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

Abstract

Provided is a chemically strengthened glass having excellent drop strength. A chemically strengthened glass in which the stress CT at the center of the sheet thickness satisfies the relationship of formula (1), and the compressive stress CS120 at a depth direction 120 [mu] m from the surface satisfies the relationship of formula (2). Formula (1) | CT | < =-170t + 175, Formula (2) 190t-124 < = CS120, in formula (1), | CT | represents the absolute value of stress CT, with the unit being MPa. In formula (1) and formula (2), t represents the sheet thickness of the chemically strengthened glass in mm. In formula (2), CS120 represents the value of compressive stress CS120, with the unit being MPa.

Description

TECHNICAL FIELD

[0001] The present application relates to a chemically strengthened glass.

[0002] Further, the present application also relates to a method for manufacturing a chemically strengthened glass.

[0003] Further, the present application also relates to a cover glass comprising the above-mentioned chemically strengthened glass and a solar cell module comprising the above-mentioned cover glass. BACKGROUND

[0004] In recent years, cover glasses have been applied in order to protect display devices such as displays for mobile phones, smartphones, tablet terminals, and car-mounted displays, and to enhance the aesthetic appearance. For cover glasses for these uses, excellent strength is required in order to suppress breakage due to impact or the like.

[0005] Further, the cover glass as described above can also be used to protect solar cell modules and the like.

[0006] Conventionally, a method for improving the surface strength of a glass by immersing the glass in a potassium nitrate molten salt or the like to perform a chemical strengthening treatment has been known. For example, Patent Literature 1 discloses a method for improving the surface strength of a glass sheet by immersing the glass in a potassium nitrate molten salt to perform a chemical strengthening treatment. More specifically, it discloses a method for improving the strength of a glass sheet by sequentially performing a chemical strengthening treatment on a glass containing Li with a molten salt containing Na and a molten salt containing K. Further, it is described that the strengthening mechanism of the strength of the glass sheet based on this chemical treatment is due to compressive stress caused by exchange of alkali metals.

[0007] PRIOR ART DOCUMENTS

[0008] PATENT LITERATURE

[0009] Patent Literature 1: International Publication No. 2022 / 004808 SUMMARY

[0010] In recent years, cover glasses can be adjusted in plate thickness due to various requirements. For example, in recent years, in order to reduce the weight and thickness of a housing, it is sometimes necessary to reduce the plate thickness of a cover glass.

[0011] The present inventors have found that the drop strength sometimes decreases when the plate thickness of a cover glass is adjusted, and thus it is necessary to improve it. In particular, in the case where the plate thickness of a cover glass is reduced, the drop strength sometimes becomes small, and thus it is necessary to improve it.

[0012] The present application was made in view of the above-described problems, and its object is to provide a chemically strengthened glass having excellent drop strength.

[0013] Further, the present application also provides a method for manufacturing chemically strengthened glass.

[0014] Further, the present application also provides a cover glass and a solar cell module.

[0015] The present inventors have intensively studied the above problem, and as a result, have found that if the relationship between the stress value and the plate thickness is a prescribed relationship, the drop strength is excellent, thereby completing the present application.

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

[0017] 〔1〕 A chemically strengthened glass, wherein a stress CT at a central position of a plate thickness satisfies the following formula (1), and a compressive stress CS at a position 120 μm from a surface in a depth direction 120 satisfies the following formula (2).

[0018] Formula (1) |CT| ≤ -170t + 175

[0019] Formula (2) 190t - 124 ≤ CS 120

[0020] In formula (1), |CT| represents the absolute value of the stress CT, and the unit is MPa.

[0021] In formula (1) and formula (2), t represents the plate thickness of the chemically strengthened glass, and the unit is mm.

[0022] In formula (2), CS 120 represents the value of the compressive stress CS 120 , and the unit is MPa.

[0023] 〔2〕 The chemically strengthened glass according to 〔1〕, wherein a depth of a compressive stress layer DOC is 0.20 times or more of the plate thickness of the chemically strengthened glass.

[0024] 〔3〕 The chemically strengthened glass according to 〔2〕, wherein the absolute value of a slope of a stress distribution curve from the depth of the compressive stress layer DOC to the central position of the plate thickness is 1.00 or less.

[0025] 〔4〕 The chemically strengthened glass according to any one of 〔1〕 to 〔3〕, wherein a compressive stress CS 50 at a position 50 μm from the surface in the depth direction satisfies formula (3).

[0026] Formula (3) 150t - 50 ≤ CS 50

[0027] In formula (3), CS 50 represents the compressive stress CS 50of 0.80 MPa • m

[0028] In formula (3), t represents the thickness of the chemically strengthened glass, in mm.

[0029] 〔5〕 The chemically strengthened glass according to any one of claims 1 to 4, wherein the Young's modulus at the in-plane central position is 80 GPa or greater.

[0030] 〔6〕 The chemically strengthened glass according to any one of claims 1 to 5, wherein the fracture toughness value K IC of 0.80 MPa • m 1 / 2 or greater at the in-plane central position.

[0031] 〔7〕 The chemically strengthened glass according to any one of claims 1 to 6, wherein the composition at the central position of the thickness, expressed in terms of mole percentage on an oxide basis, contains 55 to 75% of SiO2, 3 to 18% of Al2O3, 17 to 30% of Li2O, 0 to 3% of Na2O, 0 to 1% of K2O, 0 to 10% of MgO, 0 to 10% of CaO, 0 to 5% of SrO, 0 to 5% of ZnO, 0 to 3% of TiO2, 0 to 5% of ZrO2, 0 to 1% of SnO2, 0 to 3% of P2O5, 0 to 10% of B2O3, and 0 to 3% of Y2O3.

[0032] 〔8〕 The chemically strengthened glass according to any one of claims 1 to 7, which is a crystallized glass, and has a transmittance of 85% or greater.

[0033] 〔9〕 The chemically strengthened glass according to any one of claims 1 to 8, wherein the compressive stress CS 120 is 0 MPa or less.

[0034] 〔10〕 The chemically strengthened glass according to any one of claims 1 to 9, wherein the thickness is 0.6 mm or less.

[0035] 〔11〕 The chemically strengthened glass according to any one of claims 1 to 10, wherein the absolute value of the first derivative value of the stress distribution curve in the depth direction obtained using a scattered light photoelastic stress meter for the chemically strengthened glass is 1.80 or less at any depth from a position 120 μm from the surface in the depth direction to the central position of the thickness.

[0036] 〔12〕 The chemically strengthened glass according to claim 2 or 3, wherein the absolute value of the first derivative value of the stress distribution curve in the depth direction obtained using a scattered light photoelastic stress meter is 1.80 or less at the depth DOC of the compressive stress layer.

[0037] 〔13〕 The chemically strengthened glass according to any one of claims 2 to 3, wherein, in a stress profile in the depth direction obtained using a scattered light photoelastic stress meter, a value obtained by dividing an absolute value of a first derivative at the depth of the compressive stress layer DOC by an absolute value of a first derivative at a position 120 μm from the surface in the depth direction is 1.20 or less.

[0038] 〔14〕 A method for producing a chemically strengthened glass, which is a method for producing the chemically strengthened glass according to any one of claims 1 to 13, wherein a first chemically strengthening treatment is performed on a glass for chemical strengthening using a first molten salt containing 90 mass% or more of a Na salt and 2 mass% or more of a Li salt with respect to the total mass, and a second chemically strengthening treatment is performed on the glass for chemical strengthening subjected to the first chemically strengthening treatment using a second molten salt containing 90 mass% or more of a K salt with respect to the total mass, and the glass for chemical strengthening contains, in terms of mole percentage on an oxide basis, 60 to 72% of SiO2, 10 to 20% of Al2O3, 3 to 12% of Li2O, 0.5 to 6% of Na2O, and 1 to 3% of K2O at a central position in the thickness of the glass.

[0039] 〔15〕 The method for producing a chemically strengthened glass according to claim 14, wherein a ratio of a content of the Li salt in the first molten salt to a content of Li2O in the composition of the glass for chemical strengthening is 0.1 to 1.0 in terms of mole ratio.

[0040] 〔16〕 The method for producing a chemically strengthened glass according to claim 14 or 15, wherein a time of the first chemically strengthening treatment is 150 minutes or more, and a time of the second chemically strengthening treatment is 90 minutes or more.

[0041] 〔17〕 A cover glass comprising the chemically strengthened glass according to any one of claims 1 to 13.

[0042] 〔18〕 A solar cell module comprising the cover glass according to claim 17.

[0043] According to the present application, it is possible to provide a chemically strengthened glass having excellent drop strength.

[0044] Further, according to the present application, it is possible to provide a method for producing a chemically strengthened glass.

[0045] Further, according to the present application, it is possible to provide a cover glass and a solar cell module. BRIEF DESCRIPTION OF DRAWINGS

[0046] Figure 1 is a graph showing a method for calculating various characteristic temperatures from a DSC (Differential Scanning Calorimetry) curve of a glass.

[0047] Figure 2 The fracture toughness value K IC An explanatory view of a sample used in the present application.

[0048] Figure 3 The fracture toughness value K IC An explanatory view of a K1-v curve showing the relationship between a stress amplification coefficient K1 (unit: MPa•m 1 / 2 ) and a crack propagation speed v (unit: m / s) in the present application. DETAILED DESCRIPTION

[0049] Hereinafter, the present application will be described in detail.

[0050] The following description of the components is sometimes based on representative embodiments of the present application, but the present application is not limited to such embodiments.

[0051] 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.

[0052] In the present specification, the glass composition of the glass for chemical strengthening is sometimes referred to as the parent glass composition of the chemically strengthened glass. In the chemically strengthened glass, a compressive stress layer due to 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 parent glass composition of the chemically strengthened glass.

[0053] In the present specification, the glass composition is expressed in terms of molar percentage on an oxide basis, and the mol% is sometimes simply written as %. In addition, "~" indicating a numerical range is used in the meaning that the values written before and after it are included as lower limit values and upper limit values.

[0054] In the glass composition, "substantially not containing" means not containing, i.e., not intentionally containing, except for unavoidable impurities contained in raw materials and the like. Specifically, for components other than those described as the glass composition, for example, it is preferable to be less than 0.1 mol%, more preferable to be 0.08 mol% or less, and further preferable to be 0.05 mol% or less.

[0055] In the present specification, "stress distribution" is a pattern showing the compressive stress value with the depth from the glass surface as a variable. A negative compressive stress value refers to a tensile stress.

[0056] The stress profile of the glass can be measured using a scattered light photoelastic stress meter (SLP: Scatterd Light Photoelastic Stress Meter) and a film stress measurment (FSM: Film Stress Measurment).

[0057] In the present specification, the stress profile measured by the scattered light photoelastic stress meter (SLP) is referred to as an "SLP stress profile", and the stress profile measured by the film stress measurment (FSM) is referred to as an "FSM stress profile".

[0058] Note that the film stress measurment (FSM) can accurately measure the stress of the glass in a short time. As the FSM, for example, there is FSM-6000 manufactured by WOOLAM Co., Ltd. However, the FSM can measure the stress only in a case where the refractive index decreases from the surface of the sample toward the inside in principle. In the chemically strengthened glass, the layer in which the sodium ions inside the glass are replaced with the potassium ions outside the glass has a refractive index that decreases from the surface of the sample toward the inside, and thus the stress can be measured by the FSM. However, the stress of the layer in which the lithium ions inside the glass are replaced with the sodium ions outside the glass cannot be accurately measured by the FSM.

[0059] On the other hand, the method using the scattered light photoelastic stress meter (SLP) can measure the stress regardless of the refractive index profile. As the SLP, for example, there are SLP-1000 and SLP-2000 manufactured by WOOLAM Co., Ltd. can be cited. If these scattered light photoelastic stress meters are combined with the attached software SlpIV_up3 (Ver. 2019.01.10.001), high-precision stress measurement can be achieved. However, the SLP is easily affected by surface scattering, and sometimes the stress near the surface cannot be accurately measured.

[0060] For the above reasons, by combining the use of both the film stress measurment (FSM) and the scattered light photoelastic stress meter (SLP), accurate stress measurement can be achieved in the entire thickness range of the chemically strengthened glass.

[0061] In the present specification, the stress profile in which the SLP information and the FSM information are synthesized is referred to as a "synthesized stress profile".

[0062] The method of measuring the stress profile near the surface of the glass using the FSM can be referred to a known method. In addition, regarding the method of measuring the stress profile of the glass inside several tens of μm or more from the surface layer of the glass using the SLP, a known method can be referred to. As the above known method, for example, the method described in International Publication No. 2018 / 056121 and International Publication No. 2017 / 115811 can be cited.

[0063] In this specification, the compressive stress layer depth refers to the depth where the compressive stress value is zero.

[0064] In this specification, "fracture toughness value K" IC "The determination was performed using the DCDC method [Reference: MY He, MR Turner and AG Evans, Acta Metall. Mater. 43 (1995) 3453.]. Specifically, using..." Figure 2 The sample of the shape shown and the SHIMADZU Autograph AGS-X5KN were measured. Figure 3 The figure shows the stress amplification factor K1 (unit: MPa•m). 1 / 2 The K1-v curve showing the relationship between crack propagation rate v (unit: m / s) and Region III data was used for regression and extrapolation using a linear formula. The stress expansion factor K1 corresponding to v = 0.1 m / s was taken as the fracture toughness value K. IC .

[0065] <Chemical strengthened glass>

[0066] In the chemically strengthened glass of the present invention, the stress CT at the center of the plate thickness satisfies the following relationship (1), and the compressive stress CS at a depth of 120 μm from the surface is... 120 The following relationship (2) is satisfied.

[0067] Equation (1) |CT|≤-170t+175

[0068] Equation (2) 190t-124≤CS 120

[0069] In equation (1), |CT| represents the absolute value of stress CT, with the unit being MPa.

[0070] In equations (1) and (2), t represents the thickness of the chemically strengthened glass, in mm.

[0071] In equation (2), CS 120 Represents compressive stress CS 120 The value is in MPa.

[0072] The mechanism by which the chemically strengthened glass of the present invention, which satisfies the relationship of the above formulas (1) and (2), has excellent drop strength is still uncertain, but the inventors speculate as follows.

[0073] It can be assumed that when glass cracks, the damage on the glass surface gradually develops and leads to the crack.

[0074] In the chemically strengthened glass of the present application, a compressive stress acts on the surface of the chemically strengthened glass by chemical strengthening, and the relationship of formula (1) is satisfied, so the drop strength is easily increased. Furthermore, the chemically strengthened glass of the present application satisfies the relationship of formula (2). The relationship of formula (2) indicates that the compressive stress CS 120 is in the prescribed range, even if the damage reaches the deep portion (for example, the depth of 120 μm) of the chemically strengthened glass, the damage is difficult to progress, and the drop strength is easily increased. 120 Thus, the chemically strengthened glass of the present application satisfying the relationship of formula (2) is excellent in the drop strength.

[0075] According to the above, it can be considered that the chemically strengthened glass of the present application is excellent in the drop strength.

[0076] Hereinafter, the conditions and the like satisfied by the chemically strengthened glass of the present application will be described.

[0077] [Plate thickness]

[0078] The plate thickness of the chemically strengthened glass of the present application is preferably 0.8 mm or less, more preferably 0.7 mm or less, and further preferably 0.6 mm or less.

[0079] In addition, the plate thickness of the chemically strengthened glass of the present application is mostly 0.1 mm or more, preferably 0.2 mm or more, more preferably 0.3 mm or more, and further preferably 0.4 mm or more.

[0080] [Compressive stress]

[0081] The compressive stress (CS 120 ) at the depth of 120 μm of the chemically strengthened glass of the present application satisfies the relationship of formula (2) with respect to the plate thickness t and CS 120 .

[0082] CS 120 is preferably -30 MPa or more, more preferably -25 MPa or more, further preferably -20 MPa or more, particularly preferably -15 MPa or more, and most preferably -10 MPa or more. CS 120 may be 0 MPa or more, or 10 MPa or more. In addition, CS 120 is mostly 50 MPa or less, and when the above plate thickness is 0.6 mm or less, it is mostly 20 MPa or less. CS 120 may be 0 MPa or less.

[0083] CS 120 may be calculated from the SLP stress distribution curve.

[0084] The compressive stress (CS 50 ) at a depth of 50 μm of the chemically strengthened glass of the present application is preferably 20 MPa or more, more preferably 30 MPa or more, and further preferably 40 MPa or more. In addition, from the viewpoint of more easily increasing the drop strength, the CS 50 is preferably 200 MPa or less, more preferably 150 MPa or less, further preferably 100 MPa or less, particularly preferably 75 MPa or less, and most preferably 60 MPa or less.

[0085] The CS 50 may be obtained from the SLP stress profile.

[0086] In addition, the compressive stress (CS 50 ) at a depth of 50 μm of the chemically strengthened glass of the present application preferably satisfies the following equation (3) with respect to the plate thickness t and the CS 50 .

[0087] Equation (3) 150t - 50 ≤ CS 50

[0088] In equation (3), CS 50 represents the value of the compressive stress CS 50 , and the unit is MPa.

[0089] In equation (3), t represents the plate thickness of the chemically strengthened glass, and the unit is mm.

[0090] The compressive stress (CS0) of the surface of the chemically strengthened glass of the present application is preferably 700 MPa or more, more preferably 800 MPa or more, further preferably 900 MPa or more, and particularly preferably 1000 MPa or more.

[0091] The CS0may be obtained by a surface stress measuring device such as FSM.

[0092] Each of the above compressive stresses can be adjusted by, for example, the conditions of the chemical strengthening treatment described later.

[0093] [Depth of Compressive Stress Layer]

[0094] The depth of the compressive stress layer DOC of the chemically strengthened glass of the present application is preferably 80 μm or more, more preferably 90 μm or more, and further preferably 100 μm or more. In addition, the depth of the compressive stress layer DOC is in most cases 200 μm or less, preferably 150 μm or less, more preferably 130 μm or less, and further preferably 120 μm or less.

[0095] The depth of the compressive stress layer DOC can be obtained from the SLP stress profile.

[0096] The depth of the compressive stress layer DOC is preferably 0.16 times or more of the thickness of the sheet, more preferably 0.17 times or more of the thickness of the sheet, and further preferably 0.20 times or more of the thickness of the sheet. In addition, the depth of the compressive stress layer DOC is usually 0.30 times or less of the thickness of the sheet, and in most cases, 0.25 times or less of the thickness of the sheet, and preferably 0.23 times or less of the thickness of the sheet.

[0097] [Stretching stress]

[0098] The chemically strengthened glass of the present application has a compressive stress near the surface, and therefore, in the interior of the chemically strengthened glass, a stretching stress that balances with the compressive stress is present. That is, the stress CT at the center of the thickness of the chemically strengthened glass of the present application is usually a stretching stress (a compressive stress of a negative value).

[0099] Note that, as described above, the stress CT at the center of the thickness of the chemically strengthened glass of the present application satisfies the above-described relationship of Equation (1) with respect to the thickness t and the stress CT.

[0100] The absolute value of the stress CT is preferably 30 MPa or more, more preferably 40 MPa or more, and further preferably 50 MPa or more, and can be 70 MPa or more. In addition, the absolute value of the stress CT is preferably 100 MPa or less, more preferably 95 MPa or less, and further preferably 90 MPa or less.

[0101] [Gradient of stress distribution curve]

[0102] With respect to the SLP stress distribution curve, if an appropriate function is used for fitting, the function after fitting can be differentiated, and the SLP stress distribution curve can be further analyzed. Note that the SLP stress distribution curve has the depth (unit: pm) as the horizontal axis and the compressive stress value (unit: MPa) as the vertical axis.

[0103] The fitting of the SLP stress distribution curve can be performed using the following function (Equation (FS)).

[0104]

[0105] In the above Equation (FS), a i (i = 1 to 5) is a fitting parameter, and erfc is a complementary error function. In addition, in Equation (FS), x represents the depth.

[0106] The complementary error function (erfc(x)) is defined by the following equation.

[0107]

[0108] The fitting is performed using the attached software [SlpIV (Ver. 2019.01.10.001)] of a scattered light photoelastic stress meter (SLP-1000 manufactured by SORI Co., Ltd.). More specifically, the fitting parameters are optimized by minimizing the residual sum of squares of the obtained raw data and the function described above in accordance with the attached software specifications. The measurement processing conditions are set to a single mode, and the measurement area processing adjustment items are respectively designated as: surface selection edge method, internal surface end selection of 6.0 μm, internal left and right end selection of automatic mode, internal deep end selection of automatic (sample film thickness center) mode, and then phase curve sample thickness center extension selection of fitting curve.

[0109] The fitted function obtained by the above-described step can be subjected to first-order differentiation, and can be subjected to second-order differentiation. Hereinafter, the fitted function is also referred to as σ f (x).

[0110] The fitted function (σ f (x)) is differentiated with respect to x (depth), and a first derivative function σ f '(x) is obtained. If the value of the depth is substituted into σ f '(x), the slope (first-order differential value) of σ f (x) at the depth is obtained.

[0111] The absolute value of the above-described first-order differential value of the chemically strengthened glass of the present application is preferably 1.80 or less, more preferably 1.20 or less, further preferably 0.80 or less, and most preferably 0.60 or less at any depth from a position 120 μm from the surface in the depth direction to the center position of the plate thickness. In addition, the absolute value of the above-described first-order differential value is 0.10 or more, preferably 0.20 or more, and more preferably 0.30 or more at any depth from a position 120 μm from the surface in the depth direction to the center position of the plate thickness.

[0112] In addition, the absolute value of the above-described first-order differential of the chemically strengthened glass of the present application is preferably 1.80 or less, more preferably 1.40 or less, and further preferably 1.00 or less at the depth DOC of the compressive stress layer. In addition, the absolute value of the above-described first-order differential is preferably 0.10 or more, more preferably 0.20 or more, and further preferably 0.30 or more at the depth DOC of the compressive stress layer.

[0113] In addition, in the chemically strengthened glass of the present application, the absolute value of the slope calculated from the compressive stress value at the depth DOC of the compressive stress layer and the compressive stress value at the center position of the plate thickness is preferably 1.00 or less, more preferably 0.95 or less, and further preferably 0.90 or less. The absolute value of the slope is also preferably 0.60 or less. The absolute value of the slope is 0.20 or more, and is preferably 0.30 or more.

[0114] Note that the absolute value of the above slope can be obtained by dividing the value of the stress CT by the value obtained by subtracting the depth of the compressive stress layer DOC from the depth of the central position of the plate thickness, and taking the absolute value thereof.

[0115] In addition, in the chemically strengthened glass of the present application, in the stress distribution curve in the depth direction obtained using a scattered light photoelastic stress meter, the value obtained by dividing the absolute value of the first derivative at the depth of the compressive stress layer DOC by the absolute value of the first derivative at a position 120 μm from the surface in the depth direction (hereinafter, also referred to as "first derivative ratio") is preferably 1.20 or less. The above first derivative ratio is preferably 0.80 or more, more preferably 0.90 or more, and further preferably 1.00 or more, from the viewpoint of more excellent drop strength. In addition, the above first derivative ratio is more preferably 1.15 or less, from the viewpoint of more excellent drop strength.

[0116] [Young's modulus]

[0117] The Young's modulus at the central position in the plane of the chemically strengthened glass of the present application is preferably 80 GPa or more. The above Young's modulus is more preferably 83 GPa or more, further preferably 85 GPa or more, and particularly preferably 90 GPa or more. Note that the Young's modulus at the central position in the plane of the chemically strengthened glass refers to the Young's modulus measured at the central position in the in-plane direction of the plate-shaped chemically strengthened glass. The central position in the in-plane direction refers to the position of the center of gravity in the in-plane direction, and in the case where the chemically strengthened glass is square when viewed from above, the central position is the position of the intersection of the diagonal lines.

[0118] The above Young's modulus can be adjusted by the composition of the glass used for chemical strengthening (parent glass composition), and in addition, can be adjusted by the heat treatment conditions such as the heat treatment temperature, heat treatment time, cooling rate, and temperature profile of the glass for chemical strengthening. For example, when the parent glass composition is a composition that can become a crystalline glass, the value of the Young's modulus easily changes with the above heat treatment conditions.

[0119] In addition, in the chemically strengthened glass of the present application, the Young's modulus at the central position of the plate thickness is preferably 80 GPa or more, more preferably 83 GPa or more, further preferably 85 GPa or more, and particularly preferably 90 GPa or more. Note that the Young's modulus of the glass for chemical strengthening corresponds to the Young's modulus at the central position of the plate thickness of the chemically strengthened glass.

[0120] In the present specification, the Young's modulus at the central position in the plane of the chemically strengthened glass and the Young's modulus at the central position of the plate thickness are values measured by the ultrasonic pulse method. The detailed measurement method of the Young's modulus is shown in the following examples.

[0121] [fracture toughness value]

[0122] The fracture toughness value (K IC ) at the center of the plate thickness of the chemically strengthened glass of the present application is preferably 0.75 MPa • m 1 / 2 or more from the viewpoint of further increasing the strength of the crack. 1 / 2 More preferably, it is 0.80 MPa • m 1 / 2 or more, and further preferably, it is 0.85 MPa • m IC or more. The fracture toughness value (K 1 / 2 ) at the center of the plate thickness of the chemically strengthened glass of the present application is preferably 1.80 MPa • m 1 / 2 or less.

[0123] The method for measuring the fracture toughness value at the center of the plate thickness of the chemically strengthened glass of the present application is the method for measuring the fracture toughness value described in the following examples.

[0124] Note that the fracture toughness value of the glass for chemical strengthening corresponds to the fracture toughness value at the center of the plate thickness of the chemically strengthened glass.

[0125] The fracture toughness value (K IC ) at the center of the plate thickness of the chemically strengthened glass of the present application can be adjusted, for example, in the same manner as the Young's modulus described above.

[0126] [transmittance]

[0127] The transmittance of the chemically strengthened glass of the present application is preferably 85% or more.

[0128] The transmittance of the chemically strengthened glass is measured using a spectrophotometer.

[0129] More specifically, first, a sample for measurement having a plate thickness of 0.50 mm is prepared, and measurement is performed using the device of LAMBDA 950 manufactured by PerkinElmer. From the measurement results, the average transmittance [unit: %] at wavelengths of 380 to 780 nm is calculated as the transmittance of the chemically strengthened glass of the present application.

[0130] The transmittance of the chemically strengthened glass of the present application is preferably 90% or more, and can be 95% or more. The transmittance of the chemically strengthened glass of the present application is mostly 99% or less.

[0131] In addition, the chemically strengthened glass of the present application is a crystallized glass, and preferably has the transmittance described above.

[0132] [composition]

[0133] The chemically strengthened glass of the present application can be obtained by subjecting a plate-shaped glass (glass for chemical strengthening) before chemical strengthening to a chemical strengthening treatment.

[0134] Hereinafter, a preferred composition (parent glass composition) of the chemically strengthened glass will be described. Note that the parent glass composition coincides with the composition at the center of the plate thickness of the chemically strengthened glass.

[0135] Hereinafter, as the preferred parent glass composition, the first embodiment and the second embodiment will be described.

[0136] (First Embodiment)

[0137] The first embodiment of the parent glass composition contains, in terms of molar percentage on an oxide basis, 60 to 72% of Si02, 10 to 20% of Al203, 3 to 12% of Li20, 0.5 to 6% of Na20, and 0 to 3% (preferably 1 to 3%) of K20.

[0138] The first embodiment of the parent glass composition contains, in terms of molar percentage on an oxide basis, 60 to 72% of Si02, 10 to 20% of Al203, 3 to 12% of Li20, 0.5 to 6% of Na20, 0 to 3% of K20, 0 to 10% of MgO, 0 to 10% of CaO, 0 to 5% of SrO, 0 to 5% of ZnO, 0 to 3% of Ti02, 0 to 3% of Zr02, 0 to 1% of Sn02, 0 to 1% of P205, 0 to 10% of B203, 0 to 3% of Y203, the total of the content of Li20, the content of Na20, and the content of K20, that is, R is 5 to 20%, the ratio of the content of Li20 to R is 0.5 to 0.95, and the value of the product of the ratio of the content of Li20 to R, the ratio of the content of Na20 to R, and the ratio of the content of K20 to R is 0.001 to 0.03.

[0139] Hereinafter, each component contained in the parent glass composition will be described. Note that hereinafter, the content expressed in terms of molar percentage on an oxide basis of Si02, for example, will be referred to as "[Si02]".

[0140] Si02is a component that constitutes the network structure of the glass. In addition, it is a component that improves chemical durability and a component that reduces cracks when the glass surface is scratched.

[0141] In order to improve chemical durability, the content of Si02is more preferably 60.0% or more, further preferably 62.0% or more, particularly preferably 64.0% or more, and most preferably 66.0% or more. On the other hand, from the viewpoint of good meltability, the content of Si02is more preferably 70.0% or less, further preferably 68.0% or less, and particularly preferably 67.0% or less.

[0142] Al2O3 is a component that improves ion exchange performance during chemical strengthening and increases surface compressive stress after strengthening. From the viewpoint of achieving these effects, the content of Al2O3 is more preferably 10.0% or more, and even more preferably 10.5% or more and 11.0% or more. On the other hand, it is sometimes also required that the glass does not easily grow crystals during melting, does not easily generate devitrification defects, easily improves yield, and is easily meltable by reducing the high-temperature viscosity of the glass. From this viewpoint, the content of Al2O3 is more preferably 15.0% or less, and even more preferably 14.0% or less, 13.5% or less, and 13.0% or less.

[0143] Both SiO2 and Al2O3 are components that stabilize the structure of glass. To reduce brittleness, the combined content of SiO2 and Al2O3 is preferably 74.0% or more, more preferably 76.0% or more, and even more preferably 77.0% or more. Furthermore, both SiO2 and Al2O3 tend to increase the melting temperature of glass. Therefore, to facilitate melting, the combined content of SiO2 and Al2O3 is preferably 83.0% or less, more preferably 82.0% or less, even more preferably 81.0% or less, and particularly preferably 80.5% or less.

[0144] Li₂O is an ion-exchangeable component that improves the melt permeability of glass. Since the glass contains Li₂O, Li ions on the glass surface exchange with external Na ions to enter the glass interior. Furthermore, the Na ions exchange with external K ions, easily resulting in a stress distribution curve with high surface compressive stress and a thick compressive stress layer. From the viewpoint of easily obtaining an optimal stress distribution curve, the Li₂O content is more preferably 8.0% or more, and sequentially more preferably 9.0% or more, 9.5% or more, 10.0% or more, 10.2% or more, and 10.4% or more.

[0145] On the other hand, from the viewpoint of reducing the crystal growth rate in glass forming and making it less likely to cause a decrease in quality due to devitrification, the content of Li2O is more preferably 11.8% or less, and even more preferably 11.5% or less and 11.0% or less.

[0146] Na₂O and K₂O are components that improve the meltability of glass and reduce the crystal growth rate during glass forming. Additionally, a small amount is preferred to improve ion exchange performance.

[0147] Na₂O is an ion-exchangeable component in the chemical strengthening treatment using potassium salts, and it also reduces the viscosity of glass. To achieve the above effects, the Na₂O content is preferably 1% or more, and more preferably 1.5% or more, 2.5% or more, 3.0% or more, and 4.0% or more.

[0148] K2O is a component that suppresses devitrification by suppressing the increase in devitrification temperature and improves ion exchange performance. The content of K2O is more preferably 0.1% or more, further preferably 0.15% or more, and sequentially particularly preferably 0.2% or more, 0.5% or more, 1.0% or more.

[0149] The total of the content of Li2O, the content of Na2O, and the content of K2O, i.e., R, is more preferably 8% or more, further preferably 9% or more, and particularly preferably 12% or more, and most preferably 15% or more, from the viewpoint of suppressing the increase in devitrification temperature and reducing the crystal growth rate.

[0150] The ratio of the content of Li2O to the above R ([Li2O] / ([Li2O]+[Na2O]+[K2O]), hereinafter also referred to as "Li2O / R2O"), is more preferably 0.52 or more, and further preferably 0.55 or more, from the viewpoint of further improving the chemical strengthening properties of the compressive stress with respect to the deep portion. Li2O / R2O is more preferably 0.90 or less, further preferably 0.85 or less, and particularly preferably 0.75 or less, from the viewpoint of further improving the chemical agent durability.

[0151] The ratio of the content of Na2O to the above R ([Na2O] / ([Li2O]+[Na2O]+[K2O]), hereinafter also referred to as "Na2O / R2O"), is preferably 0.08 or more, more preferably 0.15 or more, and further preferably 0.20 or more, from the viewpoint of further improving the chemical strengthening properties of the compressive stress with respect to the deep portion. Na2O / R2O is preferably 0.60 or less, more preferably 0.50 or less, further preferably 0.40 or less, and particularly preferably 0.35 or less, from the viewpoint of further improving the chemical agent durability.

[0152] The ratio of the content of K2O to the above R ([K2O] / ([Li2O]+[Na2O]+[K2O]), hereinafter also referred to as "K2O / R2O"), is preferably 0.01 or more, more preferably 0.015 or more, further preferably 0.02 or more, and particularly preferably 0.08 or more, from the viewpoint of further improving the resistance of the glass. 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, from the viewpoint of further improving the chemical strengthening properties of the compressive stress with respect to the vicinity of the surface.

[0153] Further, the product of Li2O / R2O, Na2O / R2O, and K2O / R2O is more preferably 0.002 or more, further preferably 0.01 or more, and particularly preferably 0.015 or more from the viewpoint of suppressing an increase in devitrification temperature. Further, the product is more preferably 0.028 or less from the viewpoint of improving chemical resistance.

[0154] The ratio of the content of Al2O3 to the above R ([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 more preferably 0.50 or more. The Al2O3 / R2O is preferably 1.50 or less, more preferably 0.80 or less, further preferably 0.75 or less, particularly preferably 0.70 or less, and most preferably 0.65 or less.

[0155] Further, the ratio of the content of K2O to the content of Na2O ([K2O] / [Na2O]) is preferably 0.0 to 1.8. From the viewpoint of increasing compressive stress in the vicinity of the surface and more easily obtaining a chemically strengthened glass having a higher bending test strength, the [K2O] / [Na2O] is preferably 0.1 or more, and more preferably 0.2 or more. Further, from the above viewpoint, the [K2O] / [Na2O] is preferably 1.0 or less, more preferably 0.9 or less, further preferably 0.8 or less, and particularly preferably 0.7 or less.

[0156] The value represented by [Al2O3] - [Na2O] - [K2O] + [Li2O] is preferably 10.0 to 22.0, more preferably 10.0 to 20.0, and further preferably 12.0 to 18.0.

[0157] MgO can be contained for the purpose of reducing viscosity at the time of dissolution or the like. The content of MgO is more preferably 0.05% or more, and successively further preferably 0.1% or more, 0.2% or more, 0.9% or more, more than 0.9%, and 1.0% or more. On the other hand, from the viewpoint of easily increasing a compressive stress layer at the time of chemical strengthening treatment, the content of MgO is more preferably 8.0% or less, and successively further preferably 7.5% or less, 5.0% or less, 4.0% or less, and 3.8% or less. By setting the content of MgO to 4.0% or less, it is possible to improve acid resistance.

[0158] Further, by containing MgO, it is possible to suppress phase transition of a crystal phase from a β-quartz solid solution to a β-spodumene, and it is possible to suppress precipitation of β-spodumene crystals. Thus, in the first embodiment, it is preferable to contain MgO. From the above viewpoint, it is preferable to contain MgO of more than 0.5% and 7.0% or less. A further preferable range is as described above.

[0159] CaO is a component that improves the melting property of the glass, and can be contained. The content of CaO is more preferably 0.1% or more, and further preferably 0.15% or more. On the other hand, from the viewpoint of easily increasing the compressive stress value at the time of chemical strengthening treatment, the content of CaO is more preferably 2.0% or less, further preferably 1.0% or less, particularly preferably 0.8% or less, and most preferably 0.5% or less.

[0160] In order to improve the stability of the glass, it is more preferable to contain at least one of MgO and CaO, and it is further preferable to contain MgO. The content of the total of MgO and CaO is preferably more than 0.1%, more preferably 0.2% or more, and further preferably 0.5% or more. From the viewpoint of further improving the chemical strengthening characteristics, the content of the total of MgO and CaO is preferably 10.0% or less, and successively more preferably 5.0% or less, 3.5% or less.

[0161] SrO is a component that improves the melting property of the glass, and can be contained. The content of SrO is more preferably 0.1% or more, further preferably 0.15% or more, and particularly preferably 0.5% or more. From the viewpoint of easily increasing the compressive stress value at the time of chemical strengthening treatment, the content of SrO is more preferably 3.0% or less, further preferably 2.0% or less, particularly preferably 1.0% or less, and most preferably 0.5% or less. SrO can also be substantially not contained.

[0162] BaO is a component that improves the melting property of the glass, and can be contained. When BaO is contained, the content is preferably 0.1% or more, more preferably 0.15% or more, and further preferably 0.5% or more. From the viewpoint of easily increasing the compressive stress value at the time of chemical strengthening treatment, the content of BaO is preferably 3.0% or less, more preferably 2.0% or less, further preferably 1.0% or less, and particularly preferably 0.5% or less. BaO can also be substantially not contained.

[0163] ZnO is a component that improves the melting property of the glass. The content of ZnO is more preferably 0.1% or more, further preferably 0.15% or more, and particularly preferably 0.5% or more. From the viewpoint of easily increasing the compressive stress value at the time of chemical strengthening treatment, the content of ZnO is more preferably 3.0% or less, further preferably 2.0% or less, particularly preferably 1.0% or less, and most preferably 0.5% or less. ZnO can also be substantially not contained.

[0164] lnW is a parameter that indicates the degree of mixing of oxides calculated from the contents of alkali metal oxides, alkaline earth metal oxides, and zinc oxide contained in the glass. lnW is represented by the following formula.

[0165] InW = In (([Li20] + [Na20] + [K20] + [MgO] + [CaO] + [SrO] + [BaO] + [ZnO]) / ([Li20] x [Na20] x [K20] x [MgO] x [CaO] x [SrO] x [BaO] x [ZnO])) • • • (Wl)

[0166] In formula (Wl), [Li20], [Na20], [K20], [MgO], [CaO], [SrO], [BaO], and [ZnO] each represent the content of each component of Li20, Na20, K20, MgO, CaO, SrO, BaO, and ZnO, respectively, expressed in terms of the molar percentage on an oxide basis.

[0167] In addition, the symbol "!" represents a factorial operation on a positive number. For example, [XO]! means that the value of the content of the component XO expressed in terms of the molar percentage on an oxide basis is rounded off below the decimal point to obtain a positive number, and the factorial of the positive number is calculated. For example, when Na20 is 4.8 mol%, the factorial of "4" is calculated as 4 x 3 x 2 x 1.

[0168] If the value of InW is large, the degree of mixing of the above metal oxides is high, and the devitrification of the glass can be suppressed. From the above viewpoint, InW is preferably 10 or greater, more preferably 12 or greater, further preferably 13 or greater, and particularly preferably 14 or greater. InW is preferably 20 or less, more preferably 18 or less, and further preferably 17 or less.

[0169] Ti02is a component that significantly suppresses the effects of exposure to sunlight, and can be contained. When Ti02is contained, the content is preferably 0.02% or greater, more preferably 0.03% or greater, further preferably 0.04% or greater, particularly preferably 0.05% or greater, and most preferably 0.06% or greater. On the other hand, from the viewpoint of preventing the occurrence of devitrification, which reduces the quality of the chemically strengthened glass, the content of Ti02is preferably 2.0% or less, more preferably 1.0% or less, further preferably 0.5% or less, particularly preferably 0.25% or less, and most preferably 0.15% or less. Ti02may also be substantially not contained.

[0170] Zr02is a component that easily increases the surface compressive stress of the chemically strengthened glass. The content of Zr02is more preferably greater than 0%, and successively further preferably 0.1% or greater, 0.15% or greater, 0.2% or greater, 0.25% or greater, 0.3% or greater, or 0.4% or greater. On the other hand, from the viewpoint of suppressing the occurrence of devitrification defects and easily increasing the compressive stress value at the time of the chemical strengthening treatment, the content of Zr02is more preferably 2.0% or less, and further preferably 1.5% or less.

[0171] P2O5easily increases the compressive stress layer at the time of chemical strengthening. The content of P2O5is more preferably 0.5% or more, further preferably 1.0% or more, and particularly preferably 2.0% or more. On the other hand, from the viewpoint of improving acid resistance, the content of P2O5is more preferably 4.0% or less, and further preferably 2.0% or less. From the viewpoint of preventing the generation of stripes at the time of melting, it is preferable to contain substantially none.

[0172] B2O3reduces the brittleness of the glass and improves the crack resistance, or improves the melting property of the glass. The content of B2O3is more preferably 0.5% or more, further preferably 1.0% or more, and particularly preferably 2.0% or more. On the other hand, from the viewpoint of maintaining the acid resistance well, the content of B2O3is preferably 8.0% or less. The content of B2O3is more preferably 6.0% or less, further preferably 4.0% or less, and particularly preferably 2.0% or less. From the viewpoint of preventing the generation of stripes at the time of melting, it is preferable to contain substantially none.

[0173] Y2O3is a component that easily increases the surface compressive stress of the chemically strengthened glass and reduces the crystal growth rate. The content of Y2O3is more preferably greater than 0%, and successively further preferably 0.1% or more, 0.2% or more, 0.5% or more. On the other hand, from the viewpoint of easily increasing the compressive stress layer at the time of chemical strengthening treatment, the content of Y2O3is more preferably 2.0% or less, and further preferably 1.5% or less.

[0174] From the viewpoint of improving the initial melting property, the total of the contents of ZrO2and Y2O3is preferably 4.0% or less, and more preferably 2.4% or less. The lower limit of the total of the contents of ZrO2and Y2O3is not particularly limited, and from the viewpoint of improving the strength of the glass, it is more preferably 0.5% or more, and successively further preferably 0.7% or more, 1.0% or more, 1.2% or more.

[0175] The ratio of the content of ZrO2to the total content of ZrO2and Y2O3, [ZrO2] / ([ZrO2]+[Y2O3]), is more preferably 0.10 or more, further preferably 0.20 or more, and particularly preferably 0.25 or more. [ZrO2] / ([ZrO2]+[Y2O3]) is more preferably 0.90 or less, further preferably 0.80 or less, and particularly preferably 0.75 or less.

[0176] It is known that ZrO2and Y2O3function as nucleating agents when they are added alone, and by co-adding ZrO2and Y2O3, a eutectic of ZrO2and Y2O3is formed, and it is possible to control the devitrification temperature, the crystal growth rate, and the crystallization start temperature.

[0177] Further, by controlling the ratio of [ZrO2] / ([ZrO2] + [Y2O3]) to the above range, the diffusion of ions in the glass is suppressed, the devitrification temperature is suppressed, and devitrification is suppressed.

[0178] By controlling the ratio of [ZrO2] / ([ZrO2] + [Y2O3]) to the above range, the glass is stabilized, and further, the temperature region where nucleation occurs is separated from the temperature region where crystal growth occurs, and the overlap is avoided, the crystal growth rate is suppressed, and thus the generation of defects can be suppressed. In addition, by controlling the ratio of [ZrO2] / ([ZrO2] + [Y2O3]) to the above range, the temperature region where nucleation occurs shifts to the low temperature side, the decrease in the crystallization onset temperature is suppressed, and the manufacturing properties can be improved.

[0179] From the viewpoint of reducing defects in the glass, the value represented by 100 x [ZrO2] + 63 x [Y2O3] is preferably 250 or less, more preferably 180 or less, further preferably 175 or less, further preferably 170 or less, and particularly preferably 165 or less. The lower limit of the value represented by 100 x [ZrO2] + 63 x [Y2O3] is not particularly limited, but from the viewpoint of promoting nucleation, it is preferably 100 or more, more preferably 110 or more, further preferably 125 or more, and particularly preferably 130 or more.

[0180] La2O3 is not essential, but can be contained based on the same reasons as Y2O3. La2O3 is preferably 0.1% or more, more preferably 0.2% or more, further preferably 0.5% or more, and particularly preferably 0.8% or more. On the other hand, if it is too much, it is not easy to increase the compressive stress layer at the time of chemical strengthening treatment, so La2O3 is preferably 5.0% or less, more preferably 3.0% or less, further preferably 2.0% or less, and particularly preferably 1.5% or less. La2O3 can also be substantially not contained.

[0181] Nb2O5, Ta2O5, Gd2O3, and CeO2 have the effect of suppressing the weathering of the glass, are components that improve the melting property, and can be contained. When these components are contained, the content of each is preferably 0.03% or more, more preferably 0.1% or more, further preferably 0.5% or more, particularly preferably 0.8% or more, and most preferably 1.0% or more. On the other hand, it is preferably 3.0% or less, more preferably 2.0% or less, and further preferably 1.0% or less.

[0182] Fe2O3has an effect of improving the melting property of glass by absorbing heat radiation, and is preferably contained in the case of mass production of glass using a large melting furnace. The content in this case is preferably 0.002% or more, more preferably 0.005% or more, further preferably 0.007% or more, and particularly preferably 0.01% or more, in terms of mass% on an oxide basis. On the other hand, if Fe2O3is excessively contained, coloring occurs, and therefore the content is preferably 0.3% or less, more preferably 0.04% or less, further preferably 0.025% or less, and particularly preferably 0.015% or less, in terms of mass% on an oxide basis, from the viewpoint of improving the transparency of glass.

[0183] Further, other coloring components can be added within a range not impeding achievement of the desired chemical strengthening properties. As the other coloring components, for example, Co3O4, MnO2, NiO, CuO, Cr2O3, V2O5, Bi2O3, SeO2, Er2O3, Nd2O3, and the like can be given as appropriate components.

[0184] As a fining agent or the like at the time of melting of the glass, SO3, chloride, fluoride, and the like can be appropriately contained. It is preferable not to contain As2O3. When Sb2O3is contained, it is preferably 0.3% or less, more preferably 0.1% or less, and most preferably not to be contained.

[0185] From the viewpoint of fining of bubbles in the glass, the content of SnO2is more preferably 0.1% or more, further preferably 0.2% or more, and particularly preferably 0.3% or more. In addition, in order to suppress the generation of defects, the content of SnO2is preferably 1% or less, more preferably 0.8% or less, further preferably 0.7% or less, and particularly preferably 0.5% or less.

[0186] Next, preferred physical properties of the glass of the parent glass composition of the first embodiment will be described.

[0187] (Devitrification temperature)

[0188] The devitrification temperature of the chemically strengthened glass of the parent glass composition of the first embodiment is preferably 1300°C or lower. The devitrification temperature is more preferably 1280°C or lower, and further preferably 1250°C or lower. In order, particularly preferably 1240°C or lower, 1230°C or lower, 1220°C or lower, and 1210°C or lower. The lower limit of the devitrification temperature is not particularly limited, and is generally 1100°C or higher.

[0189] By setting the devitrification temperature to 1300°C or lower (preferably 1280°C or lower), the glass can be stably formed, and the manufacturing properties are improved. Specifically, for example, in the case where the glass is formed by a float method, if crystals are generated before the molten glass flows into a float bath, the crystals sometimes cause erosion of the bricks that constitute the float bath. By setting the devitrification temperature to 1300°C or lower (preferably 1250°C or lower), the erosion of the bricks can be suppressed.

[0190] Note that the devitrification temperature of the glass refers to the minimum value of the temperature at which no crystals are precipitated on the surface and inside of the glass by optical microscopic observation after heat treatment for 17 hours in a thermostat-controlled electric furnace, by adding 2 mm to 3 mm of glass particles to be crushed into a platinum crucible.

[0191] (Glass transition point Tg, crystallization start temperature Tcs, and crystallization peak temperature Tc)

[0192] In the present specification, the measurement by a differential scanning calorimeter (DSC) is performed by the following procedure: the glass is ground in an agate mortar, and about 70 mg of powder having a particle size of 106 to 180 μm is heated from room temperature to 1200°C at a temperature increase rate of 10°C / min.

[0193] The chemically strengthened glass of the parent glass composition of the first embodiment preferably has a crystallization start temperature Tcs of 790°C or higher, more preferably 800°C or higher, further preferably 810°C or higher, still further preferably 815°C or higher, particularly preferably 820°C or higher, and most preferably 825°C or higher, as measured by DSC. The upper limit of the crystallization start temperature is not particularly limited, and is usually 900°C or lower.

[0194] By setting the crystallization start temperature Tcs to 790°C or higher, the manufacturing properties can be improved. Specifically, for example, in a three-dimensional shaped formation (for example, 2.5D or 3D formation. Hereinafter, simply referred to as three-dimensional formation) including heat treatment after the glass is formed into a plate shape, when heated from room temperature to the formation temperature, the nucleation temperature is passed, and defects are easily caused by crystallization. By setting the crystallization start temperature Tcs to 790°C or higher, when heated from room temperature to the formation temperature, the glass can be formed without passing the nucleation temperature, and the generation of defects can be suppressed.

[0195] Figure 1 A schematic diagram for explaining Tg, Tcs, and Tc in the present specification is shown. The glass transition point Tg in the present specification is the intersection point of the auxiliary lines entering the baseline shift region in the curve obtained by DSC, as shown in Figure 1 ​

[0196] For the chemically strengthened glass of the parent glass composition of the first embodiment, the ratio of the crystallization onset temperature Tcs to the glass transition point Tg, (Tcs + 273.15) / (Tg + 273.15), is preferably 1.10 or greater, more preferably 1.15 or greater, further preferably 1.20 or greater, and particularly preferably 1.25 or greater. By making (Tcs + 273.15) / (Tg + 273.15) 1.10 or greater, the generation of defects during three-dimensional molding can be suppressed, and the molding properties can be improved. The upper limit of (Tcs + 273.15) / (Tg + 273.15) is not particularly limited, and is generally preferably 1.6 or less from the viewpoint of the moldability of the glass. Note that Tcs and Tg in "(Tcs + 273.15) / (Tg + 273.15)" are in units of "°C", and "(Tcs + 273.15) / (Tg + 273.15)" is the same as "Tcs / Tg" when the units are set to "K".

[0197] For the chemically strengthened glass of the parent glass composition of the first embodiment, the value obtained by subtracting the glass transition point Tg from the crystallization onset temperature Tcs (Tcs - Tg) is preferably 180°C or greater, more preferably 200°C or greater. Further preferably, it is 210°C or greater, more further preferably 215°C or greater, particularly preferably 225°C or greater, and most preferably 230°C or greater. By making (Tcs - Tg) 180°C or greater, the generation of defects during three-dimensional molding can be suppressed, and the molding properties can be improved. The upper limit of (Tcs - Tg) is not particularly limited, and is generally preferably 400°C or less from the viewpoint of the moldability of the glass.

[0198] From the viewpoint of reducing the warpage after chemical strengthening, the glass transition point Tg is preferably 500°C or greater, more preferably 520°C or greater, and further preferably 540°C or greater. From the viewpoint of ease of float molding, it is preferably 750°C or less, more preferably 700°C or less, further preferably 650°C or less, particularly preferably 600°C or less, and most preferably 580°C or less.

[0199] The crystallization peak temperature Tc of the chemically strengthened glass of the parent glass composition of the first embodiment is preferably 790°C or greater, more preferably 800°C or greater, and further preferably 810°C or greater. By making the crystallization peak temperature Tc 790°C or greater, stable molding can be achieved. Most preferably, no crystallization peak is observed. The upper limit of the crystallization peak temperature Tc is not particularly limited, and is generally 950°C or less.

[0200] (Crystal growth rate)

[0201] The chemically strengthened glass of the parent glass composition of the first embodiment can suppress phase transition from the β-quartz solid solution to the β-spodumene crystal phase and suppress precipitation of the β-spodumene crystal by containing MgO. Thus, even if the above chemically strengthened glass is held at 1000°C for 30 minutes, precipitation of the β-spodumene crystal is suppressed. Further, the crystal growth rate can be further reduced.

[0202] When the chemically strengthened glass of the parent glass composition of the first embodiment contains MgO, only the β-quartz solid solution is the first precipitated phase, and the crystal growth rate of the β-quartz solid solution at 1000°C is preferably 4000 μm / hr or less, more preferably 3800 μm / hr or less, further preferably 3500 μm / hr or less, particularly preferably 3200 μm / hr or less, and most preferably 2700 μm / hr or less.

[0203] In the forming process of the glass, if crystallization occurs in the glass, defects are generated. For example, in the case of forming by the float method, since the inside of the float bath is cooled from a high temperature region, the temperature region in which nucleation occurs coincides with the temperature region in which crystal growth occurs, and thus crystallization occurs.

[0204] In general, the temperature region in which nucleation occurs does not coincide with the temperature region in which crystal growth occurs, but in the glass containing a large amount of Al2O3and Li2O, the temperature region in which nucleation occurs tends to coincide with the temperature region in which crystal growth occurs around 1000°C. Here, even if the nucleation coincides with the crystal growth rate, as long as the crystal growth rate is slow, defects are not formed. Thus, by making the crystal growth rate of the β-quartz solid solution at 1000°C 600 μm / hr or less, crystallization in the forming process can be suppressed.

[0205] In the present specification, the crystal growth rate of the β-quartz solid solution at 1000°C is obtained by holding a glass sample at 1000°C for 30 minutes, measuring the length of the crystal in the glass using a polarizing microscope, and calculating the average value. Further, the crystal growth rate of the β-spodumene at 1000°C is also obtained in the same manner.

[0206] Further, the "β-OH value" can be obtained from the transmittance X1 (%) at a reference wavelength of 4000 cm -1 the minimum transmittance X2 (%) at an absorption wavelength of 3570 cm -1 nearby of the hydroxyl group, and the thickness t (unit: mm) of the glass sheet, and by the following equation.

[0207] Note that the β-OH value can be adjusted by the amount of water contained in the glass raw material, the dissolution conditions.

[0208] β-OH value = (1 / t) log 10(X1 / X2)

[0209] The β-OH value of the chemically strengthened glass of the parent glass composition of the first embodiment is preferably 0.1 mm -1 More preferably, the above is 0.15 mm -1 Further preferably, the above is 0.2 mm -1 Particularly preferably, the above is 0.22 mm -1 Most preferably, the above is 0.25 mm -1 The above.

[0210] The β-OH value is an index of the water content in the glass. The glass having a large β-OH value has a tendency to have a low softening point and to be easily bend-processed. On the other hand, from the viewpoint of improving the strength by chemical strengthening of the glass, if the β-OH value of the glass becomes large, there is a tendency that the value of the surface compressive stress (CS) after the chemical strengthening treatment becomes small. From the above viewpoint, the β-OH value is preferably 0.5 mm -1 More preferably, the above is 0.4 mm -1 Further preferably, the above is 0.3 mm -1 The above.

[0211] For the chemically strengthened glass of the parent glass composition of the first embodiment, in the preferred mode described later, when the second-stage chemical strengthening is performed using a Li-K mixed salt after the first-stage chemical strengthening is performed using a Na salt, from the viewpoint that K is easily mixed into the glass and the falling strength of the glass after the chemical strengthening is easily improved, the ratio of Na_DOL to K_DOL defined below, i.e., Na_DOL / K_DOL is preferably 26 or less, successively more preferably 25 or less, 24 or less, 23 or less, 22 or less, 21 or less, 20 or less.

[0212] Further, when the second-stage chemical strengthening is performed using a Li-K mixed salt after the first-stage chemical strengthening is performed using a Na salt, in order not to mix excessive K into the glass, from the viewpoint of preventing the glass from being broken, Na_DOL / K_DOL is preferably 15 or more, successively more preferably 16 or more, 16.5 or more, 17 or more, 17.5 or more, 18 or more.

[0213] K_DOL: the compressive stress layer depth of the chemically strengthened glass after ion exchange of the glass using a molten salt composed of 100% potassium nitrate

[0214] Na_DOL: the compressive stress layer depth of the chemically strengthened glass after ion exchange of the glass using a molten salt composed of 100% sodium nitrate

[0215] Here, the time and temperature of ion exchange in the calculation of the above K_DOL and the above Na_DOL are the same conditions.

[0216] The fracture toughness value (K IC ) of the chemically strengthened glass of the parent glass composition of the first embodiment is preferably 0.70 MPa • m 1 / 2 More preferably, the above is 0.75 MPa • m 1 / 2 Further preferably, the above is 0.80 MPa • m 1 / 2 The upper limit of the fracture toughness value is not particularly limited, and is typically 1.0 MPa • m 1 / 2 or less.

[0217] The Young's modulus of the chemically strengthened glass of the parent glass composition of the first embodiment is preferably 80 GPa or more, more preferably 85 GPa or more, further preferably 90 GPa or more, and particularly preferably 95 GPa or more. The upper limit of the Young's modulus is not particularly limited, and is typically 120 GPa or less.

[0218] (Second Embodiment)

[0219] The parent glass composition of the second embodiment contains, in terms of molar percentage on an oxide basis, 55 to 75% of SiO2, 3 to 18% of Al2O3, 17 to 30% of Li2O, 0 to 3% of Na2O, 0 to 1% of K2O, 0 to 10% of MgO, 0 to 10% of CaO, 0 to 5% of SrO, 0 to 5% of ZnO, 0 to 3% of TiO2, 0 to 5% of ZrO2, 0 to 1% of SnO2, 0 to 3% of P2O5, 0 to 10% of B2O3, and 0 to 3% of Y2O3.

[0220] In the second embodiment of the parent glass composition, the content of Li2O, the content of Na2O, and the content of K2O, that is, R is 8 to 35%, the ratio of the content of Li2O with respect to R is 0.85 to 0.99, and the value of the product of the ratio of the content of Li2O with respect to R, the ratio of the content of Na2O with respect to R, and the ratio of the content of K2O with respect to R is preferably 0 to 0.003.

[0221] Hereinafter, each component contained in the parent glass composition will be described.

[0222] SiO2is a component that constitutes the network structure of the glass. In addition, it is a component that improves chemical durability and is a component that reduces the generation of cracks when the surface of the glass is scratched.

[0223] To improve chemical durability, the content of SiO2is more preferably 57.0% or greater, further preferably 58.0% or greater, particularly preferably 59.0% or greater, and most preferably 60.0% or greater. On the other hand, from the viewpoint of good meltability, the content of SiO2is more preferably 74.0% or less, further preferably 72.0% or less, and particularly preferably 69.0% or less.

[0224] Al2O3is a component that improves ion exchange performance at the time of chemical strengthening and increases the surface compressive stress after strengthening. In addition, it contributes to the generation of crystals containing Al and Li. From the viewpoint of obtaining the above effects, the content of Al2O3is more preferably 3.5% or greater, and successively further preferably 4.0% or greater, 4.3% or greater. On the other hand, it is sometimes also required that the crystals do not easily grow and do not easily generate devitrification defects in melting, and that the yield of finished products is easily improved, and that the glass is easily melted by reducing the high-temperature viscosity of the glass. From such a viewpoint, the content of Al2O3is more preferably 18.0% or less, and successively further preferably 15.0% or less, 12.0% or less, 9.0% or less, 7.0% or less, 6.0% or less.

[0225] Both SiO2and Al2O3are components that stabilize the structure of the glass. To reduce brittleness, the total content of SiO2and Al2O3is preferably 60.0% or greater, more preferably 62.0% or greater, and further preferably 64.0% or greater. In addition, both SiO2and Al2O3tend to increase the melting temperature of the glass. Therefore, to more easily melt, the total content of SiO2and Al2O3is preferably 80.0% or less, more preferably 75.0% or less, and further preferably 74.0% or less.

[0226] Li2O is a component that can be ion exchanged and is a component that improves the meltability of the glass. Due to the glass containing Li2O, by ion exchange of Li ions on the surface of the glass with Na ions from the outside, and further ion exchange of the entered Na ions with K ions from the outside, a stress distribution in which the surface compressive stress is large and the compressive stress layer is thick is easily obtained. In addition, by including Li2O in the above range, a crystallized glass is easily obtained when a specific heat treatment is performed. From the above viewpoint, the content of Li2O is more preferably 17% or greater, and successively further preferably 18% or greater, 19% or greater, 20% or greater.

[0227] On the other hand, from the viewpoint of reducing the crystal growth rate in glass forming, and preventing quality degradation due to devitrification, the content of Li20 is more preferably 30% or less, and successively further preferably 28% or less, 26% or less, 24% or less, 23% or less.

[0228] Na20 and K20 are components that increase the melting property of the glass, and reduce the crystal growth rate in glass forming. In addition, in order to improve ion exchange performance, it is preferable to contain a small amount of

[0229] Na20 is a component that is ion-exchangeable in chemical strengthening treatment using a potassium salt, and is also a component that reduces the viscosity of the glass. In order to obtain the above effects, the content of Na20 is preferably 0.3% or more, and successively more preferably 0.5% or more, 0.8% or more, 1.0% or more, 1.2% or more, 1.5% or more. On the other hand, from the viewpoint of maintaining the glass network structure, and the viewpoint of avoiding a decrease in surface compressive stress (Na_CS) in strengthening treatment using a sodium salt, the content of Na20 is preferably 3.0% or less, more preferably 2.5% or less, and further preferably 2.3% or less.

[0230] K20 is a component that improves ion exchange performance while suppressing an increase in devitrification temperature to suppress devitrification. The content of K20 is more preferably 0.1% or more, further preferably 0.15% or more, and particularly preferably 0.2% or more, and most preferably 0.5% or more.

[0231] On the other hand, from the viewpoint of avoiding a decrease in surface compressive stress (K_CS) in strengthening treatment using a sodium salt, the content of K20 is preferably 1.0% or less, and more preferably 0.8% or less.

[0232] Note that K20 can also be substantially free.

[0233] The total of the content of Li20, the content of Na20, and the content of K20, that is, R, is more preferably 10 to 30%, further preferably 15 to 28%, and particularly preferably 18 to 25%, from the viewpoint of suppressing an increase in devitrification temperature, and reducing the crystal growth rate.

[0234] The ratio of the content of Li20 to R ([Li20] / ([Li20]+[Na20]+[K20]), hereinafter also referred to as "Li20 / R20") is more preferably 0.88 or more, and further preferably 0.90 or more, from the viewpoint of further improving the deep layer stress in chemical strengthening characteristics. Li20 / R20 is more preferably 0.98 or less, further preferably 0.95 or less, and particularly preferably 0.94 or less, from the viewpoint of further improving the resistance of the glass, and further improving the chemical resistance.

[0235] The ratio of the content of Na2O to the above R ([Na2O] / ([Li2O]+[Na2O]+[K2O]), hereinafter also referred to as "Na2O / R2O") is preferably greater than 0, more preferably 0.01 or greater, further preferably 0.03 or greater, particularly preferably 0.05 or greater, most preferably 0.06 or greater, from the viewpoint of further increasing the stress in the deep layer in the chemical strengthening characteristics. From the viewpoint of further increasing the chemical reagent resistance, the Na2O / R2O is preferably 0.40 or less, more preferably 0.30 or less, further preferably 0.20 or less, particularly preferably 0.10 or less.

[0236] The ratio of the content of K2O to the above R ([K2O] / ([Li2O]+[Na2O]+[K2O]), hereinafter also referred to as "K2O / R2O") is preferably 0.05 or greater, more preferably 0.08 or greater, further preferably 0.10 or greater, from the viewpoint of further increasing the resistance of the glass. From the viewpoint of increasing the compressive stress in the vicinity of the surface in the chemical strengthening characteristics, the K2O / R2O is preferably 0.50 or less, more preferably 0.40 or less, further preferably 0.30 or less, particularly preferably 0.20 or less.

[0237] Note that the K2O / R2O can also be 0.

[0238] In addition, the product of Li2O / R2O and Na2O / R2O and K2O / R2O is more preferably 0.008 or greater, further preferably 0.01 or greater, particularly preferably 0.02 or greater, from the viewpoint of suppressing an increase in the devitrification temperature and reducing the crystal growth rate. In addition, the above product is more preferably 0.028 or less.

[0239] Note that the above product can also be 0.

[0240] The ratio of the content of Al2O3 to the above R ([Al2O3] / ([Li2O]+[Na2O]+[K2O]), hereinafter also referred to as "Al2O3 / R2O") is preferably 0.05 or greater, more preferably 0.10 or greater, further preferably 0.15 or greater, more preferably 0.18 or greater. The Al2O3 / R2O is preferably 0.50 or less, more preferably 0.40 or less, further preferably 0.30 or less, particularly preferably 0.25 or less.

[0241] The value represented by [Al2O3]-[Na2O]-[K2O]+[Li2O] is preferably 15.0 to 35.0%, more preferably 20.0 to 30.0%.

[0242] MgO can be contained for the purpose of reducing viscosity at the time of dissolution or the like. The content of MgO is more preferably 0.05% or more, sequentially further preferably 0.5% or more, 1.0% or more, 2.0% or more, 3.0% or more, 4.0% or more. On the other hand, from the viewpoint of easily increasing the compressive stress layer at the time of chemical strengthening treatment, the content of MgO is more preferably 9.0% or less, sequentially further preferably 8.0% or less, 7.0% or less, 6.0% or less.

[0243] Further, by containing MgO, phase transition from the β-quartz solid solution to the β-spodumene crystal phase can be suppressed, and precipitation of the β-spodumene crystal can be suppressed. Thus, in Embodiment 2, it is preferable to contain MgO. From the above viewpoint, it is preferable to contain MgO in an amount of more than 0.5% and 7.0% or less. A further preferable range is as described above.

[0244] MgO can also be substantially not contained.

[0245] CaO is a component that improves the melting property of the glass, and can be contained. The content of CaO is more preferably 0.1% or more, further preferably 0.15% or more. On the other hand, from the viewpoint of easily increasing the compressive stress value at the time of chemical strengthening treatment, the content of CaO is more preferably 2.0% or less, further preferably 1.0% or less, particularly preferably 0.8% or less, most preferably 0.5% or less. CaO can also be substantially not contained.

[0246] In order to improve the stability of the glass, it is more preferable to contain at least one of MgO and CaO, further preferably to contain MgO. The total content of MgO and CaO is preferably more than 1.0%, more preferably 2.0% or more, further preferably 3.0% or more, particularly preferably 4.0% or more. From the viewpoint of further improving the chemical strengthening characteristics, the total content of MgO and CaO is preferably 10.0% or less, sequentially more preferably 8.0% or less, 7.0% or less, 6.0% or less.

[0247] SrO is a component that improves the melting property of the glass, and can be contained. The content of SrO is more preferably 0.1% or more, further preferably 0.15% or more, particularly preferably 0.5% or more.

[0248] From the viewpoint of easily increasing the compressive stress value at the time of chemical strengthening treatment, the content of SrO is more preferably 3.0% or less, further preferably 2.0% or less, particularly preferably 1.0% or less, most preferably 0.5% or less. SrO can also be substantially not contained.

[0249] BaO is a component that improves the melting property of the glass, and can be contained. When BaO is contained, the content is preferably 0.1% or more, more preferably 0.15% or more, further preferably 0.5% or more.

[0250] From the viewpoint of easily increasing the compressive stress value at the time of chemical strengthening treatment, the content of BaO is preferably 3.0% or less, more preferably 2.0% or less, further preferably 1.0% or less, and particularly preferably 0.5% or less. BaO can also be substantially not contained.

[0251] ZnO is a component that improves the melting property of the glass. The content of ZnO is more preferably 0.1% or more, further preferably 0.15% or more, and particularly preferably 0.5% or more.

[0252] From the viewpoint of easily increasing the compressive stress value at the time of chemical strengthening treatment, the content of ZnO is more preferably 3.0% or less, further preferably 2.0% or less, particularly preferably 1.0% or less, and most preferably 0.5% or less. ZnO can also be substantially not contained.

[0253] lnW is a parameter that indicates the degree of mixing of oxides calculated from the contents of alkali metal oxides, alkaline earth metal oxides, and zinc oxide contained in the glass. lnW is represented by the following formula.

[0254] lnW = ln (([Li20] + [Na20] + [K20] + [MgO] + [CaO] + [SrO] + [BaO] + [ZnO])! / ([Li20]! x [Na20]! x [K20]! x [MgO]! x [CaO]! x [SrO]! x [BaO]! x [ZnO]!)) • • • (W1)

[0255] In formula (W1), [Li20], [Na20], [K20], [MgO], [CaO], [SrO], [BaO], and [ZnO] each represent the content of each component of Li20, Na20, K20, MgO, CaO, SrO, BaO, and ZnO, respectively, expressed in terms of the molar percentage on an oxide basis.

[0256] Further,! indicates the factorial operation on a positive number. For example, [XO]! means that the value of the content expressed in terms of the molar percentage on an oxide basis of the component XO is rounded off below the decimal point to obtain a positive number, and the factorial operation is performed on the positive number. For example, when Na20 is 4.8 mol%, the factorial of "4" is calculated as 4 x 3 x 2 x 1.

[0257] If the value of lnW is large, the degree of mixing of the above metal oxides is high, and the devitrification of the glass can be suppressed. From the above viewpoint, lnW is preferably 10 or more, more preferably 12 or more, further preferably 13 or more, and particularly preferably 14 or more. lnW is preferably 20 or less, more preferably 18 or less, and further preferably 17 or less.

[0258] TiO2is a component having a high effect of suppressing exposure of the glass, and is a material for forming a crystal nucleus, and thus can be contained. When TiO2is contained, the content is preferably 0.05% or more, more preferably 0.1% or more, further preferably 0.2% or more, particularly preferably 0.5% or more, and most preferably 0.8% or more.

[0259] On the other hand, TiO2has light absorption properties, and thus from the viewpoint of preventing discoloration of the glass, the content of TiO2is preferably 2.5% or less, more preferably 2.0% or less, further preferably 1.5% or less, and particularly preferably 1.0% or less.

[0260] TiO2may also be substantially not contained.

[0261] ZrO2is a component that easily increases the surface compressive stress of the chemically strengthened glass. In addition, it is also a material for forming a crystal nucleus, and thus ZrO2may be contained. The content of ZrO2is more preferably greater than 0%, and successively further preferably 0.5% or more, 1.0% or more, 1.5% or more, 2.0% or more, and 2.5% or more.

[0262] P2O5easily increases the compressive stress layer at the time of chemical strengthening. The content of P2O5is more preferably 0.5% or more, and further preferably 0.7% or more. On the other hand, from the viewpoint of improving acid resistance, the content of P2O5is more preferably 2.0% or less. From the viewpoint of preventing the generation of streaks at the time of melting, it is preferable to be substantially not contained.

[0263] B2O3reduces the brittleness of the glass and improves the crack resistance, or improves the melting property of the glass. The content of B2O3is more preferably 0.5% or more, further preferably 1.0% or more, and particularly preferably 1.5% or more. On the other hand, from the viewpoint of maintaining good acid resistance, the content of B2O3is preferably 8.0% or less. The content of B2O3is more preferably 6.0% or less, further preferably 4.0% or less, and particularly preferably 2.0% or less. From the viewpoint of preventing the generation of streaks at the time of melting, it is preferable to be substantially not contained.

[0264] Y2O3is a component that both easily increases the surface compressive stress of the chemically strengthened glass and reduces the crystal growth rate. The content of Y2O3is more preferably greater than 0%, and successively further preferably 0.1% or more, 0.2% or more, 0.5% or more, and 0.8% or more. On the other hand, from the viewpoint of easily increasing the compressive stress layer at the time of chemical strengthening treatment, the content of Y2O3is more preferably 2.0% or less, and further preferably 1.5% or less. Y2O3may also be substantially not contained.

[0265] From the viewpoint of improving the initial melting property, the total of the contents of ZrO2and Y2O3is more preferably 5.0% or less. The lower limit of the total of the contents of ZrO2and Y2O3is not particularly limited, and from the viewpoint of improving the strength of the glass, it is more preferably 0.5% or more, and successively further preferably 1.0% or more, 1.5% or more, 2.0% or more, 2.5% or more, 3.0% or more.

[0266] The ratio of the content of ZrO2to the total content of ZrO2and Y2O3, [ZrO2] / ([ZrO2]+[Y2O3]), is more preferably 0.50 or more, and further preferably 1.00 or more. [ZrO2] / ([ZrO2]+[Y2O3]) is more preferably 8.00 or less, further preferably 7.00 or less, and particularly preferably 6.00 or less.

[0267] It is known that when ZrO2and Y2O3are added alone, they function as nucleating agents, and by co-adding ZrO2and Y2O3, a eutectic of ZrO2and Y2O3is formed, and it is possible to control the devitrification temperature, the crystal growth rate, and the crystallization start temperature.

[0268] Furthermore, by controlling [ZrO2] / ([ZrO2]+[Y2O3]) to the above range, it is possible to suppress the diffusion of ions in the glass to suppress the increase in the devitrification temperature, and to suppress devitrification.

[0269] By controlling [ZrO2] / ([ZrO2]+[Y2O3]) to the above range, the glass is stabilized, and furthermore, the temperature region where nucleation occurs is separated from the temperature region where crystal growth occurs, and the overlap is avoided, and the crystal growth rate is suppressed, and thus it is possible to suppress the generation of defects. In addition, by making [ZrO2] / ([ZrO2]+[Y2O3]) the above range, the temperature region where nucleation occurs shifts to the low temperature side, and the decrease in the crystallization start temperature is suppressed, and it is possible to improve the manufacturing properties.

[0270] La2O3is not essential, but can be contained based on the same reasons as Y2O3. La2O3is preferably 0.1% or more, more preferably 0.2% or more, further preferably 0.5% or more, and particularly preferably 0.8% or more. On the other hand, if it is too much, it is difficult to increase the compressive stress layer at the time of chemical strengthening treatment, and thus La2O3is preferably 5.0% or less, more preferably 3.0% or less, further preferably 2.0% or less, and particularly preferably 1.5% or less. It is also preferable that La2O3be substantially not contained.

[0271] Nb2O5, Ta2O5, Gd2O3, CeO2have an effect of suppressing exposure of the glass to the sun, are components that improve the melting property, and can be contained. When these components are contained, the content of each is preferably 0.03% or more, more preferably 0.1% or more, further preferably 0.5% or more, particularly preferably 0.8% or more, most preferably 1.0% or more. On the other hand, it is preferably 3.0% or less, more preferably 2.0% or less, further preferably 1.0% or less.

[0272] Fe2O3has an effect of improving the melting property of the glass due to absorption of thermal radiation, and is preferably contained when a large furnace is used to mass-produce the glass. The content in this case is preferably 0.002% or more, more preferably 0.005% or more, further preferably 0.007% or more, particularly preferably 0.01% or more, in terms of mass% on an oxide basis. On the other hand, if Fe2O3is contained excessively, coloring occurs, so from the viewpoint of improving the transparency of the glass, the content is preferably 0.3% or less, more preferably 0.04% or less, further preferably 0.025% or less, particularly preferably 0.015% or less, in terms of mass% on an oxide basis.

[0273] Further, other coloring components can also be added within a range that does not hinder achievement of the desired chemical strengthening properties. As the other coloring components, for example, Co3O4, MnO2, NiO, CuO, Cr2O3, V2O5, Bi2O3, SeO2, Er2O3, Nd2O3, and the like can be given as appropriate components.

[0274] As a fining agent or the like at the time of melting of the glass, SO3, chloride, fluoride, and the like can be appropriately contained. It is preferable not to contain As2O3. When Sb2O3is contained, it is preferably 0.3% or less, more preferably 0.1% or less, most preferably not to be contained.

[0275] From the viewpoint of fining of bubbles in the glass, the content of SnO2is more preferably 0.01% or more, further preferably 0.05% or more. In addition, in order to suppress the generation of defects, the content of SnO2is preferably 1% or less, more preferably 0.8% or less, further preferably 0.7% or less, particularly preferably 0.5% or less.

[0276] Next, the preferred physical properties of the glass of the parent glass composition of the above-described second embodiment will be described.

[0277] (Devitrification temperature)

[0278] The preferred mode of the devitrification temperature of the chemically strengthened glass of the parent glass composition of the second embodiment is the same as that of the chemically strengthened glass of the parent glass composition of the first embodiment, and thus the description is omitted.

[0279] (glass transition point Tg, crystallization onset temperature Tcs, crystallization peak temperature Tc)

[0280] The crystallization onset temperature Tcs of the chemically strengthened glass of the parent glass composition of the second embodiment is preferably 500°C or higher as measured by DSC. The upper limit of the crystallization onset temperature is not particularly limited, and is usually 800°C or lower.

[0281] If the crystallization onset temperature Tcs is within the above range, a crystal can be precipitated in the chemically strengthened glass, for example, by performing heat treatment at 500 to 600°C for 1 to 6 hours and then at 600 to 800°C for 0.5 to 6 hours, and a chemically strengthened glass of a crystallized glass can be obtained.

[0282] The above heat treatment can be performed in three stages. For example, by performing heat treatment at 500 to 600°C for 1 to 6 hours, at 550 to 650°C for 0.5 to 6 hours, and at 600 to 800°C for 0.5 to 6 hours, a chemically strengthened glass of a crystallized glass can be obtained.

[0283] From the viewpoint of reducing warpage after chemical strengthening, the glass transition point Tg is preferably 500°C or higher, more preferably 520°C or higher, and further preferably 540°C or higher. From the viewpoint of easy floatation, it is preferably 750°C or lower, more preferably 700°C or lower, further preferably 650°C or lower, particularly preferably 600°C or lower, and most preferably 580°C or lower.

[0284] The crystallization peak temperature Tc of the chemically strengthened glass of the parent glass composition of the second embodiment is preferably 600°C or higher, more preferably 650°C or higher, and further preferably 700°C or higher. By making the crystallization peak temperature Tc 600°C or higher, stable molding can be achieved. Most preferably, no crystallization peak is observed. The upper limit of the crystallization peak temperature Tc is not particularly limited, and is usually 950°C or lower.

[0285] The β-OH value of the chemically strengthened glass of the parent glass composition of the second embodiment is preferably 0.1 mm -1 or more, more preferably 0.15 mm -1 or more, further preferably 0.2 mm -1 or more, particularly preferably 0.22 mm -1 or more, most preferably 0.25 mm -1 or more.

[0286] The β-OH value is an index of the amount of water in the glass. A glass having a large β-OH value has a tendency to have a low softening point and to be easily bent and processed. On the other hand, from the viewpoint of improving the strength by chemical strengthening of the glass, if the β-OH value of the glass becomes large, the value of the surface compressive stress (CS) after the chemical strengthening treatment has a tendency to easily become small. From the above viewpoint, the β-OH value is preferably 0.5 mm -1 More preferably, 0.4 mm -1 Further preferably, 0.3 mm -1 Further preferably, 0.3 mm

[0287] The fracture toughness value (K IC ) of the chemically strengthened glass of the parent glass composition of the 2nd embodiment is preferably 0.80 MPa • m 1 / 2 More preferably, 0.85 MPa • m 1 / 2 Further preferably, 0.90 MPa • m 1 / 2 Particularly preferably, 1.0 MPa • m 1 / 2 Most preferably, 1.1 MPa • m 1 / 2 The upper limit of the fracture toughness value is not particularly limited, and is typically 1.6 MPa • m 1 / 2 Further preferably, 0.3 mm

[0288] The Young's modulus of the chemically strengthened glass of the parent glass composition of the 2nd embodiment is preferably 80 GPa or more, more preferably 90 GPa or more, further preferably 95 GPa or more, and most preferably 100 GPa or more. The upper limit of the Young's modulus is not particularly limited, and is typically 120 GPa or less.

[0289] (Method of production)

[0290] The chemically strengthened glass (parent glass composition of the 1st embodiment and parent glass composition of the 2nd embodiment) can be produced by a general method. For example, the raw materials of each component of the glass are mixed, and heated and melted in a glass melting furnace. Then, the glass is formed into a desired shape such as a glass sheet by a publicly known method, and slowly cooled.

[0291] As the forming method of the glass sheet, for example, a float method, a press method, a fusion method, and a down-draw method can be given. The float method which is suitable for mass production is particularly preferred. In addition, a continuous forming method other than the float method, for example, the fusion method and the down-draw method are preferred.

[0292] The chemically strengthened glass of the parent glass composition of the 2nd embodiment described above can be subjected to the heat treatment described above to be made into a crystallized glass.

[0293] That is, the glass for chemical strengthening can also be a crystallized glass. If a crystallized glass is used as the glass for chemical strengthening, a chemically strengthened glass as a crystallized glass can be obtained.

[0294] Then, the shaped glass is subjected to grinding and polishing processes as necessary, to form a glass substrate. Note that in the case where the glass substrate is subjected to cutting or chamfering processing to a prescribed shape and size, if the cutting, chamfering processing of the glass substrate is performed before the chemical strengthening treatment described later is performed, a compressive stress layer can be formed on the end surface as well by the subsequent chemical strengthening treatment, and thus is preferable.

[0295] The shape of the glass for chemical strengthening can also be a shape other than a plate shape, depending on the product, use, etc. to which it is applied. Also, the glass plate can be a trimmed shape in which the outer periphery has a different thickness, etc. Also, the form of the glass plate is not limited to this, and for example, the two main surfaces can not be parallel to each other, and also, one or both of the two main surfaces can be a curved surface in whole or in part. More specifically, the glass plate can be, for example, a flat glass plate that is free from warping, and also, a curved glass plate having a curved surface.

[0296] <Method for manufacturing chemically strengthened glass>

[0297] The method for manufacturing the chemically strengthened glass of the present application is not particularly limited as long as it is a method for manufacturing the above-described chemically strengthened glass of the present application, and is manufactured by subjecting the glass for chemical strengthening to a chemical strengthening treatment.

[0298] As one example of the method for manufacturing the chemically strengthened glass of the present application, a method for manufacturing a chemically strengthened glass can be given, in which a first chemical strengthening treatment is performed on a glass for chemical strengthening using a first molten salt containing 90 mass% or more of a Na salt and 2 mass% or more of a Li salt with respect to the total mass, and a second chemical strengthening treatment is performed on the glass for chemical strengthening subjected to the above-described first chemical strengthening treatment using a second molten salt containing 90 mass% or more of a K salt with respect to the total mass.

[0299] Hereinafter, one example of the method for manufacturing the chemically strengthened glass of the present application will be described.

[0300] [First chemical strengthening treatment]

[0301] In one example of the method for manufacturing the chemically strengthened glass of the present application, the first chemical strengthening treatment is performed using a first molten salt containing 90 mass% or more of a Na salt and 2 mass% or more of a Li salt with respect to the total mass.

[0302] The first chemical strengthening treatment can be performed by bringing the glass for chemical strengthening into contact with the above-described first molten salt. For example, the first chemical strengthening treatment can be performed by immersing the glass for chemical strengthening in the first molten salt.

[0303] Note that, as described above with respect to the composition of the chemically strengthened glass, such as the chemically strengthened glass of the present application, the preferable modes are also as described above.

[0304] In particular, in the case of the first embodiment of the parent glass composition of the chemically strengthened glass, one example of the production method of the chemically strengthened glass of the present application is preferably implemented.

[0305] Specifically, the composition at the central portion of the plate thickness of the chemically strengthened glass, expressed in terms of the mole percentage on the oxide basis, preferably contains 60 to 72% of SiO2, 10 to 20% of Al2O3, 3 to 12% of Li2O, 0.5 to 6% of Na2O, and 1 to 3% of K2O.

[0306] In the first molten salt, the content of the Na salt is 90% by mass or more, preferably 93% by mass or more, more preferably 95% by mass or more, and further preferably 96% by mass or more, with respect to the total mass of the first molten salt. In the first molten salt, the content of the Na salt is 98% by mass or less, and can be 97% by mass or less, or 96% by mass or less, with respect to the total mass of the first molten salt.

[0307] As the Na salt contained in the first molten salt, for example, sodium nitrate, sodium sulfate, sodium carbonate, and sodium chloride, and the like can be given, and sodium nitrate is preferable.

[0308] In the first molten salt, the content of the Li salt is 2% by mass or more, and can be 3% by mass or more, or 4% by mass or more, with respect to the total mass of the first molten salt. In the first molten salt, the content of the Li salt is 10% by mass or less, preferably 7% by mass or less, and more preferably 5% by mass or less, with respect to the total mass of the first molten salt.

[0309] As the Li salt contained in the first molten salt, lithium nitrate, lithium sulfate, lithium carbonate, and lithium chloride can be given, and lithium nitrate is preferable.

[0310] In addition, the ratio of the content of the Li salt in the first molten salt with respect to the content of Li2O in the composition of the chemically strengthened glass is preferably 0.1 or more, more preferably 0.2 or more, and can be 0.3 or more, in terms of the mole ratio. The above ratio is preferably 1.0 or less, more preferably 0.8 or less, further preferably 0.6 or less, and particularly preferably 0.5 or less.

[0311] The first molten salt can also contain components other than the Na salt and the Li salt. As the components other than the Na salt and the Li salt, K salt, Rb (rubidium) salt, Cs (cesium) salt, and Ag (silver) salt can be given.

[0312] It should be noted that the first molten salt preferably does not contain components other than Na salts and Li salts. That is, the first molten salt preferably consists of Na salts and Li salts.

[0313] The time of the first chemical strengthening treatment is preferably 30 minutes or more, more preferably 60 minutes or more, further preferably 120 minutes or more, and particularly preferably 150 minutes or more. The time of the first chemical strengthening treatment is in most cases 720 minutes or less, preferably 360 minutes or less, and more preferably 180 minutes or less.

[0314] The temperature of the first chemical strengthening treatment is preferably 350°C or more, more preferably 380°C or more, and further preferably 400°C or more. The temperature of the first chemical strengthening treatment is preferably 470°C or less, more preferably 440°C or less, and further preferably 420°C or less.

[0315] It is also preferable that the time of the first chemical strengthening treatment be the preferable time and the temperature of the first chemical strengthening treatment be the preferable temperature.

[0316] According to the first chemical strengthening treatment, ion exchange can be performed to a deeper portion while reducing the amount of ion exchange, and the chemical strengthening glass of the present application described above can be easily obtained.

[0317] [Second Chemical Strengthening Treatment]

[0318] In one example of the method for producing a chemically strengthened glass of the present application, a second chemical strengthening treatment is performed on the chemically strengthened glass subjected to the first chemical strengthening treatment described above, using a second molten salt containing 90 mass% or more of K salts with respect to the total mass.

[0319] In the second chemical strengthening treatment, the chemically strengthened glass subjected to the first chemical strengthening treatment can be brought into contact with the second molten salt to perform the treatment. For example, the second chemical strengthening treatment can be performed by immersing the chemically strengthened glass subjected to the first chemical strengthening treatment in the second molten salt.

[0320] In the second molten salt, the content of K salts is 90 mass% or more, preferably 93 mass% or more, more preferably 94 mass% or more, and further preferably 95 mass% or more, with respect to the total mass of the second molten salt, and can be 98 mass% or more or 99 mass% or more. In the second molten salt, the content of K salts can also be 100 mass% with respect to the total mass of the second molten salt. That is, the second molten salt can also consist of only K salts.

[0321] As the K salts contained in the second molten salt, potassium nitrate, potassium sulfate, potassium carbonate, and potassium chloride can be given, and potassium nitrate is preferable.

[0322] The second molten salt can also contain components other than K salts. As components other than K salts, Li salts, Na salts, Rb salts, Cs salts, and Ag salts can be given.

[0323] Note that the second molten salt preferably does not contain components other than K salts as described above.

[0324] The time of the second chemical strengthening treatment is preferably 20 minutes or more, more preferably 30 minutes or more, further preferably 60 minutes or more, and particularly preferably 90 minutes or more. The time of the second chemical strengthening treatment is in most cases 360 minutes or less, preferably 180 minutes or less, and more preferably 120 minutes or less.

[0325] The temperature of the second chemical strengthening treatment is preferably 330°C or more, more preferably 360°C or more, and further preferably 380°C or more. The temperature of the second chemical strengthening treatment is preferably 460°C or less, more preferably 430°C or less, and further preferably 410°C or less.

[0326] It is also preferable that the time of the second chemical strengthening treatment be the preferable time described above and the temperature of the second chemical strengthening treatment be the preferable temperature described above.

[0327] In addition, it is also preferable that the time of the first chemical strengthening treatment be 150 minutes or more and the time of the second chemical strengthening treatment be 90 minutes or more.

[0328] The chemically strengthened glass of the present application can also be produced by a method other than the above.

[0329] Next, other examples of the production method of the chemically strengthened glass of the present application will be described.

[0330] First, a second example of the production method of the chemically strengthened glass of the present application will be described.

[0331] As the second example of the production method of the chemically strengthened glass of the present application, a production method of a chemically strengthened glass can be given, in which a third chemical strengthening treatment is performed on a chemically strengthened glass using a third molten salt containing 50 mass% or more of Na salts, 30 mass% or more of K salts, and 1 mass% or more of Li salts with respect to the total mass, and a fourth chemical strengthening treatment is performed on the chemically strengthened glass subjected to the above-described third chemical strengthening treatment using a fourth molten salt containing 90 mass% or more of K salts and 2 mass% or more of Li salts with respect to the total mass.

[0332] [Third Chemical Strengthening Treatment]

[0333] In the second example of the method for producing the chemically strengthened glass of the present application, a third chemical strengthening treatment is performed using a third molten salt containing 50% by mass or more of a Na salt, 30% by mass or more of a K salt, and 1% by mass or more of a Li salt, with respect to the total mass.

[0334] The third chemical strengthening treatment can be performed by bringing the glass for chemical strengthening into contact with the above-mentioned third molten salt. For example, the third chemical strengthening treatment can be performed by immersing the glass for chemical strengthening in the third molten salt.

[0335] Note that, as for the glass for chemical strengthening, the preferable modes are also as described above, as described in the section of the composition of the chemically strengthened glass of the present application.

[0336] In particular, in the second embodiment of the parent glass composition of the glass for chemical strengthening and in the case where the content of P2O5 is 1.0% or more, the second example of the method for producing the chemically strengthened glass of the present application is preferably performed.

[0337] In the third molten salt, the content of the Na salt is 50% by mass or more, preferably 53% by mass or more, more preferably 55% by mass or more, and further preferably 58% by mass or more, with respect to the total mass of the third molten salt. In the third molten salt, the content of the Na salt is 69% by mass or less, preferably 65% by mass or less, and more preferably 62% by mass or less, with respect to the total mass of the third molten salt.

[0338] As for the Na salt contained in the third molten salt, the same Na salts as those contained in the first molten salt can be mentioned, and the preferable components are also the same.

[0339] In the third molten salt, the content of the K salt is 30% by mass or more, preferably 32% by mass or more, more preferably 35% by mass or more, and further preferably 37% by mass or more, with respect to the total mass of the third molten salt. In the third molten salt, the content of the K salt is 49% by mass or less, preferably 45% by mass or less, more preferably 42% by mass or less, and further preferably 40% by mass or less, with respect to the total mass of the third molten salt.

[0340] As for the K salt contained in the third molten salt, the same K salts as those contained in the second molten salt can be mentioned, and the preferable components are also the same.

[0341] In the third molten salt, the content of the Li salt is 1% by mass or more, preferably 2% by mass or more, and can also be 3% by mass or more, with respect to the total mass of the third molten salt. In the third molten salt, the content of the Li salt is 20% by mass or less, preferably 10% by mass or less, and more preferably 5% by mass or less, with respect to the total mass of the third molten salt.

[0342] As the Li salt contained in the third molten salt, the same Li salt as the Li salt contained in the first molten salt can be given, and the preferable component is also the same.

[0343] In addition, the ratio of the content of Li in the third molten salt to the content of Li20 in the composition of the glass to be chemically strengthened is preferably 0.05 or more, more preferably 0.07 or more, and further preferably 0.1 or more, in terms of molar ratio. The ratio is preferably 0.6 or less, more preferably 0.5 or less, further preferably 0.35 or less, and particularly preferably 0.2 or less.

[0344] The third molten salt can also contain a component other than the Na salt, the K salt, and the Li salt. As the component other than the Na salt, the K salt, and the Li salt, a Rb salt, a Cs salt, and an Ag salt can be given.

[0345] Note that the third molten salt preferably does not contain a component other than the Na salt, the K salt, and the Li salt. That is, the third molten salt preferably consists of the Na salt, the K salt, and the Li salt.

[0346] The time of the third chemical strengthening treatment is preferably 60 minutes or more, more preferably 120 minutes or more, and further preferably 180 minutes or more. The time of the third chemical strengthening treatment is in most cases 1440 minutes or less, preferably 720 minutes or less, and more preferably 360 minutes or less.

[0347] The temperature of the third chemical strengthening treatment is preferably 350°C or more, more preferably 380°C or more, and further preferably 400°C or more. The temperature of the third chemical strengthening treatment is preferably 470°C or less, more preferably 440°C or less, and further preferably 420°C or less.

[0348] It is also preferable that the time of the above-mentioned third chemical strengthening treatment be the preferable time and the temperature of the above-mentioned third chemical strengthening treatment be the preferable temperature.

[0349] According to the third chemical strengthening treatment, ion exchange can be performed to a deeper portion while reducing the amount of ion exchange, and the above-mentioned chemically strengthened glass of the present application can be easily obtained.

[0350] [Fourth Chemical Strengthening Treatment]

[0351] In the second example of the method of manufacturing the chemically strengthened glass of the present application, a fourth chemical strengthening treatment is performed on the above-mentioned chemically strengthened glass subjected to the above-mentioned third chemical strengthening treatment, using a fourth molten salt containing 90 mass% or more of a K salt and 2 mass% or more of a Li salt with respect to the total mass.

[0352] In the fourth chemical tempering process, the chemical tempering glass subjected to the third chemical tempering process can be contacted with the above-mentioned fourth molten salt to be performed. For example, the fourth chemical tempering process can be performed by immersing the chemical tempering glass subjected to the third chemical tempering process in the fourth molten salt.

[0353] In the fourth molten salt, the content of the K salt is 90% by mass or more, preferably 91% by mass or more, more preferably 92% by mass or more, and further preferably 94% by mass or more, with respect to the total mass of the second molten salt. In the fourth molten salt, the content of the K salt is 98% by mass or less, preferably 97% by mass or less, and further preferably 96% by mass or less, with respect to the total mass of the fourth molten salt.

[0354] As the K salt contained in the fourth molten salt, the same K salt as contained in the second molten salt can be mentioned, and the preferable components are also the same.

[0355] In the fourth molten salt, the content of the Li salt is 2% by mass or more, preferably 3% by mass or more, and more preferably 4% by mass or more, with respect to the total mass of the fourth molten salt. In the fourth molten salt, the content of the Li salt is 10% by mass or less, preferably 8% by mass or less, and more preferably 7% by mass or less, with respect to the total mass of the fourth molten salt.

[0356] As the Li salt contained in the fourth molten salt, the same Li salt as contained in the first molten salt can be mentioned, and the preferable components are also the same.

[0357] The fourth molten salt can further contain components other than the K salt and the Li salt. As the components other than the K salt and the Li salt, Na salt, Rb salt, Cs salt, and Ag salt can be mentioned.

[0358] Note that the fourth molten salt preferably does not contain components other than the K salt and the Li salt.

[0359] The time of the fourth chemical tempering process is preferably 5 minutes or more, more preferably 10 minutes or more, and further preferably 20 minutes or more. The time of the fourth chemical tempering process is in most cases 360 minutes or less, preferably 180 minutes or less, more preferably 120 minutes or less, and further preferably 90 minutes or less.

[0360] The temperature of the fourth chemical tempering process is preferably 350°C or more, more preferably 380°C or more, and further preferably 400°C or more. The temperature of the fourth chemical tempering process is preferably 480°C or less, more preferably 450°C or less, and further preferably 430°C or less.

[0361] It is also preferable that the time of the above-mentioned fourth chemical tempering process is the preferable time and the preferable temperature of the above-mentioned fourth chemical tempering process.

[0362] As the third example of the method for producing a chemically strengthened glass of the present application, a method for producing a chemically strengthened glass can be exemplified, in which a fifth chemical tempering treatment is performed on a glass for chemical strengthening using a fifth molten salt containing 20% by mass or more of a Na salt and 60% by mass or more of a K salt with respect to the total mass.

[0363] [The fifth chemical tempering treatment]

[0364] In the fifth example of the method for producing a chemically strengthened glass of the present application, a fifth chemical tempering treatment is performed using a fifth molten salt containing 60% by mass or more of a K salt and 20% by mass or more of a Na salt with respect to the total mass.

[0365] The fifth chemical tempering treatment can be performed by bringing the glass for chemical strengthening into contact with the above-mentioned fifth molten salt. For example, the fifth chemical tempering treatment can be performed by immersing the glass for chemical strengthening in the fifth molten salt.

[0366] Note that, as for the glass for chemical strengthening, the preferable modes are also as mentioned above, as described in the section of the composition of the chemically strengthened glass of the present application.

[0367] In particular, in the case where the content of P2O5 is 0.5% or more in the second embodiment of the parent glass composition of the glass for chemical strengthening, the third example of the method for producing a chemically strengthened glass of the present application is preferably performed. In addition, in the case where the content of P2O5 is 0.5% or more and less than 1.0% in the second embodiment of the parent glass composition of the glass for chemical strengthening, the third example of the method for producing a chemically strengthened glass of the present application is preferably performed.

[0368] In the fifth molten salt, the content of the K salt is 60% by mass or more, preferably 63% by mass or more, more preferably 65% by mass or more, and further preferably 67% by mass or more, with respect to the total mass of the fifth molten salt. In the fifth molten salt, the content of the K salt is 80% by mass or less, preferably 77% by mass or less, more preferably 75% by mass or less, and further preferably 72% by mass or less, with respect to the total mass of the fifth molten salt.

[0369] As for the K salt contained in the fifth molten salt, the same K salt as contained in the second molten salt can be exemplified, and the preferable components are also the same.

[0370] In the fifth molten salt, the content of the Na salt is 20% by mass or more, preferably 22% by mass or more, more preferably 25% by mass or more, and further preferably 27% by mass or more, with respect to the total mass of the fifth molten salt. In the fifth molten salt, the content of the Na salt is 40% by mass or less, preferably 37% by mass or less, and more preferably 35% by mass or less, with respect to the total mass of the fifth molten salt.

[0371] As the Na salt contained in the 5th molten salt, the same Na salt as contained in the 1st molten salt can be given, and the preferable component is also the same.

[0372] The 5th molten salt can further contain a component other than the K salt and the Na salt. As the component other than the K salt and the Na salt, a Li salt, an Rb salt, a Cs salt, and an Ag salt can be given.

[0373] It should be noted that the 5th molten salt preferably does not contain a component other than the K salt and the Na salt. That is, the 5th molten salt is preferably composed of the K salt and the Na salt.

[0374] The time of the 5th chemical strengthening treatment is preferably 60 minutes or more, more preferably 120 minutes or more, and further preferably 180 minutes or more, and can be 360 minutes or more, and can be 720 minutes or more. The time of the 3rd chemical strengthening treatment is in most cases 1440 minutes or less, can be 720 minutes or less, and can be 360 minutes or less.

[0375] The temperature of the 5th chemical strengthening treatment is preferably 390°C or more, more preferably 420°C or more, and further preferably 440°C or more. The temperature of the 5th chemical strengthening treatment is preferably 510°C or less, more preferably 480°C or less, and further preferably 460°C or less.

[0376] It is also preferable that the time of the above-mentioned 5th chemical strengthening treatment is the preferable time and the temperature of the above-mentioned 5th chemical strengthening treatment is the preferable temperature.

[0377] According to the 5th chemical strengthening treatment, ion exchange of K is performed while ion exchange of Na is performed, and thus the above-mentioned chemically strengthened glass of the present application is easily obtained.

[0378] <Usage>

[0379] The chemically strengthened glass of the present application is useful as, for example, cover glass.

[0380] The above-mentioned cover glass can be appropriately used for the purpose of surface protection of displays and solar cell modules, and the like.

[0381] In particular, the chemically strengthened glass of the present application is useful as cover glass for mobile devices such as mobile phones, smart phones, portable information terminals (PDA), tablet terminals, and the like. Further, the present application is useful for cover glass for display devices such as televisions (TV), personal computers (PC), in-vehicle displays, and touch panels, cover glass provided on the surface of a solar cell module, wall surfaces (full-surface displays) of elevators, houses, and buildings, building materials such as window glass, and interior materials such as tabletops, cars, and airplanes. In addition, the present application is also useful as cover glass for the above-mentioned articles. Further, by bending processing and bending molding, the present application can also be applied to housings having a curved shape and the like.

[0382] Examples

[0383] Hereinafter, the present application will be described in further detail according to examples.

[0384] The materials, amounts, proportions, processing contents, and processing steps and the like shown in the following examples can be appropriately changed as long as the gist of the present application is not deviated. Therefore, the scope of the present application should not be interpreted limitatively by the examples shown below.

[0385] Note that Examples 1 to 3, 5, and 7 to 9 are examples, Examples 4 and 6 are comparative examples, and Examples 10 and 11 are reference examples.

[0386] <Manufacture of chemically strengthened glass>

[0387] First, glass materials A to C were manufactured by melting glass raw materials in a platinum crucible in a manner that each glass composition is expressed as a molar percentage of the oxides shown in Table 1.

[0388] Specifically, the oxides, hydroxides, carbonates, or nitrates and the like generally used as glass raw materials were appropriately selected, and 1000 g of each was weighed as glass.

[0389] Next, the mixed raw materials were put into a platinum crucible and melted in a resistance-heating type electric furnace at 1500 to 1700°C for about 3 hours, and homogenized by deaeration to obtain a molten glass. The obtained molten glass was flowed into a mold, and after being kept at a temperature of the glass transition point + 50°C for 1 hour, it was cooled to room temperature at a rate of 0.5°C / min to obtain a glass block. The obtained glass block was cut and ground to manufacture a sheet glass. Both surfaces of the obtained sheet glass were mirror finished to finally obtain a sheet glass (glass for chemical strengthening) having a size of 120 mm in length x 60 mm in width x 0.5 mm in thickness or 120 mm in length x 60 mm in width x 0.6 mm in thickness.

[0390] On the other hand, a glass block for measuring the fracture toughness value (K ICand a sample piece for measuring the Young's modulus.

[0391] Note that, with respect to the glass material B, after becoming a sheet glass, heat treatment was performed under conditions of heating to 550°C and maintaining for 2 hours, and then heating to 720°C and maintaining for 2 hours.

[0392] Further, with respect to the glass material C, after becoming a sheet glass, heat treatment was performed under conditions of heating to 540°C and maintaining for 4 hours, and then heating to 600°C and maintaining for 4 hours, and then heating to 650°C and maintaining for 4 hours.

[0393] Further, with respect to the glass materials B and C, the same heat treatment as described above was performed on the glass blocks to obtain a sample piece for measuring the fracture toughness value (K IC ) and a sample piece for measuring the Young's modulus.

[0394] [Table 1]

[0395]

[0396] Each of the chemically strengthened glasses (glass materials A to C) obtained by the above-described steps was subjected to a chemical strengthening treatment under the conditions described in Table 2 to obtain the chemically strengthened glasses of Examples 1 to 9.

[0397] Note that, Examples 10 and 11 directly used the chemically strengthened glasses (glass materials A and B) without being subjected to chemical strengthening.

[0398] <Measurement of Stress Distribution>

[0399] The stress distribution of the chemically strengthened glass was obtained by the above-described method.

[0400] <Measurement of Young's Modulus>

[0401] In the step of obtaining each of the glass materials described above, a cut sample piece was used to measure the Young's modulus of the chemically strengthened glass. Specifically, using the above-described sample piece, measurement was performed by an ultrasonic pulse method in accordance with JIS R 1602. Note that the Young's modulus of the chemically strengthened glass corresponds to the Young's modulus at the center position in the thickness direction of the chemically strengthened glass.

[0402] Further, the Young's modulus at the center position in the plane direction of the chemically strengthened glass was measured by the same method as that for measuring the above-described sample piece, and the same value as that measured using the above-described sample piece was obtained. Therefore, in the following tables, the description of the Young's modulus at the center position in the plane direction was omitted.

[0403] <Measurement of Fracture Toughness Value>

[0404] In the step of obtaining each of the above glass materials, a cut sample piece was used to measure the Young's modulus of the chemically strengthened glass. The fracture toughness value was measured by the DCDC method described above.

[0405] <Measurement of Transmittance>

[0406] The transmittance of the chemically strengthened glass was measured by the above method.

[0407] The transmittance of the chemically strengthened glass of Example 5 was 91%, and the transmittance of the chemically strengthened glass of Example 7 was 92%.

[0408] [Drop Strength Test]

[0409] The drop strength was measured according to the following procedure.

[0410] First, an aluminum alloy structure having a cuboid shape with a width of 70 mm, a length of 130 mm, and a thickness of 2 mm was prepared, and the mass was 120 g. The structure was a device simulating a mobile device such as a smartphone.

[0411] Next, the glass of each example was attached to the widest surface of the structure. The glass attachment to the structure was performed using an adhesive tape of 0.5 mm.

[0412] Next, the structure with the glass attached was dropped against the abrasive surface of a sandpaper of #80 whose abrasive is silicon carbide. The dropping was performed in a direction in which the structure side with the glass attached faced the sandpaper. At the time of dropping, whether or not a crack was generated on the glass was confirmed, the height of dropping was changed, and the height at which a crack was first generated was recorded as an index of the drop strength. Hereinafter, the height at which a crack was first generated is referred to as "#80 SP crack height".

[0413] In addition, the sandpaper used when the #80 SP crack height was measured was changed to #180, and otherwise, the height at which a crack was first generated was measured in the same manner as the method of measuring the #80 SP crack height, and the height was also used as an index of the drop strength.

[0414] When the above test was performed with the sandpaper changed to #180, the height at which a crack was first generated was referred to as "#180 SP crack height".

[0415] <Results>

[0416] The conditions of the chemical strengthening treatment of the chemically strengthened glass of each example, the measurement results, and the evaluation results are shown in Table 2 below.

[0417] In Table 2, the measurement method of each value in the "stress distribution" column is as described above. Note that the "CT" column indicates the absolute value of the stress CT at the center of the plate thickness.

[0418] In addition, the "Slope (DOC ~ 120 μm)" column is a slope calculated from the compressive stress value at the compressive stress layer depth DOC and the compressive stress value at the center of the sheet thickness, which are obtained by the above-described method.

[0419] The "Slope (@ DOC)" column is an absolute value of the first derivative at the compressive stress layer depth DOC, which is obtained by the above-described method.

[0420] The "Slope (@ 120 μm)" column is an absolute value of the first derivative at a position 120 μm from the surface in the depth direction, which is obtained by the above-described method. Note that in any stress distribution, the position 120 μm from the surface in the depth direction is the position at which the absolute value of the first derivative is the largest in the range from the position 120 μm from the surface in the depth direction to the center of the sheet thickness.

[0421] In addition, the formula (1) and the formula (2) are as described above. Note that when the requirements of the formula (1) and the formula (2) are satisfied, the values described in Table 2 are each a value of 0 or more.

[0422] [Table 2]

[0423]

[0424] According to the results shown in Table 2, it is confirmed that the stress CT at the center of the sheet thickness, the compressive stress CS at a position 120 μm from the surface in the depth direction, and the ratio of the first derivative values satisfy the above-described formula (1), formula (2), and formula (3) in Examples 4, 6, 10, and 11. 120 When the above-described formula (2) is satisfied, the drop strength (#80 SP crack height and #180 SP crack height) is excellent.

[0425] According to the comparison of Example 7 with Examples 8 and 9, it is confirmed that when the value of the ratio of the first derivative values is 0.90 to 1.15, the drop strength (#80 SP crack height and #180 SP crack height) is more excellent.

Claims

1. A chemically strengthened glass, wherein the stress CT at the center of the thickness of the glass plate satisfies the following relationship (1). The compressive stress CS at a depth of 120 μm from the surface 120 The following relationship (2) must be satisfied. Equation (1) |CT|≤-170t+175 Equation (2) 190t-124≤CS 120 In equation (1), |CT| represents the absolute value of the stress CT, in MPa. In equations (1) and (2), t represents the thickness of the chemically strengthened glass in mm. In equation (2), CS 120 The compressive stress CS is indicated 120 The value is in MPa.

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

3. The chemically strengthened glass according to claim 2, wherein, The absolute value of the slope of the stress distribution curve from the compressive stress layer depth (DOC) to the center of the plate thickness is less than 1.

00.

4. The chemically strengthened glass according to any one of claims 1 to 3, wherein, The compressive stress CS at a depth of 50 μm from the surface 50 Satisfying the relationship in equation (3), Equation (3) 150t-50≤CS 50 In equation (3), CS 50 The compressive stress CS is indicated 50 The value is in MPa. In formula (3), t represents the thickness of the chemically strengthened glass in mm.

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

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

7. The chemically strengthened glass according to any one of claims 1 to 3, wherein, The composition at the center of the plate thickness is expressed as a molar percentage based on oxides, containing 55-75% SiO2, 3-18% Al2O3, 17-30% Li2O, 0-3% Na2O, 0-1% K2O, 0-10% MgO, 0-10% CaO, 0-5% SrO, 0-5% ZnO, 0-3% TiO2, 0-5% ZrO2, 0-1% SnO2, 0-3% P2O5, 0-10% B2O3, and 0-3% Y2O3.

8. The chemically strengthened glass according to any one of claims 1 to 3, wherein it is a crystalline glass with a transmittance of 85% or more.

9. The chemically strengthened glass according to any one of claims 1 to 3, wherein, The compressive stress CS 120 Below 0 MPa.

10. The chemically strengthened glass according to any one of claims 1 to 3, wherein, The plate thickness is less than 0.6mm.

11. The chemically strengthened glass according to any one of claims 1 to 3, wherein, For the chemically strengthened glass, the absolute value of the first derivative of the stress distribution curve in the depth direction obtained by using a diffused light photoelastic stress meter is less than 1.80 at any depth from 120 μm from the surface along the depth direction to the center of the plate thickness.

12. The chemically strengthened glass according to claim 2 or 3, wherein, The absolute value of the first derivative of the stress distribution curve in the depth direction obtained using a scattered light photoelastic stress gauge is less than 1.80 at the depth DOC of the compressive stress layer.

13. The chemically strengthened glass according to claim 2 or 3, wherein, In the stress distribution curve along the depth direction obtained using a scattered light photoelastic stress meter, the absolute value of the first derivative at the depth DOC of the compressive stress layer divided by the absolute value of the first derivative at a position 120 μm from the surface along the depth direction is less than 1.

20.

14. A method for manufacturing chemically strengthened glass, comprising the method for manufacturing chemically strengthened glass according to any one of claims 1 to 3. The chemically strengthened glass is subjected to a first chemical strengthening treatment using a first molten salt comprising at least 90% by mass of Na salt and at least 2% by mass of Li salt relative to the total mass, and the chemically strengthened glass subjected to the first chemical strengthening treatment is subjected to a second chemical strengthening treatment using a second molten salt comprising at least 90% by mass of K salt relative to the total mass. The composition of the chemically strengthened glass at the center of its thickness, expressed as a molar percentage based on oxides, contains 60–72% SiO2, 10–20% Al2O3, 3–12% Li2O, 0.5–6% Na2O, and 1–3% K2O.

15. The method for manufacturing chemically strengthened glass according to claim 14, wherein, The ratio of the Li salt content in the first molten salt to the Li2O content in the chemically strengthened glass composition is 0.1 to 1.0 in molar ratio.

16. The method for manufacturing chemically strengthened glass according to claim 14, wherein, The first chemical enhancement treatment lasts for more than 150 minutes, and the second chemical enhancement treatment lasts for more than 90 minutes.

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

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

Images