Glass plate manufacturing method

Abstract

This glass sheet manufacturing method comprises: a preparation step S1 for preparing molten glass GM; a molding step S2 for molding a glass ribbon GR from the molten glass GM; and a heat treatment step S3 including an annealing step for conveying the glass ribbon GR while annealing the same. In the heat treatment step S3, the average cooling rate CR2 from the annealing point to 600° C is lower than the average cooling rate CR0 from (the annealing point + 100° C) to 200° C.

Description

[Technical Field]

[0001] The present invention relates to a method for producing a glass sheet. [Background technology]

[0002] In recent years, in the field of display panels, pixel resolution has been increasing to improve image quality. Accordingly, high dimensional accuracy is also required for the glass plates (glass substrates) used in display panels. For this reason, glass plates that are resistant to dimensional changes even when heat-treated at high temperatures during the display panel manufacturing process, i.e., glass plates with a small thermal shrinkage rate, are required.

[0003] Methods for reducing the thermal shrinkage of a glass sheet include adjusting the composition to increase the strain point of the glass and reducing the cooling rate of the glass after the forming step.

[0004] For example, Patent Document 1 discloses a method for manufacturing a glass plate, which includes a forming step of forming molten glass into a glass ribbon (sheet glass) by a downdraw method, a cooling step of cooling the glass ribbon, and a cutting step of cutting the glass ribbon to form a glass plate. In this manufacturing method, the thermal shrinkage rate of the glass plate is reduced by controlling the cooling rate of the glass ribbon in the cooling step. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2014 / 157649 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the thermal shrinkage rate of glass sheets is not sufficient, and there is a demand for further reduction in the thermal shrinkage rate of glass sheets in order to accommodate the trend toward higher resolution display panels.

[0007] Therefore, the present invention has as its technical object to reduce the thermal shrinkage rate of a glass sheet. [Means for solving the problem]

[0008] The present invention is intended to solve the above-mentioned problems, and provides a method for manufacturing a glass sheet, comprising a preparation step of preparing molten glass, a forming step of forming a glass ribbon from the molten glass, and a heat treatment step including an annealing step of annealing the glass ribbon while transporting it, wherein in the heat treatment step, 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.

[0009] As described above, by making the average cooling rate from the annealing point to 600°C in the heat treatment step smaller 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 large effect on the thermal shrinkage rate, is lengthened, and 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.

[0010] In the heat treatment step, the cooling time from the annealing point to 600° C. may be 31 seconds or longer, thereby making it possible to further improve the thermal shrinkage rate of the glass sheet.

[0011] In the heat treatment step, 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 makes it possible to improve the heat shrinkage rate regardless of the heat treatment temperature in the heat shrinkage rate measurement.

[0012] In the heat treatment step, the cooling time from the annealing point to 500° C. may be 52 seconds or longer, thereby making it possible to further improve the thermal shrinkage rate of the glass sheet.

[0013] In the heat treatment step, 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 makes it possible to efficiently improve the thermal shrinkage of the glass sheet measured using the thermal shrinkage measurement temperature.

[0014] In the heat treatment step, the cooling time from the annealing point to the thermal shrinkage measurement temperature may be 52 seconds or longer, thereby further improving the thermal shrinkage of the glass sheet.

[0015] The heat treatment process may include a heat removal process, which is a pre-process of the slow cooling process, in which the glass ribbon is cooled while being transported, and in the heat removal process, the glass ribbon may be cooled by a temperature adjustment member equipped with a cooler, with the temperature adjustment member being positioned opposite the glass ribbon.

[0016] According to this configuration, even if the cooling rate is reduced in a temperature range above the annealing point, the contribution to the thermal shrinkage rate is small. However, by actively cooling the glass ribbon in a temperature range above the annealing point through the heat removal process, the manufacturing efficiency of the glass ribbon can be improved while maintaining the thermal shrinkage rate.

[0017] Furthermore, the present method may further include, between the forming step and the heat removal step, an end cooling step of conveying the glass ribbon while pinching both end portions of the glass ribbon with rollers having a cooling mechanism, thereby making it possible to suppress shrinkage of the glass ribbon in the width direction.

[0018] In the preparing step, the molten glass may be prepared so that the water content (β-OH) of the glass ribbon is 0.30 / mm or less, thereby further improving the thermal shrinkage of the glass sheet. [Effects of the Invention]

[0019] According to the present invention, the thermal shrinkage rate of the glass sheet can be reduced. [Brief explanation of the drawings]

[0020] [Figure 1] 1 is a schematic view showing a glass sheet manufacturing apparatus according to a first embodiment. FIG. [Figure 2] 1 is a flowchart showing a method for manufacturing a glass plate. [Figure 3] 1 is a graph showing the relationship between the temperature of the glass ribbon and the cooling time in a heat treatment process. [Figure 4] FIG. 4 is a vertical cross-sectional side view showing a glass sheet manufacturing apparatus according to a second embodiment. [Figure 5] FIG. 2 is a longitudinal sectional front view of the glass sheet manufacturing apparatus. [Figure 6A] FIG. 2 is a diagram showing a method for measuring a thermal shrinkage rate. [Figure 6B] FIG. 2 is a diagram showing a method for measuring a thermal shrinkage rate. [Figure 6C] FIG. 2 is a diagram showing a method for measuring a thermal shrinkage rate. DETAILED DESCRIPTION OF THE INVENTION

[0021] [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.

[0022] 1 illustrates an example of a glass sheet manufacturing apparatus used in this method. The manufacturing apparatus 1 is an apparatus for manufacturing a glass sheet G by the overflow downdraw method. The manufacturing apparatus 1 mainly includes a forming furnace 2, an annealing furnace 3, a cooling chamber 4, and a cutting chamber 5.

[0023] Molten glass GM produced in a glass melting furnace (not shown) is supplied to the forming furnace 2. The glass melting furnace is, for example, configured as 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 only heating electrodes, without heating using a burner combustion flame. Note that heating using a burner combustion flame may be used when starting up a fully electric melting furnace.

[0024] A forming body 6 having a substantially wedge-shaped cross section and a pair of rollers 7 are arranged inside the forming furnace 2. The molten glass GM supplied to the forming furnace 2 overflows from both sides of the forming body 6 and joins at the lower end of the forming body 6. In this way, a glass ribbon GR is formed.

[0025] The roller pair 7 is disposed below the forming body 6 and has a cooling mechanism. The roller pair 7 is configured to hold both end portions of the glass ribbon GR in the width direction. The roller pair 7 transports the glass ribbon GR while cooling both end portions of the glass ribbon GR.

[0026] 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.

[0027] The annealing point Ta of the glass ribbon GR is preferably higher than 600°C. From the viewpoint of reducing the thermal shrinkage, 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. In addition, the viscosity of the molten glass GM at its liquidus temperature (liquidus viscosity) is preferably 104.5 dPa s or higher.

[0028] 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. Among these, the following glass composition examples are particularly preferred.

[0029] An example of the first glass composition preferably contains, in mole percent, 60-70% SiO, 9.5-17% AlO (particularly 11-15%), 0-9% BO (particularly 5-7%), 0-1% or less of LiO + NaO + KO (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 increases the liquidus viscosity and Young's modulus. As a result, it becomes easier to produce a thin glass sheet G, and furthermore, it becomes easier to reduce the amount of deflection of the glass sheet G.

[0030] An example of the second glass composition preferably contains, in mole percent, 62 to 72% SiO, 9.5 to 16% (especially 11 to 15%) AlO, 1 to 8% (especially 2 to 4%) BO, 0 to less than 1% (especially 0 to 0.5%) LiO + NaO + KO, 1 to 9% (especially 4 to 8%) MgO, 2 to 10% (especially 3 to 8%) CaO, 0.1 to 5% (especially 1 to 3%) SrO, and 0.1 to 5% (especially 1 to 3%) BaO. This increases the liquidus viscosity and Young's modulus. As a result, it becomes easier to produce a thin glass sheet G, and furthermore, it becomes easier to reduce the amount of deflection of the glass sheet G.

[0031] An example of the third glass composition preferably contains, in mole percent, 67-77% SiO2, 9-14% Al2O3, 0-3% (especially 0-1%) B2O3, 0-1% or less (especially 0-0.5%) Li2O+Na2O+K2O, 0-5% (especially 2-5%) MgO, 0-10% (especially 6-9%) CaO, 0-5% SrO, and 0-7% (especially 3-6%) BaO. This facilitates raising the strain point to 730°C or higher.

[0032] The annealing furnace 3 is disposed below the forming furnace 2. The annealing furnace 3 includes a plurality of heaters 8 and a plurality of roller pairs 9.

[0033] The heaters 8 are used to control the temperature inside the annealing furnace 3. The heaters 8 are set so that the temperature is higher the closer to the upstream side (higher) the heaters 8 are located and lower the temperature the closer to the downstream side (lower) the heaters 8 are located. By gradually lowering the set temperatures of the heaters 8 from the upstream side to the downstream side, a temperature gradient is formed inside the annealing furnace 3.

[0034] The plurality of roller pairs 9 are configured to hold the widthwise ends of the glass ribbon GR. The glass ribbon GR is transported by the roller pairs 9.

[0035] The cooling chamber 4 is disposed below the annealing furnace 3. The glass ribbon GR annealed in the annealing furnace 3 is cooled to near room temperature in the cooling chamber 4 by natural cooling.

[0036] The cutting chamber 5 is disposed below the cooling chamber 4. In this cutting chamber 5, the glass ribbon GR is cut along the width direction to cut out glass sheets G of predetermined dimensions. Note that the method for cutting the glass ribbon GR is not particularly limited, and various known cutting methods may be employed.

[0037] Hereinafter, a method for manufacturing a glass sheet G by using the manufacturing apparatus 1 having the above configuration will be described. As shown in Fig. 2, the method for manufacturing a glass sheet G includes a preparation step S1, a shaping step S2, a heat treatment step S3, and a cutting step S4.

[0038] The preparation step S1 includes a melting step in which glass raw materials are heated in a glass melting furnace to produce molten glass GM. The preparation step S1 may further include a fining step, a stirring step, and a condition adjustment step. The molten glass GM is supplied to a forming furnace 2 through a glass supply path. In the preparation step S1, it is desirable to produce molten glass GM so that the water content β-OH of the glass ribbon GR (glass sheet G) is 0.30 / mm or less. The water 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 water carryover, it is possible to make the water content β-OH of the glass ribbon GR (glass sheet G) 0.30 / mm or less.

[0039] 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 (T1 / T2) (1) X: Thickness of the glass plate (mm) T1: Reference wavelength 3846cm -1 Transmittance (%) T2: Hydroxyl group absorption wavelength 3600cm -1 Minimum transmittance (%) in the vicinity

[0040] In the forming step S2, the molten glass GM is supplied to the forming furnace 2, and the molten glass GM is formed into a glass ribbon GR by the forming body 6. The formed glass ribbon GR is continuously transported from the forming furnace 2 to the annealing furnace 3 in a vertical position.

[0041] The heat treatment step S3 includes a first cooling step of cooling the glass ribbon GR in a forming furnace 2, a second cooling step (slow cooling step) of slowly cooling the glass ribbon GR in a slow cooling furnace 3, and a third cooling step of cooling the glass ribbon GR in a cooling chamber 4. In addition, the heat treatment step S3 includes an edge cooling step of conveying the glass ribbon GR while holding both widthwise ends thereof with a pair of rollers 7 having a cooling mechanism. The edge cooling step is performed before the first cooling step, during the first cooling step, or after the first cooling step. In the present embodiment, an example is shown in which the edge cooling step is performed during the first cooling step.

[0042] In the first cooling step, the glass ribbon GR descending toward the annealing furnace 3 is cooled in the forming furnace 2. In the edge cooling step, both widthwise ends of the glass ribbon GR are cooled by a pair of rollers 7 located below the forming body 6. Thereafter, in the second cooling step (annealing step), the glass ribbon GR descending toward the cooling chamber 4 is annealed in the annealing furnace 3. In the third cooling step, the glass ribbon GR descending toward the cutting chamber 5 is naturally cooled in the cooling chamber 4.

[0043] FIG. 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 step S3.

[0044] As shown in FIG. 3, in the heat treatment step 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.

[0045] The "average cooling rate" is a rate obtained by calculating the time required for the central portion of the glass ribbon GR in the width direction to pass through a predetermined temperature region, and dividing the temperature difference within the predetermined temperature region by the time required for the passage.

[0046] The heat shrinkage rate measurement temperature Tx is the heat treatment temperature of the glass plate G in the measurement of the heat shrinkage rate. The heat shrinkage rate measurement temperature Tx in the present embodiment is, for example, 500°C or 600°C.

[0047] In the present embodiment, when 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)), it is set that CR1 > CR2 and CR2 < CR3.

[0048] Also, when the average cooling rate from (slow cooling point Ta + 100°C) to 200°C is CR0 (CR0 = (Ta - 100) / (t4 - t1)), it is set that CR2 < CR0. The ratio of the second average cooling rate CR2 to the average cooling rate CR0 from (slow cooling 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. On the other hand, the lower limit of this ratio can be, for example, 0.3 or more.

[0049] Regardless of the heat shrinkage rate measurement temperature Tx, the second average cooling rate CR2 may be the average cooling rate from the slow cooling 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 heat shrinkage rate measurement temperature Tx, the second average cooling rate CR2 may be the average cooling rate from the slow cooling point Ta to 500°C, and the third average cooling rate CR3 may be the average cooling rate from 500°C to 200°C.

[0050] From the viewpoint 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 to set 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-mentioned 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.

[0051] A heat shrinkage measurement temperature Tx of 500°C to 600°C is often used, and from the viewpoint 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.

[0052] 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. On the other hand, the upper limit of this cooling time can be, for example, 500 seconds or less. Furthermore, the cooling time from 600°C to 200°C is preferably 90 seconds or less, more preferably 80 seconds or less. On the other hand, the lower limit of this cooling time can be, for example, 10 seconds or more.

[0053] 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. On the other hand, the upper limit of this cooling time can be, for example, 500 seconds or less. Furthermore, the cooling time from 500°C to 200°C is preferably 70 seconds or less, more preferably 60 seconds or less. On the other hand, the lower limit of this cooling time can be, for example, 10 seconds or more.

[0054] 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, 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.

[0055] In the cutting step S4, the glass ribbon GR introduced into the cutting chamber 5 via the cooling chamber 4 is cut at its midpoint, thereby forming a glass sheet G of a predetermined size.

[0056] [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 pairs of rollers, 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).

[0057] The temperature adjustment member 10 is located between the forming body 6 and the annealing furnace 3. The temperature adjustment member 10 includes a pair of temperature adjustment members arranged at an interval in the thickness direction of the glass ribbon GR. Of the pair of temperature adjustment members 10, one temperature adjustment member 10 faces one main surface of the glass ribbon GR, and the other temperature adjustment member 10 faces the other main surface of the glass ribbon GR. Although a pair of temperature adjustment members 10 is used in this embodiment, multiple pairs of temperature adjustment members 10 arranged side by side in the conveying direction of the glass ribbon GR may also be used.

[0058] The temperature adjustment member 10 can be made of a thermally conductive material, such as a metal such as stainless steel, but is preferably made of a ceramic containing silicon carbide (SiC). Silicon carbide is characterized by high hardness, excellent heat resistance (decomposition temperature 2545°C), high thermal conductivity (approximately 270 W / m·K in the case of a sintered body), and a low thermal expansion coefficient (2.0 to 6.0 × 10-6 / °C at 40 to 400°C).

[0059] 4, each temperature adjustment member 10 includes 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 includes a cooler 14 provided therein and a refractory material (support) 15 that supports the cooler 14.

[0060] The cooler 14 is disposed at a position where its tip is spaced from the inner surface of the side wall portion 13. The refractory material 15 supports the cooler 14 with its tip exposed. A space surrounded by the refractory material 15, the upper wall portion 11, the lower wall portion 12, and the side wall portion 13 is formed inside the temperature adjustment member 10, and the tip of the cooler 14 is disposed 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.

[0061] In the manufacturing method of a glass sheet G according to this embodiment, the first cooling step of the heat treatment step includes, as a pre-step of the annealing step, a heat extraction step in which the glass ribbon GR is cooled by the temperature adjustment members 10 while being conveyed. In the heat extraction step, the glass ribbon GR conveyed downward is quenched by passing between a pair of temperature adjustment members 10.

[0062] In the heat removal step of this embodiment, the average cooling rate from (annealing point Ta + 500°C) to (annealing point Ta + 100°C) is preferably 1°C / sec or more, more preferably 3°C / sec or more. From the viewpoint 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.

[0063] Furthermore, the manufacturing method for a glass sheet G according to this embodiment includes, between the forming step and the heat removal step, an edge cooling step in which the glass ribbon GR is conveyed while being sandwiched between both end portions GRa, GRb in the width direction W by a pair of rollers 7 having a cooling mechanism. In the edge cooling step, both end portions GRa, GRb of the glass ribbon GR that has passed between a pair of temperature adjustment members 10 are cooled by the pair of rollers 7.

[0064] Other configurations of this embodiment are the same as those of the first embodiment, and in this embodiment, components common to those of the first embodiment are denoted by the same reference numerals.

[0065] The present invention is not limited to the configuration of the above-described embodiment, nor is it limited to the above-described effects. The present invention can be modified in various ways without departing from the spirit of the present invention.

[0066] In the above embodiment, an example has been shown in which the glass ribbon GR is cut in the cutting chamber 5 to produce a glass sheet G, but the present invention is not limited to this embodiment. For example, the glass ribbon GR may be wound into a roll to form a glass roll. Thereafter, the glass ribbon may be pulled out from the glass roll and cut to produce a glass sheet. [Example]

[0067] Examples of the present invention will be described below, but the present invention is not limited to these examples.

[0068] The present inventors conducted a test to measure thermal shrinkage in order to confirm the effects of the present invention. For this test, a plurality of glass plates according to Examples 1 to 9 and Comparative Example 1 were prepared. OA-31 (thickness: 0.5 mm, annealing point Ta: 810°C) manufactured by Nippon Electric Glass Co., Ltd. was used as the glass plate. 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).

[0069] 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 10 therebetween.

[0070] Next, as shown in Figure 6B, the glass plate G was cut in a direction perpendicular to the marks M1 and M2 to obtain glass plate pieces Ga and Gb. The 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.

[0071] 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. In each of Examples 1 to 9 and Comparative Example 1, the cooling time (average cooling rate) from 910°C, which is the annealing point Ta + 100°C, to 200°C was also varied.

[0072] Thereafter, as shown in FIG. 6C, with the heat-treated glass plate piece Ga and the non-heat-treated glass plate piece Gb arranged side by side and fixed with an adhesive tape, the displacement amounts Δl1 and Δl2 between the marks M1 and M2 of the glass plate piece Ga and the marks M1 and M2 of the glass plate piece Gb were measured, and the thermal shrinkage rate S was calculated based on the following formula (2).

[0073] S (ppm) = (Δl1 (μm) + Δl2 (μm)) / l0 (m) ··· (2) l0: The distance between the mark M1 and the mark M2 on the glass plate G Δl1: The distance between the mark M1 of the glass plate piece Ga and the mark M1 of the glass plate piece Gb Δl2: The distance between the mark M2 of the glass plate piece Ga and the mark M2 of the glass plate piece Gb

[0074] The test results are shown in Table 1 and Table 2.

Table 1

Table 2

[0075] As shown in Table 1 and Table 2, in Examples 1 to 9, by making the average cooling rate (the second average cooling rate CR2) from the slow cooling point Ta to the thermal shrinkage rate measurement temperature Tx (500 ° C, 600 ° C) smaller than the average cooling rate (CR0) from (the slow cooling point Ta + 100 ° C) to 200 ° C (CR2 <CR0), the thermal shrinkage rate S could be reduced compared to Comparative Example 1 (CR2> CR0).

[0076] When comparing Examples 1 to 9 with Comparative Example 1, the cooling time from the slow cooling point Ta to 600 ° C is preferably 31 seconds or more. Also, the cooling time from the slow cooling point Ta to 500 ° C is preferably 52 seconds or more.

[0077] Furthermore, it is preferable that the ratio (average cooling rate ratio: CR2 / CR0) of the average cooling rate (CR2) from the annealing point Ta to the thermal shrinkage measurement temperature Tx (500°C, 600°C) to the average cooling rate (CR0) from (the annealing point Ta+100°C) to 200°C is less than 1. [Explanation of symbols]

[0078] 7. Laura 10 Temperature control material 14 Cooler Average cooling rate from CR0 (annealing point + 100°C) to 200°C CR2 Average cooling rate from the annealing point to the heat shrinkage measurement temperature G Glass plate GM Molten Glass GR Glass Ribbon GRa End of glass ribbon GRb End of glass ribbon S1 Preparation process S2 Molding process S3 Heat treatment process Ta Annealing point Tx Heat shrinkage measurement temperature W: Width direction of glass ribbon

Claims

1. 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.

2. 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 600° C. is 31 seconds or longer.

3. 3. The method for manufacturing a glass plate according to claim 1, wherein, in the heat treatment step, an 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.

4. The method for manufacturing a glass plate according to claim 3 , wherein in the heat treatment step, a cooling time from the annealing point to 500° C. is 52 seconds or longer.

5. 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.

6. 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, a temperature adjustment member including a cooler is arranged to face the glass ribbon, and the glass ribbon is cooled by the temperature adjustment member.

7. 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.

8. 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.

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