Alkali-free glass sheet

Abstract

To provide an alkali-free glass plate that has a high strain point and can reduce manufacturing costs.SOLUTION: The alkali-free glass plate of the present invention is characterized by: containing, as glass composition, SiO2 by 60 to 74%, Al2O3 by 6 to 20%, B2O3 by 0 to 9%, MgO by 1 to 13%, CaO by 1 to 13%, SrO by 0 to 7%, BaO by 0 to 8%, and Y2O3 + La2O3 by 0 to less than 1.0%, in mol%; containing substantially no alkali metal oxide; and having a strain point of 650°C or higher.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to an alkali-free glass plate, and particularly to an alkali-free glass plate suitable for a carrier glass that holds a substrate for forming a TFT circuit or a resin substrate for forming a TFT circuit in a flat panel display such as a liquid crystal display or an organic EL display.

Background Art

[0002] As is well known, liquid crystal panels and organic EL panels are provided with thin film transistors (TFTs) for drive control.

[0003] Amorphous silicon, low-temperature polysilicon, high-temperature polysilicon, etc. are known for the thin film transistors that drive the display. In recent years, with the spread of large liquid crystal displays, smartphones, tablet PCs, etc., the need for higher resolution of displays has been increasing. Low-temperature polysilicon TFTs can meet this need, but they will undergo a high-temperature film formation process at 500 to 600°C. However, since conventional glass plates have a large thermal shrinkage before and after the high-temperature film formation process, pattern misalignment of the thin film transistors is caused. Therefore, a glass plate with low thermal shrinkage is required for higher resolution of the display. In recent years, further higher definition of the display has been studied, and in that case, it is necessary to further reduce the thermal shrinkage of the glass plate.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Disclosure of the Invention

Problems to be Solved by the Invention

[0005] As methods for reducing the thermal shrinkage of a glass plate, mainly two methods can be mentioned. The first method is a method of holding the glass plate near the heat treatment temperature of the film forming process in advance and gradually cooling it. In this method, since the glass undergoes structural relaxation and shrinks during the gradual cooling, the amount of thermal shrinkage in the subsequent high-temperature film forming process can be suppressed. However, this method causes an increase in the number of manufacturing steps and manufacturing time, resulting in an increase in the manufacturing cost of the glass plate.

[0006] The second method is a method of increasing the strain point of the glass plate. In the overflow down-draw method, generally, it is cooled from the melting temperature to the forming temperature in a relatively short time. Due to this effect, the fictive temperature of the glass plate becomes high, and the thermal shrinkage of the glass plate becomes large. Therefore, when the strain point of the glass plate is increased, the viscosity of the glass plate at the heat treatment temperature of the film forming process becomes large, and it becomes difficult for structural relaxation to proceed. As a result, the thermal shrinkage of the glass plate can be suppressed. And the higher the heat treatment temperature of the film forming process, the greater the effect of increasing the strain point on reducing the thermal shrinkage. Therefore, in the case of a low-temperature polysilicon TFT, it is desirable to increase the strain point of the glass plate as much as possible.

[0007] For example, Patent Document 1 discloses reducing the content of B2O3 in the glass composition to increase the strain point of the glass plate. Further, Patent Document 1 discloses introducing Y2O3 and / or La2O3 into the glass composition to avoid a decrease in devitrification resistance associated with a low B2O3 amount. However, since Y2O3 and La2O3 are rare earth elements, the raw material cost is high, which increases the manufacturing cost of the glass plate.

[0008] The present invention has been made in view of the above circumstances, and its technical problem is to provide an alkali-free glass plate having a high strain point and capable of reducing the manufacturing cost.

Means for Solving the Problems

[0009] As a result of intensive studies, the inventors have found that by strictly regulating the content of each component and regulating the strain point to a predetermined value or more, the above technical problems can be solved, and the inventors propose the present invention. That is, the alkali-free glass sheet of the present invention contains, as a glass composition, in mol%, 60 to 74% of SiO2, 6 to 20% of Al2O3, 0 to 9% of B2O3, 1 to 13% of MgO, 1 to 13% of CaO, 0 to 7% of SrO, 0 to 8% of BaO, and less than 0 to 1.0% of Y2O3 + La2O3, substantially does not contain alkali metal oxides, and is characterized in that the strain point is 650 °C or more. Here, "Y2O3 + La2O3" refers to the total amount of Y2O3 and La2O3. "Substantially does not contain alkali metal oxides" means a case where the content of alkali metal oxides (Li2O, Na2O, K2O) in the glass composition is less than 0.5 mol% (preferably less than 0.1 mol%). The "strain point" refers to a value measured based on the method of ASTM C336.

[0010] Further, in the alkali-free glass sheet of the present invention, the content of SrO + BaO is preferably 0 to 3 mol%. Here, "SrO + BaO" refers to the total amount of SrO and BaO.

[0011] Further, the strain point of the alkali-free glass sheet of the present invention is preferably 700 °C or more.

[0012] Further, the Young's modulus of the alkali-free glass sheet of the present invention is preferably 79 GPa or more. Here, the "Young's modulus" can be measured by the bending resonance method.

[0013] Further, the alkali-free glass sheet of the present invention has a thermal expansion coefficient of 30×10 -7 ~45×10 -7 / °C, which is preferable. By doing so, it is possible to suppress a situation in which local dimensional changes occur in the glass sheet due to temperature unevenness in the high-temperature film-forming process.

[0014] Further, the alkali-free glass sheet of the present invention has a high-temperature viscosity of 10 2.5The temperature in dPa·s is preferably 1600 °C or lower. By doing so, the melting cost can be reduced.

Embodiments for Carrying Out the Invention

[0015] The alkali-free glass sheet of the present invention contains, as a glass composition, in mol%, 60 to 74% of SiO2, 6 to 20% of Al2O3, 0 to 9% of B2O3, 1 to 13% of MgO, 1 to 13% of CaO, 0 to 7% of SrO, 0 to 8% of BaO, and less than 0 to 1.0% of Y2O3 + La2O3, and is characterized by substantially not containing an alkali metal oxide. The reasons for limiting the content of each component as described above are shown below. In the description of the content of each component, unless otherwise specified, the % indication represents mol%.

[0016] SiO2 is a component that forms the glass skeleton and is a component that increases the strain point. Therefore, the content of SiO2 is preferably 60% or more, 62% or more, 64% or more, particularly 66% or more. On the other hand, if the content of SiO2 is too high, the high-temperature viscosity increases and the meltability tends to decrease. Therefore, the content of SiO2 is preferably 74% or less, 72% or less, 70% or less, particularly 68% or less.

[0017] Al2O3 is a component that forms the glass skeleton, is a component that increases the strain point, and is a component that suppresses phase separation. Therefore, the content of Al2O3 is preferably 6% or more, 8% or more, 10% or more, particularly 12% or more. On the other hand, if the content of Al2O3 is too high, the high-temperature viscosity increases and the meltability tends to decrease. Therefore, the content of Al2O3 is preferably 20% or less, 18% or less, 16% or less, particularly 14% or less.

[0018] B2O3 is an optional component but is a component that significantly enhances meltability. Therefore, the content of B2O3 is preferably 0% or more, 0.01% or more, 0.1% or more, 0.2% or more, 0.3% or more, 0.4% or more, particularly 0.5% or more. On the other hand, if the content of B2O3 is too high, the strain point will significantly decrease or the β-OH value will significantly increase. Although details will be described later, when the β-OH value increases, the thermal shrinkage in the temperature range below the strain point becomes larger. Therefore, the content of B2O3 is preferably 9% or less, 7% or less, 5% or less, particularly 4% or less.

[0019] The molar ratio of SiO2 / B2O3 is preferably 50 or less, 40 or less, 30 or less, 25 or less, particularly preferably 20 or less. If the molar ratio of SiO2 / B2O3 is too large, it becomes difficult to achieve both a high strain point and high meltability. Note that "SiO2 / B2O3" refers to the value obtained by dividing the content of SiO2 by the content of B2O3.

[0020] MgO is a component that lowers the high-temperature viscosity and enhances meltability, and is also a component that enhances devitrification resistance depending on the balance with other components. Furthermore, from the perspective of mechanical properties, it is a component that significantly increases the Young's modulus. Therefore, the content of MgO is preferably 1% or more, 3% or more, 5% or more, 6% or more, particularly 7% or more. On the other hand, if the content of MgO is too high, the strain point is likely to decrease or the balance with other components is disrupted, resulting in a strong devitrification tendency. Therefore, the content of MgO is preferably 15% or less, 13% or less, 10% or less, particularly 8% or less.

[0021] CaO is a component that lowers the high-temperature viscosity and enhances meltability, and is also a component that enhances devitrification resistance depending on the balance with other components. Therefore, the content of CaO is preferably 1% or more, 3% or more, particularly 5% or more. On the other hand, if the content of CaO is too high, the strain point is likely to decrease. Therefore, the content of CaO is preferably 15% or less, 13% or less, 10% or less, 8% or less, particularly 7% or less.

[0022] SrO is a component that reduces high-temperature viscosity and increases fusibility, and also a component that enhances devitrification resistance through balance with other components. Therefore, the content of SrO is preferably 0% or more, 0.5% or more, 1% or more, particularly 1.5% or more. On the other hand, if the content of SrO is too high, the strain point tends to decrease. Therefore, the content of SrO is preferably 7% or less, 5% or less, 3% or less, particularly 2% or less.

[0023] BaO is a component that reduces high-temperature viscosity and increases fusibility, and also a component that enhances devitrification resistance through balance with other components. Therefore, the content of BaO is preferably 0% or more, 0.5% or more, 1% or more, particularly 1.5% or more. On the other hand, if the content of BaO is too high, the strain point tends to decrease. Therefore, the content of BaO is preferably 8% or less, 6% or less, 4% or less, 3% or less, particularly 2% or less.

[0024] The total content of SrO and BaO is preferably 0% or more, 0.5% or more, 1% or more, 1.2% or more, 1.4% or more, particularly 1.6% or more. If the total content of SrO and BaO is too small, the fusibility tends to decrease. On the other hand, if the total content of SrO and BaO is too high, the component balance of the glass composition is impaired and the devitrification resistance tends to decrease. Therefore, the total content of SrO and BaO is preferably 6% or less, 4% or less, 3% or less, 2.5% or less, 2.2% or less, particularly 2% or less.

[0025] The molar ratio B2O3 / BaO is preferably 1 or more, 2 or more, 5 or more, 8 or more, particularly 10 or more. If the molar ratio B2O3 / BaO is too small, in the glass system according to the present application, the balance of the glass components is disrupted and the devitrification resistance tends to decrease. Note that "B2O3 / BaO" refers to the value obtained by dividing the content of B2O3 by the content of BaO.

[0026] The molar ratio BaO / (SrO + BaO) is preferably 1 or less, 0.8 or less, 0.6 or less, 0.4 or less, particularly 0.2 or less. If the molar ratio BaO / (SrO + BaO) is too large, in the glass system according to the present application, the balance of the glass components is disrupted, and the devitrification resistance tends to decrease. Note that "BaO / (SrO + BaO)" refers to the value obtained by dividing the content of BaO by the total content of SrO and BaO.

[0027] The molar ratio (SiO2 + Al2O3 + B2O3) / (SrO + BaO) is preferably 10 or more, 15 or more, 20 or more, 25 or more, particularly 30 or more. If the molar ratio (SiO2 + Al2O3 + B2O3) / (SrO + BaO) is too small, it becomes difficult to achieve both a high strain point and a high Young's modulus. Note that "(SiO2 + Al2O3 + B2O3) / (SrO + BaO)" refers to the value obtained by dividing the total content of SiO2, Al2O3, and B2O3 by the total content of SrO and BaO.

[0028] If (CaO + SrO + BaO) - (Al2O3 + B2O3) is too large, the non-bridging oxygen in the glass increases, and the thermal shrinkage rate becomes large. Therefore, (CaO + SrO + BaO) - (Al2O3 + B2O3) is preferably 5% or less, 3% or less, 1% or less, 0% or less, -1% or less, -3% or less, particularly -4% or less. On the other hand, if (CaO + SrO + BaO) - (Al2O3 + B2O3) is too small, the strain point becomes low, and instead, the thermal shrinkage rate becomes large. Therefore, (CaO + SrO + BaO) - (Al2O3 + B2O3) is preferably -20% or more, -15% or more, -10% or more, -7% or more, particularly -6% or more. Note that "(CaO + SrO + BaO) - (Al2O3 + B2O3)" refers to the value obtained by subtracting the total content of Al2O3 and B2O3 from the total content of CaO, SrO, and BaO.

[0029] Y2O3 is a component that increases the strain point and Young's modulus, but if its content is too large, the density and raw material cost tend to increase. Therefore, the content of Y2O3 is preferably 0 to 0.8%, 0 to 0.7%, 0 to 0.5%, 0 to 0.2%, particularly less than 0 to 0.1%.

[0030] La2O3 is a component that increases the strain point and Young's modulus. However, if its content is too high, the density and raw material cost tend to increase. Therefore, the content of La2O3 is preferably 0 to 0.8%, 0 to 0.7%, 0 to 0.5%, 0 to 0.2%, particularly less than 0 to 0.1%.

[0031] The total content of Y2O3 and La2O3 is preferably less than 0 to 1.0%, 0 to 0.8%, 0 to 0.7%, 0 to 0.5%, 0 to 0.2%, particularly less than 0 to 0.1%. However, if the total content of Y2O3 and La2O3 is too high, the density and raw material cost tend to increase.

[0032] In addition to the above components, the alkali-free glass sheet of the present invention may also contain the following components in the glass composition.

[0033] ZnO is a component that enhances the meltability. However, if a large amount of ZnO is contained, the glass is likely to devitrify and the strain point is likely to decrease. The content of ZnO is preferably 0 to 5%, 0 to 3%, 0 to 0.5%, 0 to 0.3%, particularly 0 to 0.2%.

[0034] P2O5 is a component that significantly reduces the liquidus temperature of Al-based devitrification crystals while maintaining the strain point. However, if a large amount of P2O5 is contained, the Young's modulus decreases and the glass may phase-separate. In addition, there is a concern that P diffuses from the glass and affects the performance of the TFT. Therefore, the content of P2O5 is preferably 0 to 5%, 0 to 3%, 0 to 1%, particularly 0 to 0.5%.

[0035] TiO2 is a component that lowers the high-temperature viscosity and enhances the meltability, and is also a component that suppresses solarization. However, if a large amount of TiO2 is contained, the glass is colored and the transmittance is likely to decrease. Therefore, the content of TiO2 is preferably 0 to 3%, 0 to 1%, 0 to 0.1%, particularly 0 to 0.02%.

[0036] SnO₂ is a component that has a good clarification effect in the high-temperature range, increases the strain point, and also reduces the high-temperature viscosity. The content of SnO₂ is preferably 0 to 1%, 0.001 to 1%, 0.05 to 0.5%, particularly 0.08 to 0.2%. If the content of SnO₂ is too high, devitrification crystals of SnO₂ are likely to precipitate. In addition, if the content of SnO₂ is less than 0.001%, it becomes difficult to enjoy the above effects.

[0037] SnO₂ is suitable as a fining agent, but other fining agents may be used as long as they do not significantly impair the glass properties. Specifically, As₂O₃, Sb₂O₃, CeO₂, F₂, Cl₂, SO₃, and C may be added in a total amount of, for example, up to 0.5%, and metal powders such as Al and Si may be added in a total amount of, for example, up to 0.5%.

[0038] As₂O₃ and Sb₂O₃ are excellent in fining properties, but from an environmental perspective, it is preferably not introduced as much as possible. Furthermore, when a large amount of As₂O₃ is contained in the glass, the solarization resistance tends to decrease, so its content is preferably 0.5% or less, particularly 0.1% or less, and it is desirable not to substantially contain it. Here, "substantially free of As₂O₃" refers to the case where the content of As₂O₃ in the glass composition is less than 0.05%. Also, the content of Sb₂O₃ is preferably 1% or less, particularly 0.5% or less, and it is desirable not to substantially contain it. Here, "substantially free of Sb₂O₃" refers to the case where the content of Sb₂O₃ in the glass composition is less than 0.05%.

[0039] Cl has the effect of promoting the melting of non-alkali glass. If Cl is added, the melting temperature can be lowered, the action of the fining agent can be promoted, and as a result, the melting cost can be reduced while achieving a longer life of the glass manufacturing furnace. However, if the content of Cl is too high, the strain point is likely to decrease. Therefore, the content of Cl is preferably 0.5% or less, particularly 0.1% or less. As a raw material for introducing Cl, chlorides of alkaline earth metal oxides such as strontium chloride, or aluminum chloride, etc. can be used.

[0040] The alkali-free glass sheet of the present invention preferably has the following characteristics.

[0041] The coefficient of thermal expansion is preferably 30×10 -7 ~45×10 -7 / °C, 30×10 -7 ~42×10 -7 / °C, 30×10 -7 ~40×10 -7 / °C, 30×10 -7 ~38×10 -7 / °C, particularly 30×10 -7 ~36×10 -7 / °C. If the coefficient of thermal expansion is too high, local dimensional changes are likely to occur in the glass sheet due to temperature unevenness in the high-temperature film-forming process.

[0042] The density is preferably 2.80 g / cm 3 or less, 2.75 g / cm 3 or less, 2.70 g / cm 3 or less, 2.65 g / cm 3 or less, 2.60 g / cm 3 or less, 2.55 g / cm 3 or less, particularly 2.45 - 2.50 g / cm 3 If the density is too high, the amount of deflection of the glass sheet increases, making it easier to promote pattern deviation caused by stress in the manufacturing process of displays and the like.

[0043] The strain point is preferably 650°C or higher, 680°C or higher, 700°C or higher, 710°C or higher, 720°C or higher, 730°C or higher, particularly 740°C or higher. If the strain point is too low, the glass sheet is likely to thermally contract in the high-temperature film-forming process.

[0044] The annealing point is preferably 720°C or higher, 750°C or higher, 780°C or higher, particularly 800°C or higher. If the annealing point is too low, the glass sheet is likely to thermally contract in the high-temperature film-forming process.

[0045] The softening point is preferably 940 °C or higher, 960 °C or higher, 980 °C or higher, particularly 1000 °C or higher. If the softening point is too low, the glass plate is likely to thermally contract in the high-temperature film-forming process.

[0046] The temperature at a high-temperature viscosity of 10 2.5 dPa·s is preferably 1656 °C or lower, 1620 °C or lower, 1600 °C or lower, 1590 °C or lower, 1580 °C or lower, particularly 1570 °C or lower. When the temperature at 10 2.5 dPa·s becomes higher, the meltability and clarity are likely to decrease, and the manufacturing cost of the glass plate increases.

[0047] The Young's modulus is preferably 76 GPa or higher, 78 GPa or higher, 79 GPa or higher, 80 GPa or higher, 81 GPa or higher, 82 GPa or higher, particularly 83 GPa or higher. If the Young's modulus is too low, the amount of deflection of the glass plate increases, so in the manufacturing process of the display, etc., pattern misalignment due to stress is likely to be promoted.

[0048] The specific Young's modulus is preferably 29 GPa / g·cm -3 or higher, 30 GPa / g·cm -3 or higher, 31 GPa / g·cm -3 or higher, 32 GPa / g·cm -3 or higher, particularly 33 GPa / g·cm -3 or higher. If the specific Young's modulus is too low, the amount of deflection of the glass plate is likely to increase, so in the manufacturing process of the display, etc., pattern misalignment due to stress is likely to be promoted.

[0049] The liquidus temperature is preferably 1450 °C or lower, 1300 °C or lower, 1200 °C or lower, particularly 1150 °C or lower. In this way, devitrification crystals are less likely to occur during forming. Furthermore, since it becomes easier to form by the overflow down-draw method, it becomes easier to improve the surface quality of the glass plate and the manufacturing cost of the glass plate can be reduced. Note that the "liquidus temperature" is the temperature at which crystals precipitate after putting glass powder that passes through a standard sieve of 30 mesh (500 μm) and remains on a 50 mesh (300 μm) sieve into a platinum boat and holding it in a temperature gradient furnace for 24 hours.

[0050] The liquid-phase viscosity is preferably 10 4.6 dPa·s or more, 10 5.0 dPa·s or more, 10 5.2 dPa·s or more, particularly 10 5.5 dPa·s or more. By doing so, devitrification is less likely to occur during forming, making it easier to form by the overflow down-draw method. As a result, it becomes possible to improve the surface quality of the glass sheet and also reduce the manufacturing cost of the glass sheet. Note that the "liquid-phase viscosity" refers to the viscosity of the glass at the liquid-phase temperature and can be measured by the platinum ball pulling-up method.

[0051] The β-OH value is an index indicating the moisture content in the glass. When the β-OH value is lowered, the strain point can be increased. Also, even when the glass composition is the same, the smaller the β-OH value, the smaller the thermal shrinkage in the temperature range below the strain point. The β-OH value is preferably 0.30 / mm or less, 0.25 / mm or less, 0.20 / mm or less, 0.15 / mm or less, particularly 0.10 / mm or less. Note that if the β-OH value is too small, the meltability tends to decrease. Therefore, the β-OH value is preferably 0.01 / mm or more, particularly 0.03 / mm or more. Here, the "β-OH value" refers to the value obtained by measuring the transmittance of the glass using FT-IR and using the following formula 1. [Equation 1] β-OH value = (1 / X)log(T1 / T2) X: Plate thickness (mm) T1: Transmittance (%) at a reference wavelength of 3846 cm -1 T2: Minimum transmittance (%) near the hydroxyl absorption wavelength of 3600 cm -1 ​​The alkali-free glass sheet of the present invention preferably has an overflow confluence surface at the central portion in the plate thickness direction. That is, it is preferably formed by the overflow down-draw method. The overflow down-draw method is a method in which molten glass overflows from both sides of a wedge-shaped refractory, and the overflowed molten glass is made to converge at the lower end of the wedge while being drawn downward to form a flat plate shape. In the overflow down-draw method, the surface that should become the surface of the glass sheet does not contact the refractory and is formed in a free surface state. For this reason, a glass sheet with good surface quality can be manufactured inexpensively without polishing. Furthermore, it is easy to increase the area and reduce the thickness.

[0052] In addition to the overflow down-draw method, for example, it is also possible to form by the slot down method, the redraw method, the float method, or the roll out method.

[0053] In the alkali-free glass sheet of the present invention, the plate thickness is not particularly limited, but is preferably 1.0 mm or less, 0.7 mm or less, 0.5 mm or less, particularly 0.05 to 0.4 mm. The smaller the plate thickness, the easier it is to reduce the weight of the liquid crystal panel or the organic EL panel. The plate thickness can be adjusted by the flow rate during glass production, the forming speed (sheet drawing speed), etc.

[0054] As a method for industrially manufacturing the alkali-free glass sheet of the present invention, a melting step of obtaining molten glass by charging a glass batch prepared in the above glass composition into a melting furnace and performing energization heating by a heating electrode, and a forming step of forming the obtained molten glass into an alkali-free glass sheet by the overflow down-draw method are preferably included.

[0055] The manufacturing process of a glass plate generally includes a melting process, a fining process, a feeding process, a stirring process, and a forming process. The melting process is a process of melting a glass batch prepared from glass raw materials to obtain molten glass. The fining process is a process of fining the molten glass obtained in the melting process by the action of a fining agent or the like. The feeding process is a process of transferring the molten glass between the processes. The stirring process is a process of stirring and homogenizing the molten glass. The forming process is a process of forming the molten glass into a glass plate. In addition, if necessary, a process other than the above, for example, a state adjustment process of adjusting the molten glass to a state suitable for forming, may be incorporated after the stirring process.

[0056] When industrially manufacturing a non-alkali glass plate, it is generally melted by heating with the combustion flame of a burner. The burner is usually arranged above the melting furnace, and fossil fuels such as liquid fuels like heavy oil or gaseous fuels like LPG are used as fuels. The combustion flame can be obtained by mixing fossil fuel and oxygen gas. However, in this method, a large amount of moisture is mixed into the molten glass during melting, so the β-OH value tends to increase. Therefore, when manufacturing a non-alkali glass plate, it is preferable to perform electric heating by heating electrodes, and it is preferable to melt by electric heating with heating electrodes without performing heating by the combustion flame of the burner, that is, complete electric melting. Thereby, it becomes difficult for moisture to be mixed into the molten glass during melting, so it becomes easier to regulate the β-OH value to 0.30 / mm or less, 0.25 / mm or less, 0.20 / mm or less, 0.15 / mm or less, particularly 0.10 / mm or less. Furthermore, when performing electric heating by heating electrodes, the energy amount per mass for obtaining the molten glass decreases and the molten volatiles decrease, so the environmental load can be reduced.

[0057] Furthermore, regarding this electric current heating, the lower the moisture content in the glass batch, the easier it is to reduce the β-OH value in the glass sheet. And the raw material for introducing B2O3 is likely to be the largest source of moisture contamination. Therefore, from the perspective of manufacturing an alkali-free glass sheet with a low β-OH value, it is preferable to minimize the content of B2O3. Also, the lower the moisture content in the glass batch, the easier it is for the glass batch to spread uniformly in the melting furnace, thus making it easier to manufacture a homogeneous and high-quality glass sheet.

[0058] The electric current heating by the heating electrode is preferably performed by applying an alternating voltage to the heating electrode provided at the bottom or side of the melting furnace so as to contact the molten glass in the melting furnace. The material used for the heating electrode is preferably one having heat resistance and corrosion resistance against the molten glass. For example, tin oxide, molybdenum, platinum, rhodium, etc. can be used, and particularly from the perspective of the freedom of installation in the furnace, molybdenum is preferable.

Examples

[0059] Hereinafter, the present invention will be described based on examples. However, the following examples are merely illustrative. The present invention is not limited to the following examples at all.

[0060] Tables 1 to 28 show the examples (Sample Nos. 1 to 391) of the present invention.

[0061]

Table 1

[0062]

Table 2

[0063]

Table 3

[0064]

Table 4

[0065]

Table 5

[0066]

Table 6

[0067]

Table 7

[0068]

Table 8

[0069]

Table 9

[0070]

Table 10

[0071]

Table 11

[0072]

Table 12

[0073]

Table 13

[0074]

Table 14

[0075]

Table 15

[0076]

Table 16

[0077]

Table 17

[0078]

Table 18

[0079]

Table 19

[0080]

Table 20

[0081]

Table 21

[0082]

Table 22

[0083]

Table 23

[0084]

Table 24

[0085]

Table 25

[0086]

Table 26

[0087]

Table 27

[0088]

Table 28

[0089] The coefficient of thermal expansion is the value measured with a dilatometer for the average coefficient of thermal expansion in the temperature range of 30 - 380 °C.

[0090] The density is the value measured by the well-known Archimedes' method.

[0091] The strain point, annealing point, and softening point are the values measured based on the methods of ASTM C336 and C338.

[0092] The temperature at a high-temperature viscosity of 10 4.0 dPa·s, 10 3.0 dPa·s, 10 2.5 dPa·s is the value measured by the platinum ball pulling-up method.

[0093] The Young's modulus is the value measured by the bending resonance method.

[0094] The specific Young's modulus is the value obtained by dividing the Young's modulus by the density.

[0095] As is clear from the table, Samples No. 1 to 391 did not contain Y2O3 and La2O3 in the glass composition and had a strain point of 650°C or higher. Therefore, Samples No. 1 to 391 are considered to be suitable for a carrier glass that holds a substrate for forming a TFT circuit or a resin substrate for forming a TFT circuit in flat panel displays such as liquid crystal displays and organic EL displays.

Claims

1. As a glass composition, in mol%, SiO ２ 60 to 74%, Al ２ O ３ 11.6 to 20%, B ２ O ３ 0.01 to 9%, MgO 7.3 to 13%, CaO 1 to 13%, SrO 0.1 to 4.9%, BaO 0.5 to 4.9%, SrO + BaO 0.6 to 4.9%, Y ２ O ３ + La ２ O ３ containing 0 to less than 1.0% and substantially free of alkali metal oxides, (CaO + SrO + BaO) - (Al ２ O ３ + B ２ O ３ ) being -4.5% or more, and the strain point being 650°C or more, characterized by an alkali-free glass sheet.

2. The alkali-free glass sheet according to claim 1, characterized in that the content of SrO + BaO is 0.6 to 3 mol%.

3. The alkali-free glass sheet according to claim 1 or 2, characterized in that the Young's modulus is 79 GPa or more.

4. The coefficient of thermal expansion is 30×10 －７ to 45×10 －７ / °C, and the alkali-free glass sheet according to any one of claims 1 to 3, characterized in that it is such.

5. High-temperature viscosity 10 ２．５ The alkali-free glass sheet according to any one of claims 1 to 4, characterized in that the temperature at dPa·s is 1600°C or lower.

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