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%-66% of SiO2, 10%-23% of Al2O3, 6%-12% 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 0.5 mm-1, a Cl content of 0.1%-0.35% by mass, and a bubble growth index I represented by formula (1) of 280 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, in the formula (1), [beta]-OH] and Cl are contained in the alkali-free glass substrate, [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 with application date of June 21, 2019 and application number 201910541667.5. Technical Field

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

[0003] For various glass substrates for displays, especially glass substrates with metal or oxide thin films formed on the surface, when containing alkali metal oxides, the film properties deteriorate due to the diffusion of alkali metal ions in the thin film. Therefore, it is preferred to use alkali-free glass substrates that substantially do not contain alkali metal ions.

[0004] The alkali-free glass substrate used for the above purpose is obtained by heating and melting glass raw materials prepared in a predetermined ratio in a melting tank to vitrify the glass, clarifying the molten glass, and then forming it into a glass ribbon of a predetermined thickness by a float process or a fusion process, and cutting the glass ribbon into a predetermined shape.

[0005] For clarification of molten glass, a decompression degassing method is known: molten glass is introduced into a decompression atmosphere, bubbles in a continuously flowing molten glass flow are greatly grown in the decompression atmosphere, bubbles contained in the molten glass are floated and broken to remove the bubbles, and then the molten glass is discharged from the decompression atmosphere. For example, Patent Document 1 discloses a glass manufacturing method having a step of decompressing molten glass in a decompression degassing tank.

[0006] In order to recycle glass and improve solubility, scraps of used glass are used as part of glass raw materials.

[0007] Prior art literature

[0008] Patent Literature

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

[0010] Non-patent literature

[0011] Non-patent document 1: Chikao Tanaka, “Environmentally responsive glass melting technology: particularly degassing technology,” New Glass 83 Vol. 21, No. 4 (2006), pp. 31-36. Summary of the invention

[0012] Problems to be solved by the invention

[0013] Incidentally, in recent years, the demand for large-scale liquid crystal displays has increased, and it is expected that the glass substrates used in liquid crystal displays will be large-scale. In order to efficiently manufacture large glass substrates and increase the flow rate of molten glass, it is sometimes necessary to increase the size of the vacuum degassing device. In particular, when a molten glass conduit (vacuum degassing tank, riser or downcomer) made of platinum or platinum alloy is used in the vacuum degassing device, there is a problem of increased investment cost of the equipment.

[0014] In addition, for glass substrates, even if the average density of bubble defects in the substrates is the same, as the substrate size increases, the yield of the product decreases (see the figure of non-patent document 1). Therefore, in order to make the manufactured glass substrate larger, it is necessary to further reduce the bubble density in the substrate than before.

[0015] In order to solve the above-mentioned problems, an object of the present invention is to provide an alkali-free glass substrate from which bubbles contained in a molten glass can be easily removed in a reduced-pressure atmosphere.

[0016] Means used to solve problems

[0017] In order to achieve the above object, the present invention provides an alkali-free glass substrate, which contains 54% to 66% SiO2, 10% to 23% Al2O3, 6% to 12% B2O3, and 8% to 26% MgO+CaO+SrO+BaO, expressed in terms of mass % based on oxides, and is characterized in that:

[0018] The β-OH of the alkali-free glass substrate is 0.15 mm -1 ~0.5mm -1 , Cl content is 0.1 mass % to 0.35 mass %, and

[0019] The bubble growth index I of the alkali-free glass substrate represented by the following formula (1) is 280 or more,

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

[0021] In formula (1), [β-OH] represents the β-OH (mm -1 ), [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 invention, bubbles included in molten glass can be easily removed in 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 the temporal change 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: Rising pipe

[0033] 24: Downcomer

[0034] 25: Thermal insulation material DETAILED DESCRIPTION

[0035] [Alkali-free glass substrate]

[0036] The following describes an alkali-free glass substrate in one embodiment of the present invention. Alkali-free glass refers to glass that substantially does not contain alkali metal oxides such as Na2O and K2O. Here, substantially not containing alkali metal oxides means that the total amount of alkali metal oxides is 0.1 mass % or less.

[0037] The alkali-free glass substrate of the present invention contains 54% to 66% of SiO2, 10% to 23% of Al2O3, 6% to 12% of B2O3, and 8% to 26% of MgO+CaO+SrO+BaO, expressed in terms of 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 is 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 55% or more, more preferably 57% or more, and further preferably 58% or more.

[0041] When SiO2 is 64% or less, the solubility of the glass during melting becomes good. It is preferably 63% or less, more preferably 62% or less, and further preferably 61% or less.

[0042] When Al2O3 is 10% or more, phase separation is suppressed and the strain point of the alkali-free glass substrate is increased. It is preferably 12% or more, more preferably 14% or more, and further preferably 16% or more.

[0043] When Al2O3 is 23% or less, the solubility of the glass during melting becomes good. It is preferably 22% or less, more preferably 21% or less, and further preferably 20% or less.

[0044] When B2O3 is 6% or more, the solubility of the glass during melting becomes good, and the chemical resistance of the alkali-free glass substrate is improved. It is preferably 6.5% or more, more preferably 7% or more, and further preferably 7.4% or more.

[0045] When B2O3 is 12% or less, the strain point of the alkali-free glass substrate increases. It is preferably 11% or less, more preferably 10% or less, and further preferably 9% or less.

[0046] When the total amount of MgO, CaO, SrO, and BaO (i.e., MgO+CaO+SrO+BaO) is 8% or more, the solubility of the glass during melting becomes good. Preferably, it is 9% or more, more preferably, it is 10% or more, and further preferably, it is 12% or more.

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

[0048] MgO may be contained in order to improve the solubility of the glass during melting, and the content is preferably 0.1% or more, more preferably 1% or more, further preferably 2% or more, and particularly preferably 3% or more.

[0049] When the MgO content is 12% or less, phase separation is suppressed, which is preferred, 10% or less is more preferred, 8% or less is further preferred, and 6% or less is particularly preferred.

[0050] CaO may be contained in order to improve the solubility of the glass during melting, and the content is preferably 0.1% or more, more preferably 1.5% or more, further preferably 3% or more, and particularly preferably 3.5% or more.

[0051] When CaO is 12% or less, the impurity phosphorus in limestone (CaCO3) as the CaO raw material is less mixed, so it is preferred. It is more preferably 10% or less, further preferably 8% or less, and particularly preferably 6% or less.

[0052] SrO may be contained in order to improve the solubility of the glass during melting. The content is preferably 0.1% or more, more preferably 1% or more, further preferably 3% or more, and particularly preferably 5% or more.

[0053] When SrO is 16% or less, the acid resistance is good, so it is preferred. It is more preferably 14% or less, further preferably 12% or less, and particularly preferably 10% or less.

[0054] BaO may be contained to improve solubility, and the content is preferably 0.1% or more.

[0055] BaO is preferably 16% or less, because segregation is less likely to occur when the raw material is melted. It is more preferably 13% or less, further preferably 10% or less, and particularly preferably 7% or less.

[0056] The β-OH of the alkali-free glass substrate of the present invention is 0.15 mm -1 ~0.5mm -1 β-OH is used as an indicator of the water content in glass. β-OH is 0.15 mm -1 When the pressure is above 0.20 mm, the water in the glass flows into the bubbles in the reduced pressure atmosphere, and the bubbles become easy to grow. -1 More preferably 0.25 mm -1 above.

[0057] β-OH is 0.5mm -1 When the diameter is less than 0.45 mm, the growth of bubbles can be suppressed from becoming too large, so the escape of bubbles caused by the expansion of the bubble layer can be suppressed during the vacuum degassing treatment. -1 Less than, more preferably 0.40 mm -1 the following.

[0058] β-OH can be determined by measuring the transmittance of an alkali-free glass test piece obtained by forming a molten glass after vacuum degassing into a plate using a Fourier transform infrared spectrophotometer (FT-IR) and determining β-OH using the following formula.

[0059] β-OH=(1 / X)log 10 (T1 / T2)

[0060] X: Glass plate thickness (mm)

[0061] T1: Reference wave number 4000cm -1 Transmittance under

[0062] T2: Hydroxyl absorption wave number 3570cm -1 Minimum transmittance near

[0063] 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 in the melting tank (oxygen combustion, air combustion), etc. In particular, β-OH can be easily adjusted by adjusting the burner combustion method. Specifically, in order to increase β-OH, the oxygen combustion ratio of the burner combustion is increased, and in order to reduce β-OH, the air combustion ratio of the burner combustion is increased.

[0064] The Cl content of the alkali-free glass substrate of the present invention is 0.1% to 0.35% by mass relative to the basic composition of the glass. The Cl in the glass is a component that makes it easy for bubbles contained in the molten glass to grow in a reduced pressure atmosphere. When the Cl content is less than 0.1% by mass, the growth of the bubbles tends to become insufficient. When the Cl content is greater than 0.35% by mass, it becomes easy to form a bubble layer due to the expansion of the bubble layer during the reduced pressure degassing treatment. It is more preferably 0.15% to 0.35% by mass, and even more preferably 0.2% to 0.35% by mass.

[0065] The alkali-free glass substrate of the present invention has a bubble growth index I represented by the following formula (1) of 280 or more.

[0066] I=590.5×[β-OH] +874.1×[Cl]-5.7×[B2O3]-33.3 (1)

[0067] In formula (1), [β-OH] represents the β-OH of the alkali-free glass substrate (mm -1 ), [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.

[0068] The bubble growth index I is an index of the ease of growth of bubbles contained in the molten glass under a reduced pressure atmosphere. When the bubble growth index I is 280 or more, the bubbles contained in the molten glass are easy to grow under a reduced pressure atmosphere. It is preferably 290 or more, and more preferably 300 or more.

[0069] When the bubble growth index I is 360 or less, the reboiling of the molten glass flowing in the vacuum degassing tank can be prevented, so it is preferred. Here, reboiling refers to the phenomenon that bubbles are generated at the glass interface in contact with the molten degassing tank made of platinum, platinum alloy or dense refractory. The bubble growth index I is more preferably 340 or less, and further preferably 320 or less.

[0070] In this specification, the bubble growth index I is correlated with the value of the pressure P defined as follows.

[0071] Under the condition of constant temperature, when the vacuum degassing tank is decompressed, the volume of bubbles (diameter of bubbles) in the molten glass in the vacuum degassing tank increases according to Boyle's law. However, when the vacuum degassing tank is decompressed to a certain pressure, the volume of bubbles (diameter of bubbles) in the molten glass deviates from Boyle's law and increases sharply. This pressure is set as pressure P.

[0072] The pressure P can be calculated by the following steps.

[0073] In order to reproduce the conditions in the vacuum degassing tank, a quartz glass crucible containing cullet of alkali-free glass is placed in a vacuum decompression container. The crucible is heated to 1400°C to melt the alkali-free glass. After the alkali-free glass is completely melted, the diameter of the bubbles in the molten glass is observed while the vacuum decompression container is depressurized. In order to observe the diameter of the bubbles in the molten glass, for example, a CCD camera can be used to photograph the bubbles in the molten glass from an observation window provided in the vacuum decompression container. It should be noted that the number of bubble samples for measuring the bubble diameter is more than 20.

[0074] When the pressure in the vacuum decompression container is reduced, the diameter of the bubbles in the molten glass increases according to Boyle's law. However, when the vacuum decompression container is decompressed to a certain pressure, the diameter of the bubbles in the molten glass deviates from Boyle's law and increases sharply. The pressure in the vacuum decompression container at this time is referred to as pressure P.

[0075] The inventors of the present invention have determined the bubble growth index I based on the measurement results of the pressure P in various alkali-free glass substrates. As a result, they found that for an alkali-free glass substrate from 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 greater than 280.

[0076] The alkali-free glass substrate of the present invention may contain Fe2O3 as a trace component. The content of Fe2O3 is preferably 0.1 mass % or less, more preferably 0.05 mass % or less.

[0077] The strain point of the alkali-free glass substrate of the present invention is preferably 650° C. or higher, since heat shrinkage during panel production can be suppressed. It is more preferably 670° C. or higher, and even more preferably 680° C. or higher.

[0078] When the strain point is 700°C or less, it is not necessary to increase the temperature inside the floating kiln and at the exit of the floating kiln excessively, and this is preferred because it has little effect on the life of metal components inside the floating kiln and on the downstream side of the floating kiln.

[0079] In addition, the strain point is measured by the fiber drawing method according to the method specified in JIS R3103-2 (2001).

[0080] The substrate size of the alkali-free glass substrate of the present invention is preferably more than 2100mm on the short side and more than 2400mm on the long side, more preferably more than 2800mm on the short side and more than 3000mm on the long side, and further preferably more than 2900mm on the short side and more than 3200mm on the long side. As the substrate size becomes larger, it is necessary to reduce the bubble density in the substrate. Since the alkali-free glass substrate of the present invention has a low bubble density, the yield rate of the product is not easy to decrease even if the substrate size becomes larger, and it is suitable for the case where the substrate size is large. In addition, the substrate size is preferably less than 6000mm on the short side and less than 6500mm on the long side. This is because, when the substrate size is too large, due to the enlargement of the equipment, the investment cost of the equipment increases, and it is difficult to transport the glass substrate.

[0081] The density of bubbles having a bubble diameter larger than 100 μm in the alkali-free glass substrate of the present invention is preferably 0.06 pcs / kg or less, more preferably 0.03 pcs / kg or less, and further preferably 0.01 pcs / kg or less.

[0082] It should be noted that the density of bubbles with a diameter greater than 100 μm is calculated in the following manner: light is irradiated onto the glass substrate from the side of the glass substrate in a dark room, and the number of bubble defects with a size greater than 100 μm is investigated by edge light inspection of the main surface of the glass substrate, thereby calculating the density of bubbles with a diameter greater than 100 μm.

[0083] The alkali-free glass substrate of the present invention is preferably a float glass. The float glass is superior to the fusion glass in that it is possible to sample a glass substrate having a large substrate size (sample a glass substrate).

[0084] Regarding the alkali-free glass substrate of the present invention, when the alkali-free glass substrate is melted, reduced pressure from atmospheric pressure to 33.33 kPa in 20 minutes at a constant decompression rate while being maintained at 1400°C, and maintained at 33.33 kPa for 5 minutes, bubbles with a diameter of 0.1 mm to 0.3 mm contained in the molten glass at 1400°C before the start of decompression are defined as initial bubbles, and bubbles corresponding to the initial bubbles after being maintained at 33.33 kPa for 5 minutes are defined as growing bubbles, and the diameter of the growing bubbles is preferably at least 3 times the diameter of the initial bubbles.

[0085] When the diameter of the growing bubble is three times or more the diameter of the initial bubble, the bubble contained in the molten glass is easy to grow and float in the molten glass under the reduced pressure atmosphere. Therefore, the bubble contained in the molten glass can be easily removed.

[0086] The diameter of the initial bubble and the diameter of the growing bubble can be calculated by the following steps.

[0087] A quartz cell of broken glass with an alkali-free glass substrate is placed in a vacuum decompression container. The quartz cell is heated to 1400°C to melt the broken glass, and then the vacuum decompression container is decompressed. The bubbles contained in the molten glass are photographed from an observation window provided in the vacuum decompression container using a CCD camera, and the diameter of the bubbles (hereinafter referred to as the bubble diameter) is measured by image analysis. It should be noted that it is not necessary to measure the bubble diameter for all of the multiple bubbles observed in the image. Specifically, bubbles attached to the wall of the quartz cell, bubbles formed by merging multiple bubbles, etc. are excluded from the measurement object. The ratio of the diameter of the growing bubble to the diameter of the initial bubble in one embodiment of the present invention (hereinafter referred to as the bubble growth rate) is obtained as follows: the bubble growth rates of the multiple bubbles observed in the image are calculated respectively, and their average value is obtained.

[0088] The decompression conditions used for evaluation are: decompression from atmospheric pressure to 33.33 kPa at a constant decompression rate in 20 minutes. When the molten glass is decompressed to 33.33 kPa, the bubbles contained in the molten glass can be fully grown, so it is suitable for evaluating the growth of bubble diameters. In addition, when the decompression time is 20 minutes, the growth of bubble diameters can be appropriately evaluated while shortening the evaluation time.

[0089] The initial bubbles are selected to have a bubble diameter of 0.1 mm to 0.3 mm. When the initial bubble diameter is 0.1 mm or more, it is easy to measure the bubble diameter using a CCD camera. When the initial bubble diameter is 0.3 mm or less, it is possible to prevent the growth bubble from expanding and bursting, so that the growth of the bubble diameter can be appropriately evaluated.

[0090] The bubbles corresponding to the initial bubbles after being held at 33.33 kPa for 5 minutes are defined as growing bubbles. When the holding time is 5 minutes, the grown bubbles become sufficiently large relative to the initial bubbles, and since the bubbles can be prevented from expanding and bursting, the growth of the bubble diameter can be appropriately evaluated.

[0091] The diameter of the growing bubbles in the alkali-free glass substrate of the present invention is more preferably 5 times or more, further preferably 7 times or more, particularly preferably 9 times or more, the diameter of the initial bubbles.

[0092] The diameter of the growing bubbles of the alkali-free glass substrate of the present invention is preferably less than 20 times the diameter of the initial bubbles. When it is less than 20 times, during the vacuum degassing treatment, the bubble layer that usually exists on the surface of the molten glass at a diameter of less than about 10 mm can be suppressed from expanding to 10 mm to several hundred mm, thereby preventing the escape of bubbles. Here, the sliding of bubbles refers to the phenomenon that the bubbles that reach the surface of the glass do not break but exist stably for a long time by forming a bubble layer, and the bubbles that float up afterwards do not break but flow out as is to the subsequent process. When the escape of bubbles occurs, the problem of bubbles remaining in the molten glass after the vacuum degassing occurs.

[0093] The diameter of the growing bubbles in the alkali-free glass substrate of the present invention is more preferably 17 times or less, further preferably 15 times or less, and particularly preferably 13 times or less, the diameter of the initial bubbles.

[0094] The alkali-free glass substrate of the present invention is preferably 0.75 mm or less in thickness when used as a glass substrate for a liquid crystal display, more preferably 0.55 mm or less, and further preferably 0.45 mm or less. In addition, the thickness is preferably 0.01 mm or more. This is because when the thickness is too thin, the rigidity of the glass substrate is reduced, and it is difficult to roll the glass substrate.

[0095] [Method for producing alkali-free glass substrate]

[0096] Next, a method for producing an alkali-free glass substrate in one embodiment of the present invention will be described using the drawings. 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.

[0097] The glass manufacturing apparatus 1 includes a melting tank 10 and a vacuum degassing apparatus 20. A forming apparatus such as a float kiln is disposed after the vacuum degassing apparatus 20. The forming apparatus may be a forming apparatus used in a down-draw method.

[0098] In the method for manufacturing an alkali-free glass substrate, a molten glass G is prepared by melting glass raw materials in a melting tank 10, and the molten glass G is subjected to a reduced pressure degassing treatment by a reduced pressure degassing device 20. A strip-shaped glass ribbon formed by a forming device is slowly cooled and cut to obtain an alkali-free glass substrate.

[0099] The melting tank 10 has a burner for melting the supplied glass raw material. The burner forms a flame by mixing fuel such as natural gas and heavy oil with the gas and burning it. A burner that mainly uses air as the gas is called an air-assisted burner, and a burner that mainly uses oxygen as the gas is called an oxygen-assisted burner. The burner heats the glass raw material from above by emitting a flame to the glass raw material. In addition, the melting tank 10 may also have an electrode for heating the glass raw material.

[0100] As the glass raw material, for example, silica sand, boric acid, limestone, aluminum oxide, strontium carbonate, magnesium oxide, etc. can be used and it can be blended so that the composition of the target alkali-free glass substrate may be obtained.

[0101] As described above, the alkali-free glass substrate of the present invention can easily remove bubbles contained in molten glass under a reduced pressure atmosphere. Therefore, cullets generated when producing the alkali-free glass substrate or cullets of used alkali-free glass substrates are preferably used as the glass raw material.

[0102] It is preferred to add a chloride-based clarifier to the glass raw material. From the viewpoint of not worrying about deliquescent properties, the chloride-based clarifier is preferably BaCl2.2H2O, SrCl2.6H2O, CaCl2, MgCl2.6H2O or NH4Cl.

[0103] As for the clarifier, in order to appropriately adjust the bubble growth rate, a clarifier other than the chloride-based clarifier may be used. In this case, for example, SO3, F, SnO2, etc. can be cited as other clarifiers. The content of these other clarifiers 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.

[0104] The vacuum degassing device 20 includes a vacuum casing 21 , a vacuum degassing tank 22 , an ascending pipe 23 , a descending pipe 24 , and a heat insulating material 25 .

[0105] The reduced pressure degassing tank 22 is arranged in a cylindrical shape and is accommodated in the reduced pressure housing 21 in such a manner that its long axis is oriented in the horizontal direction. An ascending pipe 23 oriented in the vertical direction is installed on the lower surface of one end of the reduced pressure degassing tank 22, and a descending pipe 24 is installed on the lower surface of the other end. A portion of the ascending pipe 23 and the descending pipe 24 are located in the reduced pressure housing 21.

[0106] The ascending pipe 23 is connected to the vacuum degassing tank 22, and guides the molten glass G from the melting tank 10 into the vacuum degassing tank 22. The descending pipe 24 is connected to the vacuum degassing tank 22, and guides the molten glass G after the vacuum degassing to the next processing tank. In the vacuum casing 21, a heat insulating material 25 such as heat insulating bricks is arranged around the vacuum degassing tank 22, the ascending pipe 23 and the descending pipe 24 to insulate them.

[0107] The vacuum degassing tank 22, the ascending pipe 23 and the descending pipe 24 are conduits for the molten glass, and therefore are made of materials having excellent heat resistance and corrosion resistance to the molten glass. For example, they are made of platinum, platinum alloy, or reinforced platinum obtained by dispersing metal oxides in platinum or platinum alloy. In addition, they may be made of ceramic non-metallic inorganic materials, i.e., dense refractory materials. In addition, they may be made of materials obtained by lining dense refractory materials with platinum or platinum alloys.

[0108] 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. It should be noted that, from the viewpoint of productivity, the flow rate of the molten glass is preferably 1 ton / day to 200 tons / day.

[0109] 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.

[0110] When performing the decompression degassing, the air in the decompression housing 21 is evacuated from the outside by a vacuum decompression tool such as a vacuum pump through a suction opening portion provided at a predetermined position of the decompression housing 21. Thus, the air in the decompression degassing tank 22 accommodated in the decompression housing 21 is indirectly evacuated, and the inside of the decompression degassing tank 22 is decompressed to a predetermined pressure.

[0111] The pressure inside the reduced pressure degassing tank 22 is preferably 13.33 kPa to 53.33 kPa.

[0112] [Example]

[0113] Hereinafter, the present invention will be further described 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, 5, 7, 9, 11, 12, 14, 16, 17, 19, 20, and 22 are examples, and Examples 2, 3, 6, 8, 10, 13, 15, 18, and 21 are comparative examples.

[0114] [Experimental Example 1]

[0115] 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, performs a vacuum degassing treatment on the molten glass G by a vacuum degassing device 20, forms the molten glass into a plate-shaped glass ribbon by a float process, slowly cools the glass ribbon and cuts it, and prepares an alkali-free glass substrate with a thickness of 0.50 mm (Example 1, Example 2).

[0116] The glass composition of Example 1 is expressed in mass % based on oxides: 59.8% SiO2, 17.2% Al2O3, 7.8% B2O3, 3.1% MgO, 4.1% CaO, 7.7% SrO, 0.1% BaO (MgO+CaO+SrO+BaO=15%), and the Cl content is 0.2% by mass relative to the basic composition of the glass. In addition, the β-OH measured by the following method is 0.32 mm -1 .

[0117] (β-OH)

[0118] β-OH is obtained by measuring the absorbance of the glass sample to light with a wavelength of 2.75 μm to 2.95 μm and using the maximum absorbance β max Divide by the thickness of the specimen (mm).

[0119] Therefore, the bubble growth index I=590.5×0.32+874.1×0.2-5.7×7.8-33.3=286.

[0120] The glass composition of Example 2 is expressed in terms of mass % based on oxides: 62% SiO2, 18% Al2O3, 9.5% B2O3, 2% MgO, 7% CaO, 1.2% SrO, 0.1% BaO (MgO+CaO+SrO+BaO=10.3%), and 0.2% SnO2. In addition, the β-OH measured by the above method is 0.53 mm -1 .

[0121] Therefore, the bubble growth index I=590.5×0.53+874.1×0-5.7×9.5-33.3=226.

[0122] In order to reproduce the atmosphere of decompression degassing, a quartz cell containing 50g of cullet of alkali-free glass substrate was arranged in a vacuum decompression container. The vacuum decompression container used an HTO (high temperature observation) furnace manufactured by Glass Service. The quartz cell was heated from room temperature to 1400°C to melt the cullet, and then the decompression in the vacuum decompression container was started. While the vacuum decompression container was kept at 1400°C, the pressure was reduced from atmospheric pressure to 33.33kPa in 20 minutes at a constant decompression rate, and it was kept at 33.33kPa for 10 minutes. During this period, the start of decompression was set to 0 minutes, and at 0, 3, 6, 9, 12, 15, 18, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, and 30 minutes, the bubbles in the molten glass were photographed from the observation window set in the vacuum decompression container using a CCD camera, and the diameter of the bubbles was measured by image analysis. In Experimental Example 1, 0 minutes is the initial bubble, and 25 minutes from the start of decompression is the growing bubble.

[0123] Figure 2 Graph showing the time variation of bubble diameter under reduced pressure conditions of Experimental Example 1. When comparing Example 1 with Example 2, it can be seen that the diameter of the bubble in Example 1 grows larger during the period of being maintained at 33.33 kPa. In Example 1, the diameter of the initial bubble is 0.29 mm, the diameter of the growing bubble is 1.04 mm, and the diameter of the growing bubble is 3.6 times the diameter of the initial bubble. On the other hand, in Example 2, the diameter of the initial bubble is 0.24 mm, the diameter of the growing bubble is 0.59 mm, and the diameter of the growing bubble is 2.5 times the diameter of the initial bubble. It can be seen from the alkali-free glass substrate of Example 1 that the bubbles contained in the molten glass can be easily removed under a reduced pressure atmosphere.

[0124] [Experimental Example 2]

[0125] The clarification effect of molten glass in a vacuum degassing tank was evaluated by simulation. The flotation velocity of bubbles growing in the molten glass flow and floating in the molten glass is in a Stokes equation relationship with the bubble diameter. Therefore, in the simulation, the bubble diameter was calculated based on the bubble growth rate, and the behavior of bubble floating was analyzed based on the Stokes equation. It should be noted that the bubbles were set to be generated in the central part of the position where the riser was installed on the vacuum degassing tank, and the initial bubble diameter was set to 0.2 mm for calculation.

[0126] The dimensions of the vacuum degassing tank and the liquid level of the molten glass are as follows.

[0127] Horizontal length from the center of the ascending pipe to the center of the descending pipe in the vacuum degassing tank: 10 m

[0128] Inner diameter of vacuum degassing tank: 500 mm

[0129] Molten glass level: 250mm

[0130] The molten glass passing through the reduced pressure degassing tank is assumed as follows.

[0131] The glass composition is as follows. For the Cl content, refer to Table 1 described later.

[0132] (The basic composition of the glass is expressed in mass % based on oxides, and the Cl content is the mass % relative to the basic composition of the glass)

[0133] Examples 3~6, ​​8, 9, 11, 15, 16, 18, 19, 22

[0134] SiO2: 59.9%, Al2O3: 17.2%, B2O3: 8.0%, MgO: 3.0%, CaO: 4.1%, SrO: 7.7%, BaO: 0.1% (MgO+CaO+SrO+BaO=14.9%)

[0135] Examples 7, 12, 17, 20

[0136] SiO2: 60.2%, Al2O3: 18.2%, B2O3: 6.0%, MgO: 3.8%, CaO: 4.2%, SrO: 7.5%, BaO: 0.1% (MgO+CaO+SrO+BaO=15.6%)

[0137] Example 10, 21

[0138] SiO2: 58.9%, Al2O3: 14.8%, B2O3: 13.0%, MgO: 1.1%, CaO: 3.8%, SrO: 8.3%, BaO: 0.1% (MgO+CaO+SrO+BaO=13.3%)

[0139] Example 13, 14

[0140] SiO2: 59.1%, Al2O3: 15.3%, B2O3: 12.0%, MgO: 1.5%, CaO: 3.9%, SrO: 8.2%, BaO: 0.1% (MgO+CaO+SrO+BaO=13.7%)

[0141] Flow rate of molten glass: 0.6m 3 / hour, 1.2m 3 / hour or 1.79m 3 / Hour

[0142] Pressure in the vacuum degassing tank: 33.33 kPa

[0143] Temperature when passing through the vacuum degassing tank (average): 1400°C

[0144] Viscosity when passing through a vacuum degassing tank: 151 Pa·s

[0145] Density when passing through the vacuum degassing tank: 2380 kg / m 3

[0146] The degassing performance was evaluated by the distance (floating distance) from the center of the riser in the vacuum degassing tank to the position where the bubbles floated to the liquid surface of the molten glass. The smaller the floating distance, the better the degassing performance.

[0147] The results are shown in Table 1. The flow rate, B2O3, β-OH, Cl content, bubble growth index I, bubble growth rate, and floating distance of the molten glass are shown in Table 1. The bubble growth rate was measured under the same conditions as in Experimental Example 1.

[0148]

[0149] As shown in Table 1, the floating distance of the glass (Examples 3, 6, 8, 10, 13, 15, 18, 21) with a bubble growth index I less than 280 is greater than 10 m. Based on this result, it can be considered that the bubble density of the glass substrate with a bubble diameter greater than 100 μm is greater than 0.06 / kg.

[0150] In contrast, the floating distance of the glass (Examples 4, 5, 7, 9, 11, 12, 14, 16, 17, 19, 20, 22) with a bubble growth index I of 280 or more is less than 10 m. Based on this result, it can be considered that the bubble density of the glass substrate with a bubble diameter greater than 100 μm is less than 0.06 pcs / kg.

[0151] As can be seen from the above results, the glass of the embodiment does not need to increase the size of the vacuum degassing device in order to efficiently manufacture a large glass substrate, which can solve the problem of increased investment costs for the equipment. In addition, since the bubble density in the substrate can be reduced, it can be considered that the problem of reduced product yield as the substrate size increases is solved.

[0152] While the invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope of the invention.

[0153] This application is based on Japanese Patent Application No. 2019-051534 filed on March 19, 2019, the contents of which are incorporated herein by reference.

[0154] Industrial Applicability

[0155] The use of the alkali-free glass substrate includes use in a liquid crystal display, an organic EL display, a flat panel display, and other various uses.

Claims

1. An alkali-free glass substrate, expressed as mass % based on oxides, wherein the alkali-free glass substrate contains 54% to 66% SiO 2 , 10% to 23% Al 2 O 3 6% to 12% B 2 O 3 , 8%~26% MgO+CaO+SrO+BaO, It is characterized in that The β-OH of the alkali-free glass substrate is 0.15 mm -1 ~0.5mm -1 , Cl content is 0.23 mass % to 0.35 mass %, and The bubble growth index I of the alkali-free glass substrate represented by the following formula (1) is 280 or more, I=590.5×[β-OH] +874.1×[Cl]-5.7×[B 2 O 3 ]-33.3 (1) In formula (1), [β-OH] represents the β-OH (mm -1 )、[Cl] represents the Cl content (mass %) of the alkali-free glass substrate, [B 2 O 3 ] represents the B of the alkali-free glass substrate 2 O 3 Content (mass %).

2. An alkali-free glass substrate, expressed as mass % based on oxides, wherein the alkali-free glass substrate contains 54% to 66% SiO 2 , 10% to 23% Al 2 O 3 6% to 12% B 2 O 3 , 8%~26% MgO+CaO+SrO+BaO, It is characterized in that The β-OH of the alkali-free glass substrate is 0.35 mm -1 ~0.5mm -1 , Cl content is 0.1 mass % to 0.35 mass %, and The bubble growth index I of the alkali-free glass substrate represented by the following formula (1) is 280 or more, I=590.5×[β-OH] +874.1×[Cl]-5.7×[B 2 O 3 ]-33.3 (1) In formula (1), [β-OH] represents the β-OH (mm -1 )、[Cl] represents the Cl content (mass %) of the alkali-free glass substrate, [B 2 O 3 ] represents the B of the alkali-free glass substrate 2 O 3 Content (mass %).

3. An alkali-free glass substrate, expressed as mass % based on oxides, wherein the alkali-free glass substrate contains 54% to 66% SiO 2 , 10% to 23% Al 2 O 3 6% to 12% B 2 O 3 , 8%~26% MgO+CaO+SrO+BaO, It is characterized in that The β-OH of the alkali-free glass substrate is 0.15 mm -1 ~0.5mm -1 , Cl content is 0.1 mass % to 0.35 mass %, and The bubble growth index I of the alkali-free glass substrate represented by the following formula (1) is 318 or more, I=590.5×[β-OH] +874.1×[Cl]-5.7×[B 2 O 3 ]-33.3 (1) In formula (1), [β-OH] represents the β-OH (mm -1 )、[Cl] represents the Cl content (mass %) of the alkali-free glass substrate, [B 2 O 3 ] represents the B of the alkali-free glass substrate 2 O 3 Content (mass %).

4. The alkali-free glass substrate according to any one of claims 1 to 3, in, The bubble growth index I of the alkali-free glass substrate represented by the formula (1) is 360 or less.

5. The alkali-free glass substrate according to claim 1 or 3, in, The β-OH of the alkali-free glass substrate is 0.15 mm -1 ~0.40mm -1 .

6. The alkali-free glass substrate according to claim 1 or 3, in, The β-OH of the alkali-free glass substrate is 0.25 mm -1 ~0.5mm -1 .

7. The alkali-free glass substrate according to any one of claims 1 to 3, in, The alkali-free glass substrate contains, in terms of mass % based on oxides, 0% to 12% of MgO, 0% to 12% of CaO, 0% to 16% of SrO, and 0% to 16% of BaO.

8. The alkali-free glass substrate according to any one of claims 1 to 3, in, The strain point of the alkali-free glass substrate is 650°C to 700°C.

9. The alkali-free glass substrate according to any one of claims 1 to 3, in, The alkali-free glass substrate has a substrate size of not less than 2100 mm on a short side and not less than 2400 mm on a long side.

10. The alkali-free glass substrate according to any one of claims 1 to 3, in, The alkali-free glass substrate has a substrate size of 2900 mm or more on a short side and 3200 mm or more on a long side.

11. The alkali-free glass substrate according to any one of claims 1 to 3, in, The alkali-free glass substrate has a bubble density of bubbles having a diameter greater than 100 μm of 0.06 pcs / kg or less.

12. The alkali-free glass substrate according to any one of claims 1 to 3, in, The alkali-free glass substrate was melted, and the pressure was reduced from atmospheric pressure to 33.33 kPa at a constant pressure reduction rate over 20 minutes while being held at 1400° C., and then maintained at 33.33 kPa for 5 minutes. Bubbles with a diameter of 0.1 mm to 0.3 mm contained in the molten glass at 1400° C. before the start of decompression are defined as initial bubbles. The bubbles corresponding to the initial bubbles after being maintained at 33.33 kPa for 5 minutes are defined as growing bubbles. The diameter of the growing bubble is more than 3 times the diameter of the initial bubble.

13. The alkali-free glass substrate according to claim 12, in, The diameter of the growing bubble is less than 20 times the diameter of the initial bubble.

14. The alkali-free glass substrate according to any one of claims 1 to 3, in, The alkali-free glass substrate has a thickness of 0.45 mm or less.

15. The alkali-free glass substrate according to any one of claims 1 to 3, in, The floating distance of the alkali-free glass substrate is less than 10 m.

16. A method for manufacturing an alkali-free glass substrate, in, To obtain a SiO containing 54% to 66% 2 , 10% to 23% Al 2 O 3 6% to 12% B 2 O 3 , 8% to 26% of MgO+CaO+SrO+BaO, glass raw materials are prepared, the glass raw materials are melted in a melting tank to produce molten glass, the molten glass is subjected to a reduced pressure degassing treatment by a reduced pressure degassing device, and a strip-shaped glass ribbon formed by a forming device is slowly cooled and cut to obtain an alkali-free glass substrate, wherein, The β-OH of the alkali-free glass substrate is 0.15 mm -1 ~0.5mm -1 , Cl content is 0.23 mass % to 0.35 mass %, and The bubble growth index I of the alkali-free glass substrate represented by the following formula (1) is 280 or more, I=590.5×[β-OH] +874.1×[Cl]-5.7×[B 2 O 3 ]-33.3 (1) In formula (1), [β-OH] represents the β-OH (mm -1 )、[Cl] represents the Cl content (mass %) of the alkali-free glass substrate, [B 2 O 3 ] represents the B of the alkali-free glass substrate 2 O 3 Content (mass %).

17. A method for manufacturing an alkali-free glass substrate, in, To obtain a SiO containing 54% to 66% 2 , 10% to 23% Al 2 O 3 6% to 12% B 2 O 3 , 8% to 26% of MgO+CaO+SrO+BaO, glass raw materials are prepared, the glass raw materials are melted in a melting tank to produce molten glass, the molten glass is subjected to a reduced pressure degassing treatment by a reduced pressure degassing device, and a strip-shaped glass ribbon formed by a forming device is slowly cooled and cut to obtain an alkali-free glass substrate, wherein, The β-OH of the alkali-free glass substrate is 0.35 mm -1 ~0.5mm -1 , Cl content is 0.1 mass % to 0.35 mass %, and The bubble growth index I of the alkali-free glass substrate represented by the following formula (1) is 280 or more, I=590.5×[β-OH] +874.1×[Cl]-5.7×[B 2 O 3 ]-33.3 (1) In formula (1), [β-OH] represents the β-OH (mm -1 )、[Cl] represents the Cl content (mass %) of the alkali-free glass substrate, [B 2 O 3 ] represents the B of the alkali-free glass substrate 2 O 3 Content (mass %).

18. A method for manufacturing an alkali-free glass substrate, in, To obtain a SiO containing 54% to 66% 2 , 10% to 23% Al 2 O 3 6% to 12% B 2 O 3 , 8% to 26% of MgO+CaO+SrO+BaO, glass raw materials are prepared, the glass raw materials are melted in a melting tank to produce molten glass, the molten glass is subjected to a reduced pressure degassing treatment by a reduced pressure degassing device, and a strip-shaped glass ribbon formed by a forming device is slowly cooled and cut to obtain an alkali-free glass substrate, wherein, The β-OH of the alkali-free glass substrate is 0.15 mm -1 ~0.5mm -1 , Cl content is 0.1 mass % to 0.35 mass %, and The bubble growth index I of the alkali-free glass substrate represented by the following formula (1) is 318 or more, I=590.5×[β-OH] +874.1×[Cl]-5.7×[B 2 O 3 ]-33.3 (1) In formula (1), [β-OH] represents the β-OH (mm -1 )、[Cl] represents the Cl content (mass %) of the alkali-free glass substrate, [B 2 O 3 ] represents the B of the alkali-free glass substrate 2 O 3 Content (mass %).

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