JP6861056B2 - Glass substrate manufacturing method and glass substrate manufacturing equipment - Google Patents

Description

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

The overflow downdraw method may be used to manufacture a glass substrate (hereinafter referred to as "glass substrate for display") used for a flat panel display such as a liquid crystal display or a plasma display. The overflow down draw method is a step of molding a plate-shaped sheet glass below the molded body by overflowing the molten glass from the upper part of the molded body in a molding furnace, and a cooling step of slowly cooling the sheet glass in a slow cooling furnace. And include. In the slow cooling furnace, the sheet glass is pulled in between the paired rollers, and the sheet glass is stretched to a desired thickness while being conveyed downward by the rollers, and then the sheet glass is slowly cooled. After that, a glass plate is formed by cutting the sheet glass to a predetermined size.

The molten glass flowing down along the side surface of the molded body leaves the molded body and at the same time shrinks in the width direction of the sheet glass due to surface tension. In Patent Document 1, a cooling unit provided between the molded body and the tension roller below the molded body, in the vicinity of the edge portion in the width direction of the sheet glass, and separated from the sheet glass is used. A method of adjusting the temperature of the edge portion to suppress the shrinkage of the sheet glass is disclosed. After that, the sheet glass whose shrinkage is suppressed is formed by passing through a slow cooling space. In this slow cooling space, the ambient temperature is controlled so as to have a desired temperature profile (temperature distribution that does not cause distortion in the glass plate), and plate thickness deviation, warpage, and distortion of the glass plate are suppressed.

Japanese Unexamined Patent Publication No. 5-124827

In recent years, the required specifications (quality) of glass substrates for liquid crystal display devices have become stricter. The surface of the glass substrate is required to have high flatness, and in order to satisfy the required specifications, it is necessary to suppress the occurrence of veins or local plate thickness deviation due to particularly steep concave or convex. This vein is unevenness in which the thickness (height) of the sheet glass fluctuates within a predetermined width, and is caused by contraction in the width direction of the sheet glass due to surface tension at the same time as leaving the molded body. It occurs continuously in a streak pattern in the glass transport direction.

Therefore, an object of the present invention is to provide a method for manufacturing a glass substrate and an apparatus for manufacturing a glass substrate, which can suppress a local thickness deviation including veins generated in the sheet glass.

One aspect of the present invention is a method for manufacturing a glass substrate in which molten glass is supplied from a glass supply pipe to a molded body having a supply groove, and the sheet glass is molded by an overflow down draw method using the molded body. In the manufacturing method,
The supply groove has a bottom surface such that the amount of molten glass supplied to the supply groove overflowing from the supply groove is uniform in the extending direction of the supply groove and the width direction orthogonal to the extending direction. Has a shape,
A molten glass having a maximum temperature difference of 30 ° C. or less and a viscosity of the molten glass of 22000 dPa · s or more and 38000 dPa · s or less is supplied to the supply groove. , And the molding process of forming the sheet glass by merging the molten glass at the lower end of the molded body.
The sheet glass is provided with an end cooling step of cooling both ends in the width direction of the sheet glass so as to suppress a plate thickness deviation locally generated in the sheet glass molded in the molding step.

In the end cooling step, the tension applied when the molded body is not deformed in the width direction of the sheet glass and the cross-sectional shape of the sheet glass becomes the target shape is used as a reference tension, and the molded body is deformed. When not, the reference tension is controlled by cooling both ends of the sheet glass in the width direction, and when the molded body is deformed, the reference tension is adjusted according to the deformation of the molded body. It is preferable to apply the applied tension to the sheet glass.
At this time, the deformation of the molded body is a creep deformation that changes with time with the use of the molded body, and a tension corresponding to the displacement amount of the molded body at a predetermined position due to the creep deformation is applied to the reference tension. , Is preferable.
Further, it is preferable that the larger the deformation, the stronger the cooling of both ends.

The plate thickness deviation is preferably 10 μm or less.

In the molding step, it is preferable to heat the molten glass so that the temperature of the molten glass flowing down the molded product is 10 ° C. to 150 ° C. higher than the liquidus temperature of the molten glass.

Another aspect of the present invention is a glass substrate manufacturing apparatus in which molten glass is supplied from a glass supply pipe to a molded body having a supply groove, and the sheet glass is molded by the overflow down draw method using the molded body.
The molded body merges the molten glass at the lower end of the molded body with a supply groove that receives the supply of the molten glass having a maximum temperature difference of 30 ° C. or less and a viscosity of 22000 dPa · s or more and 38000 dPa · s or less. It has a wall surface for forming a sheet glass.
The supply groove has a bottom surface such that the amount of molten glass supplied to the supply groove overflowing from the supply groove is uniform in the extending direction of the supply groove and the width direction orthogonal to the extending direction. Has a shape.
The manufacturing apparatus further includes an end cooling device that cools both ends of the sheet glass in the width direction so as to suppress a plate thickness deviation locally generated in the sheet glass molded from the molded body.

According to the glass substrate manufacturing method and the glass substrate manufacturing apparatus of the above-described embodiment, the local plate thickness deviation generated in the sheet glass can be suppressed.

It is a figure which shows the flow of the manufacturing method of this embodiment. It is the schematic of the manufacturing apparatus of a glass substrate. It is a perspective view which shows an example of the molded article which can be used for the manufacturing method of this embodiment. It is a figure explaining an example of the manufacturing method of this invention using the apparatus shown in FIG. It is a figure which shows the cross section of the glass supply tube connected to the supply groove of a molded body. It is a graph which shows the temperature change of the molten glass flowing in the glass supply pipe in the longitudinal direction of the glass supply pipe used in this embodiment. It is a figure explaining the example of the shape change of the molded body acquired by the acquisition part. It is a figure which shows an example of the cross section of the glass ribbon molded by the creep deformed molded body. It is a figure which shows the relationship between the displacement amount of a molded body, and the tension T applied to a glass ribbon. (A) is an enlarged view of an example of a cross section of the seed glass along the line AA shown in FIG. 4, and (b) is a cross section of the sheet glass along the line BB shown in FIG. It is an enlarged view of an example.

Hereinafter, the method for manufacturing the glass substrate of the present embodiment will be described.
(Overview of manufacturing method of glass substrate)
FIG. 1 is a diagram showing an example of a process of the method for manufacturing a glass substrate of the present embodiment. The glass substrate manufacturing method includes 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 (ST6). Mainly has ST7). In addition to this, it may have a grinding process, a polishing process, a cleaning process, an inspection process, a packing process, and the like. The manufactured glass substrates are laminated in the packaging process as needed and transported to the supplier.

In the melting step (ST1), molten glass is produced by heating a glass raw material.
In the clarification step (ST2), the temperature of the molten glass is raised, so that _{bubbles containing oxygen, CO 2} or SO ₂ contained in the molten glass are generated. The bubbles absorb oxygen generated by the reduction reaction of the clarifying agent (tin oxide or the like) contained in the molten glass, grow, and float on the liquid surface of the molten glass and are released. After that, in the clarification step, by lowering the temperature of the molten glass, the reducing substance obtained by the reduction reaction of the clarifying agent undergoes an oxidation reaction. As a result, gas components such as oxygen in the bubbles remaining in the molten glass are reabsorbed in the molten glass, and the bubbles disappear. The oxidation reaction and reduction reaction by the fining agent are carried out by controlling the temperature of the molten glass.
In the clarification step, a decompression defoaming method in which bubbles existing in the molten glass are grown in a decompression atmosphere to defoam can also be used. The vacuum defoaming method is effective in that it does not use a fining agent. However, the decompression defoaming method complicates and increases the size of the device. Therefore, it is preferable to adopt a clarification method in which a clarifying agent is used to raise the temperature of the molten glass.

In the homogenization step (ST3), the glass component is homogenized by stirring the molten glass with a stirrer. This makes it possible to reduce the uneven composition of the glass, which is a cause of veins and the like. The homogenization step is performed in a stirring tank described later.
In the supply step (ST4), the agitated molten glass is supplied to the molding apparatus.

The molding step (ST5) and the slow cooling step (ST6) are performed by a molding apparatus.
In the molding step (ST5), the molten glass is molded into the sheet glass to create a flow of the sheet glass. The overflow down draw method is used for molding.
In the slow cooling step (ST6), the molded and flowing sheet glass has a desired thickness and is cooled so as not to cause internal strain and further to prevent warpage.
In the cutting step (ST7), a plate-shaped glass substrate is obtained by cutting the sheet glass after slow cooling to a predetermined length. The cut glass substrate is further cut to a predetermined size to make a glass substrate of a target size.

FIG. 2 is a schematic view of a glass substrate manufacturing apparatus that performs the melting step (ST1) to the cutting step (ST8) in the present embodiment. As shown in FIG. 2, the glass substrate manufacturing apparatus mainly includes a melting apparatus 100, a molding apparatus 200, and a cutting apparatus 300. The melting device 100 includes a melting tank 101, a clarification pipe 102, a stirring tank 103, transfer pipes 104 and 105, and a glass supply pipe 106.
The melting tank 101 shown in FIG. 2 is provided with a heating means such as a burner (not shown). The glass raw material to which the fining agent is added is put into the melting tank, and the melting step (ST1) is performed. The molten glass melted in the melting tank 101 is supplied to the clarification pipe 102 via the transfer pipe 104.
In the clarification tube 102, the temperature of the molten glass MG is adjusted, and the clarification step (ST2) of the molten glass is performed by utilizing the redox reaction of the fining agent. Specifically, when the temperature of the molten glass in the clarifying tube 102 is raised _{, the bubbles containing oxygen, CO 2} or SO ₂ contained in the clarifying glass absorb the oxygen generated by the reduction reaction of the clarifying agent. It grows and floats on the liquid surface of the molten glass and is released into the vapor phase space. Then, by lowering the temperature of the molten glass, the reducing substance obtained by the reducing reaction of the fining agent undergoes an oxidation reaction. As a result, gas components such as oxygen in the bubbles remaining in the molten glass are reabsorbed in the molten glass, and the bubbles disappear. The clarified molten glass is supplied to the stirring tank 103 via the transfer pipe 105.
In the stirring tank 103, the molten glass is stirred by the stirrer 103a to perform the homogenization step (ST3). The molten glass homogenized in the stirring tank 103 is supplied to the molding apparatus 200 via the glass supply pipe 106 (supply step ST4).
In the molding apparatus 200, the sheet glass SG is molded from the molten glass by the overflow down draw method (molding step ST5) and slowly cooled (slow cooling step ST6).
In the cutting device 300, a plate-shaped glass substrate cut out from the sheet glass SG is formed (cutting step ST7).

In the supply step S4, the temperature of the molten glass flowing through the glass supply tube 106 is controlled. Specifically, the glass supply pipe 106 is energized and heated to heat the molten glass flowing through the glass supply pipe 106, and the glass supply pipe 106 is surrounded by a refractory material to fill the inside of the glass supply pipe 106. Suppresses heat dissipation of flowing molten glass. In the supply step S4, the temperature of the molten glass is controlled so that the temperature of the molten glass flowing in the glass supply tube 106 gradually decreases from the upstream side to the downstream side. The glass supply pipe 106 is divided into a plurality of sections, and the temperature of the molten glass is controlled for each section. The energizing heating device that heats the glass supply tube 106 controls the current and voltage flowing through each section of the glass supply tube 106 so that the temperature of the molten glass shows a change based on the measurement data of the measuring device. By controlling the current and voltage in the glass supply pipe 106, the temperature of the molten glass supplied to the molding apparatus 200 can be appropriately changed. Here, at the downstream end of the glass supply tube 106, the tube temperature and the center temperature of the molten glass are preferably 1235 ° C to 1265 ° C, more preferably 1240 ° C to 1260 ° C.

(Composition of molded product)
Next, the configuration of the molded body 1 included in the molding apparatus 200 will be described with reference to FIGS. 3 and 4. FIG. 3 shows an example of a molded body 1 that can be used in the manufacturing method of the present embodiment, and FIG. 4 shows an example of a molding process in the manufacturing method of the present embodiment using the molded body 1 shown in FIG. The molded body 1 overflows from both sides of the upper surface 3 on which the supply groove 2 to which the molten glass is supplied is formed, and flows down from between both end portions 3a and 3b in the direction in which the supply groove 2 on the upper surface 3 extends. Both the pair of wall surfaces 5 (only one wall surface is shown in FIGS. 3 and 4) in which the molten glass is guided and fused at the lower end 4 of the molded body 1 to form a sheet glass SG, and the wall surface 5 in the width direction. It is provided with a pair of guides 6a and 6b formed at the positions of the ends 5a and 5b of the above. The guides 6a and 6b are formed so as to project from the wall surface 5 at the positions of the end portions 5a and 5b, respectively, so as to face each other. The molten glass overflowing from the supply groove 2 flows down each of the pair of wall surfaces 5. The wall surface 5 includes a vertical wall surface in which the molten glass overflowing from the supply groove 2 flows down in the vertical direction, and an inclined wall surface connected to the vertical wall surface in which the molten glass flowing down the vertical wall surface is guided to the lower end 4 of the molded body 1. Have. The pair of molten glass flows down the wall surface 5 merge at the lower end 4 of the molded body 1 and merge with each other. At this time, the widths of the molten glass flowing down along the wall surface 5 are regulated by the guides 6a and 6b, and for example, sheet glass SG having high thickness uniformity in the width direction is continuously formed. The lower end 4 of the molded body 1 forms a linear ridge line in which a pair of wall surfaces 5 (sloping wall surfaces) are connected to each other. Reference numerals 2a shown in FIGS. 3 and 4 are the bottom surface 2a of the supply groove 2, and reference numeral 7 shown in FIG. 3 is the liquid level 7 of the molten glass supplied to the supply groove 2.

Here, in the supply groove 2 of the molded body 1, the amount of the molten glass supplied to the supply groove 2 overflowing from the supply groove 2 is the extension direction of the supply groove 2 (flow direction of the molten glass) and the extension. It has the shape of the bottom surface 2a so as to be uniform in the width direction of the supply groove 2 orthogonal to the direction. The flow rate of the molten glass flowing through the supply groove 2 is calculated from an equation based on the viscosity of the molten glass, the density of the molten glass, the depth from the liquid surface of the molten glass flowing through the supply groove 2 to the bottom surface 2a, and the width of the bottom surface 2a. .. To this equation, a condition is added in which the linear density of the flow rate of the molten glass becomes constant in the flow direction from the groove start point side to the groove end point side to which the glass supply pipe 106 is connected, that is, the amount of overflow becomes uniform. Therefore, the shape of the bottom surface 2a of the supply groove 2 can be obtained. Further, in the supply grooves 2 at the positions of both end portions 3a and 3b of the molded body 1, the molten glass overflows to both sides of the supply groove 2 and is uniform from the positions of both end portions 3a and 3b of the upper surface 3 in the same manner as the other portions. It has a height from the bottom surface 2a to the top surface 3 so as to overflow. When the molten glass overflows from both ends 3a and 3b of the upper surface 3, the molten glass has a height from the upper surface 3 to the liquid surface of the molten glass. The intersection of the groove curve having the shape of the bottom surface 2a obtained by subtracting the height from the top surface 3 to the liquid surface of the molten glass from the height from the bottom surface 2a to the liquid surface of the molten glass at the time of overflow and the intersection of the top surface 3 is It becomes the groove end point of the supply groove 2. As a result, the distance from the groove start point to the groove end point of the supply groove 2 to which the glass supply pipe 106 is connected is obtained, and the shape of the molded body 1 is determined.

The cooling roller 8 is a unit that heat-treats both ends of the sheet glass SG in the width direction. The cooling roller 8 is arranged on the downstream side of the lower end 4 of the molded body 1. Further, the cooling rollers 8 are arranged on both sides of the sheet glass SG in the thickness direction and on both sides of the sheet glass SG in the width direction. That is, the cooling roller 8 heat-treats the sheet glass SG separated from the molded body 1 directly under the molded body 1. The cooling rollers 8 arranged on both sides of the sheet glass SG in the thickness direction operate in pairs. Therefore, both ends of the sheet glass SG in the width direction are sandwiched by two pairs of cooling rollers 8. The cooling roller 8 is air-cooled by an air-cooled pipe passed through the inside. The cooling roller 8 comes into contact with the end SGa of the sheet glass SG and rapidly cools the end SGa of the sheet glass SG by heat conduction (end cooling step). Cooling roller 8, the viscosity of the end SGa of the sheet glass ^SG, to quench the end SGa of the sheet glass SG to be equal to or greater than the ¹⁰ 9.0 dPa · s. The cooling rollers 8, preferably, the viscosity of the end SGa of the sheet glass ^SG, to quench the end SGa of 10 ^{9.0 to 10} 14.5 to be within the scope of dPa · s seat glass SG ..

A heater is arranged in the vicinity of each of the guides 6a and 6b so as to extend from the upper surface 3 side to the lower end 4 side of the molded body 1, and the portion in the vicinity of the guides 6a and 6b in the molten glass flowing down the pair of wall surfaces 5. And, the molten glass flowing down the wall surface 5 is heated by the heater. In this heating, the viscosity of the portions of the molten glass flowing down the wall surface 5 near the guides 6a and 6b reaches from the upper surface 3 to the lower end 4 of the molded body 1 (the portion of the molten glass flows down from the upper surface 3 of the molded body 1). The process is performed along the guides 6a and 6b so that the viscosity (to the lower end 4) of the glass composition constituting the molten glass is less than the liquidus viscosity (hereinafter, also simply referred to as “liquidus viscosity”).

In the molding of the sheet glass SG by the overflow downdraw method using the molded body 1 provided with the guide (and the production of the glass substrate obtained by cooling the sheet glass SG), in the vicinity of the guide, that is, at the end of the sheet glass SG to be molded. Devitrification is likely to occur. This is for the purpose of making the molten glass have a viscosity suitable for molding at the lower end of the molded body 1 in the molding furnace in which the molded body 1 is housed, and not only for molding the sheet glass SG but also for cooling the molten glass. Since the temperature is usually set to a temperature lower than that of the molten glass, the heat of the molten glass is taken from the guides 6a and 6b, so that the temperature of the molten glass in the vicinity of the guides 6a and 6b is set in the molten glass. Due to the fact that the temperature is likely to drop more than the temperature of other parts, and due to such a drop in temperature and physical resistance due to contact with the guides 6a and 6b, the flow rate of the molten glass in the vicinity of the guides 6a and 6b is other than that in the molten glass. It is considered that this is because it is more likely to be lowered than the portion of the above, and it takes a long time from the contact with the guides 6a and 6b to the separation from the molded body 1.

According to the technique of JP-A-2010-215428, devitrification that occurs at the lower end of the guide may be suppressed. However, with the technology of the document, it is difficult to suppress the devitrification that occurs in the region upstream of the lower end of the guide, especially in the initial stage when the molten glass comes into contact with the guide and begins to cool, and the devitrification that occurs once is treated as the lower end of the guide. It cannot be solved by heating. Further, a glass composition having a high liquidus temperature and a low liquidus viscosity, such as non-alkali glass and glass containing a trace amount of alkali suitable for use in a glass substrate of a flat panel display, is used, for example, in the production method of the present embodiment. Such devitrification occurs when forming a sheet glass composed of a glass composition having a liquid phase viscosity of 80,000 dPa · s or more and 100,000 dPa · s or less and a liquid phase temperature in the range of 1200 ° C. to 1220 ° C. It is especially likely to occur.

In the manufacturing method of the present embodiment, the viscosity of the portions near the guides 6a and 6b in the molten glass flowing down the wall surface 5 of the molded body 1 is maintained below the liquid phase viscosity from the upper surface 3 to the lower end 4 of the molded body 1. (So that the temperature of the portion is equal to or higher than the liquidus temperature from the upper surface 3 to the lower end 4 of the molded body 1), the portion in the molten glass is heated along the guides 6a and 6b. As a result, a high effect of suppressing devitrification in the portion of the molten glass near the guide (the end of the molten glass) can be obtained, and the glass composition constituting the molten glass is a small liquid phase of 80,000 dPa · s or more and 100,000 dPa · s or less. Even when the glass has a viscosity and a liquid phase temperature in the range of 1200 ° C. to 1220 ° C., the occurrence of devitrification at the end portion is suppressed.

In the present specification, the liquid phase temperature is the equilibrium temperature between the melt and the initial phase of the crystal, and the temperature at which the crystal does not exist above that temperature, and the liquid phase viscosity means that the glass is the above liquid. It is the viscosity that becomes the phase temperature.

FIG. 5 is a view showing a cross section of a glass supply pipe 106 connected to the supply groove 2 of the molded body 1. Comparing the temperature of the molten glass flowing through the central region 106a of the glass supply pipe 106 with the temperature of the molten glass flowing through the peripheral region 106b in the glass supply pipe 106, the temperature of the molten glass flowing through the central region 106a becomes higher. When the molten glass is supplied to the supply groove 2 of the molded body 1 in a state where there is a temperature difference (viscosity difference) between the central region 106a and the peripheral region 106b, the molten glass is heated in the space provided with the molded body 1. Even so, the temperature difference of the molten glass is not improved by the time the glass supply pipe 106 reaches the upper surface 3 of the molded body 1, and the temperature difference of the molten glass remains from the upper surface 3 to the lower end 4 of the molded body 1. It will overflow toward. If there is a temperature difference in the molten glass at the time of overflow on the upper surface 3 of the molded body 1, the flow of the molten glass changes (stagnate) locally, so that the molten glass does not overflow uniformly and the wall surface 5 of the molded body 1 The thickness (amount) of the molten glass flowing down the glass changes, and the thickness of the sheet glass SG formed at the lower end 4 is locally different. As a result, a local plate thickness deviation including veins occurs in the sheet glass SG. Since both ends SGa of the sheet glass are cooled by the cooling roller 8 and tension is applied to the sheet glass SG toward both ends SGa, the plate thickness deviation generated in the sheet glass SG is reduced. In order to suppress the plate thickness deviation of the sheet glass SG generated by such a principle to 10 μm or less, the maximum temperature difference of the molten glass in the glass supply pipe 106 when supplying to the supply groove 2 of the molded body 1 and the maximum temperature difference of the molten glass , The viscosity of the molten glass is important.

In the manufacturing method of the present embodiment, the maximum temperature difference of the molten glass (the central region 106a and the peripheral region 106b of the glass supply pipe 106) when the glass supply pipe 106 is supplied to the molding apparatus 200 (the supply groove 2 of the molded body 1) The temperature difference) is preferably 30 ° C. or lower, more preferably 20 ° C. or lower, and even more preferably 10 ° C. or lower. Further, the maximum viscosity difference of the molten glass (viscosity difference between the central region 106a and the peripheral region 106b of the glass supply tube 106) is preferably 19000 dPa · s or less, more preferably 12500 dPa · s or less, and 6200 dPa. -It is more preferable to set it to s or less. Since the molten glass supplied to the supply groove 2 is heated in the space where the molded body 1 is provided, the temperature difference of the molten glass from the supply groove 2 of the molded body 1 to the upper surface 3 is the temperature difference of the supply groove 2. It is even smaller than the temperature difference at the time of supply, for example, 10 ° C. or less. When the molten glass overflows from the upper surface 3 in such a temperature difference state, the molten glass overflows uniformly, and the thickness (amount) of the molten glass flowing down the wall surface 5 becomes uniform. The molten glass merged at the lower end 4 is formed into a sheet glass SG. Although the plate thickness deviation of the sheet glass SG at the lower end 4 is larger than 10 μm, the sheet glass SG is formed by cooling both ends SGa of the sheet glass by the cooling roller 8 so that tension is applied toward both ends SGa of the sheet glass. The local plate thickness deviation that occurs is 10 μm or less. The amount of plate thickness deviation that can be reduced by cooling the SGa at both ends of the sheet glass affects the viscosity of the molten glass.

In the manufacturing method of the present embodiment, the viscosity of the molten glass when the molten glass is supplied to the molding apparatus 200 (the supply groove 2 of the molded body 1) via the glass supply pipe 106 is 22000 dPa · s or more and 38000 dPa · s or less. It is preferably 25,000 dPa · s or more and 38,000 dPa · s or less, and more preferably 25,000 dPa · s or more and 35,000 dPa · s or less. When the viscosity of the molten glass supplied to the supply groove 2 of the molded body 1 is lowered, that is, when the temperature of the molten glass is raised, the creep phenomenon of the molded body 1 becomes remarkable, and the center of the sheet glass increases with the passage of time from the start of molding. Problems such as hanging parts also occur. On the other hand, if the viscosity of the molten glass supplied to the supply groove 2 of the molded body 1 is increased, that is, the temperature of the molten glass is lowered, a plate thickness deviation is likely to occur in the sheet glass, and devitrification is likely to occur. Therefore, it is necessary to supply the molded body 1 with molten glass capable of suppressing the creep phenomenon of the molded body 1 while preventing the occurrence of plate thickness deviation and devitrification. The viscosity of the molten glass when supplied to the molding apparatus 200 is preferably 22000 dPa · s or more and 38000 dPa · s or less. The above viscosity is a viscosity determined by the glass composition depending on the average temperature of the molten glass. Hereinafter, this viscosity is referred to as a viscosity based on the average temperature.

When the liquidus viscosity of the glass composition constituting the molten glass is 80,000 dPa · s or more and 100,000 dPa · s or less, devitrification is prevented at the lower end of the molded body 1 having the highest viscosity of the molten glass molded by the molded body 1. Therefore, the viscosity of the molten glass is controlled so that the viscosity of the molten glass is less than 80,000 dPa · s. In order to suppress the creep phenomenon of the molded body 1, the viscosity of the molten glass supplied to the supply groove 2 of the molded body 1 is increased so that the viscosity of the molten glass is less than 80,000 dPa · s at the lower end of the molded body 1. , The molten glass is supplied to the supply groove 2 of the molded body 1. In the manufacturing method of the present embodiment, the lower limit of the viscosity (viscosity based on the average temperature) of the molten glass supplied to the supply groove 2 of the molded body 1 is 22000 dPa · s to 25000 dPa · s, and the upper limit is 35000 dPa · s to 38000 dPa.・ S.

As the viscosity of the molten glass supplied to the supply groove 2 becomes smaller, the time from when the molten glass is supplied to the supply groove 2 until it overflows from the upper surface 3 becomes shorter. Therefore, the amount of heat received by the molten glass during this time decreases. The molten glass is heated in the supply groove 2 so that the temperature difference becomes small, but if the time from supply to overflow is short, the temperature difference cannot be eliminated and the molten glass overflows in a state where there is a temperature difference. Then, a place where the flowing speed changes locally occurs, which causes a plate thickness deviation. By changing the viscosity (viscosity based on the average temperature) of the molten glass supplied to the supply groove 2 of the molded body 1 from 22000 dPa · s to 38000 dPa · s, the sheet glass SG formed by merging at the lower end 4 of the molded body 1. Has a low viscosity and is easily affected by the cooling effect of the cooling roller 8, and is stretched toward the end side in the width direction to increase the effect of suppressing the plate thickness deviation of the sheet glass SG. On the other hand, when the viscosity of the molten glass becomes low, the time until it overflows becomes short. Therefore, if there is a temperature difference (viscosity difference) of the molten glass, a plate thickness deviation occurs due to this temperature difference (viscosity difference). Therefore, the maximum temperature difference of the molten glass supplied to the supply groove 2 is set to 30 ° C. or less. By supplying the molten glass satisfying these two conditions to the supply groove 2, the plate thickness deviation of the sheet glass SG can be reduced to 10 μm or less.

In order to keep the maximum temperature difference of the molten glass supplied to the supply groove 2 to 30 ° C. or less, it is important to control the temperature of the molten glass flowing through the glass supply pipe 106, and FIG. As shown in the above, the temperature is adjusted by dividing into a plurality of sections SC1 to SC9 and a plurality of tube divisions PP1 to PP3. FIG. 6 is a graph showing the temperature change of the molten glass flowing in the glass supply pipe 106 in the longitudinal direction of the glass supply pipe 106. In FIG. 6, the solid line L1 represents the temperature of the molten glass in contact with the inner peripheral surface of the glass supply pipe 106, that is, the change in the “tube temperature” which is the temperature of the glass supply pipe 106, and the dotted line L2 is the glass supply pipe. It represents a change in the "center temperature", which is the temperature of the molten glass at the center of the cross section of 106. In FIG. 6, the chain line L3 represents the average glass temperature weighted and averaged by the mass flow rate of the molten glass per unit cross-sectional area. Using this average temperature, the viscosity of the molten glass based on the average temperature can be determined.

Explaining the temperature change of the molten glass shown in FIG. 6, since the molten glass flowing into the glass supply pipe 106 is the molten glass homogenized in the homogenization step ST3, the first tube division PP1 (sections SC1 to SC5) The difference between the tube temperature of the molten glass flowing into) and the center temperature is zero. The first tube section PP1 is a region for cooling the molten glass to a degree not lower than the devitrification temperature of the glass. In the first tube section PP1, the tube temperature and the center temperature tend to gradually decrease, and the difference between the tube temperature and the center temperature tends to gradually increase due to heat radiation from the glass supply tube 106. At the boundary between the first tube section PP1 and the second tube section PP2, the difference between the tube temperature and the center temperature is preferably 100 ° C. or less. In FIG. 6, in the first tube section PP1, the glass average temperature drops from 1470 ° C to 1260 ° C.

In the second pipe section PP2, the decrease in pipe temperature is suppressed. The current flowing through the second pipe section PP2 is higher than the current flowing through the first pipe section PP1. Therefore, the amount of heat given to the second tube section PP2 by energization heating is larger than the amount of heat given to the first tube section PP1 by energization heating. Therefore, in the second tube division PP2, heat dissipation from the glass supply tube 106 is suppressed, and the temperature of the glass supply tube 106 is maintained substantially constant. At this time, in the second tube section PP2, heat is transferred from the molten glass at the center of the cross section of the glass supply tube 106 toward the molten glass in contact with the inner peripheral surface of the glass supply tube 106, so that the center temperature gradually increases. descend. As a result, in the second pipe section PP2, the difference between the pipe temperature and the center temperature tends to gradually decrease. At the boundary between the second tube section PP2 and the third tube section PP3, the difference between the tube temperature and the center temperature is preferably 50 ° C. or less. In FIG. 6, in the second tube section PP2, the glass average temperature drops from 1260 ° C to 1250 ° C.

In the seventh section SC7 of the second tube division PP2, the inner diameter of the glass supply tube 106 is reduced. Therefore, in the second tube section PP2, the area of the outer peripheral surface of the glass supply tube 106 is gradually reduced, so that heat dissipation of the molten glass through the glass supply tube 106 is suppressed. That is, in the second tube section PP2, the difference between the tube temperature and the center temperature gradually decreases due to the two factors of applying a high current and reducing the inner diameter.

In the third tube category PP3, the maximum temperature difference between the tube temperature of the molten glass and the center temperature is 30 ° C. or less. The heat insulating performance of the refractory material surrounding the third pipe division PP3 is superior to that of the refractory material 106 surrounding the first pipe division PP1 and the second pipe division PP2. Therefore, in the third tube section PP3, the heat dissipation of the molten glass through the glass supply tube 106 is further suppressed as compared with the first tube section PP1 and the second tube section PP2. Further, the current flowing through the third tube section PP3 is lower than the current flowing through the second tube section PP2, and the amount of heat given to the third tube section PP3 by energization heating is given to the second tube section PP2 by energization heating. Less than the amount of heat. Therefore, the temperature rise of the molten glass flowing in the third tube section PP3 is suppressed. As a result, in the third tube section PP3, the difference between the tube temperature and the center temperature is further reduced by heat transfer in the molten glass in a state where the average glass temperature is substantially constant. In FIG. 6, in the third tube section PP3, the glass average temperature is maintained at 1250 ° C.

The preferable range of the temperature of the molten glass passing through the glass supply pipe 106 is as follows. At the upstream end of the glass supply tube 106, the tube temperature and center temperature are preferably 1420 ° C to 1470 ° C. At the boundary between the first tube section PP1 and the second tube section PP2, the tube temperature is preferably 1210 ° C to 1260 ° C, and the center temperature is preferably 1300 ° C to 1350 ° C. At the boundary between the second tube section PP2 and the third tube section PP3, the tube temperature is preferably 1210 ° C to 1260 ° C, and the center temperature is preferably 1250 ° C to 1300 ° C. At the downstream end of the glass supply tube 106, the tube temperature and center temperature are preferably 1235 ° C to 12665 ° C.
By adjusting the temperature of the molten glass by the glass supply pipe 106 in this way, the maximum temperature difference of the molten glass supplied to the supply groove 2 is set to 30 ° C. or less.

Since it may be difficult to measure the center temperature of the molten glass with a thermometer, in this case, the unit time from the glass supply pipe 106, the information on the amount of heat radiation in the unit area, and the unit time of the glass supply pipe 106, It can be obtained by computer simulation from the measurement result of the tube temperature of the glass supply tube 106 by using the information of the heating amount of the unit area and the information of the temperature and the flow rate of the molten glass when flowing into the glass supply tube 106.

The tube temperature described above is measured by a thermometer (not shown) attached to each position of the glass supply tube 106. The viscosity is measured by a viscometer (not shown) attached to a portion where the glass supply tube 106 is connected to the supply groove 2 of the molded body 1. As the viscometer, for example, a thin tube viscometer or a rotary viscometer is used. The thin tube viscometer passes the molten glass to be measured through the thin tube, and measures the viscosity of the molten glass from the time (flow rate) at which the molten glass passes through the thin tube and the pressure difference between both ends of the thin tube. The rotary viscometer measures the viscosity of the molten glass by reading the viscous resistance, which is the resistance received by the molten glass from the rotating body, from the rotational torque of the rotating body or the like.

In the manufacturing method of the present embodiment, the temperature of the portions near the guides 6a and 6b in the molten glass flowing down the wall surface 5 of the molded body 1 is 10 ° C. higher than the liquidus temperature from the upper surface 3 to the lower end 4 of the molded body 1. It is preferable to heat the portion so as to have a temperature higher than that, and it is more preferable to heat the portion so as to have a temperature higher than the liquidus temperature by 15 ° C. or more. In these cases, the occurrence of devitrification at the edge of the sheet glass to be molded is more reliably suppressed. The specific liquid phase temperature depends on the composition of the glass composition.

In the manufacturing method of the present embodiment, in the molding step, the temperature of the portion near the guides 6a and 6b in the molten glass flowing down the wall surface 5 of the molded body 1 is the liquidus temperature from the upper surface 3 to the lower end 4 of the molded body 1. Heat the part along the guide so that it is 10 ° C to 150 ° C higher than (10 ° C or more higher than the liquid phase temperature and lower than the temperature obtained by adding 150 ° C to the liquid phase temperature). Is preferable. Thereby, the deformation of the molded body 1 and the shrinkage in the width direction of the sheet glass SG after molding can be suppressed. The temperature of the portions near the guides 6a and 6b in the molten glass flowing down the wall surface 5 of the molded body 1 is 15 ° C. to 100 ° C. higher than the liquid phase temperature from the upper surface 3 to the lower end 4 of the molded body 1. It is more preferred to heat the portion along the guide.

By combining with the quenching of the end portion after the molten glass is separated from the molded body 1 (quenching of the end portion SGa of the sheet glass SG), the plate thickness deviation of the sheet glass SG becomes 10 μm or less. Further, the suppression of the occurrence of devitrification at the end SGa is further ensured.

The molded body 1 flows down so that the temperature of the portions near the guides 6a and 6b in the molten glass flowing down the wall surface 5 of the molded body 1 is sufficiently higher than the liquid phase temperature from the upper surface 3 to the lower end 4 of the molded body 1. In theory, devitrification is also suppressed by setting the temperature of the entire molten glass to be sufficiently higher than the liquidus temperature. However, when producing glass having a high liquidus temperature, in reality, such a method cannot be applied to the overflow downdraw method. This is because there is an appropriate viscosity of the molten glass for forming the sheet glass by the overflow down draw method (in order to prevent the following problems of slackening of the sheet glass and shrinkage of the width of the sheet glass, as described below, The viscosity of the molten glass at the lower end 4 of the molded body 1 is preferably 40,000 dPa · s or more, and more preferably 70,000 dPa · s or more). The temperature of the entire molten glass flowing down the molded body 1 is set to be sufficiently higher than the liquidus temperature so that the temperature of the portion of the molten glass near the guide is sufficiently higher than the liquidus temperature, or the temperature of the molded body 1 If the lower end 4 is heated excessively, the viscosity of the molten glass at the lower end 4 of the molded body 1 may become smaller than the above-mentioned appropriate range. Then, the viscosity of the sheet glass after leaving the molded body 1 does not sufficiently increase, and the sheet glass falls at a speed higher than the tensile speed by the transport roller arranged on the downstream side of the molded body 1 and falls on the roll. Problems such as loosening of the sheet glass and shrinkage of the width of the sheet glass occur. Further, as the temperature of the molded body becomes higher, the creep phenomenon that changes with time with the use of the molded body becomes remarkable, and there arises a problem that the central portion of the sheet glass hangs down as time elapses from the start of molding. Considering the desired thickness of the glass substrate and the temperature control of the sheet glass carried out in the slow cooling step after molding, there is a limit to the increase in the tensile speed by the transport roller (the sheet glass carried out in the slow cooling step). In consideration of the temperature control of the sheet glass, the transport speed of the sheet glass is preferably 50 to 500 m / hour, preferably 100 to 400 m / hour, and preferably 120 to 300 m / hour).
Further, if the temperature of the portion of the molten glass near the guide is made sufficiently higher than the liquid phase temperature, the width of the sheet glass to be molded shrinks and the product width as a glass substrate cannot be secured. Further, when the temperature of the entire molten glass flowing down the molded body 1 is set to be sufficiently higher than the liquidus temperature, a creep phenomenon of the molded body 1 occurs, and when this creep phenomenon becomes remarkable, the thickness of the glass substrate to be manufactured is uniform. The sex is reduced.

It is preferable that the height of the guide protruding from the wall surface through which the molten glass flows in the molded body 1 becomes lower toward the lower position of the molding apparatus. It is preferable that the lower end 4 of the molded body 1 is a straight ridge line in which the inclined wall surfaces on both sides are connected to each other, and the height of the pair of guides on the inclined wall surface is 0 (zero) at the position of the ridge line. As a result, the end portion (ear portion) of the sheet glass is further suppressed from opening in a bifurcated shape, and the glass substrate can be produced more stably and continuously.

The amount of cooling and the amount of rotation of the cooling roller 8 are controlled by a control device (not shown). The control device is a computer mainly composed of a CPU, RAM, ROM, a hard disk, and the like. The control device controls the drive motor that drives the cooling roller 8 to acquire and adjust the contact load between the pair of cooling rollers 8 that sandwich the widthwise end SGa of the sheet glass SG and the sheet glass SG. Can be done. The control device individually controls the cooling amount of each cooling roller 8. Further, the control device controls the tension applied to the sheet glass SG by cooling by the cooling roller 8 for the purpose of making the cross-sectional shape of the sheet glass SG in the thickness direction a target shape, which will be described below. At least four programs that function as a transport unit, an acquisition unit, a determination unit, and a control unit are stored and executed.

The transport unit uses a transport roller installed below the molded body 1 to transport the sheet glass SG molded by the molded body 1 downward at a predetermined transport speed in a slow cooling space. The transport unit controls the drive motor that drives the transport roller to adjust the rotation speed of the transport roller, thereby adjusting the transport speed of the sheet glass SG.

The acquisition unit acquires shape data related to the current shape of the molded body 1 by obtaining the time change of the shape of the molded body 1 by computer simulation. Specifically, the acquisition unit acquires shape data based on the creep characteristic parameter. The creep characteristic parameter is a parameter for reproducing the relationship between the stress applied to the molded body 1, the temperature of the molded body 1, and the strain rate of the molded body 1 due to creep deformation. Here, the stress applied to the molded body 1 is a force that compresses the molded body 1 along the longitudinal direction of the molded body 1 (the extending direction of the supply groove 2). Further, it is assumed that the strain rate of the molded body 1 is constant regardless of time. First, the acquisition unit measures the temperature-dependent change in the strain rate of the molded body 1 under the condition that the stress applied to the molded body 1 is constant. Next, the acquisition unit measures the stress-dependent change of the strain rate of the molded body 1 under the condition that the temperature of the molded body 1 is constant. Next, the acquisition unit determines a creep characteristic parameter that can reproduce the measured values of the temperature-dependent change and the stress-dependent change of the strain rate of the molded body 1. Then, the acquisition unit calculates the strain rate of the molded body 1 under a predetermined temperature and stress using the determined creep characteristic parameters by computer simulation, and obtains the time change of the shape of the molded body 1 to obtain the molding. Acquire the shape data of the body 1. FIG. 7 is an example of the shape data of the molded body 1 acquired by the acquisition unit. FIG. 7 shows the molded body 1 viewed along the direction perpendicular to the surface of the sheet glass SG molded by the molded body 1. In FIG. 7, the creep deformation of the compact 1 is shown with more emphasis than it actually is. In FIG. 7, the shape of the unused molded body 1, that is, the shape of the molded body 1 before creep deformation is shown by a dotted line, and the current shape of the molded body 1 after creep deformation is shown by a solid line. ing.

The acquisition unit acquires at least the upper surface displacement amount, which is the vertical displacement amount of the upper surface 3 of the molded body 1, from the shape data based on the creep deformation of the molded body 1. In FIG. 7, the upper surface displacement amount is a vertical dimension between the upper surface 3 before creep deformation and the upper surface 3 after creep deformation. Note that FIG. 7 shows the maximum top surface displacement amount L, which is the maximum value of the top surface displacement amount in the longitudinal direction of the molded body 1. In addition, the acquisition unit acquires the thickness data of the glass substrate measured by the glass substrate shape measuring device (not shown). The thickness data is, for example, a profile in the width direction of the thickness of the glass substrate manufactured by the molding apparatus 200.

The determination unit determines whether or not the displacement amount L acquired by the acquisition unit has reached the reference amount. Here, the reference amount means that a certain tension (initial tension) is applied to the sheet glass SG to form the sheet glass SG (glass substrate) to the planned thickness (for example, 0.1 mm to 0.8 mm). This is an amount that can satisfy the plate thickness deviation of ± 10 μm. When the tension applied to the sheet glass SG is not changed from the initial value and the displacement amount L exceeds the reference amount, the plate thickness deviation of the sheet glass SG exceeds ± 10 μm. Therefore, by increasing the tension applied to the sheet glass SG from the initial tension, the thickness of the sheet glass SG is controlled so that the plate thickness deviation of the sheet glass SG is within ± 10 μm. The reference amount can be arbitrarily changed depending on the initial tension, the plate thickness of the sheet glass SG to be formed, the plate thickness deviation, and the like, and is, for example, 3 mm to 30 mm.

The control unit sets the cross-sectional shape of the sheet glass SG in the thickness direction to the target shape when the molded body 1 is not displaced along the width direction of the molded sheet glass SG (longitudinal direction of the molded body 1). The tension applied to the sheet glass SG becomes the reference tension by cooling both ends SGa in the width direction of the sheet glass SG by controlling the cooling amount of the cooling roller 8 with the tension as the reference tension (initial tension). Control. By applying a reference tension in the width direction of the sheet glass SG in a state where the molded body 1 is not displaced, the sheet glass SG becomes the plate thickness to be molded, and the plate thickness deviation satisfies ± 10 μm. If the tension applied to the sheet glass SG remains the reference tension in the state where the molded body 1 is creep-deformed, the target shape is not obtained, for example, the plate thickness to be formed is not formed, and the plate thickness deviation becomes large. It does not satisfy ± 10 μm. Therefore, the control unit applies a tension corresponding to the displacement of the molded body 1 to the sheet glass SG in addition to the reference tension. Here, the displacement of the molded body 1 is, for example, the displacement of the upper surface of the molded body 1 in the longitudinal direction. Based on the shape data of the molded body 1 acquired by the acquisition unit, the control unit makes the thickness of the sheet glass SG the thickness to be molded, and the plate thickness deviation in the width direction of the sheet glass SG is small. By controlling the cooling amount of the cooling roller 8 so as to be obtained, the tension applied to the sheet glass SG is controlled. The shape data of the molded body 1 is, for example, a shape profile which is a profile of the displacement amount of the upper surface in the longitudinal direction of the molded body 1. The control unit controls the cooling amount of the cooling roller 8 so that the larger the displacement amount of the upper surface 3 obtained from the shape profile, the greater the tension in the width direction of the sheet glass SG. As the displacement amount of the upper surface 3 obtained from the shape profile, for example, the maximum upper surface displacement amount L is used.

When the sheet glass SG formed at the lower end 4 of the molded body 1 is separated from the lower end 4, the central region SGb begins to shrink toward the center in the width direction due to its own surface tension. Therefore, the cooling roller 8 cools the SGa at both ends of the sheet glass SG to increase the viscosity of the SGa at both ends so that tension is applied from the central region SGb toward the SGa at both ends so that the sheet glass SG is in the width direction. The thickness of the central region SGb of the sheet glass SG is made uniform by suppressing the shrinkage. However, when the molded body 1 is creep-deformed, the amount of molten glass in the vicinity of the central region SGb of the sheet glass SG increases, and the thickness of the central region SGb changes. That is, the cross-sectional shape of the sheet glass SG in the thickness retention direction is no longer the target shape. FIG. 8 is a diagram showing a sheet glass SG having an increased thickness in the vicinity of the central region SGb due to creep deformation of the molded body 1. When the molded body 1 is creep-deformed, the amount of molten glass that overflows between the end 3a and the end 3b of the upper surface 3 increases, so that the thickness of the sheet glass SG near the central region SGb increases. In FIG. 8, the thickness in the vicinity of the central region SGb is D1 thicker at the maximum than the thickness to be molded, and the thickness of the central region SGb is non-uniform. Therefore, the control unit changes the cooling amount of the cooling roller 8 according to the shape data of the molded body 1 so that the sheet glass SG is tensioned from the central region SGb of the sheet glass SG toward both ends SGa. The shrinkage in the width direction is suppressed so that the thickness of the central region SGb of the sheet glass SG becomes uniform.

FIG. 9 is a diagram showing the relationship between the maximum top surface displacement amount L of the molded body 1 and the tension T applied to the sheet glass SG. In FIG. 9, the maximum top surface displacement amount L is described as the displacement amount L. When the control unit determines that the maximum top surface displacement amount L of the molded body 1 does not exceed L1, the change in the thickness of the central region SGb of the sheet glass SG due to the creep deformation of the molded body 1 can be ignored. As a matter of fact, the tension T applied to the sheet glass SG is not changed from the initial value T1 (range of displacement amount L: 0 or more and less than L1). If the displacement amount L of the molded body 1 is less than L1, the control unit maintains the tension T at the initial value T1 without changing the cooling amount of the cooling roller 8 to form the sheet glass SG plate. The thickness deviation satisfies ± 10 μm. When the control unit determines that the displacement amount L of the molded body 1 exceeds L1 by the determination unit, the tension T corresponding to the maximum top surface displacement amount L is applied to the sheet glass SG as shown in FIG. To control. When the maximum top surface displacement amount L is L1 or more, as shown in FIG. 8, the thickness of the central region SGb of the sheet glass SG increases, and the thickness becomes non-uniform. Therefore, the control unit has a tension T = T1 + A × maximum top surface displacement L (displacement L) larger than the initial value T1 from the central region SGb of the sheet glass SG toward both ends SGa so as to correspond to the displacement L. Range: L1 or more and less than Lm, A: coefficient) is controlled so as to be applied to the sheet glass SG. In the control unit, the greater the deformation of the molded body 1, the stronger the cooling of the SGa at both ends. Specifically, the cooling amount of the cooling roller 8 is increased to increase the viscosity of the SGa at both ends. When the viscosity of both ends SGa increases, the tension T from the central region SGb toward both ends SGb increases, and the molten glass in the central region SGb of the sheet glass SG is pulled by both ends SGb, so that the thickness of the central region SGb becomes thicker. The thickness becomes uniform as it approaches the planned thickness. The control unit controls the tension T to increase by increasing the viscosity of the SGa at both ends from, for example, 10 ^9.0 dPa · s to 10 ^{14.5 dPa · s.}
When the range of the maximum top surface displacement amount L is L1 or more and less than Lm, by controlling the tension T from T1 to Tm, the thickness of the central region SGb approaches the thickness to be formed, and the thickness becomes uniform. However, when the displacement amount L is displaced beyond Lm, it is difficult to make the thickness of the central region SGb close to the thickness to be molded and to make the thickness uniform only by controlling the tension T. It is determined by the part that the periodic replacement time of the molded body 1 has been reached.

Further, the creep deformation of the molded body 1 also changes the local plate thickness deviation (surface unevenness difference) of the sheet glass SG. Since the volume shrinkage amount of the sheet glass SG increases from the end portion SGa of the sheet glass SG toward the central region SGb, tensile stress acts in the central region SGb of the sheet glass SG. The thickness in the vicinity of the central region SGb becomes thicker, and the tension from both ends SGa toward the central region SGb increases, so that the difference in surface unevenness of the sheet glass SG becomes large. 10 (a) is an enlarged view of the cross section of the line AA of FIG. 4, and FIG. 10 (b) is an enlarged view of the cross section of the line BB of FIG. Before the sheet glass SG is tensioned by the cooling roller 8, the sheet glass SG contracts toward the central region SGb, so that the surface unevenness difference of the sheet glass SG is D2, and the cooling roller 8 tensions the sheet glass SG. After applying T, the difference in surface unevenness of the sheet glass SG becomes D3, which is smaller than D2. When the molded body 1 is creep-deformed, the surface unevenness differences D2 and D3 of the sheet glass SG also increase. Therefore, by applying the tension T from the central region SGb toward both ends SGa so as to correspond to the maximum upper surface displacement amount L, the sheet glass SG is pulled by both ends SGa, so that the surface unevenness difference D3 of the sheet glass SG Becomes smaller. By applying tension T so as to correspond to the maximum upper surface displacement amount L in order to bring the thickness of the central region SGb closer to the thickness to be molded, the surface unevenness difference D3 of the sheet glass SG becomes smaller, and the central region of the sheet glass SG becomes smaller. The thickness of SGb becomes uniform.

Further, the control unit can suppress the pulse that may occur in the transport direction of the sheet glass SG by applying the tension T to the sheet glass SG. The vein is a kind of distortion in which the thickness (height) of the sheet glass SG fluctuates within a predetermined width range, and is continuously generated in a streak pattern in the transport direction of the sheet glass SG. In addition, the factor of pulse includes the difference in viscosity of glass. When tension is applied in the width direction of the sheet glass SG by controlling the cooling amount of the cooling roller 8, the locally generated veins, which are a kind of surface irregularities of the sheet glass SG, are generated in the sheet glass SG. A sheet glass SG is formed which is stretched to SGa on both ends to reduce the difference in surface unevenness and satisfy a local plate thickness deviation of ± 10 μm.

As described above, at the lower end 4 of the molded body 1, the tension T in the width direction of the sheet glass SG applied to the sheet glass SG is changed according to the displacement amount due to the creep deformation of the molded body 1, thereby changing the central region. The thickness can be made uniform while making the thickness of SGb close to the thickness to be molded. When the central portion of the molded body 1 in the longitudinal direction hangs down and bends due to the creep deformation of the molded body 1, the cooling amount of the cooling roller 8 is increased and the sheet glass SG is applied to the sheet glass SG in the width direction. By increasing the tension T, the plate thickness deviation in the width direction of the sheet glass SG can be reduced. As a result, the plate thickness deviation of the glass substrate, which is the final product, can be reduced.

Further, in the manufacturing process of a glass having a high liquidus temperature and a glass substrate using a glass having a high strain point, creep deformation of the molded body 1 tends to be a problem because the temperature of the molded body 1 tends to be high. Further, in recent years, the size of the glass substrate has been increased, and the dimension of the molded body in the longitudinal direction has become longer, so that the bending of the molded body 1 due to creep deformation tends to be more remarkable. In the present embodiment, by adjusting the cooling amount of the cooling roller 8 and changing the tension T applied to the sheet glass SG, the plate thickness deviation in the width direction of the sheet glass SG due to the creep deformation of the molded body 1 is effective. Can be reduced.

According to the production method of the present embodiment, when the liquidus temperature of the glass composition constituting the molten glass is high and the liquidus viscosity is low, for example, when the glass composition is an alkali-free glass or a glass containing a trace amount of alkali. However, the effect of suppressing devitrification at the edge of the sheet glass to be molded can be obtained. That is, when the liquidus temperature of the glass composition constituting the molten glass is high and the liquidus viscosity is low, the advantages brought about by the production method of the present embodiment are great.

In the production method of the present embodiment, the liquidus viscosity of the glass composition constituting the molten glass is 10,000 dPa · s or less. With such a glass composition, the problem of devitrification at the end is likely to occur in the molding of the sheet glass by the overflow down draw method. However, in the production method of the present embodiment, the effect of suppressing devitrification can be obtained.

The liquidus viscosity of the molten glass used in the production method of this embodiment is 100,000 dPa · s or less. The problem of devitrification becomes more remarkable in a glass composition having a liquid phase viscosity of 100,000 dPa · s or less, but the production method of the present embodiment has an effect of suppressing devitrification. From the viewpoint that the sheet glass can be stably formed by the overflow down draw method, the liquidus viscosity is preferably 80,000 dPa · s or more.

The liquidus temperature of the glass composition constituting the molten glass used in the production method of the present embodiment is preferably 1200 ° C. or higher and 1220 ° C. or lower. With such a glass composition, the problem of devitrification at the end is likely to occur in the molding of the sheet glass by the overflow down draw method. However, in the production method of the present embodiment, the effect of suppressing devitrification can be obtained.

In the production method of this embodiment, the molten glass may contain zirconia and / or tin oxide. In the molten glass containing zirconia, the liquidus temperature of the glass composition rises as compared with the case where the glass composition does not contain zirconia. With such molten glass, the problem of devitrification at the end is likely to occur in the molding of sheet glass by the overflow down draw method. However, in the production method of the present embodiment, the effect of suppressing devitrification can be obtained. Zirconia is eluted into the molten glass not only when it is originally contained in the molten glass as a component of the glass composition, but also by using a melting tank and a molding apparatus constructed by using a high zirconia refractory. In particular, when the glass raw material is electrically melted using such a melting tank, the concentration of zirconia in the molten glass tends to be high. That is, the production method of the present embodiment is more suitable when the glass raw material is electrically melted by using a melting tank constructed by using a high zirconia refractory.

The melting tank constructed using a high zirconia refractory is less likely to be eroded by glass than the melting tank constructed using an alumina electrocast refractory that has been widely used in the past, and is a melting tank. Has a long life as. In addition, foaming of the molten glass can be suppressed. Therefore, it is suitable for forming a molten glass of a glass composition having a high melting temperature (a temperature at which the viscosity of the glass composition ^{becomes 10 2.5} poise), for example, non-alkali glass and glass containing a trace amount of alkali.

Further, when the molten glass formed in the melting tank is composed of non-alkali glass or glass containing a small amount of alkali, the specific resistance of the glass composition tends to be high, and the current tends to flow to the high zirconia refractory instead of the glass raw material. .. When an electric current flows through the refractory, zirconia elutes in the molten glass formed in the melting tank. That is, the production method of the present embodiment is more suitable when forming molten glass of non-alkali glass or glass containing a small amount of alkali by electric melting using a melting tank constructed by using a high zirconia refractory. Become.

As the glass substrate for FPD such as a liquid crystal display and an organic EL display, a glass substrate composed of non-alkali glass or glass containing a trace amount of alkali is preferable. This is because if the alkaline component is eluted from the glass substrate in the panel manufacturing process, the characteristics of the electronic device such as the thin film transistor (TFT) may be deteriorated. That is, the manufacturing method of the present embodiment is for a flat panel display by electromelting a glass raw material using a melting tank constructed by using a high zirconia refractory and using the obtained molten glass by an overflow down draw method. It is particularly suitable when manufacturing a glass substrate. The non-alkali glass refers to a glass composition that does not substantially contain an alkali metal oxide (content ratio is less than 0.05% by mass). The alkali trace-containing glass refers to a glass composition containing 0.05 to 2.0% by mass of an alkali metal oxide.

In molten glass containing tin oxide, devitrification is likely to occur due to the crystallization of tin oxide. Further, when coexisting with zirconia, tin oxide has an action of crystallizing zirconia. With such molten glass, the problem of devitrification at the end is particularly likely to occur in the molding of sheet glass by the overflow down draw method. However, in the production method of the present embodiment, the effect of suppressing devitrification can be obtained.

In the production method of the present embodiment, the glass composition constituting the molten glass may be non-alkali glass or glass containing a trace amount of alkali. Compared with alkaline glass containing more than 2.0% by mass of alkali metal oxide, the liquidus temperature of such non-alkali glass or glass containing a trace amount of alkali tends to be higher and the liquidus viscosity tends to be lower. In the manufacturing method of the form, the effect of suppressing devitrification can be obtained. As described above, this effect is particularly remarkable when the molten glass of non-alkali glass or glass containing a small amount of alkali is formed by electric melting using a melting tank constructed using a high zirconia refractory. Is.

From the viewpoint of preventing deterioration of the characteristics of electronic elements such as TFTs (Thin Film Transistors), non-alkali glass is suitable for the glass substrate for flat panel displays. However, from the viewpoint of meltability and clarity, a glass substrate containing a small amount of alkali is suitable for the glass substrate for a flat panel display. By intentionally adding a trace amount of alkali metal oxide to form a glass containing a trace amount of alkali, the meltability and clarity of the glass composition are improved. Clarity is contributed by the fact that the presence of the alkali metal oxide increases the basicity of the glass and facilitates the oxidation of valence-variable metals. Further, even when molten glass is formed by electric melting of a glass raw material in a melting tank constructed by using a high zirconia-based refractory material, the specific resistance of the glass can be reduced as compared with non-alkali glass, and the glass can be melted. It is possible to suppress the elution of zirconia into the glass and suppress the increase in devitrification of the molten glass.

In the production method of the present embodiment, the ^{temperature (melting temperature) indicating the viscosity of 10 2.5} poise may be 1500 ° C. to 1750 ° C. for the glass composition constituting the molten glass. Since such a glass composition requires a high temperature at the time of melting, zirconia is likely to elute when the molten glass is formed by a melting tank constructed by using a high zirconia refractory. Even for such a glass composition, the effect of suppressing devitrification can be obtained by the production method of the present embodiment.

Examples of the glass component contained in the glass substrate produced by the production method of the present embodiment include SiO ₂ , Al ₂ O ₃ , B ₂ O ₃ , MgO, CaO, SrO, BaO, Li ₂ O, Na ₂ O, K. Examples thereof include ₂ O, ZrO ₂ , TiO ₂ , ZnO, and P ₂ O _5.

SiO ₂ is a skeletal component of glass and is therefore an essential component. As the content decreases, the strain point tends to decrease and the coefficient of thermal expansion tends to increase. Further, if the SiO ₂ content is too small, it becomes difficult to reduce the density of the glass substrate. On the other hand, if the SiO ₂ content is too large, the specific resistance of the molten glass MG increases, the melting temperature becomes remarkably high, and melting tends to be difficult. If the SiO ₂ content is too high, the devitrification temperature tends to rise and the devitrification resistance tends to decrease. Further, if the SiO ₂ content is too high, the etching rate becomes slow. From this point of view, _{the content of SiO 2} is preferably in the range of, for example, 60 to 80 mol%. The content of SiO ₂ is more preferably 64 to 73 mol% or 65 to 75 mol%, even more preferably 66 to 72 mol%, and even more preferably 67 to 71 mol%.

Al ₂ O ₃ is an essential component that raises the strain point. If the Al ₂ O ₃ content is too low, the strain point will decrease. Furthermore, if the Al ₂ O ₃ content is too low, the Young's modulus and the etching rate due to the acid also tend to decrease. On the other hand, if the Al ₂ O ₃ content is too large, the devitrification temperature of the glass rises and the devitrification resistance decreases, so that the moldability tends to deteriorate. From this point of view, _{the content of Al 2} O ₃ is in the range of 8 to 20 mol%. The content of Al ₂ O ₃ is preferably in the range of 10 to 17 mol%, more preferably 10.5 to 17 mol%, more preferably 11 to 15 mol%, still more preferably 12 to 15 mol%.

B ₂ O ₃ is a component that lowers the high-temperature viscosity of glass and improves meltability. That is, since the viscosity near the melting temperature is lowered, the melting property is improved. It is also a component that lowers the devitrification temperature. If the B ₂ O ₃ content is low, the meltability and devitrification resistance tend to decrease. If the B ₂ O ₃ content is too high, the strain point and Young's modulus will decrease. In addition, devitrification is likely to occur due to volatilization of _{B 2} O _{3 during glass molding.} In particular, glass having a high strain point tends to have a high molding temperature, so that volatilization is promoted and devitrification is a significant problem. _{Further, due to the volatilization of B 2} O ₃ during glass melting, the inhomogeneity of the glass becomes remarkable, and the veins are likely to occur. From this point of view, the B ₂ O ₃ content is 0 to 15 mol%, preferably 0 to 8 mol%, more preferably 0 to 7 mol%, still more preferably 0.1 to 6 mol%. It is more preferably in the range of 1 to 5 mol%, and even more preferably in the range of 1.5 to 4.5 mol%.

MgO is a component that improves meltability. Further, since it is a component that is difficult to increase the density in alkaline earth metals, it is easy to reduce the density by relatively increasing the content thereof. By containing it, the specific resistance and melting temperature of the molten glass MG can be lowered. However, if the content of MgO is too large, the devitrification temperature of the glass rises sharply, so that devitrification is likely to occur particularly in the molding process. From such a viewpoint, the MgO content is 0 to 15 mol%, preferably 1 to 15 mol%, more preferably 0 to 6 mol%, and further preferably 1 to 6 mol%. Alternatively, the MgO content is preferably 0 to 15 mol%, more preferably 0 to 6 mol%, still more preferably 1 to 6 mol%.

CaO is an effective component for improving the meltability of glass without rapidly increasing the devitrification temperature of the glass. Further, since it is a component whose density is difficult to increase in alkaline earth metal oxides, it is easy to reduce the density by relatively increasing the content thereof. If the content is too small, the specific resistance of the molten glass MG tends to increase and the devitrification resistance tends to decrease. If the CaO content is too high, the coefficient of thermal expansion tends to increase and the density tends to increase. From such a viewpoint, the CaO content is 0 to 20 mol%, preferably 1 to 15 mol%, more preferably 2 to 11 mol%, and further preferably 4 to 9 mol%.

SrO is a component that can lower the devitrification temperature of glass. Although SrO is not essential, when it is contained, devitrification resistance and meltability are improved. However, if the SrO content is too high, the density will increase. From this point of view, the SrO content is 0 to 15 mol%, preferably 0 to 8 mol%, more preferably 0 to 3 mol%, still more preferably 0 to 1 mol%, still more preferably 0 to 0. It is in the range of 5 mol%, and more preferably, it is substantially not contained.

BaO is an essential component capable of effectively reducing the devitrification temperature of glass and the specific resistance of molten glass MG. The inclusion of BaO improves devitrification resistance and meltability. However, if the BaO content is too high, the density will increase. Further, the BaO content is 0 to 15 mol% or 0.1 to 15 mol%, preferably 1 to 15 mol%, more preferably 1 to 15 mol%, from the viewpoint of environmental load and the tendency for the coefficient of thermal expansion to increase. Is in the range of 1 to 10 mol%, more preferably 1.5 to 6 mol%.

Li ₂ O and Na ₂ O are components that increase the coefficient of thermal expansion of glass and may damage the substrate during heat treatment. It is also a component that lowers the strain point. On the other hand, since the specific resistance of the molten glass MG can be lowered, it is possible to prevent the melting tank from being eroded by containing it. From the above viewpoint, _{the content of Li 2} O is preferably 0 to 0.5 mol%, more preferably substantially not contained. The content of Na ₂ O is preferably 0 to 0.5 mol%, more preferably 0 to 0.2 mol%. Incidentally, Na ₂ O, since compared with Li ₂ O is a difficult component to lower the strain point _is preferably Na ₂ O> Li 2 O. From the viewpoint of preventing elution from the glass substrate and deteriorating the TFT characteristics, _{it is preferable that Li 2} O and Na ₂ O are not substantially contained.

K ₂ O is a component that enhances the basicity of glass and promotes clarity. Further, it is a component that lowers the specific resistance of the molten glass MG. When it is contained, the specific resistance of the molten glass MG is lowered, so that it is possible to prevent an electric current from flowing through the refractory material constituting the melting tank, and it is possible to prevent the melting tank from being eroded. Further, when the refractory material constituting the melting tank contains zirconia, it is possible to prevent the melting tank from being eroded and zirconia from being eluted from the melting tank to the molten glass MG, so that devitrification caused by zirconia is also suppressed. it can. Further, since the glass viscosity in the vicinity of the melting temperature is lowered, the melting property and the clarity are improved. On the other hand, when the content of K 2 _O is too large, there is a tendency of increase and the strain point lowers the thermal expansion coefficient. From this point of view, _{K 2} O content is preferably 0～0.8Mol%, more preferably 0.01 to 0.5 mol%, a range more preferably of 0.1~0.3mol%.

ZrO ₂ and TiO ₂ are components that improve the strain point of glass. However, if the _{amount of ZrO 2 and the} amount of TiO ₂ are too large, the devitrification temperature rises remarkably, so that the devitrification resistance tends to decrease. In particular, since ZrO ₂ has a high melting point and is difficult to melt, it causes a problem that a part of the raw material is deposited on the bottom of the melting tank. When these unmelted components are mixed in the glass substrate, the quality of the glass deteriorates as inclusions. Further, TiO ₂ is a component that colors glass, and is not preferable for a display substrate. From such a viewpoint, in the glass substrate of the present embodiment, _{the contents of ZrO 2} and TiO ₂ are preferably 0 to 5 mol%, more preferably 0 to 2 mol%, respectively, and are substantially not contained. Is even more preferable.

ZnO is a component that improves meltability. However, it is not an essential ingredient. If the ZnO content is too high, the devitrification temperature tends to rise, the strain point tends to decrease, and the density tends to increase. From such a viewpoint, the ZnO content is preferably in the range of 0 to 5 mol%, more preferably 0 to 2 mol%, and more preferably substantially not contained.

P ₂ O ₅ is a component that lowers high-temperature viscosity and improves meltability. However, it is not an essential ingredient. If the P ₂ O ₅ content is too high, the strain point will decrease. _{Further, due to the volatilization of P 2} O ₅ during glass melting, the inhomogeneity of the glass becomes remarkable, and the veins are likely to occur. From such a viewpoint, the P ₂ O ₅ content is preferably in the range of 0 to 3 mol%, more preferably 0 to 1 mol%, still more preferably 0 to 0.5 mol%, and is not substantially contained. More preferred.

The glass substrate to which this embodiment is applied is made of non-alkali glass containing, for example, the following composition.
SiO ₂ : 55-80% by mass
Al ₂ O ₃ : 8-20% by mass
B ₂ O ₃ : 0-18% by mass
RO 0 to 17 mol% (RO is the total amount of MgO, CaO, SrO and BaO),
R _'2 O 0 to 2 mol% (R' ₂ O is Li ₂ O, the total content of Na ₂ O and K ₂ O).

SiO ₂ is preferably 60 to 75% by mass, more preferably 63 to 72% by mass, from the viewpoint of reducing the heat shrinkage rate.
Of the RO, MgO is preferably 0 to 10% by mass, CaO is 0 to 10% by mass, SrO is 0 to 10% by mass, and BaO is preferably 0 to 10% by mass.

Further, it _{contains at least SiO 2} , Al ₂ O ₃ , B ₂ O ₃ , and RO, and the molar ratio ((2 × SiO ₂ ) + Al ₂ O ₃ ) / ((2 × B ₂ O ₃ ) + RO) is 4. It may be a glass having 5 or more. Further, it preferably contains at least one of MgO, CaO, SrO, and BaO, and has a molar ratio (BaO + SrO) / RO of 0.1 or more.

Further, _{the total of twice the content of B 2} O ₃ displayed in mass% and the content of RO displayed in mass% is 30% by mass or less, preferably 10 to 30% by mass.
Further, it is preferable that a total of 0.05 to 1.5% by mass of metal oxides (tin oxide, iron oxide) whose valence fluctuates in the molten glass is contained.
It is preferable that AS ₂ O ₃ , Sb ₂ O ₃ , and PbO are not substantially contained, but these may be optionally contained.
In addition, it contains a total of 0.05 to 1.5% by mass of metal oxides (tin oxide, iron oxide) whose valence fluctuates in glass, _{and substantially contains As 2} O ₃ , Sb ₂ O _3, and PbO. Not being required is not mandatory but optional.

The glass substrate manufactured in this embodiment is suitable for a glass substrate for a display including a glass substrate for a flat panel display. It is suitable for a glass substrate for an oxide semiconductor display using an oxide semiconductor such as IGZO (indium, gallium, zinc, oxygen) and a glass substrate for an LTPS display using an LTPS (low temperature polysilicon) semiconductor. Further, the glass substrate produced in the present embodiment is suitable for a glass substrate for a liquid crystal display, which is required to have an extremely low content of alkali metal oxides. It is also suitable for a glass substrate for an organic EL display. In other words, the method for manufacturing a glass substrate of the present embodiment is suitable for manufacturing a glass substrate for a display, and is particularly suitable for manufacturing a glass substrate for a liquid crystal display. In addition, it can also be used as a cover glass for displays and housings of mobile terminal devices, a touch panel plate, a glass substrate of a solar cell, and a cover glass. In particular, it is suitable for a glass substrate for a liquid crystal display using a polysilicon TFT.
Further, the glass substrate manufactured in this embodiment can be applied to a cover glass, a glass for a magnetic disk, a glass substrate for a solar cell, and the like.

Although the glass substrate manufacturing method and the glass substrate manufacturing apparatus of the present embodiment have been described in detail above, the present invention is not limited to the above embodiment, and various improvements and modifications are made without departing from the gist of the present invention. Of course, you may do.

(Example)
A molten glass was formed by electrically melting a glass raw material prepared so as to have the following composition in a melting tank using a high zirconia refractory. Next, the formed molten glass was clarified in a clarification tube made of platinum alloy, and then stirred in a stirring tank. Subsequently, the molten glass was supplied to the molding apparatus 200 (molded body 1), and the sheet glass was molded by the overflow down draw method. The end of the sheet glass was cooled with a cooling roller 8 so that the viscosity of the end was 10 ^12.5 dPa · s, and the formed sheet glass was slowly cooled and then cut to obtain a thickness of 0.4 mm. A glass substrate for a flat panel display having a size of 2200 mm × 2500 mm was obtained. The liquidus viscosity of the glass composition was 50,000 dPa · s, and the strain point was 715 ° C.
SiO ₂ : 61.5% by mass,
Al ₂ O ₃ : 20% by mass,
B ₂ O ₃ : 8.4% by mass,
CaO: 10% by mass,
SnO ₂ : 0.1% by mass.

The maximum temperature difference of the molten glass supplied from the glass supply pipe 106 to the supply groove 2 of the molded body 1 and the viscosity of the molten glass (viscosity based on the average temperature) are changed to measure the plate thickness deviation of the sheet glass (glass substrate). did. The results are shown in Table 1.

As shown in Table 1, in Examples 1 to 6, the maximum temperature difference of the molten glass is 30 ° C. or less, and the viscosity of the molten glass (viscosity based on the average temperature) is 22000 dPa · s or more and 38000 dPa · s or less, the plate thickness deviation. Was 10 μm or less, and the plate thickness deviation could be suppressed. On the other hand, Comparative Example 2 in which the maximum temperature difference of the molten glass exceeds 30 ° C., the viscosity of the molten glass (viscosity based on the average temperature) is less than 22000 dPa · s, and the viscosity of the molten glass exceeds 38000 dPa · s. In ~ 7, the plate thickness deviation was larger than 10 μm. From this, in order to reduce the plate thickness deviation of the sheet glass to 10 μm or less, the maximum temperature difference of the molten glass supplied to the supply groove 2 of the molded body 1 is set to 30 ° C. or less, and the viscosity of the molten glass (average temperature). It was confirmed that the viscosity) should be 22000 dPa · s or more and 38000 dPa · s or less.

100 Melting device 101 Melting tank 102 Clarifying pipe 103 Stirring tank 103a Stirrer 104,105 Transfer pipe 106 Glass supply pipe 200 Molding device 300 Cutting device MG Melting glass SG Sheet glass SGa (of sheet glass) End 1 Molded body 2 Supply groove 3 Top surface 3a, 3b (top surface) End 4 Bottom edge 5 Wall surface 6a, 6b Guide 7 Liquid level 8 Cooling roller

Claims (6)

It is a method for manufacturing a glass substrate in which molten glass is supplied from a glass supply pipe to a molded body having a supply groove, and the sheet glass is molded by the overflow down draw method using the molded body.
The supply groove has a bottom surface such that the amount of molten glass supplied to the supply groove overflowing from the supply groove is uniform in the extending direction of the supply groove and the width direction orthogonal to the extending direction. Has a shape,
A molten glass having a maximum temperature difference of 30 ° C. or less and a viscosity of the molten glass of 22000 dPa · s or more and 38000 dPa · s or less is supplied to the supply groove. , And the molding process of forming the sheet glass by merging the molten glass at the lower end of the molded body.
The end cooling step includes an end cooling step of cooling both ends of the sheet glass in the width direction so as to suppress a plate thickness deviation locally generated in the sheet glass molded in the molding step . The reference tension is the tension applied when the molded body is not deformed in the width direction of the sheet glass so that the cross-sectional shape of the sheet glass becomes the target shape. When the molded body is not deformed, the sheet glass is used. By cooling both ends in the width direction, the reference tension is controlled, and when the molded body is deformed, the tension applied to the reference tension according to the deformation of the molded body is applied to the sheet glass. To call
A method for manufacturing a glass substrate. The deformation of the molded body is a creep deformation that changes with time with the use of the molded body, and a tension corresponding to the amount of displacement of the molded body at a predetermined position due to the creep deformation is applied to the reference tension. The method for manufacturing a glass substrate according to 1. The method for manufacturing a glass substrate according to claim 1 or 2 , wherein the larger the deformation, the stronger the cooling of both ends. The plate thickness deviation is 10 μm or less.
The method for manufacturing a glass substrate according to any one of claims 1 to 3, wherein the glass substrate is manufactured. In the molding step, the molten glass is heated so that the temperature of the molten glass flowing down the molded product is 10 ° C. to 150 ° C. higher than the liquidus temperature of the molten glass.
The method for manufacturing a glass substrate according to any one of claims 1 to 4, wherein the glass substrate is manufactured. It is a glass substrate manufacturing apparatus that supplies molten glass from a glass supply pipe to a molded body having a supply groove and molds sheet glass by an overflow down draw method using the molded body.
The molded body merges the molten glass at the lower end of the molded body with a supply groove that receives the supply of the molten glass having a maximum temperature difference of 30 ° C. or less and a viscosity of 22000 dPa · s or more and 38000 dPa · s or less. With a wall surface for forming sheet glass,
The supply groove has a bottom surface such that the amount of molten glass supplied to the supply groove overflowing from the supply groove is uniform in the extending direction of the supply groove and the width direction orthogonal to the extending direction. Has a shape,
Further comprising an end cooling unit, which cools the both ends in the width direction of the sheet glass so as to suppress the locally thickness deviation that occurs in said sheet glass molded with the molded body, said end cooling device The tension applied when the molded body is not deformed in the width direction of the sheet glass and the cross-sectional shape of the sheet glass becomes the target shape is set as the reference tension, and when the molded body is not deformed, the sheet is used. The reference tension is controlled by cooling both ends in the width direction of the glass, and when the molded body is deformed, the tension applied to the reference tension according to the deformation of the molded body is applied to the sheet. It's something to hang on the glass,
A glass substrate manufacturing apparatus characterized in that.

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