Chemically strengthened glass and electronic apparatus housing

Abstract

To provide chemically strengthened glass having both excellent radio wave transmissivity in the high-frequency band and high strength.SOLUTION: There is provided chemically strengthened glass having a thickness of t (unit: μm) and a specific inductive capacity of 7.0 or less at 20°C and a frequency of 10 GHz, wherein Z obtained from the expression, [Z=(S2-S1)×10+X / 1000] is 0.65 or more, using the entropy function S1 calculated from the average alkali ion amount in the central part of the glass, the entropy function S2 calculated from the average alkali ion amount up to a depth of 0.05 t from the glass surface and the average compressive stress X [unit: MPa] in the region to a depth of 0.05 t from the glass surface.SELECTED DRAWING: None

Description

[Technical Field]

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

[0002] Chemically strengthened glass is widely used for the housings of electronic devices such as mobile terminals, as they require strength that prevents the mobile terminals from easily breaking even when dropped. Chemically strengthened glass is glass that is formed by ion exchange between alkali ions contained in the glass and alkali ions with a larger ionic radius contained in the molten salt, for example by immersing the glass in a molten salt such as sodium nitrate, thereby forming a compressive stress layer on the surface of the glass. For example, Patent Document 1 discloses aluminosilicate glass that has a specific composition and can achieve high surface compressive stress by chemical strengthening.

[0003] Meanwhile, in electronic devices such as mobile phones, smartphones, personal digital assistants, and communication devices like Wi-Fi devices, as well as surface acoustic wave (SAW) devices, radar components, and antenna components, signal frequencies are being increased in order to increase communication capacity and speed. In recent years, 5G (5th generation mobile communication system) is expected to become widespread as a new communication system that uses higher frequency bands.

[0004] In the high frequency bands used by 5G, cover glass can interfere with radio wave transmission and reception, so 5G-compatible mobile devices require cover glass with excellent dielectric properties, such as radio wave permeability. For example, low dielectric constant and dielectric loss are desirable as excellent dielectric properties. A reduction in the dielectric constant can suppress radio wave reflection and improve radio wave permeability. Furthermore, a reduction in dielectric loss can suppress radio wave loss.

[0005] Several alkali-free glasses have been developed to date as glasses with high radio wave transmittance in the high frequency bands used in 5G, i.e., glasses with small relative dielectric constants and dielectric loss tangents (Patent Document 2). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japan Special Publication No. 2018-520082 [Patent Document 2] International Publication No. 2019 / 181707 Summary of the Invention [Problem to be solved by the invention]

[0007] However, it is difficult to chemically strengthen alkali-free glass containing almost no alkali ions, as disclosed in Patent Document 2. In addition, the radio wave transmittance of chemically strengthened glass is difficult to predict, and it is difficult to achieve both radio wave transmittance and strength in the high frequency band.

[0008] Therefore, an object of the present invention is to provide chemically strengthened glass that has both excellent radio wave transmittance in a high frequency band and high strength. [Means for solving the problem]

[0009] The present inventors have found that there are glasses in which the radio wave transmittance in the high frequency band decreases after chemical strengthening compared to before chemical strengthening, and glasses in which the radio wave transmittance increases after chemical strengthening. Furthermore, for glasses in which the radio wave transmittance in the high frequency band increases after chemical strengthening, they have found a correlation between the surface characteristics after chemical strengthening and the radio wave transmittance, and have completed the present invention.

[0010] The present invention provides chemically strengthened glass having a thickness t (unit: μm) and a relative dielectric constant of 7.0 or less at 20 ° C. and a frequency of 10 GHz, This chemically strengthened glass has an entropy function S1 calculated from the amount of alkali ions in the center of the glass, an entropy function S2 calculated from the average amount of alkali ions from the glass surface to a depth of 0.05t, and Z calculated using the following formula from the average compressive stress X [unit: MPa] in the region from the glass surface to a depth of 0.05t, of 0.65 or more. Z = (S2 - S1) × 10 + X / 1000 However, the entropy function S is calculated from the oxide-based mole percentage contents of Li2O, Na2O, and K2O at each depth, [Li2O], [Na2O], and [K2O], using the following formula: In the formula below, if [Li2O], [Na2O], and [K2O] are zero, the entropy function S is calculated using the following formula: -4 Let's say. 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]))

[0011] In the chemically strengthened glass of the present invention (hereinafter also referred to as the present chemically strengthened glass), the value (S2-S1) obtained by subtracting the entropy function S1 from the entropy function S2 is preferably 0.04 or more.

[0012] The dielectric loss tangent of the chemically strengthened glass at 20° C. and a frequency of 10 GHz is preferably 0.02 or less.

[0013] The base composition of this chemically strengthened glass is expressed as mole percentage based on oxides, SiO2 40-80%, B2O3 0-20%, Al2O3 1-25%, It is preferable that Li2O and / or Na2O is contained in a total amount of 5 to 30%.

[0014] The chemically strengthened glass preferably has a surface compressive stress value CSO of 300 MPa or more.

[0015] This chemically strengthened glass has an internal chemical strengthening stress CS at a depth of 0.05t from the glass surface. 0.05tIt is preferable that the compressive strength is 75 MPa or more and the thickness t is 300 μm or more.

[0016] The chemically strengthened glass preferably has a compressive stress layer depth DOL of 70 μm or more and the thickness t of 350 μm or more.

[0017] The chemically strengthened glass is a lithium aluminosilicate glass, The base composition is expressed as mole percentage based on oxides, SiO2 40-70%, Al2O3 7.5-20%, It is preferable that Li2O is contained in an amount of 5 to 25%.

[0018] The chemically strengthened glass preferably has a thickness t of 100 μm or more and 2000 μm or less.

[0019] The chemically strengthened glass is preferably glass-ceramic.

[0020] The present invention also provides an electronic device housing comprising the chemically strengthened glass. [Effects of the Invention]

[0021] The chemically strengthened glass of the present invention has a specific range of Z, which is calculated using an equation expressed by the entropy function S, which represents the degree of mixing of alkali metal ions, and the average compressive stress X, and the movement of alkali metal ions in the glass is suppressed. As a result, the chemically strengthened glass of the present invention has excellent strength and excellent radio wave transmittance in the high frequency band. [Brief explanation of the drawings]

[0022] [Figure 1]Figure 1 is a graph showing the change in the total value of the relative permittivity and dielectric dissipation factor, which are important for radio wave permeability at a frequency of 10 GHz, before and after chemical strengthening, and the correlation between the change and the entropy function and compressive stress. The vertical axis represents the total value of the change in the relative permittivity and dielectric dissipation factor multiplied by 100 before and after chemical strengthening, while the horizontal axis represents the parameter Z, which can be calculated from the entropy function and compressive stress before and after chemical strengthening. Radio wave permeability is determined by both the relative permittivity and dielectric dissipation factor, but because the absolute value of the relative permittivity is larger and more effective than the dielectric dissipation factor, radio wave permeability is expressed as the total value of 100 times the relative permittivity and dielectric dissipation factor. DETAILED DESCRIPTION OF THE INVENTION

[0023] In this specification, the use of "to" to indicate a range of values ​​means that the values ​​before and after it are included as the lower and upper limits. Unless otherwise specified, "to" will be used in the same sense hereinafter in this specification.

[0024] 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.

[0025] In this specification, the "base composition of chemically strengthened glass" refers to the glass composition of glass for chemical strengthening. In chemically strengthened glass, the glass composition at a depth of 1 / 2 the thickness t is the base composition of the chemically strengthened glass, except when extreme ion exchange treatment is performed.

[0026] In this specification, unless otherwise specified, glass compositions are expressed in terms of mole percentage on an oxide basis, and mole % is simply represented as "%".

[0027] In addition, in this specification, "substantially free" means that the content is at or below the level of impurities contained in raw materials, etc., that is, that the content is not intentionally added. Specifically, for example, it is less than 0.1 mol %.

[0028] In this specification, the term "stress profile" refers to a representation of compressive stress values ​​with depth from the glass surface as a variable. The term "depth of compressive stress layer (DOL)" refers to the depth at which the compressive stress value (CS) is zero. The term "internal tensile stress value (CT)" refers to the tensile stress value at a depth of half the glass thickness t. In this specification, the tensile stress value is expressed as a negative compressive stress value.

[0029] The stress profile in this specification can be measured using a scattered light photoelastic stress meter (e.g., the SLP-1000 manufactured by Orihara Seisakusho). The scattered light photoelastic stress meter may be affected by surface scattering, which can reduce the measurement accuracy near the sample surface. However, for example, if compressive stress is generated solely by ion exchange between lithium ions in the glass and external sodium ions, the compressive stress value expressed as a function of depth follows a complementary error function, so that the surface stress value can be determined by measuring the internal stress value. In cases where the complementary error function is not followed, the surface portion can be measured using a different method, such as a surface stress meter.

[0030] <Chemically strengthened glass> The chemically strengthened glass of the present invention has a thickness t (unit: μm) and a relative dielectric constant of 7.0 or less at a frequency of 10 GHz. The entropy function S1 calculated from the amount of alkali ions in the center of the glass, the entropy function S2 calculated from the average amount of alkali ions from the glass surface to a depth of 0.05t, and the average compressive stress X [MPa] in the region from the glass surface to a depth of 0.05t are used to calculate Z, which is calculated using the following formula: Z = (S2 - S1) × 10 + X / 1000, and Z = 0.65 or more.

[0031] Here, the entropy function S is calculated from the oxide-based mole percentage contents of Li2O, Na2O, and K2O at each depth, [Li2O], [Na2O], and [K2O], using the following formula: In the formula below, if [Li2O], [Na2O], and [K2O] are zero, the entropy function S is calculated as 1×10 -4 Let's say. 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]))

[0032] Conventionally, the radio wave transmittance of chemically strengthened glass is difficult to predict because it changes with frequency, and it has been considered difficult to achieve both radio wave transmittance and strength in the high frequency band. The present inventors focused on the relationship between radio wave transmittance in the high frequency band and chemical strengthening and found that there are glasses whose radio wave transmittance in the high frequency band increases after chemical strengthening compared to before chemical strengthening, and glasses whose radio wave transmittance in the high frequency band decreases after chemical strengthening.

[0033] Furthermore, the inventors have considered that the characteristics of glass whose radio wave transmittance in the high frequency band increases after chemical strengthening compared to before chemical strengthening are that it has both of the following features: 1) the degree of alkali ion mixing before and after chemical strengthening changes significantly, and 2) high compressive stress after chemical strengthening. Features 1) and 2) are explained below.

[0034] The radio wave transmittance increases as the dielectric constant and dielectric loss decrease. Since the dielectric constant and dielectric loss are mainly caused by the movement of alkali metal ions in the glass, it is thought that the dielectric constant and dielectric loss can be reduced by suppressing the movement of alkali metal ions in the glass through chemical strengthening treatment. Regarding the above-mentioned 1) significant change in the degree of alkali ion mixing before and after chemical strengthening, it is thought that the presence and mixing of different types of alkali metal ions in the glass makes it difficult for the alkali metal ions to exchange with each other, reducing the relative permittivity and dielectric loss and improving the dielectric properties. The degree of alkali metal ion mixing is expressed by an entropy function. Regarding 2) the high compressive stress after chemical strengthening, it is thought that a strong compressive stress suppresses the movement of alkali metal ions, reduces the relative permittivity and dielectric loss, and improves the dielectric properties.

[0035] Figure 1 is a graph showing the correlation between the change in the total value of the dielectric constant and the dielectric dissipation factor (DTF) before and after chemical strengthening, which are important for determining radio wave permeability at a frequency of 10 GHz, and the entropy function and compressive stress for glass whose radio wave permeability increases after chemical strengthening compared to before chemical strengthening, as described in Experimental Example 1 below. The vertical axis of Figure 1 represents the total value obtained by multiplying the change in the dielectric constant and the DTF by 100, and the horizontal axis represents the parameter Z, which can be calculated from the entropy function and compressive stress before and after chemical strengthening. Note that while radio wave permeability is determined by both the dielectric constant and the DTF, the absolute value of the DTF is larger and more effective than the DTF. Therefore, the radio wave permeability is expressed as the total value obtained by multiplying the change in the dielectric constant and the DTF by 100. Details of Experimental Example 1 will be described later.

[0036] The content of alkali metal ions for calculating the entropy function is measured using an EPMA (Electron Probe Micro Analyzer, JEOL: JXA-8500F) under the following measurement conditions: acceleration voltage 15 kV, probe current 30 nA, integration time 1000 msec. / point, and 1 μm intervals.

[0037] According to Figure 1, when Z, expressed by the above formula [Z = (S2 - S1) × 10 + X / 1000], is 0.65 or more, the movement of alkali metal ions is suppressed after chemical strengthening compared to before chemical strengthening, and excellent radio wave transmittance is exhibited in the high frequency band.

[0038] Chemical strengthening suppresses the movement of alkali metal ions after chemical strengthening compared to before chemical strengthening, and the radio wave permeability is improved, which can be evaluated by the change in relative permittivity and the change in dielectric loss due to chemical strengthening.

[0039] Specifically, for example, the value obtained by subtracting the "dielectric constant at 20°C and 10 GHz after chemical strengthening" from the "dielectric constant at 20°C and 10 GHz before chemical strengthening" is preferably 0 or more, more preferably 0.02 or more, even more preferably 0.04 or more, even more preferably 0.06 or more, particularly preferably 0.08 or more, even more preferably 0.1 or more, and most preferably 0.12 or more. Since the dielectric constant of the glass after chemical strengthening is reduced by 0 or more compared to before chemical strengthening, it can be evaluated that the dielectric constant has been reduced by chemical strengthening and that radio wave transmittance has been improved.

[0040] Furthermore, for example, the value obtained by subtracting the "dielectric loss tangent at 20°C and 10 GHz after chemical strengthening" from the "dielectric loss tangent at 20°C and 10 GHz before chemical strengthening" is preferably 0 or more, more preferably 0.001 or more, even more preferably 0.002 or more, even more preferably 0.003 or more, and particularly preferably 0.004 or more. If the dielectric loss tangent of the glass after chemical strengthening is reduced by 0 or more compared to before chemical strengthening, it can be evaluated that the chemical strengthening has reduced the dielectric loss and improved the radio wave transmittance.

[0041] In the high frequency band, when designing circuits on a glass substrate, the dielectric properties of the glass, particularly the dielectric properties of the glass surface layer, are particularly important. In the chemically strengthened glass of the present invention, the relative dielectric constant and dielectric dissipation factor of the glass plate surface are smaller than the relative dielectric constant and dielectric dissipation factor of the glass interior in the high frequency band, allowing radio waves to pass through efficiently and providing excellent dielectric properties to the glass surface layer.

[0042] Z, represented by the formula [Z = (S2 - S1) × 10 + X / 1000], is 0.65 or more, preferably 0.7 or more, more preferably 0.8 or more, even more preferably 0.9 or more, even more preferably 1.0 or more, particularly preferably 1.25 or more, even more preferably 1.5 or more, and most preferably 2.0 or more. When Z is 0.65 or more, the movement of alkali metal ions after chemical strengthening is suppressed, resulting in excellent radio wave transmittance 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.).

[0043] In the above formula, S1 is an entropy function calculated from the amount of alkali ions in the center of the glass, and S2 is an entropy function calculated from the average amount of alkali ions from the glass surface to a depth of 0.05t.

[0044] Although the value of S1 is not particularly limited, the lower S1, the better the chemical strengthening properties can be obtained, and for example, it is preferably 0.375 or less, more preferably 0.35 or less, even more preferably 0.325 or less, even more preferably 0.30 or less, particularly preferably 0.25 or less, even more preferably 0.20 or less, and most preferably 0.15 or less. On the other hand, if 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.

[0045] The value of S2 is not particularly limited, but the higher S2, the lower the relative permittivity and dielectric loss tangent of the glass after chemical strengthening and the more likely it is to have good radio wave transmittance after chemical strengthening, and for example, it is preferably 0.2 or more, more preferably 0.25 or more, even more preferably 0.3 or more, even more preferably 0.35 or more, particularly preferably 0.40 or more, and even more preferably 0.45 or more. On the other hand, if S2 is too high, the chemical strengthening stress is not sufficiently applied, and for example, it is preferably 0.5 or less, more preferably 0.49 or less, even more preferably 0.48 or less, even more preferably 0.47 or less, and particularly preferably 0.46 or less.

[0046] The value (S2-S1) obtained by subtracting S1 from S2 is not particularly limited, but the higher it is, the lower the relative permittivity and dielectric loss tangent after chemical strengthening can be, so it is preferably 0.04 or more, more preferably 0.05 or more, even more preferably 0.1 or more, even more preferably 0.15 or more, particularly preferably 0.2 or more, even more preferably 0.25 or more, and most preferably 0.3 or more. On the other hand, if the value obtained by subtracting S1 from S2 is too high, sufficient chemical strengthening stress will not be applied, so it is preferably 0.5 or less, more preferably 0.48 or less, even more preferably 0.46 or less, even more preferably 0.44 or less, particularly preferably 0.42 or less, even more preferably 0.40 or less, and most preferably 0.38 or less.

[0047] By setting S1 and S2 within the above ranges, the degree of mixing of alkali metal ions due to chemical strengthening is increased, the movement of alkali metal ions in the surface layer of the glass is suppressed, and radio wave transmittance in the high frequency band can be improved. 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.).

[0048] In the above formula, X is the average compressive stress (unit: MPa) in the region from the glass surface to a depth of 0.05t. The value of X is not particularly limited, but is, for example, preferably 100 MPa or more, more preferably 150 MPa or more, even more preferably 200 MPa or more, even more preferably 250 MPa or more, particularly preferably 275 MPa or more, even more preferably 300 MPa or more, and most preferably 320 MPa or more. By setting X within the above range, high compressive stress is introduced into the glass surface layer, suppressing the movement of alkali metal ions in the glass surface layer and improving dielectric properties in the high-frequency band. On the other hand, if the value of X is too high, the glass will explode into small pieces when crushed. Therefore, the value of X is preferably 600 MPa or less, more preferably 500 MPa or less, even more preferably 475 MPa or less, even more preferably 450 MPa or less, particularly preferably 425 MPa or less, even more preferably 400 MPa or less, and most preferably 375 MPa or less. The value of X can be adjusted by the composition of the chemically strengthening glass and the chemical strengthening treatment conditions (molten salt composition, time, temperature, etc.).

[0049] The chemically strengthened glass is preferably in the form of a plate. The glass plate may have a rim with a different thickness around the periphery. The shape of the glass plate is not limited thereto. For example, the two main surfaces may not be parallel to each other, and one or both of the two main surfaces may be entirely or partially curved. More specifically, the glass plate may be, for example, a flat glass plate without warping, or a curved glass plate having a curved surface.

[0050] The thickness (t) is, for example, 2000 μm or less, preferably 1500 μm or less, more preferably 1000 μm or less, even more preferably 900 μm or less, particularly preferably 800 μm or less, and most preferably 700 μm or less, from the viewpoint of enhancing the effect of chemical strengthening. Also, from the viewpoint of obtaining a sufficient strength improvement effect by chemical strengthening treatment, the thickness is, for example, 100 μm or more, preferably 200 μm or more, more preferably 300 μm or more, even more preferably 350 μm or more, still more preferably 400 μm or more, and particularly preferably 500 μm or more.

[0051] The shape of the chemically strengthened glass may be a shape other than a plate shape depending on the product or use to which it is applied.

[0052] The 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, even more preferably 6.7 or less, even more preferably 6.6 or less, particularly preferably 6.5 or less, even more preferably 6.4 or less, and most preferably 6.3 or less. A small dielectric constant can suppress radio wave loss due to reflection on the glass surface, thereby improving radio wave transmittance. On the other hand, if the dielectric constant is too low, the glass will not be imparted with sufficient chemical strengthening stress, so it is preferably 4.0 or more, more preferably 4.2 or more, even more preferably 4.4 or more, even more preferably 4.6 or more, particularly preferably 4.8 or more, even more preferably 5.0 or more, and most preferably 5.2 or more. The dielectric constant at 20°C and a frequency of 10 GHz can be measured using a network analyzer by slip post dielectric resonance (SPDR) method.

[0053] The dielectric dissipation factor (tanδ) of the chemically strengthened glass at 20°C and a frequency of 10 GHz is preferably 0.02 or less, more preferably 0.018 or less, even more preferably 0.016 or less, even more preferably 0.014 or less, particularly preferably 0.012 or less, even more preferably 0.011 or less, and most preferably 0.010 or less. A small dielectric dissipation factor can suppress the loss of radio waves passing through the glass, thereby improving radio wave transmittance. On the other hand, if the dielectric dissipation factor is too low, the glass will not be able to impart sufficient chemical strengthening stress. Therefore, the dielectric dissipation factor is preferably 0.001 or more, more preferably 0.002 or more, even more preferably 0.003 or more, even more preferably 0.004 or more, particularly preferably 0.005 or more, even more preferably 0.006 or more, and most preferably 0.007 or more. The dielectric dissipation factor (tanδ) can be measured at 20°C and a frequency of 10 GHz using a network analyzer by slip post dielectric resonance (SPDR) method.

[0054] Furthermore, by making the dielectric constant and dielectric loss tangent values ​​at 20°C and a frequency of 10 GHz closer to those at higher frequencies and reducing the frequency dependency (dielectric dispersion), the frequency characteristics of the dielectric properties are less likely to change, and design changes can be minimized even when the frequency used is different, which is preferable. The dielectric constant and dielectric loss tangent can be adjusted by the glass composition and chemical strengthening conditions.

[0055] This chemically strengthened glass has an appropriate alkali content in its composition, which allows it to reduce its dielectric constant and dielectric loss tangent at a frequency of 10 GHz. Generally, in the frequency range of 10 GHz to 40 GHz, the frequency dependence of the dielectric constant and dielectric loss tangent of glass is small. Therefore, this chemically strengthened glass, which has excellent dielectric properties at a frequency of 10 GHz, also has excellent radio wave transmittance in the 28 GHz and 35 GHz bands used by 5G.

[0056] The relative permittivity and dielectric loss tangent can be measured by the slip post dielectric resonance method (SPDR method) using a network analyzer.

[0057] This chemically strengthened glass is obtained by chemically strengthening the chemically strengthened glass or crystallized glass described later. That is, the matrix composition of this chemically strengthened glass is the same as the glass composition of the chemically strengthened glass described later, and the preferred composition range is also the same. Furthermore, the average composition of this chemically strengthened glass is the same as the composition of the chemically strengthened glass or crystallized glass described later. Here, the average composition refers to the composition obtained by analyzing a glass sample that has been heat-treated from a glass state and then finely crushed.

[0058] This chemically strengthened glass has internal chemical strengthening stress CS 0.05t The surface compressive stress value CSO is preferably 100 MPa or more, more preferably 150 MPa or more, even more 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 CSO is preferably 300 MPa or more, more preferably 400 MPa or more, and even more preferably 500 MPa or more, excellent strength is easily obtained, and further, when the compressive stress value CSO at a depth of 50 μm from the surface is 50 This is preferable because the size of the slits is likely to increase.

[0059] The greater the surface compressive stress value CS0, the higher the strength; however, if the surface compressive stress value CS0 is too large, a large tensile stress will be generated inside the chemically strengthened glass, which may lead to fracture. Therefore, the surface compressive stress value CS0 is preferably 1000 MPa or less, and more preferably 800 MPa or less.

[0060] In the stress profile 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, even more preferably 100 MPa or more, and particularly preferably 125 MPa or more. 50 The large size makes chemically strengthened glass less likely to break when damaged by being dropped, etc.

[0061] The internal tensile stress value CT of the chemically strengthened glass is preferably 80 MPa or less, more preferably 75 MPa or less. A small CT makes it less likely to fracture. The internal tensile stress value CT is preferably 50 MPa or more, more preferably 60 MPa or more, and even more preferably 65 MPa or more. A CT of at least this value increases the compressive stress near the surface, resulting in increased strength.

[0062] If the compressive stress layer depth DOL of the chemically strengthened glass is too large relative to the thickness t, it will lead to an increase in CT, so it is preferably 0.25t or less, more preferably 0.2t or less, even more preferably 0.19t or less, and even more preferably 0.18t or less. In addition, from the viewpoint of improving strength, DOL is preferably 0.06t or more, more preferably 0.08t or more, even more preferably 0.10t or more, and particularly preferably 0.12t or more.

[0063] Specifically, for example, when the thickness t is 700 μm, the DOL is preferably 140 μm or less, more preferably 133 μm or less. The DOL is preferably 70 μm or more, more preferably 80 μm or more, and even more preferably 90 μm or more. The preferred thickness (t) and shape of the present chemically strengthened glass are the same as those of the present glass described above.

[0064] The Young's modulus of the chemically strengthened glass is preferably 50 GPa or more, more preferably 80 GPa or more, and even more preferably 85 GPa or more, so that it is less likely to be broken. The upper limit of the Young's modulus is not particularly limited, but since glass with a high Young's modulus may have low acid resistance, it 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 an ultrasonic pulse method.

[0065] The four-point bending strength of the chemically strengthened glass is preferably 350 MPa or more, more preferably 450 MPa or more, and even more preferably 400 MPa or more. The upper limit of the four-point bending strength is not particularly limited, but is typically 1000 MPa or less. The four-point bending strength is measured by the method specified in JIS R1601:2008.

[0066] The Vickers hardness of the surface of the chemically strengthened glass is preferably 4.4 GPa or more, more preferably 4.8 GPa or more, and even more preferably 5.2 GPa or more. The upper limit of the Vickers hardness is not particularly limited, but is typically 9.0 GPa or less. The Vickers hardness is the Vickers hardness (HV0.1) specified in JIS R1610:2003.

[0067] The thermal conductivity of the present chemically strengthened glass is preferably 2.0 W / m°C or less, more preferably 1.8 W / m°C or less, and even more preferably 1.5 W / m°C or less. The lower limit of the thermal conductivity is not particularly limited, but is typically 0.8 W / m°C or more.

[0068] This chemically strengthened glass is particularly useful as cover glass for mobile devices such as mobile phones, smartphones, personal digital assistants (PDAs), tablet devices, etc. Furthermore, it is also useful as cover glass for non-portable display devices such as televisions (TVs), personal computers (PCs), and touch panels, as well as for elevator walls, walls (full-surface displays) of buildings such as houses and buildings, construction materials such as window glass, tabletops, interiors of automobiles and airplanes, and as cover glass for these, as well as for housings with curved shapes that are not plate-like by bending or molding.

[0069] <Method of manufacturing chemically strengthened glass> The present chemically strengthened glass can be produced by chemically strengthening glass for chemical strengthening described below (hereinafter also referred to as "the present glass for chemical strengthening").

[0070] <<Glass for chemical strengthening>> The glass for chemical strengthening is preferably any one of soda-lime glass, alkali aluminosilicate glass, and alkali aluminoborosilicate glass, which are suitable for chemical strengthening treatment.

[0071] The glass for chemical strengthening is preferably lithium aluminosilicate glass, which contains lithium ions, which are alkali ions with the smallest ionic radius, and therefore can be easily strengthened by chemical strengthening using ion exchange with various molten salts to obtain chemically strengthened glass with a favorable stress profile and excellent strength.

[0072] in particular, SiO2 40-80%, B2O3 0-20%, Al2O3 1-25%, It is preferable that Li2O and / or Na2O is contained in a total amount of 5 to 30%.

[0073] Lithium aluminosilicate glass includes: SiO2 40-70%, Al2O3 7.5-20%, Preferably, the content of Li2O is 5 to 25%.

[0074] A preferred composition of the glass for chemical strengthening will be further described below.

[0075] SiO2 is a component that makes up the network of glass. SiO2 also increases chemical durability and reduces the occurrence of cracks when the glass surface is scratched.

[0076] To improve chemical durability, the SiO content is preferably 40% or more, more preferably 50% or more, even more preferably 55% or more, even more preferably 56% or more, particularly preferably 63% or more, and most preferably 65% ​​or more. To improve meltability during glass production, the SiO content is preferably 80% or less, more preferably 75% or less, even more preferably 70% or less, particularly preferably 68% or less, and most preferably 65% ​​or less.

[0077] Al2O3 is an effective component from the viewpoint of improving the ion exchange performance during chemical strengthening and increasing the surface compressive stress after strengthening.

[0078] The Al2O3 content is preferably 1% or more, more preferably 3% or more, more preferably 5% or more, even more preferably 7% or more, even more preferably 9.1% or more, even more preferably 10% or more, particularly preferably 11% or more, and most preferably 12% or more, in order to improve chemical durability and chemical strengthening properties. On the other hand, if the Al2O3 content is too high, crystals may easily grow during melting. To prevent yield reduction due to devitrification defects, the Al2O3 content is preferably 25% or less, more preferably 23% or less, even more preferably 21% or less, particularly preferably 20% or less, and most preferably 19% or less.

[0079] Both SiO2 and Al2O3 are components that stabilize the structure of glass, and in order to reduce brittleness, the total content is preferably 57.5% or more, more preferably 65% ​​or more, even more preferably 75% or more, still more preferably 77% or more, and particularly preferably 79% or more.

[0080] Both SiO2 and Al2O3 tend to increase the melting temperature of the glass, and therefore, in order to facilitate melting, their total content is preferably 95% or less, more preferably 90% or less, even more preferably 87% or less, even more preferably 85% or less, and particularly preferably 82% or less.

[0081] Li2O is a component that forms surface compressive stress through ion exchange and improves the meltability of glass. By including Li2O in chemically strengthened glass, Li ions on the glass surface are ion-exchanged with Na ions, and then the Na ions are further ion-exchanged with K ions, resulting in a large stress profile for both the surface compressive stress and the compressive stress layer.

[0082] In order to increase the surface compressive stress during chemical strengthening, the Li2O content is preferably 5% or more, more preferably 6.5% or more, even more preferably 7.1% or more, particularly preferably 7.5% or more, and most preferably 8% or more.

[0083] On the other hand, if the Li2O content is too high, the crystal growth rate during glass molding increases, which can lead to a serious problem of reduced yield due to devitrification defects. In order to suppress devitrification during the glass manufacturing process, the Li2O content is preferably 18% or less, more preferably 16% or less, even more preferably 15% or less, even more preferably 14% or less, and particularly preferably 12% or less. Furthermore, if the alkali ion content is too high, radio wave transmittance is likely to decrease, so from the viewpoint of improving radio wave transmittance, the Li2O content is preferably 12% or less, more preferably 10% or less, and even more preferably 9% or less.

[0084] To facilitate glass forming, the total content of Li2O and / or Na2O is preferably 5% or more, more preferably 7.5% or more, and even more preferably 10% or more. To prevent the glass from dissolving in water, the total content of Li2O and / or Na2O is preferably 30% or less, more preferably 25% or less, and even more preferably 20% or less.

[0085] Although neither Na2O nor K2O is essential, they are components that improve the meltability of the glass and reduce the crystal growth rate of the glass, and are preferably contained in order to improve the ion exchange performance.

[0086] Na2O is a component that forms a surface compressive stress layer in chemical strengthening treatment using potassium salts and can also improve the meltability of glass. To achieve this effect, the Na2O content is preferably 1.5% or more, more preferably 2.5% or more, even more preferably 3% or more, even more preferably 3.6% or more, and particularly preferably 4% or more. On the other hand, if the Na2O content is too high, it becomes difficult to increase the compressive stress in a relatively deep portion from the surface by chemical strengthening, so the content is preferably 10% or less, more preferably 7% or less, even more preferably 5% or less, and even more preferably 3% or less.

[0087] K2O may be contained for the purpose of suppressing devitrification during the glass manufacturing process. When K2O is contained, the content is preferably 0.1% or more, more preferably 0.15% or more, and particularly preferably 0.2% or more. To further prevent devitrification, the content is preferably 0.5% or more, and more preferably 1.2% or more. On the other hand, since a large amount of K can cause brittleness and a decrease in surface stress due to back-exchange during tempering, the content of K2O is preferably 4% or less, more preferably 3% or less, even more preferably 2% or less, even more preferably 1% or less, and particularly preferably 0.5% or less.

[0088] The total content of Na2O and K2O ([Na2O] + [K2O]) is preferably 2% or more, more preferably 2.5% or more, even more preferably 3% or more, and particularly preferably 3.5% or more in order to improve the meltability of the glass. If ([Na2O] + [K2O]) is too high, the surface compressive stress value is likely to decrease, so ([Na2O] + [K2O]) is preferably 10% or less, more preferably 8% or less, even more preferably 7% or less, and particularly preferably 6% or less. Furthermore, the coexistence of Na2O and K2O suppresses the migration of alkali components, which is preferable from the viewpoint of radio wave transmittance.

[0089] From the viewpoint of radio wave transmittance, the glass for chemical strengthening has a ratio of the LiO content to the total content of NaO and KO ([NaO] + [KO]), [[LiO] / ([NaO] + [KO])], of preferably 1 or more, more preferably 2 or more, even more preferably 3 or more, and particularly preferably 5 or more. By setting [[LiO] / ([NaO] + [KO])] within the above range, migration of alkali components can be suppressed. There is no particular upper limit for [[LiO] / ([NaO] + [KO])], but it is typically 20 or less.

[0090] Although MgO, CaO, SrO, and BaO are not essential, one or more of them may be contained from the viewpoint of increasing the stability of the glass and improving the chemical strengthening properties. When these 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 even more preferably 4% or more. Furthermore, from the viewpoint of applying sufficient chemical strengthening stress during chemical strengthening and improving radio wave transmittance, the total content of these is preferably 20% or less, more preferably 10% or less.

[0091] MgO may be added to reduce viscosity during dissolution, etc. When MgO is added, the content is preferably 1% or more, more preferably 2% or more, and even more preferably 3% or more. On the other hand, if the MgO content is too high, it becomes difficult to increase the compressive stress layer during chemical strengthening treatment. The MgO content is preferably 5% or less, more preferably 4% or less, even more preferably 3% or less, and particularly preferably 2% or less.

[0092] CaO is a component that improves the meltability of glass and may be contained. When CaO is contained, the content is preferably 0.1% or more, more preferably 0.15% or more, and even more preferably 0.5% or more. On the other hand, if the CaO content is excessive, it becomes difficult to increase the compressive stress value during chemical strengthening treatment. The CaO content is preferably 5% or less, more preferably 3% or less, even more preferably 1% or less, and typically 0.5% or less.

[0093] ZnO is a component that improves the meltability of glass and may be contained. When ZnO is contained, the content is preferably 0.2% or more, more preferably 0.5% or more. To improve the weather resistance of the glass, the ZnO content is preferably 8% or less, more preferably 5% or less, and even more preferably 3% or less.

[0094] ZnO, SrO, and BaO tend to deteriorate chemical strengthening properties, so to facilitate chemical strengthening, the content of [ZnO] + [SrO] + [BaO] is preferably less than 1%, more preferably 0.5% or less, and even more preferably substantially none of these elements is contained.

[0095] Although ZrO2 does not have to be contained, it is preferable to contain it from the viewpoint of increasing the surface compressive stress of chemically strengthened glass. The ZrO2 content is preferably 0.1% or more, more preferably 0.15% or more, even more preferably 0.2% or more, particularly preferably 0.25% or more, and typically 0.3% or more. On the other hand, if the ZrO2 content is too high, devitrification defects are likely to occur, making it difficult to increase the compressive stress value during chemical strengthening treatment. The ZrO2 content is preferably 2% or less, more preferably 1.5% or less, even more preferably 1% or less, and particularly preferably 0.8% or less.

[0096] The Y2O3 content is preferably 0.1% or more, more preferably 0.2% or more, even more preferably 0.5% or more, and particularly preferably 1% or more. On the other hand, if the content is too high, it becomes difficult to increase the compressive stress layer during chemical strengthening treatment. The Y2O3 content is preferably 10% or less, more preferably 8% or less, even more preferably 5% or less, even more preferably 3% or less, particularly preferably 2% or less, and even particularly preferably 1.5% or less.

[0097] La2O3 is not essential, but can be included for the same reasons as Y2O3. The La2O3 content is preferably 0.1% or more, more preferably 0.2% or more, even more preferably 0.5% or more, and particularly preferably 0.8% or more. On the other hand, if it is too much, it becomes difficult to increase the compressive stress layer during chemical strengthening treatment, so the La2O3 content is preferably 5% or less, more preferably 3% or less, even more preferably 2% or less, and particularly preferably 1.5% or less.

[0098] TiO2 is a component that suppresses solarization of glass and may be contained. When TiO2 is contained, the content is preferably 0.02% or more, more preferably 0.03% or more, even more preferably 0.04% or more, particularly preferably 0.05% or more, and typically 0.06% or more. On the other hand, if the TiO2 content exceeds 1%, devitrification is likely to occur, and the quality of the chemically strengthened glass may be reduced. The TiO2 content is preferably 5% or less, more preferably 3% or less, even more preferably 2% or less, even more preferably 1% or less, particularly preferably 0.5% or less, and even more particularly preferably 0.25% or less.

[0099] Although B2O3 is not essential, it may be contained for the purposes of reducing the brittleness of the glass, improving crack resistance, and improving radio wave transmittance. When B2O3 is contained, the content is preferably 1.0% or more, preferably 3.0% or more, more preferably 4.0% or more, particularly preferably 5.0% or more, even more preferably 7.0% or more, and most preferably 8.0% or more. On the other hand, since an excessively high B2O3 content tends to deteriorate acid resistance, the B2O3 content is preferably 25% or less. The B2O3 content is more preferably 16% or less, even more preferably 13% or less, and particularly preferably 12% or less. It is particularly preferably 11% or less, even more preferably 11% or less, and most preferably 10% or less. It is more preferable that B2O3 is substantially absent in order to prevent the problem of striae formation during melting.

[0100] P2O5 is not essential, but may be added for the purpose of increasing the compressive stress layer during chemical strengthening. When P2O5 is added, the content is preferably 0.25% or more, preferably 0.5% or more, more preferably 0.75% or more, particularly preferably 1.0% or more, even more 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, even more preferably 6% or less, even more preferably 4% or less, particularly preferably 3% or less, even more preferably 2.5% or less, and most preferably 2.0% or less. To prevent the formation of striae during melting, it is more preferable that P2O5 is substantially not added.

[0101] The total content of B2O3 and P2O5 is preferably 0 to 35%, more preferably 5% or more, and even more preferably 8% or more. The total content of B2O3 and P2O5 is preferably 20% or less, more preferably 17% or less, and even more preferably 15% or less.

[0102] NbO 5、Ta2O5, Gd2O3, and CeO2 are components that suppress solarization of glass and improve meltability, and may be contained. When these components are contained, the respective contents are preferably 0.03% or more, more preferably 0.1% or more, even more preferably 0.5% or more, particularly preferably 0.8% or more, and typically 1% or more. On the other hand, if the contents of these components are too high, it becomes difficult to increase the compressive stress value during chemical strengthening treatment, so the contents are preferably 3% or less, more preferably 2% or less, even more preferably 1% or less, and particularly preferably 0.5% or less.

[0103] Furthermore, coloring components may be added within a range that does not impede the achievement of the desired chemical strengthening properties. Suitable examples of coloring components include Fe2O3, Co3O4, MnO2, NiO, CuO, Cr2O3, V2O5, Bi2O3, SeO2, CeO2, Er2O3, and Nd2O3.

[0104] The total content of the coloring components, expressed as mole percentage on an oxide basis, is preferably 5% or less. If it exceeds 5%, the glass may be prone to devitrification. The content of the coloring components is preferably 3% or less, and more preferably 1% or less. If high transmittance of the glass is desired, it is preferable that these components are substantially not contained.

[0105] SO3, chlorides, fluorides, etc. may be appropriately contained as fining agents during melting of the glass. It is preferable that As2O3 is not contained. If Sb2O3 is contained, it is preferably 0.3% or less, more preferably 0.1% or less, and most preferably zero.

[0106] The β-OH value is a value used as an index of the water content of glass. It is measured by measuring the absorbance of light with a wavelength of 2.75 to 2.95 μm, and the maximum value β max This value is calculated by dividing by the glass thickness (mm).

[0107] β-OH value is 0.8mm -1By setting the thickness to 0.6 mm or less, the radio wave transmittance of the glass can be further improved, which is preferable. -1 Less than 0.5mm is preferable -1 Less than 0.4 mm is more preferable. -1 Even more preferred are the following:

[0108] On the other hand, the β-OH value is 0.05 mm -1 By setting the β-OH value at 0.1 mm or more, it is not necessary to dissolve the glass in an extremely dry atmosphere or to drastically reduce the amount of water in the raw materials, and this is preferable because it improves the productivity of the glass and the bubble quality. -1 More than 0.2 mm is more preferable. -1 The above is even more preferable.

[0109] The β-OH value can be adjusted by the glass composition, the heat source during melting, the melting time, and the raw materials.

[0110] Viscosity is 10 2 The temperature (T2) at which the viscosity becomes 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 guide to the melting temperature of the glass, and the lower the T2, the easier the glass tends to be to manufacture. There is no particular restriction on the lower limit of T2, but glass with a low T2 tends to have an excessively low glass transition point, so T2 is usually 1400°C or higher, preferably 1450°C or higher.

[0111] Also, the viscosity is 10 4 The temperature (T4) at which the viscosity becomes dPa·s is preferably 1350°C or lower, more preferably 1300°C or lower, even more preferably 1250°C or lower, and particularly preferably 1150°C or lower. The temperature (T4) is a guideline for the temperature at which glass is formed into a sheet, and glass with a high T4 tends to place a heavy load on the forming equipment. There is no particular restriction on the lower limit of T4, but glass with a low T4 tends to have an excessively low glass transition point, so T4 is usually 900°C or higher, preferably 950°C or higher, and more preferably 1000°C or higher.

[0112] The devitrification temperature of this chemically strengthened glass is 4 It is preferable that the temperature is 120°C higher than the temperature (T4) at which the viscosity becomes dPa·s because devitrification is less likely to occur during molding by the float method. The devitrification temperature is more preferably 100°C higher than T4 or lower, even more preferably 50°C higher than T4 or lower, and particularly preferably T4 or lower.

[0113] The fracture toughness of this chemically strengthened glass is 0.70 MPa m 1 / 2 It is preferable that the pressure is equal to or higher than 0.75 MPa m 1 / 2 More preferably, 0.80 MPa m 1 / 2 More than 0.83 MPa m 1 / 2 The fracture toughness value is usually 2.0 MPa m 1 / 2 Typically 1.5 MPa m 1 / 2 The high fracture toughness value makes it difficult for severe fracture to occur even when a large surface compressive stress is introduced into the glass by chemical strengthening.

[0114] The fracture toughness value can be measured, for example, by the DCDC method (Acta metall. mater. Vol. 43, pp. 3453-3458, 1995).

[0115] The Young's modulus of the present chemically strengthened glass is preferably 80 GPa or more, more preferably 82 GPa or more, even more preferably 84 GPa or more, and particularly preferably 85 GPa or more, so that the glass is less likely to fracture. The upper limit of the Young's modulus is not particularly limited, but since glass with a high Young's modulus may have low acid resistance, it is preferably, for example, 110 GPa or less, more preferably 100 GPa or less, and even more preferably 90 GPa or less. The Young's modulus can be measured, for example, by an ultrasonic pulse method.

[0116] The average linear thermal expansion coefficient (thermal expansion coefficient) of the present glass for chemical strengthening at 50 to 350°C is preferably 95 × 10 -7 / ℃ or less, more preferably 90×10 -7 / °C or less, more preferably 88 × 10 -7 / °C or less, particularly preferably 86 × 10 -7 / °C or less, most preferably 84 x 10 -7 / °C or less. Although there are no particular restrictions on the lower limit of the thermal expansion coefficient, glass with a small thermal expansion coefficient may be difficult to melt. Therefore, the average linear thermal expansion coefficient (thermal expansion coefficient) of the glass for chemical strengthening of the present invention from 50 to 350°C is, for example, 60 × 10 -7 / °C or more, and more preferably 70 × 10 -7 / °C or higher, and more preferably 74 × 10 -7 / °C or more, particularly preferably 76 × 10 -7 / ℃ or more.

[0117] From the viewpoint of reducing warpage after chemical strengthening, the glass transition point (Tg) is preferably 500° C. or higher, more preferably 520° C. or higher, and even more preferably 540° C. or higher. From the viewpoint of ease of float forming, the glass transition point (Tg) is preferably 750° C. or lower, more preferably 700° C. or lower, even more preferably 650° C. or lower, particularly preferably 600° C. or lower, and most preferably 580° C. or lower.

[0118] The chemically strengthened glass can be produced by a conventional method. For example, the raw materials for the glass components are mixed and heated and melted in a glass melting furnace. The glass is then homogenized by a known method, formed into a desired shape such as a glass plate, and slowly cooled.

[0119] Examples of glass sheet forming methods include the float method, press method, fusion method, and down-draw method. In particular, the float method, which is suitable for mass production, is preferred. Continuous forming methods other than the float method, such as the fusion method and down-draw method, are also preferred.

[0120] The molded glass is then ground and polished as necessary to form a glass substrate. When the glass substrate is cut to a predetermined shape and size or chamfered, it is preferable to perform the cutting or chamfering of the glass substrate before performing the chemical strengthening treatment described below, because a compressive stress layer is also formed on the end surface by the subsequent chemical strengthening treatment.

[0121] <<Glass-ceramics>> The present glass for chemical strengthening may be crystallized glass (hereinafter also referred to as "the present glass-ceramics"). The present glass-ceramics is crystallized glass having the glass composition of the present glass for chemical strengthening described above.

[0122] The present crystallized glass preferably contains one or more of lithium silicate crystals, lithium aluminosilicate crystals or lithium phosphate crystals, magnesium aluminosilicate crystals, magnesium silicate crystals, and silicate crystals. As the lithium silicate crystals, lithium metasilicate crystals are more preferable. As the lithium aluminosilicate crystals, petalite crystals or β-spodumene crystals, α-eucryptite, and β-eucryptite are preferable. As the lithium phosphate crystals, lithium orthophosphate crystals are preferable.

[0123] To increase transparency, crystallized glass containing lithium metasilicate crystals is more preferred.

[0124] Glass-ceramics can be obtained by heat-treating and crystallizing amorphous glass having the same composition as the present glass for chemical strengthening. The glass composition of the glass-ceramics is the same as that of the amorphous glass.

[0125] The visible light transmittance of the crystallized glass (total visible light transmittance including diffuse transmitted light) is preferably 85% or more when converted to a thickness of 700 μm, so that when used as a cover glass for a mobile display, the display screen is easy to see. A visible light transmittance of 88% or more is more preferable, and 90% or more is even more preferable. The higher the visible light transmittance, the better, but it is usually 93% or less. Note that the visible light transmittance of ordinary amorphous glass is about 90% or more.

[0126] If the thickness of the glass-ceramic is not 700 μm, the transmittance for a thickness of 700 μm can be calculated from the measured transmittance using the Lambert-Beer law.

[0127] In addition, in the case of glass having a thickness t of more than 700 μm, the thickness may be adjusted to 0.7 mm by polishing or etching, and then the actual measurement may be performed.

[0128] Furthermore, the haze value, when converted to a thickness of 700 μm, is preferably 1.0% or less, more preferably 0.4% or less, even more preferably 0.3% or less, particularly preferably 0.2% or less, and most preferably 0.15% or less. The smaller the haze value, the better, but if the crystallization rate or the crystal grain size is reduced to reduce the haze value, the mechanical strength will decrease. To increase the mechanical strength, the haze value for a thickness of 700 μm is preferably 0.02% or more, more preferably 0.03% or more. The haze value is a value measured in accordance with JIS K7136 (2000).

[0129] If the total light visible transmittance of crystallized glass with a thickness of t [μm] is 100×T [%] and the haze value is 100×H [%], then by applying the Beer-Lambert law and using the constant α, T = (1-R) 2 ×exp(-αt / 1000). Using this constant α, dH / dt ∝ exp(-αt / 1000) × (1-H) This can be expressed as:

[0130] In other words, the haze value is thought to increase in proportion to the internal linear transmittance as the thickness increases, so the haze value H for 700 μm is 0.7 is calculated using the following formula:

[0131]

number

[0132] Furthermore, in the case of glass having a thickness t greater than 700 μm, the thickness may be adjusted to 700 μm by polishing or etching, and then the actual measurement may be performed.

[0133] When tempered glass made from glass-ceramics is used as the cover glass for a mobile display, it is preferable that it has a texture and a luxurious feel different from plastic. Therefore, the refractive index of this glass-ceramics at a wavelength of 590 nm is preferably 1.52 or more, more preferably 1.55 or more, and even more preferably 1.57 or more.

[0134] The crystallization rate of the crystallized glass is preferably 5% or more, more preferably 10% or more, even more preferably 15% or more, and particularly preferably 20% or more in order to increase the mechanical strength. In order to increase the transparency, it is preferably 70% or less, more preferably 60% or less, and particularly preferably 50% or less. A small crystallization rate is also advantageous in that it is easy to heat and bend.

[0135] The crystallinity can be calculated from the X-ray diffraction intensity by the Rietveld method. The Rietveld method is described in "Crystal Analysis Handbook" (Kyoritsu Shuppan, 1999, pp. 492-499), edited by the Editorial Committee of the Crystallographic Society of Japan.

[0136] The average particle size of the precipitated crystals in the crystallized glass is preferably 80 nm or less, more preferably 60 nm or less, even more preferably 50 nm or less, particularly preferably 40 nm or less, and most preferably 30 nm or less. The average particle size of the precipitated crystals can be determined from a transmission electron microscope (TEM) image. The average particle size of the precipitated crystals can be estimated from a scanning electron microscope (SEM) image.

[0137] <<Chemical strengthening treatment>> The present chemically strengthened glass can be produced by subjecting the obtained glass plate to a chemical strengthening treatment, followed by washing and drying.

[0138] The chemical strengthening treatment can be performed by a known method. In the chemical strengthening treatment, the glass sheet is brought into contact with a melt of a metal salt (e.g., potassium nitrate) containing a metal ion with a large ionic radius (typically, K ion) by immersion or the like. As a result, the metal ion with a small ionic radius (typically, Na ion or Li ion) in the glass sheet is replaced with a metal ion with a large ionic radius (typically, K ion for Na ion, and Na ion for Li ion).

[0139] The chemical strengthening treatment (ion exchange treatment) can be carried out, for example, by immersing the glass plate for 0.1 to 500 hours in a molten salt such as potassium nitrate heated to 360 to 600° C. The heating temperature of the molten salt is preferably, for example, 375 to 500° C., and the immersion time of the glass plate in the molten salt is preferably, for example, 0.3 to 200 hours.

[0140] Examples of molten salts used in chemical strengthening include nitrates, sulfates, carbonates, and chlorides. Nitrates include lithium nitrate, sodium nitrate, potassium nitrate, cesium nitrate, and silver nitrate. Sulfates include lithium sulfate, sodium sulfate, potassium sulfate, cesium sulfate, and silver sulfate. Carbonates include lithium carbonate, sodium carbonate, and potassium carbonate. Chlorides include lithium chloride, sodium chloride, potassium chloride, cesium chloride, and silver chloride. These molten salts may be used alone or in combination.

[0141] In the present invention, the treatment conditions for the chemical strengthening treatment may be appropriately selected in consideration of the properties and composition of the glass, the type of molten salt, and the entropy function S desired for the final chemically strengthened glass, as well as the chemical strengthening properties such as the surface compressive stress and the depth of the compressive stress layer.

[0142] In the present invention, the chemical strengthening treatment may be performed only once, or multiple times under two or more different conditions (multi-stage strengthening). Here, for example, the first stage of chemical strengthening treatment is performed under conditions that increase the DOL and relatively decrease the CS. Then, the second stage of chemical strengthening treatment is performed under conditions that decrease the DOL and relatively increase the CS. This increases the CS of the outermost surface of the chemically strengthened glass, while suppressing the internal tensile stress area (St), thereby keeping the internal tensile stress (CT) low.

[0143] <Electronic device enclosure> The electronic device housing of the present invention contains the chemically strengthened glass of the present invention. Examples of electronic device housings include cover glass for the display surface and back surface of mobile terminals, and cover glass for non-portable televisions (TVs), personal computers (PCs), touch panels, and other display devices. [Example]

[0144] The present invention will be described below with reference to examples, but the present invention is not limited thereto.

[0145] [Experimental Example 1] Various glass raw materials were mixed and weighed to give 400 g of glass. The mixed raw materials were then placed in a platinum crucible and placed in an electric furnace at 1500 to 1700°C, where they were melted for about 3 hours, degassed, and homogenized.

[0146] Of the various chemically strengthened glasses obtained, glasses whose relative permittivity or dielectric dissipation factor decreased after chemical strengthening compared to before chemical strengthening were deemed to have increased radio wave transmittance due to chemical strengthening. Figure 1 shows a graph showing the correlation between radio wave transmittance at a frequency of 10 GHz and the entropy function and compressive stress for glasses whose radio wave transmittance increased after chemical strengthening. The vertical axis of Figure 1 represents the sum of the values ​​obtained by multiplying the relative permittivity and dielectric dissipation factor by 100 before and after chemical strengthening, and the horizontal axis represents the parameter Z, which can be calculated from the entropy function and compressive stress before and after chemical strengthening.

[0147] The alkali metal ion content for calculating the entropy function was measured using an EPMA (Electron Probe Micro Analyzer, JEOL: JXA-8500F) under the following measurement conditions: acceleration voltage 15 kV, probe current 30 nA, integration time 1000 msec. / point, and 1 μm intervals.

[0148] According to Figure 1, when Z, expressed by the formula [Z = (S2 - S1) × 10 + X / 1000], is 0.65 or more, the movement of alkali metal ions is suppressed after chemical strengthening compared to before chemical strengthening, and it is clear that excellent radio wave transmittance is exhibited in the high frequency band.

[0149] [Experimental Example 2] Glass raw materials were mixed to obtain the composition shown in Table 1 in terms of oxide-based mole percentage, and weighed out to give 400 g of glass. The mixed raw materials were then placed in a platinum crucible and placed in an electric furnace at 1500 to 1700°C, where they were melted for about 3 hours, degassed, and homogenized.

[0150] The resulting molten glass was poured into a metal mold and held at a temperature approximately 50°C higher than the glass transition point for 1 hour, after which it was cooled to room temperature at a rate of 0.5°C / min to obtain a glass block. The resulting glass block was cut and ground, and finally both sides were mirror-polished to obtain a glass plate with a thickness (t) of 700 μm.

[0151] For each glass, the relative permittivity and dielectric loss tangent tanδ were measured at 20°C and a frequency of 10 GHz. The results are shown in Table 2. In addition, a two-stage chemical strengthening treatment was carried out under the conditions shown in Table 2 to produce the chemically strengthened glasses of Examples 1 to 7 below. Examples 1 to 4 are working examples, and Examples 5 to 7 are comparative examples.

[0152] [Table 1]

[0153] The compressive stress of the surface layer after chemical strengthening and the depth of the compressive stress layer DOL were measured using an optical waveguide surface stress meter FSM-6000 and a scattered light photoelastic stress meter SLP-1000 manufactured by Orihara Seisakusho, and the average value of the compressive stress in the region from the surface to 0.05 μm was recorded as the internal average chemical strengthening stress.

[0154] The alkali metal ion content of the samples was measured at a depth of 0.05 mm from the glass surface and at the center of the thickness (the center of the glass) using an EPMA (Electron Probe Micro Analyzer, JEOL: JXA-8500F). The average values ​​are shown in Table 2 as the amount of alkali metal ions after strengthening and the amount of alkali metal ions at the center of the thickness.

[0155] In addition, the entropy function S was calculated from the amount of ions of the obtained alkali metal elements according to the following definition formula.

[0156] 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]))

[0157] The entropy function S2 calculated from the average amount of alkali ions from the glass surface to a depth of 0.05t is defined as S2, and the entropy function S1 calculated from the amount of alkali ions in the center of the glass is defined as S1. The alkali fixation parameter Z was calculated using the following formula from these entropy functions S1 and S2 and the average value X (unit: MPa) of compressive stress in the region from the glass surface to a depth of 0.05t. The results are shown in Table 2. In Table 2, the "change in entropy function" was obtained by subtracting the "entropy function S1 at the center of the plate thickness (glass center)" from the "entropy function S2 after chemical strengthening." Z = (S2 - S1) × 10 + X / 1000

[0158] Furthermore, the relative permittivity and tan δ of the chemically strengthened samples were measured at 20° C. and a frequency of 10 GHz. The results are shown in Table 2.

[0159] The relative permittivity and tan δ were measured by the slip post dielectric resonance method (SPDR method) using a network analyzer at a temperature of 20°C and a frequency of 10 GHz.

[0160] In Table 2, the "change in relative permittivity due to chemical strengthening" was calculated by subtracting the "relative permittivity before chemical strengthening" from the "relative permittivity after chemical strengthening." Also, the "change in dielectric loss due to chemical strengthening" was calculated by subtracting the "dielectric loss before chemical strengthening" from the "dielectric loss after chemical strengthening."

[0161] [Table 2]

[0162] As shown in Table 2, in Examples 1 to 4, which are working examples, the change in entropy function before and after chemical strengthening is very large, and the compressive stress near the surface of the glass is also high, so the alkali fixation parameter Z is 0.65 or more.As a result, it can be confirmed that the physical properties of either the relative permittivity or the dielectric loss decrease before and after chemical strengthening treatment, and the dielectric properties are improved.

[0163] On the other hand, for Examples 5 to 7, which are comparative examples, the change in the entropy function before and after chemical strengthening is small, so the alkali fixation parameter Z is below 0.65.As a result, it can be confirmed that the chemical strengthening treatment increases both the relative permittivity and dielectric loss, and the dielectric properties are reduced.

[0164] 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 Japanese patent applications filed on December 4, 2020 (Patent Application No. 2020-202039) and June 4, 2021 (Patent Application No. 2021-094715), which are incorporated by reference in their entirety. All references cited herein are incorporated by reference in their entirety.

Claims

1. A chemically strengthened glass having a thickness t (unit: μm) and a relative dielectric constant of 7.0 or less at 20 ° C. and a frequency of 10 GHz, The base composition contains the following components in mole percentages on an oxide basis: SiO ２ 40 to 65% B ２ O ３ 0 to 20%, Al ２ O ３ を12~25%、 Li ２ Oを5~12%、 Na ２ Oを1.5~10%、 K ２ O below 1% MgO 5% or less, TiO ２ 3% or less, P ２ O ５ 6% or less, Contains 10% or less of MgO + CaO + SrO + BaO, Entropy function S calculated from the amount of alkali ions in the center of the glass １ , the entropy function S calculated from the average amount of alkali ions from the glass surface to a depth of 0.05t ２ and Z calculated by the following formula from the average value X [unit: MPa] of compressive stress in a region from the glass surface to a depth of 0.05t is 0.65 or more, The entropy function S １ Chemically strengthened glass having a modulus of 0.375 or less. Z=(S ２ -S １ )×10+X / 1000 where the entropy function S is the Li ２ O, Na ２ O and K ２ O content in mole percentage based on oxide [Li ２ O], [Na ２ O] and [K ２ O] using the following formula. ２ O], [Na ２ O] and [K ２ If [O] is zero, then 1 × 10 －４ Let's say. ==-[L) ２ O] / ([L- ２ O]+[[ ２ O]+[K ２ O])OOg([L- ２ O] / ([L- ２ O]+[[ ２ O]+[K ２ O]))-[N ２ O] / ([L- ２ O]+[[ ２ O]+[K ２ O])OOg([Na ２ O] / ([L- ２ O]+[[ ２ O]+[K ２ O]))-[K ２ O] / ([L- ２ O]+[[ ２ O]+[K ２ O])OOg([K ２ O] / ([L- ２ O]+[[ ２ O]+[K ２ O]))

2. The base composition is, in mole percentage based on oxide, Li ２ O and / or Na ２ The chemically strengthened glass according to claim 1, containing 7.5 to 20% O in total.

3. The base composition is, in mole percentage based on oxide, K ２ The chemically strengthened glass according to claim 1, containing 0.5% or less of O.

4. The chemically strengthened glass according to claim 1, wherein the matrix composition contains 4% or less of MgO in mole percentage based on oxides.

5. The base composition is, in mole percentage based on oxide, Na ２ O and K ２ Li relative to the total content of O ２ The chemically strengthened glass according to claim 1, wherein the ratio of the O content is 1 or more.

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

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

8. Internal chemical strengthening stress CS at a depth of 0.05t from the glass surface ０ The chemically strengthened glass according to any one of claims 1 to 5, wherein the tensile strength (T) of the glass is 75 MPa or more and the thickness (t) is 300 μm or more.

9. Surface compressive stress value CS ０ The chemically strengthened glass according to claim 1, wherein the compressive strength is 300 MPa or more.

10. The chemically strengthened glass according to claim 1, wherein the thickness t is 100 μm or more and 2000 μm or less.

11. The chemically strengthened glass according to claim 1, which is glass-ceramic.

12. An electronic device housing comprising the chemically strengthened glass according to any one of claims 1 to 11.

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