TW201300337A - Method for producing glass plate - Google Patents

Abstract

This method for producing a glass substrate involves a fining step of fining a molten glass while making the molten glass flow through a pipe of which the outer peripheral wall made of platinum or a platinum alloy is heated. The fining step involves a bubble removal step of releasing bubbles contained in the molten glass from the liquid surface of the molten glass toward the gas phase inside the pipe. In the bubble removal step, the temperature distribution of the molten glass along the radial direction of the pipe is made uniform by stirring the molten glass.

Description

Glass plate manufacturing method

The present invention relates to a method of manufacturing a glass sheet for producing a glass sheet.

In a glass substrate used for a flat panel display such as a liquid crystal display or a plasma display (hereinafter referred to as FPD (Flat Panel Display)), for example, a thickness of 0.5 to 0.7 mm and a size of 300 × 400 mm to 2850 × 3050 mm are mainstream.

As a method of producing a glass substrate for FPD, an overflow down-draw method is known. The overflow down-draw method is formed into a sheet glass by overflowing molten glass from the upper part of the molded object in a forming furnace, and the formed sheet glass is slowly cooled and cut. Thereafter, the cut sheet glass system is cut into a specific size in accordance with the specifications of the customer, and is shipped by washing, end surface polishing, or the like.

In the glass substrate for FPD, in particular, a glass substrate for a liquid crystal display device has a semiconductor element formed on its surface. Therefore, it is preferable that the glass substrate is completely free of an alkali metal component, or that it does not affect the semiconductor element or the like even if it is contained. .

Further, since the presence of bubbles in the glass substrate causes display defects, the glass substrate in which the bubbles are present cannot be used as the glass substrate for FPD. Therefore, it is required that no bubbles remain in the glass substrate. In the production of a glass substrate, the bubble from which the molten glass is removed is referred to as clarification, and in the clarification, the bubble is removed by a redox reaction of a clarifying agent such as As ₂ O ₃ . More specifically, the temperature of the molten glass which is coarsely melted is further increased, the clarifying agent acts to defoam the bubbles, and then the vesicles remaining in the incomplete defoaming are dissolved and absorbed in the glass by lowering the temperature. Inside. As a fining agent in addition to As ₂ O _3, the viewpoint of the environmental load of recent years, the use SnO ₂ or Fe ₂ O ₃ and the like instead of As ₂ O _3. As described above, in the case where the alkali metal component or the glass substrate containing a small amount of the alkali metal component is completely absent, the high-temperature viscosity is higher than that of the glass substrate containing a large amount of alkali metal such as soda-lime glass, and the bubble is not easily detached from the molten glass in the production. Therefore, a higher clarification effect is required.

On the other hand, a technique is known in which a clarification tank (heating heating) is heated by circulating an electric current in a clarification tank of a tube made of platinum or a platinum alloy, and molten glass is circulated in the heated clarification tank. Thereby, the temperature of the molten glass is raised and clarified (Patent Document 1).

[Previous Technical Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open Publication No. 2011-502934

When the clarification tank composed of a tube of platinum or a platinum alloy is heated to raise the temperature of the molten glass, the temperature of the molten glass is not uniformly heated. For example, as shown in FIG. 5, in the molten glass passing through the tube, since the flow rate of the molten glass flowing near the center of the pipe is faster than the flow rate of the molten glass flowing near the wall surface of the pipe having a large wall resistance, Since the wall surface of the tube to be heated is farther away, the temperature of the molten glass flowing near the center of the tube is lower than that of the molten glass flowing near the wall surface of the tube, and the temperature required for clarification cannot be raised to make the clarification become Insufficient problem. The problem is also to circulate current in a clarification tank composed of a tube of platinum or platinum alloy. The problem that arises in the situation.

Further, if the heating amount of the clarification tank containing platinum or platinum alloy is increased in order to raise the temperature near the center of the tube, there is a problem that the volatilization of platinum or a platinum alloy is promoted to shorten the life of the clarification tank. In particular, in the case of environmental load in recent years, when SnO _{2 is} used as a clarifying agent instead of As ₂ O ₃ , the molten glass is made higher than As ₂ O ₃ , so platinum or platinum alloy Volatilization is even more of a problem. Therefore, excessive heating of the tube composed of platinum or a platinum alloy is not preferable.

Further, in the clarification tank, defoaming can be promoted by making the viscosity of the bubble easy to float, but in the alkali-free glass which is preferably used in a glass substrate for a liquid crystal display device or the like, the viscosity is high due to high temperature. Compared with alkali glass, it is necessary to set the temperature of the molten glass to a high temperature, so that volatilization of platinum or a platinum alloy is more problematic. Therefore, excessive heating of the tube composed of platinum or a platinum alloy is not preferable.

Accordingly, an object of the present invention is to provide a method for producing a glass substrate which can prevent the volatilization of platinum or a platinum alloy which constitutes a tube of a clarification tank and enhance the clarification effect of the molten glass when the molten glass is clarified.

One aspect of the present invention is a method of manufacturing a glass substrate, It comprises a clarification step of clarifying one side of the molten glass while flowing in a heated tube other than the platinum or platinum alloy.

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 above defoaming step, the above melting is performed by stirring the molten glass The temperature distribution of the molten glass in the radial direction of the tube is uniformized.

In the method for producing a glass substrate according to the above aspect, volatilization of platinum or a platinum alloy can be prevented at the time of clarification of the molten glass, and the clarifying effect of the molten glass can be improved.

Hereinafter, a method of producing the glass sheet of the present embodiment will be described.

(Overall outline of the manufacturing method of the glass substrate)

Fig. 1 is a step diagram showing a method of manufacturing a glass substrate of the embodiment.

The manufacturing method of the glass plate mainly has a melting step (ST1), a clarification step (ST2), a homogenization step (ST3), a supply step (ST4), a molding step (ST5), a slow cooling step (ST6), and a cutting step ( ST7). Further, there are: a grinding step, a grinding step, a washing step, an inspection step, a packing step, and the like, and the plurality of glass substrates stacked in the packing step are transported to the ordering party.

Fig. 2 is a view schematically showing an apparatus for performing a melting step (ST1) to a cutting step (ST7). As shown in FIG. 2, the apparatus mainly has a melting device 200, a forming device 300, and a cutting device 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. Further, the glass supply pipes 204, 205, and 206 and the clarification tank 202 and the agitation vessel 203 which are connected between the grooves after the melting tank 201 and the molding apparatus 300 contain a metal pipe containing a platinum alloy such as platinum or a platinum-rhodium alloy.

In the melting step (ST1), for example, a glass frit which is supplied with a clarifying agent such as SnO ₂ and supplied into the melting tank 201 is melted by a flame and an electric heater (not shown) to obtain molten glass. Specifically, the glass raw material M is supplied to the liquid surface of the molten glass G using a raw material input device (not shown). The glass raw material is heated and slowly melted by using a flame in a high-temperature gas phase, and is melted in the molten glass MG. The molten glass MG is heated by electric heating by 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, by heating the molten glass MG in the clarification tank 202, the bubbles containing O ₂ , CO ₂ or SO ₂ contained in the molten glass MG are absorbed by a reducing reaction such as a clarifying agent such as SnO ₂ . The generated O ₂ grows and floats to the liquid surface of the molten glass MG to be released (defoaming step). In the clarification step, the clarification agent such as SnO obtained by a reduction reaction of a clarifying agent such as SnO ₂ is subjected to an oxidation reaction by lowering the temperature of the molten glass MG after defoaming, thereby remaining in the molten glass MG. The gas component such as O ₂ in the bubble in the middle is absorbed in the molten glass MG to cause the bubble to disappear (absorption step). The oxidation reaction and the reduction reaction using the clarifying agent are carried out by controlling the temperature of the molten glass MG. The temperature of the molten glass MG is caused to flow between a heating electrode (not shown) provided in the glass supply pipe 204 and a heating electrode 202a (see FIG. 3) provided in the clarification tank 202, and a current is applied to the heating electrode 202a. The heating electrode 202b (see FIG. 3(a)), which is disposed on the clarification tank 202 on the downstream side of the molten glass MG, is heated to evaporate the clarification tank 202 to raise the temperature of the molten glass MG. Further, a current is passed between the heating electrode 202b and the heating electrode 202c (see FIG. 3) provided on the clarification tank 202 on the downstream side of the molten glass MG, and the molten glass MG is heated while the clarification tank 202 is heated. Cool down. This electric heating is not limited to temperature control by electric conduction heating in three regions, and electric heating of one or two regions may be performed to control the temperature of the molten glass MG. The details of the clarification step in the clarification tank 202 are explained below.

In the homogenization step (ST3), the molten glass MG in the stirring tank 203 supplied through the glass supply pipe 205 is stirred by the agitator 203a to homogenize the glass component. In the stirring tank 203, the molten glass MG is stirred by one stirrer 203a, but the molten glass MG may be stirred by 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 tube 206.

The forming step (ST5) and the slow cooling step (ST6) are performed in the molding apparatus 300.

In the molding step (ST5), the molten glass MG is formed into a sheet-like glass G, and a continuous body of the sheet-like glass G is produced. In the present embodiment, an overflow down-draw method using the molded body 310 described below is used. In the slow cooling step (ST6), the formed and continuous sheet-like glass G is cooled so as to have a desired thickness without generating internal strain.

In the cutting step (ST7), in the cutting device 400, a sheet-shaped glass substrate is obtained by cutting the sheet-like glass G supplied from the forming device 300 to a specific length. The cut glass substrate is further cut into a specific size to produce a glass substrate of a target size. Thereafter, the end surface of the glass substrate is ground, polished, and the glass substrate is washed, and the bubbles or stripes are inspected. After the presence or absence of the defect, the glass substrate of the qualified product is packaged as a final product.

(clarification step)

As described above, the defoaming step and the absorbing step of the clarification step (ST2) are performed at least in the glass supply tube 204, the clarification tank 202, and the glass supply tube 205. The defoaming step is performed primarily in the first half of the supply tube 204 and the clarification tank 202. Again, the absorption step is performed primarily in the second half of the clarification tank 202. Further, the defoaming step is sometimes performed in the second half of the clarification tank 202. In this case, the absorption step is carried out in the supply tube 205 in the latter half of the clarification tank 202 or later.

The clarification step is illustrated below from the defoaming step.

The molten glass MG supplied from the melting tank 201 to the glass supply pipe 204 is heated in the glass supply pipe 204 and the first half of the clarification tank 202 before being supplied to the clarification tank 202 to promote the oxygen release reaction of the clarifying agent such as SnO ₂ . And in order to clarify the viscosity of the bubble in the first half of the groove 202 (preferably 120 [po] to 400 [poise], 1 poise = 0.1 Pa.s). For example, in the case of an alkali-free glass or a trace amount of alkali-containing glass (high-temperature viscous glass), for example, a glass having a viscosity corresponding to a viscosity of 10 ^2.5 [poise] of 1500 ° C or more, for example, 1580 ° C It is supplied to the glass supply pipe 204 at 1600 ° C to 1620 ° C at ~1620 ° C, and is heated so that the inlet of the clarification tank 202 is, for example, 1610 ° C to 1650 ° C, more preferably 1630 ° C to 1650 ° C. Further, in the clarification tank 202, the clarification tank 202 is heated by flowing a current between the heating electrode 202a and the heating electrode 202b described below, and the molten glass MG is heated to, for example, 1670 ° C to 1710 ° C, preferably 1690 ° C to 1710. °C. That is, it is necessary to raise the temperature of the clarification tank 202 to the vicinity of the heat-resistant temperature of the platinum or platinum alloy of the metal pipe constituting the clarification tank 202.

That is, in the defoaming step, in order to heat the molten glass MG, a tube having a length of a certain length or more is required. Further, the inner diameter of the clarification tank 202 is configured to be larger than the inner diameter of the glass supply pipe 204 and to have a gas phase space between the liquid surface of the molten glass MG and the tube. With such a configuration, the defoaming started in the glass supply tube 204 can be quickly released when the viscosity of the bubble is easily released in the clarification tank 202, and an effective clarifying effect can be promoted. Here, since the tube of the clarification tank 202 has a large inner diameter as described above, the temperature distribution in the radial direction of the tube is likely to be uneven. Moreover, this problem is less likely to occur in the glass supply tube 204 having a relatively small inner diameter.

The absorption step is then explained.

In the absorption step, when a current is passed between the heating electrode 202b and the heating electrode 202c (see FIG. 3), the molten glass MG is cooled while the clarification tank 202 is heated, and when SnO _{2 is} used as a clarifying agent, The SnO obtained by the reduction reaction of SnO ₂ is subjected to an oxidation reaction, whereby a gas component such as O ₂ remaining in the bubbles in the molten glass MG is absorbed in the molten glass MG to cause the bubbles to disappear.

(clarification tank)

Fig. 3(a) is a view specifically showing the configuration of the clarification tank 202 mainly performing the above-described clarification step. The clarification tank 202 specifically has heating electrodes 202a, 202b, and 202c and a metal pipe 202d. The metal tube 202d is a tube made of platinum or a platinum alloy. The molten glass MG flows into the inside of the metal pipe 202d by using the pipe of the metal pipe 202d as a flow path. Heating electrodes 202a, 202b, 202c The current flows from the outer peripheral wall surface of the metal pipe 202d to the metal pipe 202d, and the temperature of the molten glass MG is raised to a specific temperature by using the Joule heat generated by the electric resistance of the metal pipe 202d to heat the metal pipe 202d, and the molten glass MG is used. The defoaming of the molten glass MG is carried out in the clarifying agent. That is, the metal pipe 202d contains a peripheral wall other than platinum or a platinum alloy, and the outer peripheral wall is heated.

The heating electrodes 202a, 202b, and 202c are provided with a heating electrode 202a, a heating electrode 202b, and a heating electrode 202c in this order from the upstream side in the X direction as the longitudinal direction of the metal pipe 202d, and the heating electrode 202a and the heating electrode 202c are located in the metal pipe. Both ends of 202d. The heating electrode 202b is located substantially in the middle between the heating electrode 202a and the heating electrode 202c. That is, the region between the heating electrode 202a and the heating electrode 202b becomes the first heating region, and the region between the heating electrode 202b and the heating electrode 202c becomes the second heating region.

In the present embodiment, three heating electrodes 202a to 202c are provided, but two heating electrodes may be used. That is, the area in which the metal pipe 202d is heated may be one.

Further, in the inside of the metal pipe 202d, the molten glass MG does not flow through the entire flow path section of the metal pipe 202d, and a space in which the gas phase is provided above. In order to cause the surface of the molten glass MG to be defoamed to rupture on the surface of the molten glass MG to release the gas component in the bubble to the atmosphere, a gas is provided on the upper portion of the metal pipe 202d to separate the gas component from the metal pipe 202d. The phase is released to a gas vent hole (not shown) in the atmosphere.

The metal pipe 202d preferably has a cylindrical shape. The thickness of the metal pipe 202d is preferably, for example, 1 mm to 1.5 mm. The inner diameter of the metal pipe 202d is larger than the inner diameter of the glass supply pipes 204, 205, preferably larger than the inner diameter of the glass supply pipes 204, 205 by more than 30%, more preferably more than 40%. Example of the inner diameter of the metal pipe 202d If it is more than 300 mm. By setting the inner diameter of the metal pipe 202d to an inner diameter of, for example, 300 mm or more, the flow rate of the molten glass MG flowing in the metal pipe 202d can be lowered to extend the time during which the molten glass MG stays in the metal pipe 202d, which is highly efficient. The clarification of the molten glass MG was carried out.

In the clarification tank 202, the temperature of the molten glass MG is distributed in the X direction as shown in Fig. 3(b) by circulating current through the heating electrodes 202a, 202b, and 202c. The molten glass MG sent from the melting tank 201 is heated by the glass supply pipe 204 to gradually increase the temperature, and the molten glass MG is heated between the heating electrode 202a and the heating electrode 202b so that the temperature of the molten glass MG becomes maximum, and the heating electrode 202b is heated. The molten glass MG is heated between the heating electrodes 202c so that the temperature of the molten glass MG gradually decreases. That is, the molten glass MG is heated in a region between the heating electrode 202a and the heating electrode 202b to release oxygen, for example, by SnO ₂ by reduction of a clarifying agent such as SnO ₂ (tin oxide) contained in the molten glass MG. On the other hand, the molten glass MG is cooled in a region between the heating electrode 202b and the heating electrode 202c so as to be oxidized by a clarifying agent such as SnO (a clarifying agent obtained by reducing SnO ₂ ) contained in the molten glass MG. Allow SnO to absorb oxygen. Further, the molten glass MG is gradually cooled in the glass supply tube 205.

Fig. 4 (a) is a cross-sectional view showing the metal pipe 202d which cuts the clarification tank 202 in the X direction. The metal pipe 202d is alternately provided with a plurality of plate members 202e and 202f which are walls which are orthogonal to the X direction on the inner wall surface of the metal pipe 202d which is the flow path of the molten glass MG. The plate members 202e and 202f are static stirring mechanisms composed of members made of a material such as platinum or platinum alloy fixed to the metal pipe 202d in the metal pipe 202d. That is, the plates 202e, 202f are stirred by the metal The molten glass MG flowing in the tube 202d makes the temperature distribution of the molten glass MG in the radial direction of the tube uniform. Here, the homogenization of the temperature of the molten glass MG in the radial direction means that the temperature difference in the temperature distribution is within 20 ° C, more preferably within 10 ° C, and even more preferably within 5 ° C.

It is preferable that the plate members 202e and 202f have a cross-sectional area perpendicular to the X direction of the metal pipe 202d to be one-third or more and two-thirds or less of the cross-sectional area of the metal pipe 202d perpendicular to the X direction, that is, to limit the melting. The way the glass MG flows is set. When the cross-sectional area (blocking area) of the sheets 202e and 202f that restrict the flow of the molten glass MG is too small, the stirring effect is small, and if the blocking area is too large, the element that hinders the flow of the molten glass MG becomes excessive. The blocking area is preferably about one-half of the cross-sectional area of the metal pipe 202d perpendicular to the X direction. As shown in Fig. 4 (b), the plate member 202e is disposed so as to cross the metal pipe 202d in the horizontal direction (the horizontal direction in Fig. 4(b)) through the central portion including the center of the flow path section of the metal pipe 202d. The flow of the molten glass MG on the central portion of the flow path section is restricted, and the molten glass MG can be passed through the upper portion and the lower portion of the flow path. On the other hand, as shown in Fig. 4(c), the plate member 202f and the plate member 202e are arranged differently so as to sandwich the central portion of the metal pipe 202d including the center of the flow path section and in the horizontal direction (Fig. 4(c) The horizontal direction is provided so as to cross the upper portion and the lower portion of the flow path section, and restrict the flow of the molten glass MG on the upper portion and the lower portion of the flow path section, and the molten glass MG can pass through the center of the flow path section of the metal pipe 202d. Central area. In other words, a plurality of plate members 202e and 202f which are disposed at different positions in the flow path direction of the pipe are formed so as to restrict the flow path cross section of the molten glass MG of the pipe of the metal pipe 202d. Adjacent In the group of the plates 202e and 202f, the portions of the restriction flow path are different from each other. Further, the plate member 202f is provided so as to traverse the upper portion and the lower portion of the flow path cross section in the horizontal direction (the horizontal direction in FIG. 4(c)), but the plate member 202f may be disposed in the flow. The shape obtained by rotating the surface of the road section by 90 degrees, that is, the flow path may be cross-cut in the vertical direction (the downward direction of FIG. 4(c)), respectively, in the middle of the pipe including the center of the flow path profile center. Set the part of the left and right sides of the section. In this case, it is preferable to use the shape shown in Fig. 4 (b) as the plate member 202e. Further, the shape shown in Fig. 4(c) may be used as the plate member 202f, and the plate member 202e shown in Fig. 4(b) may be rotated by 90 degrees in the plane of the flow path cross section.

In the present embodiment, the portions of the plate members 202e and 202f that restrict the flow path are different from each other, but the portions of the flow path cross-section may be the same. However, in order to prevent the molten glass MG from flowing straight from the upstream side to the downstream side while stirring the molten glass MG in the vertical direction, it is preferable that the portions of the restricting flow paths of the plates 202e and 202f are different from each other. . Further, in the present embodiment, although two plate members 202e and 202f are provided, 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 which is electrically heated by a peripheral wall including platinum or a platinum alloy. In this case, the molten glass MG flowing near the wall of the heated metal pipe 202d is easily heated by the electric heating of the metal pipe 202d, but the portion of the center of the flow path in the molten glass MG is away from the heated metal wall 202d. Therefore, it is difficult to heat up. That is, easy to follow the metal The temperature distribution of the molten glass MG is generated in the radial direction of the tube 202d. Therefore, in the previous clarification tank in which the plates 202e, 202f are not provided, the temperature distribution of the molten glass flowing in the radial direction of the tube is not uniform, and in addition, the portion of the center of the flow path which is far from the wall of the metal pipe is molten glass. The flow rate is faster than the flow rate of the molten glass flowing near the wall of the metal tube. Therefore, the molten glass MG flowing in the center of the flow path section is easily passed through the clarification tank without being heated. If the temperature distribution of the molten glass MG is generated in the radial direction of the metal pipe 202d for the above reason, it is necessary to set the heating temperature of the metal pipe 202 to be high so that the temperature at the lowest temperature portion in the temperature distribution is suitable for clarification. The agent exerts a reducing action to release defoaming of oxygen, and the molten glass MG has a temperature at which the viscosity of the bubble is easily floated. However, when the heating temperature is set as described above, volatilization of a metal component such as platinum or a platinum alloy constituting the metal pipe 202d becomes severe, and the consumption of the metal pipe 202d becomes severe. Therefore, in the present embodiment, in order to make the temperature distribution of the molten glass MG in the radial direction of the metal pipe 202d nearly uniform (for uniformity), the plate 202e as a mechanism for stirring the molten glass MG is provided on the flow path of the metal pipe 202d. 202f. Thereby, the volatilization of the platinum or platinum alloy constituting the metal pipe 202d can be prevented as compared with the prior, and the clarifying effect of the molten glass MG can be improved.

The agitation of the molten glass MG using the plate materials 202e and 202f in the present embodiment is the highest temperature formed by heating from the inlet of the molten glass MG in the metal pipe 202d to the molten glass MG in the clarification tank 202 (refer to FIG. 3). (b)) Perform at least part of the interval up to the vicinity. Since the defoaming step of the molten glass MG is performed in the above section, the defoaming step is The temperature distribution of the molten glass MG in the radial direction of the metal pipe 202d is made uniform, the excess heating of the metal pipe 202d can be suppressed, the volatilization of the platinum or platinum alloy constituting the metal pipe 202d can be prevented, and the clarification of the molten glass MG can be improved. effect. Here, "near" in the vicinity of "the highest temperature" means a range of, for example, 10 ° C or less with respect to the maximum temperature, and preferably a range of 5 ° C or less. Therefore, the above-mentioned section means the distance from the entrance of the molten glass MG in the metal pipe 202d to the edge of the above-mentioned "near" where the temperature is lowered by 10 ° C beyond the position of the highest temperature formed by heating of the molten glass MG. Interval.

In the clarification tank 202, after the molten glass MG is heated and defoamed, the temperature of the molten glass MG is lowered to be lower than the clarification tank 202 by heating and heating the metal pipe 202d between the heating electrodes 202b and 202c. The temperature of the molten glass MG in the first half is suitable for the temperature of the absorption step. Here, the temperature of the molten glass MG in the first half of the clarification tank 202 is a viscosity which promotes the release reaction of oxygen of the clarifying agent and which is easy to float the bubble in the molten glass MG (preferably 120 [po] a temperature of ~400 [poise], for example, in an alkali-free glass or a trace amount of alkali-containing glass (high-temperature viscous glass), for example, in a glass having a temperature of 1500 ° C or higher corresponding to 10 ^2.5 [poise] In the case where SnO _{2 is} used as a clarifying agent, the temperature is, for example, in the range of 1610 ° C to 1710 ° C. In the case where SnO _{2 is} used as the clarifying agent in the above alkali-free glass or a trace amount of alkali-containing glass, the temperature suitable for the absorption step is in the range of 1200 ° C to 1650 ° C. As a result, the maximum temperature of the molten glass MG in the formed clarification tank 202 is 1670 ° C to 1710 ° C or 1690 ° C to 1710 ° C. Moreover, in this case, the upper limit of the maximum temperature shown in FIG. 3(b) is, for example, 1700 to 1710 degrees.

In this manner, the clarifying agent contained in the molten glass MG is oxidized, and the oxygen contained in the bubbles remaining in the molten glass MG is absorbed in the clarifying agent to be clarified. At this time, since the temperature of the molten glass MG is higher than the temperature of the wall surface of the tube, when the stirring is not performed in the clarification tank 202, the temperature of the molten glass MG flowing near the center of the piping becomes higher than that in the tube. The temperature of the molten glass flowing near the wall surface. That is, there is a problem that the temperature cannot be completely lowered to the temperature suitable for the absorption step, and the clarification is insufficient. At this time, the clarification tank 202 can use the plate members 202e and 202f as a stirring mechanism of the molten glass MG to stir the molten glass MG. When the molten glass MG has the above temperature distribution at the time of absorption of the bubbles, it is difficult to efficiently absorb the bubbles remaining in the molten glass MG due to the above reasons. Therefore, in the present embodiment, as shown in Fig. 4(a), not only the defoaming of the molten glass MG but also the plate members 202e and 202f can be used as the stirring mechanism of the molten glass MG during the absorption of the bubbles. The temperature of the wall surface of the tube can be made lower than that of the unstirred molten glass by stirring the molten glass during defoaming of the molten glass MG or by stirring the molten glass during the absorption of the bubbles in addition to the defoaming of the molten glass MG. The situation is, for example, a few ° C ~ 10 ° ° C. That is, even if the temperature of the wall surface of the tube is lowered by, for example, several ° C to 10 ° C, the temperature may be the same as the temperature of the molten glass in the case where the molten glass is not stirred.

In the clarification step of the present embodiment, not only the defoaming of the molten glass MG but also the plate members 202e and 202f are used as the stirring mechanism of the molten glass MG when the bubble is absorbed, but the molten glass MG is heated at least. Stirring and melting in a portion where defoaming is performed in such a manner that the above temperature distribution is uniformized Glass MG can be used.

The metal pipe 202d for defoaming in the present embodiment is an enlarged pipe which is stepwise enlarged with respect to the glass supply pipe 204, but may be an enlarged pipe which is continuously expanded in diameter. Since at least the metal pipe 202d is a pipe that is enlarged with respect to the glass supply pipe 204, a gas phase space exists in the metal pipe 202d above the molten glass MG, so that the molten glass MG has a liquid surface, and is melted due to an enlarged flow path. The flow rate of the glass MG is lowered to extend the residence time in the metal pipe 202d, and since the area of the liquid surface of the molten glass MG is enlarged, defoaming can be performed efficiently.

(glass composition)

The glass substrate produced by the method for producing a glass substrate of the present embodiment can be preferably used for a glass substrate for a flat panel display. In order to effectively exhibit the effects of the present embodiment, for example, it is preferable to contain any one of Li, Na, and K, or to contain at least one of Li, Na, and K, and to contain the inside. The total amount of the components of Li, Na, and K is also a glass composition of 0.5% by mass or less. The glass composition can be preferably exemplified as follows.

The glass composition of a glass substrate is mentioned, for example.

The content rate of the composition shown below is expressed as % by mass.

Preferably, the alkali-free glass contains the following composition: SiO ₂ : 50 to 70%, B ₂ O ₃ : 5 to 18%, Al ₂ O ₃ : 0 to 25%, MgO: 0 to 10%, CaO: 0~ 20%, SrO: 0 to 20%, BaO: 0 to 10%, and RO: 5 to 20% (wherein R is selected from at least one of Mg, Ca, Sr, and Ba, and is contained in a glass plate) .

Further, the glass of the glass substrate may be exemplified by the following glass compositions: SiO ₂ : 50 to 70%, B ₂ O ₃ : 1 to 10%, Al ₂ O ₃ : 0 to 25%, MgO: 0 to 10%, and CaO: 0~20%, SrO: 0~20%, BaO: 0~10%, RO: 5~30% (where R is the sum of Mg, Ca, Sr and Ba), and the alkali-free glass containing the above composition is also It is also better.

Further, the glass of the glass substrate may be exemplified by the following glass compositions: SiO ₂ : 50 to 70%, B ₂ O ₃ : 3 to 15%, Al ₂ O ₃ : 8 to 25%, MgO: 0 to 10%, and CaO: 0~20%, SrO: 0~20%, BaO: 0~10%, RO: 5~30% (where R is the sum of Mg, Ca, Sr and Ba), and the alkali-free glass containing the above composition is also It is also better.

Further, in the present embodiment, the alkali-free glass is used, but the glass substrate may be a trace amount of alkali-containing glass containing a small amount of an alkali metal (the total content of the alkali metal is more than 0% by mass). In the case of containing an alkali metal, it is preferable to contain R0 ₂ O in a total amount of 0.10% by mass or more and 0.5% by mass or less (wherein R' is at least one selected from the group consisting of Li, Na, and K, and is a glass substrate G Included). Further, in order to make the melting glass becomes easy to reduce the specific resistance of the viewpoint, the content of iron oxide in the glass in terms of Fe ₂ O ₃ is preferably 0.01 to 0.2% by mass, more preferably 0.01 to 0.15% by mass, Further, it is preferably 0.01 to 0.10% by mass. Further, when SnO _{2 is} added as a clarifying agent, the content of SnO ₂ is more preferably 0.01 to 0.5% by mass. Further, in the present embodiment, since SnO ₂ is a component which tends to devitrify the glass, the content thereof is preferably 0.01 to 0.5% by mass, more preferably 0.05 to 0.4 by mass in order to improve the clarity and prevent devitrification. % is further preferably 0.1 to 0.3% by mass. Further, it is preferable that substantially no As ₂ O ₃ , Sb ₂ O ₃ or PbO is contained.

In addition to the above components, the glass substrate of the present embodiment may contain various other oxides in order to adjust various physical, melting, clarifying, and forming properties of the glass. The other oxide is not limited to the following, and examples thereof include TiO ₂ , MnO, ZnO, Nb ₂ O ₅ , MoO ₃ , Ta ₂ O ₅ , WO ₃ , Y ₂ O ₃ , and La ₂ O ₃ .

In the manufacturing method of the present embodiment, the molten glass MG is stirred to uniformize the temperature distribution in the radial direction of the metal pipe 202d. Therefore, even when a molten glass having a low meltability and a high viscosity of molten glass is used depending on the glass composition, the molten glass may be heated to a degree that the viscosity of the molten glass is suitable for defoaming, and it is not necessary. Previously The molten glass is further heated by raising the temperature of the molten glass flowing near the center of the metal pipe. Therefore, the volatilization of the metal pipe 202d composed of platinum or a platinum alloy can be suppressed, and the clarification step can be efficiently performed.

In other words, even a glass having a high viscosity corresponding to a temperature of 102.5 [poise] of 1500 ° C or higher (for example, 1500 ° C or higher and 1650 ° C or lower) can be preferably used as a constituent glass in the production method of the present embodiment. The glass of the substrate suppresses the volatilization of the metal tube 202d composed of platinum or a platinum alloy, and the clarification step is effectively performed.

Moreover, even in the case of glass which is not highly viscous, in the case of using environmentally important load in recent years, when SnO _{2 is} used as a clarifying agent instead of As ₂ O ₃ , it is the case where As ₂ O _{3 is} used as a clarifying agent. The ratio of the molten glass to a higher temperature makes the volatilization of platinum or a platinum alloy more problematic. However, in the manufacturing method of the present embodiment, it is not necessary to further heat the molten glass in order to increase the temperature of the molten glass flowing near the center of the metal pipe as before. Therefore, volatilization of the metal pipe 202d composed of platinum or a platinum alloy can be suppressed, and the clarification step can be efficiently performed.

(Modification)

In the present embodiment, as shown in FIG. 4(a), a plurality of plate members 202e and 202f provided in the metal pipe 202d are alternately arranged, but one set of plate members 202e and 202f may be disposed.

Further, as shown in Fig. 6(a), the metal plates 202d may be alternately provided with the plates 202e and 202f extending from the wall of the metal pipe 202d toward the inside of the pipe but having different extension heights. That is, since the heights of the adjacent plates 202e, 202f are different, a portion of the plates 202e, 202f restricts the flow path profile. Different from each other. In this case, by the agitation of the sheets 202e, 202f, the molten glass MG flows in a undulating manner as shown in the dotted line. That is, the plate members 202e and 202f shown in Fig. 6(a) are used as a stirring mechanism for stirring the molten glass MG.

Further, as shown in FIG. 6(b), a plate member 202e having a plurality of holes having a circular or semicircular shape and a plate member 202f provided with a hole different from the arrangement of the holes may be alternately arranged in the metal pipe 202d. The plates 202e and 202f shown in Figs. 4(a) and 4(b) of the embodiment.

Further, as shown in FIG. 6(c), a plate member 202e having a plurality of slit holes in one direction and a slit plate provided with a slit hole different from the direction of the slit hole may be alternately provided in the metal pipe 202d. 202f replaces the plates 202e and 202f shown in Figs. 4(a) and 4(b) of the present embodiment. In the case of Figs. 6(b) and (c), the portions of the restricting flow path sections of the groups of the plates 202e, 202f are also different from each other. Therefore, the molten glass MG can be efficiently stirred by the sheets 202e, 202f.

Further, as shown in FIG. 7, the metal plate 202d may be provided with a blade 202h provided on the rotating shaft 202g, and the agitator 202i for rotating the rotating shaft 202g as a dynamic stirring mechanism instead of using the plate member 202e as in the present embodiment. 202f agitates the molten glass MG as a mechanism (static stirring mechanism) for stirring the molten glass MG.

In the above, the method of manufacturing the glass substrate of the present invention is described in detail, but the present invention is not limited to the above-described embodiments, and various modifications and changes can be made without departing from the spirit and scope of the invention.

200‧‧‧melting device

201‧‧‧melting tank

202‧‧‧Clarification tank

202a, 202b, 202c‧‧‧ heating electrodes

202d‧‧‧Metal tube

202e, 202f‧‧‧ plates

202g‧‧‧Rotary axis

202h‧‧‧ leaves

202i‧‧‧Mixer

203‧‧‧Stirring tank

203a‧‧‧Agitator

204, 205, 206‧‧‧ glass supply tube

300‧‧‧Forming device

310‧‧‧Formed body

400‧‧‧ cutting device

Fig. 1 is a step diagram showing a method of manufacturing a glass substrate of the embodiment.

Fig. 2 is a view schematically showing an apparatus for performing the melting step to the cutting step shown in Fig. 1.

Fig. 3(a) is a view mainly showing a clarification tank for carrying out the clarification step shown in Fig. 1, and Fig. 3(b) is a view showing the temperature of the outer peripheral wall of the clarification tank.

4(a) to (c) are diagrams showing the plates used in the clarification tank.

Figure 5 is a graph showing the flow rate and temperature of the molten glass in the previous clarification tank.

6(a) to 6(c) are views showing an example of a plate material different from the plate material shown in Figs. 4(a) to 4(c).

Fig. 7 is a view showing an example of a stirring mechanism different from the stirring mechanism constituted by the plate material shown in Figs. 4(a) to 4(c).

202‧‧‧Clarification tank

202e, 202f‧‧‧ plates

204, 205‧‧‧ glass supply tube

Claims (13)

A method for producing a glass substrate, comprising: a clarification step of clarifying a molten glass while flowing in a tube containing a peripheral wall other than platinum or a platinum alloy; and the clarifying step includes causing bubbles in the molten glass a defoaming step of releasing the liquid surface of the molten glass toward the gas phase in the tube; and in the defoaming step, the temperature distribution of the molten glass in the radial direction of the tube is made uniform by stirring the molten glass. The method for producing a glass substrate according to claim 1, wherein the molten glass is stirred in at least a part of a section from the inlet of the molten glass to a vicinity of a highest temperature at which the molten glass is heated by the heating. The method for producing a glass substrate according to claim 1 or 2, wherein the tube comprises an enlarged tube which is expanded stepwise or continuously; and the defoaming step is carried out in the enlarged tube. The method for producing a glass substrate according to claim 1 or 2, wherein the molten glass contains SnO ₂ as a clarifying agent. The method for producing a glass substrate according to claim 1 or 2, wherein the glass substrate produced by the above-mentioned glass substrate has a viscosity corresponding to a viscosity of 10 ^2.5 [poise] of 1500 ° C or higher. The method for producing a glass substrate according to claim 1 or 2, wherein the viscosity of the molten glass stirred in the defoaming step is 120 to 400 [poise]. A method of producing a glass substrate according to claim 1 or 2, wherein a space of a gas phase is provided above the inside of the tube. The method for producing a glass substrate according to claim 1 or 2, wherein the glass substrate produced is composed of an alkali-free glass or a trace amount of alkali-containing glass. The method for producing a glass substrate according to claim 1 or 2, wherein the stirring of the molten glass is carried out using a static stirring mechanism constituted by a plate member fixed to the tube. The method for producing a glass substrate according to claim 9, wherein the static stirring mechanism is a plate member provided to restrict a cross section of the flow path of the molten glass in the tube. The method for producing a glass substrate according to claim 10, wherein the static stirring mechanism is a plurality of plates which are disposed at different positions in a flow path direction in the tube so as to restrict a flow path of the molten glass in the tube. The member is configured to restrict the portions of the flow path cross-section from being different from each other in at least one of the group of adjacent plate members. The method for producing a glass substrate according to claim 1 or 2, wherein the stirring of the molten glass is carried out using a dynamic stirring mechanism. The method for producing a glass substrate according to claim 1 or 2, wherein the clarifying step further comprises an absorption step of absorbing bubbles in the molten glass in the molten glass after the defoaming step; and stirring in the absorbing step The above molten glass.