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US-12623955-B2 - Chemically strengthened glass, and electronic device housing

US12623955B2US 12623955 B2US12623955 B2US 12623955B2US-12623955-B2

Abstract

The present invention relates to a chemically strengthened glass having a thickness of t (unit: μm) and a relative permittivity of 7.0 or less at 20° C. and a frequency of 10 GHz, in which a value of Z determined by the following formula is 0.65 or more, where S1 is an entropy function calculated from an amount of alkali ions in a center portion of the glass, S2 is an entropy function calculated from an average amount of alkali ions from a glass surface to a depth of 0.05t, and X (unit: MPa) is an average value of a compressive stress in a region from the glass surface to the depth of 0.05t: Z=(S2−S1)×10+X/1000.

Inventors

  • Kazuki Kanehara
  • Yutaka Kuroiwa

Assignees

  • AGC Inc.

Dates

Publication Date
20260512
Application Date
20230526
Priority Date
20201204

Claims (12)

  1. 1 . A chemically strengthened glass having a thickness of t (unit: μm) and a relative permittivity of 7.0 or less at 20° C. and a frequency of 10 GHz, and having a base composition comprising, in terms of molar percentage based on oxides: 10% or less of Al 2 O 3 ; 2% or less of K 2 O; 3% or less of MgO; and 14% or more of Li 2 O and/or Na 2 O in total, wherein a value of Z determined by the following formula is 0.65 or more and a value of S1 is 0.2 or less, where S1 is an entropy function calculated from an amount of alkali ions in a center portion of the glass, S2 is an entropy function calculated from an average amount of alkali ions from a glass surface to a depth of 0.05t, and X (unit: MPa) is an average value of a compressive stress in a region from the glass surface to the depth of 0.05t: Z =( S 2− S 1)×10+ X/ 1000, provided that an entropy function S is calculated by the following formula from [Li 2 O], [Na 2 O], and [K 2 O] which are contents of Li 2 O, Na 2 O, and K 2 O respectively in terms of molar percentage based on oxides, and in the formula, when [Li 2 O], [Na 2 O], and [K 2 O] are zero, the entropy function S is 1×10 −4 : S=−[Li 2 O]/([Li 2 O]+[Na 2 O]+[K 2 O])log([Li 2 O]/([Li 2 O]+[Na 2 O]+[K 2 O]))−[Na 2 O]/([Li 2 O]+[Na 2 O]+[K 2 O])log([Na 2 O]/([Li 2 O]+[Na 2 O]+[K 2 O]))−[K 2 O]/([Li 2 O]+[Na 2 O]+[K 2 O])log([K 2 O]/([Li 2 O]+[Na 2 O]+[K 2 O])), and a content of Li ions after the chemical strengthening at the depth of 0.05t from the glass surface is greater than or equal to 4.1 mol %.
  2. 2 . The chemically strengthened glass according to claim 1 , wherein a value of (S2−S1) obtained by subtracting the entropy function S1 from the entropy function S2 is 0.04 or more.
  3. 3 . 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.
  4. 4 . The chemically strengthened glass according to claim 1 , wherein the base composition comprises in terms of molar percentage based on oxides: 40% to 80% of SiO 2 ; 0% to 20% of B 2 O 3 ; 1% to 10% of Al 2 O 3 ; and 14% to 30% of Li 2 O and/or Na 2 O in total.
  5. 5 . The chemically strengthened glass according to claim 1 , having a surface compressive stress value CS 0 of 300 MPa or more.
  6. 6 . The chemically strengthened glass according to claim 1 , having an internal chemical strengthening stress CS 0.05t at a depth of 0.05t from the glass surface of 75 MPa or more, wherein the thickness t is 300 μm or more.
  7. 7 . The chemically strengthened glass according to claim 1 , having a depth of a compressive stress layer DOL of 70 μm or more, wherein the thickness t is 350 μm or more.
  8. 8 . The chemically strengthened glass according to claim 1 , being a lithium aluminosilicate glass, wherein the base composition comprises, in terms of molar percentage based on oxides: 40% to 70% of SiO 2 ; 7.5% to 10% of Al 2 O 3 ; and 5% to 25% of Li 2 O.
  9. 9 . The chemically strengthened glass according to claim 1 , wherein the thickness t is 100 μm or more and 2000 μm or less.
  10. 10 . The chemically strengthened glass according to claim 1 , being a glass ceramic.
  11. 11 . The chemically strengthened glass according to claim 1 , having a dielectric loss tangent of 0.018 or less at 20° C. and a frequency of 10 GHz.
  12. 12 . An electronic device housing comprising the chemically strengthened glass according to claim 1 .

Description

CROSS-REFERENCE TO RELATED APPLICATIONS This is a continuation of International Application No. PCT/JP2021/032550 filed on Sep. 3, 2021, and claims priority from Japanese Patent Application No. 2020-202039 filed on Dec. 4, 2020 and Japanese Patent Application No. 2021-094715 filed on Jun. 4, 2021, the entire content of which is incorporated herein by reference. TECHNICAL FIELD The present invention relates to a chemically strengthened glass and an electronic device housing. BACKGROUND ART A chemically strengthened glass is widely used for an electronic device housing such as a mobile terminal since the electronic device housing is required to have sufficient strength to prevent cracking even if the mobile terminal is dropped. The chemically strengthened glass is a glass in which a compressive stress layer is formed on a surface portion of the glass by using a method of immersing the glass into a molten salt such as sodium nitrate to cause ion exchange between alkali ions contained in the glass and alkali ions that have a larger ionic radius and are contained in the molten salt. For example, Patent Literature 1 discloses an aluminosilicate glass having a specific composition and capable of obtaining high surface compressive stress by chemical strengthening. Further, in an electronic device such as a communication device such as a mobile phone, a smart phone, a mobile information terminal, and a Wi-Fi device, a surface acoustic wave (SAW) device, a radar component and an antenna component, a signal frequency has been further increased in order to increase a communication capacity and a communication speed. In recent years, as a new communication system using a higher frequency band, the fifth generation mobile communication system (5G) is expected to be widely used. In the high frequency band used in 5G, the cover glass may interfere with radio wave transmission and reception, and a cover glass having excellent dielectric properties such as radio wave transparency is required for a mobile terminal compatible with 5G. As the excellent dielectric properties, for example, it is desirable that a relative permittivity and a dielectric loss are low. Reflection of radio waves can be prevented and radio wave transparency can be improved by reducing the relative permittivity. Loss of radio waves can be prevented by reducing the dielectric loss. As a glass having high radio wave transparency, that is, a glass having a low relative permittivity and a low dielectric loss tangent in the high frequency band as used in 5G, several alkali-free glasses have been developed so far (Patent Literature 2). CITATION LIST Patent Literature Patent Literature 1: JP2018-520082TPatent Literature 2: WO 2019/181707 SUMMARY OF INVENTION Technical Problem However, it is difficult to chemically strengthen an alkali-free glass containing substantially no alkali ions as disclosed in Patent Literature 2. In addition, it is difficult to predict the radio wave transparency of the chemically strengthened glass, and it is difficult to achieve both the radio wave transparency and strength in a high frequency band. Therefore, an object of the present invention is to provide a chemically strengthened glass having both excellent radio wave transparency and high strength in a high frequency band. Solution to Problem The present inventors have found that, in a high frequency band, there are both a glass whose radio wave transparency after chemical strengthening decreases and a glass whose radio wave transparency after chemical strengthening increases, compared to before the chemical strengthening. Further, the present inventors have found a correlation between surface characteristics and the radio wave transparency after the chemical strengthening of the glass whose radio wave transparency in a high frequency band increases after the chemical strengthening, thereby completing the present invention. The present invention provides a chemically strengthened glass having a thickness of t (unit: μm) and a relative permittivity of 7.0 or less at 20° C. and a frequency of 10 GHz, in which a value of Z determined by the following formula is 0.65 or more, where S1 is an entropy function calculated from an amount of alkali ions in a center portion of the glass, S2 is an entropy function calculated from an average amount of alkali ions from a glass surface to a depth of 0.05t, and X (unit: MPa) is an average value of a compressive stress in a region from the glass surface to the depth of 0.05t: Z=(S2−S1)×10+X/1000, provided that an entropy function S is calculated by the following formula from [Li2O], [Na2O], and [K2O] which are contents of Li2O, Na2O, and K2O respectively in terms of molar percentage based on oxides, and in the formula, when [Li2O], [Na2O], and [K2O] are zero, the entropy function S is 1×10−4: S=−[Li2O]/([Li2O]+[Na2O]+[K2O])log([Li2O]/([Li2O]+[Na2O]+[K2O]))−[Na2O]/([Li2O]+[Na2O]+[K2O])log([Na2O]/([Li2O]+[Na2O]+[K2O]))−[K2O]/([Li2O]+[Na2O]+[K2O])