JP7722376B2 - Glass plate manufacturing method - Google Patents

Description

The present invention relates to a method for manufacturing glass sheets.

In recent years, in the field of display panels, pixel resolution has been increasing to improve image quality. Accordingly, high dimensional precision is also required for the glass sheets (glass substrates) used in display panels. For this reason, glass sheets that are resistant to dimensional change even when heat-treated at high temperatures during the display panel manufacturing process, i.e., glass sheets with a low thermal shrinkage rate, are required.

Methods of reducing the thermal shrinkage rate of glass sheets include adjusting the composition to increase the strain point of the glass or reducing the cooling rate of the glass after the forming process.

For example, Patent Document 1 discloses a method for manufacturing a glass sheet, which includes a forming step in which molten glass is formed into a glass ribbon (sheet glass) by the downdraw method, a cooling step in which the glass ribbon is cooled, and a cutting step in which the glass ribbon is cut to form a glass sheet. In this manufacturing method, the thermal shrinkage of the glass sheet is reduced by controlling the cooling rate of the glass ribbon in the cooling step.

International Publication No. 2014/157649

However, the thermal shrinkage rate of glass sheets is insufficient, and there is a need to further reduce the thermal shrinkage rate of glass sheets in order to accommodate the ever-increasing resolution of display panels.

Therefore, the technical objective of this invention is to reduce the thermal shrinkage rate of glass sheets.

The present invention is intended to solve the above-mentioned problems, and provides a method for manufacturing a glass sheet, comprising a preparation process for preparing molten glass, a forming process for forming a glass ribbon from the molten glass, and a heat treatment process including an annealing process for annealing the glass ribbon while transporting it, wherein the heat treatment process is characterized in that the average cooling rate from the annealing point to 600°C is smaller than the average cooling rate from (the annealing point + 100°C) to 200°C.

As described above, by making the average cooling rate from the annealing point to 600°C in the heat treatment process slower than the average cooling rate from (annealing point + 100°C) to 200°C, the residence time of the glass ribbon in the temperature range from the annealing point to 600°C, which has a significant impact on the thermal shrinkage rate, is extended, while the residence time of the glass ribbon in other temperature ranges is shortened. This makes it possible to reduce the thermal shrinkage rate of the glass sheet as much as possible without increasing the time required for heat treatment.

In the heat treatment process, the cooling time from the annealing point to 600°C may be 31 seconds or more. This can further improve the thermal shrinkage rate of the glass sheet.

In the heat treatment process, the average cooling rate from the annealing point to 500°C may be smaller than the average cooling rate from (the annealing point + 100°C) to 200°C. This allows the heat shrinkage rate to be improved regardless of the heat treatment temperature in the heat shrinkage rate measurement.

In the heat treatment process, the cooling time from the annealing point to 500°C may be 52 seconds or more. This can further improve the thermal shrinkage rate of the glass sheet.

In the heat treatment process, the average cooling rate from the annealing point to the thermal shrinkage measurement temperature may be smaller than the average cooling rate from (the annealing point + 100°C) to 200°C. This allows for efficient improvement of the thermal shrinkage of the glass sheet measured using the thermal shrinkage measurement temperature.

In the heat treatment process, the cooling time from the annealing point to the thermal shrinkage measurement temperature may be 52 seconds or longer. This can further improve the thermal shrinkage of the glass sheet.

The heat treatment process includes a heat removal process, which is a process preceding the slow cooling process, in which the glass ribbon is cooled while being transported. During the heat removal process, the glass ribbon may be cooled by a temperature adjustment member equipped with a cooler, with the temperature adjustment member positioned opposite the glass ribbon.

According to this configuration, even if the cooling rate is reduced in the temperature range above the annealing point, the contribution to the thermal shrinkage rate is small. However, by actively cooling the glass ribbon in the temperature range above the annealing point through the above-mentioned heat removal process, the manufacturing efficiency of the glass ribbon can be improved while maintaining the thermal shrinkage rate.

The method may also include an end cooling process between the forming process and the heat removal process, in which both ends of the glass ribbon are clamped and conveyed by rollers having a cooling mechanism. This can suppress shrinkage of the glass ribbon in the width direction.

In the preparation process, the molten glass may be prepared so that the water content (β-OH) of the glass ribbon is 0.30/mm or less. This can further improve the thermal shrinkage rate of the glass sheet.

According to the present invention, the thermal shrinkage rate of glass sheets can be reduced.

1 is a schematic view showing a glass sheet manufacturing apparatus according to a first embodiment. FIG. 1 is a flowchart showing a method for manufacturing a glass plate. 1 is a graph showing the relationship between the temperature of the glass ribbon and the cooling time in a heat treatment process. FIG. 4 is a vertical cross-sectional side view showing a glass sheet manufacturing apparatus according to a second embodiment. FIG. 2 is a longitudinal sectional front view of the glass sheet manufacturing apparatus. FIG. 2 is a diagram showing a method for measuring a thermal shrinkage rate. FIG. 2 is a diagram showing a method for measuring a thermal shrinkage rate. FIG. 2 is a diagram showing a method for measuring a thermal shrinkage rate.

[First embodiment]
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the drawings. Figures 1 to 3 show a first embodiment of a method for producing a glass plate according to the present invention.

Figure 1 illustrates an example of a glass sheet manufacturing apparatus used in this method. The manufacturing apparatus 1 is an apparatus for manufacturing glass sheet G by the overflow downdraw method. The manufacturing apparatus 1 mainly comprises a forming furnace 2, an annealing furnace 3, a cooling chamber 4, and a cutting chamber 5.

Molten glass GM produced in a glass melting furnace (not shown) is supplied to the forming furnace 2. The glass melting furnace may be, for example, a fully electric melting furnace, but is not limited to this configuration. A fully electric melting furnace is a melting furnace that melts glass raw materials by electrical heating using heating electrodes only, without heating using a burner combustion flame. Note that heating using a burner combustion flame may also be used when starting up a fully electric melting furnace.

Inside the forming furnace 2, a forming body 6 with a roughly wedge-shaped cross section and a pair of rollers 7 are arranged. The molten glass GM supplied to the forming furnace 2 overflows from both sides of the forming body 6 and merges at the lower end of the forming body 6. This forms the glass ribbon GR.

The roller pair 7 is positioned below the forming body 6 and has a cooling mechanism. The roller pair 7 is configured to clamp both widthwise ends of the glass ribbon GR. This roller pair 7 transports the glass ribbon GR while cooling both ends of the glass ribbon GR.

The thickness of the glass ribbon GR is preferably 0.1 mm to 1.5 mm, but is not limited to this range. The width of the glass ribbon GR is preferably 500 mm or more, but is not limited to this range.

The annealing point Ta of the glass ribbon GR is preferably higher than 600°C. From the viewpoint of reducing the thermal shrinkage rate, the annealing point Ta is more preferably 650°C or higher, even more preferably 700°C or higher, and most preferably 750°C. The upper limit of the annealing point Ta is preferably 1000°C. Furthermore, the viscosity of the molten glass GM at the liquidus temperature (liquidus viscosity) is preferably 104.5 dPa·s or higher.

From the viewpoint of obtaining a glass plate suitable for a glass substrate of a display, the type of glass is preferably alkali-free glass. Specific glass compositions preferably contain, in mole percent, 60 to ₇₅ % _SiO2 , 5 to 20% _Al2O3 , ₀ to 15% _B2O3 , 0 to less than ₁ % _Li2O + _Na2O +K2O (total amount of _Li2O , _Na2O , and _K2O ), 0 to 10% MgO, 0 to 15% CaO, 0 to 10% SrO, and 0 to 10% BaO, and among these, the following glass composition examples are particularly preferred.

An example of the first glass composition preferably contains, in mole percent, 60-70% SiO ₂ , 9.5-17% Al ₂ O ₃ (particularly 11-15%), 0-9% B ₂ O ₃ (particularly 5-7%), 0% to less than 1% Li ₂ O + Na ₂ O + K ₂ O (particularly 0-0.5%), 0-8% MgO (particularly 2-6%), 2-15% CaO (particularly 6-11%), 0-10% SrO (particularly 0.1-3%), and 0.1-5% BaO. This can increase the liquidus viscosity and Young's modulus. As a result, it becomes easier to produce a thin glass sheet G, and further, it becomes easier to reduce the amount of deflection of the glass sheet G.

An example of the second glass composition preferably contains, in mole percent, 62-72% SiO ₂ , 9.5-16% (particularly 11-15%) Al ₂ O ₃ , 1-8% (particularly 2-4%) B ₂ O ₃ , 0% to less than 1% (particularly 0-0.5%) Li ₂ O + Na ₂ O + K ₂ O , 1-9% (particularly 4-8%) MgO, 2-10% (particularly 3-8%) CaO, 0.1-5% (particularly 1-3%) SrO, and 0.1-5% (particularly 1-3%) BaO. This can increase the liquidus viscosity and Young's modulus. As a result, it becomes easier to produce a thin glass sheet G, and further, it becomes easier to reduce the amount of deflection of the glass sheet G.

An example of the third glass composition preferably contains, in mole percent, _67-77 % _SiO , _9-14 % _Al , 0-3% B (particularly 0-1%), _{0-1 %} Li + Na + _K , _0-5 % MgO (particularly 2-5%), 0-10% CaO (particularly 6-9%), 0-5% SrO, and 0-7% BaO (particularly 3-6%). This makes it easier to raise the strain point to 730°C or higher.

The annealing furnace 3 is located below the forming furnace 2. The annealing furnace 3 is equipped with multiple heaters 8 and multiple roller pairs 9.

The heater 8 is used to control the temperature inside the annealing furnace 3. The heaters 8 are set so that the temperature is higher the more upstream (higher) they are located and lower the more downstream (lower) they are located. By gradually lowering the set temperature of the heaters 8 from the upstream side to the downstream side, a temperature gradient is formed inside the annealing furnace 3.

The multiple roller pairs 9 are configured to clamp the widthwise ends of the glass ribbon GR. The glass ribbon GR is transported by these roller pairs 9.

The cooling chamber 4 is located below the annealing furnace 3. The glass ribbon GR annealed in the annealing furnace 3 is cooled to near room temperature by natural cooling in this cooling chamber 4.

The cutting chamber 5 is located below the cooling chamber 4. In this cutting chamber 5, the glass ribbon GR is cut along its width to cut out glass sheets G of a predetermined size. Note that the method for cutting the glass ribbon GR is not particularly limited, and various known cutting methods may be used.

The following describes a method for manufacturing glass sheets G using the manufacturing apparatus 1 configured as described above. As shown in Figure 2, the method for manufacturing glass sheets G includes a preparation process S1, a forming process S2, a heat treatment process S3, and a cutting process S4.

The preparation process S1 includes a melting process in which glass raw materials are heated in a glass melting furnace to produce molten glass GM. The preparation process S1 may further include a fining process, a stirring process, and a condition adjustment process. The molten glass GM is supplied to the forming furnace 2 through a glass supply path. In the preparation process S1, it is desirable to produce molten glass GM so that the moisture content β-OH of the glass ribbon GR (glass sheet G) is 0.30/mm or less. The moisture content β-OH is more desirably 0.25/mm or less, and even more desirably 0.18/mm or less. For example, by producing molten glass GM using an all-electric melting furnace or glass raw materials with little moisture content, the moisture content β-OH of the glass ribbon GR (glass sheet G) can be reduced to 0.30/mm or less.

Here, "β-OH" refers to a value obtained by measuring the transmittance of glass using a Fourier transform infrared spectrophotometer (FT-IR) and using the following formula (1):
β-OH=(1/X)log ₁₀ (T ₁ /T ₂ )...(1)
X: thickness of glass plate (mm)
T ₁ : transmittance (%) at a reference wavelength of 3846 cm ⁻¹
T ₂ : Minimum transmittance (%) at a hydroxyl group absorption wavelength of around 3600 cm ⁻¹

In the forming process S2, molten glass GM is supplied to the forming furnace 2, and the forming body 6 forms a glass ribbon GR from the molten glass GM. The formed glass ribbon GR is continuously transported in a vertical position from the forming furnace 2 to the annealing furnace 3.

The heat treatment process S3 includes a first cooling process in which the glass ribbon GR is cooled in the forming furnace 2, a second cooling process (slow cooling process) in which the glass ribbon GR is slowly cooled in the annealing furnace 3, and a third cooling process in which the glass ribbon GR is cooled in the cooling chamber 4. The heat treatment process S3 also includes an edge cooling process in which the glass ribbon GR is conveyed while being clamped at both widthwise ends by a pair of rollers 7 having a cooling mechanism. The edge cooling process is performed before, during, or after the first cooling process. This embodiment shows an example in which the edge cooling process is performed during the first cooling process.

In the first cooling process, the glass ribbon GR descending toward the annealing furnace 3 is cooled in the forming furnace 2. In the end cooling process, both widthwise ends of the glass ribbon GR are cooled by a pair of rollers 7 located below the forming body 6. Then, in the second cooling process (annealing process), the glass ribbon GR descending toward the cooling chamber 4 is annealed in the annealing furnace 3. In the third cooling process, the glass ribbon GR descending toward the cutting chamber 5 is naturally cooled in the cooling chamber 4.

Figure 3 is a graph showing the relationship between the temperature (°C) of the glass ribbon GR and the cooling time (s) in the heat treatment process S3.

As shown in Figure 3, in the heat treatment process S3, the average cooling rate from (annealing point Ta + 100°C) to the annealing point Ta (from time t1 to time t2) (hereinafter referred to as the "first average cooling rate"), the average cooling rate from the annealing point Ta to the thermal shrinkage measurement temperature Tx (from time t2 to time t3) (hereinafter referred to as the "second average cooling rate"), and the average cooling rate from the thermal shrinkage measurement temperature Tx to 200°C (from time t3 to time t4) (hereinafter referred to as the "third average cooling rate") are different.

The "average cooling rate" is the rate obtained by calculating the time required for the widthwise central part of the glass ribbon GR to pass through a specified temperature region and dividing the temperature difference within the specified temperature region by the time required for passage.

The thermal shrinkage measurement temperature Tx is the heat treatment temperature of the glass sheet G when measuring the thermal shrinkage. In this embodiment, the thermal shrinkage measurement temperature Tx is, for example, 500°C or 600°C.

In this embodiment, if the first average cooling rate is CR1 (CR1 = 100/(t2-t1)), the second average cooling rate is CR2 (CR2 = (Ta-Tx)/(t3-t2)), and the third average cooling rate is CR3 (CR3 = (Tx-200)/(t4-t3)), then CR1 > CR2 and CR2 < CR3.

Furthermore, if the average cooling rate from (the annealing point Ta + 100°C) to 200°C is CR0 (CR0 = (Ta - 100) / (t4 - t1)), then CR2 < CR0. The ratio of the second average cooling rate CR2 to the average cooling rate CR0 from (the annealing point Ta + 100°C) to 200°C (average cooling rate ratio: CR2/CR0) is preferably less than 1, more preferably 0.9 or less, and most preferably 0.86 or less. Meanwhile, the lower limit of this ratio can be, for example, 0.3 or more.

Regardless of the thermal shrinkage measurement temperature Tx, the second average cooling rate CR2 may be the average cooling rate from the annealing point Ta to 600°C, and the third average cooling rate CR3 may be the average cooling rate from 600°C to 200°C. Alternatively, regardless of the thermal shrinkage measurement temperature Tx, the second average cooling rate CR2 may be the average cooling rate from the annealing point Ta to 500°C, and the third average cooling rate CR3 may be the average cooling rate from 500°C to 200°C.

From the perspective of efficiently improving the heat shrinkage measured using a specific heat shrinkage measurement temperature Tx, it is preferable to set the second average cooling rate CR2 as the average cooling rate from the annealing point Ta to the heat shrinkage measurement temperature Tx, and the third average cooling rate CR3 as the average cooling rate from the heat shrinkage measurement temperature Tx to 200°C. For example, by setting the second average cooling rate CR2 as the average cooling rate from the annealing point Ta to 600°C and the third average cooling rate CR3 as the average cooling rate from 600°C to 200°C, thereby satisfying the above relationship, the heat shrinkage measured using a heat shrinkage measurement temperature Tx of 600°C can be efficiently improved. Setting the heat shrinkage measurement temperature Tx based on the heat treatment temperature in the display panel manufacturing process is preferable, as this allows for efficient improvement of defects in the display panel manufacturing process.

Since the heat shrinkage measurement temperature Tx is often 500°C to 600°C, from the perspective of improving the heat shrinkage measured using a heat shrinkage measurement temperature Tx of 500°C to 600°C, it is preferable to set the second average cooling rate CR2 to the average cooling rate from the annealing point Ta to 500°C, and to set the third average cooling rate CR3 to the average cooling rate from 500°C to 200°C.

In the heat treatment step S3, the cooling time from the annealing point Ta to 600°C is preferably 31 seconds or more, more preferably 40 seconds or more, and most preferably 51 seconds or more. The upper limit of this cooling time can be, for example, 500 seconds or less. The cooling time from 600°C to 200°C is preferably 90 seconds or less, more preferably 80 seconds or less. The lower limit of this cooling time can be, for example, 10 seconds or more.

In the heat treatment step S3, the cooling time from the annealing point Ta to 500°C is preferably 52 seconds or more, more preferably 60 seconds or more, and most preferably 76 seconds or more. The upper limit of this cooling time can be, for example, 500 seconds or less. The cooling time from 500°C to 200°C is preferably 70 seconds or less, more preferably 60 seconds or less. The lower limit of this cooling time can be, for example, 10 seconds or more.

In the heat treatment step S3, the cooling time from (the annealing point Ta + 100°C) to the annealing point Ta (from time t1 to time t2) is preferably 100 seconds or less, and more preferably 70 seconds or less. On the other hand, the lower limit of this cooling time can be, for example, 5 seconds or more.

In the cutting process S4, the glass ribbon GR is cut midway through the cooling chamber 4 and introduced into the cutting chamber 5. This forms a glass sheet G of the specified dimensions.

[Second embodiment]
4 and 5 show a second embodiment of the present invention. The forming furnace 2 of the manufacturing apparatus 1 according to this embodiment includes a forming body 6 and a temperature adjustment member 10 arranged to face the glass ribbon GR. In addition, in the manufacturing apparatus 1 according to this embodiment, a roller pair 7 having a cooling mechanism is provided between the forming body 6 and the temperature adjustment member 10. The roller pair 7 includes two sets of roller pairs, one on the left and one on the right, so as to sandwich each end GRa, GRb of the glass ribbon GR in the width direction W (see FIG. 5 ).

The temperature adjustment element 10 is located between the forming body 6 and the annealing furnace 3. The temperature adjustment element 10 includes a pair of temperature adjustment elements arranged at a distance in the thickness direction of the glass ribbon GR. Of the pair of temperature adjustment elements 10, one temperature adjustment element 10 faces one main surface of the glass ribbon GR, and the other temperature adjustment element 10 faces the other main surface of the glass ribbon GR. Note that while this embodiment uses a pair of temperature adjustment elements 10, multiple pairs of temperature adjustment elements 10 arranged side by side in the conveying direction of the glass ribbon GR may also be used.

While the temperature adjustment member 10 can be made of a thermally conductive material, such as a metal such as stainless steel, it is preferable to make it from a ceramic containing silicon carbide (SiC). Silicon carbide is characterized by its high hardness, excellent heat resistance (decomposition temperature 2545°C), high thermal conductivity (approximately 270 W/m·K for sintered bodies), and low thermal expansion coefficient (2.0 to 6.0 x 10-6/°C at temperatures between 40 and 400°C).

As shown in Figure 4, each temperature adjustment member 10 comprises an upper wall portion 11, a lower wall portion 12, and a side wall portion 13 connecting the upper wall portion 11 and the lower wall portion 12. The temperature adjustment member 10 also comprises a cooler 14 provided therein and a refractory material (support) 15 that supports the cooler 14.

The cooler 14 is positioned so that its tip is spaced from the inner surface of the side wall 13. The refractory material 15 supports the cooler 14 with its tip exposed. A space surrounded by the refractory material 15, upper wall 11, lower wall 12, and side wall 13 is formed inside the temperature adjustment member 10, and the tip of the cooler 14 is positioned in this space. The cooler 14 can be composed of, for example, a cooling pipe through which a refrigerant (cooling gas or cooling liquid) flows, and a supply and discharge system that supplies and discharges the refrigerant to the cooling pipe.

In the manufacturing method of the glass sheet G according to this embodiment, the first cooling step of the heat treatment process includes a heat removal step, which is a step preceding the slow cooling step, in which the glass ribbon GR is cooled by a temperature adjustment member 10 while being transported. In the heat removal step, the glass ribbon GR being transported downward is rapidly cooled by passing between a pair of temperature adjustment members 10.

In the heat removal process of this embodiment, for example, the average cooling rate from (annealing point Ta + 500°C) to (annealing point Ta + 100°C) is preferably 1°C/sec or more, and more preferably 3°C/sec or more. From the perspective of ensuring the dimensional accuracy of the glass sheet, the average cooling rate from (annealing point Ta + 500°C) to (annealing point Ta + 100°C) is preferably 20°C/sec or less.

The manufacturing method for glass sheet G according to this embodiment also includes an edge cooling process between the forming process and the heat removal process, in which both end portions GRa, GRb of the glass ribbon GR in the width direction W are clamped and transported by a pair of rollers 7 having a cooling mechanism. In the edge cooling process, both end portions GRa, GRb of the glass ribbon GR that have passed between a pair of temperature adjustment members 10 are cooled by the pair of rollers 7.

The other configurations of this embodiment are the same as those of the first embodiment. In this embodiment, components that are common to the first embodiment are given the same symbols.

The present invention is not limited to the configuration of the above-described embodiment, nor is it limited to the above-described effects. Various modifications are possible to the present invention without departing from the spirit and scope of the present invention.

In the above embodiment, an example was shown in which glass sheet G was manufactured by cutting glass ribbon GR in cutting chamber 5, but the present invention is not limited to this form. For example, glass ribbon GR may be wound into a roll to form a glass roll. The glass ribbon may then be pulled out from the glass roll and cut to manufacture a glass sheet.

The following describes examples of the present invention, but the present invention is not limited to these examples.

The inventors conducted a thermal shrinkage measurement test to confirm the effects of the present invention. For this test, multiple glass plates according to Examples 1 to 9 and Comparative Example 1 were prepared. OA-31 glass plates (thickness: 0.5 mm, annealing point Ta: 810°C) manufactured by Nippon Electric Glass Co., Ltd. were used as the glass plates. In the test, each glass plate was heated and held at a temperature of 950°C for 30 minutes to cancel the thermal history, and then each glass plate was cooled under different cooling conditions (temperature gradients).

The thermal shrinkage of each glass plate was measured as follows: First, as shown in Fig. 6A, two linear marks M1 and M2 were formed at predetermined positions on the glass plate G with a distance l ₀ therebetween.

Next, as shown in Figure 6B, glass plate G was cut in a direction perpendicular to marks M1 and M2 to obtain glass plate pieces Ga and Gb. Glass plate piece Ga was then heated from room temperature to a thermal shrinkage measurement temperature (heat treatment temperature) of 500°C, maintained at this temperature for one hour, and then cooled to room temperature. Another glass plate piece Ga was heated to a thermal shrinkage measurement temperature (heat treatment temperature) of 600°C, maintained at this temperature for one hour, and then cooled to room temperature.

In each of Examples 1 to 9 and Comparative Example 1, the cooling time (average cooling rate) from the annealing point Ta of 810°C to the thermal shrinkage measurement temperature Tx (500°C, 600°C) was varied. Furthermore, in each of the examples, the cooling time (average cooling rate) from 910°C, which is the annealing point Ta + 100°C, to 200°C was varied.

Then, as shown in Figure 6C, the heat-treated glass plate Ga and the non-heat-treated glass plate Gb were lined up and fixed with adhesive tape, and the deviations _Δl1 and _Δl2 between the marks M1 and M2 on the glass plate Ga and the marks M1 and M2 on the glass plate Gb were measured, and the thermal shrinkage rate S was calculated based on the following formula (2).

S (ppm) = (Δl ₁ (μm) + Δl ₂ (μm)) / l ₀ (m)...(2)
l ₀ : Distance between mark M1 and mark M2 on glass plate G. Δl ₁ : Distance between mark M1 on glass plate piece Ga and mark M1 on glass plate piece Gb. Δl ₂ : Distance between mark M2 on glass plate piece Ga and mark M2 on glass plate piece Gb.

The test results are shown in Tables 1 and 2.

As shown in Tables 1 and 2, in Examples 1 to 9, by making the average cooling rate (second average cooling rate CR2) from the annealing point Ta to the thermal shrinkage measurement temperature Tx (500°C, 600°C) smaller than the average cooling rate (CR0) from (annealing point Ta + 100°C) to 200°C (CR2 < CR0), the thermal shrinkage rate S could be reduced more than in Comparative Example 1 (CR2 > CR0).

Comparing Examples 1 to 9 with Comparative Example 1, it is preferable that the cooling time from the annealing point Ta to 600°C be 31 seconds or longer. Furthermore, it is preferable that the cooling time from the annealing point Ta to 500°C be 52 seconds or longer.

Furthermore, it is preferable that the ratio (average cooling rate ratio: CR2/CR0) between the average cooling rate (CR2) from the annealing point Ta to the thermal shrinkage measurement temperature Tx (500°C, 600°C) and the average cooling rate (CR0) from (annealing point Ta + 100°C) to 200°C is less than 1.

7 Roller 10 Temperature adjusting member 14 Cooler CR0 Average cooling rate from (annealing point + 100°C) to 200°C CR2 Average cooling rate from annealing point to thermal shrinkage measurement temperature G Glass sheet GM Molten glass GR Glass ribbon GRA End of glass ribbon GRb End of glass ribbon S1 Preparation step S2 Forming step S3 Heat treatment step Ta Annealing point Tx Thermal shrinkage measurement temperature W Width direction of glass ribbon

Claims (8)

a preparation step of preparing molten glass;
a forming step of forming a glass ribbon from the molten glass;
a heat treatment step including a slow cooling step of slowly cooling the glass ribbon while transporting it,
In the heat treatment step, an average cooling rate from the annealing point to 600°C is smaller than an average cooling rate from (the annealing point + 100°C) to 200°C , and the average cooling rate from the annealing point to a thermal shrinkage measurement temperature is smaller than the average cooling rate from (the annealing point + 100°C) to 200°C . The method for manufacturing a glass sheet according to claim 1, wherein the cooling time from the annealing point to 600°C in the heat treatment step is 31 seconds or longer. The method for manufacturing a glass sheet according to claim 1 or 2, wherein in the heat treatment step, the average cooling rate from the annealing point to 500°C is smaller than the average cooling rate from (the annealing point + 100°C) to 200°C. The method for manufacturing a glass sheet according to claim 3, wherein the cooling time from the annealing point to 500°C in the heat treatment step is 52 seconds or longer. The method for manufacturing a glass plate according to claim 1 , wherein in the heat treatment step, a cooling time from the annealing point to the thermal shrinkage measurement temperature is 52 seconds or more. the heat treatment step includes, as a pre-step of the annealing step, a heat removal step of cooling the glass ribbon while conveying it,
The method for manufacturing a glass sheet according to any one of claims 1 to 5 , wherein in the heat removal step, the glass ribbon is cooled by a temperature adjustment member including a cooler, the temperature adjustment member being arranged so as to face the glass ribbon. The method for manufacturing a glass sheet according to claim 6 , further comprising, between the forming step and the heat removal step, an end cooling step of conveying the glass ribbon while nipping both end portions of the glass ribbon with rollers having a cooling mechanism. The method for manufacturing a glass sheet according to any one of claims 1 to 5 , wherein in the preparing step, the molten glass is prepared so that the water content (β-OH) of the glass ribbon is 0.30/mm or less.