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

Abstract

The invention relates to chemically strengthened glass, a method for producing chemically strengthened glass, and cover glass. Provided is a chemically strengthened glass having excellent drop strength. A chemically strengthened glass which is a plate-shaped chemically strengthened glass wherein the depth DOL-tail at a compressive stress value of 0 MPa measured using an optical waveguide surface stress meter is 4.5 [mu] m or more, and the compressive stress CS90 at a depth of 90 [mu] m 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): CS90gt; in formula (I), the unit of CS90 is MPa, and in formula (I), the unit of t is mm.

Description

Technical Field

[0001] The present invention relates to chemically strengthened glass and a method for manufacturing the same.

[0002] In addition, the present invention relates to a protective glass including the chemically strengthened glass. Background Art

[0003] In recent years, protective glass has been used to improve the protection and aesthetics of display devices such as mobile phones, smartphones, and tablet terminals. For the protective glass for these uses, excellent strength is required to suppress breakage caused by impact or the like.

[0004] Conventionally, a method of chemically strengthening glass by immersing the glass in a molten salt such as potassium nitrate to increase the surface strength of the glass has been known. For example, in Patent Document 1, a lithium aluminosilicate glass having a relatively large surface compressive stress layer and a compressive stress layer depth obtained by two-step chemical strengthening is disclosed. It is described that the lithium aluminosilicate glass can suppress the tensile stress generated inside the chemically strengthened glass and at the same time increase the surface stress and the stress layer depth by a two-step chemical strengthening treatment using a sodium salt in the first-step chemical strengthening treatment and a potassium salt in the second-step chemical strengthening treatment.

[0005] Prior Art Documents

[0006] Patent Documents

[0007] Patent Document 1: Japanese Patent Application Laid-Open No. 2013-520388 Summary of the Invention

[0008] Problems to be Solved by the Invention

[0009] In recent years, there has been a demand for further improving the strength of protective glass. The protective glass for portable terminals or the like sometimes breaks due to deformation when dropped, and it is required that the protective glass does not break even when dropped from a higher position (has higher drop strength).

[0010] The present inventors studied the protective glass described in Patent Document 1 and found that there is room for improvement in the drop strength.

[0011] The present invention has been made in view of the above problems, and an object thereof is to provide a chemically strengthened glass having excellent drop strength.

[0012] In addition, an object of the present invention is to provide a method for manufacturing the chemically strengthened glass.

[0013] In addition, an object of the present invention is to provide a protective glass.

[0014] Means for Solving the Problems

[0015] The present inventors have conducted in-depth research on the above problems and found that when the surface stress value of chemically strengthened glass is adjusted and the compressive stress value and plate thickness at a specific depth satisfy a specific relationship, higher drop strength can be achieved, thus completing the present invention.

[0016] That is, the inventors found that the above problems can be solved by the following configuration.

[0017] [1] A chemically strengthened glass, which is a plate-shaped chemically strengthened glass. Among them, the depth DOL-tail at which the compressive stress value measured by an optical waveguide surface stress meter is 0 MPa is 4.5 μm or more, and the compressive stress CS at a depth of 90 μm measured by a scattered light photoelastic stress meter 90 and the plate thickness t of the chemically strengthened glass satisfy the following relationship of formula (I): Formula (I) CS 90 > 240 × t - 110. In formula (I), CS 90 is in the unit of MPa, and in formula (I), t is in the unit of mm.

[0018] [2] A chemically strengthened glass, which is a plate-shaped chemically strengthened glass. Among them, the value of R obtained by the following formula (II) Na is 0.40 or more. Formula (II) R Na = M StNa / M Na In formula (II), M Na is the integral value of the curve 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 it is the integral 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. In formula (II), M C is the integral value of the curve, and it is the integral value of the region where the detection intensity is greater than the average detection intensity I of Na in the entire plate thickness range of the chemically strengthened glass StNa > I A > I.

[0019] [3] The chemically strengthened glass according to [1] or [2], wherein the absolute value of the first derivative value of the stress curve in the depth direction of the chemically strengthened glass obtained by using a scattered light photoelastic stress meter is less than 2.00 at any depth where the compressive stress value is greater than 0 MPa.

[0020] [4] The chemically strengthened glass according to any one of [1] to [3], wherein the second derivative value of the stress curve in the depth direction of the chemically strengthened glass obtained by using a scattered light photoelastic stress meter is -0.0200 to 0.0200 at any depth where the compressive stress value is greater than 0 MPa.

[0021] [5] The chemically strengthened glass according to any one of [1] to [4], wherein the diffusion depth of K obtained from the curve of the detected intensity of K in the plate thickness direction of the chemically strengthened glass by analysis using an electron probe microanalyzer is 5 μm or more.

[0022] [6] The chemically strengthened glass according to any one of [1] to [5], wherein the compressive stress on the surface of the chemically strengthened glass measured using an optical waveguide surface stress meter is 750 MPa or more.

[0023] [7] The chemically strengthened glass according to any one of [1] to [6], wherein when the chemically strengthened glass is mounted on the largest surface of a 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, and the structure is a rectangular parallelepiped structure made of aluminum alloy with a width of 70 mm, a length of 130 mm, and a thickness of 2 mm, and a mass of 120 g.

[0024] [8] The chemically strengthened glass according to any one of [1] to [7], wherein the compressive stress CS 90 is 10 MPa or more.

[0025] [9] The chemically strengthened glass according to any one of [1] to [8], wherein the Weibull coefficient of the chemically strengthened glass obtained when performing a four-point bending test is 30 or more.

[0026]

[10] A method for manufacturing a chemically strengthened glass, which is a method for manufacturing a chemically strengthened glass that performs at least one K-salt strengthening treatment, and the K-salt strengthening treatment is a chemical strengthening treatment in which chemically strengthening glass is immersed in a molten salt containing a K-salt, wherein

[0027] the content of KNO3 in the molten salt is 70% by mass or more relative to the total mass of the molten salt,

[0028] when the temperature of the molten salt is set to T K and the treatment time of the K-salt strengthening treatment is set to t K for the G value obtained by the following formula (PI), 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 K-salt strengthening treatment is 2.0 to 5.0,

[0029] ,

[0030] in formula (PI), t is the plate thickness of the chemically strengthening glass, and the unit of t is m,

[0031] In formula (PI), T K has the unit of °C,

[0032] In formula (PI), t K has the unit of seconds,

[0033] In formula (PI), E is 125000 J / mol,

[0034] In formula (PI), R is 8.31 J / (K·mol).

[0035]

[11] The method for manufacturing chemically strengthened glass according to

[10] , wherein the chemically strengthened glass is sequentially subjected to a first chemical strengthening treatment and a second chemical strengthening treatment, the internal tensile stress value of the glass after the first chemical strengthening treatment is greater than 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.

[0036]

[12] A protective glass, wherein the protective glass comprises the chemically strengthened glass according to any one of [1] to [9].

[0037] Advantages of the Invention

[0038] According to the present invention, it is possible to provide chemically strengthened glass with excellent drop strength.

[0039] In addition, according to the present invention, it is also possible to provide a method for manufacturing chemically strengthened glass.

[0040] In addition, according to the present invention, it is also possible to provide a protective glass. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 Explanatory drawing of a sample used in the measurement of the fracture toughness value K IC using the DCDC method.

[0042] Figure 2 Graph showing the K1-v curve IC showing the relationship between the stress intensity factor K1 (unit: MPa·m 1 / 2 ) and the crack growth rate v (unit: m / s) DETAILED DESCRIPTION OF THE INVENTION

[0043] Hereinafter, the chemically strengthened glass of the present invention will be described in detail, but 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.

[0044] In this specification, the glass composition is expressed in terms of mole percentages based on oxides, and mole % is sometimes simply denoted as %. Additionally, the symbol "~" indicating a numerical range is used to mean including the values recited before and after it as the lower and upper limits.

[0045] "Substantially free of" in the glass composition means free of, except for inevitable impurities contained in raw materials, etc., that is, not intentionally contained. Specifically, regarding components other than those recited as the glass composition, for example, it is preferably less than 0.1 mole %, more preferably 0.08 mole % or less, and still more preferably 0.05 mole % or less.

[0046] In this specification, "chemically strengthened glass" means glass that has undergone chemical strengthening treatment. Additionally, "glass for chemical strengthening" means glass before chemical strengthening treatment.

[0047] In this specification, a "stress curve" means a curve that represents the compressive stress value from the glass surface to the central part with the depth measured from the glass surface as a variable. Additionally, a negative compressive stress value means a tensile stress.

[0048] The stress curve of the glass can be measured by a scattered light photoelastic stress meter (SLP) and an optical waveguide surface stress meter (FSM).

[0049] In this specification, the stress curve measured by the scattered light photoelastic stress meter (SLP) is called the "SLP stress curve", and the stress curve measured by the optical waveguide surface stress meter (FSM) is called the "FSM stress curve".

[0050] It should be noted that the fiber surface stress meter (FSM) can accurately measure the stress of glass in a short time. As an FSM, for example, there is the FSM-6000 manufactured by Orihara Seisakusho Co., Ltd. However, in principle, the FSM can only measure stress when the refractive index decreases from the specimen surface to the inside. In chemically strengthened glass, the refractive index of the layer obtained by replacing sodium ions inside the glass with external potassium ions decreases from the specimen surface to the inside, so the stress can be measured using the FSM. However, the stress of the layer obtained by replacing lithium ions inside the glass with external sodium ions cannot be accurately measured by the FSM. On the other hand, the method using a scattered light photoelastic stress meter (SLP) can measure stress regardless of the refractive index distribution. As an SLP, for example, the SLP-1000 and SLP-2000 manufactured by Orihara Seisakusho Co., Ltd. can be cited. When the attached software SlpIV_up3 (Ver. 2019.01.10.001) is combined with these scattered light photoelastic stress meters, high-precision stress measurement can be performed. However, the SLP is easily affected by surface scattering, and sometimes the stress near the surface cannot be accurately measured. For the above reasons, by combining and using the two measuring devices of the fiber surface stress meter (FSM) and the scattered light photoelastic stress meter (SLP), accurate stress measurement can be performed within the entire thickness range of the chemically strengthened glass.

[0051] In this specification, the stress curve obtained by synthesizing the information of the SLP and the information of the FSM is called the "synthesized stress curve".

[0052] Regarding the method of using the FSM to measure the stress curve near the surface of the glass, a well-known method can be referred to. In addition, regarding the method of using the SLP to measure the stress curve from the glass surface layer to tens of μm or more inside the glass, a well-known method can be referred to. As the above well-known methods, for example, the methods described in International Publication No. 2018 / 056121 and International Publication No. 2017 / 115811 can be cited.

[0053] The chemically strengthened glass of the present invention can include the following first embodiment and second embodiment.

[0054] Hereinafter, each embodiment will be described.

[0055] <Chemically Strengthened Glass (First Embodiment)>

[0056] The first embodiment of the chemically strengthened glass of the present invention is a plate-shaped chemically strengthened glass. The depth measured from the surface of the chemically strengthened glass (hereinafter, also referred to as "DOL-tail") at which the compressive stress value measured using the fiber surface stress meter (FSM) is 0 MPa is 4.5 μm or more. In addition, the compressive stress at a depth of 90 μm measured using the scattered light photoelastic stress meter (SLP) (hereinafter, also referred to as "CS"90 ”) has the following relationship with the plate thickness t of chemically strengthened glass, which satisfies the following formula (I).

[0057] Formula (I) CS 90 > 240 × t - 110,

[0058] In formula (I), CS 90 is in the unit of MPa.

[0059] In formula (I), t is in the unit of mm.

[0060] By satisfying the above requirements, the first embodiment of the chemically strengthened glass of the present invention has excellent drop strength. Although the mechanism is not yet clear, the present inventors speculate as follows.

[0061] In the first embodiment of the chemically strengthened glass of the present invention, DOL-tail is 4.5 μm or more, so it is considered that a large compressive stress acts on the surface of the chemically strengthened glass.

[0062] In addition, in the first embodiment of the chemically strengthened glass of the present invention, the relationship of the above formula (I) is satisfied. It is considered that satisfying the relationship of formula (I) means that: compared with the plate thickness, the value of CS 90 is large, indicating that the compressive stress acts inside the chemically strengthened glass.

[0063] When a large compressive stress acts on the surface of the chemically strengthened glass, the surface is difficult to be damaged and has a large flexural strength. In addition, it is considered that when the relationship of the above formula (I) is satisfied, even if the surface is damaged, since the compressive stress acts inside the chemically strengthened glass, the damage is difficult to spread and it has a large drop strength.

[0064] As a result, it is considered that the first embodiment of the chemically strengthened glass of the present invention has excellent drop strength.

[0065] Hereinafter, the first embodiment of the chemically strengthened glass of the present invention will be described in detail.

[0066] [Plate Thickness]

[0067] The plate thickness t of the first embodiment of the chemically strengthened glass of the present invention satisfies the relationship of the above formula (I) with CS described below. 90 between them.

[0068] The plate thickness is mostly 2.0 mm or less, preferably 1.5 mm or less, more preferably 1.0 mm or less, further preferably 0.8 mm or less, particularly preferably 0.7 mm or less, and most preferably 0.6 mm or less.

[0069] The plate thickness is preferably 0.2 mm or more, more preferably 0.3 mm or more, and further preferably 0.4 mm or more.

[0070] [FSM Stress Curve]

[0071] In the first embodiment of the chemically strengthened glass of the present invention, in the FSM stress curve, the depth (DOL-tail) measured from the surface of the chemically strengthened glass at the point where the compressive stress value is 0 MPa is 4.5 μm or more.

[0072] From the viewpoint of excellent strength when the chemically strengthened glass is bent, the DOL-tail is preferably 5.0 μm or more, more preferably 5.5 μm or more. The DOL-tail is preferably 13.5 μm or less, more preferably 12.0 μm or less, and further preferably 10.0 μm or less.

[0073] In addition, 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 by FSM is preferably 750 MPa or more, more preferably 800 MPa or more. The above CS0 can be 900 MPa or more, or can be 1000 MPa or more. When the above CS0 increases, the strength when the chemically strengthened glass is bent is more excellent, so it is preferred.

[0074] There is no particular limitation on the upper limit of CS0, and for example, 1500 MPa can be cited.

[0075] The compressive stress (CS1) at a depth of 1 μm of the chemically strengthened glass obtained from the FSM curve is preferably 600 MPa or more, more preferably 700 MPa or more. There is no particular limitation on the upper limit of the above CS1, and for example, 1200 MPa can be cited.

[0076] The compressive stress (CS3) at a depth of 3 μm of the chemically strengthened glass obtained from the FSM curve is preferably 300 MPa or more, more preferably 450 MPa or more. There is no particular limitation on the upper limit of the above CS1, and for example, 900 MPa can be cited.

[0077] [SLP Stress Curve]

[0078] 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 curve satisfies the relationship of the above formula (I) with the plate thickness t of the chemically strengthened glass.

[0079] From the viewpoint of more excellent drop strength, CS 90 is preferably 0 MPa or more, more preferably 10 MPa or more, further preferably 20 MPa or more, and particularly preferably 30 MPa or more. From the viewpoint of further reducing the tensile stress at the center of the plate thickness, CS 90Preferably, it is 100 MPa or less, more preferably 60 MPa or less, and still more preferably 50 MPa or less.

[0080] The value obtained by subtracting the right side (240×t - 110) from the left side (CS 90 ) of the above formula (I) is greater than 0, preferably 1 or more, more preferably 2 or more, and still more preferably 3 or more. The value obtained by subtracting the right side from the left side of the above formula (I) is mostly 20 or less, preferably 12 or less, more preferably 10 or less, and still more preferably 8 or less.

[0081] From the viewpoint of more excellent dropping strength, the compressive stress (CS 50 ) at a depth of 50 μm obtained from the SLP stress curve 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. CS 50 Preferably, it is 200 MPa or less, more preferably 170 MPa or less, and still more preferably 150 MPa or less.

[0082] In addition, regarding the SLP stress curve, when fitting is performed using an appropriate function, the function after fitting can be differentiated, and further analysis related to the SLP stress curve can be performed.

[0083] The fitting of the SLP stress curve can be performed by the following function (formula (FS)).

[0084]

[0085] In the above formula (FS), a i (i = 1 to 5) are fitting parameters, and erfc is the complementary error function. In addition, in the formula (FS), x represents the depth.

[0086] The complementary error function (erfc(x)) is defined by the following formula.

[0087]

[0088] 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, in accordance with the specifications of the attached software, the fitting parameters are optimized by minimizing the sum of the squares of the residuals between the obtained raw data and the above function. The measurement processing conditions are single-shot. Regarding the measurement area processing adjustment items, the edge method is selected for the surface designation, 6.0 μm is selected for the internal surface end designation, automatic is selected for the internal left and right ends designation, automatic (center of the sample film thickness) is selected for the internal deep end designation, and the extension to the center of the sample thickness of the phase curve is selected as the fitting curve.

[0089] The fitted function obtained through the above operation steps can be differentiated once and can be differentiated twice. Hereinafter, the fitted function is denoted as σ f (x).

[0090] When differentiating the above fitted function (σ f (x)) with respect to x (depth), the first derivative σ f ’(x) is obtained. When substituting the value of the depth into σ f ’(x), the slope (first differential value) of σ f (x) at that depth is obtained.

[0091] In the first embodiment of the chemically strengthened glass of the present invention, the absolute value of the above first differential value is preferably less than 2.00 at any depth where σ f (x)>0 (the compressive stress value is greater than 0 MPa), and more preferably 1.95 or less. The absolute value of the above first differential value can be 1.80 or less at any depth, or can be 1.50 or less. It is considered that when the absolute value of the above first differential value is within the above preferred range, the slope of the stress curve as a whole becomes smaller, and the stress is more likely to act on the inside of the chemically strengthened glass, and as a result, the drop strength is more excellent.

[0092] In addition, from the viewpoint of further reducing the tensile stress at the center of the plate thickness, the absolute value of the above first differential value is preferably 0.80 or more, more preferably 1.00 or more, and further preferably 1.20 or more.

[0093] Here, the above "at any depth" means the entire range within the range of the depth at which the SLP stress curve is obtained.

[0094] In addition, when further differentiating the above σ f ’(x) with respect to x, the second derivative σ f ”(x) is obtained. When substituting the value of the depth into σ f ”(x), the value corresponding to the curvature of σ f (x) at that depth (second differential value) is obtained.

[0095] In the first embodiment of the chemically strengthened glass of the present invention, the above second differential value is preferably -0.0200 or more at any depth where σ f (x)>0 (the compressive stress value is greater than 0 MPa), more preferably -0.0180 or more, and further preferably -0.0160 or more. In addition, the above second differential value is preferably 0.0200 or less. The above second differential value can be 0.0160 or less, or can be 0.0130 or less, or can also be 0.0110 or less.

[0096] When the second-order differential value is within the above-mentioned preferred range, it indicates that the stress curve represents a linear shape.

[0097] It should be noted that it is preferably to satisfy both the preferred range of the absolute value of the first-order differential value and the preferred range of the second-order differential value mentioned above.

[0098] In the first embodiment of the chemically strengthened glass of the present invention, since compressive stress acts on the surface, tensile stress that balances it acts inside the chemically strengthened glass.

[0099] From the viewpoint that fragments are more difficult to scatter when the glass is broken, 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 still more preferably 130 MPa or less. CT Max There is no particular limitation on the lower limit of CT, and it is mostly 10 MPa or more.

[0100] CT Max is obtained from the SLP stress curve and usually acts at the central position of the plate thickness.

[0101] From the viewpoint that fragments are more difficult to scatter when the glass is broken, 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 still more preferably 90 MPa or less. CT ave There is no particular limitation on the lower limit of CT, and it is mostly 10 MPa or more.

[0102] The average value of the tensile stress is obtained by averaging the values of the tensile stress in the region representing the depth of the tensile stress according to the SLP stress curve.

[0103] In this specification, the depth of compressive stress (DOC) is the depth at which the compressive stress value is 0 MPa in the SLP stress curve.

[0104] 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 still more preferably 100 μm or more. From the viewpoint of easily adjusting the maximum value and the average value of the tensile stress to the above-mentioned preferred ranges, the upper limit of DOC is preferably 200 μm, more preferably 150 μm, and still more preferably 140 μm.

[0105] [Analysis using an electron probe microanalyzer]

[0106] For a first embodiment of chemically strengthened glass, when analysis using an electron probe microanalyzer (EPMA) is performed, the elemental distribution of each element in the plate thickness direction (depth direction) of the chemically strengthened glass can be obtained.

[0107] In the present invention, the distribution of the detection intensity of each element in the plate thickness direction of the chemically strengthened glass (hereinafter, also referred to as "elemental distribution") is obtained by the following method.

[0108] First, the chemically strengthened glass is embedded in resin, a cross-section is made using 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.

[0109] The analysis using EPMA uses JXA-8500F manufactured by JEOL. In the analysis using 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 below.

[0110] Through the above measurement, the elemental distribution in the plate thickness direction of the chemically strengthened glass was obtained. It should be noted that the horizontal axis of the above elemental distribution is depth (μm), and the vertical axis is detection intensity (cps).

[0111] The above elemental distribution can be obtained, for example, for K (potassium). Hereinafter, the elemental distribution obtained for K is referred to as the "K curve".

[0112] Regarding the first embodiment of the chemically strengthened glass of the present invention that has undergone chemically strengthening treatment including a K salt, when the above K curve is obtained, in most cases, a K curve is obtained in which the detection intensity of K gradually decreases from near the surface of the chemically strengthened glass toward the center of the plate thickness, and the detection intensity of K is substantially constant in the range from a specified depth to the center position of the plate thickness. In the above K curve, in most cases, the detection intensity of K at the depth at the center of the plate thickness is the detection intensity corresponding to the content of K in the glass before chemically strengthening treatment (chemically strengthening glass).

[0113] Here, the following situation is considered: in the above K curve, the detection intensity of K gradually decreases from near the surface of the chemically strengthened glass toward the center of the plate thickness, and the detection intensity of K is substantially constant in the range from a specified depth to the center position of the plate thickness. In such a case, the diffusion depth of K can be calculated from the K curve. Specifically, when the average value of the detection intensity of K at a depth with a width of 20 μm at the center of the plate thickness is set as I C_K and the standard deviation of the detection intensity of K within the above range is set as σ C_K and the detection intensity of K on the surface of the chemically strengthened glass is set as I S_KWhen, the diffusion depth of K is calculated by the following method.

[0114] First, obtain the above-mentioned I C_K , σ C_K and I S_K values. Then, 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 curve, obtain the depth at which the detection intensity ratio I C_K is higher than the above-mentioned I diff_K by a value of 3×σ C_K . Take the depth obtained through the above steps as the diffusion depth of K. The depth obtained in the above operation steps corresponds in the K curve to the depth at which the detection intensity of K starts to rise from the detection intensity of K at the center position of the plate thickness.

[0115] In addition, the above element distribution can be obtained for Na (sodium). Hereinafter, the element distribution obtained for Na is referred to as the "Na curve".

[0116] Regarding the Na curve of the first embodiment of the chemically strengthened glass of the present invention, the value of R Na obtained in formula (II) described later is preferably 0.40 or more. The calculation method and preferred range of the value of R Na are the same as those described in the second embodiment later, so the description is omitted.

[0117] [Drop strength]

[0118] The drop strength of the first embodiment of the chemically strengthened glass of the present invention is excellent.

[0119] The drop strength can be measured by the following operation steps.

[0120] First, prepare a rectangular parallelepiped-shaped structure made of aluminum alloy with a width of 70 mm, a length of 130 mm, and a thickness of 2 mm, and its mass is 120 g. The above structure simulates a mobile device such as a smart phone.

[0121] Next, install the chemically strengthened glass on the widest surface of the above structure. Use a 0.5 mm adhesive tape to install the chemical strengthening on the structure.

[0122] Next, let the structure with the chemically strengthened glass installed fall onto the abrasive surface of #80 sandpaper with silicon carbide as the abrasive. The above drop is performed with the side of the structure with the chemically strengthened glass facing the above sandpaper. When dropping, confirm whether the chemically strengthened glass breaks, change the dropping height, and record the height at which breakage first occurs as an index of the drop strength. Hereinafter, the above height at which breakage first occurs is referred to as the "#80SP break height".

[0123] The rupture height of the above-mentioned #80SP is preferably 62.3×t + 2.9 cm or more, more preferably 62.3×t + 7.9 cm or more. Here, t is the plate thickness in mm.

[0124] In addition, except that the sandpaper used when obtaining the rupture height of the above-mentioned #80SP is set to #180, the above height can also be an index of the drop strength in the same manner as the method for obtaining the rupture height of #80SP when obtaining the height at which rupture first occurs. Hereinafter, when the above test is performed with #180 sandpaper, the height at which rupture first occurs is referred to as the "#180 SP rupture height".

[0125] The rupture height of the above-mentioned #180 SP is preferably 86.1×t + 7.7 cm or more, more preferably 86.1×t + 12.7 cm or more. Here, t is the plate thickness in mm.

[0126] [Flexural strength]

[0127] The first embodiment of the chemically strengthened glass of the present invention preferably has excellent flexural strength.

[0128] The flexural strength of the chemically strengthened glass in this specification refers to the flexural strength obtained in a four-point bending test. For the specific method, refer to the description in the examples section later.

[0129] The above flexural strength is preferably 750 MPa or more, more preferably 800 MPa or more, and most preferably 850 MPa or more.

[0130] In addition, in the strength test of materials such as ceramics, when the cumulative failure probability is set to P, sometimes analysis is performed on a Weibull probability paper in which the natural logarithm of the fracture strength is taken on the horizontal axis and ln(ln(1 / (1 - P))) is taken on the vertical axis. On the above Weibull probability paper, when a linear plot is obtained, it can be judged that it follows the Weibull distribution, and its slope is the Weibull coefficient (generally denoted as "m").

[0131] Prepare the same samples and repeatedly perform the above four-point bending test. When the obtained results are plotted on a Weibull probability paper, the Weibull coefficient is obtained. In this specification, in the plotting on the Weibull probability paper, the natural logarithm of the flexural strength of the four-point bending test is taken on the horizontal axis.

[0132] The Weibull coefficient obtained using the results of the four-point bending test is preferably 30 or more, more preferably 40 or more, further preferably 50 or more, and particularly preferably 60 or more. There is no particular limitation on the upper limit of the Weibull coefficient, and for example, 100 can be cited.

[0133] It should be noted that the above Weibull coefficient is understood as an index of the variation in strength. The larger the Weibull coefficient, the smaller the variation in strength.

[0134] [Composition]

[0135] The first embodiment of the chemically strengthened glass of the present invention is obtained by chemically strengthening a plate-shaped glass (glass for chemical strengthening) before chemical strengthening.

[0136] Hereinafter, the preferred composition of the glass for chemical strengthening (hereinafter also referred to as "matrix glass composition") will be described. It should be noted that the matrix glass composition is the same as the composition at the central position of the plate thickness of the chemically strengthened glass.

[0137] The matrix glass composition preferably contains Li (lithium), and is preferably an aluminosilicate glass containing Li, Si, and Al.

[0138] More specifically, in terms of mol% based on oxides, the matrix glass composition preferably contains 52% to 75% of SiO2, 8% to 20% of Al2O3, and 5% to 16% of Li2O.

[0139] Hereinafter, the preferred matrix glass composition will be described. It should be noted that hereinafter, for example, the content of SiO2 in terms of mol% based on oxides may sometimes be referred to as "[SiO2]".

[0140] SiO2 is a component that constitutes the glass skeleton. In addition, SiO2 is a component that improves chemical durability and is a component that reduces the generation of cracks when the glass surface is damaged.

[0141] 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.

[0142] From the viewpoint of improving the ion exchange performance during chemical strengthening and increasing the surface compressive stress after strengthening, Al2O3 is an effective component.

[0143] 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, when the content of Al2O3 is too high, crystals are likely to grow during melting, and the yield is likely to decrease due to devitrification defects. In addition, 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.

[0144] Both SiO2 and Al2O3 are components that stabilize the structure of the glass. To reduce brittleness, the total content of SiO2 and Al2O3 is preferably 65% or more, more preferably 70% or more, and still more preferably 75% or more.

[0145] Li2O is a component that forms surface compressive stress through ion exchange and is a component that improves the meltability of the glass. By including Li2O in the base glass composition, surface compressive stress can be introduced by ion-exchanging lithium ions on the glass surface with sodium ions and then further ion-exchanging sodium ions with potassium ions. From the viewpoint of easily obtaining a preferable stress distribution, 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.

[0146] On the other hand, when the content of Li2O is excessive, the crystal growth rate during glass forming increases, and sometimes the problem of a decrease in the yield due to devitrification defects becomes significant. 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.

[0147] Neither Na2O nor K2O is essential, but Na2O and K2O are components that improve the meltability of the glass and reduce the crystal growth rate of the glass. To improve the ion exchange performance, it is preferably contained in a total amount of 2% or more. In addition, the total amount 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.

[0148] Na2O is a component that forms a surface compressive stress layer in chemical strengthening treatment using potassium salts and is a component that can improve the meltability of the glass. To obtain this 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 viewpoint of avoiding a decrease in the surface compressive stress (CS) in the strengthening treatment using sodium salts and also increasing CS 90 the content of Na2O is preferably 8% or less, more preferably 7% or less, still more preferably 6% or less, and particularly preferably 5% or less.

[0149] K2O may be contained for the purpose of improving ion exchange performance or the like. When K2O is contained, the content of K2O is preferably 0.1% or more, more preferably 0.15% or more, and particularly preferably 0.2% or more. To further prevent devitrification, the content of K2O is preferably 0.5% or more, more preferably 1.2% or more. On the other hand, when a large amount of K is contained, sometimes the surface layer stress decreases due to brittleness and reverse exchange during strengthening, and thus the content of K2O is preferably 5% or less, more preferably 3% or less.

[0150] The total of the contents of Li2O, Na2O, and K2O, namely R, is preferably 5% or more, more preferably 8% or more, further preferably 10% or more, and particularly preferably 12% or more. The above R is preferably 25% or less, more preferably 20% or less.

[0151] From the viewpoint of further improving the chemical strengthening characteristics of the compressive stress in the deep part, the ratio of the content of Li2O to the above R ([Li2O] / ([Li2O]+[Na2O]+[K2O]), also referred to as "Li2O / R2O" below) is more preferably 0.52 or more, and further preferably 0.55 or more. From the viewpoint of further improving the chemical durability, Li2O / R2O is more preferably 0.80 or less, further preferably 0.78 or less, and particularly preferably 0.75 or less.

[0152] From the viewpoint of further improving the chemical strengthening characteristics of the compressive stress in the deep part, the ratio of the content of Na2O to the above R ([Na2O] / ([Li2O]+[Na2O]+[K2O]), also referred to as "Na2O / R2O" below) is preferably 0.05 or more, more preferably 0.08 or more, and further preferably 0.10 or more. From the viewpoint of further improving the chemical durability, Na2O / R2O is preferably 0.60 or less, more preferably 0.50 or less, further preferably 0.40 or less, and particularly preferably 0.30 or less.

[0153] From the viewpoint of further improving the resistance of the glass, the ratio of the content of K2O to the above R ([K2O] / ([Li2O]+[Na2O]+[K2O]), also referred to as "K2O / R2O" below) is preferably 0.05 or more, more preferably 0.08 or more, and further preferably 0.10 or more. From the viewpoint of further improving the chemical strengthening characteristics of the compressive stress near the surface, K2O / R2O is preferably 0.50 or less, more preferably 0.40 or less, further preferably 0.30 or less, and particularly preferably 0.20 or less.

[0154] In addition, from the viewpoint of suppressing the rise of the devitrification temperature, the product of Li2O / R2O, Na2O / R2O, and K2O / R2O is preferably 0.005 or more, more preferably 0.008 or more, and further preferably 0.010 or more. In addition, from the viewpoint of improving the chemical properties, the above product is preferably 0.030 or less, more preferably 0.028 or less.

[0155] The content ratio of Al2O3 to R as described above ([Al2O3 / ([Li2O]+[Na2O]+[K2O])]), hereinafter also referred to as "Al2O3 / R2O"), is preferably 0.20 or more, more preferably 0.30 or more, further 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, further preferably 0.85 or less.

[0156] MgO may be contained to reduce the viscosity during melting, etc. The content of MgO is preferably 0.5% or more, more preferably 1% or more, further preferably 2% or more, and particularly preferably 3% or more. On the other hand, when the content of MgO is excessive, it is sometimes difficult to increase the compressive stress layer during chemical strengthening treatment. The content of MgO is preferably 15% or less, more preferably 10% or less, further preferably 8% or less, and particularly preferably 6% or less.

[0157] ZrO2 may not be contained, but from the viewpoint of increasing the surface compressive stress of chemically strengthened glass, ZrO2 is preferably contained. The content of ZrO2 is preferably 0.1% or more, more preferably 0.15% or more, further preferably 0.2% or more, particularly preferably 0.25% or more, and typically 0.3% or more. On the other hand, when the content of ZrO2 is excessive, devitrification defects are likely to occur, and it is sometimes difficult to increase the compressive stress value during chemical strengthening treatment. The content of ZrO2 is preferably 2% or less, more preferably 1.5% or less, further preferably 1% or less, and particularly preferably 0.8% or less.

[0158] The content of Y2O3 is preferably 0.1% or more, more preferably 0.2% or more, further preferably 0.5% or more, and particularly preferably 1% or more. On the other hand, when the content of Y2O3 is excessive, it is sometimes difficult to increase the compressive stress layer during chemical strengthening treatment. The content of Y2O3 is preferably 5% or less, more preferably 3% or less, further preferably 2% or less, and particularly preferably 1.5% or less.

[0159] The composition of the chemically strengthened glass for chemical strengthening (matrix glass composition) is preferably the above-described composition.

[0160] The method for obtaining the chemically strengthened glass having the matrix 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 can be appropriately formulated, heated and melted in a glass melting furnace, and then the glass is homogenized by bubbling, stirring, adding a fining agent, etc., formed into a glass plate with a specified thickness, and slowly cooled. Alternatively, it can also be formed into a plate shape by forming it into a block and slowly cooling, and then cutting.

[0161] As a method of forming into a plate shape, for example, the float process, the pressing process, the fusion process, and the down-draw process can be cited. Particularly in the case of manufacturing a large glass plate, the float process is preferred. In addition, a continuous forming process other than the float process, such as the fusion process and the down-draw process, is also preferred.

[0162] In addition, the glass for chemical strengthening can be a glass-ceramic. When the glass for chemical strengthening is a glass-ceramic, a glass-ceramic 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 crystal, lithium metasilicate crystal, lithium disilicate crystal, etc. are preferred. As the lithium phosphate crystal, lithium orthophosphate crystal, etc. are preferred. As the lithium aluminosilicate crystal, β-spodumene crystal, petalite crystal, etc. are preferred.

[0163] From the viewpoint of improving mechanical strength, the crystallization rate of the glass-ceramic is preferably 10% or more, more preferably 15% or more, further preferably 20% or more, and particularly preferably 25% or more. In addition, in order to improve transparency, the crystallization rate of the glass-ceramic is preferably 70% or less, more preferably 60% or less, further preferably 50% or less. From the viewpoints of being easily bend-formed by heating, etc., a small crystallization rate is excellent. The crystallization rate can be calculated from the X-ray diffraction intensity by the Rietveld method. Regarding the Rietveld method, it is described in "Crystal Analysis Handbook" (published by Kyoritsu Shuppan, 1999, pages 492 to 499) edited by the Editorial Committee of "Crystal Analysis Handbook" of the Crystallographic Society of Japan.

[0164] In order to improve transparency, the average particle diameter of the precipitated crystals of the glass-ceramic is preferably 300 nm or less, more preferably 200 nm or less, further preferably 150 nm or less, and particularly preferably 100 nm or less. The average particle diameter of the precipitated crystals can be determined from a transmission electron microscope (TEM) image. In addition, it can be estimated from a scanning electron microscope (SEM) image.

[0165] The Young's modulus of the glass for chemical strengthening is preferably 80 GPa or more, more preferably 83 MPa or more.

[0166] In addition, 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, further preferably 0.80 MPa·m 1 / 2 or more. The fracture toughness value K IC is mostly 2.00 MPa·m 1 / 2 or less, preferably 1.80 MPa·m 1 / 2 or less.

[0167] In this specification, "the fracture toughness value K IC"Measurement was carried out according to the reference DCDC method [References: M.Y. He, M.R. Turner and A.G. Evans, Acta Metad. Mater. 43(1995)3453.]. Specifically, using Figure 1 samples of the shape shown and SHIMADZU Autograph AGS-X5KN, the stress intensity factor K1 (unit: MPa·m Figure 2 shown) representing the relationship with the crack growth rate v (unit: m / s) of the K1-v curve was measured. The data of Region III obtained were regressed and extrapolated by a linear equation, and the stress intensity factor K1 at 0.1 m / s was taken as the fracture toughness value K 1 / 2 . IC .

[0168] <Chemically strengthened glass (second embodiment)>

[0169] The second embodiment of the chemically strengthened glass of the present invention is a plate-shaped chemically strengthened glass, and the value of R obtained by the following formula (II) Na is 0.40 or more.

[0170] Formula (II) R Na = M StNa / M Na

[0171] In formula (II), M Na is the integral value of the curve 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 integral value of the region where the detection intensity is larger than the detection intensity I of Na at the center position of the plate thickness. C

[0172] In formula (II), M StNa is the integral value of the curve of the detection intensity of Na, and is the integral value of the region where the detection intensity is larger than the average detection intensity I of Na in the entire plate thickness range of the chemically strengthened glass. A

[0173] The second embodiment of the chemically strengthened glass of the present invention has excellent drop strength by satisfying the above requirements. The mechanism is not yet clear, but the present inventors speculate as follows.

[0174] 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), it is considered that the value of M Na corresponds to the total amount of Na ions introduced into the chemically strengthened glass by ion exchange during chemical strengthening. On the other hand, it is considered that M StNa ​​The value corresponds to the amount of Na ions in the depth region where the average detection intensity is exceeded. Here, in chemically strengthened glass, it is considered that compressive stress acts in the region where the content of Na ions is more than the average content of Na ions.

[0175] Therefore, it is considered that R represented by the formula (II) Na represents the ratio of the amount of Na ions contributing to the generation of compressive stress among the Na ions introduced by ion exchange. If that is the case, a large compressive stress acts on the surface of the chemically strengthened glass that satisfies the relationship of the above formula (II).

[0176] In addition, it is considered that when the relationship of the above formula (II) is satisfied, it means that most of the Na ions are introduced into the interior of the chemically strengthened glass by the chemical strengthening treatment until the internal compressive stress of the chemically strengthened glass acts.

[0177] Therefore, it is considered that when the relationship of the above formula (II) is satisfied, a large compressive stress acts so that the surface is difficult to be damaged. In addition, even if the surface is damaged, until the internal compressive stress of the chemically strengthened glass acts, the damage is difficult to spread.

[0178] As a result, it is considered that the drop strength of the second embodiment of the chemically strengthened glass of the present invention is excellent.

[0179] Hereinafter, the second embodiment of the chemically strengthened glass of the present invention will be described in detail.

[0180] Analysis using an electron probe microanalyzer

[0181] For the second embodiment of the chemically strengthened glass, when 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.

[0182] It should be noted that the analysis method of EPMA is the same as that of the first embodiment, so the description is omitted. In addition, the names such as "K curve" and "Na curve" are also the same as above, so the description is omitted.

[0183] In the second embodiment of the chemically strengthened glass of the present invention, as described above, regarding the Na curve, R obtained from the following formula (II) Na is 0.40 to 0.60.

[0184] Formula (II) R Na = M StNa / M Na

[0185] In the formula (II), M Na As described above, is the detection intensity ratio of Na at the center position of the plate thickness to the detection intensity I of Na CThe integrated value of a large area. More specifically, M Na is the detected intensity I of Na at the central depth position of the plate thickness in the Na curve C as the baseline, and for the area where the detected intensity is greater than the detected intensity I C value, it is the value obtained by integrating the detected intensity of the Na curve for the area where the detected intensity is greater than the detected intensity I

[0186] In formula (II), M StNa As described above, it is the integrated value of the area where the detected intensity is greater than the average detected intensity I of Na in the entire plate thickness range of the chemically strengthened glass A More specifically, M StNa is when the average detected intensity of Na in the entire plate thickness range of the chemically strengthened glass in the Na curve is set to I A At this time, taking the value of I A as the baseline, for the area where the detected intensity is greater than the average detected intensity I A value, it is the value obtained by integrating the detected intensity of the Na curve for the area where the detected intensity is greater than the average detected intensity I

[0187] In addition, the above integrated value is obtained by the sum of the product of the data interval in the depth direction and the detected intensity of Na at each depth

[0188] The above R Na is preferably 0.41 or more, more preferably 0.42 or more. The upper limit of the above R Na is 0.60, preferably 0.55

[0189] Except for the above points, the preferred embodiments of the chemically strengthened glass of the present invention are the same as those of the first embodiment

[0190] <Method for manufacturing chemically strengthened glass>

[0191] The method for manufacturing the chemically strengthened glass of the present invention is a method for manufacturing a chemically strengthened glass that performs at least one K-salt strengthening treatment, and the K-salt strengthening treatment is a chemical strengthening treatment in which the glass for chemical strengthening is immersed 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

[0192] In addition, when the temperature of the molten salt is set to T K and the treatment time of the K-salt strengthening treatment is set to t K At this time, the G value obtained by the following formula (PI) satisfies the specified requirements. 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

[0193]

[0194] In formula (PI), t is the plate thickness of the chemically strengthened glass, and the unit of t is m.

[0195] In formula (PI), T K is in the unit of °C.

[0196] In formula (PI), t K is in the unit of seconds.

[0197] In formula (PI), E is 125000 J / mol.

[0198] In formula (PI), R is 8.31 J / (K·mol).

[0199] According to the manufacturing method of the chemically strengthened glass of the present invention, the above-mentioned chemically strengthened glass of the present invention (the first embodiment and the second embodiment) can be obtained.

[0200] In the manufacturing method of the chemically strengthened glass of the present invention, the K-salt strengthening treatment is carried out in such a manner 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, the treatment temperature, and the plate thickness of the chemically strengthened glass in the K-salt strengthening treatment. When the G value or the total value of the G values is 2.0 or more, it corresponds to carrying out the K-salt strengthening treatment at a high temperature, or for a long time, or at a high temperature and for a long time as compared with the plate thickness of the chemically strengthened glass. It is considered that in this case, the ions introduced by the chemical strengthening treatment are easily diffused into the interior of the chemically strengthened glass, and it is easy for the internal compressive stress of the chemically strengthened glass to take effect until the interior.

[0201] 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 into the interior of the chemically strengthened glass more than necessary, and in addition, the state where the stress introduced due to the introduction of heat is not alleviated can be adjusted.

[0202] The preferred mode of the chemically strengthened glass used in the manufacturing method of the chemically strengthened glass of the present invention is the same as the chemically strengthened glass described in the first embodiment of the chemically strengthened glass of the present invention, and thus the description is omitted.

[0203] It should be noted that the manufacturing method of the chemically strengthened glass of the present invention can perform chemical strengthening treatments other than the above K-salt strengthening treatment (hereinafter, also referred to as "other chemical strengthening treatments").

[0204] Hereinafter, the chemical strengthening treatment will be described.

[0205] [Chemical strengthening treatment]

[0206] In the method for manufacturing chemically strengthened glass of the present invention, chemical strengthening treatment is performed on the glass for chemical strengthening. In the above chemical strengthening treatment, at least one K-salt strengthening treatment is performed.

[0207] Through the chemical strengthening treatment, components in the glass for chemical strengthening (such as Li ions and Na ions, etc.) are exchanged with the ions contained in the molten salt used in the chemical strengthening treatment. Due to the difference in the ionic radius of the ions before exchange and the ionic radius of the ions after exchange, a layer with compressive stress is formed.

[0208] The chemical strengthening treatment can be performed only once or can be performed in multiple times. It should be noted that in the case where the chemical strengthening treatment is performed only once, the chemical strengthening treatment is a K-salt strengthening treatment.

[0209] As described above, the content of KNO3 in the molten salt containing K (hereinafter also referred to as "K-containing molten salt") used in the K-salt strengthening treatment is 70% by mass or more relative to the total mass of the K-containing molten salt. Relative to 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 further preferably 95% by mass or more. Relative to the total mass of the K-containing molten salt, the content of KNO3 in the K-containing molten salt can be 100% by mass.

[0210] The K-containing molten salt can contain components other than KNO3. As components other than KNO3, for example, K salts, Na salts, and Li salts other than KNO3 (potassium nitrate) can be cited. More specifically, as K salts other than potassium nitrate, for example, potassium sulfate, potassium carbonate, and potassium chloride can be cited. As Na salts, for example, sodium nitrate, sodium sulfate, sodium carbonate, and sodium chloride, etc. can be cited. As Li salts, for example, lithium nitrate, lithium sulfate, lithium carbonate, and lithium chloride can be cited.

[0211] In addition, as components other than KNO3, for example, Rb (rubidium) salts, Cs (cesium) salts, and Ag (silver) salts, etc. can be cited.

[0212] In the case where 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 relative to the total mass of the K-containing molten salt. In the case where 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 relative to the total mass of the K-containing molten salt.

[0213] The K-salt strengthening treatment can be carried out by adjusting the conditions such that the above G value or the total value of the G values is 2.0 to 5.0.

[0214] The temperature of the K-salt strengthening treatment (T in the above formula (PI)) K)Preferably, it is 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 can be 400 °C or lower.

[0215] The time of the K-salt strengthening treatment (t in the above formula (PI)) K )Preferably, it is 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 mostly 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 can be 360 minutes or shorter or 240 minutes or shorter.

[0216] The above G value or the total value of the G values is preferably 2.2 or higher, more preferably 2.3 or higher. In addition, 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.

[0217] The K-salt strengthening treatment is preferably the chemical strengthening treatment finally carried out in the chemical strengthening treatment. Finally carrying out the K-salt strengthening treatment means that no other chemical strengthening treatment is carried out after the K-salt strengthening treatment.

[0218] In the method for manufacturing the chemically strengthened glass of the present invention, a chemical strengthening treatment (other chemical strengthening treatment) other than the K-salt strengthening treatment can be carried out.

[0219] In the other chemical strengthening treatment, a molten salt other than the above-mentioned K-containing molten salt (hereinafter also referred to as "other molten salt") is used.

[0220] The other molten salt refers to a molten salt in which the content of KNO3 is less than 70% by mass relative to the total mass of the molten salt. Therefore, the other molten salt can contain KNO3.

[0221] 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. In addition, the other molten salt can contain salts other than the above (for example, Rb (rubidium) salts, Cs (cesium) salts, and Ag (silver) salts, etc.).

[0222] 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 relative to the total mass of the other molten salt. When the other molten salt contains sodium nitrate, the content of sodium nitrate can be 100% by mass relative to the total mass of the other molten salt.

[0223] When other molten salts contain Na salts, it is easier to obtain the chemically strengthened glass of the present invention (the first embodiment and the second embodiment).

[0224] In the case of performing other chemical strengthening treatments, the temperature of the other chemical strengthening treatment is preferably 350 °C or higher, more preferably 380 °C or higher, and further preferably 400 °C or higher. The temperature of the other chemical strengthening treatment is mostly 500 °C or lower, preferably 450 °C or lower, and more preferably 430 °C or lower.

[0225] In the case of performing other chemical strengthening treatments, the time of the other chemical strengthening treatment is preferably 10 minutes or longer, more preferably 30 minutes or longer, and further preferably 60 minutes or longer. The time of the other chemical strengthening treatment is mostly 480 minutes or shorter, preferably 420 minutes or shorter, and more preferably 360 minutes or shorter. The time of the other chemical strengthening treatment can be 120 minutes or shorter, or can be 90 minutes or shorter.

[0226] After performing the above other chemical strengthening treatment, performing the above K salt strengthening treatment is also one of the preferred methods. When performing the chemical strengthening treatment according to the above operation steps, the ions (such as Na ions) that have undergone ion exchange in the other chemical strengthening treatment are likely to diffuse into the interior of the glass for chemical strengthening during the K salt strengthening treatment, so it is preferred.

[0227] In the manufacturing method of the chemically strengthened glass of the present invention, the K salt strengthening treatment is performed 1 time or more, 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 can be 1 time.

[0228] In addition, in the case of performing other chemical strengthening treatments in the manufacturing method of the 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 further preferably 1 time.

[0229] In addition, in the manufacturing method of the chemically strengthened glass of the present invention, consider the case of sequentially performing the first chemical strengthening treatment and the second chemical strengthening treatment. At this time, it is preferred 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.

[0230] In this specification, the CT limit of the glass for chemical strengthening means the internal tensile stress value at which the number of fragments per 4.0 cm 2 is 10 or more.

[0231] "Per 4.0 cm 2"The internal tensile stress value with 10 or more fragments" is first tested with a diamond indenter on a platform, and every 4.0 cm when delayed fracture occurs 2 The state where the number of fragments is greater than 10.

[0232] When the requirements related to the above CT limit are met, the second chemical strengthening treatment is preferably the above K-salt strengthening treatment. In addition, at this 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 based on other molten salts containing Na salts.

[0233] <Use>

[0234] The chemically strengthened glass (first embodiment and second embodiment) of the present invention is useful as a protective glass, for example. In particular, it is useful as a protective glass for mobile devices such as mobile phones, smartphones, portable information terminals (PDAs), and tablet terminals. In addition, it is also useful for protective glasses of display devices such as televisions (TVs), personal computers (PCs), and touch panels that are not for the purpose of portability, elevator wall surfaces, wall surfaces of buildings such as houses and buildings (full-screen displays), building materials such as window glass, and interiors of desks, automobiles, and airplanes. In addition, it is also useful as a protective glass for the above items. Furthermore, through bending processing and bending forming, it can be applied to uses such as a housing having a curved surface shape.

[0235] Examples

[0236] Hereinafter, the present invention will be described in more detail based on examples.

[0237] The materials, usage amounts, ratios, treatment contents, treatment steps, 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 restrictively by the examples shown below.

[0238] It should be noted that Examples 1 to 7, 11, and 12 are examples, and Examples 8 to 10 are comparative examples.

[0239] <Production of Chemically Strengthened Glass>

[0240] First, glass was produced by melting glass raw materials in a platinum crucible in such a manner that each glass composition was in terms of molar percentage based on the oxide standard shown in Table 1.

[0241] Specifically, oxides, hydroxides, carbonates, nitrates, etc. used in the glass raw materials were appropriately selected from commonly used glass raw materials and weighed so that the glass reached 1000 g.

[0242] Next, the mixed raw materials were placed in a platinum crucible and put into a resistance heating electric furnace at 1500 °C to 1700 °C, melted for about 3 hours, degassed and homogenized to obtain molten glass. The obtained molten glass was poured into a mold material, held at a temperature of the glass transition temperature + 50 °C for 1 hour, and then cooled to room temperature at a rate of 0.5 °C / minute to obtain a glass block. The obtained glass block was cut and ground to produce a plate-shaped glass. The two surfaces of the obtained plate-shaped glass were mirror-finished, and finally a plate-shaped glass with a length of 120 mm × a width of 60 mm × a plate thickness of 0.6 mm was obtained. In addition, according to the examples, a plate-shaped glass with a plate thickness of 0.55 mm, a plate-shaped glass with a plate thickness of 0.5 mm, or a plate-shaped glass with a plate thickness of 0.7 mm was obtained.

[0243]

[0244] For each of the plate-shaped glasses obtained in the above operation steps, chemical strengthening treatment was carried out under the conditions described in Table 2, and thus chemically strengthened glasses of Examples 1 to 12 were obtained.

[0245] <Measurement and Evaluation>

[0246] [Measurement Using EPMA]

[0247] Using the obtained chemically strengthened glass, a measurement sample was prepared according to the above operation steps, and analyzed using EPMA (JXA-8500F manufactured by JEOL) to obtain a Na curve and a Si curve.

[0248] The measurement conditions of EPMA and the like are as follows.

[0249] · Spectrometer crystal: PETJ (K-Kα), TAPH (Na-Kα)

[0250] · Electron beam acceleration voltage: 15 kV

[0251] · Irradiated electron beam current: 30 nA

[0252] · Accumulation time: 1000 msec / electron

[0253] · Measurement point interval: 1 μm

[0254] [Bending Strength Test]

[0255] In the bending strength test, the chemically strengthened glass was subjected to a four-point bending test.

[0256] The four-point bending test was carried out in accordance with JIS-R1601:2008 (4PB test). The four-point bending test device used the bench-type precision universal testing machine Autograph AGS-10kNX manufactured by Shimadzu Corporation. In order to evaluate the entire damaged area, the span of the bending test was 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 / minute. The fracture stress was obtained from the measurement results of the load at which fracture occurred.

[0257] The above-mentioned fracture stress was measured for 10 samples, and the arithmetic mean of the measured fracture stresses was taken as the average fracture stress.

[0258] In addition, the data obtained during the above-mentioned measurement was plotted on Weibull probability paper, and the Weibull coefficient was obtained from the slope of this straight line. The calculation method of the Weibull coefficient is as described above.

[0259] [Drop Strength Test]

[0260] According to the above operation steps, the drop strength of the chemically strengthened glass for each case was measured. That is, the fracture heights of #80SP and #180SP were measured.

[0261] The detailed measurement steps are as described above.

[0262] [Results]

[0263] The conditions of the chemical strengthening treatment, the above-mentioned measurement results, and the above-mentioned evaluation results of the chemically strengthened glass for each case are shown in Table 2 below.

[0264] In Table 2, the measurement methods of the values in the "FSM curve" column and the "SLP curve" column are as described above.

[0265]

[0266] From the results shown in Table 2, it can be confirmed that the drop strength of the chemically strengthened glass of Examples 1 to 7, Example 11, and Example 12, whose DOL-tail is 4.5 μm or more and satisfies the relationship of the above formula (I), is more excellent than that of the chemically strengthened glass of Examples 8 to 10.

Claims

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

2. A chemically strengthened glass, which is a plate-shaped chemically strengthened glass, wherein: R is obtained from the following formula (II): Na The value is 0.40~0.60, Formula (II) R Na =M StNa / M Na , In formula (II), M Na is the integral value of the curve of the Na detection intensity in the plate thickness direction of the chemically strengthened glass obtained by analysis using an electron probe microanalyzer, which is the ratio of the Na detection intensity I at the center of the plate thickness to the Na detection intensity I C The integral value of a large area, In formula (II), M StNa is the integral value of the curve, which is the average detection intensity I of Na in the entire thickness range of the chemically strengthened glass. A The integral value of a large area.

3. The chemically strengthened glass according to claim 1 or 2, wherein: The absolute value of the first-order differential value of the stress curve in the depth direction of the chemically strengthened glass obtained using a scattered light photoelastic stress meter is less than 2.00 at any depth where the compressive stress value is greater than 0 MPa.

4. The chemically strengthened glass according to claim 1 or 2, wherein: The second-order differential value of the stress curve in the depth direction of the chemically strengthened glass obtained using a scattered light photoelastic stress meter was -0.0200 to 0.0200 at any depth where the compressive stress value was greater than 0 MPa.

5. The chemically strengthened glass according to claim 1 or 2, wherein: The diffusion depth of K obtained from a curve 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.

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

7. The chemically strengthened glass according to claim 1 or 2, wherein: The chemically strengthened glass is mounted on the largest surface of the structure, and when the structure is dropped from a height of 40 cm with the chemically strengthened glass side facing the sandpaper, the chemically strengthened glass does not crack. The structure is a rectangular parallelepiped structure made of aluminum alloy with a width of 70 mm, a length of 130 mm, a thickness of 2 mm, and a mass of 120 g.

8. The chemically strengthened glass according to claim 1 or 2, wherein: The compressive stress CS 90 It is above 10MPa.

9. The chemically strengthened glass according to claim 1 or 2, wherein: The Weibull modulus of the chemically strengthened glass obtained by a four-point bending test is 30 or more.

10. A method for producing chemically strengthened glass, the method comprising performing at least one K salt strengthening treatment, wherein the K salt strengthening treatment is a chemical strengthening treatment in which the chemically strengthened glass is immersed in a molten salt containing a K salt, wherein: The content of KNO3 in the molten salt is 70% by mass or more relative to the total mass of the molten salt, When the temperature of the molten salt is set to T K , the treatment time of the K salt enhanced treatment is set to t K When the K salt strengthening treatment is performed once, the G value obtained by the following formula (PI) is 2.0 to 5.

0. When the K salt strengthening treatment is performed twice or more, the total value of the G value of each K salt strengthening treatment is 2.0 to 5.

0. ， In the formula (PI), t is the thickness of the chemically strengthened glass, and the unit of t is m. In formula (PI), T K The unit is ℃, In formula (PI), t K The unit is seconds, In formula (PI), E is 125000 J / mole, In formula (PI), R is 8.31 J / (K·mol).

11. The method for producing chemically strengthened glass according to claim 10, wherein: The chemically strengthened glass is subjected to a first chemical strengthening treatment and a second chemical strengthening treatment in sequence. The internal tensile stress value of the glass after the first chemical strengthening treatment is greater than the CT limit of the glass for chemical strengthening, The internal tensile stress value of the glass after the second chemical strengthening treatment is smaller than the CT limit of the glass for chemical strengthening.

12. A protective glass, wherein: The protective glass comprises the chemically strengthened glass according to claim 1 or 2.

Images