Alkali-free glass plate

Abstract

This invention provides an alkali-free glass plate with excellent manufacturability and sufficiently high strain point and Young's modulus. The alkali-free glass plate of this invention is characterized by containing, by mol%, 64–72% SiO₂, 12–16% Al₂O₃, 0–3% B₂O₃, 0–0.5% Li₂O + Na₂O + K₂O, 6–12% MgO, 9–13% CaO, 0–2% SrO, and 0–1% BaO as its glass composition, and the mol% ratio of SrO / SiO₂ is 0–0.03.

Description

Technical Field

[0001] This invention relates to an alkali-free glass plate, and more particularly to an alkali-free glass plate suitable for organic EL (Electroluminescence) displays or magnetic recording media. Prior Technology

[0002] Organic EL displays and other electronic devices are used for applications such as displays in flexible devices or mobile phones because they are thin, provide excellent animation display, and consume less power.

[0003] Glass plates are widely used as substrates for organic EL displays. The following characteristics are the main requirements for glass plates used in this application. (1) In order to prevent the diffusion of alkaline ions into the semiconductor material formed by heat treatment, it contains almost no alkali metal oxides, that is, it is an alkali-free glass (glass with an alkali metal oxide content of less than 0.5 mol%). (2) In order to keep the price of glass sheets low, the overflow down-drawing method is used to form the glass sheets, which can easily improve the surface quality and has excellent manufacturability, especially excellent melting properties or devitrification resistance. (3) In LTPS (low temperature poly silicon) process and oxide TFT (thin-film transistor) process, the strain point is higher in order to reduce the thermal shrinkage of the glass plate.

[0004] Furthermore, with the advancement of information-related infrastructure technologies, the demand for information recording media such as magnetic disks and optical disks has increased rapidly.

[0005] As substrates for information recording media, glass plates are widely used to replace the previously used aluminum alloy substrates. In recent years, in order to meet the demand for further high recording density, magnetic recording media using energy-assisted magnetic recording (EMR) are being researched. EMR also uses glass plates, and a magnetic layer is formed on the surface of the glass plate. In EMR, a regular alloy with a large magnetic anisotropy coefficient Ku (hereinafter referred to as "high Ku") is used as the magnetic material for the magnetic layer. [Previous Technical Documents] [Patent Literature]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2012-106919 [Patent Document 2] Japanese Patent Application Publication No. 2021-086643 Summary of the Invention

[0007] [The problem the invention aims to solve]

[0008] Furthermore, OLED devices are widely used in OLED TVs. For OLED TVs, there is a strong demand for larger and thinner designs, and the demand for high-resolution displays such as 8K is constantly increasing. Therefore, the glass panels used in these applications must be large and thin while possessing the thermal dimensional stability to withstand the requirements of high resolution. Moreover, for OLED TVs, in order to reduce the price difference with LCD monitors, lower costs are required, and the same applies to the glass panels. However, when the glass panels are made larger and thinner, they are prone to bending, leading to increased manufacturing costs.

[0009] Glass sheets formed by glass manufacturers undergo steps such as cutting, cooling, inspection, and cleaning. During these steps, the glass sheets are placed into and removed from a box containing multiple supports. In this box, the glass sheets are typically held horizontally on opposite sides of supports formed on the left and right inner sides. However, large and thin glass sheets, due to their greater curvature, are prone to breakage when placed into the box, or become unstable due to significant swaying during removal. This type of box is also used by electronic device manufacturers, and the same problems occur. To solve this problem, increasing the Young's modulus of the glass sheet to reduce curvature is a more effective method.

[0010] Furthermore, as mentioned above, in the LTPS or oxide TFT process used to obtain high-resolution displays, it is necessary to increase the strain point of the glass plate in order to reduce the thermal shrinkage of the large glass plate.

[0011] However, increasing the Young's modulus and strain point of the glass sheet disrupts the balance of the glass composition, reduces productivity, especially significantly decreases devitrification resistance, and increases liquid phase viscosity, making it impossible to form using the overflow downdraw method. Furthermore, melt flowability decreases, or the glass forming temperature increases, potentially shortening the lifespan of the formed piece. As a result, the cost of the raw glass sheet increases.

[0012] Also, for the glass plate for magnetic recording media, it is required to have a higher stiffness (in other words, Young's modulus) in order not to cause greater deformation during high-speed rotation. In detail, in the disc-like magnetic recording media, the media is made to rotate at high speed around the center axis, and the magnetic head is moved in the radius direction while writing, reading out the information along the rotation direction. In recent years, the rotational speed used to increase that write speed or readout speed is constantly advancing in the direction of high speed from 5400 rpm to 7200 rpm, and then to 10000 rpm, but in disc-like magnetic recording media, the position of recording information is pre-assigned based on the distance from the center axis. Therefore, when the glass plate is deformed in rotation, the magnetic head will shift in position, making it difficult to perform an accurate reading.

[0013] Furthermore, in recent years, further high recording density has been achieved by carrying the DFH (Dynamic Flying Height) mechanism on the magnetic head, and the gap between the recording reproduction element part of the magnetic head and the magnetic recording media surface is significantly narrowed (i.e., the amount of float is reduced). The DFH mechanism is a heating part such as a very small heater provided in the vicinity of the recorded reproduction element portion of the magnetic head, and only a mechanism that causes the periphery of the component portion to thermally expand towards the media surface. By having such a mechanism, the distance between the magnetic head and the magnetic layer of the media is close, so that the signal of smaller magnetic particles can be picked up, thereby achieving high recording density. On the other hand, the gap between the recording reproduction element part of the magnetic head and the magnetic recording media surface becomes extremely small, for example, less than 2 nm, so the presence of some impact will cause the magnetic head to collide with the surface of the magnetic recording media. The more high-speed rotation is performed, the more significant this tendency is. Therefore, during high-speed rotation, it is more important to prevent the bending or shaking (i.e., fluttering) of the glass plate that produces that collision.

[0014] Also, in order to improve the degree of regularization (i.e., regularity) of the magnetic layer to achieve high Kuization, the substrate containing the glass plate is sometimes thermally treated at a high temperature of around 800°C during or before and after film formation of the magnetic layer. The higher the recording density, the higher the temperature of that heat treatment is required, thus requiring higher heat resistance compared to the previous glass plates for magnetic recording media, i.e., higher strain points are required. Also, sometimes laser irradiation is also executed on the substrate containing the glass plate after the magnetic layer is formed into a film. Such heat treatment or laser irradiation also has the purpose of improving the annealing temperature or magnetic retention of the magnetic layer containing FePt series alloys and the like.

[0015] However, as mentioned above, increasing the Young's modulus and strain point of the glass sheet disrupts the balance of the glass composition, reduces productivity, especially significantly decreases devitrification resistance, and increases liquid phase viscosity, making it impossible to form using the overflow pull method. Furthermore, melt flow decreases, the glass forming temperature increases, and the lifespan of the formed piece tends to shorten. As a result, the cost of the raw glass sheet increases.

[0016] Therefore, the present invention was conceived in view of the above circumstances, and its technical objective is to provide an alkali-free glass plate with excellent manufacturability and sufficiently high strain point and Young's modulus. [Technical means to solve the problem]

[0017] The inventors conducted various experiments and discovered that the aforementioned technical problems could be solved by strictly limiting the glass composition of the alkali-free glass plate, thus proposing this invention. Specifically, the alkali-free glass plate of this invention is characterized by containing, in mol%, 64-72% SiO₂, 12-16% Al₂O₃, 0-3% B₂O₃, 0-0.5% Li₂O + Na₂O + K₂O, 6-12% MgO, 9-13% CaO, 0-2% SrO, and 0-1% BaO as its glass composition, and the mol% ratio of SrO / SiO₂ is 0-0.03. Here, "Li₂O + Na₂O + K₂O" refers to the combined amount of Li₂O, Na₂O, and K₂O. "SrO / SiO₂" is the value obtained by dividing the mol% content of SrO by the mol% content of SiO₂.

[0018] Furthermore, the alkali-free glass plate of the present invention preferably contains, by mol%, 64-72% SiO2, 12-16% Al2O3, 0-less than 1% B2O3, 0-0.5% Li2O+Na2O+K2O, 6-12% MgO, 9-13% CaO, more than 0 and less than or equal to 2% SrO, and 0-1% BaO as the glass composition, and the mol% ratio of SrO / SiO2 is 0-0.008.

[0019] Furthermore, the alkali-free glass plate of the present invention is preferably substantially free of As₂O₃ and Sb₂O₃ in its glass composition. Here, "substantially free of As₂O₃" means that the As₂O₃ content is less than 0.05 mol%. "Substantially free of Sb₂O₃" means that the Sb₂O₃ content is less than 0.05 mol%.

[0020] Furthermore, the alkali-free glass plate of the present invention preferably contains 0.001~1 mol% SnO2.

[0021] Furthermore, the alkali-free glass plate of the present invention preferably has a Young's modulus of 83 GPa or higher, a strain point of 730°C or higher, and a liquidus temperature of 1350°C or lower. Here, "Young's modulus" refers to the value measured by the bending resonance method. Moreover, 1 GPa is approximately equivalent to 101.9 Kgf / mm². "Strain point" refers to the value measured based on the method of ASTM C336. "Liquidus temperature" refers to the temperature at which glass powder that has passed through a standard 30-mesh (500 μm) sieve and has residues at a 50-mesh (300 μm) sieve is placed in a platinum boat and kept in a temperature gradient furnace for 24 hours, at which crystallization occurs.

[0022] Furthermore, the alkali-free glass plate of the present invention preferably has a strain point of 735°C or higher.

[0023] Furthermore, the alkali-free glass plate of the present invention preferably has a Young's modulus higher than 84 GPa.

[0024] Furthermore, the alkali-free glass plate of the present invention preferably has an average coefficient of thermal expansion of 30×10⁻⁷ to 50×10⁻⁷ / ℃ within a temperature range of 30 to 380℃. Here, the "average coefficient of thermal expansion within a temperature range of 30 to 380℃" can be measured by a dilatometer.

[0025] Furthermore, the alkali-free glass plate of the present invention preferably has a liquid phase viscosity of 10⁴.0 dPa·s or higher. Here, "liquid phase viscosity" refers to the glass viscosity at the liquidus temperature, which can be measured by the platinum ball pulling method.

[0026] Furthermore, the alkali-free glass plate of the present invention is preferably used in organic EL devices.

[0027] Furthermore, the alkali-free glass plate of the present invention is preferably used for magnetic recording media. Simple Explanation of the Diagram

[0028] Figure 1 is a perspective view above the disc to show its shape. Implementation

[0029] The alkali-free glass plate of the present invention is characterized by containing, in mol%, 64-72% SiO₂, 12-16% Al₂O₃, 0-3% B₂O₃, 0-0.5% Li₂O+Na₂O+K₂O, 6-12% MgO, 9-13% CaO, 0-2% SrO, and 0-1% BaO as its glass composition, and the mol% ratio of SrO / SiO₂ is 0-0.03. The reasons for limiting the content of each component as described above are explained below. Furthermore, in the description of the content of each component, unless otherwise stated, the % notation represents mol%. In this specification, the numerical range indicated by "~" refers to the range including the values ​​before and after "~" as the minimum and maximum values, respectively.

[0030] SiO₂ is a component that forms the framework of glass. When the SiO₂ content is too low, the coefficient of thermal expansion increases, and the density increases. Therefore, the lower limit of SiO₂ content is preferably 64%, further preferably 64.2%, further preferably 64.5%, further preferably 64.8%, further preferably 65%, further preferably 65.5%, further preferably 65.8%, further preferably 66%, further preferably 66.3%, further preferably 66.5%, and most preferably 66.7%. On the other hand, when the SiO₂ content is too high, the Young's modulus decreases, resulting in higher high-temperature viscosity, more heat required for melting, higher melting costs, and the risk of SiO₂ residue from the introduced raw materials dissolving, leading to a decrease in yield. Furthermore, devitrifying crystals such as scorcite are more likely to precipitate, and the liquid phase viscosity is more likely to decrease. Therefore, the upper limit of SiO2 is preferably 72%, further preferably 71.8%, further preferably 71.6%, further preferably 71.4%, further preferably 71.2%, further preferably 71%, further preferably 70.8%, further preferably 70.6%, and most preferably 70.4%.

[0031] Al₂O₃ forms the framework of glass, increases Young's modulus, and raises the strain point. When the Al₂O₃ content is too low, the Young's modulus and strain point tend to decrease. Therefore, the lower limit of Al₂O₃ content is preferably 12%, more preferably 12.2%, more preferably 12.4%, more preferably over 12.4%, more preferably 12.5%, and most preferably over 12.5%. On the other hand, when the Al₂O₃ content is too high, devitrifying crystals such as mullite tend to precipitate, and the liquid phase viscosity tends to decrease. Therefore, the upper limit of Al₂O₃ is preferably 16%, more preferably 15.8%, further preferably 15.5%, further preferably 15.3%, further preferably 15%, further preferably 14.8%, further preferably 14.6%, further preferably 14.4%, further preferably 14.2%, further preferably 14%, further preferably 13.9%, further preferably 13.8%, further preferably 13.7%, and most preferably 13.6%.

[0032] B₂O₃ is not an essential component, but its presence can improve melt flowability or resistance to devitrification. Therefore, the lower limit of B₂O₃ content is preferably 0%, more preferably more than 0%, more preferably 0.1%, further preferably 0.2%, further preferably 0.3%, further preferably 0.4%, and most preferably 0.5%. On the other hand, when the content of B₂O₃ is too high, the Young's modulus or strain point tends to decrease. Therefore, the upper limit of B₂O₃ content is preferably 3%, more preferably 2.9%, more preferably 2.8%, further preferably 2.7%, further preferably 2.6%, further preferably 2.5%, further preferably 2.4%, further preferably 2.2%, further preferably 2%, further preferably 1.8%, further preferably 1.6%, further preferably 1.4%, further preferably 1.2%, further preferably 1%, and most preferably less than 1%.

[0033] Li₂O, Na₂O, and K₂O are unavoidable components mixed into the glass raw materials, and their combined content is 0-0.5%, preferably 0-0.4%, more preferably 0-0.3%, further preferably 0.005-0.2%, and most preferably 0.01-0.1%. When the combined content of Li₂O, Na₂O, and K₂O is excessive, there is a risk of alkaline ions diffusing into the semiconductor material formed by the heat treatment step. Furthermore, the content of each of Li₂O, Na₂O, and K₂O is preferably 0-0.5%, more preferably 0-0.4%, further preferably 0-0.3%, further preferably 0.005-0.2%, and most preferably 0.01-0.1%.

[0034] MgO is a component in alkaline earth metal oxides that significantly improves Young's modulus. When the content of MgO is too low, the solubility or Young's modulus tends to decrease. Therefore, the lower limit of MgO content is preferably 6%, more preferably 6.1%, more preferably 6.3%, further preferably 6.5%, further preferably 6.6%, further preferably 6.7%, further preferably 6.8%, and most preferably 7%. On the other hand, when the content of MgO is too high, devitrifying crystals such as mullite tend to precipitate, and the liquid phase viscosity tends to decrease. Therefore, the upper limit of MgO content is preferably 12%, more preferably 11.8%, more preferably 11.5%, more preferably 11.3%, more preferably 11%, more preferably less than 11%, more preferably 10.8%, more preferably 10.6%, further preferably 10.4%, further preferably 10.2%, further preferably 10%, and most preferably 9.8%.

[0035] The mol% ratio of B₂O₃ / MgO is a crucial component ratio for improving Young's modulus and devitrification resistance. When the mol% ratio of B₂O₃ / MgO is too small, devitrification resistance decreases, easily increasing the manufacturing cost of the glass plate. Therefore, the lower limit of the mol% ratio of B₂O₃ / MgO is preferably 0, more preferably 0.0001, further preferably 0.001, and most preferably 0.005. On the other hand, when the mol% ratio of B₂O₃ / MgO is too large, Young's modulus tends to decrease. Therefore, the upper limit of the mol% ratio of B₂O₃ / MgO is preferably 0.2, more preferably 0.1, further preferably 0.08, further preferably 0.05, further preferably 0.03, further preferably 0.02, and most preferably 0.01. Furthermore, "B₂O₃ / MgO" is the value obtained by dividing the mol% content of B₂O₃ by the mol% content of MgO.

[0036] CaO is a component that significantly improves meltability by reducing high-temperature viscosity without lowering the strain point. Furthermore, CaO increases Young's modulus. When the CaO content is too low, meltability tends to decrease. Therefore, the lower limit of CaO content is preferably 9%, more preferably over 9%, more preferably 9.1%, further preferably 9.2%, further preferably 9.3%, further preferably 9.4%, further preferably 9.5%, further preferably 9.6%, and most preferably 10%. On the other hand, when the CaO content is too high, the liquidus temperature increases. Therefore, the upper limit of CaO content is preferably 13%, more preferably 12.9%, more preferably 12.8%, more preferably 12.6%, more preferably 12.5%, further preferably 12.4%, further preferably 12.2%, and most preferably 12%.

[0037] The mol% MgO / CaO ratio is a crucial component ratio for improving devitrification resistance. When the mol% MgO / CaO ratio is too low, devitrification resistance tends to decrease. Therefore, the lower limit of the mol% MgO / CaO ratio is preferably 0.6, more preferably 0.7, further preferably 0.8, and most preferably 0.9. On the other hand, when the mol% MgO / CaO ratio is too high, the liquid phase viscosity decreases, which can easily increase the manufacturing cost of the glass plate. Therefore, the upper limit of the mol% MgO / CaO ratio is preferably 2.0, more preferably 1.8, further preferably 1.6, further preferably 1.4, and most preferably 1.2. Furthermore, the "mol% MgO / CaO ratio" is the value obtained by dividing the mol% content of MgO by the mol% content of CaO.

[0038] SrO is not an essential component, but its presence can improve resistance to devitrification and enhance meltability by reducing high-temperature viscosity without lowering the strain point. Furthermore, SrO inhibits the reduction of liquid phase viscosity. When the SrO content is too low, these effects are difficult to achieve. Therefore, the lower limit of SrO content is preferably 0%, more preferably more than 0%, more preferably 0.1%, further preferably more than 0.1%, further preferably 0.2%, further preferably 0.3%, further preferably more than 0.3%, further preferably 0.4%, further preferably more than 0.4%, and most preferably 0.5%. On the other hand, when the SrO content is too high, the coefficient of thermal expansion and density tend to increase. Therefore, the upper limit of SrO is preferably 2%, more preferably less than 2%, further preferably 1.8%, further preferably 1.6%, further preferably 1.5%, further preferably 1.4%, further preferably 1.2%, further preferably 1%, further preferably less than 1%, further preferably 0.9%, further preferably less than 0.9%, further preferably 0.8%, further preferably less than 0.8%, further preferably 0.7%, further preferably less than 0.7%, further preferably 0.6%, and best preferably less than 0.6%.

[0039] BaO is not an essential component, but its presence can improve devitrification resistance. Therefore, the lower limit for BaO content is preferably 0%, more preferably more than 0%, more preferably 0.1%, further preferably more than 0.1%, further preferably 0.2%, further preferably 0.3%, further preferably 0.4%, further preferably more than 0.4%, and most preferably 0.5%. On the other hand, when the BaO content is too high, the Young's modulus tends to decrease, and the density tends to increase. As a result, the Young's modulus increases, and the glass plate is prone to bending. Therefore, the upper limit for BaO content is preferably 1%, more preferably less than 1%, more preferably 0.9%, further preferably less than 0.9%, further preferably 0.8%, further preferably less than 0.8%, and most preferably 0.7%.

[0040] SrO and BaO are components that improve devitrification resistance. The lower limit of SrO+BaO is preferably 0%, more preferably more than 0%, more preferably 0.1%, further preferably more than 0.1%, further preferably 0.2%, further preferably 0.3%, further preferably 0.4%, further preferably more than 0.4%, and most preferably 0.5%. On the other hand, when the content of SrO+BaO is too high, the Young's modulus tends to decrease, and the density tends to increase. As a result, the Young's modulus increases, and the glass plate is prone to bending. Therefore, the upper limit of SrO+BaO is preferably 2%, more preferably less than 1%, more preferably 0.9%, further preferably less than 0.9%, further preferably 0.8%, further preferably less than 0.8%, and most preferably 0.7%. Here, "SrO+BaO" refers to the combined amount of SrO and BaO.

[0041] B₂O₃, SrO, and BaO are components that improve devitrification resistance. The lower limit of B₂O₃+SrO+BaO is preferably 0%, more preferably more than 0%, more preferably 0.1%, further preferably more than 0.1%, further preferably 0.2%, further preferably 0.3%, further preferably 0.4%, further preferably more than 0.4%, and most preferably 0.5%. On the other hand, when the content of B₂O₃+SrO+BaO is too high, the Young's modulus tends to decrease. Therefore, the upper limit of B₂O₃+SrO+BaO is preferably 2%, more preferably less than 1%, more preferably 0.9%, further preferably less than 0.9%, further preferably 0.8%, further preferably less than 0.8%, and most preferably 0.7%. Here, "B₂O₃+SrO+BaO" refers to the combined amount of B₂O₃, SrO, and BaO.

[0042] The mol% SrO / SiO2 ratio is a crucial component ratio for balancing Young's modulus and liquid phase viscosity. When the mol% SrO / SiO2 ratio is too small, the Young's modulus tends to decrease. Therefore, the lower limit of the mol% SrO / SiO2 ratio is preferably 0, more preferably greater than 0, further preferably 0.001, and most preferably greater than 0.001. On the other hand, when the mol% SrO / SiO2 ratio is too large, the liquid phase viscosity decreases, and the manufacturing cost of the glass plate tends to increase. Therefore, the upper limit of the mol% SrO / SiO2 ratio is preferably 0.03, more preferably 0.02, further preferably 0.015, further preferably 0.01, further preferably less than 0.01, further preferably 0.009, further preferably less than 0.009, further preferably 0.008, and most preferably less than 0.008.

[0043] The mol% ratio of (MgO+CaO) / (MgO+CaO+SrO+BaO) is a crucial component ratio for balancing Young's modulus and solubility. When the mol% ratio is too small, either the Young's modulus or solubility tends to decrease. Therefore, the lower limit of the mol% ratio is preferably 0.6, more preferably 0.7, further preferably 0.8, further preferably 0.9, and most preferably 0.95. On the other hand, when the mol% ratio is too large, the liquid phase viscosity decreases, potentially increasing the manufacturing cost of the glass plate. Therefore, the upper limit of the mol% ratio (MgO+CaO) / (MgO+CaO+SrO+BaO) is preferably 1, more preferably 0.99, further preferably 0.98, and most preferably 0.97. Furthermore, the "mol% ratio (MgO+CaO) / (MgO+CaO+SrO+BaO)" is the value obtained by dividing the total mol% content of MgO and CaO by the total mol% content of MgO, CaO, SrO, and BaO.

[0044] The mol% ratio of (B₂O₃ + SrO + BaO) / Al₂O₃ is a crucial component ratio for improving Young's modulus and devitrification resistance. When the mol% ratio of (B₂O₃ + SrO + BaO) / Al₂O₃ is too small, devitrification resistance decreases, and the manufacturing cost of the glass plate tends to increase. Therefore, the lower limit of the mol% ratio of (B₂O₃ + SrO + BaO) / Al₂O₃ is preferably 0.001, more preferably 0.005, further preferably 0.008, further preferably 0.01, further preferably 0.02, further preferably 0.03, further preferably 0.04, and most preferably 0.05. On the other hand, when the mol% ratio of (B₂O₃ + SrO + BaO) / Al₂O₃ is too large, the Young's modulus tends to decrease. Therefore, the upper limit of the mol% ratio of (B₂O₃+SrO+BaO) / Al₂O₃ is preferably 0.3, more preferably 0.25, further preferably 0.2, further preferably 0.15, further preferably 0.12, further preferably 0.1, and most preferably 0.09.

[0045] The mol% ratio of (B₂O₃ + SrO + BaO) / MgO is a crucial component ratio for improving Young's modulus and devitrification resistance. When the mol% ratio of (B₂O₃ + SrO + BaO) / MgO is too small, devitrification resistance decreases, and the manufacturing cost of the glass plate tends to increase. Therefore, the lower limit of the mol% ratio of (B₂O₃ + SrO + BaO) / MgO is preferably 0.001, more preferably 0.005, further preferably 0.008, further preferably 0.01, further preferably 0.02, further preferably 0.03, further preferably 0.04, and most preferably 0.05. On the other hand, when the mol% ratio of (B₂O₃ + SrO + BaO) / MgO is too large, Young's modulus tends to decrease. Therefore, the upper limit of the mol% ratio of (B₂O₃+SrO+BaO) / MgO is preferably 0.5, more preferably 0.4, further preferably 0.3, further preferably 0.27, further preferably 0.24, further preferably 0.22, and most preferably 0.2. Furthermore, "(B₂O₃+SrO+BaO) / MgO" is the value obtained by dividing the total mol% content of B₂O₃, SrO, and BaO by the mol% content of MgO.

[0046] The appropriate range of each component can be combined to determine the suitable glass composition range. In order to optimize the effect of the invention, it is particularly preferred that the glass composition contains 64-72% SiO2, 12-16% Al2O3, 0-less than 1% B2O3, 0-0.5% Li2O+Na2O+K2O, 6-12% MgO, 9-13% CaO, more than 0 and less than or equal to 2% SrO, and 0-1% BaO, and the mol% ratio SrO / SiO2 is set to 0-0.008.

[0047] In addition to the above-mentioned ingredients, the following ingredients may also be added as optional ingredients. Furthermore, from the viewpoint of effectively realizing the effects of the present invention, the content of other ingredients besides the above-mentioned ingredients is preferably 10% or less, especially 5% or less, in total.

[0048] P₂O₅ is a component that raises the strain point and can significantly suppress the devitrification and crystallization of alkaline earth aluminosilicates such as anorthite. However, when P₂O₅ is present in large quantities, the glass is prone to phase separation. The preferred content of P₂O₅ is 0~2.5%, more preferably 0~1.5%, further preferably 0~0.5%, further preferably 0~0.3%, and particularly preferably 0~less than 0.1%.

[0049] TiO2 is a component that reduces high-temperature viscosity and increases meltability, and it also inhibits exposure to sunlight. However, when TiO2 content is high, the glass will be colored, and the transmittance will easily decrease. The preferred TiO2 content is 0~2.5%, more preferably 0.0005~1%, further preferably 0.001~0.5%, and most preferably 0.005~0.1%.

[0050] ZnO is a component that improves Young's modulus. However, when ZnO content is high, the glass is prone to devitrification, and the strain point tends to decrease. The ZnO content is preferably 0-6%, more preferably 0-5%, further preferably 0-4%, and particularly preferably 0.001-less than 3%.

[0051] ZrO₂ is a component that improves Young's modulus. However, when ZrO₂ is present in large quantities, the glass is prone to devitrification. The preferred ZrO₂ content is 0~2.5%, more preferably 0.0005~1%, further preferably 0.001~0.5%, and especially preferably 0.005~0.1%.

[0052] Y₂O₃, Nb₂O₅, and La₂O₃ contribute to increasing the strain point and Young's modulus. The total amount and content of these components are preferably 0-5%, more preferably 0-1%, further preferably 0-0.5%, and most preferably 0-less than 0.5%. Excessive amounts of Y₂O₃, Nb₂O₅, and La₂O₃ can easily increase density or raw material costs.

[0053] SnO₂ is a component with good clarifying properties in high-temperature regions, and it also increases the strain point and reduces high-temperature viscosity. The preferred SnO₂ content is 0-1%, 0.001-1%, 0.01-0.5%, and especially 0.05-0.3%. When the SnO₂ content is too high, devitrification crystallization of SnO₂ is easily precipitated. Furthermore, when the SnO₂ content is less than 0.001%, the above-mentioned effects are difficult to achieve.

[0054] As mentioned above, SnO2 is suitable as a clarifying agent, but up to 5% (preferably up to 1%, even more preferably up to 0.5%) of metal powders such as F, SO3, C, Al, and Si can be added to replace SnO2 as a clarifying agent, or used together with SnO2 as a clarifying agent, without impairing the glass properties. Alternatively, up to 5% (preferably up to 1%, even more preferably up to 0.5%) of CeO2, F, etc., can also be added as a clarifying agent.

[0055] As a clarifying agent, As₂O₃ and Sb₂O₃ are also effective. However, As₂O₃ and Sb₂O₃ are components that increase environmental impact. Furthermore, As₂O₃ reduces resistance to sunlight exposure. Therefore, the alkali-free glass plate of the present invention is preferably substantially free of these components.

[0056] Cl is a component that promotes the initial melting of glass batches. Furthermore, the addition of Cl can enhance the effect of clarifying agents. As a result, melting costs can be reduced, and the lifespan of glass manufacturing furnaces can be extended. However, when the Cl content is too high, the strain point tends to decrease. Therefore, the Cl content is preferably 0-3%, more preferably 0.0005-1%, and particularly preferably 0.001-0.5%. Moreover, as a raw material for introducing Cl, chlorides of alkaline earth metal oxides such as strontium chloride or aluminum chloride can be used.

[0057] Fe₂O₃ is an unavoidable component mixed into glass raw materials, and it also reduces resistivity. The preferred Fe₂O₃ content is 0-300 ppm by mass, 80-250 ppm by mass, and especially 100-200 ppm by mass. When the Fe₂O₃ content is too low, raw material costs tend to increase. On the other hand, when the Fe₂O₃ content is too high, the resistivity of the molten glass increases, making electrofusion difficult.

[0058] The alkali-free glass plate of the present invention preferably has the following characteristics.

[0059] The preferred average coefficient of thermal expansion in the temperature range of 30~380℃ is 30×10⁻⁷~50×10⁻⁷ / ℃, 32×10⁻⁷~48×10⁻⁷ / ℃, 33×10⁻⁷~45×10⁻⁷ / ℃, 34×10⁻⁷~44×10⁻⁷ / ℃, especially 35×10⁻⁷~43×10⁻⁷ / ℃. If this is achieved, it is easier to match the coefficient of thermal expansion of the Si used in TFTs.

[0060] The optimal Young's modulus is 83 GPa or higher, exceeding 83 GPa, 83.3 GPa or higher, 83.5 GPa or higher, 83.8 GPa or higher, 84 GPa or higher, exceeding 84 GPa, 84.3 GPa or higher, 84.5 GPa or higher, 84.8 GPa or higher, 85 GPa or higher, 85.3 GPa or higher, 85.5 GPa or higher, 85.8 GPa or higher, and 86 GPa or higher, especially exceeding 86-120 GPa. When the Young's modulus is too low, the glass plate is prone to bending and causing adverse conditions.

[0061] The preferred Young's modulus is 32 GPa / g·cm⁻³ or higher, 32.5 GPa / g·cm⁻³ or higher, 33 GPa / g·cm⁻³ or higher, 33.3 GPa / g·cm⁻³ or higher, 33.5 GPa / g·cm⁻³ or higher, 33.8 GPa / g·cm⁻³ or higher, 34 GPa / g·cm⁻³ or higher, exceeding 34 GPa / g·cm⁻³, 34.2 GPa / g·cm⁻³ or higher, and 34.4 GPa / g·cm⁻³ or higher, especially 34.5~37 GPa / g·cm⁻³. When the Young's modulus is too low, the glass plate is prone to bending and adverse conditions.

[0062] The optimal strain point is above 730℃, above 732℃, above 734℃, above 735℃, above 736℃, above 738℃, and especially above 740~800℃. If so, the thermal shrinkage of the glass plate can be suppressed in the LTPS process.

[0063] The ideal liquidus temperature is below 1350℃, below 1300℃, below 1290℃, below 1285℃, below 1280℃, below 1275℃, below 1270℃, and especially between 1200 and 1260℃. This helps prevent devitrification crystallization during glass manufacturing, which could reduce productivity. Furthermore, it facilitates the use of overflow-drawing methods, thus improving the surface quality of the glass sheet and reducing manufacturing costs. Moreover, liquidus temperature is an indicator of devitrification resistance; the lower the liquidus temperature, the better the devitrification resistance.

[0064] The preferred liquid phase viscosity is 10⁴.0 dPa·s or higher, 10⁴.1 dPa·s or higher, 10⁴.2 dPa·s or higher, and especially 10⁴.3 to 10⁷.0 dPa·s. With this viscosity, devitrification is less likely to occur during forming, making it easier to form using the overflow pull-down method. As a result, the surface quality of the glass sheet can be improved, and the manufacturing cost of the glass sheet can be reduced. Furthermore, liquid phase viscosity is an indicator of devitrification resistance and formability; the higher the liquid phase viscosity, the higher the devitrification resistance and formability.

[0065] The optimal temperatures for achieving a high viscosity of 10 ≤ 2.5 dPa·s are below 1650℃, below 1630℃, below 1610℃, and especially between 1400 and 1600℃. If the temperature for a high viscosity of 10 ≤ 2.5 dPa·s is too high, it becomes difficult to melt the glass batch, leading to increased manufacturing costs for glass sheets. Furthermore, the temperature for a high viscosity of 10 ≤ 2.5 dPa·s is equivalent to the melting temperature; the lower this temperature, the higher the meltability.

[0066] The β-OH value is an indicator of the water content in glass. Lowering the β-OH value increases the strain point. Furthermore, even with the same glass composition, a lower β-OH value results in less thermal shrinkage at temperatures below the strain point. Preferred β-OH values ​​are 0.35 / mm or less, 0.30 / mm or less, 0.28 / mm or less, 0.25 / mm or less, and especially 0.20 / mm or less. Moreover, when the β-OH value is too low, melt permeability tends to decrease. Therefore, a β-OH value of 0.01 / mm or more, and especially 0.03 / mm or more, is preferred.

[0067] The following methods can be used to reduce the β-OH value: (1) Select raw materials with low water content. (2) Add components that reduce the β-OH value (Cl, SO3, etc.) to the glass. (3) Reduce the water content in the furnace atmosphere. (4) Introduce N2 into the molten glass. (5) Use a small melting furnace. (6) Increase the flow rate of the molten glass. (7) Use electrofusion.

[0068] Here, "β-OH value" refers to the value obtained by measuring the transmittance of glass using FT-IR (Fourier Transform Infrared Spectrometer) and using the following formula 1.

[0069] [Number 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 (%) of hydroxyl absorption wavelength near 3600 cm⁻¹

[0070] The alkali-free glass sheet of this invention is preferably formed by an overflow-drawing method. The overflow-drawing method involves allowing molten glass to overflow from both sides of a heat-resistant refractory channel-like structure, converging at the lower end of the channel-like structure, and extending downwards to form a glass sheet. In the overflow-drawing method, the surface of the glass sheet should not contact the refractory channel, but should be formed as a free surface. Therefore, unpolished glass sheets with good surface quality can be manufactured inexpensively, and thinning is also easier.

[0071] The alkali-free glass sheet of this invention is preferably formed by the float glass process. This allows for the inexpensive manufacture of large glass sheets.

[0072] The alkali-free glass plate of this invention preferably has a polished surface. Polishing the glass surface reduces the total thickness variation (TTV). As a result, a magnetic film can be appropriately formed, making it suitable as a glass substrate for magnetic recording media.

[0073] Regarding the alkali-free glass plate of this invention, the plate thickness is not particularly limited. However, when used in organic EL devices, the plate thickness is preferably less than 0.7 mm, less than 0.6 mm, or especially 0.05 to 0.5 mm. The thinner the plate, the more lightweight the organic EL device can be achieved. The plate thickness can be adjusted by adjusting the flow rate or plate drawing speed during glass manufacturing. On the other hand, when used in magnetic recording media, the plate thickness is preferably less than 1.5 mm, less than 1.2 mm, 0.2 to 1.0 mm, or especially 0.3 to 0.9 mm. When the plate thickness is too thick, etching to the required thickness is necessary, which may increase processing costs.

[0074] The alkali-free glass plate of this invention is preferably used as a substrate for organic EL devices, especially for display panels for organic EL televisions, and as a carrier for manufacturing organic EL display panels. Particularly in applications for organic EL televisions, after fabricating multiple devices on the glass plate, each device is divided and cut, thereby achieving cost reduction (so-called panelization). The alkali-free glass plate of this invention can readily meet this requirement because it is easily formed into large glass plates.

[0075] Furthermore, the alkali-free glass plate of the present invention is preferably used as a glass substrate for magnetic recording media, especially energy-assisted magnetic recording media, due to its excellent manufacturability and sufficiently high strain point and Young's modulus. To improve the regularity (i.e., uniformity) of the magnetic layer to achieve high Ku, the substrate containing the glass plate is heat-treated at a high temperature of approximately 800°C during or before and after the magnetic layer is formed. The alkali-free glass plate of the present invention can withstand this heat treatment and also withstand the impact on the substrate caused by the high rotation of the magnetic recording media. The alkali-free glass plate of the present invention is processed into a disc substrate 1 as shown in FIG. 1 by cutting and other processing. Thus, when used as a glass substrate for magnetic recording media, the disc substrate 1 preferably has a disc shape, and more preferably has a circular opening C formed at the center. [Example]

[0076] The present invention will now be described based on embodiments. However, these embodiments are merely illustrative and are not intended to limit the invention in any way.

[0077] Tables 1-3 show the embodiments of the present invention (samples No. 1-30).

[0078] [Table 1] No.1 No.2 No. 3 No. 4 No. 5 No. 6 No. 7 No. 8 No. 9 No. 10 Glass composition (mol%) SiO 2 68.9 67.4 67.4 65.9 65.9 68.9 67.4 67.4 65.9 65.9 Al₂O₃ 13.5 13.5 13.5 13.5 13.5 12.5 12.5 12.5 12.5 12.5 B2O3 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Li 2O 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 Na2O 0.010 0.010 0.010 0.010 0.010 0.010 0.010 0.010 0.010 0.010 K2O 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 MgO 7.5 9.0 7.5 10.5 9.0 8.0 9.5 8.0 11.0 9.5 High 9.5 9.5 11.0 9.5 11.0 10.0 10.0 11.5 10.0 11.5 SrO 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 Bag 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 SnO 2 0.09 0.09 0.09 0.09 0.09 0.09 0.09 0.09 0.09 0.09 Fe2O3 0.008 0.009 0.009 0.010 0.009 0.010 0.009 0.010 0.010 0.010 TiO2 0.006 0.007 0.007 0.006 0.006 0.007 0.007 0.007 0.007 0.006 ZrO2 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 Li₂O + Na₂O + K₂O 0.012 0.012 0.012 0.012 0.012 0.012 0.012 0.012 0.012 0.012 MgO / CaO 0.789 0.947 0.682 1.105 0.818 0.800 0.950 0.696 1.100 0.826 SrO / SiO2 0.007 0.007 0.007 0.008 0.008 0.007 0.007 0.007 0.008 0.008 SrO+BaO 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 B2O3+SrO+BaO 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 (B₂O₃ + SrO + BaO) / Al₂O₃ 0.037 0.037 0.037 0.037 0.037 0.040 0.040 0.040 0.040 0.040 B2O3 / MgO 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 (B2O3 + SrO + BaO) / MgO 0.067 0.056 0.067 0.048 0.056 0.063 0.053 0.063 0.045 0.053 (MgO+CaO) / (MgO+CaO+SrO+BaO) 0.971 0.974 0.974 0.976 0.976 0.973 0.975 0.975 0.977 0.977 CTE[×10 -7 / ℃] 36.8 39.2 40.4 39.4 39.5 38.3 39.5 40.4 40.7 41.6 ρ[g / cm³] 2.53 2.54 2.54 2.56 2.56 2.53 2.54 2.55 2.56 2.57 E[GPa] 88 89 89 91 90 88 89 88 90 90 E / ρ[GPa / (g·cm -3)] 35.0 35.2 34.9 35.4 35.2 34.9 35.0 34.7 35.2 34.9 Ps[℃] 762 756 757 750 750 754 747 746 740 738 Ta[℃] 817 809 810 801 801 808 800 799 792 791 Ts[℃] 1031 1018 1018 1005 1005 1022 1008 1008 996 999 10 4dPa·s[℃] 1326 1303 1305 1282 1282 1320 1298 1294 1274 1275 10 3dPa·s[℃] 1479 1452 1454 1426 1427 1473 1446 1442 1417 1418 10 2.5dPa·s[℃] 1575 1248 1551 1519 1521 1572 1542 1537 1510 1511 TL[℃] 1270 1265 1293 1260 1285 1268 1251 1273 1241 1260 Log 10ηTL 4.5 4.3 4.1 4.2 4.0 4.5 4.4 4.2 4.3 4.1

[0079] [Table 2] No. 11 No. 12 No. 13 No. 14 No. 15 No. 16 No. 17 No. 18 No. 19 No. 20 glass composition (mol%) SiO2 68.9 67.4 65.9 68.9 67.4 68.9 68.2 67.4 66.7 67.2 Al 2O 3 14.5 14.5 14.5 13.5 12.5 12.5 12.5 12.5 12.5 12.5 B2O3 0.0 0.0 0.0 0.0 0.3 0.0 0.0 0.0 0.0 0.0 Li 2O 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 Na2O 0.010 0.010 0.010 0.010 0.010 0.020 0.010 0.010 0.020 0.010 K2O 0.001 0.001 0.001 0.001 0.001 0.002 0.002 0.002 0.002 0.001 MgO 7.0 8.5 10.0 7.5 9.5 8.9 9.5 10.4 11.0 10.4 High 9.0 9.0 9.0 9.5 10.0 9.1 9.3 9.1 9.3 9.1 SrO 0.5 0.5 0.5 0.3 0.1 0.5 0.5 0.5 0.5 0.7 Bag 0.0 0.0 0.0 0.2 0.1 0.0 0.0 0.0 0.0 0.0 SnO 2 0.09 0.09 0.09 0.09 0.09 0.09 0.09 0.09 0.09 0.09 Fe 2O 3 0.009 0.009 0.009 0.008 0.009 0.009 0.009 0.009 0.009 0.009 TiO2 0.007 0.007 0.007 0.006 0.007 0.007 0.007 0.007 0.007 0.006 ZrO2 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 Li₂O + Na₂O + K₂O 0.012 0.012 0.012 0.012 0.012 0.023 0.012 0.012 0.022 0.023 MgO / CaO 0.778 0.944 1.111 0.789 0.950 0.978 1.027 1.143 1.189 1.143 SrO / SiO2 0.007 0.007 0.008 0.004 0.001 0.007 0.007 0.007 0.008 0.010 SrO+BaO 0.5 0.5 0.5 0.5 0.2 0.5 0.5 0.5 0.5 0.7 B2O3+SrO+BaO 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.7 (B₂O₃ + SrO + BaO) / Al₂O₃ 0.034 0.034 0.034 0.037 0.040 0.040 0.040 0.040 0.040 0.056 B2O3 / MgO 0.000 0.000 0.000 0.000 0.032 0.000 0.000 0.000 0.000 0.000 (B2O3 + SrO + BaO) / MgO 0.071 0.059 0.050 0.067 0.053 0.056 0.053 0.048 0.045 0.067 (MgO+CaO) / (MgO+CaO+SrO+BaO) 0.970 0.972 0.974 0.971 0.990 0.973 0.974 0.975 0.976 0.965 CTE[×10 -7 / ℃] 36.0 37.2 38.4 37.4 39.5 37.8 38.5 39.1 39.7 39.3 ρ[g / cm³] 2.52 2.54 2.55 2.53 2.53 2.52 2.53 2.54 2.55 2.55 E[GPa] 89 90 91 88 89 88 89 90 90 90 E / ρ[GPa / (g·cm -3)] 35.2 35.5 35.6 34.9 35.1 35.0 35.1 35.3 35.3 35.2 Ps[℃] 769 761 754 756 742 752 748 746 744 744 Ta[℃] 824 815 807 811 794 806 802 799 795 796 Ts[℃] 1038 1024 1012 1030 1006 1022 1015 1008 1002 1006 10 4dPa·s[℃] 1336 1312 1290 1327 1291 1317 1308 1295 1285 1292 10 3dPa·s[℃] 1486 1458 1433 1481 1442 1469 1457 1443 1431 1439 10 2.5dPa·s[℃] 1582 1552 1524 1581 1538 1568 1554 1538 1524 1534 TL[℃] 1280 1286 1289 1270 1250 1264 1250 1242 1244 1253 Log 10ηTL 4.5 4.2 4.0 4.5 4.4 4.5 4.5 4.5 4.4 4.3

[0080] [Table 3] No. 21 No. 22 No. 23 No. 24 No. 25 No. 26 No. 27 No. 28 No. 29 No. 30 glass composition (mol%) SiO2 67.2 67.0 67.4 67.2 67.9 66.4 67.4 67.4 67.5 67.6 Al 2O 3 12.5 12.5 12.5 12.5 15.0 15.5 12.5 12.5 12.5 12.5 B 2O 3 0.0 0.0 0.0 0.0 0.0 0.0 0.1 0.2 0.1 0.2 Li 2O 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 Na2O 0.020 0.010 0.010 0.010 0.010 0.010 0.010 0.010 0.020 0.010 K2O 0.003 0.001 0.001 0.001 0.001 0.002 0.002 0.002 0.002 0.002 MgO 10.4 10.4 10.2 10.2 7.0 7.0 10.4 10.4 10.2 10.0 CaO 9.1 9.1 9.1 9.1 9.5 9.5 9.1 9.1 9.1 9.1 SrO 0.5 0.7 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 BaO 0.2 0.2 0.2 0.4 0.0 1.0 0.0 0.0 0.0 0.0 SnO2 0.09 0.09 0.09 0.09 0.09 0.09 0.09 0.09 0.09 0.09 Fe2O3 0.009 0.009 0.009 0.009 0.009 0.009 0.009 0.009 0.009 0.009 TiO2 0.007 0.006 0.007 0.007 0.007 0.007 0.007 0.007 0.007 0.007 ZrO2 0.002 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 Li₂O + Na₂O + K₂O 0.012 0.012 0.012 0.012 0.012 0.012 0.023 0.000 0.000 0.000 MgO / CaO 1.143 1.143 1.121 1.121 0.737 0.737 1.143 1.143 1.121 1.099 SrO / SiO2 0.007 0.010 0.007 0.007 0.007 0.008 0.007 0.007 0.007 0.007 SrO+BaO 0.7 0.9 0.7 0.9 0.5 1.5 0.5 0.5 0.5 0.5 B2O3+SrO+BaO 0.7 0.9 0.7 0.9 0.5 1.5 0.6 0.7 0.6 0.7 (B₂O₃ + SrO + BaO) / Al₂O₃ 0.056 0.072 0.056 0.072 0.033 0.097 0.048 0.056 0.048 0.056 B2O3 / MgO 0.000 0.000 0.000 0.000 0.000 0.000 0.010 0.019 0.010 0.020 (B2O3+SrO+BaO) / MgO 0.067 0.087 0.069 0.088 0.071 0.214 0.058 0.067 0.059 0.070 (MgO+CaO) / (MgO+CaO+SrO+BaO) 0.965 0.956 0.965 0.955 0.971 0.917 0.975 0.975 0.975 0.974 CTE[×10 -7 / ℃] 39.7 39.8 39.3 39.6 36.1 38.0 39.1 39.1 39.0 38.8 ρ[g / cm³] 2.55 2.56 2.55 2.56 2.53 2.58 2.54 2.54 2.54 2.54 E[GPa] 89 89 89 89 89 89 90 89 89 89 E / ρ[GPa / (g·cm -3)] 35.0 35.0 35.0 34.8 35.3 34.7 35.2 35.2 35.2 35.2 Ps[℃] 742 742 743 743 771 768 745 744 746 745 Ta[℃] 796 795 797 796 826 822 798 797 799 799 Ts[℃] 1005 1004 1007 1006 1041 1033 1007 1005 1009 1009 10 4dPa·s[℃] 1294 1292 1297 1294 1335 1319 1293 1292 1297 1298 10 3dPa·s[℃] 1443 1443 1447 1445 1483 1464 1441 1440 1445 1447 10 2.5dPa·s[℃] 1539 1541 1544 1542 1581 1560 1536 1535 1540 1543 TL[℃] 1255 1250 1250 1247 1300 1290 1240 1240 1240 1240 Log 10ηTL 4.3 4.4 4.4 4.4 4.3 4.3 4.5 4.5 4.5 4.5

[0081] First, glass raw materials were prepared according to the glass composition shown in the table. The resulting glass batch was placed in a platinum crucible and melted at 1600–1650 °C for 24 hours. During the melting of the glass batch, a platinum stirrer was used for stirring and homogenization. Then, the molten glass was poured onto a carbon plate, shaped into a plate, and then slowly cooled for 30 minutes at a temperature near the slow cooling point. For each obtained sample, the average coefficient of thermal expansion (CTE), density (ρ), Young's modulus (E), specific Young's modulus (E / ρ), strain point (Ps), slow cooling point (Ta), softening point (Ts), temperature at a high-temperature viscosity of 10⁴ dPa·s, temperature at a high-temperature viscosity of 10³ dPa·s, temperature at a high-temperature viscosity of 10².5 dPa·s, liquidus temperature (TL), and viscosity at liquidus temperature (TL) log₁₀ηTL were evaluated within the temperature range of 30–380 °C.

[0082] The average coefficient of thermal expansion (CTE) within the temperature range of 30~380℃ is a value measured by a dilatometer.

[0083] The density ρ is a value measured using the well-known Archimedes method.

[0084] Young's modulus E is a value measured using the well-known resonance method.

[0085] The Young's modulus E / ρ is the value obtained by dividing the Young's modulus by the density.

[0086] The strain point Ps, cooling point Ta, and softening point Ts are values ​​measured based on the methods of ASTM C336 and C338.

[0087] The temperatures at high-temperature viscosities of 10⁴ dPa·s, 10⁻³ dPa·s, and 10⁻² dPa·s were measured using the platinum ball pulling method.

[0088] The liquid phase temperature (TL) is the temperature at which glass powder that has passed through a standard sieve of 30 mesh (500 μm) and remains at 50 mesh (300 μm) is placed in a platinum boat and kept in a temperature gradient furnace for 24 hours to crystallize.

[0089] The liquid phase viscosity log 10ηTL is a value obtained by measuring the viscosity of glass at liquid phase temperature TL using the platinum ball pulling method.

[0090] As shown in Tables 1-3, samples No. 1-30, due to the limited glass composition, exhibit Young's modulus above 88 GPa, strain point above 738℃, liquidus temperature below 1300℃, and liquidus viscosity above 10⁴.0 dPa·s. Therefore, samples No. 1-30, due to their excellent manufacturability and sufficiently high strain point and Young's modulus, are suitable as glass substrates for organic EL devices or magnetic recording media. [Industrial Applicability]

[0091] The alkali-free glass plate of the present invention is suitable as a substrate for organic EL devices, especially for organic EL television display panels, and as a carrier for manufacturing organic EL display panels. In addition, it is also suitable as a substrate for flat panel displays such as liquid crystal displays, a cover glass for image sensors such as charge-coupled devices (CCDs) and close proximity solid-state imaging devices (CISs), a substrate and cover glass for solar cells, and a substrate for organic EL lighting.

[0092] Furthermore, the alkali-free glass plate of this invention, due to its sufficiently high strain point and Young's modulus, is also suitable as a glass substrate for magnetic recording media. With a high strain point, even under high-temperature heat treatment such as heat-assisted treatment or laser irradiation, glass plate deformation is unlikely. As a result, higher heat treatment temperatures can be used when pursuing high Ku, thus facilitating the manufacture of magnetic recording devices with high recording density. Moreover, with a high Young's modulus, the glass plate is less prone to bending or wobbling (i.e., jitter) during high-speed rotation, thus preventing collisions between the information recording medium and the magnetic head.

[0093] 1: Disc substrate C: Opening

Claims

1. An alkali-free glass plate, characterized in that it contains, by mol%, 67.2-72% SiO2, 12-16% Al2O3, 0-3% B2O3, 0-0.5% Li2O + Na2O + K2O, 7-12% MgO, 9-13% CaO, 0-2% SrO, and 0-1% BaO as glass composition, and the mol% ratio of SrO / SiO2 is 0-0.

03.

2. The alkali-free glass plate of claim 1 contains, by mol%, 67.2-72% SiO2, 12-16% Al2O3, 0-less than 1% B2O3, 0-0.5% Li2O+Na2O+K2O, 8.5-12% MgO, 9-13% CaO, more than 0 and less than or equal to 2% SrO, and 0-1% BaO as glass composition, and the mol% ratio of SrO / SiO2 is 0-0.

008.

3. The alkali-free glass plate of claim 1 or 2 is substantially free of As2O3 and Sb2O3 in its glass composition.

4. The alkali-free glass plate of claim 1 or 2 further contains 0.001 to 1 mol% SnO2.

5. The alkali-free glass plate requested in item 1 or 2 shall have a Young's modulus of 83 GPa or higher, a strain point of 730°C or higher, and a liquidus temperature of 1350°C or lower.

6. For the alkali-free glass plate requested in item 1 or 2, the strain point is above 735℃.

7. The alkali-free glass plate of request item 1 or 2 has a Young's modulus higher than 84 GPa.

8. The alkali-free glass plate requested in item 1 or 2 has an average coefficient of thermal expansion of 30×10-7 to 50×10-7 / ℃ in the temperature range of 30 to 380℃.

9. The alkali-free glass plate of request item 1 or 2 has a liquid phase viscosity of 104.0 dPa·s or higher.

10. The alkali-free glass plate as requested in item 1 or 2, used in organic EL devices.

11. An alkali-free glass plate, as requested in item 1 or 2, for use in magnetic recording media.

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