TWI696590B - Manufacturing method of glass substrate for display - Google Patents

Abstract

The present invention provides a method for manufacturing a glass substrate for a display that can reduce the thermal shrinkage of the glass substrate compared to the prior art.

When manufacturing the glass substrate for a display, it cools until the temperature of the center part of the width direction of the flat glass formed by the forming process reaches 300 degreeC. At this time, the cooling rate of the central region, that is, the average cooling rate in the temperature region where the temperature of the central portion does not reach 450°C and above 300°C, is lower than the central region in the temperature region other than the temperature region in the cooling step For the average cooling rate, the central region is a region located on the inner side in the width direction of the sheet glass than both ends in the width direction of the sheet glass and including the central part.

Description

Manufacturing method of glass substrate for display

The invention relates to a method for manufacturing a glass substrate for display.

In the process of manufacturing the display, the glass substrate for display undergoes heat shrinkage due to heat treatment. At this time, if the thermal shrinkage rate of the glass substrate is large, it is easy to cause a shift in the arrangement offset of the elements formed on the surface of the glass substrate. Therefore, from the viewpoint of reducing the pitch deviation, the glass substrate for display is required to have a small heat shrinkage rate during heat treatment.

As a method of reducing the thermal shrinkage rate of the glass substrate, (1) the strain point of the glass is increased by adjusting the glass composition; (2) the cooling rate of the flat glass after the forming step is reduced. For example, as a technique for reducing the thermal shrinkage rate of a glass substrate, there is known a technique for improving the glass composition so that the strain point reaches 680° C. or higher (Patent Document 1).

In addition, the cooling step is divided into a first cooling step, a second cooling step, and a third cooling step. The first cooling step cools the sheet glass until the temperature of the central area of the sheet glass after forming reaches the slow cooling point. The above second cooling step cools the sheet glass until the temperature in the central region reaches the strain point -50°C from the slow cooling point, and the above third cooling step cools the sheet glass until the temperature in the central region is from the strain point -50°C It reaches the strain point -200℃. At this time, a technique is known that makes the average cooling rate in the first cooling step faster than the average cooling rate in the third cooling step, and makes the average cooling rate in the third cooling step lower than the second cooling step The average cooling rate is faster (Patent Document 2).

[Prior Technical Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Special Publication No. 2003-503301

[Patent Document 2] Japanese Patent No. 5153965

However, according to Patent Document 1, if the composition is adjusted to increase the strain point, problems of devitrification and refractory melting are likely to occur, so there is a limit in raising the strain point. In addition, there is a problem that when a glass substrate is produced by the overflow down-draw method, if the cooling rate of the flat glass is reduced in the cooling step performed after the forming step, the slow cooling path is extended, and the cost of the slow cooling device increases.

Further, according to Patent Document 2, there is a problem that even if the average cooling rate in the first cooling step is faster than the average cooling rate in the third cooling step, and the average cooling rate in the third cooling step is lower than the second cooling The average cooling rate in the step is faster, and there is a limit to reducing the heat shrinkage rate.

The displays mounted on mobile devices such as mobile phones are increasingly demanding higher definition and lower power consumption. Therefore, in recent years, there is an increasing need to further reduce the heat shrinkage rate of the glass substrate generated during the heat treatment in the manufacturing process of the display.

Therefore, an object of the present invention is to provide a method for manufacturing a glass substrate for a display, which can reduce the thermal shrinkage rate of the glass substrate in the cooling step performed after forming compared with the prior art.

The first aspect of the present invention is a method for manufacturing a glass substrate for a display. The manufacturing method includes: a forming step which forms the molten glass into a flat glass by a down-draw method; and a cooling step which cools the flat glass after forming to flow Until the temperature in the center of the width direction orthogonal to the flow direction of the above-mentioned flat glass reaches 300°C.

In the above cooling step, the cooling rate in the central region, that is, the average cooling rate in the temperature region where the temperature of the central portion does not reach 450°C and above 300°C, is lower than that in the temperature region other than the above temperature region in the cooling step The average cooling rate of the central region, the central region is a region that is located inside the width direction of the sheet glass and includes the center portion at both ends in the width direction of the sheet glass.

It is preferable that the cooling step includes: a first cooling step, after forming the sheet glass, when the temperature of the central portion of the sheet glass in the width direction is above the slow cooling point, the central area is subjected to the first average cooling rate Cooling, the central area is located in the widthwise inner side of the sheet glass than the both ends of the width direction of the sheet glass and includes the central portion; the second cooling step, the temperature in the central portion is not reached When the slow cooling point is above 450°C, the central region is cooled at the second average cooling rate; and the third cooling step, when the temperature at the central portion is not above 450°C and above 300°C, use the 3 The average cooling rate cools the central region, and the third average cooling rate is less than the first average cooling rate and the second average cooling rate.

Preferably, the cooling step further includes a fourth cooling step, which cools the central region at a fourth average cooling rate when the temperature of the central portion does not reach 300°C and is above 100°C. 4 The average cooling rate is greater than the third average cooling rate described above.

In addition, the second aspect of the present invention is a method for manufacturing a glass substrate for a display by performing heat treatment at a specific processing temperature to form a thin film on the surface. The manufacturing method includes: a forming step of forming molten glass into flat glass by a down-draw method; and In the cooling step, when the sheet glass after forming is flowed, cooling is performed until the temperature of the central portion in the width direction orthogonal to the flow direction of the sheet glass reaches a temperature lower than the processing temperature by 250° C. (the processing temperature -250℃).

In the above cooling step, the cooling rate of the central area, that is, the temperature of the central portion does not reach the temperature lower than the treatment temperature by 100°C (that is, the treatment temperature is -100°C) and is 250°C lower than the treatment temperature The average cooling rate in the temperature range above (the processing temperature-250°C) or higher is lower than the average cooling rate in the central region in the temperature region other than the temperature region in the cooling step, the central region is located above the Both ends of the width direction of the sheet glass are closer to the inner side of the sheet glass in the width direction and include the region of the center portion.

Preferably, the cooling step includes: a first cooling step, which is performed on the central area at the first average cooling rate when the temperature of the central portion of the width direction of the flat glass is above the slow cooling point after forming the flat glass Cooling, the central region is located in the widthwise inner side of the sheet glass than the both ends of the width direction of the sheet glass and includes the central part; the second cooling step, the temperature in the central part does not reach the above When the slow cooling point is a temperature 100°C lower than the treatment temperature or above (the treatment temperature -100°C) or more, the central region is cooled at the second average cooling rate; and the third cooling step is located at the center When the temperature of the part does not reach the temperature lower than the treatment temperature by 100°C, that is, it does not reach (the treatment temperature is -100°C) and is higher than the treatment temperature by 250°C or above (the treatment temperature -250°C), The third average cooling rate cools the central region, and the third average cooling rate is less than the first average cooling rate and the second average cooling rate.

It is preferable that the cooling step further includes a fourth cooling step that does not reach the above-mentioned point when the temperature in the center portion does not reach 250°C lower than the processing temperature If the treatment temperature (°C)-250°C is above 450°C lower than the treatment temperature, that is, the treatment temperature (°C)-450°C or above, the central region is cooled at the fourth average cooling rate, and the fourth average The cooling rate is greater than the third average cooling rate.

In both the first aspect and the second aspect, the first average cooling rate is preferably greater than the second average cooling rate.

In both the first aspect and the second aspect, the third average cooling rate is preferably 5.0° C./sec or less.

In both the first aspect and the second aspect, the thermal shrinkage of the glass substrate is preferably 15 ppm or less.

Here, the above-mentioned thermal shrinkage rate is a value obtained by using the shrinkage amount of the glass substrate after heat treatment maintained at 500° C. for 30 minutes, according to the following formula.

Thermal shrinkage (ppm)={shrinkage of glass substrate after heat treatment/length of glass substrate before heat treatment}×10 ⁶

In the first aspect and the second aspect, the strain point of the glass substrate is preferably 680° C. or higher.

According to the manufacturing method of the glass substrate for displays mentioned above, the heat shrinkage rate can be reduced compared with the past.

11‧‧‧ melting device

12‧‧‧Clarification device

20‧‧‧Forming room

23‧‧‧Upstream

24‧‧‧ Downstream pipe

30‧‧‧The first cooling room

40‧‧‧Forming device

41‧‧‧Formed body

41a‧‧‧Lower end

41b‧‧‧Top

41c‧‧‧Side (surface)

42‧‧‧Inflow

43‧‧‧slot

50‧‧‧Partition

51‧‧‧cooling roller

60‧‧‧Temperature adjustment unit

61‧‧‧cooling unit

80‧‧‧Second cooling room

80a‧‧‧Top plate

80b‧‧‧Insulation component

81a~81g‧‧‧ descending roller

82a~82g‧‧‧heater

90‧‧‧cutting device

91‧‧‧Control device

100‧‧‧Glass substrate manufacturing equipment

380‧‧‧thermocouple

381‧‧‧Main power switch

390‧‧‧cooling roller drive motor

391‧‧‧Lower roller drive motor

392‧‧‧cutting device drive motor

A~E‧‧‧time

C‧‧‧Central Department

CA‧‧‧Central area

FG‧‧‧Molten glass

L, R‧‧‧ both ends

P1~P5‧‧‧ point

R1‧‧‧1st temperature zone

R2‧‧‧Second temperature zone

R3‧‧‧The third temperature zone

R4‧‧‧4th temperature zone

S1‧‧‧ melting step

S2‧‧‧Clarification steps

S3‧‧‧Forming steps

S4‧‧‧cooling step

SG‧‧‧Flat glass

T1~T3‧‧‧Temperature history

TP1~TP10‧‧‧Temperature distribution

FIG. 1 is a diagram showing an example of the steps of the method for manufacturing a glass substrate for a display of this embodiment.

FIG. 2 is a schematic diagram of an example of a glass substrate manufacturing apparatus used in the method for manufacturing a glass substrate for a display of this embodiment.

FIG. 3 shows the forming in the manufacturing method of the glass substrate for a display of this embodiment A cross-sectional view of an example of the device.

FIG. 4 is a side view showing an example of a molding apparatus used in the method for manufacturing a glass substrate for a display of this embodiment.

5 is a diagram showing an example of the configuration of a control device used in the method for manufacturing a glass substrate for a display of this embodiment.

6 is a diagram showing an example of the temperature distribution used in the cooling step of the manufacturing method of the glass substrate for a display of the present embodiment.

7 is a diagram showing an example of the temperature history of the flat glass in the flow direction in the method of manufacturing a glass substrate for a display according to this embodiment.

8 is a schematic diagram of an example of a plurality of temperature histories in the cooling step of the flat glass used in the method of manufacturing a glass substrate for a display.

Hereinafter, a method of manufacturing the glass substrate for a display of this embodiment will be described. In the manufacturing method of the glass substrate for displays of this embodiment, the glass substrate is manufactured using the overflow down-draw method. In addition, in this specification, (treatment temperature-X°C) means a temperature that is X°C lower than the treatment temperature (°C) (X is a positive number).

(1) Overview of the manufacturing method of glass substrate

First, referring to FIGS. 1 and 2, a plurality of steps included in a method for manufacturing a glass substrate for a display and a glass substrate manufacturing apparatus 100 used in the plurality of steps will be described. 1 is a diagram showing an example of the steps of the method for manufacturing a glass substrate for a display of this embodiment, and FIG. 2 is a schematic diagram of an example of a glass substrate manufacturing apparatus used in the method for manufacturing a glass substrate for a display of this embodiment.

As shown in FIG. 1, the glass substrate manufacturing method mainly includes a melting step S1, a clarification step S2, a forming step S3, and a cooling step S4.

The melting step S1 is a step of melting the glass raw material. The glass raw material is prepared in such a way as to achieve the desired composition, and then charged into the melting device 11. Glass raw material in melting The device 11 melts and becomes molten glass FG. Adjust the melting temperature according to the type of glass. In the present embodiment, heating is performed so that the maximum temperature of the molten glass FG in the melting step S1 reaches 1500°C to 1650°C. The molten glass FG is sent to the clarifier 12 via the upstream pipe 23.

The clarification step S2 is a step of removing bubbles in the molten glass FG. Thereafter, the molten glass FG after removing bubbles in the clarifier 12 is sent to the forming device 40 via the downstream pipe 24.

The forming step S3 is a step of forming the molten glass FG into sheet glass, that is, sheet glass SG. Specifically, after the molten glass FG is continuously supplied to the molded body 41 (refer to FIG. 3) included in the molding apparatus 40, it overflows from the molded body 41. The overflowed molten glass FG flows down along the surface of the molded body 41. Thereafter, the molten glass FG merges at the lower end of the molded body 41 to be formed into sheet glass SG.

The cooling step S4 is a step of cooling the flat glass SG. The glass sheet is cooled to a temperature close to room temperature through the cooling step S4. Furthermore, the thickness of the glass substrate (plate thickness), the amount of warpage of the glass substrate, and the plane strain of the glass substrate are determined according to the cooling state in the cooling step S4.

In addition, the cutting step may be provided after the cooling step S4. For example, the cutting step is a step of cutting the flat glass SG whose temperature is close to room temperature into a specific size in the cutting device 90.

In addition, in the cutting step, the flat glass SG is cut into a specific size, and thereafter, it becomes a glass substrate through steps such as end surface processing. After being packaged, the glass substrate is shipped to panel manufacturers and the like. Panel manufacturers form devices on the surface of glass substrates to manufacture displays.

Furthermore, it is not necessary to provide a cutting step after the cooling step S4. That is, the flat glass SG cooled in the cooling step S4 may be directly packaged and then shipped to the panel manufacturer or the like. In this case, after the panel manufacturer forms an element on the surface of the flat glass SG, the flat glass SG is cut to a specific size and subjected to end surface processing, thereby manufacturing a display.

Hereinafter, the configuration of the forming apparatus 40 included in the glass substrate manufacturing apparatus 100 will be described with reference to FIGS. 3 to 5. In addition, in the present embodiment, the width direction of the sheet glass SG refers to a direction that intersects the flow direction (flow direction) of the sheet glass SG in the in-plane direction of the surface of the sheet glass SG, that is, the horizontal direction.

(2) Structure of the forming device

First, FIGS. 3 and 4 show the schematic configuration of the molding device 40. FIG. 3 is a cross-sectional view of the forming device 40. 4 is a side view of the forming apparatus 40.

The forming device 40 has a path through which the sheet glass SG passes and a space surrounding the path. The space surrounding the passage is composed of, for example, the molded body chamber 20, the first cooling chamber 30, and the second cooling chamber 80.

In this embodiment, when the sheet glass SG flows downward from the following position, in the temperature region along the flow direction of the sheet glass SG, the temperature of the central portion C (see FIG. 4) of the sheet glass SG does not reach 450°C and The average cooling rate in the temperature range of 300°C or higher is as follows, which is lower than the temperature of the central portion C in the cooling step S4 that does not reach 450°C and is the average cooling rate in a temperature range other than the temperature range of 300°C or higher, above The position is a position where the molten glass FG merges at the lower end 41a of the molded body 41 to form the sheet glass SG. This content will be described later. Furthermore, a temperature region where the average cooling rate is compared with the average cooling rate of the temperature region of the central portion C that does not reach 450°C and is 300°C or higher is, for example, a temperature at which the temperature difference between the upstream side and the downstream side is at least 10°C or higher area.

In addition, the both ends of the width direction of the sheet glass SG refer to the area in the width direction from the both ends of the sheet glass SG to the position that advances 200 mm inward in the width direction of the sheet glass SG. The area on the inner side in the width direction of both end portions is called the central area CA of the sheet glass SG (refer to FIG. 4 ). Both end portions R and L of the sheet glass SG are regions that include parts that are cut off and removed after manufacture, while the central region CA of the sheet glass SG is a region that includes parts that make the plate thickness uniform. The central area CA of the flat glass SG is a self-flat glass whose width in the width direction of the flat glass SG The half of the width of the center of the glass SG in the width direction is within 85%, for example. The central portion C refers to the center position of the sheet glass SG in the width direction. The so-called average cooling rate refers to the average cooling rate of the central area CA including the central portion C, which is the temperature difference in the flow direction at the position of the same width direction in the determined temperature area, divided by the plate glass SG passing through The value obtained by the passage time of the temperature range. In the temperature range below X1°C and above X2°C, as in the temperature range below 450°C and above 300°C, the temperature difference at the center C is regarded as X1-X2(°C), and the center is calculated The average cooling rate of C. The average cooling rate of the portion other than the central portion C of the central area CA is also a value obtained by dividing the temperature difference in the temperature area by the passage time.

The molded body chamber 20 is a space for forming the molten glass FG transferred from the clarification device 12 into flat glass SG.

The first cooling chamber 30 is a space arranged below the molded body chamber 20 and used to adjust the thickness and the amount of warpage of the sheet glass SG. In the first cooling chamber 30, the sheet glass SG in a state where the temperature of the central portion C of the sheet glass SG is higher than the slow cooling point is cooled. The center portion C of the plate glass SG is the center in the width direction of the plate glass SG.

The second cooling chamber 80 is a space disposed below the molded body chamber 20 and the first cooling chamber 30 and used to adjust the warpage, thermal shrinkage, and strain value of the sheet glass SG. In the second cooling chamber 80, the sheet glass SG passing through the first cooling chamber 30 is cooled to at least a temperature of 100°C lower than the strain point through the slow cooling point and the strain point. However, in the second cooling chamber 80, the sheet glass SG may be cooled to a temperature near room temperature. Furthermore, the inside of the second cooling chamber 80 may be divided into a plurality of spaces by the heat insulating member 80b. The plurality of heat insulating members 80b are arranged between the plurality of descending rollers 81a to 81g on both sides in the thickness direction of the sheet glass SG. With this, the temperature management of the flat glass SG can be performed with better accuracy.

The molding device 40 includes, for example, a molded body 41, a partition member 50, a cooling roller 51, a temperature adjustment unit 60, descending rollers 81a to 81g, and heaters 82a to 82g. Furthermore, the molding device 40 includes a control device 91 (see FIG. 5 ). The control device 91 includes the forming device 40 The drive unit of each structure controls.

Hereinafter, each configuration included in the molding device 40 will be described in detail.

(2-1) Shaped body

The molded body 41 is provided in the molded body chamber 20. The molded body 41 shapes the molten glass FG into sheet glass SG which is sheet glass by overflowing the molten glass FG. As shown in FIG. 3, the molded body 41 has a shape with a substantially pentagonal cross-sectional shape (similar to a wedge shape). The substantially pentagonal front end corresponds to the lower end 41a of the molded body 41.

In addition, the molded body 41 has an inflow port 42 at the first end (see FIG. 4 ). A groove 43 is formed on the upper surface of the molded body 41. The inflow port 42 is connected to the downstream pipe 24 described above, and the molten glass FG flowing out of the clarifier 12 flows into the tank 43 from the inflow port 42. The molten glass FG flowing into the groove 43 of the molded body 41 overflows from the pair of tops 41 b and 41 b of the molded body 41 and flows down along the pair of side surfaces (surfaces) 41 c and 41 c of the molded body 41. After that, the molten glass FG merges at the lower end 41 a of the molded body 41 to become flat glass SG.

(2-2) Partition member

The partition member 50 is a member that blocks heat from moving from the molded body chamber 20 to the first cooling chamber 30. The partition member 50 is arranged near the confluence point of the molten glass FG. Moreover, as shown in FIG. 3, the partition member 50 is arrange|positioned at both sides of the thickness direction of the molten glass FG (flat glass SG) which merged at the junction. The partition member 50 is, for example, a heat insulating material. The partition member 50 partitions the upper side environment and the lower side environment of the confluence point of the molten glass FG, thereby blocking the heat movement between the upper side and the lower side of the partition member 50.

(2-3) Cooling roller

The cooling roller 51 is provided in the first cooling chamber 30. More specifically, the cooling roller 51 is arranged directly below the partition member 50. Moreover, the cooling roller 51 is arrange|positioned at both sides of the thickness direction of sheet glass SG, and is arrange|positioned at the position of the both ends R and L of the width direction of sheet glass SG. The cooling rollers 51 arranged on both sides in the thickness direction of the sheet glass SG operate in pairs. That is, the two ends of the sheet glass SG in the width direction are sandwiched by two pairs of cooling rollers 51.

For example, the cooling roller 51 is cooled by an air-cooled tube or a water-cooled tube that passes inside. The cooling roller 51 is in contact with both end portions R, L of the sheet glass SG, and rapidly cools both end portions R, L of the sheet glass SG by thermal conduction. The viscosity of both ends R, L of the sheet glass SG in contact with the cooling roller 51 is, for example, 10 ^9.0 poise or more.

The cooling roller 51 is rotationally driven by a cooling roller drive motor 390 (see FIG. 5 ). The cooling roller 51 also has a function of cooling both end portions R and L of the sheet glass SG and lowering the sheet glass SG downward. Furthermore, the cooling roller 51 cooling both ends R and L of the sheet glass SG will affect the uniformity of the width of the sheet glass SG and the thickness of the sheet glass SG.

(2-4) Temperature adjustment unit

The temperature adjustment unit 60 is a unit installed in the first cooling chamber 30 and cooling the sheet glass SG to near the slow cooling point. The temperature adjustment unit 60 is arranged below the partition member 50 and above the top plate 80a of the second cooling chamber 80.

The temperature adjusting unit 60 cools the sheet glass SG until the temperature of the central portion C of the sheet glass SG reaches the vicinity of the slow cooling point. Thereafter, the central portion C of the sheet glass SG is cooled in the second cooling chamber 80 to a temperature near room temperature through the slow cooling point and the strain point.

The temperature adjustment unit 60 may also have a cooling unit 61. A plurality of (three in this case) cooling units 61 are arranged in the width direction of the sheet glass SG, and a plurality of cooling units 61 are arranged in the flow direction of the sheet glass SG. Specifically, the cooling units 61 are arranged one by one so as to face the surfaces of both ends R and L of the sheet glass SG, and face the surfaces of the central area CA (see FIG. 4) described later. Way to configure a cooling unit 61.

(2-5) Lowering roller

The descending rollers 81a to 81g are provided in the second cooling chamber 80, and lower the sheet glass SG passing through the first cooling chamber 30 in the flow direction of the sheet glass SG. Falling rollers 81a~81g on the 2nd The inside of the cooling chamber 80 is arranged at specific intervals in the flow direction. A plurality of descending rollers 81a to 81g are arranged on both sides in the thickness direction of the sheet glass SG (refer to FIG. 3) and the positions of both ends R and L in the width direction of the sheet glass SG (refer to FIG. 4). That is, the lowering rollers 81a to 81g are in contact with the positions of both end portions R and L in the width direction of the sheet glass SG, and are in contact with both sides in the thickness direction of the sheet glass SG, and lower the sheet glass SG downward.

The descending rollers 81a to 81g are driven by a descending roller drive motor 391 (see FIG. 5). It is preferable that the lower rollers 81 a to 81 g are provided on the downstream side, the greater the peripheral speed of the lower rollers 81 a to 81 g. That is, among the plurality of descending rollers 81a to 81g, the peripheral speed of the descending roller 81a is the smallest, and the peripheral speed of the descending roller 81g is the largest. The descending rollers 81a to 81g arranged on both sides in the thickness direction of the sheet glass SG operate in pairs, and the pair of descending rollers 81a, 81a, ... lowers the sheet glass SG downward.

(2-6) Heater

The heaters 82a to 82g are provided inside the second cooling chamber 80, and adjust the temperature of the internal space of the second cooling chamber 80. Specifically, a plurality of heaters 82a to 82g are arranged in the flow direction of the sheet glass SG and the width direction of the sheet glass SG. For example, 7 heaters are arranged in the flow direction of the sheet glass SG, and 3 heaters are arranged in the width direction of the sheet glass. The three heaters arranged in the width direction control the temperature of the central area CA of the sheet glass SG and the both ends R and L of the sheet glass SG. The outputs of the heaters 82a to 82g are controlled by the control device 91 described later. With this, the ambient temperature in the vicinity of the sheet glass SG passing through the inside of the second cooling chamber 80 is controlled. The temperature of the sheet glass SG is controlled by controlling the ambient temperature in the second cooling chamber 80 by the heaters 82a to 82g. Furthermore, by temperature control, the sheet glass SG transitions from the viscoelastic region to the elastic region through the viscoelastic region. In this way, under the control of the heaters 82a to 82g, in the second cooling chamber 80, the temperature of the sheet glass SG is cooled from the temperature near the slow cooling point to the temperature near room temperature.

Furthermore, a ring for detecting the ambient temperature can also be provided near the flat glass SG Ambient temperature detection mechanism (thermocouple in this embodiment) 380 (refer to FIG. 5). For example, a plurality of thermocouples 380 are arranged in the flow direction of the sheet glass SG and the width direction of the sheet glass SG. Thermocouple 380 can detect the surface temperature of flat glass SG. For example, the thermocouple 380 detects the temperature of the central portion C of the sheet glass SG and the temperatures of the two end portions R and L of the sheet glass SG, respectively. The output of the heaters 82a to 82g is controlled based on the ambient temperature detected by the thermocouple 380.

(2-7) Cutting device

The cutting device 90 cuts the sheet glass SG that has been cooled to a temperature near room temperature in the second cooling chamber 80 to a specific size. With this, the flat glass SG becomes a plurality of glass plates. The cutting device 90 is driven by a cutting device driving motor 392 (see FIG. 5 ). In addition, the cutting device 90 may not necessarily be installed directly under the second cooling chamber 80. The sheet glass SG may not be cut by the cutting device 90, and the sheet glass SG may be wound into a roll shape to produce a roll-shaped sheet glass.

(2-8) Control device

FIG. 5 is a diagram showing an example of the configuration of the control device 91.

The control device 91 includes a CPU (Central Processing Unit), a RAM (Random Access Memory), a ROM (Read Only Memory), a hard disk, and the like. Various devices contained in 100 are controlled. Specifically, as shown in FIG. 5, the control device 91 receives signals from various sensors (for example, thermocouple 380) or switches (for example, main power switch 381) included in the glass substrate manufacturing device 100, and controls the temperature adjustment unit. 60. The heaters 82a to 82g, the cooling roller driving motor 390, the lowering roller driving motor 391, the cutting device driving motor 392, etc. are controlled.

(3) Temperature management

In the cooling step S4 of the manufacturing method of the glass substrate of the present embodiment, the cooling rate of the central area CA, that is, the temperature of the central portion C does not reach 450°C and is a temperature range of 300°C or higher The average cooling rate in the region is less than the average cooling rate of the central region CA in the temperature region other than the above-mentioned temperature region where the temperature of the central portion C in the cooling step S4 does not reach 450°C and is 300°C or higher. That is, in the cooling step S4, in the temperature region where the temperature of the central portion C does not reach 450°C and is 300°C or higher, the average cooling rate in the central region CA is the smallest. By adjusting the average cooling rate in the above manner, an extremely low heat shrinkage rate can be achieved on the manufacturing line of the glass substrate. In this case, the average cooling rate is adjusted using the cooling roller 51, the temperature adjustment unit 60, and the heaters 82a to 82g. Of course, at this time, the temperature distributions TP1 to TP10 in the width direction of the sheet glass SG as shown in FIG. 6 are set as the target temperature distribution in each temperature region in the flow direction, and the first cooling chamber 30 and the second cooling chamber 80 The temperature is controlled so that the thickness, warpage, and strain of the flat glass SG can be adjusted.

FIG. 6 is a diagram illustrating temperature distributions TP1 to TP10 as an example of the target temperature distribution in the cooling step. In the temperature distribution TP1, the temperature of the central area CA of the sheet glass SG is uniform, and both end portions R, L of the sheet glass SG are lower than the temperature of the central area CA. Both ends R and L of the sheet glass SG are cooled using the cooling roll 51 after forming so that the sheet glass SG may reach the above-mentioned temperature distribution TP1. In the temperature distributions TP2 to TP5, while lowering the temperature of the entire flat glass SG, the temperature distribution of the central area CA changes from a rectangular shape to a substantially parabolic shape that is convex upward, and gradually reduces the degree of convexity of the substantially parabolic shape. In the temperature distribution TP6, the temperatures in both end portions R, L and the central area CA are fixed. After that, in the temperature distributions TP7 to TP10, a substantially parabolic shape temperature distribution protruding downward is formed, while reducing the overall temperature of the plate glass SG, while increasing the degree that the temperature distribution in the central area CA protrudes downward. The temperature of the first cooling chamber 30 and the second cooling chamber 80 is adjusted using the cooling unit 61 and the heaters 82a to 82g so that the temperature of the sheet glass SG reaches the temperature distribution as described above.

In addition, when the temperature of the first cooling chamber 30 and the second cooling chamber 80 is adjusted, the measured value of the temperature of the plate glass SG can be used for the temperature of the plate glass SG, and, A value calculated by simulation based on the ambient temperature of the flat glass SG controlled by the heaters 82a to 82g can be used.

7 is a diagram showing an example of the temperature history (temporal change in temperature) of the sheet glass SG at the central portion C in the present embodiment along the flow direction. In FIG. 7, at time point A, sheet glass SG is formed on the lower end 41 a of the molded body 41. The temperature of the flat glass SG at this time is, for example, 1200°C. At time point B, the temperature of the flat glass SG reaches the slow cooling point (temperature of the glass with a viscosity of 10 ¹³ poise, for example, 775°C), and at time C, the temperature of the flat glass SG reaches 450°C. At the time point D, the temperature of the sheet glass SG reaches 300° C., and at the time point E, the temperature of the sheet glass SG reaches 200° C. or less, the sheet glass SG is cut by the cutting device 90. At this time, the temperature region of the sheet glass SG from the time point A to the time point B (after forming the sheet glass SG, the temperature region above the slow cooling point) is set as the first temperature region R1, and after the time point B passes until The temperature area of the plate glass SG up to the time point C (the temperature area where the slow cooling point does not reach 450° C. or higher) is set as the second temperature area R2, and the temperature area of the plate glass SG up to the time point D after the time point C passes (Temperature area below 450°C and above 300°C) is set as the third temperature area R3, and the temperature area of the flat glass SG after time point D is reached until time point E (under 300°C and above 100°C) Temperature range) is set as the fourth temperature range R4. At this time, in the first temperature region R1 to the fourth temperature region R4, the third average cooling rate in the third temperature region R3 is lower than the other first temperature region R1, the second temperature region R2, and the fourth temperature region R4. 1 Average cooling rate, 2nd average cooling rate, 4th average cooling rate. The cooling step of the sheet glass SG in the first temperature region R1 is the first cooling step, and the cooling steps of the sheet glass SG in the second temperature region R2 to the fourth temperature region R4 are the second cooling step to the fourth cooling step, respectively.

In the present embodiment, even when the temperature region (temperature region having a temperature difference of 10° C. or higher) is arbitrarily divided into ranges other than the temperature region R3, the third average cooling rate in the temperature region R3 is the smallest.

Furthermore, considering that the heat shrinkage rate can be effectively reduced, it is preferably in the first temperature region R1 The first average cooling rate is greater than the second average cooling rate in the second temperature region. Specifically, from the viewpoint of effectively reducing the heat shrinkage rate, in order to quickly relax the glass in the first temperature region R1, it is preferable to make the cooling rate of the second temperature region R2 to the fourth temperature region R4 lower than that of the first The cooling rate in the temperature region R1 is slower.

In addition, considering that there is no need to change the length of the path of the plate glass SG in the cooling step S4 and to suppress the reduction in the production efficiency of the glass substrate, the fourth average cooling rate in the fourth temperature region R4 of the fourth cooling step is preferred Greater than the third average cooling rate in the third temperature range.

In addition, in consideration of reducing the heat shrinkage rate, the third average cooling rate in the third temperature region R3 is preferably 5° C./sec or less. In addition, the lower limit of the third average cooling rate is not particularly limited, but considering that the length of the path of the plate glass SG is not changed, or considering that the reduction in the production efficiency of the glass substrate can be suppressed, the lower limit of the third average cooling rate is, for example, It is preferably 0.5°C/sec or more. Furthermore, from the viewpoint of maintaining productivity and reducing the heat shrinkage rate, the third average cooling rate is preferably 1°C/sec to 4.5°C/sec.

In addition, the first average cooling rate in the first temperature region R1 is preferably, for example, 5°C/sec to 50°C/sec, and more preferably 15°C/sec to 35°C/sec. The second average cooling rate in the second temperature region R2 is, for example, 5°C/sec or less, preferably 1°C/sec to 5°C/sec, more preferably 2°C/sec to 5°C/sec.

In addition, as in the present embodiment, in consideration of lowering the heat shrinkage rate without extending the path of the sheet glass SG, it is preferable that the temperature in the central portion C does not reach 300°C and is the fourth in the fourth temperature region R4 of 100°C or more The average cooling rate is greater than the third average cooling rate in the third temperature region R3.

The temperature history shown in FIG. 7 is the temperature history at the center portion C, but for the time history of the temperature at the same position in the width direction of the other parts of the center area CA of the center portion C, similarly, the third temperature area R3 The average cooling rate is also the smallest.

The first average cooling rate in the first temperature region R1 to the fourth temperature region R4 to the fourth level The average cooling rate is obtained by adjusting the ambient temperature of the first cooling chamber 30 and the second cooling chamber 80, which is a lower speed than natural cooling at normal temperature.

Generally speaking, glass is amorphous, and for high-temperature glass, its molecular structure changes to its optimal structure due to heat, that is, thermal relaxation and shrinkage. Therefore, in order to produce a glass substrate with a small heat shrinkage rate, it is preferable to cool slowly so that the heat of the sheet glass SG is sufficiently relaxed. If the cooling rate of the sheet glass SG is fast and the sheet glass SG is cooled without sufficient thermal relaxation, the change in molecular structure in the glass will be suppressed or prevented due to high viscosity during the thermal relaxation. Therefore, if the glass substrate obtained from the flat glass SG as described above is reheated for the purpose of heat treatment, the suppression or prevention of the heat relaxation is released, and the heat relaxation starts again from the way of the heat relaxation.

However, glass has multiple types of relaxations with different speeds, and the relaxation of glass can be expressed by the coincidence of relaxations with different relaxation speeds (hereinafter, the relaxations with different relaxation speeds are called "components" of relaxation). As described above, as the glass relaxing component, there are various components such as a component that rapidly thermally relaxes and shrinks, a component that smoothly thermally relaxes and shrinks, and a component that further thermally relaxes and shrinks at an intermediate speed. Therefore, in the cooling step, it is preferable to set a temperature history that sufficiently relaxes heat in all the above-mentioned components. However, as shown in FIG. 4, the path of the sheet glass SG in the cooling step S4 is a path from the vertical upward direction to the downward direction of the forming device 40, and is provided in a structure such as a building. It is difficult to extend the path because the objects are rebuilt, expanded, etc. to extend the path. Therefore, it is preferable to appropriately perform the temperature history of the sheet glass SG in the existing transport path, so as to efficiently reduce the thermal shrinkage rate of the glass substrate in the cooling step S4. In the present embodiment, the average cooling rate in the third temperature region R3 is lower than the average cooling rate in the temperature region other than the third temperature region R3 in the cooling step S4, whereby the glass substrate can be efficiently reduced Heat shrinkage. This reason is assumed as follows.

8 is a schematic diagram of the temperature history T1 to T3 (solid line) in the cooling step of the sheet glass SG in the cooling step S4 in which the horizontal axis represents time and the vertical axis represents temperature. Time points A and E in the figure correspond to time points A and E in FIG. 7. Here, the temperature history T1 is an example of the temperature history of the embodiment, and the temperature history T2 is a form in which the cooling rate is reduced relative to the temperature history T1 in a high temperature state, and thereafter, relative to the temperature history T1 Increase the cooling rate, and then make the cooling rate equal to the cooling rate of the temperature history T1. The temperature history T3 is in the form of reaching the cooling rate equivalent to the temperature history T1 in a high temperature state. The cooling rate is decreased during the temperature history T1, and thereafter, the cooling rate is increased relative to the temperature history T1.

For the temperature histories T1 and T3, the above-mentioned component that thermally relaxes and shrinks smoothly (this component is referred to as component X) cannot follow the cooling rate in a high-temperature state, and at point P1, the molecular structure related to component X The change is suppressed or prevented due to viscosity. For the temperature history T2, the cooling rate in the high-temperature state is small. Therefore, at the point P2, the change in molecular structure related to the component X is suppressed or prevented due to the viscosity.

On the other hand, in the temperature history T1, a component that rapidly thermally relaxes and shrinks (this component is referred to as component Y) cannot follow the cooling rate at point P3, and at point P3, the molecular structure related to component Y The change (heat relaxation) is suppressed or prevented due to viscosity. For temperature history T2, component Y cannot follow the cooling rate at point P4, and at point P4, the molecular structure change (heat relaxation) related to component Y is suppressed or prevented due to viscosity. For temperature history T3, component Y cannot follow the cooling rate at point P5, and at point P5, the molecular structure change (heat relaxation) related to component Y is suppressed or prevented due to viscosity.

For the temperature history T1~T3 as described above, the temperature at which the molecular structure change (heat relaxation) at points P1 and P2 is suppressed or prevented is not much different between points P1 and P2, but it is different from the composition The temperature at points P3~P5 where the changes in the molecular structure related to Y are suppressed is very different. Specifically, the temperature at the point P3 is the lowest. Therefore, for the temperature history T1 In terms of ~T3, the lower the temperature for suppressing or preventing thermal relaxation, the faster the thermal relaxation. Therefore, the lower the temperature at the time point when the molecular structure change related to component Y is suppressed or prevented, the thermal shrinkage rate can be The smaller. Therefore, in the temperature history T1 to T3, the temperature history T1 that suppresses or prevents the change of the molecular structure related to the component Y at the lowest temperature can sufficiently thermally relax before the flat glass SG is cut, thereby providing efficiency Flat glass SG with a good thermal shrinkage reduction.

In addition, the first average cooling rate to the fourth average cooling rate in the first temperature range to the fourth temperature range may be set such that the thermal shrinkage rate of the sheet glass SG reaches a specific target value. For example, under a plurality of cooling conditions, the thermal shrinkage rate of the flat glass SG is actually measured, and a calibration curve is prepared based on the obtained measured value. Furthermore, the thermal shrinkage of the plate glass SG can reach a specific target value, using the calibration curve made, along the flow direction of the target temperature distribution TP1~TP10 in the width direction of the set plate glass SG The temperature distribution is adjusted to thereby set the first average cooling rate to the fourth average cooling rate in the first temperature range to the fourth temperature range.

In the present embodiment, the temperature range of the third temperature region R3 is set to not more than 450°C and not less than 300°C, but when it is applied to a glass substrate for a display for forming a thin film on the surface by performing heat treatment at a specific processing temperature In this case, the third temperature region R3 may be set to a temperature region not exceeding (treatment temperature-100°C) and not less than (the treatment temperature-250°C). In this case, the treatment temperature is preferably 300°C or higher, and more preferably 400°C or higher.

For example, TFTs such as low-temperature polysilicon TFT (Thin Film Transistor) and thin films represented by oxide semiconductors such as IGZO (Indium, Gallium, Zinc, Oxygen) are formed on the surface of a glass substrate. When forming a thin film such as a semiconductor, for example, the glass substrate is heat-treated at a processing temperature of 300°C or higher or 400°C or higher. Therefore, for the glass substrate, the temperature range of the third temperature region R3 can be determined according to the processing temperature of the heat treatment. Furthermore, the processing temperature of the heat treatment when forming the thin film is, for example, 300°C to 700°C or 400°C to 650°C.

In the above case, after forming the sheet glass SG, the temperature region where the temperature of the central portion C is above the slow cooling point is set as the first temperature region R1, and the temperature of the central portion C is not reached the slow cooling point (processing temperature (℃)-100℃) When the temperature region above is set as the second temperature region R2, it is preferable that the third average cooling rate in the third temperature region R3 is lower than the first average cooling rate and the first in the first temperature region R1 2 The second average cooling rate in the temperature region R2.

In addition, the temperature region of the temperature of the central portion C that does not reach (processing temperature (°C)-250°C) and above (processing temperature (°C)-450°C) is set as the fourth temperature region R4, considering that the conveying path is not extended In order to reduce the heat shrinkage rate, it is preferable that the fourth average cooling rate in the fourth temperature region R4 is greater than the third average cooling rate in the third temperature region R3.

In this embodiment, in consideration of providing a glass substrate suitable as a glass substrate for a display, it is preferable to determine the temperature history as described above in the cooling step S4, thereby setting the thermal shrinkage rate of the glass substrate to 15 ppm or less . More preferably, the thermal shrinkage rate of the glass substrate is 10 ppm or less.

In addition, from the viewpoint of reducing the thermal shrinkage rate of the glass substrate, the strain point of the glass substrate (the temperature at which the glass viscosity is 10 ^14.5 poise) is preferably 680°C or higher, more preferably 700°C or higher, and further preferably 720°C the above. However, if the glass composition is adjusted to increase the strain point, the devitrification temperature tends to increase. Therefore, the upper limit of the strain point of the glass substrate is preferably 780°C or less, and more preferably 760°C or less .

In addition, the devitrification temperature is preferably 1280° C. or lower. From the viewpoint of taking into consideration the reduction in heat shrinkage rate and devitrification resistance, it is preferably 1100° C. to 1270° C., and more preferably 1150° C. to 1240° C.

(Glass composition)

As the glass composition of the glass substrate manufactured in this embodiment, for example, the following glass compositions are exemplified in mole %.

Including SiO ₂ 55%~80%, B ₂ O ₃ 0%~18%, Al ₂ O ₃ 3%~20%, MgO 0%~20%, CaO 0%~20%, SrO 0%~20%, BaO 0% ~ 20%, RO 5% ~ 25% ( wherein, R is at least one element selected from Mg, Ca, Sr, and Ba _{of), R '2 O 0%} ~ 2.0% ( wherein R' is selected from Li , Na and K at least one element).

The total content rate of the metal oxides in which the price value in the molten glass changes is not particularly limited. For example, it may contain 0.05% to 1.5%. Furthermore, it is preferable that As ₂ O ₃ , Sb ₂ O ₃ and PbO are not substantially contained.

(Application example of glass substrate)

The glass substrate manufactured by the manufacturing method of the glass substrate of this embodiment is particularly suitable as a glass substrate for a display of a liquid crystal display, a plasma display, an organic EL display, etc., or a cover glass for protecting a display. A display using a glass substrate for a display includes, in addition to a flat display with a flat display surface, an organic EL display, a liquid crystal display, or a curved display with a curved display surface. The glass substrate is preferably used as a glass substrate for high-definition displays, for example, as a glass substrate for liquid crystal displays, a glass substrate for organic EL (Electro-Luminescence) displays, and LTPS (Low Temperature Poly-silicon) ) Thin-film semiconductors, or glass substrates for displays using oxide semiconductors such as IGZO (Indium, Gallium, Zinc, Oxide, indium gallium zinc oxide).

Alkali-free glass or glass containing a small amount of alkali can be used as a glass substrate for displays. The glass substrate for display has high viscosity at high temperature. For example, the temperature of molten glass with a viscosity of 10 ^2.5 poise is above 1500°C. Furthermore, the alkali-free glass is a glass that does not substantially contain a composition of alkali metal oxide (R′ ₂ O). The term "substantially does not contain alkali metal oxides" refers to glass that does not contain alkali metal oxides as a glass raw material except for impurities mixed from raw materials. For example, the content of alkali metal oxides is less than 0.1% by mass.

(Heat shrinkage)

Heat treatment was performed to measure the heat shrinkage rate in this embodiment.

The glass substrate was cut into rectangles of a specific size, scored on both ends of the long side, cut at the center of the short side, and divided into two to obtain two glass samples. One of the glass samples was heat-treated (500°C, 30 minutes). Measure the length of another glass sample without heat treatment. Furthermore, by comparing the heat-treated glass sample and the untreated glass sample, the deviation of the scribed line is measured using a laser microscope, etc., and the difference in the length of the glass sample is obtained, whereby the thermal shrinkage of the sample can be obtained the amount. Using the heat shrinkage amount, that is, the difference and the length of the glass sample before heat treatment, the heat shrinkage rate was determined according to the following formula. The thermal contraction rate of this glass sample is set as the thermal contraction rate of the glass substrate.

Thermal shrinkage (ppm) = (differential) / (length of glass sample before heat treatment) × 10 ⁶

(Experimental example)

Using the glass substrate manufacturing apparatus 100 and the glass substrate manufacturing method described above, the glass substrates of Examples 1 to 3 and Comparative Examples were manufactured under the following conditions. The composition (mol%) of glass is SiO ₂ 70.5%, B ₂ O ₃ 7.2%, Al ₂ O ₃ 11.0%, K ₂ O 0.2%, CaO 11.0%, SnO ₂ 0.09%, Fe ₂ O ₃ 0.01%. The devitrification temperature of glass is 1206℃, and the viscosity of liquid phase is 1.9×10 ⁵ dPa‧s. The slow cooling point of the glass is 758°C and the strain point is 699°C. In addition, the width of the sheet glass SG was 1600 mm, and the thickness was 0.7 mm (Example 1, Comparative Example 1), 0.5 mm (Example 2, Comparative Example 2), and 0.4 mm (Example 3, Comparative Example 3). In addition, the heat treatment temperature for forming a thin film on the glass substrate is 550°C.

The average cooling rate when the temperature of the central portion C in the width direction of the sheet glass SG is equal to or higher than the slow cooling point is set as the first average cooling rate, and the temperature of the central portion C does not reach the slow cooling point and The average cooling rate when the temperature is 450° C. or higher is the second average cooling rate, and the average cooling rate when the temperature of the central portion C is 450° C. or less and 300° C. or higher is the third average cooling rate. In Examples 1 to 3, the third average cooling rate is slower than the first average cooling rate and the second average cooling rate. On the other hand, in Comparative Examples 1 to 3, the second average cooling rate is slower than the second average cooling rate of Examples 1 to 3, and the third average cooling rate is lower than the third average of Examples 1 to 3 The cooling rate is faster, so the second average cooling rate of Comparative Examples 1 to 3 is slower than the third average cooling rate of Comparative Examples 1 to 3. As a result, the thermal shrinkage of Examples 1 to 3 is 15 ppm or less, but the thermal shrinkage of Comparative Examples 1 to 3 exceeds 15 ppm.

Based on the above, the effect of this embodiment is obvious.

The method of manufacturing the glass substrate of the present invention has been described in detail above, but the present invention is not limited to the above-mentioned embodiments and examples, and of course various improvements or changes can be made without departing from the scope of the present invention.

A~E‧‧‧time

R1‧‧‧1st temperature zone

R2‧‧‧Second temperature zone

R3‧‧‧The third temperature zone

R4‧‧‧4th temperature zone

Claims (10)

A method for manufacturing a glass substrate for a display, comprising: a forming step of forming a molten glass into a flat glass by a down-draw method; and a cooling step of cooling the flat glass after forming into the above-mentioned flat glass Until the temperature of the central part of the width direction orthogonal to the flow direction of the sheet glass reaches 300°C, in the above cooling step, the cooling rate of the central region, that is, the temperature of the central part does not reach 450°C and is above 300°C The average cooling rate is less than the average cooling rate of the central region in the temperature region other than the temperature region in the cooling step, the central region is located closer to the flat glass than the widthwise ends of the flat glass The area inside the width direction and including the center portion. A method for manufacturing a glass substrate for a display, which is a method for manufacturing a glass substrate for a display for performing heat treatment according to a specific processing temperature to form a thin film on the surface, including: a forming step of forming a molten glass by a down-draw method Is flat glass; and a cooling step, which is to cool the flat glass after forming until the temperature of the central portion in the width direction orthogonal to the flow direction of the flat glass reaches a temperature lower than the processing temperature by 250°C So far, in the above cooling step, the cooling rate in the central region, that is, the temperature in the central part has not reached the temperature lower than the processing temperature by 100°C and is the average cooling rate in the temperature region lower than the processing temperature by 250°C or higher Is less than the average cooling rate of the central region in the temperature region other than the temperature region in the cooling step, the central region is located closer to the width direction of the sheet glass than both ends of the sheet glass in the width direction Inside and above The central area. The method for manufacturing a glass substrate for a display according to claim 1, wherein the cooling step includes: a first cooling step, after forming the sheet glass, the temperature of the central portion of the sheet glass in the width direction is equal to or more than a slow cooling point At the time, the central area is cooled at the first average cooling rate, the central area is located in the widthwise inner side of the flat glass than the both ends of the width direction of the flat glass, and includes the central portion; the second cooling Step, when the temperature in the center portion does not reach the slow cooling point and is above 450°C, the center area is cooled at the second average cooling rate; and in the third cooling step, the temperature in the center portion is not reached When the temperature is 450°C and 300°C or higher, the central region is cooled at a third average cooling rate, and the third average cooling rate is less than the first average cooling rate and the second average cooling rate. The method for manufacturing a glass substrate for a display according to claim 3, wherein the cooling step further includes a fourth cooling step, the fourth cooling step is based on the fourth average when the temperature of the central portion does not reach 300°C and is above 100°C The cooling rate cools the central region, and the fourth average cooling rate is greater than the third average cooling rate. The method for manufacturing a glass substrate for a display according to claim 2, wherein the cooling step includes: a first cooling step, after forming the flat glass, the temperature of the central portion of the flat glass in the width direction is above the slow cooling point , The central area is cooled at the first average cooling rate, the central area is located more inward in the width direction of the sheet glass than the both ends in the width direction of the sheet glass, and includes The central area; the second cooling step, which cools the central area at the second average cooling rate when the temperature of the central portion does not reach the slow cooling point and is 100°C or more lower than the processing temperature ; And the third cooling step, when the temperature of the central portion does not reach a temperature lower than the processing temperature of 100 ℃ lower than the processing temperature of 250 ℃ or higher, the third average cooling rate is performed on the central region For cooling, the third average cooling rate is lower than the first average cooling rate and the second average cooling rate. The method for manufacturing a glass substrate for a display according to claim 5, wherein the cooling step further includes a fourth cooling step, the temperature of the fourth cooling step at the central portion does not reach a temperature lower than 250°C lower than the processing temperature and is higher than the above When the treatment temperature is lower than 450° C. or higher, the central region is cooled at the fourth average cooling rate, and the fourth average cooling rate is greater than the third average cooling rate. The method for manufacturing a glass substrate for a display according to any one of claims 3 to 6, wherein the first average cooling rate is greater than the second average cooling rate. The method for manufacturing a glass substrate for a display according to any one of claims 3 to 6, wherein the third average cooling rate is 5.0°C/sec or less. The method for manufacturing a glass substrate for a display according to any one of claims 1 to 6, wherein the thermal shrinkage rate of the glass substrate is 15 ppm or less, wherein the thermal shrinkage rate is obtained by performing heat treatment maintained at 500°C for 30 minutes The shrinkage of the glass substrate is a value determined according to the following formula, and the heat shrinkage rate (ppm) = {shrinkage of the glass substrate after heat treatment/length of the glass substrate before heat treatment}×10 ⁶ . The method for manufacturing a glass substrate for a display according to any one of claims 1 to 6, wherein the strain point of the glass substrate is 680°C or higher.

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