alkali-free glass plate

Abstract

The alkali-free glass plate of the present invention is characterized by containing, in mol% as a glass composition, SiO2 60~74%, Al2O3 6~20%, B2O3 0~9%, MgO 1~13%, CaO 1~13%, SrO 0~7%, BaO 0~8%, and Y2O3+La2O3 0~1.0%, substantially not containing alkali metal oxides, and having a deformation point of 650°C or higher.

Description

Technology Field

[0001] The present invention relates to an alkali-free glass plate, and in particular to an alkali-free glass plate suitable for a substrate for forming a TFT circuit or a carrier glass for holding 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 Technology

[0002] Liquid crystal panels or organic EL panels are equipped with thin-film transistors (TFTs) for driving control, as is well known.

[0003] Amorphous silicon, low-temperature polysilicon, and high-temperature polysilicon are known thin-film transistors used to drive displays. Recently, with the proliferation of large liquid crystal displays, smartphones, and tablet PCs, the need for higher resolution displays has increased. Low-temperature polysilicon TFTs can meet this need, but they undergo a high-temperature deposition process of 500 to 600°C. However, conventional glass plates experience significant thermal shrinkage before and after the high-temperature deposition process, which causes pattern misalignment in thin-film transistors. Therefore, glass plates with low thermal shrinkage are required for high-resolution displays. Recently, further miniaturization of displays is being considered, and in such cases, it is necessary to make the glass plates even lower in thermal shrinkage. Prior art literature

[0004] Japanese Patent Publication No. 5769617 The problem to be solved

[0005] There are mainly two methods for reducing the thermal shrinkage of glass plates. The first method is to maintain the glass plate at a temperature near the heat treatment temperature of the film deposition process and then slow-cool it. With this method, the amount of thermal shrinkage during the subsequent high-temperature film deposition process can be suppressed because the glass undergoes structural relaxation and shrinkage during slow cooling. However, this method leads to an increase in the number of manufacturing processes and manufacturing time, which results in higher manufacturing costs for the glass plates.

[0006] The second method involves increasing the deformation point of the glass plate. The overflow downdraw method generally involves cooling from the melting temperature to the forming temperature in a relatively short time. As a result, the virtual temperature of the glass plate increases, and the thermal shrinkage of the glass plate increases. Therefore, increasing the deformation point of the glass plate increases the viscosity of the glass plate at the heat treatment temperature of the film deposition process, making it difficult for structural relaxation to proceed. Consequently, the thermal shrinkage of the glass plate can be suppressed. Furthermore, the higher the heat treatment temperature of the film deposition process, the greater the effect of high deformation point on reducing thermal shrinkage. Therefore, in the case of low-temperature polysilicon TFTs, it is desirable to make the glass plate as high a deformation point as possible.

[0007] For example, Patent Document 1 discloses reducing the content of B2O3 in the glass composition to increase the deformation of the glass plate. Additionally, Patent Document 1 discloses introducing Y2O3 and / or La2O3 into the glass composition to avoid the decrease in permeability that occurs with a low amount of B2O3. However, since Y2O3 and La2O3 are rare earth elements, the raw material costs are high, which increases the manufacturing cost of the glass plate.

[0008] The present invention has been made in consideration of the above circumstances, and its technical objective is to provide an alkali-free glass plate that has a high deformation point and can reduce manufacturing costs. means of solving the problem

[0009] As a result of careful examination, the inventors have discovered that the above technical problem can be solved by strictly regulating the content of each component and regulating the deformation point to a value greater than or equal to a predetermined value, and thus propose this invention. That is, the alkali-free glass plate of the present invention is characterized by containing, in mol% as a glass composition, SiO2 60~74%, Al2O3 6~20%, B2O3 0~9%, MgO 1~13%, CaO 1~13%, SrO 0~7%, BaO 0~8%, and Y2O3+La2O3 0~1.0%, substantially not containing alkali metal oxides, and having a deformation point of 650°C or higher. Here, "Y2O3+La2O3" refers to the sum of Y2O3 and La2O3. "Substantially not containing alkali metal oxides" refers to the 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%). "Strain point" refers to a value measured according to the method of ASTM C336.

[0010] In addition, the alkali-free glass plate of the present invention preferably has a SrO+BaO content of 0 to 3 mol%. Here, "SrO+BaO" refers to the total amount of SrO and BaO.

[0011] In addition, it is preferable that the alkali-free glass plate of the present invention has a deformation point of 700°C or higher.

[0012] In addition, the alkali-free glass plate of the present invention preferably has a Young's modulus of 79 GPa or higher. Here, "Young's modulus" can be measured by the bending resonance method.

[0013] In addition, the alkali-free glass plate of the present invention has a coefficient of thermal expansion of 30×10 -7 ~45×10 -7 It is desirable that the value be / ℃. By doing so, localized dimensional changes in the glass plate caused by temperature non-uniformity during the high-temperature film deposition process can be suppressed.

[0014] In addition, the alkali-free glass plate of the present invention has a high-temperature viscosity of 102.5 It is desirable that the temperature at dPa·s be 1600℃ or lower. This allows for lowering melting costs. Specific details for implementing the invention

[0015] The alkali-free glass plate of the present invention is characterized by containing, in mol% as a glass composition, SiO2 60~74%, Al2O3 6~20%, B2O3 0~9%, MgO 1~13%, CaO 1~13%, SrO 0~7%, BaO 0~8%, and Y2O3+La2O3 0~1.0% or less, and substantially not containing alkali metal oxides. The reasons for limiting the content of each component as described above are shown below. Furthermore, unless otherwise specifically stated in the description of the content of each component, % indicates mol%.

[0016] SiO2 is a component that forms a glass framework and increases the deformation point. Therefore, the SiO2 content is preferably 60% or more, 62% or more, 64% or more, and particularly 66% or more. On the other hand, if the SiO2 content is excessively high, the high-temperature viscosity increases, making it prone to reduced meltability. Therefore, the SiO2 content is preferably 74% or less, 72% or less, 70% or less, and particularly 68% or less.

[0017] Al2O3 is a component that forms a glass framework, raises the deformation point, and suppresses powdering. Therefore, the content of Al2O3 is preferably 6% or more, 8% or more, 10% or more, and particularly 12% or more. On the other hand, if the content of Al2O3 is excessively high, the high-temperature viscosity increases, making it prone to reduced meltability. Therefore, the content of Al2O3 is preferably 20% or less, 18% or less, 16% or less, and particularly 14% or less.

[0018] B2O3 is an optional component that significantly increases 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, and particularly 0.5% or more. On the other hand, if the content of B2O3 is excessively high, the deformation point is significantly lowered or the β-OH value is significantly increased. As will be described in detail later, if the β-OH value increases, thermal shrinkage in the temperature range below the deformation point increases. Therefore, the content of B2O3 is preferably 9% or less, 7% or less, 5% or less, and particularly 4% or less.

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

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

[0021] CaO is a component that lowers high-temperature viscosity and increases meltability, and also a component that increases permeability through balance with other components. Therefore, the CaO content is preferably 1% or more, 3% or more, and particularly 5% or more. On the other hand, if the CaO content is excessively high, the deformation point is prone to lowering. Therefore, the CaO content is preferably 15% or less, 13% or less, 10% or less, 8% or less, and particularly 7% or less.

[0022] SrO is a component that lowers high-temperature viscosity and increases meltability, and also a component that increases air permeability through balance with other components. Therefore, the SrO content is preferably 0% or more, 0.5% or more, 1% or more, and particularly 1.5% or more. On the other hand, if the SrO content is excessively high, the deformation point is prone to lowering. Therefore, the SrO content is preferably 7% or less, 5% or less, 3% or less, and particularly 2% or less.

[0023] BaO is a component that lowers high-temperature viscosity and increases meltability, and also a component that increases permeability through balance with other components. Therefore, the BaO content is preferably 0% or more, 0.5% or more, 1% or more, and particularly 1.5% or more. On the other hand, if the BaO content is excessively high, the deformation point is prone to lowering. Therefore, the BaO content is preferably 8% or less, 6% or less, 4% or less, 3% or less, and particularly 2% or less.

[0024] The total amount of SrO and BaO is preferably 0% or more, 0.5% or more, 1% or more, 1.2% or more, 1.4% or more, and particularly 1.6% or more. If the total amount of SrO and BaO is excessively low, meltability is prone to deterioration. On the other hand, if the total amount of SrO and BaO is excessively high, the component balance of the glass composition is damaged, and the internal permeability is prone to deterioration. Therefore, the total amount of SrO and BaO is preferably 6% or less, 4% or less, 3% or less, 2.5% or less, 2.2% or less, and particularly 2% or less.

[0025] The molar ratio B2O3 / BaO is preferably 1 or more, 2 or more, 5 or more, 8 or more, and particularly 10 or more. If the molar ratio B2O3 / BaO is excessively small, the balance of glass components in the glass system according to the present invention is disrupted, and the internal permeability is prone to deterioration. In addition, "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, and particularly 0.2 or less. If the molar ratio BaO / (SrO+BaO) is excessively large, the balance of glass components in the glass system according to the present invention is disrupted, making it easy for internal permeability to decrease. In addition, “BaO / (SrO+BaO)” refers to the value obtained by dividing the BaO content by the sum 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, and particularly 30 or more. If the molar ratio (SiO2+Al2O3+B2O3) / (SrO+BaO) is excessively small, it becomes difficult to achieve both a high deformation point and a high Young's modulus. In addition, "(SiO2+Al2O3+B2O3) / (SrO+BaO)" refers to the value obtained by dividing the total amount of SiO2, Al2O3, and B2O3 by the total amount of SrO and BaO.

[0028] If (CaO+SrO+BaO)-(Al2O3+B2O3) is excessively high, the amount of non-crosslinked oxygen in the glass increases, and the thermal shrinkage rate increases. 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, and particularly -4% or less. On the other hand, if (CaO+SrO+BaO)-(Al2O3+B2O3) is excessively low, the deformation point is lowered, and conversely, the thermal shrinkage rate increases. Therefore, (CaO+SrO+BaO)-(Al2O3+B2O3) is preferably -20% or more, -15% or more, -10% or more, -7% or more, and particularly -6% or more. Also, “(CaO+SrO+BaO)-(Al2O3+B2O3)” refers to the value obtained by subtracting the sum of Al2O3 and B2O3 from the sum of CaO, SrO, and BaO.

[0029] Y2O3 is a component that increases the deformation point and Young's modulus, but if its content is excessively high, it tends to increase density and raw material costs. Therefore, the content of Y2O3 is preferably 0~0.8%, 0~0.7%, 0~0.5%, 0~0.2%, and particularly less than 0~0.1%.

[0030] La2O3 is a component that increases the deformation point and Young's modulus, but if its content is excessively high, it tends to increase density and raw material costs. Therefore, the content of La2O3 is preferably 0~0.8%, 0~0.7%, 0~0.5%, 0~0.2%, and particularly less than 0~0.1%.

[0031] The combined amount of Y2O3 and La2O3 is preferably less than 0~1.0%, 0~0.8%, 0~0.7%, 0~0.5%, 0~0.2%, and particularly less than 0~0.1%. However, if the combined amount of Y2O3 and La2O3 is excessively high, the density and raw material costs are likely to increase.

[0032] The alkali-free glass plate of the present invention may include the following components in addition to the above components in the glass composition.

[0033] ZnO is a component that increases meltability, but if a large amount of ZnO is included, the glass becomes prone to devitrification and also prone to lowering the deformation point. The content of ZnO is preferably 0~5%, 0~3%, 0~0.5%, 0~0.3%, and particularly 0~0.2%.

[0034] P2O5 is a component that significantly lowers the liquid phase temperature of Al-based devitrified crystals while maintaining the deformation point, but if P2O5 is contained in large amounts, the Young's modulus decreases or the glass becomes pulverized. In addition, there is a concern that P may diffuse from the glass and affect the performance of the TFT. Therefore, the content of P2O5 is preferably 0~5%, 0~3%, 0~1%, and particularly 0~0.5%.

[0035] TiO2 is a component that lowers high-temperature viscosity and increases meltability, as well as a component that suppresses solarization; however, if a large amount of TiO2 is contained, the glass becomes colored and the transmittance is prone to decreasing. Therefore, the content of TiO2 is preferably 0~3%, 0~1%, 0~0.1%, and particularly 0~0.02%.

[0036] SnO2 is a component that exhibits good clarification activity in the high-temperature range, as well as a component that raises the deformation point and also lowers high-temperature viscosity. The content of SnO2 is preferably 0 to 1%, 0.001 to 1%, 0.05 to 0.5%, and particularly 0.08 to 0.2%. If the content of SnO2 is excessively high, devitrified crystals of SnO2 are prone to precipitating. Furthermore, if the content of SnO2 is less than 0.001%, it becomes difficult to enjoy the above effects.

[0037] SnO2 is suitable as a clarifying agent, but clarifying agents other than SnO2 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 total amount, for example, up to 0.5%, and metal powders such as Al and Si may be added in total amount, for example, up to 0.5%.

[0038] Although As2O3 and Sb2O3 have excellent clarity properties, it is desirable to avoid introducing them as much as possible from an environmental perspective. In addition, since the solarization resistance of As2O3 tends to decrease when contained in large amounts in the glass, its content is preferably 0.5% or less, particularly 0.1% or less, and it is desirable not to contain it substantially at all. Here, "substantially not containing As2O3" refers to the case where the content of As2O3 in the glass composition is less than 0.05%. In addition, the content of Sb2O3 is preferably 1% or less, particularly 0.5% or less, and it is desirable not to contain it substantially at all. Here, "substantially not containing 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 alkali-free glass. Adding Cl can lower the melting temperature and promote the action of the clarifying agent, thereby enabling the longevity of the glass manufacturing furnace while reducing melting costs. However, if the Cl content is excessively high, the deformation point is prone to lowering. Therefore, the Cl content is preferably 0.5% or less, particularly 0.1% or less. In addition, chlorides of alkaline earth metal oxides such as strontium chloride, or aluminum chloride, can be used as raw materials for introducing Cl.

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

[0041] The coefficient of thermal expansion is preferably 30×10 -7 ~45×10 -7 / ℃, 30×10 -7 ~42×10 -7 / ℃, 30×10 -7 ~40×10 -7 / ℃, 30×10 -7 ~38×10 -7 / ℃, especially 30×10 -7 ~36×10 -7It is / ℃. If the coefficient of thermal expansion is excessively high, localized dimensional changes in the glass plate are prone to occur due to temperature non-uniformity during the high-temperature film deposition process.

[0042] The density is preferably 2.80 g / cm³ or less, 2.75 g / cm³ or less, 2.70 g / cm³ or less, 2.65 g / cm³ or less, 2.60 g / cm³ or less, 2.55 g / cm³ or less, and particularly 2.45 to 2.50 g / cm³. If the density is excessively high, the amount of bending of the glass plate increases, making it easy to promote pattern misalignment caused by stress during the manufacturing process of a display, etc.

[0043] The deformation 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, and particularly 740°C or higher. If the deformation point is excessively low, the glass plate is prone to thermal shrinkage during the high-temperature film deposition process.

[0044] The slow cooling point is preferably 720°C or higher, 750°C or higher, 780°C or higher, and particularly 800°C or higher. If the slow cooling point is excessively low, the glass plate is prone to thermal shrinkage during the high-temperature film formation process.

[0045] The softening point is preferably 940°C or higher, 960°C or higher, 980°C or higher, and particularly 1000°C or higher. If the softening point is excessively low, the glass plate is prone to thermal shrinkage during the high-temperature film formation process.

[0046] High temperature viscosity 10 2.5 The temperature in dPa·s is preferably 1656°C or lower, 1620°C or lower, 1600°C or lower, 1590°C or lower, 1580°C or lower, and particularly 1570°C or lower. 10 2.5 As the temperature in dPa·s increases, meltability and clarity tend 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, and particularly 83 GPa or higher. If the Young's modulus is excessively low, the amount of bending of the glass plate increases, making it easy to promote stress-induced pattern misalignment in the manufacturing process of a display, etc.

[0048] The specific Young's modulus is preferably 29 GPa / g·cm -3 Above, 30 GPa / g·cm -3 Above, 31 GPa / g·cm -3 Above, 32 GPa / g·cm -3 Above, particularly 33 GPa / g·cm -3 That is all. If the specific modulus is excessively low, the amount of bending of the glass plate tends to increase, which makes it easy to promote stress-induced pattern misalignment in the manufacturing process of displays, etc.

[0049] The liquid phase temperature is preferably 1450°C or lower, 1300°C or lower, 1200°C or lower, and particularly 1150°C or lower. This makes it difficult for devitrification crystals to occur during molding. In addition, since it becomes easier to mold using the overflow downdraw method, it is easier to improve the surface quality of the glass plate and, at the same time, reduce the manufacturing cost of the glass plate. Furthermore, the “liquid phase temperature” is the temperature at which crystals precipitate after glass powder that has passed through a standard 30-mesh (500 μm) sieve and remains on a 50-mesh (300 μm) sieve is placed in a platinum boat and maintained in a temperature gradient for 24 hours.

[0050] The liquid viscosity is preferably 10 4.6 dPa·s or higher, 10 5.0 dPa·s or higher, 10 5.2 dPa·s or higher, especially 10 5.5It is greater than dPa·s. By doing so, devitrification becomes less likely to occur during forming, making it easier to form using the overflow downdraw method; consequently, it is possible to improve the surface quality of the glass plate and also reduce the manufacturing cost of the glass plate. In addition, "liquid viscosity" refers to the viscosity of the glass at the liquid temperature and can be measured by the platinum-ball pull method.

[0051] The β-OH value is an indicator of the moisture content in the glass, and lowering the β-OH value can raise the deformation point. In addition, even if the glass composition is the same, a smaller β-OH value results in less thermal shrinkage in the temperature range below the deformation 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, and particularly 0.10 / mm or less. Furthermore, if the β-OH value is excessively low, meltability tends to decrease. Therefore, the β-OH value is preferably 0.01 / mm or more, and particularly 0.03 / mm or more. Here, "β-OH value" refers to the value obtained by measuring the transmittance of the glass using FT-IR and using the following Equation 1.

[0052] [Number 1]

[0053] β-OH value = (1 / X)log(T1 / T2)

[0054] X: Plate thickness (mm)

[0055] T1: Reference wavelength 3846 cm -1 Transmittance (%) in

[0056] T2: Hydroxyl absorption wavelength 3600 cm -1 Minimum transmittance (%) in the vicinity

[0057] The alkali-free glass plate of the present invention preferably has an overflow joining surface in the center of the plate thickness direction. That is, it is preferable that it be formed by the overflow downdraw method. The overflow downdraw method is a method of forming a flat plate shape by allowing molten glass to overflow from both sides of a wedge-shaped refractory material and forming the overflowed molten glass downward while joining it at the bottom of the wedge. With the overflow downdraw method, the surface of the glass plate does not come into contact with the refractory material and is formed as a free surface. For this reason, a glass plate with good surface quality and no polishing can be manufactured at a low cost. In addition, it is easy to increase the surface area or thin the wall.

[0058] In addition to the overflow downdraw method, it is also possible to form using methods such as the slot-down method, lead-draw method, float method, and roll-out method.

[0059] In the alkali-free glass plate of the present invention, the plate thickness is not particularly limited, but preferably 1.0 mm or less, 0.7 mm or less, 0.5 mm or less, and particularly 0.05 to 0.4 mm. The smaller the plate thickness, the easier it is to lighten the liquid crystal panel or organic EL panel. In addition, the plate thickness can be adjusted by the flow rate or forming speed (plate pulling speed) during glass manufacturing.

[0060] As a method for industrially manufacturing the alkali-free glass plate of the present invention, it is preferable to have a melting process in which a glass batch combined with the glass composition is introduced into a melting furnace and heated by an electric current using a heating electrode to obtain molten glass, and a forming process in which the obtained molten glass is formed into an alkali-free glass plate by an overflow downdraw method.

[0061] The manufacturing process of a glass plate generally includes a melting process, a clarification process, a feeding process, a stirring process, and a forming process. The melting process is a process of obtaining molten glass by melting a glass batch composed of glass raw materials. The clarification process is a process of clarifying the molten glass obtained from the melting process through the action of a clarifying agent or the like. The feeding process is a process of transporting the molten glass between each process. 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, processes other than those mentioned above, such as a state control process for adjusting the molten glass to a state suitable for forming, may be introduced after the stirring process.

[0062] When alkali-free glass plates are manufactured industrially, they are generally melted by heating with a combustion flame from a burner. The burner is typically positioned above the melting furnace, and fossil fuels, specifically liquid fuels such as heavy oil or gaseous fuels such as LPG, are used as fuel. The combustion flame can be obtained by mixing fossil fuels with oxygen gas. However, with this method, a large amount of moisture is incorporated into the molten glass during melting, which tends to increase the β-OH value. Therefore, when manufacturing alkali-free glass plates, it is desirable to perform electric heating using a heating electrode, and it is preferable to melt by electric heating using a heating electrode without heating with a combustion flame from a burner—that is, to achieve complete electric melting. As a result, it becomes difficult for moisture to be incorporated into the molten glass during melting, making it 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, and particularly 0.10 / mm or less. In addition, when electric heating is performed using a heating electrode, the amount of energy per mass required to obtain molten glass is reduced, and since molten volatilities are reduced, the environmental burden can be reduced.

[0063] In addition, regarding this electric heating, the lower the moisture content in the glass batch, the easier it is to reduce the β-OH value in the glass plate. Also, the raw material for introducing B2O3 is prone to becoming the largest source of moisture incorporation. Therefore, from the perspective of manufacturing alkali-free glass plates with low β-OH values, it is desirable to keep the B2O3 content as low as possible. Furthermore, the lower the moisture content in the glass batch, the easier it is for the glass batch to diffuse uniformly within the melting furnace, making it easier to manufacture homogeneous, high-quality glass plates.

[0064] It is preferable to perform electric heating by means of a heating electrode by applying an alternating voltage to a heating electrode formed at the bottom or side of the molten furnace so as to come into contact with the molten glass inside the molten furnace. The material used for the heating electrode is preferably equipped with heat resistance and corrosion resistance to the molten glass, and, for example, tin oxide, molybdenum, platinum, rhodium, etc., may be used, and molybdenum is particularly preferred from the perspective of the degree of freedom of installation inside the furnace.

[0065] (Example)

[0066] The present invention will be explained below based on examples. However, the following examples are merely illustrative. The present invention is not limited in the least to the following examples.

[0067] Tables 1 to 28 show embodiments of the present invention (samples No. 1 to 391).

[0068]

[0069]

[0070]

[0071]

[0072]

[0073]

[0074]

[0075]

[0076]

[0077]

[0078]

[0079]

[0080]

[0081]

[0082]

[0083]

[0084]

[0085]

[0086]

[0087]

[0088]

[0089]

[0090]

[0091]

[0092]

[0093]

[0094]

[0095]

[0096] First, a glass batch prepared by combining glass raw materials to achieve the glass composition shown in the table was placed in a platinum crucible and melted at 1600–1650°C for 24 hours. During the melting of the glass batch, stirring was performed using a platinum stirrer, and homogenization was carried out. Subsequently, the molten glass was poured onto a carbon plate, formed into a plate shape, and then slow-cooled for 30 minutes at a temperature near the slow-cooling point. For each obtained sample, the coefficient of thermal expansion, density, deformation point, slow-cooling point, softening point, and high-temperature viscosity were 10 4.0 Temperature at dPa·s, high temperature viscosity 10 3.0 Temperature at dPa·s, high temperature viscosity 10 2.5 Temperature, Young's modulus, and specific Young's modulus at dPa·s were evaluated. In addition, some glass properties are not actual measured values, but estimated values ​​calculated from past data.

[0097] The coefficient of thermal expansion is the average coefficient of thermal expansion over a temperature range of 30 to 380°C, measured by a dilatometer.

[0098] Density is a value measured by the well-known Archimedes' method.

[0099] The deformation point, slow cooling point, and softening point are values ​​measured according to the ASTM C336 and C338 methods.

[0100] High temperature viscosity 10 4.0 dPa·s, 10 3.0 dPa·s, 10 2.5 The temperature in dPa·s is a value measured by the platinum-ball pull method.

[0101] Young's modulus is a value measured by the bending resonance method.

[0102] Specific Young's modulus is the value obtained by dividing Young's modulus by density.

[0103] As is evident from the table, samples No. 1 to 391 did not contain Y2O3 and La2O3 in their glass composition, and their deformation point was 650°C or higher. Therefore, samples No. 1 to 391 are considered suitable as substrates for forming TFT circuits in flat panel displays such as liquid crystal displays and organic EL displays, or as carrier glasses for holding resin substrates for forming TFT circuits.

Claims

Claim 1 An alkali-free glass plate characterized by containing, in mol% as a glass composition, SiO2 60~74%, Al2O3 6~20%, B2O3 0~2.7%, MgO 6.6~13%, CaO 1~13%, SrO 0~7%, BaO 1~8%, and Y2O3+La2O3 0~1.0%, substantially not containing alkali metal oxides, and having a deformation point of 717°C or higher. Claim 2 An alkali-free glass plate according to claim 1, characterized in that the SrO+BaO content is 1 to 3 mol%. Claim 3 An alkali-free glass plate according to claim 1 or 2, characterized in that the Young's modulus is 79 GPa or higher. Claim 4 In claim 1 or 2, the coefficient of thermal expansion is 30×10 -7 ~45×10 -7 Alkali-free glass plate characterized by being / ℃. Claim 5 In claim 1 or 2, high temperature viscosity 10 2.5 An alkali-free glass plate characterized by a temperature of 1600℃ or less in dPa·s. Claim 6 delete

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