Alkali-free glass plate

Abstract

Provided is an alkali-free glass plate which has a high strain point, is excellent in terms of productivity, and also has fewer internal defects and has excellent optical and physical characteristics. The alkali-free glass plate is particularly suitable for use in a front panel of a display.　This alkali-free glass plate has a glass composition that contains, in mass%, 59-62% of SiO2, 18-21% of Al2O3, 3-6% of B2O3, 1-5% of MgO, 4-7% CaO, 0.1-6% of SrO, 0.01-7% of BaO, 0.005-0.1% of ZrO2, 0.15-0.35% of SnO2, 0.005-0.03% of TiO2, and 0.00-0.02% of Fe2O3.

Description

Alkali-free glass plate

[0001] The present invention relates to an alkali-free glass plate, and more particularly to a glass plate for displays used in displays equipped with thin film transistors (TFTs) made of oxides such as IGZO or TFTs having low-temperature polysilicon (LTPS), and particularly to a glass plate suitable for an opposing substrate (also called a front panel, front plane, CF (color filter) substrate, or cap glass) that does not have a TFT.

[0002] In general, a glass plate is used as a support substrate for a flat panel display. Electrical circuit patterns such as TFTs are formed on the surface of this glass plate. For this reason, alkali-free glass plates that are substantially free of alkali metal components are used for this type of glass plate so as not to adversely affect the TFTs and other components.

[0003] Glass plates are exposed to high-temperature atmospheres during processes for forming electric circuit patterns, such as thin film formation processes and thin film patterning processes. When a glass plate is exposed to a high-temperature atmosphere, structural relaxation of the glass progresses, resulting in a shrinkage of the volume of the glass plate (hereinafter referred to as "thermal shrinkage"). If thermal shrinkage occurs in a glass plate during the electric circuit pattern formation process, the shape and dimensions of the electric circuit pattern formed on the glass plate deviate from the design values, making it difficult to obtain a flat panel display with the desired electrical performance. For this reason, a small thermal shrinkage rate is desired for glass plates, such as glass plates for flat panel displays, on whose surfaces thin film patterns such as electric circuit patterns are formed.

[0004] In particular, glass plates for high-definition displays equipped with TFTs having oxide films such as IGZO are exposed to relatively high temperature atmospheres of 400°C to 500°C during the formation of the oxide films, which makes them susceptible to thermal shrinkage. Furthermore, because the electrical circuit patterns are highly precise, even slight thermal shrinkage makes it difficult to achieve the desired electrical performance. Therefore, glass plates used for such applications are strongly desired to have an extremely small thermal shrinkage rate.

[0005] Incidentally, known methods for forming glass sheets used in flat panel displays and the like include the float method and the down-draw method represented by the overflow down-draw method.

[0006] The float process is a method for forming a glass sheet by flowing molten glass onto a float bath filled with molten tin, stretching it horizontally to form a glass ribbon, and then annealing the glass ribbon in an annealing furnace located downstream of the float bath. In the float process, the conveying direction of the glass ribbon is horizontal, so it is easy to make the annealing furnace long. This makes it easy to sufficiently reduce the cooling rate of the glass ribbon in the annealing furnace. Therefore, the float process has the advantage of easily obtaining a glass sheet with a small thermal shrinkage rate.

[0007] On the other hand, the downdraw method is a method in which molten glass is stretched downward to form a sheet. The overflow downdraw method, which is one type of downdraw method, is a method in which molten glass overflowing from both sides of a forming body having a generally wedge-shaped cross section is stretched downward to form a glass ribbon. The molten glass overflowing from both sides of the forming body flows down along both side surfaces of the forming body and joins below the forming body. Therefore, in the overflow downdraw method, the surface of the glass ribbon is formed by surface tension without contact with anything other than air, and therefore a glass sheet with a flat surface free from foreign matter can be obtained without polishing the surface after forming. The overflow downdraw method also has the advantage of being easy to form a thin glass sheet.

[0008] On the other hand, in the down-draw method, since molten glass flows downward from a forming body, if a long annealing furnace is to be placed below the forming body, the forming body must be placed at a high position. However, in practice, there are restrictions on the height at which the forming body can be placed due to restrictions on the ceiling height of the factory, etc. In other words, in the down-draw method, there are restrictions on the length of the annealing furnace, and it may be difficult to place a sufficiently long annealing furnace. If the length of the annealing furnace is short, the cooling rate of the glass ribbon increases, making it difficult to form a glass sheet with a small thermal shrinkage rate.

[0009] Therefore, it has been proposed to increase the strain point of glass to reduce the thermal shrinkage of the glass. For example, Patent Document 1 discloses a low-alkali glass composition with a high strain point. The same document also describes that the lower the β-OH value, which represents the amount of water in the glass, the higher the strain point.

[0010] JP 2013-151407 A

[0011] Generally, there is a correlation between strain point and thermal shrinkage, and the higher the strain point, the smaller the thermal shrinkage. However, glass designed to have a high strain point has the problem of poor productivity due to the large load it places on melting and molding during the manufacturing process.

[0012] Glass plates used in flat panel displays such as liquid crystal displays are broadly divided into rear panels (backplanes) on which TFTs are formed and front panels (frontplanes) on which TFTs are not formed. Because front panels do not have TFTs, they do not require the same high heat resistance and low thermal shrinkage as rear panels. However, they must meet the optical properties, physical properties, dimensional accuracy, surface precision, and other requirements for display substrates.

[0013] Furthermore, because this front panel glass plate is placed on the front side (viewer side) of the display, there are very strict requirements for glass internal defects, etc. In addition, because the rear panel and front panel are placed very close to each other and are bonded together with ultraviolet curing resin, etc., the two panels must have compatible glass compositions and glass properties.

[0014] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an alkali-free glass plate which has a high strain point, excellent productivity, few internal defects, and excellent optical and physical properties, and is particularly suitable for use in the front panel of a display.

[0015] As a result of extensive research, the present inventors have found that the above problems can be solved by using an alkali-free glass plate having a predetermined glass composition.

[0016] (1) That is, the alkali-free glass plate of the present invention has a glass composition containing, in mass %, SiO ２59-62%, Al ２ O ３ 18-21%, B ２ O ３ 3-6%, MgO 1-5%, CaO 4-7%, SrO 0.1-6%, BaO 0.01-7%, ZrO ２ 0.005-0.1%, SnO ２ 0.15-0.35%, TiO ２ 0.005-0.03%, Fe ２ O ３ Here, "alkali-free glass" refers to glass to which alkali metal oxide components are not added in excess of the amount of impurities that are mixed in from raw materials or during the manufacturing process. Specifically, the glass composition does not contain alkali metal oxides (Li ２ O, Na ２ O and K ２ O) content in the glass composition is 1000 ppm or less by mass. ２ The O content is preferably 500 ppm or less, more preferably 300 ppm or less.

[0017] (2) The alkali-free glass plate of the present invention is the glass plate of (1) above, which contains, in mass %, SiO ２ 59-62%, Al ２ O ３ 18-21%, B ２ O ３ 3-6%, MgO 1-4%, CaO 4-7%, SrO 0.1-5%, BaO 0.01-7%, ZrO ２ 0.005-0.1%, SnO ２ 0.15-0.35%, TiO ２ 0.005-0.03%, Fe ２ O ３ It is preferable that the content be 0.005 to 0.02%.

[0018] (3) In the alkali-free glass plate of the present invention described above in (1) or (2), the glass composition preferably contains, in mass %, 4.5 to 6% of CaO.

[0019] (4) The alkali-free glass plate of the present invention, in any one of the above (1) to (3), contains, in mass ratio, SnO ２ / ZrO ２ is preferably 5 to 30. In this specification, "x / y" means the value obtained by dividing the content of the x component by the content of the y component.

[0020] (5) The alkali-free glass plate of the present invention has a thermal expansion coefficient of 37±2×10 in any one of the above (1) to (4). －７ / ° C. This makes it easier to achieve compatibility with the rear panel of the display, making it suitable for use as a front panel.

[0021] (6) In any of the above (1) to (5), the alkali-free glass plate of the present invention preferably has a thermal shrinkage of 13 to 40 ppm when heated from 25° C. to 500° C. at a rate of 5° C. / min, held at 500° C. for 1 hour, and then cooled to 25° C. at a rate of 5° C. / min. In this way, even when exposed to a high-temperature atmosphere in a process for forming an electric circuit pattern, such as a thin film formation process or a thin film patterning process, the shape and dimensions of the electric circuit pattern are less likely to deviate from the design values, making it easier to obtain a flat panel display having the desired electrical performance.

[0022] (7) In any one of (1) to (6) above, the alkali-free glass plate of the present invention preferably has a transmittance of 89% or more at a wavelength of 360 nm and a transmittance of 90% or more at a wavelength of 400 nm when the plate has a thickness of 0.5 mm. In a display, light emitted obliquely to the front panel passes through the front panel over a relatively long optical path. In this case, if the transmittance of the glass plate, particularly the transmittance of light at short wavelengths around 360 to 400 nm, is low, the color reproducibility of the image is likely to deteriorate. Specifically, there is a concern that even white light may appear blue-green, green, or brownish. Therefore, by restricting the transmittance at wavelengths of 360 nm and 400 nm as described above, it is possible to improve the color reproducibility of the display.

[0023] (8) In any one of the above items (1) to (7), the alkali-free glass plate of the present invention preferably has a Young's modulus of 75 to 83 GPa. This makes it possible to suppress deformation of the glass plate, such as warping, in electronic displays such as high-resolution OLED displays, and to suppress deterioration of display performance, such as light leakage.

[0024] (9) In any one of the above items (1) to (8), the alkali-free glass plate of the present invention preferably has a strain point of 680 to 720° C. In this way, the thermal shrinkage can be reduced to a required level.

[0025] (10) In any one of the above items (1) to (9), the alkali-free glass plate of the present invention preferably has a β-OH value of less than 0.45 / mm. This makes it possible to increase the strain point.

[0026] (11) The alkali-free glass plate of the present invention, in any one of the above (1) to (10), has a density of 2.46 to 2.6 g / cm ３ In this way, the weight of the display can be reduced.

[0027] (12) The alkali-free glass plate of the present invention, in any one of (1) to (11) above, has a plate thickness of 0.51 mm or less and a substrate area of ​​4 m ２ It is preferable that this is equal to or greater than this.

[0028] (13) In any one of the above items (1) to (12), the alkali-free glass plate of the present invention is preferably used for a front panel of a display.

[0029] (14) In any one of the above items (1) to (13), the alkali-free glass plate of the present invention is preferably for use in a high-definition liquid crystal display or an OLED display.

[0030] (15) In any one of the above items (1) to (12), the alkali-free glass plate of the present invention is preferably a dummy glass plate used in the manufacturing process of a liquid crystal display or an OLED display.

[0031] In the manufacturing process of liquid crystal displays or OLED displays, a wide variety of equipment is used, including various film formation equipment, equipment for exposure and etching in photolithography processes, and equipment for ion doping and heat treatment. In these manufacturing processes, at the start of daily production or when changing the type of product, an alkali-free glass plate of the same size as the product is used for setting and adjusting conditions, called a dummy glass plate. The alkali-free glass plate of the present invention is also suitable as the dummy glass plate.

[0032] According to the present invention, it is possible to provide an alkali-free glass plate which has a high strain point, excellent productivity, few internal defects, and excellent optical and physical properties, and is particularly suitable for use in the front panel of a display.

[0033] FIG. 2 is a plan view illustrating a procedure for measuring the thermal shrinkage of a glass plate.

[0034] The alkali-free glass plate of the present invention has a glass composition comprising, in mass %, SiO ２ 59-62%, Al ２ O ３ 18-21%, B ２ O ３ 3-6%, MgO 1-5%, CaO 4-7%, SrO 0.1-6%, BaO 0.01-7%, ZrO ２ 0.005-0.1%, SnO ２ 0.15-0.35%, TiO ２ 0.005-0.03%, Fe ２ O ３ The glass composition is characterized by containing 0.005 to 0.02% of ammonium hydroxide. The reasons for limiting the glass composition in this way are explained below. In the following description of the content of each glass component, "%" means "mass %" unless otherwise specified. In addition, an alkali-free glass plate may be simply referred to as a "glass plate." In this specification, a numerical range indicated using "to" means a range that includes the numerical values ​​before and after "to" as the minimum and maximum values, respectively.

[0035] SiO ２ is a component that forms the skeleton of glass. ２The lower limit of the content of SiO is preferably 59% or more, particularly preferably 59.5% or more. ２ The upper limit of the content of SiO is preferably 62% or less, and particularly preferably 61.5% or less. ２ If the content of SiO is too small, the density of the glass becomes too high and the acid resistance tends to decrease. ２ If the content is too high, the high-temperature viscosity increases, the melting property tends to decrease, and devitrified crystals such as cristobalite tend to precipitate, which tends to increase the liquidus temperature.

[0036] Al ２ O ３ Al is a component that forms the skeleton of the glass, increases the strain point and Young's modulus, and also has the effect of suppressing phase separation. ２ O ３ The lower limit of the Al content is preferably 18% or more, 19% or more, particularly preferably 19.5% or more. ２ O ３ The upper limit of the Al content is 21% or less, particularly 20.5% or less, and preferably 20% or less. ２ O ３ If the content of Al is too small, the strain point and Young's modulus tend to decrease. ２ O ３ If the content is too large, devitrified crystals such as mullite and anorthite are likely to precipitate, and the liquidus temperature is likely to rise.

[0037] B ２ O ３ is a component that enhances the melting property and also enhances the devitrification resistance. ２ O ３ The lower limit of the content of B is preferably 3%, particularly preferably 3.5% or more. ２ O ３ The upper limit of the content of B is preferably 6% or less, 5.5% or less, and particularly preferably 5% or less. ２ O ３ If the content of B is too small, the melting property and devitrification resistance tend to decrease. In addition, the chemical durability tends to decrease, and in particular, the durability against hydrofluoric acid-based chemicals such as buffered hydrofluoric acid tends to decrease. ２ O ３If the content of B is too high, the strain point and Young's modulus tend to decrease. ２ O ３ When the content is relatively low, the viscosity is generally high and it is difficult to achieve a high foam quality. Therefore, it is necessary to use SnO, which has a low β-OH value and a fining effect at a relatively high temperature. ２ When the compound is contained as an essential component, it becomes easier to achieve high foam quality.

[0038] The above-mentioned SiO ２ , Al ２ O ３ and B ２ O ３ These three components constitute the skeleton of the glass of the present invention and are very important for maintaining the physical and mechanical properties of the glass, such as heat resistance, chemical durability, thermal expansion coefficient, and density. Therefore, the total amount of these three components is preferably in the range of 80% to 90%, 82 to 86%, and particularly preferably 83% to 85%.

[0039] MgO is a component that reduces high-temperature viscosity and improves meltability, and among alkaline earth metal oxides, it is a component that significantly increases Young's modulus. The lower limit of the MgO content is preferably 1% or more, 2% or more, and particularly 2.5% or more. On the other hand, the upper limit of the MgO content is preferably 5% or less, 4% or less, and particularly 3.5% or less. If the MgO content is too low, the Young's modulus tends to decrease. On the other hand, if the MgO content is too high, the devitrification resistance tends to decrease and the strain point tends to decrease. In addition, the thermal expansion coefficient increases, which may reduce the affinity with the rear glass when used as a front glass.

[0040] CaO is a component that reduces high-temperature viscosity and significantly improves meltability without lowering the strain point. Furthermore, among alkaline earth metal oxides, CaO is a component that reduces raw material costs because its raw material introduction cost is relatively low. The lower limit of the CaO content is preferably 4% or more, 4.5% or more, 5% or more, and particularly 5.1% or more. On the other hand, the upper limit of the CaO content is preferably 7% or less, 6.5% or less, and particularly 6% or less. If the CaO content is too low, meltability tends to decrease. On the other hand, if the CaO content is too high, the glass tends to devitrify and the thermal expansion coefficient increases, which may reduce affinity with the rear glass when used as a front glass.

[0041] SrO is a component that suppresses phase separation and improves devitrification resistance. Furthermore, it is a component that reduces high-temperature viscosity and improves meltability without lowering the strain point. It is also a component that suppresses an increase in liquidus temperature. The lower limit of the SrO content is preferably 0.1% or more, 0.5% or more, 1% or more, 1.5% or more, and particularly 2% or more. On the other hand, the upper limit of the SrO content is preferably 6% or less, 5% or less, 4.5% or less, 4% or less, 3.5% or less, 3% or less, and particularly 2.5% or less. If the SrO content is too low, it becomes difficult to achieve the above-mentioned effects. On the other hand, if the SrO content is too high, reaction products are generated during HF etching, and the smoothness of the glass surface is easily lost.

[0042] BaO is a component that significantly improves devitrification resistance. The lower limit of the BaO content is preferably 0.01% or more, 0.1% or more, 1% or more, 2% or more, and particularly preferably 3% or more. On the other hand, the upper limit of the BaO content is preferably 7% or less, 6% or less, and particularly preferably 5.5% or less. If the BaO content is too high, the density becomes too high and the melting property tends to decrease.

[0043] The lower limit of the SrO+BaO content is preferably 0.1% or more, 1% or more, 3% or more, 5% or more, and particularly preferably 6% or more. On the other hand, the upper limit of the SrO+BaO content is preferably 9% or less, 8% or less, and particularly preferably 7% or less. If the SrO+BaO content is too low, the devitrification resistance of the glass becomes insufficient, and if it is too high, the density and thermal expansion coefficient of the glass tend to be high. In this specification, "x+y" means the total amount of the x component and the y component.

[0044] To obtain the above-mentioned effects of SrO and BaO, one of the following combinations is preferable: 2 to 5% SrO and 0.01 to 2% BaO, or 0.1 to 3% SrO and 3 to 6% BaO.

[0045] The total amount of the above-mentioned MgO, CaO, SrO and BaO affects the physical properties, mechanical properties, liquidus temperature, bubble quality, etc. of the glass of the present invention. Therefore, this total amount is preferably in the range of 14 to 17%, particularly 14.5 to 16%.

[0046] ZrO ２ is a component that improves chemical durability such as acid resistance. ２ The lower limit of the content of ZrO is preferably 0.005% or more, particularly preferably 0.01% or more. ２ The upper limit of the content of ZrO is preferably 0.1% or less, 0.07% or less, and particularly preferably 0.05% or less. ２ If the content of ZrO is too small, it becomes difficult to obtain the above-mentioned effects. ２ If the content is too high, the glass tends to become inhomogeneous and devitrification particles tend to occur.

[0047] SnO ２ is a component that has a good fining effect in the high temperature range. ２ The lower limit of the content of SnO is preferably 0.15% or more, particularly preferably 0.17% or more. ２ The upper limit of the SnO content is preferably 0.35% or less, 0.3% or less, and particularly preferably 0.28% or less. ２ If the content of SnO is too small, it becomes difficult to obtain the above-mentioned effects. ２If the content is too high, SnO ２ Devitrification crystals of ZrO are easily precipitated. ２ The precipitation of devitrified crystals of SnO is likely to be promoted. Also, the transmittance of the glass in the short wavelength region is likely to decrease. ２ is a component that has a significant effect on the oxidation-reduction of glass, and as a result, TiO ２ and Fe ２ O ３ From this viewpoint, SnO ２ It is preferable to restrict the content to the above range.

[0048] In addition, ZrO ２ and SnO ２ The coexistence of SnO in an appropriate ratio can suppress the precipitation of devitrification crystals. ２ / ZrO ２ is preferably 5 to 30, particularly preferably 8 to 25.

[0049] TiO ２ is a component that absorbs near-ultraviolet rays, and when the glass plate of the present invention is used as, for example, the front panel of a display, it can suppress deterioration of light-emitting materials such as OLEDs, liquid crystal materials, resin adhesives, and peripheral components that constitute the display due to ultraviolet rays. It also blocks ultraviolet rays emitted from the display, which has a beneficial effect on users. ２ The lower limit of the content of TiO is preferably 0.005% or more. ２ The upper limit of the TiO content is preferably 0.03% or less, 0.025% or less, 0.02% or less, particularly preferably 0.018% or less. ２ If the content of TiO is too small, it becomes difficult to obtain the above-mentioned effects. ２ If the content is too high, the transmittance in the short wavelength region decreases, and the glass may become colored.

[0050] Fe ２ O ３ Also TiO ２ For example, when used as the front panel of a display, it can suppress deterioration of resin adhesives and peripheral components due to ultraviolet rays.２ O ３ The lower limit of the content is preferably 0.005% or more. ２ O ３ The upper limit of the content is preferably 0.02% or less, 0.018% or less, and particularly preferably 0.015% or less.

[0051] In addition, TiO ２ and Fe ２ O ３ These components affect each other and cause coloring. Therefore, it is preferable to control the total amount of both components. Specifically, TiO ２ +Fe ２ O ３ The upper limit of the content of TiO is preferably 0.05% or less, 0.04% or less, 0.035% or less, and particularly preferably 0.03% or less. ２ +Fe ２ O ３ The lower limit of the content is preferably 0.01% or more, and particularly preferably 0.015% or more.

[0052] The alkali-free glass plate of the present invention may contain the following components in addition to the components described above.

[0053] Cr ２ O ３ and CeO ２ Even a small amount of Cr can cause coloring, so it is preferable to keep the content as low as possible. ２ O ３ The content of CeO is preferably 5 ppm or less, particularly preferably 3 ppm or less. ２ The content is preferably 10 ppm or less, 5 ppm or less, and particularly preferably 3 ppm or less.

[0054] As ２ O ３ and Sb ２ O ３ are environmentally undesirable components. Furthermore, when the alkali-free glass plate of the present invention is used for a display, there is a risk of corrosion of the electrodes formed on the surface of the glass plate. Furthermore, if these components are contained in the raw materials, they corrode the molybdenum electrodes during melting, making it difficult to achieve stable electrical melting over a long period of time. Therefore, As ２O ３ and Sb ２ O ３ It is preferable that the glass obtained does not substantially contain arsenic. Here, "substantially does not contain" means that glass raw materials or glass cullets containing these components are not intentionally added to the glass batch in an amount exceeding the level at which they are mixed as impurities. More specifically, the glass obtained does not contain arsenic in the amount of As ２ O ３ 50 ppm or less as antimony, Sb ２ O ３ This means that the concentration is 50 ppm or less.

[0055] It is also possible to include Cl or F in the glass as a fining agent, but As ２ O ３ and Sb ２ O ３ Similarly, from the viewpoints of the environment and electrode erosion, it is preferable that the content be less than 0.1%, particularly less than 0.05%.

[0056] Next, the properties of the alkali-free glass plate of the present invention will be described.

[0057] The strain point of the glass plate of the present invention is preferably 680°C or higher, particularly 690°C or higher. If the strain point is too low, the thermal shrinkage tends to be large. On the other hand, the upper limit of the strain point is preferably 720°C or lower, 715°C or lower, 710°C or lower, particularly 705°C or lower. If the strain point is too high, the temperatures during molding and melting become too high, which tends to increase the production cost of the glass plate.

[0058] For example, in electronic displays such as high-resolution OLED displays, deformation of the glass plate, such as warping, can cause light leakage and other degradation in display performance. Therefore, the rigidity of the glass plate is important. To ensure rigidity, the glass plate of the present invention is desirably high in Young's modulus. Specifically, the Young's modulus is preferably 75 to 83 GPa, particularly 77 to 83 GPa.

[0059] The thermal shrinkage of the glass plate of the present invention is preferably 13 to 40 ppm, 15 to 35 ppm, and particularly preferably 17 to 30 ppm. Here, "thermal shrinkage" refers to the value measured after heat treatment under conditions in which the glass is heated from room temperature to 500°C at a rate of 5°C / min, held at 500°C for 1 hour, and then cooled to room temperature at a rate of 5°C / min. If the thermal shrinkage is too large, when exposed to a high-temperature atmosphere in an electric circuit pattern formation process such as a thin film formation process or a thin film patterning process, the shape and dimensions of the electric circuit pattern are likely to deviate from the designed values, making it difficult to obtain a flat panel display with the desired electrical performance. On the other hand, if the thermal shrinkage is too small, the glass manufacturing efficiency tends to decrease and the manufacturing cost tends to increase. When the glass plate of the present invention is used as a front panel of a display, it can be used even if the thermal shrinkage is relatively large; for example, the thermal shrinkage may be 20 ppm or more. Setting the thermal shrinkage in this range allows for high glass manufacturing efficiency and the production of glass plates at low cost.

[0060] The glass plate of the present invention is preferably colorless and highly transparent, particularly when used as the front panel of a display. When used in OLED displays, low transmittance of obliquely emitted light, particularly light with a short wavelength around 400 nm, can affect the color reproducibility of the display. Specifically, there is concern that even white light may appear blue-green, green, or brownish. Recently, new liquid crystal displays (LCDs), such as QD-LCDs, have been developed and put into practical use, using backlights that employ quantum dots. These quantum dots are also employed as color filters in OLED displays. In such displays, light is incident from various angles to enhance the color conversion efficiency of the quantum dot layer, and the color-converted light is emitted.

[0061] Therefore, the glass plate of the present invention preferably has high transmittance for light with short wavelengths in the range of about 360 to 400 nm. Specifically, the transmittance for a wavelength of 360 nm is preferably 89% or more and the transmittance for a wavelength of 400 nm is preferably 90% or more at a plate thickness of 0.5 mm.

[0062] When the glass plate of the present invention is used as a front panel, it is precisely bonded to a TFT substrate glass to form a display. At this time, if the difference in thermal expansion coefficient between the glass plate and the TFT substrate is large, distortion occurs during bonding, resulting in problems such as pattern misalignment. Therefore, when the glass plate of the present invention is used as a front panel, it is preferable to strictly control the thermal expansion coefficient. Specifically, the thermal expansion coefficient measured in the temperature range of 30 to 380°C is 37±2×10 －７ / °C.

[0063] In order to reduce the weight of the display, the glass plate of the present invention is preferably lightweight. Specifically, its density is 2.46 to 2.6 g / cm ３ , particularly 2.48 to 2.56 g / cm ３ It is preferable that the temperature is in the range of

[0064] The glass plate of the present invention preferably has a β-OH value of less than 0.45 / mm, 0.4 / mm or less, particularly 0.3 / mm or less. If the β-OH value is too large, the bubble quality of the glass may be reduced. The lower limit of the β-OH value is preferably 0.05 / mm or more, 0.1 / mm or more, 0.15 / mm or more, particularly 0.2 / mm or more. If the β-OH value is too small, the initial melting temperature of the glass base may be high, which may increase the erosion of refractories in contact with the molten glass and increase the amount of foreign matter originating from the refractories in the glass. Furthermore, the life of the melting equipment may be shortened.

[0065] The alkali-free glass plate of the present invention is ２．５ The temperature at viscosity dPa·s is preferably 1610°C or less, 1600°C or less, 1590°C or less, 1580°C or less, 1570°C or less, particularly preferably 1560°C or less. ２．５ If the temperature at 10 dPa·s is too high, the glass becomes difficult to melt, the manufacturing cost of the glass sheet increases, and defects such as bubbles are likely to occur. ２．５ If the temperature at dPa·s is too low, it is difficult to design a high viscosity at the liquidus temperature. ２．５ The temperature corresponding to dPa·s is preferably 1500° C. or higher, 1510° C. or higher, and particularly preferably 1520° C. or higher. ２．５The "temperature corresponding to dPa·s" is a value measured by the platinum sphere pull-up method.

[0066] The alkali-free glass plate of the present invention preferably has a liquidus temperature of 1200°C or lower, 1190°C or lower, 1180°C or lower, or 1170°C or lower, particularly preferably 1160°C or lower. This reduces the likelihood of devitrification crystals occurring during glass production, thereby improving productivity. Furthermore, since the glass plate can be easily formed by the overflow downdraw method, the surface quality of the glass plate can be easily improved and the manufacturing cost of the glass plate can be reduced. Furthermore, in view of the recent trend toward larger glass plates and higher resolution displays, improving devitrification resistance is extremely important in order to minimize the formation of devitrification products that can become surface defects. The lower limit of the liquidus temperature is not particularly limited, but in reality it is 1050°C or higher, or even 1100°C or higher. The liquidus temperature is an indicator of devitrification resistance, and the lower the liquidus temperature, the better the devitrification resistance. The "liquidus temperature" refers to the temperature at which devitrification (inclusion of crystals) is observed in the glass when a glass powder that passes through a standard 30 mesh (500 μm) sieve and remains on a 50 mesh (300 μm) sieve is placed in a platinum boat and held in a temperature gradient furnace set at 1100 to 1350°C for 24 hours, and then the platinum boat is removed.

[0067] The alkali-free glass plate of the present invention has a viscosity of 10 at the liquidus temperature. ５．０ dPa·s or more, 10 ５．２ dPa·s or more, especially 10 ５．４ It is preferable that the viscosity is dPa·s or more. In this way, devitrification is less likely to occur during forming, making it easier to form a glass sheet by the overflow downdraw method, and as a result, it is possible to improve the surface quality of the glass sheet. In addition, the manufacturing cost of the glass sheet can be reduced. Note that the viscosity at the liquidus temperature is an index of formability, and the higher the viscosity at the liquidus temperature, the more improved the formability. Note that the viscosity at the liquidus temperature can be measured, for example, by the platinum sphere pulling method.

[0068] The alkali-free glass plate of the present invention has a substrate area of ​​4 m ２ Above, especially 5m ２If the substrate area is too small, it becomes difficult to efficiently manufacture large LCDs or OLED displays driven by oxide TFTs such as IGZO. From the viewpoint of weight reduction, the thickness of the alkali-free glass plate of the present invention is preferably 0.51 mm or less, and desirably 0.5 mm or less.

[0069] Furthermore, when the glass plate of the present invention is used for mobile applications such as laptop computers, it is thinned by an etching process called slimming using a hydrofluoric acid-based chemical solution. Therefore, it is important that the glass plate of the present invention has chemical durability that allows the slimming process to be carried out without any problems.

[0070] The method for producing an alkali-free glass plate of the present invention will be described below.

[0071] The alkali-free glass sheet of the present invention includes, for example, a batch preparation step of preparing a raw material batch, a melting step of melting the raw material batch, a fining step of fining the molten glass, and a forming step of shaping the fined glass. Each step will be described in detail below.

[0072] (1) Batch Preparation Step First, glass raw materials are prepared so as to have the above-mentioned glass composition. The glass raw materials having the main components are as follows:

[0073] Silica sand, stone powder (SiO ２ ) etc. can be used.

[0074] Alumina (Al) was used as an aluminum source. ２ O ３ ), aluminum hydroxide (Al(OH) ３ ) etc. can be used.

[0075] The boron source is orthoboric acid (H ３ BO ３ ) and boric anhydride (B ２ O ３ ) can be used. Since orthoboric acid contains water of crystallization, when the proportion of orthoboric acid used is large, the water content in the glass can be adjusted to a relatively high level. For this reason, it is preferable to use both orthoboric acid and boric acid anhydride and adjust their proportions to match the desired β-OH value.

[0076] Alkaline earth metal sources include calcium carbonate (CaCO ３ ), magnesium oxide (MgO), magnesium hydroxide (Mg(OH) ２ ), barium carbonate (BaCO ３ ), barium nitrate (Ba(NO ３ ) ２ ), strontium carbonate (SrCO ３ ), strontium nitrate (Sr(NO ３ ) ２ ) etc. can be used.

[0077] The zirconia source is ZrO ２ In addition to using oxide raw materials such as those mentioned above, when a Zr-containing refractory such as an electrocast zirconia refractory or dense zircon is used as the refractory material constituting the melting furnace, Zr may be contained in the glass by eluting it from the refractory as a zirconia component.

[0078] Tin oxide (SnO) was used as the tin source. ２ When tin oxide is used, the average particle size D ５０ It is preferable to use tin oxide having an average particle size D of 0.3 to 50 μm, 2 to 50 μm, and particularly 5 to 50 μm. ５０ If the particle size is too small, aggregation between particles occurs, which may cause clogging in the compounding plant and may increase the amount of SnO ２ On the other hand, the average particle size D of the tin oxide powder ５０ If the ratio is too large, the dissolution reaction of the tin oxide powder into the molten glass is delayed, making it difficult to proceed with the fining of the molten glass. As a result, oxygen gas cannot be sufficiently released at the appropriate time during glass melting, bubbles tend to remain in the glass product, and it becomes difficult to obtain a product with excellent bubble quality. In addition, if the SnO ２ There is a risk that undissolved crystalline particles may remain.

[0079] The reduced batch may contain a nitrate source, such as SnO, which is a fining agent. ２ The nitrate raw material can be, for example, barium nitrate (Ba(NO ３ ) ２), strontium nitrate (Sr(NO ３ ) ２ ) etc. can be used.

[0080] In addition to the glass raw materials described above, glass cullet may be used. Here, "glass cullet" refers to defective glass generated during glass production or recycled glass recovered from the market. When glass cullet is used, the proportion of glass cullet used relative to the total amount of the raw material batch is preferably 1% by mass or more, 5% by mass or more, and particularly 10% by mass or more. There is no upper limit on the proportion of glass cullet used, but in order to accurately obtain the desired glass composition, it is preferably 50% by mass or less, 40% by mass or less, and particularly 30% by mass or less. It is also desirable that at least a portion of the glass cullet used be low-moisture glass cullet consisting of glass with a β-OH value of 0.45 / mm or less, 0.4 / mm or less, 0.3 / mm or less, and particularly 0.25 / mm or less. This makes it easier to obtain a glass plate with a low β-OH value. The lower limit of the β-OH value of low-moisture glass cullet is not particularly limited, but in practice it is 0.05 / mm or more.

[0081] (2) Melting Step Next, the prepared raw material batch is melted.

[0082] To melt the raw material batch, a melting furnace capable of heating by radiant heat from burner combustion or Joule heat generated by passing current between electrodes is used. It is particularly preferable to use a melting furnace capable of electric melting. By adopting this configuration, it is possible to suppress the increase in moisture in the atmosphere. As a result, it is possible to suppress the supply of moisture from the atmosphere to the glass, making it easier to produce glass with a high strain point. Furthermore, since the heat generated by the glass itself (Joule heat) is used to heat the molten glass, the glass can be heated efficiently. This makes it possible to melt the raw material batch at a relatively low temperature.

[0083] An electric melting furnace has multiple electrodes made of molybdenum, platinum, tin, or the like. By applying electricity between these electrodes, electricity is passed through the molten glass, and the resulting Joule heat continuously melts the glass. Although radiant heating using a heater or burner may be used as an auxiliary method, electric melting is preferred from the viewpoint of reducing the β-OH value of the glass. When heating with a burner, moisture produced by combustion is absorbed into the glass, increasing the moisture content of the glass. Therefore, it is preferable to appropriately adjust the amount of combustion, temperature, the number of burners used in the melting equipment, and the raw materials to adjust the moisture content in the glass.

[0084] It is preferable to use molybdenum electrodes as the electrodes. Molybdenum electrodes have a high degree of freedom in terms of placement location and electrode shape, making it easy to apply electrical heating to non-alkali glass, which is difficult to conduct electricity. The electrode shape is preferably rod-shaped. If the electrodes are rod-shaped, it is possible to place a desired number of electrodes at any position on the side wall surface or bottom wall surface of the melting furnace while maintaining a desired inter-electrode distance. It is desirable to arrange multiple pairs of electrodes on the wall surface (side wall surface, bottom wall surface, etc.) of the melting furnace, particularly on the bottom wall surface, with a short inter-electrode distance.

[0085] (3) Fining Step Next, the molten glass is heated and refined. The fining step may be carried out in an independent fining tank or in a downstream portion of a melting furnace.

[0086] Polyvalent oxides such as tin compounds contained in the raw material batch dissolve in the molten glass and act as fining agents. For example, tin components release oxygen bubbles during the temperature rise process. The released oxygen bubbles expand the bubbles contained in the molten glass, causing them to float and be removed from the glass. Furthermore, tin components absorb oxygen bubbles during the temperature drop process, eliminating any bubbles remaining in the glass. In this case, the greater the temperature difference between the melting temperature and the fining temperature, the greater the fining effect. Therefore, it is desirable to keep the melting temperature as low as possible.

[0087] (4) Forming Step Next, the refined glass is supplied to a forming device and formed into a sheet. A stirring tank, conditioning tank, or the like may be disposed between the refining tank and the forming device, and the glass may be passed through these tanks before being supplied to the forming device. Furthermore, in order to prevent contamination of the glass, it is preferable that at least the surface of the communication channel connecting the melting furnace, refining tank, and forming device (or each tank disposed between them) that comes into contact with the glass be made of platinum or a platinum alloy.

[0088] Although the forming method is not particularly limited, the effects of the present invention can be more easily achieved by adopting a down-draw method, which is limited by the length of the annealing furnace and makes it difficult to reduce the thermal shrinkage rate. The overflow down-draw method is preferably used as the down-draw method. The overflow down-draw method is a method in which molten glass is allowed to overflow from both sides of a trough-shaped refractory having a wedge-shaped cross section, and the overflowed molten glass is drawn downward while joining at the lower end of the trough-shaped refractory to form glass into a sheet. In the overflow down-draw method, the surface that will become the glass sheet does not come into contact with the trough-shaped refractory and is formed in a free surface state. This allows for inexpensive production of unpolished glass sheets with good surface quality, and also makes it easy to increase the size and thickness of the glass.

[0089] The structure and material of the trough-shaped refractory used in the overflow downdraw method are not particularly limited as long as they can achieve the desired dimensions and surface accuracy. Furthermore, the method of applying force when performing downward stretching is also not particularly limited. For example, a method of stretching the glass by bringing a plurality of pairs of heat-resistant rolls into contact with only the vicinity of the end face of the glass can be employed. In addition to the overflow downdraw method, for example, a slot-down method can also be employed.

[0090] The glass thus formed into a plate is cut to a predetermined size and, if necessary, subjected to various chemical or mechanical processes to form a glass plate.

[0091] The alkali-free glass plate of the present invention will be described in detail below based on examples, but the present invention is not limited to these examples in any way.

[0092] Tables 1 to 3 show examples (Nos. 1 to 15) of the present invention.

[0093]

[0094]

[0095]

[0096] First, raw material batches were prepared by mixing and compounding silica sand, aluminum oxide, orthoboric acid, boric acid anhydride, calcium carbonate, strontium carbonate, strontium nitrate, barium carbonate, stannic oxide, etc. to obtain the compositions shown in Tables 1 to 3. Glass cullet (β-OH value = 0.4 / mm) having the same composition as the target composition was used in an amount of 35 mass% relative to the total amount of the raw material batch.

[0097] Next, the raw material batch was fed into a melting furnace that combined burner combustion and electric melting and melted therein, and then the molten glass was clarified and homogenized in a fining tank and an adjusting tank, and the viscosity was adjusted to a value suitable for forming. The maximum temperature in the fining tank was set to 1500 to 1610°C. The maximum temperature in the fining tank was confirmed by monitoring the temperature of platinum or platinum alloy lined on the inner wall of the fining tank.

[0098] The molten glass was then fed into an overflow downdraw forming apparatus, formed into a plate, and cut to obtain a glass sample having a thickness of 0.5 mm.

[0099] The obtained glass samples were evaluated for β-OH value, thermal expansion coefficient α, strain point Ps, annealing point Ta, softening point Ts, viscosity characteristics, liquidus temperature TL, density ρ, Young's modulus E, specific Young's modulus E / ρ, transmittance, bubble quality, and thermal shrinkage. The results are shown in Tables 1 to 3.

[0100] As is clear from Tables 1 to 3, the glasses of Example Nos. 1 to 15 had low β-OH values ​​of 0.43 / mm or less, high strain points of 700°C or more, thermal shrinkages of 15 to 25 ppm, high T360 values ​​of 89% or more and T400 values ​​of 90% or more, and excellent bubble quality with bubble counts per unit weight of 0.008 bubbles / kg or less.

[0101] The properties were measured as follows.

[0102] The β-OH value was determined by measuring the transmittance of the glass by FT-IR (Fourier transform infrared spectroscopy) and using the following formula:

[0103] β-OH value = (1 / X) log １０ (T １ / T ２ ) X: Glass thickness (mm) T １ :Reference wavelength 3846cm －１ Transmittance (%) at T ２ : Hydroxyl group absorption wavelength 3600 cm －１ Minimum transmittance (%) in the vicinity

[0104] The thermal expansion coefficient is a value measured in the temperature range of 30 to 380°C using a dilatometer.

[0105] The strain point Ps, annealing point Ta, and softening point Ts were measured in accordance with ASTM C336 and C338.

[0106] Viscosity characteristics: high temperature viscosity 10 ４ dPa·s, 10 ３ dPa·s, 10 ２．５ The temperature at dPa·s was measured by the platinum sphere pull-up method.

[0107] The liquidus temperature TL is the temperature at which crystals precipitate when a glass powder that passes through a standard 30 mesh (500 μm) sieve and remains on a 50 mesh (300 μm) sieve is placed in a platinum boat and held in a temperature gradient furnace for 24 hours.

[0108] The density ρ is a value measured by the well-known Archimedes method.

[0109] The Young's modulus E refers to a value measured by the well-known resonance method.

[0110] The specific Young's modulus E / ρ is the value obtained by dividing the Young's modulus by the density.

[0111] The transmittance was measured for glass samples with mirror polished surfaces on both sides using a UH-4150 manufactured by Hitachi High-Tech Corp. The table shows the transmittance T360 at a wavelength of 360 nm and the transmittance T400 at a wavelength of 400 nm.

[0112] The bubble quality was evaluated by determining the number of bubbles having a diameter of 100 μm or more contained in a glass sample per unit mass.

[0113] The thermal shrinkage was measured by the following method. First, as shown in FIG. 1( a), a rectangular sample G measuring 160 mm x 30 mm was prepared as a glass plate sample. Markings M were formed on both ends of the long side of the rectangular sample G at positions 20 to 40 mm away from the edges using #1000 waterproof abrasive paper. Then, as shown in FIG. 1( b), the rectangular sample G with markings M formed thereon was folded in two along the direction perpendicular to the markings M to produce sample pieces Ga and Gb. Then, only one of the sample pieces, Ga, was subjected to a heat treatment in which the temperature was raised from room temperature (25°C) to 500°C at a rate of 5°C / min, held at 500°C for 1 hour, and then cooled to room temperature at a rate of 5°C / min. After the heat treatment, as shown in FIG. 1( c), a sample piece Gb that had not been subjected to heat treatment and a sample piece Ga that had been subjected to heat treatment were arranged in parallel, and the positional deviation (ΔL) of the markings M on the two sample pieces Ga and Gb was measured. １ and ΔL ２ ) was read using a laser microscope, and the thermal shrinkage was calculated using the following formula: ０ is the distance between the initial markings M.

[0114] Heat shrinkage rate (ppm) = [{ΔL １ (μm) + ΔL ２ (μm)} × 10 ３ ] / l ０ (mm)

[0115] The alkali-free glass plate of the present invention is used for OLED displays, high-definition LCDs, etc., and is particularly suitable as a glass plate for a front panel facing a rear panel on which oxide TFTs such as IGZO are formed. The alkali-free glass plate of the present invention is also suitable as a dummy glass plate used in the manufacturing process of liquid crystal displays or OLED displays.

Claims

1. The glass composition, by mass%, is SiO ２ 59-62%, Al ２ O ３ 18-21%, B ２ O ３ 3-6%, MgO 1-5%, CaO 4-7%, SrO 0.1-6%, BaO 0.01-7%, ZrO ２ 0.005-0.1%, SnO ２ 0.15-0.35%, TiO ２ 0.005-0.03%, Fe ２ O ３ An alkali-free glass sheet containing 0.005 to 0.02%.

2. The glass composition, by mass%, is SiO ２ 59-62%, Al ２ O ３ 18-21%, B ２ O ３ 3-6%, MgO 1-4%, CaO 4-7%, SrO 0.1-5%, BaO 0.01-7%, ZrO ２ 0.005-0.1%, SnO ２ 0.15-0.35%, TiO ２ 0.005-0.03%, Fe ２ O ３ The alkali-free glass sheet according to claim 1, containing 0.005 to 0.02%.

3. The alkali-free glass sheet according to claim 1, which contains, as a glass composition, 4.5 to 6% by mass of CaO.

4. SnO by mass ratio ２ / ZrO ２ The alkali-free glass plate according to claim 1, wherein the alkali-free glass plate has a viscosity of 5 to 30.

5. Thermal expansion coefficient is 37±2×10 －７ The alkali-free glass sheet according to claim 1 , wherein the temperature is within the range of 100° C. / ° C.

6. The alkali-free glass sheet according to claim 1, which has a thermal shrinkage of 13 to 40 ppm when heated from 25°C to 500°C at a rate of 5°C / min, held at 500°C for 1 hour, and then cooled to 25°C at a rate of 5°C / min.

7. The alkali-free glass sheet according to claim 1, which has a transmittance of 89% or more at a wavelength of 360 nm and a transmittance of 90% or more at a wavelength of 400 nm when the sheet has a thickness of 0.5 mm.

8. The alkali-free glass sheet according to claim 1, having a Young's modulus of 75 to 83 GPa.

9. The alkali-free glass sheet according to claim 1, having a strain point of 680 to 720°C.

10. The alkali-free glass sheet according to claim 1, having a β-OH value of less than 0.45 / mm.

11. Density is 2.46 to 2.6 g / cm ３ The alkali-free glass sheet according to claim 1 , 12. The board thickness is 0.51 mm or less and the board area is 4 m ２ The alkali-free glass sheet according to claim 1 .

13. The alkali-free glass sheet according to any one of claims 1 to 12, which is used for a front panel of a display.

14. The alkali-free glass sheet according to claim 13, which is for a high-definition liquid crystal display or an OLED display.

15. The alkali-free glass plate according to any one of claims 1 to 12, which is a dummy glass plate used in the manufacturing process of a liquid crystal display or an OLED display.

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