Glass manufacturing methods

Abstract

A method for manufacturing glass includes: a first etching step S1, in which glass is etched using a first etching solution; and a second etching step S2, in which glass is etched using a second etching solution after the first etching step S1. The first etching solution, in a dehydrated state, comprises, by mass%,: hydrofluoric acid: 30-90% and hydrochloric acid: 10-70%. The second etching solution, in a dehydrated state, comprises, by mass%,: hydrofluoric acid: 10-50% and sulfuric acid: 50-90%.

Description

Manufacturing Method of Glass The present invention relates to a manufacturing method of glass. Glass is widely used in cover components of various electronic terminal devices and display devices. Such glass is required to have improved mechanical strength and smoothness. Therefore, in order to improve the mechanical strength and smoothness of glass, etching is sometimes performed on the glass. For example, Patent Document 1 discloses that in order to improve the smoothness of glass, a first etching is first performed using an etching solution (surface polishing solution) containing 40 to 90% by weight of sulfuric acid and 0.4 to 4% by weight of hydrofluoric acid, and then a second etching is performed using an etching solution (post-polishing solution) containing 2 to 30% by weight of hydrofluoric acid. It should be noted that the etching solution used in the second etching is similar to the etching solution used in the first etching, and an etching solution containing hydrofluoric acid and sulfuric acid is exemplified. [Prior Art Documents] [Patent Documents] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-297228 [Problems to be Solved by the Present Invention] However, the conventional etching method cannot sufficiently improve the mechanical strength of glass, and there is still room for improvement. An object of the present invention is to provide glass with high mechanical strength. [Means for Solving the Problems] (1) The manufacturing method of glass according to the present invention for solving the above problems includes: a first etching step of etching the glass with a first etching solution; a second etching step of etching the glass with a second etching solution after the first etching step; characterized in that: the first etching solution in a dehydrated state contains, by mass%, hydrofluoric acid: 30 to 90%, hydrochloric acid: 10 to 70%, and the second etching solution in a dehydrated state contains, by mass%, hydrofluoric acid: 10 to 50%, sulfuric acid: 50 to 90%. In this way, the first etching solution is a hydrofluoric acid-hydrochloric acid system. Therefore, in the first etching step, rough processing is performed to make the steep shape of the glass surface caused by scars such as microcracks become gentle. On the other hand, the second etching solution is a hydrofluoric acid-sulfuric acid system. Therefore, in the second etching step, fine processing is performed to remove the gentle unevenness (scar traces) on the glass surface remaining in the first etching step, making the glass surface smooth. Therefore, through the first etching step and the second etching step, the scars or their traces that cause breakage on the glass surface can be removed, thereby obtaining glass with high mechanical strength. (2) In the configuration of the above (1), it is preferable that at least one of the first etching solution and the second etching solution contains ammonium bifluoride. In this way, the surface quality of the glass is improved, and it is easier to achieve high mechanical strength. (3) In the structure of (2) above, in the dehydrated state, the first etching solution preferably contains, by mass percentage: hydrofluoric acid: 40 - 80%, hydrochloric acid: 10 - 40%, ammonium bifluoride: 3 - 20%. In this way, the surface quality of the glass is improved, and it is easier to achieve high mechanical strength. (4) In the structure of (2) or (3) above, in the dehydrated state, the second etching solution preferably contains, by mass percentage: hydrofluoric acid: 10 - 30%, sulfuric acid: 50 - 80%, ammonium bifluoride: 3 - 20%. In this way, the surface quality of the glass is improved, and it is easier to achieve high mechanical strength. (5) In any of the structures of (1) - (4) above, the water content of the first etching solution is preferably 50 - 95% by mass, and the water content of the second etching solution is preferably 50 - 90% by mass. In this way, the concentrations of solutes such as hydrofluoric acid in the first etching solution and the second etching solution can be maintained within an appropriate range, and it is easier to obtain glass with high mechanical strength. (6) In any of the structures of (1) - (5) above, when the etching rate of the first etching step is set as R1 (μm / min) and the etching rate of the second etching step is set as R2 (μm / min), it is preferably R1 / R2 ≤ 20. In this way, the etching rates of the first etching step and the second etching step can be maintained within an appropriate range, and it is easier to obtain glass with high mechanical strength. (7) In any of the structures of (1) - (6) above, when the etching rate of the first etching step is set as R1 (μm / min) and the etching rate of the second etching step is set as R2 (μm / min), it is preferably R1 ≤ 9.5 μm / min and R2 ≥ 0.5 μm / min. In this way, the etching rates of the first etching step and the second etching step can be maintained within an appropriate range, and it is easier to obtain glass with high mechanical strength. (8) In any of the structures of (1) - (7) above, when the etching amount of the first etching step is set as V1 (μm) and the etching amount of the second etching step is set as V2 (μm), it is preferably V1 / V2 ≤ 80. In this way, the etching amounts of the first etching step and the second etching step can be maintained within an appropriate range, and it is easier to obtain glass with high mechanical strength. (9) In any of the above configurations (1) to (8), when the etching amount of the first etching step is set to V1 (μm) and the etching amount of the second etching step is set to V2 (μm), it is preferable that V1 ≤ 80 μm and V2 ≤ 10 μm. In this way, the etching amounts of the first etching step and the second etching step can be maintained within an appropriate range, and it is easier to obtain glass with high mechanical strength. In addition, since the amount of glass removed by etching can be suppressed, the production efficiency can also be improved. (10) In any of the above configurations (1) to (9), in the first etching step, the temperature of the first etching solution is 1 to 50 °C, and the time for treating the glass with the first etching solution is 0.5 to 50 minutes. In the second etching step, the temperature of the second etching solution is 1 to 50 °C, and the time for treating the glass with the second etching solution is 0.5 to 50 minutes is preferable. In this way, the etching solution temperature and treatment time of the first etching step and the second etching step can be maintained within an appropriate range, and it is easier to obtain glass with high mechanical strength. (11) In any of the above configurations (1) to (10), the glass is an alkali-containing glass containing an alkali metal component as a glass composition. After the first etching step and before the second etching step, an ion exchange step of performing an ion exchange treatment on the glass is further included. In this way, since the glass is chemically strengthened by the ion exchange treatment, it is easier to improve the mechanical strength of the glass. In addition, since the first etching step is performed before the ion exchange step, in the ion exchange step, an even ion exchange treatment can be performed on the glass surface that has removed the sudden unevenness caused by microcracks, etc. Furthermore, since the second etching step is performed after the ion exchange step, even if a defect (surface roughness) is formed on the glass surface due to the ion exchange step, the defect can be removed. (12) In any of the above configurations (1) to (10), the glass is an alkali-containing glass containing an alkali metal component as a glass composition. Before the first etching step, an ion exchange step of performing an ion exchange treatment on the glass is further included. In this way, since the glass is chemically strengthened, it is easier to improve the mechanical strength of the glass. In addition, since the first etching step and the second etching step are performed after the ion exchange step, even if a defect (surface roughness) is formed on the glass surface due to the ion exchange step, the defect can be removed. (13) In the structure of (11) or (12) above, the glass after the second etching step has a surface compressive stress layer. When the maximum compressive stress value of the surface compressive stress layer is set as CS (MPa), the depth of the surface compressive stress layer is set as DOL (μm), and the thickness of the glass after the second etching step is set as t1 (μm), it is preferable that CS ≧ 450 MPa and DOL / t1 ≧ 0.15. In this way, the mechanical strength of the glass can be further improved. (14) In any of the structures of (11) to (13) above, the glass composition of the alkali-containing glass contains, in mol%, 2 : 40 - 80%, Al 2 O 3 : 5 - 25%, B 2 O 3 : 0 - 30%, Li 2 O: 0 - 25%, Na 2 O: 1 - 25%, K 2 O: 0 - 15%, MgO: 0 - 20%, ZnO: 0 - 10%, P 2 O 5 : 0 - 15%, SnO 2 : 0 - 1%, which is preferable as the glass composition. In this way, through the ion exchange treatment, it is easier to improve the mechanical strength of the glass. (15) In any of the structures of (1) to (10) above, the glass can also be an alkali-free glass that substantially does not contain alkali metal components as the glass composition. Even when the glass is an alkali-free glass (in the case of non-strengthened glass), the present invention can improve its mechanical strength through the first etching step and the second etching step. (16) In any of the structures of (1) to (15) above, it is preferable that the glass after the second etching step is in the form of a sheet with a thickness of 0.3 mm or less. Such a thin sheet of glass is easily damaged, so the present invention is particularly useful in this case. (17) The present invention for solving the above problems is a method for manufacturing glass, which includes: a first etching step of etching glass with a first etching solution; a second etching step of etching glass with a second etching solution after the first etching step; and is characterized in that: the first etching solution contains, by mass%, water: 50 to 95%, hydrofluoric acid: 2 to 45%, hydrochloric acid: 0.5 to 30%, and the second etching solution contains, by mass%, water: 50 to 90%, hydrofluoric acid: 1 to 25%, sulfuric acid: 5 to 45%. In this way, through the first etching step and the second etching step, scars or traces on the glass surface that cause damage can be removed, and thus glass with high mechanical strength can be obtained. (18) The present invention for solving the above problems is a method for manufacturing glass, which includes: a first etching step of etching glass with a first etching solution; a second etching step of etching glass with a second etching solution after the first etching step; and is characterized in that: the first etching solution is an etching solution containing hydrochloric acid, and the second etching solution is an etching solution containing sulfuric acid. (19) In the configuration of the above (18), it is preferable that at least one of the first etching solution and the second etching solution contains ammonium bifluoride. [Invention Effect] According to the present invention, glass with high mechanical strength can be provided. Hereinafter, embodiments of the present invention will be described with reference to the drawings. In addition, in each embodiment, if only a part of the configuration is described, the other parts of the configuration can be applied to the configurations of other previously described embodiments. Furthermore, in the description of each embodiment, not only the explicitly indicated combinations of configurations can be adopted, but also the constituent parts of multiple embodiments can be combined as long as the combination does not cause any obstacles even if not explicitly indicated. (First Embodiment) As shown in FIG. 1, the method for manufacturing glass in the first embodiment sequentially includes: a first etching step S1 of etching glass by immersing the glass in a first etching solution, and a second etching step S2 of etching glass by immersing the glass in a second etching solution. It should be noted that the etching steps S1 and S2 are not limited to immersing the glass in the etching solution, and as long as the glass can be brought into contact with the etching solution, for example, methods such as applying or spraying the etching solution onto the glass can be adopted. Before the first etching step S1, the glass is preferably in the form of a sheet. The sheet glass can be obtained, for example, by cutting a sheet-shaped mother glass obtained by forming methods such as the Overflow downdraw method, the Slot downdraw method, the Float method, the Redraw method, etc. into small pieces of glass. In order to obtain a smooth surface, the forming method preferably uses the Overflow downdraw method; in order to obtain thin glass over a large area, the Slot downdraw method is preferably used. Before the first etching step S1, the thickness t0 of the glass is preferably 1.1 mm (1100 μm) or less, more preferably 0.7 - 0.02 mm (700 - 20 μm), and still more preferably 0.5 - 0.025 mm (500 - 25 μm). The glass can be an alkaline glass containing an alkali metal component as a glass composition, or a non-alkali glass substantially free of an alkali metal component as a glass composition. Here, "substantially free of an alkali metal component" means, for example, a case where the content of alkali metal oxides (Li₂O, Na₂O, and K₂O) in the glass composition is 0.5 mol% or less. The non-alkali glass used in the present invention preferably contains, in mol%, SiO₂: 60 - 75%, Al₂O₃: 5 - 20%, B₂O₃: 0 - 15%, Li₂O + Na₂O + K₂O (total amount of Li₂O, Na₂O, and K₂O): 0 - 0.5%, MgO: 0 - 10%, CaO: 0 - 15%, SrO: 0 - 10%, BaO: 0 - 10% as the glass composition. The first etching solution used in the first etching step S1, in a dehydrated state, contains, by mass%, hydrofluoric acid: 30 - 90% and hydrochloric acid: 10 - 70%. The first etching solution preferably contains, in a dehydrated state, by mass%, hydrofluoric acid 40 - 90% and hydrochloric acid 10 - 60%. The first etching solution preferably contains ammonium hydrogen fluoride (acidic ammonium hydrogen fluoride) in order to improve the surface quality of the glass. If ammonium hydrogen fluoride is included, the first etching solution preferably contains, in a dehydrated state, by mass%, (1) hydrofluoric acid: 40 - 80%, hydrochloric acid: 10 - 40%, ammonium hydrogen fluoride: 3 - 20%; more preferably (2) hydrofluoric acid: 42 - 78%, hydrochloric acid: 12 - 38%, ammonium hydrogen fluoride: 4 - 18%; and still more preferably (3) hydrofluoric acid: 45 - 75%, hydrochloric acid: 15 - 35%, ammonium hydrogen fluoride: 5 - 15%. The second etching solution used in the second etching step S2, in a dehydrated state, contains, by mass%, hydrofluoric acid: 10 - 50% and sulfuric acid: 0 - 90%. For the second etching solution, in order to improve the surface quality of the glass, it is preferably to contain ammonium bifluoride. If ammonium bifluoride is included, in the dehydrated state, the second etching solution preferably contains, by mass%: (1) hydrofluoric acid: 10 - 30%, sulfuric acid: 50 - 80%, ammonium bifluoride: 3 - 20%; more preferably contains, by mass%: (2) hydrofluoric acid: 12 - 28%, sulfuric acid: 52 - 78%, ammonium bifluoride: 4 - 18%; most preferably contains, by mass%: (3) hydrofluoric acid: 15 - 25%, sulfuric acid: 55 - 75%, ammonium bifluoride: 5 - 15%. In addition, the content of hydrofluoric acid in the second etching solution is preferably less than that in the first etching solution. The first etching solution preferably has a water content of 50 - 95 mass%, more preferably 50 - 90 mass%. Similarly, the second etching solution preferably has a water content of 50 - 90 mass%. Specifically, in the water-containing state, the first etching solution preferably contains, by mass%: water: 50 - 95%, hydrofluoric acid: 2 - 45%, hydrochloric acid: 0.5 - 30%; more preferably contains: water: 50 - 90%, hydrofluoric acid: 4 - 45%, hydrochloric acid: 1 - 30%. In the water-containing state, the second etching solution preferably contains, by mass%: water: 50 - 90%, hydrofluoric acid: 1 - 25%, sulfuric acid: 5 - 45%. If ammonium bifluoride is included, in the water-containing state, the first etching solution preferably contains, by mass%: water: 50 - 90%, hydrofluoric acid: 4 - 40%, hydrochloric acid: 1 - 20%, ammonium bifluoride: 0.3 - 10. In the water-containing state, the second etching solution preferably contains, by mass%: water: 50 - 90%, hydrofluoric acid: 1 - 15%, sulfuric acid: 5 - 40%, ammonium bifluoride: 0.3 - 10. Additionally, both the first etching solution and the second etching solution may contain no ammonium bifluoride. At least one of the first etching solution and the second etching solution may contain 0.6 to 1.0% by mass of an additive in a water-containing state. The additive may include, for example, a surfactant and / or a chelating agent. The chelating agent may be, for example, a compound having two or more carboxyl groups or two or more hydroxyl groups. Specifically, citric acid, gluconic acid, succinic acid, oxalic acid, tartaric acid, ethylenediaminetetraacetic acid (EDTA), hydroxyethylidene diphosphonic acid (HEDP), nitrilotriacetic acid, diethylenetriaminepentaacetic acid, dihydroxyethylglycine, hydroxyethylethylenediaminetriacetic acid, etc. may be cited. When the etching rate of the first etching step S1 is set as R1 (μm / min) and the etching rate of the second etching step S2 is set as R2 (μm / min), the upper limit range of the etching rate ratio R1 / R2 is preferably 20 or less, 18 or less, 15 or less, 10 or less, 7 or less, 5 or less, 3 or less, 2 or less. The lower limit range of the etching rate ratio R1 / R2 is preferably 0.8 or more, 0.9 or more, 1.0 or more. The upper limit range of the etching rate R1 is preferably 9.5 μm / min or less, 9.3 μm / min or less, 9.0 μm / min or less. The lower limit range of the etching rate R1 is preferably 0.5 μm / min or more, 0.55 μm / min or more, 0.6 μm / min or more. The upper limit range of the etching rate R2 is preferably 7 μm / min or less, 6.5 μm / min or less, 6.0 μm / min or less, 5.5 μm / min or less. The lower limit range of the etching rate R2 is preferably 0.5 μm / min or more, 0.55 μm / min or more, 0.6 μm / min or more. When the etching amount of the first etching step S1 is set as V1 (μm) and the etching amount of the second etching step is set as V2 (μm), the upper limit range of the etching amount ratio V1 / V2 is preferably 80 or less, 70 or less, 50 or less, 30 or less, 20 or less, 10 or less, 5 or less, 3 or less. The lower limit range of the etching amount ratio V1 / V2 is preferably 0.5 or more, 0.8 or more, 1 or more, 1.2 or more. The upper limit range of the etching amount V1 is preferably 80 μm or less, 60 μm or less, 50 μm or less. The lower limit range of the etching amount V1 is preferably 0.5 μm or more, 0.6 μm or more, 0.8 μm or more. The upper limit range of the etching amount V2 is preferably 10 μm or less, 8 μm or less, 6 μm or less. The lower limit range of the etching amount V2 is preferably 0.5 μm or more, 0.6 μm or more, 0.8 μm or more. For display applications that do not require bending deformation, the glass thickness t1 after the second etching step S2 is preferably 1000 μm or less, 700 μm or less, 500 μm or less, 300 μm or less. For display applications that require bending deformation, the glass thickness t1 after the second etching step S2 is preferably 100 μm or less, 70 μm or less, 50 μm or less, 35 μm or less. In the first etching step S1, when the temperature of the first etching solution is H1 and the time (processing time) for immersing the glass in the first etching solution is P1, the temperature H1 is preferably 1 to 50 °C, and the immersion time P1 is preferably 0.5 to 50 minutes. In the second etching step S2, when the temperature of the second etching solution is H2 and the time (processing time) for immersing the glass in the second etching solution is P2, the temperature H2 is preferably 1 to 50 °C, and the immersion time P2 is preferably 0.5 to 50 minutes. The upper limit range of the temperature ratio H1 / H2 is preferably 1.5 or less, 1.3 or less, 1.2 or less. The lower limit range of the temperature ratio H1 / H2 is preferably 0.9 or more, 0.8 or more, 0.6 or more. The upper limit range of the immersion time ratio P1 / P2 is preferably 80 or less, 50 or less, 40 or less, 30 or less. The lower limit range of the immersion time ratio P1 / P2 is preferably 0.7 or more, 0.8 or more, 0.9 or more, 1.0 or more. Based on the manufacturing method of the above first embodiment, the first etching solution used in the first etching step S1 is a hydrofluoric acid-hydrochloric acid system. Therefore, in the first etching step S1, for rough machining, the steep shape of the glass surface caused by scars such as microcracks is effectively smoothed. On the other hand, the second etching solution used in the second etching step S2 is a hydrofluoric acid-sulfuric acid system. Therefore, in the second etching step S2, for finishing machining, the gentle unevenness (scar traces) on the glass surface left by the first etching step S1 is removed, making the glass surface smooth. Thus, through the first etching step S1 and the second etching step S2, the scars or their traces that cause damage to the glass surface can be removed, thereby obtaining glass with high mechanical strength. The breaking stress of the glass after the second etching step S2, measured by the Ring-on-Ring test or the two-point bending test, is preferably 2500 MPa or more, more preferably 2600 MPa or more, still more preferably 2800 MPa or more, and 3000 MPa or more. (Second Embodiment) As shown in FIG. 2, the method for manufacturing the glass of the second embodiment sequentially includes: a first etching step S3 of etching the glass by immersing it in a first etching solution, an ion exchange step S4 of performing an ion exchange treatment by immersing the glass in a molten salt (ion exchange solution), and a second etching step S5 of etching the glass by immersing it in a second etching solution. It should be noted that the ion exchange step S4 is not limited to immersing the glass in a molten salt, and any method that can bring the glass into contact with the molten salt is acceptable, such as applying or spraying the molten salt onto the glass. The first etching step S3 is the same as the first etching step S1 in the first embodiment, and the second etching step S5 is the same as the second etching step S2 in the first embodiment. Therefore, the ion exchange step S5 will be mainly described below. The glass is an alkali-containing glass containing an alkali metal component as a glass composition for performing ion exchange treatment. The alkali-containing glass is preferably an aluminosilicate glass. The glass composition of the aluminosilicate glass preferably contains the following components (in mol%): SiO₂: 40 - 80%, Al₂O₃: 5 - 25%, B₂O₃: 0 - 30%, Li₂O: 0 - 25%, Na₂O: 1 - 25%, K₂O: 0 - 15%, MgO: 0 - 20%, ZnO: 0 - 10%, P₂O₅: 0 - 15%, SnO₂ 0 - 1%. It should be noted that in the description of the content range of each component, % means mol% unless otherwise specified. SiO₂ is a component that forms the glass network. When the content of SiO₂ is too small, vitrification becomes difficult and the coefficient of thermal expansion will be too high, easily reducing the thermal shock resistance. Therefore, the appropriate lower limit range of SiO₂ is 40% or more, 50% or more, 55% or more, 57% or more, 59% or more, especially 61% or more. On the other hand, when the content of SiO₂ is too large, the meltability and formability are easily reduced, and the coefficient of thermal expansion will be too low, making it difficult to match the coefficient of thermal expansion of surrounding materials. Therefore, the appropriate upper limit range of SiO₂ is 80% or less, 70% or less, 68% or less, 66% or less, 65% or less, especially 64.5% or less. Al₂O₃ is a component that improves ion exchange performance and also increases the strain point, Young's modulus, fracture toughness, and Vickers hardness. Therefore, the appropriate lower limit range of Al₂O₃ is 5% or more, 8% or more, 10% or more, 11% or more, 11.2% or more. On the other hand, when the content of Al₂O₃ is excessive, the high-temperature viscosity will increase, making it easy to reduce the meltability and formability. In addition, devitrification crystals are likely to precipitate in the glass, making it difficult to form into a plate shape by methods such as the overflow down-draw method. Especially when using alumina-based refractory materials as the refractory material of the formed body and forming a glass plate by the overflow down-draw method, spinel devitrification crystals are likely to precipitate at the interface with the alumina-based refractory material. Furthermore, the acid resistance will also decrease, making it difficult to apply to the acid treatment process. Therefore, the appropriate upper limit range of Al₂O₃ is 25% or less, 21% or less, 20.5% or less, 20% or less, 19.9% or less, 19.5% or less, 19.0% or less, especially 18.9% or less. B₂O₃ is a component that reduces the high-temperature viscosity and density, stabilizes the glass so that it is not easy to precipitate crystals, and reduces the liquidus temperature. In addition, it is also a component that suppresses Young's modulus and increases the bending strength and crack resistance. However, when the content of B₂O₃ is excessive, after ion exchange treatment, it is easy to cause the so-called burning phenomenon on the surface and change color, or reduce the water resistance, or reduce the compressive stress value of the compressive stress layer. Therefore, the appropriate lower limit range of B₂O₃ is 0% or more, 0.01% or more, 0.02% or more, 0.1% or more, 0.3% or more, and the appropriate upper limit range is 30% or less, 25% or less, 22% or less, 20% or less, especially 15% or less. In addition, from the perspective of preferentially increasing the maximum compressive stress value CS of the surface compressive stress layer, the content of B₂O₃ is preferably 0.2 - 5%, 0.3 - 1%. Also, from the perspective of improving chemical durability to suppress defects during etching treatment and other purposes, the lower limit range of the content of B₂O₃ is preferably 1% or more, 1.5% or more, 2% or more, and the upper limit range can be 5% or less, 4.5% or less, 4% or less, 3% or less. On the other hand, from the perspective of preferentially suppressing Young's modulus, the content of B₂O₃ is preferably 10 - 25%, 15 - 23%, 18 - 22%. Li₂O is an ion-exchange component. Specifically, through the ion exchange of Li ions in the glass with K ions in the molten salt, a component with a high surface compressive stress value is obtained. In addition, Li₂O is also a component that reduces the high-temperature viscosity and improves the meltability and formability. Therefore, the appropriate lower limit range of Li₂O is above 0%, above 3%, above 4%, above 4.2%, above 5%, above 5.5%, above 6.5%, above 7%, above 7.3%, above 7.5%, above 7.8%, especially above 8%. The appropriate upper limit range of Li₂O is below 25%, below 20%, below 15%, below 13%, below 12%, below 11.5%, below 11%, below 10.5%, less than 10%, below 9.9%, below 9%, especially below 8.9%. Na₂O is an ion-exchange component and a component that reduces the high-temperature viscosity and improves the meltability and formability. In addition, Na₂O is also a component that improves the devitrification resistance and the reactivity devitrification resistance of the shaped refractory, especially with alumina refractory. Therefore, the appropriate lower limit range of Na₂O is above 1%, above 5%, above 7%, above 8%, above 8.5%, above 9%, above 9.5%, above 10%, above 11%, above 12%, especially above 12.5%. On the other hand, when the content of Na₂O is excessive, it is easy to reduce the viscosity at which phase separation occurs. And it may reduce the acid resistance or cause the component balance of the glass composition to be失调, instead reducing the devitrification resistance. Therefore, the appropriate upper limit range of Na₂O is below 25%, below 20%, below 19.5%, below 19%, below 18%, below 17%, below 16.5%, below 16%, below 15.5%, especially below 15%. K₂O is a component that reduces the high-temperature viscosity and improves the meltability and formability. In addition, K₂O is also a component that improves the devitrification resistance and increases the Vickers hardness. Therefore, the appropriate lower limit range of K₂O is above 0%, above 0.01%, above 0.02%, above 0.1%, above 0.5%, above 1%, above 1.5%, above 2%, above 2.5%, above 3%, especially above 3.5%. On the other hand, when the content of K₂O is excessive, it is easy to reduce the viscosity at which phase separation occurs. And it may reduce the acid resistance or cause the component balance of the glass composition to be失调, instead having a tendency to reduce the devitrification resistance. Therefore, the appropriate upper limit range of K₂O is below 15%, below 10%, below 5.5%, below 5%, especially less than 4.5%. MgO is a component that reduces the high-temperature viscosity, improves the meltability and formability, or increases the strain point and Young's modulus. Among alkaline earth metal oxides, it is the component that most significantly improves the ion exchange performance. Therefore, the appropriate lower limit range of MgO is 0% or more, 0.1% or more, 0.5% or more, 1% or more, especially 2% or more. However, when the MgO content is excessive, it is likely to increase the density and thermal expansion coefficient, and make the glass prone to devitrification. Therefore, the appropriate upper limit range of MgO is 20% or less, 12% or less, 10% or less, 8% or less, 6% or less, especially 5% or less. ZnO is a component that improves the ion exchange performance, especially with the effect of significantly increasing the compressive stress value. In addition, ZnO is a component that does not reduce the low-temperature viscosity but reduces the high-temperature viscosity. However, when the ZnO content is excessive, the glass is prone to phase separation, or the devitrification resistance is reduced, or the density is increased, or the stress depth of the compressive stress layer becomes smaller. Therefore, the content of ZnO is preferably 0 - 10%, 0 - 6%, 0 - 5%, 0 - 1%, 0 - 0.5%, especially 0 - less than 0.1%. P2O5 is a component that improves the ion exchange performance, especially a component that increases the stress depth of the compressive stress layer. In addition, P2O5 is also a component that inhibits the Young's modulus. Therefore, the appropriate lower limit range of P2O5 is 0% or more, 2% or more, 2.1% or more, 2.5% or more, 3% or more, 4% or more, 4.5% or more. However, when the P2O5 content is excessive, the glass is prone to turbidity due to phase separation, or the water resistance is reduced. Therefore, the appropriate upper limit range of P2O5 is 15% or less, 10% or less, 8.5% or less. SnO2 is a component that improves the ion exchange performance. Therefore, the content of SnO2 is preferably 0% - 1%, 0.01% - 1%, 0.05% - 1%, especially 0.1% - 1%. In addition to the above components, the glass may also contain, for example, the following components as the glass composition. Compared with other components, CaO has the effect of reducing the high-temperature viscosity without reducing the devitrification resistance, improving the meltability and formability, or significantly increasing the strain point and Young's modulus. The content of CaO is preferably 0 - 10%. However, when the CaO content is excessive, it will increase the density and thermal expansion coefficient, and disrupt the component balance of the glass composition, instead making the glass more prone to devitrification or reducing the ion exchange performance. Therefore, the appropriate content of CaO is 0 - 5%, 0.01 - 4%, 0.1 - 3%, especially 1 - 2.5%. SrO is a component that reduces the high-temperature viscosity without reducing the devitrification resistance, improves the meltability and formability, or increases the strain point and Young's modulus. However, when the SrO content is excessive, it will increase the density and thermal expansion coefficient, or reduce the ion exchange performance, or disrupt the compositional balance of the glass composition, making the glass more prone to devitrification. The appropriate content range of SrO is 0 to 5%, 0 to 3%, 0 to 1%, especially 0 to less than 0.1%. BaO is a component that reduces the high-temperature viscosity without reducing the devitrification resistance, improves the meltability and formability, or increases the strain point and Young's modulus. However, when the BaO content is excessive, it will increase the density and thermal expansion coefficient, or reduce the ion exchange performance, or disrupt the compositional balance of the glass composition, making the glass more prone to devitrification. The appropriate content range of BaO is 0 to 5%, 0 to 3%, 0 to 1%, especially 0 to less than 0.1%. ZrO 2 is a component that significantly improves the ion exchange performance and also increases the viscosity and strain point near the liquidus viscosity. However, when its content is excessive, it may significantly reduce the devitrification resistance and may also result in too high a density. Therefore, 2 the appropriate upper limit range of ZrO is 10% or less, 8% or less, 6% or less, especially 5% or less. In addition, if it is desired to improve the ion exchange performance, ZrO should be introduced into the glass composition. 2 In this case, 2 the appropriate lower limit range of ZrO is 0.001% or more, 0.01% or more, 0.5% or more, especially 1% or more. As a fining agent, one or more selected from the group consisting of As 2 O 3 , Sb 2 O 3 , F, Cl, SO 3 group (preferably the Cl, SO 3 group) can be introduced, and the content is 0 to 30000 ppm (3%). Nd 2 O 3 , La 2 O 3 Rare earth oxides such as are components for increasing the Young's modulus, and by adding complementary colors, the color can be eliminated, thereby controlling the color tone of the glass. However, the cost of the raw materials themselves is relatively high, and when introduced in large quantities, the devitrification resistance is likely to decrease. Therefore, the content of rare earth oxides is preferably 4% or less, 3% or less, 2% or less, 1% or less, and particularly 0.5% or less. As 2 O 3 、F, PbO, Bi 2 O 3 Based on environmental considerations, it is preferably substantially not contained. Here, "substantially not contained" means that it is not actively added as a glass component, but it is allowed to be mixed in as an impurity. Specifically, it means that the content of each of the above components is less than 500 ppm. In the ion exchange step S4, the glass is subjected to ion exchange treatment. In this embodiment, the glass is immersed in a molten salt for ion exchange treatment. By thus subjecting the glass to be treated to ion exchange treatment to produce chemically strengthened glass, the mechanical strength of the glass can be improved. The molten salt is a salt containing a component capable of ion exchange with the components in the glass, typically an alkali metal nitrate. Alkali metal nitrates include NaNO 3 、KNO3、LiNO 3 etc., and can be used alone (100% by mass) or in combination of multiple kinds. When multiple kinds of alkali metal nitrates are mixed, the mixing ratio can be determined arbitrarily. For example, by mass%, it can be NaNO 3 : 5 to 95%, KNO3: 5 to 95%, preferably NaNO 3 : 30 to 80%, KNO3: 20 to 70%, more preferably NaNO 3 : 50 to 70%, KNO3: 30 to 50%. The temperature of the molten salt is, for example, 350°C to 500°C, preferably 355°C to 470°C, 360°C to 450°C, 365°C to 430°C, 370°C to 410°C. In addition, the immersion time is, for example, 3 to 300 minutes, preferably 5 to 120 minutes, 7 to 100 minutes. Of course, conditions such as the temperature of the molten salt and the immersion time can be appropriately changed according to the glass composition within the range of obtaining the above stress characteristics. The glass after the ion exchange step S4 has a compressive stress layer (surface compressive stress layer) in the surface layer of the glass, and a tensile stress layer in the interior of the glass deeper than the compressive stress layer. In other words, the glass after the second etching step S5, although the surface is slightly removed by etching, still has a compressive stress layer and a tensile stress layer. The lower limit range of the maximum compressive stress value CS of the compressive stress layer after the second etching step S5 is preferably 450 MPa or more, 470 MPa or more, 500 MPa or more, 530 MPa or more. In this way, higher mechanical strength can be obtained. In addition, when the maximum compressive stress value CS becomes larger, the internal tensile stress tends to become larger, and a dangerous failure mode may occur during failure. Therefore, the upper limit range of the maximum compressive stress value CS is preferably 1500 MPa or less, 1300 MPa or less, 1100 MPa or less, 1000 MPa or less, 900 MPa or less. The lower limit range of the depth DOL of the compressive stress layer after the second etching step S5 is preferably 2 μm or more, 3 μm or more, 4 μm or more. In this way, higher mechanical strength can be obtained. In addition, in order to control the integrated value of the compressive stress value at a lower level, the upper limit range of the depth DOL of the compressive stress layer is preferably 50 μm or less, 40 μm or less, 20 μm or less, 19 μm or less, 18 μm or less, 17 μm or less. When the depth of the compressive stress layer after the second etching step S5 is set as DOL and the thickness of the glass after the second etching step S5 is set as t1, DOL / t1 is preferably 0.1 or more, 0.12 or more, 0.13 or more, 0.14 - 0.3, 0.15 - 0.28. By setting DOL / t1 within this range, while having high mechanical strength, it is possible to ensure that a dangerous failure mode does not occur during failure, thereby ensuring safety. In addition, CS and DOL can be obtained by measuring the stress distribution of the glass using, for example, a surface stress meter FSM - 6000 or SLP - 1000 manufactured by Orihara Seisakusho. According to the manufacturing method of the above - mentioned second embodiment, since the glass is chemically strengthened in the ion exchange step S4, it is easier to improve the mechanical strength of the glass. In addition, since the first etching step S3 is performed before the ion exchange step S4, in the ion exchange step S4, an even ion exchange treatment can be performed on the glass surface that has removed the sharp irregularities caused by microcracks and the like. Furthermore, since the second etching step S5 is performed after the ion exchange step S4, even if defects (surface roughness caused by the molten salt) are formed on the glass surface due to the ion exchange step S4, these defects can be removed. (Third Embodiment) As shown in Fig. 3, the manufacturing method of the glass in the third embodiment sequentially includes: an ion exchange step S6 of immersing the glass in a molten salt (ion exchange liquid) to perform ion exchange treatment, a first etching step S7 of immersing the glass in a first etching liquid to perform etching, and a second etching step S8 of immersing the glass in a second etching liquid to perform etching. The ion exchange step S6 is the same as the ion exchange step S4 in the second embodiment, the first etching step S7 is the same as the first etching step S1 in the first embodiment, and the second etching step S8 is the same as the second etching step S2 in the first embodiment. The difference between the third embodiment and the first and second embodiments is that the ion exchange step S6 is performed before the first etching step S7. In this way, since the glass is chemically strengthened in the ion exchange step S6, it is easier to improve the mechanical strength of the glass. In addition, since the first etching step S7 and the second etching step S8 are performed after the ion exchange step S6, even if defects (surface roughness caused by the molten salt) are formed on the glass surface due to the ion exchange step S6, these defects can be removed. Although the embodiments of the present invention have been described, the embodiments of the present invention are not limited thereto, and various modifications can be made without departing from the gist of the present invention. In the above embodiments, although the case where the ion exchange step is performed before the first etching step, or after the first etching step and before the second etching step has been described, the ion exchange step can also be performed after the second etching step. However, in this case, if defects (surface roughness caused by the molten salt) are formed on the glass surface due to the ion exchange step, these defects cannot be removed through the first etching step or the second etching step. Therefore, when the glass surface defects caused by the ion exchange step become a problem, it is preferably to further perform a third etching step equivalent to the second etching step (finishing), which uses a sulfuric acid-based etching liquid, after the ion exchange step. In the above embodiments, the shape of the glass is not particularly limited. From a plan view, the shape of the glass can be, for example, rectangular (square, rectangle), circular, elliptical, etc. In the above embodiments, three-dimensional bending processing of the glass can be performed as needed. Specifically, the entire or part of the glass is three-dimensionally bent in advance so that the finally manufactured glass has a three-dimensional bent shape. In the above embodiments, the glass can be bendable. In this case, the glass has a thin portion and a thick portion thicker than the thin portion, and can be bent at the thin portion. Such a bendable glass is suitable for use as a cover glass of a foldable device, etc. In the above-described embodiments, although the case of performing the ion exchange step once is illustrated, the ion exchange step may be performed two or three or more times. In addition, heat treatment may be performed before and after the ion exchange. Through the heat treatment, stress can be relaxed, and ion diffusion can be promoted to control the depth of the surface compressive stress layer and the like. In addition, if the ion exchange step is performed multiple times, the stress distribution of the strengthened glass may have one or more of a buckling point, a maximum value, a minimum value, or an inflection point in the region of the compressive stress layer. [Examples] Hereinafter, a glass article according to the present invention will be described based on examples. Note that the following examples are merely illustrative, and the present invention is not limited by any of the following examples. Specimens were prepared as follows. First, glasses having the glass compositions listed in Table 1 were prepared. The glass of Composition A is an alkali-free glass, and the glass of Composition B is an alkali-containing glass (aluminosilicate glass). [Table 1] Specifically, the glass raw materials were formulated into the compositions listed in Table 1 and melted in a test melting furnace. Thereafter, the obtained molten glass was formed into a sheet by the overflow down-draw method and cut into a predetermined size to prepare the glass. Next, the glass was subjected to various treatments under the conditions listed in Tables 2 and 3, including one or two etching steps. Nos. 1 to 7 shown in Table 2 are examples of the present invention, and Nos. 8 to 11 shown in Table 3 are comparative examples. [Table 2] [Table 3] In Example No. 1, an etching step (first time) of a hydrochloric acid system using a first etching solution of a hydrofluoric acid-hydrochloric acid-ammonium bifluoride system and an etching step (second time) of a sulfuric acid system using a second etching solution of a hydrofluoric acid-sulfuric acid-ammonium bifluoride system (hydrochloric acid system etching step → sulfuric acid system etching step) were sequentially performed on the alkali-free glass of Composition A having a size of 300 mm × 400 mm and a thickness t0 of 500 μm. In each etching step, the alkali-free glass was immersed in each etching solution. The etching amount V1 in the first hydrochloric acid system etching step was 100 μm, and the etching amount V2 in the second sulfuric acid system etching step was 100 μm. As a result, the total etching amount was 200 μm, and the thickness t1 of the alkali-free glass after the treatment was 300 μm. As shown in Table 2, in Example No. 1, the concentrations of the respective components of the etching solution in the first hydrochloric acid system etching step, in the dehydrated state, satisfied: hydrofluoric acid: 40 to 90% by mass, hydrochloric acid: 10 to 60% by mass; the concentrations of the respective components of the etching solution in the second sulfuric acid system etching step, in the dehydrated state, satisfied: hydrofluoric acid: 10 to 50% by mass, sulfuric acid: 50 to 90% by mass. In Example No. 2, for the alkali-containing glass of Composition B with dimensions of 300 mm × 400 mm and a thickness t0 of 500 μm, an etching step (first time) of a hydrochloric acid-based etching solution using a first etching solution of a hydrofluoric acid-hydrochloric acid-ammonium bifluoride system, an ion exchange step using a molten salt containing KNO3, and an etching step (second time) of a sulfuric acid-based etching solution using a second etching solution of a hydrofluoric acid-sulfuric acid-ammonium bifluoride system (hydrochloric acid-based etching step → ion exchange step → sulfuric acid-based etching step) were carried out in sequence. In each etching step, the alkali-containing glass was immersed in each etching solution, and in the ion exchange step, the alkali-containing glass was immersed in the molten salt. The etching amount V1 in the first hydrochloric acid-based etching step was 198 μm, and the etching amount V2 in the second sulfuric acid-based etching step was 2 μm. As a result, the total etching amount was 200 μm, and the thickness t1 of the treated alkali-containing glass was 300 μm. As shown in Table 2, in Example No. 2, the concentrations of the respective components of the etching solution in the first hydrochloric acid-based etching step, in the dehydrated state, met the requirements: hydrofluoric acid: 40 to 90% by mass, hydrochloric acid: 10 to 60% by mass; the concentrations of the respective components of the etching solution in the second sulfuric acid-based etching step, in the dehydrated state, met the requirements: hydrofluoric acid: 10 to 50% by mass, sulfuric acid: 50 to 90% by mass. In Example No. 3, for the alkali-containing glass of Composition B with dimensions of 65 mm × 160 mm and a thickness t0 of 35 μm, an ion exchange step using a molten salt containing KNO3, an etching step of a hydrochloric acid-based etching solution using a first etching solution of a hydrofluoric acid-hydrochloric acid-ammonium bifluoride system, and an etching step (second time) of a sulfuric acid-based etching solution using a second etching solution of a hydrofluoric acid-sulfuric acid-ammonium bifluoride system (ion exchange step → hydrochloric acid-based etching step → sulfuric acid-based etching step) were carried out in sequence. In each etching step, the alkali-containing glass was immersed in each etching solution, and in the ion exchange step, the alkali-containing glass was immersed in the molten salt. The etching amount V1 in the first hydrochloric acid-based etching step was 2 μm, and the etching amount V2 in the second sulfuric acid-based etching step was 1 μm. As a result, the total etching amount was 3 μm, and the thickness t1 of the treated alkali-containing glass was 32 μm. As shown in Table 2, in Example No. 3, the concentrations of the respective components of the etching solution in the first hydrochloric acid-based etching step, in the dehydrated state, met the requirements: hydrofluoric acid: 40 to 90% by mass, hydrochloric acid: 10 to 60% by mass; the concentrations of the respective components of the etching solution in the second sulfuric acid-based etching step, in the dehydrated state, met the requirements: hydrofluoric acid: 10 to 50% by mass, sulfuric acid: 50 to 90% by mass. In Example No. 4, for the alkali-containing glass of Composition B with dimensions of 65 mm × 160 mm and a thickness t0 of 35 μm, an etching step (first time) of the hydrochloric acid-based etching solution using the first etching solution of the hydrofluoric acid-hydrochloric acid-ammonium bifluoride system, an ion exchange step using a molten salt containing KNO3, and an etching step (second time) of the sulfuric acid-based etching solution using the second etching solution of the hydrofluoric acid-sulfuric acid-ammonium bifluoride system (hydrochloric acid-based etching step → ion exchange step → sulfuric acid-based etching step) were carried out in sequence. In each etching step, the alkali-containing glass was immersed in each etching solution, and in the ion exchange step, the alkali-containing glass was immersed in the molten salt. The etching amount V1 in the first hydrochloric acid-based etching step was 3 μm, and the etching amount V2 in the second sulfuric acid-based etching step was 2 μm. As a result, the total etching amount was 5 μm, and the thickness t1 of the alkali-containing glass after treatment was 30 μm. As shown in Table 2, in Example No. 4, the concentrations of the respective components of the etching solution in the first hydrochloric acid-based etching step, in the dehydrated state, conformed to: hydrofluoric acid: 40 to 90 mass%, hydrochloric acid: 10 to 60 mass%; the concentrations of the respective components of the etching solution in the second sulfuric acid-based etching step, in the dehydrated state, conformed to: hydrofluoric acid: 10 to 50 mass%, sulfuric acid: 50 to 90 mass%. In Example No. 5, for the alkali-containing glass of Composition B with dimensions of 65 mm × 160 mm and a thickness t0 of 35 μm, an etching step (first time) of the hydrochloric acid-based etching solution using the first etching solution of the hydrofluoric acid-hydrochloric acid system (without ammonium bifluoride), an ion exchange step using a molten salt containing KNO3, and an etching step (second time) of the sulfuric acid-based etching solution using the second etching solution of the hydrofluoric acid-sulfuric acid-ammonium bifluoride system (hydrochloric acid-based etching step → ion exchange step → sulfuric acid-based etching step) were carried out in sequence. In each etching step, the alkali-containing glass was immersed in each etching solution, and in the ion exchange step, the alkali-containing glass was immersed in the molten salt. The etching amount V1 in the first hydrochloric acid-based etching step was 3 μm, and the etching amount V2 in the second sulfuric acid-based etching step was 2 μm. As a result, the total etching amount was 5 μm, and the thickness t1 of the alkali-containing glass after treatment was 30 μm. As shown in Table 2, in Example No. 5, the concentrations of the respective components of the etching solution in the first hydrochloric acid-based etching step, in the dehydrated state, conformed to: hydrofluoric acid: 40 to 90 mass%, hydrochloric acid: 10 to 60 mass%; the concentrations of the respective components of the etching solution in the second sulfuric acid-based etching step, in the dehydrated state, conformed to: hydrofluoric acid: 10 to 50 mass%, sulfuric acid: 50 to 90 mass%. In Example No. 6, for the alkali-containing glass of Composition B with dimensions of 65 mm × 160 mm and a thickness t0 of 35 μm, an etching step (first time) of a hydrochloric acid-based etching solution using a hydrofluoric acid-hydrochloric acid-based first etching solution (without ammonium bifluoride), an ion exchange step using a molten salt containing KNO3, and an etching step (second time) of a sulfuric acid-based etching solution using a hydrofluoric acid-sulfuric acid-based second etching solution (without ammonium bifluoride) were carried out in sequence (hydrochloric acid-based etching step → ion exchange step → sulfuric acid-based etching step). In each etching step, the alkali-containing glass was immersed in each etching solution, and in the ion exchange step, the alkali-containing glass was immersed in the molten salt. The etching amount V1 in the first hydrochloric acid-based etching step was 4 μm, and the etching amount V2 in the second sulfuric acid-based etching step was 1 μm. As a result, the total etching amount was 5 μm, and the thickness t1 of the treated alkali-containing glass was 30 μm. As shown in Table 2, in Example No. 6, the concentrations of the respective components of the etching solution in the first hydrochloric acid-based etching step, in the dehydrated state, met the requirements: hydrofluoric acid: 40 to 90 mass%, hydrochloric acid: 10 to 60 mass%; the concentrations of the respective components of the etching solution in the second sulfuric acid-based etching step, in the dehydrated state, met the requirements: hydrofluoric acid: 10 to 50 mass%, sulfuric acid: 50 to 90 mass%. In Example No. 7, for the alkali-containing glass of Composition B with dimensions of 65 mm × 160 mm and a thickness t0 of 55 μm, an etching step (first time) of a hydrochloric acid-based etching solution using a hydrofluoric acid-hydrochloric acid-ammonium bifluoride-based first etching solution, an ion exchange step using a molten salt containing KNO3, and an etching step (second time) of a sulfuric acid-based etching solution using a hydrofluoric acid-sulfuric acid-ammonium bifluoride-based second etching solution were carried out in sequence (hydrochloric acid-based etching step → ion exchange step → sulfuric acid-based etching step). In each etching step, the alkali-containing glass was immersed in each etching solution, and in the ion exchange step, the alkali-containing glass was immersed in the molten salt. The etching amount V1 in the first hydrochloric acid-based etching step was 4 μm, and the etching amount V2 in the second sulfuric acid-based etching step was 1 μm. As a result, the total etching amount was 5 μm, and the thickness t1 of the treated alkali-containing glass was 50 μm. As shown in Table 2, in Example No. 7, the concentrations of the respective components of the etching solution in the first hydrochloric acid-based etching step, in the dehydrated state, met the requirements: hydrofluoric acid: 40 to 90 mass%, hydrochloric acid: 10 to 60 mass%; the concentrations of the respective components of the etching solution in the second sulfuric acid-based etching step, in the dehydrated state, met the requirements: hydrofluoric acid: 10 to 50 mass%, sulfuric acid: 50 to 90 mass%. In Comparative Example No. 8, for the composition A E-glass with dimensions of 300 mm × 400 mm and a thickness t0 of 500 μm, a hydrochloric acid-based etching step using an etching solution of the hydrofluoric acid-hydrochloric acid-ammonium bifluoride system was performed. That is, the etching step was only carried out once. In the etching step, the E-glass was immersed in the etching solution. The etching amount in the etching step was 200 μm. As a result, the thickness t1 of the processed E-glass was 300 μm. As shown in Table 3, in Comparative Example No. 8, the concentrations of the respective components of the etching solution in the hydrochloric acid-based etching step, in the dehydrated state, met the requirements: hydrofluoric acid: 40 to 90% by mass, hydrochloric acid: 10 to 60% by mass, but the sulfuric acid-based etching step using an etching solution of the hydrofluoric acid-sulfuric acid-ammonium bifluoride system was not carried out. In Comparative Example No. 9, for the composition A E-glass with dimensions of 300 mm × 400 mm and a thickness t0 of 500 μm, a hydrochloric acid-based etching step (first time) using an etching solution of the hydrofluoric acid-hydrochloric acid-ammonium bifluoride system and a sulfuric acid-based etching step (second time) using an etching solution of the hydrofluoric acid-sulfuric acid-ammonium bifluoride system (hydrochloric acid-based etching step → sulfuric acid-based etching step) were carried out in sequence. In each etching step, the E-glass was immersed in the respective etching solution. The etching amount V1 in the first hydrochloric acid-based etching step was 100 μm, and the etching amount V2 in the second sulfuric acid-based etching step was 100 μm. As a result, the total etching amount was 200 μm, and the thickness t1 of the processed E-glass was 300 μm. As shown in Table 3, in Comparative Example No. 9, the concentrations of the respective components of the etching solution in the first hydrochloric acid-based etching step, in the dehydrated state, the hydrofluoric acid met the requirement of 40 to 90% by mass, but the hydrochloric acid did not meet the requirement of 10 to 60% by mass. In addition, the concentrations of the respective components of the etching solution in the second sulfuric acid-based etching step, in the dehydrated state, the sulfuric acid met the requirement of 50 to 90% by mass, but the hydrofluoric acid did not meet the requirement of 10 to 50% by mass. In Comparative Example No. 10, for the composition B alkali-containing glass with dimensions of 65 m × 160 mm and a thickness t0 of 35 μm, an ion exchange step using a molten salt containing KNO3 and a sulfuric acid-based etching step using an etching solution of the hydrofluoric acid-sulfuric acid-ammonium bifluoride system (ion exchange step → sulfuric acid-based etching step) were carried out in sequence. That is, the etching step was only carried out once. In the ion exchange step, the alkali-containing glass was immersed in the molten salt, and in the etching step, the alkali-containing glass was immersed in the etching solution. The etching amount V1 in the etching step was 3 μm. As a result, the thickness t1 of the processed alkali-free glass was 32 μm. As shown in Table 3, in Comparative Example No. 10, the concentrations of the respective components of the etching solution in the sulfuric acid-based etching step, in the dehydrated state, met the requirements: hydrofluoric acid: 10 to 50% by mass, sulfuric acid: 50 to 90% by mass, but the hydrochloric acid-based etching step using an etching solution of the hydrofluoric acid-hydrochloric acid-ammonium bifluoride system was not carried out. In Comparative Example No. 11, for a soda-containing glass of Composition B with dimensions of 65 m × 160 mm and a thickness t0 of 35 μm, an ion exchange step using a molten salt containing KNO3, a sulfuric acid-based etching step (first time) using an etching solution of a hydrofluoric acid-sulfuric acid-ammonium bifluoride system, and a hydrochloric acid-based etching step (second time) using an etching solution of a hydrofluoric acid-hydrochloric acid-ammonium bifluoride system (ion exchange step → sulfuric acid-based etching step → hydrochloric acid-based etching step) were carried out in sequence. In the ion exchange step, the soda-containing glass was immersed in the molten salt, and in each etching step, the soda-containing glass was immersed in each etching solution. The etching amount V1 in the first sulfuric acid-based etching step was 2 μm, and the etching amount V2 in the second hydrochloric acid-based etching step was 1 μm. As a result, the total etching amount was 3 μm, and the thickness t1 of the processed alkali-free glass was 32 μm. As shown in Table 3, in Comparative Example No. 11, the concentrations of the respective components of the etching solution in the first sulfuric acid-based etching step, in the dehydrated state, met the following: hydrofluoric acid: 40 to 90% by mass, hydrochloric acid: 10 to 60% by mass; the concentrations of the respective components of the etching solution in the second hydrochloric acid-based etching step, in the dehydrated state, met the following: hydrofluoric acid: 10 to 50% by mass, sulfuric acid: 50 to 90% by mass. However, the sulfuric acid-based etching step was carried out prior to the hydrochloric acid-based etching step, which was the reverse of the order in the examples. For some of the examples (No. 2 to 7) and comparative examples (No. 10, 11) where the ion exchange step was carried out, the CS (maximum compressive stress value) and DOL (depth of the surface compressive stress layer) of each processed glass were measured. The CS and DOL shown in Tables 2 and 3 are the values obtained by measuring each processed glass using a surface stress meter FSM-6000LE manufactured by Orie Seisakusho. To compare the performance of the above examples (No. 1 to 7) and comparative examples (No. 8 to 11), a strength test was carried out on each glass. For the glasses of No. 1, 2, 8, and 9 with relatively thick processed thicknesses, the breaking stress was measured through a ring-on-ring test (ROR test). On the other hand, for the glasses of No. 3 to 7, 10, and 11 with relatively thin processed thicknesses, the breaking stress was measured through a two-point bending test. As shown in Fig. 4, in the ring-on-ring test, with the relatively larger-diameter support ring 1 supporting the glass 2 from below, the relatively smaller-diameter piston ring 3 is lowered from above while applying a load to the glass 2, and the fracture stress value at the time of glass 2 fracture is measured. The size of the glass 2 is 50 mm × 50 mm, and the thickness (thickness after treatment) is 300 μm. The diameter of the support ring 1 is 12.5 mm, the diameter of the piston ring 3 is 6.25 mm, and the lowering speed of the piston ring 3 is 5 mm / min. For the ring-on-ring test, 20 pieces of each of the glasses of No. 1, 2, 8, and 9 are each tested, and the median, maximum, and minimum values of the fracture stress of each glass are evaluated. In addition, if the fracture stress in the ring-on-ring test is 2500 MPa or more, the glass is considered to have sufficient mechanical strength. As shown in Table 2, the minimum value of the fracture stress in the ring-on-ring test for Examples No. 1 and No. 2 exceeded 2500 MPa, obtaining good results. On the other hand, as shown in Table 3, for Comparative Example No. 8, microcracks were removed by the action of the hydrochloric acid-based etching solution, and the lowest value of the fracture stress in the ring-on-ring test exceeded 1800 MPa, but since the sulfuric acid-based etching solution was not used, the lowest value of the fracture stress in the ring-on-ring test was lower than 2500 MPa. In addition, although Comparative Example No. 9 used both the hydrochloric acid-based etching solution and the sulfuric acid-based etching solution, the concentrations of the respective components were inappropriate, resulting in insufficient improvement in surface quality, and even the median value of the fracture stress in the ring-on-ring test was lower than 2500 MPa. As shown in Fig. 5, in the two-point bending test, the glass 4 is sandwiched between two plate-like bodies 5 and 6 on the upper and lower sides, and while lowering the upper plate-like body 5, the glass 4 is bent into a U shape, and the fracture stress is measured and evaluated by so-called two-point bending. In the two-point bending test, the fracture stress is calculated based on the distance between the two plate-like bodies 5 and 6 at the time of glass fracture. The size of the glass 4 is 65 mm × 160 mm, and the thickness (thickness after treatment) is 30 μm. The glass 4 is bent into a U shape along the long side (the 160-mm side) and placed between the plate-like bodies 5 and 6. The lowering speed of the plate-like body 5 is 20 mm / min. For each of the various glasses of No. 3 to 7, 10, and 11, 20 two-point bending tests are performed for each, and the median, maximum, and minimum values of the fracture stress of each glass are evaluated. In addition, if the fracture stress in the two-point bending test reaches 2500 MPa or more, the glass is considered to have sufficient mechanical strength. As shown in Table 2, the minimum values of the fracture stress in the three-point bending tests of Examples No. 3 to 7 all exceeded 2500 MPa, obtaining good results. In particular, in Example No. 4, since the ion exchange step was carried out after the etching step in the hydrochloric acid system and before the etching step in the sulfuric acid system, good strengthening quality was obtained in the ion exchange step, and the fracture stress in the three-point bending test was very high. In addition, in Example No. 4, both the first etching solution and the second etching solution contained fluoride ammonium, which was also considered to be one of the factors for increasing the fracture stress. On the other hand, as shown in Table 3, in Comparative Example No. 10, only the sulfuric acid-based etching solution was used, so the removal of microcracks was insufficient, the fracture stress in the three-point bending test changed greatly, and the lowest value of the fracture stress was much lower than 2500 MPa. In Comparative Example No. 11, the order of the hydrochloric acid-based etching solution and the sulfuric acid-based etching solution was reversed, showing a form in which rough machining was carried out after finishing. As a result, although the lowest value of the fracture stress in the three-point bending test exceeded 2000 MPa, it did not reach 2500 MPa. [Industrial Applicability] The glass article of the present invention can be used for, for example, protective glasses of smartphones, mobile phones, tablet computers, personal computers, digital cameras, touch panel displays, other display devices, in-vehicle display devices, in-vehicle panels, and the like. 1: Support ring 2, 4: Glass 3: Piston ring 5, 6: Plate-like body S1, S3, S7: First etching step S2, S5, S8: Second etching step S4, S6: Ion exchange step FIG. 1 is a flowchart of a method for manufacturing glass according to a first embodiment of the present invention. FIG. 2 is a flowchart of a method for manufacturing glass according to a second embodiment of the present invention. FIG. 3 is a flowchart of a method for manufacturing glass according to a third embodiment of the present invention. FIG. 4 is a perspective view of an embodiment of a Ring-on-Ring test (ROR test). FIG. 5 is a side view of an embodiment of a three-point bending test. S1~S2: Steps

Claims

1. A method for manufacturing glass, characterized in that it comprises: The first etching step involves etching the glass with a first etching solution; The second etching step, following the first etching step, involves etching the glass with a second etching solution. An ion exchange step is performed on the glass after the first etching step and before the second etching step; the first etching solution, in a dehydrated state, contains, by mass%, 30-90% hydrofluoric acid and 10-70% hydrochloric acid; the second etching solution, in a dehydrated state, contains, by mass%, 10-50% hydrofluoric acid and 50-90% sulfuric acid.

2. The method of manufacturing glass as claimed in claim 1, wherein at least one of the first etching solution and the second etching solution comprises ammonium bifluoride.

3. The method for manufacturing glass as claimed in claim 2, wherein the first etching solution, in a dehydrated state, comprises, by mass%,: hydrofluoric acid: 40-80%, hydrochloric acid: 10-40%, and ammonium bifluoride: 3-20%.

4. A method for manufacturing glass as claimed in claim 2 or 3, wherein the second etching solution, in a dehydrated state, comprises, by mass%,: hydrofluoric acid: 10-30%, sulfuric acid: 50-80%, and ammonium bifluoride: 3-20%.

5. A method for manufacturing glass as claimed in claim 1 or 2, wherein the first etching solution has a water content of 50-95% by mass, and the second etching solution has a water content of 50-90% by mass.

6. A method for manufacturing glass as claimed in claim 1 or 2, wherein when the etching rate in the first etching step is set to R1 (μm / min) and the etching rate in the second etching step is set to R2 (μm / min), then R1 / R2 ≦ 20.

7. A method for manufacturing glass as claimed in claim 1 or 2, wherein when the etching rate in the first etching step is set to R1 (μm / min) and the etching rate in the second etching step is set to R2 (μm / min), then R1 ≦ 9.5 μm / min and R2 ≧ 0.5 μm / min.

8. A method for manufacturing glass as claimed in claim 1 or 2, wherein when the etching amount in the first etching step is set to V1 (μm) and the etching amount in the second etching step is set to V2 (μm), then V1 / V2≦80.

9. A method for manufacturing glass as claimed in claim 1 or 2, wherein when the etching amount in the first etching step is set to V1 (μm) and the etching amount in the second etching step is set to V2 (μm), then V1 ≦ 80 μm and V2 ≦ 10 μm.

10. A method for manufacturing glass as claimed in claim 1 or 2, wherein in the first etching step, the temperature of the first etching solution is 1~50°C, and the glass is treated with the first etching solution for 0.5~50 minutes; and in the second etching step, the temperature of the second etching solution is 1~50°C, and the glass is treated with the second etching solution for 0.5~50 minutes.

11. A method of manufacturing glass as claimed in claim 1 or 2, wherein the glass is an alkali-containing glass comprising an alkali metal component as part of the glass composition.

12. A method for manufacturing glass as claimed in claim 11, wherein the glass after the second etching step has a surface compressive stress layer, wherein the maximum compressive stress value of the surface compressive stress layer is set as CS (MPa), the depth of the surface compressive stress layer is set as DOL (μm), and the thickness of the glass after the second etching step is set as t1 (μm), then CS ≥ 450 MPa and DOL / t1 ≥ 0.

15.

13. A method for manufacturing glass as claimed in claim 11, wherein the alkali-containing glass comprises, in mole percent: SiO2: 40-80%, Al2O3: 5-25%, B2O3: 0-30%, Li2O: 0-25%, Na2O: 1-25%, K2O: 0-15%, MgO: 0-20%, ZnO: 0-10%, P2O5: 0-15%, SnO2: 0-1%, as a glass composition.

14. A method for manufacturing glass as claimed in claim 1 or 2, wherein the glass after the second etching step is a sheet with a thickness of less than 0.3 mm.

15. A method for manufacturing glass, characterized in that it comprises: The first etching step involves etching the glass with a first etching solution; The second etching step, following the first etching step, involves etching the glass with a second etching solution. An ion exchange step is performed on the glass after the first etching step and before the second etching step; the first etching solution contains, by mass%, water: 50-95%, hydrofluoric acid: 2-45%, hydrochloric acid: 0.5-30%; the second etching solution contains, by mass%, water: 50-90%, hydrofluoric acid: 1-25%, sulfuric acid: 5-45%.

16. A method for manufacturing glass, characterized in that it comprises: The first etching step involves etching the glass with a first etching solution; The second etching step, following the first etching step, involves etching the glass with a second etching solution. An ion exchange step is performed on the glass after the first etching step and before the second etching step; the first etching solution is an etching solution containing hydrochloric acid, and the second etching solution is an etching solution containing sulfuric acid.

17. A method of manufacturing glass as claimed in claim 16, wherein at least one of the first etching solution and the second etching solution comprises ammonium bifluoride.

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