Chemically strengthened glass and method of making the same

Abstract

The present invention relates to a chemically strengthened glass and a method for producing the same. The present invention relates to a chemically strengthened glass or the like, wherein the chemically strengthened glass has a first main surface, a second main surface opposite to the first main surface, and an end portion which is in contact with the first main surface and the second main surface, when a compressive stress value in the interior of the glass is represented with a depth from the first main surface as a variable, (1a) in a range of ±10 μm from the depth at which the compressive stress value is 0 in the thickness direction of the sheet, a gradient of a stress curve and a gradient of a Na concentration curve are within a certain range; (2a) in a range between the first main surface and the depth at which the compressive stress value is 0 in the thickness direction, the gradient of the Na concentration curve monotonously decreases; (3a) the thickness is 1 mm or less; and (4a) contains 10 mol% or more of Li2O in terms of a molar percentage on an oxide basis.

Description

[0001] This application is a divisional application of the Chinese patent application No. 202080046785.X, filed on April 9, 2020. TECHNICAL FIELD

[0002] The present application relates to chemically strengthened glass and a method for manufacturing the same. BACKGROUND

[0003] For the protection and the improvement of the appearance of display devices of mobile phones, smartphones, tablet terminals, and the like, a protective glass including chemically strengthened glass is used.

[0004] In the chemically strengthened glass, the higher the surface compressive stress (value) (CS) and the depth of the compressive stress layer (DOL) are, the higher the strength tends to be. On the other hand, in order to maintain the balance with the compressive stress of the surface layer of the glass, internal tensile stress (value) (CT) is generated in the inside of the glass, and thus the larger CS and DOL are, the larger CT is. The glass having a large CT explosively increases the number of fragments at the time of damage, and the risk of scattering of the fragments increases.

[0005] In Patent Literature 1, it is described that by two-step chemical strengthening, it is possible to increase the surface compressive stress while suppressing the internal tensile stress. Specifically, it is disclosed that a method of using a KNO3 / NaNO3 mixed salt having a low K concentration for the first step chemical strengthening and a KNO3 / NaNO3 mixed salt having a high K concentration for the second step chemical strengthening is used.

[0006] In addition, in Patent Literature 2, a lithium-containing glass having a relatively large surface compressive stress and a depth of the compressive stress layer by two-step chemical strengthening is disclosed. The lithium-containing glass is capable of increasing CS and DOL while suppressing CT by two-step chemical strengthening treatment of using a sodium salt in the first step chemical strengthening treatment and a potassium salt in the second step chemical strengthening treatment.

[0007] In Patent Literature 3, a glass article including a concentration gradient of a metal oxide is described, and a chemical strengthening stress distribution of a conventional lithium-free glass is disclosed (Patent Literature 3, Figure 2 ).

[0008] Prior Art Documents

[0009] Patent Literature

[0010] Patent Literature 1: U.S. Patent Application Publication No. 2015 / 0259244 Specification

[0011] Patent Literature 2: Japanese Patent Application Laid-Open No. 2013-520388

[0012] Patent Literature 3: Japanese Patent Application Laid-Open No. 2019-510726 SUMMARY

[0013] Problem to be solved by the invention

[0014] In Figure 1 the stress distribution of the conventional lithium-free chemically strengthened glass is shown, and in Figure 2 the stress distribution of the conventional lithium-containing chemically strengthened glass is shown. In the case of chemically strengthening the lithium-containing glass, since the diffusion speed of lithium is fast, stress relaxation also occurs, and therefore in order to increase the surface compressive stress, ion exchange needs to be performed to a deep depth in the plate thickness direction. Therefore, in the case of chemically strengthening the lithium-containing glass, the stress distribution becomes parabolic as shown in Figure 2 , and has a tendency that the tensile stress increases together with the surface compressive stress. In addition, there is a problem that Na-Li exchange is practically performed to the center of the plate thickness.

[0015] Conventionally, in order to improve such a problem, two-step chemical strengthening is performed, but the two-step chemical strengthening process is complicated, and there is a problem in terms of production efficiency. In addition, when the content of lithium (content of Li20) in the lithium-containing glass becomes high (for example, 10 mol% or more on the oxide basis), the stress distribution of the chemically strengthened glass becomes parabolic, and the tendency that the tensile stress also increases becomes particularly significant, and therefore it is required to effectively increase the compressive stress.

[0016] In view of such circumstances, an object of the present invention is to provide a lithium-containing chemically strengthened glass and a manufacturing method thereof, which has a high surface compressive stress while having the same stress distribution as the conventional lithium-free glass and introduces the compressive stress only in the vicinity of the surface layer.

[0017] Means for solving the problem

[0018] As a result of studies on the above problem, the present inventors and others have found that in a chemically strengthened glass containing 10 mol% or more of Li20, by adjusting the Na concentration gradient and the stress gradient, the ductility of the surface of the glass can be increased to improve the strength. Based on these findings, the present invention has been completed.

[0019] That is, the present invention is as described below.

[0020] 1. A chemically strengthened glass, wherein the chemically strengthened glass has a first main surface, a second main surface opposite to the first main surface, and an end portion which is in contact with the first main surface and the second main surface,

[0021] when the compressive stress value inside the glass is represented with the depth from the first main surface as a variable,

[0022] the chemically strengthened glass satisfies the following (la) to (4a):

[0023] (1a) the gradient of the stress curve in a thickness range of ±10 μm from the depth at which the compressive stress value is 0 is -15 MPa / μm to -3 MPa / μm, and

[0024] the gradient of the Na concentration curve defined below has an absolute value of 0.02 / μm to 0.12 / μm.

[0025] Na concentration curve: a Na concentration curve obtained by converting the Na ion concentration distribution in the plate thickness direction of the chemically strengthened glass measured by EPMA into a molar percentage on an oxide basis.

[0026] (2a) the gradient of the Na concentration curve monotonously decreases in a range between the first main face and the depth at which the compressive stress value is 0 in the plate thickness direction.

[0027] (3a) the thickness is 1 mm or less.

[0028] (4a) contains 10 mol% or more of Li20 on a molar percentage basis on an oxide basis.

[0029] 2. The chemically strengthened glass according to the above 1, wherein the thickness of the chemically strengthened glass is t (μm), and the average value of the gradient of the stress curve in a range between the plate thickness center tc (μm) and (tc - 0.20xt) (μm) in the plate thickness direction has an absolute value of less than 1 MPa / μm.

[0030] 3. The chemically strengthened glass according to the above 1 or 2, wherein, in a range between the first main face and the depth at which the compressive stress value is 0 in the plate thickness direction,

[0031] the compressive stress curve measured using a birefringence imaging system Abrio-IM manufactured by Tokyo Instruments Co., Ltd. contains an inflection point, and

[0032] the Na concentration curve does not contain an inflection point.

[0033] 4. The chemically strengthened glass according to the above 3, wherein the compressive stress curve contains an inflection point in a range between a position at a depth of 10 μm from the first main face and the depth at which the compressive stress value is 0 in the plate thickness direction.

[0034] 5. The chemically strengthened glass according to any one of the above 1 to 4, wherein the chemically strengthened glass is a microcrystalline glass.

[0035] 6. The chemically strengthened glass according to the above 5, wherein the crystallization rate of the microcrystalline glass is 10% or more.

[0036] 7. The chemically strengthened glass according to the above 5 or 6, wherein the crystallized glass contains lithium metasilicate crystals.

[0037] 8. The chemically strengthened glass according to any one of the preceding claims 5 to 7, wherein a haze value of transmitted light of the chemically strengthened glass converted to a thickness of 0.7 mm is 0.01 to 0.2% as measured by a method complying with JIS K7136 (2000).

[0038] 9. The chemically strengthened glass according to any one of the preceding claims 5 to 8, wherein a visible light transmittance of the chemically strengthened glass converted to a thickness of 0.7 mm is 85% or more.

[0039] 10. A method for producing a chemically strengthened glass, wherein a chemically strengthened glass is produced by chemically strengthening a glass, the glass having a first main face, a second main face opposite to the first main face, and an end portion which is a boundary between the first main face and the second main face, the glass having a thickness of 1 mm or less, and containing 10 mol% or more of Li20 in terms of molar percentage on an oxide basis, wherein

[0040] the chemical strengthening is chemical strengthening using a strengthening salt containing sodium and having a potassium content of less than 5 mass%,

[0041] when a compressive stress value inside the glass is represented with a depth from the first main face as a variable,

[0042] the obtained chemically strengthened glass satisfies the following (lb) and (2b):

[0043] (lb) a gradient of a stress curve is -15 MPa / μm to -3 MPa / μm in a thickness range of ±10 μm of a depth at which the compressive stress value is 0, and

[0044] a gradient of a Na concentration curve defined below has an absolute value of 0.02 / μm to 0.12 / μm.

[0045] Na concentration curve: a Na concentration curve obtained by converting a Na ion concentration distribution in a plate thickness direction of the chemically strengthened glass measured by EPMA to a molar percentage on an oxide basis.

[0046] (2b) a gradient of the Na concentration curve monotonously decreases in a range between the first main face and a depth at which the compressive stress value is 0 in the plate thickness direction.

[0047] 11. The method for producing a chemically strengthened glass according to claim 10, wherein the glass is a glass-ceramic.

[0048] 12. The method for producing a chemically strengthened glass according to claim 11, wherein the glass-ceramic contains, in terms of molar percentage on an oxide basis:

[0049] 40 to 65% of SiO2,

[0050] 0 to 10% of Al2O3,

[0051] 20 to 40% of Li2O,

[0052] 0 to 10% of Na2O, and

[0053] 0.1 to 10% of K2O.

[0054] 13. The method for producing a chemically strengthened glass according to any one of 11 to 12 above, wherein the visible light transmittance of the glass-ceramic when converted to a thickness of 0.7 mm is 85% or more.

[0055] 14. The method for producing a chemically strengthened glass according to any one of 11 to 13 above, wherein the glass-ceramic contains lithium metasilicate crystals.

[0056] Effects of the Invention

[0057] The chemical strengthened glass of the present application has a Na concentration gradient and a stress gradient in a specific range, whereby while containing 10 mol% or more of Li2O on an oxide basis, the same stress distribution as that of the conventional lithium-free glass is obtained, breakage at the time of damage is suppressed, and excellent strength and weather resistance are exhibited. BRIEF DESCRIPTION OF DRAWINGS

[0058] Figure 1 A graph showing an example of the stress distribution of the conventional lithium-free chemical strengthened glass.

[0059] Figure 2 A graph showing an example of the stress distribution of the conventional lithium-containing chemical strengthened glass.

[0060] Figure 3 A graph showing one mode of the stress distribution of the chemical strengthened glass of the present application.

[0061] Figure 4 (a) and Figure 4 (b) are graphs showing one mode of the ion concentration distribution of the chemical strengthened glass of the present application. Figure 4 (a) is a graph showing the signal intensity of the main ions of Example 1, Figure 4 (b) is a graph showing the calculated Na ion concentration distribution.

[0062] Figure 5 (a) and Figure 5 (b) are schematic diagrams showing the state of the sample used for measuring the surface compressive stress (CS) of the chemical strengthened glass. Figure 5 (a) shows the sample before polishing, Figure 5(b) indicates a sample after polishing of the thinned sample. DETAILED DESCRIPTION

[0063] Hereinafter, the chemically strengthened glass according to the present application is explained in detail, but the present application is not limited to the following embodiments, and can be arbitrarily modified to be implemented within the scope of the gist of the present application.

[0064] In the present specification, "chemically strengthened glass" refers to glass after chemical strengthening treatment. In addition, "glass for chemical strengthening" refers to glass before chemical strengthening treatment.

[0065] In the present specification, the glass composition of the glass for chemical strengthening is sometimes referred to as the basic composition of the chemically strengthened glass. In the chemically strengthened glass, a compressive stress layer resulting from ion exchange is generally formed in the surface portion of the glass, and thus the glass composition of the portion not subjected to ion exchange coincides with the basic composition of the chemically strengthened glass. In addition, even in the portion subjected to ion exchange, the concentration of components other than alkali metal oxides does not substantially change.

[0066] In the present specification, the glass composition is expressed in terms of molar percentage on an oxide basis, and molar % is sometimes abbreviated as %. In addition, "~" indicating a numerical range is used in the meaning that the numerical values recited before and after it are included as lower limit value and upper limit value.

[0067] In the glass composition, "substantially not containing" means not containing, that is, not intentionally containing, except for unavoidable impurities contained in raw materials and the like. Except for transition metal oxides and the like that cause coloring, for example, the content in the glass composition is less than 0.1 mol%.

[0068] In the present specification, "stress distribution" is a graph in which the depth from the surface of the glass is taken as a variable to express the compressive stress value. A negative compressive stress value refers to tensile stress. In addition, "depth of compressive stress layer (DOC)" is the depth at which the compressive stress value (CS) is 0. "Internal tensile stress value (CT)" is the tensile stress value at the depth of 1 / 2 of the plate thickness t of the glass.

[0069] Generally, stress distribution is measured using an optical waveguide surface stress meter (for example, FSM-6000 manufactured by KOTATSU Engineering Corporation). However, for the optical waveguide surface stress meter, in terms of measurement principle, stress cannot be measured if the refractive index is not lower from the surface to the inside. As a result, in the case where lithium aluminosilicate glass is chemically strengthened with a sodium salt, compressive stress cannot be measured. Therefore, in the present specification, stress distribution is mainly measured using a scattered light photoelastic stress meter (for example, SLP-1000 manufactured by KOTATSU Engineering Corporation). With the scattered light photoelastic stress meter, stress values can be measured regardless of the refractive index distribution in the glass interior. However, the scattered light photoelastic stress meter is easily affected by surface scattered light, and thus it is difficult to accurately measure stress values near the surface of the glass. For a surface layer portion up to a depth of 10 μm from the surface, stress values can be estimated based on the measured values of a portion deeper than that by a method of extrapolation using a complementary error function. In addition, for example, a birefringence imaging system Abrio-IM manufactured by Tokyo Instruments Inc. can be used, and measurement is performed using a thinned sample as described later.

[0070] 1. Chemically strengthened glass

[0071] The chemically strengthened glass of the present application is a chemically strengthened glass sheet having a first main surface, a second main surface opposite to the first main surface, and an end portion that is a boundary between the first main surface and the second main surface,

[0072] When a compressive stress value in the interior of the glass is represented with a depth from the first main surface as a variable,

[0073] The chemically strengthened glass satisfies the following (1) to (4):

[0074] (1) In a thickness range of ± 10 μm from a depth at which the compressive stress value is 0,

[0075] The gradient of the stress curve is -15 MPa / μm to -3 MPa / μm, and

[0076] The gradient of the Na concentration curve defined below has an absolute value of 0.02 / μm to 0.12 / μm.

[0077] Na concentration curve: A Na concentration curve obtained by converting the Na ion concentration distribution in the sheet thickness direction of the chemically strengthened glass measured by EPMA into a molar percentage on an oxide basis.

[0078] (2) In a range between the first main surface and a depth at which the compressive stress value is 0 in the sheet thickness direction, the gradient of the Na concentration curve monotonously decreases.

[0079] (3) The thickness is 1 mm or less.

[0080] (4) contains 10 mol% or more of Li20 on a molar percentage basis on an oxide basis.

[0081] <Stress distribution and Na concentration distribution>

[0082] Figure 3 A graph showing one mode of stress distribution of the chemically strengthened glass of the present application. Figure 3 The stress distribution shown in the center indicates the distribution in one main surface. In the present application, the stress distribution in one main surface can be the same as or different from that in the other main surface. Figure 4 (a) and Figure 4 (b) is a graph showing one mode of ion concentration distribution of the chemically strengthened glass of the present application.

[0083] The chemically strengthened glass of the present application has a gradient of the stress curve of -15 MPa / μm to -3 MPa / μm and a gradient of the Na concentration curve having an absolute value of 0.02 / μm to 0.12 / μm in a range of ±10 μm from the depth at which the compressive stress value is 0 in the plate thickness direction.

[0084] In the present application, the "Na concentration curve" refers to a Na concentration curve obtained by converting the Na ion concentration distribution in the plate thickness direction of the above chemically strengthened glass plate determined by EPMA (electron probe microanalyzer) into a molar percentage on an oxide basis.

[0085] In the stress distribution, the depth at which the compressive stress value is 0 indicates the depth of layer of compressive stress (DOL). The DOL of the chemically strengthened glass can be appropriately adjusted by adjusting the chemical strengthening conditions, the composition of the glass, and the like. The DOL of the chemically strengthened glass of the present application is the depth from the glass surface of the portion at which the stress is zero in the stress distribution, and is a value determined using a scattered light photoelastic stress meter (for example, manufactured by Oryuka Co., Ltd., SLP-1000). In addition, the determination can be performed using a birefringence imaging system Abrio-IM manufactured by Tokyo Instruments Inc. using a thinned sample as described later.

[0086] The chemically strengthened glass of the present application has a gradient of the stress curve of -15 MPa / μm to -3 MPa / μm, preferably -13 MPa / μm to -3.5 MPa / μm, and more preferably -11 MPa / μm to -4 MPa / μm in a range of ±10 μm from the depth at which the compressive stress value is 0 in the plate thickness direction. By making the gradient of the stress curve in a range of ±10 μm from the depth at which the compressive stress value is 0 in the plate thickness direction -15 MPa / μm to -3 MPa / μm, energy loss due to the concentration gradient is suppressed, and conversion to stress is efficiently performed, and thus sufficient surface compressive stress can be obtained, showing excellent strength.

[0087] The chemical strengthening glass of the present application has an absolute value of the gradient of the Na concentration curve in the range of ±10 μm from the depth at which the compressive stress value is 0 in the plate thickness direction of 0.02 / μm to 0.12 / μm, preferably 0.03 / μm to 0.11 / μm, and more preferably 0.04 / μm to 0.10 / μm. By having an absolute value of the gradient of the Na concentration curve in the range of ±10 μm from the depth at which the compressive stress value is 0 in the plate thickness direction of 0.02 / μm to 0.12 / μm, the increase in the tensile stress can be suppressed.

[0088] The chemical strengthening glass of the present application has a gradient of the Na concentration curve monotonously decreasing in the range between the first main surface and the depth at which the compressive stress value is 0 in the plate thickness direction. By having a gradient of the Na concentration curve monotonously decreasing in the range, the increase in the tensile stress can be suppressed, and the breakage at the time of damage can be suppressed. In the present application, "the gradient of the Na concentration curve is monotonously decreasing" means that the gradient of the Na concentration curve has a non-zero negative slope in the direction from the glass surface toward the glass interior at any point in the range.

[0089] In one embodiment, the chemical strengthening glass of the present application has a value obtained by dividing the gradient of the stress curve by the gradient of the concentration curve of Na in the range of ±10 μm from the depth at which the compressive stress value is 0 in the plate thickness direction preferably in the range of 80 to 200, more preferably in the range of 90 to 180, and further preferably in the range of 100 to 150. By having a value obtained by dividing the gradient of the stress curve by the gradient of the concentration curve of Na in the range of ±10 μm from the depth at which the compressive stress value is 0 in the plate thickness direction in the range of 80 to 200, the dissipation of energy caused by the concentration gradient can be further suppressed, and the stress can be effectively converted, so that a sufficient surface compressive stress can be exhibited, and the increase in the tensile stress can be suppressed, and the breakage at the time of damage can be suppressed.

[0090] In one embodiment, the chemical strengthening glass of the present application has an absolute value of the average of the gradient of the stress curve in the range between the plate thickness center tc (μm) and (tc - 0.20xt) (μm) in the plate thickness direction when the plate thickness center is set to tc (μm) is preferably less than 1 MPa / μm, more preferably 0.9 MPa / μm or less, and further preferably 0.8 MPa / μm or less. By having an absolute value of the average of the gradient of the stress curve less than 1 MPa / μm, the increase in the tensile stress can be suppressed, and the breakage at the time of damage can be suppressed, as compared with the conventional lithium-free chemical strengthening glass shown in FIG. 1. Figure 1 The chemical strengthening glass of the present application has a substantially flat tensile stress distribution, and can increase the surface compressive stress while suppressing the internal tensile stress, as with the conventional lithium-free chemical strengthening glass shown in FIG. 1.

[0091] In addition, the absolute value of the gradient of the stress curve at each point in the thickness range of tc±0.20t (μm) is preferably less than 1 MPa / μm, more preferably 0.9 MPa / μm or less, and further preferably 0.8 MPa / μm or less. By having the absolute value of the gradient of the stress curve less than 1 MPa / μm, a substantially flat stress distribution is obtained in a wider range of the tensile stress region, and it is possible to increase the surface compressive stress region while suppressing internal tensile stress.

[0092] In one embodiment, the chemically strengthened glass of the present application preferably has a compressive stress curve that includes an inflection point and a Na concentration curve that does not include an inflection point in the range between the first main surface and the depth at which the compressive stress value is 0 in the plate thickness direction, as measured using a birefringence imaging system Abrio-IM manufactured by Tokyo Instruments Inc.

[0093] The measurement of compressive stress using the birefringence imaging system Abrio-IM manufactured by Tokyo Instruments Inc. was performed according to the following procedure. Figure 5 (a) and Figure 5 (b) is a schematic diagram showing the case of a sample prepared for measuring the surface compressive stress (CS) of a chemically strengthened glass. Figure 5 (a) shows a sample before polishing, Figure 5 (b) shows a thinned sample after polishing. As Figure 5 As shown in (b), a cross section of a chemically strengthened glass having a size of 10 mm x 10 mm or more and a thickness of about 0.2 mm to about 2 mm was polished to a range of 150 μm to 750 μm to be thinned.

[0094] As a procedure for polishing, a diamond plated grinding wheel #1000 was used to grind to a target thickness + about 50 μm, then a diamond plated grinding wheel #2000 was used to grind to a target thickness + about 10 μm, and finally mirror polishing was performed using cerium oxide, thereby obtaining the target thickness. For a sample thinned to about 200 μm as prepared as described above, measurement using transmitted light was performed using monochromatic light of λ = 546 nm as a light source, measurement of the phase difference (retardation) possessed by the chemically strengthened glass was performed using a birefringence imaging system, and the stress was calculated using the obtained values and the following equation (1).

[0095] F = δ / (C x t')... Equation (1)

[0096] In equation (1), F represents the stress (MPa), δ represents the phase difference (retardation) (nm), C represents the photoelastic constant (nm / cm - 1 MPa), and t' represents the thickness of the sample (cm).

[0097] In the present application, the "inflection point" refers to a point at which the second differential of the curve is zero. That is, it refers to a point at which the curvature of the curve changes sign. Note that, in calculating the differential, it is preferable to do so after reducing measurement noise by smoothing or the like. For example, the well-known Savitzky-Golay method can be used for the preprocessing.

[0098] In the case where the glass sheet is deflected by an impact, when the deflection amount thereof becomes large, the glass breaks due to a large tensile stress applied to the glass surface. In the present specification, such a break is referred to as "glass breakage due to bending mode".

[0099] In the range between the first main surface and the depth at which the compressive stress value is 0 in the sheet thickness direction, the compressive stress curve contains an inflection point, and the Na concentration curve does not contain an inflection point, whereby particularly in the glass sheet surface, there is a tendency for the stress to relax while maintaining the concentration gradient. That is, it is indicated that the remaining portion of the energy caused by the concentration gradient is sufficiently dissipated. Therefore, it is possible to suppress the glass breakage due to bending mode while introducing a sufficient amount of compressive stress to the glass surface, and it is possible to suppress the reduction in weather resistance. From the viewpoint of further improving the strength, in one mode, the chemically strengthened glass of the present application preferably contains an inflection point in the compressive stress curve in the range between the position at a depth of 10 μm from the first main surface and the depth at which the compressive stress value is 0 in the sheet thickness direction.

[0100] In the past, in the case where such a stress curve is made for a glass not containing lithium, annealing or the like is performed after ion exchange, and also the concentration gradient is moderated. However, by this, since the energy due to the concentration gradient itself is moderated, the stress is excessively relaxed, and the degradation of the surface stress is large. In addition, in a glass containing 10 mol% or more of Li20, as described above, the diffusion speed of the ions is large, and a method of introducing stress in a relatively wide range on the surface, particularly in the vicinity of the surface, until stress relaxation occurs is unknown.

[0101] The chemically strengthened glass of the present application is manufactured by performing ion exchange treatment on a lithium aluminosilicate glass. Compared with the sodium aluminosilicate glass which has been widely used as a glass for chemical strengthening in the past, the lithium aluminosilicate glass has a tendency to have a large fracture toughness value, and not to break even if damaged. In addition, it has a tendency not to easily produce violent breakage even if the compressive stress value of the glass surface is increased.

[0102] In one embodiment, the CSo of the chemically strengthened glass of the present application is preferably 500 MPa or more, more preferably 550 MPa or more, and further preferably 600 MPa or more. By having a CSo of 500 MPa or more, the tensile stress generated by a fall is offset, and thus breakage is less likely to occur, and breakage due to a bending mode can be suppressed. In addition, the total amount of compressive stress in the surface layer of the glass is constant, and when the CSo is too high, the CS 50 inside the glass decreases. Thus, from the viewpoint of preventing breakage at the time of impact, the CSo is preferably 1000 MPa or less, more preferably 950 MPa or less, and further preferably 900 MPa or less.

[0103] In one embodiment, the CS 50 of the chemically strengthened glass of the present application is preferably 150 MPa or more, more preferably 170 MPa or more, and further preferably 180 MPa or more. By having a CS 50 of 150 MPa or more, the strength can be improved. However, when the CS 50 is too high, the internal tensile stress CT increases and breakage is more likely to occur. From the viewpoint of suppressing breakage (explosive breakage at the time of damage), the CS 50 is preferably 250 MPa or less, more preferably 240 MPa or less, and further preferably 230 MPa or less.

[0104] When the depth at which the compressive stress value is 0 (DOL) is too large with respect to the thickness t [unit: pm], an increase in CT results, and thus the DOL is preferably 0.2t or less, more preferably 0.19t or less, and further preferably 0.18t or less. Specifically, for example, in the case where the plate thickness t is 0.8 mm, the DOL is preferably 160 pm or less. In addition, from the viewpoint of improving the strength, the DOL is preferably 0.06t or more, more preferably 0.08t or more, further preferably 0.10t or more, and particularly preferably 0.12t or more.

[0105] Since the CT limit of a glass having a large fracture toughness value is large, even if a large surface compressive stress is introduced into the glass by chemical strengthening, violent breakage is less likely to occur. From the viewpoint of suppressing breakage at the time of damage, in one embodiment, the fracture toughness value of the matrix glass of the chemically strengthened glass of the present application is preferably 0.8 MPa-m 1 / 2 or more, more preferably 0.85 MPa-m 1 / 2 or more, and further preferably 0.9 MPa-m 1 / 2 or more. In addition, the fracture toughness value is typically 2.0 MPa-m 1 / 2 or less, and typically 1.5 MPa-m 1 / 2 or less.

[0106] The fracture toughness value is determined, for example, using the DCDC method (Acta metall. mater. Vol. 43: p. 3453-3458, 1995). The fracture toughness value can be evaluated simply by the indenter press-in method. As a method for bringing the fracture toughness value within the above range, for example, there can be mentioned a method of adjusting the crystallization rate, the fictive temperature, and the like by adjusting the crystallization conditions (time and temperature of heat treatment), the glass composition, the cooling rate, and the like of the glass-ceramic. Specifically, for example, in the case of a glass-ceramic, it is preferable that the crystallization rate of the glass-ceramic described later be 15% or more, more preferably 18% or more, and further preferably 20% or more. In addition, in order to ensure the transmittance, the crystallization rate of the glass-ceramic is preferably 60% or less, more preferably 55% or less, and further preferably 50% or less.

[0107] The weather resistance of the chemically strengthened glass can be evaluated by a weather resistance test. The change in the haze value of the chemically strengthened glass of the present application before and after standing at 80% humidity, 80°C for 120 hours is preferably 5% or less (i.e., |haze value after test [%] - haze value before test [%]| ≤ 5), more preferably 4% or less, and further preferably 3% or less. The haze value is determined using a haze meter and by a method conforming to JIS K7136 (2000).

[0108] The shape of the chemically strengthened glass of the present application can also be other than a plate shape depending on the product, use, and the like to which it is applied. In addition, the glass plate can have a frame shape or the like in which the thickness of the outer periphery is different. In addition, the form of the glass plate is not limited thereto, and for example, the two main surfaces can be parallel to each other, and in addition, all or a part of one or both of the two main surfaces can be curved surfaces. More specifically, the glass plate can be, for example, a flat glass plate without warping, and in addition, can be a curved glass plate having a curved surface.

[0109] The chemically strengthened glass of the present application can be used as a protective glass used in mobile electronic devices such as mobile phones, smartphones, portable information terminals (PDA), tablet terminals, and the like. It is also useful for a protective glass of electronic devices such as televisions (TV), personal computers (PC), touch panels, and the like, which are not intended for carrying. In addition, it is also useful as a building material such as a window glass, a desk surface, an interior material of an automobile or an airplane, and the like, or a protective glass thereof.

[0110] The chemically strengthened glass of the present application can be subjected to bending processing, molding, and the like before or after chemical strengthening to be made into a shape other than a flat plate, and thus is also useful in applications such as a housing having a curved shape.

[0111] <Thickness>

[0112] The chemical-strengthened glass of the present application has a thickness (t) of 1 mm or less, preferably 0.9 mm or less, more preferably 0.8 mm or less, and particularly preferably 0.7 mm or less. In addition, in order to obtain sufficient strength, the thickness is, for example, 0.1 mm or more, preferably 0.2 mm or more, more preferably 0.4 mm or more, and further preferably 0.5 mm or more.

[0113] < Lithium-containing glass >

[0114] The chemical-strengthened glass of the present application contains 10 mol% or more of Li20, on the basis of the mole percentage of oxides. Li20 is a component for forming surface compressive stress by ion exchange, and is essential. The content of Li20 is preferably 15 mol% or more, more preferably 20 mol% or more, and further preferably 25 mol% or more. On the other hand, in order to maintain chemical durability, the content of Li20 is preferably 50 mol% or less, more preferably 45 mol% or less, and further preferably 40 mol% or less.

[0115] The chemical-strengthened glass of the present application is a lithium-containing glass, and is preferably a lithium aluminosilicate glass. The lithium aluminosilicate glass is not particularly limited in form as long as it is a glass containing Si02, Al203, and Li20, and for example, a crystallized glass and an amorphous glass can be given. From the viewpoint of being able to increase the fracture toughness, a crystallized glass is preferred. Hereinafter, the crystallized glass and the amorphous glass will be described.

[0116] < Crystallized glass >

[0117] In the case where the lithium-containing glass in the present application is a crystallized glass, as one mode, the crystallized glass preferably contains, on the basis of the mole percentage of oxides:

[0118] 40 to 65% of Si02,

[0119] 0 to 10% of Al203,

[0120] 20 to 40% of Li20,

[0121] 0 to 10% of Na20, and

[0122] 0 to 10% of K20.

[0123] The crystallized glass is obtained by crystallizing an amorphous glass to be described later by heat treatment. The glass composition of the crystallized glass is the same as that of the amorphous glass before crystallization, and will be described in the item of the amorphous glass to be described later.

[0124] The total light visible light transmittance of the glass-ceramic, including diffused transmitted light, is preferably 85% or more when converted to a thickness of 0.7 mm, whereby the screen of the display is easily seen in the case of a protective glass for a portable display. The total light visible light transmittance is preferably 88% or more, further preferably 90% or more. The higher the total light visible light transmittance, the more preferable, and is usually 91% or less. Note that the total light visible light transmittance of a general non-crystalline glass is about 90%. Note that for 0.7 mm, conversion is performed in the following manner.

[0125] In the case where the total light transmittance of the glass-ceramic of a plate thickness t [mm] is 100 x T [%], and the surface reflectance of one side is 100 x R [%], by citing the Lambert-Beer law, using the constant a, there is a relationship of T = (1 - R) x exp(-at). 2

[0126] Here, R, T, t represent a, and if t = 0.7 mm, R does not change with the plate thickness, and thus the total light transmittance T converted to 0.7 mm 0.7 can be calculated as

[0127] T 0.7 = 100 x T 0.7 / t / (1 - R)^(1.4 / t - 2) [%].

[0128] where X^Y represents X Y .

[0129] The surface reflectance can be calculated from the refractive index, or can be actually measured.

[0130] In addition, in the case of a glass having a plate thickness t of more than 0.7 mm, the plate thickness can be adjusted to 0.7 mm by polishing, etching, or the like, and actually measured.

[0131] In addition, the transmitted haze value is preferably 1.0% or less, more preferably 0.4% or less, further preferably 0.3% or less, particularly preferably 0.2% or less, and most preferably 0.15% or less when converted to a thickness of 0.7 mm. The smaller the transmitted haze value, the more preferable, but when the crystallization rate or the crystal grain size is reduced in order to reduce the transmitted haze value, the mechanical strength decreases. In order to increase the mechanical strength, the transmitted haze value in the case of a thickness of 0.7 mm is preferably 0.02% or more, more preferably 0.03% or more. The transmitted haze value is a value measured by a method conforming to JIS K7136 (2000). Note that the haze value converted to 0.7 mm can be calculated in the following manner.

[0132] ​In the case where the total light ray visible light transmittance of the glass-ceramic having a plate thickness t [mm] is 100 x T [%] and the transmittance haze is 100 x H [%], the constant α used above is used,

[0133] dH / dt ∞ exp(-αt) x (1-H)

[0134] That is, it can be considered that the transmittance haze increases in proportion to the internal straight transmittance as the plate thickness increases.

[0135] This is integrated to convert the transmittance haze H at 0.7 mm 0.7 This can be calculated as

[0136] H 0.7 = 100 x [1 - (1-H)A((1-R 2 -T 0.7 ) / ((1-R 2 -T)] [%].

[0137] where "XΛY" means "X Y ".

[0138] In addition, in the case of a glass having a plate thickness t of more than 0.7 mm, the plate thickness can be adjusted to 0.7 mm by polishing, etching, or the like, and actual measurement can be performed.

[0139] The Y value in the XYZ colorimetric system calculated from the total light ray transmittance spectrum of the glass-ceramic including the diffused transmitted light is preferably 87 or more, more preferably 88 or more, further preferably 89 or more, and particularly preferably 90 or more. In addition, in the case of a protective glass for a portable display, in order to improve the reproducibility of the displayed color in the case of being used on the display screen side, and in order to maintain the design in the case of being used on the housing side, it is preferred that the coloring of the glass itself be suppressed as much as possible. Therefore, the excitation purity Pe of the glass-ceramic is preferably 1.0 or less, more preferably 0.75 or less, further preferably 0.5 or less, particularly preferably 0.35 or less, and most preferably 0.25 or less.

[0140] In the case where the strengthened glass obtained by strengthening the glass-ceramic is used as a protective glass for a portable display, it is preferred to have a different texture / sense of luxury from plastic. Therefore, the dominant wavelength λd of the glass-ceramic is preferably 580 nm or less, and the refractive index is preferably 1.52 or more, more preferably 1.55 or more, and further preferably 1.57 or more.

[0141] The glass-ceramics is preferably a glass-ceramics containing lithium metasilicate crystals. The lithium metasilicate crystals are represented as Li2SiO3, and are generally crystals showing diffraction peaks at Bragg angles (2Θ) of 26.98° ± 0.2°, 18.88° ± 0.2°, 33.05° ± 0.2° in powder X-ray diffraction spectrum.

[0142] The glass-ceramics containing lithium metasilicate crystals has a high fracture toughness value, and is less likely to be fractured severely even when a large compressive stress is formed by chemical strengthening, compared to a general non-crystalline glass. The non-crystalline glass capable of precipitating lithium metasilicate crystals sometimes precipitates lithium disilicate depending on the heat treatment conditions and the like.

[0143] The lithium disilicate is represented as Li2Si2O5, and is generally crystals showing diffraction peaks at Bragg angles (2Θ) of 24.89° ± 0.2°, 23.85° ± 0.2°, 24.40° ± 0.2° in powder X-ray diffraction spectrum. In the case of containing lithium disilicate crystals, when the lithium disilicate crystal particle size calculated from the X-ray diffraction peak width by the Scherrer equation is 45 nm or less, transparency is easily obtained, and thus is preferable, and more preferably 40 nm or less. Note that, although a shape factor is present in the Scherrer equation, in this case it can be represented by a dimensionless number of 0.9.

[0144] However, when both lithium metasilicate crystals and lithium disilicate crystals are contained in the glass-ceramics, the transparency of the glass-ceramics is easily reduced, and thus it is preferable that the glass-ceramics does not contain lithium disilicate. Here, "does not contain lithium disilicate" means that no diffraction peaks of lithium disilicate crystals are detected in the X-ray diffraction spectrum.

[0145] In order to improve the mechanical strength, the crystallization rate of the glass-ceramics is preferably 5% or more, more preferably 10% or more, further preferably 15% or more, and particularly preferably 20% or more. In order to improve the transparency, the crystallization rate is preferably 70% or less, more preferably 60% or less, and particularly preferably 50% or less. From the viewpoint of easily performing bending forming by heating and the like, a small crystallization rate is also excellent.

[0146] The crystallization rate can be calculated from the X-ray diffraction intensity using the Rietveld method. The Rietveld method is described in "Crystalline Analysis Manual" edited by the Crystalline Analysis Manual Editing Committee of the Crystallographic Society of Japan (Kyoritsu Shuppan, published in 1999, pp. 492-499).

[0147] The average particle size of the precipitated crystals of the glass-ceramics is preferably 80 nm or less, more preferably 60 nm or less, further preferably 50 nm or less, particularly preferably 40 nm or less, and most preferably 30 nm or less. The average particle size of the precipitated crystals is determined from a transmission electron microscope (TEM) image. The average particle size of the precipitated crystals can be estimated from a scanning electron microscope (SEM) image.

[0148] The average coefficient of thermal expansion of the glass-ceramics in the range of 50°C to 350°C is preferably 90 x 10 -7 / °C or more, more preferably 100 x 10 -7 / °C or more, further preferably 110 x 10 -7 / °C or more, particularly preferably 120 x 10 -7 / °C or more, and most preferably 130 x 10 -7 / °C or more.

[0149] When the coefficient of thermal expansion is too large, it is possible that cracking occurs due to a difference in the rate of thermal expansion during chemical strengthening, and thus the coefficient of thermal expansion is preferably 160 x 10 -7 / °C or less, more preferably 150 x 10 -7 / °C or less, and further preferably 140 x 10 -7 / °C or less. In addition, when the coefficient of thermal expansion is such, it is suitable as a support substrate for semiconductor packages in which the resin component is large.

[0150] The glass-ceramics has a large hardness because it contains crystals. Thus, it is not easily damaged and has excellent wear resistance. In order to increase the wear resistance, the Vickers hardness is preferably 600 or more, more preferably 700 or more, further preferably 730 or more, particularly preferably 750 or more, and most preferably 780 or more. When the hardness is too high, it is not easily processed, and thus the Vickers hardness of the glass-ceramics is preferably 1100 or less, more preferably 1050 or less, and further preferably 1000 or less.

[0151] In order to suppress warping caused by strengthening during chemical strengthening, the Young's modulus of the glass-ceramics is preferably 85 GPa or more, more preferably 90 GPa or more, further preferably 95 GPa or more, and particularly preferably 100 GPa or more. The glass-ceramics is sometimes used after polishing. In order to easily polish, the Young's modulus is preferably 130 GPa or less, more preferably 125 GPa or less, and further preferably 120 GPa or less.

[0152] The fracture toughness value of the glass-ceramics is preferably 0.8 MPa m 1 / 2 or more, more preferably 0.85 MPa m 1 / 2 or more, and further preferably 0.9 MPa m 1 / 2The above is preferable when chemical strengthening is performed because the fragments are less likely to scatter at the time of breakage.

[0153] In the case where the lithium aluminosilicate glass in the present application is a glass-ceramic, as one embodiment, it is preferable to contain, in terms of molar percentage on an oxide basis, 40 to 60% of SiO2, 0.5 to 10% of Al2O3, 10 to 50% of Li2O, 0 to 4% of P2O5, 0 to 6% of ZrO2, 0 to 7% of Na2O, and 0 to 5% of K2O. That is, it is preferable to perform crystallization by performing heat treatment on an amorphous glass (hereinafter sometimes referred to as a crystallizable amorphous glass) containing, in terms of molar percentage on an oxide basis, 40 to 60% of SiO2, 0.5 to 10% of Al2O3, 10 to 50% of Li2O, 0 to 4% of P2O5, 0 to 6% of ZrO2, 0 to 7% of Na2O, and 0 to 5% of K2O.

[0154] <<Crystallizable Amorphous Glass>>

[0155] As one embodiment, the amorphous glass in the present application preferably contains, in terms of molar percentage on an oxide basis, 40 to 60% of SiO2, 0.5 to 10% of Al2O3, 10 to 50% of Li2O, 0 to 4% of P2O5, 0 to 6% of ZrO2, 0 to 7% of Na2O, and 0 to 5% of K2O.

[0156] Hereinafter, the glass composition will be described.

[0157] In the crystallizable amorphous glass, SiO2is a component that forms a network structure of the glass. In addition, SiO2is a component that improves chemical durability, and is also a constituent component of lithium metasilicate that precipitates as a crystal. The content of SiO2is preferably 40% or greater. The content of SiO2is more preferably 42% or greater, and further preferably 45% or greater. In order to sufficiently increase the stress generated by chemical strengthening, the content of SiO2is preferably 60% or less, more preferably 58% or less, and further preferably 55% or less.

[0158] Al2O3is a component that increases the surface compressive stress generated by chemical strengthening, and is indispensable. The content of Al2O3is preferably 0.5% or greater. In order to increase the stress generated by chemical strengthening, the content of Al2O3is more preferably 1% or greater, and further preferably 2% or greater. On the other hand, in order to reduce the transmission haze value of the glass-ceramic, the content of Al2O3is preferably 10% or less, more preferably 8% or less, and further preferably 6% or less.

[0159] Li2O is a component for forming surface compressive stress by ion exchange, and is indispensable as a constituent component of lithium silicate crystals, lithium aluminosilicate crystals, and lithium phosphate crystals. The content of Li2O is preferably 10% or more, more preferably 15% or more, still more preferably 20% or more, and further more preferably 25% or more. On the other hand, in order to maintain chemical durability, the content of Li2O is preferably 50% or less, more preferably 45% or less, and further more preferably 40% or less.

[0160] Na2O is a component for improving the melting property of the glass. Although Na2O is not indispensable, it is preferably 0.1% or more, more preferably 0.5% or more, still more preferably 1% or more, and particularly preferably 2% or more. When Na2O is too much, lithium metasilicate crystals are not easily precipitated or the chemical strengthening characteristics are reduced, and thus the content of Na2O is preferably 7% or less, more preferably 6% or less, and further more preferably 5% or less.

[0161] K2O is also a component for lowering the melting temperature of the glass, and K2O can be contained. In the case where K2O is contained, the content of K2O is preferably 0.1% or more, more preferably 0.5% or more, still more preferably 1% or more, further more preferably 1.5% or more, and particularly preferably 2% or more. When K2O is too much, the chemical strengthening characteristics are reduced, and thus the content of K2O is preferably 5% or less, more preferably 4% or less, further more preferably 3% or less, and particularly preferably 2% or less.

[0162] In addition, the total content of Na2O and K2O (Na2O + K2O) is preferably 0.5% or more, and more preferably 1% or more. In addition, Na2O + K2O is preferably 7% or less, more preferably 6% or less, and further more preferably 5% or less.

[0163] In the case of the glass-ceramics containing lithium silicate or lithium aluminosilicate, P2O5 is not indispensable, but P2O5 has an effect of promoting phase separation of the glass and promoting crystallization, and thus P2O5 can be contained. In the case of the glass-ceramics containing lithium phosphate crystals, P2O5 is an indispensable component. In the case where P2O5 is contained, the content of P2O5 is preferably 0.5% or more, more preferably 1% or more, and further more preferably 1.5% or more. On the other hand, when the content of P2O5 is too much, phase separation is easily caused at the time of melting, and in addition, the acid resistance is significantly reduced. The content of P2O5 is preferably 5% or less, more preferably 4% or less, and further more preferably 3% or less.

[0164] ZrO2is a component that can form a crystal nucleus when a crystallization treatment is performed, and ZrO2may be contained. The content of ZrO2is preferably 1% or more, more preferably 2% or more, further preferably 2.5% or more, and particularly preferably 3% or more. On the other hand, in order to suppress devitrification at the time of melting, the content of ZrO2is preferably 6% or less, more preferably 5.5% or less, and further preferably 5% or less.

[0165] TiO2is a component that can form a crystal nucleus when a crystallization treatment is performed, and TiO2may be contained. Although TiO2is not essential, when TiO2is contained, the content of TiO2is preferably 0.5% or more, more preferably 1% or more, further preferably 2% or more, particularly preferably 3% or more, and most preferably 4% or more. On the other hand, in order to suppress devitrification at the time of melting, the content of TiO2is preferably 10% or less, more preferably 8% or less, and further preferably 6% or less.

[0166] SnO2has an effect of promoting the generation of a crystal nucleus, and SnO2may be contained. Although SnO2is not essential, when SnO2is contained, the content of SnO2is preferably 0.5% or more, more preferably 1% or more, further preferably 1.5% or more, and particularly preferably 2% or more. On the other hand, in order to suppress devitrification at the time of melting, the content of SnO2is preferably 6% or less, more preferably 5% or less, further preferably 4% or less, and particularly preferably 3% or less.

[0167] Y2O3is a component that makes it difficult for a chip to fly when a chemically strengthened glass is broken, and Y2O3may be contained. The content of Y2O3is preferably 1% or more, more preferably 1.5% or more, further preferably 2% or more, particularly preferably 2.5% or more, and extremely preferably 3% or more. On the other hand, in order to suppress devitrification at the time of melting, the content of Y2O3is preferably 5% or less, and more preferably 4% or less.

[0168] Although B2O3is not essential, B2O3is a component that improves the chipping resistance of a glass for chemical strengthening or a chemically strengthened glass and improves the meltability, and B2O3may be contained. In order to improve the meltability, when B2O3is contained, the content of B2O3is preferably 0.5% or more, more preferably 1% or more, and further preferably 2% or more. On the other hand, when the content of B2O3is greater than 5%, moiré occurs at the time of melting, and the quality of the glass for chemical strengthening easily decreases, and thus is preferably 5% or less. The content of B2O3is more preferably 4% or less, further preferably 3% or less, and particularly preferably 2% or less.

[0169] BaO, SrO, MgO, CaO, ZnO are components for improving the melting property of the glass, and BaO, SrO, MgO, CaO, ZnO can be contained. In the case where these components are contained, the total content of BaO, SrO, MgO, CaO, ZnO, BaO+SrO+MgO+CaO+ZnO is preferably 0.5% or more, more preferably 1% or more, further preferably 1.5% or more, and particularly preferably 2% or more. On the other hand, since the ion exchange rate decreases, the content of BaO+SrO+MgO+CaO+ZnO is preferably 8% or less, more preferably 6% or less, further preferably 5% or less, and particularly preferably 4% or less.

[0170] BaO, SrO, ZnO can be contained in order to increase the refractive index of the residual glass, to approach the precipitated crystal phase, to increase the transmittance of the glass-ceramics, and to decrease the haze value. In this case, the total content of BaO, SrO, ZnO, BaO+SrO+ZnO is preferably 0.3% or more, more preferably 0.5% or more, further preferably 0.7% or more, and particularly preferably 1% or more. On the other hand, these components sometimes decrease the ion exchange rate. In order to improve the chemical strengthening characteristics, BaO+SrO+ZnO is preferably 2.5% or less, more preferably 2% or less, further preferably 1.7% or less, and particularly preferably 1.5% or less.

[0171] In addition, CeO2may be contained. CeO2has an effect of oxidizing the glass, and sometimes suppresses coloring. In the case where CeO2is contained, the content of CeO2is preferably 0.03% or more, more preferably 0.05% or more, and further preferably 0.07% or more. In the case where CeO2is used as an oxidizing agent, in order to improve the transparency, the content of CeO2is preferably 1.5% or less, and more preferably 1.0% or less.

[0172] In the case where the strengthened glass is colored and used, coloring components can be added within a range not hindering the achievement of desired chemical strengthening characteristics. As the coloring components, for example, Co3O4, MnO2, Fe2O3, NiO, CuO, Cr2O3, V2O5, Bi2O3, SeO2, Er2O3, and Nd2O3 can be listed as appropriate components.

[0173] The content of the coloring components is preferably within a range of 1% or less in total. In the case where it is desired to further improve the visible light transmittance of the glass, it is preferable that these components are not substantially contained.

[0174] In addition, SO3, chloride, fluoride, and the like can be appropriately contained as a fining agent at the time of melting the glass. It is preferable that As2O3is not contained. In the case where Sb2O3is contained, the content of Sb2O3is preferably 0.3% or less, more preferably 0.1% or less, and most preferably Sb2O3is not contained.

[0175] Hereinafter, the mol% of a certain component A is denoted as C-A. The present application is established regardless of what kind of crystal is precipitated as a crystal phase, and in order to obtain a microcrystalline glass having higher transparency, the mol% ratio of Li20 to Si02, C-Li20 / C-Si02, is preferably 0.4 or more, more preferably 0.45 or more, and further preferably 0.5 or more. In addition, it is preferably 0.85 or less, more preferably 0.80 or less, and further preferably 0.75 or less. Thereby, lithium metasilicate is easily obtained, and as a result, a microcrystalline glass having high transparency can be obtained by controlling the particle size.

[0176] In addition, C-Li20 / C-Na20 is preferably 4 or more, more preferably 8 or more, and further preferably 12 or more. In addition, it is preferably 30 or less, more preferably 28 or less, and further preferably 25 or less. Thereby, a stress distribution in which the surface is relaxed while sufficiently introducing a compressive stress generated by chemical strengthening is easily obtained.

[0177] 2. Method for manufacturing chemically strengthened glass

[0178] As one mode of the method for manufacturing chemically strengthened glass of the present application, for example, a method in which a crystalline amorphous glass described above is subjected to heat treatment to obtain a microcrystalline glass, and the obtained microcrystalline glass is subjected to chemical strengthening treatment to manufacture can be exemplified.

[0179] <Manufacture of amorphous glass>

[0180] The amorphous glass can be manufactured, for example, by the following method. Note that the following manufacturing method is an example in the case of manufacturing a plate-shaped chemically strengthened glass.

[0181] The glass raw material is prepared to obtain a glass having a preferable composition, and is subjected to heating and melting in a glass melting furnace. Then, the molten glass is homogenized by bubbling, stirring, addition of a fining agent, or the like, and is formed into a glass sheet having a predetermined thickness by a publicly known forming method, and is subjected to slow cooling. Alternatively, it can be formed into a plate shape by forming the molten glass into a block shape, and then subjected to slow cooling and then cutting.

[0182] As the forming method of the plate-shaped glass, for example, a float method, a press method, a fusion method, and a down-draw method can be exemplified. In particular, in the case of manufacturing a large glass sheet, the float method is preferable. In addition, a continuous forming method other than the float method, such as the fusion method and the down-draw method, is also preferable.

[0183] <Crystallization treatment>

[0184] In the case where the lithium aluminosilicate glass in the present application is a microcrystalline glass, the crystalline amorphous glass obtained by the above step is subjected to heat treatment, and a microcrystalline glass can be obtained.

[0185] The heat treatment is preferably a two-step heat treatment in which the temperature is raised from room temperature to a first treatment temperature and held for a certain period of time, and then held for a certain period of time at a second treatment temperature higher than the first treatment temperature.

[0186] In the case of the two-step heat treatment, the first treatment temperature is preferably a temperature range in which the nucleation rate increases for the glass composition, and the second treatment temperature is preferably a temperature range in which the crystal growth rate increases for the glass composition. In addition, with respect to the holding time at the first treatment temperature, it is preferable to hold for a long time so that a sufficient number of crystal nuclei are generated. By generating a large number of crystal nuclei, the size of each crystal becomes small, thereby obtaining a glass-ceramic having high transparency.

[0187] The first treatment temperature is, for example, 450°C to 700°C, and the second treatment temperature is, for example, 600°C to 800°C, and the holding time at the first treatment temperature is 1 hour to 6 hours, and then the holding time at the second treatment temperature is 1 hour to 6 hours.

[0188] The glass-ceramic obtained by the above operation steps is subjected to grinding and polishing treatment as necessary, thereby forming a glass-ceramic sheet. In the case where the glass-ceramic sheet is cut into a prescribed shape and size, or subjected to chamfering processing, it is preferable to perform the cutting, chamfering processing before the chemical strengthening treatment is performed, because a compressive stress layer is formed on the end surface by the subsequent chemical strengthening treatment.

[0189] <Manufacture of chemically strengthened glass>

[0190] The chemically strengthened glass of the present application is manufactured by chemically strengthening a lithium-containing glass. The lithium-containing glass preferably has the above composition.

[0191] The lithium-containing glass can be manufactured by a general method. For example, the raw materials of each component of the glass are prepared, and heating and melting are performed in a glass melting furnace. Then, the glass is homogenized by a known method, formed into a desired shape such as a glass sheet, and subjected to slow cooling.

[0192] As the forming method of the glass, for example, a float method, a press method, a fusion method, and a down-draw method can be exemplified. The float method which is suitable for mass production is particularly preferable. In addition, a continuous forming method other than the float method, such as the fusion method and the down-draw method, is also preferable.

[0193] Then, the glass substrate is subjected to grinding and polishing treatment as necessary, thereby forming a glass substrate. Note that, in the case where the glass substrate is cut into a prescribed shape and size, or subjected to chamfering processing of the glass substrate, it is preferable to perform the cutting, chamfering processing of the glass substrate before the chemical strengthening treatment described later is performed, because a compressive stress layer is formed on the end surface by the subsequent chemical strengthening treatment.

[0194] The chemical strengthening in the method for producing the chemically strengthened glass of the present application is preferably chemical strengthening using a strengthening salt containing sodium and having a potassium content of less than 5 mass%. In the method for producing the chemically strengthened glass of the present application, chemical strengthening treatment can be performed in two or more steps, but in order to improve productivity, it is preferable to perform one-step strengthening.

[0195] The treatment conditions of the chemical strengthening treatment can be appropriately selected in consideration of the composition (properties) of the glass, the kind of the molten salt, and the desired chemical strengthening properties, and the like. The chemical strengthening treatment is performed, for example, by immersing the glass sheet in a molten salt such as sodium nitrate heated to 360°C to 600°C for 0.1 hour to 500 hours. Note that the heating temperature of the molten salt is preferably 375°C to 500°C, and the immersion time of the glass sheet in the molten salt is preferably 0.3 hours to 200 hours.

[0196] The strengthening salt used in the method for producing the chemically strengthened glass of the present application is a strengthening salt containing sodium and having a potassium content of less than 5 mass%. The potassium content in the strengthening salt is preferably 2 mass% or less, and more preferably substantially free of potassium. By "substantially free of potassium" is meant that the glass is completely free of potassium or can contain potassium as an impurity unavoidably mixed during production.

[0197] As the strengthening salt, for example, nitrates, sulfates, carbonates, chlorides, and the like can be given. Among these, as the nitrates, for example, lithium nitrate, sodium nitrate, and the like can be given. As the sulfates, for example, lithium sulfate, sodium sulfate, and the like can be given. As the carbonates, for example, lithium carbonate, sodium carbonate, and the like can be given. As the chlorides, for example, lithium chloride, sodium chloride, cesium chloride, silver chloride, and the like can be given. These strengthening salts can be used alone or in combination of a plurality of kinds.

[0198] Example

[0199] Hereinafter, the present application will be described using examples, but the present application is not limited thereto. Note that for each of the measured results in the tables, a blank indicates that the measurement was not performed. Examples 1 to 4 are examples, and Example 5 is a comparative example.

[0200] [Production and Evaluation of Amorphous Glass]

[0201] The glass raw materials were prepared so as to obtain the glass composition described in Table 1 in terms of molar percentage on an oxide basis, and melting, grinding processing were performed, thereby producing a glass sheet. As the glass raw materials, a general glass raw material such as an oxide, a hydroxide, a carbonate, and the like was appropriately selected so as to obtain 900 g of glass. The mixed glass raw materials were put in a platinum crucible, and melting, deaeration were performed at 1700°C. The glass was made to flow onto a carbon plate, thereby obtaining a glass block. A part of the obtained block was used, and the evaluation results are shown in Table 1. A blank in the table indicates that the evaluation was not performed.

[0202] [Manufacture and evaluation of glass-ceramics]

[0203] The obtained glass block was processed to 50 mm x 50 mm x 1.5 mm, and then heat-treated under the conditions described in Table 1, whereby glass-ceramics were obtained. The upper row in the crystallization condition column in the table is the nucleation treatment condition, and the lower row is the crystal growth treatment condition, for example, in the case of 550-2 in the upper row and 730-2 in the lower row, it means that 2 hours of retention at 550°C, followed by 2 hours of retention at 730°C. Using a part of the obtained glass-ceramics, it was confirmed by powder X-ray diffraction that lithium metasilicate was contained.

[0204] The obtained glass-ceramics were processed and mirror-polished, whereby glass-ceramic plates having a thickness t of 0.7 mm were obtained. In addition, rod-shaped samples for measuring the thermal expansion coefficient were prepared. A part of the remaining glass-ceramics was pulverized and used for analysis of precipitated crystals. The results obtained by evaluating the glass-ceramics are shown in Table 1. The empty column in the table indicates that the evaluation was not performed.

[0205] [Manufacture and evaluation of chemically strengthened glass]

[0206] The obtained glass-ceramics were subjected to chemical strengthening treatment under the strengthening conditions described in Table 2, whereby chemically strengthened glass was obtained. Examples 1 to 4 are examples, and Example 5 is a comparative example. In Table 2, "Na 100%" means a molten salt in which sodium nitrate is 100%, "Na 99.7% Li 0.3%" means a molten salt obtained by mixing 0.3% by weight of lithium nitrate in 99.7% by weight of sodium nitrate, and "K 100%" means a molten salt in which potassium nitrate is 100%. The results obtained by evaluating the obtained chemically strengthened glass are shown in Table 2. The empty column in the table indicates that the evaluation was not performed.

[0207] [Method of evaluation]

[0208] (Glass transition temperature Tg, thermal expansion coefficient)

[0209] According to JIS R1618:2002, using a thermal dilatometer (manufactured by Bruker AXS; TD5000SA), the temperature increase rate was set to 10°C / min, whereby a thermal expansion curve was obtained, and the glass transition temperature Tg [unit: °C] and the thermal expansion coefficient were calculated from the obtained thermal expansion curve.

[0210] (Specific gravity)

[0211] It was measured by the Archimedes method.

[0212] (Young's modulus)

[0213] Young's modulus was measured by the ultrasonic wave method.

[0214] (refractive index)

[0215] The mirror surface was polished to 15 mm x 15 mm x 0.8 mm, and the refractive index was measured using a precision refractometer KPR-2000 (manufactured by Shimadzu Corporation) by the V-block method.

[0216] (Vickers hardness)

[0217] The Vickers hardness was measured according to the test method prescribed in JIS-Z-2244 (2009) (ISO 6507-1, ISO 6507-4, ASTM-E-384) using a Vickers hardness tester (MICRO HARDNESS TESTER HMV-2) manufactured by Shimadzu in a normal temperature and humidity environment (in this case, maintained at room temperature 25°C and humidity 60% RH). Ten sites were measured per 1 sample, and the average value thereof was taken as the Vickers hardness of the trial production example. In addition, the indentation load of the Vickers indenter was set to 0.98 N, and the indentation was performed for 15 seconds.

[0218] (fracture toughness value)

[0219] Regarding the fracture toughness value, a sample of 6.5 mm x 6.5 mm x 65 mm was prepared, and the measurement was performed by the DCDC method. At this time, a 2 mm Φ through-hole was formed on the 65 mm x 6.5 mm face of the sample and evaluated.

[0220] (total light visible light transmittance)

[0221] The transmittance of the glass-ceramic plate at a wavelength of 380 nm to 780 nm was measured using an integrating sphere unit (150 mm InGaAs Int. Sptere) as a detector in a spectrophotometer (manufactured by PerkinElmer; LAMBDA 950). Note that, in the measurement, the glass plate was brought into close contact with the integrating sphere, and the measurement including the diffuse transmitted light was performed. The average transmittance, which is the arithmetic average of the transmittance, was taken as the visible light transmittance [unit: %].

[0222] (haze value)

[0223] The haze value [unit: %] under a C light source was measured by a method conforming to JIS K7136 (2000) using a haze meter (Suga Test Instruments; HZ-V3).

[0224] (X-ray diffraction: precipitated crystal and crystallization rate)

[0225] The powder X-ray diffraction was measured under the following conditions, and the precipitated crystal was identified. In addition, the crystallization rate was calculated by the Rietveld method from the obtained diffraction intensity.

[0226] Measurement device: SmartLab manufactured by Rigaku Corporation, Japan

[0227] Using X-rays: CuKα rays

[0228] Measurement range: 2θ = 10°~80°

[0229] Speed: 10° / minute

[0230] Step size: 0.02°

[0231] The detected crystals are shown in the main crystal column of Table 1. In the table, LS represents lithium metasilicate.

[0232] (Stress distribution)

[0233] First, the stress distribution was measured using an SLP-2000 stress measuring machine manufactured by Orihara Manufacturing Co., Ltd., and the stress characteristics (compressive stress value CS at a depth of 50 μm) were determined. 50 [Unit: MPa], CT [Unit: MPa], Depth DOL when compressive stress is zero [Unit: μm]). For the obtained stress distribution, the gradient (MPa / μm) of the stress curve within a thickness range of 2 μm DOL ± 10 μm and the gradient (MPa / μm) of the stress curve within a thickness range of ± 0.20 × t (μm) from the center of the plate thickness were calculated, and the maximum absolute value was determined. In addition, the compressive stress value CS0 [Unit: MPa] of the glass surface and the position (μm) of the inflection point of the compressive stress curve between the main surface and DOL were analyzed by using the Abrio-IM birefringent imaging system manufactured by Tokyo Instruments Co., Ltd. and the method of thin-film sample. The results are shown in Table 2. In addition, the stress distribution of Example 1 is shown in Table 2. Figure 3 middle.

[0234] It should be noted that in the Abrio-IM and thinning method, the thickness of the thinned plate was set to 0.5 mm. Furthermore, to correct for stress changes caused by thinning, the obtained stress distribution was multiplied by 1 / (1-ν). Here, ν is the Poisson's ratio of the glass.

[0235] (Ion concentration obtained from EPMA)

[0236] The ion concentration of the glass surface was measured using EPMA (manufactured by JEOL Co., Ltd., JXA-8500F). The sample was subjected to chemical strengthening, then embedded in a resin, mirror-polished to expose a cross section in the thickness direction of the plate. The position of the outermost surface was the position where the signal intensity of Si, which was considered to have almost no change in content, was half the signal intensity at the center of the thickness of the plate, which corresponded to the glass composition before strengthening, and the ion concentration was calculated in a manner that the concentration was proportional to the signal intensity. Regarding the gradient in the Na concentration profile obtained in the range of DOL ± 10 μm in the thickness direction, and the presence or absence of an inflection point in the range between the first main surface and the depth at which the compressive stress value was 0 in the thickness direction, as shown in Table 2. In addition, the signal intensity of the main ions of Example 1 is shown in Figure 4 (a). The calculated Na ion concentration profile is shown in Figure 4 (b). Note that, in Figure 4 (b), the Na ion concentration at the center of the thickness was twice the Na2O concentration in the glass composition.

[0237] (Weather resistance test)

[0238] After being left at 80% humidity and 80°C for 10 hours, the haze value was measured. The haze value did not change due to the chemical strengthening treatment, but increased when left at 80% humidity and 80°C for 120 hours. The difference from the haze value before the test (i.e., |haze value after the test [%] - haze value before the test [%]|) was set as [haze change (%)] and shown in Table 2.

[0239] (Breakage number)

[0240] Using a Vickers tester, a Vickers indenter with an angle of 90° at the leading end was punched into the central portion of the test glass plate to break the glass plate, and the number of fragments was counted as the breakage number. (The breakage number was 2 in the case where the glass plate was broken into two.) In the case where very fine fragments were produced, the number of fragments that did not pass through a 1 mm sieve was counted as the breakage number.

[0241] In addition, the test was started from a punching load of the Vickers indenter of 3 kgf, and in the case where the glass plate was not broken, the punching load was increased by 1 kgf each time, and the test was repeated until the glass plate was broken, and the breakage number at the time of the initial breakage was counted.

[0242] (Drop test)

[0243] With regard to the drop test, the obtained glass sample of 120 mm x 60 mm x 0.6 mm t was mounted to a structure body adjusted in mass and rigidity to the size of a common smartphone currently in use, thereby preparing a simulated smartphone, and then dropped freely onto #180 SiC sandpaper. With regard to the drop height, in the case where the sample was not broken when dropped from a height of 5 cm, the drop height was increased by 5 cm and the sample was dropped again, and this operation was repeated until breakage, and the average of 10 heights at the time of first breakage is shown in Table 1.

[0244] Table 1

[0245]

[0246] Table 2

[0247]

[0248] As shown in Table 2, Examples 1 to 4 as embodiments, by having the Na concentration gradient and the stress gradient within the prescribed range of the present application, containing 10 mol% or more of Li20 and at the same time having the same stress distribution as the conventional lithium-free glass, compared with the Comparative Examples, breakage at the time of damage was suppressed, and excellent strength and weather resistance were exhibited. In addition, Examples 1 to 3, in the range between the position of 10 μm in depth from the first main surface and the depth at which the compressive stress value is 0, the compressive stress curve contained an inflection point, and compared with Example 4 in which the compressive stress curve did not contain an inflection point in this range, exhibited higher strength.

[0249] Although the present application has been described in detail with reference to particular embodiments, various modifications and alterations are possible without departing from the spirit and scope of the present application, which will be apparent to those skilled in the art. It should be noted that this application is based on Japanese Patent Application (Japanese Patent Application No. 2019-118969) filed on June 26, 2019, the entire contents of which are incorporated herein by reference. In addition, all references cited herein are incorporated in their entirety.

Claims

1. A chemically strengthened glass, wherein, The chemically strengthened glass has a first main surface, a second main surface opposite to the first main surface, and an end portion that is in contact with the first main surface and the second main surface, When a depth from the first main surface is taken as a variable to express a compressive stress value inside the glass, the chemically strengthened glass satisfies (1a) to (4a) below, The Young's modulus is 100 GPa or more and 130 GPa or less, (1a) In a thickness range of ± 10 μm from a depth at which the compressive stress value is 0, a gradient of a stress curve is -15 MPa / μm to -3 MPa / μm, and A gradient of a Na concentration curve defined below has an absolute value of 0.02 / μm to 0.12 / μm, The Na concentration curve: a Na concentration curve obtained by converting a Na ion concentration distribution in a plate thickness direction of the chemically strengthened glass measured by EPMA into a molar percentage on an oxide basis; (2a) In a range between the first main surface and a depth at which the compressive stress value is 0 in the plate thickness direction, the gradient of the Na concentration curve monotonously decreases, where "the gradient of the Na concentration curve monotonously decreases" means that the gradient of the Na concentration curve has a non-zero negative slope in the glass interior direction from the glass surface at any point in the range; (3a) The thickness is 1 mm or less; (4a) Contains 10 mol% or more of Li2O on a molar percentage on an oxide basis.

2. The chemically strengthened glass of claim 1, wherein, The fracture toughness value is 0.9 MPa.m 1 / 2 The above.

3. The chemically strengthened glass of claim 1 or 2, wherein, The Vickers hardness is 700 or more and 1100 or less.

4. The chemically strengthened glass of claim 1 or 2, wherein, The Vickers hardness is 801 or more.

5. The chemically strengthened glass of claim 1 or 2, wherein, 50 to 350°C, and the average thermal expansion coefficient is 90 x 10 -7 / °C or more and 160 x 10 -7 / °C or more and 160 x 10 6. The chemically strengthened glass of claim 1 or 2, wherein, The chemically strengthened glass is a glass-ceramic.

7. The chemically strengthened glass of claim 6, wherein, The crystallization rate of the glass-ceramic is 10% or more.

8. The chemically strengthened glass of claim 6, wherein, The crystallization rate of the glass-ceramic is 70% or less.

9. The chemically strengthened glass of claim 1 or 2, wherein, A haze value of transmitted light of the chemically strengthened glass converted to a thickness of 0.7 mm measured by a method conforming to JIS K7136:2000 is 0.01% to 0.2%.

10. The chemically strengthened glass of claim 1 or 2, wherein, The visible light transmittance of the chemically strengthened glass converted to a thickness of 0.7 mm is 85% or more.

11. The chemically strengthened glass of claim 1 or 2, wherein, ZrO2 is 3 mol% or more on a molar percentage on an oxide basis.

12. The chemically strengthened glass of claim 1 or 2, wherein, The Young's modulus is 100 GPa or more but does not include 100 GPa.

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