Glass substrate

Abstract

This glass substrate is characterized by having a strain point of 695-740ºC, a temperature of 1300ºC or less at 104.5 dPa・s, a liquid phase viscosity of 104.5 dPa・s or more, a Young's modulus of 78 GPa or more, and a thermal shrinkage rate of 20 ppm or less when subjected to heat treatment for one hour at 500ºC.

Description

[Technical Field]

[0001] The present invention relates to a glass substrate, and more particularly to a glass substrate suitable for organic light-emitting diode (OLED) displays and liquid crystal displays, and further to a glass substrate suitable for oxide TFT and low-temperature p-Si TFT (LTPS) driven displays. [Background technology]

[0002] Glass substrates have been widely used for flat panel displays such as liquid crystal displays, hard disks, filters, sensors, etc. In recent years, in addition to conventional liquid crystal displays, OLED displays have been actively developed due to their self-luminescence, high color reproducibility, wide viewing angle, fast response, high definition, etc., and some of them have already been put into practical use.

[0003] Furthermore, LCD and OLED displays for mobile devices such as smartphones are required to display a large amount of information in a small area, so they require ultra-high-definition screens.Furthermore, they also need to have high-speed response times to display moving images.

[0004] For such applications, OLED displays or liquid crystal displays driven by LTPS are suitable. OLED displays emit light when current flows through the OLED elements that make up the pixels. For this reason, low-resistance, high-electron-mobility materials are used as the driving TFT elements. In addition to LTPS, oxide TFTs, such as IGZO (indium, gallium, zinc oxide), have attracted attention. Oxide TFTs have low resistance, high mobility, and can be fabricated at relatively low temperatures. Conventional p-Si TFTs, especially LTPS, suffer from instability in the excimer laser used to polycrystallize amorphous silicon (a-Si) films, resulting in inconsistent TFT characteristics when fabricated on large glass substrates. This can lead to uneven display in TV applications. On the other hand, oxide TFTs offer excellent uniformity of TFT characteristics when fabricated on large glass substrates, drawing attention as a promising TFT fabrication material, and some applications have already been implemented.

[0005] Glass substrates used in high-definition displays are required to have many properties, particularly the following properties (1) and (2):

[0006] (1) If the glass contains a large amount of alkaline components, alkaline ions will diffuse into the semiconductor material during heat treatment, causing deterioration of the film properties. Therefore, the content of alkaline components (especially Li and Na components) must be low or essentially zero.

[0007] (2) During processes such as film formation, dehydrogenation, crystallization of semiconductor layers, and annealing, glass substrates are heat-treated at several hundred degrees Celsius. One problem that can occur during heat treatment is pattern misalignment caused by factors such as thermal shrinkage of the glass substrate. The higher the resolution of the display, the higher the heat treatment temperature, but conversely, the smaller the tolerance for pattern misalignment. Therefore, glass substrates are required to have minimal dimensional change during heat treatment. The main causes of dimensional change during heat treatment are thermal shrinkage and film stress after film formation. Therefore, to minimize dimensional change during heat treatment, glass substrates are required to have a high strain point and a high Young's modulus (or specific Young's modulus), for example, 78 GPa or higher.

[0008] Furthermore, from the viewpoint of manufacturing the glass substrate, the glass substrate is required to have the following properties (3) to (5). (3) The molding temperature is low to extend the life of molding equipment. (4) It has excellent melting properties to prevent melting defects such as bubbles, lumps, and striae. (5) Excellent resistance to devitrification in order to prevent devitrification crystals from being mixed into the glass substrate. Summary of the Invention [Problem to be solved by the invention]

[0009] One approach to reducing the thermal shrinkage is to design the strain point to be high, as mentioned above. However, if the strain point is too high, the melting temperature and molding temperature will increase, which has the disadvantage of shortening the life of the melting equipment and molding equipment.

[0010] One approach to reducing the thermal shrinkage is to slow down the cooling rate during molding, as described above. However, slowing down the cooling rate has the disadvantage of reducing the production efficiency of glass substrates.

[0011] The present invention has been made in view of the above circumstances, and its technical object is to provide a glass substrate that can reduce dimensional changes during heat treatment without reducing production efficiency. [Means for solving the problem]

[0012] As a result of extensive research, the present inventors have found that the above technical problems can be solved by restricting the glass properties of the glass substrate to a predetermined range, and have proposed this as the present invention. 4.5 The temperature at dPa·s is 1300°C or less, and the liquidus viscosity is 10 4.5It is characterized by a Young's modulus of 78 GPa or more, a thermal shrinkage of 20 ppm or less when heat treated at 500°C for 1 hour. Here, "strain point" refers to a value measured based on the method of ASTM C336. 4.5 "Temperature at dPa·s" refers to the value measured using the platinum ball pull-up method. "Liquidus viscosity" refers to the viscosity of glass at the liquidus temperature, measured using the platinum ball pull-up method. "Liquidus temperature" refers to the temperature at which devitrification crystals (crystalline inclusions) were observed in the glass after glass powder that passed through a 30-mesh (500 μm) standard sieve and remained on the 50-mesh (300 μm) sieve was placed in a platinum boat and held in a temperature gradient furnace set at 1100°C to 1350°C for 24 hours. "Young's modulus" refers to the value measured using the dynamic elastic modulus measurement method (resonance method) based on JIS R1602. "Thermal shrinkage after heat treatment at 500°C for 1 hour" was measured using the following method. First, a 160 mm x 30 mm rectangular sample G was prepared as the measurement sample, as shown in Figure 1(a). Markings M were formed on both ends of the long side of the rectangular specimen G using #1000 waterproof abrasive paper at positions 20–40 mm from the edge. Then, as shown in Figure 1(b), the rectangular specimen G with markings M formed thereon was folded in two along the direction perpendicular to the markings M to produce specimens Ga and Gb. Then, one specimen, Gb, was subjected to heat treatment by increasing the temperature from room temperature to 500°C at a rate of 5°C / min, holding at 500°C for 1 hour, and then decreasing the temperature at a rate of 5°C / min. After the heat treatment, as shown in Figure 1(c), the unheated specimen Ga and the heat-treated specimen Gb were arranged in parallel. The positional deviations (ΔL1, ΔL2) of the markings M on the two specimens Ga and Gb were measured using a laser microscope, and the thermal shrinkage was calculated using the following formula: Note that 10 mm in the formula below refers to the initial distance between the markings M.

[0013] Heat shrinkage rate (ppm)=[{ΔL1(μm)+ΔL2(μm)}×10 3 ] / l0(mm)

[0014] In the glass substrate of the present invention, the strain point is 695 to 740°C, 4.5The temperature at dPa·s is 1300°C or less, and the liquidus viscosity is 10 4.5 The glass substrates are regulated to have a Young's modulus of 78 GPa or more, a thermal shrinkage of 20 ppm or less when heat treated at 500°C for 1 hour, and a glass substrate with reduced dimensional change during heat treatment without reducing production efficiency.

[0015] The glass substrate of the present invention has a strain point of 740°C or less and a thermal shrinkage of 20 ppm or less when subjected to heat treatment at 500°C for 1 hour. While it is difficult to achieve both of these properties with conventional manufacturing equipment and methods, it is possible to achieve both properties by, for example, extending the annealing path and slowing the annealing rate. While this method may result in a decrease in productivity of glass substrates, glass substrate production efficiency can be maintained by forming an extra-large G10.5 glass substrate and then extracting two G6-sized glass substrates from the glass substrate.

[0016] Furthermore, the glass substrate of the present invention preferably contains, in mole percent, as a glass composition: 60 to 70% SiO2, 10 to 15% Al2O3, 0 to 5% B2O3, 0 to 0.1% Li2O, 0 to 0.1% Na2O, 0 to 1% K2O, 0 to 8% MgO, 0 to 10% CaO, 0 to 10% SrO, 0 to 10% BaO, 0 to 10% ZnO, 50 to 10% P2O, and 0 to 1% SnO2. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 2 is an explanatory diagram for explaining a method for measuring a thermal shrinkage rate. DETAILED DESCRIPTION OF THE INVENTION

[0018] In the glass substrate of the present invention, the thermal shrinkage rate when subjected to heat treatment at 500°C for 1 hour is 20 ppm or less, preferably 19 ppm or less, 18 ppm or less, 17 ppm or less, 16 ppm or less, 15 ppm or less, 14 ppm or less, 13 ppm or less, and particularly 12 ppm or less. This makes it less likely that defects such as pattern misalignment will occur even when subjected to heat treatment in the LTPS manufacturing process. If the thermal shrinkage rate is too low, the production efficiency of the glass substrate will be easily reduced. Therefore, the thermal shrinkage rate is preferably 1 ppm or more, 2 ppm or more, 3 ppm or more, 4 ppm or more, and particularly 5 ppm or more.

[0019] The higher the strain point, the more the thermal shrinkage can be reduced. The strain point is 695°C or higher, preferably 697°C or higher, 700°C or higher, 702°C or higher, 705°C or higher, 710°C or higher, 711°C or higher, 712°C or higher, 713°C or higher, 714°C or higher, and particularly 715°C or higher. On the other hand, if the strain point is too high, the melting temperature and molding temperature become high, which tends to reduce the production efficiency of glass substrates. Therefore, the strain point is 740°C or lower, preferably 735°C or lower, 730°C or lower, 725°C or lower, 720°C or lower, and particularly 715°C or lower. The most preferred range of the strain point is 715 to 735°C.

[0020] 10 4.5 The lower the temperature in dPa·s, the less strain can be placed on the molding equipment. 4.5 The temperature at dPa·s is 1300°C or less, preferably 1290°C or less, 1280°C or less, 1275°C or less, 1270°C or less, 1265°C or less, 1260°C or less, 1255°C or less, particularly 1250°C or less. 4.5 If the temperature at dPa·s is too low, it will be impossible to design a high strain point. 4.5 The temperature in dPa·s is preferably 1150°C or higher, 1170°C or higher, 1180°C or higher, 1185°C or higher, 1190°C or higher, 1195°C or higher, in particular 1200°C or higher.

[0021] When forming into a plate by the overflow downdraw method or the like, devitrification resistance becomes important. Considering the forming temperature of glass containing SiO2, Al2O3, B2O3, and alkaline earth metal oxides (RO) in the glass composition, the liquidus temperature is preferably 1300°C or less, 1280°C or less, 1270°C or less, 1250°C or less, 1240°C or less, 1230°C or less, 1220°C or less, 1210°C or less, and particularly preferably 1200°C or less. In addition, the liquidus viscosity is 10 4.5 dPa·s or more, preferably 10 4.6 dPa·s or more, 10 4.7 dPa·s or more, 10 4.8 dPa·s or more, 10 4.9 dPa·s or more, 10 5.0 dPa·s or more, 10 5.2 dPa·s or more, especially 10 5.3 It is dPa·s or more.

[0022] The higher the Young's modulus, the more difficult it is for the glass substrate to deform. The Young's modulus is 78 GPa or more, preferably 78.5 GPa or more, 79 GPa or more, or 79.5 GPa or more, and particularly 80 to 120 GPa.

[0023] In addition to the above properties, the glass substrate of the present invention preferably has the following properties.

[0024] The preferred upper limit of the thermal expansion coefficient is 45 x 10 -7 / ℃ or less, 42×10 -7 / ℃ or less, 41×10 -7 / ℃ or less, especially 40×10 -7 / °C or less, and the preferred lower limit is 35×10 -7 / ℃ or more, 36×10 -7 / ℃ or more, especially 37×10 -7 / °C or more. If the thermal expansion coefficient is outside the above range, it will be inconsistent with the thermal expansion coefficient of various films (e.g., a-Si, p-Si), and problems such as film peeling and dimensional changes during heat treatment will be more likely to occur. Note that the "thermal expansion coefficient" refers to the average thermal expansion coefficient measured in a temperature range of 30 to 380°C, and can be measured, for example, with a dilatometer.

[0025] The etching depth when immersed in a 10 mass % HF aqueous solution at room temperature for 30 minutes is preferably 20 μm or more, 23 μm or more, 25 μm or more, 27 μm or more, 28 μm or more, 29 to 50 μm, and particularly preferably 30 to 40 μm. If the etching depth is too small, it becomes difficult to thin the glass substrate in the slimming process. The etching depth is an index of the etching rate. That is, a large etching depth results in a high etching rate, and a small etching depth results in a low etching rate.

[0026] The β-OH value is preferably 0.50 / mm or less, 0.45 / mm or less, 0.40 / mm or less, 0.35 / mm or less, 0.30 / mm or less, 0.25 / mm or less, 0.20 / mm or less, 0.15 / mm or less, and particularly 0.10 / mm or less. Reducing the β-OH value can increase the strain point. The following methods can be used to reduce the β-OH value: (1) Select raw materials with a low water content; (2) Add components (e.g., Cl, SO3) that reduce the water content in the glass; (3) Reduce the water content in the furnace atmosphere; (4) Bubble N2 in the molten glass; (5) Use a small melting furnace; (6) Increase the flow rate of the molten glass; or (7) Use an electric melting method. Here, the "β-OH value" refers to the value calculated using the following formula after measuring the transmittance of the glass using FT-IR.

[0027] β-OH value = (1 / X)log(T1 / T2) X: Glass thickness (mm) T1: Reference wavelength 3846cm -1 Transmittance (%) T2: Hydroxyl group absorption wavelength 3600cm -1 Minimum transmittance (%) in the vicinity

[0028] The glass substrate of the present invention preferably contains, in mole percent, 60-70% SiO2, 10-15% Al2O3, 0-5% BO3, 0-0.1% Li2O, 0-0.1% Na2O, 0-1% KO, 0-8% MgO, 0-10% CaO, 0-10% SrO, 0-10% BaO, 0-10% ZnO, 50-10% PO, and 0-1% SnO as a glass composition. The reasons for limiting the content range of each component as described above are as follows. Note that, in the explanation of the content range of each component, % means mol%.

[0029] If the SiO2 content is too low, chemical resistance, especially acid resistance, tends to decrease, and the strain point tends to decrease. On the other hand, if the SiO2 content is too high, the etching rate with hydrofluoric acid or a mixed solution of hydrofluoric acid tends to be slow, the high-temperature viscosity tends to increase, the melting property tends to decrease, and further, SiO2-based crystals, especially cristobalite, tend to precipitate, causing a decrease in liquidus viscosity. Therefore, the preferred upper limit of the SiO2 content is 70%, 69.5%, 69%, 68.5%, 68%, and particularly 67.5%, and the preferred lower limit is 60%, 61%, 62%, 62.5%, 63%, 63.5%, 64%, 64.5%, and particularly 65%. The most preferred content range is 65 to 67.5%.

[0030] If the Al2O3 content is too low, the strain point will be lowered, the amount of thermal shrinkage will be increased, and the Young's modulus will be reduced, making the glass substrate more prone to warping. On the other hand, if the Al2O3 content is too high, the BHF (buffered hydrofluoric acid) resistance will be reduced, the glass surface will be more likely to become cloudy, and crack resistance will be reduced. Furthermore, SiO2-Al2O3 crystals, especially mullite, will precipitate in the glass, making the liquidus viscosity more likely to be reduced. The preferred upper limit of the Al2O3 content is 15%, 14.5%, and especially 14%, and the preferred lower limit is 10%, 10.5%, 11%, 11.5%, and especially 12%. The most preferred content range is 12 to 14%.

[0031] B2O3 acts as a fluxing agent, lowering viscosity and improving meltability. If the B2O3 content is too low, it will not function adequately as a fluxing agent, and BHF resistance and crack resistance will likely decrease. Furthermore, the liquidus temperature will likely increase. On the other hand, if the B2O3 content is too high, the strain point, heat resistance, and acid resistance will likely decrease, particularly the strain point. Furthermore, the glass will likely undergo phase separation. The upper limit of B2O3 content is preferably 5%, particularly 4.5%, and the lower limit is preferably 0%, 1%, 1.5%, 2%, particularly 2.5%. The most preferred range is 2.5 to 4.5%.

[0032] Alkali metal oxides (Li2O, Na2O, and K2O) deteriorate the properties of various films formed on glass substrates and semiconductor elements, so it is preferable to reduce their respective contents to 0.1% (preferably 0.06%, 0.05%, 0.02%, and particularly 0.01%).

[0033] MgO is a component that reduces high-temperature viscosity without lowering the strain point, improving meltability. Although MgO has the greatest effect of lowering density in RO, excessive addition of MgO can precipitate SiO2-based crystals, particularly cristobalite, reducing liquidus viscosity. Furthermore, MgO is a component that easily reacts with BHF to form products. These reaction products can adhere to elements on the glass substrate surface or to the glass substrate, causing opacity in the elements or glass substrate. Furthermore, impurities such as Fe2O3 from MgO-introducing raw materials, such as dolomite, can be introduced into the glass, potentially reducing the transmittance of the glass substrate. Therefore, the preferred upper limit of MgO content is 8%, 7.5%, 7%, 6.5%, or especially 6%, and the preferred lower limit is 0%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, or especially 4.5%. The most preferred content range is 4.5 to 6%.

[0034] Like MgO, CaO reduces high-temperature viscosity without lowering the strain point, significantly improving meltability. However, excessive CaO content can lead to the precipitation of SiO2-Al2O3-RO crystals, particularly anorthite, which can reduce liquidus viscosity and BHF resistance. This can lead to reaction products adhering to the glass surface or to the glass substrate, potentially causing opacity of the glass. Therefore, the preferred upper limit of CaO content is 10%, 9.5%, or 9%, particularly 8.5%, and the preferred lower limit is 0%, 1%, 2%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 5.6%, or 6%, particularly 6.5%. The most preferred range is 6.5 to 8.5%.

[0035] SrO is a component that improves chemical resistance and devitrification resistance, but if its proportion in the overall RO is too high, meltability tends to decrease and the density and thermal expansion coefficient tend to increase. Therefore, the SrO content is preferably 0 to 10%, 0 to 9%, 0 to 8%, 0 to 7%, 0 to 6%, and particularly preferably 0 to 5%.

[0036] BaO is a component that improves chemical resistance and devitrification resistance, but if its content is too high, the density tends to increase. Furthermore, since SiO2-Al2O3-B2O3-RO-based glasses are generally difficult to melt, improving meltability and reducing the defect rate due to bubbles, foreign matter, and the like are extremely important from the perspective of inexpensively and mass-producing high-quality glass substrates. However, BaO has little effect in improving meltability in RO. Therefore, the preferred upper limit of BaO content is 10%, 9%, 8%, 7%, 6%, and particularly 5%, and the preferred lower limit is 0%, 0.1%, 0.3%, and particularly 0.2%.

[0037] ZnO is a component that improves meltability and BHF resistance, but if its content is too high, the glass becomes more susceptible to devitrification and the strain point decreases, making it difficult to ensure heat resistance. Therefore, the ZnO content is preferably 0 to 10%, 0 to 5%, 0 to 3%, 0 to 2%, and particularly preferably 0 to 1%.

[0038] P2O5 is a component that lowers the liquidus temperature of SiO2-Al2O3-CaO crystals (especially anorthite) and SiO2-Al2O3 crystals (especially mullite). However, if a large amount of P2O5 is incorporated, the glass becomes prone to phase separation. Therefore, the P2O5 content is preferably 0 to 10%, 0 to 5%, 0 to 3%, 0 to 2%, 0 to 1%, and particularly 0 to 0.1%.

[0039] SnO2 acts as a fining agent to reduce bubbles in glass. On the other hand, if the SnO2 content is too high, devitrification crystals of SnO2 tend to occur in the glass. The upper limit of the SnO2 content is preferably 1%, 0.5%, 0.4%, and particularly 0.3%, and the lower limit is preferably 0%, 0.01%, 0.03%, and particularly 0.05%. The most preferred range is 0.05 to 0.3%.

[0040] In addition to the above components, other components may be incorporated, preferably in an amount of 5% or less, 3% or less, and particularly preferably 1% or less.

[0041] ZrO2 is a component that improves chemical durability, but if the amount incorporated is too large, ZrSiO4 crystals are more likely to form. The upper limit of ZrO2 content is preferably 1%, 0.5%, 0.3%, 0.2%, and particularly 0.1%, and from the viewpoint of chemical durability, it is preferable to incorporate 0.001% or more. The most preferable content range is 0.001% to 0.1%. ZrO2 may be incorporated from the raw materials or by elution from the refractory.

[0042] TiO2 is a component that reduces high-temperature viscosity and improves melting properties, and also improves chemical durability. However, if incorporated in excess, it can easily reduce UV transmittance. The TiO2 content is preferably 3% or less, 1% or less, 0.5% or less, 0.1% or less, 0.05% or less, 0.03%, and particularly 0.01% or less. Furthermore, incorporating a very small amount of TiO2 (e.g., 0.0001% or more) can effectively suppress coloration due to UV rays. The most preferred content range is 0.0001 to 0.01%.

[0043] As2O3 and Sb2O3 are components that act as fining agents, but because they are environmentally hazardous chemicals, it is desirable to avoid their use as much as possible. The As2O3 and Sb2O3 contents are preferably less than 0.3%, less than 0.1%, less than 0.09%, less than 0.05%, less than 0.03%, less than 0.01%, and less than 0.005%, and especially less than 0.003%, respectively.

[0044] Iron is an impurity that is introduced from raw materials. However, excessive iron content can reduce UV transmittance. This can lead to problems during the photolithography process for TFT fabrication, the UV-based liquid crystal alignment process, and the laser lift-off process in the plastic OLED manufacturing process. Therefore, the preferred lower limit of the iron content, calculated as Fe2O3, is 0.0001%, 0.0005%, 0.001%, or particularly 0.0015%. The preferred upper limit of the iron content, calculated as Fe2O3, is 0.01%, 0.009%, 0.008%, 0.007%, or particularly 0.006%. The most preferred range is 0.0015% to 0.006%.

[0045] Cr2O3 is a component that is introduced as an impurity from raw materials. However, if the Cr2O3 content is too high, light transmission becomes difficult when light is incident from the edge of the glass substrate and scattered light is used to inspect the interior of the glass substrate for foreign objects, which can lead to defects in the foreign object inspection. This defect is particularly likely to occur when the substrate size is 730 mm × 920 mm or larger. Furthermore, when the glass substrate thickness is small (e.g., 0.5 mm or less, 0.4 mm or less, particularly 0.3 mm or less), less light is incident from the edge of the glass substrate, making it increasingly important to regulate the Cr2O3 content. The preferred upper limit of Cr2O3 content is 0.001%, 0.0008%, 0.0006%, 0.0005%, particularly 0.0003%, and the preferred lower limit is 0.00001%. The most preferred content range is 0.00001 to 0.0003%.

[0046] SO3 is a component that is mixed in as an impurity from the raw materials, but if the SO3 content is too high, bubbles called reboils will form during melting and molding, which may cause defects in the glass. The preferred upper limit of SO3 content is 0.005%, 0.003%, 0.002%, and particularly 0.001%, and the preferred lower limit is 0.0001%. The most preferred content range is 0.0001% to 0.001%.

[0047] The glass substrate of the present invention is preferably formed by the overflow downdraw method. The overflow downdraw method is a method for forming a glass substrate by overflowing molten glass from both sides of a wedge-shaped trough-shaped refractory and drawing the overflowing molten glass downward while joining at the lower end of the wedge. In the overflow downdraw method, the surface that will become the surface of the glass substrate does not come into contact with the refractory and is formed in a free surface state. This makes it easy to produce an unpolished glass substrate with good surface quality, and also makes it easy to make a large-area and thin glass substrate.

[0048] In addition to the overflow downdraw method, it is also possible to form a glass substrate by other downdraw methods (slot down method, redraw method, etc.), a float method, etc.

[0049] The thickness of the glass substrate of the present invention is not particularly limited, but is preferably 0.5 mm or less, 0.4 mm or less, 0.35 mm or less, and particularly 0.3 mm or less. The smaller the thickness, the easier it is to reduce the weight of the device. On the other hand, the thinner the thickness, the more easily the glass substrate bends. However, since the glass substrate of the present invention has a high Young's modulus and specific Young's modulus, defects caused by bending are unlikely to occur. The thickness can be adjusted by the flow rate, sheet drawing speed, etc. during glass production. [Example]

[0050] The present invention will be described in detail below based on examples. Note that the following examples are merely illustrative and are not intended to limit the scope of the present invention.

[0051] Tables 1 to 5 show examples of the present invention (samples Nos. 1 to 51).

[0052] [Table 1]

[0053] [Table 2]

[0054] [Table 3]

[0055] [Table 4]

[0056] [Table 5]

[0057] Each sample was prepared as follows. First, a glass batch prepared by blending glass raw materials to obtain the glass composition shown in the table was placed in a platinum crucible and melted at 1600°C for 24 hours. When melting the glass batch, the mixture was stirred using a platinum stirrer to homogenize it. Next, the molten glass was poured onto a carbon plate and formed into a flat plate. Each sample obtained was measured for its β-OH value, density, thermal expansion coefficient, Young's modulus, strain point, and 10 4.5 The temperature, liquidus temperature, liquidus viscosity and thermal shrinkage in dPa·s were evaluated.

[0058] The β-OH value is a value calculated by the above formula.

[0059] The density is a value measured by the well-known Archimedes method.

[0060] The thermal expansion coefficient is an average thermal expansion coefficient measured with a dilatometer in the temperature range of 30 to 380°C.

[0061] The Young's modulus is a value measured by a dynamic elastic modulus measurement method (resonance method) based on JIS R1602.

[0062] The strain point is a value measured based on the method of ASTM C336.

[0063] High temperature viscosity 10 4.5 The temperature at dPa·s was measured by the platinum sphere pulling method.

[0064] The liquidus temperature was determined by crushing each sample, passing it through a standard 30-mesh (500 μm) sieve, placing the glass powder remaining on the 50-mesh (300 μm) sieve in a platinum boat, and holding it in a temperature gradient furnace set at 1100 to 1350°C for 24 hours.The platinum boat was then removed, and the temperature at which devitrification crystals (crystalline foreign matter) were observed in the glass.The liquidus viscosity was the viscosity of the glass at the liquidus temperature, measured using the platinum sphere pulling method.

[0065] A sample for measuring thermal shrinkage was prepared as follows. First, a 160 mm x 30 mm glass substrate was prepared. It was heated to 900°C, then cooled to 500°C over approximately 180 seconds, and then allowed to cool naturally. These cooling conditions correspond to the cooling conditions used in the overflow downdraw method, where the cooling path was longer and the cooling rate was slower than in conventional methods. The thermal shrinkage of this sample was measured according to the above measurement method.

[0066] Samples No. 1 to 51 have a thermal expansion coefficient of 37 × 10 -7 ~40×10 -7 / °C, Young's modulus of 80 GPa or more, strain point of 715°C or more, and heat shrinkage of 14.0 ppm or less, it is considered that the dimensional change during heat treatment can be reduced. 4.5 The temperature at dPa·s is 1270°C or less, the liquidus temperature is 1260°C or less, and the liquidus viscosity is 10 4.5 dPa·s or more, it can improve the production efficiency of glass substrates. [Example]

[0067] Glass batches having the glass compositions of Samples No. 1 to 51 listed in Tables 1 to 5 were melted in a test melting furnace to obtain molten glass, which was then formed into a G10.5 size glass substrate with a thickness of 0.5 mm using the overflow downdraw method. This glass substrate was then cut to obtain two G6 size glass substrates. During forming, the annealing path was lengthened and the annealing rate was slower than in the past, thereby obtaining glass substrates with thermal shrinkage rates corresponding to Samples No. 1 to 51 listed in Tables 1 to 5.

Claims

1. The glass composition is, in mol%, SiO ２ 60-67.97%, Al 2 O 3 12.57-15%, B ２ O ３ 2 to 4.5%, MgO 0 to 7%, and a strain point of 713 to 740°C. ４．５ The temperature at dPa·s is 1300°C or less, and the liquidus viscosity is 10 ４．５ A glass substrate having a Young's modulus of 78 GPa or more, and a thermal shrinkage rate of 20 ppm or less when subjected to a heat treatment at 500°C for 1 hour.

2. The glass composition is, in mol%, Li ２ O 0-0.1%, Na ２ O 0-0.1%, K ２ O 0-1%, CaO 0-10%, SrO 0-10%, BaO 0-10%, ZnO 0-10%, P ２ O ５ 0-10% SnO ２ 2. The glass substrate according to claim 1, wherein the content is 0 to 1%.

3. The glass substrate according to claim 1, wherein the glass composition contains, in mol %, 0 to 7.07% CaO.

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