TWI725140B - Method and apparatus for making glass substrate - Google Patents

Abstract

The present invention provides a method for manufacturing a glass substrate that can suppress local deviations in plate thickness in plate glass. A method for manufacturing a glass substrate, which supplies molten glass from a glass supply pipe to a shaped body having a supply tank, and uses the shaped body to shape flat glass by an overflow down-draw method, and the supply tank has a molten glass supplied to the supply tank The amount of glass overflowing from the supply tank forms a uniform bottom surface shape in the extension direction of the supply tank and the width direction orthogonal to the extension direction. The manufacturing method of the glass substrate includes: a forming step, which is from the glass supply tube The maximum temperature difference of the molten glass supplied to the supply tank is 30°C or less and the viscosity of the molten glass is 22,000 dPa·s or more and 38,000 dPa·s or less. The molten glass is supplied to the supply tank, and the molten glass is converged at the lower end of the molded body. And forming the flat glass; and the end cooling step, which cools the both ends of the flat glass in the width direction in a manner that suppresses the locally generated plate thickness deviation in the flat glass formed in the forming step.

Description

Manufacturing method of glass substrate and manufacturing device of glass substrate

The present invention relates to a manufacturing method of a glass substrate and a manufacturing device of the glass substrate.

In order to manufacture glass substrates used for flat panel displays such as liquid crystal displays and plasma displays (hereinafter referred to as "glass substrates for displays"), the overflow down-draw method is sometimes used. The overflow down-draw method includes a step of forming a plate-shaped plate glass under the forming body by overflowing the molten glass from the upper part of the forming body in the forming furnace, and cooling the plate glass slowly in a slow cooling furnace step. In the slow cooling furnace, the plate glass is introduced between the pair of rollers, the plate glass is transported to the lower side by the rollers and drawn to the required thickness, and then the plate glass is slowly cooled. Thereafter, a glass plate is formed by cutting the plate glass into a specific size.

The molten glass flowing down the side of the formed body shrinks in the width direction of the plate glass due to surface tension while leaving the formed body. Patent Document 1 discloses a method of adjusting the plate between the formed body and the tension roller under the formed body, near the edge of the plate glass in the width direction, using a cooling unit provided at a distance from the plate glass. The temperature of the edge of the glass suppresses the shrinkage of the flat glass. After that, the plate glass whose shrinkage is suppressed passes through the slow cooling space to be formed. In the slow cooling space, the ambient temperature is controlled in such a way that it becomes the required temperature distribution (the temperature distribution that does not produce strain in the glass plate), thereby suppressing the thickness deviation, warpage, and strain of the glass plate.

[Prior Technical Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open No. 5-124827

In recent years, in the glass substrates for liquid crystal display devices, the requirements for specifications (quality) have become increasingly strict. High flatness is required for the surface of the glass substrate. In order to meet the required specifications, it is especially necessary to suppress the occurrence of striae or local thickness deviations caused by steep concavities or convexities. The fringe is caused by the unevenness of the thickness (height) of the plate glass in a specific width, and is caused by shrinking in the width direction of the plate glass due to surface tension while leaving the molded body, and is used in the conveying of the plate glass In the direction, the pattern is continuously produced.

Therefore, the object of the present invention is to provide a method of manufacturing a glass substrate and a manufacturing device of a glass substrate that can suppress local thickness deviations including streaks generated on flat 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 shaped body having a supply tank, and the above-mentioned shaped body is used to shape a glass substrate of plate glass by an overflow down-draw method. In this manufacturing method, the supply tank has an amount of molten glass supplied to the supply tank overflowing from the supply tank to form a uniform bottom shape in the extending direction of the supply tank and the width direction orthogonal to the extending direction. The manufacturing method of the glass substrate has: a forming step, which is to supply the molten glass from the glass supply pipe to the supply tank with a maximum temperature difference of 30°C or less and the viscosity of the molten glass to be 22000dPa‧s or more and 38000 The molten glass below dPa‧s is supplied to the supply tank, and the molten glass is converged at the lower end of the molded body to form a flat glass; and the end cooling step is to suppress the flat plate formed in the above-mentioned forming step The method of locally generated plate thickness deviation in the glass is to cool the two ends of the plate glass in the width direction.

In the end cooling step, it is preferable that the tension applied when the molded body is not deformed in the width direction of the plate glass and the cross-sectional shape of the plate glass becomes the target shape is set as the reference tension. At the time of deformation, it is controlled so that the both ends in the width direction of the plate glass are cooled to become the reference tension, and when the formed body is deformed, the plate glass is subjected to the deformation according to the formed body. The tension added to the above-mentioned reference tension.

At this time, it is preferable that the deformation of the molded body is a creep deformation that changes with time due to the use of the molded body, and the reference tension is added to the specific position of the molded body caused by the creep deformation. The tension corresponding to the displacement.

Furthermore, it is preferable that the greater the deformation, the more enhanced the cooling of the both ends.

Preferably, the above-mentioned plate thickness deviation is 10 μm or less.

Preferably, in the forming step, the molten glass is heated in such a way that the temperature of the molten glass flowing downward in the formed body is increased by 10°C to 150°C compared to the liquidus temperature of the molten glass.

Another aspect of the present invention is a manufacturing device that supplies molten glass from a glass supply pipe to a molded body having a supply tank, and uses the molded body to shape a glass substrate of plate glass by an overflow down-draw method.

The above-mentioned molded body has a maximum temperature difference of 30℃ or less and a viscosity of 22000dPa‧s The supply tank for supplying the molten glass below 38000dPa•s and the wall surface for forming the plate glass by converging the molten glass at the lower end of the above-mentioned forming body.

The supply tank has an amount of molten glass supplied to the supply tank overflowing from the supply tank to form a uniform bottom surface shape in the extension direction of the supply tank and the width direction orthogonal to the extension direction.

The manufacturing apparatus further includes an end cooling device that cools both ends of the sheet glass in the width direction in a manner that suppresses the thickness deviation locally generated in the sheet glass obtained by the molding of the molded body.

According to the manufacturing method of the glass substrate and the manufacturing apparatus of the glass substrate of the above aspect, it is possible to suppress the local thickness deviation in the flat glass.

1: formed body

2: supply tank

2a: bottom surface

3: upper surface

3a, 3b: (upper surface) end

4: bottom

5: wall surface

5a, 5b: end

6a, 6b: guide

7: Liquid level

8: Cooling roll

100: Dissolving device

101: Dissolving tank

102: Clarification tube

103: Stirring tank

103a: Stirring stick

104, 105: Transmission tube

106: Glass supply pipe

106a: central area

106b: Surrounding area

200: forming device

300: cutting device

D1: Thickness

D2, D3: Surface unevenness of flat glass SG

L(L1~Lm): displacement

MG: molten glass

PP1~PP3: multiple pipe sections

SC1~SC9: multiple areas

SG: Flat glass

SGa: (of flat glass) end

SGb: (of flat glass) central area

T(T1~Tm): Tension

Fig. 1 is a diagram showing the flow of the manufacturing method of this embodiment.

Fig. 2 is a schematic diagram of a manufacturing apparatus of a glass substrate.

Fig. 3 is a perspective view showing an example of a molded body that can be used in the manufacturing method of this embodiment.

FIG. 4 is a diagram illustrating an example of the manufacturing method of the present invention using the device shown in FIG. 3.

Fig. 5 is a view showing a cross-section of a glass supply pipe connected to a supply tank of a formed body.

Fig. 6 is a graph showing 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.

Fig. 7 is a diagram illustrating an example of the shape change of the formed body obtained by the obtaining section.

Fig. 8 is a diagram showing an example of a cross-section of a glass ribbon formed by using a molded body that has undergone creep deformation.

Fig. 9 is a diagram showing the relationship between the displacement of the formed body and the tension T applied to the glass ribbon.

Fig. 10(a) is an enlarged view of an example of the section of the plate glass along the line AA shown in Fig. 4, and (b) is an enlarged view of an example of the section of the plate glass along the line BB shown in Fig. 4 The resulting figure.

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

(Overall summary of manufacturing method of glass substrate)

FIG. 1 is a diagram showing an example of the steps of the manufacturing method of the glass substrate of the present embodiment. The manufacturing method of a glass substrate mainly includes: a dissolution step (ST1), a clarification step (ST2), a homogenization step (ST3), a supply step (ST4), a forming step (ST5), a slow cooling step (ST6), and a cutting step (ST7). Others may have a grinding step, a grinding step, a cleaning step, an inspection step, a packing step, etc. The manufactured glass substrates are laminated in the packaging step as needed, and then transported to the supplier of the ordering party.

The dissolving step (ST1) is to prepare molten glass by heating the glass raw material.

The clarification step (ST2) is to raise the temperature of the molten glass to generate bubbles _{containing oxygen, CO 2} or SO _{2 contained in the molten glass.} The bubble absorbs oxygen generated by the reduction reaction of the clarifying agent (tin oxide, etc.) contained in the molten glass, grows, and floats to the liquid surface of the molten glass to be released. After that, in the clarification step, since the temperature of the molten glass is lowered, an oxidation reaction is performed using the reducing substance obtained by the reduction reaction of the clarifying agent. Thereby, gas components such as oxygen in the bubbles remaining in the molten glass are absorbed into the molten glass again, and the bubbles are collapsed. The oxidation reaction and the reduction reaction performed by the clarifying agent are performed by controlling the temperature of the molten glass.

Furthermore, the clarification step can also adopt a vacuum defoaming method in which bubbles existing in the molten glass grow under a reduced pressure environment and then defoam. Decompression defoaming method is more effective in that no clarifying agent is used effect. However, the reduced pressure defoaming method leads to the complexity and enlargement of the device. Therefore, it is preferable to adopt a clarification method that uses a clarifying agent to increase the temperature of the molten glass.

The homogenization step (ST3) is to homogenize the glass components by stirring the molten glass with a stirrer. By this, it is possible to reduce the unevenness of the composition of the glass which is the cause of streaks and the like. The homogenization step is carried out in the stirring tank described below.

The supply step (ST4) is to supply the stirred molten glass to the forming device.

The forming step (ST5) and the slow cooling step (ST6) are performed in a forming device.

The forming step (ST5) is to shape the molten glass into plate glass to form a flow of plate glass. In forming, the overflow down-draw method is used.

The slow cooling step (ST6) is to cool the flowed flat glass after forming to the required thickness without generating internal strain, and thus without causing warpage.

The cutting step (ST7) is to cut the slow-cooled plate glass into a specific length to obtain a plate-shaped glass substrate. The cut glass substrate is then cut to a specific size to prepare a glass substrate of the target size.

Fig. 2 is a schematic diagram of a glass substrate manufacturing apparatus that performs the dissolving step (ST1) to the cutting step (ST8) in this embodiment. The manufacturing apparatus of the glass substrate mainly includes a dissolving device 100, a forming device 200, and a cutting device 300 as shown in FIG. 2. The dissolving device 100 has a dissolving tank 101, a clarification pipe 102, a stirring tank 103, transfer pipes 104 and 105, and a glass supply pipe 106.

The dissolving tank 101 shown in FIG. 2 is provided with a heating mechanism such as a burner (not shown). The glass raw material to which the clarifier has been added is put into the dissolution tank, and the dissolution step (ST1) is performed. The molten glass that has been melted in the dissolution tank 101 is supplied to the clarification pipe 102 via the transfer pipe 104.

In the clarification pipe 102, the temperature of the molten glass MG is adjusted, and the clarification step (ST2) of the molten glass is performed by the oxidation-reduction reaction of a clarifier. Specifically, by raising the temperature of the molten glass in the clarification pipe 102, the _{bubbles containing oxygen, CO 2} or SO ₂ contained in the molten glass absorb the oxygen generated by the reduction reaction of the clarifying agent and grow, and float to the molten glass. The liquid surface of the glass is released into the gas phase space. Thereafter, by lowering the temperature of the molten glass, the reducing substance obtained by the reduction reaction of the clarifying agent undergoes an oxidation reaction. Thereby, gas components such as oxygen in the bubbles remaining in the molten glass are absorbed into the molten glass again, and the bubbles are collapsed. The molten glass after clarification is supplied to the stirring tank 103 via the transfer pipe 105.

In the stirring tank 103, the molten glass is stirred by the stirring rod 103a to perform a homogenization step (ST3). The molten glass homogenized in the stirring tank 103 is supplied to the forming apparatus 200 via the glass supply pipe 106 (supply step ST4).

In the forming apparatus 200, the sheet glass SG is formed from the molten glass by the overflow down-draw method (forming step ST5), and slow cooling is performed (slow cooling step ST6).

In the cutting device 300, a plate-shaped glass substrate cut from the sheet glass SG is formed (cutting step ST7).

The supply step S4 is to control the temperature of the molten glass flowing in the glass supply pipe 106. Specifically, the glass supply pipe 106 is energized and heated to heat the molten glass flowing in the glass supply pipe 106, and the glass supply pipe 106 is surrounded by a refractory material, thereby suppressing the flow in the glass supply pipe 106 The heat dissipation of 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 pipe 106 gradually decreases from the upstream side to the downstream side. The glass supply pipe 106 is divided into a plurality of zones, and the temperature of the molten glass is controlled by zone. The energized heating device for heating the glass supply pipe 106 is based on the measurement data of the measuring device, and controls the current and voltage flowing into each zone of the glass supply pipe 106 in a manner that the temperature of the molten glass changes. The temperature of the molten glass supplied to the forming device 200 can be appropriately changed by controlling the current and voltage in the glass supply pipe 106. Here, Yu Bo At the downstream end of the glass supply pipe 106, the pipe temperature and the center temperature of the molten glass are preferably 1235°C to 1265°C, more preferably 1240°C to 1260°C.

(The composition of the formed body)

Next, referring to FIGS. 3 and 4, the configuration of the molded body 1 included in the molding apparatus 200 will be described. FIG. 3 shows an example of a molded body 1 that can be used in the manufacturing method of this embodiment, and FIG. 4 shows an example of a forming step in the manufacturing method of this embodiment using the molded body 1 shown in FIG. 3. The molded body 1 has: an upper surface 3 formed with a supply groove 2 for supplying molten glass; a pair of wall surfaces 5 (only one wall surface is shown in FIGS. 3 and 4), which are guided from both sides of the supply groove 2 After overflowing, the molten glass flowing downward from the ends 3a, 3b in the direction in which the supply groove 2 in the upper surface 3 extends, merges into the sheet glass SG at the lower end 4 of the molded body 1; and a pair of guides 6a , 6b, etc. are formed at the positions of both ends 5a, 5b in the width direction of the wall surface 5. The guides 6a and 6b are formed to face each other so as to protrude from the wall surface 5 at the positions of the end portions 5a and 5b, respectively. The molten glass overflowing from the supply tank 2 flows downward on each of the pair of wall surfaces 5. The wall surface 5 has a vertical wall surface in which the molten glass overflowing from the supply tank 2 flows downward in the vertical direction, and an inclined wall surface in which the molten glass flowing downward in the vertical wall surface is guided to the lower end 4 of the molded body 1 and connected to the vertical wall surface. A convective system of molten glass flowing downward on the wall surface 5 converges at the lower end 4 of the formed body 1, thereby converging with each other. At this time, the width of the molten glass flowing downward along the wall surface 5 is restricted by the guides 6a and 6b, thereby continuously forming, for example, a sheet glass SG having high thickness uniformity in the width direction. The lower end 4 of the molded body 1 forms a linear ridge formed by connecting a pair of wall surfaces 5 (inclined wall surfaces). The symbol 2a shown in FIGS. 3 and 4 is the bottom surface 2a of the supply tank 2, and the symbol 7 shown in FIG. 3 is the liquid surface 7 of the molten glass supplied to the supply tank 2.

Here, the supply tank 2 of the molded body 1 has the shape of a bottom surface 2a as follows. The shape of the bottom surface 2a is the amount of molten glass supplied to the supply tank 2 overflowing from the supply tank 2 in the extending direction of the supply tank 2 (The flow direction of the molten glass) and the width direction of the supply tank 2 orthogonal to the extending direction are formed uniformly. The flow rate of the molten glass flowing in the supply tank 2 is based on the formula based on the viscosity of the molten glass, the density of the molten glass, the depth from the liquid level to the bottom surface 2a of the molten glass flowing in the supply tank 2, and the width of the bottom surface 2a Calculate. By adding to this formula, the linear density of the flow rate of the molten glass becomes a constant in the flow direction from the tank start point side to the tank end point side where the glass supply pipe 106 is connected, that is, the condition that the overflow amount becomes uniform, and obtain The shape of the bottom surface 2a of the supply tank 2 is shown. In addition, the supply tank 2 at the positions of the two ends 3a, 3b of the molded body 1 has overflow from the molten glass to both sides of the supply tank 2, and the positions of the two ends 3a, 3b of the upper surface 3 are the same as the other parts The height from the bottom surface 2a to the top surface 3 where the ground uniformly overflows. When the molten glass overflows from both ends 3a, 3b of the upper surface 3, the molten glass has a height from the upper surface 3 to the liquid level of the molten glass. The intersection of the groove curve and the upper surface 3 of the shape of the bottom surface 2a obtained by subtracting the height from the upper 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 becomes the supply groove 2 The end of the slot. Thereby, the distance from the start point of the groove to the end of the groove of the supply tank 2 to which the glass supply pipe 106 is connected is calculated, and the shape of the molded body 1 is determined.

The cooling roll 8 is a unit that heat-treats both ends in the width direction of the sheet glass SG. The cooling roll 8 is arranged further downstream than the lower end 4 of the molded body 1. In addition, the cooling rollers 8 are arranged on both sides of the thickness direction of the sheet glass SG, and on both sides of the width direction of the sheet glass SG. That is, the cooling roll 8 heat-treats the sheet glass SG separated from the molded body 1 directly below the molded body 1. The cooling rolls 8 arranged on both sides of the thickness direction of the sheet glass SG operate in an opposing manner. Therefore, both ends of the width direction of the sheet glass SG are sandwiched by the two pairs of cooling rollers 8. The cooling roller 8 is air-cooled by an air cooling pipe leading to the inside. The cooling roller 8 is in 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). The cooling roller 8 rapidly cools the end SGa of the sheet glass SG so that the viscosity of the end SGa of the sheet glass SG reaches 10 ^9.0 dPa·s or more. Furthermore, the cooling roller 8 preferably rapidly cools the end SGa of the sheet glass SG so that the viscosity of the end SGa of the sheet glass SG is within the range of ^{10 9.0} to 10 ^{14.5 dPa·s.}

In the vicinity of each of the guides 6a and 6b, a heater is arranged to extend from the upper surface 3 side of the molded body 1 to the lower end 4 side, and the molten glass flows downward on the pair of wall surfaces 5 by the heater The parts near the guides 6a, 6b and the molten glass flowing downward on the wall surface 5 are heated. The heating is based on the viscosity of the part near the guides 6a, 6b in the molten glass flowing downward on the wall surface 5 from the upper surface 3 to the lower end 4 of the forming body 1 (the part of the molten glass is from the upper surface of the forming body 1 (3) It flows downward until it reaches the lower end 4), and does not reach the liquid phase viscosity (hereinafter, also referred to as "liquid viscosity") of the glass composition constituting the molten glass, along the guides 6a, 6b.

In the forming of the sheet glass SG (and the manufacture of the glass substrate obtained by cooling the sheet glass SG) using the overflow down-draw method of the forming body 1 equipped with the guide, it is easy to be near the guide, that is, the formed sheet glass Devitrification occurs at the end of the SG. This situation is considered to be caused by the following reasons. That is, the purpose is to set the molten glass to a viscosity suitable for molding in the molding furnace containing the molded body 1 at the lower end of the molded body 1, and it is usually set not only for the molding of the sheet glass SG For the purpose and also for the purpose of cooling the molten glass, the temperature is lower than the temperature of the molten glass. Therefore, the heat of the molten glass is captured from the guides 6a and 6b, resulting in the temperature of the molten glass near the guides 6a and 6b. It is easy to be lower than the temperature of other parts in the molten glass; and, due to the temperature drop and the physical resistance caused by the contact with the guides 6a, 6b, the downward flow speed of the molten glass near the guides 6a, 6b is likely to be low For other parts in the molten glass, it takes a long time from contact with the guides 6a, 6b until it leaves the molded body 1.

According to Japanese Patent Laid-Open No. 2010-215428, there is a possibility that devitrification generated at the lower end of the guide can be suppressed. However, in the technique of this document, it is difficult to suppress the lower end of the guide The region further upstream, especially the devitrification generated in the initial stage when the molten glass contacts the guide member and begins to cool, so that the devitrification generated at one time cannot be eliminated by heating the lower end of the guide member. In addition, it is used in a glass composition containing a glass substrate suitable for use in flat-panel displays such as alkali-free glass and a glass containing trace alkali, which have a high liquid phase temperature and a low liquid phase viscosity, such as the manufacturing method of this embodiment Such devitrification is especially prone to occur when forming flat glass of glass composition with liquid phase viscosity of 80,000 dPa‧s or more and 100,000 dPa‧s and liquid temperature in the range of 1200°C to 1220°C.

In the manufacturing method of this embodiment, the viscosity of the portions near the guides 6a and 6b in the molten glass flowing downward on the wall surface 5 of the molded body 1 is kept constant from the upper surface 3 to the lower end 4 of the molded body 1. To reach the liquid phase viscosity (the temperature of the part becomes higher than the liquidus temperature from the upper surface 3 to the lower end 4 of the molded body 1), the part in the molten glass is heated along the guides 6a and 6b. Thereby, a high effect of suppressing devitrification in the part near the guide of the molten glass (the end of the molten glass) is obtained, so that even if the glass composition constituting the molten glass has a smaller value of 80,000dPa‧s or more and 100000dPa‧s or less When the liquid phase viscosity is in the range of 1200℃~1220℃, the devitrification in the end can also be suppressed.

In this specification, the so-called liquidus temperature refers to the equilibrium temperature between the melt and the initial phase of the crystal, and if it exceeds this temperature, there is no crystallization temperature. The so-called liquid phase viscosity refers to the viscosity of the glass at the above liquidus temperature .

FIG. 5 is a view showing a cross-section of the glass supply pipe 106 connected to the supply tank 2 of the molded body 1. In the glass supply pipe 106, if the temperature of the molten glass flowing in the central area 106a of the glass supply pipe 106 is compared with the temperature of the molten glass flowing in the peripheral area 106b, the temperature of the molten glass flowing in the central area 106a rises high. If there is a temperature difference (difference in viscosity) between the central area 106a and the peripheral area 106b, the molten glass is supplied to the supply tank 2 of the molded body 1 In the space where the molded body 1 is installed, even if the molten glass is heated, the temperature difference of the molten glass from the glass supply pipe 106 to the upper surface 3 of the molded body 1 is not improved. In the state of the temperature difference, it overflows from the upper surface 3 of the molded body 1 toward the lower end 4. If there is a temperature difference in the molten glass at the time when the upper surface 3 of the molded body 1 overflows, the flow of the molten glass changes locally (stagnation). Therefore, the molten glass does not overflow uniformly, and the molten glass flows toward the wall surface 5 of the molded body 1. The thickness (amount) of the molten glass flowing downward is changed, and the thickness of the sheet glass SG formed at the lower end 4 is locally different. As a result, in the sheet glass SG, local thickness deviations including streaks are generated. Since both end portions SGa of the sheet glass are cooled by the cooling roll 8 and tension is applied to the sheet glass SG in the direction of the end portions SGa, the thickness deviation generated in the sheet glass SG is reduced. In order to use such a principle to suppress the thickness deviation of the generated sheet glass SG to 10 μm or less, the maximum temperature difference of the molten glass in the glass supply pipe 106 when the molded body 1 is supplied to the supply tank 2 and the viscosity of the molten glass Becomes more important.

In the manufacturing method of this embodiment, the maximum temperature difference of molten glass (the difference between the central area 106a and the peripheral area 106b of the glass supply pipe 106) when the glass supply pipe 106 is supplied to the forming device 200 (the supply tank 2 of the formed body 1) The temperature difference) is preferably 30°C or less, more preferably 20°C or less, and even more preferably 10°C or less. In addition, the maximum viscosity difference of the molten glass (the difference in viscosity between the central area 106a and the peripheral area 106b of the glass supply pipe 106) is preferably set to 19000dPa‧s or less, more preferably 12500dPa‧s or less, and more preferably Set it below 6200dPa‧s. Since the molten glass supplied to the supply tank 2 is heated in the space where the molded body 1 is provided, the temperature difference of the molten glass from the supply tank 2 of the molded body 1 to the upper surface 3 becomes further smaller than that of the supply tank 2. The temperature difference at the time of supply is, for example, 10°C or less. In the state of such a temperature difference, if the molten glass overflows from the upper surface 3, the molten glass overflows uniformly, and the thickness (amount) of the molten glass flowing downward on the wall surface 5 becomes uniform. Converge at the bottom 4 The molten glass is formed into sheet glass SG. The thickness deviation of the plate glass SG in the lower end 4 is greater than 10 μm, but by applying tension to the two ends SGa of the plate glass, the two ends SGa of the plate glass are cooled by the cooling roller 8, and the plate glass SG is The resulting local thickness deviation becomes 10 μm or less. The amount of sheet thickness deviation that can be reduced by cooling the two ends SGa of the sheet glass has an effect on the viscosity of the molten glass.

In the manufacturing method of this embodiment, the viscosity of the molten glass when the molten glass is supplied to the forming device 200 (supply tank 2 of the molded body 1) through the glass supply pipe 106 is preferably 22000dPa‧s or more and 38000dPa‧s or less, more Preferably it is 25000dPa‧s or more and 38000dPa‧s or less, and more preferably 25000dPa‧s or more and 35000dPa‧s or less. If the viscosity of the molten glass supplied to the supply tank 2 of the molded body 1 is lowered, that is, if the temperature of the molten glass is increased, the creep phenomenon of the molded body 1 becomes significant, which also results in the time since the start of molding. After passing, the central part of the plate glass sags and other problems. On the other hand, if the viscosity of the molten glass supplied to the supply tank 2 of the molded body 1 is increased, that is, if the temperature of the molten glass is lowered, the plate glass tends to vary in thickness and devitrification tends to occur. Therefore, it is necessary to supply molten glass to the molded body 1 that can prevent the occurrence of plate thickness deviation and devitrification while suppressing the creep phenomenon of the molded body 1. The viscosity of the molten glass when supplied to the forming device 200 is preferably 22000dPa•s or more and 38000dPa•s or less. The above-mentioned viscosity is determined by the composition of the glass due to the average viscosity of the molten glass. Hereinafter, this viscosity is referred to as the viscosity based on the average viscosity.

When the liquid phase viscosity of the glass composition constituting the molten glass is 80,000dPa‧s or more and 100000dPa‧s or less, in order to prevent devitrification at the lower end of the molded body 1 where the viscosity of the molten glass formed by the molded body 1 becomes the highest, The viscosity of the molten glass is controlled in such a way that the viscosity of the molten glass becomes less than 80,000dPa·s. In order to suppress the creep phenomenon of the formed body 1, the viscosity of the molten glass supplied to the supply tank 2 of the formed body 1 is increased, and the formed body 1. At the lower end, the molten glass is supplied to the supply tank 2 of the forming body 1 in a way that the viscosity of the molten glass is less than 80,000 dPa·s. In the manufacturing method of this embodiment, the viscosity (viscosity based on the average temperature) of the molten glass supplied to the supply tank 2 of the formed body 1 has a lower limit of 22000dPa‧s to 25000dPa‧s, and an upper limit of 35000dPa‧s to 35000dPa‧s 38000dPa‧s.

Since the viscosity of the molten glass supplied to the supply tank 2 becomes small, the time from when the molten glass is supplied to the supply tank 2 to overflow from the upper surface 3 becomes short. Therefore, during this time, the amount of heat received by the molten glass is reduced. The molten glass is heated in the supply tank 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 it overflows in a state where there is a temperature difference. As a result, a part where the speed of the downward flow changes locally, which becomes the cause of the thickness deviation. By setting the viscosity (viscosity based on the average temperature) of the molten glass supplied to the supply tank 2 of the forming body 1 to 22000dPa‧s to 38000dPa‧s, the sheet glass SG formed by converging at the lower end 4 of the forming body 1 becomes low The viscosity is susceptible to the cooling effect of the cooling roll 8 and is drawn to the end side in the width direction, so that the effect of suppressing the thickness deviation of the sheet glass SG becomes greater. On the other hand, if the molten glass has a low viscosity, the time to overflow becomes shorter. Therefore, if there is a temperature difference (bad viscosity) of the molten glass, a thickness deviation will occur due to the temperature difference (bad viscosity). Therefore, the maximum temperature difference of the molten glass supplied to the supply tank 2 shall be 30 degrees C or less. By supplying the molten glass satisfying these two conditions to the supply tank 2, the thickness deviation of the sheet glass SG can be 10 micrometers or less.

In order to set the maximum temperature difference of the molten glass supplied to the supply tank 2 to 30°C or less, the temperature management of the molten glass flowing in the glass supply pipe 106 is more important, and in the longitudinal direction of the glass supply pipe 106, such as As shown in Fig. 6, it is divided into a plurality of zones SC1~SC9 and a plurality of pipe sections PP1~PP3 for temperature adjustment. 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. Yu Tu In 6, the solid line L1 represents the change in the "tube temperature" as the temperature of the molten glass in contact with the inner peripheral surface of the glass supply pipe 106, that is, the temperature of the glass supply pipe 106, and the dashed line L2 represents the change in the "tube temperature" as the glass supply pipe 106 The change in the "center temperature" of the temperature of the molten glass at the center of the section. In FIG. 6, the chain line L3 represents the average glass temperature obtained by weighted average of the mass flow rate of the molten glass in each unit cross-sectional area. Using this average temperature, the viscosity based on the average temperature of the molten glass is calculated.

The temperature change of the molten glass shown in FIG. 6 will be described. The molten glass flowing into the glass supply pipe 106 is the molten glass obtained in the homogenization step ST3, and therefore flows into the first pipe section PP1 (zones SC1 to SC5). The difference between the tube temperature and the core temperature of the molten glass in) is zero. The first pipe section PP1 is used to cool the molten glass to an area not lower than the devitrification temperature of the glass. In the first pipe section PP1, there is a tendency that the pipe temperature and the center temperature gradually decrease, and due to heat dissipation from the glass supply pipe 106, the difference between the pipe temperature and the center temperature gradually increases. At the junction of the first pipe section PP1 and the second pipe section PP2, the difference between the pipe temperature and the core temperature is preferably 100°C or less. In Fig. 6, in the first pipe section PP1, the average glass temperature dropped from 1470°C to 1260°C.

In the second pipe section PP2, the decrease in pipe temperature is suppressed. The current flowing in the second pipe section PP2 is higher than the current flowing in the first pipe section PP1. Therefore, the amount of heat imparted to the second pipe section PP2 by energization heating is greater than the amount of heat imparted to the first pipe section PP1 by energization heating. Therefore, in the second pipe section PP2, heat dissipation from the glass supply pipe 106 is suppressed, and the temperature of the glass supply pipe 106 is maintained substantially constant. At this time, in the second pipe section PP2, heat is transferred from the molten glass in the center of the cross section of the glass supply pipe 106 to the molten glass in contact with the inner peripheral surface of the glass supply pipe 106, so the center temperature gradually decreases. As a result, in the second pipe section PP2, there is a tendency that the difference between the pipe temperature and the core temperature gradually decreases. In the second pipe section PP2 and the third pipe section At the junction of PP3, the difference between the tube temperature and the core temperature is preferably 50°C or less. In Fig. 6, in the second pipe section PP2, the average glass temperature dropped from 1260°C to 1250°C.

Furthermore, in the seventh zone SC7 of the second pipe section PP2, the inner diameter of the glass supply pipe 106 is reduced. Therefore, in the second pipe section PP2, the area of the outer peripheral surface of the glass supply pipe 106 gradually decreases, and therefore, the heat dissipation of the molten glass through the glass supply pipe 106 is suppressed. That is, in the second pipe section PP2, the difference between the pipe temperature and the core temperature gradually decreases due to the two main factors of the application of high current and the decrease of the inner diameter.

In the third pipe section PP3, the maximum temperature difference between the pipe temperature of the molten glass and the core temperature is less than 30°C. The heat insulation performance of the refractory material surrounding the third pipe section PP3 is better than the refractory material 106 surrounding the first pipe section PP1 and the second pipe section PP2. Therefore, compared with the first pipe section PP1 and the second pipe section PP2 in the third pipe section PP3, the heat dissipation of the molten glass through the glass supply pipe 106 is further suppressed. In addition, the current flowing in the third pipe section PP3 is lower than the current flowing in the second pipe section PP2, and the amount of heat imparted to the third pipe section PP3 by energization heating is less than the amount of heat imparted to the second pipe section PP2 by energization heating. Therefore, the temperature rise of the molten glass flowing in the third pipe section PP3 is suppressed. Thereby, in the third pipe section PP3, in a state where the average glass temperature becomes substantially constant, the difference between the pipe temperature and the core temperature is further reduced due to heat transfer in the molten glass. In Fig. 6, in the third pipe section PP3, the average glass temperature is maintained at 1250°C.

Furthermore, the preferable range of the temperature of the molten glass passing through the glass supply pipe 106 is as follows. At the end of the upstream side of the glass supply pipe 106, the pipe temperature and the center temperature are preferably 1420°C to 1470°C. At the junction of the first pipe section PP1 and the second pipe section PP2, preferably, the pipe temperature is 1210°C to 1260°C, and the core temperature is 1300°C to 1350°C. At the junction of the second pipe section PP2 and the third pipe section PP3, preferably, the pipe temperature is 1210°C to 1260°C, and the core temperature is 1250°C to 1300°C. At the end of the downstream side of the glass supply pipe 106, the pipe temperature and the center The temperature is preferably 1235°C to 1265°C.

With the temperature adjustment of the molten glass performed by such a glass supply pipe 106, the maximum temperature difference of the molten glass supplied to the supply tank 2 is made into 30 degrees C or less.

Furthermore, it is difficult to use a thermometer to measure the core temperature of molten glass. In this case, the unit time from the glass supply pipe 106, the heat dissipation per unit area information, and the unit of the glass supply pipe 106 can be used. The information of time, the amount of heating per unit area, and the information of the temperature and flow rate of the molten glass flowing into the glass supply pipe 106 are obtained by computer simulation based on the measurement result of the pipe temperature of the glass supply pipe 106.

In addition, the above-mentioned tube temperature is measured with a thermometer (not shown) installed at each position of the glass supply tube 106. The viscosity is measured by a viscometer (not shown) installed in the part where the glass supply pipe 106 is connected to the supply tank 2 of the molded body 1. The viscometer uses, for example, a thin tube viscometer or a rotary viscometer. The slim tube viscometer is to make the molten glass of the measuring object pass through the slim tube, and measure the viscosity of the molten glass based on the time (flow rate) the molten glass passes through the slim tube and the pressure difference between the two ends of the slim tube. The rotary viscometer measures the viscosity of the molten glass by reading the resistance of the molten glass from the rotating body, which is the viscous resistance, based on the torque of the rotating body.

In the manufacturing method of this embodiment, it is preferable that the temperature of the part near the guides 6a, 6b in the molten glass flowing downward on the wall surface 5 of the molded body 1 becomes from the upper surface 3 to the lower end 4 of the molded body 1 As far as the temperature of the liquid phase is higher than the liquidus temperature by more than 10°C, the part is heated, and it is more preferable to heat the part to a temperature higher than the liquidus temperature by 15°C or more. Under these circumstances, the occurrence of devitrification in the end of the formed flat glass is more surely suppressed. The specific liquidus temperature varies with the composition of the glass composition.

In the manufacturing method of this embodiment, it is preferable that in the forming step, the temperature of the part near the guides 6a and 6b in the molten glass flowing downward on the wall surface 5 of the formed body 1 becomes the temperature of the self-formed body 1. From the upper surface 3 to the lower end 4, the liquidus temperature is 10℃~150℃ higher than the liquid phase temperature (the liquidus temperature is higher than the liquidus temperature 10℃ or more, and the liquidus temperature is added to the temperature below 150℃), Heat the part along the guide. Thereby, deformation of the molded body 1 and shrinkage in the width direction in the sheet glass SG after molding can be suppressed. It is more preferable that the temperature of the part near the guides 6a, 6b in the molten glass flowing downward on the wall surface 5 of the molded body 1 becomes 15 higher than the liquidus temperature from the upper surface 3 to the lower end 4 of the molded body 1. ℃~100℃, heat the part along the guide.

By combining with the rapid cooling of the end of the molten glass after leaving the molded body 1 (the rapid cooling of the end SGa of the sheet glass SG), the thickness deviation of the sheet glass SG becomes 10 μm or less. In addition, the occurrence of devitrification in the end portion SGa is reliably suppressed.

Even if the temperature of the part near the guides 6a and 6b in the molten glass flowing downward on the wall surface 5 of the molded body 1 is sufficiently higher than the liquidus temperature from the upper surface 3 to the lower end 4 of the molded body 1, The temperature of the entire molten glass flowing downward in the molded body 1 is sufficiently higher than the liquidus temperature, and devitrification can also be suppressed theoretically. However, in the case of manufacturing glass with a high liquidus temperature, in reality, such a method cannot be applied to the overflow down-draw method. The reason is that there is a viscosity of the molten glass suitable for the forming of the plate glass by the overflow down-draw method (in order to avoid the following problems of the slack of the plate glass or the width contraction of the plate glass, the molten glass in the lower end 4 of the forming body 1 The viscosity is preferably more than 40000dPa‧s, more preferably more than 70000dPa‧s). If the temperature of the part near the guide in the molten glass becomes sufficiently higher than the liquidus temperature, the temperature of the entire molten glass flowing downward in the molded body 1 becomes sufficiently higher than the liquidus temperature, or Excessive heating of the lower end 4 of the molded body 1 may cause the viscosity of the molten glass in the lower end 4 of the molded body 1 to become less than the above-mentioned appropriate range. As a result, the following problem arises. That is, the viscosity of the plate glass after leaving the forming body 1 does not rise sufficiently, and the plate glass falls at a speed higher than the stretching speed of the conveying roller arranged on the downstream side of the forming body 1, resulting in level The plate glass relaxes on the roller, or the width of the plate glass shrinks. In addition, the higher the temperature of the molded body, the more significant the creep phenomenon that changes with time due to the use of the molded body becomes more pronounced, resulting in problems such as the central portion of the flat glass sagging with the passage of time from the start of molding. Considering the thickness required as a glass substrate and the temperature control of the plate glass implemented in the slow cooling step after forming, there is a limit to the increase in the stretching speed of the conveying roller (if the temperature control of the plate glass implemented in the slow cooling step is considered , The conveying speed of the plate glass is preferably 50~500m/hour, preferably 100~400m/hour, and preferably 120~300m/hour).

In addition, if the temperature of the part near the guide in the molten glass is sufficiently higher than the liquidus temperature, the width of the plate glass to be formed shrinks, and the product width as a glass substrate cannot be ensured. In addition, if the temperature of the entire molten glass flowing downward in the molded body 1 becomes sufficiently higher than the liquidus temperature, a creep phenomenon of the molded body 1 will occur, and if the creep phenomenon becomes significant, it will be manufactured. The thickness uniformity of the glass substrate decreases.

The height of the guide protruding from the wall surface where the molten glass in the forming body 1 flows is preferably as low as the position below the forming device. Preferably, the lower end 4 of the molded body 1 is a straight ridge line formed by connecting the inclined wall surfaces on both sides with each other, and the height of the pair of guides on the inclined wall surfaces is 0 (zero) at the position of the ridge line. Thereby, it is possible to further suppress the bifurcated opening of the ends (ears) of the plate glass, so that the glass substrate can be continuously produced more stably.

The cooling amount and the rotation amount of the cooling roller 8 are controlled by a control device (not shown). The control device is a computer that mainly includes CPU, RAM, ROM, and hard disk. The control device can control the driving motor driving the cooling roller 8 to obtain and adjust the contact load between the cooling roller 8 and the plate glass SG, which is one of the ends SGa of the width direction clamping the plate glass SG. The control device individually controls the cooling amount of each cooling roll 8 respectively. Furthermore, the control device uses the cooling control of the cooling roller 8 for the purpose of making the cross-sectional shape of the sheet glass SG in the thickness direction described below the target shape. The tension applied to the sheet glass SG is prepared, and at least 4 programs functioning as a conveying unit, an acquiring unit, a determining unit, and a control unit are memorized and executed.

The conveying part uses a conveying roller provided below the forming body 1 to convey the sheet glass SG obtained by forming the forming body 1 to the lower side at a specific conveying speed in the slow cooling space. The conveying part controls the driving motor that drives the conveying roller to adjust the rotation speed of the conveying roller, thereby adjusting the conveying speed of the sheet glass SG.

The acquiring unit obtains the shape data related to the current shape of the molded body 1 by calculating the time change of the shape of the molded body 1 by computer simulation. Specifically, the acquiring unit acquires shape data based on creep characteristic parameters. The creep characteristic parameter is a parameter used to reproduce the relationship between the stress applied to the forming body 1, the temperature of the forming body 1, and the strain rate of the forming body 1 due to creep deformation. Here, the stress applied to the molded body 1 is a force that compresses the molded body 1 in the longitudinal direction of the molded body 1 (the extending direction of the supply groove 2). In addition, the strain rate of the molded body 1 is assumed to be constant without changing with time. Initially, the acquiring unit measures the temperature-dependent change of the strain rate of the molded body 1 under the condition that the stress applied to the molded body 1 is constant. Then, the acquiring unit measures the stress-dependent change of the strain rate of the formed body 1 with respect to the stress applied to the formed body 1 under the condition that the temperature of the formed body 1 is fixed. Then, the acquiring unit determines the creep characteristic parameters 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 part uses the determined creep characteristic parameters to calculate the strain rate of the formed body 1 under a specific temperature and stress by computer simulation, and obtains the time change of the shape of the formed body 1, thereby obtaining the formed body 1. Shape information. FIG. 7 is an example of the shape data of the formed body 1 acquired by the acquiring unit. FIG. 7 shows the formed body 1 obtained when viewed in a direction perpendicular to the surface of the sheet glass SG formed by the formed body 1. In FIG. 7, the creep deformation of the molded body 1 is shown in an intensified manner compared to the actual situation. In FIG. 7, the shape of the unused molded body 1 is shown by a broken line, that is, the shape of the molded body 1 before creep deformation, and a solid line is shown Shows the current shape of the formed body 1 after creep deformation.

The acquiring unit acquires at least the displacement amount of the upper surface 3 of the upper surface 3 of the upper surface 3 in the vertical direction, that is, the displacement amount of the upper surface, based on the shape data of the formed body 1 based on the creep deformation. In Fig. 7, the displacement of the upper surface is the vertical dimension between the upper surface 3 before the creep deformation and the upper surface 3 after the creep deformation. Furthermore, in FIG. 7, the maximum upper surface displacement amount L, which is the maximum value of the upper surface displacement amount in the longitudinal direction of the molded body 1, is shown. Moreover, the acquisition part acquires the thickness data of the glass substrate measured by the glass substrate shape measuring apparatus (not shown). The thickness data is, for example, the distribution in the width direction of the thickness of the glass substrate manufactured by the forming device 200.

The determining unit determines whether the displacement L acquired by the acquiring unit reaches the reference amount. Here, the so-called reference amount refers to the deviation of the plate thickness when a fixed tension (initial tension) is applied to the sheet glass SG and the sheet glass SG (glass substrate) is formed into a predetermined thickness (for example, 0.1mm~0.8mm) It can meet the amount of ±10μm. When the tension applied to the sheet glass SG is not changed from the initial value, if the displacement L exceeds the reference amount, the thickness deviation of the sheet glass SG exceeds ±10 μm. Therefore, by increasing the tension applied to the sheet glass SG compared to the initial tension, the thickness of the sheet glass SG is controlled so that the thickness deviation of the sheet glass SG is within ±10 μm. The reference amount can be arbitrarily changed according to the initial tension, the thickness of the sheet glass SG, and the thickness deviation, etc., and is, for example, 3 mm to 30 mm.

The control unit sets the tension applied when the formed body 1 is not displaced along the width direction of the formed sheet glass SG (long side direction of the formed body 1) and the cross-sectional shape of the thickness direction of the sheet glass SG becomes the target shape. The reference tension (initial tension) is controlled by controlling the cooling amount of the cooling roller 8 to cool the both ends SGa of the sheet glass SG in the width direction, whereby the tension applied to the sheet glass SG becomes the reference tension . In the state where the forming body 1 is not displaced, the sheet glass SG becomes a forming preform by applying a reference tension in the width direction of the sheet glass SG. The plate thickness is determined so that the plate thickness deviation satisfies ±10μm. If the tension applied to the sheet glass SG is always the reference tension under the creep deformation of the molded body 1, the target shape cannot be achieved, for example, it cannot be molded to a predetermined thickness for molding, and the thickness deviation cannot satisfy ±10 μm. Therefore, the control unit not only applies the reference tension, but also applies the tension corresponding to the displacement of the molded body 1 to the sheet glass SG. 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. The control unit controls the cooling so that the thickness of the sheet glass SG becomes the predetermined thickness for forming based on the shape data of the formed body 1 acquired by the acquisition unit, and the thickness deviation of the sheet glass SG in the width direction is reduced. The amount of cooling of the roller 8 thereby controls the tension applied to the sheet glass SG. The shape information of the molded body 1 is, for example, the distribution of the displacement amount of the upper surface in the longitudinal direction of the molded body 1, that is, the shape distribution. The control unit controls the cooling amount of the cooling roller 8 in such a manner that the greater the displacement of the upper surface 3 is obtained from the shape distribution, the greater the tension in the width direction of the sheet glass SG becomes. As the displacement amount of the upper surface 3 obtained from the shape distribution, for example, the maximum upper surface displacement amount L is used.

After the sheet glass SG formed at the lower end 4 of the forming body 1 leaves the lower end 4, due to its own surface tension, the central area SGb begins to shrink toward the center in the width direction. Therefore, the cooling roller 8 cools the both ends SGa of the sheet glass SG to increase the viscosity of the both ends SGa, and suppresses the sheet glass SG from shrinking in the width direction by applying tension from the central area SGb to the both ends SGa, so that The thickness of the central area SGb of the sheet glass SG is uniform. However, if the molded body 1 undergoes creep deformation, the amount of molten glass in the vicinity of the central area SGb of the sheet glass SG increases, and the thickness of the central area SGb changes. That is, the cross-sectional shape of the thickness direction of the sheet glass SG is no longer the target shape. FIG. 8 is a diagram showing the sheet glass SG whose thickness near the central region SGb increases due to the creep deformation of the molded body 1. FIG. If the molded body 1 undergoes creep deformation, the amount of molten glass overflowing between the end 3a and the end 3b of the upper surface 3 increases, so the central area SGb of the sheet glass SG The thickness nearby increases. In FIG. 8, the thickness in the vicinity of the central region SGb is thicker than the predetermined thickness by D1 at most, so that the thickness of the central region SGb becomes non-uniform. Therefore, the control unit changes the cooling amount of the cooling roll 8 according to the shape data of the molded body 1, and suppresses the sheet glass SG from shrinking in the width direction by applying tension from the central area SGb of the sheet glass SG toward the both ends SGa, so as to prevent the sheet glass SG from shrinking in the width direction. The thickness of the central area SGb of the sheet glass SG is made uniform.

FIG. 9 is a diagram showing the relationship between the maximum upper surface displacement L of the molded body 1 and the tension T applied to the sheet glass SG. In FIG. 9, the maximum upper surface displacement amount L is referred to as the displacement amount L. The control unit is set to ignore the change in the thickness of the central area SGb of the sheet glass SG caused by the creep deformation of the molded body 1 when the judgment unit determines that the maximum upper surface displacement L of the molded body 1 does not exceed L1, and does not cause The tension T applied to the sheet glass SG changes from the initial value T1 (the range of the displacement L: 0 or more but not L1). If the displacement L of the formed body 1 does not reach L1, the control unit does not change the cooling amount of the cooling roll 8 and maintains the tension T at the initial value T1, whereby the thickness deviation of the formed sheet glass SG satisfies ±10 μm. When the control unit determines that the displacement L of the molded body 1 exceeds L1 by the determination unit, as shown in FIG. 9, it controls so that the tension T corresponding to the maximum upper surface displacement L is applied to the sheet glass SG. If the maximum upper surface displacement L reaches L1 or more, as shown in FIG. 8, the thickness of the central area SGb of the sheet glass SG increases, and the thickness is no longer uniform. Therefore, the control unit performs control in the following manner: corresponding to the displacement L, the tension T=T1+A×the maximum upper surface displacement L that is greater than the initial value T1 (the range of the displacement L: L1 or more is less than Lm , A: coefficient) is applied to the sheet glass SG from the central area SGb of the sheet glass SG toward the two ends SGa. The greater the deformation of the control portion formed body 1, the more enhanced the cooling of the both ends SGa. Specifically, the cooling amount of the cooling roll 8 is increased, and the viscosity of the both ends SGa is increased. When the viscosity of the two ends SGa increases, the tension T from the central area SGb toward the two ends SGa increases, and the molten glass located in the central area SGb of the sheet glass SG is stretched to the two ends SGa, so that the central area SGb The thickness is close to the predetermined thickness for forming, and the thickness is uniform. The control part is controlled by increasing the viscosity of the two ends SGa from, for example, 10 ^9.0 dPa·s to 10 ^14.5 dPa·s, thereby increasing the tension T.

Furthermore, when the range of the maximum upper surface displacement L is greater than or equal to L1 but less than Lm, by controlling the tension T from T1 to Tm, the thickness of the central region SGb is close to the predetermined thickness for forming, and the thickness becomes uniform. However, when the amount of displacement L exceeds Lm and the displacement occurs, only by controlling the tension T, it is difficult to make the thickness of the central area SGb approach the predetermined thickness while making the thickness uniform. Therefore, the determination section determines that the thickness is uniform. The regular replacement period of the formed body 1 is reached.

In addition, due to the creep deformation of the molded body 1, the local thickness deviation (surface unevenness) of the sheet glass SG also changes. The volume shrinkage of the sheet glass SG increases as it goes from the end SGa of the sheet glass SG toward the central area SGb, and therefore, tensile stress acts on the central area SGb of the sheet glass SG. As the thickness in the vicinity of the central area SGb becomes thicker, the tension from the end portions SGa toward the central area SGb becomes larger, so that the unevenness of the surface of the sheet glass SG becomes larger. Fig. 10(a) is an enlarged view of the cross section taken along the line A-A in Fig. 4, and Fig. 10(b) is an enlarged view taken on the line B-B of Fig. 4. Before the tension T is applied to the sheet glass SG by the cooling roller 8, the sheet glass SG shrinks toward the central area SGb. Therefore, the surface unevenness of the sheet glass SG becomes D2, after the tension T is applied to the sheet glass SG by the cooling roller 8 , The surface unevenness of the sheet glass SG becomes D3 which is smaller than D2. When the molded body 1 undergoes creep deformation, the surface unevenness D2 and D3 of the sheet glass SG also increase. Therefore, by applying a tension T from the central area SGb to the two ends SGa in a manner corresponding to the maximum upper surface displacement L, the sheet glass SG is stretched toward the two ends SGa, so that the surface of the sheet glass SG is uneven The difference D3 becomes smaller. In order to make the thickness of the central area SGb close to the predetermined thickness for forming, the tension T is applied in a manner corresponding to the maximum upper surface displacement L, so that the surface unevenness D3 of the sheet glass SG becomes smaller, so that the central area of the sheet glass SG Of SGb The thickness is uniform.

In addition, the control unit can also suppress the occurrence of streaks that may occur in the conveying direction of the sheet glass SG by applying the tension T to the sheet glass SG. Streaks are a kind of strain caused by the variation of the thickness (height) of the sheet glass SG in a specific width range, and are continuously generated in a pattern in the conveying direction of the sheet glass SG. In addition, the main factor of streaks also includes the viscosity difference of the glass. If tension is applied in the width direction of the sheet glass SG by controlling the cooling amount of the cooling roller 8 by the control unit, one of the irregularities on the surface of the sheet glass SG, that is, locally generated streaks, is stretched to the both ends of the sheet glass SG SGa, so as to form a sheet glass SG whose surface unevenness is reduced and the local thickness deviation satisfies ±10μm.

As explained above, the lower end 4 of the formed body 1 can change the tension T in the width direction of the sheet glass SG applied to the sheet glass SG in accordance with the displacement caused by the creep deformation of the formed body 1, while simultaneously changing The thickness of the central region SGb is close to the predetermined thickness for forming, and the thickness is made uniform on one side. In the case where the center of the longitudinal direction of the molded body 1 sags downward due to the creep deformation of the molded body 1 and bends, the cooling amount of the cooling roll 8 can be increased to apply the heat to the sheet glass SG The tension T in the width direction of the sheet glass SG becomes larger, and the thickness deviation of the width direction of the sheet glass SG is reduced. As a result, the thickness deviation of the glass substrate as the final product can be reduced.

Furthermore, in the manufacturing process of a glass substrate using glass with a higher liquidus temperature and glass with a higher strain point, the creep deformation of the molded body 1 is particularly likely to become a problem because the temperature of the molded body 1 is easily increased. In addition, in recent years, as glass substrates have continued to increase in size, the dimensions of the molded body in the longitudinal direction have continued to increase, and therefore, there has been a tendency that the deflection of the molded body 1 caused by creep deformation has become more pronounced. In this embodiment, the tension T applied to the sheet glass SG can be changed by adjusting the amount of cooling of the cooling roller 8, thereby effectively reducing the sheet glass SG caused by the creep deformation of the formed body 1. The thickness deviation in the width direction.

According to the manufacturing method of this embodiment, even when the liquid phase temperature of the glass composition constituting the molten glass is high and the liquid phase viscosity is small, for example, when the glass composition is alkali-free glass, glass containing a trace amount of alkali, etc. , Can also obtain the effect of suppressing the devitrification in the end of the formed flat glass. That is, when the liquid phase temperature of the glass composition constituting the molten glass is high and the liquid phase viscosity is small, the advantages obtained by the manufacturing method of this embodiment are greater.

In the manufacturing method of this embodiment, the liquid phase viscosity of the glass composition constituting the molten glass is 10000dPa•s or less. Such a glass composition is prone to devitrification problems in the end during the forming of flat glass by the overflow down-draw method. However, in the manufacturing method of this embodiment, the effect of suppressing devitrification can be obtained.

The liquid phase viscosity of the molten glass used in the manufacturing method of this embodiment is 100,000dPa•s or less. In a glass composition with a liquid phase viscosity of 100,000 dPa·s or less, the above-mentioned devitrification problem becomes more significant, but the manufacturing method of this embodiment has the effect of suppressing devitrification. From the viewpoint that the forming of flat glass can be stably implemented by the overflow down-draw method, the viscosity of the liquid phase is preferably 80,000 dPa·s or more.

The liquidus temperature of the glass composition constituting the molten glass used in the manufacturing method of this embodiment is preferably 1200°C or more and 1220°C or less. Such a glass composition is prone to devitrification problems in the end during the forming of flat glass by the overflow down-draw method. However, the manufacturing method of this embodiment has the effect of suppressing devitrification.

In the manufacturing method of this embodiment, the molten glass may contain zirconium oxide and/or tin oxide. In the molten glass containing zirconia, the liquidus temperature of the glass composition increases compared to the case without zirconia. Such molten glass is prone to devitrification problems in the end during the forming of flat glass by the overflow down-draw method. However, the manufacturing method of this embodiment has Through the effect. Even if zirconia is not originally contained in molten glass as a component of the glass composition, it can be eluted in molten glass by using a dissolving tank and a forming device composed of a high zirconia-based refractory material. In particular, when using such a dissolving tank to electrolytically dissolve the glass material, the concentration of zirconia in the molten glass tends to increase. That is, the manufacturing method of this embodiment is more suitable for the case where the glass raw material is electrolytically dissolved in a dissolution tank composed of a high zirconia refractory material.

Furthermore, the dissolving tank made of high zirconia refractory material is less likely to be corroded by glass than the dissolving tank made of alumina electroformed refractory, which is widely used in the past, and thus has a longer service life as a dissolving tank. In addition, foaming of molten glass can also be suppressed. Therefore, it is suitable for forming glass compositions with a higher melting temperature (the temperature at which the viscosity of the glass composition reaches 10 ^2.5 poise), such as alkali-free glass and molten glass containing a trace amount of alkali glass.

In addition, when the molten glass formed by the dissolving tank contains alkali-free glass or glass containing a trace amount of alkali, the resistivity of the glass composition tends to become higher, so that there is a problem that current flows into the high zirconia refractory material without flowing into the glass raw material. tendency. If electric current flows into the refractory material, zirconia is eluted in the molten glass formed by the dissolving tank. That is, the manufacturing method of this embodiment is further suitable for the case where an alkali-free glass or a molten glass containing a trace amount of alkali glass is formed by electrolytic dissolution using a dissolution tank composed of a high zirconia-based refractory material.

Among the glass substrates for FPD (Flat Panel Display) such as liquid crystal displays, organic EL displays, etc., it is preferable to include alkali-free glass or glass substrates containing a trace amount of alkali glass. The reason is that if the alkali component is eluted from the glass substrate in the panel manufacturing step, the characteristics of electronic components such as thin-film transistors (TFTs) may deteriorate. That is, the manufacturing method of this embodiment is particularly suitable for electrolytically dissolving the glass raw material in a dissolving tank composed of a high zirconia refractory material, and using the resulting molten glass to manufacture a flat panel display by the overflow down-draw method. The case of the glass substrate used for the display. In addition, the so-called alkali-free glass refers to a glass composition that does not substantially contain alkali metal oxides (in terms of the content rate is less than 0.05% by mass). The so-called trace alkali-containing glass refers to a glass composition containing 0.05 to 2.0% by mass of alkali metal oxides.

In molten glass containing tin oxide, devitrification is likely to occur due to the crystallization of tin oxide. In addition, when coexisting with zirconia, tin oxide has the effect of crystallizing zirconia. Such molten glass is particularly prone to devitrification problems in the end during the previous process of forming flat glass by the overflow down-draw method. However, the manufacturing method of this embodiment has the effect of suppressing devitrification.

In the manufacturing method of this embodiment, the glass composition constituting the molten glass may also be alkali-free glass or glass containing a trace amount of alkali. Compared with alkali glass containing more than 2.0% by mass of alkali metal oxides, such an alkali-free glass or a trace alkali-containing glass tends to have a higher liquid phase temperature and a lower liquid phase viscosity. The effect of inhibiting devitrification. As described above, this effect becomes particularly remarkable when a dissolution tank composed of a high zirconia refractory is used to form an alkali-free glass or a molten glass containing a trace amount of alkali glass by electrolytic dissolution.

Furthermore, from the viewpoint of preventing the deterioration of the characteristics of electronic components such as TFT (Thin Film Transistor), alkali-free glass is suitable for glass substrates for flat panel displays. Among them, from the viewpoints of solubility and clarity, a trace amount of alkali-containing glass is suitable for glass substrates for flat panel displays. By deliberately containing a small amount of alkali metal oxide, the glass containing a small amount of alkali is made, so that the solubility and clarity of the glass composition are improved. Due to the presence of alkali metal oxides, the alkalinity of the glass increases, so that metals with varying valences become easy to oxidize, which contributes to clarification. In addition, even when molten glass is formed by electrolytic dissolution of glass raw materials in a dissolution tank composed of high zirconia refractory materials, the resistivity of the glass can be made smaller than that of alkali-free glass, so that the zirconium oxide can be prevented from turning into a molten glass. The elution of molten glass prevents the increase in devitrification of molten glass.

In the manufacturing method of this embodiment, for the glass composition constituting the molten glass, ^{the temperature (melting temperature) exhibiting a viscosity of 10 2.5} poise may also be 1500°C to 1750°C. Such a glass composition requires a high temperature during melting, and therefore, when a molten glass is formed by using a melting tank made of a high zirconia-based refractory material, zirconia is easily eluted. Even for such a glass composition, the manufacturing method of this embodiment has the effect of suppressing devitrification.

Examples of glass components contained in the glass substrate manufactured by the manufacturing method of this embodiment include SiO ₂ , Al ₂ O ₃ , B ₂ O ₃ , MgO, CaO, SrO, BaO, Li ₂ O, Na ₂ O , K ₂ O, ZrO ₂ , TiO ₂ , ZnO, and P ₂ O ₅ .

SiO ₂ is the skeleton component of glass, so it is an essential component. If the content decreases, the strain point decreases and the thermal expansion coefficient tends to increase. In addition, if the SiO ₂ content is too small, it will be difficult to reduce the density of the glass substrate. On the other hand, if the _{content of SiO 2 is} too large, the resistivity of the molten glass MG increases, and the melting temperature becomes remarkably high, making it difficult to dissolve. If the _{content of SiO 2 is} too large, the devitrification temperature will also increase and the devitrification resistance will tend to decrease. Furthermore, if the _{content of SiO 2 is} too large, the etching rate becomes slow. From such a viewpoint, _{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%, still more preferably 66 to 72 mol%, and still more preferably in the range of 67 to 71 mol%.

Al ₂ O ₃ is an essential component for raising the strain point. If the _{content of Al 2} O _{3 is} too small, the strain point decreases. Furthermore, if the _{content of Al 2} O _{3 is} too small, the Young's modulus and the etching rate by oxygen tend to also decrease. On the other hand, if the _{content of Al 2} O _{3 is} too large, the devitrification temperature of the glass increases and the devitrification resistance decreases, so the formability tends to deteriorate. According to this viewpoint, _{the content of Al 2} O ₃ is in the range of 8-20 mol%. The content of Al ₂ O ₃ is preferably 10-17 mol%, more preferably 10.5-17 mol%, more preferably 11-15 mol%, and still more preferably 12-15 mol%.

B ₂ O ₃ is a component that reduces the high-temperature viscosity of glass and improves the meltability. That is, since the viscosity near the melting temperature is reduced, the solubility is improved. In addition, B ₂ O _{3 is} also a component that lowers the devitrification temperature. If the _{content of B 2} O _{3 is} small, the solubility and devitrification resistance tend to decrease. If the B ₂ O ₃ content is too large, the strain point and Young's modulus will decrease. In addition, due to _{the volatilization of B 2} O ₃ during glass forming, devitrification is likely to occur. In particular, glass with a higher strain point tends to increase the molding temperature, which promotes the above-mentioned volatilization, and the occurrence of devitrification becomes a significant problem. In addition, due to _{the volatilization of B 2} O ₃ when the glass is dissolved, the non-homogeneity of the glass becomes significant and it becomes easy to produce streaks. From such a viewpoint, the _{content of B 2} O ₃ is 0-15 mol%, preferably 0-8 mol%, more preferably 0-7 mol%, still more preferably 0.1-6 mol%, more preferably 1-5 mol%, More preferably, it is in the range of 1.5 to 4.5 mol%.

MgO is a component that improves solubility. In addition, the MgO-based alkaline earth metal is a component that makes it difficult to increase the density. Therefore, if the content is relatively increased, the density can be easily reduced. By containing MgO, the resistivity and melting temperature of the molten glass MG can be reduced. Among them, if the content of MgO is too large, the devitrification temperature of the glass rises sharply, so devitrification is likely to occur especially in the forming step. From such a viewpoint, the MgO content is 0-15 mol%, preferably 1-15 mol%, more preferably 0-6 mol%, and still more preferably 1-6 mol%. Alternatively, the MgO content is preferably 0-15 mol%, more preferably 0-6 mol%, and still more preferably 1-6 mol%.

CaO is an effective component for improving the solubility of glass without increasing the devitrification temperature of glass sharply. In addition, the CaO-based alkaline earth metal oxide is a component that makes it difficult to increase the density. Therefore, if the content is relatively increased, the density can be easily reduced. If the content is too small, the resistivity of the molten glass MG will increase and the devitrification resistance will tend to decrease. If the content of CaO is too large, the coefficient of thermal expansion increases and the density tends to increase. From such a viewpoint, the CaO content is 0-20 mol%, preferably 1-15 mol%, more preferably 2-11 mol%, and still more preferably 4-9 mol%.

SrO is a component that can reduce the devitrification temperature of glass. SrO is not necessary, but if it contains SrO improves the devitrification resistance and solubility. However, if the SrO content is too large, the density will increase. From such a viewpoint, the SrO content is 0-15 mol%, preferably 0-8 mol%, more preferably 0-3 mol%, still more preferably 0-1 mol%, more preferably 0-0.5 mol%, It is more preferable not to contain it substantially.

BaO is an essential component that can effectively reduce the devitrification temperature of the glass and the resistivity of the molten glass MG. If BaO is contained, devitrification resistance and solubility are improved. However, if the content of BaO is too large, the density will increase. In addition, due to the viewpoint of environmental load and the tendency of thermal expansion coefficient to increase, the content of BaO is 0-15 mol% or 0.1-15 mol%, preferably 1-15 mol%, more preferably 1-10 mol%, and still more preferably It is in the range of 1.5~6mol%.

Li ₂ O and Na ₂ O are components that increase the thermal expansion coefficient of glass and cause the risk of damage to the substrate during heat treatment. In addition, Li ₂ O and Na ₂ O are also components that lower the strain point. On the other hand, since the resistivity of the molten glass MG can be reduced, the corrosion of the dissolution tank can be suppressed _{by containing Li 2} O and Na _{2 O.} From the above viewpoints, _{the content of Li 2} O is preferably 0 to 0.5 mol%, and more preferably not contained substantially. The content of Na ₂ O is preferably 0 to 0.5 mol%, more preferably 0 to 0.2 mol%. Furthermore, Na ₂ O is a component that makes it more difficult to lower the strain point than _{Li 2 O, so it is preferably Na 2} O>Li ₂ O. Furthermore, from the viewpoint of preventing elution from the glass substrate from deteriorating the TFT characteristics, it is _{preferable that Li 2} O and Na ₂ O are not contained substantially.

K ₂ O is a component that enhances the alkalinity of glass and promotes clarity. In addition, K ₂ O is a component that lowers the resistivity of molten glass MG. If K ₂ O is contained, the resistivity of the molten glass MG decreases, so that the current can be prevented from flowing into the refractory material constituting the dissolution tank, and the erosion of the dissolution tank can be suppressed. In addition, when the refractory material constituting the dissolution tank contains zirconia, the dissolution tank can be prevented from being corroded and the zirconia can be eluted from the dissolution tank into the molten glass MG. Therefore, devitrification caused by the zirconia can also be suppressed. In addition, since the viscosity of the glass near the melting temperature can be reduced, the solubility and clarity are improved. On the other hand, if the K ₂ O content is too large, the coefficient of thermal expansion increases and the strain point tends to decrease. From such a viewpoint, the K ₂ O content is preferably 0 to 0.8 mol%, more preferably 0.01 to 0.5 mol%, and still more preferably in the range of 0.1 to 0.3 mol%.

ZrO ₂ and TiO ₂ are components that increase 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 the devitrification resistance tends to decrease. In particular, ZrO ₂ is difficult to melt due to its high melting point, which causes problems such as a part of the raw material being deposited on the bottom of the dissolving tank. If these undissolved components are mixed into the glass body, they will cause deterioration of the glass quality as inclusions. In addition, TiO ₂ is a component for coloring glass, so it is not good for substrates for displays. From such a viewpoint, in the glass substrate of this embodiment, _{the contents of ZrO 2} and TiO ₂ are preferably 0-5 mol%, more preferably 0-2 mol%, and more preferably not contained substantially.

ZnO is a component that improves solubility. But it is not an essential ingredient. If the ZnO content is too large, the devitrification temperature will increase, the strain point will decrease, and the density will tend to increase. From such a viewpoint, the ZnO content is preferably 0-5 mol%, more preferably in the range of 0-2 mol%, and still more preferably not contained substantially.

P ₂ O ₅ is a component that reduces high-temperature viscosity and improves solubility. But it is not an essential ingredient. If the _{content of P 2} O _{5 is} too large, the strain point decreases. _{In addition, due to the volatilization of P 2} O ₅ when the glass is dissolved, the non-homogeneity of the glass becomes significant and streaks are easily generated. From such a viewpoint, the _{content of P 2} O _{5 is} preferably 0 to 3 mol%, more preferably 0 to 1 mol%, still more preferably in the range of 0 to 0.5 mol%, and even more preferably not substantially contained.

The glass substrate to which this embodiment is applied includes, for example, an alkali-free glass containing 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 0~17mol% (RO is the total amount of MgO, CaO, SrO and BaO)

R _'2 O 0 ~ ₂ mole% (R' ₂ O is Li ₂ O, Na ₂ O and K ₂ O of the total).

From the viewpoint of reducing the thermal shrinkage rate, SiO ₂ is preferably 60 to 75% by mass, and furthermore, 63 to 72% by mass.

Among RO, it is preferable that MgO is 0-10% by mass, CaO is 0-10% by mass, SrO is 0-10% by mass, and BaO is 0-10% by mass.

In addition, it may include 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 4.5 or more glass. Furthermore, it is preferable to include at least any one of MgO, CaO, SrO, and BaO, and the molar ratio (BaO+SrO)/RO is 0.1 or more.

Furthermore, it is preferable that the _{total of twice the content of B 2} O ₃ expressed by mass% and the content of RO expressed by mass% is 30 mass% or less, and preferably 10 to 30 mass %.

Furthermore, it is preferable that the metal oxides (tin oxide, iron oxide) whose valences fluctuate in the molten glass are contained in a total of 0.05 to 1.5% by mass.

It is preferable that AS ₂ O ₃ , Sb ₂ O ₃ , and PbO are not contained substantially, but they may be contained arbitrarily.

In addition, the total content of metal oxides (tin oxide, iron oxide) of varying valence in the glass is 0.05 to 1.5% by mass, and _{the case where As 2} O ₃ , Sb ₂ O ₃ and PbO are not substantially contained is optional and not essential. .

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. The glass substrate produced in this embodiment is suitable for use as 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. Also, this embodiment The glass substrate made in China is suitable for glass substrates for liquid crystal displays that require very little alkali metal oxide content. It is also suitable for glass substrates for organic EL displays. In other words, the manufacturing method of the glass substrate of this embodiment is suitable for manufacturing a glass substrate for a display, especially suitable for manufacturing a glass substrate for a liquid crystal display. In addition, it can also be used as cover glass for displays or housings of mobile terminal equipment, touch panels, glass substrates or cover glass for solar cells. The glass substrate manufactured in this embodiment is particularly suitable for glass substrates for liquid crystal displays using polysilicon TFTs.

In addition, the glass substrate manufactured in this embodiment can also be applied to cover glass, glass for magnetic disks, glass substrates for solar cells, and the like.

As mentioned above, the manufacturing method of the glass substrate and the manufacturing apparatus of the glass substrate of the present embodiment have been described in detail, but the present invention is not limited to the above-mentioned embodiment. Needless to say, various modifications can be made without departing from the spirit of the present invention. Or change.

(Example)

Using a high-zirconia-based refractory material in a dissolution tank, the glass raw material formulated in the following composition is electrolytically dissolved to form molten glass. Then, after clarifying the formed molten glass with a clarification tube made of platinum alloy, it stirred with a stirring tank. Then, the molten glass is supplied to the forming apparatus 200 (formed body 1), and the sheet glass is formed by the overflow down-draw method. The end of the flat glass is cooled by the cooling roller 8 in such a way that the viscosity of the end becomes 10 ^12.5 dPa‧s. The shaped flat glass is slowly cooled and then cut to obtain a flat plate with a thickness of 0.4mm and a size of 2200mm×2500mm. Glass substrates for displays. Furthermore, the liquid phase viscosity of the glass composition is 50000dPa‧s, and the strain point is 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, and SnO ₂ : 0.1% by mass.

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

As shown in Table 1, in Examples 1 to 6 where the maximum temperature difference of molten glass is 30℃ or less and the viscosity of molten glass (viscosity based on average temperature) is 22000dPa‧s or more and 38000dPa‧s or less, the thickness deviation reaches 10μm or less, so that the thickness deviation can be suppressed. On the other hand, when the maximum temperature difference of molten glass exceeds 30℃, when the viscosity of molten glass (viscosity based on average temperature) does not reach 22000dPa‧s, and when the viscosity of molten glass exceeds 38000dPa‧s In Comparative Examples 2 to 7, the plate thickness deviation became more than 10 μm. With this, it can be confirmed It is considered that the thickness deviation of the plate glass is 10μm or less, the maximum temperature difference of the molten glass supplied to the supply tank 2 of the molded body 1 is set to 30°C or less, and the viscosity of the molten glass (viscosity based on the average temperature) is set 22000dPa‧s or more, 38000dPa‧s or less.

1‧‧‧Formed body

2‧‧‧Supply tank

2a‧‧‧Bottom

3‧‧‧Upper surface

4‧‧‧Bottom

5‧‧‧Wall

6a、6b‧‧‧Guide

7‧‧‧Liquid level

8‧‧‧Cooling roll

106‧‧‧Glass Supply Pipe

SG‧‧‧Plate glass

SGa‧‧‧(Flat glass) end

Claims (8)

A method for manufacturing a glass substrate, which is characterized in that molten glass is supplied from a glass supply pipe to a shaped body having a supply tank, and the shaped body is used to shape flat glass by an overflow down-draw method, and the supply tank has a supply to The amount of molten glass in the supply tank overflowing from the supply tank forms a uniform bottom shape in the extension direction of the supply tank and the width direction orthogonal to the extension direction. The method of manufacturing the glass substrate includes: a forming step, which The molten glass with the maximum temperature difference of the molten glass supplied from the glass supply pipe to the supply tank is 30°C or less and the viscosity of the molten glass is 22000dPa‧s to 38000dPa‧s to the supply tank, and the molten glass is formed in the above The lower end of the body allows the molten glass to flow to form the plate glass; and the end cooling step is to reduce the thickness deviation locally generated in the plate glass formed in the forming step to reduce the width of the plate glass The two ends of the direction are cooled, and the end cooling step is to set the tension applied to the shaped body when the shaped body is not deformed in the width direction of the flat glass so that the cross-sectional shape of the plate glass becomes the target shape as the reference tension. When it is not deformed, it is controlled so that the both ends in the width direction of the plate glass are cooled to become the above-mentioned reference tension, and when the shaped body is deformed, the plate glass is deformed according to the shaped body. The tension added to the above-mentioned reference tension. The method of manufacturing a glass substrate according to claim 1, wherein the deformation of the shaped body is a creep deformation that changes with time due to the use of the shaped body, and the above-mentioned reference tension is added to the above-mentioned forming caused by the creep deformation The tension corresponding to the displacement of the specific position of the body. Such as the manufacturing method of the glass substrate of claim 1, wherein the greater the deformation, the more enhanced the cooling of the two ends. Such as the manufacturing method of the glass substrate of claim 2, wherein the greater the deformation, the more the cooling of the two ends. The method for manufacturing a glass substrate according to any one of claims 1 to 4, wherein the above-mentioned plate thickness deviation is 10 μm or less. The method for manufacturing a glass substrate according to any one of claims 1 to 4, wherein in the above-mentioned forming step, the temperature of the molten glass flowing downward in the above-mentioned formed body is increased by 10℃~ the liquidus temperature of the above-mentioned molten glass. The above molten glass is heated at 150°C. The method for manufacturing a glass substrate according to claim 5, wherein in the above-mentioned forming step, the temperature of the molten glass flowing downward in the above-mentioned formed body is increased by 10℃~150℃ compared with the liquid phase temperature of the above-mentioned molten glass. The above-mentioned molten glass. A manufacturing device for a glass substrate, characterized in that it supplies molten glass from a glass supply pipe to a shaped body having a supply tank, and uses the shaped body to form a flat glass by an overflow down-draw method, and the shaped body has a maximum receiving capacity. A supply tank for supplying molten glass with a temperature difference of 30°C or less and a viscosity of 22000dPa‧s or more and 38,000dPa‧s or less, and a wall surface for forming plate glass by converging the molten glass at the lower end of the above-mentioned forming body, the said supplying tank has The amount of molten glass supplied to the supply tank overflowing from the supply tank forms a uniform bottom shape in the extension direction of the supply tank and the width direction orthogonal to the extension direction, and the manufacturing device of the glass substrate is further equipped to suppress borrowing An end cooling device for cooling both ends in the width direction of the plate glass by means of locally generated plate thickness deviations in the plate glass obtained by forming the formed body, and the end cooling device combines the formed body on the plate glass When the cross-sectional shape of the plate glass is not deformed in the width direction, the tension required to achieve the target shape is set as the reference tension. When the molded body is not deformed, it is formed by cooling both ends of the plate glass in the width direction. The method of the reference tension is controlled, and when the molded body is deformed, a tension added to the reference tension based on the deformation of the molded body is applied to the plate glass.

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