Alkali-free glass plate

Abstract

An alkali-free glass plate is characterized in that, as a glass composition, it contains, in mol%, 63-70% SiO2, 10-15% Al2O3, 3-8% B2O3, 0-0.5% Li2O + Na2O + K2O, 1-11% MgO, 2-11% CaO, 0-6% SrO, 0-8% BaO, and 13-20% MgO + CaO + SrO + BaO, with a mol% ratio of SiO2 / Al2O3 of 4.2-7 and a mol% ratio of (MgO + CaO + SrO + BaO) / Al2O3 of 0.9-2.

Description

Technical Field

[0001] This invention relates to an alkali-free glass plate, and more particularly to an alkali-free glass plate suitable for use as a substrate for organic EL displays and magnetic recording media. Background Technology

[0002] Organic EL displays and other electronic devices are used in flexible devices, mobile phone displays, and other applications because they are thin, have excellent video display capabilities, and consume little power.

[0003] Glass plates are widely used as substrates for organic EL displays (see, for example, Patent Document 1). The following characteristics are mainly required for glass plates used in this application.

[0004] (1) In order to prevent alkali ions from diffusing into the semiconductor material formed in the heat treatment process, it is necessary to be basically free of alkali metal oxides, that is, to be alkali-free glass (specifically, glass in which the content of alkali oxides in the glass composition is less than 0.5 mol%).

[0005] (2) In order to reduce the cost of glass plates, it is necessary to use the overflow down-drawing method, which is easy to improve the surface quality and has excellent productivity, especially excellent melting and devitrification resistance;

[0006] (3) In LTPS (Low Temperature Poly Silicon) process and oxide TFT (Thin Film Transistor) process, a high strain point is required in order to reduce the thermal shrinkage of the glass plate.

[0007] In addition, magnetic recording media such as magnetic disks and optical disks are used in various information devices. Glass substrates are increasingly being used as the substrates for magnetic recording media, replacing the previously used aluminum alloy substrates (see, for example, Patent Document 2). In recent years, to meet the demand for even higher recording densities, magnetic recording media using energy-assisted magnetic recording methods, i.e., energy-assisted magnetic recording media, are being researched. For energy-assisted magnetic recording media, a magnetic layer is formed on the surface of the glass substrate while using a glass substrate. In energy-assisted magnetic recording media, an ordered alloy with a large magnetic anisotropy coefficient Ku (hereinafter referred to as "high Ku") is used as the magnetic material for the magnetic layer.

[0008] Existing technical documents

[0009] Patent documents

[0010] Patent Document 1: Japanese Patent Application Publication No. 2012-106919

[0011] Patent Document 2: Japanese Patent Application Publication No. 2021-086643 Summary of the Invention

[0012] The problem that the invention aims to solve

[0013] However, OLED TVs, as a type of OLED device, strongly demand larger and thinner sizes, and the demand for high-resolution displays such as 8K is increasing. Therefore, glass panels for these applications require not only large size and thinness but also the ability to withstand the thermal dimensional stability required for high resolution. Furthermore, for OLED TVs, to reduce the price difference with LCDs, low cost is required, and the glass panels are similarly required to be low-cost. However, if the glass panels are made larger and thinner, as explained below, the glass panels become more prone to bending and breakage, or manufacturing costs increase significantly.

[0014] Glass sheets formed by glass manufacturers undergo processes such as cutting, annealing, inspection, and cleaning. During these processes, the glass sheets are fed into and discharged from cassettes with multi-layered shelves. These cassettes typically hold the glass sheets on opposite sides of shelves formed on the inner left and right sides, thus maintaining them horizontally. However, due to the large bending of large and thin glass sheets, a portion of the glass sheet may break upon contact with the cassette during feeding, or it may swing significantly during discharge. To address this problem, increasing the Young's modulus of elasticity of the glass sheet and reducing the amount of bending are effective methods.

[0015] In addition, as mentioned above, in the LTPS and oxide TFT processes 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.

[0016] However, increasing the Young's modulus and strain point of the glass sheet disrupts the balance of the glass composition, reducing productivity, particularly significantly decreasing devitrification resistance, and increasing liquid phase viscosity, thus making it impossible to use the overflow downdraw method for forming. Furthermore, reduced melt flow and higher glass forming temperatures tend to shorten the lifespan of the formed piece. As a result, the cost of the raw glass sheet increases significantly.

[0017] Furthermore, for glass plates used in magnetic recording media, a high Young's modulus is required to prevent significant deformation during high-speed rotation. Specifically, in disk-shaped magnetic recording media, information is written and read while the medium rotates at high speed around its central axis, and the magnetic head moves radially along the direction of rotation. In recent years, to improve writing and reading speeds, rotational speeds have been continuously increasing, from 5400 rpm to 7200 rpm, and further to 10000 rpm. In disk-shaped magnetic recording media, the positions for recording information are pre-allocated based on the distance from the central axis; therefore, if the glass plate deforms during rotation, it will cause the magnetic head to shift, making accurate reading difficult.

[0018] Furthermore, in recent years, by incorporating a Dynamic Flying Height (DFH) mechanism into the magnetic head, a significant reduction in the gap between the recording and playback element section of the magnetic head and the surface of the magnetic recording medium (low levitation quantization) has been achieved, thereby enabling further increases in recording density. The DFH mechanism involves placing a tiny heater or other heating element near the recording and playback element section of the magnetic head, causing thermal expansion only around the periphery of the element section towards the medium surface. With such a mechanism, the distance between the magnetic head and the magnetic layer of the medium is close, allowing the pickup of signals from even smaller magnetic particles, thus achieving high recording density. On the other hand, because the gap between the recording and playback element section of the magnetic head and the surface of the magnetic recording medium is extremely small, for example, less than 2 nm, even a small impact can cause the magnetic head to collide with the surface of the magnetic recording medium. This trend becomes more pronounced at higher rotation speeds. Therefore, preventing the bending and jitter of the glass plate, which can cause such collisions, becomes important during high-speed rotation.

[0019] Furthermore, to achieve high Ku-density by increasing the degree of ordering in the magnetic layer, the substrate containing the glass plate is heat-treated at a high temperature of around 800°C during or before and after the magnetic layer is formed. The higher the recording density, the higher the heat treatment temperature needs to be. Additionally, after the magnetic layer is formed, the substrate containing the glass plate is sometimes subjected to laser irradiation. Such heat treatment and laser irradiation also aim to increase the annealing temperature and coercivity of magnetic layers containing FePt alloys. Therefore, higher heat resistance than conventional glass plates for magnetic recording media is required, i.e., a higher strain point is needed.

[0020] However, as mentioned above, when attempting to increase the Young's modulus and strain point of the glass sheet, the balance of the glass composition is disrupted, productivity decreases, particularly devitrification resistance decreases significantly, and liquid phase viscosity increases, making it impossible to use the overflow downdraw method for forming. Furthermore, decreased melt flow or increased glass forming temperature tends to shorten the lifespan of the formed piece. As a result, the cost of the raw glass sheet increases significantly.

[0021] Therefore, the present invention was created in view of the above circumstances, and its technical challenge is to provide an alkali-free glass plate with excellent productivity and sufficiently high strain point and Young's modulus.

[0022] Methods for solving problems

[0023] The inventors conducted in-depth research and found that the above-mentioned problems can be solved by using an alkali-free glass plate with a specified composition.

[0024] (1) The alkali-free glass plate of the present invention is characterized in that, as a glass composition, it contains, in mol%, 63-70% SiO2, 10-15% Al2O3, 3-8% B2O3, 0-0.5% Li2O + Na2O + K2O, 1-11% MgO, 2-11% CaO, 0-6% SrO, 0-8% BaO, and 13-20% MgO + CaO + SrO + BaO, with a mol% ratio of SiO2 / Al2O3 of 4.2-7 and a mol% ratio of (MgO + CaO + SrO + BaO) / Al2O3 of 0.9-2. Here, "Li2O + Na2O + K2O" refers to the total amount of Li2O, Na2O, and K2O. "MgO + CaO + SrO + BaO" refers to the total amount of MgO, CaO, SrO, and BaO. "SiO2 / Al2O3" is the value obtained by dividing the SiO2 content by the Al2O3 content. "(MgO + CaO + SrO + BaO) / Al2O3" is the value obtained by dividing the total amount of MgO, CaO, SrO, and BaO by the Al2O3 content. It should be noted that "alkali-free glass" in this invention refers to glass with a Li2O + Na2O + K2O content of 0.5% or less.

[0025] (2) Preferably, in the above-mentioned (1) composition, the alkali-free glass plate of the present invention contains, in mol%, 64-68% SiO2, 11-14% Al2O3, 4.1-6% B2O3, 0-0.5% Li2O+Na2O+K2O, 2-9% MgO, 2-10% CaO, 1-4% SrO, 1-6% BaO, and 14-18% MgO+CaO+SrO+BaO, with a mol% ratio of SiO2 / Al2O3 greater than 5-5.4 and a mol% ratio of (MgO+CaO+SrO+BaO) / Al2O3 of 1.2-1.6.

[0026] (3) In the preferred form of the alkali-free glass plate of the present invention, in the above (1) or (2), the content of MgO + CaO + SrO + BaO - Al2O3 is 1 to 5% in mol%. Here, "MgO + CaO + SrO + BaO - Al2O3" is the value obtained by subtracting the content of Al2O3 from the total amount of MgO + CaO + SrO + BaO.

[0027] (4) The alkali-free glass plate of the present invention preferably contains 2.4% or more BaO in any of the above (1) to (3) components, in mol%.

[0028] (5) Preferably, in any of the above-mentioned (1) to (4), the alkali-free glass plate of the present invention does not substantially contain As2O3 and Sb2O3 in the glass composition. Here, "does not substantially contain As2O3 and Sb2O3 in the glass composition" means that the content of As2O3 and Sb2O3 is 0.05 mol% or less.

[0029] (6) The alkali-free glass plate of the present invention preferably contains 0.001 to 1% SnO2 in any of the above (1) to (5) components, in mol%.

[0030] (7) Preferably, in any of the above (1) to (6), the strain point of the alkali-free glass plate of the present invention is 680°C or higher.

[0031] (8) Preferably, in any of the above (1) to (7), the alkali-free glass plate of the present invention has a Young's modulus of 75 GPa or higher.

[0032] (9) Preferably, the alkali-free glass plate of the present invention has a specific Young's modulus of 28 GPa / g·cm in any of the above-described (1) to (8) configurations. -3 above.

[0033] (10) In the alkali-free glass plate of the present invention, the liquid phase temperature is preferably 1400°C or less in any of the above (1) to (9).

[0034] (11) Preferably, in any of the configurations described in (1) to (10) above, the alkali-free glass plate of the present invention has an average coefficient of thermal expansion of 20 × 10⁻⁶ in a temperature range of 30 to 380°C. -7 ~50×10 -7 / ℃.

[0035] (12) Preferably, in any of the above-mentioned (1) to (11), the alkali-free glass plate of the present invention has an annealing point of 730°C or higher.

[0036] (13) Preferably, in any of the above-described (1) to (12) configurations, the liquid phase viscosity of the alkali-free glass plate of the present invention is 10. 4.2 dPa·s or above.

[0037] (14) The alkali-free glass plate of the present invention is preferably used in organic EL devices in the above-described configurations (1) to (13).

[0038] (15) The alkali-free glass plate of the present invention is preferably used as a magnetic recording medium in the above-described configurations (1) to (13).

[0039] Invention Effects

[0040] According to the present invention, it is possible to provide alkali-free glass plates with excellent productivity and sufficiently high strain point and Young's modulus. Detailed Implementation

[0041] The alkali-free glass plate of the present invention is characterized in that, as a glass composition, it contains, in mol%, 63-70% SiO2, 10-15% Al2O3, 3-8% B2O3, 0-0.5% Li2O + Na2O + K2O, 1-11% MgO, 2-11% CaO, 0-6% SrO, 0-8% BaO, and 13-20% MgO + CaO + SrO + BaO, with a mol% ratio of SiO2 / Al2O3 of 4.2-7 and a mol% ratio of (MgO + CaO + SrO + BaO) / Al2O3 of 0.9-2. The reasons for limiting the content of each component as described above are given below. It should be noted that, in the description of the content of each component, % indicates mol% unless otherwise specified. Furthermore, unless otherwise specified, the upper limit indicates above the value, and the lower limit indicates below the value.

[0042] SiO2 is a component that forms the framework of glass. If 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 63%, more preferably 63.2%, further preferably 63.4%, further preferably 63.6%, further preferably 63.8%, further preferably 64%, further preferably 64.1%, further preferably 64.2%, further preferably 64.5%, further preferably 64.7%, further preferably 65%, and most preferably 65.5%. On the other hand, if the SiO2 content is too high, the Young's modulus decreases, the high-temperature viscosity increases, the heat required for melting increases, the melting cost increases, and the dissolved residue of SiO2-introducing raw materials is generated, which may lead to a decrease in yield. In addition, devitrifying crystals such as quartz are easily precipitated, and the liquid phase viscosity tends to decrease. Therefore, the upper limit of SiO2 is preferably 70%, more preferably 69.7%, even more preferably 69.5%, even more preferably 69.2%, even more preferably 69%, even more preferably 68.7%, even more preferably 68.5%, even more preferably 68.3%, and most preferably 68%.

[0043] Al₂O₃ is a component that forms the framework of glass, increases Young's modulus, and raises the strain point. If the Al₂O₃ content is too low, the Young's modulus and strain point tend to decrease. Therefore, the lower limit of Al₂O₃ is preferably 10%, more preferably 10.2%, further preferably 10.4%, further preferably 10.6%, further preferably 10.8%, further preferably 11%, further preferably 11.2%, further preferably 11.4%, and most preferably 11.6%. On the other hand, if 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 15%, more 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%.

[0044] The mol% SiO2 / Al2O3 ratio is an important component ratio used to improve the strain point and reduce high-temperature viscosity. If the mol% SiO2 / Al2O3 ratio is too low, the density tends to increase. Therefore, the lower limit of the mol% SiO2 / Al2O3 ratio is preferably 4.2, more preferably 4.4, more preferably 4.6, more preferably 4.8, more preferably 5, more preferably greater than 5, more preferably 5.1, and most preferably 5.2. On the other hand, if the mol% SiO2 / Al2O3 ratio is too high, the high-temperature viscosity increases, and the manufacturing cost of the glass plate tends to rise. Therefore, the upper limit of the mol% SiO2 / Al2O3 ratio is preferably 7, more preferably 6.5, more preferably 6, more preferably 5.9, more preferably 5.8, more preferably 5.7, more preferably 5.6, more preferably 5.5, more preferably 5.4, and most preferably 5.35.

[0045] B2O3 improves melt permeability and resistance to devitrification. Therefore, the lower limit of B2O3 is preferably 3%, more preferably 3.1%, more preferably 3.2%, more preferably 3.3%, more preferably 3.4%, more preferably 3.5%, more preferably 3.6%, more preferably 3.8%, more preferably 4%, more preferably 4.1%, and most preferably 4.3%. On the other hand, if the B2O3 content is too high, the Young's modulus and strain point tend to decrease. Therefore, the upper limit of B2O3 is preferably 8%, more preferably 7.5%, more preferably 7%, more preferably 6.8%, more preferably 6.5%, more preferably 6.3%, more preferably 6%, more preferably 5.9%, more preferably 5.8%, and most preferably 5.5%.

[0046] Li₂O, Na₂O, and K₂O are components that inevitably mix into the glass raw materials, and their total amount is 0-0.5%, preferably 0-0.1%, more preferably 0-0.09%, further preferably 0.005-0.08%, even more preferably 0.008-0.06%, and most preferably 0.01-0.05%. If the total amount of Li₂O, Na₂O, and K₂O is too high, it may lead to the diffusion of alkali ions into the semiconductor material formed in the heat treatment process. It should be noted that the individual content of Li₂O, Na₂O, and K₂O is preferably 0-0.3%, more preferably 0-0.1%, even more preferably 0-0.08%, even more preferably 0-0.07%, even more preferably 0-0.05%, and most preferably 0.001-0.04%.

[0047] MgO is a component in alkaline earth metal oxides that significantly improves Young's modulus. If the MgO content is too low, the melt permeability and Young's modulus tend to decrease. Therefore, the lower limit of MgO is preferably 1%, more preferably 1.1%, even more preferably 1.3%, further preferably 1.5%, further preferably 1.8%, further preferably 2%, further preferably 2.3%, and most preferably 2.5%. On the other hand, if the MgO 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 MgO is preferably 11%, more preferably 10.5%, further preferably 10.2%, further preferably 10%, further preferably 9.5%, further preferably 9.2%, further preferably 9%, further preferably 8.8%, further preferably 8.5%, further preferably 8.3%, and most preferably 8%.

[0048] CaO is a component that reduces high-temperature viscosity and significantly improves meltability without lowering the strain point. It also increases Young's modulus. If the CaO content is too low, meltability tends to decrease. Therefore, the lower limit of CaO is preferably 2%, more preferably 2.2%, more preferably 2.5%, further preferably 2.8%, further preferably 3%, further preferably 3.2%, further preferably 3.5%, further preferably 3.8%, and most preferably 4%. On the other hand, if the CaO content is too high, the liquidus temperature increases. Therefore, the upper limit of CaO is preferably 11%, more preferably 10.5%, more preferably 10.2%, more preferably 10%, more preferably 9.8%, further preferably 9.5%, further preferably 9.3%, and most preferably 9%.

[0049] SrO is a component that improves resistance to devitrification and reduces high-temperature viscosity and improves meltability without lowering the strain point. It also inhibits the decrease in liquid phase viscosity. Therefore, the lower limit of SrO is preferably 0%, more preferably greater than 0%, more preferably 0.1%, further preferably greater than 0.1%, further preferably 0.2%, further preferably 0.3%, further preferably greater than 0.3%, further preferably 0.4%, further preferably greater than 0.4%, further preferably 0.5%, further preferably 0.7%, and most preferably 1%. On the other hand, if the content of SrO is too high, the coefficient of thermal expansion and density tend to increase. Therefore, the upper limit of SrO is preferably 6%, more preferably less than 6%, further preferably 5.8%, further preferably 5.5%, further preferably 5.3%, further preferably 5%, further preferably 4.8%, further preferably 4.5%, further preferably 4.3%, and most preferably 4%.

[0050] BaO is a component that improves devitrification resistance. Therefore, the lower limit of BaO content is preferably 0%, more preferably greater than 0%, even more preferably 0.1%, further preferably greater than 0.1%, further preferably 0.2%, further preferably 0.3%, further preferably 0.4%, further preferably 0.5%, further preferably 0.7%, further preferably 0.9%, further preferably 1%, further preferably 1.2%, further preferably 1.4%, further preferably 1.6%, further preferably 1.8%, further preferably 2%, further preferably 2.2%, and most preferably 2.4%. On the other hand, if the BaO content is too high, the Young's modulus of elasticity tends to decrease, and the density tends to increase. As a result, the Young's modulus of elasticity decreases, and the glass plate is prone to bending. Therefore, the upper limit of BaO content is preferably 8%, more preferably 7.8%, more preferably 7.5%, further preferably 7.3%, further preferably 7%, further preferably 6.8%, further preferably 6.5%, further preferably 6.3%, and most preferably 6%.

[0051] MgO, CaO, SrO, and BaO are components that increase density and coefficient of thermal expansion. If the content of MgO + CaO + SrO + BaO is too low, the coefficient of thermal expansion tends to decrease. Therefore, the lower limit of MgO + CaO + SrO + BaO is preferably 13%, more preferably 13.3%, more preferably 13.5%, further preferably 13.8%, further preferably 14%, further preferably 14.2%, further preferably 14.4%, further preferably 14.6%, and most preferably 14.8%. On the other hand, if the content of MgO + CaO + SrO + BaO is too high, the density tends to increase. Therefore, the upper limit of MgO + CaO + SrO + BaO is preferably 20%, more preferably 19%, more preferably 18.8%, further preferably 18.5%, further preferably 18%, further preferably 17.8%, and most preferably 17.6%.

[0052] The ratio (MgO + CaO + SrO + BaO) / Al2O3 is an important parameter for reducing the coefficient of thermal expansion and improving melt permeability. If the ratio is too small, the viscosity at high temperatures increases and the melt permeability decreases, which can easily lead to higher manufacturing costs for glass sheets. Therefore, the lower limit of the ratio (MgO + CaO + SrO + BaO) / Al2O3 is preferably 0.9, more preferably 1, further preferably 1.1%, further preferably 1.2%, and most preferably 1.3. On the other hand, if the ratio (MgO + CaO + SrO + BaO) / Al2O3 is too large, the coefficient of thermal expansion can easily increase. Therefore, the upper limit of the ratio (MgO + CaO + SrO + BaO) / Al2O3 is preferably 2, more preferably 1.9, further preferably 1.8, further preferably 1.7, further preferably 1.6, further preferably 1.5, and most preferably 1.4.

[0053] The coefficient of thermal expansion (MgO + CaO + SrO + BaO - Al2O3) is an important parameter for reducing the coefficient of thermal expansion and improving melt permeability. If the value of MgO + CaO + SrO + BaO - Al2O3 is too small, the viscosity at high temperatures increases and the melt permeability decreases, thus easily leading to higher manufacturing costs for glass sheets. Therefore, the lower limit of MgO + CaO + SrO + BaO - Al2O3 is preferably 1%, more preferably 1.2%, even more preferably 1.5%, even more preferably 1.7%, even more preferably 1.8%, even more preferably 1.9%, even more preferably 2%, even more preferably 2.1%, even more preferably 2.4%, even more preferably 2.6%, even more preferably 2.8%, even more preferably 3%, even more preferably 3.2%, and most preferably 3.5%. On the other hand, if the value of MgO + CaO + SrO + BaO - Al2O3 is too large, the coefficient of thermal expansion tends to increase. Therefore, the upper limit of MgO+CaO+SrO+BaO-Al2O3 is preferably 7%, more preferably 6.8%, even more preferably 6.5%, even more preferably 6.3%, even more preferably 6%, even more preferably 5.8%, even more preferably 5.5%, even more preferably 5.3%, and most preferably 5%.

[0054] A suitable glass composition range can be set by appropriately combining the appropriate content ranges of each component. In order to optimize the effect of the present invention, the glass composition, in mol%, preferably contains 64-68% SiO2, 11-14% Al2O3, 4.1-6% B2O3, 0-0.5% Li2O+Na2O+K2O, 2-9% MgO, 2-10% CaO, 1-4% SrO, 1-6% BaO, and 14-18% MgO+CaO+SrO+BaO. The mol% ratio of SiO2 / Al2O3 is greater than 5-5.4, and the mol% ratio of (MgO+CaO+SrO+BaO) / Al2O3 is set to 1.2-1.6.

[0055] In addition to the above-mentioned components, the following components may also be added as optional components. It should be noted that, from the viewpoint of reliably enjoying the effects of the present invention, the content of the components other than those mentioned above is preferably 10% or less in total, and particularly preferably 5% or less.

[0056] P2O5 is a component that raises the strain point and also significantly suppresses the precipitation of devitrifying crystals in alkaline earth aluminosilicate systems such as anorthite. However, if a large amount of P2O5 is present, the glass is prone to phase separation. The P2O5 content is preferably 0 to 2.5%, more preferably 0 to 1.5%, further preferably 0 to 0.5%, even more preferably 0 to 0.3%, even more preferably 0 to less than 0.1%, and particularly preferably 0 to less than 0.01%.

[0057] TiO2 is a component that reduces high-temperature viscosity and improves meltability, and it also inhibits exposure discoloration. However, if TiO2 contains a large amount, the glass will be colored, and the transmittance will easily decrease. The preferred TiO2 content is 0 to 2.5%, more preferably 0.0005 to 1%, further preferably 0.001 to 0.5%, and particularly preferably 0.005 to 0.1%.

[0058] ZnO is a component that improves Young's modulus. However, if the ZnO content is too high, the glass is prone to devitrification, and the strain point tends to decrease. The ZnO content is preferably 0-3%, more preferably 0-2%, further preferably 0-1%, even more preferably 0-0.8%, even more preferably 0-0.5%, and particularly preferably 0 to less than 0.5%.

[0059] Fe2O3 is an unavoidable component in glass raw materials and also reduces resistivity. The preferred Fe2O3 content is 0–0.025%, 0.002–0.02%, and particularly preferred is 0.004–0.01%. If the Fe2O3 content is too low, raw material costs can easily increase. On the other hand, if the Fe2O3 content is too high, the resistivity of the molten glass will increase, making electrofusion difficult.

[0060] ZrO2 is a component that improves Young's modulus. However, if the ZrO2 content is too high, the glass is prone to devitrification. The ZrO2 content is preferably 0 to 2.5%, more preferably 0.0005 to 1%, even more preferably 0.001 to 0.5%, and particularly preferably 0.005 to 0.1%.

[0061] MoO3 is a component that absorbs ultraviolet light (specifically, light with a wavelength of 200-300 nm). Furthermore, MoO3 reduces the moisture content in glass. In particular, by melting the raw material batch using electrofusion heating, while containing MoO3, the moisture content in the glass can be further reduced. If the moisture content in the glass is reduced, the liquid phase viscosity and strain point increase, thereby improving the glass's resistance to devitrification and heat resistance. The minimum content of MoO3 is preferably 0.00001%, more preferably 0.00005%, further preferably 0.0001%, further preferably 0.0002%, further preferably 0.0003%, further preferably 0.0004%, and particularly preferably 0.001%. On the other hand, if the MoO3 content is too high, the transmittance of ultraviolet light decreases, which can easily reduce the yield in the display manufacturing process, especially in the laser lift-off process. Therefore, the upper limit of MoO3 is preferably 0.01%, more preferably 0.008%, even more preferably 0.006%, even more preferably 0.005%, even more preferably 0.004%, and particularly preferably 0.003%.

[0062] Y₂O₃, Nb₂O₅, and La₂O₃ have the effect of increasing the strain point and Young's modulus. The total amount and individual content of these components are preferably 0-5%, more preferably 0-1%, further preferably 0-0.5%, and particularly preferably 0 to less than 0.5%. If the total amount and individual content of Y₂O₃, Nb₂O₅, and La₂O₃ are too high, the density and raw material cost will easily increase.

[0063] SnO2 is a component with good clarifying properties in the high-temperature range, and it also increases the strain point and reduces high-temperature viscosity. The preferred SnO2 content is 0-1%, 0.001-1%, or 0.01-0.5%, and particularly preferably 0.05-0.3%. If the SnO2 content is too high, devitrified SnO2 crystals are easily precipitated.

[0064] As mentioned above, SnO2 is suitable as a clarifier; however, as long as it does not impair the glass properties, it can also be used as a clarifier in place of SnO2, or together with SnO2, metal powders such as F, SO3, C, or Al, Si, etc., each at up to 5% (preferably up to 1%, particularly up to 0.5%). Additionally, CeO2, F, etc., can also be added as a clarifier at up to 2% (preferably up to 1%, particularly up to 0.5%).

[0065] As₂O₃ and Sb₂O₃ are also effective clarifying agents. However, As₂O₃ and Sb₂O₃ are components that increase the environmental burden. In addition, As₂O₃ is a component that reduces the resistance to color change during exposure. Therefore, the alkali-free glass plate of the present invention preferably does not contain these components substantially.

[0066] Cl is a component that promotes the initial melting of the glass batch. Furthermore, the addition of Cl enhances the effect of the clarifying agent. As a result, it is possible to achieve a longer lifespan for the glass manufacturing furnace while reducing melting costs. However, if 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%. It should be noted that alkaline earth metal chlorides such as strontium chloride, or aluminum chloride, can be used as the raw material for introducing Cl.

[0067] The alkali-free glass plate of the present invention preferably has the following characteristics.

[0068] The average coefficient of thermal expansion in the temperature range of 30–380℃ is preferably 20 × 10⁻⁶. -7 ~50×10 -7 / ℃, 25×10 -7 ~48×10 -7 / ℃, 30×10 -7 ~45×10 -7 / ℃, 33×10 -7 ~44×10 -7 / ℃, preferably 35×10 -7 ~43×10 -7 / ℃. If set up like this, it is easy to match the coefficient of thermal expansion of Si used in TFTs.

[0069] The preferred Young's modulus is 75 GPa or higher, 76 GPa or higher, 76.5 GPa or higher, 77 GPa or higher, 77.5 GPa or higher, 78 GPa or higher, 78.5 GPa or higher, 78.7 GPa or higher, 79 GPa or higher, and 79.5 GPa or higher, with a particularly preferred value of 80–120 GPa. If the Young's modulus is too low, undesirable conditions may easily occur due to the bending of the glass plate.

[0070] The preferred Young's modulus is 28 GPa / g·cm. -3 Above, 28.5 GPa / g·cm -3 Above, 29 GPa / g·cm -3 Above, 29.5 GPa / g·cm -3 Above, 30 GPa / g·cm -3 Above, 30.3 GPa / g·cm -3 Above, 30.5 GPa / g·cm -3 The above values ​​are particularly preferred to be 31–37 GPa / g·cm. -3 If the modulus of elasticity is too low, undesirable conditions can easily occur due to the bending of the glass plate.

[0071] The strain point is preferably above 680℃, 685℃, 687℃, 690℃, 692℃, or 695℃, and particularly preferably 700–820℃. Setting it in this way can suppress the thermal shrinkage of the glass plate during the LTPS process.

[0072] The annealing temperature is preferably above 730℃, 732℃, 735℃, 738℃, or 740℃, and particularly preferably between 745℃ and 900℃. This setting helps to suppress thermal shrinkage of the glass sheet during the LTPS process.

[0073] The liquidus temperature is preferably below 1400℃, 1380℃, 1350℃, 1300℃, 1290℃, 1285℃, 1280℃, 1275℃, or 1270℃, and particularly preferably between 1060℃ and 1200℃. Setting it in this way easily prevents the formation of devitrifying crystals during glass manufacturing, thus reducing productivity. Furthermore, it facilitates the use of overflow-draw forming, thereby improving the surface quality of the glass sheet and reducing manufacturing costs. It should be noted that liquidus temperature is an indicator of devitrification resistance; the lower the liquidus temperature, the better the devitrification resistance.

[0074] The preferred liquid phase viscosity is 10. 4.2 dPa·s or more, 10 4.5 dPa·s or more, 10 4.8 dPa·s or more, 10 5.1 dPa·s or higher, preferably 10 7.4 Below dPa·s, 10 7.2 Below dPa·s, especially preferably 10 5.2 ~10 7.0 dPa·s. With this setting, devitrification is less likely to occur during molding, making it easier to use the overflow pull-down method for molding. As a result, the surface quality of the glass sheet can be improved, and the manufacturing cost of the glass sheet can be reduced. It should be noted that liquid phase viscosity is an indicator of devitrification resistance and formability; the higher the liquid phase viscosity, the better the devitrification resistance and formability.

[0075] High temperature viscosity 10 2.5 The preferred temperature for achieving the desired viscosity at dPa·s is below 1700℃, below 1680℃, and below 1650℃, with a particularly preferred temperature of 1450~1600℃. If the high-temperature viscosity is 10... 2.5 If the temperature at dPa·s is too high, it will be difficult to melt the glass batch, leading to a significant increase in the manufacturing cost of the glass sheet. It should be noted that a high-temperature viscosity of 10... 2.5 The temperature at dPa·s is equivalent to the melting temperature; the lower the temperature, the greater the moltenness.

[0076] The β-OH value is an indicator of the moisture 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 below the strain point. Preferably, the β-OH value is 0.35 / mm or less, 0.30 / mm or less, 0.28 / mm or less, 0.25 / mm or less, 0.20 / mm or less, or 0.17 / mm or less, and particularly preferably 0.16 / mm or less. It should be noted that if the β-OH value is too low, the melt permeability tends to decrease. Therefore, a β-OH value is preferably 0.01 / mm or more, and particularly preferably 0.03 / mm or more.

[0077] 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) Bubble N2 in the molten glass. (5) Use a small melting furnace. (6) Increase the flow rate of the molten glass. (7) Use an electro-melting method.

[0078] Here, "β-OH value" refers to the value obtained by measuring the transmittance of the glass using FT-IR (Fourier Transform Infrared Spectrophotometer) and calculating it using the following formula.

[0079] β-OH value = (1 / X)log 10 (T1 / T2)

[0080] X: Plate thickness (mm)

[0081] T1: Reference wavelength 3846cm －1 Transmittance at (%)

[0082] T2: Hydroxyl absorption wavelength 3600 cm⁻¹ －1 Minimum transmittance (%) in the vicinity

[0083] The alkali-free glass sheet of the present invention is preferably formed using the overflow-draw method. The overflow-draw method is a method of manufacturing a glass sheet by allowing molten glass to overflow from both sides of a heat-resistant trough structure, and by drawing the overflowing molten glass downwards while simultaneously allowing it to converge at the lower end of the trough structure. In the overflow-draw method, the surface to be the glass sheet does not contact the trough-shaped refractory, but is formed as a free surface. Therefore, it is possible to manufacture glass sheets with an unpolished, flame-polished surface of good quality at low cost, and thinning is also easy.

[0084] The alkali-free glass sheet of the present invention can also be a glass sheet produced by float glass forming. In this case, large glass sheets can be manufactured inexpensively.

[0085] When the alkali-free glass plate of the present invention is used as a magnetic recording medium, the surface is preferably a polished surface. Polishing the glass surface reduces the overall thickness variation (TTV). As a result, a magnetic film can be properly formed, making it suitable as a substrate for magnetic recording media. On the other hand, when used in organic EL devices, the surface is preferably a flame-polished surface (unpolished surface) formed using an overflow pull-down method.

[0086] In the alkali-free glass plate of the present invention, the plate thickness is not particularly limited; however, when used in organic EL devices, it is preferably less than 0.7 mm, less than 0.6 mm, or less than 0.6 mm, and particularly preferably 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 the flow rate, plate pulling speed, etc. 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, or 0.2 to 1.0 mm, and particularly preferably 0.3 to 0.9 mm. If the plate thickness is too thick, it must be ground (etched) to the desired thickness, which may increase processing costs.

[0087] When the alkali-free glass plate of the present invention is used in organic EL devices, the average surface roughness Ra of the surface is preferably 1.0 nm or less, 0.5 nm or less, and particularly preferably 0.2 nm or less. If the average surface roughness Ra is large, it is difficult to accurately pattern electrodes, etc., in the manufacturing process of the display. As a result, the probability of circuit electrode breakage and short circuit increases, making it difficult to ensure the reliability of the display, etc. Here, "average surface roughness Ra" refers to the average surface roughness Ra of the main surface (both surfaces) excluding the end face, which can be measured, for example, using an atomic force microscope (AFM).

[0088] When using the alkali-free glass plate of the present invention as a substrate for an organic EL television display panel or as a carrier for manufacturing an organic EL display panel, a rectangular shape is preferred. Furthermore, when using the alkali-free glass plate of the present invention as a substrate for magnetic recording media, particularly energy-assisted magnetic recording media, it is preferable to form a disk-shaped substrate by cutting or other processing. In this case, it is further preferable that the disk substrate has a circular opening at its center.

[0089] Example

[0090] The present invention will now be described based on embodiments. It should be noted that the following embodiments are merely illustrative and are not intended to limit the invention in any way.

[0091] Tables 1 and 2 show the embodiments of the present invention (samples No. 1 to 17).

[0092] [Table 1]

[0093]

[0094] [Table 2]

[0095]

[0096] First, the glass raw materials are formulated according to the glass composition shown in the table. The resulting glass batch is then added to a platinum crucible and melted at 1600–1680°C for 24 hours. During the melting of the glass batch, a platinum stirrer is used to homogenize the mixture. Next, the molten glass is poured onto a carbon plate, shaped into a plate, and then annealed at a temperature near the annealing point for 30 minutes. This process yields a glass sample.

[0097] The average coefficient of thermal expansion (CTE), density (ρ), Young's modulus (E), specific Young's modulus (E / ρ), strain point (Ps), annealing point (Ta), softening point (Ts), and high-temperature viscosity (10) of each obtained sample were evaluated within the temperature range of 30–380 °C. 4 Temperature at dPa·s, high-temperature viscosity 10 3 Temperature at dPa·s, high-temperature viscosity 10 2.5 Temperature at dPa·s, liquidus temperature TL, and viscosity at liquidus temperature TL (log liquidus viscosity) 10 ηTL.

[0098] The average coefficient of thermal expansion (CTE) in the temperature range of 30–380℃ is a value measured using a thermal dilatometer.

[0099] The density ρ is a value determined using the well-known Archimedes method.

[0100] Young's modulus of elasticity E refers to the value determined using the well-known resonance method.

[0101] The Young's modulus E / ρ is a value obtained by dividing the Young's modulus by the density.

[0102] The strain point Ps, annealing point Ta, and softening point Ts are values ​​determined based on the methods of ASTM C336 and C338.

[0103] High temperature viscosity 10 4 dPa·s, 10 3 dPa·s, 10 2.5 The temperature at dPa·s is a value determined using the platinum ball pulling method.

[0104] The liquid phase temperature TL is the temperature at which crystals precipitate after glass powder that has passed through a standard sieve of 30 mesh (500 μm) but remains at 50 mesh (300 μm) is added to a platinum boat and held in a temperature gradient furnace for 24 hours.

[0105] Liquid phase viscosity log10 ηTL is a value obtained by measuring the viscosity of glass at the liquidus temperature TL using the platinum ball pulling method.

[0106] As can be clearly seen from the table, samples No. 1 to 17, due to the glass composition being limited to the specified range, have a Young's modulus above 76.8 GPa, a strain point above 691℃, a liquidus temperature below 1206℃, and a liquidus viscosity of 10. 4.7 The strain rate is above dPa·s. Therefore, the production rate of samples No. 1 to 17 is excellent, and the strain point and Young's modulus are sufficiently high, making them suitable for use as substrates for organic EL devices and magnetic recording media.

[0107] Industrial availability

[0108] The alkali-free glass plate of the present invention is suitable for use as a substrate for organic EL devices, particularly for organic EL television display panels, and as a carrier for manufacturing organic EL display panels. In addition, the alkali-free glass plate of the present invention is also suitable for substrates for displays such as liquid crystal displays, cover glass for image sensors such as charge-coupled devices (CCDs) and contactless solid-state imaging elements (CIS), substrates and cover glass for solar cells, and substrates for organic EL lighting, etc.

[0109] Furthermore, the alkali-free glass plate of the present invention is also suitable as a glass substrate for magnetic recording media due to its sufficiently high strain point and Young's modulus. A high strain point means that even high-temperature heat treatment such as heat-assisted treatment or laser irradiation does not easily cause deformation of the glass plate. As a result, higher heat treatment temperatures can be used to achieve high Ku-density magnetic recording devices, making it easier to manufacture such devices. Additionally, a high Young's modulus reduces the likelihood of bending or jittering of the glass substrate during high-speed rotation, thus preventing collisions between the magnetic recording medium and the magnetic head.

Claims

1. An alkali-free glass plate, characterized in that, As a glass composition, it contains, in mol%, 63%–70% SiO2, 10%–15% Al2O3, 3%–8% B2O3, 0%–0.5% Li2O+Na2O+K2O, 1%–11% MgO, 2%–11% CaO, 0%–6% SrO, 0%–8% BaO, and 13%–20% MgO+CaO+SrO+BaO. The mol% ratio of SiO2 / Al2O3 is 4.2–7, and the mol% ratio of (MgO+CaO+SrO+BaO) / Al2O3 is 0.9–2.

2. The alkali-free glass plate according to claim 1, characterized in that, As a glass composition, in mol%, it contains 64%–68% SiO2, 11%–14% Al2O3, 4.1%–6% B2O3, 0%–0.5% Li2O+Na2O+K2O, 2%–9% MgO, 2%–10% CaO, 1%–4% SrO, 1%–6% BaO, and 14%–18% MgO+CaO+SrO+BaO. The mol% ratio of SiO2 / Al2O3 is greater than 5 and less than 5.4, and the mol% ratio of (MgO+CaO+SrO+BaO) / Al2O3 is 1.2–1.

6.

3. The alkali-free glass plate according to claim 1 or 2, characterized in that, On a mol% basis, MgO+CaO+SrO+BaO-Al2O3 is 1% to 5%.

4. The alkali-free glass plate according to claim 1 or 2, characterized in that, It contains more than 2.4% BaO in mol%.

5. The alkali-free glass plate according to claim 1 or 2, characterized in that, The glass composition does not actually contain As2O3 and Sb2O3.

6. The alkali-free glass plate according to claim 1 or 2, characterized in that, It contains 0.001% to 1% SnO2 on a mol% basis.

7. The alkali-free glass plate according to claim 1 or 2, characterized in that, The strain point is above 680℃.

8. The alkali-free glass plate according to claim 1 or 2, characterized in that, The Young's modulus is above 75 GPa.

9. The alkali-free glass plate according to claim 1 or 2, characterized in that, The specific Young's modulus is 28 GPa / g-cm -3 The above.

10. The alkali-free glass plate according to claim 1 or 2, characterized in that, The liquid phase temperature is below 1400℃.

11. The alkali-free glass plate according to claim 1 or 2, characterized in that, 30°C to 380°C in the temperature range of 20 x 10 -7 / °C to 50 x 10 -7 / °C.

12. The alkali-free glass plate according to claim 1 or 2, characterized in that, The annealing point is above 730℃.

13. The alkali-free glass plate according to claim 1 or 2, characterized in that, liquid viscosity of 10 4.2 dPa·s or more.

14. The alkali-free glass plate according to claim 1 or 2, characterized in that, Used in organic EL devices.

15. The alkali-free glass plate according to claim 1 or 2, characterized in that, Used for magnetic recording media.

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