Glass sheet, display device, and method for manufacturing glass sheet

Abstract

The present invention relates to a glass sheet comprising a first main surface, a second main surface, and an end surface connecting the first main surface and the second main surface, having a compressive stress layer, the length of the longest crack in a region from a position 9% of the thickness away from the end of the first main surface side of the end surface toward the second main surface side to a position 91% of the thickness away from the end of the first main surface side of the end surface toward the second main surface side is 5 μm to 20 μm, and the length of the longest crack in a region from the end of the second main surface side of the end surface to a position 6% of the thickness away from the end of the second main surface side of the end surface toward the first main surface side satisfies a specific formula.

Description

Technical Field

[0001] This invention relates to a glass plate, a display device, and a method for manufacturing a glass plate. Background Technology

[0002] In display devices mounted in vehicles, a glass panel (cover glass) is sometimes provided to cover the display surface. Such glass panels are sometimes ground on their end faces (side faces) to improve impact resistance. Patent Document 1 describes a cover glass in which the surface roughness Ra of the chamfered portion of the surface side exceeds 100 nm, and the surface roughness Ra of the chamfered portion of the back side is less than 100 nm.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: International Publication No. 2017 / 208995 Summary of the Invention

[0006] However, if the grinding degree of the end face is large, although the impact resistance is improved, the dimensional change before and after grinding may be too large, or the grinding time may be too long. Therefore, there is a need for a glass plate that is not limited to the above-mentioned applications in automotive display devices, which can suppress excessive dimensional change before and after grinding, excessive grinding time, and also suppress the reduction of impact resistance.

[0007] The present invention was made in view of the above-mentioned problems, and aims to provide a glass plate, a display device, and a method for manufacturing the glass plate that both suppresses excessive dimensional changes before and after grinding, excessive grinding time, and suppresses the reduction of impact resistance.

[0008] To address the aforementioned issues and achieve the objective, the glass plate disclosed herein comprises a first main surface, a second main surface, and an end face connecting the first main surface and the second main surface, and has a compressive stress layer. In at least a portion of the area surrounding the main surface of the glass plate, on the end face, from a position extending 9% of the thickness of the glass plate along the thickness direction of the end face towards the second main surface from the end face on the first main surface side, to a position extending 91% of the thickness of the glass plate from the end face on the first main surface side towards the second main surface side, the longest crack has a length of 5 μm to 20 μm in the direction perpendicular to the surface where the crack is formed.

[0009] The longest crack in the region from the end of the second main surface of the aforementioned end face to a position 6% of the thickness of the glass plate away from the first main surface of the aforementioned end face along the thickness direction of the aforementioned glass plate is less than a in the direction perpendicular to the surface where the crack is formed, satisfying the following formula (A).

[0010]

[0011] Where a is the crack length (μm), K IC Fracture toughness value (MPa·m) 0.5 F is the correction coefficient for the stress intensity factor, which is 1.1215, and f(x) is the compressive stress (MPa) acting on the glass plate at a depth x from the second main surface.

[0012] In order to solve the above-mentioned problems and achieve the purpose, the display device of this disclosure has the above-mentioned glass plate.

[0013] To solve the aforementioned problems and achieve the objective, the present disclosure discloses a method for manufacturing a glass plate comprising a first main surface, a second main surface, and an end face connecting the first main surface and the second main surface, and having a compressive stress layer. The method includes the following steps: on the end face of at least a portion of the periphery of the main surface of the glass plate, a length of 9% of the thickness of the glass plate is extended from the end face of the end face towards the second main surface along the thickness direction of the glass plate, from the end face of the first main surface towards the second main surface. The region is polished in such a manner that the longest crack in the region, extending from the end of the second main surface of the end face to the position 6% of the thickness of the glass plate along the thickness direction of the glass plate toward the first main surface, has a length perpendicular to the surface where the crack is formed, and the region is polished in such a manner that the longest crack in the region, extending from the end of the second main surface of the end face toward the first main surface, has a length perpendicular to the surface where the crack is formed, is less than a in the manner that satisfies formula (A) below.

[0014]

[0015] According to the present invention, it is possible to suppress excessive dimensional changes before and after grinding, as well as excessive grinding time, and to suppress the reduction of impact resistance. Attached Figure Description

[0016] Figure 1 This is a schematic diagram illustrating the vehicle-mounted display of this embodiment.

[0017] Figure 2This is a schematic diagram of the glass plate in this embodiment.

[0018] Figure 3 This is a graph showing an example of stress distribution along the thickness direction of a glass plate.

[0019] Figure 4 This is a graph illustrating an example of the relationship between crack length and fracture stress.

[0020] Figure 5 This is a diagram showing the shape of a test piece for the DCDC method.

[0021] Figure 6 It is K I A schematic diagram of the -V curve.

[0022] Figure 7 This is a diagram illustrating an example of how the distance from the second principal surface affects the bending stress and allowable crack length of the glass plate.

[0023] Figure 8 This is a diagram used to illustrate the crack length on the end face of the glass plate in this embodiment.

[0024] Figure 9 This is a diagram used to illustrate the crack length on the end face of a glass plate in other examples of this embodiment.

[0025] Figure 10 This is a diagram used to illustrate the crack length on the end face of a glass plate in other examples of this embodiment.

[0026] Figure 11 This is a cross-sectional schematic diagram of the glass plate and the functional membrane.

[0027] Figure 12 This is a graph showing the evaluation results of the intensity of each example. Detailed Implementation

[0028] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings. It should be noted that the invention is not limited to these embodiments; furthermore, when there are multiple embodiments, embodiments combining these embodiments are also included. Additionally, numerical values ​​include rounding ranges.

[0029] (In-vehicle display)

[0030] Figure 1 This is a schematic diagram illustrating the vehicle-mounted display of this embodiment. (As shown) Figure 1 As shown, the glass plate 10 of this embodiment is disposed in the vehicle display 2 and used as a cover material for the surface of the vehicle display.

[0031] The in-vehicle display 2 is a display device installed in a vehicle, for example, located inside the vehicle in front of the steering shaft 1. The in-vehicle display 2 displays various instruments such as a car navigation screen 3, a speedometer 4, and a start button 5. However, Figure 1 As an example, the automotive display 2 using the glass plate 10 can be configured in any way. Furthermore, the glass plate 10 is not limited to being used as a cover material for the surface of an automotive display; it can also be used for any other purpose.

[0032] (glass plate)

[0033] (The shape of the glass plate)

[0034] Figure 2 This is a schematic diagram of the glass plate in this embodiment. (As shown) Figure 2 As shown, the glass plate 10 in this embodiment is a transparent plate-shaped component. It should be noted that transparency here means that visible light can pass through. Hereinafter, one main surface of the glass plate 10 is designated as main surface 10A, the main surface opposite to main surface 10A is designated as main surface 10B, and the direction along the thickness direction of the glass plate 10 from main surface 10B toward main surface 10A is designated as the Z direction.

[0035] Figure 2 In the example, although the glass plate 10 appears as a rectangular flat plate when viewed from the Z direction, its shape can be arbitrary. For example, the glass plate 10 is not limited to being rectangular when viewed from the Z direction; it can also be a polygon, a circle, or an ellipse, etc. Furthermore, the glass plate 10 can also be a shape formed by bending a flat plate.

[0036] The glass panel 10 is mounted on the vehicle display 2 with the main surface 10A being the outer side (the side exposed to the outside) and the main surface 10B being the inner side (the side not exposed to the outside) of the vehicle display 2.

[0037] Here, the surface connecting the main surface 10A and the main surface 10B of the glass plate 10 is designated as the end surface 10C. The end surface 10C can also be referred to as the side surface of the glass plate 10, or the outer peripheral surface of the glass plate 10 with the Z direction as the axial direction. The end surface 10C includes a tapered surface 10C1 and a side surface 10C2.

[0038] The end face 10C can be a face formed by chamfering or a face formed by cutting. It should be noted that the end face 10C has a shape that includes a tapered face 10C1 and a side face 10C2, covering the entire circumferential area of ​​the glass plate 10 when viewed from the Z direction.

[0039] Side surface 10C2 is the surface that includes the portion of end face 10C that protrudes radially outward from the glass plate 10. Side surface 10C2 is connected to the surface of glass plate 10 via tapered face 10C1. That is, one end of tapered face 10C1 in the Z direction is connected to side surface 10C2, and the other end is connected to the surface (main surface) of glass plate 10.

[0040] More specifically, the conical face 10C1 is formed on both sides of the side surface 10C2 in the Z direction. That is, the end faces 10C are arranged in the Z direction to form one conical face 10C1, one side surface 10C2, and another conical face 10C1.

[0041] Furthermore, the end of one conical face 10C1 opposite to the Z direction is connected to the main surface 10B of the glass plate 10, and the end in the Z direction is connected to the side surface 10C2. In addition, the end of another conical face 10C1 opposite to the Z direction is connected to the side surface 10C2, and the end in the Z direction is connected to the main surface 10A of the glass plate 10.

[0042] like Figure 2 As shown, when viewed from a direction orthogonal to the Z direction, the tapered face 10C1 is inclined relative to the Z direction. The tapered face 10C1 is inclined in such a way that it tends toward the radially inward side of the glass plate 10 as it moves from the side 10C2 toward the surface side of the glass plate 10.

[0043] exist Figure 2 In the example, when viewed from a direction orthogonal to the Z direction, the tapered face 10C1 is inclined in a straight line relative to the Z direction. That is, the tapered face 10C1 is a so-called C-bevel portion. However, the tapered face 10C1 is not limited to a C-bevel; for example, it can also be a so-called R-bevel that is inclined in a curved shape relative to the Z direction.

[0044] As described above, the end face 10C is a shape consisting of a tapered face 10C1 on the main face 10A side, a side face 10C2, and a tapered face 10C1 on the main face 10B side, but the shape of the end face 10C is not limited to this.

[0045] For example, the end face 10C may not form a tapered face 10C1 on both sides of the main face 10A and the main face 10B, but may form a shape by forming a tapered face 10C1 on at least one side of the main face 10A and the main face 10B.

[0046] Furthermore, when tapered surfaces 10C1 are formed on both sides of the main surface 10A and the main surface 10B, the tapered surfaces 10C1 on the main surface 10A and the tapered surfaces 10C1 on the main surface 10B can be the same shape or different shapes.

[0047] Alternatively, for example, the end face 10C may also be a shape that does not include the tapered face 10C1. When the end face 10C is a shape that does not include the tapered face 10C1, it may be a planar shape or an R-shaped shape that is inclined in a curved manner relative to the Z direction (the end face as a whole is an R-shaped shape).

[0048] The thickness D of the glass plate 10 is preferably 0.5 mm to 3.0 mm, more preferably 0.7 mm to 2.0 mm, even more preferably 1.1 mm to 2.0 mm, and particularly preferably 1.1 mm to 1.3 mm. The thickness D of the glass plate 10 refers to the length in the Z direction from the main surface 10A to the main surface 10B. By keeping the thickness D within this range, rigidity can be appropriately improved.

[0049] (The material of the glass plate)

[0050] The material of the glass plate 10 is arbitrary; it can be amorphous glass or crystallized glass with crystals on its surface or inside.

[0051] Examples of glass plates 10 include alkali-free glass, soda-lime glass, soda-lime silicate glass, aluminosilicate glass, borosilicate glass, lithium aluminosilicate glass, and borosilicate glass.

[0052] For proper chemical strengthening, the material of the glass plate 10 is preferably alkali glass. Furthermore, aluminosilicate glass or lithium aluminosilicate glass, which are easily strengthened to produce thin but high-strength glass even when thin, are preferred for the glass plate 10. Chemically strengthened glass based on aluminosilicate glass (e.g., "Dragontrail" manufactured by AGC, a registered trademark) may also be used appropriately. It should be noted that chemical strengthening is typically performed by immersing the glass in a molten salt containing an alkali metal.

[0053] (Composition of glass)

[0054] The glass plate 10, based on the mole percentage of oxides, may contain 50%–80% SiO2, 1%–20% Al2O3, and 6%–20% Na2O. Additionally, the glass plate 10, based on the mole percentage of oxides, may contain 50%–80% SiO2, 0.1%–25% Al2O3, 3%–30% Li2O+Na2O+K2O, 0%–25% MgO, 0%–25% CaO, and 0%–5% ZrO2. Furthermore, the glass plate 10, based on the mole percentage of oxides, may contain 50%–80% SiO2, 1%–20% Al2O3, 6%–20% Na2O, 0%–11% K2O, 0%–15% MgO, 0%–6% CaO, and 0%–5% ZrO2.

[0055] It should be noted that the numerical range indicated by "~" represents the range of values ​​before and after "~" as the lower and upper limits. For example, 50% to 80% here refers to 50% to 80% when the total molar percentage of glass plate 10 is set to 100%, and the same applies to other numerical ranges. Similarly, Li₂O + Na₂O + K₂O refers to the total content of Li₂O, Na₂O, and K₂O, and the same applies to other cases using "+".

[0056] More specifically, the following glass compositions can be cited as preferred compositions for glass plate 10. It should be noted, for example, that "containing 0% to 25% MgO" means that MgO may be contained in 25% or less, although it is not essential. Glass (i) is composed of soda-lime silicate glass, glass (ii) and (iii) is composed of aluminosilicate glass, and glass (iv) and (v) is composed of lithium aluminosilicate glass.

[0057] (i) A glass containing, in mole percent based on oxides, 63%–73% SiO2, 0.1%–5.2% Al2O3, 10%–16% Na2O, 0%–1.5% K2O, 0%–5% Li2O, 5%–13% MgO and 4%–10% CaO.

[0058] (ii) A glass containing, in mole percent (based on oxides) 50%–74% SiO2, 1%–10% Al2O3, 6%–14% Na2O, 3%–11% K2O, 0%–5% Li2O, 2%–15% MgO, 0%–6% CaO and 0%–5% ZrO2, with the total content of SiO2 and Al2O3 being less than 75%, the total content of Na2O and K2O being 12%–25%, and the total content of MgO and CaO being 7%–15%.

[0059] (iii) A glass containing 68%–80% SiO2, 4%–10% Al2O3, 5%–15% Na2O, 0%–1% K2O, 0%–5% Li2O, 4%–15% MgO and 0%–1% ZrO2, expressed as mol% based on oxides.

[0060] (iv) Glass containing, in mole percent (based on oxides) 67%–75% SiO2, 0%–4% Al2O3, 7%–15% Na2O, 1%–9% K2O, 0%–5% Li2O, 6%–14% MgO and 0%–1.5% ZrO2, with a total SiO2 and Al2O3 content of 71%–75%, a total Na2O and K2O content of 12%–20%, and less than 1% CaO when present.

[0061] (v) Glass with a composition, expressed as mol% based on oxides, containing 56%–73% SiO2, 10%–24% Al2O3, 0%–6% B2O3, 0%–6% P2O5, 2%–7% Li2O, 3%–11% Na2O, 0%–5% K2O, 0%–8% MgO, 0%–2% CaO, 0%–5% SrO, 0%–5% BaO, 0%–5% ZnO, 0%–2% TiO2, and 0%–4% ZrO2.

[0062] (Compressive stress layer)

[0063] The glass plate 10 includes a compressive stress layer 12. The compressive stress layer 12 is formed over the entire surface of the glass plate 10, specifically on the main surfaces 10A and 10B and the end surface 10C. The compressive stress layer 12 is formed in the glass plate 10 through a chemical strengthening treatment.

[0064] It should be noted that the glass plate 10 is not limited to forming a compressive stress layer 12 on the main surface 10A, the main surface 10B and the end surface 10C. It may also form a compressive stress layer 12 on at least one of the main surface 10A, the main surface 10B and the end surface 10C (preferably at least the main surface 10B).

[0065] Figure 3 This is a graph illustrating an example of stress distribution along the thickness direction of the glass plate. The compressive stress layer 12 is the layer within the glass plate where compressive stress exerts its effect. (As shown...) Figure 3 As shown in the example, the compressive stress S on the surface of the glass plate plays a role, and the compressive stress decreases as it moves toward the center of the thickness direction of the glass plate.

[0066] Figure 3 In the example, the compressive stress layer 12 can be described as the portion of the entire glass plate from the surface to the depth where the stress is zero. It should be noted that tensile stresses exert their effects in layers deeper than the depth where the stress is zero. Hereinafter, the compressive stress acting on the surface of the glass plate 10, i.e., the surface of the compressive stress layer 12, will be referred to as the surface compressive stress CS.

[0067] The surface compressive stress CS of the glass plate 10 is preferably 500 MPa to 1200 MPa, more preferably 650 MPa or more, and even more preferably 750 MPa or more. By keeping the surface compressive stress CS within this range, the reduction in impact resistance can be appropriately suppressed. It should be noted that the method for measuring the surface compressive stress CS is arbitrary; for example, it can be measured by measuring the strain within the glass plate 10 using photoelastic analysis. In this embodiment, for example, the surface compressive stress CS can be measured using a surface stress gauge FSM-6000LE manufactured by Orihara Corporation.

[0068] The depth DOL of the compressive stress layer 12 of the glass plate 10 is preferably 10 μm to 100 μm, more preferably 15 μm or more, even more preferably 25 μm or more, and even more preferably 30 μm or more. Depth DOL refers to the thickness of the compressive stress layer 12 in the glass plate 10. That is, depth DOL refers to the distance in the thickness direction from the surface of the glass plate 10 where the surface compressive stress CS is exerted to the depth where the compressive stress value is 0. By having a depth DOL within this range, the glass plate 10 can appropriately suppress the reduction in impact resistance.

[0069] It should be noted that the method for measuring depth DOL is arbitrary. For example, it can be measured by using photoelastic analysis to determine the strain within the glass plate 10. In this embodiment, for example, the surface stress gauge FSM-6000LE manufactured by Orihara Corporation can be used to measure the depth DOL.

[0070] It should be noted that a typical method for obtaining chemically strengthened glass by chemically strengthening glass is to immerse the glass in molten KNO3 salt, perform ion exchange treatment, and then cool it to near room temperature. The treatment conditions, such as the temperature of the molten KNO3 salt and the immersion time, can be set in such a way that the surface compressive stress and the thickness of the compressive stress layer are the desired values.

[0071] It should be noted that the methods for chemical fortification are not limited to those based on potassium salts such as molten KNO3 salts; any method can be used. For example, sodium salts can also be used for chemical fortification.

[0072] (Impact resistance)

[0073] Glass plates used in automotive displays, such as cover materials, have their end faces ground to improve impact resistance. However, if the grinding is extensive, such as grinding the entire end face area, while it can remove cracks and improve impact resistance, the dimensional changes before and after grinding may be too large, or the grinding time may be too long.

[0074] On the other hand, if the grinding degree is too small, cracks cannot be properly removed, resulting in reduced impact resistance. To address this, the inventors focused on the fact that if bending stress is applied to one main surface 10A of the glass plate 10, the maximum tensile stress is applied to the other main surface 10B. They discovered that by manufacturing a glass plate that shortens the crack length in the region on the main surface 10B side of the end face 10C compared to that region, and does not shorten the crack length in the region on the main surface 10A side to that extent, it is possible to reduce dimensional changes and grinding time without excessive grinding, and to suppress the reduction in impact resistance. Specific details will follow.

[0075] (fracture stress)

[0076] The fracture stress of the glass plate 10 (the ultimate maximum stress that the glass can withstand without breaking) depends on the length of the crack formed in the glass plate 10. In this embodiment, the crack length a (μm) and fracture stress σ at the end face 10C of the glass plate 10 are not considered when chemically strengthened based on the compressive stress layer 12. FS The relationship (a) is expressed by equation (1). That is, equation (1) refers to the maximum limiting stress that the glass plate 10 can withstand for each length a of the crack formed on the end face 10C without considering the compressive stress layer 12.

[0077] It should be noted that, unless otherwise specified, the length of the crack in this embodiment refers to the length of the crack in the direction perpendicular to the surface where the crack is formed. That is, for example, the crack length at the location on the conical face 10C1 refers to the length of the crack in the direction orthogonal to the conical face 10C1, and the crack length at the location on the side face 10C2 refers to the length of the crack in the direction orthogonal to the side face 10C2.

[0078]

[0079] Here, K IC Fracture toughness value (MPa·m) 0.5 F is the correction coefficient for the stress intensity factor. In this embodiment, F can be denoted as 1.1215.

[0080] Figure 4 This is a graph illustrating an example of the relationship between crack length and fracture stress. Figure 4 The horizontal axis represents the crack length 'a', and the vertical axis represents the fracture stress. Figure 4 The line segment σ represents the length a (μm) of the crack at the end face 10C of the glass plate 10 without considering the chemical strengthening based on the compressive stress layer 12, and the relationship between the crack length a and the fracture stress σ. FS (a) is the relationship. That is, the line segment σ is obtained by expressing equation (1) as a curve. Among them, Figure 4 The line segment σ represents the fracture toughness value K. ICIt is 0.75 (MPa·m 0.5 Examples of the time period.

[0081] Fracture toughness value K IC Any value can be used; for example, a value obtained using the DCDC (Double Cleavage Drilled Compression) method can be used. Figure 5 This is a diagram showing the shape of a test piece for the DCDC method.

[0082] Figure 6 It is K I A schematic diagram of the -V curve. In the DC-DC method, such as... Figure 5 As shown, a sample Sa with the same composition as glass plate 10, a width W of 7.5 mm, a length D of 6.5 mm, and a height Le of 75 mm is prepared. Then, an opening H with a radius R of 1 mm is formed on the surface Sa1 along the height Le and width W of the sample Sa. The opening H extends from the surface Sa1 in a direction orthogonal to the surface on the opposite side of the surface Sa1.

[0083] Opening H is formed at the center of surface Sa1 such that its center point coincides with the center of surface Sa1. Then, compressive stress was applied to sample Sa along the height Le direction using a TENSILON UTA-5kN thermometer manufactured by ORIENTEC, and the stress intensity factor KI (MPa·m) was measured. 0.5 The curve showing the relationship between the crack propagation velocity v (m / s) and the crack propagation velocity from the opening H. Figure 6 It represents the stress intensity factor KI (MPa·m) 0.5 An example of the curve showing the relationship between ) and the stretching speed v (m / s).

[0084] In this embodiment, as follows Figure 6 The measured curves are divided into regions R1, R2, and R3. Region R1 is the region where the crack propagation rate increases with increasing stress intensity factor. Region R2 is the region where the stress intensity factor is higher than that of region R1, and the rate of increase in crack propagation rate with increasing stress intensity factor is less than that of region R1. Region R3 is the region where the stress intensity factor is higher than that of region R2, and the rate of increase in crack propagation rate with increasing stress intensity factor is greater than that of region R2.

[0085] In this embodiment, the data of region R3 is regressed and extrapolated using a linear equation to calculate the straight line R3a. The stress intensity factor KI, where the crack propagation velocity v on the straight line R3a is 0.1 m / s, is used as the fracture toughness value K of the glass plate 10. IC .

[0086] The fracture stress σ described above FS (a) represents the fracture stress without considering compressive stress layer 12. The inventors discovered that by adjusting the fracture stress σ... FS (a) By adding the average value of the compressive stress from the surface of the glass plate 10 to the depth of the crack length a, the fracture stress of the glass plate 10 after taking into account the compressive stress layer 12 can be calculated with high accuracy.

[0087] That is, in this embodiment, the crack length a (μm) of the end face 10C of the glass plate 10 under chemical strengthening based on the compressive stress layer 12 and the fracture stress σ' are considered. FS The relationship (a) is expressed as Equation (2). It can be said that Equation (2) refers to the maximum limiting stress that the glass plate 10 can withstand without breaking for each length a of the crack formed in the end face 10C of the glass plate 10 with the compressive stress layer 12.

[0088]

[0089] Here, f(x) refers to the compressive stress (MPa) acting on the glass plate 10 at a depth x from the surface of the glass plate 10. That is, equation (2) is the fracture stress σ when the compressive stress layer 12 is not considered. FS (a) The integral of the compressive stress (MPa) exerted on the glass plate 10 by the compressive stress layer 12 from the surface of the glass plate 10 to a depth of length a from the surface of the glass plate 10 is divided by the length a, and the resulting value is taken as the fracture stress σ'. FS (a).

[0090] It should be noted that f(x), i.e., the compressive stress at each location, can be determined by measuring the strain within the glass plate 10 using photoelastic analysis. In this embodiment, for example, f(x) can be measured using a surface stress gauge FSM-6000LE manufactured by Orihara Corporation.

[0091] Figure 4 The line segment σ' represents the length a (μm) of the crack at the end face 10C of the glass plate 10, considering chemical strengthening based on compressive stress layer 12, and the fracture stress σ'. FS (a) is the relationship. That is, the line segment σ' is obtained by expressing equation (2) as a curve.

[0092] in, Figure 4 The line segment σ' is taken as an example, which is the fracture toughness value K. IC It is 0.75 (MPa·m 0.5 An example is given using f(x) with a surface compressive stress CS of 757 MPa and a depth DOL of 28.8 μm.

[0093] In this embodiment, the glass plate 10 preferably has a maximum tensile stress that does not exceed the fracture stress σ' even when a hypothetical maximum tensile stress is applied. FS (a) Crack length distribution on end face 10C. That is, the crack length of the entire region of end face 10C of the glass plate 10 in this embodiment is such that the maximum tensile stress does not exceed the fracture stress σ'. FS (a) Such a length.

[0094] Hereinafter, it will be assumed that the maximum tensile stress does not exceed the fracture stress σ'. FS (a) The maximum value of such crack length, i.e., the assumed maximum tensile stress, is equal to the fracture stress σ'. FS (a) The same value of such crack length is appropriately recorded as the allowable crack length.

[0095] (Allowable crack length)

[0096] A more specific description of the allowable crack length is provided. Figure 7 This is a diagram illustrating an example of the bending stress acting on a glass plate and the allowable crack length. Figure 7 The horizontal axis represents the distance (mm) of the glass plate 10 from the second main surface (main surface 10B) along the thickness direction. That is, for example, a horizontal axis of 0mm refers to the position on the main surface 10B of the glass plate 10, and a horizontal axis of 0.1mm refers to the position of the glass plate 10 0.1mm away from the main surface 10B of the main surface 10B in the opposite direction to the Z direction.

[0097] Figure 7 Line L1 represents an example of the bending stress (tensile stress) at each location in the Z direction of the glass plate 10 when an external force is applied to the glass plate 10. It can be said to show the bending stress distribution of the glass plate 10 in the Z direction. As shown by line L1, the bending stress acting on the glass plate 10 is the largest on the main surface 10B and decreases linearly as it moves toward the side opposite to the Z direction.

[0098] In this embodiment, as shown by line L1, the maximum bending stress acting on the main surface 10B of the glass plate 10, i.e., the assumed maximum tensile stress, is set to 900 MPa. Furthermore, the slope of line L1, i.e., the degree to which the bending stress (tensile stress) decreases towards the side opposite to the Z direction, can be arbitrarily set, for example, calculated based on the measured bending stress at each location when an external force is applied to a sample made of the same material as the glass plate 10.

[0099] It should be noted that in this embodiment, the assumed maximum tensile stress is set to 900 MPa. By assuming a maximum tensile stress of 900 MPa, sufficient strength can be obtained, for example, when mounted on a display device for automotive applications. However, the maximum tensile stress is not limited to assuming 900 MPa and can be appropriately set according to the usage conditions, etc.

[0100] The allowable crack length is set for each location along the Z direction of the glass plate 10. The allowable crack length is based on the bending stress (tensile stress) at each location when the assumed maximum bending stress (tensile stress) acts on the main surface 10B of the glass plate 10, and the fracture stress σ' for each crack length a. FS (a) Configure.

[0101] Specifically, the allowable crack length at a certain location in the Z direction of the glass plate 10 is defined as the fracture stress σ', which is the same value as the assumed maximum tensile stress acting at that location. FS (a) The length a of the crack, where length a refers to the length of the crack in the direction perpendicular to the surface at that location.

[0102] For example Figure 7 Line L2 represents an example of the allowable crack length at each location. Line L2 is based on Figure 7 Line L1 and Figure 4 The line segment σ' is set. That is, line L2 represents the distribution of bending stress at each location. Figure 7 The fracture stress σ' of line L1 and each length a of the crack. FS (a) is Figure 4 The allowable crack length at each location along the Z direction of the glass plate 10 when the line segment σ' is .

[0103] For example, as shown in line L1, a tensile stress of 900 MPa is applied at a distance of 0 mm from the second main surface (main surface 10B), i.e., at the boundary between main surface 10B and end surface 10C. In this case, as... Figure 4 As shown by line segment σ', 900MPa becomes the fracture stress σ' FS The crack length in (a) is approximately 3.2 μm. Therefore, as... Figure 7 As shown by line L2, the allowable crack length at a location 0 mm from the main surface 10B in a direction orthogonal to the surface at that location (the surface at the boundary between the main surface 10B and the end surface 10C) is approximately 3.2 μm.

[0104] Additionally, for example, as shown in line L1, a tensile stress of approximately 760 MPa is applied at a location approximately 0.1 mm from the second principal surface. Figure 4 As shown by the line segment σ', approximately 760 MPa becomes the fracture stress σ'.FS The crack length in (a) is approximately 7 μm. Therefore, as Figure 7 As shown in line L2, the allowable crack length in a direction orthogonal to the surface at a location approximately 0.1 mm from the main surface 10B is approximately 7 μm.

[0105] (Crack length in the glass plate)

[0106] In this embodiment, the crack length of the glass plate 10 over the entire area of ​​the end face 10C is preferably less than or equal to an allowable crack length. That is, in this embodiment, the length of the crack at each location along the Z direction from the end face 10C on the main face 10B side to the end face 10A side is less than or equal to the allowable crack length at that location (in this example, ...). Figure 7 The settings are configured as follows (below L2).

[0107] In other words, the length of the crack at each position along the Z direction from the end of the glass plate 10C on the side of the main surface 10B to the end of the main surface 10A on the end of the glass plate 10 in this embodiment is less than or equal to the length a of the crack in the following formula (3).

[0108] It should be noted that x represents the distance from the main surface 10B, and σ(x) represents the assumed maximum tensile stress acting at a distance x from the surface. That is, σ(x) is equivalent to... Figure 7 Line L1.

[0109]

[0110] Furthermore, in this embodiment, the maximum length of the crack in the first region (i.e., the region from the end face 10B side towards the Z direction to a predetermined distance) of the glass plate 10 is preferably shorter than the maximum length of the crack in the second region (i.e., the region closer to the Z direction side of the end face 10C relative to the first region) in the direction orthogonal to the surface where the crack is formed.

[0111] That is, the glass plate 10 of this embodiment can suppress fracture from the main surface 10B where the tensile stress is high by shortening the crack length in the first region near the main surface 10B.

[0112] Furthermore, by maintaining a relatively long crack length in the second region away from the main surface 10B, the glass plate 10 of this embodiment eliminates the need for grinding in areas with lower tensile stress. Therefore, the glass plate 10 of this embodiment can reduce dimensional changes and grinding time without excessive grinding, and suppress the reduction in impact resistance.

[0113] The following provides a more detailed description of the crack length on the end face 10C of the glass plate 10. Figure 8 This is a diagram used to illustrate the crack length on the end face of the glass plate in this embodiment.

[0114] like Figure 8 As shown, in the region AR1 of the end face 10C of the glass plate 10 in this embodiment, the length of the longest crack in the direction orthogonal to the surface at the location where the crack is formed is 5 μm to 20 μm, preferably 6 μm to 18 μm, and more preferably 7 μm to 15 μm.

[0115] In other words, when the longest crack in the crack formed in region AR1 is defined as the crack with the longest length in the direction orthogonal to the surface at the location where the crack is formed, the length of the longest crack in the direction orthogonal to the surface at the location where the longest crack is formed is within the above-mentioned numerical range.

[0116] Figure 8 In the example, region AR1 refers to the area of ​​end face 10C from position P1A to position P1B in the Z direction. That is, region AR1 refers to the area of ​​the entire region of end face 10C along the Z direction from position P1A to position P1B.

[0117] Position P1A is the position on end face 10C that is located on end face 10C, away from the end face 10A side and moving towards the side opposite to the Z direction (main face 10B side), at a distance of length D1A. The length D1A is 9% of the thickness D of the glass plate 10, preferably 6%. Alternatively, the length D1A relative to the thickness D of the glass plate 10 can also be 6% to 9%.

[0118] Additionally, position P1B is the position on end face 10C that is located on end face 10C, away from the end face 10A side and moving towards the side opposite to the Z direction (main face 10B side), by a length D1B.

[0119] The length D1B is 91% of the thickness D of the glass plate 10, preferably 94%. Alternatively, the length D1B can also be 91% to 94% of the thickness D of the glass plate 10.

[0120] It should be explained that Figure 8 In the example, position P1A is located on the cone-shaped face 10C1 on the Z-direction side, and position P1B is located on the cone-shaped face 10C1 on the side opposite to the Z-direction, but is not limited to this. For example, position P1A can be located at the boundary between the cone-shaped face 10C1 and the side surface 10C2 on the Z-direction side, or it can be located on the side surface 10C2.

[0121] Similarly, position P1B can be located at the boundary between the conical face 10C1 and the side 10C2 on the side opposite to the Z direction, or it can be located on the side 10C2.

[0122] In addition, in this embodiment, the longest crack in region AR2 of the preferred end face 10C of the glass plate 10 has a length in a direction orthogonal to the surface at the location where the crack is formed, which is less than the crack length a represented by the following formula (4).

[0123] In other words, when the longest crack in region AR2 is defined as the crack with the longest length in the direction orthogonal to the surface at the location where the crack is formed, the length of the longest crack in the direction orthogonal to the surface at the location where the longest crack is formed is less than the crack length a represented by equation (4). That is, in region AR2, the fracture stress σ' FS (a) The length of a crack is greater than the assumed maximum tensile stress of 900 MPa.

[0124]

[0125] Figure 8 In the example, region AR2 refers to the area of ​​end face 10C in the Z direction from the end face 10B side to position P2. That is, region AR2 refers to the area of ​​the entire region of end face 10C in the Z direction from the end face 10B side to position P2. Position P2 is the position on end face 10C that is 6% of the thickness D of glass plate 10, preferably 9%, relative to the thickness D of glass plate 10. Alternatively, the length D2 relative to the thickness D of glass plate 10 can also be 6% to 9%.

[0126] It should be explained that Figure 8 In the example, although position P2 is a different position from position P1B, it can also refer to the same position as position P1B in the Z direction. Additionally, Figure 8 In the example, although position P2 is located on the conical face 10C1 on the side opposite to the Z direction, it is not limited to this. For example, position P2 can be located at the boundary between the conical face 10C1 and the side 10C2 on the side opposite to the Z direction, or it can be located on the side 10C2.

[0127] Thus, in this embodiment, the longest crack length in region AR1 of the glass plate 10 is 5 μm to 20 μm, and the longest crack length in region AR2 is less than the length a that satisfies equation (4). Region AR2 is formed by grinding, while region AR1 is preferably formed without grinding. In this embodiment, the glass plate 10 can suppress fractures near the main surface 10B where tensile stress is high by shortening the crack length in region AR2 near the main surface 10B.

[0128] Furthermore, the glass plate 10 of this embodiment, by maintaining a longer crack length in the region AR1 away from the main surface 10B, eliminates the need for grinding in areas with lower tensile stress. Therefore, the glass plate 10 according to this embodiment can reduce dimensional changes and grinding time without making the grinding process excessive, and suppresses the reduction in impact resistance.

[0129] It should be noted that in this embodiment, the glass plate 10 satisfies the crack length requirement specified above in the entire circumferential region of the end face 10C. That is, for example, region AR1 of the glass plate 10 (here, the region with the longest crack length of 5μm to 20μm) is formed throughout the entire circumferential region of the end face 10C, and region AR2 of the glass plate 10 (here, the region with the longest crack length less than the length a that satisfies equation (4)) is formed throughout the entire circumferential region of the end face 10C.

[0130] However, the glass plate 10 may satisfy the crack length requirement specified above in at least a portion of the circumferential region of the end face 10C. That is, for example, region AR1 of the glass plate 10 (here, the region with the longest crack length of 5μm to 20μm) is formed in a portion of the circumferential region of the end face 10C, and region AR2 of the glass plate 10 (here, the region with the longest crack length less than the length a that satisfies equation (4)) may be formed in a portion of the circumferential region of the end face 10C.

[0131] Unless otherwise specified in the description to date or in the following descriptions, the specification of the crack length of the end face 10C of the glass plate 10 may refer to the entire circumferential region or a portion of the circumferential region.

[0132] It should be noted that, in this embodiment, a portion of the circumferential region of end face 10C can refer to the same region unless otherwise specified.

[0133] When only a portion of the end face 10C meets the requirement for crack length, for example, it is preferable that only one edge meets the requirement for crack length.

[0134] The glass plate 10 of this embodiment is used as such Figure 1When the cover material for a vehicle-mounted display is being installed, the driver's head is likely to collide with the top edge (the upper edge in the vertical direction) of the cover material. Therefore, if the edge corresponding to the top edge of the cover component meets the specified crack length, the development of cracks from the top edge of the cover component during impact can be suppressed, which is therefore preferable.

[0135] Conversely, the lower and side edges of the cover component are less susceptible to impact than the upper edge, so costs can be reduced by omitting grinding of these parts. Therefore, when installed as a cover material, it is preferable that only the upper edge meets the crack length requirement. Alternatively, for example, only the portion above the upper and side edges may meet the crack length requirement, or both the upper and side edges may meet the crack length requirement.

[0136] (Methods for determining crack length)

[0137] The length of the longest crack in glass plate 10 can be determined by any method. For example, the area where the length of the longest crack is to be determined can be cut while observing whether there is a crack, and the dimensional change at the moment when no crack is visible can be used to determine the crack length. Specifically, the following methods can be used for determination.

[0138] First, the evaluation area (the area where the length of the longest crack is measured) of the glass plate 10 is ground to a specified amount, cleaned and dried, and the processed altered layer, which has become a circular pit or an elliptical pit through etching, is observed using an optical microscope.

[0139] Here, "processing alteration layer" refers to the layer of scratches, cracks, etc., that exist in the glass plate during processing steps such as chamfering and grinding.

[0140] As an optical microscope, the Olympus LEXT OLS5000 laser microscope with a 50x objective lens can be used for observation with a field of view of 258μm×258μm.

[0141] The process (to identify latent damage caused by grinding and etching) is repeated multiple times, and the amount of etching on the glass plate 10 at the moment when no circular or elliptical pits are observed in the evaluation area is taken as the "length of the longest crack".

[0142] It should be noted that "etching" can be performed by immersing the entire glass plate in an etching solution at room temperature (25°C). The etching solution can be an aqueous solution containing 5% hydrofluoric acid (HF) and 95% pure water by mass.

[0143] It should be noted that in determining the length of the longest crack, the entire region of the area where the length of the longest crack is specified can be used as the evaluation region (the region where the length of the longest crack is measured). That is, for example, the entire region AR1 and the entire region AR2 can be used as the evaluation region.

[0144] However, this is not a limitation. A portion of the region defining the longest crack length, such as a portion of region AR1 or a portion of region AR2, can also be used as the evaluation region. In this case, assuming the same surface (polished and unpolished surfaces) is uniform, as a simplified evaluation, if the region defining the longest crack length (regions AR1, AR2, etc.) includes the polished surface, the area of ​​the center of that polished surface, which is 5.0 mm, can be used. 2 The range is used as the evaluation area.

[0145] It should be noted that when multiple polished surfaces exist, an evaluation area should be set for each polished surface. Additionally, if the area defining the longest crack length includes the unpolished surface, the area of ​​the center of the unpolished surface can be 5.0 mm. 2 The range is used as the evaluation area. In other words, as long as the area near the center of each surface in different states is 5.0 mm... 2 The left and right areas can be set as evaluation areas to determine the length of the crack.

[0146] (Surface roughness of the end face of the glass plate)

[0147] The arithmetic mean roughness Ra (surface roughness) of the region AR1 of the end face 10C of the glass plate 10 is preferably 140 nm or more, more preferably 170 nm or more, and even more preferably 210 nm or more.

[0148] There is no particular upper limit, for example, it is 500 nm or less, preferably 400 nm or less. The arithmetic mean roughness Ra (surface roughness) of the region AR2 of the end face 10C of the glass plate 10 is preferably 70 nm or less, more preferably 30 nm or less, and even more preferably 10 nm or less.

[0149] It should be noted that the arithmetic mean roughness Ra refers to the arithmetic mean roughness Ra specified in JIS B 0601:2001.

[0150] (Another example of crack length in a glass plate)

[0151] Figure 9 This is a diagram used to illustrate the crack length on the end face of a glass plate in another example of this embodiment. (See diagram for example.) Figure 9 As shown, in this embodiment, region AR1 of the glass plate 10 can refer to the region of the end face 10C extending in the Z direction from the end face 10A side to position P1B. That is, region AR1 can refer to the region of the entire region of the end face 10C extending in the Z direction from the end face 10A side to position P1B.

[0152] Figure 10This is a diagram used to illustrate the crack length on the end face of a glass plate in other examples of this embodiment.

[0153] Figure 10 The region AR1 of the glass plate 10 shown is... Figure 8 Similarly, the example becomes the region from position P1A to position P1B. On the other hand, Figure 10 The glass plate 10 shown has a region AR3 on the side closer to the Z direction than region AR1. The length of the longest crack in region AR3 of end face 10C in a direction orthogonal to the surface at the location where the crack is formed is preferably less than the crack length a represented by the above formula (4).

[0154] In other words, when the longest crack in the crack formed in region AR3 is taken as the longest crack in the direction orthogonal to the surface at the location where the crack is formed, it is preferable that the length of the longest crack in the direction orthogonal to the surface at the location where the longest crack is formed is less than the crack length a represented by the above formula (4).

[0155] That is, in region AR3, the fracture stress σ' is the same as in region AR2. FS (a) Crack length greater than the assumed maximum tensile stress of 900 MPa. Region AR3 is preferably formed by grinding. It should be noted that the arithmetic mean roughness Ra of region AR3 can be the same as that of region AR2.

[0156] Region AR3 refers to the area of ​​end face 10C in the Z direction from the end of main face 10A to position P3. That is, region AR3 refers to the area of ​​the entire region of end face 10C in the Z direction from the end of main face 10A to position P3.

[0157] Position P3 is the position on end face 10C that is located on end face 10C, away from the side of main face 10A, and moving towards the side opposite to the Z direction (side of main face 10B), at a distance of length D3. The length D3 is preferably 6% of the thickness D of glass plate 10, more preferably 9%. Alternatively, the length D3 may also be 6% to 9% of the thickness D of glass plate 10. It should be noted that... Figure 10 In the example, although position P3 is a different position from position P1A, it can also refer to the same position as position P1A in the Z direction.

[0158] In addition, Figure 10 In the example, although position P3 is located on the cone-shaped face 10C1 on the Z-direction side, it is not limited to this. For example, position P3 can also be located at the boundary between the cone-shaped face 10C1 and the side face 10C2 on the Z-direction side, or it can be located on the side face 10C2.

[0159] In this way, glass plate 10 can be as follows Figure 9 As shown, the crack length can be preserved by not grinding the area near the main surface 10A, which is also possible as follows: Figure 10 The area near the main surface 10A is ground to shorten the length of the crack.

[0160] (Functional membrane)

[0161] Figure 11 This is a cross-sectional schematic diagram of the glass plate and the functional membrane. (For example...) Figure 11 As shown, a functional film 20 can be formed on the surface of the glass plate 10. Figure 11 In the example, a functional film 20 is formed on the main surface 10A of the glass plate 10. Since the functional film 20 is extremely thin, the total thickness of the functional film 20 and the glass plate 10 can be taken as the thickness D of the glass plate 10 of the present invention.

[0162] The functional film 20 can be formed by treating the surface of the glass plate 10, or by laminating other layers on the surface of the glass plate 10.

[0163] Examples of functional films 20 include anti-glare layers, anti-reflective layers, light-shielding layers, anti-fouling layers, and antibacterial layers. That is, the glass plate 10 is formed with at least one of the following as functional films 20: anti-glare layer, anti-reflective layer, light-shielding layer, anti-fouling layer, and antibacterial layer.

[0164] In other words, the glass plate 10 can have all of the anti-glare layer, anti-reflective layer, light-shielding layer, anti-fouling layer, and antibacterial layer stacked on it as the functional film 20, or it can have only a portion of the anti-glare layer, anti-reflective layer, light-shielding layer, anti-fouling layer, and antibacterial layer stacked on it. By forming the functional film 20 on the glass plate 10, it can function appropriately as an in-vehicle display.

[0165] An anti-reflective layer reduces reflectivity, thereby minimizing glare caused by external light. Furthermore, using glass with an anti-reflective layer increases the transmittance of light from the display panel, resulting in clearer displayed images.

[0166] There are no particular limitations on the material of the anti-reflective layer. Any material that can suppress light reflection can be used. For example, it can be a structure composed of a high refractive index layer and a low refractive index layer. The high refractive index layer here refers to a layer with a refractive index of 1.9 or higher at a wavelength of 550 nm, and the low refractive index layer refers to a layer with a refractive index of 1.6 or lower at a wavelength of 550 nm.

[0167] The high-refractive-index layer and the low-refractive-index layer can each contain one layer, or they can each contain two or more layers. When the high-refractive-index layer and the low-refractive-index layer each contain two or more layers, it is preferable to alternately stack the high-refractive-index layer and the low-refractive-index layer.

[0168] There are no particular restrictions on the materials used for high-refractive-index and low-refractive-index layers; the choice can be made based on factors such as the required level of anti-reflection and production efficiency.

[0169] As the material constituting the high refractive index layer, materials comprising one or more selected from niobium, titanium, zirconium, tantalum, and silicon are preferably used. Specifically, examples include niobium oxide (Nb₂O₅), titanium oxide (TiO₂), zirconium oxide (ZrO₂), tantalum oxide (Ta₂O₅), and silicon nitride.

[0170] As a material constituting the low refractive index layer, a silicon-containing material can be preferably used, for example. Specifically, examples include silicon oxide (SiO2), materials containing a mixed oxide of Si and Sn, materials containing a mixed oxide of Si and Zr, and materials containing a mixed oxide of Si and Al.

[0171] There are no particular limitations on the method for forming the anti-reflective layer; various methods can be used. Pulse sputtering, AC sputtering, and digital sputtering are particularly preferred.

[0172] The thickness of the anti-reflective layer is approximately 100–300 nm.

[0173] An anti-glare layer is a layer that reduces glare caused by reflected light from a light source by scattering external light. If a glass plate with an anti-glare layer is placed on a display panel, the reflection of external light is reduced when viewing the displayed image, thus allowing the image to be seen clearly.

[0174] There are no particular limitations on the method of forming the anti-glare layer. For example, methods such as etching the surface of glass or applying a coating liquid containing microparticles and a matrix to the surface of glass and then curing the matrix can be mentioned.

[0175] The anti-fouling layer is a layer that inhibits the adhesion of organic and inorganic substances. Alternatively, the anti-fouling layer is a layer that allows for easy removal of organic and inorganic substances even if they adhere, through cleaning methods such as wiping. With an anti-fouling layer, fingerprints will not remain on the surface of the glass panel 10 even after touching it, keeping it clean. Therefore, the displayed image can be clearly seen when viewing the image on the display panel.

[0176] (Methods for manufacturing glass plates)

[0177] Next, the manufacturing method of glass plate 10 will be described. In the manufacturing method of glass plate 10, initially, a glass blank is manufactured, and the glass blank is subjected to chemical strengthening treatment to form a compressive stress layer 12 on the surface of the glass blank. The end face of the glass blank is ground to form region AR2, thereby manufacturing glass plate 10.

[0178] The manufacturing method of the glass preform in this manufacturing method is not particularly limited and can be arbitrary. For example, the following methods can be used: down-drawing (e.g., overflow down-drawing, slot down-drawing, and re-drawing), float glass, rolling, and pressing.

[0179] In this manufacturing method, the area on the main surface 10B side of the end face of the manufactured glass blank is ground to form area AR2, and the unground portion of the end face is designated as area AR1. It should be noted that, for example... Figure 10 When forming region AR3 on the side of the main surface 10A, the region on the side of the main surface 10A of the end face of the glass blank is also ground to form region AR3. Thus, glass plate 10 is formed.

[0180] It should be noted that when forming the conical face 10C1 on the glass plate 10, after chamfering to form the conical face 10C1, regions AR2 and AR3 are formed by grinding. However, it is not limited to this; for example, the conical face 10C1 can be formed and regions AR2 and AR3 can be formed by grinding.

[0181] In this manufacturing method, a compressive stress layer 12 is formed by chemically strengthening the ground glass blank. In this embodiment, the chemical strengthening process forms the compressive stress layer 12 by contacting the manufactured glass blank with a molten salt containing alkali metal ions.

[0182] For example, in this embodiment, a glass plate is immersed in a molten salt containing alkali metal ions with a large ionic radius, in this case, a molten potassium nitrate salt containing K ions. As a result, metal ions (in this case, Na ions) in the glass plate with ionic radii smaller than those in the molten salt are replaced by alkali metal ions from the molten salt. Due to the difference in the area occupied by the alkali metal ions, compressive stress is generated on the surface of the glass plate, forming a compressive stress layer 12.

[0183] In this embodiment, the heating temperature of the molten salt (molten salt liquid) in contact with the glass blank is preferably 370°C to 480°C, more preferably 400°C to 450°C. Furthermore, in this embodiment, the contact time between the glass blank and the molten salt is preferably 0.5 hours to 32 hours, more preferably 3 hours to 6 hours.

[0184] Furthermore, salts containing potassium ions are preferably used as the molten salt in contact with the glass blank. Examples of molten salts in contact with the glass blank include basic nitrates, basic sulfates, and basic chlorides such as potassium nitrates, potassium sulfates, potassium carbonates, and potassium chlorides. These molten salts can be used alone or in combination. In addition, salts containing sodium (Na ions) and lithium (Li ions) can be mixed in to adjust the chemical strengthening properties.

[0185] Thus, in this manufacturing method, the compressive stress layer 12 is formed through chemical strengthening treatment. Therefore, it can be said that the compressive stress layer 12 of this embodiment is a layer obtained by replacing alkali metal elements with small ionic radii with alkali metal elements with large ionic radii contained in the molten salt.

[0186] In other words, if the alkali metal element contained in the molten salt is used as the substitution element, the number of substitution elements per unit volume of the compressive stress layer 12 of the glass plate 10 is greater than the number of substitution elements per unit volume of the layers other than the compressive stress layer 12. For example, potassium is used as the substitution element here.

[0187] It should be noted that, although the area not subjected to grinding is designated as region AR1 in the above description, region AR1 can also be formed through grinding. In this case, the degree of grinding in region AR1 is less than that in regions AR2 and AR3.

[0188] It should be noted that in this manufacturing method, although regions AR2 and AR3 are formed throughout the entire circumferential region by grinding the entire circumferential region of the end face 10C of the glass plate 10, it is not limited to grinding the entire circumferential region.

[0189] For example, in this manufacturing method, regions AR2 and AR3 can be formed in a circumferential portion of the end face 10C of the glass plate 10 by grinding. For example, in this manufacturing method, it is preferable to grind at least the portion that is vertically upward when mounted on a vehicle, within the entire circumferential portion of the end face 10C of the glass plate 10.

[0190] In this case, it can be said that regions AR2 and AR3 are preferably formed in the entire circumferential range of the end face 10C of the glass plate 10, including at least the range that is vertically upward when mounted on a vehicle.

[0191] (Effect)

[0192] As described above, the glass plate 10 of this embodiment includes a main surface 10A as a first main surface, a main surface 10B as a second main surface, and an end surface 10C connecting the main surface 10A and the main surface 10B, and has a compressive stress layer 12.

[0193] The longest crack in region AR1, located at least a portion of the area around the main surface of the glass plate 10 (i.e., only a portion of the area around the main surface or the entire area around the main surface), extends from the end face 10C on the main surface side of the glass plate 10 along the thickness direction (Z direction) of the glass plate 10 towards the main surface 10B at a length of 9% of the thickness D of the glass plate 10 (position P1A) to a position (position P1B) on the main surface 10C on the main surface side of the glass plate 10 at a length of 91% of the thickness D of the glass plate 10 (position P1B). The length of the longest crack in this region is 5 μm to 20 μm in the direction perpendicular to the surface where the crack is formed. In addition, in at least a portion of the area around the main surface of the glass plate 10, from the end of the main surface 10B side of the end face 10C to a position (position P2) 6% of the thickness D of the glass plate 10 along the thickness direction (Z direction) of the main surface 10A side, the length of the longest crack in region AR2 in the direction perpendicular to the surface where the crack is formed is less than a as expressed by equation (4).

[0194] The glass plate 10 of this embodiment can suppress fracture from the vicinity of the main surface 10B where tensile stress is high by shortening the crack length in the region AR2 near the main surface 10B. Furthermore, the glass plate 10 of this embodiment can eliminate the need for grinding in areas with lower tensile stress, or reduce the degree of grinding, by maintaining a longer crack length in the region AR1 away from the main surface 10B. Therefore, the glass plate 10 according to this embodiment can reduce dimensional changes and grinding time, and suppress the reduction of impact resistance.

[0195] Furthermore, the glass plate 10 according to this embodiment can also improve impact resistance in the so-called head impact test. The head impact test is, for example, the test described in International Publication No. 2016 / 194916.

[0196] Furthermore, the longest crack in region AR1, located at least a portion of the area around the main surface of the glass plate 10 (i.e., only a portion of the area around the main surface or the entire area around the main surface), from the end of ...

[0197] Furthermore, the longest crack in region AR1, located at least a portion of the area around the main surface of the glass plate 10 (i.e., only a portion of the area around the main surface or the entire area around the main surface), from the end of the end face 10C on the main surface 10A side to a position (position P1B) extending 91% of the thickness D of the glass plate 10 along the thickness direction (Z direction) of the glass plate 10 towards the main surface 10B side, has a length of 5 μm to 20 μm perpendicular to the surface of region AR1 where the crack is formed. Furthermore, the longest crack in region AR2, extending from the end of the main surface 10B of end face 10C to a position (position P2) along the thickness direction (Z direction) of glass plate 10 towards the main surface 10A, is preferably less than a as expressed in equation (4). This region AR2 extends from the end of the main surface 10B of end face 10C to a position (position P2) that is 9% of the thickness D of glass plate 10.

[0198] Furthermore, preferably, in at least a portion of the area around the main surface of the glass plate 10 (i.e., only a portion of the area around the main surface or the entire area around the main surface), from the end of ...

[0199] Furthermore, the surface compressive stress CS of the glass plate 10 is 500MPa to 1200MPa, and the depth DOL of the compressive stress layer 12 is preferably 10μm to 100μm. Therefore, the glass plate 10 can appropriately suppress the reduction in impact resistance.

[0200] Furthermore, the glass plate 10 is expressed in molar percentage based on oxides, preferably as follows: SiO2: 50%–80%, Al2O3: 1%–20%, Na2O: 6%–20%. This allows the glass plate 10 to appropriately suppress the reduction in impact resistance.

[0201] Furthermore, the glass plate 10 preferably has a thickness D of 0.5 mm to 3.0 mm, and the end face 10C includes a tapered face 10C1. Therefore, the glass plate 10 can appropriately suppress the reduction in impact resistance.

[0202] In this embodiment, the glass plate 10 is preferably provided in a vehicle-mounted display. The glass plate 10 for a vehicle-mounted display assumes that, for example, in a collision, a passenger's head collides with the main surface 10A, causing compressive stress on the main surface 10A side and tensile stress on the main surface 10B side. Therefore, by using the glass plate 10 of this embodiment in a vehicle-mounted display, impact resistance can be appropriately provided to suit the application of the vehicle-mounted display.

[0203] Furthermore, end face 10C is preferably located in a portion of the periphery of the main surface of the glass plate 10, from a position (position P1A) 9% of the thickness D of the glass plate 10 along the thickness direction (Z direction) towards the main surface 10B from the end face 10A side of the end face 10C to a position (position P1B) 91% of the thickness D of the glass plate 10 along the thickness direction (Z direction) towards the main surface 10B side of the end face 10C, in the region AR1 where the longest crack is located in the direction perpendicular to the surface where the crack is formed. The thickness is 5μm to 20μm. Furthermore, preferably, in at least a portion of the area around the main surface of the glass plate 10, from the end of the end face 10C on the main surface 10B side to a position (position P2) extending 6% of the thickness D of the glass plate 10 along the thickness direction (Z direction) of the main surface 10A side, the longest crack in region AR2 has a length in the direction perpendicular to the surface where the crack is formed that is less than a as expressed in equation (4). Therefore, the glass plate 10 can improve its impact resistance and reduce the time required for grinding.

[0204] Furthermore, the longest crack in region AR1, which extends from the end face 10C on the main surface of the glass plate 10, from a position (position P1A) 9% of the thickness D of the glass plate 10 along the thickness direction (Z direction) of the glass plate 10 towards the main surface 10B, to a position (position P1B) 91% of the thickness D of the glass plate 10 along the thickness direction (Z direction) of the glass plate 10 towards the main surface 10B, has a length of 5 μm to 20 μm in the direction perpendicular to the surface where the crack is formed, in the direction perpendicular to the surface where the crack is formed. Furthermore, preferably, in at least a portion of the area around the main surface of the glass plate 10, from the end of the end face 10C on the side of the main surface 10B to a position (position P2) 6% of the thickness D of the glass plate 10 along the thickness direction (Z direction) of the main surface 10A, the longest crack in region AR2 has a length in the direction perpendicular to the surface where the crack is formed that is less than a as expressed in equation (4). Thus, the glass plate 10 can further improve its impact resistance.

[0205] The display device of this embodiment preferably includes a glass plate 10. By including the glass plate 10, the display device can appropriately suppress the reduction of impact resistance.

[0206] The manufacturing method of this embodiment manufactures a glass plate 10 comprising a main surface 10A as a first main surface, a main surface 10B as a second main surface, and an end surface 10C connecting the main surfaces 10A and 10B, and having a compressive stress layer 12. This manufacturing method includes the following steps: in at least a portion of the area surrounding the main surface of the glass plate 10, the longest crack in region AR1, extending from the end of the end surface 10C on the main surface 10A side along the thickness direction (Z direction) of the glass plate 10 towards the main surface 10B side at a length of 9% of the thickness D of the glass plate 10 (position P1A), to a position (position P1B) extending from the end of the end surface 10C on the main surface 10A side along the thickness direction (Z direction) of the glass plate 10 towards the main surface 10B side at a length of 91% of the thickness D of the glass plate 10 (position P1B), has a length of 5 μm to 20 μm in the direction perpendicular to the surface where the crack is formed.

[0207] Furthermore, this manufacturing method includes the following step: grinding region AR2 so that the length of the longest crack in region AR2, from the end face 10C on the main face 10B side to a position (position P2) extending 6% of the thickness D of the glass plate 10 along the thickness direction (Z direction) of the glass plate 10 towards the main face 10A side, is less than a as expressed by equation (4). According to this manufacturing method, dimensional changes and grinding time can be reduced without increasing the degree of grinding, and the reduction in impact resistance can be suppressed.

[0208] Example

[0209] (sample)

[0210] Next, the embodiments will be described. In the embodiments, a glass plate sample with a length of 94 mm, a width of 223 mm, and a thickness of 1.3 mm was prepared. The composition of the sample is expressed in mol% based on oxides as follows.

[0211]

[0212] (fracture toughness value)

[0213] In addition, the fracture toughness value K IC The value was measured using the method described in this embodiment, and was 0.71 (MPa·m). 0.5 ).

[0214] (Determination of CS and DOL)

[0215] The surface compressive stress CS, the depth of the compressive stress layer DOL, and the strengthening curve f(x) representing the distribution of compressive stress values ​​in the depth direction were measured using a surface stress meter FSM-6000LE manufactured by Orihara.

[0216] (Measurement of surface roughness)

[0217] The arithmetic mean roughness Ra of the ground and unground portions of each sample was measured. An Olympus LEXT OLS5000 laser microscope was used as the measuring instrument.

[0218] (Determination of the longest crack length)

[0219] The crack lengths of each sample in the embodiments were measured using the method described in this embodiment. More specifically, a portion of the region defining the longest crack length was used as the evaluation region, and the longest crack length of each sample was measured. That is, assuming uniformity on the same surface of the sample (polished surface and unpolished surface), as a simplified evaluation, when the region defining the longest crack length includes the polished surface, the area of ​​the center of that polished surface is 5.0 mm. 2 The range is used as the evaluation area.

[0220] It should be noted that when multiple polished surfaces exist, an evaluation area is set for each polished surface. Additionally, when the area containing the unpolished surface is included in the specified longest crack length, the area of ​​the center of the unpolished surface is set at 5.0 mm. 2 The range is used as the evaluation area. In other words, the area near the center of each surface in different states is 5.0 mm. 2 The left and right areas are set as the evaluation areas, and the length of the longest crack is measured.

[0221] (Evaluation of grinding time)

[0222] The grinding time for each sample was determined in advance, and the grinding time was used to evaluate each sample.

[0223] (Evaluation of dimensional changes)

[0224] The dimensional changes of the samples from before to after grinding were measured, and the dimensional changes were used to evaluate each sample. As a method for measuring dimensional changes, the unprocessed portion of the unprocessed sample was masked with a polyethylene film, and the height difference between the processed and unprocessed portions was measured using a Mitsubishi Optical PF-60 non-contact surface property measuring device.

[0225] (Evaluation of strength)

[0226] The strength of each sample was measured, and the strength was used to evaluate each sample. Specifically, the evaluation was conducted using a four-point bending test according to JIS R 1601:2008.

[0227] The interval between the two support points was set to 40 mm, and the interval between the two load points was set to 10 mm. Data was obtained using 20 test specimens to measure bending strength. The four-point bending test was conducted using an Autograph AGS-X test specimen manufactured by Shimadzu Corporation.

[0228] Table 1 shows the conditions and evaluation results for each example.

[0229] [Table 1]

[0230]

[0231] (Example 1)

[0232] In Example 1, chamfering wheels (grit sizes: #400 and #800) are used to chamfer the ends of the prepared sample, forming chamfered sections on the front and back sides. (Angle 45°, chamfer width 0.23 mm)

[0233] Next, a belt grinder was used to grind the chamfered portion on the back side from the second main surface to a position of 0.12 mm (relative to 9.2% of the sample thickness). Two types of belts were used: diamond with a grit size of #4000 and GC with a grit size of #10000, used in the order of the former and the latter. The belt width was 27 mm, and the processing conditions were: belt tension: 30 N, vibration frequency: 20 Hz, vibration amplitude: ±2 mm, processing speed: 180 mm / min, belt conveyor speed: 200 mm / min, and the contact angle of the belt relative to the second main surface was 30°.

[0234] Then, the resulting glass plate is subjected to chemical strengthening treatment.

[0235] The chemical strengthening treatment is carried out by immersing the entire glass plate in molten KNO3 salt to achieve a surface compressive stress (CS) of 750 MPa and a depth of 30 μm in the compressive stress layer.

[0236] Next, the glass plate after the above chemical strengthening treatment was immersed in hydrochloric acid for 120 seconds for acid treatment, then rinsed several times with pure water and dried with a hair dryer. The hydrochloric acid used was prepared in a beaker with a concentration of 13.4% by mass (manufactured by Kanto Chemical Co., Ltd.) and the temperature was adjusted to 40°C using a water bath. Next, the glass plate after the above acid treatment was immersed in a sodium hydroxide aqueous solution for 120 seconds for alkali treatment, then rinsed several times with pure water and dried with a hair dryer. The sodium hydroxide aqueous solution used was prepared in a beaker with a concentration of 4.0% by mass and the temperature was adjusted to 40°C using a water bath.

[0237] In the sample of Example 1, the measured surface compressive stress CS and depth DOL were 747 MPa and 31 μm, respectively.

[0238] In Example 1, the crack length a (the allowable crack length on the second principal surface under a tensile stress of 900 MPa) that satisfies Equation (4) is 3.1 μm.

[0239] In the sample of Example 1, the longest crack length in the ground part is 1.5 μm, and the longest crack length in the unground part is 8 μm.

[0240] (Example 2~Example 8)

[0241] Examples 2 through 8 change the grinding conditions of the end face to those listed in Table 1, otherwise they are the same as in Example 1. The surface roughness, longest crack length, grinding time, and dimensional change are the values ​​shown in Table 1.

[0242] In addition, in Example 2, the measured surface compressive stress CS and depth DOL were 866 MPa and 18.7 μm, respectively, and the crack length a (the allowable crack length of the second principal surface under tensile stress of 900 MPa) that satisfies Equation (4) was 4.2 μm.

[0243] In Example 3, the surface chamfer is ground under the same conditions as the back chamfer.

[0244] In Example 4, the end face shape is a chamfer with a radius of 0.7 mm. A chamfering wheel (grit size #400 and #800) is used to create the end face shape.

[0245] In Example 6, the belt tension was set to 15N, and grinding was performed to a position 0.07mm from the main surface (relative to 5.4% of the sample thickness).

[0246] In Example 7, the entire end face was ground using a brush abrasive. The brush used was a φ292mm roller brush made of 6,6 nylon with a wire diameter of φ0.2mm, a bristle length of 15mm, and a spacing of 7mm. The slurry used was a MIREK E30J slurry prepared by Mitsui Metals Mining, adjusted to a specific gravity of 1.3 with pure water. The processing conditions were: rotation speed 600 rpm, infeed depth: 5mm, oscillation speed: 2mm / sec, oscillation amplitude: 20mm, and substrate conveying speed: 1mm / sec. The dimensional change in the amplitude direction was 0.10mm.

[0247] In Example 8, the belt of the belt grinding is set to abrasive type GC with a particle size of #4000.

[0248] (Evaluation Results)

[0249] In Examples 1 to 4, which are examples of embodiments, it is found that the grinding time is shorter and the dimensional change is less. On the other hand, in Example 7, which is a comparative example, it is found that both the grinding time and the dimensional change are greater.

[0250] Figure 12 This is a graph showing the evaluation results of the intensity of each example. Figure 12 In the figure, the maximum, minimum, and average values ​​of bending strength in each sample (each example) are plotted, along with the 90% cumulative fracture probability strength, 63.2% cumulative fracture probability strength, and 10% cumulative fracture probability strength calculated by Weibull regression (first regression).

[0251] according to Figure 12 It can be seen that in Examples 5, 6, and 8, which are comparative examples, the minimum bending strength is small, and it is not possible to adequately suppress the reduction in impact resistance. It should be noted, for example, in Example 5, there is a crack with a length of 8 μm in the region from the end of the glass plate on the second main surface side of the end face to a position along the thickness direction of the glass plate away from the first main surface side at a length of 9.2% (0.12 mm) of the thickness of the glass plate, which exceeds the allowable crack length at that position.

[0252] Additionally, for example, in Example 6, a crack with a length of 8 μm exists in the region from the end of the glass plate at a position 5.4% (0.07 mm) away from the thickness of the glass plate to a position 9.2% (0.12 mm) away from the end of the glass plate at the second main surface side of the end face towards the first main surface side, exceeding the allowable crack length at that position.

[0253] On the other hand, it can be seen that in Examples 1 to 4, which are examples of embodiments, the minimum value of bending strength is large, which can appropriately suppress the reduction of impact resistance.

[0254] The embodiments of the present invention have been described above, but the embodiments are not limited to the content of these embodiments. Furthermore, the aforementioned constituent elements include elements of substantially the same, so-called equal scope, that can be easily assumed by those skilled in the art. Moreover, the aforementioned constituent elements can be appropriately combined. Furthermore, various omissions, substitutions, or modifications of the constituent elements can be made without departing from the spirit of the aforementioned embodiments. This invention is based on Japanese Patent Application No. 2021-001081, filed January 6, 2021, the contents of which are incorporated herein by reference.

[0255] Symbol Explanation

[0256] 10 glass plates

[0257] 10A, 10B Main Face

[0258] 10C end face

[0259] 12 Compressive stress layer

[0260] AR1 and AR2 areas.

Claims

1. A glass sheet comprising a first main surface, a second main surface, and an end surface connecting the first main surface and the second main surface, having a compressive stress layer, in at least a part of the region of the end surface around the main surface of the glass sheet, a length of a longest crack in a direction perpendicular to a surface in which the crack is formed is 5 μm to 20 μm in a region from a position 9% of a thickness of the glass sheet away from the first main surface side end of the end surface toward the second main surface side along a thickness direction of the glass sheet to a position 91% of the thickness of the glass sheet away from the first main surface side end of the end surface toward the second main surface side along the thickness direction of the glass sheet, a length of a longest crack in a direction perpendicular to a surface in which the crack is formed is less than a in formula (A) that satisfies the following formula (A) in a region from the second main surface side end of the end surface to a position 6% of a thickness of the glass sheet away from the second main surface side end of the end surface toward the first main surface side along a thickness direction of the glass sheet. wherein σ' FS (a) is a breaking stress, unit: MPa, a is a length of a crack, unit: pm, K IC is a breaking toughness value, unit: MPa-m 0.5 F is a correction coefficient of a stress intensity factor, counted as 1.1215, f(x) is a compressive stress acting on the glass sheet at a position with a depth x from the 2nd main surface, unit: MPa.

2. The glass sheet of claim 1, wherein, for the end surface, in at least a part of the region of the end surface around the main surface of the glass sheet, 3. The glass sheet of claim 1, wherein, a length of a longest crack in a direction perpendicular to a surface in which the crack is formed is 5 μm to 20 μm in a region from a position 9% of a thickness of the glass sheet away from the first main surface side end of the end surface toward the second main surface side along a thickness direction of the glass sheet to a position 91% of the thickness of the glass sheet away from the first main surface side end of the end surface toward the second main surface side along the thickness direction of the glass sheet, a length of a longest crack in a direction perpendicular to a surface in which the crack is formed is less than a in formula (A) that satisfies the following formula (A) in a region from the second main surface side end of the end surface to a position 6% of a thickness of the glass sheet away from the second main surface side end of the end surface toward the first main surface side along a thickness direction of the glass sheet. for the end surface, in at least a part of the region of the end surface around the main surface of the glass sheet, 4. The glass sheet of claim 1, wherein, a length of a longest crack in a direction perpendicular to a surface in which the crack is formed is less than a in formula (A) that satisfies the following formula (A) in a region from a position 9% of a thickness of the glass sheet away from the first main surface side end of the end surface toward the second main surface side along a thickness direction of the glass sheet to a position 91% of the thickness of the glass sheet away from the first main surface side end of the end surface toward the second main surface side along the thickness direction of the glass sheet.

5. The glass sheet according to any one of claims 1-4, wherein, a surface compressive stress is 500 MPa to 1200 MPa, and a depth of the compressive stress layer is 10 μm to 100 μm.

6. The glass sheet according to any one of claims 1-4, wherein, contains SiO2: 50 to 80 mol%, Al2O3: 1 to 20 mol%, and Na2O: 6 to 20 mol%.

7. The glass sheet according to any one of claims 1-4, wherein, The thickness is 0.5 to 3.0 mm, and the end face includes a tapered surface portion.

8. The glass sheet according to any one of claims 1-4, wherein, The glass plate is provided to a display device for a vehicle.

9. The glass sheet according to any one of claims 1-4, wherein, The end face of only a part of the area around the main face of the glass plate, The length of the longest crack in the direction perpendicular to the surface in which the crack is formed is 5 to 20 μm in the area from the position at which the thickness of the glass plate is 9% of the thickness of the glass plate from the end of the first main face side of the end face toward the second main face side along the thickness direction of the glass plate to the position at which the thickness of the glass plate is 91% of the thickness of the glass plate from the end of the first main face side of the end face toward the second main face side along the thickness direction of the glass plate, The length of the longest crack in the direction perpendicular to the surface in which the crack is formed is less than a satisfying formula (A) in the area from the end of the second main face side of the end face to the position at which the thickness of the glass plate is 6% of the thickness of the glass plate from the end of the second main face side of the end face toward the first main face side along the thickness direction of the glass plate.

10. The glass sheet according to any one of claims 1-4, wherein, The end face of the entire area around the main face of the glass plate, The length of the longest crack in the direction perpendicular to the surface in which the crack is formed is 5 to 20 μm in the area from the position at which the thickness of the glass plate is 9% of the thickness of the glass plate from the end of the first main face side of the end face toward the second main face side along the thickness direction of the glass plate to the position at which the thickness of the glass plate is 91% of the thickness of the glass plate from the end of the first main face side of the end face toward the second main face side along the thickness direction of the glass plate, The length of the longest crack in the direction perpendicular to the surface in which the crack is formed is less than a satisfying formula (A) in the area from the end of the second main face side of the end face to the position at which the thickness of the glass plate is 6% of the thickness of the glass plate from the end of the second main face side of the end face toward the first main face side along the thickness direction of the glass plate.

11. A display device having the glass plate according to any one of claims 1 to 10.

12. The display device of claim 11, wherein, The glass plate is installed with the second main face as the inner side of the display device.

13. A method for manufacturing a glass plate including a first main face, a second main face, and an end face connecting the first main face and the second main face, having a compressive stress layer, The manufacturing method includes the steps of: The end face of at least a part of the area around the main face of the glass plate, the length of the longest crack in the region from the position at which the length from the end of the end surface on the first major surface side to the position at which the length from the end of the end surface on the first major surface side to the position at which the length from the end of the end surface on the first major surface side to the position at which the length from the end of the end surface on the first major surface side to the position at which the length from the end of the end surface on the first major surface side to the position at which the length from the end of the end surface on the first major surface side to the position at which the length from the end of the end surface on the first major surface side to the position at which the length from the end of the end surface on the first major surface side to the position at which the length from the end of the end surface on the first major surface side to the position at which the length from the end of the end surface on the first major surface side to the position at which the length from the end of the end surface on the first major surface side to the position at which the length from the end of the end surface on the first major surface side to the position at which the length from the end of the end surface on the first major surface side to the position at which the length from the end of the end surface on the first major surface side to the position at which the length from the end of the end surface on the first major surface side to the position at which the length from the end of the end surface on the first major surface side to the position at which the length from the end of the end surface on the first major surface side to the position at which the length from the end of the end surface on the first major surface side to the position at which the length from the end of the end surface on the first major surface side to the position at which the length from the end of the end surface on the first major surface side to the position at which the length from the end of the end surface on the first major surface side to the position at which the length from the end of the end surface on the first major surface side to the position at which the length from the end of the end surface on the first major surface side to the position at which the length from the end of the end surface on the first major surface side to the position at which the length from the end of the end surface on the first major surface side to the position at which ​ wherein, σ' FS (a) is a breaking stress, unit: MPa, a is a length of a crack, unit: pm, K IC is a breaking toughness value, unit: MPa-m 0.5 F is a correction coefficient of a stress intensity factor, counted as 1.1215, f(x) is a compressive stress acting on the glass sheet at a position with a depth x from the 2nd main surface, unit: MPa.

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