Chemically strengthened glass and electronic device case

Abstract

The invention relates to chemically strengthened glass and an electronic device case. The purpose of the present invention is to provide a chemically strengthened glass having both excellent radio wave transmissivity in a high-frequency band and high strength. The present invention relates to a chemically strengthened glass having a thickness of t (in [mu] m) and a relative dielectric constant of 7.0 or less at 20 DEG C and a frequency of 10 GHz (Z = (S2-S1) * 10 + X / 1000), where Z, as determined by the following equation, is 0.65 or more. In the formula, S1 is an entropy function calculated from the amount of alkali ions in the center of the glass, S2 is an entropy function calculated from the average amount of alkali ions in a region from the surface of the glass to a depth of 0.05 t, and X is the average value (unit: MPa) of compressive stress in a region from the surface of the glass to a depth of 0.05 t.

Description

[0001] This application is a divisional application of the Chinese Patent Application No. 202180080619.6, filed on September 3, 2021, with the title of Chemically Strengthened Glass and Electronic Device Housing. TECHNICAL FIELD

[0002] The present application relates to chemically strengthened glass and electronic device housing. BACKGROUND

[0003] For the housing of electronic devices such as portable terminals, since strength that does not easily break even if the portable terminal falls from a high place is required, chemically strengthened glass is widely used. Chemically strengthened glass is glass in which an alkali ion contained in the glass is ion-exchanged with an alkali ion having a larger ionic radius contained in a molten salt such as sodium nitrate by a method of immersing the glass in the molten salt, and a compressive stress layer is formed in a surface layer portion of the glass. For example, in Patent Literature 1, an aluminosilicate glass having a specific composition, which is chemically strengthened to obtain a high surface compressive stress, is disclosed.

[0004] On the other hand, in communication devices such as mobile phones, smartphones, portable information terminals, Wi-Fi devices, surface acoustic wave (SAW) devices, radar parts, antenna parts, and the like, in order to achieve large capacity of communication capacity, high speed of communication speed, and the like, high frequency of signal frequency is being developed. In recent years, as a new communication system using a higher frequency band, the popularization of 5G (the fifth generation mobile communication system) is expected.

[0005] In the high frequency band for 5G, the protective glass sometimes hinders transmission and reception of radio waves, and a protective glass having excellent dielectric properties such as radio wave transmittance is required for portable terminals corresponding to 5G. As excellent dielectric properties, for example, a low relative permittivity and a low dielectric loss are desired. By reducing the relative permittivity, reflection of radio waves can be suppressed, and radio wave transmittance can be improved. In addition, due to the reduction of the dielectric loss, the loss of radio waves can be suppressed.

[0006] As a glass having high radio wave transmittance in the high frequency band for 5G, that is, a glass having a small relative permittivity and a small dielectric loss tangent, several alkali-free glasses have been developed so far (Patent Literature 2).

[0007] PRIOR ART DOCUMENTS

[0008] PATENT LITERATURE

[0009] Patent Literature 1: Japanese Patent Application Laid-Open No. 2018-520082

[0010] Patent Literature 2: International Publication No. 2019 / 181707 SUMMARY

[0011] Problem to be solved by the invention

[0012] However, the alkali-free glass disclosed in Patent Literature 2, which contains almost no alkali ions, is difficult to be chemically strengthened. In addition, the radio wave transmittance of the chemically strengthened glass is difficult to predict, and it is difficult to balance the radio wave transmittance in the high frequency band and the strength.

[0013] Therefore, an object of the present invention is to provide a chemically strengthened glass which has both excellent radio wave transmittance in the high frequency band and high strength.

[0014] Means for solving the problem

[0015] The present inventors found both a glass in which the radio wave transmittance after chemical strengthening in the high frequency band is reduced compared to before chemical strengthening and a glass in which the radio wave transmittance after chemical strengthening is increased compared to before chemical strengthening. In addition, for the glass in which the radio wave transmittance in the high frequency band is increased after chemical strengthening, the correlation between the surface properties after chemical strengthening and the radio wave transmittance was found, and thus the present invention was completed.

[0016] The present invention is a chemically strengthened glass having a thickness of t (unit: pm) and a relative dielectric constant of 7.0 or less at 20°C and a frequency of 10 GHz, in which Z calculated by the following formula is 0.65 or more,

[0017] Z = (S2 - S1) x 10 + X / 1000

[0018] In the above formula,

[0019] S1 is an entropy function calculated from the amount of alkali ions in the center portion of the glass,

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

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

[0022] wherein the entropy function S is calculated from the contents of Li20, Na20 and K20 in terms of mole percentage on an oxide basis [Li20], [Na20] and [K20] at each depth by the following formula. In the formula, in the case where [Li20], [Na20] and [K20] are zero, the entropy function S is 1 x 10 -4 .

[0023] S = - [Li20] / ([Li20] + [Na20] + [K20]) log ([Li20] / ([Li20] + [Na20] + [K20])) - [Na20] / ([Li20] + [Na20] + [K20]) log ([Na20] / ([Li20] + [Na20] + [K20])) - [K20] / ([Li20] + [Na20] + [K20]) log ([K20] / ([Li20] + [Na20] + [K20])).

[0024] In the chemically strengthened glass of the present application (hereinafter, also referred to as the present chemically strengthened glass), the value of (S2 - S1), which is the value of the above-mentioned entropy function S2 minus the above-mentioned entropy function S1, is preferably 0.04 or greater.

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

[0026] The base composition of the present chemically strengthened glass preferably contains, in terms of mole percentage on an oxide basis, 40 to 80% of Si02, 0 to 20% of B203, 1 to 25% of Al203, and 5 to 30% in total of Li20 and / or Na20.

[0027] The present chemically strengthened glass preferably has a surface compressive stress value CS0 of 300 MPa or greater.

[0028] The present chemically strengthened glass preferably has an internal chemical strengthening stress CS 0.05t of 75 MPa or greater at a depth of 0.05t from the surface of the glass, and the above-mentioned thickness t is 300 μm or greater.

[0029] The present chemically strengthened glass preferably has a compressive stress layer depth DOL of 70 μm or greater, and the above-mentioned thickness t is 350 μm or greater.

[0030] The present chemically strengthened glass is preferably a lithium-aluminum-silicate glass,

[0031] The base composition of the chemically strengthened glass contains, in terms of mole percentage on an oxide basis, 40 to 70% of Si02, 7.5 to 20% of Al203, and 5 to 25% of Li20.

[0032] The present chemically strengthened glass preferably has the above-mentioned thickness t of 100 μm or greater and 2000 μm or less.

[0033] The present chemically strengthened glass is preferably a glass-ceramic.

[0034] The present application also provides an electronic device housing comprising the present chemically strengthened glass.

[0035] Inventive Effects

[0036] The Z of the chemically strengthened glass of the present application, which is calculated by a formula represented by an entropy function S indicating the degree of mixing of alkali metal ions and an average value X of compressive stress, is within a certain range, and the movement of alkali metal ions in the glass is suppressed. Thus, the chemically strengthened glass of the present application is excellent in strength while showing excellent radio wave transmission property in a high frequency band. BRIEF DESCRIPTION OF DRAWINGS

[0037] Figure 1 A graph showing the correlation between the amount of change in the sum of the relative dielectric constant and the dielectric loss tangent before and after chemical strengthening, which is important in radio wave transmission property at a frequency of 10 GHz, and the entropy function and the compressive stress. The vertical axis is the sum of the values of the relative dielectric constant and the dielectric loss tangent before and after chemical strengthening, which is 100 times the absolute value, 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. The radio wave transmission property is determined by both the relative dielectric constant and the dielectric loss tangent, but since the absolute value of the relative dielectric constant is larger than that of the dielectric loss tangent, the effect is also high, and therefore the radio wave transmission property is represented by the sum of the relative dielectric constant and the dielectric loss tangent, which is 100 times the absolute value. DETAILED DESCRIPTION

[0038] In the present specification, "~" indicating a numerical range is used in the meaning that the numerical values recited before and after it are included as lower limit values and upper limit values. The following "~" is used in the same meaning in the present specification unless otherwise specified.

[0039] In the present specification, "chemically strengthened glass" refers to glass after chemical strengthening treatment, and "glass for chemical strengthening" refers to glass before chemical strengthening treatment.

[0040] In the present specification, "the basic composition of the chemically strengthened glass" refers to the glass composition of the glass for chemical strengthening. In the chemically strengthened glass, the glass composition at a depth of 1 / 2 of the thickness t is the basic composition of the chemically strengthened glass except in the case where an extreme ion exchange treatment is performed.

[0041] In the present specification, the glass composition is expressed in terms of molar percentage on an oxide basis unless otherwise specified, and the molar % is simply denoted as "%".

[0042] In addition, in the present specification, "substantially not containing" means that it is contained at a level of impurities or the like, i.e., not intentionally contained. Specifically, for example, less than 0.1 mol%.

[0043] In the present specification, "stress profile" is a graph showing compressive stress values as a function of depth from the glass surface. In addition, "compressive stress depth of layer (DOL)" is the depth at which the compressive stress value (CS) is zero. "Tensile stress value (CT)" means the tensile stress value at the depth of 1 / 2 of the thickness t of the glass. In the present specification, the tensile stress value is expressed in the form of negative compressive stress value.

[0044] The stress profile in the present specification can be measured using a scattered light photoelastic stress meter (for example, SLP-1000 manufactured by Oryuka K.K.). The scattered light photoelastic stress meter is affected by surface scattering, and sometimes the measurement accuracy near the surface of the sample decreases. However, in the case where compressive stress is generated only by ion exchange of lithium ions in the glass with sodium ions outside, for example, since the compressive stress value expressed as a function of depth follows a complementary error function, by measuring the stress value inside, the stress value at the surface can be known. In the case where it does not follow a complementary error function or the like, the surface portion can be measured by other methods, for example, a method of measuring using a surface stress meter or the like.

[0045] <Chemically Strengthened Glass>

[0046] The chemically strengthened glass of the present application is a chemically strengthened glass having a thickness 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) x 10 + X / 1000. In the above formula, S1 is an entropy function calculated from the alkali ion amount of the center portion of the glass, S2 is an entropy function calculated from the average alkali ion amount in the region from the surface of the glass to a depth of 0.05t, and X is the average value of compressive stress [unit: MPa] in the region from the surface of the glass to a depth of 0.05t.

[0047] Here, the entropy function S is calculated from the contents [Li2O], [Na2O] and [K2O] of Li2O, Na2O and K2O in terms of mole percentage on an oxide basis at each depth by the following formula. In the formula below, in the case where [Li2O], [Na2O] and [K2O] are zero, the entropy function S is 1 x 10 -4 .

[0048] 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]))

[0049] In the past, the radio wave transmittance of chemically strengthened glass varied with frequency, and thus it was difficult to predict, and it was difficult to balance the radio wave transmittance and the strength in the high frequency band. The present inventors focused on the relationship between the radio wave transmittance in the high frequency band and chemical strengthening, and found that there are glasses in which the radio wave transmittance in the high frequency band increases after chemical strengthening compared to before chemical strengthening, and glasses in which the radio wave transmittance in the high frequency band decreases after chemical strengthening.

[0050] Furthermore, the present inventors considered that the glasses in which the radio wave transmittance in the high frequency band increases after chemical strengthening compared to before chemical strengthening have the following two characteristics: 1) the degree of mixing of alkali ions greatly changes before and after chemical strengthening; and 2) a high compressive stress is introduced after chemical strengthening. Hereinafter, the characteristics of 1) and 2) are described.

[0051] The radio wave transmittance increases due to the reduction of the relative dielectric constant and the dielectric loss. Since the relative dielectric constant and the dielectric loss are mainly generated due to the movement of alkali metal ions in the glass, it is considered that the movement of alkali metal ions in the glass is suppressed by the chemical strengthening treatment, and thus the relative dielectric constant and the dielectric loss can be reduced.

[0052] Regarding the above 1) in which the degree of mixing of alkali ions greatly changes before and after chemical strengthening, it is considered that by the presence and mixing of different kinds of alkali metal ions in the glass, the exchange of alkali metal ions with each other is not easily caused, and thus the relative dielectric constant and the dielectric loss are reduced, and the dielectric properties are improved. The degree of mixing of alkali metal ions is represented by an entropy function.

[0053] Regarding the above 2) in which 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 suppressed, and thus the relative dielectric constant and the dielectric loss are reduced, and the dielectric properties are improved.

[0054] Figure 1 A graph showing the relationship between the amount of change in the sum of the relative dielectric constant and the dielectric loss tangent at a frequency of 10 GHz of the glass in which the radio wave transmittance increases after chemical strengthening compared to before chemical strengthening, and the entropy function and the compressive stress, in Experimental Example 1 described later. Figure 1 The vertical axis is the sum of the values of 100 times the relative dielectric constant and the dielectric loss tangent before and after chemical strengthening, and the horizontal axis is a parameter Z which can be calculated from the entropy function and the compressive stress before and after chemical strengthening. Note that the radio wave transmittance is determined by both the relative dielectric constant and the dielectric loss tangent, but since the absolute value of the relative dielectric constant is larger than that of the dielectric loss tangent, and the effect is also high, the radio wave transmittance is represented by the sum of the values of 100 times the amount of change in the relative dielectric constant and the amount of change in the dielectric loss tangent. The details of Experimental Example 1 are described later.

[0055] The content of alkali metal ions used for calculating the entropy function was measured using an EPMA (Electron Probe Micro Analyzer, manufactured by JEOL Ltd.: JXA-8500F). As the measurement conditions for the 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.

[0056] According to Figure 1 It is known that, by Z represented by the above formula [Z = (S2 - S1) x 10 + X / 1000] being 0.65 or greater, the movement of alkali metal ions is suppressed after chemical strengthening compared to before chemical strengthening, and excellent radio wave transmission is exhibited in the high frequency band.

[0057] By chemical strengthening, the movement of alkali metal ions is suppressed after chemical strengthening compared to before chemical strengthening, and the radio wave transmission is improved, and these can be evaluated by the amount of change in the relative dielectric constant caused by chemical strengthening, and the amount of change in the dielectric loss caused by chemical strengthening.

[0058] Specifically, for example, the value obtained by subtracting the "relative dielectric constant at 20°C, 10 GHz after chemical strengthening" from the "relative dielectric constant at 20°C, 10 GHz before chemical strengthening" is preferably 0 or greater, more preferably 0.02 or greater, further preferably 0.04 or greater, more further preferably 0.06 or greater, particularly preferably 0.08 or greater, further preferably 0.1 or greater, and most preferably 0.12 or greater. By reducing the relative dielectric constant of the glass after chemical strengthening by 0 or greater compared to before chemical strengthening, it can be evaluated that the relative dielectric constant is reduced and the radio wave transmission is improved by chemical strengthening.

[0059] In addition, for example, the value obtained by subtracting the "dielectric loss tangent at 20°C, 10 GHz after chemical strengthening" from the "dielectric loss tangent at 20°C, 10 GHz before chemical strengthening" is preferably 0 or greater, more preferably 0.001 or greater, further preferably 0.002 or greater, more further preferably 0.003 or greater, and particularly preferably 0.004 or greater. By reducing the dielectric loss tangent of the glass after chemical strengthening by 0 or greater compared to before chemical strengthening, it can be evaluated that the dielectric loss is reduced and the radio wave transmission is improved by chemical strengthening.

[0060] In the case of designing a circuit on a glass substrate or the like, the dielectric properties of the glass, particularly the dielectric properties of the surface layer of the glass, are particularly important in the high frequency band. In the high frequency band, the relative dielectric constant and the dielectric loss tangent of the surface of the glass sheet of the chemically strengthened glass of the present application are smaller than those of the interior of the glass, and thus the radio waves can be effectively transmitted, and the dielectric properties of the surface layer of the glass are excellent.

[0061] Z represented by the above formula [Z = (S2 - S1) x 10 + X / 1000] is preferably 0.65 or greater, more preferably 0.7 or greater, further preferably 0.8 or greater, still further preferably 0.9 or greater, yet further preferably 1.0 or greater, particularly preferably 1.25 or greater, further preferably 1.5 or greater, most preferably 2.0 or greater. By making Z 0.65 or greater, the movement of alkali metal ions after chemical strengthening is suppressed, and excellent radio wave transmission in the high frequency band is exhibited. The value of Z can be adjusted by the composition of the glass for chemical strengthening and the chemical strengthening treatment conditions (composition of molten salt, time, temperature, etc.).

[0062] S1 in the above formula is an entropy function calculated from the alkali ion amount of the center portion of the glass, and S2 is an entropy function calculated from the average alkali ion amount in the region from the surface of the glass to a depth of 0.05t.

[0063] Although the value of S1 is not particularly limited, the lower S1 is, the better the chemical strengthening properties can be obtained, and thus the value of S1 is preferably, for example, 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, most preferably 0.15 or less. On the other hand, when S1 is too low, the relative dielectric constant and the dielectric loss tangent cannot be reduced even if chemical strengthening is performed, and thus is preferably 0.0 or greater.

[0064] Although the value of S2 is not particularly limited, the higher S2 is, the more easily the relative dielectric constant and the dielectric loss tangent of the glass after chemical strengthening can be reduced, and the more easily good radio wave transmission can be obtained after chemical strengthening, and thus the value of S2 is preferably, for example, 0.2 or greater, more preferably 0.25 or greater, further preferably 0.3 or greater, still further preferably 0.35 or greater, particularly preferably 0.40 or greater, further preferably 0.45 or greater. On the other hand, when S2 is too high, chemical strengthening stress cannot be sufficiently introduced, and thus the value of S2 is preferably, for example, 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.

[0065] Although the value obtained by subtracting S1 from S2, i.e., (S2-S1), is not particularly limited, the higher (S2-S1) is, the more it is possible to reduce the relative dielectric constant and the dielectric loss tangent after chemical tempering, and therefore (S2-S1) is preferably 0.04 or greater, more preferably 0.05 or greater, further preferably 0.1 or greater, more further preferably 0.15 or greater, particularly preferably 0.2 or greater, further preferably 0.25 or greater, most preferably 0.3 or greater. On the other hand, in the case where the value obtained by subtracting S1 from S2 is too high, sufficient chemical tempering stress cannot be introduced, and therefore (S2-S1) is preferably 0.5 or less, more preferably 0.48 or less, further preferably 0.46 or less, more further preferably 0.44 or less, particularly preferably 0.42 or less, further preferably 0.40 or less, most preferably 0.38 or less.

[0066] By setting S1 and S2 within the above range, the degree of mixing of alkali metal ions caused by chemical tempering can be increased, thereby suppressing the movement of alkali metal ions in the glass surface layer and improving the radio wave transmission properties in the high frequency band. S1 and S2 can be adjusted by the composition of the glass for chemical tempering and the chemical tempering treatment conditions (composition of molten salt, time, temperature, etc.).

[0067] X in the above formula is the average value of compressive stress [unit: MPa] in the region from the glass surface to a depth of 0.05t. Although the value of X is not particularly limited, it is, for example, preferably 100 MPa or greater, more preferably 150 MPa or greater, further preferably 200 MPa or greater, more further preferably 250 MPa or greater, particularly preferably 275 MPa or greater, further preferably 300 MPa or greater, most preferably 320 MPa or greater. 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, the glass explodes explosively in the form of a fine piece when it is broken, and therefore the value of X is preferably 600 MPa or less, more preferably 500 MPa or less, further preferably 475 MPa or less, more further preferably 450 MPa or less, particularly preferably 425 MPa or less, further preferably 400 MPa or less, most preferably 375 MPa or less. The value of X can be adjusted by the composition of the glass for chemical tempering and the chemical tempering treatment conditions (composition of molten salt, time, temperature, etc.).

[0068] The chemically strengthened glass is preferably in a plate shape. In addition, the glass plate can have a shape of a frame with different thicknesses of the outer periphery, or the like. In addition, the shape of the glass plate is not limited thereto, and for example, the two main surfaces can not be parallel to each other, and in addition, all or a part of one or both of the two main surfaces can be curved surfaces. More specifically, the glass plate can be, for example, a flat plate-shaped glass plate without warping, and in addition, can be a curved glass plate having a curved surface.

[0069] From the viewpoint of improving the effect of chemical strengthening, the 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 effect of improving the strength by the 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, more further preferably 400 μm or more, and particularly preferably 500 μm or more.

[0070] The shape of the chemically strengthened glass can be a shape other than a plate shape depending on the applicable product, use, or the like.

[0071] The relative dielectric constant of the chemically strengthened glass at 20°C at 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, more 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, the loss of radio waves caused by reflection at the surface of the glass can be suppressed, and thus the radio wave transmittance easily becomes good. On the other hand, in the case where the relative dielectric constant is too low, it will result in that the glass cannot be imparted with sufficient chemical strengthening stress, and thus the relative dielectric constant at 20°C at a frequency of 10 GHz is preferably 4.0 or more, more preferably 4.2 or more, further preferably 4.4 or more, more 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 at 20°C at a frequency of 10 GHz and by a split post dielectric resonance method (SPDR method).

[0072] The medium loss tangent (tan δ) at 20°C and a frequency of 10 GHz of the present chemically strengthened glass is preferably 0.02 or less, more preferably 0.018 or less, further preferably 0.016 or less, more further preferably 0.014 or less, particularly preferably 0.012 or less, further preferably 0.011 or less, most preferably 0.010 or less. With a small medium loss tangent, loss of radio waves when passing through the interior of the glass is suppressed, and thus radio wave transmission properties easily become good. On the other hand, in the case where the medium loss tangent is too low, it will result in that the glass cannot be imparted with sufficient chemical strengthening stress, and thus it is preferably 0.001 or more, more preferably 0.002 or more, further preferably 0.003 or more, more further preferably 0.004 or more, particularly preferably 0.005 or more, further preferably 0.006 or more, most preferably 0.007 or more. The medium loss tangent (tan δ) can be measured by using a network analyzer at 20°C and a frequency of 10 GHz and by a split post dielectric resonance method (SPDR method).

[0073] Note that by making the values of the relative dielectric constant and the medium loss tangent at 20°C and a frequency of 10 GHz close to the values of the relative dielectric constant and the medium loss tangent at a higher frequency, the frequency dependence (dielectric dispersion) is reduced, the frequency characteristics of the dielectric properties do not easily change, and design changes can be small when the frequency at the time of use is different, and thus it is preferable. The relative dielectric constant and the medium loss tangent can be adjusted depending on the composition of the glass and the chemical strengthening conditions.

[0074] The present chemically strengthened glass can reduce the relative dielectric constant and the medium loss tangent at a frequency of 10 GHz because the alkali content is appropriately adjusted in the glass composition. Generally, the frequency dependence of the relative dielectric constant and the medium loss tangent of the glass is small in a frequency range of about 10 GHz to about 40 GHz, and thus the present chemically strengthened glass, which has excellent medium properties at a frequency of 10 GHz, has excellent radio wave transmission properties even in the frequency bands of 28 GHz, 35 GHz, and the like used for 5G.

[0075] Note that the relative dielectric constant and the medium loss tangent can be measured by a split post dielectric resonance method (SPDR method) using a network analyzer.

[0076] The present chemically strengthened glass is obtained by chemically strengthening the glass for chemical strengthening or the glass-ceramics described later. That is, the basic composition of the present chemically strengthened glass is the same as the glass composition of the glass for chemical strengthening described later, and the preferable composition range is also the same. Further, the average composition of the present chemically strengthened glass is the same as the composition of the glass for chemical strengthening or the glass-ceramics described later. Here, the average composition means the composition obtained by finely pulverizing a glass sample after applying heat treatment from a glass state, and then analyzing the obtained sample.

[0077] Internal chemical strengthening stress CS of the present chemically strengthened glass 0.05t It is preferable that the surface compressive stress value CS0 be 300 MPa or more, more preferably 400 MPa or more, and further preferably 500 MPa or more. Further, it is preferable that the compressive stress value CS50 at a depth of 50 μm from the surface be 75 MPa or more, more preferably 90 MPa or more, and further preferably 100 MPa or more. By making the surface compressive stress value CS0 and the compressive stress value CS50 at a depth of 50 μm from the surface large, the strength of the chemically strengthened glass is easily made high. 50 It is also preferable that the internal tensile stress value CT be large.

[0078] The larger the surface compressive stress value CS0, the higher the strength, but when the surface compressive stress value CS0 is too large, a large tensile stress is generated in the interior of the chemically strengthened glass, and it can lead to breakage. Therefore, it is preferable that the surface compressive stress value CS0 be 1000 MPa or less, and more preferably 800 MPa or less.

[0079] In the stress distribution of the present chemically strengthened glass, the compressive stress value CS50 at a depth of 50 μm from the surface is preferably 75 MPa or more, more preferably 90 MPa or more, and further preferably 100 MPa or more. 50 It is preferable that the surface compressive stress value CS0 be 300 MPa or more, more preferably 400 MPa or more, and further preferably 500 MPa or more. Further, it is preferable that the compressive stress value CS50 at a depth of 50 μm from the surface be 75 MPa or more, more preferably 90 MPa or more, and further preferably 100 MPa or more. By making the surface compressive stress value CS0 and the compressive stress value CS50 at a depth of 50 μm from the surface large, the strength of the chemically strengthened glass is easily made high. 50 The chemically strengthened glass is less likely to break when damaged by falling from a high place or the like.

[0080] The internal tensile stress value CT of the present chemically strengthened glass is preferably 80 MPa or less, and 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 making CT the above value or more, the compressive stress near the surface becomes large, and the strength becomes high.

[0081] When the compressive stress layer depth DOL of the present chemically strengthened glass is excessively large relative to the thickness t, it leads to an increase in CT, and therefore the compressive stress layer depth DOL is preferably 0.25t or less, more preferably 0.2t or less, further preferably 0.19t or less, and still further 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, further preferably 0.10t or more, and particularly preferably 0.12t or more.

[0082] Specifically, for example, in the case where the thickness t is 700 μm, DOL is preferably 140 μm or less, and more preferably 133 μm or less. In addition, DOL is preferably 70 μm or more, more preferably 80 μm or more, and further preferably 90 μm or more. Note that the preferred thickness (t) and the preferred shape of the present chemically strengthened glass are the same as those of the present glass described above.

[0083] In order to be less likely to break, the Young's modulus of the present 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 a glass having a high Young's modulus is sometimes less resistant to acid, and 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, an ultrasonic pulse method.

[0084] The 4-point bending strength of the present 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 4-point bending strength, and it is typically 1000 MPa or less. The 4-point bending strength can be measured by the method prescribed in JIS R1601:2008.

[0085] The Vickers hardness of the surface of the present 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 it is typically 9.0 GPa or less. The Vickers hardness is the Vickers hardness (HV0.1) prescribed in JIS R1610:2003.

[0086] 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 further preferably 1.5 W / m°C or less. There is no particular limitation on the lower limit of the thermal conductivity, and it is typically 0.8 W / m°C or more.

[0087] This chemically strengthened glass is particularly useful as a protective glass used in mobile devices such as mobile phones, smartphones, portable information terminals (PDA), tablet terminals, and the like. In addition, it is also useful as a protective glass for display devices such as televisions (TV), personal computers (PC), touch panels, and the like, which are not intended for carrying, wall surfaces of elevators, houses, buildings, and the like (full-screen displays), building materials such as windowpanes, table surfaces, interior materials of automobiles or airplanes, and the like, their protective glasses, and in applications such as housings having a curved shape other than a plate shape by bending processing or molding.

[0088] <Method for manufacturing chemically strengthened glass>

[0089] This chemically strengthened glass can be manufactured by subjecting the chemically strengthened glass described below (hereinafter also referred to as "the present chemically strengthened glass") to a chemical strengthening treatment.

[0090] <Chemically strengthened glass>

[0091] The present chemically strengthened glass is preferably any one of soda-lime glass, alkali-aluminosilicate glass, and alkali-aluminoborosilicate glass. These glasses are suitable for chemical strengthening treatment.

[0092] The present chemically strengthened glass is more preferably lithium-aluminosilicate glass. Since lithium-aluminosilicate glass contains lithium ions, which are alkali ions having the smallest ionic radius, a chemically strengthened glass having a preferred stress distribution and excellent strength is easily obtained by chemical strengthening treatment using ion exchange with various molten salts.

[0093] Specifically, the present chemically strengthened glass preferably contains: 40% to 80% of SiO2, 0 to 20% of B2O3, 1% to 25% of Al2O3, and 5% to 30% in total of Li2O and / or Na2O.

[0094] As the lithium-aluminosilicate glass, a lithium-aluminosilicate glass containing 40% to 70% of SiO2, 7.5% to 20% of Al2O3, and 5% to 25% of Li2O is preferable.

[0095] Hereinafter, the preferred composition of the chemically strengthened glass is further described.

[0096] SiO2is a component that constitutes the network of the glass. In addition, SiO2is a component that improves chemical durability, and SiO2is a component that reduces cracks generated when the surface of the glass is damaged.

[0097] To improve chemical durability, the content of SiO2is preferably 40% or more, more preferably 50% or more, further preferably 55% or more, more further preferably 56% or more, more particularly preferably 63% or more, most preferably 65% or more. To improve the melting property at the time of manufacturing the glass, the content of SiO2is preferably 80% or less, more preferably 75% or less, further preferably 70% or less, particularly preferably 68% or less, most preferably 65% or less.

[0098] Al2O3is an effective component for improving the ion exchange property at the time of chemical strengthening and increasing the surface compressive stress after strengthening.

[0099] To improve chemical durability, and to improve the chemical strengthening property, the content of Al2O3is preferably 1% or more, preferably 3% or more, more preferably 5% or more, further preferably 7% or more, more further preferably 9.1% or more, more further preferably 10% or more, particularly preferably 11% or more, most preferably 12% or more. On the other hand, when the content of Al2O3is too much, sometimes the crystal grows easily in the melting. To prevent the reduction of the yield due to devitrification defects, the content of Al2O3is preferably 25% or less, more preferably 23% or less, further preferably 21% or less, particularly preferably 20% or less, most preferably 19% or less.

[0100] Both SiO2and Al2O3are components that stabilize the structure of the glass, and to reduce the brittleness, the content of the total of SiO2and Al2O3is preferably 57.5% or more, more preferably 65% or more, further preferably 75% or more, more further preferably 77% or more, particularly preferably 79% or more.

[0101] Both SiO2and Al2O3have a tendency to increase the melting temperature of the glass. Therefore, to easily perform the melting, the content of the total of SiO2and Al2O3is preferably 95% or less, more preferably 90% or less, further preferably 87% or less, more further preferably 85% or less, particularly preferably 82% or less.

[0102] Li2O is a component that forms a surface compressive stress by ion exchange, and is a component that improves the melting property of the glass. By containing Li2O in the chemically strengthened glass, using a method of ion exchanging Li ions on the surface of the glass to Na ions, and further ion exchanging the Na ions to K ions, a stress distribution in which both the surface compressive stress and the compressive stress layer are large can be obtained.

[0103] To increase the surface compressive stress at the time of 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, most preferably 8% or more.

[0104] On the other hand, when the content of Li20 is too much, the crystal growth rate at the time of glass forming becomes large, and the problem of reduction in yield due to devitrification defects sometimes becomes large. In order to suppress devitrification in the glass manufacturing process, the content of Li20 is preferably 18% or less, more preferably 16% or less, further preferably 15% or less, more further preferably 14% or less, and particularly preferably 12% or less. In addition, when the content of alkali ions is too much, the radio wave transmission property easily decreases, and therefore from the viewpoint of improving the radio wave transmission property, the content of Li20 is preferably 12% or less, more preferably 10% or less, and further preferably 9% or less.

[0105] From the viewpoint of easily forming the glass, the total of Li20 and / or Na20 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 or the like, the total of Li20 and / or Na20 is preferably 30% or less, more preferably 25% or less, and further preferably 20% or less.

[0106] Na20 and K20 are not essential, but are components that increase the melting property of the glass and reduce the crystal growth rate of the glass, and in order to improve the ion exchange property, it is preferable to contain Na20 and K20.

[0107] Na20 is a component that forms a surface compressive stress layer in chemical strengthening treatment using a potassium salt, and is a component that can increase the melting property of the glass. In order to obtain this effect, the content of Na20 is preferably 1.5% or more, more preferably 2.5% or more, further preferably 3% or more, more further preferably 3.6% or more, and particularly preferably 4% or more. On the other hand, when the content of Na20 is too much, it is difficult to increase the compressive stress of a relatively deep portion from the surface by chemical strengthening, and therefore the content of Na20 is preferably 10% or less, more preferably 7% or less, further preferably 5% or less, more further preferably 3% or less.

[0108] K20 can be contained for the purpose of suppressing devitrification and the like in the glass manufacturing process. When K20 is contained, the content of K20 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 K20 is preferably 0.5% or more, and more preferably 1.2% or more. On the other hand, since K is contained in a large amount, it becomes a main reason for reduction in brittleness and reduction in surface stress due to reverse exchange at the time of strengthening, and therefore the content of K20 is preferably 4% or less, more preferably 3% or less, further preferably 2% or less, more further preferably 1% or less, and particularly preferably 0.5% or less.

[0109] 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 too much, surface compressive stress values tend to decrease, and 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 alkali components can be suppressed, and therefore this is preferable from the viewpoint of radio wave permeability.

[0110] From the viewpoint of radio wave permeability, the ratio of the content of Li2O in the present chemically strengthened glass to the total content of Na2O and K2O ([Na2O] + [K2O]) [[Li2O] / ([Na2O] + [K2O])] is preferably 1 or more, more preferably 2 or more, further preferably 3 or more, and particularly preferably 5 or more. By setting [[Li2O] / ([Na2O] + [K2O])] within the above range, the movement of alkali components can be suppressed. The upper limit of [Li2O] / ([Na2O] + [K2O]) is not particularly limited, and is typically 20 or less.

[0111] None of MgO, CaO, SrO, and BaO is essential, but one or more kinds thereof can be contained from the viewpoint of improving the stability of the glass and the viewpoint of improving the chemical strengthening characteristics. In the case where these substances are contained, the total content of one or more kinds selected from the group consisting of 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 viewpoint of introducing sufficient chemical strengthening stress at the time of chemical strengthening and the viewpoint of improving radio wave permeability, the total content of these substances is preferably 20% or less, and more preferably 10% or less.

[0112] MgO can be contained in order to reduce viscosity at the time of melting and the like. In the case where 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 too much, it is difficult to increase the compressive stress layer at the time of 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.

[0113] CaO is a component that improves the melting property of the glass, and can 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 at the time of 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.

[0114] ZnO is a component that improves the melting property of the glass, and can be contained. When ZnO is contained, the content of ZnO is preferably 0.2% or more, and 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.

[0115] ZnO, SrO, and BaO have a tendency to deteriorate the chemical strengthening characteristics, and therefore, in order to easily perform chemical strengthening, [ZnO] + [SrO] + [BaO] is preferably less than 1%, and more preferably 0.5% or less. It is further preferable to substantially not contain these substances.

[0116] Zr02may not be contained, but from the viewpoint of increasing the surface compressive stress of the chemically strengthened glass, it is preferable to contain Zr02. The content of Zr02is 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 Zr02is excessive, devitrification defects are easily generated, and it is difficult to increase the compressive stress value at the time of chemical strengthening treatment. The content of Zr02is preferably 2% or less, more preferably 1.5% or less, further preferably 1% or less, and particularly preferably 0.8% or less.

[0117] The content of Y203is 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 Y203is excessive, it is difficult to increase the compressive stress layer at the time of chemical strengthening treatment. The content of Y203is preferably 10% or less, more preferably 8% or less, further preferably 5% or less, more further preferably 3% or less, particularly preferably 2% or less, and further particularly preferably 1.5% or less.

[0118] La2O3 is not essential, but can be contained for the same reason as Y2O3. 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 La2O3 is too much, it is difficult to increase the compressive stress layer at the time of chemical strengthening treatment, and therefore La2O3 is preferably 5% or less, more preferably 3% or less, further preferably 2% or less, and particularly preferably 1.5% or less.

[0119] TiO2 is a component for suppressing solarization of the glass, and can 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 more than 1%, devitrification easily occurs, and the quality of the chemically strengthened glass can be reduced. The content of TiO2 is preferably 5% or less, more preferably 3% or less, further preferably 2% or less, more further preferably 1% or less, particularly preferably 0.5% or less, and further particularly preferably 0.25% or less.

[0120] B2O3 is not essential, but can be contained for the purpose of reducing the brittleness of the glass, the purpose of improving crack resistance, and the purpose of improving radio wave transmission. 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 too much, the acid resistance easily becomes poor, and 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. It is further preferably 11% or less, and most preferably 10% or less. In order to prevent the problem of moiré occurring at the time of melting, it is more preferably substantially not contained.

[0121] P2O5 is not essential, but can be contained for the purpose of increasing the compressive stress layer at the time of chemical strengthening. In the case where 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, 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, more further preferably 4% or less, particularly preferably 3% or less, further preferably 2.5% or less, most preferably 2.0% or less. In order to prevent the generation of a wave at the time of melting, it is more preferable to substantially not contain P2O5.

[0122] The total content of B2O3 and P2O5 is preferably 0 to 35%, more preferably 5% or more, further preferably 8% or more. The total content of B2O3 and P2O5 is preferably 20% or less, more preferably 17% or less, further preferably 15% or less.

[0123] Nb2O5, Ta2O5, Gd2O3, CeO2 are components that suppress the sun exposure of the glass, and are components that improve the melting property, and these substances can be contained. In the case where 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, typically 1% or more. On the other hand, when the content of these substances is too much, it is difficult to increase the compressive stress value at the time of chemical strengthening treatment, and thus it is preferably 3% or less, more preferably 2% or less, further preferably 1% or less, particularly preferably 0.5% or less.

[0124] Furthermore, coloring components can be added within a range that does not hinder the achievement of desired chemical strengthening characteristics. As coloring components, for example, Fe2O3, Co3O4, MnO2, NiO, CuO, Cr2O3, V2O5, Bi2O3, SeO2, CeO2, Er2O3, Nd2O3, and the like can be cited as appropriate coloring components.

[0125] The total content of coloring components is preferably 5% or less in terms of mole percentage on an oxide basis. When the content of coloring components is greater than 5%, the glass sometimes easily devitrifies. The content of coloring components is preferably 3% or less, further preferably 1% or less. In the case where it is desired to improve the transmittance of the glass, it is preferable to substantially not contain these components.

[0126] As a fining agent or the like at the time of melting of the glass, SO3, chloride, fluoride, and the like can be appropriately contained. It is preferable not to contain As2O3. In the case where Sb2O3 is contained, it is preferably 0.3% or less, more preferably 0.1% or less, most preferably not to contain Sb2O3.

[0127] The β-OH value is a value used as an index of the water content of the glass, and is a value obtained by measuring the absorbance of light having a wavelength of 2.75 μm to 2.95 μm, and dividing the maximum value β max by the thickness (mm) of the glass.

[0128] The β-OH value is preferably 0.8 mm -1 The β-OH value is more preferably 0.6 mm -1 The β-OH value is further preferably 0.5 mm -1 The β-OH value is still further preferably 0.4 mm -1 The β-OH value is still further preferably 0.4 mm

[0129] On the other hand, the β-OH value is preferably 0.05 mm -1 The β-OH value is more preferably 0.1 mm -1 The β-OH value is further preferably 0.2 mm -1 The β-OH value is further preferably 0.2 mm

[0130] The β-OH value can be adjusted depending on the composition of the glass, the heat source at the time of melting, the melting time, and the raw material.

[0131] The viscosity at 10 2 The temperature (T2) at which the viscosity is 10 dPa-s is preferably 1750°C or lower, more preferably 1700°C or lower, still more preferably 1675°C or lower, and typically 1650°C or lower. The temperature (T2) is a temperature that is a general standard for the melting temperature of the glass, and the lower the T2, the more the tendency to easily manufacture the glass. There is no particular limitation on the lower limit of T2, but a glass having a low T2 tends to have a glass transition temperature that is too low, and therefore T2 is usually 1400°C or higher, and preferably 1450°C or higher.

[0132] In addition, the temperature (T4) at which the viscosity is 10 4 The temperature (T4) at which the viscosity is 10 dPa-s is preferably 1350°C or lower, more preferably 1300°C or lower, still more preferably 1250°C or lower, and particularly preferably 1150°C or lower. The temperature (T4) is a temperature that is a general standard for the temperature at which the glass is shaped into a plate, and a glass having a high T4 tends to have a tendency for the load on the shaping equipment to be high. There is no particular limitation on the lower limit of T4, but a glass having a low T4 tends to have a glass transition temperature that is too low, and therefore T4 is usually 900°C or higher, and preferably 950°C or higher, and more preferably 1000°C or higher.

[0133] When the devitrification temperature of the present chemical strengthening glass is a temperature (T4) of 120°C or lower than the temperature at which the viscosity reaches 10 4 dPa-s, devitrification is not easily caused during float forming, and thus is preferable. The devitrification temperature is more preferably a temperature of 100°C or lower than T4, further preferably a temperature of 50°C or lower than T4, and particularly preferably T4 or lower.

[0134] The fracture toughness value of the present chemical strengthening 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 typically 2.0 MPa-m 1 / 2 or less, typically 1.5 MPa-m 1 / 2 or less. By having a large fracture toughness value, even if a large surface compressive stress is introduced into the glass by chemical strengthening, violent breakage is not easily caused.

[0135] The fracture toughness value can be measured, for example, using the DCDC method (Acta metall. mater. Vol. 43, pp. 3453-3458, 1995).

[0136] In order to make the glass less likely to break, the Young's modulus of the present chemical strengthening 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 a glass having a high Young's modulus sometimes has reduced acid resistance, and thus, for example, 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, for example, using the ultrasonic pulse method.

[0137] From the viewpoint of reducing warping after chemical strengthening, the average linear thermal expansion coefficient (coefficient of thermal expansion) of the present chemical strengthening glass in the range of 50°C to 350°C is preferably 95 x 10 -7 / °C or less, more preferably 90 x 10 -7 / °C or less, further preferably 88 x 10 -7 / °C or less, particularly preferably 86 x 10 -7 / °C or less, and most preferably 84 x 10 -7 / °C or less. There is no particular limitation on the lower limit of the coefficient of thermal expansion, but a glass having a small coefficient of thermal expansion is sometimes difficult to melt, and thus, for example, the average linear thermal expansion coefficient (coefficient of thermal expansion) of the present chemical strengthening glass in the range of 50°C to 350°C is preferably 60 x 10 -7more preferably 74 x 10 -7 more preferably 74 x 10 -7 more preferably 74 x 10 -7 more preferably 74 x 10

[0138] From the viewpoint of reducing the warpage after chemical strengthening, the glass transition temperature (Tg) is preferably 500°C or higher, more preferably 520°C or higher, further preferably 540°C or higher. From the viewpoint of easiness in 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, most preferably 580°C or lower.

[0139] The present chemical strengthening glass can be produced by a usual method. For example, raw materials of each component of the glass are prepared, and heating melting is performed in a glass melting furnace. Then, the glass is homogenized by a publicly known method, formed into a desired shape such as a glass sheet, and slowly cooled.

[0140] As the forming method of the glass sheet, for example, float method, press method, fusion method, and down-draw method can be exemplified. Float method which is suitable for mass production is particularly preferable. In addition, a continuous forming method other than float method, for example, fusion method and down-draw method are preferable.

[0141] Then, the formed glass is subjected to grinding and polishing treatment as necessary, whereby a glass substrate is formed. Note that, in the case where the glass substrate is cut into a prescribed shape and size or chamfer processing of the glass substrate is performed, if the cutting, chamfer processing of the glass substrate is performed before the chemical strengthening treatment described later is performed, a compressive stress layer is formed also on the end surface by the chemical strengthening treatment thereafter, and thus is preferable.

[0142] <<Ceramic Glass>>

[0143] The present chemical strengthening glass can be a ceramic glass (hereinafter also referred to as "the present ceramic glass"). The present ceramic glass is a ceramic glass having the glass composition of the present chemical strengthening glass described above.

[0144] The present ceramic glass preferably contains any one or more of lithium silicate crystal, lithium aluminosilicate crystal, or lithium phosphate crystal, lithium aluminosilicate crystal, magnesium silicate crystal, or silica crystal. As the lithium silicate crystal, lithium metasilicate crystal is more preferable. As the lithium aluminosilicate crystal, petalite crystal or β-spodumene crystal, α-eucryptite, β-eucryptite are preferable. As the lithium phosphate crystal, lithium orthophosphate crystal is preferable.

[0145] In order to improve the transparency, a ceramic glass containing lithium metasilicate crystal is more preferable.

[0146] The glass-ceramics can be obtained by crystallizing an amorphous glass having the same composition as the chemical strengthening glass by heat treatment. The glass composition of the glass-ceramics is the same as that of the amorphous glass.

[0147] The visible light transmittance (total visible light transmittance including diffuse transmittance) of the glass-ceramics is preferably 85% or more when the thickness of the glass-ceramics is converted to 700 μm, and in the case where the glass-ceramics is used as a protective glass for a portable display, the screen of the display is easily seen. The visible light transmittance is more preferably 88% or more, and further preferably 90% or more. The higher the visible light transmittance is, the more preferable it is, but it is usually 93% or less. Note that the visible light transmittance of a general amorphous glass is about 90% or more.

[0148] In the case where the thickness of the glass-ceramics is not 700 μm, the transmittance in the case of 700 μm can be calculated from the measured transmittance using the Lambert-Beer law.

[0149] In addition, in the case of a glass having a thickness t of more than 700 μm, the thickness can be adjusted to 700 μm by polishing, etching or the like, and actual measurement can be performed.

[0150] In addition, 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 when converted to a thickness of 700 μm. The smaller the haze value is, the more preferable it is, but when the crystallization rate 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 is preferably 0.02% or more, and more preferably 0.03% or more in the case of a thickness of 700 μm. The haze value is a value measured according to JIS K7136 (2000).

[0151] Note that in the case where the total visible light transmittance of the glass-ceramics having a thickness t [μm] is 100 x T [%] and the haze value is 100 x H [%], by citing the Lambert-Beer law, using a constant α, it is written as T = (1 - R) 2 x exp (-αt / 1000). Using this constant α, it is expressed as:

[0152]

[0153] That is, it is considered that the haze value increases by an amount proportional to the internal straight transmittance as the thickness increases, and therefore the haze value H 0.7 is obtained from the following equation.

[0154]

[0155] In addition, in the case of a glass having a thickness t of more than 700 μm, the thickness can be adjusted to 700 μm by polishing, etching, or the like, and the actual measurement can be performed.

[0156] In the case where the strengthened glass obtained by strengthening the microcrystalline glass is used as a protective glass for a portable display, it is preferable to have a different texture and a high-class feel from plastics. Therefore, the refractive index of the present microcrystalline glass 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.

[0157] In order to improve the mechanical strength, the crystallization rate of the microcrystalline glass 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 microcrystalline glass is preferably 70% or less, more preferably 60% or less, and particularly preferably 50% or less. From the viewpoint of easy heating and bending forming, a small crystallization rate is preferable.

[0158] The crystallization rate can be calculated from the X-ray diffraction intensity by the Rietveld method. Regarding the Rietveld method, it is described in "Crystalline Analysis Handbook" edited by the Crystalline Society of Japan, published by Kyoritsu Shuppan, published in 1999, pp. 492 to 499.

[0159] The average particle diameter of the precipitated crystals of the microcrystalline glass 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 calculated 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.

[0160] < Chemical Strengthening Treatment >

[0161] The present chemically strengthened glass can be manufactured by subjecting the obtained glass sheet to a chemical strengthening treatment, and then performing cleaning and drying.

[0162] 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 molten solution of a metal salt (for example, potassium nitrate) containing a metal ion having a large ionic radius (typically, K ion) by immersion or the like. Thereby, metal ions having a small ionic radius (typically, Na ion or Li ion) in the glass sheet are replaced with metal ions having a large ionic radius (typically, K ion with respect to Na ion, or Na ion with respect to Li ion).

[0163] The chemical strengthening treatment (ion exchange treatment) can be performed, for example, by immersing the glass sheet in a molten salt such as potassium nitrate heated to 360°C to 600°C for 0.1 hour to 500 hours. Note that the heating temperature of the molten salt is preferably, for example, 375°C to 500°C, and the immersion time of the glass sheet in the molten salt is preferably, for example, 0.3 hour to 200 hours.

[0164] As the molten salt used for the chemical strengthening treatment, for example, nitrates, sulfates, carbonates, chlorides, and the like can be listed. Among these, as the nitrates, for example, lithium nitrate, sodium nitrate, potassium nitrate, cesium nitrate, and silver nitrate can be listed. As the sulfates, for example, lithium sulfate, sodium sulfate, potassium sulfate, cesium sulfate, silver sulfate, and the like can be listed. As the carbonates, for example, lithium carbonate, sodium carbonate, potassium carbonate, and the like can be listed. As the chlorides, for example, lithium chloride, sodium chloride, potassium chloride, cesium chloride, silver chloride, and the like can be listed. These molten salts can be used alone or in combination of a plurality of kinds.

[0165] In the present application, the treatment conditions of the chemical strengthening treatment can be selected appropriately in consideration of the properties, composition, kind of the molten salt of the glass, and the chemical strengthening properties such as the entropy function S, the surface compressive stress, the depth of the compressive stress layer, and the like of the finally obtained chemically strengthened glass.

[0166] Further, in the present application, the chemical strengthening treatment can be performed only once or can be performed a plurality of times under different conditions (multi-step strengthening). Here, for example, as the chemical strengthening treatment of the first step, the chemical strengthening treatment is performed under conditions where the DOL is large and the CS is relatively small. Then, as the chemical strengthening treatment of the second step, when the chemical strengthening treatment is performed under conditions where the DOL is small and the CS is relatively high, it is possible to increase the CS of the outermost surface of the chemically strengthened glass while suppressing the internal tensile stress area (St) and the internal tensile stress (CT) to be low.

[0167] <Electronic device housing>

[0168] The electronic device housing of the present application contains the chemically strengthened glass of the present application. 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, and the like can be listed.

[0169] Example

[0170] Hereinafter, the present application will be described by way of examples, but the present application is not limited thereto.

[0171] [Experimental Example 1]

[0172] The various glass raw materials were prepared, and 400 g was weighed based on glass. Next, the mixed raw materials were put into a platinum crucible and put into an electric furnace at 1500°C to 1700°C to be melted for about 3 hours, and defoaming and homogenization were performed.

[0173] As for the various chemically strengthened glasses obtained, the glass in which the relative dielectric constant or the dielectric loss tangent after the chemical strengthening was reduced compared to before the chemical strengthening was taken as a glass in which the radio wave transmittance was improved by the chemical strengthening. As for the glass in which the radio wave transmittance was improved by the chemical strengthening, a graph showing the correlation between the radio wave transmittance at a frequency of 10 GHz and the entropy function and the compressive stress is shown in FIG. 1. Figure 1 Figure 1 The vertical axis of FIG. 1 is the total value of the 100 times the values of the relative dielectric constant and the dielectric loss tangent before and after the chemical strengthening, and the horizontal axis is a parameter Z that can be calculated from the entropy function and the compressive stress before and after the chemical strengthening.

[0174] The content of alkali metal ions used for calculating the entropy function was measured using EPMA (electron probe micro-analyzer, manufactured by JEOL Co., Ltd.: JXA-8500F). As the measurement conditions of the 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.

[0175] According to the above Figure 1 it was found that by making Z represented by the formula [Z = (S2 - S1) x 10 + X / 1000] be 0.65 or greater, the movement of alkali metal ions was suppressed after the chemical strengthening compared to before the chemical strengthening, and excellent radio wave transmittance was exhibited in the high frequency band.

[0176] [Experimental Example 2]

[0177] The glass raw materials were prepared in accordance with the composition in Table 1 in terms of the mole percentage on an oxide basis, and 400 g was weighed based on glass. Next, the mixed raw materials were put into a platinum crucible and put into an electric furnace at 1500°C to 1700°C to be melted for about 3 hours, and defoaming and homogenization were performed.

[0178] The molten glass obtained was poured into a metal mold, maintained at a temperature of about 50°C higher than the glass transition temperature for 1 hour, and then cooled to room temperature at a rate of 0.5°C / minute, whereby a glass block was obtained. The glass block obtained was cut, ground, and finally mirror-polished on both sides, whereby a glass plate having a thickness (t) of 700 μm was obtained.

[0179] ​The relative dielectric constant and dielectric loss tangent tan δ at 20°C and a frequency of 10 GHz were measured for each glass. The results are shown in Table 2. In addition, two-step chemical strengthening treatment was performed according to the conditions shown in Table 2, and the following chemically strengthened glasses of Examples 1 to 7 were produced. Examples 1 to 4 are examples, and Examples 5 to 7 are comparative examples.

[0180]

[0181] The compressive stress and compressive stress depth of layer DOL of the surface layer after chemical strengthening were measured using an optical waveguide surface stress meter FSM-6000 and a scattered light photoelastic stress meter SLP-1000 manufactured by Kojima Corporation, and 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.

[0182] In addition, the content of alkali metal ions at a depth of 0.05t from the surface of the glass and the content of alkali metal ions at the center of the sheet thickness (glass center portion) were measured for the obtained samples using an EPMA (electron probe microanalyzer, manufactured by JEOL Ltd.: JXA-8500F). The average values thereof are shown in Table 2 as the ion content after strengthening and the ion content at the center of the sheet thickness.

[0183] In addition, the entropy function S was calculated from the ion content of the alkali metal elements according to the following definition formula.

[0184] S = - [Li20] / ([Li20] + [Na20] + [K20]) log([Li20] / ([Li20] + [Na20] + [K20])) - [Na20] / ([Li20] + [Na20] + [K20]) log([Na20] / ([Li20] + [Na20] + [K20])) - [K20] / ([Li20] + [Na20] + [K20]) log([K20] / ([Li20] + [Na20] + [K20]))

[0185] Note that the entropy function calculated from the average alkali ion content in the region from the surface of the glass to a depth of 0.05t is defined as S2, and the entropy function calculated from the alkali ion content at the center portion of the glass is defined as S1. The alkali fixation parameter Z is calculated from these entropy functions S1, S2 and the average value X [unit: MPa] of the compressive stress in the region from the surface of the glass to a depth of 0.05t according to the following formula. The results are shown in Table 2. In Table 2, the "change amount of the entropy function" is calculated by subtracting the "entropy function S1 at the center of the sheet thickness (glass center)" from the "entropy function S2 after chemical strengthening".

[0186] Z = (S2 - S1) x 10 + X / 1000

[0187] In addition, the relative dielectric constant and tan δ at 20°C and a frequency of 10 GHz were measured for the sample after chemical strengthening. The results are shown in Table 2.

[0188] Note that the relative dielectric constant and tan δ were measured using a network analyzer by a split post dielectric resonance method (SPDR method). For the measurement conditions, the temperature was set to 20°C and the frequency was set to 10 GHz.

[0189] In Table 2, the amount of change in the relative dielectric constant due to chemical strengthening was calculated by subtracting the relative dielectric constant before chemical strengthening from the relative dielectric constant after chemical strengthening. In addition, the amount of change in the dielectric loss due to chemical strengthening was calculated by subtracting the dielectric loss before chemical strengthening from the dielectric loss after chemical strengthening.

[0190]

[0191] As shown in Table 2, in Examples 1 to 4 as examples, since the amount of change in the entropy function before and after chemical strengthening was very large and the compressive stress in the vicinity of the glass surface layer was also high, the alkali fixation parameter Z was 0.65 or more, and as a result, it was confirmed that either one of the relative dielectric constant and the dielectric loss decreased before and after the chemical strengthening treatment, and the dielectric properties were improved.

[0192] On the other hand, with respect to Examples 5 to 7 as comparative examples, since the amount of change in the entropy function before and after chemical strengthening was small, the alkali fixation parameter Z was less than 0.65, and as a result, it was confirmed that both the relative dielectric constant and the dielectric loss increased by performing the chemical strengthening treatment, and the dielectric properties were reduced.

[0193] Although the present application has been described in detail and with reference to specific embodiments, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof. Note that this application is based on Japanese Patent Application (Japanese Patent Application No. 2020-202039 filed on December 4, 2020 and Japanese Patent Application No. 2021-094715 filed on June 4, 2021), the contents of which are incorporated herein by reference in their entirety. In addition, all references cited herein are incorporated by reference herein.

Claims

1. A chemically strengthened glass, wherein the thickness of the chemically strengthened glass is t (unit: μm), and the relative permittivity of the chemically strengthened glass at 20°C and 10GHz is below 7.0, wherein... The basic composition of the chemically strengthened glass, based on oxide molar percentages, contains: 40%–68% SiO2, 0-20% B2O3, 11%–25% Al2O3, K2O below 1%, and A total of 5%–30% Li₂O and / or Na₂O, The Z value obtained using the following formula is greater than 0.

65. Z = (S2 - S1) × 10 + X / 1000 In the above formula, S1 is the entropy function calculated from the amount of alkali ions in the central part of the glass. 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. X represents the average compressive stress [unit: MPa] in the region extending from the glass surface to a depth of 0.05t. The entropy function S is calculated from the molar percentages of Li₂O, Na₂O, and K₂O at each depth, based on oxides, using the following formula: [Li₂O], [Na₂O], and [K₂O], where, in the formula, when [Li₂O], [Na₂O], and [K₂O] are zero, the entropy function S is 1 × 10⁻⁶. -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 as described in claim 1, wherein, Based on the molar percentage of oxides, the ratio of Li2O content to the combined content of Na2O and K2O in the basic composition of the chemically strengthened glass is 1 or more.

3. The chemically strengthened glass as described in claim 1, wherein, The entropy function S1 is below 0.

375.

4. The chemically strengthened glass as described in claim 1, wherein, The value obtained by subtracting the entropy function S1 from the entropy function S2, i.e., (S2-S1), is 0.04 or higher.

5. The chemically strengthened glass as described in claim 1, wherein, The dielectric loss tangent of the chemically strengthened glass at 20°C and 10GHz is below 0.

02.

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

7. The chemically strengthened glass according to claim 1, wherein, The surface compressive stress value CS0 of the chemically strengthened glass is above 300 MPa.

8. The chemically strengthened glass as described in claim 1, wherein, The thickness t is greater than 100 μm and less than 2000 μm.

9. The chemically strengthened glass according to claim 1, wherein, The chemically strengthened glass is a microcrystalline glass.

10. An electronic device housing, wherein, The electronic device housing comprises the chemically strengthened glass according to any one of claims 1 to 9.

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