Alkali-free glass plate

Abstract

To provide an alkali-free glass sheet which has a high strain point and enables a reduction in manufacturing cost.SOLUTION: An alkali-free glass sheet has a glass composition including, by mol%, 55-80% of SiO2, 10-25% of Al2O3, 0-4% of B2O3, 0-30% of MgO, 0-25% of CaO, 0-15% of SrO, 0-15% of BaO, 0-5% of ZnO, and 0-1.0% (excluding 1.0%) of Y2O3+La2O3, but is substantially free of alkali metal oxide, while having a strain point of 750°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 use as a substrate for forming a TFT circuit or as a carrier glass for supporting a resin substrate for forming a TFT circuit in flat panel displays such as liquid crystal displays and organic EL displays. [Background technology]

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

[0003] Thin-film transistors that drive displays are known to be made of amorphous silicon, low-temperature polysilicon, high-temperature polysilicon, and other materials. In recent years, the widespread use of large LCD displays, smartphones, tablet PCs, and other devices has led to a growing demand for higher display resolution. Low-temperature polysilicon TFTs can meet this demand, but they require a high-temperature film-forming process at 500 to 600°C. However, conventional glass sheets experience significant thermal shrinkage before and after the high-temperature film-forming process, which can lead to pattern misalignment of thin-film transistors. Therefore, glass sheets with low thermal shrinkage are required to achieve higher display resolution. In recent years, efforts to further increase the resolution of displays have been underway, which necessitates the development of glass sheets with even lower thermal shrinkage. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 5769617 DISCLOSURE OF THE INVENTION [Problem to be solved by the invention]

[0005] There are two main methods for reducing the thermal shrinkage of glass sheets. The first method is to hold the glass sheet at a temperature close to the heat treatment temperature of the film formation process and slowly cool it. With this method, the glass undergoes structural relaxation and shrinkage during the slow cooling process, which can reduce the amount of thermal shrinkage in the subsequent high-temperature film formation process. However, this method increases the number of manufacturing steps and manufacturing time, which increases the manufacturing cost of the glass sheet.

[0006] The second method is to increase the strain point of the glass sheet. In the overflow downdraw method, the glass sheet is generally cooled from the melting temperature to the forming temperature in a relatively short time. This increases the fictive temperature of the glass sheet, resulting in greater thermal shrinkage of the glass sheet. Therefore, if the strain point of the glass sheet is increased, the viscosity of the glass sheet at the heat treatment temperature of the film formation process increases, making it more difficult for structural relaxation to occur. As a result, the thermal shrinkage of the glass sheet can be suppressed. Furthermore, the higher the heat treatment temperature of the film formation process, the greater the effect of increasing the strain point in reducing thermal shrinkage. Therefore, in the case of low-temperature polysilicon TFTs, it is desirable to increase the strain point of the glass sheet as much as possible.

[0007] Patent Document 1 discloses a high strain point glass containing Y2O3 and / or La2O3. However, because Y2O3 and La2O3 are rare earth elements, there is a problem in that the raw material costs are high, which increases the manufacturing costs of glass sheets.

[0008] The present invention has been made in view of the above circumstances, and its technical object is to create an alkali-free glass sheet that has a high strain point and can be produced at low cost. [Means for solving the problem]

[0009] After extensive research, the inventors discovered that the above technical problems can be solved by strictly controlling the content of each component and controlling the strain point to a predetermined value or higher, and have proposed this finding as the present invention. Specifically, the alkali-free glass sheet of the present invention has a glass composition containing, in mole percent, 55-80% SiO, 10-25% AlO, 0-4% BO, 0-30% MgO, 0-25% CaO, 0-15% SrO, 0-15% BaO, 0-5% ZnO, and YO + less than 0.1% LaO, is substantially free of alkali metal oxides, and has a strain point of 750°C or higher. Here, "YO + LaO" refers to the combined amount of YO and LaO. The phrase "substantially free of alkali metal oxides" refers to a glass composition containing less than 0.5 mole percent alkali metal oxides (LiO, NaO, and KO). "Strain point" refers to a value measured based on the method of ASTM C336.

[0010] The alkali-free glass plate of the present invention preferably satisfies the relationship [SiO2] + 14 × [Al2O3] - 15 × [B2O3] + 6 × [MgO] + [CaO] + 14 × [SrO] + 16 × [BaO] ≥ 360 mol%, where [SiO2] refers to the mol% content of SiO2, [SiO2] refers to the mol% content of SiO2, [Al2O3] refers to the mol% content of Al2O3, [B2O3] refers to the mol% content of B2O3, [MgO] refers to the mol% content of MgO, [CaO] refers to the mol% content of CaO, [SrO] refers to the mol% content of SrO, and [BaO] refers to the mol% content of BaO.

[0011] Furthermore, the alkali-free glass plate of the present invention preferably satisfies the relationship 17.8 × [SiO2] + 23.1 × [Al2O3] + 3.7 × [B2O3] + 12.9 × [MgO] + 14.1 × [CaO] + 15.5 × [SrO] + 15.0 × [BaO] + 7.2 × [ZnO] ≥ 1786 mol%.

[0012] The alkali-free glass plate of the present invention preferably has an Rh content of 0.1 to 3 mass ppm. Here, "Rh" includes not only Rh but also RhO2 and Rh2O3, and RhO2 and Rh2O3 are expressed in terms of Rh.

[0013] The alkali-free glass plate of the present invention preferably has a Young's modulus of 82 GPa or more. Here, "Young's modulus" can be measured by a bending resonance method. DETAILED DESCRIPTION OF THE INVENTION

[0014] The alkali-free glass plate of the present invention has a glass composition containing, in mole percent, 55-80% SiO2, 10-25% Al2O3, 0-4% B2O3, 0-30% MgO, 0-25% CaO, 0-15% SrO, 0-15% BaO, 0-5% ZnO, and 0-1.0% Y2O3 + La2O3, and is characterized by being substantially free of alkali metal oxides. The reasons for limiting the content of each component as described above are as follows. In addition, in the description of the content of each component, % denotes mol% unless otherwise specified.

[0015] SiO2 is a component that forms the glass skeleton and increases the strain point. Therefore, the SiO2 content is preferably 55% or more, 60% or more, 63% or more, 65% or more, 67% or more, and particularly 68% or more. On the other hand, if the SiO2 content is too high, the high-temperature viscosity increases and the melting property tends to decrease. Therefore, the SiO2 content is preferably 80% or less, 78% or less, 75% or less, 74% or less, 73% or less, and particularly 72% or less.

[0016] Al2O3 is a component that forms the glass skeleton, raises the strain point, and suppresses phase separation. Therefore, the Al2O3 content is preferably 10% or more, 10.5% or more, 11% or more, 11.5% or more, and particularly 12% or more. On the other hand, if the Al2O3 content is too high, the high-temperature viscosity increases and meltability tends to decrease. Therefore, the Al2O3 content is preferably 25% or less, 22% or less, 20% or less, 18% or less, 16% or less, 15% or less, and particularly 14% or less.

[0017] The total amount of SiO2 and Al2O3 is preferably 70% or more, 75% or more, 80% or more, 81% or more, 82% or more, 83% or more, 84% or more, and particularly 85% or more. If the total amount of SiO2 and Al2O3 is too small, the strain point tends to decrease. On the other hand, if the total amount of SiO2 and Al2O3 is too large, the high-temperature viscosity increases and the melting property tends to decrease. Therefore, the total amount of SiO2 and Al2O3 is preferably 90% or less, 89% or less, 88% or less, 87% or less, and particularly 86% or less.

[0018] Although B2O3 is an optional component, its incorporation in a small amount improves meltability. Therefore, the B2O3 content is preferably 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 B2O3 content is too high, the strain point will be significantly lowered and the β-OH will be significantly increased. As will be described in detail later, an increase in the β-OH will increase the thermal shrinkage. Therefore, the B2O3 content is preferably 4% or less, 3.5% or less, 3% or less, 2.5% or less, 2% or less, 1.5% or less, and particularly 1% or less.

[0019] MgO is a component that reduces high-temperature viscosity and improves meltability, and also improves devitrification resistance in 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 0% or more, 0.5% or more, 1% or more, 1.5% or more, and particularly 2% or more. On the other hand, if the MgO content is too high, the strain point tends to decrease, or the balance with other components is disrupted, increasing the tendency toward devitrification. Therefore, the MgO content is preferably 30% or less, 15% or less, 10% or less, 9% or less, 8% or less, 7.5% or less, 7% or less, 6.5% or less, and particularly 6% or less.

[0020] CaO is a component that reduces high-temperature viscosity and improves meltability, and also improves devitrification resistance in balance with other components. Therefore, the CaO content is preferably 0% or more, 0.5% or more, 1% or more, 1.5% or more, and particularly 2% or more. On the other hand, if the CaO content is too high, the strain point tends to decrease. Therefore, the CaO content is preferably 25% or less, 15% or less, 10% or less, 9% or less, 8% or less, 7.5% or less, 7% or less, 6.5% or less, and particularly 6% or less.

[0021] SrO is a component that reduces high-temperature viscosity and improves meltability, and also improves devitrification resistance in balance with other components. Therefore, the SrO content is preferably 0% or more, 0.5% or more, 1% or more, 1.5% or more, and particularly 2% or more. On the other hand, if the SrO content is too high, the strain point tends to decrease. Therefore, the SrO content is preferably 15% or less, 10% or less, 9% or less, 8% or less, 7% or less, 6% or less, 5% or less, and particularly 4% or less.

[0022] BaO is a component that reduces high-temperature viscosity and improves meltability, and also improves devitrification resistance in balance with other components. Therefore, the BaO content is preferably 0% or more, 0.5% or more, 1% or more, 1.5% or more, 2% or more, 2.5% or more, and particularly 3% or more. On the other hand, if the BaO content is too high, the strain point tends to decrease. Therefore, the SrO content is preferably 15% or less, 10% or less, 9% or less, 8% or less, 7.5% or less, 7% or less, 6.5% or less, and particularly 6% or less.

[0023] The total amount of SrO and BaO is preferably 0% or more, 2% or more, 3% or more, 4% or more, and particularly 5% or more. If the total amount of SrO and BaO is too small, meltability tends to decrease. On the other hand, if the total amount of SrO and BaO is too large, the component balance of the glass composition is impaired, and devitrification resistance tends to decrease. Therefore, the total amount of SrO and BaO is preferably 20% or less, 16% or less, 14% or less, 12% or less, 10% or less, 9% or less, and particularly 8% or less.

[0024] The total amount of MgO, CaO, SrO, and BaO is preferably 9.9% or more, 12% or more, 12.5% ​​or more, 13% or more, 13.5% or more, particularly 14% or more. If the total amount of MgO, CaO, SrO, and BaO is too small, meltability tends to decrease. On the other hand, if the total amount of MgO, CaO, SrO, and BaO is too large, the strain point decreases or the component balance of the glass composition is impaired, resulting in a decrease in devitrification resistance. Therefore, the total amount of MgO, CaO, SrO, and BaO is preferably 25% or less, 20% or less, 16% or less, 15.5% or less, 15% or less, 14.5% or less, particularly 14% or less.

[0025] The molar percentage ratio [B2O3] / ([SrO]+[BaO]) is preferably 0-0.5, 0-0.45, 0-0.4, 0-0.35, 0.01-0.3, or 0.05-0.25, and particularly preferably 0.1-0.2. If the molar percentage ratio [B2O3] / ([SrO]+[BaO]) is outside the above range, the balance of the components in the glass system according to the present invention will be lost, and devitrification resistance will be prone to decrease. Note that "[B2O3] / ([SrO]+[BaO])" refers to the value obtained by dividing the B2O3 content by the combined amount of SrO and BaO.

[0026] [SiO2] + 14 × [Al2O3] - 15 × [B2O3] + 6 × [MgO] + [CaO] + 14 × [SrO] + 16 × [BaO] is preferably 300% or more, 330% or more, 350% or more, 360% or more, 370% or more, 380% or more, 390% or more, 400% or more, 410% or more, 420% or more, or 430% or more. If [SiO2] + 14 × [Al2O3] - 15 × [B2O3] + 6 × [MgO] + [CaO] + 14 × [SrO] + 16 × [BaO] is too small, it becomes difficult to simultaneously achieve a high strain point, a high Young's modulus, and high devitrification resistance.

[0027] The ratio (17.8 × [SiO2] + 23.1 × [Al2O3] + 3.7 × [B2O3] + 12.9 × [MgO] + 14.1 × [CaO] + 15.5 × [SrO] + 15.0 × [BaO] + 7.2 × [ZnO]) is preferably 1740% or more, 1750% or more, 1760% or more, 1770% or more, 1780% or more, and particularly 1786% or more. If the ratio (17.8 × [SiO2] + 23.1 × [Al2O3] + 3.7 × [B2O3] + 12.9 × [MgO] + 14.1 × [CaO] + 15.5 × [SrO] + 15.0 × [BaO] + 7.2 × [ZnO]) is too large, the thermal shrinkage of the glass sheet is likely to increase.

[0028] [Al2O3] + [B2O3] - [CaO] - [SrO] - [BaO] is preferably 0% or more, 0.1% or more, and particularly 1.0% or more. If [Al2O3] + [B2O3] - [CaO] - [SrO] - [BaO] is too small, the amount of non-bridging oxygen in the glass increases, which can easily cause structural imbalance, making the glass sheet susceptible to thermal shrinkage during high-temperature deposition processes. On the other hand, if [Al2O3] + [B2O3] - [CaO] - [SrO] - [BaO] is too large, the melting load increases and devitrification resistance decreases, which can easily increase the manufacturing cost of the glass sheet. Therefore, [Al2O3] + [B2O3] - [CaO] - [SrO] - [BaO] is preferably 10.0% or less, 6.0% or less, 5.0% or less, 4.5% or less, 4.0% or less, 3.0% or less, particularly preferably 2.0% or less.

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

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

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

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

[0033] ZnO is a component that improves meltability, but if it is contained in a large amount, the glass becomes more susceptible to devitrification and the strain point tends to decrease. The ZnO content is preferably 0 to 5%, 0 to 3%, 0 to 0.5%, 0 to 0.3%, particularly preferably 0 to 0.2%.

[0034] P2O5 is a component that significantly lowers the liquidus temperature of Al-based devitrified crystals while maintaining the strain point. However, if a large amount of P2O5 is added, the Young's modulus decreases and the glass undergoes phase separation. Furthermore, P may diffuse from the glass and affect the performance of the TFT. Therefore, the P2O5 content is preferably 0 to 1.5%, 0 to 1.2%, 0 to 1%, and particularly 0 to 0.5%.

[0035] TiO2 is a component that reduces high-temperature viscosity, improves meltability, and suppresses solarization, but if TiO2 is contained in a large amount, the glass becomes colored and transmittance tends to decrease. Therefore, the TiO2 content is preferably 0 to 500 ppm by mass, 0.1 to 100 ppm by mass, 0.1 to 50 ppm by mass, 0.5 to 30 ppm by mass, 1 to 20 ppm by mass, 3 to 15 ppm by mass, and particularly preferably 5 to 10 ppm by mass.

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

[0037] Although SnO2 is suitable as a fining agent, fining 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 a total amount of, for example, up to 0.5%, and metal powders such as Al and Si may also be added in a total amount of, for example, up to 0.5%.

[0038] Although As2O3 and Sb2O3 have excellent clarification properties, it is preferable to avoid their incorporation as much as possible from an environmental perspective. Furthermore, since the inclusion of a large amount of As2O3 in glass tends to reduce solarization resistance, its content is preferably 1000 ppm by mass or less, 100 ppm by mass or less, and particularly less than 30 ppm by mass. Furthermore, the content of Sb2O3 is preferably 1000 ppm by mass or less, 100 ppm by mass or less, and particularly less than 30 ppm by mass.

[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 fining agent, resulting in lower melting costs and longer life for glass-making furnaces. However, if the Cl content is too high, the strain point will decrease. Therefore, the Cl content is preferably 0.5% or less, particularly 0.1% or less. Cl can be introduced from chlorides of alkaline earth metal oxides such as strontium chloride, aluminum chloride, or the like.

[0040] Rh is a component contained in melting equipment, and is a component that dissolves into the glass mass when the glass is melted at high temperatures. On the other hand, Rh is a component that colorizes the glass when coexisting with SnO2. The Rh content is preferably 0 to 3 mass ppm, 0.1 to 3 mass ppm, 0.1 to 3 mass ppm, 0.2 to 2.5 mass ppm, 0.3 to 2 mass ppm, 0.4 to 1.5 mass ppm, particularly 0.5 to 1 mass ppm. Note that lowering the melting temperature tends to reduce the Rh content.

[0041] Ir has higher heat resistance than Pt and Pt—Rh alloys and is a component that can reduce foaming of molten glass at the interface with the molten glass. Ir is also a component contained in melting equipment, and is a component that dissolves into the glass matrix when glass is melted at high temperatures. On the other hand, if the amount of Ir dissolved becomes too large, it may precipitate as a foreign substance in the glass. Therefore, the Ir content is preferably 0 to 10 ppm by mass, 0.01 to 10 ppm by mass, 0.02 to 5 ppm by mass, 0.03 to 3 ppm by mass, 0.04 to 2 ppm by mass, and particularly preferably 0.05 to 1 ppm by mass. Note that "Ir" encompasses not only Ir but also IrO2 and Ir2O3, and IrO2 and Ir2O3 are expressed in terms of Ir.

[0042] Molybdenum is a component used in electrodes in the melting step, and is a component that dissolves as MoO3 into the glass mass when the glass is melted at high temperature. The MoO3 content is preferably 0 to 50 ppm by mass, 1 to 50 ppm by mass, 3 to 40 ppm by mass, 5 to 30 ppm by mass, 5 to 25 ppm by mass, and particularly preferably 5 to 20 ppm by mass. If the MoO3 content is too low, it becomes difficult to apply electrical heating to the molten glass using a heating electrode, making it difficult to reduce β-OH.

[0043] ZrO2 is a component contained in refractories in the melting process, and is a component that dissolves into the glass matrix when the glass is melted at high temperatures. ZrO2 is also a component that increases the liquidus temperature and weather resistance. On the other hand, if the ZrO2 content is excessively reduced, it becomes necessary to use expensive refractories in the melting process, which may increase the manufacturing cost of the glass sheet. Therefore, the ZrO2 content is preferably 0 to 2000 ppm by mass, 500 to 2000 ppm by mass, 550 to 1500 ppm by mass, and particularly preferably 600 to 1200 ppm by mass.

[0044] Fe2O3 is a component that is mixed in as a raw material impurity and reduces electrical resistivity. The content of Fe2O3 is preferably 50 to 300 ppm by mass, 80 to 250 ppm by mass, and particularly 100 to 200 ppm by mass. If the content of Fe2O3 is too low, raw material costs tend to rise. On the other hand, if the content of Fe2O3 is too high, the electrical resistivity of the molten glass increases, making it difficult to perform electric melting.

[0045] The alkali-free glass sheet of the present invention is substantially free of alkali metal oxides, but this does not exclude the possibility that alkali metal oxides may be present as unavoidable impurities. When alkali metal oxides are present as unavoidable impurities, the alkali metal oxide content (total amount of Li2O, Na2O, and K2O) is preferably 10 to 1,000 mass ppm, 30 to 600 mass ppm, 50 to 300 mass ppm, 70 to 200 mass ppm, and particularly 80 to 150 mass ppm. In particular, the Na2O content is preferably 30 to 600 mass ppm, 50 to 300 mass ppm, 70 to 200 mass ppm, and particularly 80 to 150 mass ppm. If the alkali metal oxide content is too low, the use of high-purity raw materials becomes necessary, resulting in increased batch costs. In addition, the electrical conductivity becomes too low, making electrical melting difficult. On the other hand, if the alkali metal oxide content is too high, alkali ions may diffuse into the semiconductor film during the heat treatment process.

[0046] The alkali-free glass plate of the present invention preferably has the following properties.

[0047] The thermal expansion coefficient is preferably 46 x 10 ‐7 / ℃ or less, 42×10 ‐7 / ℃ or less, 40×10 ‐7 / ℃ or less, 38×10 ‐7 / ℃ or less, especially 26×10 ‐7 / ℃ or more and 36×10 ‐7 / °C or less. If the thermal expansion coefficient is too high, local dimensional changes tend to occur in the glass sheet due to temperature variations in the high-temperature film-forming process.

[0048] The density is preferably 2.80 g / cm3 Below, 2.75g / cm 3 Below, 2.70g / cm 3 Below 2.65g / cm 3 Below 2.60g / cm 3 Below 2.55g / cm 3 Below, especially 2.45 to 2.50 g / cm 3 If the density is too high, the amount of bending of the glass plate tends to increase, which tends to promote pattern misalignment due to stress during the display manufacturing process, etc.

[0049] The strain point is 750° C. or higher, preferably 760° C. or higher, 765° C. or higher, 770° C. or higher, 775° C. or higher, 780° C. or higher, 785° C. or higher, 790° C. or higher, 795° C. or higher, or 800° C. If the strain point is too low, the glass sheet is prone to thermal shrinkage in the high-temperature film formation process.

[0050] The annealing point is preferably 800° C. or higher, 805° C. or higher, 810° C. or higher, 820° C. or higher, 830° C. or higher, 840° C. or higher, particularly preferably 850° C. If the annealing point is too low, the glass sheet is likely to undergo thermal shrinkage in the high-temperature film formation process.

[0051] The softening point is preferably 1040° C. or higher, 1060° C. or higher, 1080° C. or higher, particularly preferably 1100° C. If the softening point is too low, the glass sheet is likely to undergo thermal shrinkage in the high-temperature film formation process.

[0052] High temperature viscosity 10 2.5 The temperature in dPa·s is preferably 1750°C or less, 1720°C or less, 1700°C or less, 1690°C or less, 1680°C or less, and particularly preferably 1670°C or less. 2.5 When the temperature at dPa·s becomes high, the melting property and clarity tend to decrease, and the manufacturing cost of the glass plate rises.

[0053] The Young's modulus is preferably 80 GPa or more, 81 GPa or more, 82 GPa or more, particularly 83 GPa or more. If the Young's modulus is too low, the amount of bending of the glass plate tends to increase, which tends to promote stress-induced pattern misalignment in the display manufacturing process, etc.

[0054] Specific Young's modulus is preferably 30 GPa / g cm -3 Above, 31GPa / g cm -3 Above, 32GPa / g cm -3 Above, especially 33 GPa / g cm -3 If the specific Young's modulus is too low, the amount of bending of the glass plate tends to increase, which tends to promote stress-induced pattern misalignment during the display manufacturing process and the like.

[0055] β-OH is an index showing the amount of water in glass, and reducing β-OH can increase the strain point. Furthermore, even if the glass composition is the same, a smaller β-OH results in a smaller thermal shrinkage at temperatures below the strain point. β-OH 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. If β-OH is too small, meltability tends to decrease. Therefore, β-OH is preferably 0.01 / mm or more, particularly 0.03 / mm or more.

[0056] The following methods can be used to reduce β-OH: (1) Select raw materials with low water content. (2) Add components (Cl, SO3, etc.) to the glass that reduce β-OH. (3) Reduce the amount of water 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. (7) Use an electric melting method.

[0057] Here, "β-OH" refers to a value obtained by measuring the transmittance of glass using FT-IR and using the following mathematical formula 1.

[0058] [Number 1] β-OH=(1 / X)log(T1 / T2) X: Plate thickness (mm) T1: Reference wavelength 3846cm -1 Transmittance (%) T2: Hydroxyl group absorption wavelength 3600cm -1 Minimum transmittance (%) in the vicinity

[0059] The alkali-free glass sheet of the present invention preferably has an overflow confluence surface in the center in the sheet thickness direction. That is, it is preferably formed by the overflow downdraw method. The overflow downdraw method is a method in which molten glass is allowed to overflow from both sides of a wedge-shaped refractory, and the overflowed molten glass is drawn downward while being joined at the lower end of the wedge to form a flat sheet. In the overflow downdraw method, the surface that will become the surface of the glass sheet does not come into contact with the refractory and is formed in a free surface state. Therefore, an unpolished glass sheet with good surface quality can be produced inexpensively. Furthermore, it is easy to make the glass sheet larger in area and thinner.

[0060] In addition to the overflow downdraw method, molding can also be performed by, for example, the slot down method, the redraw method, the float method, or the roll out method.

[0061] The thickness of the alkali-free glass plate of the present invention is not particularly limited, but is preferably 1.0 mm or less, 0.7 mm or less, or 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 liquid crystal panels or organic EL panels. The plate thickness can be adjusted by the flow rate and forming speed (plate drawing speed) during glass production.

[0062] A method for industrially producing the alkali-free glass plate of the present invention preferably comprises a melting step of charging a glass batch into a melting furnace and conducting electrical heating using heating electrodes to obtain molten glass, the glass batch having a glass composition containing, in mole percentages, 55 to 80% SiO, 10 to 25% AlO, 0 to 4% BO, 0 to 30% MgO, 0 to 25% CaO, 0 to 15% SrO, 0 to 15% BaO, 0 to 5% ZnO, and YO + less than 0 to 1.0% LaO, and being formulated so as to contain substantially no alkali metal oxides, and forming the molten glass into an alkali-free glass plate having a thickness of 0.1 to 0.7 mm by an overflow downdraw method.

[0063] The manufacturing process of a glass plate generally includes a melting step, a fining step, a supplying step, a stirring step, and a forming step. The melting step is a step of melting a glass batch prepared by blending glass raw materials to obtain molten glass. The fining step is a step of fining the molten glass obtained in the melting step by using a fining agent or the like. The supplying step is a step of transferring the molten glass between each step. The stirring step is a step of stirring and homogenizing the molten glass. The forming step is a step of forming the molten glass into a glass plate. Note that, if necessary, a step other than the above, for example, a conditioning step of adjusting the molten glass to a state suitable for forming, may be incorporated after the stirring step.

[0064] In industrial production of alkali-free glass sheets, the glass is generally melted by heating with a combustion flame from a burner. The burner is usually located above a melting furnace, and a fossil fuel, specifically a liquid fuel such as heavy oil or a gaseous fuel such as LPG, is used as the fuel. The combustion flame can be obtained by mixing a fossil fuel with oxygen gas. However, this method involves the incorporation of a large amount of water into the molten glass during melting, which tends to increase the β-OH. Therefore, when producing the alkali-free glass sheet of the present invention, it is preferable to perform electrical heating using a heating electrode. It is also preferable to perform melting by electrical heating using a heating electrode without heating with a burner combustion flame, i.e., complete electrical melting. This makes it difficult for water to be incorporated into the molten glass during melting, making it easier to regulate the β-OH 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. Furthermore, when electrical heating is performed using a heating electrode, the amount of energy per mass required to obtain molten glass is reduced, and the amount of molten volatiles is also reduced, thereby reducing the environmental load.

[0065] Furthermore, with regard to this electrical heating, the lower the moisture content in the glass batch, the easier it is to reduce the β-OH in the glass sheet. Furthermore, the raw material for B2O3 tends to be the largest source of moisture contamination. Therefore, from the viewpoint of producing a glass sheet with low β-OH, it is preferable 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 spread uniformly in the melting furnace, making it easier to produce a homogeneous, high-quality glass sheet.

[0066] The electrical heating using the heating electrode is preferably carried out by applying an AC voltage to the heating electrode provided at the bottom or side of the melting furnace so as to be in contact with the molten glass in the melting furnace. The material used for the heating electrode is preferably heat-resistant and corrosion-resistant to the molten glass, and examples of usable materials include tin oxide, molybdenum, platinum, and rhodium. In particular, molybdenum is preferred from the viewpoint of flexibility in installation in the furnace.

[0067] The alkali-free glass plate of the present invention is substantially free of alkali metal oxides and therefore has high electrical resistivity. Therefore, when electrical heating is performed using heating electrodes, current flows not only through the molten glass but also through the refractories constituting the melting furnace, potentially causing premature damage to the refractories constituting the melting furnace. To prevent this, it is preferable to use a zirconia-based refractory with high electrical resistivity, particularly electroformed zirconia bricks, as the furnace refractory. It is also preferable to incorporate a small amount of a component (e.g., Fe2O3) that reduces electrical resistivity into the molten glass (glass composition). The Fe2O3 content is preferably 50 to 300 ppm by mass, 80 to 250 ppm by mass, and particularly 100 to 200 ppm by mass. Furthermore, the ZrO2 content in the zirconia-based refractory is preferably 85% by mass or more, particularly 90% by mass or more. [Example]

[0068] The present invention will be described below based on examples. However, the following examples are merely illustrative and the present invention is not limited to the following examples.

[0069] Tables 1 to 49 show examples of the present invention (samples No. 1 to 679). Note that the glass properties of samples No. 281 to 679 are not actual measured values ​​but calculated values ​​calculated from composition factors.

[0070] [Table 1]

[0071] [Table 2]

[0072] [Table 3]

[0073] [Table 4]

[0074]

Table 5

[0075]

Table 6

[0076]

Table 7

[0077]

Table 8

[0078]

Table 9

[0079]

Table 10

[0080]

Table 11

[0081]

Table 12

[0082]

Table 13

[0083]

Table 14

[0084]

Table 15

[0085] Table 16

[0086] Table 17

[0087] Table 18

[0088] Table 19

[0089] Table 20

[0090] Table 21

[0091] Table 22

[0092] Table 23

[0093] Table 24

[0094] Table 25

[0095] Table 26

[0096] Table 27

[0097] Table 28

[0098] Table 29

[0099]

Table 30

[0100] Table 31

[0101] Table 32

[0102] Table 33

[0103] Table 34

[0104] Table 35

[0105] Table 36

[0106] Table 37

[0107] Table 38

[0108] Table 39

[0109] Table 40

[0110] Table 41

[0111] Table 42

[0112] Table 43

[0113] Table 44

[0114] Table 45

[0115] Table 46

[0116] [Table 47]

[0117] [Table 48]

[0118] [Table 49]

[0119] 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 1600-1650°C for 24 hours. When melting the glass batch, it was stirred using a platinum stirrer to homogenize it. Next, the molten glass was poured onto a carbon plate and formed into a plate, which was then slowly cooled at a temperature near the annealing point for 30 minutes. The thermal expansion coefficient, density, strain point, annealing point, softening point, and high-temperature viscosity (10°C) of each sample were measured. 4.5 Temperature in dPa·s, high temperature viscosity 10 4.0 Temperature in dPa·s, high temperature viscosity 10 3.0 Temperature in dPa·s, high temperature viscosity 10 2.5 The temperature, Young's modulus, specific Young's modulus, and β-OH in dPa·s were evaluated.

[0120] The thermal expansion coefficient is the average thermal expansion coefficient in the temperature range of 30 to 380°C measured with a dilatometer.

[0121] The density is a value measured by the well-known Archimedes method.

[0122] The strain point, annealing point and softening point are values ​​measured based on the methods of ASTM C336 and C338.

[0123] High temperature viscosity 10 4.5 dPa·s, 10 4.0 dPa·s, 10 3.0dPa·s, 10 2.5 The temperature in dPa·s was measured by the platinum sphere pulling method.

[0124] The Young's modulus is a value measured by a bending resonance method.

[0125] The specific Young's modulus is the Young's modulus divided by the density.

[0126] The β-OH value is measured by the above method.

[0127] As can be seen from Tables 1 to 49, Samples Nos. 1 to 679 have high strain points and do not contain Y2O3 or La2O3 in the glass composition, which is thought to enable lower manufacturing costs. [Example]

[0128] Table 50 shows data showing the relationship between β-OH and thermal shrinkage. Samples A and B have the same glass composition as Sample No. 1, but have different β-OH. The thermal shrinkage of Samples A and B was measured when they were held at 500°C for 1 hour and when they were held at 600°C for 1 hour.

[0129] [Table 50]

[0130] The thermal shrinkage rate can be measured as follows. First, two linear markings are engraved parallel to a glass plate, and then the plate is split perpendicular to the markings to obtain two glass pieces. Next, one of the glass pieces is heated from room temperature to 500°C or 600°C at a heating rate of 5°C / min, held at 500°C or 600°C for one hour, and then cooled to room temperature at a heating rate of 5°C / min. Next, the heat-treated glass piece and the unheat-treated glass piece are lined up so that their split surfaces are aligned and fixed with adhesive tape, and the deviation ΔL of the markings on both pieces is measured. Finally, the value ΔL / L0 is measured and used as the thermal shrinkage rate. L0 is the length of the glass piece before heat treatment.

[0131] Table 50 shows that even when the glass composition is the same, a glass with a lower β-OH content can reduce the thermal shrinkage rate. [Example]

[0132] Glasses having the glass compositions of Samples Nos. 1, 15, and 115 were melted under conventional temperature conditions using existing equipment and formed into glass plates by the overflow downdraw method, and the contents of trace elements were then measured by X-ray fluorescence analysis. The results are shown in Table 51.

[0133] [Table 51] [Example]

[0134] Glasses having the glass compositions of Samples Nos. 1, 15, and 115 were melted at higher temperatures than in the past using existing equipment other than that used in Example 3, and formed into glass plates by the overflow downdraw method. The contents of trace elements were then measured by X-ray fluorescence analysis. The results are shown in Table 52.

[0135] [Table 52]

Claims

1. The glass composition is, in mol%, SiO ２ 55-80%, Al ２ O ３ 10-25%, B ２ O ３ 0.01-4%, MgO 0-30%, CaO 1.5-25%, SrO 0-15%, BaO 0.5-7.1%, ZnO 0-5%, P ２ O ５ 0-1.5%, Y ２ O ３ +La ２ O ３ 17.8×[SiO 2 ]+23.1×[Al 2 O 3 ]+3.7×[B 2 O 3 ]+12.9×[MgO]+14.1×[CaO]+15.5×[SrO]+15.0×[BaO]+7.2×[ZnO]≧1792.6 mol %, is substantially free of alkali metal oxides, and has a strain point of 750°C or higher.

2. [SiO ２ ]+14×[Al ２ O ３ ]-15×[B ２ O ３ 2. The alkali-free glass plate according to claim 1, wherein the relationship of [MgO] + 6 × [MgO] + [CaO] + 14 × [SrO] + 16 × [BaO] ≥ 360 mol % is satisfied.

3. 17.8×[SiO ２ ]+23.1×[Al ２ O ３ ]+3.7×[B ２ O ３ ] + 12.9 × [MgO] + 14.1 × [CaO] + 15.5 × [SrO] + 15.0 × [BaO] + 7.2 × [ZnO] ≥ 1796.9 mol%.

4. 3. The alkali-free glass plate according to claim 1, wherein the Rh content is 0.1 to 3 ppm by mass.

5. 3. The alkali-free glass plate according to claim 1, having a Young's modulus of 82 GPa or more.

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