Chemically strengthened glass and its manufacturing method

Abstract

To provide a chemically strengthened glass exhibiting excellent flying stone resistance as compared with a conventional one, and to provide a method for producing the same.SOLUTION: Provided is a chemically strengthened glass with the ratio ICS(≥400) / ICS, which is a ratio of the integral value ICS(≥400) of compressive stress in a region from a depth of 400 μm from the surface to a depth at which the compressive stress becomes 0 to the integrated value of the compressive stress CS, being more than 0.13. Also provided is a method for producing the chemically strengthened glass, including a first ion-exchange in which the chemically strengthened glass and a lithium-containing aluminosilicate glass having a sheet thickness of 1.4 to 7 mm are brought into contact with a first inorganic salt composition containing sodium at a temperature of 430°C or higher for 10 hours or longer for ion exchange therebetween.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing chemically strengthened glass and chemically strengthened glass, and more particularly to chemically strengthened glass suitable as glass for protecting a sensor module and a sensor or oscillator, and a method for manufacturing the same. [Background technology]

[0002] Mobile devices such as cars, trains, and drones, as well as outdoor sensors and security devices such as surveillance cameras, are equipped with multiple sensors with diverse functions. The structure and materials of the protective component can sometimes impede the sensor's use, so the type of sensor placed inside the protective component is also a factor in selecting the structure and materials of the protective component.

[0003] It is desirable to select a material for the protective member that protects the sensor that has high transmittance for visible light and excellent strength. Sensor modules that use glass as a protective member that protects the sensor are known, and for example, Patent Document 1 discloses a sensor module that uses chemically strengthened glass as a protective member.

[0004] Chemically strengthened glass is glass that has a compressive stress layer formed on its surface by an ion exchange process in which the glass is exposed to an inorganic salt composition such as sodium nitrate or potassium nitrate. This ion exchange process causes ion exchange between alkali metal ions contained in the glass and alkali metal ions with a larger ionic radius contained in the inorganic salt composition, forming a compressive stress layer on the surface of the glass. The strength of chemically strengthened glass depends on the stress profile, which is expressed as compressive stress (hereinafter also abbreviated as CS), with the depth from the glass surface as a variable. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2019 / 009336 Summary of the Invention [Problem to be solved by the invention]

[0006] When a sensor is installed in a mobile device, foreign objects such as flying stones may collide with the sensor module while the device is in motion. When a momentary external impact is applied due to a collision with a flying stone or the like, the stress at the time of the collision is not alleviated and concentrated stress occurs, which may damage the glass protecting the sensor and the sensor. Therefore, the glass protecting the sensor must have excellent resistance to flying stones.

[0007] Therefore, an object of the present invention is to provide chemically strengthened glass that exhibits superior resistance to chipping stones compared to conventional glass, and a method for producing the same. [Means for solving the problem]

[0008] The present inventors have studied the above problems and have found that chemically strengthened glass having a specific stress profile that increases compressive stress in a deep layer from the surface to a depth of about 400 μm or more can improve stone chip resistance, thereby completing the present invention.

[0009] The present invention relates to chemically strengthened glass having a ratio ICS(≧400) / ICS of greater than 0.13, where ICS(≧400) is the integral of compressive stress in a region from a depth of 400 μm from the surface to a depth at which the compressive stress becomes 0, to ICS, the integral of compressive stress CS.

[0010] The present invention also relates to a method for producing chemically strengthened glass, which includes a first ion exchange step in which lithium-containing aluminosilicate glass having a plate thickness of 1.4 to 7 mm is brought into contact with a first inorganic salt composition containing sodium at a temperature of 430°C or higher for 10 hours or longer to perform ion exchange. [Effects of the Invention]

[0011] The chemically strengthened glass of the present invention has a specific stress profile and high compressive stress in a deep layer portion at a depth of 400 μm or more from the surface, and therefore exhibits excellent resistance to chipped stones. According to the method for producing chemically strengthened glass of the present invention, by subjecting lithium-containing aluminosilicate glass having a plate thickness of 1.4 mm or more to ion exchange under specific conditions, it is possible to produce chemically strengthened glass that exhibits excellent resistance to chipped stones by increasing the compressive stress in a deep layer portion at a depth of 400 μm or more from the surface. [Brief explanation of the drawings]

[0012] [Figure 1] 1(a) and 1(b) are perspective views showing examples of the configuration of a protective member formed entirely or partially from the chemically strengthened glass of the present embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0013] The present invention will be described in detail below, but the present invention is not limited to the following embodiments and can be implemented in any modified form without departing from the gist of the present invention.

[0014] In this specification, the symbol "to" indicating a range of values ​​is used to mean that the values ​​before and after it are included as the lower and upper limits. Furthermore, in this specification, the composition of the glass (the content of each component) is described in terms of mole percentage based on oxides, unless otherwise specified.

[0015] Hereinafter, "chemically strengthened glass" refers to glass after chemical strengthening treatment, and "glass for chemical strengthening" refers to glass before chemical strengthening treatment.

[0016] In this specification, unless otherwise specified, glass compositions are expressed in mole percent based on oxides, and mole percent is simply expressed as "%." Furthermore, in this specification, "substantially free" means that the content is below the impurity level contained in raw materials, i.e., it is not intentionally added. Specifically, for example, it is less than 0.1%.

[0017] In this specification, the term "stress profile" refers to a representation of compressive stress values ​​with depth from the glass surface as a variable. In the stress profile, tensile stress is represented as negative compressive stress.

[0018] Compressive stress (CS) can be measured by cutting a cross section of glass into thin slices and analyzing the sliced ​​samples with a birefringence imaging system. A birefringence imaging system birefringence stress meter is a device that measures the magnitude of retardation caused by stress using a polarizing microscope and a liquid crystal compensator, and one example is the birefringence imaging system Abrio-IM manufactured by CRi.

[0019] Measurements can also be made using scattered light photoelasticity. With this method, light is incident on the glass surface and the polarization of the scattered light is analyzed to measure CS. An example of a stress measuring instrument that uses scattered light photoelasticity is the SLP-2000 scattered light photoelasticity meter manufactured by Orihara Seisakusho.

[0020] In this specification, the "depth of compressive stress layer (DOC)" is the depth at which the compressive stress value becomes zero. Hereinafter, the surface compressive stress value is referred to as CS0, and the compressive stress value at a depth of 50 μm from the surface is referred to as CS 50 Also, "internal tensile stress (CT)" refers to the tensile stress value at a depth of 1 / 2 of the plate thickness t.

[0021] In this specification, the crack occurrence rate is evaluated according to the strength test method of ISO 20567-1 Test Method B under the following conditions. (conditions) Stepping stones: Chilled iron grit Stone size: 3.55-5mm Injection amount: 500g Injection pressure: 250kPa Sample installation angle: 54° Injection time: 8-12s Number of shots: 2 Sample impact area: 40-40mm

[0022] <Stress measurement method> In recent years, glass that has undergone two-stage chemical strengthening, in which the lithium ions inside the glass are exchanged for sodium ions (Li-Na exchange), and then the sodium ions inside the glass are exchanged for potassium ions on the surface of the glass (Na-K exchange), has become mainstream for cover glass for devices such as smartphones.

[0023] To obtain the stress profile of such two-stage chemically strengthened glass non-destructively, for example, a scattered light photoelastic stress meter (hereinafter also abbreviated as SLP) or a glass surface stress meter (hereinafter also abbreviated as FSM) can be used in combination.

[0024] The method using a scattered light photoelastic stress meter (SLP) can measure the compressive stress resulting from Li-Na exchange in the glass interior at a depth of several tens of micrometers or more from the glass surface. On the other hand, the method using a glass surface stress meter (FSM) can measure the compressive stress resulting from Na-K exchange in the glass surface layer at a depth of several tens of micrometers or less from the glass surface (e.g., WO 2018 / 056121, WO 2017 / 115811). Therefore, a combination of SLP and FSM information is sometimes used to determine the stress profile of the glass surface and interior in two-stage chemically strengthened glass.

[0025] In the present invention, stress profiles measured mainly by a scattered light photoelastic stress meter (SLP) are used. In this specification, the terms compressive stress CS, tensile stress CT, compressive stress layer depth DOC, etc. refer to values ​​in the SLP stress profile.

[0026] The scattered light photoelastic stress meter is a stress measuring device that includes a polarization phase difference variable member that varies the polarization phase difference of laser light by one or more wavelengths relative to the wavelength of the laser light, an imaging element that captures the scattered light emitted when the laser light with the varied polarization phase difference is incident on tempered glass multiple times at predetermined time intervals to obtain multiple images, and a calculation unit that measures the periodic brightness change of the scattered light using the multiple images, calculates the phase change of the brightness change, and calculates the stress distribution in the depth direction from the surface of the tempered glass based on the phase change.

[0027] A method for measuring stress profiles using a scattered light photoelastic stress meter is described in International Publication No. 2018 / 056121. Examples of scattered light photoelastic stress meters include the SLP-1000 and SLP-2000 manufactured by Orihara Seisakusho. High-precision stress measurements are possible when these scattered light photoelastic stress meters are combined with the accompanying software SlpIV_up3 (Ver. 2019.01.10.001).

[0028] In this specification, the average slope of the stress profile refers to the average obtained by determining the slope of the stress profile every 1 μm within the depth range for which the slope is to be determined.

[0029] <Chemically strengthened glass> <<Stress profile>> The chemically strengthened glass of this embodiment (hereinafter also referred to as the present chemically strengthened glass) is characterized in that the ratio ICS(≧400) / ICS, which is the integral of compressive stress in the region from a depth of 400 μm from the surface to a depth where the compressive stress becomes 0, to ICS, which is the integral of compressive stress CS, is greater than 0.13. Since ICS(≧400) / ICS is greater than 0.13, the compressive stress is increased at positions deeper than 400 μm from the surface, and excellent resistance to chipped stones is exhibited.

[0030] The chemically strengthened glass has an ICS(≧400) / ICS ratio of more than 0.13, more preferably 0.16 or more, even more preferably 0.19 or more, particularly preferably 0.22 or more, and most preferably 0.25 or more. The upper limit of ICS(≧400) / ICS is not particularly limited, but is preferably 0.8 or less, more preferably 0.7 or less, from the viewpoint of the balance with the surface layer stress.

[0031] The chemically strengthened glass preferably has an ICS(≧400), which is the integral of compressive stress in the region from a depth of 400 μm from the surface to a depth where the compressive stress becomes 0, of 9200 MPa μm or more, more preferably 9800 MPa μm or more, even more preferably 10400 MPa μm or more, and particularly preferably 11000 MPa μm or more. Having an ICS(≧400) of 9200 MPa μm or more increases the compressive stress at positions deeper than 400 μm from the surface, further improving resistance to chipping stones. From the viewpoint of productivity, the ICS(≧400) is preferably 40,000 or less, more preferably 35,000 or less, and even more preferably 30,000 or less.

[0032] In the present chemically strengthened glass, the stress depth DOL at which the compressive stress is 50 MPa is preferably 400 μm or more, more preferably 450 μm or more, even more preferably 500 μm or more, and particularly preferably 550 μm or more. By having the stress depth DOL at which the compressive stress is 50 MPa be 400 μm or more, the compressive stress at a position deeper than 400 μm from the surface can be increased, and the resistance to chipping stones can be further improved. The upper limit of the stress depth DOL at which the compressive stress is 50 MPa is not particularly limited, but it is usually preferably 1000 μm or less from the viewpoint of the balance between compressive stress and tensile stress.

[0033] In the chemically strengthened glass, the maximum negative slope of the stress profile at a position deeper than 50 μm from the surface is preferably −0.50 (MPa / μm) or more, more preferably −0.46 (MPa / μm) or more, even more preferably −0.42 (MPa / μm) or more, and particularly preferably (MPa / μm) or more. Having a maximum negative slope of −0.50 (MPa / μm) or more at a position deeper than 50 μm from the surface increases compressive stress in the deep layer, further improving resistance to chipping stones. The upper limit of the maximum negative slope is not particularly limited, but from the viewpoint of improving bending strength due to surface layer stress, it is preferably −0.05 (MPa / μm) or less, more preferably −0.09 (MPa / μm) or less.

[0034] The chemically strengthened glass has a plate thickness of t, and the value DOC / t obtained by dividing the compressive stress layer depth DOC by t is preferably 0.170 or more, more preferably 0.175 or more, even more preferably 0.180 or more, and particularly preferably 0.185 or more. By having DOC / t of 0.170 or more, the compressive stress in the deep layer can be increased, and the resistance to flying stones can be further improved. Although the upper limit of DOC / t is not particularly limited, from the viewpoint of the balance between compressive stress and tensile stress, it is preferably 0.30 or less, more preferably 0.28 or less.

[0035] From the viewpoint of improving strength, the chemically strengthened glass preferably has a maximum tensile stress CTmax of 40 MPa or more, more preferably 45 MPa or more, even more preferably 50 MPa or more, and particularly preferably 55 MPa or more. The upper limit of the maximum tensile stress CTmax is not particularly limited, but from the viewpoint of productivity, it is usually preferably 100 MPa or less.

[0036] This chemically strengthened glass has a compressive stress CS at a depth of 400 μm from the surface. 400 is preferably 60 MPa or more, more preferably 65 MPa or more, even more preferably 70 MPa or more, and particularly preferably 75 MPa or more. 400By making the CS equal to or greater than 60 MPa, the compressive stress in the deep layer can be increased, and the resistance to flying stones can be further improved. 400 Although there is no particular upper limit, it is usually preferably 200 MPa or less from the viewpoint of the balance between compressive stress and tensile stress.

[0037] This chemically strengthened glass has a compressive stress CS at a depth of 500 μm from the surface. 500 is preferably 45 MPa or more, more preferably 50 MPa or more, even more preferably 55 MPa or more, and particularly preferably 60 MPa or more. 500 By setting the CS to 45 MPa or more, the compressive stress in the deep layer can be increased, and the resistance to flying stones can be further improved. 500 Although there is no particular upper limit to the value, it is usually preferably 180 or less from the viewpoint of the balance between compressive stress and tensile stress.

[0038] This chemically strengthened glass has a compressive stress CS at a depth of 600 μm from the surface. 600 is preferably 15 MPa or more, more preferably 20 MPa or more, even more preferably 25 MPa or more, and particularly preferably 30 MPa or more. 600 By setting the CS to 15 MPa or more, the compressive stress in the deep layer can be increased, and the resistance to flying stones can be further improved. 600 Although there is no particular upper limit to the value, it is usually preferably 160 or less from the viewpoint of the balance between compressive stress and tensile stress.

[0039] Hereinafter, as a specific example of the present chemically strengthened glass, the stress profiles of the chemically strengthened glasses of the first and second embodiments will be described. The characteristics of the stress profiles described above are common to the first and second embodiments. The characteristics of the stress profile of the present chemically strengthened glass can be adjusted by its matrix composition and the conditions of the ion exchange treatment.

[0040] (Chemically strengthened glass of the first embodiment) In the chemically strengthened glass of the first embodiment, the maximum negative slope of the stress profile at a depth of 0 to 20 μm from the surface is preferably −10 (MPa / μm) or less, more preferably −12 (MPa / μm) or less, even more preferably −14 (MPa / μm) or less, and particularly preferably −16 (MPa / μm) or less. By having the maximum negative slope of the stress profile at a depth of 0 to 20 μm be −10 (MPa / μm) or less, excess stress that does not contribute to strength can be reduced. There is no particular lower limit for the maximum negative slope, but from the viewpoint of increasing deep layer stress, it is usually preferably −40 (MPa / μm) or more.

[0041] The chemically strengthened glass of the first embodiment has a compressive stress maximum value. The compressive stress maximum value is preferably 50 MPa or more, more preferably 60 MPa or more, even more preferably 70 MPa or more, and particularly preferably 80 MPa or more. When the compressive stress maximum value is 50 MPa or more, crack extension in deep layers can be suppressed, and resistance to flying stones can be further improved. There is no particular upper limit to the compressive stress maximum value, but from the viewpoint of the balance between compressive stress and tensile stress, it is usually preferably 200 MPa or less.

[0042] The chemically strengthened glass of the first embodiment has a plate thickness of t, and the position of the compressive stress maximum value is preferably within a depth range of 0.05t to 0.13t from the surface. The position of the compressive stress maximum value is more preferably 0.055t or more, even more preferably 0.060t or more, and particularly preferably 0.065t or more. The position of the compressive stress maximum value is more preferably 0.12t or less, even more preferably 0.11t or less, and particularly preferably 0.10t or less. By having the position of the compressive stress maximum value within the range of 0.05t to 0.13t, the compressive stress in the deep layer can be increased, and resistance to flying stones can be further improved.

[0043] In the chemically strengthened glass of the first embodiment, when the absolute value of the average slope of the stress profile from the surface to the position of the compressive stress maximum value is ms and the absolute value of the average slope of the stress profile from the position of the compressive stress maximum value to the depth where the compressive stress becomes zero is md, it is preferable that md > md. By having md > md, the compressive stress in the deep layer can be increased and the resistance to flying stones can be further improved.

[0044] The chemically strengthened glass of the first embodiment has a compressive stress CS at a depth of 400 μm from the surface relative to the surface compressive stress CS 400 The ratio of CS 400 / CS0 is preferably 0.10 or more, more preferably 0.12 or more, even more preferably 0.14 or more, and particularly preferably 0.16 or more. 400 By setting the ratio of CS to 0.10 or more, compressive stress in the deep layer can be increased, and resistance to flying stones can be further improved. 400 Although there is no particular upper limit for / CS0, it is usually preferably 0.50 or less from the viewpoint of improving the bending strength due to the surface layer stress.

[0045] From the viewpoint of improving bending strength, the chemically strengthened glass of the first embodiment preferably has a surface compressive stress CSO of 400 MPa or more, more preferably 450 MPa or more, and even more preferably 500 MPa or more. From the viewpoint of the balance between compressive stress and tensile stress, the surface compressive stress CSO is preferably 900 MPa or less, more preferably 800 MPa or less, and even more preferably 700 MPa or less.

[0046] The chemically strengthened glass of the first embodiment has a compressive stress CS at a depth of 0 μm from the surface. 50 Compressive stress CS at a depth of 600 μm from the surface 600 The ratio of CS 600 / CS0 is preferably 0.03 or more, more preferably 0.04 or more, even more preferably 0.05 or more, and particularly preferably 0.06 or more. 600By setting the ratio of CS to 0.03 or more, compressive stress in the deep layer can be increased, and resistance to flying stones can be further improved. 600 Although there is no particular upper limit for / CS0, it is usually preferably 0.20 or less from the viewpoint of improving the bending strength due to the surface layer stress.

[0047] (Chemically strengthened glass of second embodiment) The chemically strengthened glass of the second embodiment has a compressive stress CS at a depth of 400 μm from the surface relative to the surface compressive stress CS 400 The ratio of CS 400 / CS0 is preferably 0.32 or more, more preferably 0.34 or more, even more preferably 0.36 or more, and particularly preferably 0.38 or more. 400 By setting the ratio of CS to 0.32 or more, compressive stress in the deep layer can be increased, and resistance to flying stones can be further improved. 400 Although there is no particular upper limit for / CS0, it is usually preferably 0.50 or less from the viewpoint of improving the bending strength due to the surface layer stress.

[0048] In the chemically strengthened glass of the second embodiment, from the viewpoint of improving strength, the surface compressive stress CSO is preferably 200 MPa or more, more preferably 210 MPa or more, and even more preferably 220 MPa or more. In addition, from the viewpoint of increasing stress in the deep layer portion, the surface compressive stress CSO is preferably 320 MPa or less, more preferably 310 MPa or less, and even more preferably 300 MPa or less.

[0049] The chemically strengthened glass of the second embodiment has a compressive stress CS at a depth of 600 μm from the surface relative to a compressive stress CS at a depth of 0 μm from the surface. 600 The ratio of CS 600 / CS0 is preferably 0.03 or more, more preferably 0.04 or more, even more preferably 0.05 or more, and particularly preferably 0.06 or more. 600 By setting the ratio of CS to 0.03 or more, compressive stress in the deep layer can be increased, and resistance to flying stones can be further improved. 600Although there is no particular upper limit for / CS0, it is usually preferably 0.20 or less from the viewpoint of improving the bending strength due to the surface layer stress.

[0050] <<Crack occurrence rate>> The chemically strengthened glass preferably has a cracking rate of 10% or less, more preferably 8% or less, even more preferably 5% or less, and particularly preferably 3% or less, as evaluated in accordance with the strength test method of ISO 20567-1 Test Method B. A cracking rate of 10% or less can more effectively improve resistance to flying stones. When determining the cracking rate, n is 3 or more.

[0051] <<Plate thickness>> The chemically strengthened glass preferably has a thickness of 1.4 to 7 mm. From the viewpoint of improving strength, the thickness is more preferably 1.8 mm or more, even more preferably 2.2 mm or more, and particularly preferably 2.6 mm or more. From the viewpoint of reducing weight, the thickness is more preferably 6.6 mm or less, even more preferably 6.2 mm or less, and particularly preferably 5.8 mm or less.

[0052] <<Glass composition>> In this specification, "mother composition of chemically strengthened glass" refers to the glass composition of glass for chemical strengthening, and except when extreme ion exchange treatment is performed, the glass composition deeper than the compressive stress layer depth of the chemically strengthened glass is almost the same as the mother composition of the chemically strengthened glass.

[0053] The chemically strengthened glass of this embodiment has a matrix composition, expressed in mole percent on an oxide basis, SiO2 52-75%, Al2O3 8-20%, It is preferable that Li2O is contained in an amount of 5 to 18%.

[0054] More preferably, the chemically strengthened glass of the present embodiment has a matrix composition, expressed in mole percent on an oxide basis, SiO2 52-75%, Al2O3 8-20%, Li2O 5-18%, Na2O 0-15%, K2O 0-5%, MgO 0-20%, CaO 0-20%, SrO 0-20%, BaO 0-20%, ZnO 0-10% TiO2 0-1% ZrO2 0-8%, Contains 0-5% Y2O3. A preferred glass composition will now be described.

[0055] In the chemically strengthened glass of this embodiment, SiO2 is a component that forms the network structure of the glass. It is also a component that increases chemical durability. The SiO2 content is preferably 52% or more, more preferably 56% or more, even more preferably 60% or more, and particularly preferably 64% or more. On the other hand, to improve meltability, the SiO2 content is preferably 75% or less, more preferably 73% or less, even more preferably 71% or less, and particularly preferably 69% or less.

[0056] Al2O3 is an essential component that increases the surface compressive stress due to chemical strengthening. The Al2O3 content is preferably 8% or more, more preferably 10% or more, even more preferably 11% or more, and particularly preferably 12% or more. On the other hand, the Al2O3 content is preferably 20% or less, more preferably 18% or less, further preferably 17% or less, further preferably 16% or less, and most preferably 15% or less, in order to prevent the devitrification temperature of the glass from becoming too high.

[0057] Li2O is a component that generates surface compressive stress through ion exchange. The Li2O content is preferably 5% or more, more preferably 7% or more, even more preferably 9% or more, and particularly preferably 11% or more. On the other hand, to stabilize the glass, the Li2O content is preferably 18% or less, more preferably 17% or less, even more preferably 16% or less, and most preferably 15% or less.

[0058] MgO is a component that stabilizes glass and also increases mechanical strength and chemical resistance, so it is preferable to add it when the Al2O3 content is relatively low. The MgO content is preferably 1% or more, more preferably 2% or more, even more preferably 3% or more, and particularly preferably 4% or more. On the other hand, if too much MgO is added, the viscosity of the glass decreases, making devitrification or phase separation more likely to occur. The MgO content is preferably 20% or less, more preferably 19% or less, even more preferably 18% or less, and particularly preferably 17% or less.

[0059] CaO, SrO, BaO and ZnO are all components that improve the meltability of the glass and may be contained.

[0060] CaO is a component that improves the meltability of glass and the crushability of chemically strengthened glass, and may be contained. When CaO is contained, the content is preferably 0.5% or more, more preferably 1% or more, even more preferably 2% or more, particularly preferably 3% or more, and most preferably 5% or more. On the other hand, if the CaO content exceeds 20%, the ion exchange performance is significantly reduced, so it is preferably 20% or less. The CaO content is more preferably 14% or less, and even more preferably 10% or less, 8% or less, 6% or less, 3% or less, and 1% or less in the following stepwise manner.

[0061] SrO is a component that improves the meltability of glass and the crushability of chemically strengthened glass, and may be contained. When SrO is contained, the content is preferably 0.5% or more, more preferably 1% or more, even more preferably 2% or more, particularly preferably 3% or more, and most preferably 5% or more. On the other hand, if the SrO content exceeds 20%, the ion exchange performance significantly decreases, so it is preferably 20% or less. The SrO content is more preferably 14% or less, and even more preferably 10% or less, 8% or less, 6% or less, 3% or less, and 1% or less in the following stepwise manner.

[0062] BaO is a component that improves the meltability of glass and the crushability of chemically strengthened glass, and may be contained. When BaO is contained, the content is preferably 0.5% or more, more preferably 1% or more, even more preferably 2% or more, particularly preferably 3% or more, and most preferably 5% or more. On the other hand, if the BaO content exceeds 20%, the ion exchange performance will be significantly reduced. The BaO content is preferably 15% or less, and more preferably 10% or less, 8% or less, 6% or less, 3% or less, and 1% or less in the following stepwise order.

[0063] ZnO is a component that improves the meltability of glass and may be contained. When ZnO is contained, the content is preferably 0.25% or more, and more preferably 0.5% or more. On the other hand, if the ZnO content exceeds 10%, the weather resistance of the glass will be significantly reduced. The ZnO content is more preferably 14% or less, and even more preferably 10% or less, 8% or less, 6% or less, 3% or less, and 1% or less in the following stepwise order.

[0064] Na2O is a component that improves the meltability of glass. Na2O is not essential, but when contained, it is preferably 1% or more, more preferably 2% or more, and particularly preferably 5% or more. If the Na2O content is too high, the chemical strengthening properties will decrease, so the Na2O content is preferably 15% or less, more preferably 12% or less, particularly preferably 10% or less, and most preferably 8% or less.

[0065] Like NaO, KO is a component that lowers the melting temperature of glass and may be contained. When KO is contained, the content is preferably 0.5% or more, more preferably 0.8% or more, even more preferably 1% or more, even more preferably 1.2% or more, and particularly preferably 1.5% or more. If the KO content is too high, the chemical strengthening properties or chemical durability will decrease, so the content is preferably 5% or less, more preferably 4.8% or less, even more preferably 4.5% or less, particularly preferably 4.2% or less, and most preferably 4.0% or less.

[0066] The total content of Na2O and K2O (Na2O+K2O) is preferably 3% or more, more preferably 5% or more, to improve the meltability of the glass raw materials. Furthermore, the ratio of the K2O content to the total content of Li2O, Na2O, and K2O (hereinafter referred to as R2O), K2O / R2O, is preferably 0.2 or less, since this improves chemical strengthening properties and chemical durability. K2O / R2O is more preferably 0.15 or less, and even more preferably 0.10 or less. R2O is preferably 10% or more, more preferably 12% or more, and even more preferably 15% or more. Furthermore, R2O is preferably 20% or less, and more preferably 18% or less.

[0067] ZrO2 is a component that enhances mechanical strength and chemical durability, and is preferably contained because it significantly improves CS. The ZrO2 content is preferably 0.5% or more, more preferably 0.7% or more, even more preferably 1.0% or more, particularly preferably 1.2% or more, and most preferably 1.5% or more. On the other hand, to suppress devitrification during melting, ZrO2 is preferably 8% or less, more preferably 7.5% or less, even more preferably 7% or less, and particularly preferably 6% or less. If the ZrO2 content is too high, the viscosity decreases due to an increase in the devitrification temperature. To suppress deterioration of formability due to such a decrease in viscosity, when the forming viscosity is low, the ZrO2 content is preferably 5% or less, more preferably 4.5% or less, and even more preferably 3.5% or less.

[0068] To improve chemical durability, ZrO2 / R2O is preferably 0.02 or more, more preferably 0.04 or more, even more preferably 0.06 or more, particularly preferably 0.08 or more, and most preferably 0.1 or more. ZrO2 / R2O is preferably 0.2 or less, more preferably 0.18 or less, even more preferably 0.16 or less, and particularly preferably 0.14 or less.

[0069] Although TiO2 is not essential, if it is contained, it is preferably 0.05% or more, more preferably 0.1% or more. On the other hand, in order to suppress devitrification during melting, the TiO2 content is preferably 1% or less, more preferably 0.5% or less, and even more preferably 0.3% or less.

[0070] Although SnO2 is not essential, when it is contained, it is preferably 0.5% or more, more preferably 1% or more, even more preferably 1.5% or more, and particularly preferably 2% or more. On the other hand, in order to suppress devitrification during melting, the content of SnO2 is preferably 4% or less, more preferably 3.5% or less, even more preferably 3% or less, and particularly preferably 2.5% or less.

[0071] Y2O3 is a component that has the effect of preventing fragments from scattering when chemically strengthened glass is broken, and may be contained. The Y2O3 content is preferably 0.3% or more, more preferably 0.5% or more, even more preferably 0.7% or more, and particularly preferably 1.0% or more. On the other hand, in order to suppress devitrification during melting, the Y2O3 content is preferably 5% or less, more preferably 4% or less.

[0072] B2O3 is a component that improves the chipping resistance and meltability of the glass for chemical strengthening or chemically strengthened glass, and may be contained. When B2O3 is contained, the content is preferably 0.5% or more, more preferably 1% or more, and even more preferably 2% or more, in order to improve meltability. On the other hand, if the B2O3 content is too high, striae may occur during melting, or phase separation may occur, which may lead to a deterioration in the quality of the glass for chemical strengthening, so the B2O3 content is preferably 10% or less. The B2O3 content is more preferably 8% or less, even more preferably 6% or less, and particularly preferably 4% or less.

[0073] La2O3, Nb2O5, and Ta2O5 are all components that prevent chemically strengthened glass from scattering fragments when broken, and may be included to increase the refractive index. When these are included, the total content of La2O3, Nb2O5, and Ta2O5 (hereinafter, La2O3 + Nb2O5 + Ta2O5) is preferably 0.5% or more, more preferably 1% or more, even more preferably 1.5% or more, and particularly preferably 2% or more. Furthermore, to prevent the glass from devitrifying during melting, La2O3 + Nb2O5 + Ta2O5 is preferably 4% or less, more preferably 3% or less, even more preferably 2% or less, and particularly preferably 1% or less.

[0074] CeO2 may also be contained. CeO2 may oxidize the glass, thereby suppressing coloration. When CeO2 is contained, the content is preferably 0.03% or more, more preferably 0.05% or more, and even more preferably 0.07% or more. In order to increase transparency, the CeO2 content is preferably 1.5% or less, and more preferably 1.0% or less.

[0075] When chemically strengthened glass is used in a colored form, coloring components may be added to the glass within a range that does not impede the achievement of the desired chemical strengthening characteristics. Examples of coloring components include Co3O4, MnO2, Fe2O3, NiO, CuO, Cr2O3, V2O5, Bi2O3, SeO2, Er2O3, and Nd2O3.

[0076] The total content of coloring components is preferably in the range of 1% or less. If a higher visible light transmittance of the glass is desired, it is preferable that these components are substantially not contained.

[0077] To improve weather resistance against ultraviolet light irradiation, HfO2, Nb2O5, and Ti2O3 may be added. When added for the purpose of improving weather resistance against ultraviolet light irradiation, the total content of HfO2, Nb2O5, and Ti2O3 is preferably 1% or less, more preferably 0.5% or less, and even more preferably 0.1% or less, in order to suppress the influence on other properties.

[0078] In addition, SO3, chlorides, and fluorides may be appropriately contained as clarifiers for melting the glass. The total content of components functioning as clarifiers is preferably 2% or less, more preferably 1% or less, and even more preferably 0.5% or less, expressed as mass% on an oxide basis, since excessive addition affects the strengthening properties. While there is no particular lower limit, typically, a total of 0.05% or more, expressed as mass% on an oxide basis, is preferred.

[0079] When SO3 is used as a fining agent, if the content is too low, no effect is observed, so the content is preferably 0.01% or more, more preferably 0.05% or more, and even more preferably 0.1% or more, expressed as mass% on the oxide basis. Also, when SO3 is used as a fining agent, the content of SO3 is preferably 1% or less, more preferably 0.8% or less, and even more preferably 0.6% or less, expressed as mass% on the oxide basis.

[0080] When Cl is used as a fining agent, if it is added too much, it will affect physical properties such as strengthening characteristics, so the Cl content is preferably 1% or less, more preferably 0.8% or less, and even more preferably 0.6% or less, expressed as mass% on the oxide basis. Also, if the Cl content is too low when Cl is used as a fining agent, no effect will be seen, so the Cl content is preferably 0.05% or more, more preferably 0.1% or more, and even more preferably 0.2% or more, expressed as mass% on the oxide basis.

[0081] When SnO2 is used as a fining agent, the content of SnO2 is preferably 1% or less, more preferably 0.5% or less, and even more preferably 0.3% or less, expressed as mass% on the oxide basis. Furthermore, when SnO2 is used as a fining agent, if the content of SnO2 is too low, the effect is not seen, so the content is preferably 0.02% or more, more preferably 0.05% or more, and even more preferably 0.1% or more, expressed as mass% on the oxide basis.

[0082] It is preferable that P2O5 is not contained. If P2O5 is contained, the content is preferably 2.0% or less, more preferably 1.0% or less, and most preferably zero.

[0083] It is preferable that As2O3 is not contained. When Sb2O3 is contained, it is preferable that it is 0.3% or less, more preferably 0.1% or less, and most preferably it is not contained.

[0084] <<Application>> Examples of uses for the present chemically strengthened glass include protective materials for sensors mounted on mobile devices such as cars and drones, outdoor sensors, and sensors mounted on surveillance cameras. Because the present chemically strengthened glass exhibits excellent resistance to stone chips, it is preferably used as a protective material for sensors mounted on mobile devices, and more preferably for in-vehicle sensors. Figures 1(a) and 1(b) are perspective views showing examples of the configuration of protective materials formed entirely or partially using the present chemically strengthened glass.

[0085] 1(a) shows a structure in which protective glass 10 is used on the lid of a cylindrical housing (protective member 1) that houses a sensor 20, and FIG. 1(b) shows a structure in which glass is used on the spherical surface of a hemisphere that houses the sensor 20. The protective member 1 is formed in part or in whole using protective glass 10, and the present chemically strengthened glass can be used for the protective glass 10.

[0086] 1(a), the protective member 1 may have a support portion 2 formed in a part of the protective member 1 to support the protective glass 10. The support portion 2 may be made of glass, but may also be made of metal such as stainless steel or anodized aluminum.

[0087] The protective member 1 is not limited to a cylindrical or hemispherical shape, and may be a three-dimensional shape such as a cylindrical or prismatic shape, or a spherical regular polyhedron. The protective member 1 can be formed by bonding together multiple sheets of glass, and when forming the support part 2, an adhesive layer can be formed between the support part 2 and the protective glass 10 to bond them together.

[0088] <Method of manufacturing chemically strengthened glass> The method for producing chemically strengthened glass of this embodiment (hereinafter also referred to as the present production method) is characterized by including a first ion exchange step in which lithium-containing aluminosilicate glass having a plate thickness of 1.4 to 7 mm is brought into contact with a first inorganic salt composition containing sodium at a temperature of 430°C or higher for 10 hours or more to perform ion exchange.

[0089] The chemical strengthening treatment for forming a compressive stress layer on the surface of glass is a treatment in which a glass plate is brought into contact with an inorganic salt composition to replace metal ions in the glass with metal ions in the inorganic salt composition that have a larger ionic radius than the metal ions in the glass.

[0090] Examples of methods for bringing glass into contact with the inorganic salt composition include a method of applying a paste-like inorganic salt composition to glass, a method of spraying an aqueous solution of the inorganic salt composition onto glass, a method of immersing a glass plate in a salt bath of a molten salt of the inorganic salt composition heated to a melting point or higher, etc. Among these, the method of immersing glass in a molten salt of the inorganic salt composition is preferred from the viewpoint of improving productivity.

[0091] As used herein, the term "inorganic salt composition" refers to a composition containing a molten salt. Examples of molten salts contained in the inorganic salt composition include nitrates, sulfates, carbonates, and chlorides. Examples of nitrates include lithium nitrate, sodium nitrate, potassium nitrate, cesium nitrate, rubidium nitrate, and silver nitrate. Examples of sulfates include lithium sulfate, sodium sulfate, potassium sulfate, cesium sulfate, rubidium sulfate, and silver sulfate. Examples of chlorides include lithium chloride, sodium chloride, potassium chloride, cesium chloride, rubidium chloride, and silver chloride. These may be used alone or in combination.

[0092] The inorganic salt composition is preferably one based on a nitrate, more preferably one based on sodium nitrate or potassium nitrate. Here, "based on" means that the content of the inorganic salt in the inorganic salt composition is 80% by mass or more.

[0093] <<First ion exchange treatment>> The composition of the first inorganic salt composition used in the first ion exchange treatment is not particularly limited as long as it does not impair the effects of the present invention, but it contains sodium as an alkali metal ion having an ionic radius larger than that of lithium contained in the lithium-containing aluminosilicate glass. Examples of sodium-containing inorganic salts include sodium nitrate, sodium sulfate, and sodium chloride, and among these, sodium nitrate is preferred.

[0094] When the first inorganic salt composition contains sodium nitrate, the content thereof is preferably 20% by mass or more, more preferably 30% by mass or more, and even more preferably 50% by mass or more.

[0095] The first inorganic salt composition preferably contains lithium. Examples of inorganic salts containing lithium include lithium nitrate, lithium sulfate, and lithium chloride, and among these, lithium nitrate is particularly preferred.

[0096] When the first inorganic salt composition contains lithium nitrate, the content thereof is preferably 0.01% by mass or more, more preferably 0.1% by mass or more, and even more preferably 0.3% by mass or more, and is preferably 5% by mass or less, more preferably 4% by mass or less, and even more preferably 3% by mass or less.

[0097] In the first ion exchange treatment, the lithium-containing aluminosilicate glass is brought into contact with a first inorganic salt composition at 430°C or higher. When the temperature of the first inorganic salt composition is 430°C or higher, ion exchange is likely to proceed. The temperature is more preferably 435°C or higher, even more preferably 440°C or higher, and particularly preferably 445°C or higher. In addition, the temperature of the first inorganic salt composition is usually 525°C or lower, from the viewpoints of the risk of evaporation and compositional changes of the inorganic salt composition.

[0098] In the first ion exchange treatment, the time for which the glass for chemical strengthening is contacted with the first inorganic salt composition is 10 hours or more. By making this time 10 hours or more, the surface compressive stress can be increased. The contact time is more preferably 20 hours or more, 40 hours or more, 60 hours or more, 80 hours or more, and even more preferably 90 hours or more, in the following order. If the contact time is too long, not only will productivity decrease, but the compressive stress may also decrease due to relaxation phenomena. Therefore, the contact time is usually 200 hours or less.

[0099] In the present production method, the ion exchange treatment may be a single-stage treatment, or may be a two-stage or more treatment under two or more different conditions (multi-stage strengthening).

[0100] <<Second ion exchange treatment>> When the ion exchange treatment in the present production method is a multi-stage strengthening treatment, it is preferable to include, after the first ion exchange, a second ion exchange in which the lithium-containing aluminosilicate glass is brought into contact with a second inorganic salt composition containing lithium to perform ion exchange.

[0101] The second inorganic salt composition is not particularly limited as long as it contains lithium and does not impair the effects of the present invention. Examples of inorganic salt compositions containing lithium include lithium nitrate, lithium sulfate, and lithium chloride, and among these, lithium nitrate is particularly preferred.

[0102] When the second inorganic salt composition contains lithium nitrate, the content is preferably 0.01% by mass or more, more preferably 0.1% by mass or more, and even more preferably 0.3% by mass or more, and is preferably 3% by mass or less, more preferably 2% by mass or less, and even more preferably 1.5% by mass or less.

[0103] As the second inorganic salt composition, it is preferable to use a lithium-containing inorganic salt composition in combination with a potassium-containing inorganic salt composition or a sodium-containing inorganic salt composition.

[0104] Examples of the potassium-containing inorganic salt composition used in the second inorganic salt composition include potassium nitrate, potassium sulfate, and potassium chloride, and among these, potassium nitrate is preferred.

[0105] When the second molten salt composition contains potassium nitrate, the content thereof is preferably 85% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more, and is preferably 99.9% by mass or less, more preferably 99.7% by mass or less, and even more preferably 99.5% by mass or less.

[0106] Examples of the sodium-containing inorganic salt composition used in the second inorganic salt composition include sodium nitrate, sodium sulfate, and sodium chloride, and among these, sodium nitrate is preferred.

[0107] From the viewpoint of increasing compressive stress in deep layers, in the present chemical strengthening method, it is preferable that the ratio of lithium to the total amount of sodium and lithium contained in the second molten salt composition is greater than the ratio of lithium to the total amount of sodium and lithium contained in the first molten salt composition.

[0108] From the viewpoint of increasing the ion exchange efficiency, in the second ion exchange treatment, the temperature of the second inorganic salt composition to be brought into contact with the lithium-containing aluminosilicate glass is preferably 400° C. or higher, more preferably 415° C. or higher, even more preferably 430° C. or higher, and particularly preferably 445° C. or higher. In addition, from the viewpoint of the risk of evaporation and compositional changes of the inorganic salt composition, the temperature of the second inorganic salt composition is usually preferably 505° C. or lower.

[0109] From the viewpoint of improving ion exchange efficiency, in the second ion exchange treatment, the time for which the glass for chemical strengthening is contacted with the second inorganic salt composition is preferably 1 hour or more, more preferably 4 hours or more, and even more preferably 8 hours or more. If the contact time is too long, not only will productivity decrease, but the compressive stress may also decrease due to relaxation. Therefore, the contact time is usually preferably 48 hours or less.

[0110] The second inorganic salt composition may contain a specific inorganic salt (hereinafter referred to as a flux) as an additive. The flux is preferably a carbonate, bicarbonate, phosphate, sulfate, hydroxide, or chloride, and preferably contains at least one salt selected from the group consisting of K2CO3, Na2CO3, KHCO3, NaHCO3, K3PO4, Na3PO4, K2SO4, Na2SO4, KOH, NaOH, KCl, and NaCl, more preferably contains at least one salt selected from the group consisting of K2CO3 and Na2CO3, and even more preferably contains K2CO3.

[0111] Examples of combinations of the first inorganic salt composition used in the first ion exchange treatment and the second inorganic salt composition used in the second ion exchange treatment include the following. (a) The first inorganic salt composition is an inorganic salt composition containing 100% by mass of sodium nitrate, and the second inorganic salt composition is an inorganic salt composition containing potassium and lithium. (b) The first inorganic salt composition is an inorganic salt composition containing 100% by mass of sodium nitrate, and the second inorganic salt composition is an inorganic salt composition containing a sodium salt and a lithium salt. The sodium salt contained in the second inorganic salt composition is preferably sodium nitrate, and the lithium salt is preferably lithium nitrate. (c) The first inorganic salt composition is an inorganic salt composition containing sodium nitrate and lithium nitrate, and the second inorganic salt composition is an inorganic salt composition containing potassium and lithium. Potassium nitrate is preferred as the potassium salt contained in the second inorganic salt composition, and lithium nitrate is preferred as the lithium salt.

[0112] <<Glass for chemical strengthening>> The chemically strengthened glass to be ion-exchanged in this manufacturing method is lithium-containing aluminosilicate glass. The preferred composition of the lithium-containing aluminosilicate glass is the same as that described in the <<Composition>> section of <<Chemically Strengthened Glass>>. That is, the matrix composition preferably contains, in mole percent on an oxide basis, 52 to 75% SiO2, 8 to 20% Al2O3, and 5 to 18% Li2O. The composition of the chemically strengthened glass and the matrix composition of the chemically strengthened glass obtained by chemically strengthening the chemically strengthened glass are the same.

[0113] In a method for producing chemically strengthened glass, glass raw materials are appropriately blended to obtain glass of the desired composition, and the glass is heated and melted in a glass melting furnace. The glass is then homogenized by bubbling, stirring, adding a fining agent, etc., formed into a glass plate of a predetermined thickness, and slowly cooled. Alternatively, the glass may be formed into a plate by forming it into a block shape, slowly cooling it, and then cutting it.

[0114] Examples of methods for forming into a plate include the float method, press method, fusion method, and down-draw method. In particular, when producing a large glass plate, the float method is preferred. In addition, continuous forming methods other than the float method, such as the fusion method and down-draw method, can be used.

[0115] The chemically strengthened glass obtained by this manufacturing method has a CS depth of 400 μm from the surface. 400 is preferably 60 MPa or more, more preferably 70 MPa or more, and even more preferably 80 MPa or more. 400 By making the compressive stress at a depth of 60 MPa or more, the compressive stress at a deep layer can be increased, and the resistance to flying stones can be further improved.

[0116] The chemically strengthened glass obtained by this manufacturing method has a CS depth of 500 μm from the surface. 500 is preferably 45 MPa or more, more preferably 50 MPa or more, and even more preferably 55 MPa or more. 500By making the compressive stress at or above 45 MPa, the compressive stress in the deep layer can be increased, and the resistance to flying stones can be further improved.

[0117] The chemically strengthened glass obtained by this manufacturing method has a CS depth of 600 μm from the surface. 600 is preferably 15 MPa or more, more preferably 20 MPa or more, and even more preferably 25 MPa or more. 600 By making the compressive stress at a depth of 15 MPa or more, the compressive stress at a deep layer can be increased, and the resistance to flying stones can be further improved. [Example]

[0118] The present invention will be described below with reference to examples, but the present invention is not limited thereto.

[0119] <Production of glass for chemical strengthening> Glass raw materials were mixed to obtain the following composition expressed in mole percentages based on oxides, and weighed out to give 400 g of glass. The mixed raw materials were then placed in a platinum crucible and placed in an electric furnace at 1500 to 1700°C, where they were melted for about 3 hours, degassed, and homogenized. Glass material A: SiO266.2%, Al2O3 11.2%, MgO 3.1%, CaO 0.2%, ZrO21.3%, Y2O30.5%, Li2O 10.4%, Na2O 5.6%, K2O 1.5%

[0120] The resulting molten glass was poured into a metal mold and held at a temperature about 50°C higher than the glass transition point for 1 hour, then cooled to room temperature at a rate of 0.5°C / min to obtain a glass block. The resulting molten glass was poured into a mold and held at a temperature near the glass transition point (714°C) for about 1 hour, then cooled to room temperature at a rate of 0.5°C / min to obtain a glass block. Glass plates measuring 50mm x 50mm x 50mm (thickness (mm) x 50mm) as shown in Table 1) were produced from the resulting glass blocks.

[0121] <Evaluation of chemical strengthening treatment and chemically strengthened glass> The glass plates obtained above were immersed in molten salt compositions under the conditions shown in Table 1 to perform a first ion exchange treatment and a second ion exchange treatment, thereby producing the chemically strengthened glasses of the following Examples 1 to 13. Examples 1 to 3, 8, 9, and 11 to 13 are working examples, and Examples 4 to 7 and 10 are comparative examples.

[0122] The obtained chemically strengthened glass was evaluated by the following method.

[0123] [Stress measurement using a scattered light photoelastic stress meter] The stress of chemically strengthened glass was measured using a scattered light photoelastic stress meter (SLP-2000 manufactured by Orihara Seisakusho) by the method described in International Publication No. 2018 / 056121. The stress profile was calculated using the attached software [SlpV (Ver. 2019.11.07.001)] of the scattered light photoelastic stress meter (SLP-2000 manufactured by Orihara Seisakusho).

[0124] The function used to obtain the stress profile is σ(x) = [a1 × erfc(a2 × x) + a3 × erfc(a4 × x) + a5]. i ( i =1 to 5) are fitting parameters, and erfc is the complementary error function. The complementary error function is defined by the following equation:

[0125]

number

[0126] In the evaluation in this specification, the fitting parameters were optimized by minimizing the residual sum of squares between the obtained raw data and the above function. The measurement processing conditions were single shot, and the measurement area processing adjustment items were specified as follows: edge method on the surface, 6.0 μm for the inner surface edge, automatic for the inner left and right edges, automatic (center of sample thickness) for the inner deep edge, and a fitting curve for the extension of the phase curve to the center of the sample thickness.

[0127] At the same time, the concentration distribution of alkali metal ions (sodium ions and potassium ions) in the cross-sectional direction was measured using SEM-EDX (EPMA), and it was confirmed that there was no inconsistency with the obtained stress profile.

[0128] Furthermore, the compressive stress CS and the compressive stress layer depth DOC were calculated from the obtained stress profile using the method described above. The results are shown in Table 1.

[0129] In Table 1, the following notations apply: Li / Li+Na in salt: mass ratio of lithium to the total amount of sodium and lithium contained in the inorganic salt composition CS0 (MPa): Compressive stress on the glass surface CS 400 (MPa): Compressive stress at a depth of 400 μm from the glass surface CS 500 (MPa): Compressive stress at a depth of 500 μm from the glass surface CS 600 (MPa): Compressive stress at a depth of 600 μm from the glass surface Surface gradient: The maximum negative gradient of the stress profile from the surface to a depth of 0 to 20 μm (MPa / μm) Depth gradient: The maximum negative gradient of the stress profile at a depth of more than 50 μm from the surface (MPa / μm) Maximum value CSlp: Maximum compressive stress value Maximum position d: Depth from the surface where the compressive stress maximum value exists (μm) d / t: Depth from the surface where the compressive stress is at its maximum value divided by the plate thickness t ms: Absolute value of the average positive slope on the shallower side than the maximum value (MPa / μm) md: Absolute value of the negative mean slope on the side deeper than the maximum value (MPa / μm) DOC: Depth of compressive stress layer (μm) DOC / t: Depth of compressive stress layer divided by plate thickness t CTmax(MPa): Maximum tensile stress DOL@50MPa: Stress depth (μm) from the surface at which compressive stress reaches 50 MPa ICS (≧400): The integral value of compressive stress in the region from a depth of 400 μm from the surface to the depth where compressive stress becomes 0 (MPa μm) ICS: Integrated value of compressive stress CS (MPa μm)

[0130] [Stepping stone test] A stone chipping test was conducted under the following conditions in accordance with the strength test method of ISO 20567-1 Test Method B, and the crack occurrence rate was calculated (n≧3). The results of evaluation using the following indexes are shown in Table 1. (conditions) Stepping stones: Chilled iron grit Stone size: 3.55-5mm Injection amount: 500g Injection pressure: 250kPa Sample installation angle: 54° Injection time: 8-12s Number of shots: 2 Sample impact area: 40-40mm (Evaluation indicators) ◎: Crack occurrence rate is 0% ○: Crack occurrence rate is 10% or more but less than 20% △: Crack occurrence rate is 20% or more but less than 60% ×: Crack occurrence rate is 60% or more and 100% or less

[0131] [Table 1]

[0132] As shown in Table 1, Examples 1 to 3, 8, 9 and 11 to 13, which are working examples, had higher compressive stress in deep layers at depths of 400 μm or more from the surface, and exhibited excellent resistance to flying stones, compared to the comparative examples. [Explanation of symbols]

[0133] 1 Protective material 2 Instruction section 5. Mounting section 10 Protective Glass 20 sensors 30 Camera

Claims

1. The ratio ICS (≧ 400) / ICS of ICS (≧ 400), which is the integral of compressive stress in a region from a depth of 400 μm from the surface to a depth where the compressive stress becomes 0, to ICS (≧ 400), which is the integral of compressive stress CS, is greater than 0.13, the plate thickness is 1.8 mm or more, and the ICS (≧ 400) is 9200 MPa μm or more, The matrix composition is expressed in mole percent based on oxides, SiO 2 52 to 75%, 8-20% Al 2 O 3; Chemically strengthened glass containing 5 to 18% of Li 2 O.

2. The chemically strengthened glass according to claim 1, wherein the ICS (≧400) is 9800 MPa μm or more.

3. The chemically strengthened glass according to claim 1 or 2, wherein a stress depth DOL at which a compressive stress becomes 50 MPa is 400 μm or more.

4. The chemically strengthened glass according to any one of claims 1 to 3, wherein the maximum negative slope of the stress profile at a position deeper than 50 μm from the surface is −0.50 (MPa / μm) or more.

5. The chemically strengthened glass according to any one of claims 1 to 4, wherein the plate thickness is t, and the value DOC / t obtained by dividing the compressive stress layer depth DOC by t is 0.170 or more.

6. The chemically strengthened glass according to any one of claims 1 to 5, having a maximum tensile stress CTmax of 40 MPa or more.

7. Compressive stress CS at a depth of 600 μm from the surface ６００ The chemically strengthened glass according to any one of claims 1 to 6, wherein the compressive strength is 15 MPa or more.

8. The chemically strengthened glass according to any one of claims 1 to 7, wherein the maximum negative slope of the stress profile at a depth of 0 to 20 μm from the surface is −10 (MPa / μm) or less.

9. The chemically strengthened glass according to any one of claims 1 to 8, having a compressive stress maximum value, wherein the compressive stress maximum value is 50 MPa or more.

10. The chemically strengthened glass according to claim 9, wherein the plate thickness is t, and the position of the compressive stress maximum value is in the range of a depth from the surface of 0.05t to 0.13t.

11. the absolute value of the average slope of the stress profile in the region from the surface to the position of the compressive stress maximum, m s; When the absolute value of the average slope of the stress profile from the position of the compressive stress maximum value to the depth where the compressive stress becomes zero is md, The chemically strengthened glass according to claim 9 or 10, wherein ms>md.

12. Surface compressive stress CS ０ Compressive stress CS at a depth of 400 μm from the surface ４００ CS is the ratio of ４００ / CS ０ The chemically strengthened glass according to any one of claims 1 to 11, wherein is 0.10 or more.

13. Compressive stress CS at a depth of 0 μm from the surface ０ Compressive stress CS at a depth of 600 μm from the surface ６００ CS is the ratio of ６００ / CS ０ The chemically strengthened glass according to any one of claims 1 to 12, wherein is 0.03 or more.

14. Surface compressive stress CS ０ Compressive stress CS at a depth of 400 μm from the surface ４００ CS is the ratio of ４００ / CS ０ The chemically strengthened glass according to any one of claims 1 to 7, wherein is 0.32 or more.

15. Compressive stress CS at a depth of 0 μm from the surface ０ Compressive stress CS at a depth of 600 μm from the surface ６００ CS is the ratio of ６００ / CS ０ The chemically strengthened glass according to any one of claims 1 to 7 and 14, wherein is 0.03 or more.

16. The chemically strengthened glass according to any one of claims 1 to 15, wherein the crack occurrence rate evaluated in accordance with the strength test method of ISO 20567-1 Test Method B is 10% or less.

17. The chemically strengthened glass according to any one of claims 1 to 16, having a plate thickness of 1.8 to 7 mm.

18. The chemically strengthened glass according to any one of claims 1 to 17, which is for an in-vehicle sensor.

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