Chemically strengthened glass, method of manufacturing the same, and glass for chemical strengthening

Abstract

The present invention relates to chemically strengthened glass, a method for producing the same, and glass for chemical strengthening. A chemically strengthened glass is a plate-shaped chemically strengthened glass having a compressive stress layer on a glass surface, in which a compressive stress value (CS0) of the glass surface is 500 MPa or greater, a plate thickness (t) is 400 μm or greater, a compressive stress layer depth (DOL) is (t x 0.15) μm or greater, a compressive stress value (CS1) at a position at a depth of 1 / 4 of the DOL from the glass surface and a compressive stress value (CS2) at a position at a depth of 1 / 2 of the DOL from the glass surface are each 50 MPa or greater, m1 represented by {m1 = (CS1-CS2) / (DOL / 4-DOL / 2)} is -1.5 MPa / μm or greater, m2 represented by {m2 = CS2 / (DOL / 2-DOL)} is 0 MPa / μm or less, and m2 is less than m1.

Description

[0001] This application is a divisional application of Chinese patent application No. 201880042555.9, filed on June 25, 2018. Technical Field

[0002] This invention relates to chemically strengthened glass. Background Technology

[0003] Chemically strengthened glass is used for protective glass in portable devices, etc.

[0004] Chemically strengthened glass is produced by contacting the glass with a molten salt containing alkali metal ions, resulting in ion exchange between the metal ions in the glass and those in the molten salt, thus forming a compressive stress layer on the glass surface. The strength of chemically strengthened glass is highly dependent on the stress distribution, expressed as a compressive stress value measured from the depth of the glass surface.

[0005] Protective glass in portable devices sometimes cracks when bent by external forces. In such cases, the crack originates at the glass surface, where tiny cracks propagate until the glass breaks. Therefore, it is believed that increasing the compressive stress on the glass surface can suppress the propagation of these tiny cracks, making it less prone to cracking.

[0006] Protective glass for portable devices sometimes cracks due to protrusions when dropped on asphalt or sand. In such cases, the crack originates deeper than the glass surface. Therefore, it is believed that increasing the depth of the compressive stress layer, forming a compressive stress layer even deeper into the glass, can make it less prone to cracking.

[0007] On the other hand, when a compressive stress layer forms on the glass surface, a tensile stress layer inevitably forms inside the glass. When the internal tensile stress is high, chemically strengthened glass breaks violently, resulting in easily scattered fragments. Therefore, research is needed on methods to increase surface compressive stress and the depth of the compressive stress layer while suppressing the internal tensile stress.

[0008] Patent Document 1 describes a chemically strengthened glass with a compressive stress layer depth of 90 μm or more obtained through one or two ion exchange treatments. Furthermore, a typical stress distribution is illustrated when two ion exchange treatments have been performed. This distribution consists of two linear components: one representing the stress distribution from the glass surface to a position X at a certain depth; and the other representing the stress distribution from position X to a position where the stress is zero (Patent Document 1, Figure 8). It is believed that using such a stress distribution can increase the surface compressive stress and the depth of the compressive stress layer while suppressing the internal tensile stress value.

[0009] Existing technical documents

[0010] Patent documents

[0011] Patent Document 1: International Publication No. 2015 / 127483 Summary of the Invention

[0012] The problem that the invention aims to solve

[0013] However, even the glass described in Patent Document 1 sometimes has insufficient strength when dropped onto sand or asphalt (hereinafter sometimes referred to as "asphalt drop strength").

[0014] The purpose of this invention is to provide a chemically strengthened glass with high asphalt drop strength and whose fragments do not easily scatter when broken.

[0015] means for solving problems

[0016] Based on the following research and experiments, the inventors believe that, in order to improve the drop strength of asphalt, the maximum depth at which a compressive stress value of 50 MPa is obtained is more important than the maximum compressive stress layer depth DOL.

[0017] When a glass plate falls onto asphalt, microcracks are created inside the glass due to protrusions on the asphalt surface. As these microcracks propagate and enlarge, the glass breaks. The propagation of these microcracks can be suppressed by applying a compressive stress of approximately 50 MPa. Therefore, it is believed that if the maximum depth required to achieve a compressive stress of 50 MPa is large, even if microcracks are created inside the glass due to relatively large protrusions, breakage is less likely.

[0018] Table 1 shows the results obtained from chemically strengthening float glass sheets and conducting the bitumen drop strength test described later, expressed as a mass percentage based on oxides. The float glass sheets contain: 60.7% SiO2, 16.8% Al2O3, 15.6% Na2O, 1.2% K2O, 5.3% MgO, and 0.4% ZrO2. In this experiment, the following tendency was observed: the greater the maximum depth at which a compressive stress of 50 MPa is obtained, the better the resistance to drops from higher positions.

[0019] Table 1

[0020] Sample 1 Sample 2 Sample 3 Depth (μm) at 30 MPa 39 64 79 Depth (μm) at 50 MPa 35 58 70 Falling height (cm) 60 95 135

[0021] Therefore, the inventors believe that, in order to improve the drop strength of asphalt, a larger maximum depth at which a compressive stress value of 50 MPa is obtained is more important than a larger compressive stress layer depth (DOL). Furthermore, they found that the stress distribution described in Patent Document 1, consisting of two or fewer straight lines, makes it difficult to suppress the internal tensile stress value (CT) and to increase the maximum depth at which a compressive stress value of 50 MPa is obtained. Therefore, they conducted research and, as a result, completed this invention.

[0022] This invention relates to the following <1> ~ <12> .

[0023] <1> A chemically strengthened glass, which is a plate-shaped chemically strengthened glass with a compressive stress layer on its surface, wherein,

[0024] The compressive stress (CS0) on the surface of the chemically strengthened glass is above 500 MPa.

[0025] The thickness (t) of the chemically strengthened glass is 400 μm or more.

[0026] The compressive stress layer depth (DOL) of the chemically strengthened glass is greater than (t×0.15) μm.

[0027] The compressive stress (CS1) at a depth of 1 / 4 of the DOL, measured from the glass surface, is 50 MPa or more.

[0028] The compressive stress (CS2) at a depth of 1 / 2 of the DOL, measured from the glass surface, is 50 MPa or more.

[0029] The following formula represents m1 as -1.5 MPa / μm or higher, and the following formula represents m2 as 0 MPa / μm or lower, wherein m2 is smaller than m1.

[0030] m1 = (CS1 - CS2) / (DOL / 4 - DOL / 2)

[0031] m2 = CS2 / (DOL / 2-DOL).

[0032] <2> A chemically strengthened glass, which is a plate-shaped chemically strengthened glass with a compressive stress layer on its surface, wherein,

[0033] The compressive stress (CS0) on the surface of the chemically strengthened glass is above 500 MPa.

[0034] The compressive stress layer depth (DOL) of the chemically strengthened glass is 100 μm or more.

[0035] The compressive stress (CS1) at a depth of 1 / 4 of the DOL, measured from the glass surface, is 50 MPa or more.

[0036] The compressive stress (CS2) at a depth of 1 / 2 of the DOL, measured from the glass surface, is 50 MPa or more.

[0037] The following formula represents m1 as -1.5 MPa / μm or higher, and the following formula represents m2 as 0 MPa / μm or lower, wherein m2 is smaller than m1.

[0038] m1 = (CS1 - CS2) / (DOL / 4 - DOL / 2)

[0039] m2 = CS2 / (DOL / 2-DOL).

[0040] <3> As mentioned above <1> or <2> The chemically strengthened glass, wherein the maximum depth of the chemically strengthened glass when the compressive stress value is 50 MPa or more is related to the DOL and is (0.55 × DOL) μm or more.

[0041] <4> As mentioned above <1> ~ <3> The chemically strengthened glass according to any one of the following methods, wherein the ratio of m1 to m2 (m1 / m2) is less than 0.9.

[0042] <5> As mentioned above <1> ~ <4> The chemically strengthened glass according to any one of the following methods, wherein m1 is less than 0.5 MPa / μm.

[0043] <6> As mentioned above <1> ~ <5> The chemically strengthened glass according to any one of the following methods, wherein the internal tensile stress value of the chemically strengthened glass is less than 100 MPa.

[0044] <7> As mentioned above <1> ~ <6> In any one of the chemically strengthened glass formulas, the m3 expressed by the following formula is related to the compressive stress value (CS3) at a depth of 2.5 μm from the glass surface and is 120 MPa / μm or more.

[0045] m3 = (CS0 - CS3) / 2.5.

[0046] <8> As mentioned above <1> ~ <7> In any one of the chemically strengthened glasses, wherein, expressed as a mass percentage based on oxides, the basic composition of the chemically strengthened glass comprises:

[0047] 55%–80% SiO2,

[0048] 15%–28% Al2O3,

[0049] 0%–10% B2O3

[0050] 2%–10% Li₂O,

[0051] 0.5%–10% Na₂O,

[0052] 0%–10% K2O,

[0053] 0%–10% of (MgO+CaO+SrO+BaO), and

[0054] 0% to 5% (ZrO2+TiO2).

[0055] <9> A method for manufacturing chemically strengthened glass, comprising the following steps:

[0056] Ion exchange is achieved by contacting chemically strengthened glass containing Li₂O with a metal salt containing Na ions.

[0057] Next, ion exchange occurs through contact with a metal salt containing Li ions.

[0058] Next, ion exchange occurs through contact with a metal salt containing K ions.

[0059] <10> A method for manufacturing chemically strengthened glass, comprising the following steps:

[0060] Ion exchange is achieved by contacting chemically strengthened glass containing Li₂O with a metal salt containing Na ions.

[0061] Next, heat treatment is performed without contact with metal salts.

[0062] Next, ion exchange occurs through contact with a metal salt containing K ions.

[0063] <11> As mentioned above <9> or <10> The method for manufacturing chemically strengthened glass, wherein, expressed as a mass percentage based on oxides, the chemically strengthened glass contains: 55%–80% SiO2, 15%–28% Al2O3, 0%–10% B2O3, 2%–10% Li2O, 0.5%–10% Na2O, 0%–10% K2O, 0%–10% (MgO+CaO+SrO+BaO), and 0%–5% (ZrO2+TiO2).

[0064] <12> A chemically strengthened glass, wherein, expressed as a mass percentage based on oxides, the chemically strengthened glass contains: 55%–75% SiO2, 15%–25% Al2O3, 0%–10% B2O3, 2%–10% Li2O, 1%–10% Na2O, 0.5%–10% K2O, 0%–10% (MgO+CaO+SrO+BaO), and 0%–5% (ZrO2+TiO2).

[0065] Invention Effects

[0066] According to the present invention, a chemically strengthened glass with high pitch drop strength and suppressed fragmentation upon breakage is obtained. Attached Figure Description

[0067] Figure 1 A diagram showing a portion of the stress distribution in chemically strengthened glass 1.

[0068] Figure 2 A diagram showing a portion of the stress distribution in chemically strengthened glass 3.

[0069] Figure 3 A diagram showing a portion of the stress distribution in chemically strengthened glass 5.

[0070] Figure 4 A diagram showing a portion of the stress distribution in chemically strengthened glass 7.

[0071] Figure 5 A diagram showing a portion of the stress distribution in chemically strengthened glass 12. Detailed Implementation

[0072] In this specification, the symbol “~” indicating a numerical range is used to mean that the numerical values ​​before and after it are included as the lower limit and upper limit, unless otherwise specified, “~” will be used in the same sense in this specification.

[0073] In this specification, "stress distribution" refers to the compressive stress value expressed as a variable based on the depth measured from the glass surface. Additionally, "compressive stress layer depth DOL" is the depth at which the compressive stress value CS is zero. For example, in... Figure 1 In the stress distribution shown, the depth of the location indicated by arrow C is DOL.

[0074] Stress distribution can be obtained, for example, by analyzing a sample obtained by forming a thin section of glass and then using a birefringence imaging system. An example of a birefringence imaging system is the Abrio-IM birefringence imaging system manufactured by Tokyo Instrument Co., Ltd. Alternatively, it can be measured using the photoelasticity of scattered light. In this method, incident light is incident from the surface of the glass, and the polarization of the scattered light is analyzed.

[0075] "Internal tensile stress CT" refers to the tensile stress value at a depth of 1 / 2 the thickness t of the glass plate.

[0076] In this specification, "chemically strengthened glass" refers to glass that has undergone chemical strengthening treatment, and "glass for chemical strengthening" refers to glass that has not undergone chemical strengthening treatment.

[0077] In this specification, "basic composition of chemically strengthened glass" refers to the glass composition of chemically strengthened glass. Except in cases where extreme ion exchange treatment has been performed, the glass composition of the portion deeper than the DOL of the chemically strengthened glass is the basic composition of the chemically strengthened glass.

[0078] In this specification, unless otherwise specified, the glass composition is expressed as a mass percentage based on oxides, and mass % is simply referred to as "%".

[0079] Furthermore, in this specification, "substantially not containing" means below the level of impurities contained in raw materials, etc., i.e., not intentionally contained. Specifically, for example, less than 0.1%.

[0080] Chemically strengthened glass

[0081] The chemically strengthened glass of the present invention (hereinafter, sometimes referred to as "the strengthened glass") is in the form of a plate, usually a flat plate, but it can also be curved.

[0082] This tempered glass has a compressive stress layer on its surface, with a thickness (t) of 400 μm or more and a compressive stress layer depth (DOL) of (t × 0.15) μm or more, or a compressive stress layer depth (DOL) of 100 μm or more. Alternatively, the thickness (t) can be 400 μm or more, and the compressive stress layer depth (DOL) can be both (t × 0.15) μm or more and 100 μm or more.

[0083] The thickness (t) of this tempered glass is preferably 400 μm or more, more preferably 600 μm or more, and even more preferably 700 μm or more. This is because the strength of the glass is increased. To increase strength, the greater the thickness (t), the better; however, when t is too large, the weight increases. Therefore, it is preferably 2000 μm or less, more preferably 1000 μm or less.

[0084] The large DOL of this tempered glass makes it less prone to breakage even in the event of damage such as a drop from a chemically tempered glass, making it a preferred choice. The DOL of this tempered glass is preferably (t × 0.15) μm or more, more preferably (t × 0.18) μm or more, even more preferably (t × 0.19) μm or more, and particularly preferably (t × 0.2) μm or more.

[0085] On the other hand, the DOL is preferably (t×0.3) μm or less, more preferably (t×0.25) μm or less, and even more preferably (t×0.22) μm or less. This is because it can suppress internal tensile stress (CT).

[0086] The DOL of this tempered glass is preferably 100 μm or more, more preferably 120 μm or more, and even more preferably 140 μm or more.

[0087] It should be noted that when the CT is below 110 MPa, the fragments of chemically strengthened glass are less likely to scatter when it breaks, and therefore this is preferred. A CT below 100 MPa is more preferable, and below 90 MPa is even more preferable.

[0088] The compressive stress CS0 on the surface of this tempered glass is 500 MPa or more, making it less prone to breakage even in cases where chemically strengthened glass deforms due to impact, thus it is preferred. CS0 is preferably 600 MPa or more, more preferably 700 MPa or more, and even more preferably 800 MPa or more. On the other hand, to suppress CT (coal stress), CS0 is preferably 1500 MPa or less, more preferably 1300 MPa or less, even more preferably 1100 MPa or less, and particularly preferably 900 MPa or less.

[0089] The compressive stress (CS1) at a depth of DOL / 4 from the glass surface of this tempered glass is 50 MPa or more, thus making it less prone to breakage when dropped onto sand or asphalt. To increase the asphalt drop strength, CS1 is preferably 60 MPa or more, more preferably 70 MPa or more. If CS1 is too high, CT becomes large, and the glass fragments are more likely to scatter when broken. Therefore, CS1 is preferably 120 MPa or less, more preferably 100 MPa or less, and even more preferably 80 MPa or less.

[0090] The compressive stress (CS2) at a depth of DOL / 2 from the glass surface of this tempered glass is 50 MPa or more, thus it is not easily broken even if damage occurs when it falls onto sand or asphalt. To increase the asphalt drop strength, CS2 is preferably 60 MPa or more, more preferably 70 MPa or more. If CS2 is too large, the possibility of fragments scattering when the glass breaks increases. This is because CT increases. Therefore, CS2 is preferably 120 MPa or less, more preferably 100 MPa or less, and even more preferably 80 MPa or less.

[0091] Furthermore, the tempered glass exhibits a strength m1 of -1.5 MPa / μm or higher, as expressed by the following formula, thus suppressing CT and reducing the likelihood of severe breakage. Preferably, m1 is -1.0 MPa / μm or higher, and more preferably -0.8 MPa / μm or higher.

[0092] m1 = (CS1 - CS2) / (DOL / 4 - DOL / 2)

[0093] On the other hand, when m1 is too large, cracks are prone to form on the end faces of chemically strengthened glass. Chemically strengthened glass is glass in which a compressive stress layer is formed on the glass surface. Therefore, as a whole, the compressive stress value on the outer side of the glass is greater than that on the inner side. Thus, the compressive stress value CS1 on the outer side is usually greater than that on the inner side, and m1 is usually negative. It is also possible to make m1 positive by adjusting the stress distribution, but in this case, a localized portion occurs inside the glass sheet where the compressive stress value on the outer side is less than that on the inner side, making it prone to strain. Consequently, cracks are easily formed on the end faces.

[0094] m1 is preferably 0.5 MPa / μm or less, more preferably 0.3 MPa / μm or less, even more preferably 0 MPa / μm or less, and particularly preferably -0.2 MPa / μm or less. This is because it can suppress the formation of cracks at the end face.

[0095] Furthermore, m2, as expressed by the following formula, is below 0 MPa / μm and less than m1. That is, the ratio of m1 to m2 (m1 / m2) is less than 1.

[0096] m2 = CS2 / (DOL / 2 - DOL)

[0097] The m1 / m2 ratio is preferably 0.9 or less, more preferably 0.85 or less, even more preferably 0.8 or less, even more preferably 0.75 or less, and particularly preferably 0.7 or less. A small m1 / m2 ratio suppresses CT.

[0098] On the other hand, m1 / m2 is preferably -0.2 or more, more preferably 0 or more, even more preferably 0.1 or more, and particularly preferably 0.25 or more. This is because cracks are less likely to form on the end face of the glass.

[0099] For this tempered glass, when the compressive stress value at a depth of 2.5 μm is set as CS3, m3, expressed by the following formula, is preferably 120 MPa / μm or higher. Therefore, even if CS0 is increased, CT can be reduced.

[0100] m3 = (CS0 - CS3) / 2.5

[0101] More preferably, m3 is 150 MPa / μm or more, even more preferably 180 MPa / μm or more, even more preferably 200 MPa / μm or more, and particularly preferably 220 MPa / μm or more. On the other hand, if m3 is too large, the strength is easily reduced due to minor damage to the glass surface. Therefore, m3 is preferably 500 MPa / μm or less, more preferably 400 MPa / μm or less, and even more preferably 300 MPa / μm or less.

[0102] The maximum depth (D) of this tempered glass when the compressive stress value is above 50 MPa. 50M The micrometer diameter is preferably (0.55 × DOL) μm or more, more preferably (0.6 × DOL) μm or more, and even more preferably (0.65 × DOL) μm or more. This improves the drop strength of the asphalt.

[0103] <Chemically Strengthened Glass>

[0104] The chemically strengthened glass of the present invention (hereinafter, sometimes referred to as the strengthened glass) preferably exhibits a compressive stress (CS) of 200 MPa or more on its surface after being immersed in molten sodium nitrate (NaNO3) at 450°C for 1 hour. Furthermore, the diameter at which the glass surface (DOL) reaches a depth of 40 μm or more at this time.

[0105] The CS (Coefficient of Performance) of glass immersed in molten sodium nitrate at 450°C for 1 hour is more preferably 250 MPa or more, further preferably 300 MPa or more, particularly preferably 350 MPa or more, and most preferably 400 MPa or more. Such glass can easily achieve high CS through chemical strengthening.

[0106] Furthermore, the DOL (diameter of glass) after immersion in molten sodium nitrate at 450°C for 1 hour is more preferably 50 μm or more, even more preferably 60 μm or more, and particularly preferably 70 μm or more. When this is used for chemically strengthened glass, the strengthening treatment time can be shortened.

[0107] Generally, when the CS (Coefficient of Stress) is too high, the DOL (Density of Oxygen Surface) becomes lighter; when the DOL is too deep, the CS becomes smaller. Considering a balance between the two, the CS after immersion in molten sodium nitrate at 450°C for 1 hour is preferably 700 MPa or less, more preferably 600 MPa or less, and even more preferably 500 MPa or less. The DOL is preferably 170 μm or less, more preferably 150 μm or less, and even more preferably 130 μm or less.

[0108] The glass for strengthening is preferably prepared by impregnation in potassium nitrate (KNO3) molten salt at 450°C for 1 hour, resulting in a CS of 500 MPa or higher. Furthermore, it is preferable that the DOL (Density Oxide) reaches 3 μm or higher at this point.

[0109] The CS (chemical strength) of chemically strengthened glass after immersion in molten potassium nitrate at 450°C for 1 hour is more preferably 600 MPa or more, even more preferably 700 MPa or more, and even more preferably 800 MPa or more. Such chemically strengthened glass readily yields high CS, thus readily producing high-strength chemically strengthened glass.

[0110] The DOL (Density Oxide) of glass that has been immersed in molten potassium nitrate at 450°C for 1 hour is more preferably 4 μm or more, even more preferably 5 μm or more, and even more preferably 6 μm or more. Such strengthening glass can shorten the strengthening process time.

[0111] Generally, when the CS (coal pressure) is too high, the DOL (diameter of nitrate) becomes lighter; when the DOL is too deep, the CS becomes smaller. Considering a balance between the two, the CS after immersion in molten potassium nitrate salt at 450°C for 1 hour is preferably 1400 MPa or less. More preferably, it is 1300 MPa or less; even more preferably, it is 1100 MPa or less; and particularly preferably, it is 900 MPa or less. The DOL after immersion in molten potassium nitrate salt at 450°C for 1 hour is preferably 20 μm or less; more preferably, it is 15 μm or less; and even more preferably, it is 10 μm or less.

[0112] The glass for strengthening is more preferably impregnated in sodium nitrate (NaNO3) molten salt at 450°C for 1 hour with a DOL of 40 μm or more, and in potassium nitrate (KNO3) molten salt at 450°C for 1 hour with a CS of 500 MPa or more.

[0113] This is because, with such strengthened glass, chemically strengthened glass with large CS, large DOL, and suppressed CT can be easily obtained by using sodium and potassium salts for chemical strengthening treatment.

[0114] To suppress stress relaxation during chemical strengthening, the glass transition temperature (Tg) of the glass for strengthening is preferably 480°C or higher. To suppress stress relaxation and obtain a large compressive stress, Tg is more preferably 500°C or higher, and even more preferably 520°C or higher.

[0115] Furthermore, to accelerate ion diffusion during chemical strengthening, Tg is preferably below 700°C. For easier attainment of deep DOL, Tg is more preferably below 650°C, and even more preferably below 600°C.

[0116] The Young's modulus of the glass used for strengthening is preferably 70 GPa or higher. A higher Young's modulus tends to result in less fragmentation when the strengthened glass breaks. Therefore, a Young's modulus of 75 GPa or higher is more preferred, and 80 GPa or higher is even more preferred. On the other hand, an excessively high Young's modulus tends to result in slow ion diffusion during chemical strengthening, making it difficult to obtain deep DOL (dielectric-to-glass) crystals. Therefore, a Young's modulus of 110 GPa or lower is preferred, 100 GPa or lower is more preferred, and 90 GPa or lower is even more preferred.

[0117] The Vickers hardness of the glass used for strengthening is preferably 575 or higher. The higher the Vickers hardness of the chemically strengthened glass, the easier it is for the Vickers hardness to increase after chemical strengthening, and the less likely it is to be damaged when dropped. Therefore, the Vickers hardness of the chemically strengthened glass is preferably 600 or higher, and more preferably 625 or higher.

[0118] It should be noted that the Vickers hardness after chemical strengthening is preferably 600 or higher, more preferably 625 or higher, and even more preferably 650 or higher.

[0119] A higher Vickers hardness reduces the likelihood of damage and is therefore preferred; however, the Vickers hardness of the glass used for strengthening is typically below 850. Glasses with excessively high Vickers hardness tend to have difficulty achieving sufficient ion exchange capacity. Therefore, a Vickers hardness of 800 or below is preferred, and more preferably below 750.

[0120] The preferred fracture toughness value of this reinforced glass is 0.7 MPa·m. 1 / 2 The higher the fracture toughness value, the more it suppresses the tendency for fragments to scatter when chemically strengthened glass breaks. A fracture toughness value of 0.75 MPa·m is more preferred. 1 / 2 The above is further preferably 0.8 MPa·m 1 / 2 above.

[0121] The fracture toughness value is typically 1 MPa·m 1 / 2 the following.

[0122] The average coefficient of thermal expansion (α) of this strengthened glass in the range of 50℃ to 350℃ is preferably 100×10⁻⁶. -7 Below ℃. A smaller average coefficient of thermal expansion (α) means the glass is less prone to warping during glass forming or cooling after chemical strengthening. A more preferred average coefficient of thermal expansion (α) is 95 × 10⁻⁶. -7 Below / ℃, further preferably 90×10 -7 / ℃ below.

[0123] To suppress warping of chemically strengthened glass, a smaller average coefficient of thermal expansion (α) is preferred, but it is typically 60 × 10⁻⁶. -7 / ℃ or above.

[0124] The viscosity of this reinforced glass reaches 10. 2 The temperature (T2) at dPa·s is preferably 1750°C or lower, more preferably 1700°C or lower, and even more preferably 1680°C or lower. T2 is typically 1400°C or higher.

[0125] The viscosity of this reinforced glass reaches 10. 4 The temperature (T4) at dPa·s is preferably 1350°C or lower, more preferably 1300°C or lower, and even more preferably 1250°C or lower. T4 is typically 1000°C or higher.

[0126] The liquidus temperature of chemically strengthened glass is preferably below (T4+50)°C. This is because such glass is easily manufactured using the float glass process. More preferably, the liquidus temperature is below (T4+25)°C, and even more preferably below T4°C.

[0127] Expressed as a mass percentage based on oxides, the glass for strengthening this application preferably contains: 50%–80% SiO2, 15%–25% Al2O3, 0%–10% B2O3, 2%–10% Li2O, 0%–10% Na2O, 0%–10% K2O, a total content of MgO, CaO, SrO, and BaO (MgO+CaO+SrO+BaO) of 0%–10%, and a total content of ZrO2 and TiO2 (ZrO2+TiO2) of 0%–5%.

[0128] Expressed as a mass percentage based on oxides, the glass for strengthening this application more preferably contains: 55% to 80% SiO2, 15% to 28% Al2O3, 0% to 10% B2O3, 2% to 10% Li2O, 0.5% to 10% Na2O and 0% to 10% K2O, the total content of MgO, CaO, SrO and BaO (MgO+CaO+SrO+BaO) is 0% to 10%, and the total content of ZrO2 and TiO2 (ZrO2+TiO2) is 0% to 5%.

[0129] Expressed as a mass percentage based on oxides, the glass for strengthening this product is further preferably composed of: 55%–75% SiO2, 15%–25% Al2O3, 0%–10% B2O3, 2%–10% Li2O, 1%–10% Na2O, 0.5%–10% K2O, 0%–10% (MgO+CaO+SrO+BaO), and 0%–5% (ZrO2+TiO2).

[0130] Such glass can easily achieve a preferred stress distribution through chemical strengthening treatment. The preferred glass composition is described below.

[0131] SiO2 is a component that forms the framework of glass. Furthermore, SiO2 is a component that improves chemical durability and reduces the formation of cracks when damage occurs on the glass surface. The SiO2 content is preferably 50% or more, more preferably 55% or more, and even more preferably 58% or more.

[0132] In addition, in order to improve the meltability of the glass, the SiO2 content is preferably 80% or less, more preferably 75% or less, and even more preferably 70% or less.

[0133] Al2O3 is an effective component for improving ion exchange capacity during chemical strengthening and increasing surface compressive stress after strengthening. It is also a component for increasing glass transition temperature (Tg) and Young's modulus. The content of Al2O3 is preferably 13% or more, and more preferably 15% or more.

[0134] In addition, in order to improve meltability, the Al2O3 content is preferably 28% or less, more preferably 26% or less, and even more preferably 25% or less.

[0135] B2O3 is not a necessary component, but it can be added to improve the meltability during glass manufacturing. When B2O3 is present, the content of B2O3 is preferably 0.5% or more, more preferably 1% or more, and even more preferably 2% or more.

[0136] Furthermore, the B2O3 content is preferably 10% or less, more preferably 5% or less, even more preferably 3% or less, and most preferably 1% or less. This prevents the formation of ripples during melting and avoids a decline in the quality of chemically strengthened glass. It should be noted that, to improve acid resistance, it is preferable to have virtually no B2O3.

[0137] Li₂O is a component that forms surface compressive stress through ion exchange. To increase the depth of the compressive stress layer (DOL), the content of Li₂O is preferably 2% or more, more preferably 3% or more, and even more preferably 4% or more.

[0138] In addition, in order to improve the chemical durability of the glass, the Li2O content is preferably 10% or less, more preferably 8% or less, and even more preferably 7% or less.

[0139] Na₂O is a component that forms a surface compressive stress layer through ion exchange using a potassium-containing molten salt, and it also improves the meltability of glass. The content of Na₂O is preferably 0.5% or more, more preferably 1% or more, and even more preferably 1.5% or more.

[0140] In addition, the Na2O content is preferably 10% or less, more preferably 8% or less, and even more preferably 6% or less.

[0141] K2O is not an essential component, but it can be included to improve the meltability of the glass and suppress devitrification. The K2O content is preferably 0.5% or more, and more preferably 1% or more.

[0142] In addition, in order to increase the compressive stress value generated by ion exchange, the K2O content is preferably 10% or less, more preferably 9% or less, and even more preferably 8% or less.

[0143] Alkali metal oxides such as Li₂O, Na₂O, and K₂O are all components that lower the melting temperature of glass, and it is preferable that the glass contains a total of 5% or more of alkali metal oxides such as Li₂O, Na₂O, and K₂O. The total content of Li₂O, Na₂O, and K₂O (Li₂O + Na₂O + K₂O) is preferably 5% or more, more preferably 7% or more, and even more preferably 8% or more.

[0144] To maintain the strength of the glass, the content of (Li2O+Na2O+K2O) is preferably 20% or less, more preferably 18% or less.

[0145] Alkaline earth metal oxides such as MgO, CaO, SrO, and BaO are all components that improve the melting properties of glass, but they tend to reduce ion exchange performance.

[0146] The total content of MgO, CaO, SrO and BaO (MgO+CaO+SrO+BaO) is preferably 10% or less, more preferably 5% or less.

[0147] In the case of containing any one of MgO, CaO, SrO, and BaO, MgO is preferred in order to improve the strength of chemically strengthened glass.

[0148] In the case of MgO, the MgO content is preferably 0.1% or more, more preferably 0.5% or more.

[0149] In addition, to improve ion exchange performance, the MgO content is preferably 10% or less, more preferably 5% or less.

[0150] In the case of CaO, the CaO content is preferably 0.5% or more, more preferably 1% or more. To improve ion exchange performance, the CaO content is preferably 5% or less, more preferably 1% or less, and even more preferably substantially free of CaO.

[0151] In the case of SrO, the SrO content is preferably 0.5% or more, more preferably 1% or more. To improve ion exchange performance, the SrO content is preferably 5% or less, more preferably 1% or less, and even more preferably substantially free of SrO.

[0152] In the case of BaO, the BaO content is preferably 0.5% or more, more preferably 1% or more. To improve ion exchange performance, the BaO content is preferably 5% or less, more preferably 1% or less, and even more preferably substantially free of BaO.

[0153] ZnO is a component that improves the meltability of glass and may be present in the glass. When ZnO is present, its 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 1% or less, and even more preferably substantially free of ZnO.

[0154] TiO2 is a component that suppresses the scattering of fragments when chemically strengthened glass breaks, and may contain TiO2. In the case of TiO2, the TiO2 content is preferably 0.1% or more. To suppress devitrification during melting, the TiO2 content is preferably 5% or less, more preferably 1% or less, and even more preferably substantially free of TiO2.

[0155] ZrO2 is a component that increases the surface compressive stress generated through ion exchange and may be present in the sample. When ZrO2 is present, its content is preferably 0.5% or more, more preferably 1% or more. Furthermore, to suppress devitrification during melting, the ZrO2 content is preferably 5% or less, more preferably 3% or less.

[0156] In addition, the content of TiO2 and ZrO2 (TiO2+ZrO2) is preferably 5% or less, more preferably 3% or less.

[0157] Y₂O₃, La₂O₃, and Nb₂O₅ are components that suppress the breakage of chemically strengthened glass, and the glass may contain Y₂O₃, La₂O₃, and Nb₂O₅. When these components are present, their respective contents are preferably 0.5% or more, more preferably 1% or more, further preferably 1.5% or more, particularly preferably 2% or more, and most preferably 2.5% or more.

[0158] Furthermore, the combined content of Y₂O₃, La₂O₃, and Nb₂O₅ is preferably 9% or less, more preferably 8% or less. In this case, the glass is less prone to devitrification during melting, preventing a decline in the quality of the chemically strengthened glass. Additionally, the content of each of Y₂O₃, La₂O₃, and Nb₂O₅ is preferably 3% or less, more preferably 2% or less, further preferably 1% or less, particularly preferably 0.7% or less, and most preferably 0.3% or less.

[0159] To suppress the breakage of chemically strengthened glass, it may contain a small amount of Ta2O5 and Gd2O3. However, due to the increase in refractive index and reflectivity, the content of Ta2O5 and Gd2O3 is preferably less than 1%, more preferably less than 0.5%, and even more preferably substantially free of Ta2O5 and Gd2O3.

[0160] To improve ion exchange performance, P2O5 may be included. When P2O5 is included, the P2O5 content is preferably 0.5% or more, more preferably 1% or more. To improve chemical durability, the P2O5 content is preferably 2% or less, more preferably substantially free of P2O5.

[0161] When coloring glass, coloring components can be added within a range that does not impede achieving the desired chemical strengthening properties. Examples of coloring components include Co3O4, MnO2, Fe2O3, NiO, CuO, Cr2O3, V2O5, Bi2O3, SeO2, TiO2, CeO2, Er2O3, and Nd2O3. They can be used alone or in combination.

[0162] The total content of the coloring components is preferably 7% or less. This helps to suppress devitrification of the glass. More preferably, the content of the coloring components is 5% or less, even more preferably 3% or less, and particularly preferably 1% or less. When it is desirable to improve the visible light transmittance of the glass, it is preferable that these components are substantially absent.

[0163] Additionally, SO3, chlorides, fluorides, etc., may be appropriately included as clarifying agents during glass melting. It is preferable that the glass does not contain substantially As2O3. When Sb2O3 is present, the Sb2O3 content is preferably 0.3% or less, more preferably 0.1% or less, and most preferably substantially free of Sb2O3.

[0164] It should be noted that the tempered glass is preferably a chemically tempered glass obtained by chemically strengthening the tempered glass with the above composition, and its basic composition is the same as that of the chemically tempered glass.

[0165] That is, for example, expressed as a mass percentage based on oxides, this tempered glass preferably contains: 55% to 80% SiO2, 15% to 28% Al2O3, 0% to 10% B2O3, 2% to 10% Li2O, 0.5% to 10% Na2O and 0% to 10% K2O, the total content of MgO, CaO, SrO and BaO (MgO+CaO+SrO+BaO) is 0% to 10%, and the total content of ZrO2 and TiO2 (ZrO2+TiO2) is 0% to 5%.

[0166] <Manufacturing Methods of Chemically Strengthened Glass>

[0167] Chemically strengthened glass is manufactured by chemically strengthening glass produced using conventional glass manufacturing methods.

[0168] Chemical strengthening is a process that involves ion exchange on the surface of glass to form a surface layer with compressive stress. Specifically, ion exchange is performed at a temperature below the glass transition temperature of the chemically strengthened glass, replacing metal ions with small ionic radii (typically Li or Na ions) present near the glass surface with ions with larger ionic radii (typically Na or K ions for Li ions, and K ions for Na ions).

[0169] This tempered glass can be manufactured, for example, by chemically strengthening a chemically strengthened glass having the above-described composition.

[0170] Chemically strengthened glass can be manufactured, for example, in the following manner. It should be noted that the following manufacturing method is an example of manufacturing sheet-shaped chemically strengthened glass.

[0171] For example, glass raw materials are blended to obtain glass with the preferred composition described above, and then heated and melted in a glass melting furnace. The glass is then homogenized by bubbling, stirring, adding a clarifying agent, etc., and formed into a glass sheet of a specified thickness using conventional forming methods, followed by slow cooling. Alternatively, it can be formed into a sheet by cutting it after forming it into a block and slow cooling.

[0172] Methods for forming glass sheets include, for example, float glass, pressing, fusion, and drawing. Float glass is particularly preferred when manufacturing large glass sheets. Other continuous forming methods besides float glass, such as fusion and drawing, are also preferred.

[0173] Then, the glass obtained by forming is ground and polished as needed to form a glass sheet. It should be noted that if the glass sheet is cut into a specified shape and size, or if the glass sheet is beveled, the cutting or beveling is performed before the chemical strengthening treatment described later, and a compressive stress layer is formed on the end face by the chemical strengthening treatment, which is therefore preferred.

[0174] The resulting glass plate is then chemically strengthened, cleaned, and dried to obtain chemically strengthened glass.

[0175] <Chemical Enhancement Treatment>

[0176] Chemical strengthening treatment involves contacting the glass with a metal salt (e.g., potassium nitrate) by means of immersion in a molten liquid containing metal ions with large ionic radii (typically Na or K ions), thereby replacing the metal ions with small ionic radii (typically Na or Li ions) in the glass with metal ions with large ionic radii (typically Na or K ions for Li ions, and K ions for Na ions).

[0177] To accelerate the chemical strengthening process, "Li-Na exchange," which involves exchanging Li ions with Na ions in the glass, is preferred. Furthermore, to generate large compressive stress through ion exchange, "Na-K exchange," which involves exchanging Na ions with K ions in the glass, is preferred.

[0178] Examples of molten salts used for chemical fortification treatment include nitrates, sulfates, carbonates, and chlorides. Examples of nitrates include lithium nitrate, sodium nitrate, potassium nitrate, cesium nitrate, and silver nitrate. Examples of sulfates include lithium sulfate, sodium sulfate, potassium sulfate, cesium sulfate, and silver sulfate. Examples of carbonates include lithium carbonate, sodium carbonate, and potassium carbonate. Examples of chlorides include lithium chloride, sodium chloride, potassium chloride, cesium chloride, and silver chloride. These molten salts can be used alone or in combination.

[0179] This tempered glass can be manufactured, for example, using the strengthening treatment method 1 or strengthening treatment method 2 described below.

[0180] (Enhanced processing method 1)

[0181] In strengthening treatment method 1, firstly, chemically strengthened glass containing Li₂O is brought into contact with a metal salt containing sodium (Na) ions (the first metal salt), thereby causing ion exchange between Na ions in the metal salt and Li ions in the glass. Hereinafter, this ion exchange treatment is sometimes referred to as "step 1 treatment".

[0182] In the first step of the process, for example, chemically strengthened glass is immersed in a metal salt containing Na ions (e.g., sodium nitrate) at a temperature of about 350°C to about 500°C for about 0.1 hours to about 24 hours. To improve productivity, the first step processing time is preferably 12 hours or less, more preferably 6 hours or less.

[0183] The first step of the process creates a deep compressive stress layer on the glass surface, resulting in a stress distribution with a CS exceeding 200 MPa and a DOL exceeding 1 / 8 of the plate thickness. Furthermore, a large D... 50M The absolute value of the slope of the stress distribution in the range of DOL / 4 to DOL / 2 corresponding to m1 in the glass that has undergone the first step of processing is greater than the absolute value of the slope of the stress distribution in the range of DOL / 2 to DOL in the glass that has undergone the first step of processing. Furthermore, the glass that has undergone the first step of processing has a large CT (Crystal Pressure), so it is prone to scattering fragments when broken. However, since the scattering of fragments is improved through subsequent processing, a large CT at this stage is actually preferred. The CT of the glass that has undergone the first step of processing is preferably 90 MPa or more, more preferably 100 MPa or more, and even more preferably 110 MPa or more. This is because, therefore, D... 50M It gets bigger.

[0184] The first metal salt is an alkali metal salt, and the most abundant alkali metal ion is Na ion. Li ions may also be present, but the content of Li ions is preferably 2% or less, more preferably 1% or less, and even more preferably 0.2% or less, relative to 100% of the molar amount of alkali metal ions in the first metal salt. Additionally, K ions may also be present. The content of K ions is preferably 20% or less, more preferably 5% or less, relative to 100% of the molar amount of alkali metal ions in the first metal salt.

[0185] Next, the glass that has undergone the first step treatment is brought into contact with a metal salt containing lithium (Li) ions (the second metal salt). Through ion exchange between the Li ions in the metal salt and the Na ions in the glass, the compressive stress near the surface is reduced. This treatment is sometimes referred to as the "second step treatment".

[0186] Specifically, for example, the sample is immersed in a metal salt containing Na and Li (e.g., a mixture of sodium nitrate and lithium nitrate) at a temperature of about 350°C to about 500°C for about 0.1 hours to about 24 hours. To improve productivity, the second step processing time is preferably 12 hours or less, more preferably 6 hours or less.

[0187] Through the second step of processing, the absolute value of the slope of the stress distribution within the range of DOL / 4 to DOL / 2 of m1 is less than the absolute value of the slope of the stress distribution within the range of DOL / 2 to DOL of m2. As a result, CT decreases. On the other hand, the second step of processing does not affect the stress curve of the deeper portion of the glass; therefore, D... 50M It will not be reduced by the second step of processing.

[0188] The glass that has undergone step 2 processing is able to maintain a large D-shape. 50M At the same time, it reduces internal tensile stress, preventing violent rupture upon fracture.

[0189] The second metal salt is an alkali metal salt, and preferably contains Na and Li ions as alkali metal ions. Nitrates are also preferred. The total molar percentage of Na and Li ions is preferably 50% or more, more preferably 70% or more, and even more preferably 80% or more, relative to 100% of the molar percentage of alkali metal ions in the second metal salt. By adjusting the Na / Li molar ratio, the stress distribution within the range of DOL / 4 to DOL / 2 can be controlled.

[0190] The optimal Na / Li molar ratio for the second metal salt varies depending on the glass composition, but is preferably 0.3 or higher, more preferably 0.5 or higher, and even more preferably 1 or higher. When the Na / Li ratio is too high, it becomes difficult to increase D while simultaneously reducing CT. 50M The Na / Li ratio is preferably 100 or less, more preferably 60 or less, and even more preferably 40 or less.

[0191] When the second metal salt is a sodium nitrate-lithium nitrate mixed salt, the mass ratio of sodium nitrate to lithium nitrate is preferably 25:75 to 99:1, more preferably 50:50 to 98:2, and more preferably 70:30 to 97:3.

[0192] Next, the glass that has undergone the second step treatment is brought into contact with a metal salt containing potassium (K) ions (the third metal salt). Through ion exchange between the K ions in the metal salt and the Na ions in the glass, a large compressive stress is generated on the glass surface. This ion exchange treatment is sometimes referred to as the "third step treatment".

[0193] Specifically, for example, the glass is immersed in a metal salt containing K ions (e.g., potassium nitrate) at a temperature of about 350°C to about 500°C for about 0.1 hours to about 10 hours. This step allows for the formation of large compressive stress in a region of 0 μm to about 10 μm on the glass surface.

[0194] Step 3 only increases the compressive stress in the shallow portion of the glass surface, having almost no effect on the interior, thus maintaining a large D. 50M Furthermore, it suppresses the formation of large compressive stress on the surface layer while maintaining internal tensile stress.

[0195] The third metal salt is an alkali metal salt. As an alkali metal ion, it may contain Li ions, but the Li ion content is preferably 2% or less, more preferably 1% or less, and even more preferably 0.2% or less, relative to 100% of the alkali metal atoms. In addition, the Na ion content is preferably 2% or less, more preferably 1% or less, and even more preferably 0.2% or less.

[0196] In the enhanced processing method 1, the total processing time for steps 1 to 3 is less than 24 hours, resulting in high productivity, which is preferred. More preferably, the total processing time is less than 15 hours, and even more preferably less than 10 hours.

[0197] (Enhanced processing method 2)

[0198] In strengthening treatment method 2, firstly, a first step treatment is performed in which chemically strengthened glass containing Li2O is brought into contact with a first metal salt containing sodium (Na) ions, thereby causing ion exchange between Na ions in the metal salt and Li ions in the glass.

[0199] The first step of the process is the same as the first reinforcement method, so the explanation is omitted.

[0200] Next, heat treatment is performed without allowing the glass that has undergone step 1 to come into contact with the metal salt. This is called step 2.

[0201] The second step of the treatment is performed, for example, by holding the glass that has undergone the first step treatment in the atmosphere at a temperature of 350°C or higher for a certain period of time. The holding temperature is below the strain point of the chemically strengthened glass, preferably below a temperature 10°C higher than the temperature of the first step treatment, and more preferably the same as the temperature of the first step treatment.

[0202] It is believed that by using this treatment, the alkali metal ions introduced into the glass surface through the first step of the treatment undergo thermal diffusion, thereby reducing the CT.

[0203] Next, the glass that has undergone the second step treatment is brought into contact with a third metal salt containing potassium (K) ions. Through ion exchange between the K ions in the metal salt and the Na ions in the glass, a large compressive stress is generated on the glass surface. This ion exchange treatment is sometimes referred to as the "third step treatment".

[0204] The third step is the same as the first step of the enhancement process, so the explanation is omitted.

[0205] In enhanced processing method 2, high productivity is preferred because the total processing time for steps 1 to 3 can be less than 24 hours. More preferably, the total processing time is less than 15 hours, and even more preferably less than 10 hours.

[0206] According to the strengthening treatment method 1, stress distribution can be precisely controlled by adjusting the composition of the second metal salt used in the second step of the treatment and the treatment temperature.

[0207] According to strengthening treatment method 2, chemically strengthened glass with excellent properties can be obtained at low cost through a relatively simple process.

[0208] Regarding the processing conditions for chemical strengthening treatment, the appropriate time and temperature should be selected by considering the characteristics and composition of the glass, the type of molten salt, etc.

[0209] The chemically strengthened glass of this invention is particularly useful as protective glass for use in mobile devices such as mobile phones and smartphones. Furthermore, it is also useful as protective glass for display devices such as televisions, personal computers, and touch panels that are not intended for portability; elevator walls; and walls of buildings such as houses or buildings (full-screen displays). Additionally, it is useful as building materials such as window glass; desktops; interior decorations for automobiles or aircraft; or protective glass for these applications; and in casings with curved shapes.

[0210] Example

[0211] The present invention will be described below through examples, but the present invention is not limited thereto.

[0212] The glass raw materials were prepared to obtain the compositions of glass 1, 2, 4 to 8, expressed as oxide-based mass percentages as shown in Table 2, and weighed in such a way that the glass content reached 1000g. Next, the mixed raw materials were placed in a platinum crucible and melted in an electric furnace at 1500°C to 1700°C for about 3 hours to remove bubbles and homogenize.

[0213] The molten glass obtained was poured into a mold and held at (glass transition temperature + 50) °C for 1 hour, then cooled to room temperature at a rate of 0.5 °C / min to obtain a glass block. The obtained glass block was cut, ground, and finally mirror-polished on both sides to obtain a glass plate with a thickness (t) of 800 μm. In addition, glass 3 was manufactured using the float glass process.

[0214] The following properties were evaluated on the obtained glass.

[0215] Average linear expansion coefficient (α) (×10) -7 The glass transition temperature (Tg) (°C) and the glass transition temperature (T4) (°C) were determined according to JIS R 3102 (1995), "Test method for mean linear expansion coefficient of glass". Young's modulus (E) (GPa) was determined using the ultrasonic pulse method (JIS R1602 (1995)). T4 (°C) and T2 (°C) were determined using a rotational viscometer according to ASTM C 965-96 (2012).

[0216] Liquid phase temperature (T) L )>

[0217] The glass before chemical strengthening is crushed, graded using sieves with 4mm and 2mm apertures, washed, and then dried to obtain glass shards. 2-5g of the glass shards are placed in a platinum dish and kept in an electric furnace at a controlled temperature for 17 hours. Afterward, they are removed and cooled to room temperature. The presence of devitrification is then observed using a polarizing microscope. This process is repeated, and the average of the highest temperature at which devitrification was observed (T1) and the lowest temperature at which no devitrification was observed (T2) is taken as T0. L However, it should be done in a way that keeps the difference between T1 and T2 within 20°C.

[0218] Table 2

[0219] Glass 1 Glass 2 Glass 3 Glass 4 Glass 5 Glass 6 Glass 7 Glass 8 SiO2 68.6 59.2 60.9 62.5 61.1 59.8 60.4 57.4 Al2O3 16.6 22.7 12.8 18.0 19.5 20.9 19.5 24.2 B2O3 0.0 0.0 0.0 0.0 7.4 Li2O 4.9 6.3 5.3 5.2 5.2 5.2 3.2 <![CDATA[Na2O]]> 3.0 1.9 12.2 2.8 2.8 2.7 2.8 3.9 <![CDATA[K2O]]> 1.5 7.3 5.9 6.2 6.1 6.1 6.2 0.1 MgO 3.3 0.6 6.7 3.2 3.1 3.1 3.8 0.6 CaO 0.1 0.2 0.2 0.2 0.2 1.3 SrO 0.2 0.0 0.0 0.0 0.0 1.8 BaO 0.2 0.0 0.0 0.0 0.0 0 <![CDATA[ZrO2]]> 2.0 1.9 1.0 2.0 2.0 1.9 2.0 0 <![CDATA[TiO2]]> 0.0 0.0 0.0 0.0 0 Tg 586 534 604 543 552 562 552 α 63 87 98 82 82 82 83 E 84 84 74 82 82 83 83 75 <![CDATA[T2]]> 1675 1620 1601 1592 1581 1579 1554 1625 <![CDATA[T4]]> 1211 1150 1176 1135 1139 1145 1122 1220 <![CDATA[T L ]]> 1195 1150 1150 1087 1175 No rating 1142 1110

[0220] Chemically strengthened glasses, as described in Examples 1 to 12 below, were prepared using glass 1 to 8 and evaluated. It should be noted that Examples 1 to 3 and 8 to 12 are exemplary cases, while Examples 4 to 7 are comparative examples.

[0221] (Example 1)

[0222] The glass plate 1 was immersed in sodium nitrate at 450°C for 3 hours. Next, it was immersed in a sodium nitrate-lithium nitrate mixed salt solution (mass ratio 85:15) at 375°C for 3 hours. Then, it was immersed in potassium nitrate at 400°C for 1 hour, thus obtaining a chemically strengthened glass plate (total strengthening time 7 hours).

[0223] (Example 2)

[0224] The glass plate 1 was immersed in sodium nitrate at 450°C for 3 hours, and then kept at 450°C in the atmosphere for 3 hours, instead of immersion in a sodium nitrate-lithium nitrate mixed salt as in Example 1. Otherwise, a chemically strengthened glass plate was obtained in the same manner as in Example 1 (total strengthening time was 7 hours).

[0225] (Example 3)

[0226] Glass 2 was immersed in sodium nitrate at 450°C for 3 hours, then kept at 450°C in the atmosphere for 3 hours, and then immersed in potassium nitrate at 400°C for 0.5 hours to obtain chemically strengthened glass (total strengthening time was 6.5 hours).

[0227] (Example 4)

[0228] Glass 1 was immersed in a potassium nitrate-sodium nitrate mixed salt (mass ratio 90:10) at 450°C for 1.5 hours to obtain a chemically strengthened glass plate (total strengthening time was 1.5 hours).

[0229] (Example 5)

[0230] The glass plate 1 was immersed in sodium nitrate at 450°C for 2 hours, followed by immersion in potassium nitrate at 450°C for 4 hours, thus obtaining a chemically strengthened glass plate (total strengthening time was 6 hours).

[0231] (Example 6)

[0232] The glass plate 1 was immersed in sodium nitrate at 450°C for 3 hours, followed by immersion in potassium nitrate at 400°C for 1 hour, thus obtaining a chemically strengthened glass plate (total strengthening time was 4 hours).

[0233] (Example 7)

[0234] Glass 3 was immersed in potassium nitrate at 450°C for 4 hours, then kept at 500°C in the atmosphere for 5 hours, and then immersed in potassium nitrate at 400°C for 15 minutes to obtain a chemically strengthened glass plate (total strengthening time was 9.25 hours).

[0235] (Example 8)

[0236] The glass plate 4 was immersed in sodium nitrate at 450°C for 4 hours, then kept at 450°C in the atmosphere for 1 hour, and then immersed in potassium nitrate at 400°C for 1 hour to obtain a chemically strengthened glass plate (total strengthening time was 6 hours).

[0237] (Examples 9~11)

[0238] The glass plates listed in Table 4 were each immersed in sodium nitrate at 450°C for 4 hours, then kept in the atmosphere at 450°C for 3 hours, and then immersed in potassium nitrate at 400°C for 1 hour to obtain chemically strengthened glass plates (total strengthening time was 8 hours).

[0239] (Example 12)

[0240] Glass plate 8 was immersed in sodium nitrate at 450°C for 3 hours, then kept at 450°C in the atmosphere for 1 hour, and then immersed in potassium nitrate at 450°C for 1 hour to obtain chemically strengthened glass plate (total strengthening time is 5 hours).

[0241] The chemically strengthened glass plates of Examples 1 to 12 were evaluated as follows.

[0242] [Stress Distribution]

[0243] Stress values ​​were measured using an FSM-6000 surface stress meter manufactured by Orihara Seisakusho and an SLP1000 measuring instrument manufactured by Orihara Seisakusho that utilizes photoelasticity based on scattered light. The measurement results for chemically strengthened glass 1, 3, 5, 7, and 12 are shown below. Figure 1 , 2 In figures 3, 4, and 5, the depth at the location indicated by arrow c (where the compressive stress value is 0) is DOL [unit: μm]. Additionally, the compressive stress values ​​(CS1 [unit: MPa]) at depths reaching DOL / 4 (indicated by arrow a), (CS2 [unit: MPa] at depths reaching DOL / 2 (indicated by arrow b), (CS0 [unit: MPa] at the glass surface (where the depth is 0), and (CS3 [unit: MPa] at a depth of 2.5 μm) are also recorded.

[0244] Based on these results, calculate m1 [unit: MPa / μm], m2 [unit: MPa / μm], m3 [unit: MPa / μm] and m1 / m2 using the following formula.

[0245] m1 = (CS1 - CS2) / (DOL / 4 - DOL / 2)

[0246] m2 = CS2 / (DOL / 2 - DOL)

[0247] m3 = (CS0 - CS3) / 2.5

[0248] Additionally, the maximum depth (D) when the CS reaches 50 MPa or higher. 50M [Unit: μm] and tensile stress (CT) at a depth of (t×1 / 2) [Unit: MPa].

[0249] [Asphalt Drop Strength Test]

[0250] A chemically strengthened glass plate was used as the protective glass for a smartphone, mounted on a simulated smartphone casing, and then dropped onto a flat asphalt surface. The combined mass of the chemically strengthened glass plate and the casing was approximately 140g.

[0251] The test begins at a height of 30 cm. If the chemically strengthened glass plate does not break, the height is increased by 10 cm and the test is repeated, recording the height at which it breaks [unit: cm]. This test is considered a group, and 10 groups are repeated. The average height at which it breaks is taken as the "drop height" (cm).

[0252] The blank columns in Tables 3 and 4 indicate that no measurements were taken.

[0253] [Fragmentation Count]

[0254] Using a diamond indenter with a relative angle of 90 degrees, a 20mm square chemically strengthened glass plate is broken by pressing it with an indenter bearing a load of 3kgf to 10kgf for 15 seconds. The number of fragments of the chemically strengthened glass after breakage is then determined.

[0255]

[0256]

[0257] Example 1, with its preferred stress distribution, exhibits excellent asphalt drop resistance and a low number of fractures. For Examples 4 and 5, with their large m1 / m2 ratios, although CS1 and CS2 are large, the asphalt drop strength is poor. For Example 6, with its small m1 and m2 ratios, severe fracture occurs due to a large CT ratio. Example 7, with its small DOL ratio, exhibits low asphalt drop strength.

[0258] In addition, although Examples 2, 3 and 8-12 are embodiments in which the strengthening conditions or glass composition have been changed relative to Example 1, they are the same as Example 1, with a preferred stress distribution, and high asphalt drop strength can be expected.

[0259] The present invention has been described in detail with reference to specific embodiments, but various changes or modifications can be made without departing from the spirit and scope of the invention, which will be apparent to those skilled in the art. This application is based on Japanese patent applications filed on June 28, 2017 (Japanese Patent Application No. 2017-126357) and October 26, 2017 (Japanese Patent Application No. 2017-207310), the contents of which are incorporated herein by reference.

Claims

1. A chemically strengthened glass, which is a plate-shaped chemically strengthened glass having a compressive stress layer on its surface, wherein, The compressive stress (CS0) on the surface of the chemically strengthened glass is above 500 MPa. The thickness (t) of the chemically strengthened glass is 400 μm or more. The compressive stress layer depth (DOL) of the chemically strengthened glass is greater than (t×0.15) μm. The compressive stress (CS1) at a depth of 1 / 4 of the DOL, measured from the glass surface, is 50 MPa or more. The compressive stress (CS2) at a depth of 1 / 2 of the DOL, measured from the glass surface, is 50 MPa or more. The following formula represents m1 as being greater than or equal to -1.5 MPa / μm and less than or equal to 0.5 MPa / μm, and the following formula represents m2 as being less than or equal to 0 MPa / μm, wherein m2 is less than m1. m1=(CS1-CS2) / (DOL / 4-DOL / 2) m2 = CS2 / (DOL / 2 - DOL) The m3 expressed by the following formula is related to the compressive stress value (CS3) at a depth of 2.5 μm from the glass surface and is greater than or equal to 150 MPa / μm. m3 = (CS0 - CS3) / 2.5 The basic composition of the chemically strengthened glass, expressed as a mass percentage based on oxides, contains: 58%–70% SiO2, 15%–25% Al2O3, 0%~5% B2O3, 3%–8% Li2O, 1%–6% Na2O, 1%–8% K2O, 0.5%–5% MgO, 0%–5% (MgO+CaO+SrO+BaO), and 0% to 3% (ZrO2 + TiO2).

2. A chemically strengthened glass, which is a plate-shaped chemically strengthened glass having a compressive stress layer on its surface, wherein, The compressive stress (CS0) on the surface of the chemically strengthened glass is above 500 MPa. The compressive stress layer depth (DOL) of the chemically strengthened glass is 100 μm or more. The compressive stress (CS1) at a depth of 1 / 4 of the DOL, measured from the glass surface, is 50 MPa or more. The compressive stress (CS2) at a depth of 1 / 2 of the DOL, measured from the glass surface, is 50 MPa or more. The following formula represents m1 as being greater than or equal to -1.5 MPa / μm and less than or equal to 0.5 MPa / μm, and the following formula represents m2 as being less than or equal to 0 MPa / μm, wherein m2 is less than m1. m1=(CS1-CS2) / (DOL / 4-DOL / 2) m2 = CS2 / (DOL / 2 - DOL) The m3 expressed by the following formula is related to the compressive stress value (CS3) at a depth of 2.5 μm from the glass surface and is greater than or equal to 150 MPa / μm. m3 = (CS0 - CS3) / 2.5 The basic composition of the chemically strengthened glass, expressed as a mass percentage based on oxides, contains: 58%–70% SiO2, 15%–25% Al2O3, 0%~5% B2O3, 3%–8% Li2O, 1%–6% Na2O, 1%–8% K2O, 0.5%–5% MgO, 0%–5% (MgO+CaO+SrO+BaO), and 0% to 3% (ZrO2 + TiO2).

3. The chemically strengthened glass as described in claim 1 or 2, wherein, The maximum depth of the chemically strengthened glass when the compressive stress value is 50 MPa or more is related to the DOL and is (0.55 × DOL) μm or more.

4. The chemically strengthened glass as described in claim 1 or 2, wherein, The m3 is above 180 MPa / μm.

5. The chemically strengthened glass as described in claim 1 or 2, wherein, The m3 is above 200 MPa / μm.

6. The chemically strengthened glass as described in claim 1 or 2, wherein, The m3 is above 220 MPa / μm.

7. The chemically strengthened glass as described in claim 1 or 2, wherein, The value of m1 is below -0.2 MPa / μm.

8. The chemically strengthened glass as described in claim 1 or 2, wherein, The ratio of m1 to m2 (m1 / m2) is 0.1 or higher.

9. The chemically strengthened glass as described in claim 1 or 2, wherein, The internal tensile stress value of the chemically strengthened glass is less than 100 MPa.

10. The chemically strengthened glass according to claim 1 or 2, wherein, The basic composition of the chemically strengthened glass, expressed as a mass percentage based on oxides, contains: 0%–5% CaO, and 0% to 5% BaO.

11. The chemically strengthened glass as described in claim 1 or 2, wherein, The basic composition of the chemically strengthened glass, expressed as a mass percentage based on oxides, contains: 0.5% to 3% ZrO2.

12. The chemically strengthened glass as described in claim 1 or 2, wherein, The basic composition of the chemically strengthened glass, expressed as a mass percentage based on oxides, contains: 5% to 18% (Li2O+Na2O+K2O).

13. A method for manufacturing chemically strengthened glass according to any one of claims 1 to 12, comprising the following steps: Ion exchange is achieved by contacting chemically strengthened glass containing Li₂O with a metal salt containing Na ions. Next, ion exchange occurs through contact with a metal salt containing Li ions, wherein the Na / Li molar ratio in the Li ion-containing metal salt is 0.3 or more and 60 or less. Next, ion exchange occurs through contact with a metal salt containing K ions. The chemically strengthened glass, expressed as a mass percentage based on oxides, contains: 58%–70% SiO2, 15%–25% Al2O3, 0%~5% B2O3, 3%–8% Li2O, 1%–6% Na2O, 1%–8% K2O, 0.5%–5% MgO, 0%–5% (MgO+CaO+SrO+BaO), and 0% to 3% (ZrO2 + TiO2).

14. The method for manufacturing chemically strengthened glass as described in claim 13, wherein, The chemically strengthened glass, expressed as a mass percentage based on oxides, contains: 0%–5% CaO, and 0% to 5% BaO.

15. The method for manufacturing chemically strengthened glass as described in claim 13 or 14, wherein, The chemically strengthened glass, expressed as a mass percentage based on oxides, contains: 0.5% to 3% ZrO2.

16. The method for manufacturing chemically strengthened glass as described in claim 13 or 14, wherein, The chemically strengthened glass, expressed as a mass percentage based on oxides, contains: 5% to 18% (Li2O+Na2O+K2O).

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