JP6043550B2 - Glass substrate manufacturing method and glass substrate manufacturing apparatus - Google Patents

Description

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

In general, as described in Patent Document 1 (Japanese Translation of PCT International Publication No. 2006-522001), a glass substrate manufacturing method includes a melting step of heating a glass raw material to generate a molten glass, and a glass from the molten glass. A molding process for molding the substrate. The method for producing a glass substrate further includes a refining step for removing minute bubbles contained in the molten glass between the melting step and the forming step. In the clarification step, bubbles in the molten glass are removed by an oxidation-reduction reaction of the clarifier by passing the molten glass containing a clarifier such as As ₂ O ₃ through a high-temperature clarifier tube. Specifically, first, by raising the temperature of the molten glass and causing the fining agent to function, bubbles contained in the molten glass are floated and removed on the liquid surface of the molten glass in the clarification tube. Next, the temperature of the molten glass is lowered, and fine bubbles remaining in the molten glass are absorbed by the molten glass and removed. The refining tube through which the molten glass passes has a gas phase space between the upper inner wall surface and the liquid surface of the molten glass. The gas phase space communicates with outside air, which is an external space of the clarification tube, through a ventilation tube connected to the clarification tube.

  In order to mass-produce a high-quality glass substrate from high-temperature molten glass, it is desirable that foreign substances that cause defects in the glass substrate do not enter the molten glass. Therefore, the inner wall of the member in contact with the molten glass needs to be made of an appropriate material according to the temperature of the molten glass in contact with the member and the required quality of the glass substrate. A platinum group metal is usually used for the inner wall of the member that contacts the molten glass. Hereinafter, the “platinum group metal” means a metal composed of a single platinum group element and a metal alloy 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). Platinum group metals are expensive, but have a high melting point and excellent corrosion resistance against molten glass.

The temperature of the molten glass passing through the inside of the clarification tube varies depending on the composition of the glass substrate to be molded, and is 1000 ° C. to 1700 ° C. in the case of a glass substrate for a flat panel display (FPD). In recent years, SnO ₂ has been used as a refining agent instead of As ₂ O ₃ from the viewpoint of reducing environmental burden. SnO ₂ has a small refining effect as compared with As ₂ O _3, in order to obtain the same refining effect and As ₂ O ₃ is required to raise the temperature of the molten glass. Specifically, when using SnO ₂ as a fining agent, the temperature of the molten glass passing through the inside of the fining tube is set to 1500 ° C. to 1700 ° C.

In the method for producing a glass substrate using SnO ₂ as a fining agent, the inner wall of the fining tube is in contact with the high-temperature molten glass. Therefore, the platinum group metal gradually volatilizes from the inner wall of the clarification tube by using the clarification tube over a long period of time. This volatile matter is discharged together with bubbles in the molten glass to the outside air through the gas phase space of the clarification tube and the ventilation tube. However, the platinum group metal volatiles become supersaturated as the temperature drops in the process of being discharged to the outside air. Therefore, solidified volatiles are likely to deposit on the inner walls of the clarification tube and the ventilation tube. Hereinafter, the substance deposited on the inner wall of the clarification tube and the ventilation tube is referred to as “platinum foreign matter”. Since the inside of the ventilation pipe communicates with the outside air, the temperature tends to decrease, and platinum foreign matter is particularly likely to deposit on the inner wall of the ventilation pipe. When the platinum foreign matter grows with the passage of time, it may be peeled off by its own weight from the inner walls of the clarification tube and the aeration tube, and may fall onto the molten glass in the clarification tube. Further, when removing the platinum foreign matter deposited on the inner wall of the vent pipe, the platinum foreign matter may fall onto the molten glass in the clarification tube. And when a platinum foreign material mixes in molten glass, it will become difficult to mass-produce a high quality glass substrate.

  The objective of this invention is providing the manufacturing method of the glass substrate which can suppress that a foreign material mixes in molten glass in the clarification process of molten glass, and the manufacturing apparatus of a glass substrate.

The method for producing a glass substrate according to the present invention includes a melting step for producing a molten glass by heating a glass raw material, a clarification step for clarifying the molten glass, a molding step for forming a glass substrate from the clarified molten glass, Is provided. In the clarification step, the molten glass flows through a platinum or platinum alloy clarification tube so that a gas phase space is formed. The gas phase space is a space above the liquid surface of the molten glass inside the clarification tube. The clarification pipe has a vent pipe protruding outward from the outer wall surface of the clarification pipe. The vent pipe communicates the gas phase space and the external space of the clarification pipe. The vent pipe is provided in the highest temperature region of the temperature profile of the fine pipe in the longitudinal direction of the fine pipe. The maximum temperature region is preferably a temperature region in the range of (T _max −20) ° C. to T _max ° C., and more preferably (T _max −10) when the maximum temperature of the clarification tube is expressed as T _max ° C. ) A temperature range within the range of ° C to _Tmax ° C, and particularly preferably a temperature range within the range of ( _Tmax- 5) ° C to _Tmax ° C.

  In the manufacturing method of the glass substrate which concerns on this invention, the molten glass produced | generated by heating a glass raw material is heated by passing the inside of a high temperature clarification pipe | tube. Inside the clarification tube, bubbles contained in the molten glass grow by absorbing oxygen generated by the reduction reaction of the clarifier mixed in the molten glass. The grown bubbles rise to the liquid surface of the molten glass, break up and disappear. The gas contained in the extinguished bubbles is released into the gas phase space in the clarification tube and is discharged from the clarification tube via the vent tube.

  In the method for producing a glass substrate according to the present invention, the clarification 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 is therefore suitable as a material for a fining tube that comes into contact with high-temperature molten glass. However, the platinum component gradually volatilizes from the inner wall of the clarification tube by using the clarification tube for a long period of time. Volatile materials including platinum are discharged from the clarification tube through the vent tube together with bubbles in the molten glass. Volatile materials including platinum are likely to be supersaturated when the temperature decreases in the process of passing through the gas phase space of the clarification tube and the ventilation tube. Therefore, solidified volatiles may adhere as platinum foreign matter to the inner walls of the clarification tube and the ventilation tube.

  In the method for manufacturing a glass substrate according to the present invention, the vent pipe is connected to the outer wall surface of the clarification pipe. Electrodes used for electric heating of the clarification tube are attached to both ends of the clarification tube. Usually, since an electrode has a flange shape with a large heat dissipation effect, both ends of the clarification tube are more easily radiated than an intermediate portion between both ends of the clarification tube. Therefore, the temperature profile in the longitudinal direction of the clarification tube has an upwardly convex shape in which the temperature of the intermediate portion of the clarification tube tends to be higher than the temperature at both ends of the clarification tube. The ventilation pipe is provided in a portion where the temperature is highest in the longitudinal direction of the clarification pipe, that is, in the highest temperature region of the temperature profile of the clarification pipe. Thereby, the volatile matter containing platinum generated in the clarification pipe flows into the inside of the ventilation pipe through the space having the highest temperature in the gas phase space. Therefore, since the volatile matter containing platinum flows from the low temperature part to the high temperature part and is discharged from the vent pipe in the gas phase space, the supersaturated state of the volatile matter containing platinum in the gas phase space can be suppressed. . Thereby, it is suppressed that a platinum foreign material adheres to the inner wall in the gaseous-phase space of a clarification tube, and the inner wall of a ventilation pipe. Therefore, it is suppressed that platinum foreign materials fall from the inner wall of a clarification pipe | tube and the inner wall of a ventilation pipe, and mix with molten glass.

Further, molten glass preferably contains SnO ₂ as a fining agent. The method of manufacturing a glass substrate using SnO ₂ as a fining agent, as compared with the case of using As ₂ O ₃ as a fining agent, it is necessary to raise the temperature of the molten glass passing through the interior of the finer tube. Therefore, when SnO ₂ is used as a clarifier, the platinum component is likely to volatilize from the inner wall of the clarifier tube, and platinum foreign matter tends to adhere to the inner wall of the clarifier tube and the inner wall of the vent tube. Therefore, method of manufacturing a glass substrate according to the present invention is suitable for manufacturing method of a glass substrate using SnO ₂ as a fining agent.

A method of manufacturing a glass substrate according to the present invention, molten glass having a temperature of more than 1500 ° C. If the viscosity is 10 ^2.5 poise, when refining a high molten glass viscosity at high temperature, it is suitable. A molten glass having a high high temperature viscosity needs to have a higher temperature in the refining process than a normal alkali glass molten glass. Therefore, the problem that the platinum component volatilizes from the inner wall of the clarification tube becomes prominent, and platinum foreign matters are likely to adhere to the inner wall of the clarification tube and the inner wall of the ventilation tube.

  The manufacturing method of the glass substrate which concerns on this invention is suitable for the manufacturing method of the glass substrate using the molten glass which has a high high temperature viscosity, ie, the molten glass which needs to be made higher temperature than a normal molten glass in a refining process.

  The apparatus for producing a glass substrate according to the present invention includes a melting tank that heats a glass raw material to generate a molten glass, a clarification tube that clarifies the molten glass generated in the melting tank, and a molten glass clarified by the clarification tube. A molding apparatus for molding a glass substrate. The fining tube is a platinum or platinum alloy tube through which molten glass flows so that a gas phase space is formed. The gas phase space is a space above the liquid surface of the molten glass inside the clarification tube. The clarification pipe has a vent pipe protruding outward from the outer wall surface of the clarification pipe. The vent pipe communicates the gas phase space and the external space of the clarification pipe. The vent pipe is provided in the highest temperature region of the temperature profile of the fine pipe in the longitudinal direction of the fine pipe.

  The method for manufacturing a glass substrate and the apparatus for manufacturing a glass substrate according to the present invention can prevent foreign matters from being mixed into the molten glass in the clarification step of the molten glass.

It is a flowchart which shows the process of the glass substrate manufacturing method which concerns on embodiment. It is a schematic diagram which shows the structure of the glass substrate manufacturing apparatus which concerns on embodiment. It is an external view of the clarification pipe concerning an embodiment. It is sectional drawing in the longitudinal direction of the clarification pipe | tube which concerns on embodiment. It is a figure showing the correspondence of the side view of the clarification pipe | tube which concerns on embodiment, and the temperature profile of a clarification pipe | tube.

(1) Overall Configuration of Glass Substrate Manufacturing Apparatus An embodiment of a glass substrate manufacturing method and a glass substrate manufacturing apparatus according to the present invention will be described with reference to the drawings. FIG. 1 is a flowchart showing an example of steps of the 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 clarification step S2, a stirring step S3, a forming 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 molten glass. The molten glass is stored in a melting tank and energized and heated to have a desired temperature. A fining agent is added to the glass raw material. From the viewpoint of reducing environmental burden, SnO ₂ is used as a clarifying agent.

In the clarification step S2, the molten glass flows through the clarification tube. First, the temperature of the molten glass is raised. The refining agent causes a reduction reaction with an increase in 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 reductive reaction of the fining agent. Bubbles that have grown by absorbing oxygen float on the liquid surface of the molten glass, break up and disappear. The gas contained in the extinguished bubbles is discharged into the gas phase space in the clarification tube and finally discharged to the outside air. Next, in the refining step S2, the temperature of the molten glass is lowered. Thereby, the reduced fining agent causes an oxidation reaction and absorbs gas components such as oxygen remaining in the molten glass.

  In the stirring step S3, the clarified molten glass is stirred, and the components of the molten glass are homogenized. Thereby, the composition nonuniformity of the molten glass which is a cause of the striae etc. of a glass substrate is reduced. The homogenized molten glass is sent to the forming step S4.

  In the forming step S4, a glass ribbon is continuously formed from the molten glass by the overflow downdraw method or the float method.

  In the slow cooling step S5, the glass ribbon continuously formed in the forming step S4 is gradually cooled so as to have a desired thickness and to prevent distortion and warpage.

  In the cutting step S6, the glass ribbon slowly cooled in the slow cooling step S5 is cut into a predetermined length to obtain a glass sheet. The glass sheet is further cut into a predetermined size to obtain a glass substrate. Thereafter, the end surface of the glass substrate is ground and polished, and the glass substrate is cleaned. Further, the glass substrate is inspected for defects such as scratches, and the glass substrate that has passed the inspection is packed and shipped as a product.

  FIG. 2 is a schematic diagram illustrating an example of the configuration of the glass substrate manufacturing apparatus 200 according to the present embodiment. The glass substrate manufacturing apparatus 200 includes a melting tank 40, a clarification tube 41, a stirring device 100, a molding device 42, and transfer tubes 43a, 43b, and 43c. The transfer pipe 43 a connects the melting tank 40 and the clarification pipe 41. The transfer pipe 43 b connects the clarification pipe 41 and the stirring device 100. The transfer pipe 43 c connects the stirring device 100 and the molding device 42.

  The molten glass G produced in the melting tank 40 passes through the transfer pipe 43a and flows into the clarification pipe 41. The molten glass G clarified by the clarification tube 41 passes through the transfer tube 43b and flows into the stirring device 100. The molten glass G stirred by the stirring device 100 passes through the transfer pipe 43 c and flows into the molding device 42. In the forming apparatus 42, the glass ribbon GR is formed from the molten glass G by the overflow downdraw method. The glass ribbon GR is cut into a predetermined size in a later process, and a glass substrate is manufactured. The dimension of the glass substrate in the width direction is, for example, 500 mm to 3500 mm. The dimension of the glass substrate in the length direction is, for example, 500 mm to 3500 mm.

The glass substrate manufactured by the glass substrate manufacturing method and the glass substrate manufacturing apparatus 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. ing. As the glass substrate for FPD, non-alkali glass or alkali-containing glass is used. A glass substrate for FPD has high viscosity at high temperatures. For example, the temperature of the molten glass having a viscosity of 10 ^2.5 poise is 1500 ° C. or higher.

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

Moreover, you may use the alkali trace amount glass which contains a trace amount of alkali metals as a glass substrate for FPD. The alkali-containing glass contains 0.1% by mass to 0.5% by mass of R ′ ₂ O as a component, and preferably 0.2% by mass to 0.5% by mass of R ′ ₂ O. 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.

In addition to the above components, the glass produced according to the present invention includes SnO ₂ : 0.01% by mass to 1% by mass (preferably 0.01% by mass to 0.5% by mass), Fe ₂ O ₃ : 0. You may further contain mass%-0.2 mass% (preferably 0.01 mass%-0.08 mass%). The glass produced by the present invention, in consideration of the environmental load, substantially free of _{As 2 O 3, Sb 2 O} 3 , and PbO.

  The glass raw material prepared as described above is charged into the melting tank 40 using a raw material charging machine (not shown). The raw material input machine may input a glass raw material using a screw feeder, or may input a glass raw material using a bucket. In the melting tank 40, the glass raw material is heated and melted at a temperature according to its composition. Thereby, in the melting tank 40, the high temperature molten glass G of 1500-1600 degreeC is obtained, for example. In the melting tank 40, the molten glass G between the electrodes may be energized and heated by flowing a current between at least one pair of electrodes formed of molybdenum, platinum, tin oxide or the like. In addition, the glass raw material may be heated by supplementarily providing a flame with a burner.

  The molten glass G obtained in the melting tank 40 passes through the transfer pipe 43 a from the melting tank 40 and flows into the clarification pipe 41. The clarification tube 41 and the transfer tubes 43a, 43b, and 43c are tubes made of platinum or a platinum alloy. The clarification tube 41 is provided with a heating means similar to the melting tank 40. In the clarification tube 41, the molten glass G is clarified by further raising the temperature. For example, in the clarification tube 41, the temperature of the molten glass G is raised to 1500 ° C to 1700 ° C.

  The molten glass G clarified in the clarification tube 41 passes through the transfer tube 43b from the clarification tube 41 and flows into the stirring device 100. The molten glass G is cooled when passing through the transfer tube 43b. In the stirring device 100, the molten glass G is stirred at a temperature lower than the temperature of the molten glass G passing through the clarification tube 41. For example, in the stirring device 100, the temperature of the molten glass G is 1250 ° C to 1450 ° C. For example, in the stirring device 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 device 100.

  The molten glass G homogenized by the stirrer 100 flows from the stirrer 100 through the transfer pipe 43 c and flows into the molding device 42. When the molten glass G passes through the transfer tube 43c, it is cooled so as to have a viscosity suitable for forming the molten glass G. For example, the molten glass G is cooled to around 1200 ° C. In the shaping | molding apparatus 42, the molten glass G is shape | molded by the overflow downdraw method. Specifically, the molten glass G that has flowed into the molding apparatus 42 is supplied to a molded body 52 installed inside a molding furnace (not shown). The formed body 52 is formed of refractory bricks and has a wedge-shaped cross-sectional shape. A groove is formed on the upper surface of the molded body 52 along the longitudinal direction of the molded body 52. The molten glass G is supplied to the groove on the upper surface of the molded body 52. The molten glass G overflowing from the groove flows down along the pair of side surfaces of the molded body 52. A pair of molten glass G which flowed down the side surface of the molded body 52 joins at the lower end of the molded body 52, and the glass ribbon GR is continuously molded. The glass ribbon GR is gradually cooled as it flows downward, and then cut into a glass sheet having a desired length.

(2) Structure of clarification tube Next, the detailed structure of the clarification tube 41 is demonstrated. FIG. 3 is an external view of the clarification tube 41. FIG. 4 is a cross-sectional view of the clarification tube 41 cut vertically along the longitudinal direction of the clarification tube 41. The clarification tube 41 has, for example, a thickness of 0.5 mm to 1.5 mm and an inner diameter of 300 mm to 500 mm. A ventilation pipe 41a and a pair of heating electrodes 41b are attached to the clarification pipe 41. Inside the clarification tube 41, the molten glass G flows in a state where the gas phase space 41c is formed upward. That is, the liquid surface LS of the molten glass G exists in the clarification tube 41 as shown in FIG. The internal space of the vent pipe 41a communicates with the gas phase space 41c. Moreover, the clarification tube 41 is energized and heated by passing a current between the pair of heating electrodes 41b. Thereby, the molten glass G which passes the inside of the clarification tube 41 is heated and clarified. In the clarification process of the molten glass G, bubbles containing gaseous components such as CO ₂ , N ₂ , and SO ₂ contained in the molten glass G absorb oxygen generated by the reductive reaction of the clarifier. Bubbles grown by absorbing oxygen float on the liquid surface LS of the molten glass G, break up and disappear. The gas contained in the extinguished bubbles is released into the gas phase space 41c in the clarification tube 41, and is discharged to the outside air through the vent tube 41a.

  The ventilation pipe 41 a is attached to the outer wall surface of the clarification pipe 41 and projects outward from the clarification pipe 41. In the present embodiment, as shown in FIG. 4, the ventilation pipe 41 a is attached to the upper end portion of the outer wall surface of the clarification pipe 41 and protrudes in a chimney shape toward the upper side of the clarification pipe 41. The ventilation pipe 41 a communicates the gas phase space 41 c that is a part of the internal space of the clarification pipe 41 and the outside air that is the external space of the clarification pipe 41. The ventilation pipe 41a is formed of platinum or a platinum alloy in the same manner as the clarification pipe 41. The vent pipe 41a has a thickness of 0.5 mm to 1.5 mm, for example, and an inner diameter of 10 mm to 100 mm.

The heating electrode 41 b is a flange-shaped electrode plate that is attached to each of both ends of the clarification tube 41. The heating electrode 41b is connected to a power source (not shown). By supplying electric power to the heating electrode 41b, a current flows through the clarification tube 41 between the pair of heating electrodes 41b, and the clarification tube 41 is energized and heated. Thereby, finer tube 41, for example, is heated to 1700 ° C., molten glass G flowing in the finer tube 41, the temperature of the reduction reaction of SnO ₂ is a fining agent contained in the molten glass G occurs, for example, 1600 C. to 1650.degree. By controlling the current flowing through the clarification tube 41, the temperature of the molten glass flowing inside the clarification tube 41 can be controlled.

  FIG. 5 is a diagram illustrating a correspondence relationship between the side view of the clarification tube 41 and the temperature profile of the clarification tube 41. The upper diagram in FIG. 5 is a side view of the clarification tube 41. The lower diagram of FIG. 5 is a graph showing the temperature profile of the clarification tube 41. In the graph representing the temperature profile of the clarification tube 41, the horizontal axis represents the position in the longitudinal direction of the clarification tube 41, and the vertical axis represents the temperature of the clarification tube 41.

Since the heating electrode 41b having the flange shape has a high heat dissipation effect, the both ends of the clarification tube 41 are more easily radiated than the intermediate portion between the both ends of the clarification tube 41. Therefore, as shown in FIG. 5, both ends of the clarification tube 41, that is, the vicinity of the pair of heating electrodes 41 b are regions where the temperature is lowest in the longitudinal direction of the clarification tube 41. On the other hand, a region having the highest temperature in the longitudinal direction of the clarification tube 41 exists in an intermediate portion of the clarification tube 41. That is, the temperature profile of the clarification tube 41 has an upwardly convex shape in which the temperature of the intermediate portion of the clarification tube 41 tends to be higher than the temperature of both ends of the clarification tube 41. The ventilation pipe 41 a is provided in the maximum temperature region R of the temperature profile of the clarification pipe 41 in the longitudinal direction of the clarification pipe 41. As shown in FIG. 5, the maximum temperature region R is a region in the vicinity of the maximum temperature point P, which is a point where the temperature profile of the clarification tube 41 indicates the maximum temperature. When the maximum temperature region R represents the maximum temperature of the clarification tube 41, that is, the temperature of the clarification tube 41 at the maximum temperature point P as T _max ° C, it is preferably in the range of (T _max -20) ° C to T _max ° C. More preferably, it is a temperature range within the range of (T _max −10) ° C. to T _max ° C, and particularly preferably a temperature within the range of (T _max −5) ° C. to T _max ° C. It is an area.

  In addition, the temperature profile of the molten glass G which passes through the inside of the clarification tube 41 in the longitudinal direction of the clarification tube 41 shows the same tendency as the temperature profile of the clarification tube 41, and has an upwardly convex shape. The peak of the temperature profile of the molten glass G is located on the downstream side of the molten glass G compared to the peak of the temperature profile of the clarification tube 41. This is because the molten glass G flows inside the clarification tube 41 along the longitudinal direction of the clarification tube 41 and flows while exchanging heat with the clarification tube 41.

  Although not shown in FIGS. 3 and 4, a refractory protective layer made of alumina cement or the like is provided on the outer wall surface of the clarification tube 41. A refractory brick is further provided on the outer wall surface of the refractory protective layer. The refractory brick is placed on a base (not shown). That is, the clarification tube 41 is supported from below by the refractory protective layer and the refractory brick.

(3) Features (3-1)
In the glass substrate manufacturing method according to the present embodiment, the molten glass G generated by heating the glass raw material is heated when passing through the clarification tube 41. Inside the clarification tube 41, bubbles containing CO ₂ or SO ₂ contained in the molten glass G are removed by an oxidation-reduction reaction of SnO ₂ which is a clarifier added to the molten glass G. Specifically, first, the temperature of the molten glass G is raised to reduce the fining agent, thereby generating oxygen bubbles in the molten glass G. Bubbles containing gaseous components such as CO ₂ , N ₂ and SO ₂ contained in the molten glass G absorb oxygen generated by the reductive reaction of the fining agent. Bubbles grown by absorbing oxygen float on the liquid surface LS of the molten glass G, break up and disappear. The gas contained in the extinguished bubbles is released into the gas phase space 41c and discharged to the outside air through the vent pipe 41a. Next, the temperature of the molten glass G is lowered to oxidize the reduced fining agent. Thereby, the bubbles of oxygen remaining in the molten glass G are absorbed by the molten glass G. In this way, bubbles contained in the molten glass G are removed by the oxidation-reduction reaction of the clarifying agent.

  The clarification tube 41 is made of platinum or a platinum alloy. Platinum or a platinum alloy has a high melting point and is excellent in corrosion resistance to the molten glass G. Therefore, platinum or a platinum alloy is suitable as a material for the fining tube 41 in contact with the high temperature molten glass G. However, the platinum component gradually evaporates from the inner wall of the clarification tube 41 by using the clarification tube 41 for a long period of time. The volatile matter containing platinum is discharged into the gas phase space 41c together with the bubbles contained in the molten glass G, and discharged to the outside air through the vent pipe 41a.

  However, the volatile matter containing platinum is likely to be in a supersaturated state due to a decrease in temperature in the process of passing through the vent pipe 41a. Therefore, the solidified volatile matter adheres to the inner wall of the vent pipe 41a as platinum foreign matter. And the platinum foreign material adhering to the inner wall of the vent pipe 41a grows with progress of time. The grown platinum foreign matter may be peeled off from the inner wall surface of the vent pipe 41a due to its own weight. Further, during the maintenance work of the clarification tube 41, the platinum foreign matter may fall when the platinum foreign matter is removed from the inner wall surface of the vent pipe 41a.

  In addition, the volatile matter containing platinum may flow from the high temperature part toward the low temperature part in the process of passing through the gas phase space 41c of the clarification pipe 41 toward the vent pipe 41a, and the temperature may decrease. In this case, also in the gas phase space 41c, the volatile matter containing platinum tends to be supersaturated, and the solidified volatile matter may adhere to the inner wall of the clarification tube 41 as a platinum foreign matter. And the platinum foreign material adhering to the inner wall of the clarification pipe | tube 41 grows with progress of time, and may peel and fall from the inner wall surface of the clarification pipe | tube 41 with dead weight.

  In the present embodiment, the ventilation pipe 41 a is provided in a portion where the temperature is highest in the longitudinal direction of the clarification pipe 41, that is, in the maximum temperature region of the temperature profile of the clarification pipe 41. Thereby, the volatile matter containing platinum generated in the clarification pipe 41 flows into the ventilation pipe 41a through the space having the highest temperature in the gas phase space 41c. Therefore, since the volatile matter containing platinum flows from the low temperature portion toward the high temperature portion and is discharged from the vent pipe 41a in the gas phase space 41c, the supersaturated state of the volatile matter containing platinum in the gas phase space 41c is suppressed. The Thereby, it is suppressed that a platinum foreign material adheres to the inner wall in the gas phase space 41c of the clarification tube 41. Moreover, since the temperature of the gas flowing through the vent pipe 41a is kept as high as possible, it is possible to prevent the platinum foreign matter from adhering to the inner wall of the vent pipe 41a. Accordingly, it is possible to suppress the platinum foreign matter from falling from the inner wall of the clarification tube 41 and the inner wall of the ventilation tube 41a and being mixed into the molten glass G.

  If the vent pipe 41a is not provided in the maximum temperature region of the temperature profile of the clarification pipe 41, the temperature of the volatiles including platinum may decrease before flowing into the vent pipe 41a. In this case, there is a possibility that the volatile matter containing platinum is solidified on the inner wall of the vent pipe 41a, and platinum foreign matter adheres to the inner wall of the vent pipe 41a.

  Further, when the vent pipe 41a is not provided in the maximum temperature region of the temperature profile of the clarification pipe 41, in the gas phase space 41c of the clarification pipe 41, volatile matter containing platinum flows from the high temperature portion toward the low temperature portion. Thereby, in the gas phase space 41c, the volatile matter containing platinum whose temperature has been lowered becomes supersaturated, and solidifies on the inner wall of the clarification tube 41 and the inner wall of the ventilation tube 41a, and there is a possibility that platinum foreign matter adheres to these inner walls. is there.

  And the platinum foreign material which peeled and fell from the inner wall face of the clarification pipe | tube 41 and the inner wall face of the ventilation pipe | tube 41a may mix with the molten glass G. FIG. If platinum foreign matter is mixed into the molten glass G, there is a risk of a quality defect of the glass substrate to be manufactured. In the present embodiment, the ventilation pipe 41a is provided in the maximum temperature region of the temperature profile of the clarification pipe 41, so that platinum foreign matter is prevented from being mixed into the molten glass G, and a high-quality glass substrate is mass-produced with a high yield. be able to.

(3-2)
The glass substrate manufacturing apparatus 200 according to the present embodiment is particularly effective when SnO ₂ is used as a clarifier in the clarification tube 41 made of platinum or platinum alloy. In recent years, SnO ₂ is used as a refining agent instead of As ₂ O ₃ from the viewpoint of environmental burden. When SnO ₂ is used, the molten glass G needs to be heated to a higher temperature in the refining tube 41 than when As ₂ O ₃ is used, and thus the problem of volatilization of platinum or platinum alloy becomes significant. And if volatilization of platinum or a platinum alloy is accelerated | stimulated, a platinum foreign material will become easy to adhere to the inner wall of the clarification tube 41, and the inner wall of the ventilation pipe 41a.

In the present embodiment, even in the situation where platinum or platinum alloy volatilization is promoted and platinum foreign matter is likely to adhere to the inner wall of the clarification tube 41 and the inner wall of the ventilation tube 41a, the ventilation tube 41a has the highest temperature in the temperature profile of the clarification tube 41. By being provided in the region, the solidification of platinum or the platinum alloy is suppressed, so that the contamination of the molten glass G with the platinum foreign matter is suppressed. Therefore, the glass substrate manufacturing method according to the present embodiment is particularly effective for the manufacturing process of a glass substrate using SnO ₂ as a fining agent.

(3-3)
The glass substrate manufacturing apparatus 200 according to the present embodiment is generated from a glass raw material suitable for manufacturing a glass substrate for FPD such as a liquid crystal display, a plasma display, and an organic EL display in a clarification tube 41 made of platinum or a platinum alloy. This is particularly effective when refining molten glass.

In the clarification tube 41, the molten glass G is clarified by adjusting the viscosity of the molten glass G to a value at which bubbles contained in the molten glass G can easily float on the liquid surface. However, non-alkali glass and glass containing a small amount of alkali suitable for a glass substrate for FPD have high viscosity at high temperatures. For example, a molten glass used for forming an alkali-free glass and a glass containing a trace amount of alkali has a temperature of 1500 ° C. or higher when the viscosity is 10 ^2.5 poise. Therefore, in the refining process, it is necessary to increase the temperature of the molten glass as compared with the temperature of a normal alkali glass molten glass, and thus the problem of volatilization of platinum or a platinum alloy described above becomes significant. And if volatilization of platinum or a platinum alloy is accelerated | stimulated, a platinum foreign material will become easy to adhere to the inner wall of the clarification tube 41, and the inner wall of the ventilation pipe 41a.

  In the present embodiment, even in the situation where platinum or platinum alloy volatilization is promoted and platinum foreign matter is likely to adhere to the inner wall of the clarification tube 41 and the inner wall of the ventilation tube 41a, the ventilation tube 41a has the highest temperature in the temperature profile of the clarification tube 41. By being provided in the region, the solidification of platinum or the platinum alloy is suppressed, so that the contamination of the molten glass G with the platinum foreign matter is suppressed. Therefore, the glass substrate manufacturing method according to the present embodiment is particularly effective for the manufacturing process of the FPD glass substrate.

(4) Modification In the glass substrate manufacturing apparatus 200 according to the present embodiment, the clarification tube 41 and the vent tube 41a are formed of platinum or a platinum alloy, but may be formed of other platinum group metals. “Platinum group metal” means a metal composed 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). Platinum group metals are expensive, but have a high melting point and excellent corrosion resistance against molten glass.

41 Clearing tube 41a Venting tube 41b Heating electrode 41c Gas phase space 41d Receiving part 200 Glass substrate manufacturing apparatus G Molten glass LS Liquid glass surface R Maximum temperature region

JP 2006-522001 Gazette

Claims (4)

A melting process for heating the glass raw material to produce a molten glass;
A refining step of refining the molten glass;
A molding step of molding a glass substrate from the clarified molten glass;
With
In the clarification step, the molten glass flows inside a clarification tube made of platinum or a platinum alloy so that a gas phase space which is a space above the liquid level of the molten glass is formed,
The clarification pipe has a ventilation pipe protruding outward from the outer wall surface of the clarification pipe,
The vent pipe communicates the gas phase space and the external space of the clarification pipe, and is provided in the highest temperature region of the temperature profile of the clarification pipe in the longitudinal direction of the clarification pipe ,
The temperature profile shows a tendency that the temperature of the intermediate portion in the longitudinal direction of the clarification tube is higher than the temperature at both ends in the longitudinal direction of the clarification tube,
A method for producing a glass substrate. The molten glass contains SnO ₂ as a fining agent,
The manufacturing method of the glass substrate of Claim 1. The molten glass has a temperature of 1500 ° C. or higher when the viscosity is 10 ^2.5 poise.
The manufacturing method of the glass substrate of Claim 1 or 2. A melting tank for heating glass raw material to produce molten glass;
A refining tube for refining the molten glass produced in the melting tank;
A molding apparatus for molding a glass substrate from the molten glass clarified by the clarification tube;
With
The clarified tube is a tube made of platinum or a platinum alloy in which the molten glass flows inside so that a gas phase space that is a space above the liquid level of the molten glass is formed,
The clarification pipe has a ventilation pipe protruding outward from the outer wall surface of the clarification pipe,
The vent pipe communicates the gas phase space and the external space of the clarification pipe, and is provided in the highest temperature region of the temperature profile of the clarification pipe in the longitudinal direction of the clarification pipe ,
The temperature profile shows a tendency that the temperature of the intermediate portion in the longitudinal direction of the clarification tube is higher than the temperature at both ends in the longitudinal direction of the clarification tube,
Glass substrate manufacturing equipment.

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