Chemically strengthened glass plate and method for producing same

Abstract

A chemically strengthened glass plate (1) is provided with a thin section (2), a thick section (3), and compressive stress layers (6a, 6b) formed on the respective surface sections of the thin section (2) and the thick section (3), and is bendable in the thin section (2). The chemically strengthened glass plate (1) has the relationship DOC2 > DOC1 and the relationship DOC2 / t2 > = 0.05, where DOC1 is the maximum compressive stress depth of the thin-walled section (2), DOC2 is the maximum compressive stress depth of the thick-walled section (3), and t2 is the thickness of the thick-walled section (3).

Description

Technical Field

[0001] The present invention relates to a chemically strengthened glass plate and a method for producing the same. Background Art

[0002] In recent years, so-called foldable devices, such as smartphones and tablet PCs, have been developed, whose display surfaces can be folded. The cover glass of such foldable devices must be bendable. Therefore, when using a chemically strengthened glass sheet as the cover glass, the chemically strengthened glass sheet must also be bendable.

[0003] To make chemically strengthened glass sheets bendable, one approach is to thin the entire sheet to impart flexibility (softness). However, while thin-walled chemically strengthened glass sheets can be bent, they have the problem of being difficult to impart high impact resistance.

[0004] On the other hand, when a chemically strengthened glass sheet is made thick throughout, while it is easy to impart high impact resistance to the sheet, it is difficult to impart flexibility to the sheet. As a result, a chemically strengthened glass sheet made thick throughout has the problem of being difficult to bend.

[0005] Therefore, a chemically strengthened glass sheet has been developed that has a thin portion and a thick portion thicker than the thin portion, and in which the thin portion is bendable (see, for example, Patent Document 1).

[0006] Prior art literature

[0007] Patent Literature

[0008] Patent Document 1: International Publication No. 2020 / 065132 Summary of the Invention

[0009] Problems to be solved by the invention

[0010] Even in chemically strengthened glass sheets with thin-walled and thick-walled portions, where the thin-walled portion is bendable, there is still room for improvement in achieving both high impact resistance and flexibility. In particular, in such chemically strengthened glass sheets, increasing the impact resistance of either the thick-walled or thin-walled portion tends to reduce the impact resistance of the other portion.

[0011] For example, if the depth of the compressive stress layer (DOC) is increased to improve the impact resistance of thick-walled sections, then if ion exchange is carried out deeply in a single ion exchange process, ions will diffuse excessively in the thin-walled sections, spreading throughout the entire thickness of the glass. This makes it difficult to create a difference in ion concentration between the center and the surface of the glass, and high compressive stress may not be achieved on the surface of the thin-walled sections. Conversely, if the ion exchange depth is set shallow to achieve high compressive stress on the surface of the thin-walled sections, the DOC will also be reduced in the thick-walled sections. As such, conventional technologies have made it difficult to achieve high impact resistance in both thick and thin-walled sections.

[0012] An object of the present invention is to provide a chemically strengthened glass plate having high impact resistance and flexibility.

[0013] Means for solving problems

[0014] (1) The present invention, which was first created to solve the above-mentioned problems, is characterized in that it includes a thin-walled portion, a thick-walled portion thicker than the thin-walled portion, and a compressive stress layer formed on each surface portion of the thin-walled portion and the thick-walled portion, and is capable of being bent at the thin-walled portion. When the maximum compressive stress depth of the thin-walled portion is set to DOC1, the maximum compressive stress depth of the thick-walled portion is set to DOC2, and the thickness of the thick-walled portion is set to t2, the relationship DOC2>DOC1 is maintained, and the relationship DOC2 / t2≥0.05 is maintained.

[0015] With this arrangement, the maximum compressive stress depth DOC2 in the thick-walled portion is greater than the maximum compressive stress depth DOC1 in the thin-walled portion (DOC2 > DOC1). Furthermore, the maximum compressive stress depth DOC2 in the thick-walled portion is sufficient relative to the thickness of the thick-walled portion (DOC2 / t2 ≥ 0.05). Consequently, the compressive stress layer can be formed to an appropriate depth corresponding to the thickness of the thin-walled and thick-walled portions, respectively. In other words, while the thin-walled portion imparts flexibility to the chemically strengthened glass sheet, high impact resistance can be achieved in both the thin-walled and thick-walled portions.

[0016] (2) In the configuration of (1) above, when the maximum compressive stress depth of the thin portion is defined as DOC1 and the thickness of the thin portion is defined as t1, it is preferable that the relationship DOC1 / t1≦0.20 is satisfied.

[0017] In thin-walled sections, there's less glass inside to suppress the volume expansion of the ion-exchange portion. Therefore, if the maximum compressive stress depth DOC1 is too large, it becomes difficult to increase the maximum compressive stress value CS1. Therefore, the maximum compressive stress depth DOC1 in thin-walled sections is preferably 20% or less of the thickness t1 of the thin-walled section (DOC1 / t1 ≤ 0.20). This increases the maximum compressive stress value CS1 in the thin-walled section, facilitating improved impact resistance in the thin-walled section.

[0018] (3) In the configuration of (1) or (2) above, preferably, the thickness t1 of the thin portion is 0.01 mm or more and 0.2 mm or less, and the thickness t2 of the thick portion is greater than 0.2 mm and 2.0 mm or less.

[0019] With this arrangement, the thin-walled portion is thin enough to easily improve the flexibility of the chemically strengthened glass plate, and the thick-walled portion is thick enough to easily improve the impact resistance of the entire chemically strengthened glass plate.

[0020] (4) In any of the above configurations (1) to (3), when the maximum compressive stress depth of the thin portion is DOC1 and the maximum compressive stress depth of the thick portion is DOC2, the relationship DOC2 / DOC1≥5 is preferably satisfied.

[0021] This configuration can achieve higher impact resistance in each of the thin-walled portion and the thick-walled portion.

[0022] (5) In any one of the above configurations (1) to (4), it is preferred that the maximum compressive stress depth DOC1 of the thin-walled portion is 2 to 20 μm, and the maximum compressive stress depth DOC2 of the thick-walled portion is 10 to 200 μm.

[0023] This configuration can achieve higher impact resistance in each of the thin-walled portion and the thick-walled portion.

[0024] (6) In any one of the above configurations (1) to (5), it is preferred that the maximum compressive stress value CS1 of the thin-walled portion is 100 to 1500 MPa, and the maximum compressive stress value CS2 of the thick-walled portion is 200 to 2000 MPa.

[0025] This configuration can achieve higher impact resistance in each of the thin-walled portion and the thick-walled portion.

[0026] (7) In any of the above configurations (1) to (6), when the maximum compressive stress value of the thin portion is CS1 and the maximum compressive stress value of the thick portion is CS2, it is preferable that the relationship CS2 / CS1≤20 is satisfied.

[0027] This configuration can achieve higher impact resistance in each of the thin-walled portion and the thick-walled portion.

[0028] (8) In any one of the above configurations (1) to (7), preferably, in the compressive stress layer of the thick portion, stress distribution in the depth direction has an inflection point.

[0029] By doing so, it is possible to increase the maximum compressive stress depth DOC2 of the thick portion while reducing the maximum tensile stress value CT2 of the thick portion.

[0030] (9) In any one of the above-mentioned structures (1) to (8), the glass composition preferably contains Li2O and Na2O.

[0031] With this arrangement, it is easy to manufacture a chemically strengthened glass plate having the aforementioned stress characteristics by performing the ion exchange treatment multiple times (e.g., twice). Specifically, for example, a chemically strengthened glass plate having the aforementioned stress characteristics can be manufactured easily using a molten salt containing NaNO3 and a molten salt containing KNO3.

[0032] (10) In the composition of (9) above, the glass composition preferably contains, in mol%, 50 to 80% of SiO2, 8 to 25% of Al2O3, 0 to 10% of B2O3, 3 to 15% of Li2O, 3 to 21% of Na2O, 0 to 10% of K2O, 0 to 10% of MgO, and 0 to 15% of P2O5.

[0033] With this configuration, it is easy to manufacture a chemically strengthened glass plate having the above-mentioned stress characteristics by performing ion exchange treatment multiple times (for example, in two stages).

[0034] (11) The present invention, which was first devised to solve the above-mentioned problems, is characterized in that it is a method for manufacturing a chemically strengthened glass plate having a thin-walled portion, a thick-walled portion thicker than the thin-walled portion, and a compressive stress layer formed on each surface portion of the thin-walled portion and the thick-walled portion, and the thin-walled portion can be bent. The manufacturing method comprises: a preparation step of preparing a strengthening glass having the thick-walled portion and the thin-walled portion; and an ion exchange treatment step of performing a two-stage ion exchange treatment on the strengthening glass. In the ion exchange treatment step, the two-stage ion exchange treatment is performed in such a manner that the chemically strengthened glass plate after the ion exchange treatment satisfies the relationship DOC2>DOC1 and the relationship DOC2 / t2≥0.05, when the maximum compressive stress depth of the thin-walled portion is set to DOC1, the maximum compressive stress depth of the thick-walled portion is set to DOC2, and the thickness of the thick-walled portion is set to t2.

[0035] By setting it in this way, a chemically strengthened glass plate having high impact resistance and flexibility can be manufactured.

[0036] (12) In the configuration of (11) above, the tempered glass plate preferably contains Li2O and Na2O as the glass composition, and the ion exchange treatment step includes a first ion exchange treatment in which ion exchange is performed using a molten salt containing 10% or more of NaNO3, and a second ion exchange treatment in which ion exchange is performed using a molten salt containing 30% or more of KNO3 after the first ion exchange treatment.

[0037] In this manner, the maximum compressive stress value CS1 can be increased in the thin-walled portion by K ion exchange, and the maximum compressive stress value CS2 can be increased in the thick-walled portion by increasing the maximum compressive stress depth DOC2 by Na ion exchange.

[0038] Furthermore, the present invention can also adopt the following aspects as another aspect.

[0039] (13) In another embodiment, the chemically strengthened glass plate of the present invention may have the following characteristics, namely, it includes a thin-walled portion, a thick-walled portion thicker than the thin-walled portion, and a compressive stress layer formed on the surface of each of the thin-walled portion and the thick-walled portion, the thin-walled portion is bendable, the thickness t1 of the thin-walled portion is not more than 0.2 mm, and the stress distribution in the depth direction has an inflection point in the compressive stress layer of the thick-walled portion.

[0040] Effects of the Invention

[0041] According to the present invention, a chemically strengthened glass plate having high impact resistance and flexibility can be provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 This is a plan view of a chemically strengthened glass plate according to an embodiment of the present invention.

[0043] Figure 2 yes Figure 1 AA cross-sectional view.

[0044] Figure 3 It will Figure 2 The cross-sectional view showing the enlarged periphery of the thin-walled portion is a diagram showing the compressive stress layer and the tensile stress layer of the thin-walled portion and the thick-walled portion.

[0045] Figure 4 This is an example of stress distribution in a thick wall section. DETAILED DESCRIPTION

[0046] Hereinafter, a chemically strengthened glass plate and a method for producing the same according to an embodiment of the present invention will be described.

[0047] (Chemically strengthened glass plate)

[0048] like Figure 1 and Figure 2 As shown, the chemically strengthened glass plate 1 of this embodiment includes a thin portion 2 and a thick portion 3 that is thicker than the thin portion 2 .

[0049] In this embodiment, the chemically strengthened glass plate 1 is exemplified as a rectangular shape having long sides 1a and short sides 1b in a plan view. The length La of the long side 1a of the chemically strengthened glass plate 1 is preferably 50 mm to 500 mm, 65 mm to 450 mm, 60 mm to 400 mm, 70 mm to 300 mm, 75 mm to 200 mm, or 80 mm to 160 mm. The length Lb of the short side 1b of the chemically strengthened glass plate 1 is preferably 40 mm to 400 mm, 45 mm to 350 mm, 50 mm to 300 mm, 55 mm to 120 mm, or 60 mm to 80 mm.

[0050] The chemically strengthened glass plate 1 can be bent at the thin portion 2. The chemically strengthened glass plate 1 has flexibility such that the minimum bending radius is 10 mm or less without being damaged when the thin portion 2 is bent.

[0051] The thin-walled portion 2 separates the two thick-walled portions 3. The two separated thick-walled portions 3 are connected to each other by the thin-walled portion 2. In other words, the thin-walled portion 2 extends in a strip-like shape from one end of the chemically strengthened glass plate 1 to the other end. More specifically, the thin-walled portion 2 is provided parallel to the short side 1b so as to cross the main surface of the chemically strengthened glass plate 1 from the center of one long side 1a to the center of the other long side 1a.

[0052] The two thick portions 3 are preferably line-symmetrical with respect to the thin portion 2. This configuration allows the chemically strengthened glass plate 1 to be bent with the two thick portions 3 overlapping, making it suitable for applications such as foldable devices.

[0053] The thickness t1 of the thin-walled portion 2 is preferably 0.01 mm to 0.2 mm, 0.01 mm to 0.15 mm, 0.01 mm to 0.095 mm, 0.02 mm to 0.085 mm, or 0.03 mm to 0.075 mm. This arrangement makes it easier to ensure the flexibility and impact resistance of the thin-walled portion 2. It should be noted that if the thickness t1 of the thin-walled portion 2 is too thin, not only will the mechanical strength be reduced, but it will also be difficult to increase the surface compressive stress value, which may in turn impair flexibility.

[0054] The thickness t1 of the thin portion 2 is preferably constant. If the thickness of the thin portion 2 is not constant, the thickness of the thinnest portion of the thin portion 2 (minimum thickness) can be determined as t1.

[0055] The width W of the thin portion 2 is preferably 3 mm to 50 mm, or 5 mm to 30 mm. This ensures a sufficient movable area required for bending the chemically strengthened glass sheet 1. The width W of the thin portion 2 is preferably constant.

[0056] The thickness t2 of the thick-walled portion 3 is preferably greater than 0.2 mm and less than 2.0 mm, greater than 0.2 mm and less than 0.8 mm, greater than 0.2 mm and less than 0.7 mm, greater than 0.2 mm and less than 0.65 mm, or greater than 0.2 mm and less than 0.6 mm. This configuration appropriately suppresses the deformation of the thick-walled portion 3 and improves the handling during assembly and manufacturing of the device.

[0057] The thickness t2 of the thick portion 3 is preferably constant. If the thickness of the thick portion 3 is not constant, the thickness of the thickest portion of the thick portion 3 (maximum thickness) can be determined as t2.

[0058] The chemically strengthened glass plate 1 has a groove 4 on one main surface 1c. The groove 4 includes a bottom surface 4a formed as a plane parallel to the main surfaces 1c and 1d, and a side surface 4b formed as a plane inclined relative to the main surfaces 1c and 1d. The shape of the groove 4 is not particularly limited. The side surface 4b may be, for example, a plane perpendicular to the main surfaces 1c and 1d, or a concave curved surface recessed toward the main surface 1d. The bottom surface 4a may be, for example, a concave curved surface recessed toward the main surface 1d.

[0059] The thin portion 2 is formed by a residual portion 5 on the other main surface 1d side formed at a position corresponding to the groove 4. The chemically strengthened glass plate 1 can be oriented in a direction such that the groove 4 side is outward ( Figure 2 By enabling bending in this direction, the flat surface without the groove 4 can be used as the touch surface of the foldable device, protecting the touch surface when the foldable device is folded. It should be noted that the thin-walled portion 2 can also be formed by forming the groove 4 on both main surfaces 1c and 1d.

[0060] like Figure 3 As shown, the chemically strengthened glass plate 1 includes a compressive stress layer 6 formed on the surface portion including the surface, and a tensile stress layer 7 formed on the inner side (center side in the thickness direction) relative to the compressive stress layer 6. In this embodiment, the compressive stress layer 6 includes a compressive stress layer 6a formed on the thin-walled portion 2 and a compressive stress layer 6b formed on the thick-walled portion 3. The tensile stress layer 7 includes a tensile stress layer 7a formed on the thin-walled portion 2 and a tensile stress layer 7b formed on the thick-walled portion 3. However, the stress characteristics of the thin-walled portion 2 and the thick-walled portion 3 differ from each other.

[0061] The maximum compressive stress depth DOC1 of the thin-walled portion 2 is smaller than the maximum compressive stress depth DOC2 of the thick-walled portion 3. In other words, the relationship DOC1 < DOC2 holds. This arrangement results in a relatively smaller depth of the compressive stress layer 6a in the thin-walled portion 2, while a relatively larger depth of the compressive stress layer 6b in the thick-walled portion 3. Therefore, by adjusting the depths of the compressive stress layers 6a and 6b according to the respective thicknesses of the thin-walled portion 2 and the thick-walled portion 3, high impact resistance can be easily achieved in both the thin-walled portion 2 and the thick-walled portion 3. It should be noted that DOC1 refers to the depth of the compressive stress layer 6a in the thin-walled portion 2, and DOC2 refers to the depth of the compressive stress layer 6b in the thick-walled portion 3. If the thickness of the thin-walled portion 2 is not constant, the maximum compressive stress depth at the thinnest portion of the thin-walled portion 2 (i.e., the portion with thickness t1) can be determined as DOC1. CS1 and CT1, described later, can also be determined at the same location as DOC1.

[0062] The lower limit of DOC2 / DOC1 is preferably 5 or greater, 7 or greater, or 10 or greater. This makes it easier to optimize the depths of the compressive stress layers 6a and 6b according to the thicknesses of the thin-walled portion 2 and the thick-walled portion 3. On the other hand, the upper limit of DOC2 / DOC1 is preferably 200 or less, 100 or less, or 50 or less. It should be noted that DOC2 / DOC1 is the value obtained by dividing the maximum compressive stress depth DOC2 of the thick-walled portion 3 by the maximum compressive stress depth DOC1 of the thin-walled portion 2.

[0063] The lower limit of the maximum compressive stress depth DOC1 of the thin-walled portion 2 is preferably 2 μm or greater, 3 μm or greater, 4 μm or greater, or 5 μm or greater. The upper limit of the maximum compressive stress depth DOC1 of the thin-walled portion 2 is preferably 20 μm or less, 15 μm or less, or 10 μm or less. The lower limit of the maximum compressive stress depth DOC2 of the thick-walled portion 3 is preferably 10 μm or greater, 30 μm or greater, 40 μm or greater, 50 μm or greater, or 80 μm or greater. The upper limit of the maximum compressive stress depth DOC2 of the thick-walled portion 3 is preferably 200 μm or less and 150 μm or less.

[0064] The lower limit of DOC2 / t2 is preferably 0.05 or greater, 0.08 or greater, 0.10 or greater, 0.12 or greater, or 0.15 or greater. If this is done, the proportion of the compressive stress layer 6b in the thick-walled portion 3 is sufficiently large, enabling high impact resistance to be achieved. On the other hand, the upper limit of DOC2 / t2 is preferably 0.3 or less, 0.25 or less, or 0.23 or less. If this is done, the proportion of the compressive stress layer 6b in the thick-walled portion 1 is prevented from becoming excessively large, making it easier to increase the maximum compressive stress value CS2 of the thick-walled portion 1. It should be noted that DOC2 / t2 is the value obtained by dividing the maximum compressive stress depth DOC2 of the thick-walled portion 3 by the thickness t2 of the thick-walled portion 3.

[0065] The lower limit range of DOC1 / t1 is preferably above 0.01, above 0.02, and above 0.05. If set in this way, the proportion of the compressive stress layer 6b in the thick-walled portion 3 is sufficiently large, and high impact resistance can be achieved. On the other hand, the upper limit range of DOC1 / t1 is preferably below 0.02, below 0.10, below 0.08, and below 0.05. If set in this way, the proportion of the compressive stress layer 6a in the thin-walled portion 2 is suppressed from being too large, and it is easy to increase the maximum compressive stress value CS1 of the thin-walled portion 2. In the case of the thin-walled portion 2, in particular, since there is less glass inside to suppress the volume expansion of the ion exchange portion, if the maximum compressive stress depth DOC1 becomes too large, it is difficult to increase the maximum compressive stress value CS1. It should be noted that DOC1 / t1 is the value obtained by dividing the maximum compressive stress depth DOC1 of the thin-walled portion 2 by the thickness t1 of the thin-walled portion 2.

[0066] Between DOC2 / t2 and DOC1 / t1, the relationship DOC2 / t2 ≥ DOC1 / t1 is optionally established. For example, DOC2 / t2 may be 1.3 times or more, 1.5 times or more, or 2 times or more of DOC1 / t1.

[0067] When the maximum compressive stress value of the thin-walled portion 2 is set to CS1 and the maximum compressive stress value of the thick-walled portion 3 is set to CS2, the upper limit range of CS2 / CS1 is preferably less than 20, less than 15, less than 12, less than 10, less than 5, less than 4, less than 2, or less than 1.5. The lower limit range of CS2 / CS1 is preferably more than 1, more than 1.05, more than 1.1, or more than 1.1. If set in this way, it is easy to further improve the impact resistance of the thin-walled portion 2 and the thick-walled portion 3. It should be noted that the maximum compressive stress value CS1 is the compressive stress value at the surface of the thin-walled portion 2. The maximum compressive stress value CS2 is the compressive stress value at the surface of the thick-walled portion 3. CS2 / CS1 is the value obtained by dividing the maximum compressive stress value CS2 of the thick-walled portion 3 by the maximum compressive stress value CS1 of the thin-walled portion 2.

[0068] The lower limit range of the maximum compressive stress value CS1 of the thin-walled portion 2 is preferably 100 MPa or more, 200 MPa or more, 300 MPa or more, 400 MPa or more, or 500 MPa or more. The upper limit range of the maximum compressive stress value CS1 of the thin-walled portion 2 is preferably 1500 MPa or less, 1300 MPa or less, 1100 MPa or less, 1000 MPa or less, or 900 MPa or less.

[0069] The lower limit of the maximum compressive stress value CS2 of the thick-walled portion 3 is preferably 200 MPa or more, 300 MPa or more, 400 MPa or more, 500 MPa or more, 600 MPa or more, 700 MPa or more, 800 MPa or more, or 900 MPa or more. The upper limit of the maximum compressive stress value CS2 of the thick-walled portion 3 is preferably 2000 MPa or less, 1500 MPa or less, 1300 MPa or less, or 1200 MPa or less.

[0070] The upper limit range of the maximum tensile stress value CT1 of the thin-walled portion 2 is preferably 1000 MPa or less, 500 MPa or less, 400 MPa or less, 285 MPa or less, 250 MPa or less, 240 MPa, 230 MPa or less, 220 MPa or less, 210 MPa or less, 200 MPa or less, 190 MPa or less, 180 MPa or less, 170 MPa or less, 160 MPa or less, 150 MPa or less, 145 MPa or less, 140 MPa or less, 130 MPa or less, 120 MPa or less, 110 MPa or less, 100 MPa or less, 95 MPa or less, 85 MPa or less, or 70 MPa or less. On the other hand, the lower limit range of the maximum tensile stress value CT1 of the thin-walled portion 2 is preferably 20 MPa or more, 50 MPa or more, or 60 MPa or more. If set in this way, while ensuring safety in that the failure mode does not become dangerous, it is possible to ensure strength against bending.

[0071] The upper limit range of the maximum tensile stress value CT2 of the thick-walled portion 3 is preferably 1000 MPa or less, 500 MPa or less, 400 MPa or less, 285 MPa or less, 250 MPa or less, 240 MPa, 230 MPa or less, 220 MPa or less, 210 MPa or less, 200 MPa or less, 190 MPa or less, 180 MPa or less, 170 MPa or less, 160 MPa or less, 150 MPa or less, 145 MPa or less, 140 MPa or less, 130 MPa or less, 120 MPa or less, 110 MPa or less, 100 MPa or less, 95 MPa or less, 85 MPa or less, or 70 MPa or less. On the other hand, the lower limit range of the maximum tensile stress value CT1 of the thick-walled portion 3 is preferably 20 MPa or more, 50 MPa or more, or 60 MPa or more. This ensures safety by preventing dangerous failure modes during failure.

[0072] Numerical values ​​related to stress, such as DOC1, DOC2, CS1, CS2, CT1, and CT2, can be derived by measuring the stress distribution of the chemically strengthened glass plate 1 using a measuring device such as FSM-6000 or SLP-2000 manufactured by Orihara Seisakusho.

[0073] The entire surface of the chemically strengthened glass plate 1, namely, both principal surfaces including the thin-walled portion 2 and the thick-walled portion 3, and the end faces, are preferably formed of etched surfaces. Etching the entire surface reduces defects and provides high strength. The surface roughness Ra of the etched surface is, for example, 10.0 to 0.1 nm. The term "principal surface" refers to the front and back surfaces of the entire surface of the glass plate, excluding the end faces.

[0074] In this embodiment, the chemically strengthened glass plate 1 contains Li 2 O and Na 2 O as a glass composition. This configuration makes it easy to manufacture the chemically strengthened glass plate 1 having the above-mentioned stress characteristics by performing ion exchange treatment multiple times (for example, twice).

[0075] Specifically, the chemically strengthened glass plate 1 preferably contains, in mol%, 50-80% SiO2, 8-25% Al2O3, 0-10% B2O3, 3-15% Li2O, 3-21% Na2O, 0-10% K2O, 0-10% MgO, and 0-15% P2O5. The reasons for limiting the content ranges of each component are as follows. It should be noted that, unless otherwise specified, the percentages in the description of the content ranges of each component refer to mole %.

[0076] SiO2 is a component that forms the glass network. If the SiO2 content is too low, vitrification becomes difficult, and the thermal expansion coefficient becomes too high, which tends to reduce thermal shock resistance. Therefore, the appropriate lower limit range of SiO2 is 50% or more, 55% or more, 57% or more, 59% or more, and particularly 61% or more. On the other hand, if the SiO2 content is too high, the meltability and formability tend to decrease, and the thermal expansion coefficient becomes too low, making it difficult to match the thermal expansion coefficient of the surrounding materials. Therefore, the appropriate upper limit range of SiO2 is 80% or less, 70% or less, 68% or less, 66% or less, 65% or less, and particularly 64.5% or less.

[0077] Al2O3 is a component that improves ion exchange performance and is also a component that improves strain point, Young's modulus, fracture toughness, and Vickers hardness. Thus, the appropriate lower limit range of Al2O3 is 8% or more, 10% or more, 12% or more, 13% or more, 14% or more, 14.4% or more, 15% or more, 15.3% or more, 15.6% or more, 16% or more, 16.5% or more, 17% or more, 17.2% or more, 17.5% or more, 17.8% or more, 18% or more, greater than 18%, 18.3% or more, and particularly 18.5% or more, 18.6% or more, 18.7% or more, or 18.8% or more. On the other hand, if the content of Al2O3 is too much, the high-temperature viscosity increases, and the meltability and formability are easily reduced. Moreover, devitrified crystals are easily precipitated in the glass, making it difficult to form it into a sheet using overflow downdraw methods or the like. In particular, when an alumina-based refractory is used as a formed body refractory and formed into a plate shape by an overflow downdraw method, spinel devitrified crystals tend to precipitate at the interface with the alumina-based refractory. Furthermore, acid resistance is reduced, making it difficult to apply to an acid treatment process. Therefore, the appropriate upper limit range of Al2O3 is 25% or less, 21% or less, 20.5% or less, 20% or less, 19.9% ​​or less, 19.5% or less, 19.0% or less, and particularly 18.9% or less.

[0078] B2O3 is a component that reduces high-temperature viscosity and density, stabilizes the glass, makes crystals difficult to precipitate, and lowers the liquidus temperature. If the B2O3 content is too low, the stress depth of ion exchange between the Li ions contained in the glass and the Na ions in the molten salt becomes too large, resulting in a tendency for the maximum compressive stress value CS2 to decrease. Furthermore, the glass may become unstable and its resistance to devitrification may be reduced. Therefore, the suitable lower limit range of B2O3 is 0% or more, 0.01% or more, 0.05% or more, 0.1% or more, 0.2% or more, 0.5% or more, 0.6% or more, 0.7% or more, 0.8% or more, 0.9% or more, and particularly 1% or more. On the other hand, if the B2O3 content is too high, the stress depth may decrease. In particular, the efficiency of ion exchange between the Na ions contained in the glass and the K ions in the molten salt tends to decrease, and the maximum compressive stress depth DOC tends to decrease. Therefore, the appropriate upper limit range of B2O3 is less than 10%, less than 5%, less than 4%, less than 3.8%, less than 3.5%, less than 3.3%, less than 3.2%, less than 3.1%, less than 3%, and especially less than 2.9%.

[0079] Li2O is an ion exchange component, particularly necessary for exchanging Li ions contained in the glass with Na ions in the molten salt, thereby increasing the maximum compressive stress depth DOC2. Furthermore, Li2O reduces high-temperature viscosity, thereby improving meltability and formability, and is also a component that increases Young's modulus. Therefore, the appropriate lower limit range of Li2O is 3% or more, 4% or more, 5% or more, 5.5% or more, 6.5% or more, 7% or more, 7.3% or more, 7.5% or more, 7.8% or more, and particularly 8% or more. Therefore, the appropriate upper limit range of Li2O is 15% or less, 13% or less, 12% or less, 11.5% or less, 11% or less, 10.5% or less, less than 10%, and particularly 9.9% or less, 9% or less, and 8.9% or less.

[0080] Na2O is an ion exchange component that reduces high-temperature viscosity, improving meltability and formability. Furthermore, Na2O improves devitrification resistance, particularly suppressing devitrification caused by reactions with alumina-based refractories. Therefore, the appropriate lower limit range for Na2O is 3% or more, 4% or more, 5% or more, 6% or more, 7% or more, 7.5% or more, 8% or more, 8.5% or more, 8.8% or more, and particularly 9% or more. On the other hand, excessive Na2O content increases the thermal expansion coefficient excessively, tending to reduce thermal shock resistance. Furthermore, the component balance of the glass composition may be disrupted, which in turn reduces devitrification resistance. Therefore, the appropriate upper limit range for Na2O is 21% or less, 20% or less, 19% or less, particularly 18% or less, 15% or less, 13% or less, 11% or less, and particularly 10% or less.

[0081] K2O is a component that reduces high-temperature viscosity, improving meltability and formability. However, if the K2O content is too high, the thermal expansion coefficient becomes excessively high, and thermal shock resistance tends to decrease. Furthermore, the compressive stress value at the outermost surface tends to decrease. Therefore, the appropriate upper limit range of K2O is 10% or less, 7% or less, 6% or less, 5% or less, 4% or less, 3% or less, 2% or less, 1.5% or less, 1% or less, less than 1%, 0.5% or less, and particularly less than 0.1%. It should be noted that, with emphasis on increasing stress depth, the appropriate lower limit range of K2O is 0% or more, 0.1% or more, 0.3% or more, and particularly 0.5% or more.

[0082] MgO reduces high-temperature viscosity, improving meltability and formability, and raising strain point and Vickers hardness. Among alkaline earth metal oxides, it is the most effective component in improving ion exchange performance. However, excessive MgO content can reduce devitrification resistance, making it difficult to suppress devitrification caused by reactions with alumina-based refractories. Therefore, suitable MgO contents are 0-10%, 0-5%, 0.1-4%, 0.2-3.5%, and particularly 0.5 to less than 3%.

[0083] P2O5 is a component that enhances ion exchange performance, particularly increasing the maximum compressive stress depth DOC2. It also improves acid resistance. If the P2O5 content is too low, the ion exchange performance may not be fully realized. In particular, the efficiency of ion exchange between Na ions in the glass and K ions in the molten salt is likely to decrease. Furthermore, the glass may become unstable and its devitrification resistance may be reduced. Therefore, the appropriate lower limit range for P2O5 is 0% or more, 0.1% or more, 0.4% or more, 0.7% or more, 1% or more, 1.2% or more, 1.4% or more, 1.6% or more, 2% or more, 2.3% or more, 2.5% or more, and particularly 3% or more. On the other hand, if the P2O5 content is too high, the glass may experience phase separation and water resistance may be reduced. Furthermore, the stress depth of ion exchange between Li ions in the glass and Na ions in the molten salt becomes excessive, resulting in a decrease in the maximum compressive stress value CS2. Therefore, the upper limit range of the appropriate P2O5 is 15% or less, 10% or less, 5% or less, 4.5% or less, or 4% or less. In other words, in one embodiment, P2O5 may be substantially not contained.

[0084] Alkali metal oxides are ion-exchange components that reduce high-temperature viscosity, improving meltability and formability. Excessive alkali metal oxide content ([Li2O] + [Na2O] + [K2O]) can increase the thermal expansion coefficient and reduce acid resistance. Therefore, the appropriate lower limit range for the alkali metal oxide ([Li2O] + [Na2O] + [K2O]) content is 10% or higher, 11% or higher, 12% or higher, 13% or higher, 14% or higher, and 15% or higher. The appropriate upper limit range for the alkali metal oxide ([Li2O] + [Na2O] + [K2O]) content is 25% or lower, 23% or lower, 20% or lower, 19% or lower, and 18% or lower.

[0085] The molar ratio [Li2O] / ([Na2O] + [K2O]) is preferably 0.4 to 1.0, 0.5 to 0.9, and particularly 0.6 to 0.8. If the molar ratio [Li2O] / ([Na2O] + [K2O]) is too low, the ion exchange performance may not be fully exerted. In particular, the efficiency of ion exchange between the Li ions contained in the glass and the Na ions in the molten salt tends to decrease. On the other hand, if the molar ratio [Li2O] / ([Na2O] + [K2O]) is too high, devitrified crystals tend to precipitate in the glass, making it difficult to form the glass into a sheet using methods such as overflow downdraw. It should be noted that "[Li2O] / ([Na2O] + [K2O])" refers to the value obtained by dividing the Li2O content by the combined amount of Na2O and K2O.

[0086] The molar ratio ([Na2O] - [Li2O]) / ([Al2O3] + [B2O3] + [P2O5]) is preferably 0.29 or less, 0.27 or less, 0.26 or less, 0.25 or less, 0.23 or less, 0.20 or less, and particularly 0.15 or less. If the molar ratio ([Na2O] - [Li2O]) / ([Al2O3] + [B2O3] + [P2O5]) is too high, the ion exchange performance may not be fully exerted. In particular, the efficiency of ion exchange between Li ions contained in the glass and Na ions in the molten salt tends to decrease.

[0087] The molar ratio ([B2O3] + [Na2O] - [P2O5]) / ([Al2O3] + [Li2O]) is preferably 0.30 or greater, 0.35 or greater, 0.40 or greater, 0.42 or greater, 0.43 or greater, and particularly 0.45 or greater. If the molar ratio ([B2O3] + [Na2O] - [P2O5]) / ([Al2O3] + [Li2O]) is too low, devitrified crystals are likely to precipitate in the glass, making it difficult to form the glass into a sheet using methods such as overflow downdraw.

[0088] ([SiO2] + 1.2 × [P2O5] - 3 × [Al2O3] - 2 × [Li2O] - 1.5 × [Na2O] - [K2O] - [B2O3]) is preferably -40% or more, -30% or more, -25% or more, -24% or more, -23% or more, -22% or more, -21% or more, -20% or more, -19% or more, and particularly -18% or more. If ([SiO2] + 1.2 × [P2O5] - 3 × [Al2O3] - 2 × [Li2O] - 1.5 × [Na2O] - [K2O] - [B2O3]) is too low, acid resistance tends to decrease. On the other hand, if the ratio ([SiO2] + 1.2 × [P2O5] - 3 × [Al2O3] - 2 × [Li2O] - 1.5 × [Na2O] - [K2O] - [B2O3]) is too high, the ion exchange performance may not be fully exerted. Therefore, ([SiO2] + 1.2 × [P2O5] - 3 × [Al2O3] - 2 × [Li2O] - 1.5 × [Na2O] - [K2O] - [B2O3]) is preferably 30 mol% or less, 20 mol% or less, 15 mol% or less, 10 mol% or less, 5 mol% or less, and particularly 0 mol% or less.

[0089] In addition to the above-mentioned components, for example, the following components may be added.

[0090] Compared to other components, CaO improves meltability and formability without reducing devitrification resistance, lowering high-temperature viscosity, or increasing strain point and Vickers hardness. However, excessive CaO content can reduce ion exchange performance or degrade the ion exchange solution during ion exchange. Therefore, the appropriate upper limit range for CaO is 6% or less, 5% or less, 4% or less, 3.5% or less, 3% or less, 2% or less, 1% or less, less than 1%, 0.5% or less, and particularly less than 0.1%.

[0091] SrO and BaO are components that lower high-temperature viscosity, improving meltability and formability, or increasing the strain point and Young's modulus. However, excessive amounts of these components can hinder ion exchange reactions, increase density and thermal expansion coefficient inappropriately, and increase the likelihood of devitrification. Therefore, suitable SrO and BaO contents are 0-2%, 0-1.5%, 0-1%, 0-0.5%, 0-0.1%, and particularly 0 to less than 0.1%, respectively.

[0092] ZnO is a component that improves ion exchange performance, and is particularly effective in increasing the maximum compressive stress value CS2. Furthermore, it does not reduce low-temperature viscosity, but rather reduces high-temperature viscosity. The appropriate lower limit range for ZnO is 0% or more, 0.1% or more, 0.3% or more, 0.5% or more, 0.7% or more, and particularly 1% or more. On the other hand, excessive ZnO content can lead to phase separation in the glass, reduced devitrification resistance, increased density, or reduced stress depth. Therefore, the appropriate upper limit range for ZnO is 10% or less, 6% or less, 5% or less, 4% or less, 3% or less, 2% or less, 1.5% or less, 1.3% or less, 1.2% or less, and particularly 1.1% or less.

[0093] ZrO2 is a component that increases Vickers hardness and increases viscosity and strain point near liquidus viscosity. However, if its content is too high, devitrification resistance may be significantly reduced. Therefore, the appropriate ZrO2 content is 0-3%, 0-1.5%, 0-1%, and particularly 0-0.1%.

[0094] TiO2 is a component that improves ion exchange performance and reduces high-temperature viscosity. However, if its content is too high, transparency and devitrification resistance tend to decrease. Therefore, the appropriate TiO2 content is 0-3%, 0-1.5%, 0-1%, 0-0.1%, and particularly 0.001-0.1 mol%.

[0095] SnO2 is a component that improves ion exchange performance, but if its content is too high, the devitrification resistance tends to decrease. Therefore, the appropriate lower limit range of SnO2 is 0.005% or more, 0.01% or more, and particularly 0.1% or more, and the appropriate upper limit range is 3% or less, 2% or less, and particularly 1% or less.

[0096] Cl is a clarifier, but excessive Cl content can negatively impact the environment and equipment. Therefore, the appropriate lower limit for Cl is 0.001% or higher, particularly 0.01% or higher, and the appropriate upper limit is 0.3% or lower, 0.2% or lower, particularly 0.1% or lower.

[0097] The Young's modulus of the chemically strengthened glass plate 1 is preferably 70 to 100 GPa, 75 to 100 GPa, and particularly 76 to 90 GPa. A low Young's modulus can easily cause the cover glass to bend when the plate thickness is thin. The Young's modulus can be calculated using the well-known resonance method.

[0098] <Method for Manufacturing Chemically Strengthened Glass Sheet>

[0099] The method for producing the chemically strengthened glass plate 1 includes a preparation step of preparing a chemically strengthened glass plate and an ion exchange treatment step of performing an ion exchange treatment on the chemically strengthened glass plate.

[0100] In the preparation step, a chemically strengthened glass plate is prepared. The chemically strengthened glass plate is an unstrengthened glass plate having the same shape, dimensions, and glass composition as the chemically strengthened glass plate 1 described above. Specifically, the chemically strengthened glass plate is a rectangular plate containing Li2O and Na2O as its glass composition.

[0101] Chemically strengthened glass sheets can be obtained by, for example, cutting a sheet of mother glass obtained by a forming method such as overflow downdraw, orifice downdraw, float, or redraw into small pieces of glass and processing them. In order to obtain a smooth surface, overflow downdraw is preferably used as the forming method.

[0102] The cut glass pieces are subjected to groove forming processing to form the thin-walled portion 2. The grooves are formed by processing such as etching and grinding. The groove forming processing is performed before the ion exchange treatment step.

[0103] The end faces of the chemically strengthened glass plate are preferably chamfered or treated to improve strength by grinding, heat treatment, etching, or the like.

[0104] The main surface of the chemically strengthened glass plate may be polished. Alternatively, if the main surface is previously smoothed by the overflow down-draw method, and the plate is formed to a uniform thickness and high precision, the main surface of the chemically strengthened glass plate may be left as an unpolished surface. The unpolished surface formed by the overflow down-draw method becomes a forged surface. Chemically strengthened glass may also be subjected to a thinning treatment to reduce its thickness by etching.

[0105] In the ion exchange treatment step, the chemically strengthened glass plate obtained as described above is subjected to multiple ion exchange treatments. The multiple ion exchange treatments include a first ion exchange treatment in which the chemically strengthened glass plate is immersed in a first molten salt containing 10% by mass or more of NaNO3, and a second ion exchange treatment in which, after the first ion exchange treatment, the chemically strengthened glass plate is immersed in a second molten salt containing 30% by mass or more of KNO3.

[0106] In the first ion exchange treatment, the NaNO3 contained in the first molten salt is preferably more than 10 mass %, more than 20 mass %, more than 30 mass %, more than 50 mass %, more than 70 mass %. The first molten salt can be a molten salt containing only NaNO3, or it can be a mixed molten salt of NaNO3 and KNO3, etc. When using a mixed molten salt of NaNO3 and KNO3 as the first molten salt, KNO3 concentration is preferably more than 0 mass %, more than 1 mass %, more than 5 mass %, more than 7 mass %, more than 10 mass %, more than 15 mass %, or 20 to 90 mass %. KNO3 concentration is preferably higher than NaNO3 concentration. If KNO3 concentration is too high, the compressive stress value formed when the Li ions contained in the glass are ion-exchanged with the Na ions in the molten salt is likely to be excessively reduced. On the other hand, if KNO3 concentration is too low, it is likely to be difficult to measure stress using a surface stress meter FSM-6000.

[0107] In the first ion exchange treatment, since the first molten salt contains NaNO3, the Li ions contained in the glass are ion-exchanged with the Na ions in the molten salt. When a mixed molten salt of NaNO3 and KNO3 is used as the first molten salt, in addition to this ion exchange, an ion exchange is also performed between the Na ions contained in the glass and the K ions in the molten salt. Here, the ion exchange between the Li ions contained in the glass and the Na ions in the molten salt is faster than the ion exchange between the Na ions contained in the glass and the K ions in the molten salt, and the ion exchange efficiency is high.

[0108] In this case, if the conditions for the first ion exchange treatment are set based on the thin-walled portion of the chemically strengthened glass plate, the maximum compressive stress depth in the thin-walled portion can be adjusted appropriately relative to the thickness of the thin-walled portion. However, in the thick-walled portion of the chemically strengthened glass plate, Na ions do not diffuse to a sufficient depth relative to the thickness of the thick-walled portion. As a result, the maximum compressive stress depth in the thick-walled portion is too small relative to the thickness of the thick-walled portion. In this case, the strength of the thick-walled portion to withstand damage caused by, for example, intrusion from protrusions is reduced.

[0109] Therefore, in this embodiment, the conditions for the first ion exchange treatment are set based on the thick-walled portion. As a result, in the thick-walled portion of the chemically strengthened glass plate, Na ions diffuse to a depth sufficient for the thickness of the thick-walled portion. As a result, the maximum compressive stress depth in the thick-walled portion is optimized relative to the thickness of the thick-walled portion. However, in this case, the Na ions diffuse to a depth that is too great for the thickness of the thin-walled portion, and a gradient in the Na ion concentration distribution is not generated along the thickness direction of the thin-walled portion. The compressive stress layer is formed due to the gradient in the concentration distribution of the diffused ions, and therefore, the thin-walled portion is not sufficiently strengthened by the first ion exchange treatment. Therefore, in this embodiment, the thick-walled portion is strengthened using the first and second ion exchange treatments, while the thin-walled portion is strengthened using the second ion exchange treatment.

[0110] In the second ion exchange treatment, the KNO contained in the second molten salt is preferably more than 30 mass %, more than 50 mass %, more than 70 mass %, more than 90 mass %. The second molten salt can be a molten salt comprising only KNO, or it can be a mixed molten salt of KNO and NaNO. When using a mixed molten salt of KNO and NaNO as the second molten salt, NaNO concentration is preferably greater than 0 to 5 mass %, greater than 0 to 3 mass %, greater than 0 to 2 mass %, 0.5 to 2 mass %. However, KNO concentration is preferably higher than NaNO concentration. If NaNO concentration is too low, the Na ions near the glass surface are easily detached and become the main cause of stress reduction. On the other hand, if NaNO concentration is too high, the compressive stress value formed by the ion exchange of the Na ions near the glass surface and the K ions in the molten salt is likely to be excessively reduced.

[0111] It should be noted that the second molten salt can be a mixed molten salt of KNO 3 , NaNO 3 and LiNO 3 , or a mixed molten salt of KNO 3 and LiNO 3 . In either case, it is preferred that the content of KNO 3 in the second molten salt is the highest compared to the other salts.

[0112] In the second ion exchange process, because the second molten salt contains KNO₃, Na ions near the glass surface (a shallow area from the outermost surface to 20% of the glass thickness) are exchanged with K ions in the molten salt. When a mixed molten salt of KNO₃ and LiNO₃ is used as the second molten salt, in addition to this ion exchange, Na ions near the glass surface are also exchanged with Li ions in the molten salt. In other words, the second ion exchange process allows the removal of Na ions near the glass surface while simultaneously introducing K ions with a larger ionic radius.

[0113] In this case, the introduction of K ions in the thick-walled portion can increase the maximum compressive stress value while maintaining the relatively high maximum compressive stress depth formed in the first ion exchange treatment. Meanwhile, in the thin-walled portion, the introduction of K ions can form a relatively low maximum compressive stress depth while increasing the maximum compressive stress value. In other words, the chemically strengthened glass plate 1 manufactured through this ion exchange treatment exhibits different stress characteristics (e.g., DOC1 < DOC2) in the thick-walled portion 3 and the thin-walled portion 2. It should be noted that in the thick-walled portion 3, there are gradients in the concentration distribution of K and Na ions. Meanwhile, in the thin-walled portion 2, there is a gradient in the concentration distribution of K ions, but there is virtually no gradient in the concentration distribution of Na ions. In other words, in the thick-walled portion 3, the concentration distributions of K and Na ions each show a decreasing trend toward the center of the plate thickness. Meanwhile, in the thin-walled portion 2, while the concentration distribution of K ions shows a decreasing trend toward the center of the plate thickness, the concentration distribution of Na ions does not change significantly toward the center of the plate thickness, but remains nearly constant. Here, in the “concentration distribution showing a decreasing trend”, as long as the concentration distribution as a whole shows a decreasing trend, it also includes cases where there is an inflection point (bottom) where the concentration changes from decreasing to increasing, an inflection point (peak) where the concentration changes from increasing to decreasing, etc. on the way toward the center of the plate thickness.

[0114] The stress distribution in the depth direction of the compressive stress layer of the thick wall portion 3 after the second ion exchange treatment is as follows: Figure 3 As shown, it has an inflection point e. Figure 4 In FIG. 1 , the vertical axis represents the compressive stress value, and the horizontal axis represents the depth from the surface of the chemically strengthened glass plate 1. Figure 4 As shown, the stress distribution of the thick-walled portion 3 has a maximum compressive stress value CS2 at the surface, which decreases with a relatively steep gradient α toward the depth, reaching the inflection point e. Furthermore, the compressive stress value within the same stress distribution gradually decreases from the inflection point e to the depth DOC2 with a relatively gentle gradient β. This stress distribution achieves both a high maximum compressive stress value CS2 and a low maximum tensile stress value CT2 in the thick-walled portion 3, thereby achieving high impact resistance. It should be noted that, for example, if the stress distribution can be approximated by a broken line consisting of two straight lines, the inflection point e can be determined as the point on the stress distribution at the depth of the intersection of the two straight lines (the point where the broken line bends). Linear approximation can be performed using well-known methods such as the least squares method.

[0115] In the first ion exchange treatment, the temperature of the first molten salt is preferably 360-400°C, and the ion exchange time is preferably 30 minutes to 6 hours. In the second ion exchange treatment, the temperature of the second molten salt is preferably 370-400°C, and the ion exchange time is preferably 15 minutes to 3 hours. The ion exchange time of the second ion exchange treatment is preferably shorter than that of the first ion exchange treatment. This is because if the ion exchange time of the second ion exchange treatment is excessively extended, the maximum compressive stress depth DOC1 of the thin-walled portion 2 becomes too large, making it difficult to increase the maximum compressive stress value CS1.

[0116] It should be noted that although the embodiments of the present invention have been described, the embodiments of the present invention are not limited thereto, and various modifications can be made without departing from the scope of the present invention.

[0117] In the above embodiment, the chemically strengthened glass plate and the glass plate for chemical strengthening contain Li2O as the glass composition, but the present invention is not limited thereto. The chemically strengthened glass plate and the glass plate for chemical strengthening may not contain substantially Li2O as the glass composition.

[0118] Specifically, the chemically strengthened glass plate and the glass plate for chemical strengthening may contain, in terms of mol%, 40% to 80% of SiO2, 10% to 30% of Al2O3, 0% to 3% of B2O3, 5% to 25% of Na2O, 0% to 5.5% of K2O, 0% to 0.09% of Li2O, and 0% to 10% of MgO as a glass composition.

[0119] Even in the case of a chemically strengthened glass plate whose glass composition substantially does not contain Li₂O, it is preferable to perform a first ion exchange treatment and a second ion exchange treatment as ion exchange treatment steps. In this case, the first molten salt used in the first ion exchange treatment and the second molten salt used in the second ion exchange treatment preferably both contain KNO₃. The concentration of KNO₃ in the first molten salt is preferably higher than the concentration of KNO₃ in the second molten salt. The ion exchange time for the first ion exchange treatment is preferably longer than the ion exchange time for the second ion exchange treatment. Through such ion exchange treatment, the maximum compressive stress value CS1 can be increased in the thin-walled portion 2 of the chemically strengthened glass plate 1 due to the introduction of K ions during the second ion exchange treatment. Furthermore, in the thick-walled portion 3 of the chemically strengthened glass plate 1, the maximum compressive stress depth DOC2 can be increased due to the introduction of K ions during the first ion exchange treatment, while the maximum compressive stress value CS2 can be increased due to the introduction of K ions during the second ion exchange treatment.

[0120] Example

[0121] Hereinafter, the glass article of the present invention will be described based on Examples. It should be noted that the following Examples are merely illustrative and the present invention is not limited in any way by the following Examples.

[0122] As chemically strengthened glass plates, prepared were alkali aluminosilicate glass having the following glass composition A and alkali aluminosilicate glass having the following glass composition B. Each chemically strengthened glass plate had a thin portion (thickness t1) and a thick portion (thickness t2).

[0123] (Glass composition A)

[0124] Glass composition A contains, in mol%, 60.35% SiO2, 18.90% Al2O3, 0.20% B2O3, 7.20% Li2O, 8.20% Na2O, 0.40% K2O, 0.40% MgO, 4.30% P2O5, and 0.05% SnO2.

[0125] (Glass composition B)

[0126] Glass composition B contains, in mol%, 66.38% SiO2, 11.5% Al2O3, 0.5% B2O3, 0.02% Li2O, 15.2% Na2O, 1.4% K2O, 4.8% MgO, 0.1% CaO, and 0.1% SnO2.

[0127] The chemically strengthened glass plates were ion exchanged under the conditions shown in Table 1 to produce chemically strengthened glass plates, and various stress characteristics were evaluated. Nos. 1 to 4 are examples of the present invention, and No. 5 is a comparative example.

[0128] [Table 1]

[0129]

[0130] In addition, No. 1 to 4, the ion exchange treatment was performed twice in total, namely, the first ion exchange treatment and the second ion exchange treatment, and in No. 5, only the first ion exchange treatment was performed once in total.

[0131] Regarding stress characteristics, Nos. 1 to 4 were measured twice in total, after the first ion exchange treatment and after the second ion exchange treatment, while No. 5 was measured once in total, only after the first ion exchange treatment.

[0132] In the table, "K70 / Na30" means ion exchange treatment performed by immersion in a molten salt with a KNO3 concentration of 70% by mass and a NaNO3 concentration of 30% by mass. "Na100" means ion exchange treatment performed by immersion in a molten salt with a NaNO3 concentration of 100% by mass. "K100" means ion exchange treatment performed by immersion in a molten salt with a KNO3 concentration of 100% by mass.

[0133] In the table, “FSM” refers to FSM-6000LE manufactured by Orihara Seisakusho. “SLP” refers to SLP-2000 manufactured by Orihara Seisakusho. “FSM+SLP” means that the stress characteristics were determined by combining the measurement results of the two measuring devices, FSM-6000LE and SLP-2000.

[0134] The results in Table 1 also confirm that the depth of the compressive stress layer (DOC2) in the thick-walled portion of Examples Nos. 1 to 4 is significantly greater than the depth of the compressive stress layer (DOC2) in the thick-walled portion of Comparative Example No. 5. Furthermore, although the ion exchange treatment conditions in Comparative Example No. 5 were set based on the thin-walled portion, the depth of the compressive stress layer (DOC1) in the thin-walled portion of Examples Nos. 1 to 4 is comparable to the depth of the compressive stress layer (DOC1) in the thin-walled portion of Comparative Example No. 5, which is a good result. Therefore, the chemically strengthened glass sheets of Examples Nos. 1 to 4 can achieve high impact resistance in both the thick and thin-walled portions while maintaining flexibility in the thin-walled portion. Consequently, the chemically strengthened glass sheets of Examples Nos. 1 to 4 are suitable for applications such as foldable devices.

[0135] It should be noted that the glass composition of the above-mentioned embodiment is an example, and the present invention can also be applied to the following glass composition C, glass composition D, etc.

[0136] (Glass composition C)

[0137] Glass composition C contains, in mol%, 68.2% SiO2, 9.5% Al2O3, 0.1% B2O3, 8.0% Li2O, 8.2% Na2O, 3.0% K2O, 3.0% MgO, and 0.1% SnO2.

[0138] (Glass composition D)

[0139] Glass composition C contains, in mol%, 66.9% SiO2, 15.6% Al2O3, 1.7% B2O3, 7.5% Li2O, 7.5% Na2O, 0.3% K2O, 0.4% MgO, and 0.1% SnO2.

[0140] Description of Reference Numerals

[0141] 1: Chemically strengthened glass plate; 2: Thin-walled portion; 3: Thick-walled portion; 4: Groove; 5: Residual portion; 6: Compressive stress layer; 7: Tensile stress layer.

Claims

1. A chemically strengthened glass plate comprising: Thin-walled parts, a thick-walled portion thicker than the thin-walled portion, and A compressive stress layer is formed on the surface of each of the thin-walled portion and the thick-walled portion. The chemically strengthened glass plate is bendable at the thin-walled portion. When the maximum compressive stress depth of the thin-walled portion is defined as DOC1, the maximum compressive stress depth of the thick-walled portion is defined as DOC2, and the thickness of the thick-walled portion is defined as t2, There is a relationship DOC2>DOC1, and There is a relationship of DOC2 / t2≥0.

05.

2. The chemically strengthened glass plate according to claim 1, wherein When the maximum compressive stress depth of the thin-walled portion is set as DOC1 and the thickness of the thin-walled portion is set as t1, There is a relationship of DOC1 / t1≤0.

20.

3. The chemically strengthened glass plate according to claim 1 or 2, wherein The thickness t1 of the thin-walled portion is greater than or equal to 0.01 mm and less than or equal to 0.2 mm. The thickness t2 of the thick portion is greater than 0.2 mm and is equal to or less than 2.0 mm.

4. The chemically strengthened glass plate according to claim 1 or 2, wherein When the maximum compressive stress depth of the thin-walled portion is defined as DOC1 and the maximum compressive stress depth of the thick-walled portion is defined as DOC2, There is a relationship of DOC2 / DOC1≥5.

5. The chemically strengthened glass plate according to claim 1 or 2, wherein The maximum compressive stress depth DOC1 of the thin-walled portion is 2 μm to 20 μm. The maximum compressive stress depth DOC2 of the thick-walled portion is 10 μm to 200 μm.

6. The chemically strengthened glass plate according to claim 1 or 2, wherein The maximum compressive stress value CS1 of the thin-walled portion is 100 MPa to 1500 MPa. The maximum compressive stress value CS2 of the thick-walled portion is 200 MPa to 2000 MPa.

7. The chemically strengthened glass plate according to claim 1 or 2, wherein When the maximum compressive stress value of the thin-walled portion is CS1 and the maximum compressive stress value of the thick-walled portion is CS2, There is a relationship of CS2 / CS1≤20.

8. The chemically strengthened glass plate according to claim 1 or 2, wherein In the compressive stress layer of the thick portion, a stress curve in the depth direction has an inflection point.

9. The chemically strengthened glass plate according to claim 1 or 2, It contains Li2O and Na2O as glass components.

10. The chemically strengthened glass plate according to claim 9, wherein The glass composition, in mol%, includes 50-80% SiO2, 8-25% Al2O3, 0-10% B2O3, 3-15% Li2O, 3-21% Na2O, 0-10% K2O, 0-10% MgO, and 0-15% P2O5.

11. A method for producing a chemically strengthened glass plate, the chemically strengthened glass plate comprising: Thin-walled parts, a thick-walled portion thicker than the thin-walled portion, and A compressive stress layer is formed on the surface of each of the thin-walled portion and the thick-walled portion. The chemically strengthened glass plate is bendable at the thin-walled portion. The manufacturing method comprises: a step of preparing a tempered glass having the thick portion and the thin portion, and an ion exchange treatment step of subjecting the tempered glass to a two-stage ion exchange treatment, In the ion exchange treatment step, the two-stage ion exchange treatment is performed so that the chemically strengthened glass sheet after the ion exchange treatment satisfies the following relationship: when the maximum compressive stress depth of the thin-walled portion is set to DOC1, the maximum compressive stress depth of the thick-walled portion is set to DOC2, and the thickness of the thick-walled portion is set to t2, The relationship DOC2>DOC1 is satisfied, and The relationship DOC2 / t2≥0.05 is satisfied.

12. The method for producing a chemically strengthened glass plate according to claim 11, wherein: The tempered glass plate contains Li2O and Na2O as glass composition, The ion exchange treatment process includes: A first ion exchange treatment using a molten salt containing 10% or more of NaNO3 for ion exchange, and After the first ion exchange treatment, a second ion exchange treatment is performed using a molten salt containing 30% or more of KNO 3 .

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