Chemically strengthened glass, method for producing chemically strengthened glass, cover glass, and solar cell module

Abstract

To provide a chemically strengthened glass having superior drop strength.SOLUTION: Provided is a chemically strengthened glass in which a stress CT at a central position in a plate thickness satisfies a relationship of the following formula (1), and a compressive stress CS120 at 120 μm in a depth direction from a surface satisfies a relationship of the following formula (2). Formula (1): |CT|≤-170t+175. Formula (2): 190t-124≤CS120. In formula (1), |CT| represents an absolute value of a stress CT, and a unit is MPa. In formula (1) and formula (2), t represents a plate thickness of the chemically strengthened glass, and the unit is mm. In formula (2), CS120 represents a value of a compressive stress CS120, and the unit is MPa.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to chemically strengthened glass. The present invention also relates to a method for manufacturing the chemically strengthened glass. The present invention also relates to a cover glass including the above chemically strengthened glass, and a solar cell module including the above cover glass.

Background Art

[0002] In recent years, cover glasses have been used for the purpose of protecting and enhancing the aesthetics of display devices such as mobile phones, smartphones, tablet terminals, and in-vehicle displays. Cover glasses for these applications are required to have excellent strength in order to suppress breakage due to impacts and the like. In addition, the cover glass as described above may be used for protecting a solar cell module or the like.

[0003] Conventionally, a method of increasing the surface strength of glass by immersing the glass in a molten salt of potassium nitrate or the like and performing a chemical strengthening treatment has been known. For example, Patent Document 1 discloses improving the surface strength of a glass plate by immersing the glass in a molten salt of potassium nitrate and performing a chemical strengthening treatment. More specifically, it is disclosed that the strength of a glass plate is improved by sequentially performing chemical strengthening treatments on a glass containing Li with a molten salt containing Na and a molten salt containing K. Further, it is described that the mechanism of strengthening the strength of the glass plate by such a chemical treatment is due to the compressive stress generated by the exchange of alkali metals.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In recent years, cover glass may have its plate thickness adjusted due to various requirements. For example, in recent years, cover glass may be required to have a thinner plate thickness for weight reduction and thinning of the housing. When the inventor adjusted the plate thickness of the cover glass, the drop strength sometimes decreased, and improvement was required. In particular, when the plate thickness of the cover glass was adjusted to be thinner, the drop strength sometimes decreased, and improvement was required.

[0006] The present invention has been made in view of the above problems, and an object thereof is to provide chemically strengthened glass having excellent drop strength. Another object of the present invention is to provide a method for manufacturing chemically strengthened glass. Another object of the present invention is also to provide cover glass and a solar cell module.

Means for Solving the Problems

[0007] As a result of intensive studies on the above problems, the present inventors have found that when the relationship between the stress value and the plate thickness satisfies a predetermined relationship, the drop strength is excellent, and the present invention has been completed.

[0008] That is, the inventors have found that the above problems can be solved by the following configuration. 〔1〕 The stress CT at the central position of the plate thickness satisfies the relationship of the following formula (1), The compressive stress CS at a depth of 120 μm in the depth direction from the surface 120 satisfies the relationship of the following formula (2), chemically strengthened glass. Formula (1) |CT|≦-170t + 175 Formula (2) 190t - 124≦CS 120 In formula (1), |CT| represents the absolute value of the stress CT, and the unit is MPa. In formula (1) and formula (2), t represents the plate thickness of the chemically strengthened glass, and the unit is mm. In formula (2), CS 120 represents the value of the compressive stress CS 120 and the unit is MPa. 〔2〕 The chemically strengthened glass according to 〔1〕, wherein the depth DOC of the compressive stress layer is 0.20 times or more of the plate thickness of the chemically strengthened glass. 〔3〕 The chemically strengthened glass according to 〔2〕, wherein the absolute value of the slope of the stress profile from the depth DOC of the compressive stress layer to the central position of the plate thickness is 1.00 or less. 〔4〕 The compressive stress CS at a depth of 50 μm in the depth direction from the surface 50 satisfies the relationship of formula (3), and is the chemically strengthened glass according to any one of 〔1〕 to 〔3〕. Formula (3) 150t - 50 ≤ CS 50 In formula (3), CS 50 represents the value of the compressive stress CS 50 and the unit is MPa. In formula (3), t represents the plate thickness of the chemically strengthened glass, and the unit is mm. 〔5〕 The chemically strengthened glass according to any one of 〔1〕 to 〔4〕, wherein the Young's modulus at the in-plane central position is 80 GPa or more. 〔6〕 The fracture toughness value K at the in-plane central position IC is 0.80 MPa·m 1 / 2 or more, and is the chemically strengthened glass according to any one of 〔1〕 to 〔5〕. 〔7〕 The composition at the central position of the plate thickness is expressed in mole percentage based on oxides, SiO2 is 55 to 75% Al2O3 is 3 to 18% Li2O is 17 to 30% Na2O is 0 to 3% K2O is 0 to 1% MgO is 0 to 10% CaO is 0 to 10% SrO is 0 to 5% ZnO is 0 to 5% TiO2 is 0 to 3% ZrO2 is 0 to 5% SnO2 is 0 to 1% P2O5 is 0 to 3% B2O3 is 0 to 10% Y2O3 is 0 to 3% and contains the chemically strengthened glass according to any one of 〔1〕 to 〔6〕. 〔8〕The chemically strengthened glass according to any one of 〔1〕 to 〔7〕, which is crystallized glass and has a transmittance of 85% or more. 〔9〕The above-mentioned compressive stress CS 120 is 0 MPa or less, and the chemically strengthened glass according to any one of 〔1〕 to 〔8〕. 〔10〕The chemically strengthened glass according to any one of 〔1〕 to 〔9〕, having a plate thickness of 0.6 mm or less. 〔11〕The absolute value of the first derivative of the stress profile in the depth direction obtained using a scattered light photoelastic stress meter of the above-mentioned chemically strengthened glass is 1.80 or less at any depth from a position 120 μm in the depth direction from the surface to the center position of the plate thickness, and the chemically strengthened glass according to any one of 〔1〕 to 〔10〕. 〔12〕The absolute value of the first derivative of the stress profile in the depth direction obtained using a scattered light photoelastic stress meter is 1.80 or less at the depth DOC of the compressive stress layer, and the chemically strengthened glass according to 〔2〕 or 〔3〕. 〔13〕In the stress profile in the depth direction obtained using a scattered light photoelastic stress meter, the value obtained by dividing the absolute value of the first derivative at the depth DOC of the compressive stress layer by the first derivative at a position 120 μm in the depth direction from the surface is 1.20 or less, and the chemically strengthened glass according to 〔2〕 or 〔3〕. 〔14〕A method for manufacturing a chemically strengthened glass for manufacturing the chemically strengthened glass according to any one of 〔1〕 to 〔13〕, a first chemical strengthening treatment is performed on the glass for chemical strengthening using a first molten salt containing 90% by mass or more of a Na salt and 2% by mass or more of a Li salt based on the total mass, and a second chemical strengthening treatment is performed on the glass for chemical strengthening that has undergone the above-mentioned first chemical strengthening treatment using a second molten salt containing 90% by mass or more of a K salt based on the total mass, the composition at the center position of the plate thickness of the above-mentioned glass for chemical strengthening is expressed in terms of molar percentage on an oxide basis, SiO2 is 60 to 72% Al2O3 is 10 to 20% Li2O is 3 to 12% Na2O is 0.5 to 6% A method for manufacturing chemically strengthened glass containing 1 to 3% of K2O. 〔15〕 The method for manufacturing chemically strengthened glass according to 〔14〕, wherein the ratio of the content of the Li salt in the first molten salt to the content of Li2O in the composition of the glass for chemical strengthening is 0.1 to 1.0 in terms of molar ratio. 〔16〕 The method for manufacturing chemically strengthened glass according to 〔14〕 or 〔15〕, wherein the time of the first chemical strengthening treatment is 150 minutes or more, and the time of the second chemical strengthening treatment is 90 minutes or more. 〔17〕 A cover glass including the chemically strengthened glass according to any one of 〔1〕 to 〔13〕. 〔18〕 A solar cell module including the cover glass according to 〔17〕.

Advantages of the Invention

[0009] According to the present invention, it is possible to provide chemically strengthened glass having excellent drop strength. Further, according to the present invention, it is also possible to provide a method for manufacturing chemically strengthened glass. Further, according to the present invention, it is also possible to provide a cover glass and a solar cell module.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Embodiments for Carrying Out the Invention

[0011] Hereinafter, the present invention will be described in detail. The description of the constituent elements given below may be based on representative embodiments of the present invention, but the present invention is not limited to such embodiments.

[0012] In this specification, "chemically strengthened glass" refers to the glass after the chemical strengthening treatment. Also, "glass for chemical strengthening" refers to the glass before the chemical strengthening treatment.

[0013] In this specification, the glass composition of the glass for chemical strengthening may be referred to as the parent glass composition of the chemically strengthened glass. In the chemically strengthened glass, usually, a compressive stress layer is formed on the glass surface portion by ion exchange, so the glass composition of the portion that has not been ion-exchanged coincides with the parent glass composition of the chemically strengthened glass. In this specification, the glass composition is shown in terms of molar percentages on an oxide basis, and mol% may be simply denoted as %. Also, "~" indicating a numerical range is used in the sense of including the numerical values described before and after it as the lower limit value and the upper limit value.

[0014] "Substantially not contained" in the glass composition means not contained except for inevitable impurities contained in raw materials, etc., that is, not intentionally contained. Specifically, for components other than those described as the glass composition, for example, less than 0.1 mol% is preferable, less than 0.08 mol% is more preferable, and less than 0.05 mol% is even more preferable.

[0015] In this specification, the "stress profile" is a pattern representing the compressive stress value with the depth from the glass surface as a variable. A negative compressive stress value means a tensile stress.

[0016] The stress profile of the glass can be measured with a scattered light photoelastic stress meter (SLP) and a film stress measurement (FSM). In this specification, the stress profile measured by a scattered light photoelastic stress meter (SLP) is referred to as the "SLP stress profile", and the stress profile measured by an optical waveguide surface stress meter (FSM) is referred to as the "FSM stress profile". Note that the optical waveguide surface stress meter (FSM) can accurately measure the stress of glass in a short time. Examples of FSM include the FSM-6000 manufactured by Orihara Seisakusho Co., Ltd. However, in principle, FSM can only measure stress when the refractive index decreases from the sample surface toward the interior. In chemically strengthened glass, a layer obtained by replacing sodium ions inside the glass with external potassium ions can have its stress measured by FSM because the refractive index decreases from the sample surface toward the interior. However, the stress of a layer obtained by replacing lithium ions inside the glass with external sodium ions cannot be accurately measured by FSM. On the other hand, the method using a scattered light photoelastic stress meter (SLP) can measure stress regardless of the refractive index distribution. Examples of SLP include the SLP-1000 and SLP-2000 manufactured by Orihara Seisakusho Co., Ltd. Combining these scattered light photoelastic stress meters with the attached software SlpIV_up3 (Ver. 2019.01.10.001) enables high-precision stress measurement. However, SLP is easily affected by surface scattering and may not be able to accurately measure the stress near the surface. For the above reasons, by combining and using two types of measuring devices, namely the optical waveguide surface stress meter (FSM) and the scattered light photoelastic stress meter (SLP), accurate stress measurement becomes possible across the entire thickness of chemically strengthened glass. In this specification, the stress profile synthesized from the information of SLP and the information of FSM is referred to as the "synthesized stress profile".

[0017] Regarding the method of measuring the stress profile near the surface of glass using FSM, reference can be made to known methods. Also, regarding the method of measuring the stress profile in the glass interior more than several tens of μm from the glass surface layer using SLP, reference can be made to known methods. Examples of the above-known methods include the methods described in International Publication No. WO2018 / 056121 and International Publication No. WO2017 / 115811.

[0018] In this specification, the depth of the compressive stress layer is the depth at which the compressive stress value becomes zero.

[0019] In this specification, "fracture toughness value K IC " is measured with reference to the DCDC method [Reference: M.Y. He, M.R. Turner and A.G. Evans, Acta Metall. Mater. 43 (1995) 3453.]. Specifically, using a sample with the shape shown in Figure 2 and a SHIMADZU autograph AGS-X5KN, a K1-v curve showing the relationship between the stress intensity factor K1 (unit: MPa·m 1 / 2 ) and the crack propagation rate v (unit: m / s) as shown in Figure 3 is measured. The data in Region III obtained is regressed and extrapolated with a linear equation, and the stress intensity factor K1 of 0.1 m / s is taken as the fracture toughness value K IC .

[0020] <Chemically strengthened glass> The chemically strengthened glass of the present invention satisfies the following relationship for the stress CT at the central position of the plate thickness, and the compressive stress CS at a depth of 120 μm in the depth direction from the surface 120 satisfies the following relationship. Equation (1) |CT| ≦ -170t + 175 Equation (2) 190t - 124 ≦ CS 120 In Equation (1), |CT| represents the absolute value of the stress CT, and the unit is MPa. In Equations (1) and (2), t represents the plate thickness of the chemically strengthened glass, and the unit is mm. In Equation (2), CS 120 represents the value of the compressive stress CS 120 , and the unit is MPa.

[0021] According to the chemically strengthened glass of the present invention that satisfies the relationships of the above Equations (1) and (2), the mechanism for excellent drop strength is not necessarily clear, but the present inventor speculates as follows. When the glass breaks, it is considered that the crack generated on the surface of the glass propagates and leads to cracking. In the chemically strengthened glass of the present invention, due to chemical strengthening, a compressive stress acts on the surface of the chemically strengthened glass and satisfies the relationship of formula (1), so the drop strength is likely to increase. Further, in the chemically strengthened glass of the present invention, the relationship of formula (2) is satisfied. The relationship of formula (2) indicates that the compressive stress CS 120 at a depth of 120 μm is equal to or greater than a predetermined value with respect to the plate thickness. Then, in the chemically strengthened glass of the present invention that satisfies the relationship of formula (2), even if a scratch reaches the deep part (for example, a depth of 120 μm) of the chemically strengthened glass, the compressive stress CS 120 is within a predetermined range, so the scratch is less likely to progress and the drop strength is likely to increase. From the above, the chemically strengthened glass of the present invention is considered to have excellent drop strength.

[0022] Hereinafter, the conditions satisfied by the chemically strengthened glass of the present invention will be described.

[0023] [Plate thickness] The plate thickness of the chemically strengthened glass of the present invention is preferably 0.8 mm or less, more preferably 0.7 mm or less, and even more preferably 0.6 mm or less. In addition, the plate thickness of the chemically strengthened glass of the present invention is often 0.1 mm or more, preferably 0.2 mm or more, more preferably 0.3 mm or more, and even more preferably 0.4 mm or more.

[0024] [Compressive stress] The compressive stress (CS 120 ) at a depth of 120 μm in the chemically strengthened glass of the present invention satisfies the relationship of the above formula (2) with respect to the plate thickness t and CS 120 . CS 120 is preferably -30 MPa or more, more preferably -25 MPa or more, even more preferably -20 MPa or more, particularly preferably -15 MPa or more, and most preferably -10 MPa or more. CS 120 may be 0 MPa or more, or may be 10 MPa or more. Further, CS 120 is often 50 MPa or less, and when the above plate thickness is 0.6 mm or less, it is often 20 MPa or less.120 may be 0 MPa or less. CS 120 is determined from the SLP stress profile.

[0025] The compressive stress (CS 50 ) at a depth of 50 μm in the chemically strengthened glass of the present invention is preferably 20 MPa or more, more preferably 30 MPa or more, and still more preferably 40 MPa or more. Also, CS 50 is preferably 200 MPa or less, more preferably 150 MPa or less, still more preferably 100 MPa or less, particularly preferably 75 MPa or less, and most preferably 60 MPa or less in terms of the drop strength being more likely to increase. CS 50 is determined from the SLP stress profile.

[0026] Also, the compressive stress (CS 50 ) at a depth of 50 μm in the chemically strengthened glass of the present invention preferably satisfies the relationship of the following formula (3) with respect to the plate thickness t and CS 50 . Formula (3) 150t - 50 ≤ CS 50 In formula (3), CS 50 represents the value of the compressive stress CS 50 , and the unit is MPa. In formula (3), t represents the plate thickness of the chemically strengthened glass, and the unit is mm.

[0027] The compressive stress (CS0) on the outermost surface of the chemically strengthened glass of the present invention is preferably 700 MPa or more, more preferably 800 MPa or more, still more preferably 900 MPa or more, and particularly preferably 1000 MPa or more. CS0 is determined by a surface stress measuring device such as FSM.

[0028] Each of the above compressive stresses can be adjusted, for example, by the conditions of the chemical strengthening treatment described later.

[0029] [Compressive stress layer depth] The depth of the compressive stress layer DOC of the chemically strengthened glass of the present invention is preferably 80 μm or more, more preferably 90 μm or more, and even more preferably 100 μm or more. Further, the depth of the compressive stress layer DOC is often 200 μm or less, preferably 150 μm or less, more preferably 130 μm or less, and even more preferably 120 μm or less. The depth of the compressive stress layer DOC is determined from the SLP stress profile.

[0030] The depth of the compressive stress layer DOC is preferably 0.16 times or more of the plate thickness, more preferably 0.17 times or more of the plate thickness, and even more preferably 0.20 times or more of the plate thickness. Further, the depth of the compressive stress layer DOC is usually 0.30 times or less of the plate thickness, often 0.25 times or less of the plate thickness, and preferably 0.23 times or less.

[0031] [Tensile stress] Since the chemically strengthened glass of the present invention has compressive stress near the surface, tensile stress that balances with it acts inside the chemically strengthened glass. That is, the stress CT, which is the stress at the center position of the plate thickness of the chemically strengthened glass of the present invention, is usually tensile stress (compressive stress with a negative value). As described above, the stress CT at the center position of the plate thickness of the chemically strengthened glass of the present invention satisfies the relationship of the above formula (1) with respect to the plate thickness t and the stress CT. The absolute value of the stress CT is preferably 30 MPa or more, more preferably 40 MPa or more, even more preferably 50 MPa or more, and may be 70 MPa or more. Further, the absolute value of the stress CT is preferably 100 MPa or less, more preferably 95 MPa or less, and even more preferably 90 MPa or less.

[0032] [Slope of stress profile] Regarding the SLP stress profile, when fitting is performed using an appropriate function, the function after fitting can be differentiated, and further analysis regarding the SLP stress profile becomes possible. Note that the SLP stress profile has the depth (unit: μm) on the horizontal axis and the compressive stress value (unit: MPa) on the vertical axis. The fitting of the SLP stress profile can be performed using the following function (Equation (FS)).

[0033] [Number]

[0034] In the above Equation (FS), a i (i = 1 to 5) are fitting parameters, and erfc is the complementary error function. Also, in Equation (FS), x represents the depth. The complementary error function (erfc(x)) is defined by the following equation.

[0035] [Number]

[0036] The fitting is performed using the attached software [SlpIV (Ver.2019.01.10.001)] of the scattered light photoelastic stress meter (SLP-1000 manufactured by Oriehara Seisakusho). More specifically, according to the specifications of the attached software, the fitting parameters are optimized by minimizing the sum of the squared residuals between the obtained raw data and the above function. The measurement processing condition is single-shot, and for the measurement region processing adjustment items, the edge method is used at the surface, 6.0 μm at the internal surface edge, automatic at the internal left and right edges, automatic (at the center of the sample film thickness) at the internal deep edge, and the extension of the phase curve to the center of the sample thickness is the fitting curve, which are each specified and selected. The function after fitting obtained by the above procedure is differentiable with respect to the first order and differentiable with respect to the second order. Hereinafter, the function after fitting is also denoted as σ f (x).

[0037] When the above function after fitting (σ f (x)) is differentiated with respect to x (depth), the first derivative σ f ’(x) is obtained. When the depth value is substituted into σ f ’(x), the slope (first derivative value) of σ f (x) at that depth is obtained.

[0038] The absolute value of the first-order derivative of the chemically strengthened glass of the present invention is preferably 1.80 or less, more preferably 1.20 or less, still more preferably 0.80 or less, and most preferably 0.60 or less at any depth from the position 120 μm deep from the surface to the center position of the plate thickness. Also, the absolute value of the first-order derivative is often 0.10 or more, preferably 0.20 or more, and more preferably 0.30 or more at any depth from the position 120 μm deep from the surface to the center position of the plate thickness.

[0039] Also, the absolute value of the first-order derivative of the chemically strengthened glass of the present invention is preferably 1.80 or less, more preferably 1.40 or less, and still more preferably 1.00 or less at the depth DOC of the compressive stress layer. Also, the absolute value of the first-order derivative is preferably 0.10 or more, more preferably 0.20 or more, and still more preferably 0.30 or more at the depth DOC of the compressive stress layer.

[0040] Also, in the chemically strengthened glass of the present invention, the absolute value of the slope calculated from the compressive stress value at the depth DOC of the compressive stress layer and the compressive stress value at the center position of the plate thickness is preferably 1.00 or less, more preferably 0.95 or less, and still more preferably 0.90 or less. The absolute value of the slope is also preferably 0.60 or less. The absolute value of the slope is often 0.20 or more, and preferably 0.30 or more. The absolute value of the slope is obtained by dividing the value of the stress CT by the value obtained by subtracting the value of the depth of the compressive stress layer DOC from the depth at the center position of the plate thickness and taking the absolute value.

[0041] Further, in the chemically strengthened glass of the present invention, in the stress profile in the depth direction obtained using a scattered light photoelastic stress meter, the absolute value of the first derivative value at the depth DOC of the compressive stress layer is divided by the first derivative value at a position 120 μm in the depth direction from the surface (hereinafter, also referred to as "first derivative value ratio"). It is also preferable that this value is 1.20 or less. The above first derivative value ratio is preferably 0.80 or more, more preferably 0.90 or more in terms of better drop strength, and even more preferably 1.00 or more. Further, the above first derivative value ratio is more preferably 1.15 or less in terms of better drop strength.

[0042] [Young's modulus] The Young's modulus at the in-plane central position of the chemically strengthened glass of the present invention is preferably 80 GPa or more. The above Young's modulus is more preferably 83 GPa or more, even more preferably 85 GPa or more, and particularly preferably 90 GPa or more. The Young's modulus at the in-plane central position of the chemically strengthened glass means the Young's modulus measured at the central position in the in-plane direction of the plate-shaped chemically strengthened glass. The central position in the in-plane direction is the centroid position in the in-plane direction. When the chemically strengthened glass is square, the central position is the position of the intersection of the diagonals. The above Young's modulus can be adjusted not only by the composition (parent glass composition) of the glass (glass for chemical strengthening) used for the chemically strengthened glass, but also by heat treatment conditions such as the heat treatment temperature, heat treatment time, cooling rate, and temperature profile of the glass for chemical strengthening. For example, when the parent glass composition is a composition that can become a crystallized glass, the value of the Young's modulus is likely to change depending on the above heat treatment conditions. Further, in the chemically strengthened glass of the present invention, the Young's modulus at the central position of the plate thickness is preferably 80 GPa or more, more preferably 83 GPa or more, even more preferably 85 GPa or more, and particularly preferably 90 GPa or more. The Young's modulus of the glass for chemical strengthening corresponds to the Young's modulus at the central position of the plate thickness of the chemically strengthened glass. In this specification, the Young's modulus at the in-plane central position and the Young's modulus at the central position of the plate thickness of the chemically strengthened glass are measured by the ultrasonic pulse method. The detailed measurement method of the Young's modulus follows the method shown in the examples in the following section.

[0043] [Fracture toughness value] The fracture toughness value (K IC ) at the center of the plate thickness of the chemically strengthened glass of the present invention is preferably 0.75 MPa·m 1 / 2 or more in terms of higher crack strength, more preferably 0.80 MPa·m 1 / 2 or more, and even more preferably 0.85 MPa·m 1 / 2 or more. K IC is often 2.00 MPa·m 1 / 2 or less, and preferably 1.80 MPa·m 1 / 2 or less. The method for measuring the fracture toughness value at the center of the plate thickness of the chemically strengthened glass of the present invention follows the method for measuring the fracture toughness value in the examples in the later stage. Note that the fracture toughness value of the glass for chemical strengthening corresponds to the fracture toughness value at the center of the plate thickness of the chemically strengthened glass. K IC can be adjusted, for example, in the same manner as the above Young's modulus.

[0044] [Transmittance] The transmittance of the chemically strengthened glass of the present invention is preferably 85% or more. The transmittance of the chemically strengthened glass is measured with a spectrophotometer. More specifically, first, a measurement sample with a plate thickness of 0.50 mm is prepared and measured with an apparatus of PerkinElmer; LAMBDA950. From the measurement results, the average transmittance [unit: %] at wavelengths of 380 to 780 nm is calculated and taken as the transmittance of the chemically strengthened glass of the present invention. The transmittance of the chemically strengthened glass of the present invention is preferably 90% or more, and may be 95% or more. The transmittance of the chemically strengthened glass of the present invention is often 99% or less. Also, the chemically strengthened glass of the present invention is preferably a crystallized glass and has the above transmittance.

[0045] [Composition] The chemically strengthened glass of the present invention is obtained by chemically strengthening a plate glass (glass for chemical strengthening) before chemical strengthening. The preferred composition of the glass for chemical strengthening (parent glass composition) will be described below. The parent glass composition is the same as the composition at the center of the plate thickness of the chemically strengthened glass. The following describes the first embodiment and the second embodiment as preferred parent glass compositions.

[0046] (First Embodiment) The first embodiment of the parent glass composition is expressed in mole percentages based on oxides, SiO2 is 60 to 72% Al2O3 is 10 to 20% Li2O is 3 to 12% Na2O is 0.5 to 6% Contains 0 to 3% of K2O (preferably 1 to 3%). Among them, the first embodiment of the parent glass composition is expressed in mole percentages based on oxides, SiO2 is 60 to 72% Al2O3 is 10 to 20% Li2O is 3 to 12% Na2O is 0.5 to 6% K2O is 0 to 3% MgO is 0 to 10% CaO is 0 to 10% SrO is 0 to 5% ZnO is 0 to 5% TiO2 is 0 to 3% ZrO2 is 0 to 3% SnO2 is 0 to 1% P2O5 is 0 to 1% B2O3 is 0 to 10% Contains 0 to 3% of Y2O3, R, which is the total of the contents of Li2O, Na2O, and K2O, is 5 to 20%, the content of Li2O relative to R is 0.5 to 0.95, and the value of the product of the content of Li2O relative to R, the content of Na2O relative to R, and the content of K2O relative to R is 0.001 to 0.03. The following describes each component contained in the parent glass composition. Hereinafter, for example, the content in mole percentage based on oxides of SiO2 may be described as "[SiO2]".

[0047] SiO2 is a component that constitutes the glass network. It is also a component that improves chemical durability and reduces the occurrence of cracks when the glass surface is scratched.

[0048] The content of SiO2 is more preferably 60.0% or more, still more preferably 62.0% or more, particularly preferably 64.0% or more, and most preferably 66.0% or more in order to improve chemical durability. On the other hand, from the viewpoint of improving meltability, the content of SiO2 is more preferably 70.0% or less, still more preferably 68.0% or less, and particularly preferably 67.0% or less.

[0049] Al2O3 is a component that improves the ion exchange performance during chemical strengthening and increases the surface compressive stress after strengthening. From the viewpoint of obtaining the above effects, the content of Al2O3 is more preferably 10.0% or more, still more preferably 10.5% or more, and 11.0% or more in this order. On the other hand, it is required that crystals are less likely to grow during melting, devitrification defects are less likely to occur and the yield is more likely to be higher, and the high-temperature viscosity of the glass is reduced to make it easier to melt. From such a viewpoint, the content of Al2O3 is more preferably 15.0% or less, still more preferably 14.0% or less, 13.5% or less, and 13.0% or less in this order.

[0050] Both SiO2 and Al2O3 are components that stabilize the glass structure. In order to lower brittleness, the total content of SiO2 and Al2O3 is preferably 74.0% or more, more preferably 76.0% or more, and still more preferably 77.0% or more. Also, both SiO2 and Al2O3 tend to increase the melting temperature of the glass. Therefore, in order to make it easier to melt, the total content of SiO2 and Al2O3 is preferably 83.0% or less, more preferably 82.0% or less, still more preferably 81.0% or less, and particularly preferably 80.5% or less.

[0051] Li2O is a component capable of ion exchange and is a component that improves the meltability of the glass. When the glass contains Li2O, the Li ions on the glass surface are ion-exchanged with external Na ions and taken into the glass, and then the incorporated Na ions are ion-exchanged with external K ions. In this way, a stress profile with a large surface compressive stress and a thick compressive stress layer is easily obtained. From the viewpoint of easily obtaining a preferable stress profile, the content of Li2O is more preferably 8.0% or more, and still more preferably, in the following order, 9.0% or more, 9.5% or more, 10.0% or more, 10.2% or more, 10.4% or more.

[0052] On the other hand, from the viewpoint of reducing the crystal growth rate during glass forming and making it less likely to cause a quality deterioration due to devitrification, the content of Li2O is more preferably 11.8% or less, and still more preferably, in the following order, 11.5% or less, 11.0% or less.

[0053] Na2O and K2O are components that improve the meltability of the glass and reduce the crystal growth rate during glass forming. Also, it is preferable to contain a small amount in order to improve the ion exchange performance.

[0054] Na2O is a component capable of ion exchange in chemical strengthening treatment using a potassium salt and is a component that lowers the viscosity of the glass. In order to obtain the above effects, the content of Na2O is preferably 1% or more, and more preferably, in the following order, 1.5% or more, 2.5% or more, 3.0% or more, 4.0%.

[0055] K2O is a component that suppresses the rise of the devitrification temperature to suppress devitrification and improves the ion exchange performance. The content of K2O is more preferably 0.1% or more, and still more preferably 0.15% or more, and particularly preferably, in the following order, 0.2% or more, 0.5% or more, 1.0% or more.

[0056] R, which is the total content of Li2O, Na2O, and K2O, is more preferably 8% or more, even more preferably 9% or more, particularly preferably 12% or more, and most preferably 15% or more from the viewpoint of suppressing the increase in the devitrification temperature and reducing the crystal growth rate.

[0057] The ratio of the content of Li2O to the above R ([Li2O] / ([Li2O]+[Na2O]+[K2O]), hereinafter also referred to as "Li2O / R2O") is more preferably 0.52 or more, even more preferably 0.55 or more from the viewpoint of further improving the chemical strengthening characteristics with respect to the compressive stress in the deep layer. Li2O / R2O is more preferably 0.90 or less, even more preferably 0.85 or less, and particularly preferably 0.75 or less from the viewpoint of further enhancing the chemical durability.

[0058] The ratio of the content of Na2O to the above R ([Na2O] / ([Li2O]+[Na2O]+[K2O]), hereinafter also referred to as "Na2O / R2O") is preferably 0.08 or more, more preferably 0.15 or more, and even more preferably 0.20 or more from the viewpoint of further improving the chemical strengthening characteristics with respect to the compressive stress in the deep layer. Na2O / R2O is preferably 0.60 or less, more preferably 0.50 or less, even more preferably 0.40 or less, and particularly preferably 0.35 or less from the viewpoint of further enhancing the chemical durability.

[0059] The ratio of the content of K2O to the above R ([K2O] / ([Li2O]+[Na2O]+[K2O]), hereinafter also referred to as "K2O / R2O") is preferably 0.01 or more, more preferably 0.015 or more, even more preferably 0.02 or more, and particularly preferably 0.08 or more from the viewpoint of further improving the electrical resistance of the glass. K2O / R2O is preferably 0.50 or less, more preferably 0.40 or less, even more preferably 0.30 or less, and particularly preferably 0.20 or less from the viewpoint of further enhancing the chemical strengthening characteristics with respect to the compressive stress near the surface.

[0060] Also, the product of Li2O / R2O, Na2O / R2O, and K2O / R2O is more preferably 0.002 or more, even more preferably 0.01 or more, and particularly preferably 0.015 or more from the viewpoint of suppressing the increase in the devitrification temperature. Also, from the viewpoint of improving chemical resistance, the above product is more preferably 0.028 or less.

[0061] The ratio of the content of Al2O3 to R ([Al2O3] / ([Li2O]+[Na2O]+[K2O]), hereinafter also referred to as "Al2O3 / R2O") is preferably 0.20 or more, more preferably 0.30 or more, even more preferably 0.40 or more, and still more preferably 0.50 or more. Al2O3 / R2O is preferably 1.50 or less, more preferably 0.80 or less, even more preferably 0.75 or less, particularly preferably 0.70 or less, and most preferably 0.65 or less.

[0062] Also, the ratio of the content of K2O to the content of Na2O ([K2O] / [Na2O]) is preferably 0.0 to 1.8. [K2O] / [Na2O] is preferably 0.1 or more, more preferably 0.2 or more in that it improves the compressive stress near the surface layer and makes it easier to obtain chemically strengthened glass with a greater bending test strength. Also, [K2O] / [Na2O] is preferably 1.0 or less, more preferably 0.9 or less, even more preferably 0.8 or less, and particularly preferably 0.7 or less in the above respect.

[0063] The value represented by [Al2O3]-[Na2O]-[K2O]+[Li2O] is preferably 10.0 to 22.0, more preferably 10.0 to 20.0, and even more preferably 12.0 to 18.0.

[0064] MgO may be contained to lower the viscosity during melting. The content of MgO is more preferably 0.05% or more, and even more preferably, in order, 0.1% or more, 0.2% or more, 0.9% or more, more than 0.9%, 1.0% or more. On the one hand, in terms of being more likely to increase the compressive stress layer during chemical strengthening treatment, the MgO content is more preferably 8.0% or less, and even more preferably, in the following order, 7.5% or less, 5.0% or less, 4.0% or less, 3.8% or less. By setting the MgO content to 4.0% or less, the acid resistance can be improved.

[0065] Also, by containing MgO, the phase transition of the crystal phase from β - quartz solid solution to β - spodumene can be suppressed, and the precipitation of β - spodumene crystals can be suppressed. Therefore, in Embodiment 2, it is preferable to contain MgO. From the above viewpoints, it is preferable to contain more than 0.5% and 7.0% or less of MgO. The more preferable range is as described above.

[0066] CaO is a component that improves the meltability of the glass and may be contained. The CaO content is more preferably 0.1% or more, and even more preferably 0.15% or more. On the other hand, in terms of being more likely to increase the compressive stress value during chemical strengthening treatment, the CaO content is more preferably 2.0% or less, and even more preferably 1.0% or less, particularly preferably 0.8% or less, and most preferably 0.5% or less.

[0067] To enhance the stability of the glass, it is more preferable to contain at least one of MgO and CaO, and it is even more preferable to contain MgO. The total content of MgO and CaO is preferably more than 0.1%, more preferably 0.2% or more, and even more preferably 0.5% or more. In terms of further improving the chemical strengthening characteristics, the total content of MgO and CaO is preferably 10.0% or less, and more preferably, in the following order, 5.0% or less, 3.5% or less.

[0068] SrO is a component that improves the meltability of the glass and may be contained. The SrO content is more preferably 0.1% or more, and even more preferably 0.15% or more, and particularly preferably 0.5% or more. In terms of facilitating an increase in the compressive stress value during chemical strengthening treatment, the content of SrO is more preferably 3.0% or less, still more preferably 2.0% or less, particularly preferably 1.0% or less, and most preferably 0.5% or less. SrO may not be substantially contained.

[0069] BaO is a component that improves the meltability of the glass and may be contained. When BaO is contained, the content is preferably 0.1% or more, more preferably 0.15% or more, and still more preferably 0.5% or more. In terms of facilitating an increase in the compressive stress value during chemical strengthening treatment, the content of BaO is preferably 3.0% or less, more preferably 2.0% or less, still more preferably 1.0% or less, and particularly preferably 0.5% or less. BaO may not be substantially contained.

[0070] ZnO is a component that improves the meltability of the glass. The content of ZnO is more preferably 0.1% or more, still more preferably 0.15% or more, and particularly preferably 0.5% or more. In terms of facilitating an increase in the compressive stress value during chemical strengthening treatment, the content of ZnO is more preferably 3.0% or less, still more preferably 2.0% or less, particularly preferably 1.0% or less, and most preferably 0.5% or less. ZnO may not be substantially contained.

[0071] lnW is a parameter representing the degree of mixing of oxides, which is calculated from the contents of alkali metal oxides, alkaline earth metal oxides, and zinc oxide contained in the glass. lnW is represented by the following formula. lnW = ln(([Li2O] + [Na2O] + [K2O] + [MgO] + [CaO] + [SrO] + [BaO] + [ZnO])! / ([Li2O]! × [Na2O]! × [K2O]! × [MgO]! × [CaO]! × [SrO]! × [BaO]! × [ZnO]!)) ··· Formula (W1) In formula (W1), [Li2O], [Na2O], [K2O], [MgO], [CaO], [SrO], [BaO] and [ZnO] respectively represent the contents in terms of molar percentage based on the oxides of the respective components of Li2O, Na2O, K2O, MgO, CaO, SrO, BaO and ZnO. Also,! indicates taking the factorial of a positive number. For example, [XO]! means truncating the decimal part of the numerical value of the content in terms of molar percentage based on the oxide of component XO to a positive number and taking the factorial of that positive number. For example, when Na2O is 4.8 mol%, it is calculated as the factorial of "4", that is, 4×3×2×1. The larger the value of lnW, the higher the degree of mixing of the above metal oxides, and the more the devitrification of the glass can be suppressed. From the above perspective, lnW is preferably 10 or more, more preferably 12 or more, still more preferably 13 or more, and particularly preferably 14 or more. lnW is preferably 20 or less, more preferably 18 or less, and still more preferably 17 or less.

[0072] TiO2 is a component with a high effect of suppressing the solarization of glass and may be contained. When TiO2 is contained, the content is preferably 0.02% or more, more preferably 0.03% or more, still more preferably 0.04% or more, particularly preferably 0.05% or more, and most preferably 0.06% or more. On the other hand, from the perspective of preventing the occurrence of devitrification and the deterioration of the quality of chemically strengthened glass, the content of TiO2 is preferably 2.0% or less, more preferably 1.0% or less, still more preferably 0.5% or less, particularly preferably 0.25% or less, and most preferably 0.15% or less. TiO2 may not be substantially contained.

[0073] ZrO2 is a component that tends to increase the surface compressive stress of chemically strengthened glass. The content of ZrO2 is more preferably more than 0%, and still more preferably, in the following order, 0.1% or more, 0.15% or more, 0.2% or more, 0.25% or more, 0.3% or more, 0.4% or more. On the one hand, in terms of suppressing the generation of devitrification defects and making it easier to increase the compressive stress value during chemical strengthening treatment, the content of ZrO2 is more preferably 2.0% or less, and even more preferably 1.5% or less.

[0074] P2O5 is likely to increase the compressive stress layer during chemical strengthening. The content of P2O5 is more preferably 0.5% or more, even more preferably 1.0% or more, and particularly preferably 2.0% or more. On the other hand, from the perspective of enhancing acid resistance, the content of P2O5 is more preferably 4.0% or less, and even more preferably 2.0% or less. From the perspective of preventing the occurrence of veining during melting, it is also preferable to be substantially free of it.

[0075] B2O3 reduces the brittleness of the glass and improves crack resistance, or improves the meltability of the glass. The content of B2O3 is more preferably 0.5% or more, even more preferably 1.0% or more, and particularly preferably 2.0% or more. On the one hand, in terms of maintaining good acid resistance, the content of B2O3 is preferably 8.0% or less. The content of B2O3 is more preferably 6.0% or less, even more preferably 4.0% or less, and particularly preferably 2.0% or less. From the perspective of preventing the occurrence of veining during melting, it is also preferable to be substantially free of it.

[0076] Y2O3 is a component that makes it easier to increase the surface compressive stress of chemically strengthened glass while reducing the crystal growth rate. The content of Y2O3 is more preferably more than 0%, and even more preferably, in order, 0.1% or more, 0.2% or more, 0.5% or more. On the one hand, in terms of making it easier to increase the compressive stress layer during chemical strengthening treatment, the content of Y2O3 is more preferably 2.0% or less, and even more preferably 1.5% or less.

[0077] From the viewpoint of improving the initial solubility, the total content of ZrO2 and Y2O3 is preferably 4.0% or less, more preferably 2.4% or less. The lower limit of the total content of ZrO2 and Y2O3 is not particularly limited, but from the viewpoint of enhancing the strength of the glass, it is more preferably 0.5% or more, still more preferably 0.7% or more, 1.0% or more, and 1.2% or more in this order.

[0078] The ratio [ZrO2] / ([ZrO2]+[Y2O3]) of the content of ZrO2 to the total content of ZrO2 and Y2O3 is more preferably 0.10 or more, still more preferably 0.20 or more, and particularly preferably 0.25 or more. [ZrO2] / ([ZrO2]+[Y2O3]) is more preferably 0.90 or less, still more preferably 0.80 or less, and particularly preferably 0.75 or less.

[0079] ZrO2 and Y2O3 are known as nucleating agents when added alone, but when ZrO2 and Y2O3 are co-added, a eutectic of ZrO2 and Y2O3 is formed, so that the devitrification temperature, crystal growth rate, and crystallization start temperature can be controlled. Furthermore, by setting [ZrO2] / ([ZrO2]+[Y2O3]) within the above range, the diffusion of ions in the glass is suppressed, the increase in the devitrification temperature is suppressed, and devitrification can be suppressed. By setting [ZrO2] / ([ZrO2]+[Y2O3]) within the above range, the glass is stabilized, and furthermore, the temperature range where nucleation occurs and the temperature range where crystal growth occurs do not overlap and are separated to suppress the increase in the crystal growth rate, so that the occurrence of defects can be suppressed. Also, by setting [ZrO2] / ([ZrO2]+[Y2O3]) within the above range, the temperature range where nucleation occurs shifts to the low-temperature side to suppress the decrease in the crystallization start temperature, and the manufacturing characteristics can be improved.

[0080] From the perspective of reducing the drawbacks of glass, the value represented by 100×[ZrO2]+63×[Y2O3] is preferably 250 or less, more preferably 180 or less, still more preferably 175 or less, even more preferably 170 or less, and particularly preferably 165 or less. The lower limit of the value represented by 100×[ZrO2]+63×[Y2O3] is not particularly limited, but from the perspective of promoting nucleation, it is preferably 100 or more, more preferably 110 or more, still more preferably 125 or more, and particularly preferably 130 or more.

[0081] La2O3 is not essential, but can be contained for the same reasons as Y2O3. La2O3 is preferably 0.1% or more, more preferably 0.2% or more, still more preferably 0.5% or more, and particularly preferably 0.8% or more. On the other hand, if it is too much, it becomes difficult to increase the compressive stress layer during chemical strengthening treatment, so La2O3 is preferably 5.0% or less, more preferably 3.0% or less, still more preferably 2.0% or less, and particularly preferably 1.5% or less. It is also preferable that La2O3 is substantially not contained.

[0082] Nb2O 5、 Ta2O5, Gd2O3, and CeO2 have the effect of suppressing the solarization of glass and are components that improve the meltability, and may be contained. When these components are contained, the respective contents are preferably 0.03% or more, more preferably 0.1% or more, still more preferably 0.5% or more, particularly preferably 0.8% or more, and most preferably 1.0% or more. On the other hand, it is preferably 3.0% or less, more preferably 2.0% or less, and still more preferably 1.0% or less.

[0083] Since Fe2O3 absorbs heat rays, it has the effect of improving the solubility of glass. When producing glass in large quantities using a large melting furnace, it is preferably contained. In that case, the content is preferably 0.002% or more, more preferably 0.005% or more, still more preferably 0.007% or more, and particularly preferably 0.01% or more in terms of mass% based on oxides. On the other hand, if Fe2O3 is contained in excess, coloring occurs. Therefore, from the viewpoint of enhancing the transparency of the glass, the content is preferably 0.3% or less, more preferably 0.04% or less, still more preferably 0.025% or less, and particularly preferably 0.015% or less in terms of mass% based on oxides.

[0084] Furthermore, other coloring components may be added as long as they do not inhibit the achievement of the desired chemical strengthening characteristics. Examples of other coloring components include Co3O4, MnO2, NiO, CuO, Cr2O3, V2O5, Bi2O3, SeO2, Er2O3, Nd2O3, etc.

[0085] As a fining agent or the like during the melting of glass, SO3, chlorides, fluorides, etc. may be appropriately contained. It is preferably not to contain As2O3. When containing Sb2O3, it is preferably 0.3% or less, more preferably 0.1% or less, and most preferably not to contain it. From the viewpoint of clarifying the bubbles in the glass, the content of SnO2 is more preferably 0.1% or more, still more preferably 0.2% or more, and particularly preferably 0.3% or more. Also, the content of SnO2 is preferably 1% or less, more preferably 0.8% or less, still more preferably 0.7% or less, and particularly preferably 0.5% or less in order to suppress the occurrence of defects.

[0086] Hereinafter, the preferable physical properties of the glass of the parent glass composition of the first embodiment will be described.

[0087] (Devitrification temperature) The glass for chemical strengthening of the parent glass composition of the first embodiment preferably has a devitrification temperature of 1300 °C or lower. The devitrification temperature is more preferably 1280 °C or lower, and even more preferably 1250 °C or lower. Particularly preferably, in order, it is 1240 °C or lower, 1230 °C or lower, 1220 °C or lower, 1210 °C or lower. The lower limit of the devitrification temperature is not particularly limited, but is usually 1100 °C or higher.

[0088] When the devitrification temperature is 1300 °C or lower (preferably 1250 °C or lower), the glass can be stably formed and the manufacturing characteristics can be improved. Specifically, for example, when forming glass by the float process, if crystals form before pouring the molten glass into the float bath, the bricks constituting the float bath may be eroded by the crystals. When the devitrification temperature is 1300 °C or lower (preferably 1250 °C or lower), erosion of the bricks can be suppressed. The devitrification temperature of the glass is the minimum value of the temperature at which, when glass particles of 2 mm to 3 mm crushed in a platinum dish are placed and heat-treated in an electric furnace controlled at a constant temperature for 17 hours, no crystals precipitate on the surface and inside of the glass as observed by an optical microscope after the heat treatment.

[0089] (Glass transition temperature Tg, crystallization start temperature Tcs, crystallization peak temperature Tc) In this specification, the measurement by differential scanning calorimetry (DSC) is performed by grinding the glass in an agate mortar, preparing about 70 mg of powder with a particle size of 106 to 180 μm, and heating from room temperature to 1200 °C at a heating rate of 10 °C / min.

[0090] The glass for chemical strengthening of the parent glass composition of the first embodiment preferably has a crystallization start temperature Tcs measured by DSC of 790 °C or higher, more preferably 800 °C or higher, even more preferably 810 °C or higher, still more preferably 815 °C or higher, particularly preferably 820 °C or higher, and most preferably 825 °C or higher. The upper limit of the crystallization start temperature is not particularly limited, but is usually 900 °C or lower.

[0091] When the crystallization start temperature Tcs is 790 °C or higher, the manufacturing characteristics can be improved. Specifically, for example, in the molding including a three-dimensional shape (for example, 2.5D or 3D molding; hereinafter also abbreviated as three-dimensional molding) that is heat-treated after glass is formed into a plate, when the temperature is raised from room temperature to the molding temperature, the nucleation temperature is passed through, and defects due to crystallization are likely to occur. When the crystallization start temperature Tcs is 790 °C or higher, it is possible to perform molding without passing through the nucleation temperature when the temperature is raised from room temperature to the molding temperature, and the occurrence of defects can be suppressed.

[0092] FIG. 1 shows a schematic diagram for explaining Tg, Tcs, and Tc in the present specification. The glass transition point Tg in the present specification is, as shown in FIG. 1, the intersection point where an auxiliary line is drawn in the curve obtained by DSC. The glass crystallization start temperature Tcs in the present specification refers to the temperature at the peak apex when the glass is heated at 10 °C / min using DSC.

[0093] For the glass for chemical strengthening of the parent glass composition of the first embodiment, the ratio (Tcs + 273.15) / (Tg + 273.15) of the crystallization start temperature Tcs to the glass transition point Tg is preferably 1.10 or higher, more preferably 1.15 or higher, still more preferably 1.20 or higher, and particularly preferably 1.25 or higher. When (Tcs + 273.15) / (Tg + 273.15) is 1.10 or higher, the occurrence of defects in three-dimensional molding can be suppressed, and the molding characteristics can be improved. The upper limit of (Tcs + 273.15) / (Tg + 273.15) is not particularly limited, but from the viewpoint of the moldability of the glass, it is usually preferably 1.6 or lower. In addition, the units of Tcs and Tg in "(Tcs + 273.15) / (Tg + 273.15)" are "°C", and "(Tcs + 273.15) / (Tg + 273.15)" is the same as "Tcs / Tg" when the unit is "K".

[0094] For the glass for chemical strengthening of the parent glass composition of the first embodiment, the value obtained by subtracting the glass transition point Tg from the crystallization start temperature Tcs (Tcs - Tg) is preferably 180°C or higher, more preferably 200°C or higher. Even more preferably 210°C or higher, still more preferably 215°C or higher, particularly preferably 225°C or higher, and most preferably 230°C or higher. When (Tcs - Tg) is 200°C or higher, the occurrence of defects in three-dimensional molding can be suppressed and the molding characteristics can be improved. The upper limit of (Tcs - Tg) is not particularly limited, but from the viewpoint of the moldability of the glass, it is usually preferably 400°C or lower. For the glass for chemical strengthening of the parent glass composition of the first embodiment, the value obtained by subtracting the glass transition point Tg from the crystallization start temperature Tcs (Tcs - Tg) is preferably 180°C or higher, more preferably 185°C or higher.

[0095] From the viewpoint of reducing the warp after chemical strengthening, the glass transition point Tg is preferably 500°C or higher, more preferably 520°C or higher, and even more preferably 540°C or higher. From the viewpoint of easy float forming, it is preferably 750°C or lower, more preferably 700°C or lower, even more preferably 650°C or lower, particularly preferably 600°C or lower, and most preferably 580°C or lower.

[0096] For the glass for chemical strengthening of the parent glass composition of the first embodiment, the crystallization peak temperature Tc is preferably 790°C or higher, more preferably 800°C or higher, and even more preferably 810°C or higher. When the crystallization peak temperature Tc is 790°C or higher, stable molding can be achieved. It is most preferable that no crystallization peak is observed. The upper limit of the crystallization peak temperature Tc is not particularly limited, but it is usually 950°C or lower.

[0097] (Crystal growth rate) When the glass for chemical strengthening of the parent glass composition of the first embodiment contains MgO, the phase transition of the crystal phase from β - quartz solid solution to β - spodumene can be suppressed, and the precipitation of β - spodumene crystals can be suppressed. Therefore, even when the glass for chemical strengthening is held at 1000 °C for 30 minutes, the precipitation of β - spodumene is suppressed. Also, the crystal growth rate can be further decreased. When the glass for chemical strengthening of the parent glass composition of the first embodiment contains MgO, only the β - quartz solid solution is the first precipitation phase, and the crystal growth rate of the β - quartz solid solution at 1000 °C is preferably 4000 μm / hr or less, more preferably 3800 μm / hr or less, still more preferably 3500 μm / hr or less, particularly preferably 3200 μm / hr or less, and most preferably 2700 μm / hr or less.

[0098] In the glass forming process, crystallization in the glass causes defects. For example, when forming by the float method, crystallization occurring in the float bath occurs where the temperature range where nucleation occurs and the temperature range where crystal growth occurs overlap because it is cooled from a high - temperature part.

[0099] In ordinary glass, the temperature range where nucleation occurs and the temperature range where crystal growth occurs do not overlap, but glass containing a large amount of Al2O3 and Li2O tends to have the temperature range where nucleation occurs and the temperature range where crystal growth occurs overlap near 1000 °C. Here, even if the nucleation and the crystal growth rate overlap, it is not a defect if the crystal growth rate is slow. Therefore, by setting the crystal growth rate of the β - quartz solid solution at 1000 °C to 600 μm / hr or less, crystallization in the forming process can be suppressed.

[0100] In this specification, the crystal growth rate of the β - quartz solid solution at 1000 °C is obtained by holding a glass sample at 1000 °C for 30 minutes, measuring the length of the crystals in the glass with a polarized light microscope, and calculating the average value. Also, the crystal growth rate of β - spodumene at 1000 °C is obtained by the same method.

[0101] In addition, the "β-OH value" is obtained by the formula (1) from the transmittance X1 (%) at the reference wavelength of 4000 cm -1 measured by the FT-IR method, the minimum transmittance X2 (%) in the vicinity of 3570 cm -1 which is the absorption wavelength of the hydroxyl group, and the plate thickness t (unit: mm) of the glass plate. β-OH value = (1 / t) log 10 (X1 / X2) ····· (1) Note that the β-OH value can be adjusted according to the moisture content in the glass raw material and the melting conditions.

[0102] For the glass for chemical strengthening of the parent glass composition of the first embodiment, the β-OH value is preferably 0.1 mm -1 or more, more preferably 0.15 mm -1 or more, still more preferably 0.2 mm -1 or more, particularly preferably 0.22 mm -1 or more, most preferably 0.25 mm -1 or more.

[0103] The β-OH value is an index of the moisture content in the glass. Glass with a large β-OH value tends to have a lower softening point and is easier to bend. On the other hand, from the viewpoint of improving the strength by chemical strengthening of the glass, when the β-OH value of the glass increases, the value of the surface compressive stress (CS) after the chemical strengthening treatment tends to decrease. From the above viewpoints, the β-OH value is preferably 0.5 mm -1 or less, more preferably 0.4 mm -1 or less, still more preferably 0.3 mm -1 or less.

[0104] For the glass for chemical strengthening of the parent glass composition of the first embodiment, in the preferred embodiment described later, when performing the second-stage chemical strengthening with a Li-K mixed salt after the first-stage chemical strengthening with a Na salt, since K is incorporated into the glass and the drop strength of the glass after chemical strengthening is likely to be improved, the ratio of Na_DOL to K_DOL, which is the ratio of Na_DOL to K_DOL defined below, is preferably 26 or less, more preferably, in the following order, 25 or less, 24 or less, 23 or less, 22 or less, 21 or less, 20 or less. Further, when performing the second-stage chemical strengthening with a Li-K mixed salt after the first-stage chemical strengthening with a Na salt, from the viewpoint of preventing the glass from being damaged by preventing excessive incorporation of K into the glass, Na_DOL / K_DOL is preferably 15 or more, more preferably 16 or more, 16.5 or more, 17 or more, 17.5 or more, 18 or more in the following order. K_DOL: Depth of the compressive stress layer of chemically strengthened glass obtained by ion-exchanging glass using a molten salt composed of 100% potassium nitrate Na_DOL: Depth of the compressive stress layer of chemically strengthened glass obtained by ion-exchanging glass using a molten salt composed of 100% sodium nitrate Here, the time and temperature of ion exchange in the calculation of the above K_DOL and the above Na_DOL are set under the same conditions.

[0105] The glass for chemical strengthening of the parent glass composition of the first embodiment has a fracture toughness value (K IC ) of preferably 0.70 MPa·m 1 / 2 or more, more preferably 0.75 MPa·m 1 / 2 or more, and even more preferably 0.80 MPa·m 1 / 2 or more. The upper limit of the fracture toughness value is not particularly limited, but is typically 1.0 MPa·m 1 / 2 or less.

[0106] The glass for chemical strengthening of the parent glass composition of the first embodiment preferably has a Young's modulus of 80 GPa or more, more preferably 85 GPa or more, even more preferably 90 GPa or more, and particularly preferably 95 GPa or more. The upper limit of the Young's modulus is not particularly limited, but is typically 120 GPa or less.

[0107] (Second Embodiment) The second embodiment of the parent glass composition is expressed in terms of molar percentage based on oxides, SiO2 is 55 - 75% Al2O3 is 3 - 18% Li2O is 17 - 30% Na2O is 0 - 3% K2O is 0 - 1% 0 to 10% of MgO 0 to 10% of CaO 0 to 5% of SrO 0 to 5% of ZnO 0 to 3% of TiO2 0 to 5% of ZrO2 0 to 1% of SnO2 0 to 3% of P2O5 0 to 10% of B2O3 contains 0 to 3% of Y2O3. Among them, the second embodiment of the mother glass composition is expressed in mole percentage based on oxides, 55 to 75% of SiO2 3 to 18% of Al2O3 17 to 30% of Li2O 0 to 3% of Na2O 0 to 1% of K2O 0 to 10% of MgO 0 to 10% of CaO 0 to 5% of SrO 0 to 5% of ZnO 0 to 3% of TiO2 0 to 5% of ZrO2 0 to 1% of SnO2 0 to 3% of P2O5 0 to 10% of B2O3 contains 0 to 3% of Y2O3, R, which is the sum of the contents of Li2O, Na2O, and K2O, is 8 to 35%, the content of Li2O relative to R is 0.85 to 0.99, and the value of the product of the content of Li2O relative to R, the content of Na2O relative to R, and the content of K2O relative to R is preferably 0 to 0.003. Hereinafter, each component contained in the mother glass composition will be described.

[0108] SiO2 is a component that constitutes the glass network. It is also a component that improves chemical durability and reduces the occurrence of cracks when the glass surface is scratched.

[0109] The content of SiO2 is more preferably 57.0% or more, still more preferably 58.0% or more, particularly preferably 59.0% or more, and most preferably 60.0% or more in order to improve chemical durability. On the other hand, from the viewpoint of improving meltability, the content of SiO2 is more preferably 74.0% or less, still more preferably 72.0% or less, and particularly preferably 69.0% or less.

[0110] Al2O3 is a component that improves the ion exchange performance during chemical strengthening and increases the surface compressive stress after strengthening. It also contributes to the formation of crystals containing Al and Li. From the viewpoint of obtaining the above effects, the content of Al2O3 is more preferably 3.5% or more, still more preferably 4.0% or more, and 4.3% or more in this order. On the other hand, in some cases, it is required that crystals are less likely to grow during melting, devitrification defects are less likely to occur, the yield is more likely to be higher, and the high-temperature viscosity of the glass is reduced to make melting easier. From such a viewpoint, the content of Al2O3 is more preferably 18.0% or less, still more preferably 15.0% or less, 12.0% or less, 9.0% or less, 7.0% or less, and 6.0% or less in this order.

[0111] Both SiO2 and Al2O3 are components that stabilize the structure of the glass. In order to reduce brittleness, the total content of SiO2 and Al2O3 is preferably 60.0% or more, more preferably 62.0% or more, and still more preferably 64.0% or more. In addition, both SiO2 and Al2O3 tend to increase the melting temperature of the glass. Therefore, in order to make melting easier, the total content of SiO2 and Al2O3 is preferably 80.0% or less, more preferably 75.0% or less, and still more preferably 74.0% or less.

[0112] Li2O is a component capable of ion exchange and is a component that improves the meltability of the glass. When the glass contains Li2O, the Li ions on the glass surface are ion-exchanged with external Na ions and taken into the glass interior, and further, the incorporated Na ions are ion-exchanged with external K ions. In this way, a stress profile with a large surface compressive stress and a thick compressive stress layer is easily obtained. Also, by including Li2O within the above range, it is easy to obtain a crystallized glass when a specific heat treatment is performed. From the above viewpoints, the content of Li2O is more preferably 17% or more, and even more preferably, in the following order, 18% or more, 19% or more, 20% or more.

[0113] On the other hand, from the viewpoint of reducing the crystal growth rate during glass forming and making it less likely to cause a quality decline due to devitrification, the content of Li2O is more preferably 30% or less, and even more preferably, in the following order, 28% or less, 26% or less, 24% or less, 23% or less.

[0114] Na2O and K2O are components that improve the meltability of the glass and reduce the crystal growth rate during glass forming. Also, it is preferably contained in a small amount to improve the ion exchange performance.

[0115] Na2O is a component capable of ion exchange in chemical strengthening treatment using a potassium salt and is a component that lowers the viscosity of the glass. To obtain the above effects, the content of Na2O is preferably 0.3% or more, and more preferably, in the following order, 0.5% or more, 0.8% or more, 1.0% or more, 1.2% or more, 1.5% or more. On the other hand, from the viewpoint of maintaining the glass network and avoiding a decrease in the surface compressive stress (Na_CS) in the strengthening treatment with a sodium salt, the content of Na2O is preferably 3.0% or less, more preferably 2.5% or less, and even more preferably 2.3% or less.

[0116] K2O is a component that suppresses devitrification by suppressing the rise in the devitrification temperature and improves the ion exchange performance. The content of K2O is more preferably 0.1% or more, still more preferably 0.15% or more, particularly preferably 0.2% or more, and most preferably 0.5% or more. On the other hand, from the viewpoint of avoiding a decrease in the surface compressive stress (K_CS) in the strengthening treatment with a sodium salt, the content of K2O is preferably 1.0% or less, and more preferably 0.8% or less. Note that K2O may not be substantially contained.

[0117] R, which is the total of the contents of Li2O, Na2O, and K2O, is more preferably 10 to 30%, still more preferably 15 to 28%, and particularly preferably 18 to 25% from the viewpoint of suppressing the rise in the devitrification temperature and reducing the crystal growth rate.

[0118] The ratio of the content of Li2O to the above R ([Li2O] / ([Li2O]+[Na2O]+[K2O]), hereinafter also referred to as "Li2O / R2O") is more preferably 0.88 or more, and still more preferably 0.90 or more from the viewpoint of further improving the deep layer stress in the chemical strengthening characteristics. Li2O / R2O is more preferably 0.98 or less, still more preferably 0.95 or less, and particularly preferably 0.94 or less from the viewpoint of further increasing the electrical resistance of the glass and further enhancing the chemical resistance.

[0119] The ratio of the content of Na2O to the above R ([Na2O] / ([Li2O]+[Na2O]+[K2O]), hereinafter also referred to as "Na2O / R2O") is preferably more than 0, more preferably 0.01 or more, still more preferably 0.03 or more, particularly preferably 0.05 or more, and most preferably 0.06 or more from the viewpoint of further improving the deep layer stress in the chemical strengthening characteristics. Na2O / R2O is preferably 0.40 or less, more preferably 0.30 or less, still more preferably 0.20 or less, and particularly preferably 0.10 or less from the viewpoint of further enhancing the chemical resistance.

[0120] The ratio of the content of K2O to R above ([K2O] / ([Li2O]+[Na2O]+[K2O]), hereinafter also referred to as "K2O / R2O") is preferably 0.05 or more, more preferably 0.08 or more, and even more preferably 0.10 or more from the viewpoint of further increasing the electrical resistance of the glass. K2O / R2O is preferably 0.50 or less, more preferably 0.40 or less, even more preferably 0.30 or less, and particularly preferably 0.20 or less from the viewpoint of increasing the compressive stress near the surface in chemical strengthening characteristics. Note that K2O / R2O may be 0.

[0121] Also, the product of Li2O / R2O, Na2O / R2O, and K2O / R2O is more preferably 0.008 or more, even more preferably 0.01 or more, and particularly preferably 0.02 or more from the viewpoint of suppressing the increase in devitrification temperature and reducing the crystal growth rate. Also, the above product is more preferably 0.028 or less. Note that the above product may be 0.

[0122] The ratio of the content of Al2O3 to R above ([Al2O3] / ([Li2O]+[Na2O]+[K2O]), hereinafter also referred to as "Al2O3 / R2O") is preferably 0.05 or more, more preferably 0.10 or more, even more preferably 0.15 or more, and still more preferably 0.18 or more. Al2O3 / R2O is preferably 0.50 or less, more preferably 0.40 or less, even more preferably 0.30 or less, and particularly preferably 0.25 or less.

[0123] The value represented by [Al2O3]-[Na2O]-[K2O]+[Li2O] is preferably 15.0 to 35.0%, and more preferably 20.0 to 30.0%.

[0124] MgO may be contained to lower the viscosity during melting. The content of MgO is more preferably 0.05% or more, and even more preferably, in order, 0.5% or more, 1.0% or more, 2.0% or more, 3.0% or more, 4.0% or more. On the one hand, in terms of being easy to increase the compressive stress layer during chemical strengthening treatment, the MgO content is more preferably 9.0% or less, and even more preferably, in the following order, 8.0% or less, 7.0% or less, and 6.0% or less.

[0125] Moreover, by containing MgO, the phase transition of the crystal phase from β-quartz solid solution to β-spodumene can be suppressed, and the precipitation of β-spodumene crystals can be suppressed. Therefore, in Embodiment 2, it is preferable to contain MgO. From the above viewpoints, it is preferable to contain more than 0.5% and 7.0% or less of MgO. The more preferable range is as described above. MgO may not be substantially contained.

[0126] CaO is a component that improves the meltability of the glass and may be contained. The CaO content is more preferably 0.1% or more, and even more preferably 0.15% or more. On the other hand, in terms of being easy to increase the compressive stress value during chemical strengthening treatment, the CaO content is more preferably 2.0% or less, and even more preferably 1.0% or less, particularly preferably 0.8% or less, and most preferably 0.5% or less. CaO may not be substantially contained.

[0127] To increase the stability of the glass, it is more preferable to contain at least one of MgO and CaO, and it is even more preferable to contain MgO. The total content of MgO and CaO is preferably more than 1.0%, more preferably 2.0% or more, even more preferably 3.0% or more, and particularly preferably 4.0% or more. In terms of further improving the chemical strengthening characteristics, the total content of MgO and CaO is preferably 10.0% or less, and more preferably, in the following order, 8.0% or less, 7.0% or less, and 6.0% or less.

[0128] SrO is a component that improves the meltability of the glass and may be contained. The SrO content is more preferably 0.1% or more, even more preferably 0.15% or more, and particularly preferably 0.5% or more. In terms of making it easier to increase the compressive stress value during chemical strengthening treatment, the content of SrO is more preferably 3.0% or less, still more preferably 2.0% or less, particularly preferably 1.0% or less, and most preferably 0.5% or less. SrO may not be substantially contained.

[0129] BaO is a component that improves the meltability of the glass and may be contained. When BaO is contained, the content is preferably 0.1% or more, more preferably 0.15% or more, and still more preferably 0.5% or more. In terms of making it easier to increase the compressive stress value during chemical strengthening treatment, the content of BaO is preferably 3.0% or less, more preferably 2.0% or less, still more preferably 1.0% or less, and particularly preferably 0.5% or less. BaO may not be substantially contained.

[0130] ZnO is a component that improves the meltability of the glass. The content of ZnO is more preferably 0.1% or more, still more preferably 0.15% or more, and particularly preferably 0.5% or more. In terms of making it easier to increase the compressive stress value during chemical strengthening treatment, the content of ZnO is more preferably 3.0% or less, still more preferably 2.0% or less, particularly preferably 1.0% or less, and most preferably 0.5% or less. ZnO may not be substantially contained.

[0131] lnW is a parameter representing the degree of mixing of oxides, which is calculated from the contents of alkali metal oxides, alkaline earth metal oxides, and zinc oxide contained in the glass. lnW is represented by the following formula. lnW = ln(([Li2O] + [Na2O] + [K2O] + [MgO] + [CaO] + [SrO] + [BaO] + [ZnO])! / ([Li2O]! × [Na2O]! × [K2O]! × [MgO]! × [CaO]! × [SrO]! × [BaO]! × [ZnO]!)) ··· Formula (W1) In formula (W1), [Li2O], [Na2O], [K2O], [MgO], [CaO], [SrO], [BaO] and [ZnO] respectively represent the contents in terms of mole percentage on the basis of the oxides of the respective components of Li2O, Na2O, K2O, MgO, CaO, SrO, BaO and ZnO. Also,! indicates taking the factorial of a positive number. For example, [XO]! means truncating the decimal part of the numerical value of the content in terms of mole percentage on the basis of the oxide of component XO to a positive number and taking the factorial of that positive number. For example, when Na2O is 4.8 mol%, it is calculated as the factorial of "4", i.e., 4×3×2×1. The larger the value of lnW, the higher the degree of mixing of the above metal oxides, and the more the devitrification of the glass can be suppressed. From the above perspective, lnW is preferably 10 or more, more preferably 12 or more, still more preferably 13 or more, and particularly preferably 14 or more. lnW is preferably 20 or less, more preferably 18 or less, still more preferably 17 or less.

[0132] TiO2 is a component with a high effect of suppressing the solarization of glass and is a material for forming crystal nuclei, so it may be contained. When TiO2 is contained, the content is preferably 0.05% or more, more preferably 0.1% or more, still more preferably 0.2% or more, particularly preferably 0.5% or more, and most preferably 0.8% or more. On the other hand, since TiO2 has light absorption characteristics, from the perspective of preventing the coloring of the glass, the content of TiO2 is preferably 2.5% or less, more preferably 2.0% or less, still more preferably 1.5% or less, and particularly preferably 1.0% or less. TiO2 may not be substantially contained.

[0133] ZrO2 is a component that easily increases the surface compressive stress of chemically strengthened glass. Also, since it is a material for forming crystal nuclei, ZrO2 may be contained. The content of ZrO2 is more preferably more than 0%, and still more preferably, in the following order, 0.5% or more, 1.0% or more, 1.5% or more, 2.0% or more, 2.5% or more.

[0134] P2O5 is likely to increase the compressive stress layer during chemical strengthening. The content of P2O5 is more preferably 0.5% or more, still more preferably 0.7% or more. On the other hand, from the perspective of enhancing acid resistance, the content of P2O5 is more preferably 2.0% or less. From the perspective of preventing the occurrence of veins during melting, it is also preferable to be substantially free of P2O5.

[0135] B2O3 reduces the brittleness of the glass and improves crack resistance, or improves the meltability of the glass. The content of B2O3 is more preferably 0.5% or more, still more preferably 1.0% or more, and particularly preferably 1.5% or more. On the other hand, from the point of maintaining good acid resistance, the content of B2O3 is preferably 8.0% or less. The content of B2O3 is more preferably 6.0% or less, still more preferably 4.0% or less, and particularly preferably 2.0% or less. From the perspective of preventing the occurrence of veins during melting, it is also preferable to be substantially free of B2O3.

[0136] Y2O3 is a component that makes it easier to increase the surface compressive stress of chemically strengthened glass while reducing the crystal growth rate. The content of Y2O3 is more preferably more than 0%, still more preferably, in order, 0.1% or more, 0.2% or more, 0.5% or more, 0.8% or more. On the other hand, from the point of making it easier to increase the compressive stress layer during chemical strengthening treatment, the content of Y2O3 is more preferably 2.0% or less, and even more preferably 1.5% or less. Y2O3 may not be substantially contained.

[0137] From the perspective of improving the initial solubility, the total content of ZrO2 and Y2O3 is more preferably 5.0% or less. The lower limit of the total content of ZrO2 and Y2O3 is not particularly limited, but from the perspective of enhancing the strength of the glass, 0.5% or more is more preferably, still more preferably, in order, 1.0% or more, 1.5% or more, 2.0% or more, 2.5% or more, 3.0% or more.

[0138] The ratio of the content of ZrO2 to the total content of ZrO2 and Y2O3, [ZrO2] / ([ZrO2]+[Y2O3]), is more preferably 0.50 or more, and even more preferably 1.00 or more. [ZrO2] / ([ZrO2]+[Y2O3]) is more preferably 8.00 or less, even more preferably 7.00 or less, and particularly preferably 6.00 or less.

[0139] When ZrO2 and Y2O3 are added alone, they are known as nucleating agents. However, when ZrO2 and Y2O3 are co-added, a eutectic of ZrO2 and Y2O3 is formed, so the devitrification temperature, crystal growth rate, and crystallization start temperature can be controlled. Furthermore, by setting [ZrO2] / ([ZrO2]+[Y2O3]) within the above range, the diffusion of ions in the glass is suppressed, the increase in the devitrification temperature is suppressed, and devitrification can be suppressed. By setting [ZrO2] / ([ZrO2]+[Y2O3]) within the above range, the glass is stabilized, and furthermore, the temperature range where nucleation occurs and the temperature range where crystal growth occurs do not overlap and are separated, suppressing the increase in the crystal growth rate, so the occurrence of defects can be suppressed. Also, by setting [ZrO2] / ([ZrO2]+[Y2O3]) within the above range, the temperature range where nucleation occurs shifts to the low-temperature side, suppressing the decrease in the crystallization start temperature, and the manufacturing characteristics can be improved.

[0140] 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, even more preferably 0.5% or more, and particularly preferably 0.8% or more. On the other hand, if there is too much, it becomes difficult to increase the compressive stress layer during chemical strengthening treatment, so La2O3 is preferably 5.0% or less, more preferably 3.0% or less, even more preferably 2.0% or less, and particularly preferably 1.5% or less. It is also preferable that La2O3 is substantially not contained.

[0141] Nb2O 5、Ta2O5, Gd2O3, and CeO2 have the effect of suppressing the solarization of glass and are components that improve the fusibility, and they may be contained. When these components are contained, their respective contents are preferably 0.03% or more, more preferably 0.1% or more, still more preferably 0.5% or more, particularly preferably 0.8% or more, and most preferably 1.0% or more. On the other hand, it is preferably 3.0% or less, more preferably 2.0% or less, still more preferably 1.0% or less.

[0142] Since Fe2O3 absorbs heat rays, it has the effect of improving the solubility of glass, and when glass is mass-produced using a large melting furnace, it is preferably contained. In that case, the content in terms of mass% on an oxide basis is preferably 0.002% or more, more preferably 0.005% or more, still more preferably 0.007% or more, and particularly preferably 0.01% or more. On the other hand, if Fe2O3 is contained in excess, coloring will occur, so from the viewpoint of enhancing the transparency of the glass, the content is preferably 0.3% or less, more preferably 0.04% or less, still more preferably 0.025% or less, and particularly preferably 0.015% or less in terms of mass% on an oxide basis.

[0143] Furthermore, other coloring components may be added within a range that does not inhibit the achievement of the desired chemical strengthening characteristics. Examples of other coloring components include Co3O4, MnO2, NiO, CuO, Cr2O3, V2O5, Bi2O3, SeO2, Er2O3, Nd2O3, etc.

[0144] As a fining agent or the like during the melting of glass, SO3, chlorides, fluorides, etc. may be appropriately contained. It is preferably not to contain As2O3. When containing Sb2O3, it is preferably 0.3% or less, more preferably 0.1% or less, and most preferably not to contain it. From the perspective of clarification of bubbles in the glass, the SnO₂ content is more preferably 0.01% or more, and even more preferably 0.05% or more. Also, in order to suppress the occurrence of defects, the SnO₂ content is preferably 1% or less, more preferably 0.8% or less, even more preferably 0.7% or less, and particularly preferably 0.5% or less.

[0145] Hereinafter, the preferable physical properties of the glass of the mother glass composition of the second embodiment will be described.

[0146] (Devitrification temperature) Since the preferable aspect of the devitrification temperature of the chemically strengthened glass of the mother glass composition of the second embodiment is the same as that of the chemically strengthened glass of the mother glass composition of the first embodiment, the description thereof will be omitted.

[0147] (Glass transition point Tg, crystallization start temperature Tcs, crystallization peak temperature Tc) For the chemically strengthened glass of the mother glass composition of the second embodiment, the crystallization start temperature Tcs measured by DSC is preferably 500°C or higher. The upper limit of the crystallization start temperature is not particularly limited, but is usually 800°C or lower.

[0148] When the crystallization start temperature Tcs is within the above range, for example, after holding at 500 to 600°C for 1 to 6 hours and then holding at 600 to 800°C for 0.5 to 6 hours, crystals can be precipitated in the chemically strengthened glass, and a chemically strengthened glass that is a crystallized glass can be obtained. The above heat treatment may be performed in three steps. For example, it may be held at 500 to 600°C for 1 to 6 hours, held at 550 to 650°C for 0.5 to 6 hours, and held at 600 to 800°C for 0.5 to 6 hours to obtain a chemically strengthened glass that is a crystallized glass.

[0149] From the perspective of reducing the warp after chemical strengthening, the glass transition point Tg is preferably 500°C or higher, more preferably 520°C or higher, and even more preferably 540°C or higher. From the viewpoint of easy float forming, it is preferably 750°C or lower, more preferably 700°C or lower, even more preferably 650°C or lower, particularly preferably 600°C or lower, and most preferably 580°C or lower.

[0150] For the glass for chemical strengthening of the parent glass composition of the second embodiment, the crystallization peak temperature Tc is preferably 600 °C or higher, more preferably 650 °C or higher, and still more preferably 700 °C or higher. By having the crystallization peak temperature Tc of 600 °C or higher, it can be stably formed. Most preferably, no crystallization peak is observed. The upper limit of the crystallization peak temperature Tc is not particularly limited, but is usually 950 °C or lower.

[0151] For the glass for chemical strengthening of the parent glass composition of the second embodiment, the β-OH value is preferably 0.1 mm -1 or more, more preferably 0.15 mm -1 or more, still more preferably 0.2 mm -1 or more, particularly preferably 0.22 mm -1 or more, and most preferably 0.25 mm -1 or more.

[0152] The β-OH value is an index of the moisture content in the glass. Glass with a large β-OH value tends to have a lower softening point and be easier to bend. On the other hand, from the viewpoint of improving the strength by chemical strengthening of the glass, when the β-OH value of the glass increases, the value of the surface compressive stress (CS) after the chemical strengthening treatment tends to decrease. From the above viewpoints, the β-OH value is preferably 0.5 mm -1 or less, more preferably 0.4 mm -1 or less, and still more preferably 0.3 mm -1 or less.

[0153] For the glass for chemical strengthening of the parent glass composition of the second embodiment, the fracture toughness value (K IC ) is preferably 0.80 MPa·m 1 / 2 or more, more preferably 0.85 MPa·m 1 / 2 or more, still more preferably 0.90 MPa·m 1 / 2 or more, particularly preferably 1.0 MPa·m 1 / 2 or more, and most preferably 1.1 MPa·m 1 / 2 or more. The upper limit of the fracture toughness value is not particularly limited, but is typically 1.6 MPa·m1 / 2 The following is the case.

[0154] The glass for chemical strengthening of the mother glass composition of the second embodiment preferably has a Young's modulus of 80 GPa or more, more preferably 90 GPa or more, still more preferably 95 GPa or more, and most preferably 100 GPa or more. The upper limit of the Young's modulus is not particularly limited, but is typically 120 GPa or less.

[0155] (Manufacturing method) The glass for chemical strengthening (the mother glass composition of the first embodiment and the mother glass composition of the second embodiment) can be manufactured by a normal method. For example, raw materials of each component of the glass are prepared and heated and melted in a glass melting furnace. Then, the glass is homogenized by a known method, formed into a desired shape such as a glass plate, and gradually cooled.

[0156] Examples of the forming method of the glass plate include a float method, a press method, a fusion method, and a down-draw method. In particular, the float method suitable for mass production is preferable. Also, continuous forming methods other than the float method, such as the fusion method and the down-draw method, are also preferable.

[0157] The glass for chemical strengthening of the mother glass composition of the second embodiment described above may be subjected to the above-described heat treatment to be a crystallized glass. That is, the glass for chemical strengthening may be a crystallized glass. When the crystallized glass is used as the glass for chemical strengthening, a chemically strengthened glass that is a crystallized glass can be obtained.

[0158] Thereafter, the formed glass is ground and polished as necessary to form a glass substrate. When cutting or chamfering the glass substrate into a predetermined shape and size, if the cutting or chamfering of the glass substrate is performed before the chemical strengthening treatment described later, a compressive stress layer is also formed on the end face by the subsequent chemical strengthening treatment, which is preferable.

[0159] The shape of the glass for chemical strengthening may be other than plate shape according to the product to which it is applied, the use, etc. Further, the glass plate may have a beveled shape with different thicknesses at the outer periphery. Further, the form of the glass plate is not limited to this. For example, the two main surfaces may not be parallel to each other, and all or part of one or both of the two main surfaces may be a curved surface. More specifically, the glass plate may be, for example, a flat glass plate without warping, or a curved glass plate having a curved surface.

[0160] <Method for manufacturing chemically strengthened glass> The method for manufacturing the chemically strengthened glass of the present invention is not particularly limited as long as the chemically strengthened glass of the present invention described above is manufactured, but it is manufactured by performing a chemical strengthening treatment on the glass for chemical strengthening. As an example of the method for manufacturing the chemically strengthened glass of the present invention, a first chemical strengthening treatment is performed on the glass for chemical strengthening using a first molten salt containing 90% by mass or more of a Na salt and 2% by mass or more of a Li salt based on the total mass, and a second chemical strengthening treatment is performed on the glass for chemical strengthening that has undergone the first chemical strengthening treatment using a second molten salt containing 90% by mass or more of a K salt based on the total mass. Hereinafter, an example of the method for manufacturing the chemically strengthened glass of the present invention will be described.

[0161] [First chemical strengthening treatment] In an example of the method for manufacturing the chemically strengthened glass of the present invention, a first chemical strengthening treatment is performed using a first molten salt containing 90% by mass or more of a Na salt and 2% by mass or more of a Li salt based on the total mass. In the first chemical strengthening treatment, it can be carried out by bringing the glass for chemical strengthening into contact with the first molten salt. For example, the first chemical strengthening treatment can be carried out by immersing the glass for chemical strengthening in the first molten salt.

[0162] Note that the glass for chemical strengthening is as described above in the part of the composition of the chemically strengthened glass of the present invention, and the preferred embodiments are also as described above. Particularly, when it is the first embodiment of the mother glass composition of the chemically strengthened glass, it is preferable to implement an example of the manufacturing method of the chemically strengthened glass of the present invention. Specifically, the composition at the center position of the plate thickness of the chemically strengthened glass is expressed in mol percentage based on oxides, SiO2 is 60 to 72% Al2O3 is 10 to 20% Li2O is 3 to 12% Na2O is 0.5 to 6% It is preferable to contain 1 to 3% of K2O.

[0163] In the first molten salt, the content of the Na salt is 90% by mass or more, preferably 93% by mass or more, more preferably 95% by mass or more, and even more preferably 96% by mass or more with respect to the total mass of the first molten salt. In the first molten salt, the content of the Na salt is 98% by mass or less, may be 97% by mass or less, and may be 96% by mass or less with respect to the total mass of the first molten salt. Examples of the Na salt contained in the first molten salt include sodium nitrate, sodium sulfate, sodium carbonate, and sodium chloride, etc., and sodium nitrate is preferable.

[0164] In the first molten salt, the content of the Li salt is 2% by mass or more, may be 3% by mass or more, and may be 4% by mass or more with respect to the total mass of the first molten salt. In the first molten salt, the content of the Li salt is 10% by mass or less, preferably 7% by mass or less, and more preferably 5% by mass or less with respect to the total mass of the first molten salt. Examples of the Li salt contained in the first molten salt include lithium nitrate, lithium sulfate, lithium carbonate, and lithium chloride, and lithium nitrate is preferable. Also, the ratio of the content of the Li salt in the first molten salt to the content of Li2O in the composition of the chemically strengthened glass is preferably 0.1 or more, more preferably 0.2 or more, and may be 0.3 or more in molar ratio. The above ratio is preferably 1.0 or less, more preferably 0.8 or less, even more preferably 0.6 or less, and particularly preferably 0.5 or less.

[0165] The first molten salt may contain components other than Na salts and Li salts. Examples of components other than Na salts and Li salts include K salts, Rb (rubidium) salts, Cs (cesium) salts, and Ag (silver) salts. It is also preferable that the first molten salt does not contain components other than Na salts and Li salts. That is, it is also preferable that the first molten salt consists of Na salts and Li salts.

[0166] The time of the first chemical strengthening treatment is preferably 30 minutes or more, more preferably 60 minutes or more, even more preferably 120 minutes or more, and particularly preferably 150 minutes or more. The time of the first chemical strengthening treatment is often 720 minutes or less, preferably 360 minutes or less, and more preferably 180 minutes or less. The temperature of the first chemical strengthening treatment is preferably 350°C or more, more preferably 380°C or more, and even more preferably 400°C or more. The temperature of the first chemical strengthening treatment is preferably 470°C or less, more preferably 440°C or less, and even more preferably 420°C or less. It is also preferable that the time is the preferable time of the first chemical strengthening treatment and the temperature is the preferable temperature of the first chemical strengthening treatment.

[0167] According to the first chemical strengthening treatment, ion exchange can be performed to a deeper part while reducing the amount of ion exchange, and the chemically strengthened glass of the present invention can be easily obtained.

[0168] [Second Chemical Strengthening Treatment] In an example of the method for manufacturing the chemically strengthened glass of the present invention, a second chemical strengthening treatment is performed on the chemically strengthened glass that has undergone the first chemical strengthening treatment, using a second molten salt containing 90% by mass or more of K salt based on the total mass. In the second chemical strengthening treatment, it can be carried out by bringing the chemically strengthened glass that has undergone the first chemical strengthening treatment into contact with the second molten salt. For example, the chemically strengthened glass that has undergone the first chemical strengthening treatment can be immersed in the second molten salt to perform the second chemical strengthening treatment.

[0169] In the second molten salt, the content of the potassium salt is 90% by mass or more, preferably 93% by mass or more, more preferably 94% by mass or more, still more preferably 95% by mass or more, may be 98% by mass or more, and may be 99% by mass or more, based on the total mass of the second molten salt. In the second molten salt, the content of the potassium salt may be 100% by mass based on the total mass of the second molten salt. That is, the second molten salt may consist only of the potassium salt. Examples of the potassium salt contained in the second molten salt include potassium nitrate, potassium sulfate, potassium carbonate, and potassium chloride, with potassium nitrate being preferred.

[0170] The second molten salt may contain components other than the potassium salt. Examples of the components other than the potassium salt include lithium salts, sodium salts, rubidium salts, cesium salts, and silver salts. Note that, as described above, it is also preferable that the second molten salt does not contain components other than the potassium salt.

[0171] The time of the second chemical strengthening treatment is preferably 20 minutes or more, more preferably 30 minutes or more, still more preferably 60 minutes or more, and particularly preferably 90 minutes or more. The time of the second chemical strengthening treatment is often 360 minutes or less, preferably 180 minutes or less, and more preferably 120 minutes or less. The temperature of the second chemical strengthening treatment is preferably 330°C or more, more preferably 360°C or more, still more preferably 380°C or more. The temperature of the second chemical strengthening treatment is preferably 460°C or less, more preferably 430°C or less, and still more preferably 410°C or less. It is also preferable that the time is the preferred time of the second chemical strengthening treatment and the temperature is the preferred temperature of the second chemical strengthening treatment. Also, it is preferable that the time of the first chemical strengthening treatment is 150 minutes or more and the time of the second chemical strengthening treatment is 90 minutes or more.

[0172] The chemically strengthened glass of the present invention may be manufactured by other methods than those described above. Hereinafter, other examples of the method for manufacturing the chemically strengthened glass of the present invention will be described.

[0173] First, a second example of the method for manufacturing chemically strengthened glass of the present invention will be described. As a second example of the method for manufacturing chemically strengthened glass of the present invention, a third chemical strengthening treatment is performed on chemically strengthening glass using a third molten salt containing 50% by mass or more of a Na salt, 30% by mass or more of a K salt, and 1% by mass or more of a Li salt with respect to the total mass, and a fourth chemical strengthening treatment is performed on the chemically strengthening glass that has undergone the third chemical strengthening treatment using a fourth molten salt containing 90% by mass or more of a K salt and 2% by mass or more of a Li salt with respect to the total mass. There is provided a method for manufacturing chemically strengthened glass.

[0174] [Third Chemical Strengthening Treatment] In the second example of the method for manufacturing chemically strengthened glass of the present invention, a third chemical strengthening treatment is performed using a third molten salt containing 50% by mass or more of a Na salt, 30% by mass or more of a K salt, and 1% by mass or more of a Li salt with respect to the total mass. In the third chemical strengthening treatment, the chemically strengthening glass can be brought into contact with the third molten salt. For example, the third chemical strengthening treatment can be performed by immersing the chemically strengthening glass in the third molten salt.

[0175] Note that the chemically strengthening glass is as described above in the part of the composition of the chemically strengthened glass of the present invention, and the preferred embodiments are also as described above. In particular, when it is the second embodiment of the mother glass composition of the chemically strengthening glass and the content of P2O5 is 1.0% or more, it is preferable to implement the second example of the method for manufacturing chemically strengthened glass of the present invention.

[0176] In the third molten salt, the content of the Na salt is 50% by mass or more with respect to the total mass of the third molten salt, preferably 53% by mass or more, more preferably 55% by mass or more, and even more preferably 58% by mass or more. In the third molten salt, the content of the Na salt is 69% by mass or less with respect to the total mass of the third molten salt, preferably 65% by mass or less, and more preferably 62% by mass or less. The Na salt contained in the third molten salt may be the same as the Na salt contained in the first molten salt, and the same ones are preferred.

[0177] In the third molten salt, the content of the K salt is 30% by mass or more, preferably 32% by mass or more, more preferably 35% by mass or more, and still more preferably 37% by mass or more with respect to the total mass of the third molten salt. In the third molten salt, the content of the K salt is 49% by mass or less, preferably 45% by mass or less, more preferably 42% by mass or less, and still more preferably 40% by mass or less with respect to the total mass of the third molten salt. The K salt contained in the third molten salt may be the same as the K salt contained in the second molten salt, and the same ones are preferred.

[0178] In the third molten salt, the content of the Li salt is 1% by mass or more, preferably 2% by mass or more, and may be 3% by mass or more with respect to the total mass of the third molten salt. In the third molten salt, the content of the Li salt is 20% by mass or less, preferably 10% by mass or less, and more preferably 5% by mass or less with respect to the total mass of the third molten salt. The Li salt contained in the third molten salt may be the same as the Li salt contained in the first molten salt, and the same ones are preferred. Further, the ratio of the content of Li in the third molten salt to the content of Li2O in the composition of the chemically strengthened glass is preferably 0.05 or more, more preferably 0.07 or more, and still more preferably 0.1 or more in terms of molar ratio. The above ratio is preferably 0.6 or less, more preferably 0.5 or less, still more preferably 0.35 or less, and particularly preferably 0.2 or less.

[0179] The third molten salt may contain components other than the Na salt, K salt, and Li salt. Examples of the components other than the Na salt, K salt, and Li salt include Rb salt, Cs salt, and Ag salt. Note that it is also preferable that the third molten salt does not contain components other than the Na salt, K salt, and Li salt. That is, it is also preferable that the third molten salt consists of the Na salt, K salt, and Li salt.

[0180] The time for the third chemical strengthening treatment is preferably 60 minutes or more, more preferably 120 minutes or more, and even more preferably 180 minutes or more. The time for the third chemical strengthening treatment is often 1440 minutes or less, preferably 720 minutes or less, and more preferably 360 minutes or less. The temperature for the third chemical strengthening treatment is preferably 350 °C or more, more preferably 380 °C or more, and even more preferably 400 °C or more. The temperature for the third chemical strengthening treatment is preferably 470 °C or less, more preferably 440 °C or less, and even more preferably 420 °C or less. It is also preferable that the time for the third chemical strengthening treatment is a preferable time and the temperature for the third chemical strengthening treatment is a preferable temperature.

[0181] According to the third chemical strengthening treatment, ion exchange can be performed to a deeper part while reducing the amount of ion exchange, and the chemically strengthened glass of the present invention can be easily obtained.

[0182] [Fourth Chemical Strengthening Treatment] In the second example of the method for manufacturing the chemically strengthened glass of the present invention, a fourth chemical strengthening treatment is performed on the chemically strengthened glass that has undergone the third chemical strengthening treatment using a fourth molten salt containing 90% by mass or more of a K salt and 2% by mass or more of a Li salt based on the total mass. In the fourth chemical strengthening treatment, the chemically strengthened glass that has undergone the third chemical strengthening treatment can be brought into contact with the fourth molten salt. For example, the chemically strengthened glass that has undergone the third chemical strengthening treatment can be immersed in the fourth molten salt to perform the fourth chemical strengthening treatment.

[0183] In the fourth molten salt, the content of the K salt is 90% by mass or more based on the total mass of the second molten salt, preferably 91% by mass or more, more preferably 92% by mass or more, and even more preferably 94% by mass or more. In the fourth molten salt, the content of the K salt is 98% by mass or less based on the total mass of the fourth molten salt, preferably 97% by mass or less, and even more preferably 96% by mass or less. The K salt contained in the fourth molten salt is preferably the same as the K salt contained in the second molten salt.

[0184] In the fourth molten salt, the content of the Li salt is 2% by mass or more, preferably 3% by mass or more, and more preferably 4% by mass or more, based on the total mass of the fourth molten salt. In the fourth molten salt, the content of the Li salt is 10% by mass or less, preferably 8% by mass or less, and more preferably 7% by mass or less, based on the total mass of the fourth molten salt. Examples of the Li salt contained in the fourth molten salt include the same ones as those contained in the first molten salt, and the same ones are preferred.

[0185] The fourth molten salt may contain components other than the K salt and the Li salt. Examples of the components other than the K salt and the Li salt include Na salts, Rb salts, Cs salts, and Ag salts. It is also preferable that the fourth molten salt does not contain components other than the K salt and the Li salt.

[0186] The time of the fourth chemical strengthening treatment is preferably 5 minutes or more, more preferably 10 minutes or more, and even more preferably 20 minutes or more. The time of the fourth chemical strengthening treatment is often 360 minutes or less, preferably 180 minutes or less, more preferably 120 minutes or less, and even more preferably 90 minutes or less. The temperature of the fourth chemical strengthening treatment is preferably 350 °C or more, more preferably 380 °C or more, and even more preferably 400 °C or more. The temperature of the fourth chemical strengthening treatment is preferably 480 °C or less, more preferably 450 °C or less, and even more preferably 430 °C or less. It is also preferable that the time is the preferable time of the fourth chemical strengthening treatment and the temperature is the preferable temperature of the fourth chemical strengthening treatment.

[0187] As a third example of the method for producing chemically strengthened glass of the present invention, there is provided a method for producing chemically strengthened glass, which comprises performing a fifth chemical strengthening treatment on chemically strengthening glass using a fifth molten salt containing 20% by mass or more of a Na salt and 60% by mass or more of a K salt based on the total mass.

[0188] [Fifth Chemical Strengthening Treatment] In the fifth example of the method for manufacturing chemically strengthened glass of the present invention, a fifth chemical strengthening treatment is performed using a fifth molten salt containing 60% by mass or more of a K salt and 20% by mass or more of a Na salt with respect to the total mass. In the fifth chemical strengthening treatment, the chemically strengthened glass can be brought into contact with the fifth molten salt. For example, the fifth chemical strengthening treatment can be performed by immersing the chemically strengthened glass in the fifth molten salt.

[0189] Note that the chemically strengthened glass is as described above in the part of the composition of the chemically strengthened glass of the present invention, and the preferred embodiments are also as described above. In particular, when it is the second embodiment of the parent glass composition of the chemically strengthened glass and the content of P2O5 is 0.5% or more, it is preferable to carry out the third example of the method for manufacturing the chemically strengthened glass of the present invention. Further, when it is the second embodiment of the parent glass composition of the chemically strengthened glass and the content of P2O5 is 0.5% or more and less than 1.0%, it is more preferable to carry out the third example of the method for manufacturing the chemically strengthened glass of the present invention.

[0190] In the fifth molten salt, the content of the K salt is 60% by mass or more with respect to the total mass of the fifth molten salt, preferably 63% by mass or more, more preferably 65% by mass or more, and still more preferably 67% by mass or more. In the fifth molten salt, the content of the K salt is 80% by mass or less with respect to the total mass of the fifth molten salt, preferably 77% by mass or less, more preferably 75% by mass or less, and still more preferably 72% by mass or less. Examples of the K salt contained in the fifth molten salt include the same ones as the K salt contained in the second molten salt, and the same ones are preferred.

[0191] In the fifth molten salt, the content of the Na salt is 20% by mass or more with respect to the total mass of the fifth molten salt, preferably 22% by mass or more, more preferably 25% by mass or more, and still more preferably 27% by mass or more. In the fifth molten salt, the content of the Na salt is 40% by mass or less with respect to the total mass of the fifth molten salt, preferably 37% by mass or less, and more preferably 35% by mass or less. The Na salt contained in the fifth molten salt is preferably the same as the Na salt contained in the first molten salt.

[0192] The fifth molten salt may contain components other than the K salt and the Na salt. Examples of the components other than the K salt and the Na salt include Li salt, Rb salt, Cs salt, and Ag salt. Note that it is also preferable that the fifth molten salt does not contain components other than the K salt and the Na salt. That is, it is also preferable that the fifth molten salt consists of the K salt and the Na salt.

[0193] The time of the fifth chemical strengthening treatment is preferably 60 minutes or more, more preferably 120 minutes or more, further preferably 180 minutes or more, and may be 360 minutes or more, or may be 720 minutes or more. The time of the third chemical strengthening treatment is often 1440 minutes or less, and may be 720 minutes or less, or may be 360 minutes or less. The temperature of the fifth chemical strengthening treatment is preferably 390°C or more, more preferably 420°C or more, and further preferably 440°C or more. The temperature of the fifth chemical strengthening treatment is preferably 510°C or less, more preferably 480°C or less, and further preferably 460°C or less. It is also preferable that the time is the preferable time of the fifth chemical strengthening treatment and the temperature is the preferable temperature of the fifth chemical strengthening treatment.

[0194] According to the fifth chemical strengthening treatment, by performing K ion exchange while performing Na ion exchange, the chemically strengthened glass of the present invention can be easily obtained.

[0195] <Use> The chemically strengthened glass of the present invention is useful, for example, as a cover glass. The cover glass can also be suitably used for the purpose of surface protection of displays, solar cell modules, and the like. In particular, the chemically strengthened glass of the present invention is useful as a cover glass for mobile devices such as mobile phones, smartphones, personal digital assistants (PDAs), and tablet terminals. Furthermore, it is useful as a cover glass for display devices such as televisions (TVs), personal computers (PCs), in-vehicle displays, and touch panels that are not intended for portability, a cover glass provided on the surface of a solar cell module, an elevator wall surface, a wall surface of a building such as a house and a building (full-surface display), a building material such as window glass, and an interior of a tabletop, an automobile, an airplane, etc. It is also useful as a cover glass for the above articles. Furthermore, it can be applied to uses such as a housing having a curved surface shape by bending and bending forming.

Examples

[0196] The present invention will be described in more detail based on the following examples. The materials, amounts used, ratios, treatment contents, treatment procedures, etc. shown in the following examples can be appropriately changed as long as they do not deviate from the gist of the present invention. Therefore, the scope of the present invention should not be construed as being limited by the examples shown below. Note that Examples 1 to 3, 5, and 7 to 9 are examples, Examples 4 and 6 are comparative examples, and Examples 10 and 11 are reference examples.

[0197] <Production of Chemically Strengthened Glass> First, glass raw materials were melted in a platinum crucible to produce frit materials A to C so as to have each glass composition shown in Table 1 in terms of molar percentage based on oxides. Specifically, oxides, hydroxides, carbonates, nitrates, etc. used as glass raw materials were appropriately selected from generally used glass raw materials and weighed so as to be 1000 g as glass. Next, the mixed raw materials were put into a platinum crucible, charged into a resistance heating electric furnace at 1500 - 1700 °C, melted for about 3 hours, defoamed and homogenized to obtain molten glass. The obtained molten glass was poured into a profile, held at a temperature of glass transition point + 50 °C for 1 hour, and then cooled to room temperature at a rate of 0.5 °C / min to obtain a glass block. The obtained glass block was cut and ground to obtain sheet glass. Both sides of the obtained sheet glass were mirror-finished to finally obtain sheet glass (chemically strengthened glass) with a length of 120 mm × width of 60 mm × thickness of 0.5 mm, or a length of 120 mm × width of 60 mm × thickness of 0.6 mm. On the other hand, from the above glass block, sample pieces for measuring the fracture toughness value (K IC ), and sample pieces for measuring the Young's modulus were cut out by the method described above. Regarding the glass material B, after forming it into sheet glass, it was heated to 550 °C, held for 2 hours, then heated up to 720 °C and maintained for 2 hours for heat treatment. Regarding the glass material C, after forming it into sheet glass, it was heated to 540 °C, held for 4 hours, then heated up to 600 °C and held for 4 hours, then heated up to 650 °C and held for 4 hours for heat treatment. Regarding the glass materials B and C, the same heat treatment as above was performed on the glass block to obtain sample pieces for measuring the fracture toughness value (K IC ), and sample pieces for measuring the Young's modulus.

[0198]

Table 1

[0199] For each of the chemically strengthened glasses (glass materials A - C) obtained by the above procedure, chemical strengthening treatment was performed under the conditions described in Table 2 to obtain the chemically strengthened glasses of Examples 1 - 9. Note that in Examples 10 and 11, no chemical strengthening was performed.

[0200] <Measurement of stress profile> The stress profile of the chemically strengthened glass was obtained by the method described above.

[0201] <Measurement of Young's modulus> In the procedure for obtaining each of the above-mentioned glass materials, the Young's modulus of the chemically strengthened glass was measured using the cut-out sample pieces. Specifically, using the above-mentioned sample pieces, the measurement was carried out in accordance with JIS R 1602 by the ultrasonic pulse method. The Young's modulus of the chemically strengthened glass corresponds to the Young's modulus at the central position of the plate thickness of the chemically strengthened glass. Also, when the Young's modulus at the in-plane central position of the chemically strengthened glass was measured in the same manner as the method for measuring the above-mentioned sample pieces, it was the same value as the value measured using the above-mentioned sample pieces. Therefore, in the table in the subsequent stage, the description of the Young's modulus at the in-plane central position is omitted.

[0202] <Measurement of fracture toughness value> In the procedure for obtaining each of the above-mentioned glass materials, the Young's modulus of the chemically strengthened glass was measured using the cut-out sample pieces. The fracture toughness value was measured by the DCDC method described above.

[0203] <Measurement of transmittance> The transmittance of the chemically strengthened glass was measured by the method described above. The transmittance of the chemically strengthened glass in Example 5 was 91%, and the transmittance of the chemically strengthened glass in Example 7 was 92%.

[0204] [Drop strength test] The drop strength was measured by the following procedure. First, a rectangular parallelepiped structure made of an aluminum alloy with a width of 70 mm, a length of 130 mm, and a thickness of 2 mm and having a mass of 120 g was prepared. The above-mentioned structure simulated a mobile device such as a smartphone. Next, the chemically strengthened glass was attached to the widest surface of the above-mentioned structure. The attachment of the chemical strengthening to the structure was carried out using an adhesive tape with a thickness of 0.5 mm. Next, a structure with chemically strengthened glass attached was dropped onto the abrasive surface of #80 sandpaper where the abrasive is silicon carbide. The above dropping was performed with the side of the structure to which the chemically strengthened glass was attached facing the above sandpaper. When dropping, it was confirmed whether cracks occurred in the chemically strengthened glass, the dropping height was changed, and the height at which cracks first occurred was recorded and used as an index of the dropping strength. Hereinafter, the height at which cracks first occurred is also referred to as the "#80SP crack height".

[0205] Also, in the same manner as the method for obtaining the #80SP crack height, except that the sandpaper used when obtaining the #80SP crack height was changed to #180, the height at which cracks first occurred was obtained, and this height was also used as an index of the dropping strength. When the above test was performed with the sandpaper being #180, the height at which cracks first occurred is also referred to as the "#180SP crack height".

[0206] <Results> Regarding the conditions of the chemical strengthening treatment of the chemically strengthened glass for each example, the above measurement results and the above evaluation results are shown in Table 2 below. In Table 2, the measurement method for each value in the "stress profile" column is as described above. Note that the "CT" column shows the absolute value of the stress CT at the center position of the plate thickness. Also, the "slope (DOC~120μm)" column is the slope calculated from the compressive stress value at the compressive stress layer depth DOC obtained by the above method and the compressive stress value at the center position of the plate thickness. The "slope (@DOC)" column is the absolute value of the first derivative at the compressive stress layer depth DOC obtained by the above method. The "slope (@120μm)" column is the absolute value of the first derivative at the position 120μm in the depth direction from the surface obtained by the above method. In any of the stress profiles, in the range from the position 120μm in the depth direction from the surface to the center position of the plate thickness, the absolute value of the first derivative was the largest at the position 120μm in the depth direction from the surface. Also, regarding Formula (1) and Formula (2), it is as described above. When the requirements of Formula (1) and Formula (2) are met, the values described in Table 2 are each values of 0 or more.

[0207]

Table 2

[0208] From the results shown in Table 2, when comparing Examples 4, 6, 10, and 11 with other examples, the stress CT at the central position of the plate thickness satisfies the relationship of the above Formula (1), and the compressive stress CS at a depth of 120 μm in the depth direction from the surface 120 is confirmed to be excellent in the drop strength (#80SP crack height and #180SP crack height) when it satisfies the relationship of the above Formula (2). From the comparison between Example 7 and Examples 8 and 9, it was confirmed that when the value of the above first derivative ratio is 0.90 to 1.15, it is more excellent in the drop strength (#80SP crack height and #180SP crack height).

Claims

1. The stress CT at the center of the plate thickness satisfies the following formula (1), Compressive stress CS at 120 μm depth from the surface １２０ A chemically strengthened glass satisfying the following formula (2). Formula (1) |CT|≦-170t+175 Formula (2) 190t-124≦CS １２０ In formula (1), |CT| represents the absolute value of the stress CT, and its unit is MPa. In formula (1) and formula (2), t represents the plate thickness of the chemically strengthened glass, and is measured in mm. In formula (2), CS １２０ is the compressive stress CS １２０ The unit of this expression is MPa.

2. The chemically strengthened glass according to claim 1, wherein the compressive stress layer depth DOC is 0.20 times or more the plate thickness of the chemically strengthened glass.

3. The chemically strengthened glass according to claim 2, wherein an absolute value of a slope of a stress profile from the compressive stress layer depth DOC to a center position of a plate thickness is 1.00 or less.

4. Compressive stress CS at 50 μm depth from the surface ５０ The chemically strengthened glass according to any one of claims 1 to 3, wherein the relationship of formula (3) is satisfied. Formula (3) 150t-50≦CS ５０ In formula (3), CS ５０ is the compressive stress CS ５０ The value is expressed in units of MPa. In formula (3), t represents the plate thickness of the chemically strengthened glass, and is measured in mm.

5. The chemically strengthened glass according to any one of claims 1 to 3, wherein the Young's modulus at the in-plane central position is 80 GPa or more.

6. Fracture toughness value K at the center position in the plane ＩＣ However, 0.80 MPa m １／２ The chemically strengthened glass according to any one of claims 1 to 3.

7. The composition at the center of the plate thickness is expressed as mole percentage based on oxides. SiO ２ 55 to 75% Al ２ O ３ を3~18% Li ２ Oを17~30% Na ２ Oを0~3% K ２ O 0 to 1% MgO 0-10% CaO 0-10% SrO 0-5% ZnO 0-5% TiO ２ 0 to 3% ZrO ２ 0 to 5% SnO ２ 0 to 1% P ２ O ５ 0 to 3% B ２ O ３ 0 to 10% Y ２ O ３ を0~3% The chemically strengthened glass according to any one of claims 1 to 3, comprising:

8. The chemically strengthened glass according to any one of claims 1 to 3, which is a crystallized glass and has a transmittance of 85% or more.

9. The compressive stress CS １２０ The chemically strengthened glass according to any one of claims 1 to 3, wherein the compressive strength is 0 MPa or less.

10. The chemically strengthened glass according to any one of claims 1 to 3, having a plate thickness of 0.6 mm or less.

11. The absolute value of the first-order differential value of the stress profile in the depth direction obtained using a scattered light photoelastic stress meter of the chemically strengthened glass is 1.80 or less at any depth from a position 120 μm in the depth direction from the surface to the center position of the plate thickness. The chemically strengthened glass according to any one of claims 1 to 3.

12. The chemically strengthened glass according to claim 2 or 3, wherein an absolute value of a first-order differential value of a stress profile in the depth direction obtained using a scattered light photoelastic stress meter is 1.80 or less at the compressive stress layer depth DOC.

13. 4. In a depth direction stress profile obtained using a scattered light photoelastic stress meter, the absolute value of the first-order differential value at the compressive stress layer depth DOC is divided by the first-order differential value at a position 120 μm in the depth direction from the surface, which is 1.20 or less. The chemically strengthened glass according to claim 2 or 3.

14. A method for producing chemically strengthened glass according to any one of claims 1 to 3, A first chemical strengthening treatment is performed on the chemically strengthened glass using a first molten salt containing 90 mass% or more of Na salt and 2 mass% or more of Li salt with respect to the total mass, and a second chemical strengthening treatment is performed on the chemically strengthened glass that has been subjected to the first chemical strengthening treatment using a second molten salt containing 90 mass% or more of K salt with respect to the total mass, The composition at the center of the thickness of the glass for chemical strengthening is expressed in mole percentage based on oxides, SiO ２ 60 to 72% Al ２ O ３ を10~20% Li ２ Oを3~12% Na ２ Oを0.5~6% K ２ A method for producing chemically strengthened glass containing 1 to 3% O.

15. Li in the composition of the chemically strengthened glass ２ The method for producing chemically strengthened glass according to claim 14, wherein a ratio of the Li salt content in the first molten salt to the O content is 0.1 to 1.0 in molar ratio.

16. The method for producing chemically strengthened glass according to claim 14, wherein a time for the first chemical strengthening treatment is 150 minutes or more, and a time for the second chemical strengthening treatment is 90 minutes or more.

17. A cover glass comprising the chemically strengthened glass according to any one of claims 1 to 3.

18. A solar cell module comprising the cover glass of claim 17.

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