JPWO2012133467A1 - Manufacturing method of glass plate - Google Patents

Abstract

A step of conveying molten glass containing at least SnO2 from the melting tank (101) to the clarification tank (102) via the first transfer pipe (105a) (connection pipe) made of platinum or a platinum alloy, It is a manufacturing method of the glass plate which has the clarification process which defoams the foam contained in a molten glass in the clarification tank (102) made from platinum or a platinum alloy which has the space to accommodate. In the manufacturing method of the said glass plate, the temperature of a molten glass is heated at 1500 to 1690 degreeC in a 1st transfer pipe | tube (105a) (connection pipe), and the temperature of a molten glass is 1600-1780 in a clarification tank (102). Heat to ° C. The temperature of the molten glass in the clarification tank (102) is higher than the temperature of the molten glass in the first transfer pipe (105a) (connection pipe).

Description

  The present invention relates to a method for producing a glass plate.

  Glass manufacturers have been plagued by bubbles that form in the glass during the manufacturing process. In particular, a glass plate for a glass substrate or a cover glass of a liquid crystal display device is required to have an extremely small bubble content. Therefore, clarification of molten glass is performed to remove bubbles, but various methods for clarification have been developed. For example, Patent Document 1 (Japanese translations of PCT publication No. 2008-539162) proposes a technique for controlling the atmosphere around the clarification tank in order to clarify the molten glass effectively.

The clarification is also performed by using a clarifier such as As ₂ O ₃ . However, in recent years, from the viewpoint of reducing the environmental burden, it has been demanded to limit the use of highly used As ₂ O ₃ which has been conventionally used. Therefore, instead of As ₂ O _3, poor refining capabilities compared to As ₂ O _3, and the temperature which exhibits the fining (defoaming) function, that is, as vigorously temperature is high, such as SnO ₂ is fining agent to release oxygen It is used. Therefore, when using such SnO ₂ as a fining agent, there is a problem that it is impossible to sufficiently reduce the number of bubbles in the glass plate in as compared with the case of using As ₂ O ₃ as a fining agent.

Here, the technique described in Patent Document 1 cannot sufficiently extract the clarification function of the clarifier when a clarifier such as SnO ₂ other than As ₂ O ₃ which is an environmental load factor is used. was there. In recent years, the demand for the number of bubbles of glass plates used in electrical products such as displays has been increasing day by day, and the technology described in Patent Document 1 alone has not been able to sufficiently meet the demand. .

  The above method requires complicated atmosphere control, and the equipment becomes complicated. Therefore, there is still a need for a simple and effective method for refining molten glass.

The object of the present invention has been made in view of the above problems, and is a glass plate capable of sufficiently reducing the number of bubbles even when a clarifying agent such as SnO ₂ other than As ₂ O ₃ is used. It is to provide a manufacturing method. Another object of the present invention is to provide a method for producing a glass plate that is capable of clarifying molten glass simply and effectively.

The method for producing a glass plate according to the present invention includes a step of transporting molten glass containing at least SnO ₂ from a melting tank to a clarification tank via a platinum or platinum alloy connecting tube, and a space for storing gas by defoaming. The clarification tank made of platinum or platinum alloy has a clarification step of defoaming bubbles contained in the molten glass out of the molten glass. The temperature of the molten glass is heated to 1500 ° C. to 1690 ° C. in the connecting pipe, the molten glass temperature is heated to 1600 to 1780 ° C. in the clarification tank, and the molten glass temperature in the clarification tank is higher than the temperature of the molten glass in the connecting pipe. It is also characterized by high.

In the method for producing a glass plate according to the present invention, the molten glass is already heated to a temperature suitable for clarification in the connecting pipe before being sent to the clarification tank, so the clarification of the molten glass is sent to the clarification tank. It is promoted immediately after being done. Therefore, according to the manufacturing method for a glass plate according to the present invention, even when using a clearing agent such as SnO ₂ other than As ₂ O _3, it is possible to pull out the refining effect sufficiently, the glass plate in The number of bubbles can be sufficiently reduced.

  Moreover, it is preferable that the manufacturing method of the glass plate which concerns on this invention heats the temperature of a molten glass to 1550 to 1690 degreeC within a connecting pipe, and heats the molten glass temperature to 1620 to 1780 degreeC within a clarification tank.

  In addition, the method for producing a glass plate according to the present invention includes a melting step in which a glass material is heated and melted in a melting tank to generate molten glass, and a molten glass is connected from the melting tank to a connecting tube made of platinum or a platinum alloy. Through a clarification tank made of platinum or platinum alloy, and a clarification process in which the molten glass is heated and clarified in the clarification tank. The molten glass flowing through the connecting pipe is heated to about 1600 ° C. to about 1650 ° C. by the connecting pipe, and the molten glass in the clarification tank is heated to about 1650 to about 1700 ° C. by the clarification tank.

  Here, since the molten glass is already heated to a temperature suitable for clarification in the connecting pipe before being sent to the clarification tank, clarification of the molten glass is promoted immediately after the molten glass is sent to the clarification tank. Thus, according to the manufacturing method of the glass plate which concerns on this invention, a molten glass can be clarified simply and effectively.

  Moreover, it is preferable that the manufacturing method of the glass plate which concerns on this invention has a higher pressure concerning the molten glass in a connection pipe than the pressure concerning the molten glass in a clarification tank.

  Moreover, the manufacturing method of the glass plate which concerns on this invention WHEREIN: It is preferable that the viscosity of the molten glass in a connection pipe is 500-2000 poise, and the viscosity of the molten glass in a clarification tank is 200-800 poise.

  Moreover, it is preferable that the manufacturing method of the glass plate which concerns on this invention has a cross-sectional area perpendicular | vertical to the longitudinal direction of a connecting pipe smaller than a cross-sectional area perpendicular | vertical to the longitudinal direction of a clarification tank.

  Moreover, it is preferable that the manufacturing method of the glass plate which concerns on this invention performs heating of a connection pipe by electrical heating, and performs heating of a clarification tank by electrical heating.

In the method for producing a glass plate according to the present invention, the glass plate is R ′ ₂ O exceeding 0.10% by mass and not more than 2.0% by mass (where R ′ is selected from Li, Na, and K). At least one selected from the group consisting of In this specification, R ′ ₂ O represents the total amount of Li ₂ O, Na ₂ O, and K ₂ O.

Further, in the method for producing a glass plate according to the present invention, the glass plate does not substantially contain R ′ ₂ O (where R ′ is at least one selected from Li, Na, and K). Alkali glass is preferred.

  Moreover, it is preferable that the temperature of log (eta) = 2.5 is 1500 to 1750 degreeC in the manufacturing method of the glass plate which concerns on this invention.

  Moreover, the manufacturing method of the glass plate which concerns on this invention is a temperature drop rate of 2 degree-C / min or more in the temperature range of 1600 degreeC to 1500 degreeC after a molten glass is heated to 1600 degreeC or more by a clarification tank. It is preferable to lower the temperature.

  Moreover, it is preferable that the manufacturing method of the glass plate which concerns on this invention flows a molten glass in contact with a connection pipe in the perimeter of the internal diameter of a connection pipe.

Moreover, as for the manufacturing method of the glass plate which concerns on this invention, it is preferable that a glass plate contains the following composition.
(A) SiO ₂ : 50 to 70% by mass,
(B) B ₂ O ₃ : 5 to 18% by mass,
(C) Al ₂ O ₃ : 10 to 25% by mass,
(D) MgO: 0 to 10% by mass,
(E) CaO: 0 to 20% by mass,
(F) SrO: 0 to 20% by mass,
(O) BaO: 0 to 10% by mass,
(P) RO: 5 to 20% by mass (provided that R is at least one selected from Mg, Ca, Sr and Ba).

  Moreover, it is preferable that the manufacturing method of the glass plate which concerns on this invention connects a dissolution tank and a clarification tank so that a connection pipe may incline from a dissolution tank to a clarification tank.

  In the method for producing a glass plate according to the present invention, it is preferable that the clarification tank has a wall having a predetermined thickness, and the connecting pipe has a wall made of a refractory metal that is thicker than the thickness of the wall of the clarification tank.

  In addition, in this specification, RO shows the total amount of MgO, CaO, SrO, and BaO.

According to the method for producing a glass plate of the present invention, the number of bubbles can be sufficiently reduced even when a clarifying agent such as SnO ₂ other than As ₂ O ₃ is used. Alternatively, the molten glass can be clarified simply and effectively.

The flowchart of the manufacturing method of the glass plate concerning embodiment of this invention. Schematic of the glass plate manufacturing line concerning embodiment of this invention. The enlarged view of a dissolution tank, a connection pipe, and a clarification tank.

  Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings. The following description relates to an example of the present invention, and the present invention is not limited to these.

(1) Manufacturing method of glass plate The manufacturing method of the glass plate which concerns on one Embodiment of this invention includes the series of processes which the flowchart of FIG. 1 shows, and uses the glass plate manufacturing line 100 which FIG. 2 shows.

(1-1) Process Performed in the First Furnace The glass raw material is first melted in the melting process (step S101). The raw material is put into a melting tank 101 which is a first furnace and heated to a predetermined first temperature (T1). T1 is preferably, for example, 1450 ° C. to 1650 ° C., and preferably 1500 ° C. to 1630 ° C. T1 is, for example, R ′ ₂ O (provided that it is preferable for a glass plate for a liquid crystal display or a glass substrate for an organic EL display in the case of a glass substrate for a flat panel display having the following composition (2): R ′ is at least one selected from Li, Na, and K) in the case of a non-alkali glass plate substantially not containing R ′ ₂ O or more than 0.10% by mass and 2.0% by mass In the case of a glass plate containing a trace amount of alkali containing only the following, it is more preferably 1500 ° C. to 1650 ° C., and preferably 1550 ° C. or more and less than 1630 ° C. By setting it as the above minimum temperature, it becomes possible to fully melt | dissolve a glass raw material, and generation | occurrence | production of the bubble resulting from undissolved substances, such as a silica, can be suppressed. On the other hand, by setting the upper limit temperature as described above, it is possible to prevent the clarifier such as SnO _{2 from} violently releasing gas components (for example, oxygen) in the dissolution tank 101, and to clarify the clarifier in the clarification step. It becomes possible to demonstrate the function. The heated raw material melts to form molten glass. Molten glass is sent through the first transfer pipe 105a (connection pipe) to the clarification tank 102 where the next clarification step (step S102) is performed. In other words, the molten glass is conveyed from the melting tank 101 to the clarification tank 102 via the first transfer pipe 105a (platinum or platinum alloy connecting pipe).

  In addition, it is preferable that the temperature of the molten glass in the area | region vicinity where the melting tank 101 and the 1st transfer pipe 105a (platinum or platinum alloy connection pipe) are connected is 1500 to 1690 degreeC, and 1550 to 1650 degreeC. It is more preferable that

(1-2) Step in connecting pipe In the first transfer pipe 105a (connecting pipe), the molten glass is preferably heated to a third temperature (T3) higher than T1. Specifically, T3 is preferably higher by 50 ° C. or more than T1. Furthermore, T3 is preferably higher by 100 ° C. or more than T1. T1 is 1450 ° C. to 1650 ° C., whereas T3 is preferably 1500 ° C. to 1720 ° C., more preferably about 1550 ° C. to about 1690 ° C. At this time, the viscosity of the molten glass in the first transfer pipe 105a (connection pipe) is preferably 500 to 2000 poise. For example, in the case of a glass substrate for a flat panel display having the following composition (2), T1 is about 1500 ° C. to 1610 ° C. (eg, about 1550 ° C.), whereas T3 is 1550 ° C. to 1690 ° C. It is preferably about 1600 ° C to about 1650 ° C. At this time, the viscosity of the molten glass in the first transfer pipe 105a (connection pipe) is preferably 500 to 2000 poise. By doing so, the molten glass can be sent to the clarification tank 102 (second furnace) where the next clarification step (step S102) is performed at a temperature suitable for clarification described below or a temperature close thereto. The clarification of the molten glass can be effectively promoted from the entrance of the clarification tank 102. Thereby, the residence time of the molten glass in the clarification tank 102 can be made relatively short, and the time during which the molten glass is exposed to the atmosphere can be shortened, so that SO ₂ in the existing bubbles in the molten glass can be reduced. Promotion of diffusion can be suppressed. Moreover, it can prevent that nitrogen etc. in atmosphere melt | dissolve in a molten glass. Here, when the diffusion of SO ₂ into the existing bubbles in the molten glass is promoted, SO ₂ having a low solubility in the molten glass may remain as bubbles in the glass plate. On the other hand, when nitrogen or the like dissolves in the molten glass, it is considered that N ₂ is generated as a reboil bubble in the process of lowering the temperature of the molten glass. That is, if the residence time of the molten glass in the clarification tank 102 can be made relatively short, reboiling bubbles such as SO ₂ and N ₂ can be suppressed, and the number of bubbles in the glass plate can be reduced. On the other hand, when the temperature of the molten glass is made higher than the upper limit temperature, the temperature of the first transfer pipe 105a (connection pipe) is increased to the vicinity of the melting point of platinum or the platinum alloy constituting the first transfer pipe 105a (connection pipe). Heating may be necessary, and the first transfer pipe 105a (connection pipe) may be melted, which is not preferable. In addition, it is preferable that T3 is below 2nd temperature (T2) reached when a molten glass is heated in the clarification tank 102 mentioned later.

Here, the temperature suitable for clarification of molten glass varies depending on the clarifier used and the composition of the glass. The glass plate of this embodiment contains SnO ₂ as a fining agent. The temperature at which SnO ₂ functions as a fining agent, that is, the temperature at which oxygen begins to be released effectively is 1600 ° C. or higher, and oxygen is released violently as the temperature rises. That is, when SnO ₂ is contained as a fining agent, the temperature suitable for fining is 1620 ° C. or higher, more preferably 1650 ° C. or higher. On the other hand, the glass plate shown in the present embodiment is an alkali-free glass plate or R ′ that does not substantially contain R ′ ₂ O (where R ′ is at least one selected from Li, Na, and K). ₂ O is a glass plate containing a trace amount of alkali and containing only 0.10% by mass and 2.0% by mass or less. Thus, the alkali-free glass or the alkali trace-containing glass glass has a higher viscosity (high temperature viscosity) at a higher temperature than a glass containing more than 2.0% by mass of alkali. For example, the temperature when the non-alkali glass or the alkali-containing glass contains log η = 2.5 is 1500 ° C. to 1750 ° C.
Here, the speed at which the bubbles in the molten glass rise is affected by the viscosity of the molten glass. The lower the viscosity of the molten glass, the higher the rising speed of the bubbles. In order to perform clarification efficiently, it is preferable that the viscosity of the molten glass in the clarification tank 102 is, for example, 200 to 800 poise. Therefore, in order to clarify the alkali-free glass or the alkali-containing glass, it is necessary to further increase the temperature of the molten glass as compared with the alkali glass in order to lower the viscosity of the molten glass. More specifically, in the production of the alkali-free glass plate or the alkali-containing glass plate, the temperature of the molten glass in the clarification tank 102 is preferably set to, for example, 1650 ° C. or higher. The clarification referred to above means that bubbles in the molten glass are discharged out of the molten glass and defoamed.

The molten glass is heated by energizing the first transfer pipe 105a (connection pipe) made of a refractory metal with an electric heating device 201 provided with power supply terminals 201a and 201b and generating heat by the Joule heat. preferable. The power supply terminals 201a and 201b are preferably attached to both ends of the first transfer pipe 105a (connection pipe). By thus electrically heating the first transfer tube 105a made of platinum or platinum alloy (connecting pipe), even in the production of glass plates containing SnO ₂ as a fining agent, to elicit the fining effect by SnO ₂ sufficiently The temperature control of the molten glass can be easily realized.

  Moreover, it is preferable that the cross-sectional area perpendicular to the longitudinal direction of the first transfer pipe 105 a (connection pipe) is smaller than the cross-sectional area perpendicular to the longitudinal direction of the clarification tank 102. That is, the cross-sectional area perpendicular to the longitudinal direction of the clarification tank 102 is preferably larger than the cross-sectional area perpendicular to the longitudinal direction of the first transfer pipe 105a (connecting pipe).

Specifically, the cross-sectional area of the clarification tank 102 is preferably larger than the cross-sectional area related to the inner diameter of the first transfer pipe 105a (connection pipe) by more than 100%. The cross-sectional area of the clarification tank 102 is more preferably 150% or more larger than the cross-sectional area related to the inner diameter of the first transfer pipe 105a (connection pipe). For example, if the inner diameter of the first transfer pipe 105a (connection pipe) is 200 mm (cross-sectional area of about 31416 mm ² ), the inner diameter of the clarification tank 102 is about 316 mm and the cross-sectional area perpendicular to the longitudinal direction is about 78540 mm ² or more. preferable. Thereby, the pressure applied to the molten glass when the molten glass comes out from the first transfer pipe 105a (connection pipe) to the clarification tank 102 is reduced, and the gas component in the molten glass easily escapes out of the molten glass as bubbles, The clarification of the molten glass is promoted from the entrance of the clarification tank 102. Here, the clarification tank 102 has a space for accommodating the gas degassed from the molten glass in the clarification tank 102. That is, by making the pressure applied to the molten glass in the first transfer pipe 105a (connection pipe) higher than the pressure applied to the molten glass in the clarification tank 102, bubbles generated in the molten glass are transferred to the clarification tank 102. It can discharge | emit to the said provided space.

  The first transfer pipe 105a (connecting pipe) may connect the dissolution tank 101 and the clarification tank 102 substantially horizontally as shown in FIG. 3, but the dissolution tank 101 and the clarification tank 102 are connected to the dissolution tank 101. To the clarification tank 102 is preferably connected so as to rise with an inclination. That is, the first transfer pipe 105a (connection pipe) is melted so that the molten glass passing through the first transfer pipe 105a (connection pipe) climbs an inclined slope from the melting tank 101 toward the clarification tank 102. It is desirable that the tank 101 and the clarification tank 102 are connected. The inclination is preferably 15 degrees or more and less than 90 degrees, more preferably 20 degrees or more and less than 90 degrees, and further preferably 30 degrees or more and less than 90 degrees. By doing so, the molten glass flowing in the first transfer pipe 105a (connection pipe) excluding the downstream end of the first transfer pipe 105a (connection pipe) is subjected to pressure due to its own weight, but the first transfer pipe 105a ( Such pressure is not applied at the downstream end of the connection pipe), that is, the outlet to the clarification tank 102, and the pressure applied to the molten glass is reduced at the outlet of the first transfer pipe 105a (connection pipe) to the clarification tank 102. To do. In such a reduced pressure environment, gas components in the molten glass easily escape from the molten glass as bubbles, and clarification of the molten glass is promoted from the entrance of the clarification tank 102.

  Further, since high-temperature molten glass is poured into the first transfer pipe 105a (connection pipe), it is desirable that the first transfer pipe 105a (connection pipe) has a wall made of a refractory metal. It is preferably made of platinum or a platinum alloy. The wall thickness of the first transfer pipe 105a (connection pipe) is preferably thicker. For example, the wall thickness is preferably about 1 mm or more. The wall of the first transfer pipe 105a (connection pipe) is preferably thicker than the wall of the clarification tank 102, which is a second furnace described later. The wall of the first transfer pipe 105a (connection pipe) is preferably 10% or more thicker than the wall of the clarification tank 102. For example, if the wall of the clarification tank 102 is 1 mm, the first transfer pipe 105a (connection pipe) The wall of the tube is preferably 1.1 mm. Furthermore, the wall of the first transfer pipe 105a (connection pipe) is preferably 20% or more thicker than the wall of the clarification tank 102. For example, if the thickness of the wall of the clarification tank 102 is 1 mm, the first transfer pipe 105a The wall of the (connection pipe) is preferably 1.2 mm. Furthermore, the wall of the first transfer pipe 105a (connection pipe) is preferably 50% or more thicker than the wall of the clarification tank 102. For example, if the thickness of the wall of the clarification tank 102 is 1 mm, the first transfer pipe 105a The wall of the (connection pipe) is preferably 1.5 mm. By doing so, the first transfer pipe 105a (connection pipe) can be endured even when the molten glass is heated to a high temperature of, for example, 1600 ° C. or higher. Further, the strength of the wall of the first transfer pipe 105a (connection pipe) against the pressure from the inside caused by the molten glass is also increased.

  In addition, if there is a gap between the wall of the first transfer pipe 105a (connection pipe) and the molten glass, the air in the gap becomes hotter than the molten glass, thereby the first transfer pipe 105a (connection pipe). ) Also becomes high temperature, promotes oxidation or volatilization of refractory metals such as platinum or platinum alloys, and significantly reduces the durability of the first transfer pipe 105a (connection pipe). Therefore, in the first transfer pipe 105a (connection pipe), the molten glass is in contact with the entire circumference of the inner diameter of the first transfer pipe 105a (connection pipe), that is, the molten glass and the first transfer pipe 105a (connection pipe). It is preferable to pour in a state where there is no gap between the wall of the tube). By doing so, it is possible to prevent the first transfer pipe 105a (connection pipe) from being damaged and shortening its life.

(1-3) Process performed in 2nd furnace Molten glass is clarified in the following clarification process (step S102). Specifically, when the molten glass is heated up to a predetermined second temperature (T2) in the clarification tank 102, the gas component contained in the molten glass forms bubbles or vaporizes to form the outside of the molten glass. Get out. T2 is preferably higher than T1 and preferably higher than T3. T2 is preferably 1600 ° C to 1780 ° C, more preferably 1620 ° C to 1780 ° C. For example, in the case of a glass substrate for a flat panel display having the following composition (2), T2 is preferably 1620 ° C to 1780 ° C, more preferably 1650 ° C to 1740 ° C, and about 1650 ° C. More preferably, it is about 1700 degreeC. Accordingly, the viscosity of the molten glass can be sufficiently reduced while preventing the clarification tank 102 from being damaged, so that a sufficient bubble rising speed can be realized, and the molten glass can be clarified effectively. The molten glass is heated by energizing the clarification tank 102 itself having a refractory metal wall with an electric heating device (not shown) having a power supply terminal (not shown) and generating heat by the Joule heat. It is preferable. The wall made of refractory metal is preferably made of platinum or a platinum alloy. By electrically heating the thus fining vessel 102 made of platinum or platinum alloy, in the manufacturing of the glass plate containing SnO ₂ as a fining agent, the temperature control of the molten glass to draw a fining effect by SnO ₂ sufficiently Can be realized easily.

Moreover, when raising melting temperature in the 1st transfer pipe | tube 105a (connection pipe) and the clarification tank 102, the temperature of a molten glass is 1630 degreeC or more with the temperature increase rate of 2 degree-C / min or more, More preferably, it is 1650-1740 degreeC. It is preferable to raise the temperature to This is because when the rate of temperature rise is 2 ° C./min or more, the amount of released O ₂ gas increases rapidly. That is, when the temperature of the molten glass is increased to 1630 ° C. or higher at a temperature increase rate of 2 ° C./min or higher, the volatilization of the first transfer pipe 105a (connection pipe) and the clarification tank 102 is promoted. Even if it is not heated so much (for example, even if it does not exceed 1740 ° C.), it becomes possible to sufficiently extract the clarification function of SnO ₂ and prevent damage to the first transfer pipe 105a (connection pipe) and the clarification tank 102. Meanwhile, the number of bubbles in the glass plate can be reduced.

  The clarified molten glass is sent through the second transfer pipe 105b to the agitation tank 103 where the next step, the homogenization step (step S103), is performed.

  At this time, the molten glass is heated to 1600 ° C. or higher, more preferably 1600 ° C. to 1780 ° C., and still more preferably 1620 ° C. to 1780 ° C. in the clarification tank 102 to perform defoaming treatment. It is preferable to cause the molten glass to absorb bubbles in the molten glass by lowering the temperature at a temperature decreasing rate of 2 ° C./min or more in the temperature range from 1 ° C. to 1500 ° C. The reason why the temperature of the molten glass is preferably lowered at a temperature drop rate of 2 ° C./min or more in the temperature range of 1600 ° C. to 1500 ° C. is as follows.

In the clarification tank 102, the temperature of the molten glass is raised to 1600 ° C. or higher, which is the temperature at which SnO ₂ releases oxygen and is reduced, so that the oxygen present in the molten glass is taken up by the oxygen released by SnO _2. Besides being promoted, the diffusion of O ₂ , CO ₂ and SO ₂ dissolved in the molten glass at a high temperature is promoted, and O ₂ , CO ₂ and SO ₂ dissolved in the molten glass are also taken into the bubbles. It is. The solubility of the gas component in the molten glass varies depending on the glass component, but in the case of SO ₂ , the glass having a high content of the alkali metal component has a relatively high solubility, but does not contain an alkali metal component. In the case of a plate or a glass plate containing a trace amount of alkali even if it is contained, the solubility that can be dissolved in molten glass is low. In an alkali-free glass plate or a glass plate containing a trace amount of alkali, it is preferable that an S (sulfur) component is not added artificially as a glass raw material, but a combustion gas used as an impurity in the raw material or in the dissolution tank 101 (Natural gas, city gas, propane gas, etc.) are contained in trace amounts as impurities. For this reason, the S component contained as these impurities is oxidized to SO ₂ and diffuses into the bubbles contained in the molten glass. SO ₂ remains as foam because it is difficult to be reabsorbed. This phenomenon appears very prominently when SnO ₂ is used as a fining agent, compared to when conventional As ₂ O ₃ is used as a fining agent.

In the case of a glass composition using SnO ₂ as a fining agent, the longer the holding time of the molten glass at a high temperature, the more the diffusion of SO ₂ into the existing bubbles in the molten glass is promoted. This is presumably because the diffusion rate of SO _{2 in} the molten glass increased as the temperature increased, and it was easier to enter the bubbles.

Thereafter, when the temperature of the molten glass is lowered, SnO obtained by the reduction of SnO ₂ tries to oxidize by absorbing oxygen by an oxidation reaction. Therefore, O ₂ in the bubbles remaining in the molten glass is absorbed by SnO. However, the diffusion of SO ₂ and CO _{2 in} the molten glass into the existing bubbles is still maintained. For this reason, the gas component in the foam downstream of the clarification tank 102 has a higher concentration of SO ₂ and CO ₂ than the foam in the clarification tank 102. Particularly, in the case of a molten glass containing no alkali or a trace amount of alkali, the solubility of SO _{2 in} the molten glass MG is small. Therefore, when the SO ₂ is captured once it bubbles as gas, the SO ₂ is less likely to be absorbed into the molten glass in the absorption process.

As described above, for example, in the process from the latter half of the clarification tank 102 to the stirring tank 103, O ₂ in the bubbles is absorbed by SnO due to the oxidation reaction of SnO, and diffusion of SO ₂ and CO ₂ into the existing bubbles still remains. Therefore, by making this period short, the diffusion of SO ₂ and CO ₂ into the existing bubbles can be reduced and the growth of the bubbles can be suppressed.

(1-4) Process after the above In the next homogenization process (step S103), the molten glass is homogenized. Specifically, the molten glass is homogenized in the stirring tank 103 by being stirred by a stirring blade (not shown) provided in the stirring tank 103. The molten glass fed into the stirring vessel 103 is heated so as to be in a predetermined temperature range. For example, in the case of a glass substrate for a flat panel display having the following composition (2), the predetermined temperature range is preferably 1440 ° C to 1500 ° C. The homogenized molten glass is sent from the stirring tank 103 to the third transfer pipe 105c.

  In the next supply process (step S104), the molten glass is heated to a temperature suitable for molding in the third transfer pipe 105c, and sent to the molding apparatus 104 where the next molding process (step S105) is performed. It is. For example, in the case of a glass substrate for a flat panel display having the following composition (2), the temperature suitable for molding is preferably about 1200 ° C. In particular, when the overflow downdraw method is used in the molding step described below, the temperature is preferably about 1300 to 1200 ° C. in the most downstream region of the third transfer pipe 105c.

  In the next forming step (step S105), the molten glass is formed into a plate-like glass. In the present embodiment, the molten glass is continuously formed into a ribbon shape by the overflow downdraw method. The formed ribbon-shaped glass is cut into a glass plate. The overflow downdraw method is a method known per se. For example, as described in U.S. Pat. No. 3,338,696, the molten glass poured into the molded body and overflowed, It is a method of forming a ribbon-like glass by drawing down the outer surface and flowing down and joining the bottom of the molded body downward.

(2) Mixing of glass raw materials The method for producing a glass plate according to the present invention can be applied to the production of any glass plate, particularly for flat panel displays such as liquid crystal display devices, organic EL display devices and plasma display devices. It is suitable for manufacture of the glass substrate of this, or the cover glass which covers a display part.

In order to produce a glass plate according to the present invention, glass raw materials are first prepared so as to have a desired glass composition. For example, when manufacturing a glass substrate for a flat panel display, it is preferable to mix the raw materials so as to have the following composition.
(A) SiO ₂ : 50 to 70% by mass,
(B) B ₂ O ₃ : 5 to 18% by mass,
(C) Al ₂ O ₃ : 10 to 25% by mass,
(D) MgO: 0 to 10% by mass,
(E) CaO: 0 to 20% by mass,
(F) SrO: 0 to 20% by mass,
(O) BaO: 0 to 10% by mass,
(P) RO: 5 to 20% by mass (wherein R is at least one selected from Mg, Ca, Sr and Ba),
(Q) R ′ ₂ O: more than 0.10% by mass and 2.0% by mass or less (provided that R ′ is Li, Na,
And at least one selected from K),
(R) 0.05 to 1.5% by mass in total of at least one metal oxide selected from tin oxide, iron oxide, cerium oxide, and the like.

In addition, since (q) R ′ ₂ O is not essential, it may not be contained. In this case, 'becomes alkali-free glass containing no ₂ O in substantially from the glass plate R' R can reduce the risk of destroying the TFT ₂ O flows out. On the other hand, by deliberately containing (q) R ′ ₂ O exceeding 0.10% by mass and not more than 2.0% by mass, the base of the glass is suppressed while suppressing deterioration of TFT characteristics and thermal expansion of the glass within a certain range. It is possible to enhance the clarity, facilitate the oxidation of the metal whose valence varies, and improve the clarity. Furthermore, since the specific resistance of the glass can be reduced, it is suitable for performing electric melting in the melting tank 101.

Furthermore, in order to realize further high definition in recent years, displays using P-Si (low-temperature polysilicon) / TFT and oxide semiconductors instead of α-Si / TFT are required. Here, in the process of forming a P-Si (low-temperature polysilicon) TFT or an oxide semiconductor, there is a heat treatment process at a higher temperature than the process of forming an α-Si · TFT. Therefore, a glass plate on which a P-Si (low temperature polysilicon) TFT or an oxide semiconductor is formed is required to have a low thermal shrinkage rate. In order to reduce the heat shrinkage rate, it is preferable to increase the strain point of the glass. However, a glass having a high strain point tends to have a high viscosity at high temperature (high temperature viscosity). Therefore, although it is necessary to raise the temperature of a molten glass more in the clarification tank 102, if the clarification tank 102 is heated too much in order to raise the temperature of a molten glass, there exists a possibility that the clarification tank 102 may be damaged. That is, in the clarification tank 102, the present invention that can sufficiently bring out the clarification effect of SnO ₂ is suitable for the production of high strain point glass that tends to have high-temperature viscosity.

  That is, for example, the present invention is suitable for manufacturing a glass plate having a strain point of 655 ° C. or higher. In particular, a glass plate having a strain point of 675 ° C. or higher suitable for P-Si (low-temperature polysilicon) / TFT or oxide semiconductor is suitable for the present invention, and a glass plate having a strain point of 680 ° C. or higher is more preferred. A glass plate having a strain point of 690 ° C. or higher is particularly suitable.

  Examples of the composition of a glass plate having a strain point of 675 ° C. or higher include those in which the glass plate is represented by mass% and contains the following components.

SiO ₂ 52-78 mass%, Al ₂ O ₃ 3~25 wt%, B ₂ O ₃ 3~15 wt%, RO (where, RO is MgO, CaO, SrO and BaO in total amount) from 3 to 20 wt% The mass ratio (SiO ₂ + Al ₂ O ₃ ) / B ₂ O ₃ is preferably in the range of 7 or more. Further, in order to further increase the strain point, the mass ratio (SiO ₂ + Al ₂ O ₃ ) / RO is preferably 7.5 or more. Furthermore, in order to raise a strain point, it is preferable to make (beta) -OH value into 0.1-0.3 mm < ^-1 >. On the other hand, R ₂ O (where R ₂ O is the total amount of Li ₂ O, Na ₂ O and K ₂ O) 0.01 to 0 so that no current flows through the melting tank 101 instead of glass during melting. It is preferable to reduce the specific resistance of the glass as .8% by mass. Alternatively, it is preferable that the Fe ₂ O ₃ 0.01 to 1% by weight to lower the specific resistance of the glass. Further, CaO / RO is preferably set to 0.65 or more in order to prevent an increase in the devitrification temperature while realizing a high strain point. Alternatively, the weight ratio _{(SiO 2 + Al 2 O 3} ) / B 2 O 3 is preferably in the range of 7.5 to 20. By setting the devitrification temperature to 1250 ° C. or lower, the overflow downdraw method can be applied. In consideration of application to mobile devices, the total content of SrO and BaO is preferably 0 to less than 2% by mass from the viewpoint of weight reduction.

In addition, it is preferable that said glass substrate for flat panel displays does not contain arsenic substantially, and it is more preferable that arsenic and antimony are not included substantially. That is, even if these substances are included, they are as impurities. Specifically, these substances include 0.1% by mass including oxides of As ₂ O ₃ and Sb ₂ O _3. The following is preferable.

In addition to the components described above, the glasses of the present invention may contain various other oxides to adjust the various physical, melting, fining, and forming characteristics of the glass. Examples of such other oxides, but are not limited _{to, SnO 2, TiO 2, MnO} , ZnO, Nb 2 O 5, MoO 3, Ta 2 O5, WO 3, Y 2 O 3, and , La ₂ O ₃ . Here, since the glass substrate for flat panel displays, such as a liquid crystal display and an organic EL display, has a particularly severe requirement for bubbles, it is preferable to contain at least SnO ₂ having a high clarification effect among the oxides.

  Nitrate and carbonate can be used for the supply source of RO in (p) in the above (a) to (r). In order to increase the oxidizability of the molten glass, it is more desirable to use nitrate as a supply source of RO at a ratio suitable for the process.

  The glass plate manufactured in the present embodiment is continuously manufactured, unlike a method in which a certain amount of glass raw material is supplied to a melting furnace and batch processing is performed. The glass plate applied in the production method of the present invention may be a glass plate having any thickness and width.

(3) Specific Example As described below, when the method for producing a glass plate according to the present invention is actually used, bubbles in the glass can be effectively suppressed.

(Example)
First, composition, SiO _2: 60.9 wt%, B ₂ O _3: 11.6 wt%, Al ₂ O _3: 16.9 wt%, MgO: 1.7 wt%, CaO: 5.1 Weight %, SrO: 2.6 mass%, BaO: 0.7 mass%, K ₂ O: 0.25 mass%, Fe ₂ O ₃ : 0.15 mass%, SnO ₂ : 0.13 mass% The raw materials were mixed so that Subsequently, the raw material was put into the melting tank 101, and the glass plate was manufactured by performing the series of steps of the glass plate manufacturing method according to the present invention described above using the glass plate manufacturing line 100. That is, the glass raw material is heated and melted to about 1550 ° C. in the melting tank 101 to form molten glass, and the molten glass is clarified through the first transfer pipe 105a (connection pipe) made of an alloy of platinum and rhodium. The molten glass was heated to about 1700 ° C. in the clarification tank 102. The cross-sectional area of the inner diameter of the first transfer pipe 105a (connection pipe) was about 40% of the cross-sectional area perpendicular to the longitudinal direction of the clarification tank 102. In the first transfer pipe 105a (connection pipe), the molten glass was heated to about 1650 ° C. Glass was formed into a plate shape using the overflow downdraw method, and a glass plate having a thickness of 0.7 mm and a length of 2000 mm in the width direction and a length of 2500 mm in the length direction was produced. When the number of bubbles contained in the produced glass plate was measured, the number of bubbles was 0.05 in 1 kg of glass.

(Comparative Example 1)
As Comparative Example 1, a glass raw material is heated and melted to about 1550 ° C. in a melting tank 101 to form a molten glass, and the molten glass is made of a first transfer pipe 105a (connection pipe) made of an alloy of platinum and rhodium. The molten glass is fed to the clarification tank 102 through the heating point, and the molten glass is heated to about 1700 ° C. in the clarification tank 102, and the molten glass is heated to about 1480 ° C. in the first transfer pipe 105a (connection pipe). A glass plate was produced by the same method as in the example except for. When the number of bubbles contained in the produced glass plate was measured, the number of bubbles was 0.2 to 0.3 in 1 kg of glass. In addition, the area | region where molten glass reaches about 1700 degreeC in the clarification tank 102 was the downstream of the flow direction of molten glass compared with the Example. Moreover, compared with the Example, the temperature of the clarification tank 102 became high, and the volatilization amount of the clarification tank 102 after manufacturing a glass plate for one year increased 50 to 66% compared with Example 1. FIG.

(Comparative Example 2)
As Comparative Example 2, the glass raw material is heated to about 1550 ° C. in the melting tank 101 to be melted to form a molten glass, and the molten glass is made of a first transfer pipe 105a (connection pipe) made of an alloy of platinum and rhodium. The glass plate was produced by the same method as in Example, except that the molten glass was heated to about 1630 ° C. in the clarification tank 102. When the number of bubbles contained in the produced glass plate was measured, the number of bubbles was 50 to 200 in 1 kg of glass.

(4) Features In the above embodiment, the glass raw material is heated to the first temperature (T1), for example, about 1550 ° C., in the melting tank 101, which is the first furnace, and is melted to become molten glass. Is sent to a first transfer pipe 105a (connection pipe) which is a connection pipe connecting the melting tank 101 and the clarification tank 102 which is the second furnace. In the first transfer pipe 105a (connection pipe), the molten glass is heated to a third temperature (T3) higher than the heating temperature in the melting tank 101, for example, about 1650 ° C. In the clarification tank 102, the molten glass is further heated to a second temperature (T2) higher than the first temperature (T1). The second temperature (T2) is a temperature suitable for clarification of the molten glass. For example, in the case of the glass substrate for a flat panel display according to the above-described embodiment, it is 1650 ° C. to 1700 ° C. Here, since the molten glass is already heated to a temperature suitable for clarification in the first transfer pipe 105a (connection pipe) before being sent to the clarification tank 102, the molten glass is clarified in the clarification tank 102. It is promoted immediately after being sent. Therefore, according to the manufacturing method for a glass plate according to the present invention, even when using a clearing agent such as SnO ₂ other than As ₂ O _3, it is possible to pull out the refining effect sufficiently, the glass plate in The number of bubbles can be sufficiently reduced. In addition, the molten glass can be clarified simply and effectively.

100 Glass plate production line 101 Dissolution tank 102 Clarification tank 105a First transfer pipe (connection pipe)
201 Electric heating device

Special table 2008-539162

Claims (13)

A step of conveying molten glass containing at least SnO ₂ from a melting tank to a clarification tank via a connecting tube made of platinum or a platinum alloy;
In a clarification tank made of platinum or a platinum alloy having a space for storing gas due to defoaming, a clarification step of defoaming bubbles contained in the molten glass out of the molten glass,
Have
The temperature of the molten glass is heated to 1500 ° C. to 1690 ° C. in the connecting pipe,
In the clarification tank, the temperature of the molten glass is heated to 1600-1780 ° C.,
The temperature of the molten glass in the clarification tank is higher than the temperature of the molten glass in the connecting pipe,
Manufacturing method of glass plate. The temperature of the molten glass is heated to 1550 ° C. to 1690 ° C. in the connecting pipe,
The temperature of the molten glass is heated to 1620 ° C to 1780 ° C in the clarification tank.
The manufacturing method of the glass plate of Claim 1. Melting the glass material by heating it in a melting tank to produce molten glass;
Flowing the molten glass from the melting tank through a platinum or platinum alloy connecting pipe to a platinum or platinum alloy clarification tank;
A clarification step of heating and melting the molten glass in the clarification tank;
Including
The molten glass flowing through the connecting tube is heated to about 1600 ° C. to about 1650 ° C. by the connecting tube;
The molten glass in the clarification tank is heated to about 1650 to about 1700 ° C. by the clarification tank,
Manufacturing method of glass plate. The pressure applied to the molten glass in the connecting pipe is higher than the pressure applied to the molten glass in the clarification tank,
The manufacturing method of the glass plate in any one of Claims 1-3. The viscosity of the molten glass in the connecting pipe is 500 to 2000 poise,
The viscosity of the molten glass in the clarification tank is 200 to 800 poise,
The manufacturing method of the glass plate in any one of Claims 1-4. The cross-sectional area perpendicular to the longitudinal direction of the connecting pipe is smaller than the cross-sectional area perpendicular to the longitudinal direction of the clarification tank,
The manufacturing method of the glass plate in any one of Claims 1-5. The connection pipe is heated by energization heating,
The clarification tank is heated by energization heating.
The manufacturing method of the glass plate in any one of Claims 1-6. The glass plate contains 0.10% by mass and less than or equal to 2.0% by mass of R ′ ₂ O (provided that R ′ is at least one selected from Li, Na, and K).
The manufacturing method of the glass plate in any one of Claims 1-7. The glass plate is a non-alkali glass that does not substantially contain R ′ ₂ O (where R ′ is at least one selected from Li, Na, and K).
The manufacturing method of the glass plate in any one of Claims 1-7. the temperature of log η = 2.5 is 1500 ° C. to 1750 ° C.,
The manufacturing method of the glass plate in any one of Claims 1-9. After the molten glass is heated to 1600 ° C. or higher by the clarification tank, the molten glass is cooled at a temperature decreasing rate of 2 ° C./min or higher in a temperature range of 1600 ° C. to 1500 ° C.,
The manufacturing method of the glass plate in any one of Claims 1-10. The molten glass is caused to flow in contact with the connecting pipe in the entire circumference of the inner diameter of the connecting pipe,
The manufacturing method of the glass plate in any one of Claims 1-11. The said glass plate is a manufacturing method of the glass plate in any one of Claims 1-12 containing the following composition.
(A) SiO ₂ : 50 to 70% by mass,
(B) B ₂ O ₃ : 5 to 18% by mass,
(C) Al ₂ O ₃ : 10 to 25% by mass,
(D) MgO: 0 to 10% by mass,
(E) CaO: 0 to 20% by mass,
(F) SrO: 0 to 20% by mass,
(O) BaO: 0 to 10% by mass,
(P) RO: 5 to 20% by mass (provided that R is at least one selected from Mg, Ca, Sr and Ba).

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