KR101644218B1 - Method for manufacturing glass substrate and apparatus for manufacturing glass substrate - Google Patents

Abstract

It is an object of the present invention to provide a method of manufacturing a glass substrate and an apparatus for manufacturing a glass substrate that can prevent foreign matter from being mixed into the molten glass in the finishing step of the molten glass.
The manufacturing method of the glass substrate includes a melting step, a refining step, and a molding step. In the refining process, the molten glass G flows inside the cleaning tube 41 made of platinum or platinum alloy so as to form the gas phase space 41c. The vapor phase space 41c is a space above the molten glass G liquid surface LS in the inside of the cleaning tube 41. [ The purifying pipe 41 has a vent pipe 41a protruding outward from the outer wall surface of the purifying pipe 41 and a receiving portion 41d provided above the liquid surface LS of the molten glass G. The vent pipe (41a) communicates the vapor space (41c) with the outer space of the purifying pipe (41). The accommodating portion 41d covers a part of the cross section of the vent pipe 41a when the vent pipe 41a is viewed along the longitudinal direction of the vent pipe 41a.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a method of manufacturing a glass substrate,

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

Generally, as disclosed in Patent Document 1 (Japanese Patent Application Laid-Open No. 2006-522001), a manufacturing method of a glass substrate is generally classified into a melting process for heating a glass raw material to produce a molten glass, . The manufacturing method of the glass substrate further includes a cleaning step of removing minute bubbles contained in the molten glass between the melting step and the molding step. In the refining step, bubbles in the molten glass are removed by redox reaction of the refining agent by passing the molten glass containing the refining agent such as As ₂ O ₃ through a high-temperature refining tube. Specifically, by initially raising the temperature of the molten glass and functioning the refining agent, the bubbles contained in the molten glass are floated and removed on the surface of the molten glass in the purifying tube. Subsequently, the temperature of the molten glass is lowered, and minute bubbles remaining in the molten glass are absorbed and removed by the molten glass. The cleaning tube through which the molten glass passes has a vapor phase space between the upper inner wall surface and the molten glass liquid surface. The gas phase space communicates with the outside air, which is the outside space of the purifying pipe, through a vent pipe connected to the purifying pipe.

In order to mass-produce a high-quality glass substrate from a molten glass at a high temperature, it is preferable that a foreign matter which causes a defect in the glass substrate is not mixed into the molten glass. Therefore, the inner wall of the member contacting the molten glass needs to be made of a suitable material, depending on the temperature of the molten glass contacting the member, the quality of the glass substrate required, and the like. A platinum group metal is generally used for the inner wall of the member contacting the molten glass. Hereinafter, the term " platinum group metal " means an alloy of a metal composed of a single platinum group element and a metal composed of a platinum group element. The platinum group elements are six elements of platinum (Pt), palladium (Pd), rhodium (Rh), ruthenium (Ru), osmium (Os) and iridium (Ir). Although platinum group metals are expensive, they have a high melting point and are excellent in corrosion resistance to molten glass.

The temperature of the molten glass passing through the inside of the purifying tube differs depending on the composition of the glass substrate to be formed, and in the case of a glass substrate for a flat panel display (FPD), it is 1000 ° C to 1700 ° C. In recent years, SnO ₂ has been used as a fining agent instead of As ₂ O ₃ in view of environmental load reduction. SnO ₂ has a refining effect to small as compared to As ₂ O ₃ to obtain the refining effect same as As ₂ O ₃ is required to increase the temperature of the molten glass. Specifically, when SnO ₂ is used as the fining agent, the temperature of the molten glass passing through the interior of the finishing tube is set at 1500 ° C to 1700 ° C.

Japanese Patent Publication No. 2006-522001

In the manufacturing method of a glass substrate using SnO ₂ as a fining agent, the inner wall of the cleaning tube is in contact with the hot molten glass. Therefore, the platinum group metal slowly volatilizes from the inner wall of the purifying tube by the use of the purifying tube over a long period of time. The volatiles are discharged to the outside air through the gas-phase space of the purifying tube and the vent pipe together with the bubbles in the molten glass. However, the volatile matter of the platinum group metal decreases in temperature during the discharge to the outside air, and becomes a supersaturated state. Therefore, solidified volatiles are liable to precipitate on the inner wall of the purifying tube and the vent tube. Hereinafter, the substance deposited on the inner wall of the purifying tube and the vent pipe is referred to as " platinum foreign substance ". Since the inside of the vent pipe is in communication with the outside air, the temperature tends to lower, and the platinum foreign matter is likely to precipitate particularly on the inner wall of the vent pipe. If the platinum foreign object grows with the elapse of time, it may be peeled off from the inner wall of the purifying pipe and the vent pipe by its own weight, and may fall into the molten glass in the purifying pipe. Further, when the platinum foreign matter deposited on the inner wall of the vent pipe is removed, there is a possibility that the platinum foreign matter falls into the molten glass in the purifying pipe. Further, if a platinum foreign matter is mixed in the molten glass, it becomes difficult to mass-produce a high-quality glass substrate.

It is an object of the present invention to provide a method of manufacturing a glass substrate and an apparatus for manufacturing a glass substrate that can prevent foreign matter from being mixed into the molten glass in the finishing step of the molten glass.

A manufacturing method of a glass substrate according to the present invention comprises a melting step of heating a glass raw material to produce a molten glass, a refining step of refining the molten glass, and a forming step of molding the glass substrate from the refined molten glass. In the refining process, the molten glass flows inside the purifying tube made of platinum or platinum alloy so as to form a vapor phase space. The vapor phase space is a space above the liquid level of the molten glass in the inside of the purifying tube. The purifying tube has a vent pipe projecting outward from the outer wall surface of the purifying tube and a receiving portion provided above the liquid surface of the molten glass. The vent pipe communicates the meteorological space with the outer space of the clarifying tube. The receiving portion covers a part of the cross section of the vent pipe when the vent pipe is viewed along the longitudinal direction of the vent pipe.

In the glass substrate manufacturing method according to the present invention, the molten glass produced by heating the glass raw material is heated by passing through the inside of the high-temperature purifying tube. In the inside of the purifying tube, the bubbles contained in the molten glass absorb the oxygen generated by the reduction reaction of the refining agent incorporated in the molten glass and grow. The grown bubbles float on the surface of the molten glass, and the bubbles burst and disappear. The gas contained in the disappearing bubbles is discharged into the vapor phase space inside the purifying pipe and discharged from the purifying pipe via the vent pipe.

In the method for manufacturing a glass substrate according to the present invention, the purifying tube is made of platinum or a platinum alloy. Platinum or a platinum alloy has a high melting point and is excellent in corrosion resistance against molten glass, and thus is suitable as a material of a cleaning pipe in contact with a molten glass at a high temperature. However, by the use of the purifying tube over a long period of time, the platinum component gradually evaporates from the inner wall of the purifying tube. Volatiles containing platinum are discharged from the purifying tube via the vent pipe together with the bubbles in the molten glass. Volatiles containing platinum tend to become supersaturated if the temperature drops during the passage through the vent tube. Therefore, solidified volatiles may adhere to the inner wall of the vent pipe as platinum foreign matter.

In the method of manufacturing a glass substrate according to the present invention, the accommodating portion is provided in the ventilating pipe inner space or the vaporizing space of the purifying pipe. Platinum foreign substances adhered to the inner wall of the vent pipe may peel off from the inner wall surface due to its own weight and fall when it grows with the lapse of time. In addition, there is a possibility that the foreign matter of platinum falls when the platinum foreign object is removed from the inner wall surface of the vent pipe at the time of maintenance work of the cleaning tube. The receiving portion receives the platinum foreign material falling off from the inner wall surface of the vent pipe. Therefore, the accommodating portion inhibits the platinum foreign matter adhering to the inner wall of the vent pipe from being mixed into the molten glass.

Preferably, the accommodating portion is provided below the portion having a temperature at which the gas containing platinum existing in the gas phase coagulates in the vent pipe. In order to more effectively receive the platinum foreign material separated from the inner wall surface of the vent pipe, it is preferable that the receiving portion is provided at a position through which volatiles as high as possible pass through the internal space of the vent pipe. That is, it is preferable that the accommodating portion is disposed as close as possible to the vapor phase space in the purifying tube.

Further, it is preferable that the molten glass contains SnO ₂ as a refining agent. It is necessary to raise the temperature of the molten glass passing through the inside of the purifying pipe in comparison with the case where As ₂ O ₃ is used as the purifying agent in the method of manufacturing the glass substrate using SnO ₂ as the purifying agent. Therefore, when SnO ₂ is used as the refining agent, the platinum component is liable to volatilize from the inner wall of the refining tube, and foreign matter of platinum tends to adhere to the inner wall of the air tube. Therefore, the method for producing a glass substrate according to the present invention is suitable for a method for producing a glass substrate using SnO ₂ as a fining agent.

The method of manufacturing a glass substrate according to the present invention is suitable for refining molten glass having a high temperature viscosity such as a molten glass having a temperature of 1,500 ° C or more when the viscosity is 10 ^{2 5} poise. The molten glass having a high temperature viscosity is required to have a higher temperature in the refining step than the ordinary molten glass of alkali glass. Therefore, the problem of platinum component volatilization from the inner wall of the purifying tube becomes remarkable, and foreign matter of platinum easily attaches to the inner wall of the vent pipe.

The method for producing a glass substrate according to the present invention is suitable for a method for producing a glass substrate using a molten glass having a high high-temperature viscosity, that is, a molten glass which needs to be higher in temperature than ordinary molten glass in a refining process.

The apparatus for manufacturing a glass substrate according to the present invention comprises a melting vessel for heating a glass raw material to produce a molten glass, a purifying tube for purifying the molten glass produced in the molten bath, and a glass substrate from the molten glass refined in the purifying tube And a molding apparatus. The purifying tube is a tube made of platinum or platinum alloy in which molten glass flows inside so as to form a gas phase space. The vapor phase space is a space above the liquid level of the molten glass in the inside of the purifying tube. The purifying tube has a vent pipe projecting outward from the outer wall surface of the purifying tube and a receiving portion provided above the liquid surface of the molten glass. The vent pipe communicates the meteorological space with the outer space of the clarifying tube. The receiving portion covers a part of the cross section of the vent pipe when the vent pipe is viewed along the longitudinal direction of the vent pipe.

A glass substrate manufacturing method according to the present invention comprises a melting step of heating a glass raw material to produce a molten glass, a refining step of refining the molten glass, and a forming step of molding the glass substrate from the refined molten glass. In the refining process, the molten glass flows inside the purifying tube made of platinum or platinum alloy so as to form a vapor phase space. The vapor phase space is a space above the liquid level of the molten glass in the inside of the purifying tube. The purifying tube has a vent pipe projecting outward from the outer wall surface of the purifying tube. The vent pipe communicates the meteorological space with the outer space of the clarifying tube. The vent pipe is installed in the highest temperature region of the temperature profile of the purifying pipe in the longitudinal direction of the purifying pipe. The maximum temperature range is preferably a temperature range within a range of (T _max -20) ° C to T _max ° C, more preferably (T _max -10) when the maximum temperature of the purifying tube is represented by T _max ° C, _Deg.] C to T _{max [} deg.] C, and particularly preferably is a temperature range within the range of (T _max -5) C to T _max [

In the glass substrate manufacturing method according to the present invention, the molten glass produced by heating the glass raw material is heated by passing through the inside of the high-temperature purifying tube. In the inside of the purifying tube, the bubbles contained in the molten glass grow by absorbing the oxygen generated by the refining agent reduction reaction combined with the molten glass. The grown bubbles float on the surface of the molten glass, and the bubbles burst and disappear. The gas contained in the disappearing bubbles is discharged into the vapor phase space inside the purifying pipe and discharged from the purifying pipe via the vent pipe.

In the method for manufacturing a glass substrate according to the present invention, the purifying tube is made of platinum or a platinum alloy. Platinum or a platinum alloy has a high melting point and is excellent in corrosion resistance against molten glass, and thus is suitable as a material of a cleaning pipe in contact with a molten glass at a high temperature. However, by the use of the purifying tube over a long period of time, the platinum component gradually evaporates from the inner wall of the purifying tube. Volatiles containing platinum are discharged from the purifying tube via the vent pipe together with the bubbles in the molten glass. Volatiles containing platinum tend to become supersaturated when the temperature is lowered in the process of passing through the vapor phase space and the vent pipe of the purifying tube. Therefore, solidified volatiles may adhere to the inner wall of the purifying pipe and the vent pipe as platinum foreign matter.

In the method of manufacturing a glass substrate according to the present invention, the vent pipe is connected to the outer wall face of the purifying pipe. At both ends of the clarifying tube, there is provided an electrode used for heating the clarifying tube electrically. Generally, since the electrode has a flange shape having a large heat radiating effect, both ends of the clarifying tube are more likely to radiate heat than the middle portion between both ends of the clarifying tube. Therefore, the temperature profile in the longitudinal direction of the cleaning tube has a convex shape that indicates a higher temperature at the middle portion of the cleaning tube than at both ends of the cleaning tube. The vent pipe is provided in the highest temperature region of the temperature profile of the purifying pipe, that is, the portion where the temperature is highest in the longitudinal direction of the purifying pipe. Thus, the volatiles containing platinum generated in the purifying tube are introduced into the inside of the vent pipe via the space having the highest temperature in the vapor phase space. Therefore, volatiles containing platinum flow out from the low temperature portion toward the high temperature portion in the vapor phase space and are discharged from the vent pipe, so that the supersaturated state of the volatiles including platinum in the vapor phase space can be suppressed. As a result, the platinum foreign matter is prevented from adhering to the inner wall of the purifying tube in the vapor phase space and the inner wall of the vent pipe. Therefore, the platinum foreign matter falls from the inner wall of the purifying pipe and the inner wall of the vent pipe, and is prevented from being mixed into the molten glass.

Further, it is preferable that the molten glass contains SnO ₂ as a refining agent. It is necessary to raise the temperature of the molten glass passing through the inside of the purifying pipe in comparison with the case where As ₂ O ₃ is used as the purifying agent in the method of manufacturing the glass substrate using SnO ₂ as the purifying agent. Therefore, when SnO ₂ is used as the refining agent, the platinum component is easily volatilized from the inner wall of the refining tube, and foreign matter of platinum is liable to adhere to the inner wall of the refining tube and the inner wall of the air tube. Therefore, the method for producing a glass substrate according to the present invention is suitable for a method for producing a glass substrate using SnO ₂ as a fining agent.

Further, the method of manufacturing a glass substrate according to the present invention, if the viscosity is 10 ^2. fining the molten glass or the like, the high temperature high viscosity molten glass having at least 1500 ℃ temperature when the ⁵ poise, is suitable. The molten glass having a high temperature viscosity is required to have a higher temperature in the refining step than the ordinary molten glass of alkali glass. Therefore, the problem of platinum component volatilization from the inner wall of the purifying tube becomes remarkable, and foreign matter of platinum easily attaches to the inner wall of the purifying tube and the inner wall of the vent tube.

The method for producing a glass substrate according to the present invention is suitable for a method for producing a glass substrate using a molten glass having a high high-temperature viscosity, that is, a molten glass which needs to be higher in temperature than ordinary molten glass in a refining process.

The apparatus for manufacturing a glass substrate according to the present invention comprises a melting vessel for heating a glass raw material to produce a molten glass, a purifying tube for purifying the molten glass produced in the molten bath, and a glass substrate from the molten glass refined in the purifying tube And a molding apparatus. The purifying tube is a tube made of platinum or platinum alloy in which molten glass flows inside so as to form a gas phase space. The vapor phase space is a space above the liquid level of the molten glass in the inside of the purifying tube. The purifying tube has a vent pipe projecting outward from the outer wall surface of the purifying tube. The vent pipe communicates the meteorological space with the outer space of the clarifying tube. The vent pipe is installed in the highest temperature region of the temperature profile of the purifying pipe in the longitudinal direction of the purifying pipe.

INDUSTRIAL APPLICABILITY The method for manufacturing a glass substrate and the apparatus for manufacturing a glass substrate according to the present invention can suppress foreign matter from being mixed into a molten glass in a finishing process of the molten glass.

1 is a flowchart showing a process of a glass substrate manufacturing method according to the first embodiment;
2 is a schematic diagram showing a configuration of a glass substrate manufacturing apparatus according to the first embodiment;
3 is an external view of a cleaning tube according to the first embodiment;
4 is a cross-sectional view in the longitudinal direction of the cleaning tube according to the first embodiment;
Fig. 5 is an external view of the vent pipe viewed along the direction of the arrow V shown in Fig. 4; Fig.
6 is a cross-sectional view of the cleaning tube according to Modification A of the first embodiment in the longitudinal direction.
Fig. 7 is an external view of the vent pipe taken along the direction of arrow VII shown in Fig. 6; Fig.
8 is a cross-sectional view of the cleaning tube according to Modification B of the first embodiment in the longitudinal direction.
Fig. 9 is an external view of the vent pipe viewed along the direction of the arrow IX shown in Fig. 8; Fig.
10 is a cross-sectional view of the cleaning tube according to Modification C of the first embodiment in the longitudinal direction.
Fig. 11 is an external view of the vent pipe viewed along the direction of the arrow XI shown in Fig. 10; Fig.
12 is a flowchart showing a process of the glass substrate manufacturing method according to the second embodiment.
13 is a schematic diagram showing a configuration of a glass substrate manufacturing apparatus according to a second embodiment.
14 is an external view of a cleaning tube according to a second embodiment;
15 is a cross-sectional view in the longitudinal direction of the clarifying tube according to the second embodiment;
16 is a diagram showing a correspondence relationship between a side view of the cleaning tube according to the second embodiment and a temperature profile of the cleaning tube;

- First Embodiment -

(1) Overall construction of glass substrate manufacturing apparatus

A method of manufacturing a glass substrate and a glass substrate manufacturing apparatus according to a first embodiment of the present invention will be described with reference to the drawings. 1 is a flowchart showing an example of a process of a glass substrate manufacturing method according to the present embodiment.

As shown in Fig. 1, the glass substrate manufacturing method mainly includes a melting step S1, a clarifying step S2, a stirring step S3, a molding step S4, a slow cooling step S5, and a cutting step S6.

In the melting step S1, the glass raw material is heated to obtain a molten glass. The molten glass is stored in the melting tank, and is heated by conduction so as to have a desired temperature. A cleaning agent is added to the glass raw material. From the viewpoint of environmental load reduction, SnO ₂ is used as a refining agent.

In the finishing step S2, the molten glass flows through the inside of the purifying pipe. Initially, the temperature of the molten glass is raised. The refining agent causes a reduction reaction by raising the temperature to release oxygen. Bubbles containing gaseous components such as CO ₂ , N ₂ and SO ₂ contained in the molten glass absorb oxygen generated by the reduction reaction of the fining agent. The bubbles grown by absorbing oxygen float on the surface of the molten glass, and the bubbles burst and disappear. The gas contained in the extinct bubble is discharged to the vapor phase space in the purifying tube and finally discharged to the outside air. Subsequently, in the finishing step S2, the temperature of the molten glass is lowered. Thereby, the reduced refining agent causes an oxidation reaction to absorb gas components such as oxygen remaining in the molten glass.

In the stirring step S3, the refined molten glass is stirred to homogenize the components of the molten glass. This reduces unevenness in the composition of the molten glass, which is a cause of spalling of the glass substrate and the like. The homogenized molten glass is sent to the molding step S4.

In the molding step S4, the glass ribbon is continuously formed from the molten glass by the overflow down-draw method or the float method.

In the gradual cooling step S5, the glass ribbon continuously formed in the molding step S4 has a desired thickness and is gradually cooled so that distortion and warping do not occur.

In the cutting step S6, the glass ribbon that has been slowly cooled in the gradual cooling step S5 is cut to a predetermined length, and a glass sheet is obtained. The glass sheet is further cut to a predetermined size to obtain a glass substrate. Thereafter, grinding and polishing of the end face of the glass substrate and cleaning of the glass substrate are performed. Further, the presence or absence of defects such as scratches on the glass substrate is inspected, and the glass substrate that passes the inspection is packed and shipped as a product.

2 is a schematic diagram showing an example of the configuration of the glass substrate production apparatus 200 according to the present embodiment. The glass substrate manufacturing apparatus 200 includes a melting vessel 40, a clarifying tube 41, a stirring device 100, a molding device 42, and transfer tubes 43a, 43b and 43c. The transfer pipe (43a) connects the melting tank (40) and the cleaning pipe (41). The transfer pipe 43b connects the purifying pipe 41 and the agitation device 100. The transfer pipe 43c connects the agitation apparatus 100 and the molding apparatus 42.

The molten glass G generated in the melting tank 40 flows into the cleaning pipe 41 through the transfer pipe 43a. The molten glass G refined in the cleaning tube 41 passes through the transfer pipe 43b and flows into the stirring device 100. [ The molten glass G stirred in the stirring apparatus 100 passes through the transfer pipe 43c and flows into the molding apparatus 42. [ In the molding apparatus 42, the glass ribbon GR is formed from the molten glass G by an overflow down-draw method. The glass ribbon GR is cut to a predetermined size in the subsequent process, and a glass substrate is produced. The dimension in the width direction of the glass substrate is, for example, 500 mm to 3500 mm. The dimension in the longitudinal direction of the glass substrate is, for example, 500 mm to 3500 mm.

The glass substrate produced by the method for manufacturing a glass substrate and the apparatus for manufacturing a glass substrate according to the present invention is particularly suitable as a glass substrate for a flat panel display (FPD) such as a liquid crystal display, a plasma display, and an organic EL display. As the glass substrate for FPD, an alkali-free glass or a glass containing a small amount of alkali is used. The glass substrate for FPD has a high viscosity at a high temperature. For example, 10 ^2. Temperature of the molten glass having a viscosity of ⁵ poise is not less than 1500 ℃.

The melting tank 40 is provided with heating means (not shown) such as a burner. In the melting tank 40, the glass raw material is dissolved by the heating means, and molten glass G is produced. The glass raw material is prepared so as to obtain substantially the glass of the desired composition. As an example of the composition of the glass, a non-alkali glass suitable as a glass substrate for an FPD is a glass containing 50% by mass to 70% by mass of SiO ₂ , 0 to 25% by mass of Al ₂ O ₃ , 1% by mass of B ₂ O _3, 0 to 15 mass% MgO: 0 mass% to 10 mass%, CaO: 0 mass% to 20 mass%, SrO: 0 mass% to 20 mass%, and BaO: 0 mass% to 10 mass%. Here, the total content of MgO, CaO, SrO, and BaO is 5% by mass to 30% by mass.

As the glass substrate for FPD, an alkali-containing glass containing a trace amount of alkali metal may be used. The alkali-small-content glass contains R ' ₂ O in an amount of 0.1 mass% to 0.5 mass%, and preferably 0.2 mass% to 0.5 mass% of R' ₂ O as a component. Here, R 'is at least one selected from Li, Na and K. The total content of R ' ₂ O may be less than 0.1% by mass.

As the glass substrate for FPD, polysilicon (low-temperature polysilicon) other than amorphous silicon may be used. For example, glass plates containing the following components in mass% are exemplified. (1) SiO ₂ : 52 to 78%, (2) Al ₂ O ₃ : 3 to 25%, (3) B ₂ O ₃ : 3 to 15% (SiO ₂ + Al ₂ O ₃ ) / B ₂ O ₃ : 7 to 20), CaO, SrO and BaO, the total amount of all the components contained in the glass plate): 3% to 20%;

The glass produced by the present invention contains SnO _{2 in an} amount of 0.01 to 1% by mass (preferably 0.01 to 0.5% by mass), Fe ₂ O ₃ : 0 to 0.2% by mass, (Preferably, 0.01% by mass to 0.08% by mass). Further, the glass produced by the present invention is substantially free of As ₂ O ₃ , Sb ₂ O ₃ and PbO in consideration of environmental load.

The glass raw material thus prepared is put into the dissolution tank 40 by using a raw material introducing device (not shown). The raw material dispenser may be charged with a glass raw material by using a screw feeder, or may be charged with a glass raw material by using a bucket. In the melting tank 40, the glass raw material is heated and melted at a temperature according to the composition or the like. Thereby, in the melting tank 40, for example, a molten glass G at a high temperature of 1500 to 1600 占 폚 is obtained. In addition, in the melting tank 40, the molten glass G between the electrodes may be heated by conduction by flowing an electric current between at least a pair of electrodes made of molybdenum, platinum or tin oxide. In addition to energization heating, The glass raw material may be heated.

The molten glass G obtained in the melting tank 40 flows into the cleaning pipe 41 from the melting tank 40 through the transfer pipe 43a. The cleaning tube 41 and the transfer tubes 43a, 43b and 43c are made of platinum or platinum alloy. A heating means is provided in the purifying tube 41 in the same manner as the melting vessel 40. In the purifying pipe (41), the molten glass G is further heated up and cleaned. For example, in the cleaning tube 41, the temperature of the molten glass G may be raised to 1500 to 1700 占 폚.

The refined molten glass G in the purifying pipe 41 flows from the purifying pipe 41 through the transfer pipe 43b and flows into the stirring device 100. [ The molten glass G is cooled when it passes through the transfer pipe 43b. In the stirring apparatus 100, the molten glass G is stirred at a temperature lower than the temperature of the molten glass G passing through the purifying pipe 41. For example, in the stirring apparatus 100, the temperature of the molten glass G is 1250 캜 to 1450 캜. For example, in the stirring apparatus 100, the viscosity of the molten glass G is 500 poise to 1300 poise. The molten glass G is stirred and homogenized in the stirring apparatus 100.

The molten glass G homogenized in the stirring apparatus 100 is introduced into the molding apparatus 42 from the stirring apparatus 100 through the transfer pipe 43c. The molten glass G is cooled so as to have a viscosity suitable for forming the molten glass G when it passes through the transfer pipe 43c. For example, the molten glass G is cooled to about 1200 ° C. In the molding apparatus 42, the molten glass G is formed by an overflow down-draw method. Specifically, the molten glass G introduced into the molding machine 42 is supplied to a molding body 52 provided inside a molding furnace (not shown). The molded body 52 is molded by refractory bricks and has a wedge-shaped cross-sectional shape. On the upper surface of the molded body 52, a groove is formed along the longitudinal direction of the molded body 52. The molten glass G is supplied to the grooves on the upper surface of the molded body 52. The molten glass G flowing over the groove flows downward along a pair of side surfaces of the molded body 52. The pair of molten glass G, which has flowed down the side surface of the molded body 52, joins at the lower end of the formed body 52, and the glass ribbon GR is continuously formed. The glass ribbon GR is gradually cooled as it flows downward, and is then cut into glass sheets of desired length.

(2) Composition of the purifying tube

Next, the detailed structure of the cleaning tube 41 will be described. Fig. 3 is an external view of the cleaning tube 41. Fig. Fig. 4 is a cross-sectional view of the cleaning tube 41 cut vertically along the longitudinal direction of the cleaning tube 41. Fig. The cleaning tube 41 has a thickness of, for example, 0.5 mm to 1.5 mm and an inner diameter of 300 mm to 500 mm. The purifying pipe 41 is provided with a vent pipe 41a and a pair of heating electrodes 41b. In the inside of the cleaning tube 41, the molten glass G flows in a state in which the vapor space 41c is formed above. That is, in the inside of the cleaning tube 41, as shown in Fig. 4, the liquid surface LS of the molten glass G exists. The inner space of the vent pipe 41a communicates with the vapor space 41c. Further, by flowing a current between the pair of heating electrodes 41b, the cleaning tube 41 is energized and heated. As a result, the molten glass G passing through the inside of the purifying pipe 41 is heated and refined. Bubbles containing gaseous components such as CO ₂ , N ₂ and SO ₂ contained in the molten glass G in the refining process of the molten glass G absorb the oxygen generated by the refining reaction of the refining agent. The bubbles grown by absorbing the oxygen float on the liquid surface LS of the molten glass G, and the bubbles burst and disappear. The gas contained in the exhausted bubble is discharged into the vapor phase space 41c in the purifying pipe 41 and discharged to the outside air via the vent pipe 41a.

The vent pipe 41a is provided on the outer wall surface of the purifying pipe 41 and protrudes to the outside of the purifying pipe 41. [ In this embodiment, as shown in Fig. 4, the vent pipe 41a is provided at the upper end of the outer wall surface of the purifying pipe 41 and protrudes in the form of a chimney toward the upper side of the purifying pipe 41. [ The vent pipe 41a communicates with the outside space, which is the outer space of the purifying pipe 41, with the vapor space 41c, which is a part of the internal space of the purifying pipe 41. [ Like the purifying pipe 41, the vent pipe 41a is formed of platinum or a platinum alloy. The vent tube 41a has a thickness of, for example, 0.5 mm to 1.5 mm and an inner diameter of 10 mm to 100 mm.

The vent tube 41a has a receiving portion 41d. 4, the accommodating portion 41d is located above the liquid surface LS of the molten glass G and is provided on the inner wall surface of the vent pipe 41a. Like the vent pipe 41a, the receiving portion 41d is formed of platinum or a platinum alloy. Fig. 5 is an external view of the vent pipe 41a taken along the direction of the arrow V shown in Fig. 5 shows a state in which the vent pipe 41a is viewed from the upper side downward along the longitudinal direction of the vent pipe 41a, that is, the vertical direction. In other words, FIG. 5 shows how the inside of the purifying pipe 41 is viewed from the vent pipe 41a. The accommodating portion 41d covers a part of the cross section of the vent pipe 41a. The accommodating portion 41d is a circular plate having a hole at the center thereof. The outer periphery of the accommodating portion 41d is joined to the inner wall surface of the vent pipe 41a. The vapor space 41c of the purifying pipe 41 communicates with the outside air by the hole in the central portion of the accommodating portion 41d.

The heating electrode 41b is a flange-shaped electrode plate provided at each of both end portions of the cleaning tube 41. [ The heating electrode 41b is connected to a power source (not shown). Electric power is supplied to the heating electrode 41b so that current flows through the cleaning tube 41 between the pair of heating electrodes 41b and the cleaning tube 41 is energized and heated. Thus, the fining tube 41 is, for example, heated to 1700 ℃, flowing the melt to the interior of the fining tube 41, a glass G is temperature reduction of the refining agent SnO ₂ contained in the molten glass G that occur, for example, Lt; RTI ID = 0.0 > 1600 C < / RTI > The temperature of the molten glass flowing inside the cleaning tube 41 can be controlled by controlling the current flowing through the cleaning tube 41. [ The number and positions of the heating electrodes 41b provided in the cleaning tube 41 may be appropriately determined depending on the material, inner diameter and length of the cleaning tube 41, the position of the air tube 41a, and the like.

3 and 4, a refractory material protecting layer made of alumina cement or the like is provided on the outer wall surface of the cleaning tube 41. As shown in Fig. A refractory brick is further provided on the outer wall surface of the refractory protective layer. The refractory bricks are mounted on a base (not shown). That is, the cleaning pipe 41 is supported from below by the refractory protection layer and the refractory brick.

(3) Features

(3-1)

In the glass substrate manufacturing method according to the present embodiment, the molten glass G produced by heating the glass raw material is heated when passing through the inside of the cleaning tube 41. [ In the inside of the cleaning tube 41, bubbles containing CO ₂ or SO ₂ contained in the molten glass G are removed by redox reaction of SnO ₂ , which is a cleaning agent added to the molten glass G. Specifically, the temperature of the molten glass G is first raised to reduce the refining agent, thereby generating bubbles of oxygen in the molten glass G. Bubbles containing gas components such as CO ₂ , N ₂ and SO ₂ contained in the molten glass G absorb oxygen generated by the reduction reaction of the fining agent. The bubbles grown by absorbing the oxygen float on the liquid surface LS of the molten glass G, and the bubbles burst and disappear. The gas contained in the disappearing bubbles is discharged to the gas phase space 41c and discharged to the outside air via the vent pipe 41a. Then, the temperature of the molten glass G is lowered to oxidize the reduced fining agent. Thereby, bubbles of oxygen remaining in the molten glass G are absorbed into the molten glass G. Thus, the bubbles contained in the molten glass G are removed by the redox reaction of the cleaning agent.

The cleaning tube (41) is made of platinum or platinum alloy. The platinum or platinum alloy has a high melting point and is excellent in corrosion resistance against the molten glass G, so that the platinum or platinum alloy is suitable as a material of the cleaning pipe 41 in contact with the molten glass G at a high temperature. However, by the use of the purifying pipe 41 over a long period of time, the platinum component slowly volatilizes from the inner wall of the purifying pipe 41. Volatiles containing platinum are discharged into the gas phase space 41c together with the bubbles contained in the molten glass G, and are discharged to the outside air via the vent pipe 41a. However, volatiles containing platinum tend to be in a supersaturated state due to a decrease in temperature in the process of passing through the vent pipe 41a. Therefore, solidified volatiles are attached to the inner wall of the vent pipe 41a as platinum foreign matter. The platinum foreign matter adhered to the inner wall of the vent pipe 41a grows with the lapse of time. There is a possibility that the platinum foreign object is peeled off from the inner wall surface of the vent pipe 41a due to its own weight and falls. In addition, there is a possibility that the platinum foreign matter falls when the platinum foreign object is removed from the inner wall surface of the vent pipe 41a during the repair work of the cleaning tube 41. [

In the glass substrate manufacturing apparatus 200 according to the present embodiment, the accommodating portion 41d is provided on the inner wall surface of the vent pipe 41a serving as the exhaust pipe of the purifying pipe 41. [ The receiving portion 41d is a member for receiving the platinum foreign material that has fallen off from the inner wall surface of the vent pipe 41a. The platinum foreign material peeled off from the inner wall surface of the vent pipe 41a falls down to the inner space of the purifying pipe 41 and the molten metal passing through the purifying pipe 41 There is a fear that it may be mixed into the glass G. If a platinum foreign matter is mixed with the molten glass G, there is a possibility that the quality of the glass substrate to be produced becomes defective. The accommodating portion 41d suppresses the platinum foreign material that has fallen off from the inner wall surface of the vent pipe 41a and falls down to the liquid surface LS of the molten glass G in the purifying pipe 41. [ Therefore, the incorporation of the platinum foreign matter into the molten glass G is suppressed by the accommodating portion 41d, so that a high-quality glass substrate can be mass-produced at a high yield.

(3-2)

In the present embodiment, the accommodating portion 41d is provided below the portion having the temperature at which volatiles containing platinum existing in the vapor space 41c of the purifying pipe 41 are solidified in the vent pipe 41a . That is, it is preferable that the accommodating portion 41d is provided at a position through which the volatiles as high as possible pass through the internal space of the vent pipe 41a. In other words, the accommodating portion 41d is desirably provided as close as possible to the vapor phase space 41c in the cleaning tube 41. [

The temperature of the vent pipe 41a is the highest at the connecting portion between the purifying pipe 41 and the vent pipe 41a and tends to decrease as it goes upward at the connecting portion. In other words, the temperature of the internal space of the vent pipe 41a also has the highest part that communicates with the vapor space 41c, and shows a tendency to decrease as it goes upward. As a result, the gas containing platinum gradually evaporated from the inner wall of the purifying pipe 41 is gradually cooled and becomes supersaturated in the process of flowing upwardly through the vent pipe 41a. Therefore, the inner space of the vent pipe 41a has a platinum coagulation point, which is a point indicating the temperature at which volatiles containing platinum solidify along the longitudinal direction of the vent pipe 41a. Therefore, the volatiles containing platinum coagulate above the platinum solidification point, and foreign matter of platinum easily attaches to the inner wall of the vent pipe 41a.

Therefore, by disposing the accommodating portion 41d below the platinum coagulation point, the accommodating portion 41d can more effectively receive the platinum foreign object that has fallen off from the inner wall surface of the vent pipe 41a. In the case where the accommodating portion 41d is provided above the platinum solidification point, foreign matter of platinum is likely to adhere to the inner wall of the vent pipe 41a below the accommodating portion 41d. In this case, there is a possibility that the accommodating portion 41d can not receive the platinum foreign material falling off from the inner wall surface of the vent pipe 41a.

(3-3)

The glass substrate manufacturing apparatus 200 according to the present embodiment is particularly effective when SnO ₂ is used as a fining agent in the cleaning tube 41 made of platinum or platinum alloy. Recently, from the viewpoint of environmental load, SnO ₂ is used as a refining agent instead of As ₂ O ₃ . In the case of using SnO ₂ , since the molten glass G needs to be heated to a higher temperature in the cleaning tube 41 than in the case of using As ₂ O ₃ , the problem of the volatilization of platinum or platinum alloy becomes remarkable. If the volatilization of the platinum or platinum alloy is promoted, foreign matter of platinum easily attaches to the inner wall of the vent pipe 41a.

The accommodating portion 41d can receive the platinum foreign material falling off from the inner wall surface of the vent pipe 41a even when the platinum foreign matter tends to adhere to the inner wall of the vent pipe 41a, G is prevented from being mixed with the platinum foreign matter. Therefore, the glass substrate manufacturing method according to the present embodiment is particularly effective in the process of manufacturing a glass substrate using SnO ₂ as a fining agent.

(3-4)

The glass substrate manufacturing apparatus 200 according to the present embodiment is a glass substrate manufacturing apparatus that is suitable for manufacturing a glass substrate for FPD such as a liquid crystal display, a plasma display, and an organic EL display in a cleaning tube 41 made of platinum or platinum alloy It is particularly effective in refining the molten glass produced from the molten glass.

In the purifying pipe (41), the molten glass (G) is refined by adjusting the viscosity of the molten glass (G) such that the bubbles contained in the molten glass (G) float on the surface of the molten glass. However, an alkali-free glass and an alkali-containing glass suitable for a glass substrate for an FPD have a high viscosity at a high temperature. Therefore, in the refining process, the temperature of the molten glass needs to be higher than the temperature of the molten glass of ordinary alkali glass, so that the problem of volatilization of the above-mentioned platinum or platinum alloy becomes remarkable. If the volatilization of the platinum or platinum alloy is promoted, foreign matter of platinum easily attaches to the inner wall of the vent pipe 41a.

The accommodating portion 41d can receive the platinum foreign material falling off from the inner wall surface of the vent pipe 41a even when the platinum foreign matter tends to adhere to the inner wall of the vent pipe 41a, G is prevented from being mixed with the platinum foreign matter. Therefore, the glass substrate manufacturing method according to the present embodiment is particularly effective for the manufacturing process of the glass substrate for FPD.

(4) Variations

(4-1) Variation Example A

In the glass substrate manufacturing apparatus 200 according to the present embodiment, the vent pipe 41a has a receiving portion 41d for receiving the platinum foreign material that has been peeled off from the inner wall surface of the vent pipe 41a. The housing portion 41d is an annular plate provided on the inner wall surface of the vent pipe 41a as shown in Fig. However, the receiving portion 41d may have a different shape as long as the receiving portion 41d has a shape capable of receiving the platinum foreign object that has fallen off from the inner wall surface of the vent pipe 41a.

Figs. 6 and 7 are views showing another embodiment of the accommodating portion 41d. Fig. 6 is a cross-sectional view of the cleaning tube 141 cut vertically along the longitudinal direction of the cleaning tube 141, as in Fig. Fig. 7 is an external view of the vent pipe 141a taken along the direction of the arrow VII shown in Fig. 6 as in Fig. 7 shows a state in which the vent pipe 141a is viewed from above to below along the longitudinal direction of the vent pipe 141a.

As shown in Fig. 7, the accommodating portion 141d is provided on the inner wall surface of the vent pipe 141a. The receiving portion 141d is composed of an image receiving portion 141d1 and a lower receiving portion 141d2. The image receiving portion 141d1 and the lower receiving portion 141d2 each have a semicircular shape. The image receiving portion 141d1 and the lower receiving portion 141d2 are provided at different positions along the longitudinal direction of the vent pipe 141a. More specifically, the image receiving portion 141d1 is provided at a higher position than the lower receiving portion 141d2. The upper and lower accommodating portions 141d1 and 141d2 cover a part of a cross section of the vent pipe 141a. Therefore, the gas in the vapor phase space 141c in the cleaning tube 141 passes through the vent pipe 141a and is discharged to the outside air.

Also in this modified example, since the accommodating portion 141d suppresses the incorporation of the platinum foreign matter into the molten glass G, it is possible to mass-produce a glass substrate of high quality at a high yield. Also, like the present embodiment, it is preferable that the accommodating portion 141d is provided below the platinum solidification point. Thereby, the accommodating portion 141d can more effectively receive the platinum foreign object that has fallen off from the inner wall surface of the vent pipe 141a.

(4-2) Variation B

In the glass substrate manufacturing apparatus 200 according to the present embodiment, the accommodating portion 41d is provided on the inner wall surface of the vent pipe 41a. However, the accommodating portion 41d may be provided above the liquid surface LS of the molten glass G, and may be provided in the vapor space 41c of the cleaning tube 41, for example.

8 and 9 are views showing another embodiment of the accommodating portion 41d. Fig. 8 is a cross-sectional view of the clarifying tube 241 cut vertically along the longitudinal direction of the purifying tube 241, as in Fig. Fig. 9 is an external view of the vent pipe 241a taken along the direction of the arrow IX shown in Fig. 8, as in Fig. Fig. 9 shows a state in which the vent pipe 241a is viewed from above to below along the longitudinal direction of the vent pipe 241a.

As shown in Fig. 8, the accommodating portion 241d is provided on the inner wall surface above the purifying pipe 241. As shown in Fig. The accommodating portion 241d is located above the liquid level LS of the molten glass G. Further, as shown in Fig. 9, the receiving portion 241d is a net-like plate having a large number of holes when viewed from above. The cross section of the vent pipe 241a is covered by the mesh member 241d of the accommodating portion 241d when the vent pipe 241a is viewed from the upper side downward along the longitudinal direction of the vent pipe 241a. The accommodating portion 241d covers a part of the cross section of the vent tube 241a. Therefore, the gas in the vapor phase space 241c in the purifying pipe 241 passes through the vent pipe 241a and is discharged to the outside air.

Also in this modified example, incorporation of platinum foreign matter into the molten glass G is suppressed by the accommodating portion 241d, so that a high-quality glass substrate can be mass-produced at a high yield.

(4-3) Variation C

In the glass substrate manufacturing apparatus 200 according to the present embodiment, the vent pipe 41a has a receiving portion 41d for receiving the platinum foreign material that has been peeled off from the inner wall surface of the vent pipe 41a. The housing portion 41d is an annular plate provided on the inner wall surface of the vent pipe 41a as shown in Fig. However, the accommodating portion 41d may be formed as a part of the purifying pipe 41. [

10 and 11 are views showing another embodiment of the accommodating portion 41d. 10 is a cross-sectional view of the cleaning tube 341 cut vertically along the longitudinal direction of the cleaning tube 341 as in Fig. 11 is an external view of the vent pipe 341a taken along the direction of the arrow XI shown in Fig. 10, as in Fig. 11 shows a state in which the vent pipe 341a is viewed from the upper side downward along the longitudinal direction of the vent pipe 341a.

As shown in Fig. 11, the cleaning tube 341 has a circular exhaust hole 341e. The exhaust hole 341e is formed at the upper end of the purifying pipe 341. [ The exhaust hole 341e communicates the vapor space 341c in the purifying pipe 341 with the inside space of the vent pipe 341a provided in the purifying pipe 341. As shown in Fig. 11, the inner diameter of the exhaust hole 341e is smaller than the inner diameter of the vent pipe 341a. When the vent pipe 341a is viewed along the longitudinal direction of the vent pipe 341a, the center of the circular cross-sectional shape of the vent pipe 341a is at the same position as the center of the vent hole 341e. 11, a part of the outer wall of the purifying pipe 341 which is located outside the outer periphery of the exhaust hole 341e and inside the inner wall surface of the vent pipe 341a is a part of the outer wall of the purifying pipe 341 from the inner wall of the vent pipe 341a And has a function of a receiving portion 341d for receiving the separated platinum foreign object. The gas in the vapor phase space 341c in the purifying pipe 341 passes through the vent pipe 341a and is discharged to the outside air.

Also in this modified example, the incorporation of the platinum foreign matter into the molten glass G is suppressed by the accommodating portion 341d constituted by the part of the cleaning tube 341, so that a high-quality glass substrate can be mass-produced at a high yield.

(4-4) Modification D

In the glass substrate manufacturing apparatus 200 according to the present embodiment, the cleaning tube 41, the vent tube 41a and the accommodating portion 41d are formed of platinum or platinum alloy, but may be formed of other platinum group metals. &Quot; Platinum group metal " means a metal consisting of a single platinum group element and an alloy of a metal composed of a platinum group element. The platinum group elements are six elements of platinum (Pt), palladium (Pd), rhodium (Rh), ruthenium (Ru), osmium (Os) and iridium (Ir). Although platinum group metals are expensive, they have a high melting point and are excellent in corrosion resistance to molten glass.

- Second Embodiment -

(1) Overall construction of glass substrate manufacturing apparatus

A method of manufacturing a glass substrate and an apparatus for manufacturing a glass substrate according to the present invention will be described with reference to the drawings. 12 is a flowchart showing an example of a process of a glass substrate manufacturing method according to the present embodiment.

The glass substrate manufacturing method mainly includes a melting step S1, a clarifying step S2, a stirring step S3, a molding step S4, a slow cooling step S5, and a cutting step S6, as shown in Fig.

In the melting step S1, the glass raw material is heated to obtain a molten glass. The molten glass is stored in the melting tank, and is heated by conduction so as to have a desired temperature. A refining agent is added to the glass raw material. From the viewpoint of environmental load reduction, SnO ₂ is used as a refining agent.

In the finishing step S2, the molten glass flows through the inside of the purifying pipe. Initially, the temperature of the molten glass is raised. The refining agent causes a reduction reaction by raising the temperature to release oxygen. Bubbles containing gas components such as CO ₂ , N ₂ and SO ₂ contained in the molten glass absorb oxygen generated by the refining agent reduction reaction. The bubbles grown by absorbing oxygen float on the surface of the molten glass, and the bubbles burst and disappear. The gas contained in the extinct bubble is discharged to the vapor phase space in the purifying tube and finally discharged to the outside air. Subsequently, in the finishing step S2, the temperature of the molten glass is lowered. Thereby, the reduced refining agent causes an oxidation reaction to absorb gas components such as oxygen remaining in the molten glass.

In the stirring step S3, the refined molten glass is stirred to homogenize the components of the molten glass. This reduces unevenness in the composition of the molten glass, which is a cause of spalling of the glass substrate and the like. The homogenized molten glass is sent to the molding step S4.

In the molding step S4, the glass ribbon is continuously formed from the molten glass by the overflow down-draw method or the float method.

In the gradual cooling step S5, the glass ribbon continuously formed in the molding step S4 has a desired thickness and is gradually cooled so that distortion and warping do not occur.

In the cutting step S6, the glass ribbon that has been slowly cooled in the gradual cooling step S5 is cut to a predetermined length, and a glass sheet is obtained. The glass sheet is further cut to a predetermined size, and a glass substrate is obtained. Thereafter, grinding and polishing of the end face of the glass substrate and cleaning of the glass substrate are performed. Further, the presence or absence of defects such as scratches on the glass substrate is inspected, and the glass substrate that passes the inspection is packed and shipped as a product.

13 is a schematic diagram showing an example of the configuration of a glass substrate production apparatus 200 according to the present embodiment. The glass substrate manufacturing apparatus 200 includes a melting vessel 40, a clarifying tube 41, a stirring device 100, a molding device 42, and transfer tubes 43a, 43b and 43c. The transfer pipe (43a) connects the melting tank (40) and the cleaning pipe (41). The transfer pipe 43b connects the purifying pipe 41 and the agitation device 100. The transfer pipe 43c connects the agitation apparatus 100 and the molding apparatus 42.

The molten glass G generated in the melting tank 40 flows into the cleaning pipe 41 through the transfer pipe 43a. The molten glass G refined in the cleaning tube 41 passes through the transfer pipe 43b and flows into the stirring device 100. [ The molten glass G stirred in the stirring apparatus 100 passes through the transfer pipe 43c and flows into the molding apparatus 42. [ In the molding apparatus 42, the glass ribbon GR is formed from the molten glass G by an overflow down-draw method. The glass ribbon GR is cut to a predetermined size in the subsequent process, and a glass substrate is produced. The dimension in the width direction of the glass substrate is, for example, 500 mm to 3500 mm. The dimension in the longitudinal direction of the glass substrate is, for example, 500 mm to 3500 mm.

The glass substrate produced by the method for manufacturing a glass substrate and the apparatus for manufacturing a glass substrate according to the present invention is particularly suitable as a glass substrate for a flat panel display (FPD) such as a liquid crystal display, a plasma display, and an organic EL display. As the glass substrate for FPD, an alkali-free glass or a glass containing a small amount of alkali is used. The glass substrate for FPD has a high viscosity at a high temperature. For example, 10 ^2. Temperature of the molten glass having a viscosity of ⁵ poise is not less than 1500 ℃.

The melting tank 40 is provided with heating means (not shown) such as a burner. In the melting tank 40, the glass raw material is dissolved by the heating means, and molten glass G is produced. The glass raw material is prepared so as to obtain substantially the glass of the desired composition. As an example of the composition of the glass, a non-alkali glass suitable as a glass substrate for an FPD is a glass containing 50% by mass to 70% by mass of SiO ₂ , 0 to 25% by mass of Al ₂ O ₃ , 1% by mass of B ₂ O _3, 0 to 15 mass% MgO: 0 mass% to 10 mass%, CaO: 0 mass% to 20 mass%, SrO: 0 mass% to 20 mass%, and BaO: 0 mass% to 10 mass%. Here, the total content of MgO, CaO, SrO, and BaO is 5% by mass to 30% by mass.

As the glass substrate for FPD, an alkali-containing glass containing a trace amount of alkali metal may be used. The alkali-small-content glass contains R ' ₂ O in an amount of 0.1 mass% to 0.5 mass%, and preferably 0.2 mass% to 0.5 mass% of R' ₂ O as a component. Here, R 'is at least one selected from Li, Na and K. The total content of R ' ₂ O may be less than 0.1% by mass.

As the glass substrate for FPD, polysilicon (low-temperature polysilicon) other than amorphous silicon may be used. For example, glass plates containing the following components in mass% are exemplified. (1) SiO ₂ : 52 to 78%, (2) Al ₂ O ₃ : 3 to 25%, (3) B ₂ O ₃ : 3 to 15% (SiO ₂ + Al ₂ O ₃ ) / B ₂ O ₃ : 7 to 20), CaO, SrO and BaO, the total amount of all the components contained in the glass plate): 3% to 20%;

The glass produced by the present invention contains SnO _{2 in an} amount of 0.01 to 1% by mass (preferably 0.01 to 0.5% by mass), Fe ₂ O ₃ : 0 to 0.2% by mass, (Preferably, 0.01% by mass to 0.08% by mass). Further, the glass produced by the present invention is substantially free of As ₂ O ₃ , Sb ₂ O ₃ and PbO in consideration of environmental load.

The glass raw material thus prepared is put into the dissolution tank 40 by using a raw material introducing device (not shown). The raw material injector may be charged with the glass raw material by using a screw feeder, or may be charged with the glass raw material by using the bucket. In the melting tank 40, the glass raw material is heated and melted at a temperature according to the composition and the like. Thereby, in the melting tank 40, for example, a molten glass G at a high temperature of 1500 to 1600 占 폚 is obtained. Further, in the melting tank 40, the molten glass G between the electrodes may be heated by conduction by flowing a current between at least a pair of electrodes formed of molybdenum, platinum or tin oxide. In addition to the conduction heating, By supplementing the flame, the glass raw material may be heated.

The molten glass G obtained in the melting tank 40 flows into the cleaning pipe 41 from the melting tank 40 through the transfer pipe 43a. The cleaning tube 41 and the transfer tubes 43a, 43b and 43c are made of platinum or platinum alloy. A heating means is provided in the cleaning tube 41 in the same manner as the melting tank 40. In the cleaning tube (41), the molten glass (G) is further refined by heating. For example, in the cleaning tube 41, the temperature of the molten glass G may be raised to 1500 to 1700 占 폚.

The refined molten glass G in the purifying pipe 41 flows from the purifying pipe 41 through the transfer pipe 43b and flows into the stirring device 100. [ The molten glass G is cooled when it passes through the transfer pipe 43b. In the stirring apparatus 100, the molten glass G is stirred at a temperature lower than the temperature of the molten glass G passing through the purifying pipe 41. For example, in the stirring apparatus 100, the temperature of the molten glass G is 1250 캜 to 1450 캜. For example, in the stirring apparatus 100, the viscosity of the molten glass G is 500 poise to 1300 poise. The molten glass G is stirred and homogenized in the stirring apparatus 100.

The molten glass G homogenized in the stirring apparatus 100 is introduced into the molding apparatus 42 from the stirring apparatus 100 through the transfer pipe 43c. The molten glass G is cooled so as to have a viscosity suitable for forming the molten glass G when it passes through the transfer pipe 43c. For example, the molten glass G is cooled to about 1200 ° C. In the molding apparatus 42, the molten glass G is formed by an overflow down-draw method. Specifically, the molten glass G introduced into the molding machine 42 is supplied to a molding body 52 provided inside a molding furnace (not shown). The molded body 52 is molded by refractory bricks and has a wedge-shaped cross-sectional shape. On the upper surface of the molded body 52, a groove is formed along the longitudinal direction of the molded body 52. The molten glass G is supplied to the grooves on the upper surface of the molded body 52. The molten glass G flowing over the groove flows downward along a pair of side surfaces of the molded body 52. The pair of molten glass G, which has flowed down the side surface of the molded body 52, joins at the lower end of the formed body 52, and the glass ribbon GR is continuously formed. The glass ribbon GR is gradually cooled as it flows downward, and is then cut into glass sheets of desired length.

(2) Composition of the purifying tube

Next, the detailed structure of the cleaning tube 41 will be described. 14 is an external view of the cleaning tube 41. Fig. 15 is a cross-sectional view of the cleaning tube 41 cut vertically along the longitudinal direction of the cleaning tube 41. Fig. The cleaning tube 41 has a thickness of, for example, 0.5 mm to 1.5 mm and an inner diameter of 300 mm to 500 mm. The purifying pipe 41 is provided with a vent pipe 41a and a pair of heating electrodes 41b. In the inside of the cleaning tube 41, the molten glass G flows in a state in which the vapor space 41c is formed above. That is, as shown in Fig. 15, the liquid surface LS of the molten glass G is present in the inside of the cleaning tube 41. [ The inner space of the vent pipe 41a communicates with the vapor space 41c. Further, by flowing a current between the pair of heating electrodes 41b, the cleaning tube 41 is energized and heated. As a result, the molten glass G passing through the inside of the purifying pipe 41 is heated and refined. Bubbles containing gaseous components such as CO ₂ , N ₂ and SO ₂ contained in the molten glass G in the refining process of the molten glass G absorb the oxygen generated by the refining reaction of the refining agent. The bubbles grown by absorbing the oxygen float on the liquid surface LS of the molten glass G, and the bubbles burst and disappear. The gas contained in the disappearing bubble is discharged into the vapor phase space 41c in the cleaning tube 41 and discharged to the outside air via the vent pipe 41a.

The vent pipe 41a is provided on the outer wall surface of the purifying pipe 41 and protrudes to the outside of the purifying pipe 41. [ In this embodiment, as shown in Fig. 15, the vent pipe 41a is provided at the upper end of the outer wall surface of the purifying pipe 41 and protrudes in the form of a chimney toward the upper side of the purifying pipe 41. [ The vent pipe 41a communicates with the outside space, which is the outer space of the purifying pipe 41, with the vapor space 41c, which is a part of the internal space of the purifying pipe 41. [ Like the purifying pipe 41, the vent pipe 41a is formed of platinum or a platinum alloy. The vent tube 41a has a thickness of, for example, 0.5 mm to 1.5 mm and an inner diameter of 10 mm to 100 mm.

The heating electrode 41b is a flange-shaped electrode plate provided at each of both end portions of the cleaning tube 41. [ The heating electrode 41b is connected to a power source (not shown). Electric power is supplied to the heating electrode 41b so that current flows through the cleaning tube 41 between the pair of heating electrodes 41b and the cleaning tube 41 is energized and heated. Thus, the fining tube 41 is, for example, is heated to 1700 ℃, melt flowing in the interior of the fining tube 41, a glass G is temperature reduction of the refining agent SnO ₂ contained in the molten glass G that occur, for example, Lt; RTI ID = 0.0 > 1600 C < / RTI > The temperature of the molten glass flowing inside the cleaning tube 41 can be controlled by controlling the current flowing through the cleaning tube 41. [

16 is a diagram showing the correspondence between the side view of the cleaning tube 41 and the temperature profile of the cleaning tube 41. Fig. The upper part of Fig. 16 is a side view of the cleaning tube 41. Fig. 16 is a graph showing the temperature profile of the cleaning tube 41. As shown in Fig. In the graph showing the temperature profile of the cleaning tube 41, the horizontal axis indicates the longitudinal position of the cleaning tube 41, and the vertical axis indicates the temperature of the cleaning tube 41.

The heating electrode 41b having a flange shape has a high heat dissipation effect and both end portions of the cleaning tube 41 are more likely to radiate heat than the middle portion between both ends of the cleaning tube 41. [ 16, the both ends of the cleaning tube 41, that is, the vicinity of the pair of heating electrodes 41b, is the region having the lowest temperature in the longitudinal direction of the cleaning tube 41. On the other hand, , And in the middle portion of the purifying pipe (41), there exists a region having the highest temperature in the longitudinal direction of the purifying pipe (41). That is, the temperature profile of the cleaning tube 41 has a convex shape that indicates a higher temperature at the middle portion of the cleaning tube 41 than the temperatures at both ends of the cleaning tube 41. The vent pipe 41a is installed in the maximum temperature region R of the temperature profile of the purifying pipe 41 in the longitudinal direction of the purifying pipe 41. [ As shown in Fig. 16, the maximum temperature region R is a region in the vicinity of the maximum temperature point P, at which the temperature profile of the cleaning tube 41 is the point at which the maximum temperature is indicated. The maximum temperature region R, if the highest temperature, i.e. the temperature of the fining tube 41 according to the maximum temperature point P of the fining tube 41 is shown as T _max ℃, preferably (T _max -20) ℃ to T _max ° C, more preferably in the range of (T _max -10) ° C to T _max ° C, and particularly preferably in the range of (T _max -5) ° C to T _max ° C Lt; / RTI >

The temperature profile of the molten glass G passing through the inside of the purifying pipe 41 in the longitudinal direction of the purifying pipe 41 shows the same tendency as the temperature profile of the purifying pipe 41, I have. The temperature profile peak of the molten glass G is located on the downstream side of the molten glass G as compared with the peak of the temperature profile of the cleaning tube 41. This is because the molten glass G flows through the inside of the purifying pipe 41 along the longitudinal direction of the purifying pipe 41 and flows through heat exchange with the purifying pipe 41.

14 and 15, a refractory material protecting layer made of alumina cement or the like is provided on the outer wall surface of the cleaning tube 41. [ A refractory brick is further provided on the outer wall surface of the refractory protective layer. The refractory bricks are mounted on a base (not shown). That is, the cleaning pipe 41 is supported from below by the refractory protection layer and the refractory brick.

The outer wall surface of the cleaning tube 41, the inner wall surface of the cleaning tube 41, the molten glass G in the cleaning tube 41, the cleaning tube 41 The temperature profile on the inner wall surface of the purifying pipe 41 and the temperature profile on the inner wall surface of the purifying pipe 41 are different from each other in the temperature of the purifying pipe 41. [ The temperature profile of the molten glass G in the cooling pipe 41, and the temperature profile of the vapor space 41c in the cleaning pipe 41. [ The temperature of the molten glass G in contact with the bottom surface of the cleaning pipe 41 and the temperature of the molten glass G in contact with the vapor phase space 41c in the cleaning pipe 41 and the temperature of the molten glass G in contact with the molten glass G in the cleaning pipe 41 The temperature of the space 41c and the temperature of the vapor space 41c in contact with the inner wall surface of the cleaning tube 41 are different from each other, but a temperature profile formed by measuring any one temperature may be used. Therefore, the cleaning tube 41 may be provided in the vicinity of the maximum temperature point P of any one of the temperature profiles.

(3) Features

(3-1)

In the glass substrate manufacturing method according to the present embodiment, the molten glass G produced by heating the glass raw material is heated when passing through the inside of the cleaning tube 41. [ In the inside of the cleaning tube 41, bubbles containing CO ₂ or SO ₂ contained in the molten glass G are removed by redox reaction of SnO ₂ , which is a cleaning agent added to the molten glass G. Specifically, the temperature of the molten glass G is first raised to reduce the fining agent, thereby generating bubbles of oxygen in the molten glass G. Bubbles containing gas components such as CO ₂ , N ₂ and SO ₂ contained in the molten glass G absorb oxygen generated by the reduction reaction of the fining agent. The bubbles grown by absorbing the oxygen float on the liquid surface LS of the molten glass G, and the bubbles burst and disappear. The gas contained in the disappearing bubbles is discharged to the gas phase space 41c and discharged to the outside air via the vent pipe 41a. Then, the temperature of the molten glass G is lowered to oxidize the reduced fining agent. Thereby, bubbles of oxygen remaining in the molten glass G are absorbed into the molten glass G. Thus, the bubbles contained in the molten glass G are removed by the redox reaction of the cleaning agent.

The cleaning tube 41 is made of platinum or platinum alloy. The platinum or platinum alloy has a high melting point and is excellent in corrosion resistance against the molten glass G, so that it is suitable as a material of the cleaning pipe 41 in contact with the molten glass G of high temperature. However, by the use of the purifying pipe 41 over a long period of time, the platinum component slowly volatilizes from the inner wall of the purifying pipe 41. Volatiles containing platinum are discharged into the gas phase space 41c together with the bubbles contained in the molten glass G, and are discharged to the outside air via the vent pipe 41a.

However, volatiles containing platinum tend to be in a supersaturated state due to a decrease in temperature in the process of passing through the vent pipe 41a. Therefore, solidified volatiles are attached to the inner wall of the vent pipe 41a as platinum foreign matter. The platinum foreign matter adhered to the inner wall of the vent pipe 41a grows with the lapse of time. There is a possibility that the platinum foreign object is peeled off from the inner wall surface of the vent pipe 41a due to its own weight and falls. In addition, there is a possibility that the platinum foreign matter falls when the platinum foreign object is removed from the inner wall surface of the vent pipe 41a during the repair work of the cleaning tube 41. [

In addition, volatiles containing platinum may flow from the high temperature portion toward the low temperature portion in the course of passing through the vapor space 41c of the purifying pipe 41 toward the vent pipe 41a, thereby lowering the temperature. In this case, volatiles containing platinum are liable to be supersaturated even in the vapor phase space 41c, and solidified volatiles may adhere to the inner wall of the purifying pipe 41 as platinum foreign matter. The platinum foreign matter adhered to the inner wall of the purifying pipe 41 grows with the lapse of time and may peel off from the inner wall surface of the purifying pipe 41 due to its own weight and fall down.

In the present embodiment, the vent pipe 41a is provided at the highest temperature region of the temperature profile of the purifying pipe 41, that is, the portion where the temperature is highest in the longitudinal direction of the purifying pipe 41. [ Thus, volatiles containing platinum generated in the purifying pipe 41 flow into the inside of the vent pipe 41a via the space having the highest temperature in the vapor phase space 41c. Therefore, volatiles containing platinum flow from the low temperature portion toward the high temperature portion in the gas phase space 41c and are discharged from the vent pipe 41a, so that the supersaturated state of volatiles containing platinum in the gas phase space 41c is suppressed do. As a result, the platinum foreign matter is prevented from adhering to the inner wall of the vapor-phase space 41c of the purifying pipe 41. [ Further, since the temperature of the gas flowing through the vent pipe 41a is maintained as high as possible, adhesion of platinum foreign matter to the inner wall of the vent pipe 41a is suppressed. Therefore, the platinum foreign matter falls from the inner wall of the purifying pipe 41 and the inner wall of the vent pipe 41a and is prevented from being mixed into the molten glass G.

In the case where the vent pipe 41a is not provided in the highest temperature region of the temperature profile of the purifying pipe 41, the volatiles containing platinum may be lowered in temperature before flowing into the vent pipe 41a . In this case, volatiles containing platinum solidify on the inner wall of the vent pipe 41a, and foreign matter of platinum may adhere to the inner wall of the vent pipe 41a.

When the vent pipe 41a is not provided in the highest temperature region of the temperature profile of the purifying pipe 41, the volatilized material containing platinum is supplied from the high temperature portion to the low temperature portion 41c in the vapor phase space 41c of the purifying pipe 41, Lt; / RTI > As a result, in the vapor phase space 41c, volatiles containing platinum whose temperature has dropped become supersaturated and solidify on the inner wall of the purifying pipe 41 and on the inner wall of the vent pipe 41a, There is a possibility that a platinum foreign matter adheres.

There is a possibility that the platinum foreign material falling off from the inner wall surface of the purifying pipe 41 and the inner wall surface of the vent pipe 41a is mixed into the molten glass G. If a platinum foreign matter is mixed with the molten glass G, there is a possibility that the quality of the glass substrate to be manufactured becomes defective. In the present embodiment, since the vent pipe 41a is provided at the highest temperature region of the temperature profile of the cleaning pipe 41, the platinum foreign matter is prevented from being mixed with the molten glass G, and a high quality glass substrate can be mass- have.

(3-2)

The glass substrate manufacturing apparatus 200 according to the present embodiment is particularly effective when SnO ₂ is used as a fining agent in the cleaning tube 41 made of platinum or platinum alloy. Recently, from the viewpoint of environmental load, SnO ₂ is used as a refining agent instead of As ₂ O ₃ . In the case of using SnO ₂ , since the molten glass G needs to be heated to a higher temperature in the cleaning tube 41 than in the case of using As ₂ O ₃ , the problem of the volatilization of platinum or platinum alloy becomes remarkable. When the volatilization of platinum or platinum alloy is promoted, foreign matter of platinum tends to adhere to the inner wall of the purifying pipe 41 and the inner wall of the vent pipe 41a.

In this embodiment, even when the platinum or the platinum alloy is volatilized and the platinum foreign matter adheres to the inner wall of the purifying pipe 41 and the inner wall of the vent pipe 41a, By being installed in the highest temperature region of the temperature profile, the coagulation of the platinum or the platinum alloy is suppressed, so that the ingress of the platinum foreign matter into the molten glass G is suppressed. Therefore, the glass substrate manufacturing method according to the present embodiment is particularly effective in the process of manufacturing a glass substrate using SnO ₂ as a fining agent.

(3-3)

The glass substrate manufacturing apparatus 200 according to the present embodiment is a glass substrate manufacturing apparatus that is suitable for manufacturing a glass substrate for FPD such as a liquid crystal display, a plasma display, and an organic EL display in a cleaning tube 41 made of platinum or platinum alloy It is particularly effective in refining the molten glass produced from the molten glass.

In the purifying pipe 41, the molten glass G is refined by adjusting the viscosity of the molten glass G to a value at which bubbles contained in the molten glass G float on the liquid surface. However, an alkali-free glass and an alkali-containing glass suitable for a glass substrate for an FPD have a high viscosity at a high temperature. For example, a molten glass used for molding an alkali-free glass and an alkali-low-content glass has a temperature of 1,500 ° C or more when the viscosity is 10 ^{2 5} poise. Therefore, in the refining process, the temperature of the molten glass needs to be higher than the temperature of the molten glass of ordinary alkali glass, so that the problem of volatilization of the above-mentioned platinum or platinum alloy becomes remarkable. When the volatilization of platinum or platinum alloy is promoted, foreign matter of platinum tends to adhere to the inner wall of the purifying pipe 41 and the inner wall of the vent pipe 41a.

In this embodiment, even when the platinum or the platinum alloy is volatilized and the platinum foreign matter adheres to the inner wall of the purifying pipe 41 and the inner wall of the vent pipe 41a, By being installed in the highest temperature region of the temperature profile, the coagulation of the platinum or the platinum alloy is suppressed, so that the ingress of the platinum foreign matter into the molten glass G is suppressed. Therefore, the glass substrate manufacturing method according to the present embodiment is particularly effective in the manufacturing process of the glass substrate for FPD.

(4) Variations

In the glass substrate manufacturing apparatus 200 according to the present embodiment, the cleaning tube 41 and the vent tube 41a are formed of platinum or a platinum alloy, but may be formed of other platinum group metals. The term " platinum group metal " means a metal consisting of a single platinum group element and an alloy of a metal composed of a platinum group element. The platinum group elements are six elements of platinum (Pt), palladium (Pd), rhodium (Rh), ruthenium (Ru), osmium (Os) and iridium (Ir). Although platinum group metals are expensive, they have a high melting point and are excellent in corrosion resistance to molten glass.

41: Purification Hall
41a: vent pipe
41b: heating electrode
41c: weather space
41d:
200: glass substrate manufacturing apparatus
G: molten glass
LS: liquid surface of molten glass
R: Maximum temperature range

Claims (8)

A melting step of heating the glass raw material to produce a molten glass,
A refining step of refining the molten glass;
A molding process for molding a glass substrate from the refined molten glass
And,
In the refining step, the molten glass flows in a purifying tube made of platinum or platinum alloy so as to form a gas-phase space, which is a space above the surface of the molten glass,
Wherein the purifying tube has a vent pipe projecting outward from the outer wall surface of the purifying pipe and a receiving portion provided above the liquid surface of the molten glass and below the upper end of the vent pipe,
Wherein the vent pipe communicates the vapor space with an outer space of the purifying pipe,
Wherein the accommodating portion covers a part of the cross section of the vent pipe when the vent pipe is viewed along the longitudinal direction of the vent pipe. The method according to claim 1,
Wherein the accommodating portion is provided below the portion having a temperature at which the gas containing platinum present in the vapor phase solidifies in the vent pipe. 3. The method according to claim 1 or 2,
Wherein the molten glass contains SnO ₂ as a refining agent. A melting vessel for heating the glass raw material to produce a molten glass,
A purifying tube for purifying the molten glass generated in the molten bath;
And a molding apparatus for molding a glass substrate from the molten glass cleaned in the cleaning tube,
Wherein the cleaning tube is made of a platinum or platinum alloy in which the molten glass flows inside so as to form a vapor phase space which is a space above the surface of the molten glass,
Wherein the purifying tube has a vent pipe projecting outward from the outer wall surface of the purifying pipe and a receiving portion provided above the liquid surface of the molten glass and below the upper end of the vent pipe,
Wherein the vent pipe communicates the vapor space with an outer space of the purifying pipe,
Wherein the accommodating portion covers a part of an end face of the vent pipe when the vent pipe is viewed along the longitudinal direction of the vent pipe. delete delete delete delete

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