Chemically strengthened glass, method for producing chemically strengthened glass and cover glass

Abstract

To provide a chemically strengthened glass excellent in shatter strength.SOLUTION: It is a plate-shaped chemically strengthened glass, where a depth DOL-tail where the compression stress value measured using an optical waveguide surface stress gauge is 0 MPa is 4.5 μm or more, the compression stress CS90 measured using a scattered light photoelastic stress gauge at 90 μm and the thickness t of the chemically strengthened glass satisfy the relationship described by the following formula (I): Formula (I) CS90>240×t-110. In formula (I), the unit of CS90 is MPa, and the unit of t is mm.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to chemically strengthened glass and a method for manufacturing the same. The present invention also relates to a cover glass including the chemically strengthened 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, and tablet terminals. Cover glasses for these applications are required to have excellent strength in order to suppress breakage due to impacts and 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 for chemical strengthening treatment has been known. For example, Patent Document 1 discloses a lithium aluminosilicate glass that can obtain a relatively large surface compressive stress layer and a compressive stress layer depth by two-stage chemical strengthening. The lithium aluminosilicate glass is described to be able to increase both the surface stress and the stress layer depth while suppressing the tensile stress generated inside the chemically strengthened glass by a two-stage chemical strengthening treatment using a sodium salt in the first-stage chemical strengthening treatment and a potassium salt in the second-stage chemical strengthening treatment.

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 has been required to have further improved strength. Cover glass for mobile terminals and the like may crack due to deformation when dropped, and it is required that the cover glass does not crack even when dropped from a higher position (has a higher drop strength). When the inventors examined the cover glass described in Patent Document 1, they found that there was room for improvement in terms of drop strength.

[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 to provide cover glass.

Means for Solving the Problems

[0007] As a result of intensive studies on the above problems, the inventors have found that by adjusting the surface stress value of chemically strengthened glass and satisfying a specific relationship with respect to the compressive stress value and the plate thickness at a specific depth, higher drop strength can be achieved, leading to the present invention. That is, the inventors have found that the above problems can be solved by the following configuration.

[0008] 〔1〕 A plate-shaped chemically strengthened glass, The depth DOL-tail at which the compressive stress value measured using an optical waveguide surface stress meter is 0 MPa is 4.5 μm or more, The compressive stress CS at a depth of 90 μm measured using a scattered light photoelastic stress meter 90 and the plate thickness t of the above chemically strengthened glass satisfy the following relationship of the following formula (I): Chemically strengthened glass. Formula (I) CS 90 > 240×t - 110 In formula (I), CS 90 The unit of is MPa. In formula (I), the unit of t is mm. 〔2〕 A plate-shaped chemically strengthened glass, R obtained by the following formula (II) NaThe chemically strengthened glass in which the value of Formula (II) R Na =M StNa / M Na In formula (II), M Na is the integrated value of the profile of the detection intensity of Na in the plate thickness direction of the above-mentioned chemically strengthened glass obtained by analysis using an electron probe microanalyzer, and is the integrated value of the region where the detection intensity of Na is higher than the detection intensity I C at the central position of the plate thickness. In formula (II), M StNa is the integrated value of the above profile, and is the integrated value of the region where the detection intensity of Na is higher than the average detection intensity I A of Na over the entire plate thickness range of the above-mentioned chemically strengthened glass. 〔3〕 The absolute value of the first derivative of the stress profile in the depth direction obtained using the scattered light photoelastic stress gauge of the above-mentioned chemically strengthened glass is less than 2.00 at any depth where the compressive stress value exceeds 0 MPa, and the chemically strengthened glass according to 〔1〕 or 〔2〕. 〔4〕 The second derivative of the stress profile in the depth direction obtained using the scattered light photoelastic stress gauge of the above-mentioned chemically strengthened glass is -0.0200 to 0.0200 at any depth where the compressive stress value exceeds 0 MPa, and the chemically strengthened glass according to any one of 〔1〕 to 〔3〕. 〔5〕 The diffusion depth of K obtained from the profile of the detection intensity of K in the plate thickness direction of the above-mentioned chemically strengthened glass obtained by analysis using an electron probe microanalyzer is 5 μm or more, and the chemically strengthened glass according to any one of 〔1〕 to 〔4〕. 〔6〕 The compressive stress on the surface of the above-mentioned chemically strengthened glass measured using an optical waveguide surface stress gauge is 750 MPa or more, and the chemically strengthened glass according to any one of 〔1〕 to 〔5〕. 〔7〕 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, having a mass of 120 g. The chemically strengthened glass is attached to the widest surface of the structure. When the structure is dropped from a height of 40 cm with the chemically strengthened glass side facing the abrasive surface of #80 sandpaper whose abrasive is silicon carbide, no crack occurs in the chemically strengthened glass. The chemically strengthened glass according to any one of 〔1〕~〔6〕. 〔8〕 The compressive stress CS 90 is 10 MPa or more. The chemically strengthened glass according to any one of 〔1〕~〔7〕. 〔9〕 The Weibull coefficient obtained when a four-point bending test is performed is 30 or more. The chemically strengthened glass according to any one of 〔1〕~〔8〕. 〔10〕 A method for manufacturing a chemically strengthened glass, which comprises performing at least one K-salt strengthening treatment, which is a chemical strengthening treatment of immersing the glass for chemical strengthening in a molten salt containing K-salt. The content of KNO3 in the molten salt is 70% by mass or more based on the total mass of the molten salt. Let the temperature of the molten salt be T K and the treatment time of the K-salt strengthening treatment be t K When the above is the case, regarding the G value obtained by the following formula (PI), when the K-salt strengthening treatment is performed once, the G value is 2.0~5.0, and when the K-salt strengthening treatment is performed two or more times, the total value of the G values of each K-salt strengthening treatment is 2.0~5.0. A method for manufacturing a chemically strengthened glass. 〔Equation 1〕 JPEG2025103785000001.jpg21112 In formula (PI), t is the plate thickness of the glass for chemical strengthening, and the unit of t is m. In formula (PI), T K The unit of is °C. In formula (PI), t K The unit of is seconds. In formula (PI), E is 125000 J / mol. In formula (PI), R is 8.31 J / (K·mol). 〔11〕Perform the first chemical strengthening treatment and the second chemical strengthening treatment on the above chemically strengthened glass in this order. The internal tensile stress value of the glass after the above first chemical strengthening treatment exceeds the CT limit of the above chemically strengthened glass. The manufacturing method of the chemically strengthened glass according to 〔10〕, wherein the internal tensile stress value of the glass after the above second chemical strengthening treatment is less than the CT limit of the above chemically strengthened glass. 〔12〕A cover glass including the chemically strengthened glass according to any one of 〔1〕 to 〔9〕.

Advantages of the Invention

[0009] According to the present invention, a chemically strengthened glass excellent in drop strength can be provided. Further, according to the present invention, a manufacturing method of a chemically strengthened glass can also be provided. Further, according to the present invention, a cover glass can also be provided.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0011] Hereinafter, the chemically strengthened glass of the present invention will be described in detail. However, the present invention is not limited to the following embodiments, and can be arbitrarily modified and implemented without departing from the gist of the present invention. In this specification, the glass composition is shown in terms of mol percentage based on oxides, and mol% may be simply described as %. Further, "~" 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.

[0012] In the glass composition, "substantially not contained" 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, 0.08 mol% or less is more preferable, and 0.05 mol% or less is even more preferable.

[0013] 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.

[0014] In this specification, the "stress profile" refers to a representation of the compressive stress value from the glass surface to the central part with the depth from the glass surface as a variable. Note that a negative compressive stress value means a tensile stress.

[0015] 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 the scattered light photoelastic stress meter (SLP) is called the "SLP stress profile", and the stress profile measured by the film stress measurement (FSM) is called the "FSM stress profile". Note that an optical waveguide surface stress meter (FSM) can accurately measure the stress of glass in a short time. Examples of FSMs include the FSM-6000 manufactured by Orihara Seisakusho Co., Ltd. However, in principle, an FSM can only measure stress when the refractive index decreases from the sample surface toward the inside. In chemically strengthened glass, a layer obtained by replacing sodium ions inside the glass with external potassium ions has a refractive index that decreases from the sample surface toward the inside, so the stress can be measured with an FSM. However, the stress of a layer obtained by replacing lithium ions inside the glass with external sodium ions cannot be accurately measured with an 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. High-precision stress measurement is possible by combining these scattered light photoelastic stress meters with the attached software SlpIV_up3 (Ver. 2019.01.10.001). However, an 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, an optical waveguide surface stress meter (FSM) and a scattered light photoelastic stress meter (SLP), accurate stress measurement becomes possible over the entire thickness of chemically strengthened glass. In this specification, a stress profile obtained by synthesizing SLP information and FSM information is referred to as a "synthesized stress profile."

[0016] For the method of measuring the stress profile near the surface of glass using an FSM, a known method can be referred to. Also, for the method of measuring the stress profile in the glass more than several tens of μm from the surface layer of the glass using an SLP, a known method can be referred to. Examples of the above-known methods include the methods described in International Publication No. 2018 / 056121 and International Publication No. 2017 / 115811.

[0017] The chemically strengthened glass of the present invention includes the first embodiment and the second embodiment described later. Hereinafter, each embodiment will be described.

[0018] <Chemically strengthened glass (first embodiment)> The first embodiment of the chemically strengthened glass of the present invention is a plate-shaped chemically strengthened glass, and the depth from the surface of the chemically strengthened glass (hereinafter, also referred to as "DOL-tail") at which the compressive stress value measured using a fiber optic surface stress meter (FSM) is 0 MPa is 4.5 μm or more. Further, the compressive stress (hereinafter, also referred to as "CS") at a depth of 90 μm measured using a scattered light photoelastic stress meter (SLP) and the plate thickness t of the chemically strengthened glass satisfy the following relationship of formula (I). 90 ” also) and t which is the plate thickness of the chemically strengthened glass satisfy the relationship of the following formula (I). Formula (I) CS 90 > 240 × t - 110 In formula (I), the unit of CS 90 is MPa. In formula (I), the unit of t is mm.

[0019] Although the mechanism by which the first embodiment of the chemically strengthened glass of the present invention excels in drop strength is not necessarily clear by satisfying the above requirements, the present inventors presume as follows. In the first embodiment of the chemically strengthened glass of the present invention, since DOL-tail is 4.5 μm or more, it is considered that a large compressive stress is acting on the surface of the chemically strengthened glass. Further, in the first embodiment of the chemically strengthened glass of the present invention, the relationship of formula (I) is satisfied. Satisfying the relationship of formula (I) indicates that the value of CS 90 is large compared to the plate thickness, and it is considered that compressive stress is acting up to the inside of the chemically strengthened glass. When a large compressive stress acts on the surface of the chemically strengthened glass, it is difficult for the surface to be scratched and it has a large bending strength. Further, when the relationship of formula (I) is satisfied, even if the surface is scratched, since compressive stress acts up to the inside of the chemically strengthened glass, it is considered that the scratch hardly progresses and it has a large drop strength. As a result, the first embodiment of the chemically strengthened glass of the present invention is considered to be excellent in drop strength.

[0020] Hereinafter, the first embodiment of the chemically strengthened glass of the present invention will be described in detail.

[0021] [Thickness of the plate] In the first embodiment of the chemically strengthened glass of the present invention, the plate thickness t satisfies the relationship of the above formula (I) with CS described later. 90 and. The plate thickness is often 2.0 mm or less, preferably 1.5 mm or less, more preferably 1.0 mm or less, still more preferably 0.8 mm or less, particularly preferably 0.7 mm or less, and most preferably 0.6 mm or less. The plate thickness is preferably 0.2 mm or more, more preferably 0.3 mm or more, and still more preferably 0.4 mm or more.

[0022] [FSM stress profile] In the first embodiment of the chemically strengthened glass of the present invention, in the FSM stress profile, the depth (DOL-tail) from the surface of the chemically strengthened glass where the compressive stress value is 0 MPa is 4.5 μm or more. DOL-tail is preferably 5.0 μm or more and more preferably 5.5 μm or more in terms of excellent strength when bending the chemically strengthened glass. DOL-tail is preferably 13.5 μm or less, more preferably 12.0 μm or less, and still more preferably 10.0 μm or less.

[0023] Also, as described above, in FSM, the stress near the surface of the chemically strengthened glass can be accurately measured. The compressive stress (CS0) on the surface of the chemically strengthened glass measured using FSM is preferably 750 MPa or more, more preferably 800 MPa or more. The above CS0 may be 900 MPa or more, or may be 1000 MPa or more. When the above CS0 increases, the strength when bending the chemically strengthened glass is more excellent and preferable. The upper limit of CS0 is not particularly limited, and for example, 1500 MPa can be mentioned.

[0024] The compressive stress (CS1) at a depth of 1 μm of the chemically strengthened glass obtained from the FSM profile is preferably 600 MPa or more, more preferably 700 MPa or more. The upper limit of the above CS1 is not particularly limited, and for example, 1200 MPa can be mentioned.

[0025] The compressive stress (CS3) at a depth of 3 μm of the chemically strengthened glass obtained from the FSM profile is preferably 300 MPa or more, more preferably 450 MPa or more. The upper limit of the above CS1 is not particularly limited, and for example, 900 MPa can be mentioned.

[0026] [SLP stress profile] In the first embodiment of the chemically strengthened glass of the present invention, the compressive stress (CS 90 ) at a depth of 90 μm obtained from the SLP stress profile and the plate thickness t of the chemically strengthened glass satisfy the relationship of the above formula (I). CS 90 is preferably 0 MPa or more, more preferably 10 MPa or more, still more preferably 20 MPa or more, and particularly preferably 30 MPa or more in terms of excellent drop strength. CS 90 is preferably 100 MPa or less, more preferably 60 MPa or less, still more preferably 50 MPa or less in terms of further reducing the tensile stress at the center of the plate thickness.

[0027] The value obtained by subtracting the right side (240 × t - 110) from the left side (CS 90 ) of the above formula (I) is more than 0, preferably 1 or more, more preferably 2 or more, still more preferably 3 or more. The value obtained by subtracting the right side from the left side of the above formula (I) is often 20 or less, preferably 12 or less, more preferably 10 or less, still more preferably 8 or less.

[0028] The compressive stress (CS 50 ) at a depth of 50 μm obtained from the SLP stress profile is preferably 50 MPa or more, more preferably 70 MPa or more, still more preferably 80 MPa or more, and particularly preferably 90 MPa or more in terms of excellent drop strength. CS 50 is preferably 200 MPa or less, more preferably 170 MPa or less, still more preferably 150 MPa or less.

[0029] Regarding the SLP stress profile, if fitting is performed using an appropriate function, the function after fitting can be differentiated, enabling further analysis of the SLP stress profile. The fitting of the SLP stress profile can be performed using the following function (Equation (FS)).

[0030] [Number]

[0031] 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.

[0032] [Number]

[0033] 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 area processing adjustment items, the edge method is used on the surface, 6.0 μm for the internal surface edge, automatic for the internal left and right edges, automatic (at the center of the sample film thickness) for the internal deep edge, and the fitting curve is specified and selected for the extension of the phase curve to the center of the sample thickness. 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).

[0034] Differentiating the above function after fitting (σ f (x)) with respect to x (depth) gives the first derivative σ fThe σ’(x) is obtained. f When substituting the depth value into σ’(x), the slope (first derivative value) of σ(x) at that depth is obtained. f (x) is obtained. In the first embodiment of the chemically strengthened glass of the present invention, the absolute value of the above first derivative value is preferably less than 2.00, more preferably 1.95 or less, at any depth where σ(x)>0 (compressive stress value exceeds 0 MPa). The absolute value of the above first derivative value may be 1.80 or less, or may be 1.50 or less, at any depth. When the absolute value of the above first derivative value is within the above preferred range, the slope of the stress profile is generally small, and stress is more likely to act even inside the chemically strengthened glass, and as a result, it is considered to be more excellent in drop strength. f (x)>0 (compressive stress value exceeds 0 MPa), and at any depth, it is preferably less than 2.00, more preferably 1.95 or less. The absolute value of the above first derivative value may be 1.80 or less, or may be 1.50 or less, at any depth. When the absolute value of the above first derivative value is within the above preferred range, the slope of the stress profile is generally small, and stress is more likely to act even inside the chemically strengthened glass, and as a result, it is considered to be more excellent in drop strength. In addition, the absolute value of the above first derivative value is preferably 0.80 or more, more preferably 1.00 or more, and even more preferably 1.20 or more, in terms of further reducing the tensile stress at the center of the plate thickness. Here, the above "at any depth" means within the entire range of the depth at which the SLP stress profile is obtained.

[0035] Also, when the above σ f ’(x) is further differentiated with respect to x, the second derivative function σ f ’’(x) is obtained. f When substituting the depth value into σ’’(x), the value corresponding to the curvature of σ(x) at that depth (second derivative value) is obtained. f (x) is obtained. In the first embodiment of the chemically strengthened glass of the present invention, the above second derivative value is preferably -0.0200 or more, more preferably -0.0180 or more, and even more preferably -0.0160 or more, at any depth where σ(x)>0 (compressive stress value exceeds 0 MPa). Also, the above second derivative value is preferably 0.0200 or less. The above second derivative value may be 0.0160 or less, may be 0.0130 or less, or may be 0.0110 or less. f (x)>0 (compressive stress value exceeds 0 MPa), and at any depth, it is preferably -0.0200 or more, more preferably -0.0180 or more, and even more preferably -0.0160 or more. Also, the above second derivative value is preferably 0.0200 or less. The above second derivative value may be 0.0160 or less, may be 0.0130 or less, or may be 0.0110 or less. When the above second derivative value is within the above preferred range, it indicates that the stress profile shows a linear shape. It is also preferable to simultaneously satisfy the preferable range of the absolute value of the first-order differential value and the preferable range of the second-order differential value.

[0036] In the first embodiment of the chemically strengthened glass of the present invention, since a compressive stress acts on the surface, a tensile stress that balances with it acts inside the chemically strengthened glass. The maximum value of the tensile stress (CT Max ) in the first embodiment of the chemically strengthened glass of the present invention is preferably 200 MPa or less, more preferably 150 MPa or less, and even more preferably 130 MPa or less in that the fragments are less likely to scatter when the glass breaks. The lower limit of CT Max is not particularly limited, but is often 10 MPa or more. CT Max is obtained from the SLP stress profile and usually acts at the center position of the plate thickness.

[0037] The average value of the tensile stress (CT ave ) in the first embodiment of the chemically strengthened glass of the present invention is preferably 150 MPa or less, more preferably 120 MPa or less, and even more preferably 90 MPa or less in that the fragments are less likely to scatter when the glass breaks. The lower limit of CT ave is not particularly limited, but is often 10 MPa or more. The average value of the tensile stress is obtained by averaging the tensile stress values in the region of the depth indicating the tensile stress from the SLP stress profile.

[0038] In this specification, the compressive stress depth (DOC) is the depth at which the compressive stress value is 0 MPa in the SLP stress profile. In the first embodiment of the chemically strengthened glass of the present invention, DOC is preferably 50 μm or more, more preferably 70 μm or more, and even more preferably 100 μm or more. The upper limit of DOC is preferably 200 μm, more preferably 150 μm, and even more preferably 140 μm in that it is easy to adjust the maximum value of the tensile stress and the average value of the tensile stress to the above preferable ranges.

[0039] [Analysis using an electron beam microprobe analyzer] Regarding the first embodiment of chemically strengthened glass, when analysis is performed using an Electron Probe Micro Analyzer (EPMA), the elemental distribution of each element in the plate thickness direction (depth direction) of the chemically strengthened glass can be obtained. In the present invention, the profile of the detection intensity of each element in the plate thickness direction of the chemically strengthened glass (hereinafter, also referred to as "element profile") is obtained by the following method.

[0040] First, the chemically strengthened glass is embedded in resin, a cross-section is made on a plane parallel to the plate thickness direction of the chemically strengthened glass, and the cross-section is mirror-polished to obtain a measurement sample. The surface of the cross-section of the chemically strengthened glass of the obtained measurement sample is analyzed by EPMA. For the analysis by EPMA, JXA-8500F manufactured by JEOL is used. In the analysis by EPMA, line scan analysis is performed along the plate thickness direction of the chemically strengthened glass of the measurement sample. The detailed measurement conditions follow the method described in the examples in the subsequent section. By the above measurement, the element profile in the plate thickness direction of the chemically strengthened glass is obtained. Note that in the above element profile, the horizontal axis is depth (μm) and the vertical axis is detection intensity (count per second: cps).

[0041] The above element profile can be obtained, for example, for K (potassium). Hereinafter, the element profile obtained for K is also referred to as "K profile". Regarding the first embodiment of the chemically strengthened glass of the present invention that has undergone a chemical strengthening treatment containing a K salt, when the above K profile is obtained, the detection intensity of K gradually decreases from near the surface of the chemically strengthened glass toward the center of the plate thickness, and in many cases, a K profile in which the detection intensity of K is substantially constant from a predetermined depth to the center position of the plate thickness is obtained. In the above K profile, the detection intensity of K at the depth of the center of the plate thickness often corresponds to the detection intensity of the K content of the glass before the chemical strengthening treatment (chemically strengthened glass).

[0042] Here, in the above K profile, consider the case where the detected intensity of K gradually decreases from near the surface of the chemically strengthened glass toward the center of the plate thickness, and the detected intensity of K is substantially constant from a predetermined depth to the center position of the plate thickness. In such a case, the diffusion depth of K can be calculated from the K profile. Specifically, the diffusion depth of K is the average value of the detected intensity of K at a depth within a width of 20 μm at the center of the plate thickness, denoted as I C_K Let the standard deviation of the detected intensity of K in the above range be σ C_K Let the detected intensity of K at the surface of the chemically strengthened glass be I S_K When this is the case, it is calculated by the following method. First, obtain the values of the above I C_K , σ C_K and I S_K . Next, calculate the value obtained by subtracting I S_K from I C_K (hereinafter also referred to as "I diff_K "). Then, in the K profile, obtain the depth at which the detected intensity is higher by the value of 3×σ of the above I diff_K C_K than the value of I C_K . The depth obtained by the above procedure is defined as the diffusion depth of K. The depth obtained by the above procedure corresponds to the depth at which the detected intensity of K starts to rise from the detected intensity of K at the center position of the plate thickness in the K profile.

[0043] Also, the above element profile can be obtained for Na (sodium). Hereinafter, the element profile obtained for Na is also referred to as the "Na profile". Regarding the Na profile of the first embodiment of the chemically strengthened glass of the present invention, it is also preferable that the value of R Na obtained by the formula (II) described later is 0.40 or more. Since the calculation method of the value of R Na , the preferable range, etc. are the same as those described in the second embodiment later, the description is omitted.

[0044] [Drop strength] The first embodiment of the chemically strengthened glass of the present invention is excellent in drop strength. The drop strength can be measured by the following procedure. First, prepare 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. The above structure simulates a mobile device such as a smartphone. Next, attach chemically strengthened glass to the widest surface of the above structure. The attachment of chemical strengthening to the structure is performed using an adhesive tape with a thickness of 0.5 mm. Next, drop the structure with the chemically strengthened glass attached onto the abrasive surface of #80 sandpaper whose abrasive is silicon carbide. The above dropping is performed with the side of the structure to which the chemically strengthened glass is attached facing the above sandpaper. When dropping, check whether cracks occur in the chemically strengthened glass, change the dropping height, record the height at which cracks first occur, and use it as an index of the dropping strength. Hereinafter, the above height at which cracks first occur is also referred to as the "#80SP crack height". The above #80SP crack height is preferably 62.3×t + 2.9 cm or more, and more preferably 62.3×t + 7.9 cm or more. Here, t is the plate thickness and the unit is mm.

[0045] Also, when the sandpaper used to obtain the above #80SP crack height is changed to #180 and the height at which cracks first occur is obtained in the same manner as the method for obtaining the #80SP crack height, the above height can also be used as an index of the dropping strength. Hereinafter, when the above test is performed with the sandpaper being #180, the height at which cracks first occur is also referred to as the "#180SP crack height". The above #180SP crack height is preferably 86.1×t + 7.7 cm or more, and more preferably 86.1×t + 12.7 cm or more. Here, t is the plate thickness and the unit is mm.

[0046] [Bending strength] It is also preferable that the first embodiment of the chemically strengthened glass of the present invention is excellent in bending strength. The bending strength of the chemically strengthened glass in this specification refers to the bending strength obtained in a four-point bending test. For a specific method, refer to the description in the example section in the following text. The bending strength is preferably 750 MPa or more, more preferably 800 MPa or more, and most preferably 850 MPa or more.

[0047] In addition, in a material strength test such as for ceramics, when the cumulative fracture probability is P, analysis may be performed using a Weibull probability paper where the natural logarithm value of the fracture strength is plotted on the horizontal axis and ln(ln(1 / (1 - P))) is plotted on the vertical axis. When a linear plot is obtained on the Weibull probability paper, it can be determined that it follows a Weibull distribution, and the slope is the Weibull coefficient (generally, "m" is used). When the four-point bending test is repeatedly performed with similar samples prepared and the obtained results are plotted on a Weibull probability paper, the Weibull coefficient can be obtained. In this specification, in plotting on the Weibull probability paper, the horizontal axis takes the natural logarithm value of the bending strength of the four-point bending test. The Weibull coefficient obtained using the results of the four-point bending test is preferably 30 or more, more preferably 40 or more, still more preferably 50 or more, and particularly preferably 60 or more. The upper limit of the Weibull coefficient is not particularly limited, and for example, 100 can be mentioned. Note that the above Weibull coefficient is understood as an index of the variation in strength, and the larger the Weibull coefficient, the smaller the variation in strength.

[0048] [Composition] The first embodiment of the chemically strengthened glass of the present invention is obtained by chemically strengthening a sheet glass (glass for chemical strengthening) before chemical strengthening. Hereinafter, the preferred composition of the glass for chemical strengthening (hereinafter, also referred to as "mother glass composition") will be described. Note that the mother glass composition coincides with the composition at the center of the plate thickness of the chemically strengthened glass.

[0049] The mother glass composition preferably contains Li (lithium), and an aluminosilicate glass containing Li, Si, and Al is preferred. More specifically, as the mother glass composition, in terms of mol% based on oxides, SiO2 is 52 to 75%, Al2O3 is 8 to 20%, It is preferable to contain 5 to 16% of Li2O. Hereinafter, the preferable mother glass composition will be described. In the following, for example, the content in terms of the molar percentage based on the oxide of SiO2 may be described as "[SiO2]".

[0050] SiO2 is a component that constitutes the glass skeleton. It is also a component that improves chemical durability and reduces the generation of cracks when the glass surface is scratched. The content of SiO2 is preferably 52% or more, more preferably 55% or more, and particularly preferably 60% or more. On the other hand, from the viewpoint of improving meltability, the content of SiO2 is preferably 75% or less, more preferably 72% or less, further preferably 70% or less, and particularly preferably 68% or less.

[0051] Al2O3 is an effective component from the viewpoint of improving the ion exchange performance during chemical strengthening and increasing the surface compressive stress after strengthening. The content of Al2O3 is preferably 8% or more, more preferably 9% or more, further preferably 10% or more, particularly preferably 11% or more, and typically 12% or more. On the other hand, if the content of Al2O3 is too high, crystals are likely to grow during melting, and the yield is likely to decrease due to the devitrification defect. Also, the viscosity of the glass increases and the meltability decreases. The content of Al2O3 is preferably 20% or less, more preferably 19% or less, and further preferably 18% or less.

[0052] Both SiO2 and Al2O3 are components that stabilize the glass structure, and for reducing brittleness, the total content is preferably 65% or more, more preferably 70% or more, and further preferably 75% or more.

[0053] Li2O is a component that forms surface compressive stress through ion exchange and is a component that improves the meltability of glass. By including Li2O in the parent glass composition, it is possible to introduce surface compressive stress by ion-exchanging lithium ions on the glass surface with sodium ions and further ion-exchanging sodium ions with potassium ions. From the perspective of easily obtaining a preferable stress profile, the content of Li2O is preferably 5% or more, more preferably 7% or more, still more preferably 9% or more, particularly preferably 10% or more, and most preferably 11% or more. On the other hand, if the content of Li2O is too high, the crystal growth rate during glass forming increases, and there may be a significant problem of reduced yield due to devitrification defects. The content of Li2O is preferably 20% or less, more preferably 16% or less, still more preferably 14% or less, and particularly preferably 12% or less.

[0054] Neither Na2O nor K2O is essential, but they are components that improve the meltability of glass and reduce the crystal growth rate of glass, and it is preferable to contain a total of 2% or more in order to improve ion exchange performance. Also, the total is preferably 10% or less, preferably 9% or less, more preferably 8% or less, still more preferably 7% or less, and particularly preferably 5% or less.

[0055] Na2O is a component that forms a surface compressive stress layer in chemical strengthening treatment using a potassium salt and is also a component that can improve the meltability of glass. In order to obtain its effect, the content of Na2O is preferably 1% or more, more preferably 2% or more, still more preferably 3% or more, and particularly preferably 4% or more. On the other hand, from the perspective of avoiding a decrease in surface compressive stress (CS) in the strengthening treatment with a sodium salt and from the perspective of increasing CS 90 it is preferably 8% or less, more preferably 7% or less, still more preferably 6% or less, and particularly preferably 5% or less.

[0056] K2O may be contained for the purpose of improving ion exchange performance or the like. When K2O is contained, the content is preferably 0.1% or more, more preferably 0.15% or more, and particularly preferably 0.2% or more. In order to further prevent devitrification, 0.5% or more is preferable, and 1.2% or more is more preferable. On the other hand, since containing a large amount of K may cause brittleness and a factor for reducing the surface stress due to reverse exchange during strengthening, 5% or less is preferable, and 3% or less is more preferable.

[0057] R, which is the total of the content of Li2O, the content of Na2O, and the content of K2O, is preferably 5% or more, more preferably 8% or more, still more preferably 10% or more, and particularly preferably 12% or more. The above R is preferably 25% or less, and more preferably 20% or less.

[0058] 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, and still 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 0.80 or less, still more preferably 0.78 or less, and particularly preferably 0.75 or less, from the viewpoint of further enhancing chemical durability.

[0059] The ratio of the content of Na2O to the above R ([Na2O] / ([Li2O]+[Na2O]+[K2O]), hereinafter also referred to as "Na2O / R2O") is preferably 0.05 or more, more preferably 0.08 or more, and still more preferably 0.10 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, still more preferably 0.40 or less, and particularly preferably 0.30 or less, from the viewpoint of further enhancing chemical durability.

[0060] 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 improving the electrical resistance of the glass. From the viewpoint of further enhancing the chemical strengthening characteristics with respect to the compressive stress near the surface, 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.

[0061] Also, the product of Li2O / R2O, Na2O / R2O, and K2O / R2O is preferably 0.005 or more, more preferably 0.008 or more, and even more preferably 0.010 or more from the viewpoint of suppressing the increase in the devitrification temperature. Also, from the viewpoint of improving the chemical resistance, the above product is preferably 0.030 or less, more preferably 0.028 or less.

[0062] The ratio of the content of Al2O3 to R above ([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 0.90 or less, more preferably 0.88 or less, and even more preferably 0.85 or less.

[0063] MgO may be contained to lower the viscosity during melting. The content of MgO is preferably 0.5% or more, more preferably 1% or more, even more preferably 2% or more, and particularly preferably 3% or more. On the other hand, if the content of MgO is too high, it may be difficult to increase the compressive stress layer during the chemical strengthening treatment. The content of MgO is preferably 15% or less, more preferably 10% or less, even more preferably 8% or less, and particularly preferably 6% or less.

[0064] ZrO2 does not necessarily have to be contained, but it is preferably contained from the viewpoint of increasing the surface compressive stress of the chemically strengthened glass. The content of ZrO2 is preferably 0.1% or more, more preferably 0.15% or more, still more preferably 0.2% or more, particularly preferably 0.25% or more, and typically 0.3% or more. On the other hand, if the content of ZrO2 is too high, devitrification defects are likely to occur, and it may be difficult to increase the compressive stress value during the chemical strengthening treatment. The content of ZrO2 is preferably 2% or less, more preferably 1.5% or less, still more preferably 1% or less, and particularly preferably 0.8% or less.

[0065] The content of Y2O3 is preferably 0.1% or more, more preferably 0.2% or more, still more preferably 0.5% or more, and particularly preferably 1% or more. On the other hand, if it is too much, it may be difficult to increase the compressive stress layer during the chemical strengthening treatment. The content of Y2O3 is preferably 5% or less, more preferably 3% or less, still more preferably 2% or less, and particularly preferably 1.5% or less.

[0066] The composition of the chemically strengthened glass (parent glass composition) to be subjected to chemical strengthening is preferably the above composition. The method for obtaining the chemically strengthened glass having the parent glass composition is not particularly limited, and known methods can be applied. For example, in order to obtain the glass having the above composition, glass raw materials are appropriately blended, heated and melted in a glass melting furnace, and then the glass is homogenized by bubbling, stirring, addition of a fining agent, etc., formed into a glass plate having a predetermined thickness, and slowly cooled. Also, it may be formed into a plate shape by a method of forming into a block shape, slowly cooling, and then cutting.

[0067] Examples of the method for forming into a plate shape include the float method, the press method, the fusion method, and the down-draw method. In particular, when manufacturing a large-sized glass plate, the float method is preferable. Also, continuous forming methods other than the float method, such as the fusion method and the down-draw method, are also preferable.

[0068] Alternatively, the glass for chemical strengthening may be a crystallized glass. When the glass for chemical strengthening is a crystallized glass, a crystallized glass containing one or more crystals selected from the group consisting of lithium silicate crystals, lithium aluminosilicate crystals, and lithium phosphate crystals is preferred. As the lithium silicate crystals, lithium metasilicate crystals, lithium disilicate crystals, etc. are preferred. As the lithium phosphate crystals, lithium orthophosphate crystals, etc. are preferred. As the lithium aluminosilicate crystals, β-spodumene crystals, petalite crystals, etc. are preferred.

[0069] The crystallization rate of the crystallized glass is preferably 10% or more, more preferably 15% or more, still more preferably 20% or more, and particularly preferably 25% or more in terms of improving mechanical strength. Also, in order to enhance transparency, it is preferably 70% or less, more preferably 60% or less, and still more preferably 50% or less. The fact that the crystallization rate is small is also excellent in terms of being easy to heat and bend-mold. The crystallization rate can be calculated by the Rietveld method from the X-ray diffraction intensity. The Rietveld method is described in "Crystallography Handbook" edited by the Editorial Committee of the Crystallographic Society of Japan, "Crystallography Handbook" (published by Kyoritsu Shuppan in 1999, p492-499).

[0070] The average particle size of the precipitated crystals of the crystallized glass is preferably 300 nm or less, more preferably 200 nm or less, still more preferably 150 nm or less, and particularly preferably 100 nm or less in order to enhance transparency. The average particle size of the precipitated crystals can be obtained from a transmission electron microscope (TEM) image. Also, it can be estimated from a scanning electron microscope (SEM) image.

[0071] The Young's modulus of the glass for chemical strengthening is preferably 80 GPa or more, more preferably 83 MPa or more. Also, the fracture toughness value (K IC ) of the glass for chemical strengthening is preferably 0.70 MPa·m 1 / 2 or more, more preferably 0.75 MPa·m 1 / 2 or more, still more preferably 0.80 MPa·m 1 / 2 or more. The fracture toughness value K IC is 2.00 MPa·m 1 / 2In many cases, 1.80 MPa·m 1 / 2 is preferably as follows. In this specification, the "fracture toughness value K IC " is measured with reference to the DCDC method [References: 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 Fig. 1 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 speed v (unit: m / s) as shown in Fig. 2 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 .

[0072] <Chemically strengthened glass (second embodiment)> The second embodiment of the chemically strengthened glass of the present invention is a plate-shaped chemically strengthened glass, and the value of R Na obtained by the following formula (II) is 0.40 or more. Formula (II) R Na = M StNa / M Na In formula (II), M Na is the integrated value of the profile of the detection intensity of Na in the plate thickness direction of the chemically strengthened glass obtained by analysis using an electron probe microanalyzer, and is the integrated value of the region where the detection intensity is greater than the detection intensity I C of Na at the center position of the plate thickness. In formula (II), M StNa is the integrated value of the profile of the detection intensity of Na, and is the integrated value of the region where the detection intensity is greater than the average detection intensity I A of Na in the entire plate thickness range of the chemically strengthened glass.

[0073] Although the mechanism by which the second embodiment of the chemically strengthened glass of the present invention excels in drop strength is not necessarily clear when it satisfies the above requirements, the present inventors presume as follows. In the second embodiment of the chemically strengthened glass of the present invention, the relationship of the above formula (II) is satisfied. In formula (II), M Na The value of is considered to correspond to the total amount of Na ions introduced into the chemically strengthened glass by ion exchange during chemical strengthening. On the other hand, M StNa The value of is considered to correspond to the amount of Na ions in the depth region deeper than the average detection intensity. Here, in the chemically strengthened glass, it is considered that a compressive stress acts in a region where the content of Na ions is higher than the average content of Na ions. Therefore, the value of R Na represented by formula (II) is considered to represent the ratio of the amount of Na ions contributing to the generation of compressive stress among the Na ions introduced by ion exchange. Then, it is considered that a large compressive stress acts on the surface of the chemically strengthened glass satisfying the relationship of the above formula (II). Also, when the relationship of the above formula (II) is satisfied, Na ions are often introduced into the chemically strengthened glass up to the inside of the chemically strengthened glass by the chemical strengthening treatment, and it is considered to indicate that a compressive stress acts up to the inside of the chemically strengthened glass. Therefore, when the relationship of the above formula (II) is satisfied, a large compressive stress acts and it is difficult for the surface to be scratched. Also, even if the surface is scratched, since the compressive stress acts up to the inside of the chemically strengthened glass, it is considered that the scratch is difficult to progress. As a result, the second embodiment of the chemically strengthened glass of the present invention is considered to be excellent in drop strength.

[0074] Hereinafter, the second embodiment of the chemically strengthened glass of the present invention will be described in detail.

[0075] [Analysis using an electron probe microanalyzer] Regarding the second embodiment of the chemically strengthened glass, when an analysis using an electron probe microanalyzer (EPMA) is performed, the element distribution of each element in the plate thickness direction (depth direction) of the chemically strengthened glass can be obtained. The analysis method by EPMA is the same as that in the first embodiment, and thus the description thereof is omitted. In addition, the terms such as "K profile" and "Na profile" are the same as those described above, and thus the description thereof is omitted.

[0076] In the second embodiment of the chemically strengthened glass of the present invention, as described above, for the Na profile, R obtained by the following formula (II) Na is 0.40 to 0.60. Formula (II) R Na =M StNa / M Na In formula (II), M Na is the integrated value of the region where the detection intensity is greater than the detection intensity I of Na at the central position of the plate thickness, as described above. More specifically, M C is the integrated value of the detection intensity of the Na profile for the region where the detection intensity is greater than the value of the detection intensity I of Na at the central depth position of the plate thickness, with the value of the detection intensity I of Na at the central depth position of the plate thickness in the Na profile as the baseline. Na is the integrated value of the region where the detection intensity is greater than the detection intensity I of Na at the central depth position of the plate thickness, as described above. More specifically, M C is the integrated value of the detection intensity of the Na profile for the region where the detection intensity is greater than the value of the detection intensity I of Na at the central depth position of the plate thickness, with the value of the detection intensity I of Na at the central depth position of the plate thickness in the Na profile as the baseline. C is the integrated value of the detection intensity of the Na profile for the region where the detection intensity is greater than the value of the detection intensity I of Na at the central depth position of the plate thickness, with the value of the detection intensity I of Na at the central depth position of the plate thickness in the Na profile as the baseline. In formula (II), M StNa is the integrated value of the region where the detection intensity is greater than the average detection intensity I of Na over the entire plate thickness range of the chemically strengthened glass, as described above. More specifically, M A is the integrated value of the detection intensity of the Na profile for the region where the detection intensity is greater than the average detection intensity I of Na over the entire plate thickness range of the chemically strengthened glass, with the average detection intensity I of Na over the entire plate thickness range of the chemically strengthened glass in the Na profile as the baseline. StNa is the integrated value of the detection intensity of the Na profile for the region where the detection intensity is greater than the average detection intensity I of Na over the entire plate thickness range of the chemically strengthened glass, with the average detection intensity I of Na over the entire plate thickness range of the chemically strengthened glass in the Na profile as the baseline. A When the average detection intensity I of Na over the entire plate thickness range of the chemically strengthened glass in the Na profile is set as I A is the integrated value of the detection intensity of the Na profile for the region where the detection intensity is greater than the average detection intensity I of Na over the entire plate thickness range of the chemically strengthened glass, with the value of the average detection intensity I of Na over the entire plate thickness range of the chemically strengthened glass in the Na profile as the baseline. A is the integrated value of the detection intensity of the Na profile for the region where the detection intensity is greater than the average detection intensity I of Na over the entire plate thickness range of the chemically strengthened glass, with the value of the average detection intensity I of Na over the entire plate thickness range of the chemically strengthened glass in the Na profile as the baseline. In addition, the above integrated value is obtained by the sum of the product of the data interval in the depth direction and the detection intensity of Na at each depth.

[0077] The above R Na is preferably 0.41 or more, and more preferably 0.42 or more. The upper limit of the above R Na is 0.60, and 0.55 is preferable.

[0078] The second embodiment of the chemically strengthened glass of the present invention is the same as the first embodiment in preferred aspects, except for the above points.

[0079] <Method for manufacturing chemically strengthened glass> The method for manufacturing chemically strengthened glass of the present invention is a method for manufacturing chemically strengthened glass that performs at least one K-salt strengthening treatment, which is a chemical strengthening treatment of immersing a glass for chemical strengthening in a molten salt containing a K-salt. Here, the content of KNO3 in the molten salt used for the K-salt strengthening treatment is 70% by mass or more based on the total mass of the molten salt. Also, when the temperature of the molten salt is T K and the treatment time of the K-salt strengthening treatment is t K the G value obtained by the following formula (PI) satisfies a predetermined requirement. Specifically, when the K-salt strengthening treatment is performed once, the G value is 2.0 to 5.0, and when the K-salt strengthening treatment is performed two or more times, the total value of the G values of each K-salt strengthening treatment is 2.0 to 5.0.

[0080]

Equation

[0081] In formula (PI), t is the plate thickness of the glass for chemical strengthening, and the unit of t is m. In formula (PI), T K The unit of is °C. In formula (PI), t K The unit of is seconds. In formula (PI), E is 125000 J / mol. In formula (PI), R is 8.31 J / (K·mol).

[0082] According to the method for manufacturing chemically strengthened glass of the present invention, the above-described chemically strengthened glass of the present invention (the first embodiment and the second embodiment) can be obtained. In the method for manufacturing chemically strengthened glass of the present invention, the K-salt strengthening treatment is carried out such that the above G value or the total value of the G values is 2.0 to 5.0. As can be seen from the above formula (PI), the G value is a parameter related to the length of the treatment time of the K-salt strengthening treatment, the treatment temperature, and the plate thickness of the glass for chemical strengthening. That the G value or the total value of the G values is 2.0 or more corresponds to the K-salt strengthening treatment being carried out at a high temperature, or for a long time, or at a high temperature and for a long time compared to the plate thickness of the glass for chemical strengthening. Then, it is considered that the ions introduced by the chemical strengthening treatment easily diffuse to the inside of the chemically strengthened glass, and the compressive stress easily acts on the inside of the chemically strengthened glass. On the other hand, when the G value or the total value of the G values is adjusted to 5.0 or less, the ions introduced by the chemical strengthening treatment are not introduced more than necessary into the chemically strengthened glass, and the stress introduced by the introduction of heat can be adjusted to a state where it is not relaxed.

[0083] A preferred embodiment of the glass for chemical strengthening used in the method for manufacturing chemically strengthened glass of the present invention is the same as the glass for chemical strengthening described in the first embodiment of the chemically strengthened glass of the present invention, and thus the description is omitted.

[0084] Note that in the method for manufacturing chemically strengthened glass of the present invention, a chemical strengthening treatment other than the above K-salt strengthening treatment (hereinafter, also referred to as "other chemical strengthening treatment") may be performed. Hereinafter, the chemical strengthening treatment will be described.

[0085] [Chemical Strengthening Treatment] In the method for manufacturing chemically strengthened glass of the present invention, a chemical strengthening treatment is performed on the glass for chemical strengthening. Among the above chemical strengthening treatments, the K-salt strengthening treatment is performed at least once. By the chemical strengthening treatment, components (for example, Li ions and Na ions, etc.) in the glass for chemical strengthening are exchanged with ions contained in the molten salt used for the chemical strengthening treatment, and a layer having compressive stress is formed due to the difference between the ionic radius of the ions before the exchange and the ionic radius of the exchanged ions. The chemical strengthening treatment may be performed only once or may be performed in multiple steps. When the chemical strengthening treatment is performed only once, the chemical strengthening treatment is a K-salt strengthening treatment.

[0086] As described above, the content of KNO3 in the molten salt used for the K-salt strengthening treatment (hereinafter also referred to as "K-containing molten salt") is 70% by mass or more based on the total mass of the K-containing molten salt. The content of KNO3 in the K-containing molten salt is preferably 85% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more based on the total mass of the K-containing molten salt. The content of KNO3 in the K-containing molten salt may be 100% by mass based on the total mass of the K-containing molten salt.

[0087] The K-containing molten salt may contain components other than KNO3. Examples of components other than KNO3 include K salts, Na salts, and Li salts other than KNO3 (potassium nitrate). More specifically, examples of K salts other than potassium nitrate include potassium sulfate, potassium carbonate, and potassium chloride. Examples of Na salts include sodium nitrate, sodium sulfate, sodium carbonate, and sodium chloride. Examples of Li salts include lithium nitrate, lithium sulfate, lithium carbonate, and lithium chloride. In addition, examples of components other than KNO3 also include Rb (rubidium) salts, Cs (cesium) salts, and Ag (silver) salts. When the K-containing molten salt contains components other than KNO3, sodium nitrate (NaNO3) is preferred, and the content of sodium nitrate is preferably 10% by mass or less, more preferably 5% by mass or less based on the total mass of the K-containing molten salt. When the K-containing molten salt contains sodium nitrate, the content of sodium nitrate is preferably 1% by mass or more, more preferably 2% by mass or more based on the total mass of the K-containing molten salt.

[0088] The K-salt strengthening treatment may be carried out by adjusting the conditions so that the above-described G value or the total value of the G values is 2.0 to 5.0. The temperature of the K-salt strengthening treatment (T in the above formula (PI)) K) is preferably 350 °C or higher, more preferably 360 °C or higher, and still more preferably 370 °C or higher. The temperature of the K-salt strengthening treatment is preferably 450 °C or lower, more preferably 430 °C or lower. The temperature of the K-salt strengthening treatment may be 400 °C or lower. The time of the K-salt strengthening treatment (t in the above formula (PI)) K ) is preferably 60 minutes or longer, more preferably 120 minutes or longer, still more preferably 160 minutes or longer, and particularly preferably 240 minutes or longer. The time of the K-salt strengthening treatment is often 1440 minutes or shorter, preferably 960 minutes or shorter, more preferably 720 minutes or shorter, and still more preferably 480 minutes or shorter. The time of the K-salt strengthening treatment may be 360 minutes or shorter, or 240 minutes or shorter. The above-described G value or the total value of the G values is preferably 2.2 or higher, more preferably 2.3 or higher. Also, the G value or the total value of the G values is preferably 4.8 or lower, more preferably 4.4 or lower, still more preferably 4.0 or lower, and particularly preferably 3.5 or lower.

[0089] The K-salt strengthening treatment is preferably the chemical strengthening treatment carried out last among the chemical strengthening treatments. Conducting the K-salt strengthening treatment last means not performing other chemical strengthening treatments after the K-salt strengthening treatment.

[0090] In the method for producing chemically strengthened glass of the present invention, a chemical strengthening treatment other than the K-salt strengthening treatment (other chemical strengthening treatment) may be performed. In the other chemical strengthening treatment, a molten salt other than the above-described K-containing molten salt (hereinafter also referred to as "other molten salt") is used. The other molten salt refers to a molten salt in which the content of KNO3 is less than 70% by mass based on the total mass of the molten salt. Therefore, the other molten salt may contain KNO3. Examples of the salts contained in the other molten salt include K salts, Na salts, and Li salts. Specific examples of each salt are as described above. Also, the other molten salt may contain salts other than the above (for example, Rb (rubidium) salts, Cs (cesium) salts, Ag (silver) salts, etc.). Among them, the other molten salt preferably contains 70% by mass or more of a Na salt (preferably sodium nitrate). When the other molten salt contains sodium nitrate, the content of sodium nitrate is more preferably 80% by mass or more, still more preferably 90% by mass or more, and particularly preferably 95% by mass or more, based on the total mass of the other molten salt. When the other molten salt contains sodium nitrate, the content of sodium nitrate may be 100% by mass based on the total mass of the other molten salt. When the other molten salt contains a Na salt, the chemically strengthened glass (first embodiment and second embodiment) of the present invention is more easily obtained.

[0091] When performing other chemical strengthening treatment, the temperature of the other chemical strengthening treatment is preferably 350°C or higher, more preferably 380°C or higher, and still more preferably 400°C or higher. The temperature of the other chemical strengthening treatment is often 500°C or lower, preferably 450°C or lower, and more preferably 430°C or lower. When performing other chemical strengthening treatment, the time of the other chemical strengthening treatment is preferably 10 minutes or longer, more preferably 30 minutes or longer, and still more preferably 60 minutes or longer. The time of the other chemical strengthening treatment is often 480 minutes or shorter, preferably 420 minutes or shorter, and more preferably 360 minutes or shorter. The time of the other chemical strengthening treatment may be 120 minutes or shorter, or 90 minutes or shorter.

[0092] Performing the above-mentioned K-salt strengthening treatment after performing the above-mentioned other chemical strengthening treatment is also one of the preferred embodiments. When performing the chemical strengthening treatment in the above order, ions (for example, Na ions) ion-exchanged in the other chemical strengthening treatment are likely to diffuse to the inside of the glass for chemical strengthening during the K-salt strengthening treatment, which is preferable.

[0093] In the method for manufacturing the chemically strengthened glass of the present invention, the K-salt strengthening treatment is performed one or more times, and the number of times of performing the K-salt strengthening treatment is preferably 1 to 3 times, more preferably 1 or 2 times. The number of times of performing the K-salt strengthening treatment may be 1 time. Further, when performing other chemical strengthening treatments in the method for manufacturing chemically strengthened glass of the present invention, the number of times of performing the other chemical strengthening treatment is preferably 1 to 3 times, more preferably 1 or 2 times, and even more preferably 1 time.

[0094] Also, consider the case where the first chemical strengthening treatment and the second chemical strengthening treatment are performed in this order in the method for manufacturing chemically strengthened glass of the present invention. At this time, it is also preferable that the internal tensile stress value of the glass after the first chemical strengthening treatment exceeds the CT limit of the glass for chemical strengthening, and the internal tensile stress value of the glass after the second chemical strengthening treatment is less than the CT limit of the glass for chemical strengthening. In this specification, the CT limit of the glass for chemical strengthening refers to the internal tensile stress value at which the number of fragments is 10 or more per 4.0 cm 2 impact. "The internal tensile stress value at which the number of fragments is 10 or more per 4.0 cm 2 impact" is first determined by performing an indenter test using a diamond chip on an anvil, and the number of fragments when causing delayed fracture is 4.0 cm 2 when it exceeds 10 per impact.

[0095] When the requirements regarding the above CT limit are satisfied, the second chemical strengthening treatment is preferably the above K-salt strengthening treatment. Also, at that time, the first chemical strengthening treatment is preferably the above other chemical strengthening treatment, and the above other chemical strengthening treatment is preferably a chemical strengthening treatment using another molten salt containing Na salt.

[0096] <Use> The chemically strengthened glass of the present invention (first and second embodiments) is useful, for example, as a cover glass. In particular, it 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), and touch panels that are not intended for portability, elevator wall surfaces, wall surfaces of buildings such as houses and buildings (full-surface displays), building materials such as window glass, and table tops, interiors of automobiles and airplanes, etc. It is also useful as a cover glass for the above-mentioned articles. Furthermore, it can be applied to uses such as a housing having a curved surface shape by bending and bending molding.

Examples

[0097] The present invention will be described in more detail below based on 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 in a limited manner by the examples shown below. Note that Examples 1 to 7, Example 11, and Example 12 are examples, and Examples 8 to 10 are comparative examples.

[0098] <Production of Chemically Strengthened Glass> First, glass was produced by melting glass raw materials in a platinum crucible so as to obtain each glass composition expressed in mol percentage based on oxides shown in Table 1. Specifically, oxides, hydroxides, carbonates, nitrates, etc. used as glass raw materials were appropriately selected from commonly 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 to 1700 °C, melted for about 3 hours, defoamed and homogenized to obtain molten glass. The obtained molten glass was poured into a shaped material, held at a temperature of the 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 with a length of 120 mm × width of 60 mm × thickness of 0.6 mm. Also, depending on the example, sheet glass with a thickness of 0.55 mm, sheet glass with a thickness of 0.5 mm, or sheet glass with a thickness of 0.7 mm was obtained.

[0099]

Table 1

[0100] For each sheet glass obtained by the above procedure, chemical strengthening treatment was performed under the conditions described in Table 2 to obtain chemically strengthened glasses of Examples 1 to 12.

[0101] <Measurement and Evaluation> [Measurement by EPMA] Using the obtained chemically strengthened glass, a measurement sample was prepared by the above-described procedure, and analysis was performed by EPMA (JXA-8500F manufactured by JEOL) to obtain a Na profile and an Si profile. The measurement conditions of EPMA and the like were as follows. · Spectrometer crystal: PETJ (K-Kα), TAPH (Na-Kα) · Electron beam acceleration voltage: 15 kV · Irradiated electron beam current: 30 nA · Integration time: 1000 msec / point · Measurement point interval: 1 μm

[0102] [Bending Strength Test] In the bending strength test, the chemically strengthened glass was subjected to a four-point bending test. The four-point bending test was carried out in accordance with JIS-R1601:2008 (4PB test). An autograph AGS-10kNX, a tabletop precision universal testing machine manufactured by Shimadzu Corporation, was used for the four-point bending test apparatus. In order to evaluate the entire area of the damaged region, the spans of the bending test were set to 20 mm on the upper side and 40 mm on the lower side. The moving speed of the crosshead was set to 5 mm / min. The fracture stress was determined from the measurement results of the load at which cracks occurred. The above measurement of the fracture stress was performed on 10 samples, and the arithmetic mean value of the measured fracture stresses was defined as the average fracture stress. Also, the data obtained when the above measurements were carried out were plotted on Weibull probability paper, and the Weibull coefficient was determined from the slope of the straight line. The calculation method of the Weibull coefficient is as described above.

[0103] [Drop Strength Test] The drop strength of the chemically strengthened glass of each example was measured according to the above-described procedure. That is, the #80SP crack height and the #180SP crack height were measured. The detailed measurement procedure is as described above.

[0104] [Results] The conditions of the chemical strengthening treatment, the above measurement results, and the above evaluation results of the chemically strengthened glass of each example are shown in Table 2 below. In Table 2, the measurement methods of the values in the "FSM profile" column and the "SLP profile" column are as described above.

[0105] [Table 2]

[0106] From the results shown in Table 2, it was confirmed that the chemically strengthened glasses of Examples 1 to 7, Example 11, and Example 12, in which the DOL-tail is 4.5 μm or more and the relationship of the above formula (I) is satisfied, are superior in drop strength to the chemically strengthened glasses of Examples 8 to 10.

Claims

1. A plate-shaped chemically strengthened glass, wherein the depth DOL-tail at which the compressive stress value measured using an optical waveguide surface stress meter is 0 MPa is 4.5 μm or more, Compressive stress CS at a depth of 90 μm measured using a scattered light photoelastic stress meter ９０ A chemically strengthened glass, wherein the compressive stress CS at a depth of 90 μm measured using a scattered light photoelastic stress meter and the plate thickness t of the chemically strengthened glass satisfy the relationship of the following formula (I). Formula (I) CS ９０ > 240 × t - 110 In formula (I), CS ９０ is in MPa units. In formula (I), the unit of t is mm.

2. A plate-shaped chemically strengthened glass, R obtained by the following formula (II) Ｎａ The chemically strengthened glass, wherein the value of is 0.40 to 0.

60. Formula (II) R Ｎａ = M ＳｔＮａ / M Ｎａ In formula (II), M Ｎａ is the integrated value of the profile of the detection intensity of Na in the plate thickness direction of the chemically strengthened glass obtained by analysis using an electron probe microanalyzer, and is the integrated value of the region where the detection intensity is higher than the detection intensity I Ｃ of Na at the central position of the plate thickness. In formula (II), M ＳｔＮａ is the integrated value of the profile, which is the integrated value of the region where the detection intensity is higher than the average detection intensity I of Na in the entire plate thickness range of the chemically strengthened glass Ａ ​

3. The absolute value of the first derivative of the stress profile in the depth direction obtained using the scattered light photoelastic stress meter of the chemically strengthened glass is less than 2.00 at any depth where the compressive stress value is more than 0 MPa. The chemically strengthened glass according to Claim 1 or 2.

4. The second derivative of the stress profile in the depth direction obtained using the scattered light photoelastic stress meter of the chemically strengthened glass is -0.0200 to 0.0200 at any depth where the compressive stress value is more than 0 MPa. The chemically strengthened glass according to Claim 1 or 2.

5. The diffusion depth of K obtained from the profile of the detection intensity of K in the plate thickness direction of the chemically strengthened glass obtained by analysis using an electron probe microanalyzer is 5 μm or more. The chemically strengthened glass according to Claim 1 or 2.

6. The compressive stress on the surface of the chemically strengthened glass measured using an optical waveguide surface stress meter is 750 MPa or more. The chemically strengthened glass according to Claim 1 or 2.

7. 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, having a mass of 120 g. When the chemically strengthened glass is attached to the widest surface of the structure and the structure is dropped from a height of 40 cm with the chemically strengthened glass side facing the abrasive surface of #80 sandpaper with silicon carbide as the abrasive, no crack occurs in the chemically strengthened glass. The chemically strengthened glass according to Claim 1 or 2.

8. The compressive stress CS ９０ is 10 MPa or more, the chemically strengthened glass according to claim 1 or 2.

9. The Weibull coefficient obtained when a four-point bending test is performed is 30 or more. The chemically strengthened glass according to Claim 1 or 2.

10. A method for manufacturing a chemically strengthened glass, which comprises performing at least one K-salt strengthening treatment, which is a chemical strengthening treatment of immersing a glass for chemical strengthening in a molten salt containing a K-salt, The content of KNO in the molten salt ３ is 70% by mass or more based on the total mass of the molten salt, Let the temperature of the molten salt be T Ｋ and let the treatment time of the K-salt strengthening treatment be t Ｋ When the G value obtained by the following formula (PI) is considered, in the case where the K-salt strengthening treatment is performed once, the G value is 2.0 to 5.0, and in the case where the K-salt strengthening treatment is performed two or more times, the total value of the G values of each of the K-salt strengthening treatments is 2.0 to 5.

0. A method for manufacturing chemically strengthened glass. 【Number 1】 In formula (PI), t is the plate thickness of the glass for chemical strengthening, and the unit of t is m. In formula (PI), T Ｋ is in the unit of °C. In formula (PI), t Ｋ is in units of seconds. In formula (PI), E is 125000 J / mol. In formula (PI), R is 8.31 J / (K·mol).

11. The first chemical strengthening treatment and the second chemical strengthening treatment are sequentially performed on the chemically strengthened glass, the internal tensile stress value of the glass after the first chemical strengthening treatment exceeds the CT limit of the chemically strengthened glass, and the internal tensile stress value of the glass after the second chemical strengthening treatment is less than the CT limit of the chemically strengthened glass. The method for manufacturing a chemically strengthened glass according to claim 10.

12. A cover glass including the chemically strengthened glass according to claim 1 or 2.

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