Chemically strengthened glass and electronic device housing

Abstract

An object of the present invention is to provide chemically strengthened glass having excellent radio wave transmissivity in a high frequency band and high strength. The present invention relates to chemically strengthened glass having a thickness of t (unit: μm), the relative dielectric constant of the chemically strengthened glass at 20 °C and a frequency of 10 GHz being 7.0 or less, wherein Z obtained by the following formula is 0.65 or more, Z = (S2 - S1) × 10 + X / 1000. In the above formula, S1 is an entropy function calculated from the amount of alkali ions in the central portion of the glass, S2 is an entropy function calculated from the average amount of alkali ions in the region from the glass surface to a depth of 0.05t, and X is the average value of the compressive stress [unit: MPa] in the region from the glass surface to a depth of 0.05t.

Description

Technical Field

[0001] The present invention relates to chemically strengthened glass and a housing for an electronic device. Background Art

[0002] For the housing of an electronic device such as a portable terminal, chemically strengthened glass is widely used because it is required to have a strength such that the portable terminal is not easily broken even when it falls from a height. Chemically strengthened glass is glass in which alkali ions contained in the glass are ion-exchanged with alkali ions having a larger ionic radius contained in a molten salt by a method such as immersing the glass in a molten salt such as sodium nitrate, thereby forming a compressive stress layer in the surface layer portion of the glass. For example, aluminosilicate glass having a specific composition and obtaining a high surface compressive stress by chemical strengthening is disclosed in Patent Document 1.

[0003] On the other hand, in electronic devices such as communication devices such as mobile phones, smartphones, portable information terminals, and Wi-Fi devices, surface acoustic wave (SAW) devices, radar components, and antenna components, the high-frequency of signal frequencies has been developed in order to achieve a large communication capacity and a high communication speed. In recent years, the spread of 5G (fifth-generation mobile communication system) has been expected as a new communication system using a higher-frequency band.

[0004] In a high-frequency band for 5G, the protective glass sometimes hinders the transmission and reception of radio waves, and a protective glass having excellent dielectric properties such as radio wave transmissivity is required for a portable terminal corresponding to 5G. As excellent dielectric properties, for example, a low relative dielectric constant and a low dielectric loss are desired. By reducing the relative dielectric constant, reflection of radio waves can be suppressed and radio wave transmissivity can be improved. In addition, since the dielectric loss is reduced, loss of radio waves can be suppressed.

[0005] As glass having high radio wave transmissivity in a high-frequency band for 5G, that is, glass having a small relative dielectric constant and a small dielectric loss tangent, several kinds of alkali-free glass have been developed so far (Patent Document 2).

[0006] Prior Art Documents

[0007] Patent Documents

[0008] Patent Document 1: Japanese Patent Application Laid-Open No. 2018-520082

[0009] Patent Document 2: WO 2019 / 181707 Summary of the Invention

[0010] Problems to be Solved by the Invention

[0011] However, an alkali-free glass that contains almost no alkali ions as disclosed in Patent Document 2 is difficult to be chemically strengthened. In addition, the radio wave transmissivity of chemically strengthened glass is difficult to predict, and it is difficult to balance the radio wave transmissivity and strength in the high-frequency band.

[0012] Therefore, an object of the present invention is to provide a chemically strengthened glass that has excellent radio wave transmissivity in the high-frequency band and high strength.

[0013] Means for Solving the Problem

[0014] The present inventors found that there are both glasses in which the radio wave transmissivity after chemical strengthening in the high-frequency band decreases compared with that before chemical strengthening and glasses in which the radio wave transmissivity after chemical strengthening increases compared with that before chemical strengthening. In addition, for glasses in which the radio wave transmissivity in the high-frequency band increases after chemical strengthening, the correlation between the surface properties after chemical strengthening and the radio wave transmissivity was found, and thus the present invention was completed.

[0015] The present invention provides a chemically strengthened glass having a thickness of t (unit: μm), and the relative permittivity of the chemically strengthened glass at 20 °C and a frequency of 10 GHz is 7.0 or less, wherein

[0016] Z calculated by the following formula is 0.65 or more,

[0017] Z = (S2 - S1) × 10 + X / 1000

[0018] In the above formula,

[0019] S1 is the entropy function calculated from the amount of alkali ions in the central part of the glass,

[0020] S2 is the entropy function calculated from the average amount of alkali ions in the region from the glass surface to a depth of 0.05t,

[0021] X is the average value of the compressive stress in the region from the glass surface to a depth of 0.05t [unit: MPa],

[0022] wherein the entropy function S is calculated by the following formula from the contents [Li2O], [Na2O], and [K2O] in terms of the molar percentage based on the oxide of Li2O, Na2O, and K2O at each depth. In the following formula, when [Li2O], [Na2O], and [K2O] are zero, the entropy function S is 1 × 10 -4 .

[0023] S = -[Li2O] / ([Li2O] + [Na2O] + [K2O]) log([Li2O] / ([Li2O] + [Na2O] + [K2O])) - [Na2O] / ([Li2O] + [Na2O] + [K2O]) log([Na2O] / ([Li2O] + [Na2O] + [K2O])) - [K2O] / ([Li2O] + [Na2O] + [K2O]) log([K2O] / ([Li2O] + [Na2O] + [K2O])).

[0024] In the chemically strengthened glass of the present invention (hereinafter, also referred to as the present chemically strengthened glass), the value obtained by subtracting the above entropy function S1 from the above entropy function S2, that is, the value of (S2 - S1), is preferably 0.04 or more.

[0025] The dielectric loss tangent of the present chemically strengthened glass at 20 °C and a frequency of 10 GHz is preferably 0.02 or less.

[0026] In terms of molar percentage based on oxides, the basic composition of the present chemically strengthened glass preferably contains:

[0027] 40% to 80% of SiO2,

[0028] 0 to 20% of B2O3,

[0029] 1% to 25% of Al2O3, and

[0030] A total of 5% to 30% of Li2O and / or Na2O.

[0031] The surface compressive stress value CS0 of the present chemically strengthened glass is preferably 300 MPa or more.

[0032] The internal chemical strengthening stress CS at a depth of 0.05t measured from the glass surface of the present chemically strengthened glass 0.05t is 75 MPa or more, and the above thickness t is 300 μm or more.

[0033] The depth of the compressive stress layer DOL of the present chemically strengthened glass is preferably 70 μm or more, and the above thickness t is 350 μm or more.

[0034] The present chemically strengthened glass is preferably a lithium aluminosilicate glass,

[0035] In terms of molar percentage based on oxides, the basic composition of the chemically strengthened glass contains:

[0036] 40% to 70% of SiO2,

[0037] 7.5% to 20% of Al2O3, and

[0038] 5% to 25% of Li2O.

[0039] Preferably, the thickness t of the chemically strengthened glass is 100 μm or more and 2000 μm or less.

[0040] Preferably, the chemically strengthened glass is a glass-ceramic.

[0041] The present invention also provides an electronic device housing including the chemically strengthened glass.

[0042] Advantageous Effects of the Invention

[0043] In the chemically strengthened glass of the present invention, the Z value obtained by the formula represented by the entropy function S indicating the mixing degree of alkali metal ions and the average value X of the compressive stress is within a specific range, and the movement of alkali metal ions in the glass is suppressed. As a result, the chemically strengthened glass of the present invention exhibits excellent strength and excellent radio wave transmissivity in the high frequency band. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 A graph showing the correlation between the change amount of the sum of the relative dielectric constant and the dielectric loss tangent, which are important in the radio wave transmissivity at a frequency of 10 GHz, before and after chemical strengthening, and the entropy function and the compressive stress. The vertical axis represents the sum of 100 times the values of the relative dielectric constant and the dielectric loss tangent that change before and after chemical strengthening, and the horizontal axis represents the parameter Z that can be calculated from the entropy function and the compressive stress before and after chemical strengthening. The radio wave transmissivity is determined by both the relative dielectric constant and the dielectric loss tangent. However, since the absolute value of the relative dielectric constant is larger than the absolute value of the dielectric loss tangent and the effect is also higher, the radio wave transmissivity is represented by the sum of 100 times the relative dielectric constant and the dielectric loss tangent. DETAILED DESCRIPTION OF THE INVENTION

[0045] In this specification, "~" indicating a numerical range is used to mean including the numerical values described before and after it as the lower limit value and the upper limit value. Unless otherwise specified, "~" is used with the same meaning hereinafter in this specification.

[0046] In this specification, "chemically strengthened glass" refers to glass after chemical strengthening treatment, and "glass for chemical strengthening" refers to glass before chemical strengthening treatment.

[0047] In this specification, "basic composition of the chemically strengthened glass" refers to the glass composition of the glass for chemical strengthening. In the chemically strengthened glass, except in the case of extreme ion exchange treatment, the glass composition at a depth of 1 / 2 of the thickness t is the basic composition of the chemically strengthened glass.

[0048] In this specification, unless otherwise specified, the glass composition is expressed in terms of molar percentages on an oxide basis, and "mol%" is abbreviated as "%".

[0049] In addition, in this specification, "substantially free of" means below the impurity level contained in raw materials, etc., that is, not intentionally contained. Specifically, for example, less than 0.1 mol%.

[0050] In this specification, the "stress distribution" is a graph representing the compressive stress value with the depth measured from the glass surface as a variable. In addition, the "depth of the compressive stress layer (DOL)" is the depth at which the compressive stress value (CS) is zero. The "internal tensile stress value (CT)" refers to the tensile stress value at a depth of 1 / 2 of the glass thickness t. In this specification, the tensile stress value is expressed in the form of a negative compressive stress value.

[0051] The stress distribution in this specification can be measured using a scattered light photoelastic stress meter (for example, manufactured by Orihara Seisakusho, SLP-1000). The scattered light photoelastic stress meter is affected by surface scattering, and sometimes the measurement accuracy near the specimen surface decreases. However, for example, in the case where compressive stress is generated only by the ion exchange of lithium ions in the glass with sodium ions outside, since the compressive stress value expressed as a function of depth follows the complementary error function, by measuring the internal stress value, the surface stress value can be known. In cases where it does not follow the complementary error function, etc., the surface part can be measured by other methods, such as a method using a surface stress meter.

[0052] <Chemically strengthened glass>

[0053] The chemically strengthened glass of the present invention is a chemically strengthened glass with a thickness of t (unit: μm) and a relative dielectric constant of 7.0 or less at a frequency of 10 GHz, wherein Z calculated by the following formula is 0.65 or more. Z = (S2 - S1) × 10 + X / 1000. In the above formula, S1 is the entropy function calculated from the alkali ion amount in the central part of the glass, S2 is the entropy function calculated from the average alkali ion amount in the region from the glass surface to a depth of 0.05t, and X is the average value of the compressive stress [unit: MPa] in the region from the glass surface to a depth of 0.05t.

[0054] Here, the entropy function S is calculated by the following formula from the contents [Li2O], [Na2O], and [K2O] in terms of molar percentages on an oxide basis of Li2O, Na2O, and K2O at each depth. In the following formula, when [Li2O], [Na2O], and [K2O] are zero, the entropy function S is 1×10 -4 。

[0055] S = -[Li2O] / ([Li2O] + [Na2O] + [K2O]) log([Li2O] / ([Li2O] + [Na2O] + [K2O])) - [Na2O] / ([Li2O] + [Na2O] + [K2O]) log([Na2O] / ([Li2O] + [Na2O] + [K2O])) - [K2O] / ([Li2O] + [Na2O] + [K2O]) log([K2O] / ([Li2O] + [Na2O] + [K2O]))

[0056] Conventionally, the radio wave transmissivity of chemically strengthened glass changes with frequency, so it is difficult to predict and it is difficult to balance the radio wave transmissivity and strength in the high-frequency band. The present inventors focused on the relationship between the radio wave transmissivity in the high-frequency band and chemical strengthening, and found that there are glasses in which the radio wave transmissivity in the high-frequency band increases after chemical strengthening compared with before chemical strengthening and glasses in which the radio wave transmissivity in the high-frequency band decreases.

[0057] In addition, the present inventors believe that the glass in which the radio wave transmissivity in the high-frequency band increases after chemical strengthening compared with before chemical strengthening has the following two characteristics: 1) the mixing degree of alkali ions changes significantly before and after chemical strengthening; 2) a high compressive stress is introduced after chemical strengthening. Hereinafter, the characteristics of 1) and 2) will be described.

[0058] Due to the decrease in relative permittivity and dielectric loss, the radio wave transmissivity increases. Since the relative permittivity and dielectric loss are mainly caused by the movement of alkali metal ions in the glass, it is considered that by chemically strengthening the treatment to inhibit the movement of alkali metal ions in the glass, the relative permittivity and dielectric loss can be reduced.

[0059] Regarding the above 1) the mixing degree of alkali ions changes significantly before and after chemical strengthening, it is considered that by having and mixing different types of alkali metal ions in the glass, the exchange between alkali metal ions is not likely to occur, so that the relative permittivity and dielectric loss are reduced and the dielectric properties are improved. The mixing degree of alkali metal ions is represented by an entropy function.

[0060] Regarding the above 2) a high compressive stress is introduced after chemical strengthening, it is considered that when the compressive stress is strong, the movement of alkali metal ions is inhibited, so that the relative permittivity and dielectric loss are reduced and the dielectric properties are improved.

[0061] Figure 1 A graph showing the relationship between the change amounts before and after chemical strengthening of the total value of the relative permittivity and the tangent of the dielectric loss angle, which are important for the radio wave transmissivity at a frequency of 10 GHz of the glass in which the radio wave transmissivity increases after chemical strengthening compared with before chemical strengthening, and the entropy function and the compressive stress in Experimental Example 1 described later. Figure 1The vertical axis is the total value of 100 times the relative permittivity and the tangent of the dielectric loss angle that have changed before and after chemical strengthening, and the horizontal axis is the parameter Z that can be calculated from the entropy function and the compressive stress before and after chemical strengthening. It should be noted that the radio wave transmissivity is determined by both the relative permittivity and the tangent of the dielectric loss angle. However, since the absolute value of the relative permittivity is larger than the absolute value of the tangent of the dielectric loss angle and the effect is also higher, the radio wave transmissivity is represented by the total value of 100 times the change amount of the relative permittivity and the change amount of the tangent of the dielectric loss angle. The details of Experimental Example 1 will be described later.

[0062] The content of the alkali metal ions used to calculate the entropy function was measured using EPMA (Electron Probe MicroAnalyzer, manufactured by JEOL Ltd.: JXA-8500F). As the measurement conditions of EPMA, the acceleration voltage was set to 15 kV, the probe current was set to 30 nA, the accumulation time was set to 1000 milliseconds per point, and the interval was set to 1 μm.

[0063] According to Figure 1 It can be seen that when Z represented by the above formula [Z = (S2 - S1) × 10 + X / 1000] is 0.65 or more, compared with before chemical strengthening, the movement of alkali metal ions is suppressed after chemical strengthening, and excellent radio wave transmissivity is shown in the high-frequency band.

[0064] By chemical strengthening, compared with before chemical strengthening, the movement of alkali metal ions is suppressed and the radio wave transmissivity is improved after chemical strengthening, and these can be evaluated by the change amount of the relative permittivity caused by chemical strengthening and the change amount of the dielectric loss caused by chemical strengthening.

[0065] Specifically, for example, the value obtained by subtracting the "relative permittivity at 20 °C and 10 GHz after chemical strengthening" from the "relative permittivity at 20 °C and 10 GHz before chemical strengthening" is preferably 0 or more, more preferably 0.02 or more, further preferably 0.04 or more, still further preferably 0.06 or more, particularly preferably 0.08 or more, further preferably 0.1 or more, and most preferably 0.12 or more. By making the relative permittivity of the glass after chemical strengthening decrease by 0 or more compared with before chemical strengthening, it can be evaluated that the relative permittivity is reduced by chemical strengthening and the radio wave transmissivity is improved.

[0066] In addition, for example, the value obtained by subtracting the "dielectric loss tangent at 20°C and 10 GHz before chemical strengthening" from the "dielectric loss tangent at 20°C and 10 GHz after chemical strengthening" is preferably 0 or more, more preferably 0.001 or more, further preferably 0.002 or more, still further preferably 0.003 or more, and particularly preferably 0.004 or more. By making the dielectric loss tangent of the glass after chemical strengthening decrease by 0 or more compared to before chemical strengthening, it can be evaluated that the dielectric loss is reduced and the radio wave transmissivity is improved by chemical strengthening.

[0067] In the high-frequency band, in cases such as circuit design of a glass substrate, the dielectric properties of the glass, particularly the dielectric properties of the glass surface layer, are particularly important. In the high-frequency band, the relative dielectric constant and dielectric loss tangent of the surface of the glass plate of the chemically strengthened glass of the present invention are smaller than those of the interior of the glass, so radio waves can be effectively transmitted, and the dielectric properties of the glass surface layer are excellent.

[0068] Z represented by the above formula [Z = (S2 - S1) × 10 + X / 1000] is 0.65 or more, preferably 0.7 or more, more preferably 0.8 or more, further preferably 0.9 or more, still further preferably 1.0 or more, particularly preferably 1.25 or more, further preferably 1.5 or more, and most preferably 2.0 or more. By making Z 0.65 or more, the movement of alkali metal ions after chemical strengthening is suppressed, and excellent radio wave transmissivity is exhibited in the high-frequency band. The value of Z can be adjusted by the composition of the glass for chemical strengthening and the chemical strengthening treatment conditions (molten salt composition, time, temperature, etc.).

[0069] In the above formula, S1 is the entropy function calculated from the amount of alkali ions in the central part of the glass, and S2 is the entropy function calculated from the average amount of alkali ions in the region from the glass surface to a depth of 0.05t.

[0070] Although there is no particular limitation on the value of S1, the lower S1 is, the better the chemical strengthening characteristics can be obtained. Therefore, the value of S1 is, for example, preferably 0.375 or less, more preferably 0.35 or less, further preferably 0.325 or less, still further preferably 0.30 or less, particularly preferably 0.25 or less, further preferably 0.20 or less, and most preferably 0.15 or less. On the other hand, when S1 is too low, the relative dielectric constant and dielectric loss tangent cannot be reduced even by chemical strengthening, so it is preferably 0.0 or more.

[0071] Although there is no particular limitation on the value of S2, the higher S2 is, the lower the relative dielectric constant and the tangent of the dielectric loss angle of the chemically strengthened glass are likely to be, and the better the radio wave transmissivity is likely to be obtained after chemical strengthening. Therefore, the value of S2 is preferably 0.2 or more, more preferably 0.25 or more, further preferably 0.3 or more, still further preferably 0.35 or more, particularly preferably 0.40 or more, and further preferably 0.45 or more. On the other hand, when S2 is too high, sufficient chemical strengthening stress cannot be introduced. Therefore, the value of S2 is preferably 0.5 or less, more preferably 0.49 or less, further preferably 0.48 or less, still further preferably 0.47 or less, particularly preferably 0.46 or less.

[0072] Although there is no particular limitation on the value obtained by subtracting S1 from S2, that is, (S2 - S1), the higher (S2 - S1) is, the more the relative dielectric constant and the tangent of the dielectric loss angle can be reduced after chemical strengthening. Therefore, (S2 - S1) is preferably 0.04 or more, more preferably 0.05 or more, further preferably 0.1 or more, still further preferably 0.15 or more, particularly preferably 0.2 or more, and further preferably 0.25 or more, and most preferably 0.3 or more. On the other hand, when the value obtained by subtracting S1 from S2 is too high, sufficient chemical strengthening stress cannot be introduced. Therefore, (S2 - S1) is preferably 0.5 or less, more preferably 0.48 or less, further preferably 0.46 or less, still further preferably 0.44 or less, particularly preferably 0.42 or less, and further preferably 0.40 or less, and most preferably 0.38 or less.

[0073] By making S1 and S2 within the above ranges, the mixing degree of alkali metal ions caused by chemical strengthening can be increased, thereby suppressing the movement of alkali metal ions in the glass surface layer and improving the radio wave transmissivity in the high-frequency band. S1 and S2 can be adjusted by the composition of the glass for chemical strengthening and the chemical strengthening treatment conditions (molten salt composition, time, temperature, etc.).

[0074] In the above formula, X is the average value of the compressive stress in the region from the glass surface to a depth of 0.05t [unit: MPa]. Although there is no particular limitation on the value of X, for example, it is preferably 100 MPa or more, more preferably 150 MPa or more, further preferably 200 MPa or more, still further preferably 250 MPa or more, particularly preferably 275 MPa or more, further preferably 300 MPa or more, and most preferably 320 MPa or more. By setting X within the above range, a high compressive stress can be introduced into the glass surface layer, thereby suppressing the movement of alkali metal ions in the glass surface layer and improving the dielectric properties in the high-frequency band. On the other hand, when the value of X is too high, it explodes and breaks in the form of small pieces when the glass is broken, so the value of X is preferably 600 MPa or less, more preferably 500 MPa or less, further preferably 475 MPa or less, still further preferably 450 MPa or less, particularly preferably 425 MPa or less, further preferably 400 MPa or less, and most preferably 375 MPa or less. The value of X can be adjusted by the composition of the glass for chemical strengthening and the chemical strengthening treatment conditions (molten salt composition, time, temperature, etc.).

[0075] This chemically strengthened glass is preferably plate-shaped. In addition, the glass plate may have a border shape with different peripheral thicknesses, etc. In addition, the form of the glass plate is not limited to this. For example, the two main surfaces may not be parallel to each other. In addition, all or part of one or both of the two main surfaces may be a curved surface. More specifically, the glass plate can be, for example, a flat glass plate without warping, or a curved glass plate with a curved surface.

[0076] From the viewpoint of improving the effect of chemical strengthening, its thickness (t) is, for example, 2000 μm or less, preferably 1500 μm or less, more preferably 1000 μm or less, further preferably 900 μm or less, particularly preferably 800 μm or less, and most preferably 700 μm or less. In addition, from the viewpoint of obtaining a sufficient strength improvement effect through chemical strengthening treatment, the thickness is, for example, 100 μm or more, preferably 200 μm or more, more preferably 300 μm or more, further preferably 350 μm or more, still further preferably 400 μm or more, and particularly preferably 500 μm or more.

[0077] The shape of this chemically strengthened glass can be a shape other than plate-shaped according to the applicable products, uses, etc.

[0078] The relative dielectric constant of this chemically strengthened glass at 20°C and a frequency of 10 GHz is 7.0 or less, preferably 6.9 or less, more preferably 6.8 or less, further preferably 6.7 or less, still further preferably 6.6 or less, particularly preferably 6.5 or less, further preferably 6.4 or less, and most preferably 6.3 or less. By having a small relative dielectric constant, it is possible to suppress the loss of radio waves caused by reflection at the glass surface, and thus the radio wave transmissivity is likely to be good. On the other hand, when the relative dielectric constant is too low, it will result in insufficient chemical strengthening stress being imparted to the glass. Therefore, the relative dielectric constant at 20°C and a frequency of 10 GHz is preferably 4.0 or more, more preferably 4.2 or more, further preferably 4.4 or more, still further preferably 4.6 or more, particularly preferably 4.8 or more, further preferably 5.0 or more, and most preferably 5.2 or more. The relative dielectric constant can be measured by using a network analyzer and the split post dielectric resonator method (SPDR method) for the value at 20°C and a frequency of 10 GHz.

[0079] The dielectric loss tangent (tanδ) of this chemically strengthened glass at 20°C and a frequency of 10 GHz is preferably 0.02 or less, more preferably 0.018 or less, further preferably 0.016 or less, still further preferably 0.014 or less, particularly preferably 0.012 or less, further preferably 0.011 or less, and most preferably 0.010 or less. By having a small dielectric loss tangent, it is possible to suppress the loss of radio waves when passing through the glass interior, and thus the radio wave transmissivity is likely to be good. On the other hand, when the dielectric loss tangent is too low, it will result in insufficient chemical strengthening stress being imparted to the glass. Therefore, it is preferably 0.001 or more, more preferably 0.002 or more, further preferably 0.003 or more, still further preferably 0.004 or more, particularly preferably 0.005 or more, further preferably 0.006 or more, and most preferably 0.007 or more. The dielectric loss tangent (tanδ) can be measured by using a network analyzer and the split post dielectric resonator method (SPDR method) for the value at 20°C and a frequency of 10 GHz.

[0080] It should be noted that by making the values of the relative dielectric constant and the dielectric loss tangent at 20°C and a frequency of 10 GHz approach the values of the relative dielectric constant and the dielectric loss tangent at higher frequencies respectively, reducing the frequency dependence (dielectric dispersion), the frequency characteristics of the dielectric properties are less likely to change, and when the frequencies during use are different, the design changes can also be small. Therefore, this is preferred. The relative dielectric constant and the dielectric loss tangent can be adjusted according to the composition of the glass and the chemical strengthening conditions.

[0081] This chemically strengthened glass can reduce the relative dielectric constant and the tangent of the dielectric loss angle at a frequency of 10 GHz because the alkali content in the glass composition is appropriately adjusted. Generally, in the frequency range of about 10 GHz to about 40 GHz, the frequency dependence of the relative dielectric constant and the tangent of the dielectric loss angle of the glass is small. Therefore, this chemically strengthened glass with excellent dielectric properties at a frequency of 10 GHz also has excellent radio wave transmissibility even in frequency bands such as 28 GHz and 35 GHz used for 5G.

[0082] It should be noted that the relative dielectric constant and the tangent of the dielectric loss angle can be measured by the split post dielectric resonator method (SPDR method) using a network analyzer.

[0083] This chemically strengthened glass is obtained by chemically strengthening the glass for chemical strengthening or the glass-ceramics described below. That is, the basic composition of this chemically strengthened glass is the same as the glass composition of the glass for chemical strengthening described below, and the preferred composition ranges are also the same. In addition, the average composition of this chemically strengthened glass is the same as the composition of the glass for chemical strengthening or the glass-ceramics described below. Here, the average composition refers to the composition obtained by finely pulverizing a glass sample after heat treatment in a glass state and then analyzing the obtained sample.

[0084] The internal chemical strengthening stress CS of this chemically strengthened glass 0.05t is preferably 100 MPa or more, more preferably 150 MPa or more, further preferably 200 MPa or more, still more preferably 225 MPa or more, and particularly preferably 250 MPa or more. In addition, when the surface compressive stress value CS0 is preferably 300 MPa or more, more preferably 400 MPa or more, further preferably 500 MPa or more, excellent strength can be easily obtained. In addition, the compressive stress value CS at a depth of 50 μm from the surface 50 also tends to be large, so it is preferred.

[0085] The larger the surface compressive stress value CS0, the higher the strength. However, when the surface compressive stress value CS0 is too large, a large tensile stress is generated inside the chemically strengthened glass, which may cause damage. Therefore, the surface compressive stress value CS0 is preferably 1000 MPa or less, more preferably 800 MPa or less.

[0086] In the stress distribution of this chemically strengthened glass, the compressive stress value CS at a depth of 50 μm from the surface 50 is preferably 75 MPa or more, more preferably 90 MPa or more, further preferably 100 MPa or more, and particularly preferably 125 MPa or more. Due to the large CS 50 the chemically strengthened glass is not easily broken when damaged by falling from a height or the like.

[0087] The internal tensile stress value CT of this chemically strengthened glass is preferably 80 MPa or less, more preferably 75 MPa or less. Since CT is small, breakage is less likely to occur. The internal tensile stress value CT is preferably 50 MPa or more, more preferably 60 MPa or more, and further preferably 65 MPa or more. By having CT above the above values, the compressive stress near the surface becomes larger and the strength becomes higher.

[0088] When the depth of the compressive stress layer DOL of this chemically strengthened glass is too large relative to the thickness t, it causes an increase in CT. Therefore, the depth of the compressive stress layer DOL is preferably 0.25t or less, more preferably 0.2t or less, further preferably 0.19t or less, and even more preferably 0.18t or less. Additionally, from the perspective of improving strength, DOL is preferably 0.06t or more, more preferably 0.08t or more, further preferably 0.10t or more, and particularly preferably 0.12t or more.

[0089] Specifically, for example, when the thickness t is 700 μm, DOL is preferably 140 μm or less, more preferably 133 μm or less. Additionally, DOL is preferably 70 μm or more, more preferably 80 μm or more, and further preferably 90 μm or more. It should be noted that the preferred thickness (t) and the preferred shape of this chemically strengthened glass are the same as the preferred thickness (t) and shape of the above-mentioned glass.

[0090] In order to be less likely to break, the Young's modulus of this chemically strengthened glass is preferably 50 GPa or more, more preferably 80 GPa or more, and further preferably 85 GPa or more. There is no particular limitation on the upper limit of the Young's modulus, but sometimes the acid resistance of glass with a high Young's modulus decreases. Therefore, the Young's modulus 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 by, for example, the ultrasonic pulse method.

[0091] The four-point bending strength of this chemically strengthened glass is preferably 350 MPa or more, more preferably 400 MPa or more, and further preferably 450 MPa or more. There is no particular limitation on the upper limit of the four-point bending strength, and typically it is 1000 MPa or less. The four-point bending strength can be measured by the method specified in JIS R1601:2008.

[0092] The Vickers hardness of the surface of this chemically strengthened glass is preferably 4.4 GPa or more, more preferably 4.8 GPa or more, and further preferably 5.2 GPa or more. There is no particular limitation on the upper limit of the Vickers hardness, and typically it is 9.0 GPa or less. The Vickers hardness is the Vickers hardness (HV0.1) specified in JIS R1610:2003.

[0093] The thermal conductivity of this chemically strengthened glass is preferably 2.0 W / m°C or less, more preferably 1.8 W / m°C or less, and still more preferably 1.5 W / m°C or less. There is no particular limitation on the lower limit of the thermal conductivity, and typically it is 0.8 W / m°C or more.

[0094] This chemically strengthened glass is particularly useful as a protective glass for use in mobile devices such as mobile phones, smartphones, portable information terminals (PDAs), tablet terminals, etc. In addition, it is also useful as a protective 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 (full-screen displays) of buildings such as houses and buildings, building materials such as window glass, table tops, interior fittings of automobiles or airplanes, etc., their protective glasses, and in applications such as cases with a curved surface shape that is not plate-shaped through bending processing and forming.

[0095] <Manufacturing method of chemically strengthened glass>

[0096] This chemically strengthened glass can be manufactured by chemically strengthening the glass for chemical strengthening (hereinafter also referred to as "this glass for chemical strengthening") described below.

[0097] 《Glass for chemical strengthening》

[0098] This glass for chemical strengthening is preferably any one of soda-lime glass, alkali aluminosilicate glass, and alkali aluminoborosilicate glass. These glasses are suitable for chemical strengthening treatment.

[0099] This glass for chemical strengthening is more preferably lithium aluminosilicate glass. Since lithium aluminosilicate glass contains lithium ions which are alkali ions with the smallest ionic radius, through chemical strengthening treatment by ion exchange using various molten salts, it is easy to obtain a chemically strengthened glass with a preferred stress distribution and excellent strength.

[0100] Specifically, this glass for chemical strengthening preferably contains:

[0101] 40% to 80% of SiO2,

[0102] 0 to 20% of B2O3,

[0103] 1% to 25% of Al2O3 and

[0104] A total of 5% to 30% of Li2O and / or Na2O.

[0105] As lithium aluminosilicate glass, it preferably contains

[0106] 40% to 70% of SiO2,

[0107] 7.5% to 20% of Al2O3 and

[0108] 5% to 25% of Li2O

[0109] lithium aluminosilicate glass

[0110] Hereinafter, the preferred composition of the glass for chemical strengthening will be further described.

[0111] SiO2 is a component that constitutes the network of the glass. In addition, SiO2 is a component that improves chemical durability, and SiO2 is a component that reduces the generation of cracks when the glass surface is damaged.

[0112] In order to improve chemical durability, the content of SiO2 is preferably 40% or more, more preferably 50% or more, further preferably 55% or more, still further preferably 56% or more, particularly preferably 63% or more, and most preferably 65% or more. In order to improve the meltability during glass manufacturing, the content of SiO2 is preferably 80% or less, more preferably 75% or less, further preferably 70% or less, particularly preferably 68% or less, and most preferably 65% or less.

[0113] Al2O3 is an effective component that improves the ion exchange performance during chemical strengthening and increases the surface compressive stress after strengthening.

[0114] In order to improve chemical durability, and in addition, in order to improve chemical strengthening characteristics, the content of Al2O3 is preferably 1% or more, preferably 3% or more, more preferably 5% or more, further preferably 7% or more, still further preferably 9.1% or more, still further preferably 10% or more, particularly preferably 11% or more, and most preferably 12% or more. On the other hand, when the content of Al2O3 is too high, crystals tend to grow easily during melting. In order to prevent the reduction in the yield caused by devitrification defects, the content of Al2O3 is preferably 25% or less, more preferably 23% or less, further preferably 21% or less, particularly preferably 20% or less, and most preferably 19% or less.

[0115] Both SiO2 and Al2O3 are components that stabilize the structure of the glass. In order to reduce brittleness, the total content of SiO2 and Al2O3 is preferably 57.5% or more, more preferably 65% or more, further preferably 75% or more, still further preferably 77% or more, particularly preferably 79% or more.

[0116] Both SiO2 and Al2O3 tend to increase the melting temperature of the glass. Therefore, in order to facilitate melting, their total content is preferably 95% or less, more preferably 90% or less, further preferably 87% or less, still further preferably 85% or less, particularly preferably 82% or less.

[0117] Li2O is a component that forms surface compressive stress through ion exchange and is a component that improves the fusibility of glass. By chemically strengthening glass containing Li2O, a stress distribution with a large surface compressive stress and a large compressive stress layer can be obtained by the method of ion-exchanging Li ions on the glass surface with Na ions and further ion-exchanging Na ions with K ions.

[0118] In order to increase the surface compressive stress during chemical strengthening, the content of Li2O is preferably 5% or more, more preferably 6.5% or more, further preferably 7.1% or more, particularly preferably 7.5% or more, and most preferably 8% or more.

[0119] On the other hand, when the content of Li2O is excessive, the crystal growth rate during glass forming becomes large, and the problem of reduced yield caused by devitrification defects sometimes becomes large. In order to suppress devitrification in the glass manufacturing process, the content of Li2O is preferably 18% or less, more preferably 16% or less, further preferably 15% or less, still further preferably 14% or less, and particularly preferably 12% or less. In addition, when the content of alkali ions is excessive, the radio wave transmissivity is likely to decrease. Therefore, from the viewpoint of improving the radio wave transmissivity, the content of Li2O is preferably 12% or less, more preferably 10% or less, and further preferably 9% or less.

[0120] From the viewpoint of facilitating glass forming, the total of Li2O and / or Na2O is preferably 5% or more, more preferably 7.5% or more, and further preferably 10% or more. In addition, from the viewpoint of making the glass insoluble in water, etc., the total of Li2O and / or Na2O is preferably 30% or less, more preferably 25% or less, and further preferably 20% or less.

[0121] Neither Na2O nor K2O is essential, but both are components that improve the fusibility of glass and reduce the crystal growth rate of glass. In order to improve the ion exchange performance, it is preferable to contain Na2O and K2O.

[0122] Na2O is a component that forms a surface compressive stress layer in the chemical strengthening treatment using potassium salts and is a component that can improve the fusibility of glass. In order to obtain this effect, the content of Na2O is preferably 1.5% or more, more preferably 2.5% or more, further preferably 3% or more, still further preferably 3.6% or more, and particularly preferably 4% or more. On the other hand, when the content of Na2O is excessive, it is difficult to increase the compressive stress in a relatively deep part starting from the surface by chemical strengthening. Therefore, the content of Na2O is preferably 10% or less, more preferably 7% or less, further preferably 5% or less, and still further preferably 3% or less.

[0123] K2O may be contained for the purpose of suppressing devitrification in the glass manufacturing process. When K2O is contained, the content of K2O is preferably 0.1% or more, more preferably 0.15% or more, and particularly preferably 0.2% or more. In order to further prevent devitrification, the content of K2O is preferably 0.5% or more, more preferably 1.2% or more. On the other hand, since a large amount of K is contained, it becomes the main cause of reduced brittleness and reduced surface stress due to reverse ion exchange during strengthening. Therefore, the content of K2O is preferably 4% or less, more preferably 3% or less, further preferably 2% or less, still further preferably 1% or less, and particularly preferably 0.5% or less.

[0124] In order to improve the meltability of the glass, the total content of Na2O and K2O ([Na2O]+[K2O]) is preferably 2% or more, more preferably 2.5% or more, further preferably 3% or more, and particularly preferably 3.5% or more. When ([Na2O]+[K2O]) is excessive, a decrease in the surface compressive stress value is likely to occur. Therefore, ([Na2O]+[K2O]) is preferably 10% or less, more preferably 8% or less, further preferably 7% or less, and particularly preferably 6% or less. In addition, by coexisting Na2O and K2O, the movement of the alkali components can be suppressed, which is preferable from the viewpoint of radio wave transmissivity.

[0125] From the viewpoint of radio wave transmissivity, the ratio [[Li2O] / ([Na2O]+[K2O])] of the content of Li2O in this chemically strengthened glass to the total content of Na2O and K2O ([Na2O]+[K2O]) is preferably 1 or more, more preferably 2 or more, further preferably 3 or more, and particularly preferably 5 or more. By making [[Li2O] / ([Na2O]+[K2O])] within the above range, the movement of the alkali components can be suppressed. There is no particular limitation on the upper limit of [Li2O] / ([Na2O]+[K2O]), and typically it is 20 or less.

[0126] MgO, CaO, SrO, and BaO are not essential, but from the viewpoints of improving the stability of the glass and improving the chemical strengthening characteristics, any one or more of them may be contained. When these substances are contained, the total content of one or more selected from MgO, CaO, SrO, and BaO [MgO]+[CaO]+[SrO]+[BaO] is preferably 1% or more, more preferably 2% or more, and further preferably 4% or more. In addition, from the viewpoints of introducing sufficient chemical strengthening stress during chemical strengthening and improving radio wave transmissivity, the total content of these substances is preferably 20% or less, more preferably 10% or less.

[0127] MgO may be contained to reduce the viscosity during melting, etc. When MgO is contained, the content of MgO is preferably 1% or more, more preferably 2% or more, and further preferably 3% or more. On the other hand, when the content of MgO is excessive, it is difficult to increase the compressive stress layer during chemical strengthening treatment. The content of MgO is preferably 5% or less, more preferably 4% or less, further preferably 3% or less, and particularly preferably 2% or less.

[0128] CaO is a component that improves the meltability of the glass, and CaO may be contained. When CaO is contained, the content of CaO is preferably 0.1% or more, more preferably 0.15% or more, and further preferably 0.5% or more. On the other hand, when the content of CaO is excessive, it is difficult to increase the compressive stress value during chemical strengthening treatment. The content of CaO is preferably 5% or less, more preferably 3% or less, further preferably 1% or less, and typically 0.5% or less.

[0129] ZnO is a component that improves the meltability of the glass, and ZnO may be contained. When ZnO is contained, the content of ZnO is preferably 0.2% or more, more preferably 0.5% or more. In order to improve the weather resistance of the glass, the content of ZnO is preferably 8% or less, more preferably 5% or less, and further preferably 3% or less.

[0130] ZnO, SrO, and BaO tend to deteriorate the chemical strengthening characteristics. Therefore, in order to facilitate chemical strengthening, [ZnO] + [SrO] + [BaO] is preferably less than 1%, and more preferably 0.5% or less. It is further preferably substantially free of these substances.

[0131] ZrO2 may not be contained, but from the viewpoint of increasing the surface compressive stress of chemically strengthened glass, it is preferably contained. The content of ZrO2 is preferably 0.1% or more, more preferably 0.15% or more, further preferably 0.2% or more, particularly preferably 0.25% or more, and typically 0.3% or more. On the other hand, when the content of ZrO2 is excessive, devitrification defects are likely to occur, and it is difficult to increase the compressive stress value during chemical strengthening treatment. The content of ZrO2 is preferably 2% or less, more preferably 1.5% or less, further preferably 1% or less, particularly preferably 0.8% or less.

[0132] The content of Y2O3 is preferably 0.1% or more, more preferably 0.2% or more, further preferably 0.5% or more, and particularly preferably 1% or more. On the other hand, when the content of Y2O3 is excessive, it is difficult to increase the compressive stress layer during chemical strengthening treatment. The content of Y2O3 is preferably 10% or less, more preferably 8% or less, further preferably 5% or less, still further preferably 3% or less, particularly preferably 2% or less, and further particularly preferably 1.5% or less.

[0133] Although La2O3 is not essential, it may be contained for the same reasons as Y2O3. The content of La2O3 is preferably 0.1% or more, more preferably 0.2% or more, further preferably 0.5% or more, and particularly preferably 0.8% or more. On the other hand, when the amount of La2O3 is excessive, it is difficult to increase the compressive stress layer during chemical strengthening treatment. Therefore, the content of La2O3 is preferably 5% or less, more preferably 3% or less, further preferably 2% or less, and particularly preferably 1.5% or less.

[0134] TiO2 is a component for suppressing the solarization of glass and may be contained. When TiO2 is contained, the content of TiO2 is preferably 0.02% or more, more preferably 0.03% or more, further preferably 0.04% or more, particularly preferably 0.05% or more, and typically 0.06% or more. On the other hand, when the content of TiO2 is greater than 1%, devitrification is likely to occur, and the quality of chemically strengthened glass may deteriorate. The content of TiO2 is preferably 5% or less, more preferably 3% or less, further preferably 2% or less, still further preferably 1% or less, particularly preferably 0.5% or less, and further particularly preferably 0.25% or less.

[0135] B2O3 is not essential, but it may be contained for the purpose of reducing the brittleness of the glass, improving the crack resistance, and improving the radio wave transmittance. When B2O3 is contained, the content of B2O3 is preferably 1.0% or more, preferably 3.0% or more, further preferably 4.0% or more, particularly preferably 5.0% or more, further preferably 7.0% or more, and most preferably 8.0% or more. On the other hand, when the content of B2O3 is excessive, the acid resistance is likely to deteriorate. Therefore, the content of B2O3 is preferably 25% or less. The content of B2O3 is more preferably 16% or less, further preferably 13% or less, particularly preferably 12% or less. Further preferably 11% or less, and most preferably 10% or less. In order to prevent the problem of ripple formation during melting, it is more preferable that B2O3 is substantially not contained.

[0136] P2O5 is not essential, but it may be contained for the purpose of increasing the compressive stress layer during chemical strengthening. When P2O5 is contained, the content of P2O5 is preferably 0.25% or more, more preferably 0.5% or more, further preferably 0.75% or more, particularly preferably 1.0% or more, further preferably 1.25% or more, and most preferably 1.5% or more. On the other hand, from the viewpoint of improving acid resistance, the content of P2O5 is preferably 10% or less, more preferably 8% or less, further preferably 6% or less, still further preferably 4% or less, particularly preferably 3% or less, further preferably 2.5% or less, and most preferably 2.0% or less. In order to prevent striae from occurring during melting, it is more preferable that substantially no P2O5 is contained.

[0137] The total content of B2O3 and P2O5 is preferably 0% to 35%, more preferably 5% or more, and further preferably 8% or more. The total content of B2O3 and P2O5 is preferably 20% or less, more preferably 17% or less, and further preferably 15% or less.

[0138] Nb2O5, Ta2O5, Gd^2O3, CeO2 are components that inhibit solarization of the glass and are components that improve meltability, and these substances may be contained. When these components are contained, the content of each is preferably 0.03% or more, more preferably 0.1% or more, further preferably 0.5% or more, particularly preferably 0.8% or more, and typically 1% or more. On the other hand, when the content of these substances is excessive, it is difficult to increase the compressive stress value during chemical strengthening treatment, and therefore it is preferably 3% or less, more preferably 2% or less, further preferably 1% or less, and particularly preferably 0.5% or less.

[0139] In addition, coloring components can be added within the range that does not hinder the achievement of the desired chemical strengthening characteristics. As coloring components, for example, Fe2O3, Co3O4, MnO2, NiO, CuO, Cr2O3, V2O5, Bi2O3, SeO2, CeO2, Er2O3, Nd2O3, etc. can be cited as appropriate coloring components.

[0140] In terms of the molar percentage based on oxides, the total content of the coloring components is preferably 5% or less. When the content of the coloring components is greater than 5%, the glass may be prone to devitrification. The content of the coloring components is preferably 3% or less, and further preferably 1% or less. When it is desired to improve the transmittance of the glass, it is preferably that substantially no such components are contained.

[0141] As a fining agent or the like during glass melting, SO3, chlorides, fluorides, etc. can be appropriately contained. It is preferably that no As2O3 is contained. When Sb2O3 is contained, it is preferably 0.3% or less, more preferably 0.1% or less, and most preferably no Sb2O3 is contained.

[0142] The β-OH value refers to the value used as an index of the water content of the glass, and is a value obtained by measuring the absorbance of light with wavelengths from 2.75 μm to 2.95 μm and dividing the maximum value β max by the thickness (mm) of the glass.

[0143] When the β-OH value is 0.8 mm -1 or less, the radio wave transmittance of the glass can be further improved, so it is preferable. The β-OH value is more preferably 0.6 mm -1 or less, still more preferably 0.5 mm -1 or less, and even more preferably 0.4 mm -1 or less.

[0144] On the other hand, by setting the β-OH value to 0.05 mm -1 or more, the productivity of the glass, the quality of the bubbles, etc. can be improved without extremely reducing the amount of water in the raw materials during melting in an extremely dry atmosphere, so it is preferable. The β-OH value is more preferably 0.1 mm -1 or more, still more preferably 0.2 mm -1 or more.

[0145] The β-OH value can be adjusted according to the composition of the glass, the heat source during melting, the melting time, and the raw materials.

[0146] The temperature (T2) at a viscosity of 10 2 dPa·s is preferably 1750 °C or lower, more preferably 1700 °C or lower, particularly preferably 1675 °C or lower, and typically 1650 °C or lower. The temperature (T2) is a temperature that serves as a rough standard for the melting temperature of the glass. The lower T2 is, the more likely it is to be easy to manufacture the glass. There is no particular limitation on the lower limit of T2, but glass with a low T2 tends to have too low a glass transition temperature, so T2 is usually 1400 °C or higher, preferably 1450 °C or higher.

[0147] In addition, the temperature (T4) at a viscosity of 10 4 dPa·s is preferably 1350 °C or lower, more preferably 1300 °C or lower, further preferably 1250 °C or lower, and particularly preferably 1150 °C or lower. The temperature (T4) is a temperature that serves as a rough standard for the temperature at which the glass is formed into a plate shape. Glass with a high T4 tends to have a higher load on the forming equipment. There is no particular limitation on the lower limit of T4, but glass with a low T4 tends to have too low a glass transition temperature, so T4 is usually 900 °C or higher, preferably 950 °C or higher, and more preferably 1000 °C or higher.

[0148] When the devitrification temperature of this chemically strengthened glass is at a temperature 120 °C or lower than the temperature (T4) at which the specific viscosity reaches 10 4 dPa·s, devitrification is less likely to occur during float forming, and thus it is preferred. The devitrification temperature is more preferably 100 °C or lower than T4, further preferably 50 °C or lower than T4, and particularly preferably T4 or lower.

[0149] The fracture toughness value of this chemically strengthened glass is preferably 0.70 MPa·m 1 / 2 or more, more preferably 0.75 MPa·m 1 / 2 or more, further preferably 0.80 MPa·m 1 / 2 or more, particularly preferably 0.83 MPa·m 1 / 2 or more. In addition, the fracture toughness value is usually 2.0 MPa·m 1 / 2 or less, typically 1.5 MPa·m 1 / 2 or less. With a large fracture toughness value, even if a large surface compressive stress is introduced into the glass by chemical strengthening, intense breakage is less likely to occur.

[0150] The fracture toughness value can be measured, for example, using the DCDC method (Acta metall. mater., Vol. 43, pp. 3453 - 3458, 1995).

[0151] In order to make the glass less likely to break, the Young's modulus of this chemically strengthened glass is preferably 80 GPa or more, more preferably 82 GPa or more, further preferably 84 GPa or more, and particularly preferably 85 GPa or more. There is no particular limitation on the upper limit of the Young's modulus, but glass with a high Young's modulus sometimes has reduced acid resistance, so for example, it is preferably 110 GPa or less, more preferably 100 GPa or less, and further preferably 90 GPa or less. The Young's modulus can be measured by, for example, the ultrasonic pulse method.

[0152] From the viewpoint of reducing the warpage after chemical strengthening, the average linear thermal expansion coefficient (thermal expansion coefficient) of this chemically strengthened glass in the range of 50 °C to 350 °C is preferably 95×10 -7 / °C or less, more preferably 90×10 -7 / °C or less, further preferably 88×10 -7 / °C or less, particularly preferably 86×10 -7 / °C or less, most preferably 84×10 -7 / °C or less. There is no particular limitation on the lower limit of the thermal expansion coefficient, but glass with a small thermal expansion coefficient is sometimes difficult to melt, so the average linear thermal expansion coefficient (thermal expansion coefficient) of this chemically strengthened glass in the range of 50 °C to 350 °C is, for example, preferably 60×10 -7 / °C or higher, more preferably 70×10 -7 / °C or higher, further preferably 74×10 -7 / °C or higher, particularly preferably 76×10 -7 / °C or higher.

[0153] From the viewpoint of reducing warpage after chemical strengthening, the glass transition temperature (Tg) is preferably 500 °C or higher, more preferably 520 °C or higher, and further preferably 540 °C or higher. From the viewpoint of facilitating float forming, the glass transition temperature (Tg) is preferably 750 °C or lower, more preferably 700 °C or lower, further preferably 650 °C or lower, particularly preferably 600 °C or lower, and most preferably 580 °C or lower.

[0154] This glass for chemical strengthening can be produced by a conventional method. For example, raw materials of each component of the glass are formulated 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 slowly cooled.

[0155] As a method for forming a glass plate, for example, there can be mentioned: the float process, the pressing process, the fusion process, and the down-draw process. The float process, which is particularly suitable for mass production, is preferably used. In addition, continuous forming processes other than the float process, such as the fusion process and the down-draw process, are preferably used.

[0156] Then, if necessary, the formed glass is subjected to grinding and polishing treatment to form a glass substrate. It should be noted that when the glass substrate is cut into a specified shape and size or chamfered, if the cutting and chamfering of the glass substrate are performed before the chemical strengthening treatment described below, a compressive stress layer is also formed on the end face by the subsequent chemical strengthening treatment, so this is preferred.

[0157] 《Glass-ceramics》

[0158] This glass for chemical strengthening can be glass-ceramics (hereinafter also referred to as "this glass-ceramics"). This glass-ceramics is glass-ceramics having the glass composition of the above-mentioned glass for chemical strengthening.

[0159] This glass-ceramics preferably contains any one or more of lithium silicate crystals, lithium aluminosilicate crystals or lithium phosphate crystals, magnesium aluminosilicate crystals, magnesium silicate crystals, and silicon crystals. As the lithium silicate crystal, metasilicate lithium crystal is more preferably used. As the lithium aluminosilicate crystal, spodumene crystal or β-spodumene crystal, α-eucryptite, β-eucryptite is preferably used. As the lithium phosphate crystal, lithium orthophosphate crystal is preferably used.

[0160] In order to improve transparency, glass-ceramics containing metasilicate lithium crystals are more preferably used.

[0161] The glass-ceramics can be obtained by subjecting an amorphous glass having the same composition as the glass for chemical strengthening to a heat treatment for crystallization. The glass composition of the glass-ceramics is the same as that of the amorphous glass.

[0162] When the thickness of the glass-ceramics is converted to 700 μm, the visible light transmittance (total visible light transmittance including diffused transmitted light) of the glass-ceramics is preferably 85% or more. When the glass-ceramics is used as a protective glass for a portable display, the screen of the display can be easily seen. The visible light transmittance is more preferably 88% or more, and further preferably 90% or more. The higher the visible light transmittance, the more preferable it is, but it is usually 93% or less. It should be noted that the visible light transmittance of a general amorphous glass is about 90% or more.

[0163] When the thickness of the glass-ceramics is not 700 μm, the Lambert-Beer law can be used to calculate the transmittance at 700 μm from the measured transmittance.

[0164] In addition, in the case of a glass with a thickness t greater than 700 μm, the thickness can be adjusted to 0.7 mm by grinding, etching, etc. and actually measured.

[0165] In addition, when converted to a thickness of 700 μm, the haze value is preferably 1.0% or less, more preferably 0.4% or less, further preferably 0.3% or less, particularly preferably 0.2% or less, and most preferably 0.15% or less. The smaller the haze value, the more preferable it is. However, when the crystallization rate is reduced or the crystal grain size is reduced in order to reduce the haze value, the mechanical strength is reduced. In order to improve the mechanical strength, the haze value at a thickness of 700 μm is preferably 0.02% or more, and more preferably 0.03% or more. The haze value is a value measured according to JIS K7136 (2000).

[0166] It should be noted that when the total visible light transmittance of the glass-ceramics with a thickness t [μm] is 10,000 × T [%] and the haze value is 10,000 × H [%], by referring to the Lambert-Beer law and using the constant α, it is described as T = (1 - R) 2 × exp(-αt / 1000). Using this constant α, it is expressed as:

[0167] dH / dt ∝ exp(-αt / 1000) × (1 - H).

[0168] That is, it is considered that the increase in the haze value with the increase in thickness is proportional to the internal direct transmittance. Therefore, the haze value H at 700 μm 0.7 is obtained by the following formula.

[0169]

[0170] In addition, in the case of glass with a thickness t greater than 700 μm, the thickness can be adjusted to 700 μm by grinding, etching, etc. and actual measurement can be carried out.

[0171] When the strengthened glass obtained by strengthening the glass-ceramics is used as the protective glass of a portable display, it is preferably provided with a texture and a sense of luxury different from those of plastics. Therefore, the refractive index of this glass-ceramics is preferably 1.52 or more, more preferably 1.55 or more, and further preferably 1.57 or more at a wavelength of 590 nm.

[0172] In order to improve the mechanical strength, the crystallization rate of the glass-ceramics is preferably 5% or more, more preferably 10% or more, further preferably 15% or more, and particularly preferably 20% or more. In order to improve the transparency, the crystallization rate of the glass-ceramics is preferably 70% or less, more preferably 60% or less, and particularly preferably 50% or less. From the viewpoints of easy heating and bending forming, etc., a small crystallization rate is preferred.

[0173] The crystallization rate can be calculated from the X-ray diffraction intensity by the Rietveld method. Regarding the Rietveld method, it is described in "Crystal Analysis Handbook" edited by the Editorial Committee of "Crystal Analysis Handbook" of the Crystallographic Society of Japan (published by Kyoritsu Shuppan Co., Ltd. in 1999, pages 492 to 499).

[0174] The average particle diameter of the precipitated crystals of the glass-ceramics is preferably 80 nm or less, more preferably 60 nm or less, further preferably 50 nm or less, particularly preferably 40 nm or less, and most preferably 30 nm or less. The average particle diameter of the precipitated crystals can be obtained from a transmission electron microscope (TEM) image. The average particle diameter of the precipitated crystals can be estimated from a scanning electron microscope (SEM) image.

[0175] "Chemical Strengthening Treatment"

[0176] This chemically strengthened glass can be manufactured by subjecting the obtained glass plate to chemical strengthening treatment and then performing cleaning and drying.

[0177] The chemical strengthening treatment can be carried out by a known method. In the chemical strengthening treatment, the glass plate is brought into contact with a melt of a metal salt (e.g., potassium nitrate) containing metal ions with a large ionic radius (typically K ions) by impregnation or the like. Thereby, the metal ions with a small ionic radius (typically Na ions or Li ions) in the glass plate are replaced with metal ions with a large ionic radius (typically K ions relative to Na ions and Na ions relative to Li ions).

[0178] 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°C to 600°C for 0.1 hour to 500 hours. It should be noted that as the heating temperature of the molten salt, for example, it is preferably 375°C to 500°C. In addition, the immersion time of the glass plate in the molten salt is, for example, preferably 0.3 hour to 200 hours.

[0179] As the molten salt used for the chemical strengthening treatment, for example, the following can be listed: nitrates, sulfates, carbonates, chlorides, etc. Among them, as nitrates, for example, lithium nitrate, sodium nitrate, potassium nitrate, cesium nitrate, and silver nitrate can be listed. As sulfates, for example, lithium sulfate, sodium sulfate, potassium sulfate, cesium sulfate, silver sulfate, etc. can be listed. As carbonates, for example, lithium carbonate, sodium carbonate, potassium carbonate, etc. can be listed. As chlorides, for example, lithium chloride, sodium chloride, potassium chloride, cesium chloride, silver chloride, etc. can be listed. These molten salts can be used alone or in combination of multiple kinds.

[0180] In the present invention, the treatment conditions of the chemical strengthening treatment can be appropriately selected considering the characteristics, composition of the glass, the type of the molten salt, and the chemical strengthening characteristics such as the entropy function S, surface compressive stress, and depth of the compressive stress layer of the finally obtained chemically strengthened glass.

[0181] In addition, in the present invention, the chemical strengthening treatment can be carried out only once, or multiple chemical strengthening treatments (multi-step strengthening) can be carried out under two or more different conditions. Here, for example, as the first-step chemical strengthening treatment, the chemical strengthening treatment is carried out under the condition that DOL is large and CS is relatively small. Then, as the second-step chemical strengthening treatment, when the chemical strengthening treatment is carried out under the condition that DOL is small and CS becomes relatively high, the CS of the outermost surface of the chemically strengthened glass can be increased, and at the same time, the internal tensile stress area (St) can be suppressed, and the internal tensile stress (CT) can be suppressed to a low level.

[0182] <Electronic device housing> <FSD

[0183] The electronic device housing of the present invention includes the chemically strengthened glass of the present invention. As the electronic device housing, for example, the protective glass of the display surface and the back surface of a portable terminal, the protective glass of a display device such as a television (TV), a personal computer (PC), or a touch panel that is not for portable use, etc. can be listed.

[0184] Examples

[0185] Hereinafter, the present invention will be described by way of examples, but the present invention is not limited thereto.

[0186] [Experimental Example 1]

[0187] Prepare various glass raw materials and weigh 400 g based on the glass. Then, put the mixed raw materials into a platinum crucible and place it in an electric furnace at 1500 °C to 1700 °C for melting for about 3 hours to perform defoaming and homogenization.

[0188] Regarding the various chemically strengthened glasses obtained, the glass in which the relative dielectric constant or the tangent of the dielectric loss angle after chemical strengthening is reduced compared to before chemical strengthening is defined as the glass with improved radio wave transmissivity by chemical strengthening. Regarding the glass with improved radio wave transmissivity by chemical strengthening, the graph showing the correlation between the radio wave transmissivity at a frequency of 10 GHz, the entropy function, and the compressive stress is shown in Figure 1 in. Figure 1 The vertical axis of is the total value of 100 times the values of the relative dielectric constant and the tangent of the dielectric loss angle that change before and after chemical strengthening, and the horizontal axis is the parameter Z that can be calculated from the entropy function and the compressive stress before and after chemical strengthening.

[0189] The content of alkali metal ions used to calculate the entropy function is measured using EPMA (electron probe microanalyzer, manufactured by JEOL Ltd.: JXA-8500F). As the measurement conditions of EPMA, the acceleration voltage is set to 15 kV, the probe current is set to 30 nA, the integration time is set to 1000 milliseconds / point, and the interval is set to 1 μm.

[0190] According to Figure 1 it is known that by making Z represented by the formula [Z = (S2 - S1) × 10 + X / 1000] be 0.65 or more, the movement of alkali metal ions is suppressed after chemical strengthening compared to before chemical strengthening, and excellent radio wave transmissivity is shown in the high-frequency band.

[0191] [Experimental Example 2]

[0192] Prepare glass raw materials according to the composition in terms of mole percentage based on oxides in Table 1 and weigh 400 g based on the glass. Then, put the mixed raw materials into a platinum crucible and place it in an electric furnace at 1500 °C to 1700 °C for melting for about 3 hours, and perform defoaming and homogenization.

[0193] Pour the obtained molten glass into a metal mold, hold it at a temperature about 50 °C higher than the glass transition temperature for 1 hour, and then cool it to room temperature at a rate of 0.5 °C / minute to obtain a glass block. Cut and grind the obtained glass block, and finally perform mirror polishing on both sides to obtain a glass plate with a thickness (t) of 700 μm.

[0194] The relative permittivity and the dielectric loss tangent tanδ of each glass were measured at 20 °C and a frequency of 10 GHz. The results are shown in Table 2. In addition, two-step chemical strengthening treatments were carried out according to the conditions shown in Table 2, and the following chemically strengthened glasses of Examples 1 to 7 were fabricated. Examples 1 to 4 are examples, and Examples 5 to 7 are comparative examples.

[0195] Table 1

[0196]

[0197] The surface compressive stress and the depth of the compressive stress layer DOL of the chemically strengthened surface layer were measured using the optical waveguide surface stress meter FSM-6000 and the scattered light photoelastic stress meter SLP-1000 manufactured by Oriehara Manufacturing Co., Ltd. The average value of the compressive stress in the region from the surface layer to 0.05t μm was recorded as the internal average chemical strengthening stress.

[0198] In addition, the obtained samples were measured using EPMA (electron probe microanalyzer, manufactured by JEOL Ltd.: JXA-8500F) to obtain the content of alkali metal ions after chemical strengthening at a depth of 0.05t from the glass surface and the content of alkali metal ions at the center of the plate thickness (glass center part). The average values are shown in Table 2 as the ion amount after strengthening and the ion amount at the center of the plate thickness.

[0199] In addition, according to the ion amount of the obtained alkali metal element, the entropy function S was calculated according to the following definition formula.

[0200] S = -[Li2O] / ([Li2O]+[Na2O]+[K2O]) log([Li2O] / ([Li2O]+[Na2O]+[K2O])) - [Na2O] / ([Li2O]+[Na2O]+[K2O]) log([Na2O] / ([Li2O]+[Na2O]+[K2O])) - [K2O] / ([Li2O]+[Na2O]+[K2O]) log([K2O] / ([Li2O]+[Na2O]+[K2O]))

[0201] It should be noted that the entropy function calculated from the average alkali ion amount in the region from the glass surface to a depth of 0.05t is defined as S2, and the entropy function calculated from the alkali ion amount in the center part of the glass is defined as S1. From these entropy functions S1, S2 and the average value X [unit: MPa] of the compressive stress in the region from the glass surface to a depth of 0.05t, the alkali fixation parameter Z was calculated according to the following formula. The results are shown in Table 2. In Table 2, the "change amount of the entropy function" was obtained by subtracting the "entropy function S1 of the center of the plate thickness (glass center)" from the "entropy function S2 after chemical strengthening".

[0202] Z = (S2 - S1) × 10 + X / 1000

[0203] In addition, the relative permittivity and tanδ of the chemically strengthened sample were measured at 20 °C and a frequency of 10 GHz. The results are shown in Table 2.

[0204] It should be noted that the relative permittivity and tanδ were measured by the split post dielectric resonator method (SPDR method) using a network analyzer. For the measurement conditions, the temperature was set to 20 °C and the frequency was set to 10 GHz.

[0205] In Table 2, the "change amount of relative permittivity caused by chemical strengthening" was obtained by subtracting the "relative permittivity before chemical strengthening" from the "relative permittivity after chemical strengthening". In addition, the "change amount of dielectric loss caused by chemical strengthening" was obtained by subtracting the "dielectric loss before chemical strengthening" from the "dielectric loss after chemical strengthening".

[0206]

[0207] As shown in Table 2, in Examples 1 to 4 as the examples, since the change amount of the entropy function before and after chemical strengthening was very large and the compressive stress near the glass surface layer was also high, the alkali fixation parameter Z was 0.65 or more. As a result, it was confirmed that either physical property of the relative permittivity and the dielectric loss decreased and the dielectric characteristics improved before and after the chemical strengthening treatment.

[0208] On the other hand, regarding Examples 5 to 7 as the comparative examples, since the change amount of the entropy function before and after chemical strengthening was small, the alkali fixation parameter Z was less than 0.65. As a result, it was confirmed that both the relative permittivity and the dielectric loss increased and the dielectric characteristics decreased by performing the chemical strengthening treatment.

[0209] Although the present invention has been described in detail and with reference to specific modes, various changes and modifications can be made without departing from the spirit and scope of the present invention, which will be apparent to those skilled in the art. It should be noted that this application is based on a Japanese patent application (Japanese Patent Application No. 2020-202039) filed on December 4, 2020 and a Japanese patent application (Japanese Patent Application No. 2021-094715) filed on June 4, 2021, the entire text of which is incorporated herein by reference. In addition, all references cited herein are incorporated herein by reference.

Claims

1. A chemically strengthened glass, wherein the thickness of the chemically strengthened glass is t (unit: μm), and the relative dielectric constant of the chemically strengthened glass at 20 °C and a frequency of 10 GHz is 7.0 or less, wherein in terms of the molar percentage based on oxides, the basic composition of the chemically strengthened glass contains: 40% to 80% of SiO2, 0 to 20% of B2O3, 1% to 25% of Al2O3, 7.1% or more of Li2O, 2% or less of K2O, 3% or less of CaO, 3% or less of MgO + CaO + SrO + BaO, and a total of 5% to 30% of Li2O and / or Na2O, Z obtained by the following formula is 0.65 or more, Z = (S2 - S1) × 10 + X / 1000 In the above formula, S1 is the entropy function calculated from the alkali ion amount in the central part of the glass, S2 is the entropy function calculated from the average alkali ion amount in the region from the glass surface to a depth of 0.05t, X is the average value of the compressive stress in the region from the glass surface to a depth of 0.05t [unit: MPa], Among them, the entropy function S is obtained from the contents [Li2O], [Na2O], and [K2O] in terms of the molar percentages based on oxides of Li2O, Na2O, and K2O at each depth by the following formula. In the following formula, when [Li2O], [Na2O], and [K2O] are zero, the entropy function S is 1×10 -4 , S = -[Li2O] / ([Li2O] + [Na2O] + [K2O]) log([Li2O] / ([Li2O] + [Na2O] + [K2O])) - [Na2O] / ([Li2O] + [Na2O] + [K2O]) log([Na2O] / ([Li2O] + [Na2O] + [K2O])) - [K2O] / ([Li2O] + [Na2O] + [K2O]) log([K2O] / ([Li2O] + [Na2O] + [K2O])).

2. The chemically strengthened glass according to claim 1, wherein, The value obtained by subtracting the entropy function S1 from the entropy function S2, that is, the value of (S2 - S1) is 0.04 or more.

3. The chemically strengthened glass according to claim 1 or 2, wherein The chemically strengthened glass has a dielectric loss tangent of 0.02 or less at 20 °C and a frequency of 10 GHz.

4. The chemically strengthened glass according to any one of claims 1 to 3, wherein, The surface compressive stress value CS0 of the chemically strengthened glass is 800 MPa or less, and the internal tensile stress value CT is 80 MPa or less.

5. The chemically strengthened glass according to any one of claims 1 to 4, wherein, The surface compressive stress value CS0 of the chemically strengthened glass is 300 MPa or more.

6. The chemically strengthened glass according to any one of claims 1 to 5, wherein, The internal chemical strengthening stress CS at a depth of 0.05t measured from the glass surface of the chemically strengthened glass 0.05t is 75 MPa or more, and the thickness t is 300 μm or more.

7. The chemically strengthened glass according to any one of claims 1 to 6, wherein, The depth of the compressive stress layer DOL of the chemically strengthened glass is 70 μm or more, and the thickness t is 350 μm or more.

8. The chemically strengthened glass according to any one of claims 1 to 7, wherein, The chemically strengthened glass is a lithium aluminosilicate glass, in terms of the molar percentage based on oxides, the basic composition of the chemically strengthened glass contains: 40% to 70% of SiO2, 7.5% to 20% of Al2O3, and 7.1% to 25% of Li2O.

9. The chemically strengthened glass according to any one of claims 1 to 5 and 8, wherein, The thickness t is 100 μm or more and 2000 μm or less.

10. The chemically strengthened glass according to any one of claims 1 to 9, wherein, The chemically strengthened glass is a glass-ceramic.

11. An electronic device housing, wherein, The electronic device housing includes the chemically strengthened glass according to any one of claims 1 to 10.

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