JP5952311B2 - Glass substrate manufacturing method and glass substrate manufacturing apparatus - Google Patents

Description

  The present invention relates to a glass substrate manufacturing method and a glass substrate manufacturing apparatus by a downdraw method.

  Conventionally, a method of manufacturing a glass substrate using a downdraw method has been used. When manufacturing a glass substrate by such a downdraw method, in order to reduce the thickness deviation, warpage, or distortion of the glass substrate, in advance, the sheet glass cooling rate in the sheet glass flowing direction or the sheet glass flowing direction. An orthogonal width direction sheet glass temperature profile may be designed. In this case, the temperature management of the ambient temperature surrounding the sheet glass is performed so that the temperature of the sheet glass realizes the temperature of this temperature profile.

  For example, as an example of the town draw method, a method for manufacturing a glass substrate described in Patent Document 1 is known. This manufacturing method discloses that the temperature distribution in the width direction of the sheet glass is reduced in the slow cooling step.

Japanese Patent No. 3586142

  However, in the above manufacturing method, when unintended heat transfer occurs, there is a possibility that the cooling rate in the sheet glass flow direction and the temperature distribution in the width direction of the sheet glass cannot be sufficiently reduced in the sheet glass cooling stage. .

  In recent years, in glass substrates used for flat panel displays such as liquid crystal display devices and organic EL displays, quality requirements regarding thickness deviation, warpage, distortion, heat shrinkage, and the like of glass substrates have become strict. When a glass substrate is manufactured by the downdraw method, the temperature of the ambient temperature surrounding the sheet glass must be managed with higher accuracy than in the past in accordance with recent quality requirements.

  Therefore, the present invention provides a glass substrate manufacturing method that satisfies the quality requirements of the glass substrate by accurately controlling the temperature of the ambient temperature around the sheet glass when manufacturing the glass substrate by the downdraw method. For the purpose.

  The present invention includes the following aspects.

One embodiment of the present invention is a method for manufacturing a glass substrate.
[Aspect 1]
A method of manufacturing a glass substrate,
A molding step of molding a sheet glass from molten glass by a downdraw method using a molded body provided in a molding furnace chamber;
When the sheet glass flows through the slow cooling furnace chamber adjacent to the forming furnace chamber, while controlling the cooling rate in the flow direction of the sheet glass and the temperature distribution in the width direction of the sheet glass, A cooling step of gradually cooling the sheet glass including a center part closer to the center in the width direction of the sheet glass than the end part, and
The cooling step includes a first cooling rate control step of cooling the central portion at a first average cooling rate until the temperature of the central portion of the sheet glass reaches a slow cooling point,
A second cooling rate control step of cooling the central portion at a second average cooling rate until the temperature of the central portion reaches a strain point of −50 ° C. from the annealing point;
A third cooling rate control step of cooling the central portion at a third average cooling rate until the temperature of the central portion reaches the strain point of -200 ° C from the strain point of -50 ° C,
The slow cooling furnace chamber is divided into at least two spaces, a partition wall between the forming furnace chamber and the slow cooling furnace chamber, and a partition wall provided in the space provided in the slow cooling furnace chamber, The upper space where the cooling rate control step, the second cooling rate control step, and the third cooling rate control step are performed, and the temperature of the central portion is less than the strain point of −200 ° C. A heat insulating plate is used for a partition wall that divides the region from a lower space that cools more rapidly than cooling in the region from the annealing point + 100 ° C. to the strain point −200 ° C. ,
By making the thermal resistance of the heat insulating plate 0.07 m ² · K / W or more,
(1) The first average cooling rate is set to 5.0 ° C./second or more and 50.0 ° C./second or less,
(2) realizing that the first average cooling rate is faster than the second average cooling rate and the third average cooling rate;
The glass substrate manufactured by the cooling step has a heat shrinkage rate of 75 ppm or less and a strain retardation value of 1.0 nm or less.

[Aspect 2]
Said third average cooling rate, said second average that are controlled to be faster than the cooling rate, manufacturing method for a glass substrate according to Embodiment 1.

[Aspect 3]
In the temperature region where the temperature of the center portion of the sheet glass is equal to or higher than the glass softening point from the lowermost end portion of the molded body, the end portion in the width direction of the sheet glass is more than the temperature of the center region sandwiched between the end portions. The manufacturing method of the glass substrate of the aspect 1 or 2 with which the 1st temperature control process which controls temperature so that it is low and the temperature of the said center area | region becomes uniform is performed.

[Aspect 4]
The temperature of the central portion of the sheet glass is lower than the glass softening point, and the temperature control is performed so that the temperature in the width direction of the sheet glass decreases from the central portion toward the end portion in the temperature region near the glass strain point. The manufacturing method of the glass substrate as described in any one of the aspects 1-3 by which the 2nd temperature control process to perform is performed.

[Aspect 5]
A third temperature at which the temperature of the central portion of the sheet glass is controlled so that the temperature gradient between the end portion in the width direction of the sheet glass and the central portion approaches 0 in the temperature region near the glass strain point. The manufacturing method of the glass substrate as described in any one of the aspects 1-4 with which a control process is performed.

[Aspect 6]
In the third cooling rate control step, the sheet glass has a temperature in the width direction of the sheet glass in a temperature range from a glass strain point of −50 ° C. to a glass strain point of −200 ° C. The manufacturing method of the glass substrate as described in any one of the aspects 1-5 which controls so that it may become low toward the center part from the edge part of the width direction of glass.

[Aspect 7]
Another embodiment of the present invention is a glass substrate manufacturing apparatus. The manufacturing equipment
A molding apparatus comprising a molding furnace chamber, and molding a sheet glass from molten glass by a downdraw method using a molded body provided in the molding furnace chamber;
The sheet glass includes a slow cooling furnace chamber adjacent to the forming furnace chamber, and controls the cooling rate in the flow direction of the sheet glass and the temperature distribution in the width direction of the sheet glass when the sheet glass flows in the slow cooling furnace chamber. And a slow cooling device that slowly cools the sheet glass including the end portions on both sides and a center portion closer to the center in the width direction of the sheet glass than the end portions,
In the slow cooling apparatus,
A first cooling rate control step of cooling the central portion at a first average cooling rate until the temperature of the central portion of the sheet glass reaches a slow cooling point ;
A second cooling rate control step of cooling the central portion at a second average cooling rate until the temperature of the central portion reaches a strain point of −50 ° C. from the annealing point ;
Performing a third cooling rate control step of cooling the central portion at a third average cooling rate until the temperature of the central portion reaches the strain point of -200 ° C from the strain point of -50 ° C.
The slow cooling furnace chamber is divided into at least two spaces, a partition wall between the forming furnace chamber and the slow cooling furnace chamber, and a partition wall provided in the space provided in the slow cooling furnace chamber, the cooling rate controlling step, the second cooling rate controlling step, and the upper space to perform the third cooling rate controlling step, the sheet glass temperature of the central portion is less than the temperature of the strain point -200 ° C. A heat insulating plate is used for a partition wall that divides the region from a lower space that cools more rapidly than cooling in the region from the annealing point + 100 ° C. to the strain point −200 ° C. ,
By making the thermal resistance of the heat insulating plate 0.07 m ² · K / W or more,
(1) The first average cooling rate is 5.0 ° C./second or more and 50.0 ° C./second or less,
(2) realizing that the first average cooling rate is faster than the second average cooling rate and the third average cooling rate;
The glass substrate manufactured by the cooling step has a heat shrinkage rate of 75 ppm or less, and has a strain retardation value of 1.0 nm or less.

  According to the glass substrate manufacturing method and manufacturing apparatus using the downdraw method described above, the temperature of the ambient temperature around the sheet glass can be accurately controlled, for example, the warpage and distortion of the glass substrate can be reduced, and the glass substrate quality requirements can be reduced. Can be provided.

The flowchart of a part of manufacturing method of the glass substrate which concerns on this embodiment. The schematic diagram which mainly shows the melting apparatus contained in the manufacturing apparatus of the glass substrate used for the manufacturing method of the glass substrate which concerns on this embodiment. The schematic front view of the shaping | molding apparatus shown in FIG. The schematic side view of the shaping | molding apparatus shown in FIG. The control block diagram of the control apparatus used for the manufacturing method of the glass substrate which concerns on this embodiment. The figure which shows the temperature of the sheet glass SG in each temperature profile used at the temperature control process performed with the manufacturing method of the glass substrate which concerns on this embodiment. The graph of the temperature profile in the table | surface shown in FIG. The figure which shows the cooling rate and temperature gradient in the temperature control process performed with the manufacturing method of the glass substrate which concerns on this embodiment. The figure explaining the temperature control process and cooling rate control process which concern on this embodiment by contrast.

The following words and phrases in this specification are defined as follows.
-The edge part (R, L) of a sheet glass means the range within 50 mm from the edge of the width direction of a sheet glass.
-The center area | region (CA) of sheet glass means the part except the edge part of sheet glass.
The right part (CR) and the left part (CL) of the sheet glass are a part of the central area (CA), are adjacent to the end part of the sheet glass, and are areas within a range of 150 mm from the end part.
-The center part (C) of sheet glass is an area | region except the right part (CR) and the left part (CL) from the said center area | region (CA) of sheet glass, From the edge of the both sides of the width direction of sheet glass The portion inside 200 mm in the width direction from the position 200 mm inside in the width direction.
The strain point is the temperature of the glass when the glass viscosity is 10 ^14.5 dPa · sec.
-An annealing point means the temperature of glass when a glass viscosity will be 10 < ¹³ > dPa * second.
- The softening point refers to the temperature of the glass when the glass viscosity of ¹⁰ 7.6 dPa · s.

  Hereinafter, a glass substrate manufacturing method for manufacturing a glass substrate using the glass substrate manufacturing apparatus 100 of the present embodiment will be described with reference to the drawings.

FIG. 1 is a partial flowchart of the glass substrate manufacturing method according to the present embodiment.
Hereinafter, the manufacturing method of a glass substrate is demonstrated using FIG.

  As shown in FIG. 1, the glass substrate is manufactured through various processes including a melting process ST1, a clarification process ST2, a homogenization process ST3, a molding process ST4, a cooling process ST5, and a cutting process ST6. The Hereinafter, these steps will be described.

In the melting step ST1, the glass raw material is heated and melted to form molten glass.
In the clarification step ST2, the molten glass is clarified. Specifically, the gas component contained in the molten glass is released from the molten glass, or the gas component contained in the molten glass is absorbed into the molten glass.
In the homogenization step ST3, the molten glass is homogenized.
In the forming step ST4, the molten glass is formed into a sheet-like glass, that is, a sheet glass SG (see FIGS. 3 and 4) by a downdraw method (specifically, an overflow downdraw method).
In the cooling step ST5, the sheet glass SG formed in the forming step ST4 is gradually cooled. In the cooling step ST5, the sheet glass SG is cooled to near room temperature.
In the cutting step ST6, the sheet glass SG cooled to near room temperature is cut every predetermined length to obtain a cut sheet glass SG1 (see FIG. 3). Note that the cutting step ST6 may not be performed immediately after the cooling step.

  FIG. 2 is a schematic view mainly showing a melting apparatus 200 included in the glass substrate manufacturing apparatus 100. FIG. 3 is a schematic front view of a forming apparatus 300 included in the glass substrate manufacturing apparatus 100. FIG. 4 is a schematic side view of the molding apparatus 300. The glass substrate manufacturing apparatus 100 will be described below.

  The glass substrate manufacturing apparatus 100 mainly includes a melting apparatus 200 and a forming apparatus 300.

The melting apparatus 200 is an apparatus for performing the melting process ST1, the clarification process ST2, and the homogenization process ST3.
As shown in FIG. 2, the melting apparatus 200 includes a melting tank 201, a clarification tank 202, a stirring tank 203, a first pipe 204, and a second pipe 205.
The melting tank 201 is a tank for melting a glass raw material. In the melting tank 201, the melting step ST1 is performed.
The clarification tank 202 is a tank for removing bubbles from the molten glass melted in the melting tank 201. By further heating the molten glass fed from the melting tank 201 in the clarification tank 202, defoaming of bubbles in the molten glass is promoted. In the clarification tank 202, a clarification step ST2 is performed.
The stirring tank 203 stirs the molten glass with a stirrer. In the stirring tank 203, the homogenization step ST3 is performed.

The molding apparatus 300 is an apparatus for performing the molding process ST4 and the cooling process ST5, and is provided in the furnace chamber S1 that is an internal space surrounded by the furnace wall 301.
As shown in FIGS. 3 and 4, the molding apparatus 300 includes a molded body 310, an atmosphere partition member 320, a cooling roller 330, a cooling unit 340, pulling rollers 350 a to 350 e, heaters 360 a to 360 e, 1st-5th partition 355a-355d and the furnace wall 301 are provided. Hereinafter, these configurations will be described.

  The furnace chamber S1 is divided into a forming furnace chamber S2 and a slow cooling furnace chamber S3 by a first partition 355a. Therefore, the forming furnace chamber S2 and the slow cooling furnace chamber S3 are adjacent rooms. The forming furnace chamber S2 is surrounded by the furnace wall 301 and the first partition 355a. The slow cooling furnace chamber S3 is surrounded by the furnace wall 301 and the first partition 355a. The molding furnace chamber S2 is further divided into an upper molding furnace chamber S2U and a lower molding furnace chamber S2B by an atmosphere partition member 320. On the other hand, the slow cooling furnace chamber S3 includes a first slow cooling chamber S3A, a second slow cooling chamber S3B, a third slow cooling chamber S3C, and a fourth slow cooling chamber S3D by the second partition 355b, the third partition 355c, and the fourth partition 355d. And the fifth annealing chamber S3E.

The molded body 310 is an apparatus for performing the molding step ST4, and is provided in the molding furnace chamber S2, more specifically, the upper molding furnace chamber S2U.
As shown in FIG. 3, the molded body 310 is located in the upper part of the molding apparatus 300, and the molten glass flowing from the melting apparatus 200 is molded into a sheet-like glass substrate (sheet glass SG) by the overflow down draw method. It has the function to do.
The molten glass MG that has flowed into the groove 312 of the molded body 310 overflows at the top of the groove 312 and flows down along both side surfaces 313 of the molded body 310. And the molten glass MG which flows down along the both side surfaces 313 of the molded object 310 joins at the lowest end part 314 of the molded object 310, and becomes sheet glass SG. The sheet glass SG is supplied to the lower forming furnace chamber S2B through a slit-like gap between the pair of atmosphere partition members 320.

As shown in FIGS. 3 and 4, the atmosphere partition member 320 is a plate-like member disposed in the vicinity of the lowermost end portion 314 of the molded body 310 and is a heat insulating member.
The atmosphere partition member 320 is disposed so as to be substantially horizontal on both sides in the thickness direction of the sheet glass SG flowing down from the lowermost end portion 314 of the molded body 310. The atmosphere partition member 320 suppresses the movement of heat from the upper side to the lower side of the atmosphere partition member 320 by partitioning the upper and lower air.

The cooling roller 330 is disposed in the lower molding furnace chamber S2B located below the atmosphere partition member 320. Moreover, the cooling roller 330 is arrange | positioned so as to oppose the edge part of the both sides of the width direction on the both sides of the thickness direction of the sheet glass SG. The cooling roller 330 is air-cooled by, for example, an air-cooling tube passed through the inside. Therefore, the sheet glass SG is in contact with the cooled cooling roller 330 on both side portions in the thickness direction and on both end portions in the width direction (hereinafter, the portions are the ear portions R and L of the sheet glass SG (FIG. 4). And also referred to as FIG. 7) is cooled. Thereby, the viscosities of the ear portions R and L are adjusted to a predetermined value or more, specifically, 10 ^9.0 dPa · sec or more. The cooling roller 330 also pulls the sheet glass SG downward as a driving force from the cooling roller drive motor 390 (see FIG. 5) is transmitted.

The cooling unit 340 (see FIG. 4) is disposed in the lower forming furnace chamber S2B. The cooling unit 340 cools the cooling roller 330 and the ambient temperature of the sheet glass SG passing therebelow.
The cooling unit 340 includes a plurality of cooling sources in the width direction of the sheet glass SG and a plurality of cooling sources in the flow-down direction thereof. The number of cooling sources is not particularly limited, but a larger number can perform temperature control with higher accuracy.

  The pulling rollers 350a to 350e are located below the cooling roller 330. Specifically, the pulling rollers 350a to 350e are arranged in the slow cooling furnace chamber S3 with a predetermined interval in the flow direction of the sheet glass SG. The pulling rollers 350a and 350b are disposed in the first slow cooling furnace chamber S3A, the pulling roller 350c is disposed in the second slow cooling furnace chamber S3B, the pulling roller 350d is disposed in the third slow cooling furnace chamber S3C, and the pulling roller 350e is 4 Arranged in the slow cooling furnace chamber S3D.

  The pulling rollers 350a to 350e are respectively arranged on both sides in the thickness direction of the sheet glass SG and so as to face ends on both sides in the width direction of the sheet glass SG. The pulling rollers 350a to 350e are in contact with the end portions on both sides in the thickness direction of the sheet glass SG in which the viscosity of the lugs R and L is equal to or higher than a predetermined value in the cooling roller 330. However, the sheet glass SG is pulled downward. The peripheral speed of the pulling rollers 350 a to 350 e is larger than the peripheral speed of the cooling roller 330.

  A plurality of heaters are arranged in the flow direction of the sheet glass SG and a plurality of heaters in the width direction of the sheet glass SG. The heaters 360a to 360e control the ambient temperature in the vicinity of the sheet glass SG pulled downward by the pulling rollers 350a to 350e by controlling the output by the control device 500 described later (specifically, the temperature rises). It functions as a temperature control device.

Here, the ambient temperature of the sheet glass SG pulled downward by the pulling rollers 350a to 350e is controlled by the heaters 360a to 360e (specifically, the ambient temperature around the sheet glass SG is controlled). Thus, the sheet glass SG is controlled in temperature), so that the sheet glass SG is cooled from the viscous region to the elastic region through the viscoelastic region.
In addition, in the vicinity of each of the heaters 360a to 360e, a plurality of thermocouples (here, thermocouple units 380 (see FIG. 5)) serving as ambient temperature detection means for detecting the ambient temperature of each region of the sheet glass SG. ) Are arranged to correspond to each of the heaters 360a to 360e. That is, a plurality of thermocouples are arranged in the flow direction of the sheet glass SG and a plurality in the width direction.
As described above, the cooling process ST5 is a process in which the sheet glass SG is cooled by the cooling roller 330, the cooling unit 340, and the heaters 360a to 360e in the region below the lowermost end 314 of the molded body 310. Therefore, the cooling process is performed in the upper forming furnace chamber S2B, the first slow cooling furnace chamber S3A, the second slow cooling furnace chamber S3B, the third slow cooling furnace chamber S3C, and the fourth slow cooling furnace chamber S3D.

  In the cutting device 400, the cutting step ST6 is performed. In the present embodiment, the cutting device 400 is disposed on the outside lower side of the furnace chamber S1, but is not limited thereto. Further, the cutting device 400 is not provided, and the sheet glass SG may be formed into a predetermined shape, for example, rolled into a roll shape, and conveyed to the next step.

FIG. 5 is a control block diagram of the control device 500.
The control device 500 is provided outside the furnace wall 301. The control device 500 includes a CPU, a ROM, a RAM, a hard disk, and the like, and functions as a control unit that controls various devices included in the glass substrate manufacturing apparatus 100.
The control device 500 controls the cooling unit 340, the heaters 360a to 360e, the cooling roller driving motor 390, the pulling roller driving motor 391, the cutting device driving motor 392, and the like. As described below, the temperature control by the control device 500 can make the temperature distribution of the sheet glass SG coincide with a predetermined temperature profile.

  FIG. 6 shows a table showing an example of the temperature of the sheet glass SG in each temperature profile (described later). FIG. 7 shows a graph of the temperature profile in the table of FIG. FIG. 8 shows a table showing cooling rates and temperature gradients in the temperature control steps ST11 to ST14. FIG. 9 is a diagram illustrating a temperature control step and a cooling rate control step, which will be described later, in comparison.

  In cooling process ST5, temperature control process ST10 (refer FIG. 8) which temperature-controls sheet glass SG is performed. The temperature control step ST10 is a step of performing temperature control in the width direction of the sheet glass SG in a temperature range from the lower part of the molded body 310 to a temperature range near the glass strain point. Specifically, in the temperature control step ST10, the control device 500 controls the temperature of the sheet glass SG by controlling the cooling roller 330. In the temperature control step ST10, the control device 500 controls the cooling unit 340 and the heaters 360a to 360e to directly or indirectly control the temperature of the sheet glass SG. The temperature of the sheet glass SG shown in FIGS. 6 and 7 is a value calculated by simulation based on the ambient temperature around the sheet glass SG controlled by the cooling unit 340 and the heaters 360a to 360e.

  In the cooling step ST5, by performing the temperature control step ST10, the temperature of the sheet glass SG enters a predetermined temperature range at a predetermined height position, and the temperature of the sheet glass SG is a predetermined temperature in the width direction. Have a distribution. That is, the temperature of the sheet glass SG is controlled in the flow-down direction and the width direction.

  As shown in FIG. 8, the temperature control step ST10 includes a glass strain point upper temperature control step ST10a and a strain point lower temperature control step ST14. Hereinafter, each temperature control process will be described.

  The temperature control step ST10a on the glass strain point is the temperature of the sheet glass SG from the lowermost end portion 314 of the molded body 310 to the temperature at which the temperature of the central portion C of the sheet glass SG is located in the temperature region near the glass strain point. And includes a first temperature control step ST11, a second temperature control step ST12, and a third temperature control step ST13. That is, the high-temperature sheet glass SG immediately after being obtained by molding is cooled according to the temperature control to a temperature located in the temperature region near the glass strain point by the glass strain point upper temperature control step ST10a. The temperature range near the glass strain point is the temperature obtained by adding the glass strain point and the glass annealing point and dividing by 2 ((glass strain point + glass annealing point) / 2), and 50 ° C. from the glass strain point. The region between the temperature (glass strain point −50 ° C.) minus.

1st temperature control process ST11 is performed when the temperature of the center part of the width direction of the sheet glass SG is more than a glass softening point.
In the first temperature control step ST11, the temperature profile is controlled to be the first temperature profile TP11.

  As shown in FIG. 7, the first temperature profile TP11 is a central region CA in which the temperature of the ears R and L of the sheet glass SG is lower than the temperature of the central region CA and is sandwiched between the ears R and L. This is a temperature profile in which the temperature in the width direction becomes uniform. Here, “the temperature in the central area CA width direction is uniform” means that the temperature difference in the width direction in the central area CA falls within a range from −20 ° C. to 20 ° C.

  In the first temperature control step ST11, for example, the ears R and L of the sheet glass SG are cooled by the cooling roller 330, and the ambient temperature of the sheet glass SG is controlled by the cooling unit 340, thereby the ears R. , L is lower than the temperature of the central area CA by a predetermined temperature, and the temperature profile in which the temperature in the width direction of the central area CA is uniform is formed and maintained. Thereby, the plate | board thickness of center area | region CA of the sheet glass SG can be made uniform as much as possible. Here, as described above, since the cooling unit 340 includes a plurality of cooling sources in the width direction, the temperatures of the ear portions R and L of the sheet glass SG and the temperature of the central region CA are independent. Temperature can be controlled.

In the second temperature control step ST12, the temperature of the central portion C of the sheet glass SG is lower than the glass softening point, that is, the temperature of the central portion C is close to the glass annealing point after the glass softening point is lowered. This is done up to a certain temperature located in the temperature region near the glass strain point. The temperature range near the glass annealing point is the temperature obtained by adding 100 ° C. to the glass annealing point (glass annealing point + 100 ° C.), the glass strain point and the glass annealing point, and dividing by 2. The region between ((glass strain point + glass annealing point) / 2).
In the second temperature control step ST12, the temperature profile is controlled to be the second temperature profile TP20.

The second temperature profile TP20 is a temperature profile in which the temperature in the width direction of the sheet glass SG decreases from the central portion C toward the ear portions R and L, and has a shape that draws a convex curve upward. That is, in 2nd temperature control process ST12, the temperature of the center part C of the sheet glass SG is the highest in the width direction, and the temperature of the ear | edge parts R and L of the sheet glass SG is the lowest. In the second temperature profile TP20, the temperature continuously decreases from the center C toward the ears R and L in the width direction.
The second temperature profile TP20 includes a plurality of temperature profiles (for example, in the present embodiment, the 2a temperature profile TP21 and the 2b temperature profile TP22). The 2a temperature profile TP21 and the 2b temperature profile TP22 are sequentially located from the upstream side in the flow-down direction of the sheet glass SG toward the downstream side.

As the second temperature profile TP20 moves toward the downstream side in the flow direction of the sheet glass SG (that is, after the temperature of the central region CA of the sheet glass SG falls below the glass softening point, the temperature of the sheet glass SG becomes the glass strain point). In the width direction of the sheet glass SG, the absolute value of the temperature difference between the temperatures of the ear portions R and L and the temperature of the central portion C (herein referred to as the temperature difference absolute value) decreases in the width direction of the sheet glass SG. . Therefore, the absolute value of the temperature difference of the 2b temperature profile TP22 is smaller than the absolute value of the temperature difference of the 2a temperature profile TP21.
Here, the fact that the absolute value of the temperature difference becomes smaller toward the downstream side in the flow direction of the sheet glass SG, in other words, the second temperature profile TP20, as it goes to the downstream side in the flow direction of the sheet glass SG, That is, the temperature gradient between the temperatures of the ears R and L of the sheet glass SG and the temperature of the central part C is reduced. The temperature gradient between the temperatures of the ears R and L of the sheet glass SG and the temperature of the center C is a value obtained by subtracting the temperature of the ears R from the temperature of the center C as shown by the two-dot chain line in FIG. Is the value obtained by dividing the width W of the sheet glass SG by 2 (the absolute value of the first gradient here) or the value obtained by subtracting the temperature of the ear L from the temperature of the center C. Is a value obtained by dividing the width W of the sheet glass SG by 2, and is an absolute value (herein referred to as a second gradient absolute value). In the following description, the temperature gradient between the temperatures of the ear portions R and L and the temperature of the central portion C of the sheet glass SG means an average value of the first gradient absolute value and the second gradient absolute value. Shall.
In the second temperature control step ST12, the temperature gradient TG21 of the second-a temperature profile TP21 and the temperature gradient TG22 of the second-b temperature profile TP22 are increased in this order.

In the second temperature control step ST12, the heater is controlled so that the temperature profile becomes the second temperature profile TP20.
Specifically, the 2a temperature profile TP21 is formed by controlling the heater 360a, and the 2b temperature profile TP22 is formed by controlling the heater 360b.
In the present embodiment, five approximate temperature curves of the ears R and L, the right part CR, the left part CL, and the center part C are set to be the second temperature profile TP20.
Moreover, in 2nd temperature control process ST12, the heater is controlled so that the cooling rate of the center part C becomes the fastest in the width direction of the sheet glass SG. That is, the heater is controlled so that the cooling rate of the temperature at the center C is faster than the cooling rate of the temperatures at the ears R and L in the width direction of the sheet glass SG. Thereby, the 2a temperature profile TP21 and the 2b temperature profile TP22 can be formed.

The third temperature control step ST13 is performed while the temperature of the central portion C of the sheet glass SG is in the temperature region near the glass strain point.
In the third temperature control step ST13, the temperature profile is controlled to be the third temperature profile TP31.

The third temperature profile TP31 is a temperature profile in which the temperature in the width direction of the sheet glass SG is uniform. In other words, the third temperature profile TP31 is a temperature profile in which the temperature gradient between the temperature ear portions R and L and the central portion C disappears (the temperature gradient approaches 0) in the width direction of the sheet glass SG. is there.
Here, “becomes uniform” and “no temperature gradient” means that the value (temperature difference) obtained by subtracting the temperatures of the ears R and L from the temperature of the center C in the width direction of the sheet glass SG is − It is in the range from 20 ° C to 20 ° C.

  In the third temperature control step ST13, the temperature profile is set to the third temperature profile TP31 by controlling the heater. Here, the heater 360c is controlled so that the absolute value of the temperature difference in the cooling process ST5 is minimized.

  In the third temperature control step ST13, similarly to the second temperature control step ST12, the heater 360c is controlled so that the cooling rate of the temperature of the central portion C is the fastest in the width direction of the sheet glass SG. . That is, the heater 360c is controlled so that the cooling rate of the temperature of the central portion C is faster than the cooling rate of the temperature of the ear portions R and L of the sheet glass SG.

The strain point lower temperature control step ST14 is performed when the temperature of the central portion C of the sheet glass SG is lower than the temperature region in the vicinity of the glass strain point and until the temperature obtained by subtracting 200 ° C. from the glass strain point. Done.
In the strain point lower temperature control step ST14, the temperature profile is controlled to be the fourth temperature profile TP40.

The fourth temperature profile TP40 is a temperature profile in which the temperature in the width direction of the sheet glass SG decreases from the ears R and L toward the center C, and has a shape that draws a downwardly convex curve. That is, in the strain point lower temperature control step ST14, in the width direction, the temperatures of the ear portions R and L of the sheet glass SG are the highest, and the temperature of the central portion C of the sheet glass SG is the lowest.
The fourth temperature profile TP40 includes a plurality of temperature profiles (specifically, in the present embodiment, the 4a temperature profile TP41 and the 4b temperature profile TP42). The 4a temperature profile TP41 and the 4b temperature profile TP42 are sequentially positioned from the upstream side to the downstream side in the flow direction of the sheet glass SG.
As the fourth temperature profile TP40 moves toward the downstream side in the flow direction of the sheet glass SG (that is, after the temperature of the sheet glass SG falls below the temperature region near the glass strain point, 200 ° C. is subtracted from the glass strain point. The temperature difference absolute value increases as the temperature range increases. Therefore, in the strain point lower temperature control step ST14, the temperature difference absolute value in the 4a temperature profile TP41 is smaller than the temperature difference absolute value in the 4b temperature profile TP42.

Here, the fact that the absolute value of the temperature difference increases toward the downstream side in the flow direction of the sheet glass SG, in other words, the fourth temperature profile TP40, as it goes to the downstream side in the flow direction of the sheet glass SG, That is, the temperature gradient between the temperature of the ear portions R and L of the sheet glass SG and the temperature of the central portion C is increased.
Therefore, in the strain point lower temperature control step ST14, the magnitude of the temperature gradient becomes the temperature gradient TG42 of the 4b temperature profile TP42 and the temperature gradient TG41 of the 4a temperature profile TP41 in descending order.

In the strain point lower temperature control step ST14, the temperature profile becomes the fourth temperature profile TP40 by controlling the heater.
Specifically, the heater 360d is controlled so as to be the 4a temperature profile TP41, and the heater 360e is controlled so as to be the 4b temperature profile TP42.
In the present embodiment, the temperature approximate curves of the five temperatures of the ears R and L, the right part CR, the left part CL, and the center part C are set to be the fourth temperature profile TP40.

  Further, as shown in FIG. 8, in the strain point lower temperature control step ST14, the heater is controlled so that the cooling rate of the temperature of the central portion C is the fastest in the width direction of the sheet glass SG. That is, the heater is controlled so that the cooling rate of the temperature of the central portion C is faster than the cooling rate of the temperature of the ear portions R and L of the sheet glass SG.

  In the second temperature control step ST12, the third temperature control step ST13, and the strain point lower temperature control step ST14, the outputs of the heaters 360a to 360e are controlled based on the ambient temperature detected by the thermocouple unit 380. Thus, the temperature distribution of the sheet glass SG is set to a temperature profile in each process.

Further, the sheet glass SG subjected to the strain point lower temperature control step ST14 is cooled in the fifth slow cooling chamber S3E until reaching the cutting device 400. The fifth slow cooling chamber S3E is surrounded by the furnace wall 301 and the fifth partition 355e. The temperature region of the sheet glass SG in the fifth annealing chamber S3E is less than the temperature of the central portion C of the sheet glass SG (glass strain point -200 ° C.), and the temperature of the sheet glass SG is the sheet glass. Since it is cooled to a temperature that does not affect the sheet thickness deviation and warpage of SG, it can be rapidly cooled to room temperature within a range in which the sheet glass is not broken by the primary strain due to rapid cooling. For this reason, the temperature difference between the fourth slow cooling chamber S3D and the fifth slow cooling chamber S3E is large.
Thus, the sheet glass SG formed by the molten glass MG flowing down the lowermost end portion 314 of the molded body 310 has a highly accurate temperature distribution in the lower molding space S2B and the first to fourth annealing furnace chambers S3A to S3D. After the control is performed, the fifth slow cooling furnace chamber S3E is rapidly cooled to room temperature. From such a point, the lower forming space S2B and the first to fourth slow cooling furnace chambers S3A to S3D that require the control of the temperature distribution of the sheet glass SG are referred to as the upper space and do not require the control of the temperature distribution of the sheet glass SG. The 5 slow cooling furnace chamber S3E is also referred to as a lower space.

In the slow cooling process of the present embodiment, the cooling rate is controlled along the flowing direction of the sheet glass SG as described below, in addition to the temperature control process described above. By controlling the cooling rate, the sheet glass SG can provide a glass substrate that satisfies the quality requirements of the glass substrate such as warpage and distortion.
For example, in the cooling step ST5, as shown in FIG. 9, the first cooling rate that cools the central portion C at the first average cooling rate until the temperature of the central portion C of the sheet glass SG reaches the annealing point. The control step, the second cooling rate control step of cooling the central portion C at the second average cooling rate until the temperature of the central portion C reaches the strain point −50 ° C. from the annealing point, and the temperature of the central portion Includes a third cooling rate control step of cooling the central portion C at the third average cooling rate until the strain point reaches −200 ° C. from the strain point of −50 ° C.
The first average cooling rate is 5.0 ° C./second or more and 50.0 ° C./second or less in order to maintain productivity. The first average cooling rate is faster than the second average cooling rate and the third average cooling rate in order to accurately control the temperature in the width direction of the sheet glass in the second average cooling step and the third average cooling step. . The third average cooling rate is preferably faster than the second average cooling rate. The sheet glass thus cooled has, for example, a thermal shrinkage of 100 ppm or less and a strain retardation value of 1.0 nm or less.

At this time, it is preferable that the second average cooling rate is 0.5 ° C./second to 5.5 ° C./second, and the third average cooling rate is 1.5 ° C./second to 7.0 ° C./second. In the third cooling rate control step, it is preferable to control the temperature in the width direction of the sheet glass SG so as to decrease from the end portion in the width direction of the sheet glass toward the central portion C.
Further, when it is desired to further reduce the thermal shrinkage, the following cooling rate control is performed.
The cooling step includes a fourth cooling rate control step for cooling the central portion C at the fourth average cooling rate until the temperature of the central portion C in the width direction of the sheet glass SG reaches the annealing point, and the temperature of the central portion C. Until the temperature reaches the strain point from the annealing point, the fifth cooling rate control step of cooling the central portion C at the fifth average cooling rate, and the temperature of the central portion C changes from the strain point (strain point -100 ° C). And the sixth cooling step of cooling the central portion C at the sixth average cooling rate.
At this time, the fourth average cooling rate is controlled to be faster than the fifth average cooling rate and the sixth average cooling rate, and the sixth average cooling rate is controlled to be slower than the fifth average cooling rate.
At this time, the fourth average cooling rate is 5.0 to 50.0 ° C./second, the fifth average cooling rate is 0.8 to 5.0 ° C./second, and the sixth average cooling rate is 0.5 to The temperature is preferably 4.0 ° C./second. Furthermore, the ratio of the second average cooling rate and the third average cooling rate (third average cooling rate / second average cooling rate) is 0.2 or more and less than 1, maintaining productivity. However, it is preferable from the viewpoint of reducing thermal shrinkage.

By controlling the cooling rate of the sheet glass SG as described above, preferably further controlling the temperature distribution, the thickness deviation, warpage, distortion, and heat shrinkage of the glass substrate made of the sheet glass SG and the sheet glass SG can be reduced. As will be described later, this can be reduced.
In order to realize such control of the cooling rate of the sheet glass SG and preferably further control of the temperature distribution, around the sheet glass SG of the lower forming furnace chamber S2B and the first slow cooling furnace chamber S3A to the fourth slow cooling furnace chamber S3D. It is necessary that the ambient temperature of the is controlled. Since the atmosphere temperature of the lower forming furnace chamber S2B and the first annealing furnace chamber S3A to the fourth annealing furnace chamber S3D decreases toward the downstream side in the flow direction of the sheet glass SG, the atmosphere partition member 320 or the partition walls 355a to 355e are opened from the upstream side. It is necessary to prevent heat from being transferred to the downstream space. For this reason, the atmosphere partition member 320 and the partition walls 355a to 355e are provided with heat insulating plates having heat insulating properties. At this time, it is preferable that the heat resistance of the heat insulating plate is 0.07 m ² · K / W or more. Thereby, the heat transfer which arises between each chamber divided | segmented in lower molding furnace chamber S2B and slow cooling furnace chamber S3 can be suppressed, and the width direction of sheet glass SG other than control of the cooling rate of sheet glass SG The temperature distribution can be controlled with high accuracy. Thereby, the plate | board thickness deviation, curvature, and distortion of a glass substrate can be reduced. Furthermore, thermal shrinkage of the glass substrate can be reduced. As the heat insulating plate used for the atmosphere partition member 320 and the partition walls 355a to 355e, an alumina fiber board in which alumina fibers are hardened is preferably used.
The heat resistance of the atmosphere partition member 320 is preferably at least 0.2m ² · K / W, more preferably at least 0.4m ² · K / W, more 0.6m ² · K / W is more preferred. The thermal resistance of the partition walls 355a~355e is a 0.07m ² · K / W or more, preferably at least ^{0.15m 2 · K / W, 0.5m} 2 · K / W or more is more preferable. In addition, although the upper limit of the heat resistance of a heat insulating board is not specifically limited, From a viewpoint of suppressing that the thickness of a heat insulating board becomes thick in order to achieve high heat resistance, heat resistance is 2 m < ² > * K / W. The following is preferable.

In particular, a glass substrate on which LTPS (Low Temperature Poly Silicon) / TFT (Thin Film Transistor) or an oxide semiconductor is formed is required to have low thermal shrinkage. For this reason, in order to manufacture a glass substrate having a small heat shrinkage rate, for example, a glass substrate having a heat shrinkage rate of 75 ppm or less, in the temperature control step ST10, for example, from a glass annealing point + 100 ° C. to a glass strain point −200 ° C. It is preferable to cool relatively slowly in this region, and to cool rapidly after the temperature control step ST10 on the downstream side of this region. Accordingly, the fifth partition 355e that defines the space between the upper space that needs to control the temperature distribution of the sheet glass SG and the lower space that does not need to control the temperature distribution of the sheet glass SG and is desired to be rapidly cooled is another partition. The temperature difference is large compared to. For this reason, in the 5th partition 355e, suppression of heat transfer is more important to other partitions. From this point, the thermal resistance of the fifth partition wall 355e is preferably 0.5 m ² · K / W or more, and more preferably 1.5 m ² · K / W or more. At this time, the upper limit of the thermal resistance is preferably 3 m ² · K / W. Thereby, the heat transfer from the upper space to the lower space can be further suppressed. For this reason, the temperature distribution of the sheet glass SG can be accurately controlled. Thereby, it is possible to stably produce a glass substrate in which warpage, distortion, and thermal shrinkage of the glass substrate are further reduced while suppressing the enlarging of the slow cooling furnace. Unlike the first to fourth partition walls 355a to 355d, a material having a low thermal conductivity can be used for the fifth partition wall 355e. The fifth partition wall 355e may be made of the same material as the atmosphere partition member 320 or the partition walls 355a to 355d, but a heat insulating plate having a larger plate thickness and higher thermal resistance than the partition walls 355a to 355d may be used. .
Therefore, in this embodiment, a glass substrate having a heat shrinkage rate of 75 ppm or less can be stably manufactured. Here, the heat shrinkage rate is a value obtained by the following equation using the amount of shrinkage of the glass substrate after heat treatment at a heating / cooling rate of 10 ° C./min and 550 ° C. for 2 hours. is there.
Thermal shrinkage (ppm)
= {Shrinkage of glass substrate after heat treatment / length of glass substrate before heat treatment} × 10 ⁶

The warp value of the glass substrate is 0.15 mm or less. The maximum birefringence when the magnitude of the birefringence of the glass substrate is measured is 1.0 nm or less, more preferably 0.6 nm or less.
In the central area CA of the glass substrate, when the thickness deviation is measured at intervals of 5 mm in the width direction, the thickness deviation of the glass substrate is 10 μm to 15 μm.

(Feature)
In the present embodiment, the first to third cooling rate control steps are included. At this time, the heat insulating plate used for the atmosphere partition member 320 and the partition walls 355a to 355e has a first average cooling rate of 5.0 ° C./second or more. And 50.0 ° C./second or less, the first average cooling rate is faster than the second average cooling rate and the third average cooling rate, and by this slow cooling, the sheet glass SG has a heat shrinkage of 100 ppm or less. And has a heat insulation property that can be controlled so that the retardation value of the strain has a value of 1.0 nm or less. For this reason, a plate thickness deviation, a curvature, and distortion can be reduced, and the quality requirement of a glass substrate can be satisfied.
Further, in the present embodiment, the fourth to sixth cooling rate control steps are included. At this time, the fourth average cooling rate of the heat insulating plate used for the atmosphere partition member 320 and the partition walls 355a to 355e is the fifth average cooling rate. The sixth average cooling rate is higher than the speed and the sixth average cooling rate, and the sixth average cooling rate has an adiabatic property that can be controlled to be slower than the fifth average cooling rate. For this reason, in addition to plate thickness deviation, warpage, and distortion, thermal shrinkage can be reduced to satisfy the quality requirements of the glass substrate.
It is preferable that the heat resistance of such a heat insulating plate is 0.07 m ² · K / W or more. In the present embodiment, the heat resistance of the first to fifth partition walls 355a to 355e is 0.07 m ² · K / W or more, and a heat insulating plate is used, but between the forming furnace chamber S2 and the slow cooling furnace chamber S3. At least one thermal resistance of the first partition wall 355a and the second to fifth partition walls 355b to 355e provided in the slow cooling furnace chamber S3 may be 0.07 m ² · K / W or more. Thereby, in any partition, the thermal resistance is not limited, and the temperature control of the sheet glass SG can be efficiently performed as compared with the case where the thermal resistance is less than 0.07 m ² · K / W.

In the present embodiment, the glass strain point upper temperature control step ST10a is performed in the cooling step ST5. The glass strain point upper temperature control step ST10a includes a first temperature control step ST11 and a second temperature control step ST12.
Here, generally, the sheet glass that has left the formed body tends to shrink due to its surface tension. Moreover, there is a concern that the flatness of the sheet glass is deteriorated.
Therefore, in the present embodiment, in the temperature region where the temperature of the central portion C of the sheet glass SG is equal to or higher than the glass softening point, the sheet glass is cooled by the cooling roller 330 disposed immediately below the molded body 310 in the first temperature control step ST11. While pulling SG downward, the ears R and L of the sheet glass SG are rapidly cooled. Thus, the ear portion R of the utmost fast sheet glass SG, can increase the viscosity of the L (specifically, it is possible to the viscosity to more than 10 ^{9.0 dPa} · s), the sheet glass SG by surface tension Can be prevented from shrinking. Here, when the sheet glass SG is shrunk in the width direction, the thickness of the shrunk end portions on both sides is increased, and the width of the part having a uniform thickness at the center of the sheet glass is narrowed. Therefore, by making the temperature of the ear portions R and L of the sheet glass SG lower than the temperature of the central area CA in the first temperature control step ST11, the effective width of the sheet glass SG and eventually the glass substrate is contracted. Can be suppressed.

  Moreover, in 1st temperature control process ST11, the viscosity of center area | region CA becomes uniform by making temperature of center area | region CA of sheet glass SG uniform. Thereby, the plate | board thickness of the sheet glass SG can be equalize | homogenized.

In general, it is said that distortion (residual stress) is likely to occur if there is a temperature difference in the width direction of the sheet glass in the temperature region near the glass strain point.
Therefore, in the present embodiment, by performing the third temperature control step ST13, there is no temperature gradient between the edge portions R and L in the width direction of the sheet glass SG and the central portion C in the temperature region near the glass strain point. As such, the ambient temperature is controlled. That is, in the third temperature control step ST13, the absolute value of the temperature difference in the cooling step ST5 is made the smallest. If the sheet glass SG has a temperature difference at the glass strain point, the sheet glass SG is distorted after being cooled to room temperature. That is, in the third temperature control step ST13, by reducing the temperature gradient between the edge portions R and L and the central portion C in the width direction of the sheet glass SG toward the temperature region near the glass strain point, the sheet glass is reduced. SG distortion can be reduced. The temperature difference between the ears R and L and the central part C is such that the value obtained by subtracting the temperature of the ears R and L from the temperature of the central part C of the sheet glass SG is in the range from −20 ° C. to 20 ° C. It is preferable to enter.
Thereby, distortion (residual stress) of sheet glass SG and by extension, a glass substrate can be reduced.

In the present embodiment, the temperature in the width direction of the sheet glass SG becomes uniform from the second temperature profile TP20 in which the temperature in the width direction of the sheet glass SG decreases from the central portion C toward the ear portions R and L. A three-temperature profile TP31 is set. That is, in this embodiment, in the temperature region where the temperature of the central portion C of the sheet glass SG is lower than the glass softening point, in the second temperature control step ST12 and the third temperature control step ST13, the center in the width direction of the sheet glass SG. The cooling rate of the temperature of the part C is made faster than the cooling rate of the temperature of the ear parts R and L.
Thereby, in 2nd temperature control process ST12 and 3rd temperature control process ST13, since the volumetric shrinkage of sheet glass SG becomes large as it goes to the center part C from the ear | edge parts R and L of sheet glass SG, sheet glass SG Tensile stress is applied to the central portion C. In particular, tensile stress acts on the center portion C of the sheet glass SG in the flow-down direction and the width direction of the sheet glass SG. In addition, it is preferable that the tensile stress which works in the flow direction of the sheet glass SG is larger than the tensile stress which works in the width direction of the sheet glass SG. Since the sheet glass SG can be cooled while maintaining the flatness of the sheet glass SG due to the tensile stress, the warpage of the sheet glass SG and, consequently, the glass substrate can be further reduced.

In the present embodiment, a tensile stress is always applied to the central portion C of the sheet glass SG also in the strain point lower temperature control step ST14. Also in the first temperature control step ST11, the cooling roller 330 promptly increases the viscosity of the ear portions R and L to a predetermined value or more, thereby applying a tensile stress to the central portion C of the sheet glass SG.
Therefore, in the cooling process ST5 of the present embodiment, not only the tensile stress in the width direction and the downflow direction is applied to the sheet glass SG by the cooling roller 330 or the pulling rollers 350a to 350e, but also the sheet glass SG ( In particular, a tensile stress in the width direction and the flow-down direction is applied to the central portion C). Therefore, the curvature of sheet glass SG and by extension, a glass substrate can be reduced.

  In this embodiment, in the temperature region lower than the temperature region in the vicinity of the glass strain point, the temperature below the strain point is set such that the temperature in the width direction of the sheet glass SG decreases from the ear portions R and L toward the center portion C. Step ST14 is performed. Thereby, the volumetric shrinkage of the sheet glass SG increases as it goes from the ears R, L of the sheet glass SG toward the center C. Therefore, tensile stress acts on the center part C of the sheet glass SG in the flow-down direction and the width direction of the sheet glass SG. Therefore, the sheet glass SG can be cooled while maintaining the flatness of the sheet glass SG due to the tensile stress, so that the warpage of the sheet glass SG can be reduced.

(Glass composition)
The following glass composition is illustrated as a glass composition of the glass substrate manufactured by this embodiment.
Glass substrate is less, _SiO 2 50-70 _wt% is the glass substrate for a flat panel display, _Al 2 O 3 5~25 _{wt%, B} 2 O 3 _0~15 wt%, MgO 0 mass%, CaO 0-20 wt%, SrO 0 to 20 wt%, BaO 0 _wt%, a glass substrate containing ZrO 2 0% by weight.
Alkali metal oxides such as Li ₂ O, Na ₂ O and K ₂ O may elute from the glass and deteriorate the TFT characteristics, so that a glass substrate for a display (for example, a liquid crystal display) on which a TFT is mounted. When applied as, it is preferable that the alkali metal oxide is substantially free of alkali glass. However, a glass containing a trace amount of alkali in which the above components are intentionally contained in the glass can suppress the degradation of the TFT characteristics, and can also prevent the melting tank from being damaged. Therefore, the alkaline trace containing glass, it is preferred that Li ₂ O, Na ₂ O and K ₂ O is contained 0.05 to 2.0 wt%, more to contain 0.2 to 0.5 wt% preferable.

The glass substrate of this embodiment is used suitably for the glass substrate for flat panel displays. The glass substrate can also be used for a glass substrate which is formed with LTPS / TFT or an oxide semiconductor and is subjected to high temperature treatment, which is particularly required to have a low thermal shrinkage rate. Furthermore, it can also be used for a cover glass for a display device, a glass substrate for a magnetic disk, a glass substrate for a solar cell, and the like.

[Experimental example]
Example 1
In order to examine the effects of the atmosphere partition member 320 and the partition walls 355a to 355d of the present embodiment, a sheet glass SG was produced using a molding apparatus 300 shown in FIGS. Specifically, the glass raw material was melted in the melting tank 201 to obtain a molten glass MG. And molten glass MG was conveyed to the clarification tank 202 via piping made from a platinum alloy, and the molten glass MG was clarified in the clarification tank 202 made from a platinum alloy. Next, after the clarified molten glass MG was stirred in the stirring tank 203, the molten glass MG was supplied to the molded body 310, and the sheet glass SG was molded by the overflow down draw method. The sheet glass SG was cooled while performing temperature control, and then the sheet glass SG was cut to produce a glass substrate for a flat panel display having a thickness of 0.7 mm and a size of 2200 mm × 2500 mm. At this time, the thermal resistance of the atmosphere partition member 320, the partition walls 355a to 355d, and the fifth partition wall 355e was set to 0.15 m ² · K / W.
The composition of the glass used is as follows.
SiO ₂ 60 mass%, Al ₂ O ₃ 19.5 mass%, B ₂ O ₃ 10 mass%, CaO 5.3 mass%, SrO 5 mass%, SnO ₂ 0.2 mass%.
The strain point of the glass substrate produced in Example 1 was 713 ° C.

(Example 2)
A sheet glass SG was produced in the same manner as in Example 1 to produce a glass substrate. The difference from Example 1 is only the glass composition. The glass composition in Example 2 is as follows.
SiO ₂ 61.5 wt%, Al ₂ O ₃ 20 wt%, B ₂ O ₃ 8.4 wt%, CaO 10% by weight, SnO ₂ 0.1% by mass.
The strain point of the glass substrate produced in Example 2 was 715 ° C.

Example 3
A sheet glass SG was produced in the same manner as in Example 1 to produce a glass substrate. The difference from Example 1 is only the glass composition. The glass composition in Example 3 is as follows.
SiO ₂ 61.2 wt%, Al ₂ O ₃ 19.5 wt%, B ₂ O ₃ 9.0 wt%, K ₂ O 0.19 wt%, CaO 10 wt%, Fe ₂ O ₃ 0.01 wt %, SnO ₂ 0.1 mass%.
The strain point of the glass substrate produced in Example 3 was 699 ° C.

(Examples 4 to 6)
A sheet glass SG was produced in the same manner as in Example 3 to produce a glass substrate. The difference from Example 3 is that the thermal resistance of the partition walls 355a to 355e is 0.3 m ² · K / W (Example 4), 0.6 m ² · K / W (Example 5), 1.2 m ² · K. / W (Example 6) only.

(Comparative Example 1)
A sheet glass SG was produced using a glass having the same glass composition as in Example 1 to produce a glass substrate. In the manufacturing method of the glass substrate in the comparative example, the thermal partitioning member 320, the partition walls 355a to 355d, and the thermal resistance of the fifth partition wall 355e are different from those in the first embodiment, and the others are the same as in the first embodiment. In the comparative example, the thermal resistance of the atmosphere partition member 320, the partition walls 355a to 355d, and the fifth partition wall 355e was set to 0.05 m ² · K / W.
(Comparative Example 2)
A sheet glass SG was produced using a glass having the same glass composition as in Example 3 to produce a glass substrate. In the manufacturing method of the glass substrate in the comparative example, the thermal resistance of the atmosphere partition member 320 and the partition walls 355a to 355e is different from that in the third embodiment, and the others are the same as in the third embodiment. In the comparative example, the thermal resistance of the atmosphere partition member 320 and the partition walls 355a to 355e was set to 0.05 m ² · K / W.

(Cooling rate)
In Examples 1 to 6, the first average cooling rate is 5.0 ° C./second or more and 50.0 ° C./second or less, and the first average cooling rate is the second average cooling rate and the third average cooling rate. The sheet glass that was faster than the average cooling rate and cooled by this cooling step had a heat shrinkage rate of 100 ppm or less, and a strain retardation value of 1.0 nm or less.
In Comparative Examples 1 and 2, the first average cooling rate is 5.0 ° C./second or more and 50.0 ° C./second or less, and the first average cooling rate is the second average cooling rate or the second average cooling rate. 3 is faster than the average cooling rate of 3, and the sheet glass cooled by this cooling step has a heat shrinkage rate of 100 ppm or less and does not satisfy the condition that the retardation value of strain is 1.0 nm or less. It was.

(Strain measurement)
As the performance evaluation of the glass substrates manufactured in Examples 1 to 6 and Comparative Examples 1 and 2, the retardation value resulting from the birefringence of the glass substrate serving as a strain index was measured. For the measurement of the retardation value, a birefringence measuring device ABR-10A manufactured by UNIOPT was used. As for the retardation value, the measurement values of Examples 1 to 4 are all 0.6 nm or less, the measurement value of Example 5 is 0.5 nm or less, the measurement value of Example 6 is 0.4 nm or less, It was within the range of allowable values of strain. On the other hand, in Comparative Examples 1 and 2, the measured value exceeded 1.0 nm, which was outside the range of allowable strain values.

(Warpage measurement)
Furthermore, the curvature of the glass substrate was measured as performance evaluation of the glass substrate manufactured in Examples 1-6 and Comparative Examples 1-2.
The measurement of the curvature of the glass substrate was performed by the following method.
Eight small plates of the first to second generation sizes were cut out from the effective area of the glass substrate, and the small plates were placed on a glass surface plate. And a clearance gauge is used for the gap between each small plate and the glass surface plate at a plurality of locations (in this embodiment, four corners, two central portions on the long side, and two central portions on the short side). The warpage was measured by measuring.
The measured values of warpage in Examples 1 to 6 were all 0.15 mm or less, and were within the range of allowable values of warpage, but the measured values of warpage in Comparative Examples 1 and 2 exceeded 0.25 mm. Therefore, it was out of the range of allowable values of warpage.

(Heat shrinkage measurement)
As a performance evaluation of the glass substrate manufactured in Examples 1 to 6, the thermal shrinkage rate of the glass substrate was measured. The heat shrinkage rate was determined by the following equation using the amount of shrinkage of the glass substrate after heat treatment at a heating / cooling rate of 10 ° C./min and 550 ° C. for 2 hours.
Thermal shrinkage (ppm)
= {Shrinkage of glass substrate after heat treatment / length of glass substrate before heat treatment} × 10 ⁶
The heat shrinkage rates of Examples 1 to 6 were all 50 ppm or less.
From this, the effect of this embodiment is clear.

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

DESCRIPTION OF SYMBOLS 100 Glass substrate manufacturing apparatus 310 Molded body 313 Lower section 320 of molded body Atmosphere partition members 355a to 355e Partition C Central portion R, L of sheet glass Ear portion (width direction end) of sheet glass
ST10a Glass strain point upper temperature control step ST11 First temperature control step ST12 Second temperature control step ST13 Third temperature control step

Claims (7)

A method of manufacturing a glass substrate,
A molding step of molding a sheet glass from molten glass by a downdraw method using a molded body provided in a molding furnace chamber;
When the sheet glass flows through the slow cooling furnace chamber adjacent to the forming furnace chamber, while controlling the cooling rate in the flow direction of the sheet glass and the temperature distribution in the width direction of the sheet glass, A cooling step of gradually cooling the sheet glass including a center part closer to the center in the width direction of the sheet glass than the end part, and
The cooling step includes a first cooling rate control step of cooling the central portion at a first average cooling rate until the temperature of the central portion of the sheet glass reaches a slow cooling point,
A second cooling rate control step of cooling the central portion at a second average cooling rate until the temperature of the central portion reaches a strain point of −50 ° C. from the annealing point;
A third cooling rate control step of cooling the central portion at a third average cooling rate until the temperature of the central portion reaches the strain point of -200 ° C from the strain point of -50 ° C,
The slow cooling furnace chamber is divided into at least two spaces, a partition wall between the forming furnace chamber and the slow cooling furnace chamber, and a partition wall provided in the space provided in the slow cooling furnace chamber, The upper space where the cooling rate control step, the second cooling rate control step, and the third cooling rate control step are performed, and the temperature of the central portion is less than the strain point of −200 ° C. A heat insulating plate is used for a partition wall that divides the region from a lower space that cools more rapidly than cooling in the region from the annealing point + 100 ° C. to the strain point −200 ° C. ,
By making the thermal resistance of the heat insulating plate 0.07 m ² · K / W or more,
(1) The first average cooling rate is set to 5.0 ° C./second or more and 50.0 ° C./second or less,
(2) realizing that the first average cooling rate is faster than the second average cooling rate and the third average cooling rate;
The glass substrate manufactured by the cooling step has a heat shrinkage rate of 75 ppm or less and a strain retardation value of 1.0 nm or less.   The method for producing a glass substrate according to claim 1, wherein the third average cooling rate is controlled to be faster than the second average cooling rate.   In the temperature region where the temperature of the center portion of the sheet glass is equal to or higher than the glass softening point from the lowermost end portion of the molded body, the end portion in the width direction of the sheet glass is more than the temperature of the center region sandwiched between the end portions. The manufacturing method of the glass substrate of Claim 1 or 2 with which the 1st temperature control process which controls temperature so that it is low and the temperature of the said center area | region becomes uniform is performed.   The temperature of the central portion of the sheet glass is lower than the glass softening point, and the temperature control is performed so that the temperature in the width direction of the sheet glass decreases from the central portion toward the end portion in the temperature region near the glass strain point. The manufacturing method of the glass substrate of any one of Claims 1-3 in which the 2nd temperature control process to perform is performed.   A third temperature at which the temperature of the central portion of the sheet glass is controlled so that the temperature gradient between the end portion in the width direction of the sheet glass and the central portion approaches 0 in the temperature region near the glass strain point. The manufacturing method of the glass substrate of any one of Claims 1-4 with which a control process is performed.   In the third cooling rate control step, the sheet glass has a temperature in the width direction of the sheet glass in a temperature range from a glass strain point of −50 ° C. to a glass strain point of −200 ° C. The manufacturing method of the glass substrate of any one of Claims 1-5 controlled so that it becomes low toward the center part from the edge part of the width direction of glass. An apparatus for manufacturing a glass substrate,
A molding apparatus comprising a molding furnace chamber, and molding a sheet glass from molten glass by a downdraw method using a molded body provided in the molding furnace chamber;
The sheet glass includes a slow cooling furnace chamber adjacent to the forming furnace chamber, and controls the cooling rate in the flow direction of the sheet glass and the temperature distribution in the width direction of the sheet glass when the sheet glass flows in the slow cooling furnace chamber. And a slow cooling device that slowly cools the sheet glass including the end portions on both sides and a center portion closer to the center in the width direction of the sheet glass than the end portions,
In the slow cooling apparatus,
A first cooling rate control step of cooling the central portion at a first average cooling rate until the temperature of the central portion of the sheet glass reaches a slow cooling point ;
A second cooling rate control step of cooling the central portion at a second average cooling rate until the temperature of the central portion reaches a strain point of −50 ° C. from the annealing point ;
Performing a third cooling rate control step of cooling the central portion at a third average cooling rate until the temperature of the central portion reaches the strain point of -200 ° C from the strain point of -50 ° C.
The slow cooling furnace chamber is divided into at least two spaces, a partition wall between the forming furnace chamber and the slow cooling furnace chamber, and a partition wall provided in the space provided in the slow cooling furnace chamber, the cooling rate controlling step, the second cooling rate controlling step, and the upper space to perform the third cooling rate controlling step, the sheet glass temperature of the central portion is less than the temperature of the strain point -200 ° C. A heat insulating plate is used for a partition wall that divides the region from a lower space that cools more rapidly than cooling in the region from the annealing point + 100 ° C. to the strain point −200 ° C. ,
By making the thermal resistance of the heat insulating plate 0.07 m ² · K / W or more,
(1) The first average cooling rate is 5.0 ° C./second or more and 50.0 ° C./second or less,
(2) realizing that the first average cooling rate is faster than the second average cooling rate and the third average cooling rate;
The glass substrate manufactured by the cooling step has a heat shrinkage rate of 75 ppm or less, and has a strain retardation value of 1.0 nm or less.

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