TWI552972B - A molten glass manufacturing apparatus, a method for producing a molten glass, and a method for manufacturing the same - Google Patents

Description

Molten glass manufacturing apparatus, molten glass manufacturing method, and sheet glass manufacturing method using same

The present invention relates to a molten glass manufacturing apparatus, a molten glass manufacturing method, and a sheet glass manufacturing method using the same. More specifically, it relates to a molten glass manufacturing apparatus for producing high-quality alkali-free glass having high homogeneity, a method for producing molten glass, and a method for producing a sheet glass using the same.

In the production of a glass substrate for a flat panel display (FPD), it is preferred to use an alkali-free glass substantially free of alkali metal ions to improve the insulating properties of the glass substrate. Further, in terms of a small coefficient of thermal expansion, alkali-free glass is also preferable in the production of a glass substrate for FPD.

In the production of a glass substrate for FPD, it is required to produce a high-quality glass substrate having a higher quality, that is, a higher homogeneity. Therefore, various methods are conceivable in order to improve the homogeneity of the molten glass in the melting tank (melting furnace) in which the molten glass is obtained by melting the glass raw material.

In the melting furnace described in Patent Document 1, the melting furnace is divided into an upstream zone and a downstream zone by a cross sill, and a circulating flow of molten glass is formed in each zone (upstream side circulation flow, downstream side) The circulating flow) is used to melt the raw material and homogenize the molten glass. More specifically, the glass raw material is melted by forming an upstream side circulating flow in the upstream zone, and the downstream side circulating flow is formed in the downstream zone to homogenize the molten glass. In the melting furnace described in Patent Document 1, a bubbler is provided on the upstream side of the diaphragm for controlling the upstream side circulation flow and the downstream side circulation flow.

The melting furnace (melting tank) described in Patent Document 2 does not have a patent equivalent In the structure of the crosspiece in the melting furnace described in Document 1, there is described a case where at least one row of bubblers and at least two burners opposed to each other are used to melt and clarify the glass.

However, the melting furnaces described in Patent Documents 1 and 2 are not necessarily suitable for producing high-quality alkali-free glass.

T _η is used in the index of the melting temperature of the glass, that is, the glass viscosity η becomes 10 ² [dPa. s] The temperature, _T η of alkali-free glass is 1500 ~ 1760 ℃, typically of soda lime glass and alkali-containing glass and the like as compared to _T η higher than 100 deg.] C, it is difficult to homogenize. Therefore, it is not possible to sufficiently homogenize the melting furnace of a general mass production such as soda lime glass described in Patent Documents 1 and 2, and it is not necessarily suitable for producing a glass product (FPD) which is particularly strict in terms of homogeneity. Glass substrate, etc.).

Further, as described above, since the alkali-free glass has a higher T _η than the alkali-containing glass such as soda lime glass, the temperature of the molten glass in the melting furnace is also inevitably increased. If the temperature of the molten glass is high, the erosion effect of the molten glass on the structure in the furnace is enhanced. Therefore, in the case of the alkali-free glass, the molten glass flow is affected at the bottom of the melting furnace as compared with the clarification table in the melting furnace described in Patent Document 1 or the clarification stage in the melting furnace described in Patent Document 2. The step of the ladder, the erosion of the steps of the molten glass, and the generation of impurities caused by erosion become a problem.

In the case of the alkali-free glass, the temperature of the molten glass in the melting furnace is inevitably increased. Therefore, as in Patent Document 1, the structure having a long downstream band or a large melting as in Patent Document 2 is used. In the furnace, the range in which the burner is heated is widened, which is disadvantageous in terms of energy efficiency. Also, molten glass The erosion and the generation of impurities caused by erosion, or the change in the flow rate of the molten glass, also become a problem.

In order to solve the above problem, the applicant of the present invention has proposed a molten glass manufacturing apparatus described in Patent Document 3. In the molten glass manufacturing apparatus described in Patent Document 3, a bubbler (first and second bubblers 13, 14) provided in the vicinity of the bottom surface of the melting tank 10 for melting the glass raw material, and a heating and melting tank 10 are provided. The burners 15 in the upper space are arranged in a specific arrangement, whereby the stepped structure which affects the flow of the molten glass as described in Patent Documents 1 and 2 is provided at the bottom of the molten glass flow path, and the melting in the melting tank 10 is promoted. The glass circulation flow (the upstream side circulation flow 100 and the downstream side circulation flow 101) is formed, and is controlled such that the flow velocity of the upstream side circulation flow 100 and the flow velocity of the downstream side circulation flow 101 have a specific relationship, whereby the production can be performed. A high-quality alkali-free glass having high homogeneity (the symbols in the text are as described in Patent Document 3).

Prior technical literature Patent literature

Patent Document 1: Japanese Patent Laid-Open No. Hei 9-124323

Patent Document 2: Japanese Patent Laid-Open No. 7-144923

Patent Document 3: International Publication No. 2011/036939

As described above, by using the glass manufacturing apparatus described in Patent Document 3, it is possible to produce a high-quality alkali-free glass having high homogeneity.

However, even when the glass manufacturing apparatus described in Patent Document 3 is used, the operation of the melting tank is started or the operation of the melting tank is changed. In the case of the conditions, it takes a long time to homogenize the molten glass for the following reasons.

When the operation of the melting tank is started, in order to increase the efficiency of the melting operation, the upper space of the melting tank is heated by the burner, and the glass cullet is poured into the melting tank to melt the glass cullet, thereby ensuring melting in the melting tank. The depth of the glass. For example, the depth of the molten glass is ensured by melting of the glass frit until it is about 50% or more of the target depth of the molten glass in the melting tank.

The time required until the target depth of the molten glass in the melting tank is about 50% or more differs depending on the size of the melting tank. In the case of a melting tank having a glass production capacity of 20 to 100 tons/day, since the size thereof is relatively large, it takes a long time to become about 50% or more of the target depth of the molten glass in the melting tank.

In the case of producing an alkali-free glass, glass swarf composed of an alkali-free glass is used, and in the case of an alkali-free glass composition, a component which is easily volatilized, such as B ₂ O ₃ or Cl, is contained in the glass composition (hereinafter referred to as "dissipation" The composition "), so the composition of the molten glass differs from the target composition due to the volatilization from the molten glass.

Therefore, when the glass raw material is started to be charged, the raw material of the volatilized component is added to the target composition, and the time until the molten glass becomes the target composition is shortened.

As described above, in the molten glass manufacturing apparatus described in Patent Document 3, the gas 16 and 17 are supplied from the bubblers (the first and second bubblers 13 and 14) provided near the bottom surface of the melting tank 10 to promote the gas. The circulating flow of the molten glass in the melting tank 10 (the upstream side circulating stream 100 and the downstream side circulating stream 101) is formed, and the flow rate of the upstream side circulating stream 100 and the flow rate of the downstream side circulating stream 101 are formed. Controlling the manner of the specific relationship, thereby promoting the homogenization of the molten glass (the symbols in the text are as described in Patent Document 3).

However, a volatilized component having a smaller molecular weight is lighter in weight than other glass raw materials, and therefore has a tendency that the lighter raw material does not melt in the upstream side circulating stream, but floats on the upstream side circulating stream and flows toward the melting tank. The downstream side moves. Therefore, homogenization of the molten glass in the melting tank takes a long time.

Further, when the operating conditions of the melting tank are changed, there is a case where the molten glass stays on the upstream side of the melting tank from the upstream side circulating flow. The retention of such molten glass is responsible for delaying the homogenization of the molten glass. In addition, in the case where the amount of the glass raw material is increased, for example, there is a tendency that the glass raw material having a specific gravity lower than that of the molten glass in the melting tank is added to adjust the specific gravity of the glass to be produced. Further, there is a tendency that, for some reason, the depth of the molten glass in the melting tank is lowered, or when the temperature of the molten glass existing on the upstream side of the melting tank is lowered.

The present invention is to solve the above problems of the prior art, and an object of the present invention is to provide a high-quality alkali-free glass which is suitable for producing homogenization with high homogenization when the operation of the melting tank is started or when the operating conditions of the melting tank are changed. A molten glass manufacturing apparatus, a molten glass manufacturing method, and a sheet glass manufacturing method using the same.

In order to achieve the above object, the present invention provides a molten glass manufacturing apparatus characterized in that it has a melting tank for melting a glass raw material, and the melting tank has a burner for heating an upper space of the melting tank. when the length of molten glass flow path of the groove to above the melting L _F, the distance from the upstream side of the melting vessel becomes 0.4 L _F ~ midstream domain frothing unit is provided with a position of 0.6 L _F on which the self- An upstream domain bubbling unit is disposed at a position where the distance from the upstream side of the melting tank is 0.05 L _F to 0.2 L _F , and the midstreaming bubbling unit is a molten glass that crosses the melting tank near the bottom surface of the melting tank The bubbler group of the plurality of bubblers is disposed in the width direction of the flow path, and the upstream region foaming unit is arranged side by side in the width direction of the molten glass flow path of the melting tank near the bottom surface of the melting tank. The plurality of bubblers are configured to include at least a pair of bubblers disposed at positions symmetrical with respect to a center in a width direction of the molten glass flow path.

Moreover, the present invention provides a method for producing a molten glass by using the molten glass manufacturing apparatus of the present invention to produce molten glass from a bubbler supply gas constituting the midstream bubbling unit and the upstream domain bubbling unit.

Moreover, the present invention provides a method for producing a sheet glass which is formed into a sheet glass by the molten glass obtained by the method for producing molten glass of the present invention.

According to the molten glass manufacturing apparatus and the molten glass manufacturing method of the present invention, it is possible to promote the homogenization of the molten glass at the start of the operation of the melting tank or when the operating conditions of the melting tank are changed, so that it is suitable for high quality non-alkali having high homogeneity. The production of glass can shorten the time required for the production of the alkali-free glass.

The method for producing a sheet glass of the present invention can produce a sheet glass having high homogeneity and high transparency, and is therefore suitable for the production of a substrate for FPD.

Hereinafter, the present invention will be described with reference to the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a cross-sectional view showing an embodiment of a melting tank in a molten glass manufacturing apparatus of the present invention, and Fig. 2 is a plan view showing a melting tank shown in Fig. 1. However, the upper wall surface of the melting tank 10 is omitted for easy understanding.

An input port 11 for glass raw material is provided at an end portion on the upstream side of the melting tank 10. The glass raw material introduced from the inlet port 11 is melted by heating by the burner 16 to become the molten glass G, and is held in the melting tank 10. At the end portion on the downstream side of the melting tank 10, an extraction port 12 for extracting the molten glass G to the next step is provided. The suction port 12 is in communication with the conduit 20 on the downstream side.

In the vicinity of the bottom surface of the melting tank 10 shown in Figs. 1 and 2, an upstream domain bubbling unit and a midstream bubbling unit each composed of a plurality of bubblers 13, 14, and 15 are provided. The details are as follows. The bubbler 13 constituting the upstream domain bubbling unit is disposed in the upstream region of the molten glass flow path of the melting tank 10, and the bubblers 14, 15 constituting the middle-stream bubbling unit are disposed in the melting tank. 10 of the molten glass flow path among the swimming areas.

On both side faces of the melting tank 10 shown in Figs. 1 and 2, the burner 16 is disposed so as to be positioned above the molten glass G held in the melting tank 10. The burners 16 are disposed at equal intervals across the longitudinal direction of the melting tank 10 except for the following exceptions.

The upstream domain foaming unit is in the melting tank near the bottom surface of the melting tank 10 A plurality of bubblers 13 arranged in parallel in the width direction of the molten glass flow path of 10.

In the aspect shown in Fig. 2, the upstream domain bubbling unit is constituted by a pair of bubblers 13 disposed at positions symmetrical with respect to the center in the width direction of the molten glass flow path of the melting tank 10.

As described below, in the melting tank 10 in the molten glass manufacturing apparatus of the present invention, the gas bubbles 18 and 15 are supplied from the bubblers 14, 15 constituting the middle-bubble bubbling unit, thereby being able to be at the bottom of the molten glass flow path. The stepped structure that affects the flow of the molten glass as described in Patent Documents 1 and 2 is not provided, and the formation of the circulating flow of the molten glass G in the melting tank 10 (the upstream circulating flow 100 and the downstream circulating flow 101) is promoted. Further, the flow rate of the upstream side circulation stream 100 and the flow rate of the downstream side circulation stream 101 are controlled in a specific relationship. Hereinafter, in the present specification, the case where the gas bubbles 18 and 15 from the bubblers 14 and 15 constituting the mid-stream bubbling unit are supplied to the gas 18 and 19 is referred to as "foaming from the mid-stream foaming unit".

However, in the case of foaming only from the mid-stream foaming unit, it takes a long time to homogenize the molten glass G in the melting tank 10 at the start of the operation of the melting tank 10 or when the operating conditions of the melting tank are changed.

In the case of producing an alkali-free glass, when the operation of the melting tank 10 is started, the time until the molten glass G in the melting tank 10 becomes the target composition is shortened, and the raw material of the volatilized component is more than the target composition, but the molecular weight is small. Since the volatilized component has a lighter specific gravity than other glass raw materials, there is a tendency that the lighter raw material does not melt in the upstream side circulating stream 100 and floats on the upstream side circulating stream 100 and moves toward the downstream side of the melting tank 10. ,therefore, The homogenization of the molten glass G in the melting tank 10 takes a long time.

Further, when the operating conditions of the melting tank 10 are changed, the molten glass G may be retained on the upstream side of the melting tank 10 from the upstream side circulating flow 100. In the present specification, the case where the molten glass G on the upstream side of the melting tank 10 in the upstream side circulation flow 100 is retained is referred to as "the retention of the molten glass G on the upstream side of the melting tank 10".

The retention of the molten glass G on the upstream side of the melting tank 10 causes the homogenization of the molten glass G in the melting tank 10 to be delayed. Therefore, the molten glass G in the melting tank 10 after the operating conditions of the melting tank 10 is changed is homogeneous. It takes a long time.

In the melting tank 10, the gas is supplied from the bubbler 13 constituting the upstream region bubbling unit, whereby the molten glass G in the melting tank 10 can be promoted at the start of the operation of the melting tank 10 or when the operating conditions of the melting tank are changed. Homogenization. Hereinafter, in the present specification, the case where the gas is supplied from the bubbler 13 constituting the upstream region bubbling unit is referred to as "foaming from the upstream domain bubbling unit".

At the start of the operation of the melting tank 10, the raw material which promotes the volatilization component is melted in the upstream circulating flow 100 by performing foaming from the upstream domain foaming unit. Thereby, the homogenization of the molten glass G in the melting tank 10 is promoted.

Further, when the operating conditions of the melting tank 10 are changed, the foaming of the foaming unit from the upstream region can be suppressed, and the retention of the molten glass G on the upstream side of the melting tank 10 can be suppressed, and the difference can be eliminated depending on the case. The retention of molten glass G.

In order to exert the above effects, the bubbler 13 constituting the upstream domain bubbling unit is In the relationship of the length of the molten glass flow path of the melting tank 10, it is necessary to satisfy the conditions described below.

When the molten glass producing apparatus of the present invention in the melting vessel 10, to the length of molten glass flow path of the melting tank 10 is set to L _F, from the upstream terminus of the molten glass flow path of the upstream domain to the configuration of each of the frothing unit The distance from the bubbler 13 is 0.05 L _F ~ 0.2 L _F .

If the distance from the upstream end of the molten glass flow path to each of the bubblers 13 is less than 0.05 L _F , the upstream side wall surface of the melting tank 10 is too close to each of the bubblers 13 and thus is implemented by the upstream The foaming of the domain bubbling unit promotes erosion of the upstream side wall surface of the melting tank 10.

On the other hand, when the distance from the upstream end of the molten glass flow path to the bubbler 13 is more than 0.2 L _F , even if foaming from the upstream domain foaming unit is performed at the start of the operation of the melting tank 10, The raw material which cannot promote the volatilization component melts in the upstream side circulation flow 100, and the homogenization of the molten glass G in the melting tank 10 cannot be accelerated. Further, when the operating conditions of the melting tank 10 are changed, even if foaming from the upstream region foaming unit is performed, the retention of the molten glass G on the upstream side of the melting tank 10 cannot be suppressed.

In the melting tank 10 in the molten glass manufacturing apparatus of the present invention, the distance from the upstream end of the molten glass flow path to each of the bubblers 13 constituting the upstream domain foaming unit is preferably 0.1 L _F to 0.2 L _F More preferably, it is 0.1 L _F ~ 0.15 L _F .

As described above, in the melting tank 10 shown in Fig. 2, a pair of bubblers 13 are provided at positions symmetrical with respect to the center in the width direction of the molten glass flow path of the melting tank 10. Hereinafter, in the present specification, it is provided at a position symmetrical with respect to the center in the width direction of the molten glass flow path of the melting tank 10. The case where the bubbler 13 is placed is referred to as "the bubbler 13 is provided in a symmetrical manner in the width direction of the melting tank 10." In the melting tank 10 in the molten glass manufacturing apparatus of the present invention, it is necessary to provide the bubbler 13 in a symmetrical manner in the width direction of the melting tank 10. As an example in which the bubbler 13 is not provided symmetrically in the width direction of the melting tank 10, one of the bubblers 13 shown in Fig. 2 is not provided. In this case, when foaming from the upstream domain bubbling unit is performed, the flow of the molten glass G in the melting tank 10 is not symmetrical with respect to the width direction of the melting tank 10, and flows toward the side wall of the melting tank 10. It is promoted and thus has a tendency to erode the side walls of the melting tank 10. Further, there is a problem that the chaos in the upstream side circulation flow 100 adversely affects the homogenization of the molten glass G.

Further, as an example in which the bubbler 13 is not provided symmetrically in the width direction of the melting tank 10, one bubbler is provided in the vicinity of the center in the width direction of the molten glass flow path of the melting tank 10. 13 situation. In this case as well, when the foaming from the upstream domain bubbling unit is performed, the flow of the molten glass G toward the side wall of the melting tank 10 is promoted, so that the side wall of the melting tank 10 is eroded.

Further, it is necessary to provide the bubbler 13 in a symmetrical manner in the width direction of the melting tank 10, and therefore it is necessary to provide at least two bubblers 13. Further, in the case of more than two bubblers 13, it is necessary to set the number of bubblers 13 to an even number. For example, in the case where four bubblers 13 are provided, it is necessary to arrange two pairs of bubblers 13 in a symmetrical manner in the width direction of the melting tank 10.

It is also preferable that the bubbler 13 constituting the upstream region bubbling unit has the following conditions in the relationship with the width of the molten glass flow path of the melting tank 10.

In the melting tank 10 in the molten glass manufacturing apparatus of the present invention, when the width of the molten glass flow path of the melting tank 10 is W, each of the bubblers 13 constituting the upstream-stage foaming unit is preferably provided in self-melting. The distance from the center of the glass flow path in the width direction is 0.25 W or more.

When the distance from the center of the width direction of the molten glass flow path is less than 0.25 W, the bubbler 13 is provided in the vicinity of the center in the width direction of the molten glass flow path, so that foaming from the upstream domain foaming unit is performed. At this time, the flow of the molten glass G in the direction of the side wall of the melting tank 10 is promoted, so that the side wall of the melting tank 10 is eroded.

In the melting tank 10 in the molten glass manufacturing apparatus of the present invention, each of the bubblers 13 constituting the upstream-stage foaming unit is preferably provided at a distance of 0.27 W or more from the center in the width direction of the molten glass flow path. The position is further preferably a position at a distance of 0.4 W or more from the center in the width direction of the molten glass flow path.

However, each of the bubblers 13 constituting the upstream domain bubbling unit is preferably disposed at a position where the distance from the side wall of the melting tank 10 is 400 mm or more. When the bubbler 13 is disposed at a position where the distance from the side wall of the melting tank 10 is less than 400 mm, the side wall of the melting tank 10 is too close to the bubbler 13, so that there is foaming from the upstream region. The implementation of the foaming of the unit promotes the erosion of the sidewalls of the melting tank 10.

In the melting tank 10 in the molten glass manufacturing apparatus of the present invention, each of the bubblers 13 constituting the upstream domain bubbling unit is preferably provided at a position of 1000 mm or more from the side wall of the melting tank 10.

Further, the length L _F of the molten glass flow path of the melting tank 10 of the present invention differs depending on the width W of the molten glass flow path, and is preferably 10 to 30 m, more preferably 10 to 25 m, and further preferably 15~22 m.

On the other hand, the width W of the molten glass flow path is preferably 5 to 10 m, more preferably 5.5 to 9 m, and still more preferably 6.5 to 8 m.

In the melting tank 10 shown in Figs. 1 and 2, each of the bubblers 13 constituting the upstream-stage bubbling unit is disposed on the upstream side of the burner 16 located on the most upstream side in the longitudinal direction of the molten glass flow path. In the melting tank 10 of the molten glass manufacturing apparatus of the present invention, it is preferable that each of the bubblers 13 constituting the upstream domain bubbling unit is disposed on the upstream side of the burner 16 located on the most upstream side. : The effect of promoting the homogenization of the molten glass by the foaming from the foaming unit of the upstream domain is exhibited.

Further, depending on the melting tank, there is a case where the flue for exhausting the combustion exhaust gas of the burner 16 is disposed on the upstream side of the burner 16 located on the most upstream side. In this case, each of the bubblers 13 constituting the upstream domain bubbling unit is preferably disposed on the upstream side of the flue.

However, in order to promote the homogenization of the molten glass by the foaming from the upstream domain bubbling unit, it is preferable to form the bubblers of the upstream domain bubbling unit in the longitudinal direction of the molten glass flow path. 13. The distance from the burner 16 located on the most upstream side is not too large. In the melting tank 10 in the molten glass manufacturing apparatus of the present invention, the distance between the respective bubblers 13 constituting the upstream domain bubbling unit and the molten glass flow path of the burner 16 located on the most upstream side is preferably in the longitudinal direction. It is within 2000 mm, more preferably within 1500 mm, and even more preferably within 1000 mm.

The middle cell foaming unit is spanned by the bottom surface of the melting tank 10 and the melting In the width direction of the molten glass flow path of the tank 10, a bubbler group of a plurality of bubblers 14, 15 is provided.

In the melting tank 10 in the molten glass manufacturing apparatus of the present invention, by the foaming from the bubble cell in the middle region, the molten glass flow as described in Patent Documents 1 and 2 can be provided at the bottom of the molten glass flow path. The stepped structure that affects the formation of the circulating flow of the molten glass G in the melting tank 10 (the upstream side circulating stream 100, the downstream side circulating stream 101), and the flow rate of the upstream side circulating stream 100 and the downstream side circulating stream 101 The flow rate is controlled in a specific relationship.

In the melting tank 10 of the molten glass manufacturing apparatus of the present invention, since it is not necessary to provide a stepped structure in which the erosion of the molten glass is a problem at the bottom of the molten glass flow path, it is suitable for producing T _η of 1500 to 1760 ° C and soda lime glass. An alkali-free glass having a height of 100 ° C or higher compared with an alkali-containing glass.

In the melting tank 10 shown in Figs. 1 and 2, the midstreaming foaming unit is composed of two bubbler groups in which the positions of the molten glass flow paths of the melting tank 10 are different from each other in the longitudinal direction, that is, a first bubbler group in which a plurality of bubblers 14 are disposed across a width direction of the molten glass flow path, and a second bubbler group in which a plurality of bubblers 15 are disposed across a width direction of the molten glass flow path .

However, in the melting tank 10 in the molten glass manufacturing apparatus of the present invention, the mid-stream foaming unit may be a single bubbler group. Specifically, for example, only one of the first bubbler group and the second bubbler group may be provided.

However, the mid-stream foaming unit is made up of the molten glass flow path of the melting tank 10. The case where a plurality of bubbler groups having different positions in the degree direction are formed is preferable in that the effect of the foaming from the mid-stream foaming unit is exerted.

Further, in the case where a plurality of bubbler groups constitute a mid-stream foaming unit, three or more bubbler groups having different positions in the longitudinal direction of the molten glass flow path of the melting tank 10 may be used. In view of the cost-effectiveness, it is more preferable that the two foamers are different in the longitudinal direction of the molten glass flow path of the melting tank 10 as in the melting tank 10 shown in Figs. Group composition.

In order to exhibit the above effects, the relationship between the bubblers 14, 15 constituting the bubble region of the middle region and the length of the molten glass flow path of the melting tank 10 must satisfy the following conditions.

When the molten glass producing apparatus of the present invention in the melting vessel 10, to the length of molten glass flow path of the melting tank 10 is set to L _F, from the upstream terminus of the molten glass flow path to the frothing unit constituting each domain midstream The distance from each of the bubblers 14 and 15 of the bubbler (the first bubbler group and the second bubbler group) is 0.4 L _F to 0.6 L _F .

Therefore, the length of the melting tank 10 is shorter than that of the previous melting tank (melting furnace) described in Patent Documents 1 and 2, and the length of the portion where the downstream side circulating stream is formed in the melting tank is also short.

Here, as in the case of the melting tank 10 shown in FIGS. 1 and 2, the two bubbler groups (the first bubbler group, which are different in position in the longitudinal direction of the molten glass flow path of the melting tank 10, In the case of the second bubbler group, from the upstream end of the molten glass flow path to the bubblers 14, 15 constituting each of the bubbler groups The distance is preferably such that the following conditions are respectively satisfied.

The distance from the upstream end of the molten glass flow path to each of the bubblers 14 constituting the first bubbler group is preferably 0.4 L _F to 0.5 L _F , more preferably 0.43 L _F to 0.46 L _F . On the other hand, the distance from the upstream end of the molten glass flow path to each of the bubblers 15 constituting the second bubbler group is preferably 0.45 L _F to 0.55 L _F , more preferably 0.46 L _F to 0.53 L _F.

In the same manner as the melting tank 10 shown in Figs. 1 and 2, the two bubbler groups are different in the longitudinal direction of the molten glass flow path of the melting tank 10 (the first bubbler group, the second In the case of the bubbler group, when the distance between each of the bubblers 14 constituting the first bubbler group and each of the bubblers 15 constituting the second bubbler group is L _P , L _P is The case of 500 to 1000 mm is preferable in that the effect of the foaming from the foaming unit in the middle region is exerted, and the L _{P is} preferably 600 to 800 mm.

Further, the pitch p between the bubblers of each of the bubbler groups constituting the bubble generating unit in the midstream region, that is, the distance between the bubblers in the width direction of the molten glass flow path of the melting tank 10 is 400 to 700 mm This case is preferable in view of cost-effectiveness and exerts the effect of the above-described foaming from the mid-stream foaming unit.

In the same manner as the melting tank 10 shown in Figs. 1 and 2, the two bubbler groups are different in the longitudinal direction of the molten glass flow path of the melting tank 10 (the first bubbler group, the second In the case of the bubbler group, when the direction of the flow path of the molten glass in the melting tank 10 is set to the axis, the bubbler 14 of the first bubbler group and the second bubbler group are formed. The bubbler 15 is preferably arranged in such a manner as not to exist on the same axis.

In the melting tank 10 shown in FIG. 2, the protrusions of the bubbler 14 constituting the first bubbler group and the protrusions of the bubbler 15 constituting the second bubbler group are arranged in a zigzag shape, and The protrusions of the bubbler 14 constituting the first bubbler group and the protrusions of the bubbler 15 constituting the second bubbler group are not present on the same axis.

In the case of such an arrangement, even if the projections of the bubblers 14 constituting the first bubbler group do not function, they may be arranged in a zigzag manner on the downstream side. The presence of the protrusion of the bubbler 15 of the bubbler group does not impair the effect of promoting the formation of the circulating flow of the molten glass G in the melting tank 10 (the upstream side circulation stream 100, the downstream side circulation stream 101), and is circulated upstream. The flow rate of the stream 100 is controlled in such a manner that the flow rate of the downstream side circulation stream 101 has a specific relationship.

In the melting tank 10 in the molten glass manufacturing apparatus of the present invention, the foamer 13 constituting the upstream region bubbling unit and the constituent materials of the bubblers 14, 15 constituting the intermediate-field foaming unit are required to have flame resistance and Since it is excellent in corrosion resistance of molten glass, it is preferable that it is platinum or a platinum alloy.

Further, in terms of the gas 17 supplied from the bubbler 13 constituting the bubble generating unit in the upstream domain and the gases 18 and 19 supplied from the bubblers 14, 15 constituting the bubble generating unit in the middle region, it is preferable to use the molten glass G. And the components of the melting tank 10 such as the bubblers 13, 14, 15 and the like cause adverse effects. Specific examples of such a gas include air, nitrogen, oxygen, helium, argon, and the like. In the case where platinum or a platinum alloy is used as the constituent material of the bubblers 13, 14, 15, the gases 17, 18, 19 supplied from the bubblers 13, 14, 15 are preferably nitrogen, helium, and argon. An oxygen-free gas such as gas. Especially among these Nitrogen.

On both side faces of the melting tank 10 shown in Figs. 1 and 2, a burner 16 is disposed at equal intervals across the longitudinal direction of the melting tank 10. However, the burner 16 is not disposed above the bubbler 15 constituting the second bubbler group.

The burner 16 is not disposed above the bubbler 15 constituting the second bubbler group because the following aspects of the control are implemented in the molten glass manufacturing method of the present invention (control 2) In the case of the above, it is necessary to make the ambient temperature T ₂ above the bubbler 15 constituting the second bubbler group lower than the ambient temperature T ₁ above the bubbler 14 constituting the first bubbler group.

In the case of the implementation (Control 2), it is preferable that the bubbler 15 constituting the second bubbler group and the burner 16 close to the downstream side of the bubbler 15 are disposed to be separated to some extent. Specifically, it is preferable that the distance L _B2 between the bubbler 15 constituting the second bubbler group and the burner 16 on the downstream side with respect to the bubbler 15 is 800 mm or more.

However, if the bubbler 15 constituting the second bubbler group and the burner 16 on the downstream side with respect to the bubbler 15 are excessively separated, there is the following: the formation of the second bubbler group The ambient temperature above the bubbler 15 is too low, and conversely, there is a problem that the homogenization of the molten glass is insufficient. Further, there is a case where the temperature of the molten glass G taken out from the suction port 12 provided at the end portion on the downstream side of the melting tank 10 becomes low, and it is difficult to defoam when the vacuum defoaming is performed in the subsequent step. And other issues. Therefore, L _{B2 is} preferably set to 2500 mm or less. Further, L _{B2 is} preferably 1000 to 2000 mm, and L _{B2 is} preferably 1000 to 1600 mm.

Further, in the case of the implementation (Control 2), it is necessary to make the ambient temperature T ₂ above the bubbler 15 constituting the second bubbler group lower than the bubbler 14 constituting the first bubbler group. Since the ambient temperature T ₁ is preferably a distance L _B1 between the bubbler 14 constituting the first bubbler group and the burner 16 on the upstream side with respect to the bubbler 14, and the distance L _B2 becomes L _B2 >L _B1 relationship. Therefore, as shown in Fig. 2, it is preferable that the burner 16 is provided above the bubbler 14 constituting the first bubbler group. With such an arrangement, the ambient temperature T ₂ above the bubbler 15 constituting the second bubbler group can be made lower than the ambient temperature T ₁ above the bubbler 14 constituting the first bubbler group. .

In the present invention, L _{B2 -} L _B1 ≧ 300 mm is preferable, and L _{B2 -} L _B1 ≧ 500 mm is more preferable, and further preferably L _{B2 -} L _B1 ≧ 800 mm.

On the other hand, in the melting tank 10 shown in Fig. 2, the burner 16 immediately above the bubbler 14 constituting the first bubbler group is provided, but as long as the relationship of L _B2 > L _B1 is satisfied, The bubbler 14 constituting the first bubbler group and the burner 16 on the upstream side with respect to the bubbler 14 can be disposed to be separated to some extent. However, if the bubbler 14 constituting the first bubbler group is excessively separated from the burner 16 on the upstream side with respect to the bubbler 14, there is a problem that the environment above the bubbler 14 When the temperature is too low, the upstream side circulation flow 100 is weakened, the melting of the glass raw material is insufficient, and the homogenization of the molten glass G in the downstream region of the melting tank 10 is insufficient. From this point of view, L _{B1 is} preferably 2000 mm or less. Furthermore, L _{B1 is} preferably 500 to 1500 mm.

Further, the distance between adjacent burners 16 also depends on the type of the burner 16 or the layout of the melting tank 10, preferably 600 to 2600 mm, more preferably 800 to 2400 mm.

The combustion in the combustor 16 allows the fuel to be mixed with oxygen for combustion, or the fuel is mixed with oxygen and air for combustion. By using these methods, water can be contained in the molten glass. In the subsequent step of the molten glass conveyed from the melting tank 10 to the downstream side of the conduit 20, when the foam in the molten glass is defoamed by vacuum degassing, it is preferred that the molten glass contains moisture, so Good for burning as described above.

Further, in order to prevent the deposit on the surface of the inner wall of the melting tank 10 (for example, the vitreous material from the brick, the raw material or the volatilized material of the molten glass, etc.) from falling onto the burner portion, it is preferably in the melting tank. A groove (not shown) is provided in the upper portion of the burner 16 in the inner wall of 10.

The constituent material of the portion of the melting tank 10 that is in contact with the molten glass G is required to have heat resistance and excellent corrosion resistance to molten glass. Therefore, a refractory brick containing ZrO ₂ is preferably used, and a melting tank 10 for forming a molten glass flow path is preferably used. In the bottom surface, from the bubbler 14 constituting the first bubbler group to the upstream side of 0.1 L _F to 0.3 L _F , ZrO ₂ is used in an amount of 85% or more and 97% or less, and the remainder is SiO _{2 .} A glassy hot melt refractory as a main body. The reason for this is that the temperature of the molten glass flowing through the melting tank 10 is higher on the upstream side than on the downstream side, and in the case of the preferred control form in the method for producing molten glass of the present invention (Control 1). The flow rate of the gas 18 from the bubbler 14 constituting the first bubbler group is larger than the flow rate of the gas 19 from the bubbler 15 constituting the second bubbler group, thereby forming the melting tank 10 of the molten glass flow path. The constituent material of the bottom surface is easily corroded.

Further, from the viewpoint of preventing corrosion of the constituent material of the bottom surface of the melting tank 10 which forms the molten glass flow path, it is preferable to constitute the upstream region foaming unit. The hot melt refractory described above is used for the peripheral portion of the bubbler 13.

Further, in the case where the length L _F of the molten glass flow path of the melting tank 10 is 10 to 30 m (preferably 10 to 25 m, more preferably 15 to 22 m) as described above, it is preferably The above-mentioned hot melting is used in a portion of the range of 100 to 600 mm, preferably 150 to 400 mm, in the longitudinal direction of the molten glass flow path centering on the bubbler 13 constituting the upstream region foaming unit. Refractory.

Further, in the case where the width W of the molten glass flow path of the melting tank 10 is 5 to 10 m (preferably 5.5 to 9 m, more preferably 6.5 to 8 m) as described above, it is preferable to The bubbler 13 constituting the upstream region foaming unit is in the range of 100 to 600 mm, preferably 150 to 400 mm, and more preferably 150 to 300 mm in the width direction of the molten glass flow path. For the part of the range, the above-mentioned hot-melt refractory is used.

In such cases, the thickness of the hot-melt refractory is preferably 50 to 400 mm, and the hot-melt refractory is preferably 2 to 3 layers. Further, on the outer side of the layer of the hot-melt refractory formed in this manner, 2 to 5 layers of other refractory bricks containing ZrO ₂ may be laminated. Further, it is preferable that the hot-melt refractory having the above composition constitutes all of the portions of the melting tank 10 which are in contact with the molten glass G. Further, each of the refractory bricks may be laminated with a tamping material such as alumina-zircon.

Further, in order to prevent the molten glass from invading the joint of the refractory brick at the bottom of the melting tank 10 and eroding the refractory brick, it is preferable to laminate the refractory bricks under the joint to block the joint.

If a cooling mechanism for cooling the refractory brick by air cooling or water cooling is provided on the outer side of the refractory brick at the bottom of the melting tank 10, the life of the refractory brick Life is better, so it is better.

Further, it is preferable that a water pipe for cooling the annular shape or the horseshoe shape of the pipe is provided around the inside of the refractory brick at the bottom of the melting tank 10 or the piping of the bubblers 13, 14, 15 outside the refractory brick.

Next, a method of producing a molten glass of the present invention will be described.

In the method for producing a molten glass according to the present invention, the molten glass manufacturing apparatus is used to perform foaming from the intermediate-field foaming unit and to foam from the upstream-stage foaming unit in the melting tank 10 of the molten glass manufacturing apparatus. Molten glass is produced on one side.

As described above, by performing foaming from the bubble cell in the middle region, the stepped structure which affects the flow of the molten glass as described in Patent Documents 1 and 2 can be provided at the bottom of the molten glass flow path, and the melting tank can be promoted. The formation of the circulating flow of the molten glass G (the upstream side circulating flow 100 and the downstream side circulating flow 101) in 10 is controlled such that the flow velocity of the upstream side circulating flow 100 and the flow velocity of the downstream side circulating flow 101 have a specific relationship. Therefore, it is suitable for producing an alkali-free glass having a T _η of 1500 to 1760 ° C and high homogeneity.

Further, by performing foaming from the bubble cell in the middle region, it is possible to promote the homogenization of the molten glass G in the melting tank 10 at the start of the operation of the melting tank 10 or when the operating conditions of the melting tank are changed, thereby shortening The time required for the manufacture of the alkali-free glass.

Specific examples of the alkali-free glass having a T _η of 1500 to 1760 ° C are exemplified by the alkali-free glass compositions 1 to 4 having the following composition.

Alkali-free glass composition 1

SiO ₂ : 50 to 73%, preferably 50 to 66%

Al ₂ O ₃ : 10.5~24%

B ₂ O ₃ : 0~12%

MgO: 0~10%, preferably 0~8%

CaO: 0~14.5%

SrO: 0~24%

BaO: 0~13.5%

MgO+CaO+SrO+BaO: 8~29.5%, preferably 9~29.5%

ZrO ₂ : 0~5%

When the strain point is high and the meltability is considered, the alkali-free glass composition is preferred.

SiO ₂ : 58~66%

Al ₂ O ₃ : 15~22%

B ₂ O ₃ : 5~12%

MgO: 0~8%

CaO: 0~9%

SrO: 3~12.5%

BaO: 0~2%

MgO+CaO+SrO+BaO: 9~18%

Especially in the case of considering the solubility, it is preferably an alkali-free glass composition 3

SiO ₂ : 50~61.5%

Al ₂ O3: 10.5~18%

B ₂ O ₃ : 7~10%

MgO: 2~5%

CaO: 0~14.5%

SrO: 0~24%

BaO: 0~13.5%

MgO+CaO+SrO+BaO: 16~29.5%

Especially in the case of considering a high strain point, it is preferably an alkali-free glass composition 4

SiO ₂ : 54~73%

Al ₂ O ₃ : 10.5~22.5%

B ₂ O ₃ : 0~5.5%

MgO: 0~10%

CaO: 0~9%

SrO: 0~16%

BaO: 0~2.5%

MgO+CaO+SrO+BaO: 8~26%

In the method for producing a molten glass of the present invention, the average flow rate of the gases 18 and 19 supplied from the respective bubblers 14, 15 constituting the intermediate-zone foaming unit is set to 0.5 to 5.0 liters/min, which is compared in the following respects. It is preferable to promote the formation of the circulating flow of the molten glass G in the melting tank 10 (the upstream side circulating stream 100 and the downstream side circulating stream 101), and the flow velocity of the upstream side circulating stream 100 and the flow velocity of the downstream side circulating stream 101 are in a specific relationship. The way to control.

Here, as in the case of the melting tank 10 shown in FIGS. 1 and 2, when the mid-bubble bubbling unit is composed of the first and second bubbler groups, the following (Control 1) and (Control) are implemented. 2) This case is preferable in that the circulation flow (the upstream side circulation stream 100, the downstream side circulation stream 101) of the molten glass G in the melting tank 10 is promoted, and the flow rate and downstream of the upstream side circulation stream 100 are advanced. The flow rate of the side circulation stream 101 is controlled in such a manner as to have a specific relationship. In this way, when the molten glass having a T _η of 1500 to 1760 ° C is produced, homogenization of the molten glass can be promoted, and high-quality molten glass having high homogeneity can be obtained.

(Control 1)

The average flow rate V ₂ of the gas 19 from the bubbler 15 constituting the second bubbler group is made smaller than the average flow rate V ₁ of the gas 18 from the bubbler 14 constituting the first bubbler group.

(Control 2)

The ambient temperature T ₂ above the second bubbler 15 is made lower than the ambient temperature T ₁ above the first bubbler 14.

In the case of the implementation (Control 1), the above V _{1 is} preferably 0.5 to 20 liters/min, more preferably 0.7 to 5 liters/minute, further preferably 0.9 to 3 liters/minute, and particularly preferably 1.8 to 2.6. l / min. Further, the above V _{2 is} preferably from 0.3 to 19.8 liters/min, more preferably from 0.4 to 4.8 liters/min, further preferably from 0.5 to 2 liters/min, and particularly preferably from 0.9 to 2.0 liters/min.

Further, it is preferably V ₁ - V ₂ ≧ 0.2 liter / minute, more preferably V ₁ - V ₂ ≧ 0.4 liter / minute, further preferably V ₁ - V ₂ ≧ 0.6 liter / minute, and particularly preferably V ₁ -V ₂ ≧ 1.0 l / min.

In the case of the implementation (Control 2), the above T _{1 is} preferably from 1590 to 1710 ° C, more preferably from 1600 to 1695 ° C. Further, the above T _{2 is} preferably from 1570 to 1690 ° C, more preferably from 1580 to 1675 ° C.

Further, T _{1 -} T _{2 is} preferably 10 to 35 ° C, and T _{1 -} T _{2 is more} preferably 15 to 30 ° C, and still more preferably 19 to 26 ° C.

Further, T ₁ and T ₂ can be measured by the following methods.

(measurement position)

T ₁ : an intermediate position between the burner 16 on the upstream side of the bubbler 14 constituting the first bubbler group and the burner 16 on the upstream side of the burner 16 .

T ₂ : intermediate position between the burner 16 on the downstream side of the bubbler 15 constituting the second bubbler group and the burner 16 on the downstream side of the bubbler.

(test methods)

The inner wall surface temperature of the melting tank on the side of the opposite side is measured by a radiation thermometer (for example, CHINO IR-AH3SU (measurement wavelength: 0.65 μm, ε = 1.0)) from the observation window provided on the side surface of the melting tank.

In the method for producing a molten glass of the present invention, the average flow rate of the gas 17 supplied from each of the bubblers 13 constituting the upstream domain foaming unit is set to 0.1 to 5.0 liters/min. In this case, the operation of the melting tank 10 is included. At the beginning or at the time of changing the operating conditions of the melting tank 10, the homogenization of the molten glass G in the melting tank 10 can be continuously promoted.

Here, the average flow rate of the gas 17 supplied from each of the bubblers 13 constituting the bubble generating unit of the upstream domain may further require utilization from the upstream domain as in the start of the operation of the melting tank 10 or when the operating conditions of the melting tank 10 are changed. The foaming of the foaming unit is carried out to promote the homogenization of the molten glass G in the melting tank 10, and the normal operation of the melting tank 10 is changed. For example, it is preferable that the average flow rate of the gas 17 supplied from each of the bubblers 13 constituting the upstream region foaming unit is 0.5 to 3.0 liters at the start of the operation of the melting tank 10 or when the operating conditions of the melting tank 10 are changed. The average flow rate of the gas 17 supplied from each of the bubblers 13 constituting the upstream region foaming unit is 0.1 to 1.0 in the normal operation of the melting tank 10 at a time of 1.0 to 2.0 liters/min. L/min is preferably set to 0.2 to 0.5 liters/min. Here, in the normal operation of the melting tank 10, for example, when B ₂ O ₃ is contained in the glass composition, it means that the mass percentage based on the oxide indicates that B ₂ O ₃ is ±1% with respect to the target composition. Preferably, it is ±0.5%, more preferably ±0.3%.

In the method for producing molten glass of the present invention, when the average flow velocity of the upstream side circulation stream 100 is F ₁ [m/hr] and the average flow velocity of the downstream side circulation stream 101 is F ₂ [m/hr], it is preferably It is controlled in such a manner that F ₁ = 5 to 20 m / hour and F ₂ = 0.5 to 7 m / hour. In this way, when the molten glass having a T _η of 1500 to 1760 ° C is produced, homogenization of the molten glass can be promoted, and high-quality molten glass having high homogeneity can be obtained.

More preferably, it is controlled by F ₁ = 8 to 15 m / hour and F ₂ = 1 to 4 m / hour.

Further, F ₁ and F ₂ can be measured by the following methods.

(measurement position)

F ₁ : The distance from the upstream end of the molten glass flow path is 0.30 L _F to 0.34 L _F and is near the center in the width direction of the molten glass flow path.

F ₂ : The distance from the downstream end of the molten glass flow path is 0.22 L _F to 0.30 L _F and is near the center in the width direction of the molten glass flow path.

(test methods)

The video of the bubble in the surface layer of the molten glass was subjected to video photography, and the movement time of the bubble with respect to the moving distance was measured as the flow rate. This procedure was repeated 2 to 3 times and the average flow rate was determined.

Next, a method for producing a sheet glass of the present invention will be described.

In the method for producing a sheet glass according to the present invention, the molten glass obtained by the method for producing molten glass of the present invention is formed into a sheet glass. As a method of forming molten glass by molding molten glass, various molding methods such as a float method and a down-draw method can be used. In the case where the T _η is 1500 to 1760 ° C glass, it is particularly preferable to be a floating method.

In the method for producing a sheet glass according to the present invention, before the molten glass obtained by the method for producing molten glass of the present invention is formed into a sheet glass, the bubbles in the molten glass may be removed by defoaming under reduced pressure. bubble.

In the method for producing a sheet glass of the present invention, the molten glass having high homogeneity obtained by the method for producing molten glass of the present invention is molded into a sheet glass, whereby a sheet glass having high homogeneity and high transparency can be obtained. .

The sheet glass manufacturing apparatus of the present invention can be applied to the production of sheet glass for various purposes, and can be used for manufacturing a glass substrate having high homogeneity and high transparency, and is particularly suitable for manufacturing a glass substrate such as FPD. Plate glass for extremely demanding applications.

Example

The glass raw material is supplied to the input port of the melting tank 10 shown in Figs. 1 and 2 so as to have a desired composition, and an alkali-free glass having a T _η of 1500 to 1760 ° C is produced. Specifically, the above-described alkali-free glass composition is produced. ~4. The dimensions of the respective portions of the melting tank 10 shown in Figs. 1 and 2 are as follows.

Length of molten glass flow path L _F : 16~25 m

The width of the molten glass flow path is W: 5.5~9 m

Distance from the upstream end of the molten glass flow path to each of the bubblers 13 constituting the upstream side bubble unit: 0.1 L _F

Distance from the center of the width direction of the molten glass flow path to each of the bubblers 13 constituting the upstream side bubble unit: 0.5 W

Distance from the upstream end of the molten glass flow path to each of the bubblers 14 constituting the first bubbler group: 0.43 L _F ~ 0.46 L _F

Distance from the downstream end of the molten glass flow path to each of the bubblers 15 constituting the second bubbler group: 0.47 L _F ~ 0.54 L _F

The distance L _p of each of the bubblers 14 constituting the first bubbler group and each of the bubblers 15 constituting the second bubbler group is 600 to 800 mm

The distance between each bubbler 14 constituting the first bubbler group is p: 400~700 mm

The distance between each bubbler 15 constituting the second bubbler group is p: 400~700 mm

Distance from the upstream end of the molten glass flow path to the burner 16 on the most upstream side in the direction of the flow path of the molten glass in the melting tank: 0.15 L _F

The distance L _B1 between the bubbler 14 constituting the first bubbler group and the burner 16 on the upstream side of the bubbler 14 in the direction of the flow path of the molten glass in the melting tank: 500 to 1500 mm

The distance L _B2 of the bubbler 15 constituting the second bubbler group and the burner 16 on the downstream side of the bubbler 15 in the direction of the flow path of the molten glass in the melting tank: 1000 to 2000 mm

L _B2 -L _B1 ≧500 mm

The distance between the burners 16 in the direction of the flow path of the molten glass in the melting tank: 800~2400 mm

The average flow rate of the gas 17 from the bubbler 13 constituting the upstream side bubble generating unit is adjusted to 0.25 to 0.5 liter/min.

The average flow rate V ₁ of the gas 18 from the bubbler 14 constituting the first bubbler group and the average flow rate V ₂ of the gas 19 from the bubbler 15 constituting the second bubbler group are as follows. The way to adjust.

V ₁ : 1.8 to 2.6 liters / minute

V ₂ : 0.9~2.0 l/min

V ₁ -V ₂ ≧0.6 l/min

The ambient temperature T ₁ above the bubbler 14 constituting the first bubbler group and the ambient temperature T ₂ above the bubbler 15 constituting the second bubbler group are utilized by combustion by the burner 16. The conditions are as follows. Further, T ₁ and T ₂ were measured by the above method.

T ₁ : 1590~1710 °C

T ₂ : 1580~1675°C

T ₁ -T ₂ : 10~35°C

At the start of the operation of the melting tank 10, the time required for homogenization of the molten glass in the melting tank 10 is shortened by foaming from the bubbler 13 constituting the upstream side foaming unit.

By the above-described method for measuring the upstream side of the melting vessel 10 within the circulation flow F ₁ of the average flow rate of 100 and the downstream circulation flow 101 of the average flow rate F _2. The results are as follows.

F ₁ =8~15 m/hour

F ₂ =1~4 m/hour

By carrying out under the above conditions, a high-quality alkali-free glass having a T _η of 1500 to 1760 ° C and high homogeneity is produced, and the time required for the production of the alkali-free glass can be shortened.

The invention has been described in detail and with reference to specific embodiments, but It will be apparent to those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention.

The present application is based on Japanese Patent Application No. 2011-277287, filed on Dec.

Industrial availability

According to the molten glass manufacturing apparatus and the molten glass manufacturing method of the present invention, it is possible to promote homogenization of the molten glass at the start of the operation of the melting tank or when the operating conditions of the melting tank are changed, so that it is suitable for producing high quality with high homogeneity. Alkali-free glass, and can shorten the time required for the production of the alkali-free glass.

The method for producing a sheet glass of the present invention can produce a sheet glass having high homogeneity and high transparency, and is therefore suitable for producing a substrate for FPD.

10‧‧‧melting tank

11‧‧‧ Input

12‧‧‧Extracted

13‧‧‧Blisters (upstream domain foaming unit)

14‧‧‧Blisters (Middle Foaming Unit, 1st Bubbler Group)

15‧‧‧Blisters (Middle Foaming Unit, 2nd Bubbler Group)

16‧‧‧ burner

17‧‧‧Gas from the bubbler (upstream domain bubbling unit)

18‧‧‧Gas from bubbler (middle-zone foaming unit, first bubbler group)

19‧‧‧Gas from bubbler (messional bubbler unit, second bubbler group)

20‧‧‧Tube on the downstream side

100‧‧‧ upstream circulation

101‧‧‧ downstream side circulation

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a cross-sectional view showing an embodiment of a melting tank in a molten glass manufacturing apparatus of the present invention.

Figure 2 is a plan view of the melting tank 10 shown in Figure 1. However, the upper wall surface of the melting tank 10 is omitted.

Claims (12)

A molten glass manufacturing apparatus characterized in that it has a melting tank for melting a glass raw material, and a burner for heating an upper space of the melting tank on both sides of the melting tank, the burner system When the length of the molten glass flow path of the melting tank is LF, the distance from the upstream side of the melting tank is 0.4 L _F when the molten glass is held above the molten glass in the melting tank. ~ field provided midstream of the frothing unit on 0.6L _F position at a distance from the upstream of the melting vessel from the upstream side is provided with a blowing unit domain position of 0.05L _F ~ 0.2L _F on the midstream region foaming The unit includes a bubbler group having a plurality of bubblers disposed in a width direction of the molten glass flow path of the melting tank near a bottom surface of the melting tank, wherein the upstream domain foaming unit is included on a bottom surface of the melting tank a plurality of bubblers arranged side by side in the width direction of the molten glass flow path of the melting tank, wherein the upstream domain foaming unit is disposed at least in a width direction with respect to the molten glass flow path A pair of bubblers in a position where the heart is symmetrical. The molten glass manufacturing apparatus according to claim 1, wherein when the width of the molten glass flow path of the melting tank is W, each of the bubblers constituting the upstream bubble generating unit is disposed at a position that satisfies the following condition. : the distance from the center of the width direction of the molten glass flow path is 0.25W The distance from the side wall of the melting tank is 400 mm or more. The molten glass manufacturing apparatus according to claim 1 or 2, wherein each of the bubblers constituting the upstream-stage bubbling unit is disposed on the upstream side of the burner located on the most upstream side in the longitudinal direction of the molten glass flow path. The molten glass manufacturing apparatus according to claim 1 or 2, wherein the mid-stream foaming unit includes a plurality of bubbler groups having different positions in the longitudinal direction of the molten glass flow path. The molten glass manufacturing apparatus according to claim 1 or 2, wherein each of the bubblers constituting the midstream bubbling unit and the upstream domain bubbling unit is made of platinum or a platinum alloy, and is supplied from the buffers. The gas system does not contain oxygen. A method for producing a molten glass using the molten glass manufacturing apparatus according to any one of claims 1 to 5, wherein a gas is supplied from each of the bubble generating unit and the bubble generating unit of the upstream region Manufacture of molten glass. The method for producing molten glass according to claim 6, which is to produce a glass viscosity η of 10 ² [dPa. s] The molten glass having a temperature T _η of 1500 to 1760 ° C. The method for producing a molten glass according to claim 6 or 7, wherein the average flow rate of the gas supplied from each of the bubblers constituting the bubble unit of the midstream region is set to 0.5 to 5.0 liters/min, which will foam from the upstream region. The average flow rate of the gas supplied by each bubbler of the unit is set to 0.1 to 5.0 liters/min. A method of producing a sheet glass, which is formed into a sheet glass by a molten glass obtained by the method for producing molten glass according to any one of claims 6 to 8. The molten glass manufacturing apparatus according to claim 1 or 2, wherein the molten glass is expressed by mass percentage of the oxide standard, and the alkali-free glass containing the following components: SiO ₂ : 50 to 73% Al ₂ O ₃ : 10.5 to 24% B ₂ O ₃ : 0~12% MgO: 0~10% CaO: 0~14.5% SrO: 0~24% BaO: 0~13.5% MgO+CaO+SrO+BaO: 8~29.5% ZrO ₂ :0~5 %. The method for producing molten glass according to claim 6 or 7, wherein the molten glass is expressed by mass percentage of the oxide standard, and the alkali-free glass containing the following components: SiO ₂ : 50 to 73% Al ₂ O ₃ : 10.5 to 24% B ₂ O ₃ : 0~12% MgO: 0~10% CaO: 0~14.5% SrO: 0~24% BaO: 0~13.5% MgO+CaO+SrO+BaO: 8~29.5% ZrO ₂ :0~5 %. The method for producing a sheet glass according to claim 9, wherein the molten glass is expressed by mass percentage of the oxide standard, and the alkali-free glass containing the following components: SiO ₂ : 50 to 73% Al ₂ O ₃ : 10.5 to 24% B ₂ O ₃ : 0~12% MgO: 0~10% CaO: 0~14.5% SrO: 0~24% BaO: 0~13.5% MgO+CaO+SrO+BaO: 8~29.5% ZrO ₂ :0~5% .