Alkali-free glass substrate

Abstract

The invention relates to an alkali-free glass substrate. The present invention provides an alkali-free glass substrate capable of easily removing bubbles contained in molten glass in a reduced pressure atmosphere. The present invention relates to an alkali-free glass substrate containing 54%-68% of SiO2, 10%-25% of Al2O3, 0.1%-5.5% of B2O3, and 8%-26% of MgO + CaO + SrO + BaO in terms of mass% of oxides, characterized in that the alkali-free glass substrate has a [beta]-OH of 0.15 mm-1 to 0.35 mm-1, a Cl content of 0.15%-0.3% by mass, and a bubble growth index I represented by formula (1) of 320 or more, I = 590.5 [[beta]-OH] + 874.1 [Cl]-5.7 [B2O3]-33.3 (1) in which [beta]-OH] and Cl are contained in the alkali-free glass substrate, and in which [beta]-OH] and Cl are not contained in the alkali-free glass substrate, and B2O3 is [beta-OH] represents beta-OH (mm-1) of the alkali-free glass substrate, [Cl] represents the Cl content (mass%) of the alkali-free glass substrate, and [B2O3] represents the B2O3 content (mass%) of the alkali-free glass substrate.

Description

[0001] This application is a divisional application of the Chinese Patent Application No. 201910541488.1 with a filing date of June 21, 2019 and a title of Alkali-free glass substrate. TECHNICAL FIELD

[0002] The present application relates to an alkali-free glass substrate suitable as a glass substrate for various displays. BACKGROUND

[0003] For a glass substrate for various displays, particularly a glass substrate on the surface of which a metal or oxide thin film or the like is formed, when an alkali metal oxide is contained, film properties are deteriorated due to diffusion of alkali metal ions in the thin film, and therefore, it is preferable to use an alkali-free glass substrate which does not substantially contain an alkali metal ion.

[0004] An alkali-free glass substrate used for the above purpose is obtained by melting and vitrifying glass raw materials prepared in a prescribed ratio in a melting tank, refining the molten glass, and then forming the glass into a glass ribbon of a prescribed thickness by a float method or a fusion method, and cutting the glass ribbon into a prescribed shape.

[0005] For refining of the molten glass, a reduced pressure defoaming method is known in which the molten glass is introduced into a reduced pressure atmosphere, and under the reduced pressure atmosphere, bubbles in the continuously flowing molten glass stream are greatly grown, the bubbles contained in the molten glass are floated and broken to remove the bubbles, and then the molten glass is discharged from the reduced pressure atmosphere. For example, a glass manufacturing method having a process of defoaming the molten glass in a reduced pressure defoaming tank is disclosed in Patent Literature 1.

[0006] For recycling of the glass and improving the melting property, scraps of used glass are used as a part of the glass raw materials.

[0007] PRIOR ART DOCUMENTS

[0008] PATENT LITERATURE

[0009] Patent Literature 1: International Publication No. 2008 / 093580

[0010] NON-PATENT LITERATURE

[0011] Non-Patent Literature 1: TANAKA Sirofu, “Environmentally compatible glass melting technology: particularly on defoaming technology”, New Glass 83 Vol. 21, No. 4 (2006), pp. 31-36. SUMMARY

[0012] PROBLEMS TO BE SOLVED BY THE INVENTION

[0013] Incidentally, in recent years, the demand for large-sized liquid crystal displays has increased, and the large-sizing of glass substrates used in liquid crystal displays is desired. In order to efficiently manufacture large-sized glass substrates, increase the flow rate of molten glass, there is sometimes a need to increase the size of a reduced-pressure defoaming apparatus. In particular, in the case where a molten glass conduit (reduced-pressure defoaming tank, riser, or downcomer) made of platinum or platinum alloy is used in the reduced-pressure defoaming apparatus, there is a problem of an increase in the capital investment cost of the equipment.

[0014] In addition, with respect to glass substrates, even if the average density of bubble defects in the substrates is the same, as the size of the substrates increases, the yield of products decreases (see FIG. in Non-Patent Literature 1). Therefore, in order to make the glass substrates manufactured large-sized, it is necessary to further reduce the bubble density in the substrates than in the past.

[0015] In order to solve the above problems, the object of the present application is to provide an alkali-free glass substrate capable of easily removing bubbles contained in molten glass under a reduced-pressure atmosphere.

[0016] Means for solving the problems

[0017] In order to achieve the above object, the present application provides an alkali-free glass substrate containing, in mass% on an oxide basis, 54 to 68% of SiO2, 10 to 25% of Al2O3, 0.1 to 5.5% of B2O3, and 8 to 26% of MgO + CaO + SrO + BaO, characterized in that

[0018] the β-OH of the alkali-free glass substrate is 0.15 mm -1 to 0.35 mm -1 the Cl content is 0.15 mass% to 0.3 mass%, and

[0019] the bubble growth index I represented by the following formula (1) of the alkali-free glass substrate is 320 or more,

[0020] I = 590.5 x [β-OH] + 874.1 x [Cl] - 5.7 x [B2O3] - 33.3 (1)

[0021] where, in formula (1), [β-OH] represents the β-OH (mm -1 ) of the alkali-free glass substrate, [Cl] represents the Cl content (mass%) of the alkali-free glass substrate, and [B2O3] represents the B2O3 content (mass%) of the alkali-free glass substrate.

[0022] Effects of the Invention

[0023] According to the alkali-free glass substrate of the present application, bubbles contained in molten glass can be easily removed under a reduced-pressure atmosphere. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a cross-sectional view showing one structural example of a glass manufacturing apparatus for manufacturing the alkali-free glass substrate of the present invention.

[0025] Figure 2 Graph showing temporal changes in bubble diameter under the reduced pressure conditions of Experimental Example 1.

[0026] Reference numerals

[0027] 1: Glass manufacturing equipment

[0028] 10: Melting tank

[0029] 20: Decompression degassing device

[0030] 21: Decompression housing

[0031] 22: Decompression degassing tank

[0032] 23: Riser

[0033] 24: Downcomer

[0034] 25: Thermal insulation materials DETAILED DESCRIPTION

[0035] [Alkali-free glass substrate]

[0036] The following describes an alkali-free glass substrate according to one embodiment of the present invention. Alkali-free glass refers to glass that is substantially free of alkali metal oxides such as Na2O and K2O. Here, "substantially free of alkali metal oxides" means that the total amount of alkali metal oxides is 0.1% by mass or less.

[0037] The alkali-free glass substrate of the present invention contains 54% to 68% of SiO2, 10% to 25% of Al2O3, 0.1% to 5.5% of B2O3, and 8% to 26% of MgO+CaO+SrO+BaO, expressed in mass % based on oxides.

[0038] Hereinafter, in this specification, mass % based on oxides will be simply referred to as “%”.

[0039] Next, the composition range of each component will be described.

[0040] When SiO2 is 54% or more, the strain point of the alkali-free glass substrate increases and the chemical resistance becomes good. It is preferably 57% or more, more preferably 58.5% or more, and further preferably 59.5% or more.

[0041] When SiO2 is 68% or less, the melting property at the time of melting of the glass becomes good. It is preferably 67.5% or less, more preferably 66% or less, and further preferably 65% or less.

[0042] When Al2O3 is 10% or more, the phase separation is suppressed, and the strain point of the alkali-free glass substrate is increased. It is preferably 16% or more, more preferably 17% or more, and further preferably 18% or more.

[0043] When Al2O3 is 25% or less, the melting property at the time of melting of the glass becomes good. It is preferably 24% or less, more preferably 23% or less, and further preferably 22% or less.

[0044] When B2O3 is 0.1% or more, the melting property at the time of melting of the glass becomes good. It is preferably 0.5% or more, more preferably 1% or more, and further preferably 1.8% or more.

[0045] When B2O3 is 5.5% or less, the strain point of the alkali-free glass substrate is increased. It is preferably 4.5% or less, more preferably 3.0% or less, and further preferably 2.5% or less.

[0046] When the total amount of MgO, CaO, SrO, and BaO (i.e., MgO + CaO + SrO + BaO) is 8% or more, the melting property at the time of melting of the glass becomes good. It is preferably 10% or more, more preferably 12% or more, and further preferably 14% or more.

[0047] When MgO + CaO + SrO + BaO is 26% or less, the strain point of the alkali-free glass substrate is increased. It is preferably 24% or less, more preferably 22% or less, and further preferably 20% or less.

[0048] In order to improve the melting property at the time of melting of the glass, MgO can be contained. The content is preferably 2% or more, more preferably 3% or more, further preferably 4% or more, and particularly preferably 4.5% or more.

[0049] When MgO is 12% or less, the phase separation is suppressed, and thus it is preferable. It is more preferably 8.5% or less, further preferably 7.5% or less, and particularly preferably 7% or less.

[0050] In order to improve the melting property at the time of melting of the glass, CaO can be contained. The content is preferably 1.5% or more, more preferably 3% or more, and further preferably 4% or more.

[0051] When CaO is 15% or less, the mixing of impurities phosphorus in limestone (CaCO3) as a raw material of CaO is small, and thus it is preferable. It is more preferably 8.5% or less, further preferably 8% or less, and particularly preferably 7% or less.

[0052] SrO can be contained in order to improve the melting property at the time of melting the glass. The content is preferably 0.5% or more, more preferably 2% or more, and further preferably 2.5% or more.

[0053] SrO is preferably 16% or less because the acid resistance is good. More preferably, it is 10% or less, further preferably 8.5% or less, and particularly preferably 8% or less.

[0054] BaO can be contained in order to improve the melting property. The content is preferably 0.1% or more.

[0055] BaO is preferably 15% or less because segregation is not easily generated at the time of melting the raw material. More preferably, it is 10% or less, further preferably 8% or less, and more further preferably 4% or less, and particularly preferably 2.5% or less.

[0056] The first mode of the preferred composition of the alkali-free glass substrate of the present application contains:

[0057] 58.5% to 67.5% of SiO2,

[0058] 18% to 24% of Al2O3,

[0059] 0.1% to 1.7% of B2O3,

[0060] 4% to 8.5% of MgO,

[0061] 3% to 8.5% of CaO,

[0062] 2% to 10% of SrO,

[0063] 0% to 2.5% of BaO.

[0064] The second mode of the preferred composition of the alkali-free glass substrate of the present application contains:

[0065] 57% to 67.5% of SiO2,

[0066] 17% to 25% of Al2O3,

[0067] 1.8% to 5.5% of B2O3,

[0068] 2% to 8.5% of MgO,

[0069] 1.5% to 8% of CaO,

[0070] 0.5% to 8.5% of SrO,

[0071] 0% to 1% of BaO.

[0072] The β-OH of the alkali-free glass substrate of the present application is 0.15 mm -1~ 0.35 mm -1 β-OH is used as an index of water content in the glass. β-OH is 0.15 mm -1 When the above, the water in the glass flows into the bubbles under a reduced pressure atmosphere, and the bubbles easily grow. It is preferable that the β-OH be 0.18 mm -1 When the above, more preferably 0.2 mm -1 When the above, further preferably 0.22 mm -1 When the above.

[0073] β-OH is 0.35 mm -1 When the below, the growth of the bubbles can be inhibited from becoming too large, and thus in the reduced pressure defoaming treatment, the escape (suri-nukeri) of the bubbles due to the expansion of the bubble layer can be inhibited. It is preferable that the β-OH be 0.32 mm -1 When the below, more preferably 0.3 mm -1 When the below, further preferably 0.28 mm -1 When the below.

[0074] The β-OH can be found by measuring the transmittance of an alkali-free glass test piece obtained by forming the molten glass after the reduced pressure defoaming into a plate shape using a Fourier transform infrared spectrophotometer (FT-IR), and finding the β-OH using the following equation.

[0075] β-OH = (1 / X) log 10 (T1 / T2)

[0076] X: thickness of the glass plate (mm)

[0077] T1: transmittance (%) at a reference wave number of 4000 cm -1

[0078] T2: minimum transmittance (%) near a hydroxyl absorption wave number of 3570 cm -1

[0079] The β-OH is controlled by the water content in the glass raw material, the water vapor concentration in the melting tank, the burner combustion method (oxygen combustion, air combustion) in the melting tank, and the like. In particular, the β-OH can be easily adjusted by adjusting the burner combustion method. Specifically, in order to increase the β-OH, the oxygen combustion ratio of the burner combustion is increased, and in order to decrease the β-OH, the air combustion ratio of the burner combustion is increased.

[0080] ​​The content of Cl in the alkali-free glass substrate of the present application is 0.15 to 0.3 mass% relative to the base composition of the glass. Cl in the glass is a component that facilitates the growth of bubbles contained in the molten glass under a reduced pressure atmosphere. When the content of Cl is less than 0.15 mass%, the growth of bubbles tends to become insufficient. It is preferable that the content of Cl be 0.18 mass% or more, more preferably 0.2 mass% or more. When the content of Cl is more than 0.3 mass%, a bubble layer tends to be formed due to the expansion of the bubble layer in the reduced pressure defoaming treatment. It is more preferable that the content of Cl be 0.28 mass% or less, further preferably 0.25 mass% or less.

[0081] The bubble growth index I represented by the following formula (1) in the alkali-free glass substrate of the present application is 320 or more.

[0082] I = 590.5 x [β-OH] + 874.1 x [Cl] - 5.7 x [B203] - 33.3 (1)

[0083] In formula (1), [β-OH] represents the β-OH (mm -1 ) of the alkali-free glass substrate, [Cl] represents the content of Cl (mass%) of the alkali-free glass substrate, and [B203] represents the content of B203 (mass%) of the alkali-free glass substrate.

[0084] The bubble growth index I is an index of the easiness of the growth of bubbles contained in the molten glass under a reduced pressure atmosphere. When the bubble growth index I is 320 or more, the bubbles contained in the molten glass tend to grow under a reduced pressure atmosphere. It is preferable that the bubble growth index I be 330 or more, more preferably 340 or more.

[0085] When the bubble growth index I is 400 or less, the occurrence of reboiling in the molten glass flowing in the reduced pressure defoaming tank can be prevented, and thus it is preferable. Here, reboiling refers to a phenomenon in which bubbles are generated at the glass interface in contact with the molten defoaming tank made of platinum, platinum alloy, or dense refractory. It is more preferable that the bubble growth index I be 390 or less, further preferably 380 or less.

[0086] In the present specification, the bubble growth index I is correlated with the value of the pressure P defined in the following manner.

[0087] Under the condition that the temperature is constant, in the case where the reduced pressure defoaming tank is reduced in pressure, the volume of the bubbles (the diameter of the bubbles) present in the molten glass in the reduced pressure defoaming tank increases according to Boyle's law. However, when the reduced pressure defoaming tank is reduced in pressure to a certain pressure, the volume of the bubbles (the diameter of the bubbles) in the molten glass sharply increases deviating from Boyle's law. This pressure is set as the pressure P.

[0088] The pressure P can be obtained by the following steps.

[0089] In order to reproduce the conditions in the decompression bubble-removing tank, a crucible made of quartz glass, in which crushed glass of an alkali-free glass was placed, was arranged in a vacuum decompression vessel. The crucible was heated to 1450°C to melt the alkali-free glass. After the alkali-free glass was completely melted, the diameter of the bubbles in the molten glass was observed while the pressure in the vacuum decompression vessel was reduced. In order to observe the diameter of the bubbles in the molten glass, for example, a CCD camera can be used to take pictures of the bubbles in the molten glass from an observation window provided in the vacuum decompression vessel. Note that the number of samples of the bubbles for which the bubble diameter was measured was 20 or more.

[0090] When the pressure in the vacuum decompression vessel was reduced, the diameter of the bubbles in the molten glass increased according to Boyle's law. However, when the vacuum decompression vessel was reduced to a certain pressure, the diameter of the bubbles in the molten glass sharply increased, deviating from Boyle's law. The pressure in the vacuum decompression vessel at this time was set as the pressure P.

[0091] The present inventors et al. derived a bubble growth index I based on the results of the measurement of the pressure P in a variety of alkali-free glass substrates, and found that, for an alkali-free glass substrate in which bubbles contained in the molten glass can be easily removed under a reduced pressure atmosphere, the bubble growth index I represented by formula (1) is 320 or more.

[0092] The alkali-free glass substrate of the present application can contain Fe2O3 as a trace component. Fe2O3 is preferably 0.1% by mass or less, more preferably 0.05% by mass or less.

[0093] The alkali-free glass substrate of the present application is preferably one in which the strain point is 690°C or higher, because the thermal shrinkage during panel manufacturing can be suppressed. More preferably, the strain point is 700°C or higher.

[0094] The alkali-free glass substrate of the present application is preferably one in which the strain point is 750°C or lower, because the temperature in the floatation furnace and at the outlet of the floatation furnace does not need to be excessively high, and the impact on the life of the metal members located in the floatation furnace and on the downstream side of the floatation furnace is small. More preferably, the strain point is 740°C or lower, and further preferably 730°C or lower.

[0095] Note that the strain point was measured by the fiber elongation method according to the method prescribed in JIS R3103-2 (2001).

[0096] The alkali-free glass substrate of the present application is preferably one in which the Young's modulus is 78 GPa or higher, because the deflection of the glass substrate during transportation is suppressed as the glass substrate is enlarged and thinned. More preferably, the Young's modulus is 79 GPa or higher, further preferably 80 GPa or higher, and particularly preferably 82 GPa or higher. On the other hand, when the Young's modulus is excessively high, the cuttability of the glass deteriorates, and thus the Young's modulus is preferably 95 GPa or lower, further preferably 92 GPa or lower, and further preferably 90 GPa or lower.

[0097] Note that the Young's modulus was measured by an ultrasonic method.

[0098] The substrate size of the alkali-free glass substrate of the present application is preferably 2100 mm or more in the short side and 2400 mm or more in the long side, more preferably 2800 mm or more in the short side and 3000 mm or more in the long side, further preferably 2900 mm or more in the short side and 3200 mm or more in the long side. As the substrate size becomes larger, it is necessary to reduce the bubble density in the substrate, and the alkali-free glass substrate of the present application has a low bubble density, so that the yield of the product is not easily reduced even if the substrate size becomes larger, and is suitable for a large substrate size. In addition, the substrate size is preferably 6000 mm or less in the short side and 6500 mm or less in the long side. This is because, when the substrate size is too large, the investment cost of the equipment increases due to the enlargement of the equipment, and it is difficult to transport the glass substrate.

[0099] The bubble density of the alkali-free glass substrate of the present application in which the bubble diameter is greater than 100 μm is preferably 0.06 pieces / kg or less, more preferably 0.03 pieces / kg or less, further preferably 0.01 pieces / kg or less.

[0100] Note that the bubble density of the bubble having a diameter greater than 100 μm is calculated by irradiating light from the side surface of the glass substrate in a dark room, investigating the number of bubble defects having a size greater than 100 μm by edge light inspection of the main surface of the glass substrate, and thereby calculating the bubble density of the bubble having a diameter greater than 100 μm.

[0101] The alkali-free glass substrate of the present application is preferably a float glass. The float method is superior to the fusion method in terms of taking out a large substrate size glass substrate.

[0102] With respect to the alkali-free glass substrate of the present application, when the alkali-free glass substrate is melted, maintained at 1450°C, and depressurized from the atmospheric pressure to 44 kPa at a constant depressurization rate for 20 minutes, and maintained at 44 kPa for 5 minutes, the bubble having a diameter of 0.1 mm to 0.3 mm contained in the molten glass at 1450°C before the start of the depressurization is set as an initial bubble, the bubble corresponding to the initial bubble after the maintenance at 44 kPa for 5 minutes is set as a grown bubble, and the diameter of the grown bubble is preferably 3 times or more the diameter of the initial bubble.

[0103] When the diameter of the grown bubble is 3 times or more the diameter of the initial bubble, the bubble contained in the molten glass easily grows under the depressurized atmosphere, and easily floats up in the molten glass. Therefore, the bubble contained in the molten glass can be easily removed.

[0104] The diameter of the initial bubble and the diameter of the grown bubble can be found by the following steps.

[0105] A quartz cell containing crushed glass of an alkali-free glass substrate was disposed in a vacuum decompression vessel. The quartz cell was heated to 1450°C to melt the crushed glass, and then the vacuum decompression vessel was decompressed. A CCD camera was used to take an image of bubbles contained in the molten glass from an observation window provided in the vacuum decompression vessel, and the diameters of the bubbles (hereinafter referred to as bubble diameters) were measured by image analysis. Note that it is not necessary to measure the bubble diameters of all of the bubbles observed in the image. Specifically, bubbles attached to the wall surface of the quartz cell, bubbles formed by merging of a plurality of bubbles, and the like were excluded from the measurement targets. The ratio of the diameter of the grown bubble to the diameter of the initial bubble (hereinafter referred to as the bubble growth rate) in one embodiment of the present application was obtained by calculating the bubble growth rate for each of the bubbles observed in the image and averaging the results.

[0106] The decompression condition for evaluation was decompression from atmospheric pressure to 44 kPa at a constant decompression rate over 20 minutes. The bubbles contained in the molten glass were allowed to grow sufficiently when the molten glass was decompressed to 44 kPa, and thus this condition was suitable for evaluation of the growth of the bubble diameters. Further, when the decompression time was 20 minutes, the growth of the bubble diameters could be evaluated appropriately while shortening the evaluation time.

[0107] The initial bubble was selected to be a bubble having a bubble diameter of 0.1 mm to 0.3 mm. When the diameter of the initial bubble was 0.1 mm or more, the measurement of the bubble diameter by the CCD camera became easy. When the diameter of the initial bubble was 0.3 mm or less, the growth of the bubble diameters could be evaluated appropriately because the grown bubbles were prevented from bursting due to expansion.

[0108] The bubble corresponding to the initial bubble after being kept at 44 kPa for 5 minutes was set as the grown bubble. When the keeping time was 5 minutes, the grown bubble became sufficiently large with respect to the initial bubble, and further, the growth of the bubble diameters could be evaluated appropriately because the grown bubbles were prevented from bursting due to expansion.

[0109] The diameter of the grown bubble of the alkali-free glass substrate of the present application is more preferably 3.5 times or more, and further preferably 4 times or more, the diameter of the initial bubble.

[0110] The diameter of the growing bubble of the alkali-free glass substrate of the present application is preferably 15 times or less the diameter of the initial bubble. When it is 15 times or less, in the reduced-pressure bubble-removal treatment, the bubble layer that is normally present on the surface of the molten glass at about 10 mm or less expands to 10 mm to several hundred mm, and thus the sliding of the bubble can be suppressed. Here, the escape of the bubble refers to a phenomenon in which a bubble that has reached the surface of the glass does not break but stably exists for a long time by forming a bubble layer, and then flows out to the subsequent process as it is without breaking. When the escape of the bubble occurs, the problem of the residual of the bubble in the molten glass after the reduced-pressure bubble-removal treatment occurs.

[0111] The diameter of the growing bubble of the alkali-free glass substrate of the present application is more preferably 10 times or less, further preferably 8 times or less, and particularly preferably 6 times or less the diameter of the initial bubble.

[0112] The alkali-free glass substrate of the present application is preferably a glass substrate for a liquid crystal display, and the thickness thereof is preferably 0.75 mm or less, more preferably 0.55 mm or less, further preferably 0.5 mm or less, and particularly preferably 0.45 mm or less. In addition, the thickness is preferably 0.1 mm or more, and more preferably 0.2 mm or more.

[0113] [Method for manufacturing alkali-free glass substrate]

[0114] Next, a method for manufacturing an alkali-free glass substrate according to one embodiment of the present application will be described with reference to the drawings. Figure 1 FIG. 1 is a cross-sectional view showing one configuration example of a glass manufacturing apparatus for manufacturing an alkali-free glass substrate of the present application.

[0115] The glass manufacturing apparatus 1 has a melting tank 10 and a reduced-pressure bubble-removal apparatus 20. A forming apparatus such as a floatation furnace is provided after the reduced-pressure bubble-removal apparatus 20. The forming apparatus can also be a forming apparatus used in a down-draw method.

[0116] In the method for manufacturing an alkali-free glass substrate, a molten glass G is produced by melting a glass raw material in the melting tank 10, the molten glass G is subjected to a reduced-pressure bubble-removal treatment by the reduced-pressure bubble-removal apparatus 20, and a ribbon-shaped glass band formed by the forming apparatus is slowly cooled and cut, thereby obtaining an alkali-free glass substrate.

[0117] The melting tank 10 has a burner for melting the glass raw material supplied. The burner forms a flame by mixing and burning a fuel such as natural gas or heavy oil with a gas. A burner that mainly uses air as the gas is referred to as an air-assisted burner, and a burner that mainly uses oxygen as the gas is referred to as an oxygen-assisted burner. The burner heats the glass raw material from above by emitting the flame toward the glass raw material. In addition, the melting tank 10 can have an electrode for heating the glass raw material.

[0118] For the glass raw material, for example, silica sand, boric acid, limestone, alumina, strontium carbonate, magnesium oxide, etc. can be used, and are adjusted in a manner so as to obtain the composition of the target non-alkali glass substrate.

[0119] As described above, the non-alkali glass substrate of the present application can easily remove the bubbles contained in the molten glass under a reduced pressure atmosphere, and therefore, the glass raw material is preferably the cullet generated when manufacturing the non-alkali glass substrate, or the cullet of the used non-alkali glass substrate.

[0120] A chloride-based fining agent is preferably added to the glass raw material. From the viewpoint of not worrying about deliquescence, the chloride-based fining agent is preferably BaCl2-2H2O, SrCl2-6H2O, CaCl2, MgCl2-6H2O, or NH4Cl.

[0121] For the fining agent, in order to appropriately adjust the bubble growth rate, a fining agent other than the chloride-based fining agent can also be used. In this case, for example, SO3, F, SnO2, etc. can be cited as the other fining agent. The content of these other fining agents in the glass raw material is preferably 2% by mass or less, more preferably 1% by mass or less, and further preferably 0.5% by mass or less.

[0122] The reduced pressure bubble removing apparatus 20 has a reduced pressure casing 21, a reduced pressure bubble removing tank 22, an upcomer 23, a downcomer 24, and a heat insulating material 25.

[0123] The reduced pressure bubble removing tank 22, which is provided in a cylindrical shape, is housed in the reduced pressure casing 21 so as to be oriented with its long axis in the horizontal direction. The upcomer 23, which is oriented in the vertical direction, is installed to the lower surface of one end of the reduced pressure bubble removing tank 22, and the downcomer 24 is installed to the lower surface of the other end. A part of the upcomer 23 and the downcomer 24 is located in the reduced pressure casing 21.

[0124] The upcomer 23 communicates with the reduced pressure bubble removing tank 22, and guides the molten glass G from the melting tank 10 into the reduced pressure bubble removing tank 22. The downcomer 24 communicates with the reduced pressure bubble removing tank 22, and guides the molten glass G after the reduced pressure bubble removing to the next processing tank. In the reduced pressure casing 21, the reduced pressure bubble removing tank 22, the upcomer 23, and the downcomer 24 are surrounded by the heat insulating material 25, such as heat insulating bricks, which insulate them.

[0125] The reduced pressure bubble removing tank 22, the upcomer 23, and the downcomer 24 are conduits for the molten glass, and therefore are made of a material having excellent heat resistance and corrosion resistance against the molten glass. For example, platinum, platinum alloy, or a reinforced platinum obtained by dispersing a metal oxide in platinum or platinum alloy. In addition, it can be a ceramic non-metallic inorganic material, i.e., a dense refractory. In addition, it can be a material obtained by lining platinum or platinum alloy in a dense refractory.

[0126] The vacuum degassing is performed by passing the molten glass G supplied from the melting tank 10 through the vacuum degassing tank 22, which is decompressed to a predetermined pressure. The molten glass G is preferably continuously supplied and discharged to the vacuum degassing tank 22. From the perspective of productivity, the flow rate of the molten glass is preferably 1 to 200 tons per day.

[0127] In order to prevent a temperature difference from the molten glass G supplied from the melting tank 10 , the vacuum degassing tank 22 is preferably heated so that the inside thereof reaches a temperature in the range of 1200° C. to 1600° C., particularly 1350° C. to 1550° C.

[0128] During decompression degassing, the air within the decompression housing 21 is evacuated from the outside using a vacuum pump or other vacuum degassing means through a suction opening provided at a predetermined position within the decompression housing 21. This indirectly evacuates the air within the decompression degassing tank 22 housed within the decompression housing 21, reducing the pressure within the decompression degassing tank 22 to a predetermined level.

[0129] The pressure inside the reduced pressure degassing tank 22 is preferably 15 kPa to 55 kPa.

[0130] [Example]

[0131] The present invention is further described below using Examples and Comparative Examples. It should be noted that the present invention is not limited to these descriptions. It should be noted that Examples 1, 4 to 7, 9, 10, 12, 13, 15, 16, and 18 are Examples, and Examples 2, 3, 8, 11, 14, and 17 are Comparative Examples.

[0132] [Experimental Example 1]

[0133] use Figure 1 The glass manufacturing apparatus 1 shown in the figure melts glass raw materials composed of alkali-free glass in a melting tank 10 to produce molten glass G, which is then subjected to a vacuum degassing treatment by a vacuum degassing apparatus 20. The molten glass is formed into a plate-shaped glass ribbon by a float process, and the glass ribbon is slowly cooled and cut to prepare alkali-free glass substrates with a thickness of 0.50 mm (Examples 1 and 2).

[0134] The glass composition of Example 1, expressed in mass % based on oxides, is: 61.2% SiO2, 20.0% Al2O3, 2.0% B2O3, 5.3% MgO, 4.5% CaO, 7.0% SrO, and 0.1% BaO (MgO+CaO+SrO+BaO=16.9%). The Cl content relative to the basic composition of the glass is 0.234% by mass. Furthermore, the β-OH content measured by the following method is 0.329 mm. -1 .

[0135] (β-OH)

[0136] β-OH is determined by measuring the absorbance of a glass sample for light having a wavelength of 2.75 μm to 2.95 μm, and using the maximum value β max divided by the thickness (mm) of the sample.

[0137] Therefore, the bubble growth index I = 590.5 x 0.329 + 874.1 x 0.234 - 5.7 x 2.0 - 33.3 = 354.

[0138] I = 590.5 x 0.329 + 874.1 x 0.234 - 5.7 x 2.0 - 33.3 = 354.

[0139] The glass composition of Example 2 was 62% of SiO2, 18% of Al2O3, 9.5% of B2O3, 2% of MgO, 7% of CaO, 1.2% of SrO, 0.1% of BaO (MgO + CaO + SrO + BaO = 10.3%), 0.2% of SnO2, expressed in mass% on an oxide basis, and the content of Cl was 0 mass% with respect to the base composition of the glass. In addition, β-OH measured by the above method was 0.47 mm -1 .

[0140] Therefore, the bubble growth index I = 590.5 x 0.329 + 874.1 x 0.234 - 5.7 x 2.0 - 33.3 = 354.

[0141] In order to reproduce the atmosphere in which the pressure reduction devitrification was carried out, a quartz cell containing 50 g of crushed glass of an alkali-free glass substrate was disposed in a vacuum pressure reduction vessel. The vacuum pressure reduction vessel used was an HTO (high temperature observation) furnace manufactured by Glass Service Co. The quartz cell was heated from room temperature to 1450°C, the crushed glass was melted, and then the pressure reduction in the vacuum pressure reduction vessel was started. While maintaining the vacuum pressure reduction vessel at 1450°C, the pressure was reduced from atmospheric pressure to 44 kPa at a constant pressure reduction rate over 20 minutes, and maintained at 44 kPa for 10 minutes. During this period, the time at which the pressure reduction was started was set to 0 minutes, and at 0, 3, 6, 9, 12, 15, 18, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30 minutes, the bubbles in the molten glass were photographed from an observation window provided in the vacuum pressure reduction vessel using a CCD camera, and the diameters of the bubbles were measured by image analysis. In Experimental Example 1, the initial bubbles were 0 minutes, and the growing bubbles were 25 minutes from the start of the pressure reduction.

[0142] Figure 2A graph showing the time change of the bubble diameter under the reduced pressure condition of Experimental Example 1 is shown. When comparing Example 1 and Example 2, it is understood that the diameter of the bubble in Example 1 grew larger during the period maintained at 44 kPa. In Example 1, the diameter of the initial bubble was 0.24 mm, and the diameter of the grown bubble was 0.97 mm, which was 4.0 times the diameter of the initial bubble. On the other hand, in Example 2, the diameter of the initial bubble was 0.25 mm, and the diameter of the grown bubble was 0.47 mm, which was 1.9 times the diameter of the initial bubble. According to the alkali-free glass substrate of Example 1, it is understood that the bubbles contained in the molten glass can be easily removed under a reduced pressure atmosphere.

[0143] Note that Experimental Example 1 and Experimental Example 2 described below differ in that the temperature of the molten glass is 1450°C and 1400°C, and the pressure in the vacuum reduced pressure vessel (reduced pressure bubble removing tank) is 44 kPa and 33.33 kPa. This is because when Experimental Example 1 was performed under the condition of a pressure of 33.33 kPa, the bubbles in the molten glass excessively expanded, and it was difficult to perform the photographing using the CCD camera.

[0144] [Experimental Example 2]

[0145] The refining effect of the molten glass in the reduced pressure bubble removing tank was evaluated by simulation. The rising speed of the bubble growing in the molten glass stream and rising in the molten glass has a relationship with the bubble diameter according to the Stokes equation. Therefore, in the simulation, the bubble diameter was calculated based on the bubble growth rate, and the behavior of the bubble rising was analyzed based on the Stokes formula. Note that the calculation was performed assuming that the bubble was generated at the central portion of the reduced pressure bubble removing tank on which the riser was installed, and the diameter of the initial bubble was set to 0.2 mm.

[0146] The size of the reduced pressure bubble removing tank and the liquid surface height of the molten glass were as follows, respectively.

[0147] The length in the horizontal direction from the central portion of the riser to the central portion of the downcomer in the reduced pressure bubble removing tank: 10 m

[0148] The inner diameter of the reduced pressure bubble removing tank: 500 mm

[0149] The liquid surface height of the molten glass: 250 mm

[0150] The molten glass passing through the reduced pressure bubble removing tank was assumed in the following manner.

[0151] The glass composition is shown below. Note that the content of Cl is referred to Table 1 described later.

[0152] (Glass basic composition is shown in mass% on an oxide basis, and the content of Cl is mass% with respect to the basic composition of the glass)

[0153] Examples 3 to 14

[0154] SiO2: 61.2%, Al2O3: 20.0%, B2O3: 2.0%, MgO: 5.3%, CaO: 4.5%, SrO: 7.0%, BaO: 0.1% (MgO + CaO + SrO + BaO = 16.9%)

[0155] Example 15

[0156] SiO2: 61.6%, Al2O3: 20.9%, B2O3: 0.1%, MgO: 6.1%, CaO: 4.6%, SrO: 6.8%, BaO: 0.1% (MgO + CaO + SrO + BaO = 17.6%)

[0157] Example 16

[0158] SiO2: 61.2%, Al2O3: 20.1%, B2O3: 1.8%, MgO: 5.4%, CaO: 4.5%, SrO: 7.0%, BaO: 0.1% (MgO + CaO + SrO + BaO = 17.0%)

[0159] Example 17

[0160] SiO2: 60.9%, Al2O3: 19.5%, B2O3: 3.5%, MgO: 4.9%, CaO: 4.4%, SrO: 7.1%, BaO: 0.1% (MgO + CaO + SrO + BaO = 16.6%)

[0161] Example 18

[0162] SiO2: 60.7%, Al2O3: 19.1%, B2O3: 5.5%, MgO: 4.6%, CaO: 4.4%, SrO: 7.3%, BaO: 0.1% (MgO + CaO + SrO + BaO = 16.3%)

[0163] Flow rate of molten glass: 0.6 m 3 / hour or 1.5 m 3 / hour

[0164] Pressure in the pressure-reducing defoaming tank: 33.33 kPa

[0165] Temperature (average) when passing through the pressure-reducing defoaming tank: 1400°C

[0166] Viscosity when passing through the pressure-reducing defoaming tank: 150 Pa-s to 200 Pa-s

[0167] Density when passing through the pressure-reducing defoaming tank: 2380 kg / m 3

[0168] As for the defoaming performance, the distance from the central portion of the riser in the defoaming tank to the position at which the bubbles float to the liquid surface of the molten glass (floating distance) was evaluated. The smaller the floating distance, the more excellent the defoaming performance.

[0169] The results are shown in Table 1. In Table 1, the flow rate of the molten glass, B2O3, β-OH, Cl content, bubble growth index I, bubble growth rate, and floating distance are shown. The bubble growth rate was measured under the same conditions as in Experimental Example 1.

[0170]

[0171] As shown in Table 1, the floating distance of the glass having a bubble growth index I of less than 320 (Examples 3, 8, 11, 14, 17) was greater than 10 m. From this result, it can be considered that the bubble density of the glass substrate having a bubble diameter of greater than 100 μm was greater than 0.06 pieces / kg.

[0172] On the other hand, the floating distance of the glass having a bubble growth index I of 320 or more (Examples 4 to 7, 9, 10, 12, 13, 15, 16, 18) was 10 m or less. From this result, it can be considered that the bubble density of the glass substrate having a bubble diameter of greater than 100 μm was 0.06 pieces / kg or less.

[0173] From the above results, it can be seen that the glass of the Examples does not need to intentionally increase the size of the defoaming device in order to efficiently produce a large glass substrate, and can solve the problem of an increase in the investment cost of the equipment. In addition, since the bubble density in the substrate can be reduced, it can be considered that, as the size of the substrate increases, the problem of a decrease in the product yield is solved.

[0174] Although the present application has been described in detail and with reference to specific embodiments, various changes and modifications can be made without departing from the spirit and scope of the application, which will be readily apparent to those skilled in the art.

[0175] This application is based on Japanese Patent Application No. 2019-051570 filed on March 19, 2019, the contents of which are incorporated herein by reference.

[0176] Industrial Applicability

[0177] The use of the alkali-free glass substrate can be cited for liquid crystal displays, for organic EL displays, for flat panel displays, or other various uses.

Claims

1. An alkali-free glass substrate, comprising, expressed in mass % based on oxides, 54% to 68% of SiO2, 10% to 25% of Al2O3, 0.1% to 4.5% of B2O3, and 8% to 26% of MgO+CaO+SrO+BaO, and containing no SnO2 or SO3, characterized in that: The β-OH of the alkali-free glass substrate is 0.15 mm -1 ~0.35mm -1 , Cl content is 0.15 mass% to 0.3 mass%, and The bubble growth index I of the alkali-free glass substrate represented by the following formula (1) is 320 or more, I=590.5×[β-OH] +874.1×[Cl]-5.7×[B2O3]-33.3 (1) Wherein, in formula (1), [β-OH] represents the β-OH of the alkali-free glass substrate, and the unit is mm -1 , [Cl] represents the mass percentage content of Cl in the alkali-free glass substrate, and [B2O3] represents the mass percentage content of B2O3 in the alkali-free glass substrate.

2. The alkali-free glass substrate according to claim 1, wherein The bubble growth index I of the alkali-free glass substrate represented by the formula (1) is 400 or less.

3. The alkali-free glass substrate according to claim 1 or 2, wherein The strain point of the alkali-free glass substrate is 690° C. to 750° C.

4. The alkali-free glass substrate according to claim 1 or 2, wherein The alkali-free glass substrate contains, expressed in mass % based on oxides, 0% to 12% of MgO, 0% to 15% of CaO, 0% to 16% of SrO, and 0% to 15% of BaO.

5. The alkali-free glass substrate according to claim 1 or 2, wherein The alkali-free glass substrate contains, expressed in mass % based on oxides, 58.5% to 67.5% of SiO2, 18% to 24% of Al2O3, 0.1% to 1.7% of B2O3, 4% to 8.5% of MgO, 3% to 8.5% of CaO, 2% to 10% of SrO, and 0% to 2.5% of BaO. The alkali-free glass substrate according to claim 1 or 2, wherein The alkali-free glass substrate contains, expressed in mass % based on oxides, 57% to 67.5% of SiO2, 17% to 25% of Al2O3, 1.8% to 4.5% of B2O3, 2% to 8.5% of MgO, 1.5% to 8% of CaO, 0.5% to 8.5% of SrO, and 0% to 1% of BaO.

7. The alkali-free glass substrate according to claim 1 or 2, wherein The alkali-free glass substrate has a Young's modulus of 78 GPa or more.

8. The alkali-free glass substrate according to claim 1 or 2, wherein The alkali-free glass substrate has a thickness of 0.1 mm to 0.5 mm.

9. The alkali-free glass substrate according to claim 1 or 2, wherein The alkali-free glass substrate has a substrate size of a short side of not less than 2100 mm and a long side of not less than 2400 mm.

10. The alkali-free glass substrate according to claim 1 or 2, wherein The alkali-free glass substrate has a substrate size of a short side of not less than 2900 mm and a long side of not less than 3200 mm.

11. The alkali-free glass substrate according to claim 1 or 2, wherein The alkali-free glass substrate has a bubble density of bubbles having a diameter greater than 100 μm and a bubble density of 0.06 / kg or less.

12. The alkali-free glass substrate according to claim 1 or 2, wherein The alkali-free glass substrate was melted, and while being held at 1450° C., the pressure was reduced from atmospheric pressure to 44 kPa at a constant rate over 20 minutes, and then maintained at 44 kPa for 5 minutes. Bubbles with a diameter of 0.1 mm to 0.3 mm contained in the molten glass at 1450°C before the start of decompression are defined as initial bubbles. The bubbles corresponding to the initial bubbles after being maintained at 44 kPa for 5 minutes are defined as growing bubbles. The diameter of the growing bubble is more than three times the diameter of the initial bubble.

13. The alkali-free glass substrate according to claim 12, wherein The diameter of the growing bubble is less than 15 times the diameter of the initial bubble.

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