JP2016069262A - Manufacturing method for glass substrate and manufacturing apparatus for glass substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method for a glass substrate etc., that can suppress part of an aggregate from being mixed as foreign matter with molten glass by suppressing aggregation of platinum group metal vaporized in a vapor phase space of a glass processing device made at least partially of a material including the platinum group metal.SOLUTION: There is provided a manufacturing method for a glass substrate which comprises a glass processing device made of platinum group metal, the method comprising: forming a vapor phase space above the liquid level of molten glass in the glass processing device; and processing the molten glass while reducing the amount of foreign matter powder dust present in the vapor phase space so as to suppress aggregation of platinum volatile matter included in the vapor phase space at a temperature at which the platinum group metal vaporizes in the glass processing device.SELECTED DRAWING: Figure 4

Description

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

A glass substrate is generally produced by forming molten glass from a glass raw material, and then forming the molten glass into a glass substrate through a clarification step and a homogenization step.
By the way, in order to mass-produce high-quality glass substrates from high-temperature molten glass, consideration should be given so that foreign substances that cause defects in the glass substrate do not enter the molten glass from any apparatus that manufactures the glass substrate. Is desired. For this reason, the inner wall of the member in contact with the molten glass in the manufacturing process of the glass substrate needs to be made of an appropriate material according to the temperature of the molten glass in contact with the member, the required quality of the glass substrate, and the like. For example, since molten glass is in a high temperature state after it is produced and supplied to the molding process, a clarification device that performs a clarification process, a stirring device that performs a homogenization process, and a glass supply pipe that transfers the molten glass Is made of platinum group metal which is platinum or platinum alloy having high heat resistance. However, platinum group metals are likely to volatilize at high temperatures required for glass melting. The volatiles of the platinum group metal aggregate on the inner wall surrounding the gas phase space to form an aggregate. A part of the aggregate separates and enters the molten glass as a foreign substance, resulting in a deterioration in the quality of the glass substrate. There was a risk of inviting.

On the other hand, there is known a glass melting furnace that can obtain a high-quality glass that is less likely to be mixed with platinum foreign matter and has few optical defects such as cord striae and foreign matter defects (Patent Document 1).
In the glass melting furnace, the lower part of the inner wall surface of the tank body closed by providing a ceiling is formed by a platinum surface made of platinum or a platinum alloy, and the platinum surface has an upper end at the upper part of the molten glass tank. It is formed so as to be a position not exposed in the atmosphere.

JP 2010-202444 A

  If the contact surface between the atmosphere of the gas phase space above the liquid surface of the molten glass and the wall surface of the platinum group metal is eliminated as in Patent Document 1, volatilization of the platinum group metal does not occur. Further, it is considered that volatilization of the platinum group metal can be reduced by reducing the contact area of the inner wall of the platinum group metal that is in contact with the atmosphere of the gas phase space. However, even when the contact area of the inner wall of the platinum group metal in contact with the atmosphere in the gas phase space is reduced, the volatilization of the platinum group metal cannot be sufficiently reduced from the wall surface, and the platinum group metal aggregates. It was. In the gas phase space, minute substances such as brick waste float. When such a minute substance floats, platinum aggregates using the suspended substance as a nucleus. In order to suppress the aggregation of the platinum group metal in the gas phase space, it is necessary to reduce the substance serving as a nucleus in the gas phase space.

  In view of this, the present invention is a method for producing foreign matter dust existing in a glass processing apparatus when processing molten glass in a glass processing apparatus that is used in a glass substrate manufacturing process and is made of a material containing at least a platinum group metal. By reducing the amount, a method for producing a glass substrate that suppresses aggregation of the platinum group metal volatilized in the gas phase space and suppresses that a part of the aggregate becomes a foreign substance and enters the molten glass. And it aims at providing the manufacturing apparatus of a glass substrate.

One aspect of the present invention is a method of manufacturing a glass substrate including a glass processing apparatus composed of a platinum group metal,
Inside the glass processing apparatus, a gas phase space is formed above the liquid surface of the molten glass,
Reduce the amount of foreign dust present in the gas phase space so as to suppress aggregation of platinum volatiles contained in the gas phase space above the temperature at which the platinum group metal volatilizes inside the glass processing apparatus. Treating the molten glass;
It is characterized by that.

  Regarding the amount of foreign matter dust in the gas phase space, the number of foreign matter dust having a particle size of 0.3 μm to less than 5 μm is 3000000 / L or less, and the number of foreign matter dust having a particle size of 5 μm or more is 300000 / L or less. It is preferable that there is.

  The amount of the foreign dust is preferably reduced by suctioning foreign dust existing in the gas phase space and / or inflow of clean gas into the gas phase space.

  The foreign dust is preferably fine particles made of one of alumina, zirconia, zircon, tin oxide, and boric acid, or a combination thereof.

Another aspect of the present invention is a glass substrate manufacturing apparatus including a glass processing apparatus made of a platinum group metal,
Inside the glass processing apparatus, a gas phase space is formed above the liquid surface of the molten glass,
Reduce the amount of foreign dust present in the gas phase space so as to suppress aggregation of platinum volatiles contained in the gas phase space above the temperature at which the platinum group metal volatilizes inside the glass processing apparatus. Treating the molten glass;
It is characterized by that.

  ADVANTAGE OF THE INVENTION According to this invention, in the process of processing the molten glass before shaping | molding of a glass substrate, aggregation of the volatile matter of the platinum group metal volatilized within the gaseous-phase space of a glass processing apparatus can be reduced. Thereby, it can suppress that a foreign material mixes in 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 the external view which mainly represented the clarification pipe | tube which concerns on embodiment. It is a schematic sectional drawing in the longitudinal direction of the clarification pipe | tube which concerns on embodiment. It is a figure showing an example of a temperature profile of a sectional view showing the inside of a clarification pipe concerning an embodiment, and a clarification pipe. It is a schematic diagram for demonstrating that the platinum group metal which volatilized by using the particle | grains of a foreign dust as a nucleus aggregates.

(Glass substrate manufacturing method and glass substrate manufacturing apparatus)
DESCRIPTION OF EMBODIMENTS Embodiments 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 refining step S2, a stirring step S3, a forming step S4, a slow cooling step S5, and a cutting step S6.
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.

In the melting step S1, molten glass is produced by melting glass raw materials. The molten glass is stored in a melting tank and heated to have a desired temperature. The molten glass contains a fining agent. From the viewpoint of reducing the environmental load, tin oxide is suitably used as a fining agent.
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 degreeC-1620 degreeC is obtained, for example. In the melting tank 40, the molten glass G between the electrodes may be energized and heated by passing an electric current between at least one pair of electrodes. In addition to the energization heating, a flame by the burner is supplementarily given. The glass raw material may be heated.

In the clarification step S2, the molten glass flows inside the transfer tube and 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 contained in the molten glass grow by absorbing the released oxygen, rise to the liquid surface of the molten glass, break up and disappear. 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.
Specifically, 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 group metal that is platinum or a platinum alloy. 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 have a high melting point and are excellent in corrosion resistance to molten glass. The clarification tube 41 is provided with a heating means similar to the melting tank 40. At least the transfer pipe 43a is also provided with a heating means. In the clarification step S2, the molten glass G is clarified by further raising the temperature. For example, the temperature of the molten glass G in the clarification tube 41 is 1600 ° C to 1720 ° 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 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.
Specifically, 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 1100 to 1300 ° C.

In the forming step S4, the sheet glass is continuously formed from the molten glass by the overflow downdraw method or the float 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). 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 sheet glass GR is continuously molded.

In the slow cooling step S5, the sheet glass continuously formed in the forming step S4 has a desired thickness and is gradually cooled so as not to be distorted and warped.
In cutting process S6, the sheet glass annealed in slow cooling process S5 is cut | disconnected by predetermined length, and a glass sheet is obtained. The glass sheet is further cut into a predetermined size to obtain a glass substrate.

As described above, the glass substrate manufacturing method of the present embodiment includes a melting step of melting glass raw material to produce a molten glass, and a processing step of processing the molten glass in the glass processing device, for example, a molten glass in a clarification device. A clarification step of clarification. The glass processing apparatus has a liquid phase in which a molten glass flows, a gas phase space formed by a liquid surface and a wall of the molten glass, and at least a part of the wall surrounding the gas phase space is a material containing a platinum group metal. It is configured.
Hereinafter, although it demonstrates using the clarification apparatus containing the clarification pipe | tube 41 as a glass processing apparatus, a glass processing apparatus is provided between the melting tank 40 and the shaping | molding apparatus 42, and is an apparatus which performs predetermined processing to the molten glass G As long as it is, it is not particularly limited. In addition to the refining device, the glass processing device can be, for example, a stirring device or a transfer pipe for transferring molten glass. Therefore, the process of the molten glass G includes the process of homogenizing the molten glass, the process of transferring the molten glass, and the like in addition to the process of clarifying the molten glass.

(Application example of glass substrate)
The glass substrate manufactured by the glass substrate manufacturing method of the present embodiment 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 and a cover glass for protecting the display. Yes. 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.

(Glass composition)
In the melting tank 40, the glass raw material is melted by heating means (not shown), and 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 : 0. 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. Alkaline trace containing glass, as component, 'comprises ₂ O, preferably, 0.2 wt% to 0.5 wt% R' of R 0.1 wt% to 0.5 wt% including the 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.

(Configuration of clarification tube)
Next, the structure of the clarification pipe | tube 41 of a clarification apparatus is demonstrated in detail. In addition to the clarification pipe 41, the clarification apparatus includes a vent pipe 41a, a heating electrode 41b, and a refractory protective layer (not shown) and a refractory brick that surround the outer periphery of the clarification pipe 41. FIG. 3 is an external view mainly showing the clarification tube 41. FIG. 4 is a schematic cross-sectional view in the longitudinal direction of the clarification tube 41.

  A ventilation pipe 41a and a pair of heating electrodes 41b are attached to the clarification pipe 41. The clarification tube 41 has a gas phase space 41 c formed therein from the liquid phase in which the molten glass G flows, the liquid level LS of the molten glass G, and the wall of the clarification tube 41. The gas phase space 41 c is formed along the flow direction of the molten glass G. At least a part of the wall surrounding the gas phase space 41c is made of a material containing a platinum group metal. In the present embodiment, the entire wall surrounding the gas phase space 41c is made of a material containing a platinum group metal.

  The vent pipe 41a is provided in the middle of the direction in which the molten glass G flows and is provided on a wall in contact with the gas phase space 41c, and communicates the gas phase space 41c with the atmosphere outside the clarification tube 41. The vent pipe 41a is preferably formed of a platinum group metal, like the clarification pipe 41. Since the temperature of the vent pipe 41a is likely to decrease due to the heat dissipation function, the vent pipe 41a may be provided with a heating mechanism for heating the vent pipe 41a.

The pair of heating electrodes 41b are flange-shaped electrode plates provided at both ends of the clarification tube 41a. The heating electrode 41b allows a current supplied from a power source (not shown) to flow through the clarification tube 41, and the clarification tube 41 is energized and heated by this current. When tin oxide is used as the fining agent, for example, the fining tube 41 is heated so that the maximum temperature is 1600 ° C to 1750 ° C, more preferably 1630 ° C to 1750 ° C, and the molten glass G has a maximum temperature reduction reaction of tin oxide. For example, 1600 ° C. to 1720 ° C., more preferably 1620 ° C. to 1720 ° C. By controlling the current flowing through the clarification tube 41, the temperature of the molten glass G flowing inside the clarification tube 41 can be controlled. The heating electrode 41b is provided with a cooling pipe (not shown) so as to be in contact with the heating electrode 41b in order to suppress damage due to overheating of the heating electrode 41b. When the heating electrode 41b is cooled by the cooling pipe, the clarification pipe 41a and the gas phase space 41c in the vicinity of the heating electrode 41b are also cooled. For this reason, the area | region where temperature becomes low is formed in the vicinity of the heating electrode 41b. In the region where the temperature is low, volatiles tend to aggregate. Here, the vicinity means, for example, within a range of 50 cm from a predetermined position (here, the position of the heating electrode 41b).
Although a pair of heating electrodes 41b are provided in the clarification tube 41, the number of clarification tubes 41 is not particularly limited. The temperature of the wall in contact with the gas phase space 41c of the clarification tube 41 by energization heating by the heating electrode 41b is, for example, in the range of 1500 to 1750 ° C.

Inside the clarification tube 41, bubbles containing CO ₂ or SO ₂ contained in the molten glass G are removed by a redox agent added to the molten glass G, for example, an oxidation-reduction reaction of tin oxide. 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 clarifying agent. The bubbles that have grown by absorbing oxygen float on the liquid surface of the molten glass G and release the bubbles, that is, they disappear and disappear. The gas contained in the extinguished bubbles is discharged into the gas phase space 41c and discharged to the outside of the clarification tube 41 through the vent tube 41a. Next, the temperature of the molten glass G is lowered to oxidize the reduced fining agent. Thereby, the oxygen of the bubble which remains in the molten glass G is absorbed by the molten glass G (absorption process). Thus, the remaining bubbles are reduced and disappear. In this way, bubbles contained in the molten glass G are removed by the oxidation-reduction reaction of the clarifying agent.

  Although not shown, a refractory protective layer is provided on the outer wall surface of the clarification tube 41. A refractory brick is further provided outside the refractory protective layer. The refractory brick is placed on a base (not shown).

  A dust collecting device 44 for controlling the amount of dust in the gas phase space 41 c is provided on the outer wall side of the clarification tube 41. The dust collector 44 includes, for example, a pipe 44a that sucks gas, a filter that adsorbs dust contained in the sucked gas, a dust sensor, and the like. The dust collector 44 controls the amount of dust in the gas phase space 41c by sucking the gas in the gas phase space 41c from the pipe 44a and adsorbing foreign dust contained in the gas in the gas phase space 41c. If the amount of dust in the gas phase space 41c is large, that is, if a large number of particles of foreign matter dust exist in the gas phase space 41c, the volatilized platinum group metal aggregates with the foreign matter dust as a nucleus. Here, foreign dust is generated from refractories, refractory bricks, etc., alumina, zirconia, a kind of zircon, etc., or volatiles from molten glass, such as tin oxide, boric acid, etc. Fine particles that are a combination of fine particles floating in the air and adhering to the walls. However, other components may be included without departing from the assertion of the present case. In the present embodiment, the amount of dust in the gas phase space 41 c is controlled so as to suppress the aggregation of the platinum group metal in the gas phase space 41 c of the clarification tube 41. By controlling the amount of dust in the gas phase space 41c, it is possible to prevent the platinum group metal from aggregating on the inner wall of the clarification tube 41 or the like. This point will be described later. As a method for controlling the amount of dust in the gas phase space 41c and a method for removing dust adhering to the inner wall of the clarification tube 41, known methods can be used. Further, the pipe 44a may be provided with a heating mechanism for heating the pipe 44a in the same manner as the vent pipe 41a because the temperature of the pipe 44a is likely to decrease due to the heat radiation function of the vent pipe 41a. Alternatively, the pipe 44a may be connected to the tip of the vent pipe 41a instead of putting the pipe 44a into the vent pipe 41a, and dust may be collected from the entire vent pipe 41a. Further, the effect of removing dust may be enhanced by flowing clean air from the ventilation pipe 41a or another ventilation hole opened in the wall of the clarification pipe 41a. In this case, the gas to be introduced is not limited to air, but may be, for example, nitrogen, oxygen, argon, a mixed gas thereof, or other clean gas. As another form of method, the amount of dust in the clarification tube 41 is indirectly controlled by controlling the amount of dust in the entire room where the clarification tube 41 is installed without using the pipe 44a. You may use the method of controlling. Since the gas phase space 41c and the outside of the clarification tube 41 (the room in which the clarification tube 41 is installed) are communicated with each other through the ventilation tube 41a, the amount of dust outside the clarification tube 41 is reduced, so that the inside of the gas phase space 41c The amount of dust can be reduced. Also in this case, a known method can be used as a method for controlling the amount of dust in the gas phase space 41c and a method for collecting the dust in the gas phase space 41c.

  In such a clarification step, a temperature gradient is provided along the upstream or downstream direction, which is the flow direction of the molten glass G, in the space of the gas phase space 41c and the wall of the clarification tube 41 forming the gas phase space 41c. A temperature gradient region is formed. This temperature gradient region is formed using at least one of heating and heat dissipation of the clarification tube 41. In the temperature gradient region where the temperature is high, the amount of tin oxide volatilized from the molten glass increases. In the present embodiment, the high temperature region of the gas phase space 41c is a region away from the heating electrode 41b and the vent pipe 41a. FIG. 5 shows an example of the temperature profile of the clarification tube 41 (the temperature profile of the wall in contact with the gas phase space 41c of the clarification tube 41 in the X direction) expressed in accordance with the position of the clarification tube 41 in the X direction. In the temperature profile, the temperature is the highest between the end 41d of the clarification tube 41 on the side where the molten glass G flows and the vent tube 41a. A temperature gradient is formed such that the temperature decreases from the highest temperature position P toward the end 41 d of the clarification tube 41. Similarly, a temperature gradient is formed in which the temperature decreases from the highest temperature position P toward the position of the vent pipe 41a in the X direction. In addition to the above, the temperature gradient region is also formed between the position in the X direction of the ventilation tube 41a and the end 41e of the clarification tube 41 on the side where the molten glass G flows out. Since the temperature of the clarification tube 41 and the temperature of the gas phase space 41 c have a correlation, the temperature profile of the gas phase space 41 c is the same as the temperature profile of the clarification tube 41. Here, since the low temperature regions 41f and 41g are formed in the vicinity of the heating electrode 41b and the vent pipe 41a, recrystallization of volatiles from molten glass such as tin oxide is likely to occur. For this reason, in the gas phase space 41c, in the vicinity of the heating electrode 41b and the vent pipe 41a, the low temperature regions 41f and 41g, that is, the number of foreign particles due to the volatile matter from the molten glass is large, and the aggregation of the platinum volatile matter A region where susceptibility is likely to occur is formed. In particular, since the vicinity of the vent pipe 41a is connected to the external space, there is a large amount of foreign matter inflow due to the refractory and the refractory bricks. Therefore, by reducing the amount of dust in a region where the number of foreign dusts is large and aggregation of platinum group metal volatiles is likely to occur, it is possible to suppress aggregation of platinum group metal volatiles in the gas phase space 41c.

FIG. 6 is a schematic diagram for explaining that the platinum group metal volatilized using foreign dust (for example, brick dust) as a nucleus aggregates. When the volatilized platinum group metal (Pt) touches the brick dust (D) in the gas phase space 41c, a platinum group metal solid is deposited using the brick dust as a nucleus. Volatilized platinum group metal is further adsorbed on the platinum group metal precipitates, and the precipitates grow, whereby aggregates of platinum group metals are formed in the gas phase space 41c. In addition, when there is a large amount of foreign matter dust in the gas phase space 41c, a large number of foreign matter dust is also attached to the inner wall of the gas phase space 41c. The volatilized platinum group metal generates aggregates of the platinum group metal with the foreign dust adhering to the inner wall of the gas phase space 41c as a nucleus. When the aggregate of platinum group metal formed on the inner wall of the gas phase space 41 c peels off and falls onto the molten glass M, the foreign material of the platinum group metal is mixed into the molten glass G. In general, platinum group metal is likely to precipitate at an interface with a foreign object such as brick scrap. Therefore, when the area of the interface between the foreign dust and the gas phase is large, the number of aggregates of platinum volatiles to be generated increases. For this reason, in order to suppress aggregation of platinum volatiles, it is necessary to reduce the area of the interface in contact with the gas phase. Aggregation of platinum volatiles can be suppressed by reducing the number of foreign particles and reducing the total area of the interface between foreign particles and platinum volatiles. Further, by reducing the particle size of the foreign dust, that is, by removing the foreign dust having a large particle size, the area of the interface in contact with the gas phase can be reduced, and aggregation of platinum volatiles can be suppressed. When the foreign particle dust is a sphere and the average particle size of the foreign particle dust is r, the total area S of the interface is obtained by multiplying the area 4π (r / 2) ² of the single foreign particle by the number n of the foreign particle dust. Therefore, S = n × πr ² is obtained. Therefore, in the present embodiment, the dust collection device 44 is used to remove foreign matter dust in the gas phase space 41c, thereby reducing the number n of foreign matter dust and removing foreign matter dust having a large particle size to remove foreign matter. By reducing the average particle size r of the dust, aggregation of platinum group metal volatiles is suppressed.

  In the present embodiment, when the temperature of the gas phase space 41c is, for example, 1400 ° C. or more as the temperature at which the platinum group metal volatilizes, the particle size in the gas phase space 41c is 0.3 μm or more to less than 5 μm using the dust collector 44. The gas phase space 41c is collected so that the number of foreign particles is 3000000 / L or less and the number of foreign particles having a particle diameter of 5 μm to less than 300 μm is 300000 / L. Thereby, it is possible to suppress the aggregation of platinum volatiles by using foreign matter dust as a nucleus, and it is possible to prevent foreign matters that are aggregates of platinum group metals from being mixed into the molten glass G.

The production method according to the present embodiment is particularly effective when tin oxide is used as a fining agent in the fining tube 41 made of a platinum group alloy. In recent years, tin oxide is used as a refining agent instead of As ₂ O ₃ from the viewpoint of environmental burden. When tin oxide is used, the molten glass G needs to be heated to a higher temperature in the clarification tube 41 than when As ₂ O ₃ is used, and thus the problem of volatilization of the platinum group metal becomes significant. When the volatilization of the platinum group metal is promoted, the volatiles of the platinum group metal are easily aggregated and adhered to the inner wall of the clarification tube 41 and the inner wall of the ventilation tube 41a. When the molten glass G becomes higher temperature in the clarification tube 41, the tin oxide volatiles also increase. For this reason, since the aggregation of platinum group metal volatiles can be suppressed by collecting the dust in the gas phase space 41c and reducing the number of tin oxide volatiles serving as nuclei, the manufacturing method of this embodiment is effective. It is. Moreover, since it can suppress that a platinum group metal aggregates on the inner wall etc. of the clarification pipe | tube 41 by reducing the dust amount in the gaseous-phase space 41c, it implements simply, without changing the structure of the clarification pipe | tube 41. be able to.

The production method of the present embodiment can be applied in the production of a glass substrate for FPD, the production of a cover glass for protecting a display, the production of glass for a magnetic disk, or the production of a glass substrate for a solar cell. In particular, the manufacturing method of the present embodiment uses molten glass produced 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 a platinum group metal. It is effective when clarifying.
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, the molten glass G used to mold the alkali-free glass and the alkali-containing glass has a temperature of 1500 ° C. or higher when the viscosity is 10 ^2.5 poise. Therefore, in the clarification step, it is necessary to increase the temperature of the molten glass as compared with the temperature of a normal alkali glass molten glass, so that the above-described problem of volatilization of the platinum group metal becomes remarkable. When the volatilization of the platinum group metal is promoted, the aggregates of the platinum group metal are likely to adhere to the inner wall of the clarification tube 41 and the inner wall of the ventilation tube 41a as foreign matter. In this respect, the manufacturing method of the present embodiment is effective.

  Hereinafter, the present invention will be described in more detail with reference to examples. In addition, this invention is not limited to a following example.

Example 1
Using tin oxide as a fining agent and clarifying the molten glass using the fining tube 41 shown in FIG. 3, adjusting the dust collection amount of the above embodiment, and after fining, the thickness is 2270 mm × 2000 mm, and the thickness is The glass sheet was formed into 0.5 mm sheet glass to prepare 100 glass substrates (Examples).
The amount of dust in the gas phase space 41c of the clarification tube 41 is adjusted by using the dust collector 44 to suck the gas in the gas phase space 41c from the pipe 44a and remove the dust contained in the gas in the gas phase space 41c. It was done by doing. The temperature of the gas phase space 41c was set to 1400 ° C. or higher, the amount of dust in the gas phase space 41c was adjusted, and the presence or absence of platinum foreign matter on the glass substrate was visually confirmed. The amount of dust in the gas phase space 41c is (1) the number of foreign particles having a particle size of 0.3 μm to less than 5 μm is more than 3000000 / L to 10000000 / L and foreign particles having a particle size of 5 μm to less than 300 μm Environment when the number of dust is more than 300,000 / L to 1,000,000 / L, (2) The number of foreign dust with a particle size of 0.3 μm to less than 5 μm is more than 1,000,000 / L to less than 3000000 / L And the environment when the number of foreign dust particles having a particle size of 5 μm or more and less than 300 μm is more than 10,000 / L to 300,000 particles / L, (3) The number of foreign dust particles having a particle size of 0.3 μm or more and less than 5 μm is 300,000. Environment in which the number of foreign matter dust having a particle size of 5 μm or more and less than 300 μm is more than 1000 / L to 10000 / L or less, and (4) a particle size of 0.3 μm. Was adjusted to above the number of ~5μm less foreign material dust is the number of foreign matter dust below ～300Myuemu 300000 pieces / L or less was in a particle size 5μm or the 1000 / L or less in the case of the environment. Moreover, it adjusted so that it might become an environment whose number of the foreign material dust of about 400 micrometers particle size is about 20000 pieces / L. The glass composition of the glass substrate was as follows: SiO ₂ 66.6 mol%, Al ₂ O ₃ 10.6 mol%, B ₂ O ₃ 11.0 mol%, MgO, CaO, SrO and BaO combined 11.4 Molten%, the strain point was 660 ° C., and the temperature of the molten glass when the viscosity was 10 ^2.5 poise was 1570 ° C.

  As a result, the average number of foreign platinum particles in the glass substrate produced in an environment where the number of foreign dust particles having a particle size of about 400 μm was about 2000000 / L was 250. On the other hand, (1) the number of foreign matter dust having a particle size of 0.3 μm or more and less than 5 μm is more than 3000000 / L and less than 10000000 / L, and the number of foreign matter dust having a particle size of 5 μm or more and less than 300 μm. The number of platinum foreign objects on the glass substrate produced under the environment of more than 300000 pieces / L to 1000000 pieces / L or less is an average of 25 pieces, and (2) the number of foreign matter dust particles having a particle size of 0.3 μm to less than 5 μm. Of a glass substrate produced in an environment where the number of foreign particles having a particle size of more than 1000000 / L to 3000000 / L or less and a particle size of 5 μm to less than 300 μm is more than 10,000 / L to 300000 / L The average number of foreign particles of platinum is 5, and (3) the number of foreign particles having a particle size of 0.3 μm to less than 5 μm is more than 300000 / L to 1000000 / L and the particle size is 5 μm to 300 μm. The number of platinum foreign objects on the glass substrate produced under the environment when the number of foreign object dusts is more than 1000 / L to 10000 / L or less is 1.5 on average, and (4) a particle size of 0.3 μm to 5 μm. The number of foreign foreign particles less than 300,000 / L and the number of foreign foreign particles having a particle diameter of 5 μm or more and less than 300 μm is 1000 / L or less is the average number of platinum foreign objects on the glass substrate produced in the environment. There were 0.2. Accordingly, the number of foreign dust particles having a particle size of 0.3 μm to less than 5 μm is 3000000 / L or less, and the number of foreign dust particles having a particle size of 5 μm to less than 300 μm is set to 300000 pieces / L or less. By doing this, aggregation of platinum group metal volatiles could be suppressed, and the number of platinum foreign matter could be reduced. Further, the number of foreign matter dust having a particle size of 0.3 μm or more and less than 5 μm is more than 3000000 / L to 10000000 / L or less, and the number of foreign matter dust having a particle size of 5 μm or more to less than 300 μm is more than 300000 / L to 1000000. Even under an environment of less than / L, the amount of platinum foreign matter contained in the glass substrate increases, but it was found that aggregation of platinum group metal volatiles can be suppressed.

  As mentioned above, although the manufacturing method of the glass substrate and the manufacturing apparatus of the glass substrate of this invention were demonstrated in detail, this invention is not limited to the said embodiment, In the range which does not deviate from the main point of this invention, various improvement and a change are carried out. Of course.

40 melting tank 41 clarification pipe 41a vent pipe 41b heating electrode 41c gas phase space 42d end 42 molding apparatus 43a, 43b. 43c Transfer pipe 44 Dust collector 44a Pipe 52 Molded body 100 Stirrer 200 Glass substrate manufacturing apparatus G Molten glass

Claims (5)

A method for producing a glass substrate comprising a glass processing apparatus composed of a platinum group metal,
Inside the glass processing apparatus, a gas phase space is formed above the liquid surface of the molten glass,
Reduce the amount of foreign dust present in the gas phase space so as to suppress aggregation of platinum volatiles contained in the gas phase space above the temperature at which the platinum group metal volatilizes inside the glass processing apparatus. Treating the molten glass;
A method for producing a glass substrate, comprising: Regarding the amount of foreign matter dust in the gas phase space, the number of foreign matter dust having a particle size of 0.3 μm to less than 5 μm is 3000000 / L or less, and the number of foreign matter dust having a particle size of 5 μm to less than 300 μm is 300000 / L or less,
The method for producing a glass substrate according to claim 1. The amount of foreign dust is reduced by sucking foreign dust existing in the gas phase space and / or by flowing clean gas into the gas phase space.
The manufacturing method of the glass substrate of Claim 1 or 2 characterized by the above-mentioned. The foreign matter dust is fine particles made of alumina, zirconia, zircon, tin oxide, and boric acid, or a combination thereof.
The manufacturing method of the glass substrate as described in any one of Claims 1-3 characterized by the above-mentioned. A glass substrate manufacturing apparatus comprising a glass processing apparatus made of a platinum group metal,
Inside the glass processing apparatus, a gas phase space is formed above the liquid surface of the molten glass,
Reduce the amount of foreign dust present in the gas phase space so as to suppress aggregation of platinum volatiles contained in the gas phase space above the temperature at which the platinum group metal volatilizes inside the glass processing apparatus. Treating the molten glass;
An apparatus for producing a glass substrate.

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