JP5616450B2 - Manufacturing method of glass plate - Google Patents

Description

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

  For example, glass substrates used for flat panel displays (hereinafter referred to as FPD) such as liquid crystal displays and plasma displays are mainly 0.5 to 0.7 mm in thickness and 300 to 400 mm to 2850 to 3050 mm in size. is there.

  An overflow down draw method is known as a method for manufacturing a glass substrate for FPD. In the overflow down draw method, the glass sheet is formed into a glass sheet by overflowing from the upper part of the molten glass molded body in a molding furnace, and the formed glass sheet is gradually cooled and cut. Thereafter, the cut sheet glass is further cut into a predetermined size in accordance with the customer's specifications, cleaned, end-polished, etc., and shipped.

Among the glass substrates for FPD, in particular, the glass substrate for liquid crystal display devices has a semiconductor element formed on the surface thereof, and therefore does not contain an alkali metal component at all or even if it is contained, the semiconductor element is affected. It is preferable that the amount is as small as possible.
In addition, if bubbles are present in the glass substrate, it causes a display defect. Therefore, a glass substrate in which bubbles are present cannot be used as a glass substrate for FPD. For this reason, it is calculated | required that a bubble does not remain | survive in a glass substrate. In the production of a glass substrate, removing bubbles from the molten glass is called clarification. In this clarification, the bubbles are removed by an oxidation-reduction reaction of a clarifier such as As ₂ O ₃ . More specifically, the temperature of the melted molten glass is further increased, the fining agent is caused to function by causing the fining agent to function, and then the temperature is lowered to reduce the remaining small bubbles in the glass. Dissolve and absorb. As the fining agent, SnO ₂ or Fe ₂ O ₃ is used in place of As ₂ O ₃ in addition to As ₂ O ₃ from the viewpoint of environmental load in recent years. As described above, in the case of a glass substrate that does not contain an alkali metal component at all or is in a very small amount, the high-temperature viscosity is higher than that of a glass substrate that contains a large amount of alkali metal such as soda lime glass. Since bubbles are difficult to escape from, a higher clarification effect is required.

  On the other hand, the temperature of the molten glass is controlled by heating the clarification tank by passing an electric current through a clarification tank of a tube made of platinum or a platinum alloy (conduction heating), and circulating the molten glass in the heated clarification tank. Techniques for raising and clarifying are known. (Patent Document 1).

Special table 2011-502934 gazette

When the temperature of the molten glass is raised by heating a clarification tank composed of platinum or a platinum alloy tube, the temperature of the molten glass may not be heated uniformly. For example, as shown in FIG. 5, among the molten glass that passes through the tube, the flow rate of the molten glass that flows near the center of the pipe line is faster than the flow rate of the molten glass that flows near the wall surface of the tube having a large wall resistance. Furthermore, since it is far from the wall surface of the tube to be heated, the molten glass that flows near the center of the pipe line is lower than the temperature of the molten glass that flows near the wall surface of the tube. Has the problem of becoming insufficient. This problem is also a problem that occurs when an electric current is passed through a clarification tank composed of a platinum or platinum alloy tube.
In addition, increasing the heating amount of a clarification tank made of platinum or a platinum alloy in order to increase the temperature near the center of the tube promotes volatilization of the platinum or platinum alloy and shortens the life of the clarification tank. is there. In particular, in recent years, from the viewpoint of environmental impact, when SnO ₂ is used as a refining agent instead of As ₂ O ₃ , the volatility of platinum or platinum alloys is increasingly increased in order to make molten glass higher than As ₂ O _3. Is a problem. For this reason, it is preferable to excessively heat a tube made of platinum or a platinum alloy.

  Further, in the clarification tank, defoaming is promoted by setting the viscosity at which bubbles are likely to rise. For example, non-alkali glass suitably used in a glass substrate for a liquid crystal display device, etc. Since the temperature needs to be higher than that of alkali glass, volatilization of platinum or platinum alloys becomes a problem. For this reason, it is in a situation where it is not preferable to heat excessively with respect to a pipe constituted of platinum or a platinum alloy.

  Therefore, the present invention provides a method for producing a glass substrate capable of enhancing the clarification effect of molten glass while preventing the volatilization of platinum or platinum alloy constituting the tube of the clarification tank in the clarification of molten glass, as compared with the prior art. The purpose is to provide.

One aspect of the present invention is a method of manufacturing a glass substrate,
It includes a clarification step of clarification while flowing molten glass in a tube whose outer peripheral wall made of platinum or a platinum alloy is heated.
The clarification step includes a defoaming step of discharging bubbles in the molten glass from the liquid surface of the molten glass toward the gas phase in the tube.
In the defoaming step, by stirring the molten glass, the flow of the molten glass in the central region of the flow path cross section of the tube is suppressed, and the temperature distribution along the radial direction of the tube of the molten glass is uniform. The manufacturing method of the glass substrate characterized by the above-mentioned.

  In the manufacturing method of the glass substrate of the said form, the clarification effect of molten glass can be heightened, preventing volatilization of platinum or a platinum alloy in the clarification of molten glass.

It is process drawing of the manufacturing method of the glass substrate of this embodiment. It is a figure which shows typically the apparatus which performs the melting process-cutting process shown in FIG. (A) is a figure which mainly shows the clarification tank which performs the clarification process shown in FIG. 1, (b) is a figure which shows the temperature of the outer peripheral wall of a clarification tank. (A)-(c) is a figure explaining the board | plate material used for a clarification tank. It is a figure explaining the flow velocity and temperature of the molten glass in the conventional clarification tank. (A)-(c) is a figure which shows the example of the board | plate material of a form different from the board | plate material shown to FIG. 4 (a)-(c). It is a figure which shows the example of the stirring means of a form different from the stirring means comprised with the board | plate material shown to Fig.4 (a)-(c).

  Hereinafter, the manufacturing method of the glass plate of this embodiment is demonstrated.

(Overall overview of glass substrate manufacturing method)
FIG. 1 is a process diagram of a method for producing a glass substrate according to the present embodiment.
The glass plate manufacturing method includes a melting step (ST1), a refining step (ST2), a homogenizing step (ST3), a supplying step (ST4), a forming step (ST5), and a slow cooling step (ST6). And a cutting step (ST7). In addition, a plurality of glass substrates that have a grinding process, a polishing process, a cleaning process, an inspection process, a packing process, and the like and are stacked in the packing process are transported to a supplier.

  FIG. 2 is a diagram schematically showing an apparatus for performing the melting step (ST1) to the cutting step (ST7). As shown in FIG. 2, the apparatus mainly includes a melting apparatus 200, a forming apparatus 300, and a cutting apparatus 400. The melting apparatus 200 mainly has a melting tank 201, a clarification tank 202, a stirring tank 203, and glass supply pipes 204, 205, and 206. In addition, the glass supply pipes 204, 205, and 206, the clarification tank 202, and the stirring tank 203 that connect the respective tanks from the melting tank 201 to the molding apparatus 300 are made of a metal pipe made of platinum or a platinum alloy such as a platinum rhodium alloy. Has been.

In the melting step (ST1), for example, a glass raw material to which a fining agent such as SnO ₂ is added and supplied into the melting tank 201 is heated and melted by a flame and an electric heater (not shown) to obtain a molten glass. Specifically, the glass raw material M is supplied to the liquid surface of the molten glass G using a raw material charging apparatus (not shown). The glass raw material is heated and melted gradually by the gas phase heated to a high temperature by the flame, and melted in the molten glass MG. Molten glass MG is heated by energization heating with an electric heater.
The clarification step (ST2) is performed at least in the glass supply pipe 204, the clarification tank 202, and the glass supply pipe 205. In the clarification step, when the molten glass MG in the clarification tank 202 is heated, the bubbles containing O ₂ , CO _2, or SO ₂ contained in the molten glass MG are reduced with a clarifier such as SnO _2. It grows by absorbing O ₂ generated by the reaction, floats on the liquid surface of the molten glass MG, and is released (defoaming step). In the clarification step, after defoaming, the temperature of the molten glass MG is lowered, and for example, a clarifier such as SnO obtained by a reduction reaction of a clarifier such as SnO ₂ undergoes an oxidation reaction, thereby Gas components such as O ₂ in the foam remaining in the MG are absorbed into the molten glass MG, and the foam disappears (absorption process). The oxidation reaction and reduction reaction by the fining agent are performed by controlling the temperature of the molten glass MG. As for the temperature of the molten glass MG, an electric current is passed between a heater electrode (not shown) provided in the glass supply pipe 204 and a heater electrode 202a (see FIG. 3) provided in the clarification tank 202, which will be described later. The clarification tank 202 is heated by flowing an electric current between 202a and the heater electrode 202b (see FIG. 3A) provided in the clarification tank 202 on the downstream side of the molten glass MG as compared with the heater electrode 202a. The molten glass MG is heated. Furthermore, the clarification tank 202 is heated by passing an electric current between the heater electrode 202b and the heater electrode 202c (see FIG. 3) provided in the clarification tank 202 on the downstream side of the molten glass MG as compared with the heater electrode 202b. Meanwhile, the temperature of the molten glass MG is lowered. This energization heating is not limited to the temperature control by the energization heating in the three regions, and the temperature control of the molten glass MG can be performed by performing the energization heating in one or two regions. The detail about the clarification process in the clarification tank 202 is mentioned later.

In the homogenization step (ST3), the glass component is homogenized by stirring the molten glass MG in the stirring tank 203 supplied through the glass supply pipe 205 using the stirrer 203a. The stirring tank 203 stirs the molten glass MG using one stirrer 203a, but can also stir the molten glass MG using two or more stirrers 203a.
In the supply step (ST4), the molten glass MG is supplied to the molding apparatus 300 through the glass supply pipe 206.

In the molding apparatus 300, a molding process (ST5) and a slow cooling process (ST6) are performed.
In the forming step (ST5), the molten glass MG is formed into a sheet glass G, and a flow of the sheet glass G is created. In the present embodiment, an overflow down draw method using a molded body 310 described later is used. In the slow cooling step (ST6), the sheet-like glass G that is formed and flows is cooled to have a desired thickness and no internal distortion occurs.
In a cutting process (ST7), in the cutting device 400, the sheet-like glass G supplied from the shaping | molding apparatus 300 is cut | disconnected to predetermined length, and a plate-shaped glass substrate is obtained. The cut glass substrate is further cut into a predetermined size to produce a glass substrate of a target size. After this, the end face of the glass substrate is ground, polished and the glass substrate is cleaned. Further, after checking for defects such as bubbles and striae, the glass substrate that has passed the inspection is packed as a final product. .

(Clarification process)
As described above, the defoaming step and the absorption step of the clarification step (ST2) are performed at least in the glass supply pipe 204, the clarification tank 202, and the glass supply pipe 205. The defoaming step is mainly performed in the first half of the supply pipe 204 and the clarification tank 202. The absorption process is mainly performed in the latter half of the clarification tank 202. The defoaming step may be performed in the latter half of the clarification tank 202. In this case, the absorption step is performed in the supply pipe 205 in the latter half of the clarification tank 202 or later.

Hereinafter, the clarification process will be described from the defoaming process.
The molten glass MG supplied from the melting tank 201 to the glass supply pipe 204 is clarified in the first half of the glass supply pipe 204 and the clarification tank 202 so that the oxygen release reaction of a clarifier such as SnO ₂ is promoted. It is heated before being supplied to the clarification tank 202 so that the viscosity of the bubbles easily rises in the first half of the tank 202 (preferably 120 [poise] to 400 [poise]: 1 poise = 0.1 Pa · sec). . For example, in the case of glass having a temperature corresponding to a viscosity of 10 ^2.5 [poise] of 1500 ° C. or more, for example, 1580 ° C. to 1620 ° C. More preferably, it is supplied to the glass supply tube 204 at 1,600 ° C. to 1620 ° C., and is heated at, for example, 1610 ° C. to 1650 ° C., more preferably 1630 ° C. to 1650 ° C. at the entrance of the clarification tank 202. Further, in the clarification tank 202, by passing an electric current between a heater electrode 202a and a heater electrode 202b described later, the clarification tank 202 is heated and the molten glass MG is, for example, 1670 ° C. to 1710 ° C., preferably 1690 ° C. The temperature is raised to 1710 ° C. That is, it is necessary to raise the temperature of the clarification tank 202 to the vicinity of the heat resistance temperature of platinum or a platinum alloy of the metal tube constituting the clarification tank 202.
That is, in the defoaming step, a tube having a certain length or more is required to heat the molten glass MG. Moreover, the inner diameter of the clarification tank 202 is larger than the inner diameter of the glass supply pipe 204 and is configured to have a gas phase space between the liquid surface of the molten glass MG and the pipe. With such a configuration, defoaming started in the glass supply pipe 204 can be rapidly released when the viscosity of the foam is likely to rise in the clarification tank 202, and an effective clarification effect can be obtained. Can be promoted. Here, since the pipe of the clarification tank 202 has a large inner diameter as described above, the temperature distribution in the radial direction of the pipe tends to be uneven. This problem hardly occurs in the glass supply tube 204 having a relatively small inner diameter.

Next, the absorption process will be described.
In the absorption process, when flowing current between the heater electrode 202b and the heater electrode 202c (see FIG. 3), the temperature of the molten glass MG is lowered while heating the clarification tank 202, and SnO ₂ is used as a clarifier. When SnO obtained by the reduction reaction of SnO ₂ undergoes an oxidation reaction, gas components such as O ₂ in bubbles remaining in the molten glass MG are absorbed in the molten glass MG, and the bubbles disappear.

(Clarification tank)
FIG. 3A is a diagram specifically illustrating the configuration of the clarification tank 202 that mainly performs the above-described clarification step. Specifically, the clarification tank 202 includes heater electrodes 202a, 202b, and 202c, and a metal tube 202d. The metal tube 202d is a tube made of platinum or a platinum alloy. The molten glass MG flows through the inside of the metal tube 202d using the pipe line of the metal tube 202d as a flow path. The heater electrodes 202a, 202b, and 202c cause a current to flow from the outer peripheral wall surface of the metal tube 202d to the metal tube 202d and heat the metal tube 202d using Joule heat generated by the resistance of the metal tube 202d to set the temperature of the molten glass MG to a predetermined value. The molten glass MG is defoamed using a fining agent in the molten glass MG. That is, the metal tube 202d is made of an outer peripheral wall of platinum or a platinum alloy, and the outer peripheral wall is heated.

The heater electrodes 202a, 202b, and 202c are sequentially provided with the heater electrode 202a, the heater electrode 202b, and the heater electrode 202c in order from the upstream side in the X direction, which is the longitudinal direction of the metal tube 202d, and the heater electrode 202a and the heater electrode 202c are , Located at both ends of the metal tube 202d. The heater electrode 202b is located approximately in the middle between the heater electrode 202a and the heater electrode 202c. That is, a region between the heater electrode 202a and the heater electrode 202b is a first heating region, and a region between the heater electrode 202b and the heater electrode 202c is a second heating region.
In the present embodiment, three heater electrodes 202a to 202c are provided, but two heater electrodes may be provided. That is, the number of regions for heating the metal tube 202d may be one.

  Further, inside the metal tube 202d, the molten glass MG does not flow through the entire flow path section of the metal tube 202d, but a gas phase space is provided above. In order to cause bubbles to be defoamed in the molten glass MG to break up on the liquid surface of the molten glass MG and to release gas components in the bubbles to the atmosphere, the upper part of the metal tube 202d is from the gas phase of the metal tube 202d. A gas exhaust hole (not shown) for releasing a gas component to the atmosphere is provided.

  The metal tube 202d preferably has a cylindrical shape. The thickness of the metal tube 202d is preferably 1 mm to 1.5 mm, for example. The inner diameter of the metal tube 202d is larger than the inner diameter of the glass supply tubes 204 and 205, preferably 30% or more larger than the inner diameter of the glass supply tubes 204 and 205, and more preferably 40% or more. The inner diameter of the metal tube 202d is, for example, 300 mm or more. By setting the inner diameter of the metal tube 202d to an inner diameter of 300 mm or more, for example, the flow rate of the molten glass MG flowing in the metal tube 202d can be reduced, and the time for the molten glass MG to stay in the metal tube 202d can be increased. The glass MG can be clarified efficiently.

In the clarification tank 202, the temperature of the molten glass MG is distributed along the X direction as shown in FIG. 3B by passing a current through the heater electrodes 202a, 202b, and 202c. The molten glass MG sent from the melting tank 201 is heated by the glass supply pipe 204 and gradually heated, and further, the temperature of the molten glass MG is maximized between the heater electrode 202a and the heater electrode 202b. The molten glass MG is heated, and the molten glass MG is heated between the heater electrode 202b and the heater electrode 202c so that the temperature of the molten glass MG gradually decreases. That is, in the region between the heater electrode 202a and the heater electrode 202b, the molten glass is released so that, for example, SnO ₂ releases oxygen by the reducing action of the fining agent contained in the molten glass MG, for example, SnO ₂ (tin oxide). MG is heated. On the other hand, in the region between the heater electrode 202b and the heater electrode 202c, so that SnO absorbs oxygen by the oxidizing action of a fining agent contained in the molten glass MG, for example, SnO (a fining agent obtained by reducing SnO ₂ ). Molten glass MG is cooled. Furthermore, the temperature of the molten glass MG is gradually lowered in the glass supply pipe 205.

  FIG. 4A is a cross-sectional view of the metal tube 202d of the clarification tank 202 cut in the X direction. In the metal tube 202d, a plurality of plate materials 202e and 202f that are walls orthogonal to the X direction are alternately provided on the inner wall surface of the metal tube 202d that is a flow path of the molten glass MG. The plate members 202e and 202f are static stirring means constituted by a member made of a material such as platinum or a platinum alloy fixed to the metal tube 202d in the metal tube 202d. That is, the plate materials 202e and 202f agitate the molten glass MG flowing in the metal tube 202d, thereby uniformizing the temperature distribution along the radial direction of the tube of the molten glass MG. Here, the homogenization of the temperature along the radial direction of the molten glass MG means that the temperature difference in the temperature distribution is within 20 ° C, more preferably within 10 ° C, and more preferably within 5 ° C. That means.

  The plate members 202e and 200f are formed so that the cross-sectional area perpendicular to the X direction of the metal tube 202d is not less than one third and not more than two thirds of the cross-sectional area perpendicular to the X direction of the metal tube 202d. It is preferable to be provided so as to regulate the flow of If the cross-sectional areas (blocking areas) of the plate members 202e and 200f that regulate the flow of the molten glass MG are too small, the stirring effect is small, and if the blocking area is too large, the elements that inhibit the flow of the molten glass MG become too large. Preferably, the blocking area is about one half of the cross-sectional area perpendicular to the X direction of the metal tube 202d. As shown in FIG. 4B, the plate member 202e is provided so as to pass through the central region including the center of the cross section of the metal tube 202d and cross the metal tube 202d in the horizontal direction (left and right direction in FIG. 4B). In addition, while restricting the flow of the molten glass MG in the central region of the flow path cross section, the molten glass MG can pass through the upper part and the lower part of the flow path. On the other hand, as shown in FIG. 4C, the plate member 202f is different from the arrangement of the plate member 202e in that the upper and lower portions of the cross section of the flow path are horizontally arranged across the central region including the flow path cross section center of the metal tube 202d. Is provided so as to cross in the direction (left and right direction in FIG. 4C) and regulates the flow of the molten glass MG at the upper and lower portions of the flow path cross section, while the molten glass MG is the center of the flow path cross section of the metal tube 202d. Can pass through a central area including That is, it is composed of a plurality of plate members 202e, 202f provided at different positions in the flow path direction of the pipe so as to regulate the cross section of the molten glass MG in the pipe of the metal pipe 202d. In the set of adjacent plate members 202e and 202f, the portions where the flow path cross section is regulated are different from each other. The plate member 202f is provided so as to cross the upper and lower portions of the cross section of the channel in the horizontal direction (left and right direction in FIG. 4C) across the central region. The shape rotated in the plane of the cross section, that is, the left and right portions of the cross section of the flow path in the vertical direction (vertical direction in FIG. ) May be provided across. In this case, it is preferable to use the plate 202e having the shape shown in FIG. Further, the plate member 202f having the shape shown in FIG. 4C is used, while the plate member 202e shown in FIG. 4B is rotated by 90 degrees in the plane of the channel cross section. Good.

  In this embodiment, although the part which controls the flow-path cross section of board | plate material 202e, 202f mutually differs, the part which controls a flow-path cross section may be the same. However, it is possible to prevent the molten glass MG from flowing linearly from the upstream side to the downstream side, and to flow the molten glass MG while stirring it in the vertical direction. Preferably they are different. In the present embodiment, two plate members 202e and 202f are provided, but only one plate member may be provided to restrict the flow path cross section of the molten glass MG.

  In the clarification tank 202, the molten glass MG supplied from the glass supply pipe 204 is defoamed while flowing through the metal pipe 202 whose outer peripheral wall made of platinum or platinum alloy is energized and heated. In this case, the molten glass MG flowing near the wall of the metal tube 202d to be heated is likely to rise in temperature as the metal tube 202d is energized and heated, but the central portion of the flow path cross section of the molten glass MG is heated. It is difficult to raise the temperature because it is away from the metal wall 202d. That is, the temperature distribution of the molten glass MG tends to occur along the radial direction of the metal tube 202d. For this reason, in the conventional clarification tank in which the plate materials 202e and 202f are not provided, the temperature distribution along the radial direction of the flowing molten glass tube is not uniform, and the melting of the central portion of the flow path section far from the wall of the metal tube The flow rate of the glass is faster than the flow rate of the molten glass flowing near the wall of the metal tube. Therefore, the molten glass MG flowing through the center of the channel cross section is likely to pass through the clarification tank without being heated. If the temperature distribution of the molten glass MG occurs along the radial direction of the metal tube 202d for the above-mentioned reason, the temperature at the lowest temperature in the temperature distribution is the desorption that the fining agent exhibits a reducing action and releases oxygen. The heating temperature of the metal tube 202 must be set high so that the molten glass MG has a viscosity at which the molten glass MG can easily float. However, when such a heating temperature is set, the volatilization of metal components such as platinum and platinum alloy constituting the metal tube 202d becomes violent, and the metal tube 202d is consumed greatly. For this reason, in this embodiment, in order to make the temperature distribution in the radial direction of the metal tube 202d of the molten glass MG closer to uniform (in order to make it uniform), means for stirring the molten glass MG in the flow path of the metal tube 202d The plate materials 202e and 202f are provided. Thereby, compared with the past, the clarification effect of molten glass MG can be improved, preventing volatilization of the platinum or platinum alloy which comprises the metal pipe 202d.

  Stirring of the molten glass MG using the plate materials 202e and 202f of the present embodiment is the highest temperature formed by heating the molten glass MG from the inlet of the molten glass MG in the metal tube 202d of the clarification tank 202 (FIG. 3 (b ) See) It is performed in at least a part of the section to the vicinity. Since the defoaming step of the molten glass MG is performed in the above section, in this defoaming step, the temperature distribution along the radial direction of the metal tube 202d of the molten glass MG is made uniform so that extra heating of the metal tube 202d is performed. It is possible to suppress the volatilization of platinum or the platinum alloy constituting the metal tube 202d and to enhance the clarification effect of the molten glass MG. Here, “near the highest temperature” means a range within 10 ° C., preferably within 5 ° C. with respect to the highest temperature. Therefore, the section is from the entrance of the molten glass MG in the metal tube 202d to the end of the “near” where the temperature has dropped by 10 ° C. beyond the position of the highest temperature formed by heating the molten glass MG. Refers to a section.

In the clarification tank 202, after the molten glass MG is heated and defoamed, the temperature of the molten glass MG is energized and heated in the metal tube 202d between the heater electrodes 202b and 202c, thereby the first half of the clarification tank 202. The temperature is lowered to a temperature suitable for the absorption process, which is lower than the temperature of the molten glass MG. Here, the temperature of the molten glass MG in the first half of the clarification tank 202 is a viscosity (preferably, 120 [poise] to 120 [poise] to which the oxygen release reaction of the clarifier is promoted and bubbles in the molten glass MG easily float. 400 [poise]). This temperature is, for example, a non-alkali glass or a glass containing only a trace amount of alkali (high-temperature viscous glass), for example, a temperature corresponding to 10 ^2.5 [poise] is 1500 ° C. When SnO ₂ is used as a fining agent in the glass as described above, for example, it is in the range of 1610 ° C. to 1710 ° C. Temperature suitable for the absorption step, the case of using SnO ₂ as a fining agent in the alkali glass or alkali-trace-containing glass is in the range of 1200 ° C. to 1650 ° C.. The maximum temperature of the molten glass MG in the clarification tank 202 resulting from this is 1670 ° C to 1710 ° C, or 1690 ° C to 1710 ° C. In this case, the upper limit of the maximum temperature shown in FIG. 3B is, for example, 1700 degrees to 1710 degrees.
In this way, the fining agent contained in the molten glass MG exhibits an oxidizing action, and the fining agent absorbs the oxygen contained in the bubbles remaining in the molten glass MG and performs fining. At this time, since the temperature of the molten glass MG is higher than the temperature of the wall surface of the tube, when stirring is not performed in the clarification tank 202, the molten glass MG flowing near the center of the tube is near the wall surface of the tube. Higher than the temperature of the molten glass flowing through That is, there is a problem that the temperature is not lowered to a temperature suitable for the absorption process and the clarification becomes insufficient. At this time, the clarification tank 202 can stir the molten glass MG using the plate materials 202e and 202f as stirring means for the molten glass MG. If the temperature distribution described above exists in the molten glass MG during the absorption of bubbles, it becomes difficult to efficiently absorb the bubbles remaining in the molten glass MG for the reasons described above. For this reason, in this embodiment, as shown to Fig.4 (a), not only at the time of defoaming of molten glass MG, but also at the time of absorption of foam, plate material 202e, 202f serves as a stirring means of molten glass MG. Used. When the molten glass is not agitated by stirring the molten glass at the time of defoaming the molten glass MG, or by stirring the molten glass at the time of absorbing bubbles in addition to the defoaming of the molten glass MG As compared with the above, the temperature of the wall surface of the tube can be lowered by several degrees C. to several ten degrees C., for example. That is, even if the temperature of the wall surface of the tube is lowered by, for example, several to 10 ° C., it can be set to the same temperature as the molten glass when the molten glass is not stirred.
In the refining process of this embodiment, not only when defoaming the molten glass MG but also when absorbing bubbles, the plate materials 202e and 202f are used as stirring means for the molten glass MG. It is only necessary that the molten glass MG is stirred so that the temperature distribution is made uniform in the portion where the degassing is performed by heating.

  The metal tube 202d on which defoaming is performed according to the present embodiment is an expansion tube that is expanded stepwise with respect to the glass supply tube 204, but may be an expansion tube that is continuously expanded. Since at least the metal tube 202d is a tube expanded with respect to the glass supply tube 204, a gas phase space exists above the molten glass MG in the metal tube 202d, and the molten glass MG can have a liquid surface. In addition, since the flow path is widened, the flow rate of the molten glass MG is lowered and the residence time in the metal tube 202d is increased, and the area of the liquid surface of the molten glass MG is widened, so that defoaming is performed efficiently. Can do.

(Glass composition)
The glass substrate manufactured by the manufacturing method of the glass substrate of this embodiment is used suitably for the glass substrate for flat panel displays. For example, any component of Li, Na, and K is not contained, or even if at least one component of Li, Na, and K is contained, It is preferable that the total amount of the components to be contained has a glass composition of 0.5% by mass or less from the viewpoint of efficiently exhibiting the effects of the present embodiment. The glass composition is preferably exemplified as follows.

The glass composition of a glass substrate can mention the following, for example.
The content rate display of the composition shown below is mass%.
SiO _2: 50~70%,
B ₂ O _3: 5~18%,
Al ₂ O _3: 0~25%,
MgO: 0 to 10%,
CaO: 0 to 20%,
SrO: 0 to 20%,
BaO: 0 to 10%,
RO: 5 to 20% (However, R is at least one selected from Mg, Ca, Sr and Ba, and the glass plate contains),
It is preferable that it is an alkali free glass containing.

Further, _SiO 2 glass of the glass substrate, may be mentioned glass composition of the following: 50% to 70%,
B ₂ O ₃ : 1 to 10%,
Al ₂ O _3: 0~25%,
MgO: 0 to 10%,
CaO: 0 to 20%,
SrO: 0 to 20%,
BaO: 0 to 10%,
RO: 5 to 30% (where R is the total amount of Mg, Ca, Sr and Ba),
Similarly, it is also preferable that the glass be an alkali-free glass.

Further, _SiO 2 glass of the glass substrate, may be mentioned glass composition of the following: 50% to 70%,
B ₂ O ₃ : _{3 to} 15%,
Al ₂ O _3: 8~25%,
MgO: 0 to 10%,
CaO: 0 to 20%,
SrO: 0 to 20%,
BaO: 0 to 10%,
RO: 5 to 30% (where R is the total amount of Mg, Ca, Sr and Ba),
Similarly, it is also preferable that the glass be an alkali-free glass.

Although the alkali-free glass is used in this embodiment, the glass substrate may be a glass containing a trace amount of alkali metal (a total content of alkali gold images is greater than 0% by mass). When the alkali metal is contained, the total of R ′ ₂ O is 0.10% by mass or more and 0.5% by mass or less (provided that R ′ is at least one selected from Li, Na and K, and the glass substrate G is It is preferable to contain. In order to facilitate melting of the glass, the content of iron oxide in the glass is 0.01 to 0.2% by mass in terms of Fe ₂ O ₃ from the viewpoint of reducing the specific resistance. It is preferably 0.01 to 0.15% by mass, more preferably 0.01 to 0.10% by mass. Also, if the SnO ₂ is added as a refining agent, it is more preferable that the content of SnO ₂ is 0.01 to 0.5 mass%. In the present embodiment, since SnO ₂ is a component for devitrified glass, in order not to cause devitrification while improving the clarity, the content of 0.01 to 0.5 mass% It is preferable that it is 0.05-0.4 mass%, and it is further more preferable that it is 0.1-0.3 mass%. Further, it is preferable that As ₂ O ₃ , Sb ₂ O ₃ , and PbO are not substantially contained.

  In addition to the components described above, the glass substrate of this embodiment may contain various other oxides to adjust various physical, melting, fining, and forming properties of the glass. Examples of such other oxides include, but are not limited to, TiO2, MnO, ZnO, Nb2O5, MoO3, Ta2O5, WO3, Y2O3, and La2O3.

In the manufacturing method of this embodiment, the temperature distribution of the molten glass MG along the radial direction of the metal tube 202d is made uniform by stirring the molten glass MG. For this reason, even when a molten glass having a low melting property and a high viscosity of the molten glass is used, it is only necessary to heat the molten glass to a degree suitable for defoaming. Thus, there is no need to further heat the molten glass in order to increase the temperature of the molten glass flowing near the center of the metal tube. Therefore, the clarification step can be effectively performed while suppressing volatilization of the metal tube 202d made of platinum or a platinum alloy.
That is, even in the case of highly viscous glass having a temperature corresponding to 102.5 [poise] of 1500 ° C. or higher (for example, 1500 ° C. or higher and 1650 ° C. or lower), the manufacturing method according to the present embodiment preferably configures the glass substrate. It can be used as a glass to be used, and the clarification step can be effectively performed while suppressing the volatilization of the metal tube 202d made of platinum or a platinum alloy.
Even if the glass is not highly viscous, in recent years, from the viewpoint of environmental load, instead of As2O3, when SnO2 is used as a fining agent, the molten glass is made to have a higher temperature than when As2O3 is used as a fining agent. Increasingly, volatilization of platinum or platinum alloys is a problem. However, in the manufacturing method of this embodiment, it is not necessary to heat the molten glass further in order to increase the temperature of the molten glass flowing in the vicinity of the center of the metal tube, as in the prior art. Therefore, the clarification step can be effectively performed while suppressing volatilization of the metal tube 202d made of platinum or a platinum alloy.

(Modification)
In the present embodiment, as shown in FIG. 4A, a plurality of plate members 202e and 202f provided in the metal tube 202d are alternately arranged, but one set of plate members 202e and 202f may be arranged.
As shown in FIG. 6A, plate members 202e and 202f extending from the wall of the metal pipe 202d toward the inside of the pipe line but having different extending heights may be alternately provided in the metal pipe 202d. That is, since the heights of the adjacent plate members 202e and 202f are different, the portions of the set of the plate members 202e and 202f that restrict the flow path cross section are different from each other. In this case, the molten glass MG flows undulatingly as indicated by the broken line shown in the figure by stirring with the plate materials 202e and 202f. That is, the plate materials 202e and 202f shown in FIG. 6A are used as stirring means for stirring the molten glass MG.
Furthermore, instead of the plate members 202e and 202f shown in FIGS. 4A and 4B of the present embodiment, as shown in FIG. 6B, a plate member 202e having a plurality of circular or semicircular holes opened. And the plate material 202f provided with the hole which arrangement | positioning differs from this hole may be provided in the metal pipe 202d alternately.
Further, instead of the plate members 202e and 202f shown in FIGS. 4A and 4B of the present embodiment, as shown in FIG. 6C, a plate member 202e having a plurality of slit holes in one direction, The plate member 202f provided with slit holes having different slit hole directions may be alternately provided in the metal tube 202d. In the case of FIGS. 6B and 6C as well, the portions of the set of plate members 202e and 202f that restrict the cross section of the flow path are different from each other. For this reason, the molten glass MG is efficiently stirred by the plate materials 202e and 202f.

  Further, instead of using the plate materials 202e and 202f as a means for stirring the molten glass MG (static stirring means) as in the present embodiment, as shown in FIG. The molten glass MG may be stirred by providing the metal tube 202d with a stirrer 202i that rotates the shaft 202g as a dynamic stirring means.

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

200 melting apparatus 201 melting tank 202 clarification tank 202a, 202b, 202c heater electrode 202d metal tube 202e, 202f plate material 202g rotating shaft 202h blade 202i stirrer 203 stirring tank 203a stirrer 204, 205, 206 glass supply pipe 300 molding apparatus 310 molded body 400 Cutting device

Claims (13)

A method of manufacturing a glass substrate,
Including a clarification step of clarification while flowing molten glass in a tube whose outer peripheral wall made of platinum or a platinum alloy is heated,
The clarification step includes a defoaming step of releasing bubbles in the molten glass from a liquid surface of the molten glass toward a gas phase in the tube,
In the defoaming step, by stirring the molten glass, the flow of the molten glass in the central region of the flow path cross section of the tube is suppressed, and the temperature distribution along the radial direction of the tube of the molten glass is uniform. The manufacturing method of the glass substrate characterized by the above-mentioned.   The manufacturing method of the glass substrate of Claim 1 which stirs the said molten glass in at least one part of the area from the entrance of the said molten glass in the said pipe | tube to the maximum temperature vicinity formed by the heating of the said molten glass. The pipe is an enlarged pipe having a diameter larger than that of an upstream pipe provided on the upstream side of the pipe,
The said defoaming process is a manufacturing method of the glass substrate of Claim 1 or 2 performed with the said expansion tube. Wherein the molten glass, as refining agent, containing SnO _2, method of manufacturing a glass substrate according to any one of claims 1 to 3. Glass substrate prepared above ^are 10 2.5 temperature corresponding to the viscosity of [poise] is 1500 ° C. or more, a manufacturing method of a glass substrate according to any one of claims 1 to 4.   The manufacturing method of the glass substrate of any one of Claims 1-5 whose viscosity of the said molten glass stirred in the said defoaming process is 120-400 [poise].   The manufacturing method of the glass substrate of any one of Claims 1-6 which has a gaseous-phase space above the said pipe | tube.   The said glass substrate manufactured is a manufacturing method of the glass substrate of any one of Claims 1-7 comprised with an alkali free glass or alkali trace amount glass.   The method for manufacturing a glass substrate according to any one of claims 1 to 8, wherein the stirring of the molten glass is performed using a static stirring means constituted by a plate member fixed to the tube.   The said static stirring means is a manufacturing method of the glass substrate of Claim 9 which is a board member provided so that the flow-path cross section of the molten glass in the said pipe | tube may be controlled.   The static stirring means is composed of a plurality of plate members provided at different positions in the flow channel direction in the tube so as to regulate the flow channel cross section of the molten glass in the tube, and the set of adjacent plate members. The method for producing a glass substrate according to claim 10, wherein in at least one of the groups, the portions to be regulated of the cross section of the flow path are different from each other.   The method for producing a glass substrate according to any one of claims 1 to 8, wherein the stirring of the molten glass is performed using a dynamic stirring means. The clarification step further includes an absorption step of absorbing bubbles in the molten glass into the molten glass after the defoaming step,
The manufacturing method of the glass substrate of any one of Claims 1-12 with which the said molten glass is stirred at the said absorption process.

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