Alkali-free glass

Abstract

This invention relates to an alkali-free glass with a strain point above 650℃, an average coefficient of thermal expansion of 30×10⁻⁷ to 45×10⁻⁷ / ℃ at 50 to 350℃, a glass viscosity at a temperature T₂ of 102 dPa·s of 1500℃ to 1800℃, and, expressed in moles (%) based on oxides, comprising: SiO₂: 62–70%, Al₂O₃: 9–16%, B₂O₃: 0–12%, MgO: 3–10%, CaO: 4–12%, SrO: 0–6%, Fe₂O₃: 0.001–0.04%, MgO + CaO + SrO + BaO: 12–25%, and a β-OH value of 0.35–0.85 / mm.

Description

Technical Field

[0001] This invention relates to an alkali-free glass. More specifically, it relates to an alkali-free glass suitable for use as a glass substrate or support for ultraviolet transmittance in the manufacture or production of various electronic devices. Prior Technology

[0002] In recent years, the demand for glass substrates with high ultraviolet transmittance has surged. Examples of such substrates include glass substrates used in liquid crystal flat panel displays, which are constructed by bonding two glass substrates together using an ultraviolet-curing resin, and support glass substrates used in the manufacture of organic light-emitting diodes (OLEDs) (such as flexible OLEDs containing a polyimide layer) by laminating layers onto a support glass substrate. In the latter case, after the OLED manufacturing process, ultraviolet irradiation debonds the adhesive layer on the support glass substrate, allowing the support glass substrate to peel off from the OLED. Such support glass substrates are useful for devices that possess lightweight, thin, or flexible characteristics, ensuring the strength necessary for the manufacturing process.

[0003] If these glass substrates contain alkali metal oxides, the alkali metal ions diffuse into the thin film formed on the substrate, causing a deterioration in the film properties. Therefore, these glass substrates are required to be alkali-free glass that is substantially free of alkali metal ions.

[0004] Patent documents 1-3 describe an alkali-free glass substrate whose ultraviolet transmittance at a wavelength of 300 nm is 40-85% or 50-85% when converted to a thickness of 0.5 mm. Previous technical documents Patent documents

[0005] Patent Document 1: International Publication No. 2014 / 175215 Patent Document 2: Japanese Patent Application Publication No. 2006-36625 Patent Document 3: Japanese Patent Application Publication No. 2006-36626 Summary of the Invention

[0006] [The problem the invention aims to solve] Generally, mass-produced glass contains iron from raw materials or manufacturing processes. Iron exists in glass as Fe2+ or Fe3+. Since Fe3+ absorbs light at wavelengths below 300 nm, reducing the iron content in glass is considered to improve the ultraviolet transmittance of alkali-free glass (hereinafter referred to as "glass"). However, reducing the iron content decreases the infrared absorption of Fe2+ during the melting process, resulting in increased thermal conductivity. Consequently, when manufacturing glass by heating the green glass in a furnace using the heat of the burner flame, the temperature distribution of the molten green glass decreases, leading to reduced convection and potentially poorer bubble quality or homogeneity in the final product. This is because clarification (bubble removal) and homogeneity depend on sufficient convection.

[0007] The objective of this invention is to provide an alkali-free glass with high ultraviolet transmittance and adjustable thermal conductivity. [Technical means to solve the problem]

[0008] The inventors discovered that by increasing the β-OH content of the glass, infrared absorption can be improved while maintaining low iron content and high ultraviolet transmittance, thereby reducing thermal conductivity. However, it is important to note that if the thermal conductivity is reduced excessively, the molten glass billet at the bottom of the furnace will become too cold and difficult to flow. Therefore, the thermal conductivity can be controlled within an optimal range by adjusting the iron content and β-OH content.

[0009] The present invention includes the following embodiments. [1] A type of alkali-free glass, Its strain point is above 650℃, and its average coefficient of thermal expansion in the range of 50~350℃ is 30×10-7~45×10-7 / ℃. The temperature T2 at which the glass viscosity reaches 102 dPa·s is 1500℃~1800℃. Expressed in moles (%) based on oxides, comprising: SiO2: 62~70%, Al2O3: 9~16%, B2O3: 0~12%, MgO: 3~10% CaO: 4~12%, SrO: 0~6%, Fe2O3: 0.001~0.04%, The content of MgO, CaO, SrO, and BaO is 12-25%. The β-OH value is 0.35~0.85 / mm. [2] As described in [1], the alkali-free glass in which the value represented by formula A is 7~30, In formula A, [Fe2O3] is the value of all iron in moles (%) converted to Fe2O3, and [β-OH] is the value expressed in units of / mm. Formula A: (3.119×10-4T2 2-0.2014T2-17.38)[Fe2O3]+(6.434×10-7T2 2+0.0144T2-7.842)[β-OH]. [3] The alkali-free glass described in [1] or [2] has an effective thermal conductivity of 40~65 W / m·K at a temperature T2 with a glass viscosity of 102 dPa·s. [4] The alkali-free glass described in any of [1] to [3] has a transmittance of more than 50% when the plate thickness is 0.5 mm at a wavelength of 300 nm. [5] The alkali-free glass described in any of [1] to [4] is a glass plate with a thickness of 0.05 mm to 3 mm. [6] A method for manufacturing alkali-free glass as described in any of [1] to [5], comprising the step of forming molten glass using a float glass method or a melting method. [7] A display panel having alkali-free glass as described in any of [1] to [5]. [8] A semiconductor element having an alkali-free glass as described in any one of [1] to [5]. [9] An information recording medium having alkali-free glass as described in any of [1] to [5]. [Effects of the Invention]

[0010] The alkali-free glass of this invention has high ultraviolet transmittance and thermal conductivity that can be adjusted to the desired value. Therefore, this invention provides a high-quality alkali-free glass that can be manufactured efficiently by heating methods such as burner flames, and is suitable as a glass substrate or support glass substrate for various electronic devices such as thin displays or organic EL displays. Implementation

[0011] In this embodiment, "alkali-free" glass means glass that substantially does not contain alkali metal oxides such as Na₂O and K₂O. "Substantially does not contain" means that, apart from unavoidable inclusions as impurities, these components are not added. In this invention, "substantially does not contain alkali metal oxides" means, for example, that the content of alkali metal oxides is 0.5% or less, preferably 0.2% or less, more preferably 0.1% or less, more preferably 0.08% or less, and even more preferably 0.05% or less, most preferably 0.03% or less (in moles based on oxides).

[0012] In addition to SiO2 and Al2O3, which form the glass framework, the alkali-free glass of this embodiment also contains a specific amount of metal oxide components. The following describes the content of each component in the alkali-free glass of this embodiment, based on oxides. Unless otherwise stated, "%" refers to "moles %".

[0013] The SiO2 content is 62-70%. Preferably, the SiO2 content is 63% or higher, more preferably 64% or higher, further preferably 65% ​​or higher, and especially preferably 65.5% or higher. If the SiO2 content does not reach the lower limit, the strain point tends to be lower, the coefficient of thermal expansion and specific gravity tend to be higher, and consequently, the resistance to hydrofluoric acid tends to be worse. Furthermore, hydrofluoric acid and buffered hydrofluoric acid (BHF: a mixture of hydrofluoric acid and ammonium fluoride) are chemicals commonly used in etching processes related to semiconductor formation or thin-film fabrication. On the other hand, the SiO2 content is preferably 69% or lower, more preferably 68.5% or lower, further preferably 68% or lower, and especially preferably 67.5% or lower. If the SiO2 content exceeds the upper limit, the temperature (T2) at which the glass viscosity reaches 102 poise (dPa·s) tends to be higher, the solubility deteriorates, and the devitrification temperature tends to increase.

[0014] The Al2O3 content is 9-16%. Preferably, the Al2O3 content is 10% or more, more preferably 10.5% or more, further preferably 10.8% or more, and even more preferably 11% or more. If the Al2O3 content does not reach the lower limit, phase separation control becomes more difficult, the strain point decreases, and the coefficient of thermal expansion tends to increase. On the other hand, the Al2O3 content is preferably 15% or less, more preferably 14% or less, further preferably 13.8% or less, and even more preferably 13.5% or less. If the Al2O3 content exceeds the upper limit, the T2 (temperature at break) tends to increase, solubility deteriorates, and the devitrification temperature also tends to increase.

[0015] The B2O3 content is 0-12%. While not essential, B2O3 can be included to improve the melting reactivity of the glass during manufacturing, lower the devitrification temperature, and improve resistance to BHF. The B2O3 content is preferably 0.5% or more, more preferably 0.8% or more, and even more preferably 1% or more, particularly preferably 1.2% or more. Conversely, the B2O3 content is preferably 11% or less, more preferably 10% or less, even more preferably 9% or less, and particularly preferably 8.5% or less. If the B2O3 content exceeds the upper limit, there is a tendency for the strain point to decrease.

[0016] The MgO content is 3-10%. Preferably, the MgO content is 4% or more, more preferably 4.5% or more, further preferably 5% or more, and especially preferably 5.5% or more. Compared with other alkaline earth elements, MgO improves solubility and reduces specific gravity without increasing the coefficient of thermal expansion, thereby improving resistance to hydrofluoric acid. However, if its content does not reach the lower limit, it is difficult to fully obtain these effects. On the other hand, the MgO content is preferably 9.7% or less, more preferably 9.5% or less, further preferably 9.3% or less, and especially preferably 9.1% or less. If the MgO content exceeds the upper limit, there is a risk of an increased devitrification temperature.

[0017] The CaO content is 4-12%. Preferably, the CaO content is 4.2% or higher, more preferably 4.5% or higher, and even more preferably 4.7% or higher, and especially preferably 5% or higher. Following MgO in the alkaline earth group, CaO also possesses the characteristic of not increasing the coefficient of thermal expansion and not significantly lowering the strain point; similarly, it also improves solubility. If its content does not reach the lower limit, it is difficult to fully obtain these effects. On the other hand, the CaO content is preferably 11.5% or lower, more preferably 11% or lower, even more preferably 10.5% or lower, and especially preferably 10% or lower. If the CaO content exceeds the upper limit, there is a tendency for the coefficient of thermal expansion to increase. Furthermore, if the CaO content exceeds the upper limit, there is a risk of an increase in the devitrification temperature.

[0018] The SrO content is 0-6%. SrO can be included to prevent the devitrification temperature of the glass from rising and to improve its solubility during glass manufacturing. The SrO content is preferably 0.1% or more, more preferably 0.5% or more, and even more preferably 1% or more, particularly preferably 1.2% or more. On the other hand, the SrO content is preferably 5.8% or less, more preferably 5.5% or less, even more preferably 5.3% or less, and particularly preferably 5.0% or less. If the SrO content exceeds the upper limit, the specific gravity and coefficient of thermal expansion tend to increase, and the resistance to hydrofluoric acid tends to decrease.

[0019] While BaO is not an essential component, it can be included to prevent the devitrification temperature of the glass from rising and to improve its solubility. However, if the BaO content is too high, the specific gravity tends to increase, and the average coefficient of thermal expansion tends to become excessively large. Therefore, the BaO content is preferably 1% or less, more preferably 0.5% or less, and even more preferably 0.1% or less. It is especially preferable that the glass contains virtually no BaO.

[0020] The total amount of alkaline earth metal oxides in the alkali-free glass of this embodiment, namely MgO+CaO+SrO+BaO (hereinafter also referred to as "RO"), is 12-25%. RO is preferably 13% or more, more preferably 14% or more, further preferably 15% or more, and especially preferably 15.5% or more. If RO does not reach the lower limit, the solubility of the glass deteriorates. Furthermore, if RO does not reach the lower limit, there is a risk of an increase in devitrification temperature. On the other hand, RO is preferably 23% or less, more preferably 21% or less, further preferably 20.5% or less, and especially preferably 20% or less. If RO exceeds the upper limit, there is a tendency for the strain point to decrease, the specific gravity to increase, the coefficient of thermal expansion to increase, and the resistance to hydrofluoric acid to decrease.

[0021] The iron content in the alkali-free glass of this embodiment, calculated as Fe2O3, is 0.001 to 0.04%. Fe2O3 is preferably 0.002% or more, more preferably 0.003% or more, and even more preferably 0.0035% or more, and particularly preferably 0.004% or more. Furthermore, Fe2O3 is preferably 0.03% or less, more preferably 0.02% or less, even more preferably 0.018% or less, and particularly preferably 0.016% or less. As mentioned above, it is believed that since the Fe2O3 content helps reduce ultraviolet transmittance, it is preferable to set a low content in glass requiring high ultraviolet transmittance. However, if the Fe2O3 content of the glass is reduced, the infrared absorption capacity also decreases, and the thermal conductivity increases. In this embodiment, the balance with β-OH described below was studied in detail, and the above-mentioned Fe2O3 content range was found.

[0022] In addition to the components mentioned above, the glass of this embodiment may contain any one of ZrO2, ZnO, SO3, F, Cl and SnO2 alone or in combination, in order to improve its solubility, clarity and formability, up to 2% in total, preferably up to 1% or more, and even more preferably up to 0.5% in total.

[0023] On the other hand, in order to avoid deterioration of the properties of the thin film such as metal or oxide disposed on the surface of the glass plate, the glass of this embodiment is preferably substantially free of P2O5. Furthermore, in order to facilitate the reuse of the glass, it is preferably substantially free of PbO, As2O3, and Sb2O3.

[0024] In the alkali-free glass of this embodiment, the β-OH value, used as an indicator of water content, is 0.35~0.85 / mm. A β-OH value of 0.40 / mm or higher is preferred, more preferably 0.45 / mm or higher, further preferably 0.48 / mm or higher, and especially preferably 0.50 / mm or higher. Furthermore, a β-OH value of 0.8 / mm or lower is preferred, more preferably 0.77 / mm or lower, further preferably 0.75 / mm or lower, and especially preferably 0.7 / mm or lower. Increasing the β-OH value can reduce thermal conductivity without decreasing ultraviolet transmittance. However, excessively reducing thermal conductivity may also lead to the aforementioned drawbacks. The inventors analyzed the contributions of different combinations of iron content and β-OH value when thermal conductivity decreases near the melting temperature, thereby discovering the aforementioned β-OH value range that is particularly suitable for the manufacture of alkali-free glass with high ultraviolet transmittance.

[0025] The β-OH value in alkali-free glass can be adjusted using methods known to the industry. For example, the β-OH value can be adjusted to a higher level by using hydroxides as glass raw materials (especially Mg or Ca supply sources), or by increasing the partial pressure or dew point of water vapor in the molten environment.

[0026] The strain point of the alkali-free glass in this embodiment is 650°C or higher. If the strain point is lower than 650°C, thermal shrinkage may occur during the heat treatment necessary for manufacturing electronic devices, leading to a decrease in yield. The strain point is preferably 655°C or higher, more preferably 660°C or higher, further preferably 663°C or higher, and especially preferably 665°C or higher. If the strain point is too high, the temperature of the forming apparatus may need to be increased accordingly, tending to reduce the lifespan of the forming apparatus. Therefore, the strain point is preferably 770°C or lower, more preferably 750°C or lower, further preferably 740°C or lower, and especially preferably 730°C or lower.

[0027] The alkali-free glass of this embodiment has an average coefficient of thermal expansion of 30×10⁻⁷ / ℃ to 45×10⁻⁷ / ℃ at 50~350℃. Preferably, the average coefficient of thermal expansion at 50~350℃ is 33×10⁻⁷ / ℃ or higher, more preferably 35×10⁻⁷ / ℃ or higher, further preferably 36×10⁻⁷ / ℃ or higher, and even more preferably 37×10⁻⁷ / ℃ or higher. For example, in the manufacturing of the TFT (thin-film transistor) side substrate of a flat panel display, there are cases where gate metal films such as copper and gate insulating films such as silicon nitride are sequentially deposited on alkali-free glass. However, if the average coefficient of thermal expansion does not reach the lower limit, the difference in expansion rates between the gate insulating film and the glass becomes too small. Therefore, the effect of eliminating glass warpage caused by the formation of the gate metal film by the gate insulating film becomes smaller. This could lead to problems such as increased substrate warping, resulting in transport abnormalities, or increased pattern shift during exposure. On the other hand, the average coefficient of thermal expansion at 50–350°C is preferably below 43 × 10⁻⁷ / °C, more preferably below 42 × 10⁻⁷ / °C, further preferably below 40 × 10⁻⁷ / °C, and most preferably below 39 × 10⁻⁷ / °C. Glass with an average coefficient of thermal expansion below the upper limit exhibits stronger thermal shock resistance and achieves higher yields.

[0028] The temperature T2 at which the viscosity of the alkali-free glass in this embodiment reaches 102 poise (dPa·s) is 1500~1800℃. T2 is preferably 1550℃ or higher, more preferably 1570℃ or higher, more preferably 1580℃ or higher, and especially preferably 1600℃ or higher. If T2 does not reach the lower limit, the melting temperature and refining temperature of the glass may deviate, resulting in poor clarity of the glass. Furthermore, if T2 does not reach the lower limit, corrosion of the melting furnace may easily develop due to the low viscosity of the molten liquid, shortening the lifespan of the manufacturing equipment. On the other hand, T2 is preferably 1750℃ or lower, more preferably 1730℃ or lower, further preferably 1700℃ or lower, and especially preferably 1660℃ or lower. If T2 exceeds the upper limit, the melting properties of the glass are poor, increasing the burden on the manufacturing equipment due to the need for high temperatures.

[0029] The alkali-free glass of this embodiment preferably has a viscosity of 104 poise (dPa·s) at a temperature T4 of 1400°C or lower, more preferably 1370°C or lower, further preferably 1350°C or lower, and even more preferably 1320°C or lower. Glass with such a T4 is suitable for float glass forming. If the T4 is too high, there is a risk that the lifespan of the metal bath shell structure or the heater will become extremely short.

[0030] The alkali-free glass of this embodiment preferably has an effective thermal conductivity of 40-65 W / m·K at temperature T2 when the glass viscosity is 102 dPa·s. More preferably, the effective thermal conductivity at T2 is 45 W / m·K or higher, more preferably 50 W / m·K or higher, and even more preferably 55 W / m·K or higher. Furthermore, the effective thermal conductivity at T2 is more preferably 63 W / m·K or lower, more preferably 60 W / m·K or lower, and even more preferably 57 W / m·K or lower. The so-called effective thermal conductivity is the thermal conductivity measured by the steady-state method (J. Am. Cer. Soc. 44, 1961, pp.333-339), and is sometimes also called "apparent thermal conductivity". By having the above-mentioned effective thermal conductivity at temperature T2, the optimal convection rate is generated when the glass is heated and melted, the heating becomes efficient, and thus a glass product with excellent bubble quality and homogeneity can be provided.

[0031] The alkali-free glass of this embodiment is preferably 7 to 30 as represented by Formula A. Formula A: (3.119×10-4T2 2-0.2014T2-17.38)[Fe2O3]+(6.434×10-7T2 2+0.0144T2-7.842)[β-OH] Here, [Fe2O3] is the value of total iron in moles (%) converted to Fe2O3, and [β-OH] is the value expressed in units of mm. Equation A above was derived by analyzing in detail how much the amount of Fe2O3 and the value of β-OH contribute to the decrease in thermal conductivity at different temperatures. The value represented by Formula A indicates how much the thermal conductivity decreases compared to alkali-free glass that contains no moisture or iron. The larger the value of Formula A, the greater the decrease in thermal conductivity. Preferably, the value of Formula A is 10 or higher, more preferably 12 or higher, and especially preferably 14 or higher. Furthermore, the value of Formula A is preferably 25 or lower, more preferably 20 or lower, and especially preferably 17 or lower.

[0032] The alkali-free glass of this embodiment preferably has a transmittance of 50% or more when the plate thickness is 0.5 mm at a wavelength of 300 nm. This ensures suitable ultraviolet transmittance for use as a substrate or support substrate in various electronic devices. More preferably, the transmittance is 60% or more, even more preferably 70% or more, and most preferably 80% or more.

[0033] The alkali-free glass of this embodiment is preferably in the shape of a glass plate. The thickness of the glass plate is preferably 3 mm or less, more preferably 2 mm or less, more preferably 1.5 mm or less, further preferably 1.2 mm or less, and especially preferably 0.8 mm or less. Furthermore, the thickness of the glass plate is preferably 0.05 mm or more, more preferably 0.1 mm or more, more preferably 0.15 mm or more, further preferably 0.2 mm or more, and especially preferably 0.3 mm or more.

[0034] The alkali-free glass of this embodiment can be manufactured by appropriately combining methods known to the industry. For example, the raw materials for making the above-mentioned components into the above-mentioned specific composition are prepared, continuously fed into a melting furnace, and heated to 1500~1800°C to melt and obtain molten glass. The obtained molten glass is formed into a glass strip of a specific thickness using a forming device, and after slow cooling, the glass strip is cut.

[0035] The manufacturing method of the glass and glass sheet in this embodiment is not particularly limited, and various methods can be applied. For example, the raw materials are prepared in a manner that makes each component the target composition, and then heated and melted in a glass melting furnace. The glass is homogenized by means of bubbling, stirring, and adding clarifying agents, and then formed into a glass sheet of a specific thickness by means of float glass, pressing, melting, or drawing. After slow cooling, it can be processed as needed by grinding, polishing, etc., to produce a glass substrate of a specific size and shape. By using the melting method, the average cooling rate near the glass transfer point is faster, and when the obtained glass sheet is further thinned by hydrofluoric acid etching, the surface roughness of the glass sheet on the etched side becomes smaller.

[0036] From the perspective of consistently producing large panes of glass (e.g., one side is 1800 mm or more), the float glass method is preferable.

[0037] The term "large substrate" refers to a glass plate with at least one side being 1800 mm or more. Specifically, a glass plate with a long side of 1800 mm or more and a short side of 1500 mm or more is more suitable. The alkali-free glass of this embodiment is more preferably used for glass plates with at least one side being 2400 mm or more, such as glass plates with a long side of 2400 mm or more and a short side of 2100 mm or more. More preferably, it is used for glass plates with at least one side being 3000 mm or more, such as glass plates with a long side of 3000 mm or more and a short side of 2800 mm or more. It is even more preferably used for glass plates with at least one side being 3200 mm or more, such as glass plates with a long side of 3200 mm or more and a short side of 2900 mm or more. Most preferably, it is used for glass plates with at least one side being 3300 mm or more, such as glass plates with a long side of 3300 mm or more and a short side of 2950 mm or more.

[0038] Next, the display panel of one embodiment of the present invention will be described. The display panel of this embodiment uses the alkali-free glass of the above embodiment as a glass substrate. As long as the alkali-free glass of the above embodiment is used, the display panel is not particularly limited and can be a liquid crystal display panel, an organic EL (Electroluminescence) display panel, or any other type of display panel.

[0039] Taking a thin-film transistor liquid crystal display (TFT-LCD) as an example, it comprises a display surface electrode substrate (array substrate) on which gate electrode lines and a gate insulating oxide layer are formed, and pixel electrodes are formed on the surface of the oxide layer, and a color filter substrate on which RGB color filters and opposing electrodes are formed. Liquid crystal material is sandwiched between the array substrate and the color filter substrate, which are paired together, to form a cell. In addition to this cell, the liquid crystal display panel also includes other elements such as peripheral circuits. In the liquid crystal display panel of this embodiment, at least one of the pair of substrates constituting the cell uses the alkali-free glass of the above embodiment.

[0040] Secondly, in one embodiment of the present invention, the semiconductor device has the alkali-free glass of the above embodiment as a glass substrate. Specifically, for example, it has the alkali-free glass of the above embodiment as a glass substrate for image sensors such as MEMS (Micro Electro Mechanical Systems), CMOS (Complementary Metal Oxide Semiconductor), and CIS (Contact Image Sensor). Furthermore, it has the alkali-free glass of the above embodiment as an outer cover glass for display devices used for projection, such as the outer cover glass of LCOS (Liquid Crystal On Silicon).

[0041] Secondly, one embodiment of the information recording medium of the present invention uses the alkali-free glass of the above-described embodiment as a glass substrate. Specifically, for example, it uses the alkali-free glass of the above-described embodiment as a glass substrate for magnetic recording media or optical discs. As a magnetic recording medium, for example, there are energy-assisted magnetic recording media or perpendicular magnetic recording media. Example

[0042] The embodiments and comparative examples described below further illustrate the implementation of the present invention in detail, but the present invention is not limited to these embodiments.

[0043] The raw materials for each component were prepared according to the target compositions (unit: moles%) shown in Tables 1 and 2. The mixture was stirred in a platinum crucible at 1650°C in a stirrer for 6 hours. After melting, the mixture was poured onto a carbon plate and held at the glass transfer point +30°C for 60 minutes. It was then cooled to room temperature at 1°C per minute. The resulting alkali-free glass was mirror-polished to produce glass plates, which were then subjected to various evaluations. Examples 1-4 and 7-10 are embodiments of the present invention, and Examples 5, 6, 11, and 12 are comparative examples.

[0044] Using a fluorescence X-ray apparatus (XRF) (manufactured by Rigaku Corporation, ZSX100e), the X-ray intensity of each component on the surface of the glass obtained above was measured and quantitatively analyzed to confirm the composition.

[0045] The average coefficient of thermal expansion (unit: ×10⁻⁷ / ℃) from 50℃ to 350℃ was measured using a differential thermal expansion meter (TMA) according to the method specified in JIS R3102 (1995). The strain point (unit: ℃) was measured using the fiber tensile method according to the method specified in JIS R3103-2 (2001). T2 and T4 were measured using a rotational viscometer. The thermal conductivity was determined according to the steady-state method (J. Am. Cer. Soc. 44, 1961, pp.333-339), measuring the effective thermal conductivity (hereinafter also referred to as Keff) of the glass.

[0046] The effective thermal conductivity (Keff) of the glass at temperature T2 was evaluated after melting the glass samples at temperature T2 in the crucible used for effective thermal conductivity measurement to form a glass melt. The effective thermal conductivity (Keff) is determined by defining the thermal conductivity of the crucible containing molten glass as Kr, the thickness of the bottom surface of the crucible as dr, the depth of the molten glass in the crucible as dg, the temperature of the surface of the molten glass as Ts, the temperature of the inner bottom surface of the crucible at the interface between the molten glass and the inner bottom surface of the crucible as Tb, and the temperature of the outer bottom surface of the crucible as Tr. These values ​​are measured separately and obtained using formula B. Equation B: Keff=Kr{(Tb-Tr) / (Ts-Tb)}(dg / dr) The thermal conductivity Kr of the crucible is obtained by measuring the thickness dr of the bottom surface of the crucible, the depth dg of the molten glass, the temperature Ts of the surface of the molten glass, the interface temperature Tb between the molten glass and the inner bottom surface of the crucible, and the temperature Tr of the outer bottom surface of the crucible using Equation B. The ultraviolet transmittance was measured using a Hitachi U-4100 spectrophotometer according to ISO-9050:2003. The transmittance converted to a wavelength of 300 nm and a plate thickness of 0.5 mm was calculated.

[0047] The β-OH value was determined by double-sided mirror polishing of glass samples with a thickness of 0.70–2.0 mm, followed by FT-IR (Fourier transform infrared radiation) transmittance measurements in the wavenumber range of 4000–2000 cm⁻¹. The transmittance at wavenumber 4000 cm⁻¹ was defined as τ₁ [%], the minimum transmittance near wavenumber 3600 cm⁻¹ as τ₂ [%], and the glass thickness as X [mm]. The β-OH value was calculated using the following formula. Furthermore, the glass sample thickness was adjusted so that τ₂ fell within the range of 20–60%. β-OH[mm-1]=(1 / X)log10(τ1 / τ2)

[0048] [Table 1] Table 1 Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 SiO2 67.1 67.1 67.1 67.1 67.1 67.1 Al2O3 12.7 12.7 12.7 12.7 12.7 12.7 B2O3 1.3 1.3 1.3 1.3 1.3 1.3 MgO 9.1 9.1 9.1 9.1 9.1 9.1 CaO 5.4 5.4 5.4 5.4 5.4 5.4 SrO 4.4 4.4 4.4 4.4 4.4 4.4 BaO 0.0 0.0 0.0 0.0 0.0 0.0 Fe2O3 0.004 0.008 0.012 0.016 0.050 0.004 β-OH[ / mm] 0.70 0.60 0.50 0.40 0.60 0.10 MgO + CaO + SrO + BaO 18.9 18.9 18.9 18.9 18.9 18.9 Average thermal expansion coefficient [×10⁻⁷ / ℃] 39 39 39 39 39 39 Strain point [°C] 720 720 720 720 720 720 T2 [℃] 1654 1654 1654 1654 1654 1654 T4 [℃] 1304 1304 1304 1304 1304 1304 Effective thermal conductivity at T2 [W / m·K] 57 56 56 56 37 67 (3.119×10-4T2 2-0.2014T2-17.38)[Fe2O3]+(6.434×10-7T2 2+0.0144T2-7.842)[β-OH] 14.4 14.7 14.9 15.1 35.8 3.8 Transmittance at 300 nm (Conversion based on 0.5 mm plate thickness) [%] 80 69 60 51 8 80

[0049] [Table 2] Table 2 Example 7 Example 8 Example 9 Example 10 Example 11 Example 12 SiO2 65.7 65.7 65.7 65.7 65.7 65.7 Al2O3 11.0 11.0 11.0 11.0 11.0 11.0 B2O3 7.7 7.7 7.7 7.7 7.7 7.7 MgO 5.6 5.6 5.6 5.6 5.6 5.6 CaO 5.0 5.0 5.0 5.0 5.0 5.0 SrO 5.0 5.0 5.0 5.0 5.0 5.0 BaO 0.0 0.0 0.0 0.0 0.0 0.0 Fe2O3 0.004 0.008 0.012 0.016 0.050 0.004 β-OH[ / mm] 0.70 0.60 0.50 0.40 0.60 0.10 MgO + CaO + SrO + BaO 15.6 15.6 15.6 15.6 15.6 15.6 Average coefficient of thermal expansion [×10⁻⁷ / ℃] 38 38 38 38 38 38 Strain point [°C] 665 665 665 665 665 665 T2 [℃] 1645 1645 1645 1645 1645 1645 T4 [℃] 1275 1275 1275 1275 1275 1275 Effective thermal conductivity at T2 [W / m·K] 57 56 56 56 37 67 (3.119×10-4T2 2-0.2014T2-17.38)[Fe2O3]+(6.434×10-7T2 2+0.0144T2-7.842)[β-OH] 14.3 14.5 14.7 15.0 35.3 3.7 Transmittance at 300 nm (Conversion based on 0.5 mm plate thickness) [%] 80 69 60 51 8 80

[0050] [Table 3] Table 3 Glass 1 Glass 2 SiO2 71.3 69.3 Al2O3 1.0 1.1 CaO 9.1 9.0 MgO 5.7 6.9 Na2O 12.5 12.8 K2O 0.3 0.5 TiO2 0.022 0.015 Fe2O3 0.031 0.449 Co 0 0.0233 Se 0 0.0023 Cr 0 0.0040 Effective thermal conductivity (1600℃) [W / m·K] 119.0 19.7 Effective thermal conductivity (1500℃) [W / m·K] 87.4 17.4 Effective thermal conductivity (1400℃) [W / m·K] 62.8 15.2 Effective thermal conductivity (1300℃) [W / m·K] 45.2 12.9 Effective thermal conductivity (1200℃) [W / m·K] 34.5 10.7 Effective thermal conductivity (1100℃) [W / m·K] 30.7 8.4

[0051] As shown in Tables 1 and 2, the glasses in Examples 1-4 and 7-10 have the content of each component, especially Fe2O3 and β-OH values, controlled within specified ranges to maintain high ultraviolet transmittance while ensuring moderately low thermal conductivity. Therefore, these can be manufactured as alkali-free glasses with excellent bubble quality and homogeneity. They also ensure suitable physical properties for use as substrates or support substrates in various electronic devices.

[0052] In contrast, the glasses in Examples 5 and 11 have lower thermal conductivity due to their higher Fe2O3 content, and therefore cannot guarantee the necessary ultraviolet transmittance. While the glasses in Examples 6 and 12 achieve higher ultraviolet transmittance through iron reduction, their thermal conductivity also becomes excessively high. The higher thermal conductivity of the glasses in Examples 6 and 12 results in poorer bubble quality or homogeneity in the final products. It can be understood that this drawback of the glasses in Examples 6 and 12 is compensated for in Examples 1-4 and 7-10 by the β-OH value.

[0053] Although the invention has been described in detail and with reference to specific embodiments, practitioners will understand that various changes or modifications may be made without departing from the spirit and scope of the invention. This application is based on Japanese Patent Application No. 2018-086580, filed on April 27, 2018, the contents of which are incorporated herein by reference. [Industrial Applicability]

[0054] The alkali-free glass of the present invention can be used for various applications including electronic devices, and is particularly suitable for applications requiring high ultraviolet transmittance, such as glass substrates or support glass substrates for thin display devices or organic EL devices.

Claims

1. An alkali-free glass having a strain point above 650℃, an average coefficient of thermal expansion of 30×10⁻⁷ to 45×10⁻⁷ / ℃ at 50–350℃, a glass viscosity at a temperature T₂ of 10² dPa·s of 1500℃ to 1800℃, and comprising, in moles % based on oxides: SiO₂: 62–70%, Al₂O₃: 9–16%, B₂O₃: 0–12%, MgO: 5–10%, CaO: 4–12%, SrO: 0–6%, BaO: 0–0.5%, Fe₂O₃: 0.001–0.04%, MgO + CaO + SrO + BaO: 12–25%, and a β-OH value of 0.35–0.85 / mm.

2. An alkali-free glass having a strain point above 650℃, an average coefficient of thermal expansion of 30×10⁻⁷ to 45×10⁻⁷ / ℃ at 50–350℃, a glass viscosity of 10² dPa·s at a temperature T₂ of 1500℃ to 1800℃, and comprising, in moles (%) based on oxides: SiO₂: 62–70%, Al₂O₃: 9–16%, B₂O₃: 0–12%, MgO: 5–10%, CaO: 4–12%, SrO: 0–6%, BaO: 0–0.5%, Fe₂O₃: 0.001–0.04%, MgO + CaO + SrO + BaO: 12–25%, and values ​​represented by the following formula A: 7–30. In Formula A, [Fe2O3] is the value of all iron in moles (%) converted to Fe2O3, and [β-OH] is the value expressed in units of mm. Formula A: (3.119×10-4T22-0.2014T2-17.38)[Fe2O3]+(6.434×10-7T22+0.0144T2-7.842)[β-OH].

3. The alkali-free glass of claim 1 or 2 has an effective thermal conductivity of 40 to 65 W / m·K at a temperature T2 where the glass viscosity is 102 dPa·s.

4. For the alkali-free glass in request item 1 or 2, the transmittance at a wavelength of 300 nm is equivalent to that of a plate thickness of 0.5 mm or more, which is above 50%.

5. The alkali-free glass requested in item 1 or 2 is in the shape of a glass sheet with a thickness of 0.05 mm to 3 mm.

6. A method for manufacturing alkali-free glass as claimed in any one of claims 1 to 4, comprising the step of forming molten glass using a float glass method or a melting method.

7. A display panel having alkali-free glass as claimed in any one of claims 1 to 4.

8. A semiconductor device having alkali-free glass as claimed in any one of claims 1 to 4.

9. An information recording medium having alkali-free glass as claimed in any one of claims 1 to 4.