Chemically reinforced glass article, and production method of the same

Abstract

To provide a chemically reinforced glass article excellent in strength, suppressed in scattering of fragments when broken, and hard to generate chipping.SOLUTION: A chemically reinforced glass article has a first surface, a second surface facing the first surface, and an end part contacting the first surface and the second surface, wherein a compression stress value on the first surface is 400 to 1,000 MPa, a depth m[μm] giving a maximum compression stress value is more than 0 μm when expressing a compression stress value of an inner part of the glass by means of a depth from the first surface as a variable, CSm-CS0 [MPa] is 30 MPa or more when a compression stress value at the depth m [μm] is CSm [MPa], and a compression stress value on the first surface is CS0 [MPa], and a depth DOL giving a compression stress of 0 is 50 to 150 μm.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to chemically strengthened glass articles and methods for producing the same. [Background technology]

[0002] Chemically strengthened glass is used for the cover glass of mobile devices, etc. Chemically strengthened glass is produced by contacting glass with a molten salt such as sodium nitrate to cause ion exchange between alkali metal ions contained in the glass and alkali metal ions with a larger ionic radius contained in the molten salt, thereby forming a compressive stress layer on the surface of the glass. The strength of chemically strengthened glass is strongly dependent on the stress profile, which is expressed as a compressive stress value with the depth from the glass surface as a variable.

[0003] Cover glass for mobile devices, etc., can break due to deformation caused by dropping, etc. In order to prevent such breakage, i.e., breakage due to bending mode, it is effective to increase the compressive stress on the glass surface. For this reason, it has become common to create a high surface compressive stress of 700 MPa or more in recent years.

[0004] On the other hand, the cover glass of a mobile device, etc., can be broken by impact with a protruding object when the device is dropped onto asphalt or sand. To prevent such damage, i.e., damage due to impact mode, it is effective to increase the depth of the compressive stress layer and form the compressive stress layer deeper in the glass.

[0005] However, when a compressive stress layer is formed on the surface of a glass article, tensile stress corresponding to the compressive stress on the surface inevitably occurs in the center of the glass article. If this tensile stress value becomes too large, the glass article will break violently and fragments will fly when it breaks. Therefore, chemically strengthened glass is designed to increase the compressive stress on the surface and form a compressive stress layer deeper, while preventing the total compressive stress in the surface layer from becoming too large.

[0006] Patent Document 1 describes a two-stage chemical strengthening method using lithium-containing alkali aluminoborosilicate glass, while Patent Document 2 describes a three-stage ion exchange treatment method that produces chemically strengthened glass that has high drop strength and is less likely to shatter when broken. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japan Special Publication No. 2013-536155 [Patent Document 2] International Publication No. 2019 / 004124 Summary of the Invention [Problem to be solved by the invention]

[0008] According to the two-stage chemical strengthening method described in Patent Document 1, large compressive stress due to sodium-potassium exchange occurs in the surface portion of the glass, and slightly smaller compressive stress due to lithium-sodium exchange occurs in the deeper portion. This is thought to suppress both fracture due to bending mode and fracture due to impact mode.

[0009] However, the chemically strengthened glass articles described in Patent Documents 1 and 2 have very large compressive stresses formed on their outermost surfaces, and therefore, the balance of stresses is easily disrupted due to improper chemical strengthening treatment, which can result in chipping. Furthermore, if a small scratch occurs during the manufacturing process of a chemically strengthened glass article, polishing the surface can significantly reduce the strength of that part.

[0010] Therefore, an object of the present invention is to provide a chemically strengthened glass article that has excellent strength, is suppressed from scattering fragments when broken, and is less likely to chip. [Means for solving the problem]

[0011] The present invention provides a chemically strengthened glass article having a first surface, a second surface opposite to the first surface, and an end portion in contact with the first surface and the second surface, the compressive stress value on the first surface is 400 to 1000 MPa, When the compressive stress value inside the glass is expressed using the depth from the first surface as a variable, The depth m [μm] at which the compressive stress value is maximum is greater than 0 μm, The compressive stress value at a depth m [μm] is expressed as CS m [MPa], The compressive stress value on the first surface is defined as CSO [MPa], CS m -CS0 [MPa] is 30 MPa or more, A chemically strengthened glass article is provided, having a depth DOL at which the compressive stress value becomes 0 of 50 to 150 μm.

[0012] The present invention also provides a method for producing a chemically strengthened glass article, which includes immersing lithium aluminosilicate glass in a salt containing 90% by mass or more of sodium nitrate at 400 to 450°C, and, after removing the lithium aluminosilicate glass from the salt, holding the glass at 100 to 300°C for 1 minute or more. [Effects of the Invention]

[0013] According to the present invention, a chemically strengthened glass article can be obtained which has high strength, is suppressed from scattering fragments when broken, and is less susceptible to chipping. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a diagram showing one embodiment of a stress profile of a chemically strengthened glass article of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0015] In this specification, the use of "to" to indicate a range of values ​​is used to mean that the values ​​before and after it are included as the lower and upper limits, and unless otherwise specified, "to" will be used in the same sense hereinafter in this specification.

[0016] The stress profile can usually be measured by a method using a combination of an optical waveguide surface stress meter and a scattered light photoelastic stress meter. It is known that the method using an optical waveguide surface stress meter can measure the stress of glass accurately in a short time. One example of an optical waveguide surface stress meter is the FSM-6000 manufactured by Orihara Seisakusho. Combining the FSM-6000 with the accompanying software Fsm-V enables highly accurate stress measurements.

[0017] However, in principle, an optical waveguide surface stress meter can only measure stress when the refractive index decreases from the sample surface toward the inside. In chemically strengthened glass articles, the layer obtained by substituting external potassium ions for sodium ions inside the glass has a refractive index that decreases from the sample surface toward the inside, so stress can be measured with an optical waveguide surface stress meter. However, the stress of the layer obtained by substituting external sodium ions for lithium ions inside the glass article cannot be measured with an optical waveguide surface stress meter. Therefore, when a glass article containing lithium is subjected to ion exchange treatment using a sodium-containing molten salt, there is a depth (D) at which the compressive stress value measured with an optical waveguide surface stress meter becomes zero. K ) is not the true depth of the compressive stress layer.

[0018] The method using a scattered light optical waveguide stress meter can measure stress regardless of the refractive index distribution. An example of a birefringence stress meter is the SLP2000 manufactured by Orihara Seisakusho. However, it is difficult to accurately determine stress values ​​near the glass surface using a scattered light photoelastic stress meter. Therefore, when a layer formed near the surface of chemically strengthened glass is formed by replacing sodium ions inside the glass with external potassium ions, accurate stress measurement can be achieved by combining two types of measuring devices: an optical waveguide surface stress meter and a scattered light photoelastic stress meter.

[0019] However, when a layer formed near the glass surface was formed by replacing internal lithium ions with external sodium ions, it was difficult to accurately measure the stress near the surface using an optical waveguide surface stress meter. In such cases, the stress near the glass surface can be accurately measured by etching one side of the glass to a desired thickness to generate a stress difference between the front and back surfaces of the chemically strengthened glass, and then measuring the warpage of the glass that occurs in response to that stress difference.

[0020] In this specification, "chemically strengthened glass" refers to glass after chemical strengthening treatment, and "glass for chemical strengthening" refers to glass before chemical strengthening treatment. In this specification, "mother composition of chemically strengthened glass" refers to the glass composition of glass for chemical strengthening, and except in cases where extreme ion exchange treatment has been performed, the glass composition of the portion deeper than the compressive stress layer depth DOL of chemically strengthened glass is approximately the same as the mother composition of chemically strengthened glass.

[0021] 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, etc., that is, that the content is not intentionally added. Specifically, for example, it is less than 0.1%.

[0022] <Chemically strengthened glass articles> The chemically strengthened glass article of the present invention (hereinafter sometimes referred to as "the present tempered glass" or "the present tempered glass article") has a first surface, a second surface opposite to the first surface, and end portions contacting the first surface and the second surface. The present tempered glass article is usually in the form of a flat plate, but may also have a curved surface.

[0023] <<Stress profile>> Figure 1 shows one embodiment of the stress profile of the tempered glass. The stress profile shown in Figure 1 shows the profile on one of the main surfaces. In the present invention, the stress profiles on one main surface and the other main surface may be the same or different. In the present invention, the compressive stress value inside the glass is expressed using the depth from the first surface as a variable.

[0024] In the present tempered glass, the compressive stress value (CS0) at the first surface is preferably 400 MPa or more, more preferably 450 MPa or more, further preferably 500 MPa or more, and particularly preferably 550 MPa or more. The higher the CS0, the more effectively "fracture due to bending mode" can be prevented.

[0025] On the other hand, if the compressive stress value of the surface is too large, the edge may chip after chemical strengthening. This phenomenon is called chipping. To prevent this, CSO is preferably 1000 MPa or less, more preferably 900 MPa or less, and even more preferably 800 MPa or less.

[0026] In the stress profile of this tempered glass, in the thickness direction from the first surface to a depth of 10 μm, the maximum stress is not at the glass surface. That is, if the depth at which the compressive stress value is maximum is m [μm], then m>0. The glass surface usually has scratches several μm deep, and it is most effective to have the maximum stress at this point to prevent crack propagation. Furthermore, when m>0, the glass is less likely to shatter violently upon breaking, and chipping during polishing can be suppressed. Therefore, the depth at which the maximum stress occurs is preferably 0.5 μm or more, more preferably 1 μm or more, and even more preferably 1.5 μm or more.

[0027] If the scratches exceed 10 μm, the product value will decrease from the viewpoint of visibility, so the scratches on the product are usually 10 μm or less. Therefore, the depth at which the stress becomes maximum is preferably 10 μm or less, more preferably 9 μm or less, and even more preferably 8 μm or less.

[0028] It is generally believed that chemically strengthened glass can be made less susceptible to breakage by increasing the compressive stress value on the glass surface, thereby suppressing the spread of microcracks on the glass surface. It is also believed that increasing the compressive stress layer depth and forming a compressive stress layer deeper in the glass can make the glass less susceptible to breakage even when subjected to a large impact.

[0029] However, forming a compressive stress layer on the surface of glass inevitably results in the formation of a tensile stress layer inside the glass. If the internal tensile stress is large, chemically strengthened glass is likely to shatter violently and scatter fragments when broken.

[0030] In the stress profile of this tempered glass, the compressive stress value at the depth m [μm] where the compressive stress value is maximum is defined as CS m [MPa], the compressive stress value at the first surface is CS0 [MPa], and CS m and CS0 (CS m -CS0) is 30 MPa or more, preferably 35 MPa or more, more preferably 40 MPa or more, even more preferably 45 MPa or more, and particularly preferably 50 MPa or more.

[0031] (CS m By having a compressive stress of 30 MPa or more, the material is less likely to fracture violently when broken, and chipping during polishing can be suppressed. If the total amount of compressive stress becomes too large, violent fracture occurs when scratching, but in order to prevent bending fracture, (CS m -CS0) is preferably 300 MPa or less, more preferably 280 MPa or less, further preferably 250 MPa or less, and particularly preferably 200 MPa or less.

[0032] In the stress profile of the tempered glass, the depth DOL at which the compressive stress value becomes 0 is preferably 50 μm or more, more preferably 60 μm or more, even more preferably 70 μm or more, and particularly preferably 80 μm or more. A DOL of 50 μm or more introduces compressive stress into a relatively deep portion of the glass in the plate thickness direction, which is advantageous for preventing cracking due to impact. Furthermore, if the DOL is too large, the internal tensile stress becomes too large, so the DOL is preferably 150 μm or less, more preferably 135 μm or less, even more preferably 130 μm or less, and particularly preferably 125 μm or less.

[0033] The thickness (t) of the tempered glass article is preferably 300 μm or more, more preferably 500 μm or more, even more preferably 600 μm or more, even more preferably 700 μm or more, and particularly preferably 800 μm or more. The larger t, the less likely it is to break. When used in a mobile terminal or the like, t is preferably 2000 μm or less, more preferably 1000 μm or less, in order to reduce weight.

[0034] The compressive stress depth of the tempered glass (DOL) is preferably 0.1t or more, more preferably 0.11t or more, and even more preferably 0.12t or more. A DOL of 0.1t or more introduces compressive stress into a relatively deep portion of the glass in the thickness direction, which is advantageous for preventing cracking due to a collision. Furthermore, in order to balance the total amount of compressive stress and tensile stress throughout the thickness direction of the glass, the DOL is preferably 0.25t or less, more preferably 0.23t or less, and even more preferably 0.2t or less.

[0035] In the stress profile of this tempered glass, the compressive stress value CS at a depth of 60 μm from the first surface 60 is preferably 100 MPa or more, more preferably 110 MPa or more, even more preferably 120 MPa or more, and particularly preferably 130 MPa or more.

[0036] When a glass item falls onto an asphalt pavement or sand, it will collide with the sand or other protruding objects, causing cracks. The length of the cracks that occur will vary depending on the size of the sand that the glass item hits, but the compressive stress value CS 60 If the stress is 100 MPa or more, a large compressive stress value is formed near a depth of 60 μm, and destruction by an impact mode in which the material is crushed by hitting a relatively large protrusion can be prevented.

[0037] On the other hand, if a large compressive stress layer is formed inside the glass, the tensile stress value corresponding to the compressive stress on the surface will inevitably become large in the center of the glass. If the tensile stress value becomes too large, the glass will break violently and fragments will fly when it is broken. Therefore, the compressive stress value CS 60 The compressive stress is preferably 200 MPa or less, more preferably 150 MPa or less. The compressive stress value here is a value measured with a birefringence stress meter. 60 When is in the above range, the thickness t of the glass is preferably 300 μm or more.

[0038] In addition, in order to increase the asphalt drop strength, the compressive stress value CS at a depth of 50 μm from the first surface 50 is preferably 100 MPa or more, more preferably 140 MPa or more, and even more preferably 160 MPa or more.

[0039] In the stress profile of this tempered glass, the tensile stress value CT at a depth of (0.5 × t) μm from the first surface of the glass article is preferably 120 MPa or less, more preferably 110 MPa or less, and even more preferably 100 MPa or less. This makes it less likely for severe fracture to occur. Here, the depth (0.5 × t) μm corresponds to the center of the glass in the thickness direction, and the tensile stress value at this depth means the tensile stress value inside the glass.

[0040] In order to provide sufficient strengthening so that the glass article is less likely to break when dropped, the tensile stress value at a depth of (0.5×t) μm from the first surface of the glass article is preferably 50 MPa or more, more preferably 75 MPa or more.

[0041] The tempered glass is preferably made of lithium aluminosilicate glass. Lithium aluminosilicate glass can be efficiently ion-exchanged with a salt containing sodium, and large compressive stress can be introduced into the surface of the glass through sodium-potassium exchange. Furthermore, slightly smaller compressive stress can be introduced into the deeper portion of the glass through lithium-sodium exchange. Therefore, it is believed that both fracture due to bending mode and fracture due to impact mode caused by collision with a protrusion can be suppressed.

[0042] <<Glass composition>> In the present tempered glass, the glass composition at the center portion in the thickness direction, i.e., the glass composition of the mother glass of the chemically tempered glass, preferably contains, in mole % on an oxide basis, 40 to 75% SiO2, 2 to 35% Al2O3, and 4 to 35% Li2O. The glass composition in the central portion in the thickness direction is almost the same as the composition of glass for chemical strengthening, and details of this preferred glass composition will be described in the section <Glass for chemical strengthening>.

[0043] In one embodiment, the tempered glass preferably satisfies Li(0)≦Li(t / 2) and K(0)≦K(t / 2), where Li(x), Na(x), and K(x) are the ion concentrations of Li, Na, and K at a thickness of t [μm] and a depth of x [μm] from the first surface. That is, the K ion concentration at the outermost surface is preferably equal to or lower than the concentration in the interior. Furthermore, it is preferable that Na(0)>0.3×[Li(0)+Na(0)+K(0)] and Li(t / 2)>0.7×[Li(t / 2)+Na(t / 2)+K(t / 2)].

[0044] Chemically strengthened glass, in which lithium aluminosilicate glass has undergone a two-stage ion exchange process, has sometimes exhibited reduced weather resistance compared to before chemical strengthening. This is thought to be due to the large amount of potassium ions present on the glass surface chemically reacting with components in the air to form precipitates. In this embodiment, the K ion concentration at the outermost surface is lower than that in the interior, preventing chemical reactions with components in the air and resulting in excellent weather resistance. Furthermore, because the potassium ions at the outermost surface are exchanged with sodium ions in the molten salt, only surface stress can be reduced.

[0045] The ion concentration on the glass surface can be measured using an EPMA (electron probe micro analyzer).

[0046] The weather resistance of chemically strengthened glass can be evaluated by a weather resistance test. The chemically strengthened glass of the present invention preferably exhibits a haze change rate of 5% or less before and after standing at 80°C and 80% humidity for 120 hours, more preferably 4% or less, and even more preferably 3% or less. The haze value is measured using a haze meter under Illuminant C.

[0047] <Glass-ceramics> The tempered glass may be crystallized glass. When the tempered glass is crystallized glass, it is preferable that the visible light transmittance at a thickness of 0.7 mm is 85% or more, since when used as a cover glass for a mobile display, the display screen is easily visible. The visible light transmittance at a thickness of 0.7 mm is more preferably 88% or more, and even more preferably 90% or more.

[0048] Visible light transmittance is measured in accordance with JIS R 3106:2019. In this specification, "light transmittance" refers to the average transmittance for light with wavelengths of 380 nm to 780 nm. If the thickness of the chemically strengthened glass is not 0.7 mm, the transmittance for a thickness of 0.7 mm can be calculated from the measured transmittance using the Lambert-Beer law.

[0049] When the tempered glass is a crystallized glass, the haze value calculated based on a thickness of 0.7 mm is preferably 0.5% or less, more preferably 0.4% or less, and even more preferably 0.3% or less. When the haze value is 0.5% or less, the visibility of the display screen is improved when the glass is used as a cover glass for a mobile display. The haze value is measured using a C light source in accordance with JIS K3761:2000.

[0050] If the total visible light transmittance of crystallized glass with a thickness of t [mm] is 100 × T [%] and the haze value is 100 × H [%], then by applying the Beer-Lambert law and using the constant α, T = (1 - R) 2 ×exp(-αt). Using this constant α, dH / dt ∝ exp(-αt)×(1-H) Haze value H for 0.7 mm 0.7 is calculated using the following formula:

[0051]

number

[0052] If the tempered glass is glass-ceramic, the types of crystals contained therein are basically the same as those in the glass before chemical strengthening, and will be explained in the section on glass for chemical strengthening. Crystals containing alkali metal components may change near the surface of the tempered glass due to chemical strengthening treatment. This is thought to be due to ion exchange of the alkali metal ions contained in the crystals.

[0053] The shape of the tempered glass may be a shape other than a plate shape depending on the product or application to which it is applied. The glass plate may also have a rim shape with a different peripheral thickness. The shape of the glass plate is not limited thereto; for example, the two main surfaces may not be parallel to each other, and one or both of the two main surfaces may be entirely or partially curved. More specifically, the glass plate may be, for example, a flat glass plate without warping, or a curved glass plate having a curved surface.

[0054] This tempered glass is particularly useful as cover glass for mobile devices such as mobile phones and smartphones. It is also useful as cover glass for non-portable display devices such as televisions, personal computers, and touch panels, as well as elevator walls and wall surfaces (full-surface displays) for buildings such as houses and buildings. It is also useful as building materials such as window glass, tabletops, interiors of automobiles and airplanes, and their cover glass, as well as for applications such as curved housings.

[0055] <Method of manufacturing a chemically strengthened glass article> The tempered glass can be produced by subjecting the below-described glass for chemical tempering to an ion exchange treatment. The glass for chemical tempering can be produced by, for example, a general glass production method as follows.

[0056] Glass raw materials are appropriately blended to obtain glass of a desired composition, and then 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 block, slowly cooled, and then cut into a plate.

[0057] 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, are also preferred.

[0058] The formed glass ribbon is ground and polished as necessary to form a glass plate. When the glass plate is cut to a predetermined shape and size or chamfered, it is preferable to cut or chamfer the glass plate before subjecting it to the chemical strengthening treatment described below, since this will form a compressive stress layer on the edge surfaces as well. The formed glass plate is then subjected to the chemical strengthening treatment, followed by washing and drying, to obtain chemically strengthened glass.

[0059] When the chemically strengthened glass is crystallized glass, the glass plate is cut into a predetermined shape and then heat-treated to crystallize it. The crystallization treatment may be a two-stage heat treatment.

[0060] Chemical strengthening is a process in which glass is brought into contact with a metal salt (e.g., potassium nitrate) by, for example, immersing the glass in a melt of the metal salt containing metal ions with a large ionic radius (typically, sodium ions or potassium ions), and metal ions with a small ionic radius (typically, lithium ions or sodium ions) in the glass are replaced with metal ions with a large ionic radius in the metal salt (typically, sodium ions or potassium ions for lithium ions, and potassium ions for sodium ions).

[0061] The "Li-Na exchange" method, which exchanges lithium ions in the glass with sodium ions, is particularly preferred because it has a fast chemical strengthening rate. To create a large compressive stress through ion exchange, the "Na-K exchange" method, which exchanges sodium ions in the glass with potassium ions, can also be used.

[0062] Examples of molten salts for chemical strengthening include nitrates, sulfates, carbonates, and chlorides. Nitrates include lithium nitrate, sodium nitrate, potassium nitrate, cesium nitrate, and silver nitrate. Sulfates include lithium sulfate, sodium sulfate, potassium sulfate, cesium sulfate, and silver sulfate. Carbonates include lithium carbonate, sodium carbonate, and potassium carbonate. Chlorides include lithium chloride, sodium chloride, potassium chloride, cesium chloride, and silver chloride. These molten salts may be used alone or in combination.

[0063] In the present invention, it is preferable to use a molten salt containing sodium nitrate. The content of sodium nitrate in the molten salt is preferably 90% by mass or more, more preferably 95% by mass or more, and even more preferably 98% by mass or more.

[0064] The treatment conditions for the chemical strengthening treatment may be appropriately selected, such as time and temperature, taking into consideration the glass composition, the type of molten salt, etc. Specifically, the present tempered glass can be produced, for example, by the tempering treatment method described below (hereinafter referred to as "the present tempering treatment method").

[0065] This tempering method includes a step of immersing a glass sheet in a sodium nitrate-containing strengthening molten salt (hereinafter also referred to as sodium-containing strengthening salt). This step allows a high compressive stress layer to be formed deep in the glass. Furthermore, the compressive stress formed near the first surface and the compressive stress formed near the opposing second surface are approximately the same.

[0066] The sodium-containing fortifying salt preferably contains 90% by mass or more, and more preferably 95% by mass or more, of sodium ions, where the mass of metal ions contained in the fortifying salt is 100% by mass. The sodium-containing fortifying salt may contain lithium ions, but to obtain sufficient compressive stress, the lithium ion content is preferably 2% by mass or less, and more preferably 1% by mass or less.

[0067] Furthermore, when the glass plate is made of crystallized glass or high-strength glass containing 20 mol% or more of Al2O3, adding potassium ions to the molten salt makes it difficult to reduce the surface stress. In this case, the potassium ion content is preferably 2% by mass or less, more preferably 1% by mass or less. On the other hand, when the glass plate is other than those mentioned above, potassium ions may be added to the sodium-containing strengthening salt in the first stage of two-stage strengthening to sufficiently suppress the bending stress generated in the glass upon drop impact. The potassium ion content in the sodium-containing strengthening salt is typically 50% or less, where the mass of the metal ions contained in the strengthening salt is 100% by mass. Furthermore, when two-stage strengthening is performed, it is recommended to add lithium ions to the potassium-containing strengthening salt in the second stage of two-stage strengthening. This allows the sodium ions introduced near the surface in the first stage to be exchanged with the lithium ions in the molten salt, thereby reducing the surface stress. In this case, the lithium ion content is preferably 0.2% by mass or more, more preferably 0.4% by mass or more. Furthermore, it is preferably 2% by mass or less, more preferably 1.5% by mass or more.

[0068] In this tempering method, it is preferable to immerse the glass sheet in a sodium-containing reinforcing salt at 380°C to 450°C. If the temperature of the sodium-containing reinforcing salt is 380°C or higher, ion exchange is likely to proceed. It is more preferably 400°C or higher, and even more preferably 420°C or higher. Furthermore, the temperature of the sodium-containing reinforcing salt is usually 450°C or lower, from the viewpoints of the risk of evaporation and changes in the composition of the molten salt.

[0069] Furthermore, the immersion time of the glass plate in the sodium-containing strengthening salt is preferably 0.5 hours or more, since this increases the surface compressive stress. The immersion time is more preferably 1 hour or more. If the immersion time is too long, not only will productivity decrease, but the compressive stress may also decrease due to relaxation. Therefore, the immersion time is usually 20 hours or less.

[0070] The tempering method then includes a step of holding the glass article removed from the sodium-containing salt at a predetermined temperature for a certain period of time. Through this step, the Na ions introduced into the glass from the sodium-containing reinforcing salt are thermally diffused within the glass, forming a more favorable stress profile and thereby increasing the asphalt drop strength.

[0071] The temperature to be maintained is preferably 100°C or higher, more preferably 130°C or higher, and even more preferably 150°C or higher, in order to improve the drop strength of the asphalt. If the temperature is too high, the diffusion of alkali ions will proceed and the stress near the surface will become too small, so the temperature is preferably 300°C or lower, more preferably 280°C or lower, and even more preferably 250°C or lower.

[0072] From the viewpoint of improving the asphalt drop strength, the holding time is preferably 1 minute or more, more preferably 0.2 hours or more, even more preferably 0.3 hours or more, and particularly preferably 0.5 hours or more. If the holding time is too long, relaxation will proceed too much and the stress near the surface will become too small, so the holding time is preferably 4 hours or less, more preferably 3 hours or less, and even more preferably 2 hours or less.

[0073] The tempered glass may be manufactured by a two- or three-stage chemical tempering treatment. When the two- or three-stage tempering treatment is performed, the total treatment time is preferably 10 hours or less, more preferably 5 hours or less, and even more preferably 3 hours or less, from the viewpoint of production efficiency. On the other hand, in order to obtain a desired stress profile, the total treatment time is preferably 0.5 hours or more, more preferably 1 hour or more, and even more preferably 1.5 hours or more.

[0074] <Glass for chemical strengthening> The glass for chemical strengthening in the present invention (hereinafter sometimes referred to as the present glass for strengthening) is preferably lithium aluminosilicate glass. More specifically, it preferably contains, in mole percent on an oxide basis, 40 to 75% SiO2, 2 to 35% Al2O3, and 4 to 35% Li2O.

[0075] The glass having the above composition is likely to form a desirable stress profile by chemical strengthening treatment. The glass to be strengthened may be crystallized glass or amorphous glass.

[0076] When the chemically strengthened glass is crystallized glass, it is preferably crystallized glass containing one or more crystals selected from the group consisting of lithium silicate crystals, lithium aluminosilicate crystals, and lithium phosphate crystals. As the lithium silicate crystals, lithium metasilicate crystals, lithium disilicate crystals, etc. are preferred. As the lithium phosphate crystals, lithium orthophosphate crystals, etc. are preferred. As the lithium aluminosilicate crystals, β-spodumene crystals, petalite crystals, etc. are preferred.

[0077] The crystallization rate of the crystallized glass is preferably 10% or more, more preferably 15% or more, even more preferably 20% or more, and particularly preferably 25% or more in order to increase the mechanical strength. Also, in order to increase the transparency, it is preferably 70% or less, more preferably 60% or less, and particularly preferably 50% or less. A small crystallization rate is also advantageous in that it is easy to heat and bend.

[0078] The crystallinity can be calculated from the X-ray diffraction intensity by the Rietveld method. The Rietveld method is described in "Crystal Analysis Handbook" (Kyoritsu Shuppan, 1999, pp. 492-499), edited by the Editorial Committee of the Crystallographic Society of Japan.

[0079] The average particle size of the precipitated crystals in the crystallized glass is preferably 300 nm or less, more preferably 200 nm or less, even more preferably 150 nm or less, and particularly preferably 100 nm or less, in order to increase transparency. The average particle size of the precipitated crystals can be determined from a transmission electron microscope (TEM) image. It can also be estimated from a scanning electron microscope (SEM) image.

[0080] When the chemically strengthened glass is crystallized glass, one embodiment is preferably glass obtained by heat-treating amorphous glass having the following glass composition. The following glass composition is a glass composition that crystallizes by appropriate heat treatment. In this case, the heat treatment is preferably a two-stage heat treatment in which the temperature is raised from room temperature to a first treatment temperature and maintained for a certain period of time, and then maintained at a second treatment temperature that is higher than the first treatment temperature for a certain period of time. Alternatively, a one-stage heat treatment in which the temperature is maintained at a certain treatment temperature and crystallized may be performed.

[0081] The amorphous glass contains, in mole percent on an oxide basis, 40 to 75% SiO2, 2 to 15% Al2O3, 4 to 35% Li2O, 0 to 4% P2O5, 0 to 7% Na2O, and 0 to 5% K2O.

[0082] Glass having the above composition can be subjected to heat treatment to obtain crystallized glass containing any of β-spodumene crystals, petalite crystals, lithium metasilicate crystals, lithium disilicate crystals, and lithium orthophosphate crystals. To promote crystallization by heat treatment, this glass preferably contains 1 to 7% in total of SnO2, ZrO2, and TiO2, and more preferably 2 to 5% of ZrO2.

[0083] When the glass for chemical strengthening is amorphous glass, it preferably contains, for example, 40 to 65% SiO2, 15 to 35% Al2O3, 4 to 15% Li2O, and 1 to 15% Y2O3 and / or La2O3 in mole percent on an oxide basis. Such glass has a high fracture toughness value, and can achieve extremely high strength by chemical strengthening.

[0084] Alternatively, glass containing, expressed in mole percent on an oxide basis, 60 to 75% SiO2, 8 to 20% Al2O3, 5 to 20% Li2O, and 1 to 15% Na2O and / or K2O in total is preferred. The glass has excellent tempering properties and is suitable for mass production using a float method or the like. This preferred glass composition will now be described.

[0085] SiO2 is a component that constitutes the glass network. It also increases chemical durability and reduces the occurrence of cracks when the glass surface is scratched. The SiO2 content is preferably 40% or more, more preferably 45% or more, even more preferably 48% or more, and even more preferably 50% or more. When the content of Al2O3 is about 20% or less, the content of SiO2 is preferably 60% or more, and more preferably 64% or more, in order to suppress the occurrence of cracks. In order to improve the meltability of the glass, the SiO2 content is preferably 75% or less, more preferably 72% or less, and even more preferably 70% or less. In order to obtain amorphous glass with a particularly high fracture toughness value, the porosity is preferably 65% ​​or less, more preferably 62% or less, and even more preferably 60% or less.

[0086] Al2O3 is an effective component for improving ion exchangeability during chemical strengthening and increasing the surface compressive stress after strengthening, and it also increases the glass transition temperature (Tg) and Young's modulus. The Al2O3 content is preferably 2% or more, more preferably 5% or more, and even more preferably 10% or more. When the tempered glass is a glass-ceramic containing lithium silicate crystals or lithium phosphate crystals, the Al2O3 content is preferably 15% or less, more preferably 13% or less, and even more preferably 10% or less.When the tempered glass is a glass-ceramic containing lithium aluminosilicate crystals, the Al2O3 content is preferably 5% or more, more preferably 7% or more, and even more preferably 16% or more. In order to obtain amorphous glass with a particularly high fracture toughness value, the Al2O3 content is preferably 15% or more, more preferably 18% or more, and even more preferably 20% or more. In addition, in order to improve the melting property, the content of Al2O3 is preferably 35% or less, more preferably 30% or less, even more preferably 28% or less, and even more preferably 25% or less. For example, to obtain crystallized glass containing lithium phosphate crystals or lithium silicate crystals but not containing lithium aluminosilicate crystals, the Al2O3 content is preferably 15% or less, and more preferably 12% or less.

[0087] Li2O is a component that forms surface compressive stress through ion exchange and is an essential component of lithium aluminosilicate glass. Chemically strengthening lithium aluminosilicate glass can produce chemically strengthened glass with a desirable stress profile. The Li2O content is preferably 2% or more, more preferably 4% or more, even more preferably 5% or more, and particularly preferably 7% or more, in order to increase the compressive stress layer depth DOL. In the case of crystallized glass containing lithium silicate or lithium phosphate, the content is preferably 10% or more, more preferably 15% or more, in order to fully precipitate the crystals. Furthermore, in order to suppress the occurrence of devitrification during glass production, the Li2O content is preferably 35% or less, more preferably 32% or less, and even more preferably 30% or less. When the present tempered glass is amorphous glass, the content of Li2O is preferably 20% or less, more preferably 16% or less, and even more preferably 15% or less, in order to suppress crystallization during melting.

[0088] K2O is a component that improves the meltability of glass and also improves the processability of glass. Furthermore, when one-stage chemical strengthening is performed using NaNO3 molten salt, it tends to reduce surface stress. K2O does not need to be contained, but if it is contained, the content is preferably 0.5% or more, more preferably 1% or more. If the KO content is too high, tensile stress may be generated by the ion exchange treatment, which may cause cracks. To prevent cracks, the KO content is preferably 10% or less, more preferably 8% or less, even more preferably 6% or less, and particularly preferably 5% or less. Furthermore, when the present tempered glass is glass-ceramic, crystals such as lithium silicate are likely to precipitate, so the K2O content is preferably 5% or less, more preferably 4% or less, and even more preferably 2% or less.

[0089] Na2O is a component that forms a surface compressive stress layer by ion exchange using a potassium-containing molten salt and also improves the meltability of glass. The Na2O content is preferably 0.5% or more, more preferably 1% or more, and even more preferably 1.5% or more. The content of Na2O is preferably 10% or less, more preferably 8% or less, and further preferably 6% or less. Furthermore, when the present tempered glass is glass-ceramic, since crystals such as lithium silicate are likely to precipitate, the Na2O content is preferably 5% or less, more preferably 4% or less, and even more preferably 3% or less.

[0090] Both Na2O and K2O are components that lower the melting temperature of the glass, and in order to suppress crystallization when the lithium aluminosilicate glass is melted, the total content of these components is preferably 1% or more, and more preferably 2% or more.

[0091] MgO, CaO, SrO, and BaO are all components that improve the meltability of glass, but tend to reduce the ion exchange performance. The total content of MgO, CaO, SrO and BaO (MgO+CaO+SrO+BaO) is preferably 15% or less, more preferably 10% or less, and even more preferably 5% or less. In the case of crystallized glass containing lithium silicate, lithium phosphate, or lithium aluminosilicate, crystals tend to precipitate, so (MgO+CaO+SrO+BaO) is preferably 4% or less, more preferably 3% or less, and even more preferably 2% or less.

[0092] Although MgO, CaO, SrO, and BaO do not necessarily have to be contained, when at least one of them is contained, the total content (MgO + CaO + SrO + BaO) is preferably 0.1% or more, more preferably 0.5% or more. When the tempered glass is an amorphous glass and contains any of these, it is preferable to contain MgO in order to increase the strength of the chemically tempered glass. When MgO is contained, the content is preferably 0.1% or more, and more preferably 0.5% or more. In order to improve the ion exchange performance, the MgO content is preferably 10% or less, and more preferably 8% or less.

[0093] When CaO is contained, the content is preferably 0.5% or more, more preferably 1% or more. In order to improve the ion exchange performance, the CaO content is preferably 5% or less, more preferably 3% or less.

[0094] When SrO is contained, the content is preferably 0.5% or more, more preferably 1% or more. In order to improve the ion exchange performance, the content of SrO is preferably 5% or less, more preferably 3% or less. When BaO is contained, the content is preferably 0.5% or more, more preferably 1% or more. In order to improve the ion exchange performance, the content of BaO is preferably 5% or less, more preferably 1% or less, and even more preferably substantially zero.

[0095] ZnO is a component that improves the meltability of glass and may be contained. When ZnO is contained, the content is preferably 0.2% or more, more preferably 0.5% or more. To improve the weather resistance of the glass, the ZnO content is preferably 5% or less, more preferably 3% or less.

[0096] TiO2 is a component that increases the surface compressive stress due to ion exchange and may be contained. When TiO2 is contained, the content is preferably 0.1% or more. In order to suppress devitrification during melting, the content of TiO2 is preferably 5% or less, more preferably 1% or less, and even more preferably substantially zero.

[0097] ZrO2 is a component that increases the surface compressive stress due to ion exchange and may be contained. When ZrO2 is contained, the content is preferably 0.5% or more, more preferably 1% or more. In addition, in order to suppress devitrification during melting, the content is preferably 5% or less, more preferably 3% or less. When the tempered glass is glass-ceramic, the content of ZrO2 is preferably 2% or more, and more preferably 3% or more, in order to promote crystal precipitation.

[0098] In addition, since TiO2, ZrO2, and SnO2 easily promote crystallization, the total content (TiO2 + SnO2 + ZrO2) is preferably 7% or less, more preferably 5% or less, and even more preferably 3% or less. It is preferable that any one of them is contained in the crystallized glass. When TiO2, ZrO2, and SnO2 are contained, the total content is preferably 1% or more.

[0099] Y2O3 is a component that improves the strength of the glass and may be contained. When Y2O3 is contained, the content is preferably 0.2% or more, more preferably 0.5% or more, even more preferably 1% or more, even more preferably 1.5% or more, and particularly preferably 2% or more. In order to prevent the glass from devitrifying during melting and to prevent a decrease in the quality of the chemically strengthened glass, the Y2O3 content is preferably 10% or less, more preferably 8% or less, even more preferably 7% or less, even more preferably 6% or less, particularly preferably 5% or less, particularly preferably 4% or less, and most preferably 3% or less.

[0100] La2O3 and Nb2O5 are components that suppress fracture of the glass article when chemically strengthened, and may be contained. When these components are contained, the content of each is preferably 0.5% or more, more preferably 1% or more, even more preferably 1.5% or more, and particularly preferably 2% or more.

[0101] The total content of Y2O3, La2O3, and Nb2O5 is preferably 10% or less, more preferably 9% or less, and even more preferably 8% or less. This makes it difficult for the glass to devitrify during melting, preventing a decrease in the quality of the chemically strengthened glass. The contents of La2O3 and Nb2O5 are each preferably 10% or less, more preferably 7% or less, even more preferably 6% or less, even more preferably 5% or less, particularly preferably 4% or less, and most preferably 3% or less.

[0102] B2O3 can be added to improve meltability during glass production, etc. In order to reduce the gradient of the stress profile near the surface of chemically strengthened glass, the B2O3 content is preferably 0.5% or more, more preferably 1% or more, and even more preferably 2% or more. Since B2O3 is a component that makes stress relaxation more likely to occur after chemical strengthening, in order to prevent a decrease in surface compressive stress due to stress relaxation, the content is preferably 10% or less, more preferably 8% or less, even more preferably 5% or less, and most preferably 3% or less.

[0103] P2O5 may be contained to improve ion exchange performance. When P2O5 is contained, the content is preferably 0.5% or more, more preferably 1% or more. To improve chemical durability, the content of P2O5 is preferably 10% or less, more preferably 5% or less, and even more preferably 3% or less. It is preferable that crystallized glass contains P2O5 to promote crystal precipitation, and it is an essential component for crystallized glass containing lithium phosphate.

[0104] To color the glass, coloring components may be added within a range that does not impede the achievement of the desired chemical strengthening properties. Examples of coloring components include Co3O4, MnO2, Fe2O3, NiO, CuO, Cr2O3, V2O5, Bi2O3, SeO2, CeO2, Er2O3, and Nd2O3. These may be used alone or in combination.

[0105] The total content of coloring components is preferably 7% or less. This can prevent devitrification of the glass. The content of coloring components is more preferably 5% or less, even more preferably 3% or less, and particularly preferably 1% or less. If it is desired to increase the visible light transmittance of the glass, it is preferable that these components are substantially not contained.

[0106] Furthermore, SO3, chlorides, fluorides, etc. may be appropriately contained as fining agents during glass melting. It is preferable that As2O3 is not substantially contained. If Sb2O3 is contained, it is preferably 0.3% or less, more preferably 0.1% or less, and most preferably it is not substantially contained.

[0107] When the glass having the above composition is crystallized, it is preferable to carry out a two-stage heat treatment.

[0108] In the case of two-stage heat treatment, the first treatment temperature is preferably in a temperature range where the crystal nucleation rate is high in the glass composition, and the second treatment temperature is preferably in a temperature range where the crystal growth rate is high in the glass composition. Also, it is preferable to maintain the first treatment temperature for a long time so that a sufficient number of crystal nuclei are generated. By generating a large number of crystal nuclei, the size of each crystal becomes small, and highly transparent crystallized glass is obtained.

[0109] The first treatment temperature is, for example, 550°C to 800°C, and the second treatment temperature is, for example, 850°C to 1000°C. After being held at the first treatment temperature for 2 to 10 hours, the second treatment temperature is held for 2 to 10 hours.

[0110] The glass transition temperature (Tg) of the present tempering glass is preferably 480°C or higher to suppress stress relaxation during chemical tempering. Tg is more preferably 500°C or higher, and even more preferably 520°C or higher, to suppress stress relaxation and obtain large compressive stress. Furthermore, Tg is preferably 700°C or lower, since the ion diffusion rate increases during chemical tempering. Tg is more preferably 650°C or lower, and even more preferably 600°C or lower, to facilitate obtaining a deep DOL.

[0111] The Young's modulus of the present tempered glass is preferably 70 GPa or more. The higher the Young's modulus, the less likely the tempered glass is to scatter fragments when broken. Therefore, the Young's modulus is more preferably 75 GPa or more, and even more preferably 80 GPa or more. On the other hand, if the Young's modulus is too high, ion diffusion during chemical tempering tends to be slow, making it difficult to obtain a deep DOL. Therefore, the Young's modulus is preferably 110 GPa or less, more preferably 100 GPa or less, and even more preferably 90 GPa or less. The Young's modulus can be measured by an ultrasonic method.

[0112] The Vickers hardness of the present glass to be tempered is preferably 575 or more. The greater the Vickers hardness of the glass to be tempered, the greater the Vickers hardness after chemical tempering, and the chemically tempered glass is less likely to be scratched when dropped. Therefore, the Vickers hardness of the glass to be tempered is more preferably 600 or more, and even more preferably 625 or more. The Vickers hardness after chemical strengthening is preferably 600 or more, more preferably 625 or more, and even more preferably 650 or more.

[0113] A higher Vickers hardness is preferable because it makes the glass less susceptible to scratches, but the Vickers hardness of the present tempering glass is usually 850 or less. Glass with too high a Vickers hardness tends to make it difficult to obtain sufficient ion exchangeability. Therefore, a Vickers hardness of 800 or less is preferable, and 750 or less is more preferable.

[0114] The fracture toughness of this tempered glass is 0.7 MPa m 1 / 2The higher the fracture toughness value, the more likely it is that the chemically strengthened glass will not shatter into fragments when broken. The fracture toughness value is more preferably 0.75 MPa m 1 / 2 More preferably, 0.8 MPa m 1 / 2 The fracture toughness value is usually 1.0 MPa m 1 / 2 The fracture toughness value can be measured by the DCDC method (Acta metall. mater. Vol. 43, pp. 3453-3458, 1995).

[0115] The average thermal expansion coefficient (α) of this tempered glass from 50°C to 350°C is 100×10 -7 / °C or less. If the average coefficient of thermal expansion (α) is small, the glass plate is less likely to warp during glass molding or cooling after chemical strengthening. The average coefficient of thermal expansion (α) is 95 × 10 -7 / ℃ or less is more preferable, and 90×10 -7 / °C or less is more preferable. In order to suppress warping of chemically strengthened glass, the smaller the average thermal expansion coefficient (α) is, the more preferable. -7 / ℃ or more.

[0116] In this tempering glass, the viscosity is 10 2 The temperature (T2) at which the viscosity becomes dPa·s is preferably 1750° C. or lower, more preferably 1700° C. or lower, and even more preferably 1680° C. or lower. T2 is usually 1400° C. or higher.

[0117] In this tempering glass, the viscosity is 10 4 The temperature (T4) at which the viscosity becomes dPa·s is preferably 1350° C. or lower, more preferably 1300° C. or lower, and even more preferably 1250° C. or lower. T4 is usually 1000° C. or higher. [Example]

[0118] The present invention will be described below with reference to examples, but the present invention is not limited thereto. Glass raw materials were mixed to obtain the compositions of Glasses A to E shown in Table 1 in terms of oxide-based mole percentages, 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.

[0119] The resulting molten glass was poured into a metal mold and held at a temperature approximately 50°C higher than the glass transition point for 1 hour, after which it was cooled to room temperature at a rate of 0.5°C / min to obtain a glass block. The resulting glass block was cut and ground, and finally both surfaces were mirror-polished to obtain a glass plate with a thickness of 600 μm. Glasses B and D were crystallized under the conditions shown in Table 1 to obtain crystallized glass.

[0120] The fracture toughness, Young's modulus and CT limit of the obtained glass plate were measured by the following methods. The results are shown in Table 1.

[0121] [Fracture toughness value] The fracture toughness value was measured by the DC-DC method using a 6.5mm x 6.5mm x 65mm sample prepared by drilling a 2mm diameter through hole in the 65mm x 6.5mm surface of the sample.

[0122] Young's Modulus The Young's modulus was measured by an ultrasonic method.

[0123] [CT Limit] Plate glass was chemically strengthened under various conditions using NaNO3 salt or KNO3 salt, and the CT of the resulting chemically strengthened glass was measured using a scattered light photoelastic stress meter (SLP-1000, manufactured by Orihara Seisakusho).The CT limit was then evaluated by driving a diamond indenter into chemically strengthened glass plates with different CT values ​​and measuring the number of fractures.

[0124] [Table 1]

[0125] The obtained glass plates were subjected to a chemical strengthening treatment under the conditions shown in Tables 2 and 3 to produce the chemically strengthened glasses of Examples 1 to 8 below. The chemical strengthening treatment was carried out using the salt, temperature, and time shown in the first stage chemical strengthening condition column of Tables 2 and 3. Thereafter, chemical strengthening was carried out using the salt, temperature, and time shown in the second stage chemical strengthening condition column of Tables 2 and 3 to obtain chemically strengthened glass. The obtained chemically strengthened glasses were evaluated by the following methods.

[0126] Stress Profile The stress profile of the resulting chemically strengthened glass was measured using the following method. The surface area within 10 μm of the glass surface was immersed in an acid solution of 1% HF-99% HO by volume while one side was sealed, and only one side was etched to the desired thickness. This creates a stress difference between the front and back surfaces of the chemically strengthened glass, causing the glass to warp in response to this stress difference. The amount of warping was measured using a contact shape meter (Mitutoyo Surftest). The obtained amount of warping was converted into stress using the formula shown in the following document. Reference: GG Stoney, Proc. Roy. Soc. A, 82 172 (1909). The area at a depth of 10 μm or more from the glass surface was measured using a scattered light photoelastic stress meter (Orihara Seisakusho: SLP2000).

[0127] [Measurement of ion concentration using EPMA] The ion concentration on the glass surface was measured using an EPMA (JEOL JXA-8500F). After chemical strengthening, the samples were embedded in resin and mirror-polished. Because it is difficult to accurately measure the concentration on the outermost surface, we assumed that the signal intensity of ions at a position where the signal intensity of Si, which is thought to have little change in content, is half that of the signal intensity at the center of the plate thickness corresponds to the ion concentration on the outermost surface. We calculated the ion concentration on the outermost surface by assuming that the signal intensity at the center of the plate thickness corresponds to the glass composition before strengthening.

[0128] [4-point bending strength] Chemically strengthened glass was processed into 10 mm x 50 mm strips, and a four-point bending test was performed under the conditions of a 30 mm outer support distance, a 10 mm inner support distance, and a crosshead speed of 0.5 mm / min to measure the four-point bending strength. Ten test pieces were used. The results are shown in Tables 2 and 3.

[0129] [Drop test] For the drop test, the obtained glass sample, measuring 120 x 60 x 0.6 mmt, was fitted into a structure whose mass and rigidity had been adjusted to match the size of a typical smartphone currently in use, and then a mock smartphone was prepared and the sample was allowed to drop freely onto #180 SiC sandpaper. The sample was dropped from a height of 5 cm. If the sample did not break, the height was increased by 5 cm and the drop was repeated until the sample broke. The average height of the 10 samples at which the sample first broke is shown in Tables 2 and 3.

[0130] [Number of crushes] Chemically strengthened glass was processed into a square with sides of 30 mm, and a fracture test was conducted by striking the resulting glass with a diamond indenter with a 90-degree tip angle. If the glass did not break, the test was repeated while gradually increasing the load applied to the indenter, and the number of fragments at the minimum load at which fracture occurred is shown in Tables 2 and 3 as the number of fractures. If the number of fractures exceeds 10, it can be determined that the internal tensile stress CT is excessive.

[0131] The results are shown in Tables 2 and 3. Examples 1 to 6 are working examples, and Example 7 is a comparative example. In Tables 2 and 3, the symbols represent the following. CS0 (MPa): compressive stress value at the first surface CS m (MPa): Compressive stress value at a depth m [μm] from the first surface m: Depth from the first surface where the compressive stress value is maximum (μm) CS 50 (MPa): Compressive stress value at a depth of 50 μm from the first surface CS 60 (MPa): Compressive stress value at a depth of 60 μm from the first surface DOL (μm): Depth from the first surface where the compressive stress value becomes 0 C-0-Li, Na, or K (at%): ion concentration of Li, Na, or K at a depth of 0 μm from the first surface Ct / 2-Li, Na, or K (at%): ion concentration of Li, Na, or K at a depth of t / 2 [μm] from the first surface, where t [μm] is the thickness

[0132] [Table 2]

[0133] [Table 3]

[0134] As shown in Tables 2 and 3, Examples 1 to 6, which are working examples, were found to have superior strength, suppressed scattering of fragments upon breaking, and were less likely to cause chipping, compared to the comparative examples.

[0135] Although the present invention has been described in detail with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the present invention. This application is based on a Japanese patent application (Patent Application No. 2020-089755) filed on May 22, 2020, the entirety of which is incorporated by reference. All references cited herein are incorporated in their entirety.

Claims

1. A chemically strengthened glass article having a first surface which is one surface of a plate, a second surface which is the surface of the plate opposite to the first surface, and an end portion which is made up of a side surface of the plate which contacts the first surface and the second surface, respectively. the compressive stress value on the first surface is 400 to 1000 MPa; When the compressive stress value inside the glass is expressed using the depth from the first surface as a variable, The depth m [μm] at which the compressive stress value is maximum is greater than 0 μm, The compressive stress value at a depth m [μm] is CS ｍ [MPa], The compressive stress value on the first surface is CS ０ As [MPa], CS ｍ -CS ０ [MPa] is 30 MPa or more, The depth DOL at which the compressive stress value becomes 0 is 50 to 150 μm, The base glass of the chemically strengthened glass article is SiO ２ 40 to 75% Al ２ O ３ を12.4~35%、 Li ２ Oを4~35% A chemically strengthened glass article comprising:

2. Compressive stress value CS at a depth of 60 μm from the first surface ６０ The chemically strengthened glass article according to claim 1, wherein the strain is 100 MPa or more.

3. Said CS ｍ -CS ０ The chemically strengthened glass article according to claim 1 or 2, wherein [MPa] is 300 MPa or less.

4. The chemically strengthened glass article according to any one of claims 1 to 3, wherein the depth m [μm] at which the compressive stress value is maximum is 5 μm or less.

5. The chemically strengthened glass article according to any one of claims 1 to 4, which is made of lithium aluminosilicate glass.

6. The chemically strengthened glass article according to claim 5, wherein the chemically strengthened glass article is glass-ceramic.

7. The mother glass of chemically strengthened glass is expressed as mole percent based on oxides. SiO ２ 40 to 75% Al ２ O ３ を12.4~20%、 Li ２ Oを4~35%、 ZrO ２ + TiO ２ + SnO ２ The chemically strengthened glass article according to claim 6, containing 1 to 7% of

8. The mother glass of chemically strengthened glass is expressed as mole percent based on oxides. SiO ２ 40 to 65% Al ２ O ３ を15~35%、 Li ２ Oを4~15%、 Y ２ O ３ +La ２ O ３ The chemically strengthened glass article according to claim 5, which is an amorphous glass containing 1 to 15% of

9. The mother glass of chemically strengthened glass is expressed as mole percent based on oxides. SiO ２ 60 to 75% of Al ２ O ３ を12.4~20%、 Li ２ Oを5~20%、 Na ２ O+K ２ The chemically strengthened glass article according to claim 5, which is an amorphous glass containing 1 to 15% of O.

10. When the thickness is t [μm] and the ion concentrations of Li, Na, and K at a depth x [μm] from the first surface are Li(x), Na(x), and K(x), respectively, Li(0)≦Li(t / 2), K(0)≦K(t / 2), and Na(0)>0.3×[Li(0)+Na(0)+K(0)], The chemically strengthened glass article according to any one of claims 5 to 9, wherein Li(t / 2) > 0.7 × [Li(t / 2) + Na(t / 2) + K(t / 2)].

11. Immersing lithium aluminosilicate glass in a salt containing 90% by mass or more of sodium nitrate at 400 to 450°C; and and after removing the lithium aluminosilicate glass from the salt, holding the glass at 100 to 300°C for 1 minute or more and 4 hours or less, The lithium aluminosilicate glass is, in terms of mole percent on an oxide basis, SiO ２ 40 to 75% Al ２ O ３ を12.4~35%、 Li ２ Oを4~35% A method for producing a chemically strengthened glass article comprising the steps of:

12. The method for producing a chemically strengthened glass article according to claim 11, wherein the salt contains 2 mass% or less of lithium ions.

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