Glass for chemical strengthening

Abstract

To provide a glass for chemical strengthening that exhibits a high strength after chemical strengthening and is resistant to devitrification.SOLUTION: The present invention relates to a glass for chemical strengthening that contains, expressed as mol% on an oxide basis, SiO2 of 55-70%, Al2O3 of 10-25%, Li2O of 1-20%, CaO of 0-8%, SrO of 0-8%, and ZrO2 of 0-5%, with the total content of CaO and SrO being 1.5-10%, the total content of Na2O and K2O being 3-11%, and a value X represented by the formula ([Li2O]+[K2O]) / [Al2O3] of 0.1-1.1.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to glass for chemical strengthening.

Background Art

[0002] In recent years, in order to protect and enhance the aesthetics of display devices of mobile devices such as mobile phones, smartphones, personal digital assistants (PDAs), and tablet terminals, cover glass made of chemically strengthened glass has been used.

[0003] In chemically strengthened glass, the strength tends to increase as the surface compressive stress (value) (CS) and the depth of the compressive stress layer (DOC) increase. On the other hand, in order to maintain the balance with the surface compressive stress, an internal tensile stress (CT) is generated inside the glass. Therefore, the larger the CS and DOC are, the larger the CT becomes. When glass with a large CT breaks, the number of fragments increases and the fragments are likely to scatter.

[0004] Patent Document 1 describes that by forming a stress profile represented by a bent line through a two-step chemical strengthening treatment, the surface compressive stress can be increased while suppressing the internal tensile stress. Specifically, a method has been proposed in which a KNO3 / NaNO3 mixed salt with a relatively low potassium salt concentration is used for the first-stage chemical strengthening, and a KNO3 / NaNO3 mixed salt with a relatively high potassium salt concentration is used for the second-stage chemical strengthening. In addition, Patent Document 2 discloses a lithium aluminosilicate glass that can obtain a relatively large surface compressive stress and a depth of the compressive stress layer through a two-step chemical strengthening treatment. The lithium aluminosilicate glass can increase both CS and DOC by a two-step chemical strengthening treatment in which a sodium salt is used for the first-stage chemical strengthening treatment and a potassium salt is used for the second-stage chemical strengthening treatment.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

[0006] Recently, there has been an increasing demand for thinner and lighter cover glasses, as well as cover glasses processed into curved surfaces and the like. Lithium aluminosilicate glass, which can simultaneously increase the surface compressive stress value (CS) and the depth of the compressive stress layer (DOC), has attracted attention. However, lithium aluminosilicate glass tends to devitrify easily during the glass manufacturing process or during the process of bending the obtained glass. An object of the present invention is to provide chemically strengthened glass that is less likely to devitrify and can achieve a large CS and a large DOC. [Means for Solving the Problems]

[0007] The present invention provides, in terms of molar percentage based on oxides, SiO2 of 55 to 70%, Al2O3 of 10 to 25%, Li2O of 1 to 20%, CaO of 0 to 8%, SrO of 0 to 8%, and ZrO2 of 0 to 5%, the total content of CaO and SrO is 1.5 to 10%, the total content of Na2O and K2O is 3 to 11%, and provides chemically strengthened glass in which the value X represented by the following formula is 0.1 to 1.1. X = ([Li2O] + [K2O]) / [Al2O3] However, [Al2O3], [Li2O], and [K2O] are the contents in terms of molar percentage of each component.

[0008] The glass for chemical strengthening preferably has a total content of MgO, BaO, and ZnO of 0 to 5%. Also, the content of B2O3 is preferably 0 to 10%.

[0009] Also, the temperature (T4) at which the viscosity becomes 10 4 dPa·s is preferably 1050 to 1300°C. Also, the devitrification temperature is preferably at a temperature (T4 + 120°C) 120°C higher than the temperature (T4) at which the viscosity becomes 10 4 dPa·s or lower. Also, the devitrification temperature is preferably at or higher than the temperature (T5.5) at which the viscosity becomes 10 5.5 dPa·s. Also, the temperature (T2) at which the viscosity becomes 10 2 dPa·s is preferably 1400 to 1800°C. Also, when a two-stage chemical strengthening is performed by immersing a glass plate with a thickness of 0.8 mm in sodium nitrate at 450°C for 3 hours and then in potassium nitrate at 450°C for 1.5 hours, the surface compressive stress (CS2 described later) is preferably 950 MPa or more, and the surface compressive stress layer depth (DOC3 described later) is preferably 100 μm or more.

Advantages of the Invention

[0010] According to the present invention, it is possible to provide chemically strengthened glass that is less likely to devitrify and has a large surface compressive stress value (CS) and a large compressive stress layer depth (DOC).

Brief Description of the Drawings

[0011]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0012] The glass for chemical strengthening of the present invention will be described in detail below. However, the present invention is not limited to the following embodiments and can be arbitrarily modified and implemented without departing from the gist of the present invention. In this specification, "chemically strengthened glass" refers to glass after being subjected to chemical strengthening treatment. Further, "glass for chemical strengthening" refers to glass before being subjected to chemical strengthening treatment. In this specification, the glass composition of the glass for chemical strengthening may be referred to as the mother composition of the chemically strengthened glass. In a chemically strengthened glass, usually, a compressive stress layer is formed on the glass surface portion by ion exchange, so the glass composition of the portion where ion exchange has not occurred coincides with the mother composition of the chemically strengthened glass.

[0013] In this specification, the glass composition is shown in terms of mole percentage on an oxide basis, and mole % may sometimes be simply denoted as %. Also, "~" indicating a numerical range is used in the sense of including the numerical values described before and after it as the lower limit value and the upper limit value. "Substantially not contained" in the glass composition means not contained except for unavoidable impurities contained in raw materials and the like, that is, not intentionally contained. Specifically, for example, in the case of a coloring component such as a transition metal oxide, the content in the glass composition is less than 0.01 mol%. Also, in the case of an oxide other than the above coloring component, the content in the glass composition is less than 0.1 mol%.

[0014] In this specification, "stress profile" is a pattern representing the compressive stress value with the depth from the glass surface as a variable. A negative compressive stress value means a tensile stress.

[0015] Hereinafter, unless otherwise specified, the "surface compressive stress value" of the glass is the surface compressive stress value when chemical strengthening treatment is performed using a glass plate with a thickness of 0.8 mm that has been held at a temperature 50 °C higher than the glass transition point Tg for 1 hour or more and then slowly cooled at a cooling rate of 0.5 °C / min. The surface compressive stress generated by chemical strengthening treatment tends to increase as the fictive temperature of the glass is lower, and the fictive temperature of the glass is affected by the thermal history (e.g., cooling rate) that the glass has undergone. Therefore, it is evaluated by excluding the influence of the fictive temperature through heat treatment and slow cooling.

[0016] Also, the "β-OH value" is obtained from the transmittance X1 (%) at a wavenumber of 4000 cm -1 measured by the FT-IR method, the minimum transmittance X2 (%) in the vicinity of the absorption wavenumber of the hydroxyl group at 3570 cm -1 and the thickness t (unit: mm) of the glass plate according to Equation (1). β-OH value = (1 / t) log 10 (X1 / X2) ····· (1) Note that the β-OH value can be adjusted by the moisture content contained in the glass raw material and the melting conditions.

[0017] <Glass for Chemical Strengthening> The glass for chemical strengthening of the present invention (hereinafter sometimes referred to as "this glass") is expressed in terms of molar percentage based on oxides, contains 55 - 70% of SiO2, 10 - 25% of Al2O3, 1 - 20% of Li2O, 0 - 8% of CaO, 0 - 8% of SrO, and 0 - 5% of ZrO2, and the total content of CaO and SrO is preferably 1.5 - 10%, and the total content of Na2O and K2O is preferably 3 - 11%.

[0018] This glass preferably has a value X represented by the following formula in the range of 0.1 - 1.1. X = ([Li2O] + [K2O]) / [Al2O3] However, [Al2O3], [Li2O], and [K2O] are the contents in terms of molar percentages of each component.

[0019] The inventors of the present invention studied the relationship between the glass composition of chemically strengthened glass and the compressive stress value after chemical strengthening and the relationship with chemical strengthening characteristics, and found a glass composition in which a large compressive stress value can be introduced by chemical strengthening treatment and devitrification hardly occurs.

[0020] Hereinafter, the preferred glass composition will be described. SiO2 is a component that constitutes the glass network and is a component that improves chemical durability. In order to reduce the generation of cracks when the glass surface is scratched, the content of SiO2 is preferably 55% or more, more preferably 58% or more, still more preferably 61% or more, and particularly preferably 64% or more. On the other hand, in order to improve the meltability, the content of SiO2 is 70% or less, preferably 68% or less, still more preferably 66% or less.

[0021] The content of Al2O3 is preferably 10% or more, more preferably 12% or more, and still more preferably 14% or more in order to improve the ion exchange performance during chemical strengthening and increase the surface compressive stress after strengthening. On the other hand, in order to suppress devitrification, the content of Al2O3 is preferably 25% or less, more preferably 20% or less, still more preferably 18% or less, and particularly preferably 16% or less.

[0022] Li2O is a component that forms a surface compressive stress by ion exchange and is a component that improves the meltability of the glass. When the chemically strengthened glass contains Li2O, a stress profile in which both the surface compressive stress and the compressive stress layer depth are large can be obtained by ion-exchanging Li ions on the glass surface with Na ions and further ion-exchanging Na ions with K ions. In order to easily obtain a preferred stress profile, the content of Li2O is 1% or more, preferably 4% or more, more preferably 7% or more, and particularly preferably 9% or more. On the one hand, if the content of Li2O is too high, the devitrification growth rate during glass melting will increase, and the problem of yield reduction due to devitrification will become significant. Therefore, the content of Li2O is 20% or less, preferably 18% or less, more preferably 15% or less, and even more preferably 13% or less.

[0023] Neither Na2O nor K2O is essential, but they are components that improve the meltability of the glass and reduce the devitrification growth rate of the glass, and they may be added to improve the ion exchange performance. The total content of Na2O and K2O ([Na2O]+[K2O]) is preferably 0 to 11%, more preferably 3% or more, and even more preferably 5% or more. On the other hand, the total content is more preferably 8% or less, and particularly preferably 7% or less.

[0024] The ratio of the content represented by [Li2O] / ([Na2O]+[K2O]) is preferably 3 or less, more preferably 2.5 or less, and even more preferably 2 or less in order to reduce the devitrification growth rate. On the other hand, in order to increase the surface compressive stress in the chemical strengthening treatment using sodium, [Li2O] / ([Na2O]+[K2O]) is preferably 0.5 or more, more preferably 0.9 or more, and even more preferably 1.3 or more.

[0025] Also, the ratio of the content represented by ([Li2O]+[K2O]) / [Al2O3] is preferably 1.1 or less, more preferably 1.0 or less, and even more preferably 0.8 or less in order to increase the surface compressive stress by chemical strengthening treatment. In order to lower the melting temperature of the glass and suppress devitrification, ([Li2O]+[K2O]) / [Al2O3] is preferably 0.1 or more, more preferably 0.3 or more, and even more preferably 0.5 or more.

[0026] Na2O is a component that forms a surface compressive stress layer in the chemical strengthening treatment using a potassium salt, and is also a component that can improve the meltability of the glass. To obtain such an effect, the content of Na2O is preferably 1% or more, more preferably 2% or more, still more preferably 3% or more, and particularly preferably 4% or more. On the other hand, to avoid a decrease in the surface compressive stress due to the chemical strengthening treatment with a sodium salt, the content is preferably 10% or less, more preferably 8% or less, still more preferably 6% or less, and particularly preferably 5% or less.

[0027] K2O may be contained to improve the ion exchange performance or the like. When K2O is contained, the content is preferably 0.5% or more, more preferably 1% or more, still more preferably 1.5% or more, particularly preferably 2% or more, and typically 3% or more. On the other hand, to avoid a decrease in the surface compressive stress (CS) due to a potassium salt, the content is preferably 10% or less, more preferably 5% or less, still more preferably 3% or less, and particularly preferably 2% or less.

[0028] MgO, CaO, SrO, BaO, and ZnO (hereinafter, may be collectively referred to as "alkaline earth oxides, etc.") are not all essential, but it is preferable to contain one or more of them to enhance the stability of the glass. This glass is a lithium aluminosilicate glass that can obtain a high surface compressive stress by ion exchange treatment, and contains SiO2, Al2O3, and Li2O at relatively high concentrations. As a result, lithium aluminosilicate crystals are likely to precipitate during the production of the glass plate or during the thermoforming of the glass plate. Lithium aluminosilicate crystals have a high crystal growth rate, and the crystals grow in a short time, so the quality of products such as glass plates is likely to deteriorate. Alkaline earth oxides, etc., when contained in the glass composition, have the effect of suppressing the precipitation and growth of lithium aluminosilicate crystals. The total content of alkaline earth oxides, etc. ([MgO] + [CaO] + [SrO] + [BaO] + [ZnO]) is preferably 1% or more, more preferably 2% or more, still more preferably 3% or more, and particularly preferably 4% or more. On the other hand, from the viewpoint of improving the ion exchange ability by chemical strengthening, the total content is preferably 20% or less, more preferably 15% or less, still more preferably 10% or less, and even more preferably 8% or less. In order to suppress the precipitation of lithium aluminosilicate crystals, it is more preferable to contain one or more selected from MgO, CaO, SrO, and BaO.

[0029] When containing MgO and one or more of CaO, SrO, BaO, and ZnO, in order to lower the surface reflectance of the glass, the content ratio represented by [MgO] / ([CaO]+[SrO]+[BaO]+「ZnO」) is preferably 10 or more, more preferably 15 or more, still more preferably 20 or more, and particularly preferably 25 or more. Since CaO, SrO, BaO, and ZnO increase the refractive index as compared with MgO, the refractive index can be lowered by relatively increasing the content of MgO. By suppressing the refractive index, the surface reflectance of the glass is reduced. [MgO] / ([CaO]+[SrO]+[BaO]+「ZnO」) is preferably 60 or less, more preferably 55 or less, still more preferably 50 or less, and particularly preferably 45 or less in order to lower the devitrification temperature. Since MgO does not have a very large effect of lowering the devitrification temperature, if the relative content becomes too large, the devitrification temperature tends to increase.

[0030] When containing MgO, the content is preferably 0.5% or more, more preferably 1% or more, in order to increase the meltability of the chemically strengthened glass while reducing the devitrification growth rate. On the other hand, in order to increase the surface compressive stress by chemical strengthening, the content of MgO is preferably 5% or less, more preferably 3% or less, and preferably 1% or less.

[0031] CaO is an alkaline earth oxide that can enhance strength through chemical strengthening after MgO and has a greater effect of suppressing devitrification than MgO. Therefore, in order to increase strength through chemical strengthening while suppressing devitrification, it is preferable to contain CaO. When containing CaO, the content is preferably 0.1% or more, more preferably 0.15% or more, and still more preferably 0.5% or more. In order to increase the compressive stress value during chemical strengthening treatment, the content of CaO is preferably 8% or less, more preferably 5% or less, still more preferably 3% or less, and particularly preferably 1% or less.

[0032] SrO is a component that has a great effect of suppressing crystal precipitation along with BaO. Compared with BaO, there are fewer problems such as increasing the surface reflectance. Therefore, when emphasizing devitrification suppression, it is preferable to contain SrO. In that case, the SrO content is preferably 0.1% or more, more preferably 0.5% or more, and still more preferably 1% or more. In order to increase the compressive stress value during chemical strengthening treatment, the SrO content is preferably 8% or less, more preferably 5% or less, still more preferably 4% or less, particularly preferably 3% or less, and typically 2% or less.

[0033] Alkaline earth oxides, etc. can enhance the meltability of glass and have the effect of suppressing devitrification. On the other hand, if contained in excess, the improvement in strength by chemical strengthening may be inhibited. Among alkaline earth oxides, etc., CaO and SrO have a relatively high effect of suppressing devitrification and a relatively low tendency to deteriorate chemical strengthening characteristics. Therefore, in order to obtain glass with good comprehensive properties, it is preferable to contain either CaO or SrO. In that case, the total content of CaO and SrO ([CaO]+[SrO]) is preferably 1.5% or more, more preferably 2.0% or more, and still more preferably 2.5% or more. Also, in order to increase the surface compressive stress layer by chemical strengthening treatment, it is preferably 10% or less, more preferably 7% or less, and still more preferably 5% or less.

[0034] BaO is a component that improves the meltability of the chemically strengthened glass and may be contained. When BaO is contained, the content is preferably 0.1% or more, more preferably 0.15% or more, and still more preferably 0.5% or more. On the other hand, when the content of BaO is excessive, it becomes difficult to increase the surface compressive stress layer during the chemical strengthening treatment. Also, since BaO significantly increases the refractive index, in order to suppress the refractive index, lower the surface reflectance, and increase the transmittance, the content of BaO is preferably 3% or less, more preferably 2% or less, still more preferably 1% or less, and particularly preferably 0.5% or less.

[0035] ZnO is a component that improves the meltability of the chemically strengthened glass and may be contained. When ZnO is contained, the content is preferably 0.1% or more, more preferably 0.15% or more, and still more preferably 0.5% or more. On the other hand, when the content of ZnO is excessive, it becomes difficult to increase the surface compressive stress layer during the chemical strengthening treatment. The content of ZnO is preferably 3% or less, more preferably 2% or less, still more preferably 1% or less, and typically 0.5% or less.

[0036] The total content of MgO, BaO, and ZnO ([MgO]+[BaO]+[ZnO]) is preferably 5% or less, more preferably 3% or less, and still more preferably 1% or less in order to increase the surface compressive stress by chemical strengthening.

[0037] ZrO2 may not be contained, but it is preferably contained in order to increase the surface compressive stress of the chemically strengthened glass. The content of ZrO2 is preferably 0.1% or more, more preferably 0.2% or more, still more preferably 0.5% or more, particularly preferably 0.8% or more, and typically 1% or more. On the other hand, when the content of ZrO2 is too high, it becomes difficult to increase the surface compressive stress layer during the chemical strengthening treatment. The content of ZrO2 is preferably 5% or less, more preferably 3% or less, still more preferably 2% or less, and particularly preferably 1.5% or less.

[0038] When ordinary glass is irradiated with light, it is known that solarization occurs, resulting in color changes and a decrease in transmittance due to, for example, changes in the valence of transition metal ions contained in small amounts in the glass. TiO2 is not essential but may be contained to suppress solarization. When TiO2 is contained, the content is preferably 0.02% or more, more preferably 0.05% or more, still more preferably 0.1% or more, particularly preferably 0.12% or more, and typically 0.15% or more. On the other hand, when the content of TiO2 exceeds 1%, devitrification is likely to occur, and the quality of chemically strengthened glass may deteriorate. The content of TiO2 is preferably 1% or less, more preferably 0.5% or less, still more preferably 0.25% or less.

[0039] B2O3 is not essential, but it may be contained to reduce the brittleness of the glass and improve crack resistance, and also to improve the meltability of the glass. When B2O3 is contained, the content is preferably 0.5% or more, more preferably 1% or more, still more preferably 2% or more. On the other hand, if the content of B2O3 is too high, the acid resistance is likely to deteriorate, so it is preferably 10% or less. The content of B2O3 is more preferably 6% or less, still more preferably 4% or less, and typically 2% or less.

[0040] P2O5 is not essential, but it may be contained to increase the surface compressive stress layer during chemical strengthening. When P2O5 is contained, the content is preferably 0.5% or more, more preferably 1% or more, still more preferably 2% or more. On the other hand, in order to improve acid resistance, the content of P2O5 is preferably 6% or less, more preferably 4% or less, still more preferably 2% or less. In order to prevent the occurrence of veins during melting, it is more preferable not to substantially contain it.

[0041] The total content of B2O3 and P2O5 ([B2O3] + [P2O5]) is preferably 0 to 10%, more preferably 1% or more, still more preferably 2% or more. Also, it is more preferably 6% or less, still more preferably 4% or less.

[0042] La2O3, Nb2O 5、 Ta2O5, Gd2O3 are components that reduce the devitrification growth rate of the glass and improve its meltability, and may be included. When these components are included, their respective contents are preferably 0.1% or more, more preferably 0.2% or more, still more preferably 0.5% or more, particularly preferably 0.8% or more, and typically 1% or more. On the other hand, if these contents are too high, it becomes difficult to increase the surface compressive stress layer during chemical strengthening treatment, so it is preferably 3% or less, more preferably 2% or less, still more preferably 1% or less, and particularly preferably 0.5% or less.

[0043] Since Fe2O3 absorbs heat rays, it has the effect of improving the solubility of the glass. When the glass is mass-produced using a large melting furnace, it is preferably contained. In that case, the content is preferably 0.002% or more, more preferably 0.005% or more, still more preferably 0.007% or more, and particularly preferably 0.01% or more in terms of weight% based on the oxide. On the other hand, if it is contained in excess, coloring occurs. Therefore, in order to enhance the transparency of the glass, it is preferably 0.3% or less, more preferably 0.04% or less, still more preferably 0.025% or less, and particularly preferably 0.015% or less in terms of weight% based on the oxide. Here, all the iron oxides in the glass have been described as Fe2O3, but in reality, Fe(III) in the oxidized state and Fe(II) in the reduced state are usually mixed. Among these, Fe(III) causes yellow coloring, Fe(II) causes blue coloring, and the balance between the two causes green coloring in the glass.

[0044] Furthermore, coloring components may be added within a range that does not inhibit the achievement of the desired chemical strengthening characteristics. Examples of suitable coloring components include Co3O4, MnO2, NiO, CuO, Cr2O3, V2O5, Bi2O3, SeO2, CeO2, Er2O3, Nd2O3, etc. The total content of these coloring components is preferably 5% or less. If it exceeds 5%, the glass may tend to devitrify. This content is more preferably 3% or less, and even more preferably 1% or less. When it is desired to increase the transmittance of the glass, it is preferable that these components are not substantially contained.

[0045] As a fining agent during the melting of the glass, it may appropriately contain SO3, chlorides, fluorides, etc. It is preferably not to contain As2O3. When containing Sb2O3, it is preferably 0.3% or less, more preferably 0.1% or less, and most preferably not to contain it.

[0046] The β-OH value, which is an index of the water content in the glass, is preferably 0.1 mm -1 or more, more preferably 0.15 mm -1 or more, even more preferably 0.2 mm -1 or more, still more preferably 0.22 mm -1 or more, particularly preferably 0.25 mm -1 or more, and most preferably. Glass with a large β-OH value tends to have a low softening point and is prone to bending forming. On the other hand, when the β-OH value of the glass increases, the value of the surface compressive stress (CS) after chemical strengthening treatment becomes small, and it becomes difficult to improve the strength. Therefore, the β-OH value is preferably 0.5 mm -1 or less, more preferably 0.4 mm -1 or less, even more preferably 0.3 mm -1 or less, and even more preferably.

[0047] The temperature (T4) at which the viscosity becomes 10 4 dPa·s is preferably 1300 °C or less, more preferably 1250 °C or less, even more preferably 1200 °C or less, and particularly preferably 1150 °C or less. The temperature (T4) is a reference temperature for the forming temperature of forming the glass into a plate shape, and glass with a high T4 tends to have a high load on the forming equipment. Glass with a low T4 may have poor glass stability, and T4 is usually 900 °C or more, preferably 950 °C or more, more preferably 1000 °C or more, and even more preferably 1050 °C or more.

[0048] Also, the temperature (T2) at which the viscosity becomes 10 2 dPa·s is preferably 1800°C or lower, more preferably 1750°C or lower, even more preferably 1700°C or lower, particularly preferably 1650°C or lower, and typically 1600°C or lower. The temperature (T2) is a reference temperature for the melting temperature of the glass, and the lower T2 is, the easier it is to manufacture the glass. Glass with a low T2 may have poor stability. The T2 of this glass is usually 1400°C or higher, preferably 1450°C or higher.

[0049] The devitrification temperature of this glass is preferably at a temperature (T4 + 120°C) or lower, which is 120°C higher than the temperature (T4) at which the viscosity becomes 10 4 dPa·s, because devitrification is less likely to occur during forming by the float process. The devitrification temperature is more preferably at a temperature or lower that is 100°C higher than T4, even more preferably at a temperature or lower that is 50°C higher than T4, and particularly preferably at or lower than T4. The devitrification temperature of this glass is preferably at a temperature (T2 - 350°C) or lower, which is 350°C lower than the temperature (T2) at which the viscosity becomes 10 2 dPa·s, because devitrification is less likely to occur during melting of the glass. The devitrification temperature is even more preferably at or lower than T2 - 400°C.

[0050] Glass that is less likely to devitrify even in a high-viscosity state may be difficult to enhance even with chemical strengthening treatment. Therefore, the devitrification temperature is preferably at a temperature (T5.5) or higher at which the viscosity becomes 10 5.5 dPa·s, more preferably at a temperature (T5.2) or higher at which the viscosity becomes 10 5.2 dPa·s, and even more preferably at a temperature (T5) or higher at which the viscosity becomes 10 5 dPa·s.

[0051] The devitrification growth rate of this glass at 850 - 1200°C is preferably 600 μm / h or lower, because even if devitrification occurs, it will not grow significantly. The devitrification growth rate at 850 - 1200°C is more preferably 500 μm / h or lower, even more preferably 400 μm / h or lower, and particularly preferably 300 μm / h. Also, the maximum devitrification growth rate at 700 - 1200°C is preferably 600 μm / h or lower. In addition, the devitrification growth rate of this glass at 950°C is preferably 600 μm / h or less, more preferably 500 μm / h or less, still more preferably 400 μm / h or less, and particularly preferably 300 μm / h or less.

[0052] The glass transition point (Tg) is preferably 500°C or higher, more preferably 520°C or higher, still more preferably 540°C or higher, in order to reduce the warp after chemical strengthening. From the viewpoint of easy float forming, it is preferably 750°C or lower, more preferably 700°C or lower, still more preferably 650°C or lower, particularly preferably 600°C or lower, and most preferably 580°C or lower.

[0053] The softening point of this glass is preferably 900°C or lower, more preferably 850°C or lower, still more preferably 820°C or lower, and particularly preferably 790°C or lower. The lower the softening point of the glass, the lower the heat treatment temperature in bending forming, so that not only the energy consumption in the bending forming process is reduced, but also the load on the equipment is reduced. In order to lower the bending forming temperature, the lower the softening point is, the more preferable it is, but in ordinary chemically strengthened glass, it is 700°C or higher. In order to prevent the phenomenon that the stress introduced during the chemical strengthening treatment is relaxed, the softening point is preferably 700°C or higher, more preferably 720°C or higher, still more preferably 740°C or higher. The softening point can be measured by the fiber stretching method described in JIS R3103-1:2001.

[0054] It is preferable that the crystallization peak temperature of this glass is higher than the softening point. Further, it is more preferable that no crystallization peak is observed. The crystallization peak temperature can be measured using a differential scanning calorimeter (DSC) from room temperature to 1000°C at a heating rate of 10°C / min after crushing about 70 mg of the glass, grinding it in an agate mortar.

[0055] The Young's modulus of this glass is preferably 80 GPa or more, more preferably 82 GPa or more, still more preferably 84 GPa or more, and particularly preferably 85 GPa or more because the fragments are less likely to scatter when the glass breaks. Glass with a high Young's modulus may have low acid resistance. The Young's modulus of this glass is, for example, 110 GPa or less, preferably 100 GPa or less, and more preferably 90 GPa or less. The Young's modulus can be measured, for example, by the ultrasonic pulse method.

[0056] The density of this glass is preferably 3.0 g / cm 3 or less, more preferably 2.8 g / cm 3 or less, still more preferably 2.6 g / cm 3 or less, and particularly preferably 2.55 g / cm 3 or less in order to lighten the product. Glass with a low density tends to have low acid resistance and the like. The density of this glass is, for example, 2.3 g / cm 3 or more, preferably 2.4 g / cm 3 or more, and particularly preferably 2.45 g / cm 3 or more.

[0057] The refractive index of this glass is preferably 1.6 or less, more preferably 1.58 or less, still more preferably 1.56 or less, and particularly preferably 1.54 or less in order to reduce the surface reflection of visible light. Glass with a small refractive index tends to have low acid resistance. The refractive index of this glass is, for example, 1.5 or more, preferably 1.51 or more, and more preferably 1.52 or more.

[0058] The photoelastic constant of this glass is preferably 33 nm / cm / MPa or less, more preferably 32 nm / cm / MPa or less, still more preferably 31 nm / cm / MPa or less, and particularly preferably 30 nm / cm / MPa or less in order to reduce optical strain. Also, since glass with a small photoelastic constant tends to have low acid resistance, for example, 24 nm / cm / MPa or more is preferable, more preferably 25 nm / cm / MPa or more, and still more preferably 26 nm / cm / MPa or more.

[0059] The average linear thermal expansion coefficient (thermal expansion coefficient) of this glass at 50 to 350 °C is preferably 95×10 -7 / °C or less, more preferably 90×10 -7 / °C or less, still more preferably 88×10 -7 / °C or less, particularly preferably 86×10 -7 / °C or less, most preferably 84×10 -7 / °C or less. Glass with a small thermal expansion coefficient may be difficult to melt. The thermal expansion coefficient of this glass is, for example, 60×10 -7 / °C or more, preferably 70×10 -7 / °C or more, more preferably 74×10 -7 / °C or more, still more preferably 76×10 -7 / °C or more.

[0060] The fictive temperature of this glass is preferably 80 °C higher than the glass transition point (Tg) (Tg + 80 °C) or lower, more preferably Tg + 50 °C or lower, still more preferably Tg + 40 °C or lower, even more preferably Tg + 30 °C or lower, still more preferably Tg + 20 °C or lower, particularly preferably Tg + 10 °C or lower, in order to increase the surface compressive stress by chemical strengthening. The fictive temperature of glass becomes lower as the cooling rate after melting is smaller when obtaining glass by melting glass raw materials at a high temperature and then cooling. Therefore, in order to obtain glass with a very low fictive temperature, it is necessary to cool it slowly over a long period of time. When cooling the glass slowly, depending on the glass composition, a devitrification phenomenon in which crystals precipitate and grow large during cooling is likely to occur. In order to suppress devitrification during cooling, the fictive temperature is preferably Tg - 30 °C or higher, more preferably Tg - 10 °C or higher, still more preferably Tg or higher, and particularly preferably Tg + 10 °C or higher.

[0061] Note that the fictive temperature of glass can be experimentally determined from the refractive index of the glass. By the method of rapidly cooling the glass held at a certain temperature from that temperature, a plurality of glass pieces with different fictive temperatures but the same glass composition are prepared. Since the fictive temperatures of these glass pieces are the temperatures held before rapid cooling, by measuring the refractive indices of these glass pieces, a calibration curve plotting the refractive index against the fictive temperature can be created. An example is shown in Fig. 1. Even for a glass with unknown cooling rate etc., the fictive temperature can be obtained from the calibration curve by measuring the refractive index. However, since the calibration curve differs when the glass composition is different, it is necessary to use the calibration curve created using glass with the same composition as the glass for which the fictive temperature is desired.

[0062] The fictive temperature of glass depends on the cooling rate when the molten glass is cooled. If the cooling rate is fast, the fictive temperature tends to be high, and if the cooling rate is slow, the fictive temperature tends to be low. Also, the lower the fictive temperature, the greater the surface compressive stress after chemical strengthening tends to be.

[0063] When this glass is a glass plate with a thickness of 0.8 mm and is immersed in sodium nitrate at 450°C for 3 hours and then immersed in potassium nitrate at 450°C for 1.5 hours for two-stage chemical strengthening, it is preferable that the surface compressive stress is 950 MPa or more and the surface compressive stress layer depth is 100 μm or more. The surface compressive stress here is CS2 described later, that is, the surface compressive stress by the Na-K ion exchange layer, and the surface compressive stress layer depth is DOC3 described later, that is, the surface compressive stress layer depth by the Li-Na ion exchange layer.

[0064] When this glass is immersed in sodium nitrate at 450 °C for 1 hour for chemical strengthening, the surface compressive stress value (CS1) is preferably 100 MPa or more, more preferably 150 MPa or more, still more preferably 200 MPa or more, particularly preferably 250 MPa or more, and typically 300 MPa or more. To increase the strength, the larger CS1 is, the better. However, to suppress strengthening cracks in the chemical strengthening treatment process, for example, 600 MPa or less is preferable, more preferably 500 MPa or less, still more preferably 400 MPa or less.

[0065] Also, in this case, the depth of the compressive stress layer (DOC1) is preferably 70 μm or more, more preferably 80 μm or more, still more preferably 90 μm or more, and particularly preferably 100 μm or more. On the other hand, in order to prevent a decrease in yield due to strengthening cracks in the chemical strengthening treatment process, for example, 200 μm or less is preferable, more preferably 150 μm or less, still more preferably 130 μm or less, and particularly preferably 120 μm or less.

[0066] Note that CS1 and DOC1 can be measured using a scattered light photoelastic stress meter (for example, SLP-1000 manufactured by Orihara Seisakusho). Also, it can be measured using a birefringence imaging system Abrio-IM manufactured by Tokyo Instruments Co., Ltd. according to the following procedure. The cross-section of chemically strengthened glass with a size of 10 mm × 10 mm or more and a thickness of about 0.2 to 2 mm is polished in the range of 150 to 250 μm to make it into a thin slice. For the sample thinned to 150 to 250 μm thus obtained, monochromatic light with a wavelength of 546 nm is used as the light source, and measurement is performed with transmitted light. The phase difference (retardation) of the chemically strengthened glass is measured by a birefringence imaging system, and the stress is calculated from the obtained value and the following formula (2). 1.28×F = δ / (C×t’) ··· Formula (2) In formula (2), F is the stress [unit: MPa], δ is the phase difference [unit: nm], C is the photoelastic constant [unit: nm / cm / MPa], and t’ is the thickness of the sample [unit: cm].

[0067] When this glass is immersed in sodium nitrate at 450°C for 3 hours and then immersed in potassium nitrate at 450°C for 1.5 hours for chemical strengthening, the surface compressive stress value CS2 due to the Na-K ion exchange layer is preferably 950 MPa or more, more preferably 1000 MPa or more, still more preferably 1050 MPa or more, even more preferably 1100 MPa or more, and particularly 1150 MPa or more. On the other hand, the upper limit of CS2 is not particularly limited, but when it is desired to minimize the reduction in yield due to strengthening cracks in the chemical strengthening treatment process, it is preferably 1500 MPa or less, more preferably 1300 MPa or less, still more preferably 1200 MPa or less, and particularly preferably 1100 MPa or less. Also, when this glass with a thickness of 0.8 mm is immersed in sodium nitrate at 450°C for 3 hours and then immersed in potassium nitrate at 450°C for 1.5 hours for strengthening, the surface compressive stress layer depth DOC2 due to the Na-K ion exchange layer is preferably 3 μm or more, more preferably 4 μm or more, still more preferably 5 μm or more, even more preferably 7 μm or more, and particularly preferably 9 μm or more. For DOC2 to increase the yield after the strengthening treatment, it is preferably 20 μm or less, more preferably 15 μm or less, still more preferably 8 μm or less, and particularly preferably 6 μm or less. CS2 and DOC2 can be measured, for example, with a surface stress meter FSM-6000 manufactured by Orihara Seisakusho Co., Ltd.

[0068] Also, when this glass is immersed in sodium nitrate at 450°C for 3 hours and then immersed in potassium nitrate at 450°C for 1.5 hours for chemical strengthening, the compressive stress layer depth DOC3 due to the Li-Na ion exchange layer is preferably 100 μm or more, more preferably 110 μm or more, still more preferably 120 μm or more, and particularly preferably 130 μm or more. On the other hand, the upper limit of DOC3 is not particularly limited, but when considering the reduction in yield due to strengthening cracks in the chemical strengthening treatment process, for example, it is preferably 200 μm or less, more preferably 180 μm or less, still more preferably 170 μm or less, and particularly preferably 160 μm or less. When glass with a thickness of 0.8 mm is immersed in sodium nitrate at 450°C for 3 hours and then in potassium nitrate at 450°C for 1.5 hours, the compressive stress value CS3 due to the Li - Na ion exchange layer is preferably 100 MPa or more, more preferably 150 MPa or more, still more preferably 180 MPa or more, and particularly preferably 200 MPa or more. To prevent a reduction in yield due to strengthening cracks, CS3 is preferably 400 MPa or less, more preferably 350 MPa or less, still more preferably 300 MPa or less, and particularly preferably 250 MPa or less. CS3 and DOC3 can be measured by the aforementioned method using a scattered light photoelastic stress meter (for example, SLP - 1000 manufactured by Orihara Seisakusho) or a birefringence imaging system Abrio - IM manufactured by Tokyo Instruments Co., Ltd.

[0069] The chemically strengthened glass of the present invention can be manufactured by a normal method. For example, raw materials of each component of the glass are prepared and heated and melted in a glass melting furnace. Then, the glass is homogenized by a known method, formed into a desired shape such as a glass plate, and gradually cooled. Examples of the glass plate forming method include the float method, the press method, the fusion method, and the down - draw method. In particular, the float method suitable for mass production is preferable. Also, continuous forming methods other than the float method, such as the fusion method and the down - draw method, are also preferable.

[0070] Thereafter, the formed glass is ground and polished as necessary to form a glass substrate. When cutting the glass substrate into a predetermined shape and size or chamfering the glass substrate, if the cutting and chamfering of the glass substrate are performed before the chemically strengthening treatment described later, a compressive stress layer is also formed on the end face by the subsequent chemically strengthening treatment, which is preferable.

[0071] <Chemically Strengthened Glass> The chemically strengthened glass of the present invention has a base composition equal to the glass composition of the above-described glass for chemical strengthening. The surface compressive stress of the chemically strengthened glass of the present invention is preferably 800 MPa or more, more preferably 950 MPa or more, still more preferably 1000 MPa or more, and particularly preferably 1150 MPa or more. Also, the depth of the compressive stress layer is preferably 100 μm or more, more preferably 110 μm or more, still more preferably 120 μm or more, and particularly preferably 130 μm or more.

[0072] The chemically strengthened glass of the present invention can be produced by subjecting a glass plate made of the glass for chemical strengthening of the present invention to a chemical strengthening treatment and then performing washing and drying. The chemical strengthening treatment can be carried out by a known method. In the chemical strengthening treatment, a glass plate is brought into contact with a melt of a metal salt (for example, potassium nitrate) containing metal ions with a large ionic radius (typically, K ions) by immersion or the like, so that metal ions with a small ionic radius in the glass plate (typically, Na ions or Li ions) are replaced with metal ions with a large ionic radius (typically, K ions for Na ions and Na ions for Li ions).

[0073] The chemical strengthening treatment (ion exchange treatment) can be carried out, for example, by immersing a glass plate in a molten salt such as potassium nitrate heated to 360 to 600 °C for 0.1 to 500 hours. The heating temperature of the molten salt is more preferably 375 °C or more and more preferably 500 °C or less. Also, the immersion time of the glass plate in the molten salt is more preferably 0.3 hours or more and more preferably 200 hours or less.

[0074] Examples of the molten salt for performing chemical strengthening treatment include nitrates, sulfates, carbonates, chlorides, etc. Among these, examples of nitrates include lithium nitrate, sodium nitrate, potassium nitrate, cesium nitrate, silver nitrate, etc. Examples of sulfates include lithium sulfate, sodium sulfate, potassium sulfate, cesium sulfate, silver sulfate, etc. Examples of carbonates include lithium carbonate, sodium carbonate, potassium carbonate, etc. Examples of chlorides include lithium chloride, sodium chloride, potassium chloride, cesium chloride, silver chloride, etc. These molten salts may be used alone or in combination of multiple types.

[0075] In the present invention, the treatment conditions of the chemical strengthening treatment are not particularly limited, and appropriate conditions may be selected in consideration of the properties and composition of the glass, the type of the molten salt, and the chemical strengthening characteristics such as the surface compressive stress and the depth of the compressive stress layer desired for the finally obtained chemically strengthened glass.

[0076] Also, in the present invention, the chemical strengthening treatment may be performed only once, or multiple chemical strengthening treatments (multi-stage strengthening) may be performed under two or more different conditions. Here, for example, as the first-stage chemical strengthening treatment, after performing the chemical strengthening treatment under the condition that the DOC is large and the CS is relatively small, as the second-stage chemical strengthening treatment, performing the chemical strengthening treatment under the condition that the DOC is small and the CS is relatively high can increase the CS of the outermost surface of the chemically strengthened glass while suppressing the internal tensile stress area (St), and as a result, the internal tensile stress (CT) can be kept low.

[0077] When the glass for chemical strengthening of the present invention is in a plate shape (glass plate), its plate thickness (t) is, for example, 2 mm or less, preferably 1.5 mm or less, and more preferably 1 mm or less in order to enhance the effect of chemical strengthening. Further, in order to suppress devitrification by increasing the cooling rate during glass plate forming, it is more preferably 0.9 mm or less, particularly preferably 0.8 mm or less, and most preferably 0.7 mm or less. Also, from the viewpoint of obtaining a sufficient strength improvement effect by the chemical strengthening treatment, the plate thickness is, for example, 0.1 mm or more, preferably 0.2 mm or more, more preferably 0.4 mm or more, and still more preferably 0.5 mm or more.

[0078] The shape of this glass may be a shape other than a plate shape according to the product to which it is applied, the application, etc. Also, the glass plate may have a beaded shape with different thicknesses on the outer periphery. The form of the glass plate is not limited to this. For example, the two main surfaces do not have to be parallel to each other, and all or part of one or both of the two main surfaces may be a curved surface. More specifically, the glass plate may be, for example, a flat glass plate without warp, or a curved glass plate having a curved surface.

[0079] This glass is particularly useful as a cover glass for mobile devices such as mobile phones, smartphones, personal digital assistants (PDAs), tablet terminals, etc. Further, it is also suitable as a cover glass for display devices such as televisions (TVs), personal computers (PCs), touch panels, etc. that are not for the purpose of portability, elevator wall surfaces, wall surfaces of buildings such as houses and buildings (full-surface displays), building materials such as window glass, table tops, interior decorations of automobiles and airplanes, etc. and their cover glasses, and also for applications such as enclosures having a curved surface shape.

Examples

[0080] Hereinafter, the present invention will be described by way of examples, but the present invention is not limited thereto. Examples 1 to 3 are comparative examples, and Examples 4 to 11 are examples. Note that for each measurement result in the table, a blank indicates that it was not measured.

[0081] (Fabrication of Chemically Strengthened Glass) Glass plates were fabricated by melting in a platinum crucible so as to have each glass composition expressed as a molar percentage based on oxides shown in Tables 1 and 2. Glass raw materials generally used such as oxides, hydroxides, carbonates or nitrates were appropriately selected and weighed so as to be 1000 g as glass. Next, the mixed raw materials were put into a platinum crucible, charged into a resistance heating type electric furnace at 1500 to 1700 °C and melted for about 3 hours to remove bubbles and homogenize. The obtained molten glass was poured into a mold, held at a temperature of glass transition point + 50 °C for 1 hour, and then cooled to room temperature at a rate of 0.5 °C / min to obtain a glass block. The obtained glass block was cut and ground, and finally both sides were mirror polished to obtain a plate-shaped glass with a length of 50 mm × width of 50 mm × plate thickness of 0.8 mm.

[0082] The physical properties of this glass were evaluated as follows. The results are shown in Tables 1 and 2. <Density> The density (d) was measured by the Archimedes method. The unit is g / cm 3 . <Young's Modulus> For the glass before chemical strengthening, the Young's modulus (E) (unit: GPa) was measured by the ultrasonic pulse method (JIS R1602: 1995).

[0083] <Coefficient of Mean Linear Expansion and Glass Transition Point (Tg)> The coefficient of mean linear expansion (α) (unit: 10 -7 / °C) and the glass transition point (Tg) (unit: °C) at a temperature of 50 to 350 °C were measured according to the method of JIS R3102: 1995 "Test Method for Coefficient of Mean Linear Expansion of Glass". <T2, T4> For the glass before chemical strengthening, the temperature T2 (Tlogη = 2, unit: °C) at which the viscosity becomes 10 2 dPa·s and the temperature T4 (Tlogη = 4, unit: °C) at which the viscosity becomes 10 4 dPa·s were measured by a rotational viscometer (in accordance with ASTM C 965-96).

[0084] <Devitrification Growth Rate> The devitrification growth rate was measured by the following procedure. The glass pieces were crushed and classified in a mortar, and the glass particles that passed through a 3.35 mm mesh sieve and did not pass through a 2.36 mm mesh sieve were washed with ion-exchanged water and dried, and then used for the test. An elongated platinum container (platinum container 1 for devitrification evaluation) having a large number of recesses with a diameter of about 3 mm as shown in Fig. 2 was used. One glass particle 3 was placed in each recess 2, and the surface of the glass particles was heated in an electric furnace at 1000 - 1100 °C until it melted and became smooth. Next, the glass was put into a temperature gradient furnace maintained at a predetermined temperature, heat-treated for a certain time (denoted as T), taken out at room temperature, and rapidly cooled. According to this method, since an elongated container can be installed in the temperature gradient furnace and a large number of glass particles can be heat-treated simultaneously, the maximum devitrification growth rate within a predetermined temperature range can be measured. The glass after heat treatment was observed with a polarized light microscope (manufactured by Nikon Corporation: ECLIPSE LV100ND), and the diameter (denoted as L μm) of the largest crystal among the observed crystals was measured. Observation was carried out under the conditions of a 10-fold eyepiece lens, a 5-fold to 100-fold objective lens, transmitted light, and polarized light observation. Since the crystals due to devitrification can be considered to grow isotropically, the devitrification growth rate is L / (2T) [unit: μm / h]. However, as the crystal to be measured, a crystal that did not precipitate from the interface with the container was selected. The crystal growth at the metal interface has a tendency different from the devitrification growth behavior that occurs inside the glass or at the glass - atmosphere interface.

[0085] <Devitrification test> An appropriate amount of glass particles was placed in a platinum dish with a diameter of 15 - 30 mm and a depth of about 4 mm, and heat-treated at a temperature 20 °C lower than T4 for 17 hours in an electric furnace controlled at a constant temperature. The glass after heat treatment was observed with a polarized light microscope to observe the presence or absence of devitrification.

[0086] <Refractive index> Using a precision refractometer (KPR - 2000 manufactured by Shimadzu Corporation), the refractive index nd at the d line (He light source, wavelength 587.6 nm) was measured. <Photoelastic constant (photoelastic multiplier)> The measurement was carried out using a sodium lamp as the light source, applying mutatis mutandis the disk compression method described in the Journal of the Ceramic Society of Japan, Vol. 87, (1979) No. 1010, p519. The unit is nm / cm / MPa.

[0087] <Chemical strengthening properties> The surface compressive stresses CS1 and CS3 (unit: MPa), and the compressive stress layer depths DOC1 and DOC3 (unit: μm) were measured using a measuring instrument SLP1000 manufactured by Orihara Seisakusho Co., Ltd. The surface compressive stress (CS2) (unit: MPa) and the compressive stress layer depth (DOC2) (unit: μm) were measured using a surface stress meter FSM - 6000 manufactured by Orihara Seisakusho Co., Ltd. In the table, CS1 and DOC1 respectively represent the surface compressive stress and the compressive stress layer depth after one - step chemical strengthening by immersing the obtained chemically strengthened glass in sodium nitrate at 450°C for 1 hour. CS2 and DOC2 respectively represent the surface compressive stress and the compressive stress layer depth due to the Na - K ion - exchange layer after two - step chemical strengthening by immersing the obtained chemically strengthened glass in sodium nitrate at 450°C for 3 hours and then in potassium nitrate at 450°C for 1.5 hours. Also, CS3 and DOC3 respectively represent the surface compressive stress and the compressive stress layer depth due to the Li - Na ion - exchange layer after two - step chemical strengthening by immersing the obtained chemically strengthened glass in sodium nitrate at 450°C for 3 hours and then in potassium nitrate at 450°C for 1.5 hours. CS3 represents the value at a profile depth of 0 μm of the profile obtained by fitting the stress profile of the Li - Na ion - exchange layer measured in a region deeper than 50 μm with an error function. The results are shown in Tables 3 and 4.

[0088]

Table 1

[0089]

Table 2

[0090]

Table 3

[0091]

Table 4

[0092] From Tables 1 to 4, Examples 3 to 11 where X = ([Li2O] + [K2O]) / [Al2O3] is 1.1 or less have a large surface compressive stress (CS2) of 950 MPa or more, as compared with Examples 1 and 2 where X = ([Li2O] + [K2O]) / [Al2O3] is large. Also, it can be seen that Examples 4 to 7 where the total content of CaO and SrO is 1.5 mol% or more are less likely to devitrify, as compared with Example 3 where the total content of CaO and SrO is less than 1.5 mol%.

[0093] Although the present invention has been described in detail with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the present invention. This application is based on a Japanese patent application filed on April 4, 2018 (Japanese Patent Application No. 2018-072487), the content of which is incorporated herein by reference.

Explanation of Signs

[0094] 1 Platinum container for devitrification evaluation 2 Concave portion 3 Glass particles

Claims

1. In terms of molar percentage based on oxides, SiO ２ from 55% to 68%, Al ２ O ３ is 14 to 20%, Li ２ O is 4 to 13%, Na ２ O is 1 to 8%, CaO is 0.5 to 5%, SrO is 0 to 8%, ZrO ２ from 0 to 5%, and B ２ O ３ contains 2 to 10%, B ２ O ３ and P ２ O ５ and the total content thereof is 1 to 10%, Na ２ O and K ２ The total content of O is 0 to 11%, a glass in which the value X represented by the following formula is 0.1 to 1.

1. X = ([Li ２ O] + [K ２ O]) / [Al ２ O ３ ​ However, [Al ２ O ３ , [Li ２ O], [K ２ O] are the contents expressed in mole percentages of the respective components.

2. The glass according to claim 1, wherein the total content of alkaline earth oxides etc. ([MgO] + [CaO] + [SrO] + [BaO] + [ZnO]) is 8% or less. However, [MgO], [CaO], [SrO], [BaO], and [ZnO] are the contents in terms of molar percentage of each component.

3. The glass according to claim 1 or 2, wherein the total content of alkaline earth oxides etc. ([MgO] + [CaO] + [SrO] + [BaO] + [ZnO]) is 1% or more. However, [MgO], [CaO], [SrO], [BaO], and [ZnO] are the contents in terms of molar percentage of each component.

4. [Li ２ O] / ([Na ２ O]+[K ２ O]) is 3 or less, the glass according to any one of claims 1 to 3. However, [Li ２ O], [Na ２ O], [K ２ O] are the contents expressed as the molar percentages of the respective components.

5. The glass according to any one of claims 1 to 4, wherein in terms of molar percentage based on oxides, the total content of MgO, BaO and ZnO is 0 to 5%.

6. The β-OH value is 0.5 mm －１ The glass according to any one of claims 1 to 5, wherein the following conditions are satisfied

7. The β-OH value is 0.1 mm －１ The glass according to any one of claims 1 to 6, wherein the above conditions are satisfied.

8. The temperature (T4) at which the viscosity becomes 10 ４ dPa·s is 1050 to 1300°C, and the glass according to any one of claims 1 to 7.

9. The devitrification temperature is 120 °C higher than the temperature (T4) at which the viscosity becomes 10 ４ dPa·s (T4 + 120 °C) or lower, the glass according to any one of claims 1 to 8.

10. The devitrification temperature is at a temperature (T5.5) or higher at which the viscosity becomes 10 ５．５ dPa·s, for the glass according to any one of claims 1 to 9.

11. The viscosity is 10 ２ The glass according to any one of claims 1 to 10, wherein the temperature (T2) at which the viscosity becomes ２ dPa·s is 1400 to 1800 °C.

12. When a glass plate with a thickness of 0.8 mm is immersed in sodium nitrate at 450 °C for 3 hours and then immersed in potassium nitrate at 450 °C for 1.5 hours for two-stage chemical strengthening, the surface compressive stress is 950 MPa or more and the surface compressive stress layer depth is 100 μm or more. The glass according to any one of claims 1 to 11.

13. A chemically strengthened glass having a compressive stress layer on the surface, wherein the compressive stress layer depth is 100 μm or more, and the glass of the non-ion-exchanged part of the chemically strengthened glass, in terms of molar percentage based on oxides, SiO ２ is 55 to 68%, Al ２ O ３ 14 to 20%, Li ２ O is 4 to 13%, Na ２ O is 1 to 8%, CaO is 0.5 to 5%, SrO is 0 to 8%, ZrO ２ from 0 to 5%, and B ２ O ３ contains 2 to 10%, B ２ O ３ and P ２ O ５ The total content of is 1 to 10%, Na ２ O and K ２ The total content of O is 0 to 11%, and the value X represented by the following formula is 0.1 to 1.

1. Chemically strengthened glass. X = ([Li ２ O] + [K ２ O]) / [Al ２ O ３ ​ However, [Al ２ O ３ , [Li ２ O], [K ２ O] are the contents expressed as molar percentages of the respective components.

14. In the glass of the non-ion-exchanged part of the chemically strengthened glass, the total content of alkaline earth oxides etc. ([MgO] + [CaO] + [SrO] + [BaO] + [ZnO]) is 8% or less. The chemically strengthened glass according to claim 13. However, [MgO], [CaO], [SrO], [BaO], and [ZnO] are the contents in terms of molar percentage of each component.

15. In the glass of the un-ion-exchanged part of the chemically strengthened glass, [Li ２ O] / ([Na ２ O] + [K ２ O]) is 3 or less. The chemically strengthened glass according to claim 13 or 14. However, [Li ２ O], [Na ２ O], [K ２ O] are the contents expressed as molar percentages of the respective components.

16. In the glass of the un-ion-exchanged portion of the chemically strengthened glass, in terms of molar percentage based on oxides, the total content of MgO, BaO, and ZnO is 0 to 5%, and the chemically strengthened glass according to any one of claims 13 to 15.

17. In the glass of the un-ion-exchanged part of the chemically strengthened glass, the β-OH value is 0.5 mm －１ The chemically strengthened glass according to any one of claims 13 to 16, wherein the value is as follows

18. In the glass of the un-ion-exchanged portion of the chemically strengthened glass, the β-OH value is 0.1 mm －１ The chemically strengthened glass according to any one of claims 13 to 17, wherein the value is 0.1 mm or more.

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