Strengthened glass and method of manufacturing strengthened glass

Abstract

A strengthened glass and a method for manufacturing the same, the strengthened glass having a surface and a thickness T, a compressive stress being set as a positive number and a tensile stress being set as a negative number, a stress profile obtained by measuring the stress in a depth direction from the surface has: a first peak P1 where the compressive stress becomes the maximum in the surface, a first valley B1 where the stress gradually decreases in the depth direction from the first peak P1 and becomes the minimum, a second peak P2 where the stress gradually increases in the depth direction from the first valley B1 and the compressive stress becomes the maximum, and a second valley B2 where the tensile stress gradually decreases in the depth direction from the second peak P2 and becomes the minimum, the compressive stress CSmax at the first peak P1 being 500 MPa or more, the compressive stress CSp at the second peak P2 being 15 MPa to 250 MPa, and the depth DOLp of the second peak P2 being 4% to 20% of the thickness T.

Description

[0001] This application is a divisional application of PCT / JP2019 / 039632, application number: 201980066114.7, application date: October 8, 2019, invention title: "Strengthened Glass and Method for Manufacturing Strengthened Glass". Technical Field

[0002] This invention relates to tempered glass and its manufacturing method, and particularly to tempered glass suitable for cover glass of mobile phones, digital cameras, PDAs (portable terminals), and touch panel displays, and its manufacturing method. Background Technology

[0003] Mobile phones (especially smartphones), digital cameras, PDAs, touch panel displays, large televisions, and contactless power supplies are becoming increasingly popular. These applications utilize ion-exchange treated tempered glass. Furthermore, in recent years, the use of tempered glass in the outer components of digital signage, mice, and smartphones has been steadily increasing.

[0004] Tempered glass achieves high strength by having a compressive stress layer formed on its surface through ion exchange treatment, thereby suppressing the formation and propagation of cracks on the surface. It is believed that the strength of tempered glass can be improved by adjusting the formation morphology of such a compressive stress layer (e.g., Patent Document 1).

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: International Publication No. 2013 / 088856 Summary of the Invention

[0008] The problem the invention aims to solve

[0009] However, there is still room for improvement in achieving higher impact resistance.

[0010] The purpose of this invention is to provide reinforced glass with higher impact resistance compared to prior art.

[0011] means for solving problems

[0012] The present invention, created to solve the aforementioned problems, is characterized by a reinforced glass having a surface and a thickness T. When compressive stress is set to a positive number and tensile stress to a negative number, the stress distribution obtained by measuring the stress from the surface along the depth direction has the following characteristics: a first peak where the compressive stress is at its maximum value on the surface; a first valley where the stress gradually decreases along the depth direction from the first peak to a minimum value; a second peak where the compressive stress gradually increases along the depth direction from the first valley to a maximum value; and a second valley where the tensile stress gradually decreases along the depth direction from the second peak to a minimum value. The compressive stress at the first peak is 500 MPa or more, and the compressive stress at the second peak is 15 MPa to 250 MPa. The second peak exists at a depth of 4% to 20% of the thickness T. The inventors' in-depth research has confirmed that reinforced glass with such a stress distribution exhibits high impact resistance. In particular, setting the compressive stress (maximum value) of the second peak and its position along the depth direction within the aforementioned numerical range is important for improving impact resistance.

[0013] In the above configuration, it is preferable that the stress distribution has a stress zero point between the second peak and the second valley, and the stress zero point exists in the depth range of 10% to 35% of the thickness T from the surface. In this way, compressive stress can be generated at a deeper depth, and thus improved impact resistance can be expected.

[0014] In the above configuration, the stress at the first valley is preferably -50 MPa to +100 MPa. In this way, in order to maintain the balance between compressive stress and tensile stress, the tensile stress at the second valley can be relatively reduced, and thus the impact resistance can be expected to be improved.

[0015] In the above configuration, it is preferable that the stress at the first valley is 0 MPa or more and +65 MPa or less. In this way, tensile stress is not generated in the surface layer of the tempered glass, thus preventing cracking during the manufacturing process of the tempered glass.

[0016] In the above configuration, it is preferable that the stress at the first valley is -30 MPa or higher and less than 0 MPa. In this way, in order to maintain the balance between compressive stress and tensile stress, the tensile stress at the second valley is relatively smaller, and thus improved impact resistance can be expected.

[0017] In the above configuration, the first valley preferably exists in a depth range of 0.5% to 12% of the thickness T from the surface.

[0018] In the above configuration, it is preferable that the distance in the depth direction from the first valley to the second peak is 3% or more of the thickness T.

[0019] In the above configuration, the compressive stress at the first peak is preferably 700 MPa or more, and the second peak exists in the range of 7.3% or more of the thickness T from the surface.

[0020] In the above configuration, the thickness T is preferably 0.3 mm to 0.9 mm, and the stress distribution is present on the main surface and the end face.

[0021] In the above configuration, preferably, the thickness T is in the range of 0.45 mm or more and 0.85 mm or less, the compressive stress at the first peak is in the range of 700 MPa or more and 850 MPa or less, the compressive stress at the second peak is in the range of 20 MPa or more and 80 MPa or less, the second peak exists in the depth range of 7.3% or more and 20% or less of the thickness T from the surface, the stress distribution has a stress zero point between the second peak and the second valley, the stress zero point exists in the depth range of 17% or more and 25% or less of the thickness T from the surface, and the maximum absolute value of the tensile stress is in the range of 40 MPa or more and 60 MPa or less.

[0022] In the above composition, the glass composition preferably contains, by mass%, 40-70% SiO2, 10-30% Al2O3, 0-10% B2O3, 2-11% Li2O, 5-25% Na2O, 0-10% K2O, 0-6% MgO, 0-10% ZnO and 0-20% P2O5.

[0023] The present invention, created to solve the aforementioned problems, is characterized by a method for manufacturing reinforced glass by performing ion exchange treatment on reinforced glass containing a first alkali metal ion, comprising the following steps: a first ion exchange step, wherein a first molten salt containing a second alkali metal ion with an ionic radius larger than the first alkali metal ion is brought into contact with the reinforced glass, thereby introducing the second alkali metal ion into the reinforced glass; a second ion exchange step, after the first ion exchange step, wherein a second molten salt containing the first alkali metal ion is brought into contact with the reinforced glass, thereby detaching at least a portion of the second alkali metal ion from the reinforced glass; and a third ion exchange step, after the second ion exchange step, wherein a third molten salt containing the second alkali metal ion is brought into contact with the reinforced glass, thereby introducing the second alkali metal ion into the reinforced glass. A method for manufacturing reinforced glass having such steps can yield reinforced glass with high impact resistance.

[0024] In the above configuration, it is preferable that in the first ion exchange step, the second alkali metal ions are introduced into the strengthened glass up to a depth of 10.5% or more of its thickness T from the surface; in the second ion exchange step, at least a portion of the second alkali metal ions are removed from the strengthened glass up to a region shallower than 10% of its thickness T from the surface; and in the third ion exchange step, the second alkali metal ions are introduced into the strengthened glass up to a region shallower than 7% of its thickness T from the surface. In this case, it is preferable that the alkali metal ions are not introduced and removed in regions deeper than the aforementioned depths. This allows for a more reliable production of strengthened glass with high impact resistance.

[0025] In the above composition, the first alkali metal ion is preferably Na ion, the second alkali metal ion is preferably K ion, the first molten salt contains KNO3, the second molten salt contains NaNO3, and the third molten salt contains KNO3.

[0026] In the above configuration, the first alkali metal ion is preferably Na ions, the second alkali metal ion is preferably K ions, the first molten salt contains at least KNO3 among NaNO3 and KNO3, the second molten salt contains at least NaNO3 among NaNO3 and KNO3, the concentration of KNO3 in the first molten salt is higher than the concentration of NaNO3, and the concentration of NaNO3 in the second molten salt is higher than the concentration of KNO3. This allows for efficient and effective implementation of the first and second ion exchange processes.

[0027] In this case, preferably, the concentration of KNO3 in the first molten salt is 50% by mass or more, the concentration of NaNO3 in the first molten salt is less than 50% by mass, the concentration of NaNO3 in the second molten salt is 60% by mass or more, the concentration of KNO3 in the second molten salt is less than 40% by mass, the concentration of KNO3 in the third molten salt is higher than the concentration of KNO3 in the first molten salt, the ion exchange treatment temperature of the first ion exchange step is 420–500°C, the ion exchange treatment temperature of the second ion exchange step is 420–500°C, the ion exchange treatment temperature of the third ion exchange step is more than 10°C lower than the ion exchange treatment temperature of the first ion exchange step, the ion exchange treatment time of the first ion exchange step is 2–40 hours, the ion exchange treatment time of the second ion exchange step is 2–40 hours, and the ion exchange treatment time of the third ion exchange step is shorter than the respective ion exchange treatment times of the first and second ion exchange steps.

[0028] The present invention, created to solve the aforementioned problems, is characterized by a method for manufacturing reinforced glass by performing ion exchange treatment on reinforced glass containing a first alkali metal ion, comprising the following steps: a first ion exchange step in which a first molten salt containing a second alkali metal ion with an ionic radius larger than the first alkali metal ion is brought into contact with the reinforced glass, thereby introducing the second alkali metal ion into the reinforced glass; and a second ion exchange step in which, after the first ion exchange step, a second molten salt containing a third alkali metal ion with an ionic radius larger than the second alkali metal ion and the first alkali metal ion are brought into contact with the reinforced glass, thereby causing at least a portion of the second alkali metal ion to detach from the reinforced glass and introducing the third alkali metal ion into the reinforced glass. A method for manufacturing reinforced glass having such steps can yield reinforced glass with high impact resistance.

[0029] In the above configuration, it is preferable that, in the second ion exchange step, the third alkali metal ions are introduced into the strengthened glass from the surface up to a depth 7% shallower than the thickness T. In this case, it is preferable that the introduced alkali metal ions are not removed in a region deeper than the aforementioned depth. In this way, strengthened glass with high impact resistance can be obtained more reliably.

[0030] In the above composition, the preferred strengthening glass further contains a second alkali metal ion.

[0031] In the above composition, the first alkali metal ion is preferably Li ion, the second alkali metal ion is preferably Na ion, the third alkali metal ion is preferably K ion, and the concentration of Li ions contained in the second molten salt is preferably 100 ppm by mass or more.

[0032] In the above configuration, the first molten salt preferably contains NaNO3, and the second molten salt preferably contains LiNO3 and KNO3.

[0033] In the above configuration, the preferred first alkali metal ion is Li ion, the preferred second alkali metal ion is Na ion, and the preferred third alkali metal ion is K ion. The first molten salt contains at least NaNO3, either NaNO3 or KNO3, and the concentration of NaNO3 in the first molten salt is higher than the concentration of KNO3. The second molten salt contains both LiNO3 and KNO3, and the concentration of LiNO3 in the second molten salt is lower than the concentration of KNO3. This configuration allows for efficient and effective implementation of both the first and second ion exchange processes.

[0034] In this case, preferably, the concentration of NaNO3 in the first molten salt is 50% by mass or more, the concentration of KNO3 in the first molten salt is less than 50% by mass, the concentration of LiNO3 in the second molten salt is 0.5% to 5% by mass, the concentration of KNO3 in the second molten salt is 95% to 99.5% by mass, the ion exchange treatment temperature of the first ion exchange step is 350% to 480°C, the ion exchange treatment temperature of the second ion exchange step is 350% to 480°C, the ion exchange treatment time of the first ion exchange step is 1 to 20 hours, and the ion exchange treatment time of the second ion exchange step is shorter than that of the first ion exchange step.

[0035] In the above configuration, it is preferable that in the first ion exchange step, the second alkali metal ions are introduced into the strengthening glass up to a depth of 10% or more than the thickness T from the surface, and in the second ion exchange step, at least a portion of the second alkali metal ions in the strengthening glass up to a depth of 10% or more than the thickness T are removed. In this case, it is preferable that the introduction and removal of alkali metal ions are not carried out in regions deeper than the aforementioned depth.

[0036] In the above configuration, the first molten salt preferably contains a second alkali metal ion and a third alkali metal ion.

[0037] Invention Effects

[0038] According to the present invention, compared with the prior art, it is possible to obtain reinforced glass with higher impact resistance. Attached Figure Description

[0039] Figure 1 This is a schematic diagram showing the cross-section of the tempered glass according to the first embodiment of the present invention.

[0040] Figure 2 A graph showing the general stress distribution in the thickness direction of the tempered glass according to the first embodiment of the present invention.

[0041] Figure 3 This is a flowchart of a method for manufacturing tempered glass according to the first embodiment of the present invention.

[0042] Figure 4 This is a flowchart of a method for manufacturing tempered glass according to the second embodiment of the present invention.

[0043] Figure 5 A graph showing the stress distribution of the tempered glass involved in sample No.1.

[0044] Figure 6 A graph showing the stress distribution of the tempered glass involved in sample No. 2.

[0045] Figure 7A graph showing the stress distribution of the tempered glass involved in sample No. 3.

[0046] Figure 8 A graph showing the stress distribution of the tempered glass involved in sample No. 4.

[0047] Figure 9 A graph showing the stress distribution of the tempered glass involved in sample No. 10.

[0048] Figure 10 A graph showing the stress distribution of the tempered glass involved in sample No. 38.

[0049] Figure 11 A graph showing the stress distribution of the tempered glass involved in sample No. 49.

[0050] Figure 12 A graph showing the stress distribution of the tempered glass involved in sample No. 140.

[0051] Figure 13 This is a schematic diagram illustrating the drop test method in an embodiment of the present invention.

[0052] Figure 14 This is a graph illustrating the relationship between the damage height and the calculated intensity in the embodiments of the present invention.

[0053] Explanation of reference numerals in the attached figures

[0054] 1. Tempered glass, 2. Compressive stress layer, 3. Tensile stress layer, 10. Simulated frame, 20. Glass sample (tempered glass), 30. Sandpaper, 40. Platform, 50. Optical bonding film, 60. Insulating tape sheet Detailed Implementation

[0055] The following describes the reinforced glass according to embodiments of the present invention.

[0056] (First Embodiment)

[0057] like Figure 1As shown, the tempered glass 1 according to the first embodiment of the present invention is a plate-shaped chemically strengthened glass that has been chemically strengthened by ion exchange, and has a compressive stress layer 2 and a tensile stress layer 3. The thickness T of the tempered glass 1 can be arbitrarily set, but is preferably 2.0 mm or less, more preferably 1.8 mm or less, 1.6 mm or less, 1.4 mm or less, 1.2 mm or less, 1.0 mm or less, 0.9 mm or less, 0.85 mm or less, and even more preferably 0.8 mm or less. It is also preferably 0.03 mm or more, 0.05 mm or more, 0.1 mm or more, 0.15 mm or more, 0.2 mm or more, 0.25 mm or more, 0.3 mm or more, 0.35 mm or more, 0.4 mm or more, 0.45 mm or more, 0.5 mm or more, 0.6 mm or more, and even more preferably 0.65 mm or more.

[0058] The compressive stress layer 2 is formed on the surface portion of the tempered glass 1, including the main surface 1a and the end face 1b. The tensile stress layer 3 is formed inside the tempered glass 1, that is, at a depth deeper than the compressive stress layer 2.

[0059] The stress distribution (stress curve) of the tempered glass 1 is obtained by measuring the stress along the depth direction (orthogonal to the main surface 1a) from the main surface 1a side, with compressive stress set to positive and tensile stress set to negative. The stress distribution of the tempered glass 1 thus obtained is as follows: Figure 2 As shown. Figure 2 In the graph, the vertical axis represents stress, and the horizontal axis represents the position (depth) in the thickness direction with the main surface 1a on one side as a reference. Figure 2 In the curve graph, positive stress values ​​represent compressive stress, and negative stress values ​​represent tensile stress. That is, Figure 2 The larger the absolute value of the stress in the curve, the greater the stress. It should be noted that... Figure 2 This is an exaggerated diagram for the purpose of understanding; the stress distribution of the reinforced glass 1 is not limited to this method.

[0060] The stress distribution of the tempered glass 1, along the depth direction (orthogonal to the main surface 1a), has a first peak P1, a first valley B1, a second peak P2, and a second valley B2.

[0061] The first peak P1 is the maximum value of compressive stress and exists on the main surface 1a. The compressive stress CSmax of the first peak P1 is 500 MPa or more, preferably 600 MPa to 1100 MPa, more preferably 600 MPa to 1000 MPa, 700 MPa to 900 MPa, or 750 MPa to 850 MPa.

[0062] At valley B1, the stress gradually decreases along the depth direction from the first peak P1, reaching a minimum value. Figure 2Examples show the case where it is compressive stress (positive value), but there are also cases where it is tensile stress (negative value). The lower the stress CSb of the first valley B1, the lower the tensile stress CTmax of the second valley B2, making the failure process slower. The stress CSb of the first valley B1 is preferably +100MPa or less, more preferably +90MPa or less, +80MPa or less, +70MPa or less, or +60MPa or less. However, if the stress CSb of the first valley B1 is too low, cracks will form on the surface during the strengthening process, deteriorating visibility. The stress CSb of the first valley B1 is preferably -50MPa or more, more preferably -45MPa or more, -40MPa or more, -35MPa or more, or -30MPa or more. The stress CSb of the first valley B1 can be 0MPa or more and +65MPa or less, or -30MPa or more and less than 0MPa. The depth DOLb of the first valley B1 is preferably 0.5% to 12% of the thickness T, more preferably 1% to 7% of the thickness T.

[0063] At the second peak P2, the stress gradually increases along the depth direction from the first valley B1, reaching a maximum value. The stress CSp of the second peak P2 is compressive stress. The compressive stress CSp of the second peak P2 is 15MPa to 250MPa, preferably 15MPa to 240MPa, 15MPa to 230MPa, 15MPa to 220MPa, 15MPa to 210MPa, 15MPa to 200MPa, 15MPa to 190MPa, 15MPa to 180MPa, 15MPa to 175MPa, 15MPa to 170MPa, 15MPa to 165MPa, 15MPa to 160MPa, 18MPa to 100MPa, and more preferably 20MPa to 80MPa. The depth DOLp of the second peak P2 is 4% to 20% of the thickness T, preferably 4% to 19%, 4% to 18.5%, 4% to 18%, 4% to 17.5%, or 4% to 17% of the thickness T, and more preferably 4.5% to 17%, 5% to 17%, 6% to 17%, 7.3% to 17%, or 8% to 15% of the thickness T.

[0064] The distance in the depth direction from the first valley B1 to the second peak P2, i.e., DOLp-DOLb, is 3% or more of the thickness T, preferably 4% or more of the thickness T, and more preferably 5% to 13% of the thickness T.

[0065] At the second valley B2, the stress gradually decreases along the depth direction from the second peak P2, and the minimum value of the tensile stress (the absolute value is the maximum value) is taken. The absolute value of the tensile stress CTmax at the second valley B2 is 70 MPa or less, preferably 65 MPa or less, 60 MPa or less, and more preferably 40 MPa to 55 MPa.

[0066] The product of the tensile stress CTmax and the thickness T of the second valley B2 is preferably -70 MPa·mm or more, more preferably -65 MPa·mm or more, -60 MPa·mm or more, or -55 MPa·mm or more. Furthermore, the product of the tensile stress CTmax and the thickness T of the second valley B2 is preferably -5 MPa·mm or less, -10 MPa·mm or less, -15 MPa·mm or less, -20 MPa·mm or less, -25 MPa·mm or less, or -30 MPa·mm or less.

[0067] Between the second peak P2 and the second valley B2, there is a stress zero point Z where the stress is zero. Typically, the depth of the stress zero point Z, DOLzero, is difficult to exceed 20% of the thickness T, and physically around 22% is considered a limit. However, in this embodiment, a DOLzero exceeding this limit value can be obtained. The greater the depth DOLzero of the stress zero point Z, the higher the strength relative to the penetration of the protrusion. Preferably, it is 10% or more, 10.5% or more, 11% or more, 11.5% or more, 12% or more, 12.5% ​​or more, 13% or more, 13.5% or more, 14% or more, 14.5% or more, 15% or more, 15.5% or more, 16% or more, 16.5% or more, 17% or more, 17.5% or more, 18% or more, more preferably 18.5% or more, 19% or more, 19.5% or more, 20% or more, 20.5% or more, 21% or more, 21.5% or more, 22.0% or more, 22.5% or more, 23% or more, 23.5% or more, and most preferably 24% or more. However, if the depth DOLzero of the stress zero point Z becomes excessively large, excessive tensile stress may be generated in the first valley B1 and the second valley B2. Therefore, the depth DOLzero of the stress zero point Z is preferably 35% or less, 34.5% or less, 34% or less, 33.5% or less, 33% or less, 32.5% or less, 32% or less, 31.5% or less, 31% or less, 30.5% or less, 30% or less, 29.5% or less, 29% or less, 28.5% or less, or 28% or less of the thickness T, and more preferably 27% or less.

[0068] In this embodiment, the tempered glass 1 also has the same stress distribution on the end face 1b. Specifically, the stress distribution on the end face 1b has a first peak where compressive stress is at its maximum, a first valley where stress gradually decreases along the depth direction from the first peak to a minimum, a second peak where compressive stress gradually increases along the depth direction from the first valley to a maximum, and a second valley where tensile stress gradually decreases along the depth direction from the second peak to a minimum. The compressive stress at the first peak is 500 MPa or more, and the compressive stress at the second peak is 15 MPa to 250 MPa. The second peak exists at a depth of 4% to 20% of the thickness T. Furthermore, the preferred range for the stress distribution on the end face 1b can be applied in the same way to the preferred range for the stress distribution on the main surface 1a.

[0069] It should be noted that the stress and its distribution in the reinforced glass 1 can be measured and synthesized using, for example, the FSM-6000LE and SLP-1000 manufactured by Orihara Corporation.

[0070] The tempered glass 1 constructed in the above manner can be manufactured according to the following points, for example. First, as a preparation step, a sheet-shaped glass (hereinafter referred to as tempered glass) containing alkali metal oxides for tempering treatment is prepared. Next, the following steps are performed sequentially: a first ion exchange step (first tempering step) in which a first molten salt is brought into contact with the surface of the tempered glass; a second ion exchange step (mitigation step) in which a second molten salt is brought into contact with the surface of the tempered glass; and a third ion exchange step (second tempering step) in which a third molten salt is brought into contact with the surface of the tempered glass. In each ion exchange step, it is preferable to immerse the tempered glass in molten salt.

[0071] The strengthening glass prepared in the preparation process preferably contains, for example, as a glass composition, 40%–70% SiO2, 10%–30% Al2O3, 0%–3% B2O3, 5%–25% Na2O, 0%–5.5% K2O, 0%–10% Li2O, 0%–5.5% MgO, and 2%–10% P2O5 by mass%.

[0072] The rationale for the preferred composition is explained below. It should be noted that, unless otherwise specified, the percentage (%) in the description of the content range of each component refers to mass percentage.

[0073] SiO2 is a component that forms the network of glass. If the SiO2 content is too low, vitrification becomes difficult, and acid resistance is easily reduced. Therefore, the suitable lower limit range of SiO2 is 40% or more, 40.5% or more, 41% or more, 41.5% or more, 42% or more, 42.5% or more, 43% or more, 44% or more, 45% or more, 46% or more, 47% or more, 48% or more, 49% or more, and especially 50% or more. On the other hand, if the SiO2 content is too high, meltability and formability easily decrease, and the coefficient of thermal expansion becomes too low, making it difficult to match the coefficient of thermal expansion of the surrounding materials. Therefore, the suitable upper limit range of SiO2 is 70% or less, 68% or less, 65% or less, 62% or less, 60% or less, 58% or less, 57% or less, 56% or less, 55% or less, and especially 54% or less.

[0074] Al₂O₃ is a component that increases the ion exchange rate, as well as Young's modulus and Vickers hardness. It also increases the viscosity at the point of phase separation. The Al₂O₃ content is typically 10-30%. If the Al₂O₃ content is too low, the ion exchange rate and Young's modulus tend to decrease. Therefore, the suitable lower limit range for Al₂O₃ content is 10% or higher, 11% or higher, 12% or higher, 13% or higher, 14% or higher, 14.5% or higher, 15% or higher, 15.5% or higher, 16% or higher, 16.5% or higher, 17% or higher, 17.5% or higher, 18% or higher, 18.5% or higher, and especially 19.5% or higher. On the other hand, if the Al₂O₃ content is too high, devitrification crystals tend to precipitate in the glass, making it difficult to form plates using methods such as overflow pull-down. Especially when using alumina refractories as the shaped refractories and employing the overflow pull-down method for plate forming, spinel devitrification crystals easily precipitate at the interface with the alumina refractories. Furthermore, acid resistance decreases, making it unsuitable for acid treatment processes. Additionally, high-temperature viscosity tends to increase, and melting points tend to decrease. Therefore, the suitable upper limits for Al2O3 are below 30%, 28%, 26%, 25%, 24%, 23.5%, 23%, 22.5%, 22%, and 21.5%, particularly below 21%.

[0075] B₂O₃ is a component that reduces viscosity and density at high temperatures and improves resistance to devitrification. However, if the B₂O₃ content is too high, the ion exchange rate (especially the stress depth) tends to decrease. Furthermore, due to ion exchange, discoloration of the glass surface, known as scorching, can occur, or acid and water resistance can easily decrease. Therefore, suitable ranges for B₂O₃ are 0%–3%, 0%–2.5%, 0%–2%, 0%–1.9%, 0%–1.8%, 0%–1.7%, 0%–1.6%, 0%–1.5%, and 0%–1.3%, especially above 0% and below 1%.

[0076] Na₂O is an ion-exchange component, and also a component that reduces high-temperature viscosity and improves meltability and formability. Furthermore, Na₂O improves devitrification resistance and the reactivity with shaped refractories, especially alumina refractories. If the Na₂O content is too low, meltability may decrease, the coefficient of thermal expansion may decrease excessively, or the ion exchange rate may decrease. Therefore, the suitable lower limit range for Na₂O is 5% or higher, 7% or higher, 8% or higher, 8.5% or higher, 9% or higher, 9.5% or higher, 10% or higher, 11% or higher, and 12% or higher, especially 12.5% ​​or higher. On the other hand, if the Na₂O content is too high, phase separation and viscosity become easier to decrease. Additionally, acid resistance decreases, or the glass composition lacks balance, which can sometimes reduce devitrification resistance. Therefore, the suitable upper limits for Na2O are below 25%, below 22%, below 20%, below 19.5%, below 19%, below 18%, below 17%, below 16.5%, below 16%, below 15.5%, and especially below 15%.

[0077] K₂O is a component that reduces viscosity at high temperatures and improves melt flow and formability. It also improves devitrification resistance and increases Vickers hardness. However, if the K₂O content is too high, the viscosity becomes easier to decrease during phase separation. Furthermore, it reduces acid resistance or lacks a balanced glass composition, which can actually decrease devitrification resistance. Therefore, the suitable lower limit range for K₂O is 0% or more, 0.01% or more, 0.02% or more, 0.1% or more, 0.5% or more, 1% or more, 1.5% or more, 2% or more, 2.5% or more, and 3% or more, especially 3.5% or more; the suitable upper limit range is 5.5% or less, 5% or less, especially less than 4.5%.

[0078] Li₂O is an ion-exchange component that reduces viscosity at high temperatures and improves melt flow and formability. It also increases Young's modulus. The suitable lower limit range of Li₂O is above 0%, above 0.0001%, above 0.01%, above 1%, above 2%, above 2.5%, and above 2.8%. The suitable upper limit range of Li₂O is below 10%, below 5%, below 4.5%, below 2%, below 1%, less than 1%, below 0.5%, below 0.3%, below 0.1%, and below 0.05%.

[0079] MgO is a component that reduces viscosity at high temperatures and improves meltability and formability. It also increases Young's modulus, Vickers hardness, and acid resistance. Therefore, the suitable lower limit range for MgO is 0% or more, 0.1% or more, 0.5% or more, 1% or more, 1.5% or more, and especially 2% or more. However, if the MgO content is too high, the ion exchange rate tends to decrease, and the glass may become more prone to devitrification. Particularly when using alumina refractories as the shaped refractories and employing the overflow-drawing method for plate forming, spinel devitrification crystals easily precipitate at the interface with the alumina refractories. Therefore, the suitable upper limit range for MgO is 5.5% or less, 4.5% or less, 4% or less, 3.5% or less, 3% or less, and especially 2.5% or less.

[0080] P2O5 is a component that increases the ion exchange rate while maintaining compressive stress. Therefore, the suitable lower limit range for P2O5 is 2% or more, 2.1% or more, 2.5% or more, 3% or more, 4% or more, and especially 4.5% or more. However, if the P2O5 content is too high, phase separation will occur in the glass, leading to turbidity, or the water resistance will easily decrease. Therefore, the suitable upper limit range for P2O5 is 10% or less, 8.5% or less, 8% or less, 7.5% or less, 7% or less, 6.5% or less, 6.3% or less, 6% or less, 5.9% or less, 5.7% or less, 5.5% or less, 5.3% or less, 5.1% or less, and especially 5% or less.

[0081] As a clarifying agent, 0% to 3% of one or more of the group selected from Cl, SO3, and CeO2 (preferably the group of Cl and SO3) can be added.

[0082] SnO2 has the effect of improving ion exchange performance. Therefore, the content of SnO2 is 0%–3%, 0.01%–3%, 0.05%–3%, especially 0.1%–3%, and particularly preferably 0.2%–3%.

[0083] The Fe2O3 content is below 1000 ppm (less than 0.1%), below 800 ppm, below 600 ppm, below 400 ppm, and particularly preferably below 300 ppm. This makes it easier to improve the transmittance (400 nm to 770 nm) at a thickness of 1 mm.

[0084] Rare earth oxides such as Nb₂O₅ and La₂O₃ are components that improve Young's modulus. However, the raw materials themselves are expensive, and if added in large quantities, the devitrification resistance becomes easily reduced. Therefore, the content of rare earth oxides is 3% or less, 2% or less, 1% or less, or 0.5% or less, with 0.1% or less being particularly preferred.

[0085] Furthermore, from an environmental perspective, the aforementioned reinforced glass is preferably substantially free of As₂O₃, Sb₂O₃, and PbO as its glass composition. Additionally, from an environmental perspective, it is also preferable that it is substantially free of Bi₂O₃ and F.

[0086] The glass for strengthening is more preferably composed of the following components by mass: 40-70% SiO2, 10-30% Al2O3, 0.1-3% B2O3, 5-25% Na2O, 1-5.5% K2O, 0.01-10% Li2O, 0.1-5.5% MgO, 2-10% P2O5, and 0.01-3% SnO2.

[0087] It should be noted that the composition of the aforementioned strengthening glass is an example. If chemical strengthening based on ion exchange can be performed, strengthening glass with a known composition can be used. Furthermore, the strengthening glass obtained by ion-exchange treatment of the aforementioned strengthening glass has the same composition as the strengthening glass before ion-exchange treatment.

[0088] The aforementioned reinforced glass can be manufactured in the following manner.

[0089] First, glass raw materials prepared in accordance with the above-mentioned glass composition are fed into a continuous melting furnace, heated and melted at 1500°C to 1600°C, clarified, and then fed to a forming device to be formed into plates or the like, and annealed, thereby enabling the production of reinforced glass.

[0090] The overflow-draw method is preferred as a method for forming glass sheets. The overflow-draw method is capable of producing high-quality glass sheets in large quantities and easily manufacturing large glass sheets, while minimizing surface damage. It should be noted that in the overflow-draw method, alumina and dense zircon are used as the forming material. The strengthening glass of this invention exhibits good compatibility with alumina and dense zircon, particularly with alumina (it is difficult for them to react with the forming material to produce bubbles, pitting, etc.).

[0091] Besides the overflow pull-down method, various other forming methods can be used. For example, float forming, pull-down (slit pull-down, re-pulling, etc.), calendering, extrusion, and other forming methods can be used.

[0092] After the reinforced glass is formed, or simultaneously with the forming process, it can be bent as needed. Additionally, it can be cut, drilled, surface ground, chamfered, end-face ground, etched, and other processes can be performed as required.

[0093] The dimensions of the reinforced glass can be set arbitrarily, but the thickness T is preferably 2.0 mm or less, more preferably 1.0 mm or less, and even more preferably 0.3 mm to 0.9 mm.

[0094] The strengthened glass obtained in the above manner is subjected to multiple ion exchange treatments. This embodiment will describe an example of performing three ion exchange treatments. Specifically, the method for manufacturing strengthened glass according to this embodiment is as follows: Figure 3 As shown, the first ion exchange step S1, the second ion exchange step S2, and the third ion exchange step S3 are performed sequentially. It should be noted that although the illustrations are omitted, the molten salts and alkali metal ions used in each step S1 to S3 are also marked with symbols below to distinguish them.

[0095] In the first ion exchange step S1, the strengthening glass is immersed in a treatment tank filled with a first molten salt containing second alkali metal ions a2, whose ionic radius is larger than that of the first alkali metal ion a1 contained in the strengthening glass, and held at a specified temperature for a specified time, thereby performing ion exchange treatment on the surface of the strengthening glass. This process involves ion exchange between the first alkali metal ion a1 contained in the strengthening glass and the second alkali metal ion a2 contained in the first molten salt m1, introducing the second alkali metal ion a2 into the strengthening glass up to a depth of 10.5% or more of its thickness T from the surface (main surface and end face in this embodiment). As a result, a compressive stress layer is formed on the surface of the strengthening glass, and the strengthening glass is strengthened.

[0096] In the first ion exchange process S1, the first alkali metal ion a1 becomes the detached ion that is separated from the strengthening glass, and the second alkali metal ion a2 becomes the introduced ion that is introduced into the strengthening glass.

[0097] In the first ion exchange step S1, the region where the second alkali metal ion a2 is introduced into the strengthening glass is preferably the region of the strengthening glass from the surface to a depth of 12% or more of the thickness T, and more preferably the region of the strengthening glass from the surface to a depth of 13.5% or more and 30% or less of the thickness T.

[0098] The first molten salt m1 is pre-included in the composition of the strengthening glass, and is mainly composed of a mixed salt of nitrates of the first alkali metal ion a1 removed during ion exchange and nitrates of the second alkali metal ion a2 introduced into the strengthening glass through ion exchange. In this embodiment, the case where the first alkali metal ion a1 is Na ion and the second alkali metal ion a2 is K ion will be described. That is, in this embodiment, the first molten salt m1 is a mixed salt mainly composed of NaNO3 and KNO3. It should be noted that the first molten salt m1 is not limited to this, and may also be, for example, a molten salt composed only of KNO3.

[0099] Preferably, the concentration of KNO3 in the first molten salt m1 is higher than the concentration of NaNO3 in the first molten salt m1. Specifically, the concentration of NaNO3 is preferably less than 50% by mass, more preferably 5 to 40% by mass. The concentration of KNO3 is preferably 50% by mass or more, more preferably 60 to 95% by mass.

[0100] In the second ion exchange step S2, the strengthening glass that has undergone the first ion exchange step S1 is immersed in a treatment tank filled with a second molten salt m2 containing the first alkali metal ions a1, and held at a specified temperature for a specified time, thereby performing ion exchange treatment on the surface of the strengthening glass. As a result, the second alkali metal ions a2 contained in the strengthening glass and the first alkali metal ions a1 contained in the second molten salt m2 undergo ion exchange, causing at least a portion of the second alkali metal ions a2 from the surface (main surface and end face in this embodiment) to a region shallower than 10% of the thickness T of the strengthening glass to detach from the strengthening glass. Consequently, the compressive stress of the compressive stress layer formed in the strengthening glass decreases. On the other hand, the region where the compressive stress layer is formed expands into the depth of the strengthening glass.

[0101] In the second ion exchange process S2, the second alkali metal ion a2 becomes the detached ion that detaches from the strengthening glass, and the first alkali metal ion a1 becomes the introduced ion that is introduced into the strengthening glass.

[0102] In the second ion exchange step S2, the region where the second alkali metal ion a1 is removed from the strengthening glass is preferably the region of the strengthening glass from the surface to a depth of 9% or less of the thickness T, and more preferably the region of the strengthening glass from the surface to a depth of 4% or more and 8% or less of the thickness T.

[0103] The second molten salt m2 is pre-included in the composition of the strengthening glass, and is mainly composed of a mixed salt of nitrates of the second alkali metal ion a2 that has been removed during ion exchange and nitrates of the first alkali metal ion a1 that has been introduced into the strengthening glass through ion exchange. That is, in this embodiment, the second molten salt m2 is a mixed salt mainly composed of NaNO3 and KNO3. It should be noted that the second molten salt m2 is not limited to this, and may also be, for example, a molten salt composed only of NaNO3.

[0104] Preferably, the concentration of NaNO3 in the second molten salt m2 is higher than the concentration of KNO3 in the second molten salt m2. Specifically, the concentration of NaNO3 is preferably 60% by mass or more, more preferably 70 to 95% by mass. The concentration of KNO3 is preferably 40% by mass or less, more preferably 5% to 30% by mass.

[0105] In the third ion exchange step S3, the strengthening glass that has undergone the second ion exchange step S2 is immersed in a treatment tank filled with a third molten salt m3 containing the second alkali metal ions a2, and held at a specified temperature for a specified time, thereby performing ion exchange treatment on the surface of the strengthening glass. Here, the first alkali metal ions a1 contained in the strengthening glass and the second alkali metal ions a2 contained in the first molten salt m1 undergo ion exchange, introducing the second alkali metal ions a2 into the strengthening glass from the surface (main surface and end face in this embodiment) to a region shallower than 7% of the thickness T. As a result, the strengthening glass is re-strengthened, and a compressive stress layer 2 with high compressive stress is formed near the surface in the surface layer. At this time, the compressive stress layer 2 is maintained in a state where it extends to a certain depth.

[0106] In the third ion exchange process S3, the first alkali metal ion a1 becomes the detached ion that is separated from the strengthening glass, and the second alkali metal ion a2 becomes the introduced ion that is introduced into the strengthening glass.

[0107] In the third ion exchange step S3, the region where the second alkali metal ion a2 is introduced into the strengthening glass is preferably the region of the strengthening glass from the surface to a depth of 6% or less of the thickness T, and more preferably the region of the strengthening glass from the surface to a depth of 1% or more and 5% or less of the thickness T.

[0108] Preferably, the concentration of KNO3 in the third molten salt m3 is higher than the concentration of NaNO3 in the third molten salt m3.

[0109] Preferably, the concentration of NaNO3 in the third molten salt m3 is lower than the concentration of NaNO3 in the first molten salt m1. Specifically, the concentration of NaNO3 in the third molten salt m3 is preferably 10% by mass or less, more preferably 0 to 5% by mass, and even more preferably 0.1 to 5% by mass.

[0110] Preferably, the concentration of KNO3 in the third molten salt m3 is higher than the concentration of KNO3 in the first molten salt m1. Specifically, the concentration of KNO3 in the third molten salt m3 is preferably 90% by mass or more, more preferably 95 to 100% by mass, and even more preferably 95 to 99.5% by mass.

[0111] In this embodiment, the third molten salt m3 is a molten salt composed only of KNO3, but it is not limited to this, and can also be, for example, a mixed salt with NaNO3 and KNO3 as the main components.

[0112] Preferably, the proportion of alkali metal ions with small ionic radii (e.g., Li ions, Na ions, especially Na ions) in the third molten salt m3 is lower than that in the first molten salt m1. This facilitates deeper stress formation and increases the concentration of large alkali metal ions on the outermost surface. It should be noted that the order of alkali metal ion size is Li ion < Na ion < K ion (potassium ion) < Ce ion < Rb ion.

[0113] Preferably, the ion exchange treatment temperatures of the first ion exchange step S1 and the second ion exchange step S2 are higher than the ion exchange treatment temperature of the third ion exchange step S3. It should be noted that the ion exchange treatment temperature refers to the temperature of the molten salt.

[0114] Specifically, the ion exchange treatment temperature of the first ion exchange step S1 and the second ion exchange step S2 is preferably 420°C or higher, more preferably 430°C or higher, and even more preferably 440°C to 500°C. It should be noted that the ion exchange treatment temperature of the first ion exchange step S1 is preferably higher than the ion exchange treatment temperature of the second ion exchange step S2. The temperature difference between the first ion exchange step S1 and the second ion exchange step S2 is preferably 5°C or higher, more preferably 5°C to 50°C. The ion exchange treatment temperature of the first ion exchange step S1 is more preferably 440°C or higher and lower than 490°C, and even more preferably 450°C to 470°C. The ion exchange treatment temperature of the second ion exchange step S2 is more preferably 400°C to 480°C, and even more preferably 420°C to 460°C.

[0115] The ion exchange temperature of the third ion exchange step S3 is preferably 10°C, 20°C, 30°C, or more lower than the ion exchange temperature of the first ion exchange step S1, and particularly 50°C or more lower. Specifically, the ion exchange temperature of the third ion exchange step S3 is preferably 350°C or more and lower than 410°C, 360°C or more and lower than 400°C, and particularly 380°C or more and lower than 400°C.

[0116] The ion exchange treatment time of the first ion exchange step S1 and the second ion exchange step S2 is preferably more than 3 times longer than the ion exchange treatment time of the third ion exchange step S3, more preferably more than 5 times, and even more preferably 10 to 200 times longer.

[0117] The ion exchange treatment time for the first ion exchange step S1 and the second ion exchange step S2 is preferably 2 hours or more, more preferably 3 hours or more, and even more preferably 4 to 20 hours. By increasing the ion exchange treatment time of the first ion exchange step S1 and the second ion exchange step S2, a deeper compressive stress layer can be formed; therefore, it is preferable to increase the treatment time without reducing productivity. It should be noted that the ion exchange treatment time of the first ion exchange step S1 is preferably longer than the ion exchange treatment time of the second ion exchange step S2. The difference between the ion exchange treatment times of the first ion exchange step S1 and the second ion exchange step S2 is preferably 2 hours or more, more preferably 3 to 7 hours.

[0118] The ion exchange treatment time for the third ion exchange step S3 is preferably 2 hours or less, more preferably 3 hours or less, 0.2 to 2 hours, 0.3 to 1 hour, or 0.3 to 0.5 hours. By controlling the total ion exchange treatment time to a shorter duration, the tensile stress in the tensile stress layer 3 can be easily controlled to a smaller value.

[0119] The strengthening glass impregnated with molten salt in each ion exchange process S1 to S3 can be preheated to the temperature of the molten salt in the ion exchange treatment of each ion exchange process, or it can be impregnated with each molten salt at room temperature (e.g., 1℃ to 40℃).

[0120] Between the first ion exchange step S1 and the second ion exchange step S2, and / or between the second ion exchange step S2 and the third ion exchange step S3, a cleaning step for cleaning the strengthening glass extracted from the molten salt is preferably provided. By cleaning, the deposits attached to the strengthening glass can be easily removed, and the ion exchange treatment can be performed more uniformly in the second ion exchange step S2 and the third ion exchange step S3.

[0121] By appropriately adjusting the processing time and temperature within the conditions of the first to third ion exchange processes S1 to S3 described above, a reinforced glass 1 with the above-mentioned characteristics can be obtained.

[0122] It should be noted that after the third ion exchange process S3 mentioned above, various processing steps such as cutting, hole opening, surface grinding, chamfering, end face grinding, etching, and film formation can be performed.

[0123] Furthermore, in the above embodiments, examples of the first to third ion exchange processes including two strengthening processes and one tempering process have been described, but it is also possible to implement two or more ion exchange processes including at least two strengthening processes.

[0124] (Second Implementation)

[0125] In the first embodiment described above, a method for obtaining tempered glass 1 through three ion exchange treatments was illustrated. In the second embodiment, a method for obtaining tempered glass 1 through two ion exchange treatments was illustrated. Specifically, in the method for manufacturing tempered glass according to this embodiment, as follows... Figure 4 As shown, the first ion exchange step T1 and the second ion exchange step T2 are performed sequentially. It should be noted that although the illustrations are omitted, symbols are added below to distinguish the molten salts and alkali metal ions used in each step T1 to T2.

[0126] In the first ion exchange step T1, the glass for strengthening is immersed in a treatment tank filled with a first molten salt n1 containing second alkali metal ions b2, whose ionic radius is larger than that of the first alkali metal ions b1 contained in the strengthening glass, and held at a specified temperature for a specified time, thereby performing ion exchange treatment on the surface of the strengthening glass. This process involves ion exchange between the first alkali metal ions b1 contained in the strengthening glass and the second alkali metal ions b2 contained in the first molten salt n1, introducing the second alkali metal ions b2 into the vicinity of the surface of the strengthening glass (in this embodiment, the main surface and end face). As a result, a compressive stress layer is formed on the surface portion of the strengthening glass, and the strengthening glass is strengthened.

[0127] In the first ion exchange process T1, the first alkali metal ion b1 becomes the detached ion that is separated from the strengthening glass, and the second alkali metal ion b2 becomes the introduced ion that is introduced into the strengthening glass.

[0128] In the first ion exchange step T1, the region where the second alkali metal ion b2 is introduced into the strengthening glass is preferably the region of the strengthening glass from the surface to a depth of 10% or more of the thickness T, and more preferably the region of the strengthening glass from the surface to a depth of 12% or more, 14% or more, 15% or more, or 15% or more and less than 40% of the thickness T.

[0129] In the second ion exchange step T2, the strengthening glass is immersed in a treatment tank filled with a second molten salt n2 containing a third alkali ion b3 (whose ionic radius is larger than that of the second alkali metal ion b2 in the strengthening glass) and a first alkali metal ion b1, and held at a specified temperature for a specified time, thereby performing ion exchange treatment on the surface of the strengthening glass. This reverse ion exchange between the first alkali metal ion b1 and the second alkali metal ion b2 contained in the strengthening glass causes at least a portion of the second alkali metal ion b2 to detach from the strengthening glass. Simultaneously, the third alkali metal ion b3 is ion exchanged with either the first alkali metal ion b1 or the second alkali metal ion b2 contained in the strengthening glass, introducing the third alkali metal ion b3 into the strengthening glass from the surface to a region shallower than 7% of the thickness T. In other words, the compressive stress formed in the surface portion of the strengthening glass is alleviated by the reverse ion exchange, and the strengthening glass is strengthened by ion exchange, with high compressive stress only forming near the surface in the surface portion.

[0130] In the second ion exchange step T2, the region where the second alkali metal ion b2 is detached from the strengthening glass is preferably a region extending from the surface of the strengthening glass to a depth of 15% or less of the thickness T, more preferably a region extending from the surface of the strengthening glass to a depth of 14% or less, 13% or less, 12% or less, 11% or less, 10% or less, 1% or more and 10% or less, 2% or more and 10% or less, 3% or more and 10% or less, 4% or more and 10% or less, or 5% or more and 10% or less of the thickness T. Furthermore, in the second ion exchange step T2, the region where the third alkali metal ion b3 is introduced into the strengthening glass is preferably a region extending from the surface of the strengthening glass to a depth of 7% or less of the thickness T, more preferably a region extending from the surface of the strengthening glass to a depth of 6.5% or less, 6% or less, 5.5% or less, or 5% or less of the thickness T.

[0131] By appropriately adjusting the processing time and temperature within the conditions of the first and second ion exchange processes T1 and T2 described above, a reinforced glass 1 with the above-mentioned characteristics can be obtained.

[0132] Here, in the second ion exchange process T2, the rate of the reverse ion exchange is greater than the rate of the ion exchange. Therefore, the easing of compressive stress in the surface layer first proceeds to a deeper level, and then compressive stress is formed again on the surface. As a result, the stress distribution in the manufactured reinforced glass 1 is prone to form... Figure 2 Valley B1 as shown.

[0133] It should be noted that after the second ion exchange process T2 mentioned above, various processing can be performed, such as cutting, hole opening, surface grinding, chamfering, end face grinding, etching, and film formation.

[0134] In the second embodiment, the first alkali metal ion b1 is preferably Li ion, the second alkali metal ion b2 is preferably Na ion, and the third alkali metal ion b3 is preferably K ion.

[0135] Especially when the strengthening glass is a lithium aluminosilicate glass containing 2% or more Li₂O and 5% or more Na₂O by mass, the first molten salt n1 can be a molten salt composed solely of NaNO₃, or a mixed salt with NaNO₃ and KNO₃ as the main components. It should be noted that the first molten salt n1 may contain LiNO₃. In this case, the Li₂O content of the strengthening glass is preferably 2.5 to 5.0% by mass, more preferably 2.8 to 4.5% by mass.

[0136] In the second embodiment, the glass used for strengthening is preferably composed of, by mass percent, 48-60% SiO2, 21-29% Al2O3, 0-10% B2O3, 2-11% Li2O, 5-20% Na2O, 0-10% K2O, 0-6% MgO, 0-10% ZnO, and 0-20% P2O5.

[0137] In the second embodiment, the first molten salt n1 used in the first ion exchange step T1 is preferably a mixed salt of NaNO3 and KNO3. If the first molten salt n1 contains K ions, the stress and its distribution in the strengthened glass can be easily measured after the first ion exchange step T1, thus facilitating quality management of the obtained strengthened glass. The concentration of NaNO3 in the first molten salt n1, in mass percent, is preferably 100–20%, 100–30%, 100–40%, 100–50%, or 100–60%, with the balance preferably being KNO3. Preferably, the concentration of NaNO3 in the first molten salt n1 is higher than the concentration of KNO3 in the first molten salt n1. It should be noted that the first molten salt n1 can be configured to contain only NaNO3 and no KNO3. The ion exchange treatment temperature of the first ion exchange step T1 is preferably 350–480°C, more preferably 360–430°C, and even more preferably 370–400°C or 370–390°C. The ion exchange treatment time for the first ion exchange step T1 is preferably 1 to 20 hours, more preferably 1.5 to 15 hours, and even more preferably 2 to 10 hours.

[0138] In the second embodiment, the second molten salt n2 used in the second ion exchange step T2 is preferably a mixed salt of LiNO3 and KNO3. Preferably, the concentration of LiNO3 in the second molten salt n2 is lower than the concentration of KNO3 in the second molten salt n2. Specifically, the concentration of LiNO3 in the second molten salt n2, in mass %, is preferably 0.1–5%, 0.2–5%, 0.3–5%, 0.4–5%, 0.5–5%, 0.5–4%, 0.5–3%, 0.5–2.5%, 0.5–2%, or 1–2%, with the balance preferably being KNO3. Furthermore, the concentration of Li ions in the second molten salt is preferably 100 ppm or more. In this case, the concentration of Li ions in the second molten salt n2 is obtained by multiplying the mass % of LiNO3 by 0.101. The ion exchange treatment temperature of the second ion exchange step T2 is preferably 350–480°C, more preferably 360–430°C, and even more preferably 370–400°C or 370–390°C. The ion exchange treatment time of the second ion exchange step T2 is preferably shorter than the ion exchange treatment time of the first ion exchange step T1. The ion exchange treatment time of the second ion exchange step T2 is preferably 0.2 hours or more, more preferably 0.3–2 hours or 0.4–1.5 hours, and even more preferably 0.5–1 hour.

[0139] The embodiments of the present invention have been described above. Of course, the present invention is not limited to this method, and various methods can be adopted within the scope of the present invention.

[0140] For example, in the first and second embodiments described above, an example is shown where the tempered glass 1 has a compressive stress layer 2 on both sides of the main surface 1a and the end face 1b. Alternatively, the compressive stress layer 2 may be provided only on one side of the main surface 1a, or only on a portion of the surface layer of the tempered glass 1. As a method of forming the compressive stress layer 2 only on a portion of the surface layer of the tempered glass 1, an example is to form an inhibition film (e.g., a SiO2 film) in advance in the region of the tempered glass where the compressive stress layer is not formed, to inhibit the permeation of introduced ions during ion exchange treatment, and then perform ion exchange treatment locally on the portion other than the inhibition film.

[0141] In addition, the tempered glass 1 in the above embodiment is a flat plate, but the concept of plate in the present invention also includes a curved plate shape with a curved surface.

[0142] Example

[0143] The following description relates to the tempered glass based on embodiments. It should be noted that the following embodiments are merely illustrative, and the present invention is not limited to any of them.

[0144] Prepare the test specimens as follows. First, prepare strengthening glasses with compositions A to T as shown in Tables 1 to 2.

[0145] Table 1

[0146]

[0147] Table 2

[0148]

[0149] For each composition of the glass raw material, a platinum boat was used to melt it at 1600°C for 21 hours. Subsequently, the resulting molten glass was poured from the refractory molding body using an overflow-pull method to form plates of the specified thicknesses listed in Tables 3-18.

[0150] Next, the aforementioned strengthening glass is immersed in a molten salt bath under the conditions shown in Tables 3-18 to undergo ion exchange treatment, thereby obtaining plate-shaped strengthened glass. Regarding the molten salt bath, in processes marked with NaNO3 / KNO3, NaNO3 molten salt is added to the KNO3 molten salt to adjust the concentration so that the weight concentration ratio of NaNO3 to KNO3 in the molten salt is as described in the table. Regarding the molten salt bath, in processes marked with LiNO3 / KNO3, LiNO3 molten salt is added to the KNO3 molten salt to adjust the concentration so that the weight concentration ratio of LiNO3 to KNO3 in the molten salt is as described in the table.

[0151] It should be noted that samples No. 1 to 10 underwent three ion exchange treatments: a first ion exchange step (enhancing step), a second ion exchange step (mitigating step), and a third ion exchange step (enhancing step). On the other hand, sample No. 11 underwent only the first ion exchange step (enhancing step) once, and samples No. 12 to 160 underwent two ion exchange treatments: a first ion exchange step (enhancing step) and a second ion exchange step (enhancing step). Samples No. 1 to 10 and No. 13 to 160 are embodiments of the present invention, and samples No. 11 to 12 are comparative examples.

[0152] For the reinforced glass obtained in this manner, the results of various properties and strength tests as determined below are shown in Tables 3-18.

[0153] Table 3

[0154]

[0155] Table 4

[0156]

[0157] Table 5

[0158]

[0159] Table 6

[0160]

[0161] Table 7

[0162]

[0163] Table 8

[0164]

[0165] Table 9

[0166]

[0167] Table 10

[0168]

[0169] Table 11

[0170]

[0171] Table 12

[0172]

[0173] Table 13

[0174]

[0175] Table 14

[0176]

[0177] Table 15

[0178]

[0179] Table 16

[0180]

[0181] Table 17

[0182]

[0183] Table 18

[0184]

[0185] First, the stress distribution of each specimen was measured. The stress distribution of specimens No.1 to 10 and No.13 to 160 was measured using surface stress gauges FSM-6000LE and SLP-1000 manufactured by Orihara Corporation. The measurement results were synthesized using the data synthesis application pmac pre-installed on the above devices to obtain the phase difference distribution. For the applicable range of each data in the synthesis, the FSM-6000LE was set to 10 μm from the surface, and the SLP-1000 was set to 30 μm and beyond from the surface. The stress distribution was obtained from the obtained phase difference distribution through analysis as described below. First, the initial values ​​shown in the table below were set, and the following formula R(x) was calculated at each depth x of the obtained phase difference distribution. Here, Δ = 0.01 [um]. The sum of squares of the deviations between R(x) and the obtained phase difference distribution was calculated, and various variables A1, A2, A3, B1, B2, B3, and C1 were set in a manner that minimized the sum of squares of the deviations. More specifically, using Excel's solver function, the solution uses "GRG Nonlinearity," approximating various variables with the ranges and constraints given in the table below. This approximation calculation is repeated until the correlation coefficient between R(x) and the phase difference distribution exceeds 0.9995. If the correlation coefficient does not reach 0.9995, multiple measurements are performed using an SLP-1000, and the averaged measurement data is analyzed. The stress distribution is represented by the following formula σ(x) using the various variables obtained as described above. The stress distributions of samples No. 11 and No. 12 are measured using a surface stress gauge FSM-6000LE manufactured by Orihara Manufacturing Co., Ltd. For the photoelastic constant C [nm / cm / MPa], optical heterodyne interferometry is used for each sample, more specifically, using a PEL-3A-XR manufactured by Uniopt. The device constant k is a constant calculated in the SLP-1000 by inputting the refractive index of each sample into the device; more specifically, it is the value of kDP recorded in the measurement results file divided by the value of the stress correction coefficient. It should be noted that the refractive index was measured for each sample using the V-block method, and more specifically, using the KPR-2000 manufactured by Shimadzu Corporation.

[0186]

Mathematical Formula 1

[0187] σ(x)=A1·erfc(B1·x)+A2·erfc(B2·x)+A3·erfc(B3·x)+C1

[0188]

Mathematical Formula 2

[0189]

[0190] k: apparatus constant, C: photoelastic constant, λ: measurement wavelength (640 nm)

[0191] Table 19

[0192]

[0193] An example of the measured stress distribution is shown below. Figures 5-12 . Figure 5 This is a graph showing the stress distribution along the depth direction of the tempered glass in sample No.1. Figure 6 This is a graph showing the stress distribution along the depth direction of the tempered glass in sample No. 2. Figure 7 This is a graph showing the stress distribution along the depth direction of the tempered glass in sample No. 3. Figure 8 This is a graph showing the stress distribution along the depth direction of the tempered glass in sample No. 4. Figure 9 A graph showing the stress distribution along the depth direction of the tempered glass in sample No. 10. Figure 10 A graph showing the stress distribution along the depth direction of the tempered glass in sample No. 38. Figure 11 A graph showing the stress distribution along the depth direction of the tempered glass in sample No. 49. Figure 12 A graph showing the stress distribution along the depth direction of the tempered glass in sample No. 140. Figures 5-12 In the diagram, the horizontal axis represents the depth (μm) from one side of the main surface, and the vertical axis represents the magnitude of the stress (MPa). It should be noted that... Figures 5-12 In this context, compressive stress is represented by positive values, and tensile stress is represented by negative values.

[0194] Based on the stress distribution measured in the manner described above, the characteristics shown in Tables 3-18 are calculated.

[0195] In Tables 3-18, CSmax represents the stress at the first peak P1, i.e., the maximum compressive stress in compressive stress layer 2. CTmax represents the stress at the second valley B2, i.e., the minimum tensile stress in tensile stress layer 3. CSb represents the stress (minimum) at the first valley B1, and DOLb represents the depth of the first valley B1. CSp represents the stress (maximum) at the second peak P2, and DOLp represents the depth of the second peak P2. DOLzero represents the depth to the point where the stress between the second peak P2 and the second valley B2 becomes zero.

[0196] Regarding the simulated frame drop strength, such as Figure 13The diagram shows the breakage height of the glass sample 20 when it is dropped onto an iron platform 40, with the simulated frame 10, the glass sample 20 made of tempered glass 1, and the sandpaper 30 stacked in that order. Specifically, the simulated frame 10 is first attached to one main surface of the glass sample 20, which is 65 mm wide and 130 mm long and has been processed to the thickness T listed in Table 1. The simulated frame 10 is a thick polycarbonate plate component with a width of 70 mm, a length of 140 mm, a thickness of 8 mm, and a mass of 110 g, simulating a portable terminal. The simulated frame 10 and the glass sample 20 are bonded together by sandwiching a 150 μm thick optical bonding film 50 in between.

[0197] Next, on the other main surface of the glass sample 20 (the main surface opposite to the main surface adhered to the simulation frame), sandpaper 30 is attached in a manner that the surface of sandpaper 30 (the side with the abrasive material) is against it. Sandpaper 30 is 60mm wide and 120mm long, and is positioned at the center of the other main surface of the glass sample 20. At this time, the sandpaper 30 is positioned so that its peripheral edge protrudes from the glass sample 20. Multiple insulating tape sheets 60 are used to attach the peripheral edge of the protruding back side (the side without the abrasive material) of the glass sample 20 and the end of the sandpaper 30 at multiple locations, thereby attaching the sandpaper 30 to the glass sample 20. The insulating tape sheets 60 are 19mm wide, 10mm long, and 0.1mm thick, and are attached at the center of each short side of the sandpaper 30. It should be noted that, as sandpaper 30, different grades of Riken Corundum SiC sandpaper with different grit roughness (grit size) were used to measure the simulated frame drop strength for each case.

[0198] The test subject obtained in this manner is held horizontally with sandpaper 30 facing downwards, towards platform 40, and repeatedly dropped while increasing the drop height until glass sample 20 breaks. More specifically, in this application, the test subject is held in a clamping device including a cylinder, and the drop begins together with the clamping device. The cylinder-based clamping is released at a position 20cm in front of the platform 40, so that the test subject falls towards platform 40 while maintaining a horizontal posture. The test is conducted in this manner. Sandpaper 30 is replaced with a new one after each drop test. The drop height is set based on a height of 20cm from the drop surface, and is set to increase the height by 10cm if the glass sample 20 does not break.

[0199] In all examples (e.g., specimens No. 1 to No. 4) where the drop strength of the simulated frame was measured, it was confirmed that the simulated frame had a higher drop strength and higher impact resistance compared to the comparative examples (executives No. 11 and 12).

[0200] In addition, it can be confirmed that the simulated frame drop strength is correlated to some extent with the calculated strength shown below.

[0201]

Mathematical Expression 3

[0202]

[0203] Here, P(x) is the probability density function of the injury at depth x that occurs during the drop test, σ f (x) is the sum of the stress amplification factor and the compressive stress value as shown below.

[0204]

Mathematical Expression 4

[0205]

[0206] Here, Kc is the breaking toughness value of the mother glass, and σ(x) is the compressive stress value at depth x generated by strengthening. By successively observing the depth of the scratches produced in the drop test and calculating P(x) and strength, if the correlation between the breakage height in the simulated frame drop test is shown, then... Figure 14 As shown in the graph, it can be confirmed that the fall intensity is related to the calculated intensity mentioned above.

[0207] It should be noted that in the tempered glass of the present invention, the calculated strength of P180 is preferably 35 MPa or more, more preferably 40 to 200 MPa. Furthermore, the calculated strength of P120 is preferably 10 MPa or more, more preferably 20 to 150 MPa. The calculated strength of P100 is preferably 5 MPa or more, more preferably 10 to 100 MPa. The calculated strength of P80 is preferably -13 MPa or more, more preferably -10 to 50 MPa.

[0208] Industrial availability

[0209] The reinforced glass of this invention can be used as a component in, for example, mobile phones (especially smartphones), tablet computers, digital cameras, touch panel displays, large televisions, etc.

Claims

1. A type of tempered glass, characterized in that, It is a reinforced glass with a surface area and thickness T. By setting compressive stress to a positive value and tensile stress to a negative value, the stress distribution obtained by measuring the stress from the surface along the depth direction has the following characteristics: The first peak where the compressive stress reaches its maximum value in the surface. The first valley, where the stress gradually decreases along the depth direction from the first peak and reaches a minimum value, The second peak, where the compressive stress gradually increases along the depth direction from the first valley, and reaches its maximum value, and... The second valley, starting from the second peak, gradually decreases along the depth direction, where the tensile stress reaches its minimum value. The compressive stress at the first peak is above 700 MPa. The compressive stress at the second peak is 15 MPa to 100 MPa. The second peak exists in the depth range of 4% to 20% of the thickness T. The stress at the first valley is -50 MPa to +100 MPa. The stress distribution is between the second peak and the second valley, with a stress zero point where the stress is zero, and the stress zero point exists within a depth range of more than 16.5% of the thickness T from the surface.

2. The tempered glass according to claim 1, characterized in that, The stress distribution has a zero-stress point between the second peak and the second valley, where the stress is zero. The zero stress point exists within a depth range of 10% to 35% of the thickness T from the surface.

3. The tempered glass according to claim 1 or 2, characterized in that, The stress at the first valley is above 0 MPa and below +65 MPa.

4. The tempered glass according to claim 1 or 2, characterized in that, The stress at the first valley is above -30 MPa and less than 0 MPa.

5. The tempered glass according to claim 1 or 2, characterized in that, The first valley exists at a depth ranging from 0.5% to 12% of the thickness T from the surface.

6. The tempered glass according to claim 1 or 2, characterized in that, The distance in the depth direction from the first valley to the second peak is more than 3% of the thickness T.

7. The tempered glass according to claim 1 or 2, characterized in that, The compressive stress at the first peak is above 700 MPa. The second peak exists at a depth of 7.3% or more of the thickness T from the surface.

8. The tempered glass according to claim 1 or 2, characterized in that, The thickness T is 0.3mm to 0.9mm. The stress distribution is present on the main surface and the end face.

9. The tempered glass according to claim 1 or 2, wherein, The thickness T is within the range of 0.45 mm or more and 0.85 mm or less. The compressive stress at the first peak is in the range of 700 MPa or higher and 850 MPa or lower. The compressive stress at the second peak is in the range of 20 MPa or higher and 80 MPa or lower. The second peak exists in a depth range of more than 7.3% and less than 20% of the thickness T from the surface. The stress distribution has a zero-stress point between the second peak and the second valley, where the stress is zero. The zero stress point exists within a depth range of more than 17% and less than 25% of the thickness T from the surface. The maximum absolute value of the tensile stress is within the range of 40 MPa or more and 60 MPa or less.

10. The tempered glass according to claim 1 or 2, wherein, As a glass composition, it contains, by mass%, 40%–70% SiO2, 10%–30% Al2O3, 0%–10% B2O3, 2%–11% Li2O, 5%–25% Na2O, 0%–10% K2O, 0%–6% MgO, 0%–10% ZnO, and 0%–20% P2O5.

11. A method for manufacturing tempered glass, characterized in that, The method for manufacturing the tempered glass according to claim 1 is a method for manufacturing tempered glass by subjecting a tempering glass containing a first alkali metal ion to ion exchange treatment, comprising the following steps: In the first ion exchange process, a first molten salt containing a second alkali metal ion with an ionic radius larger than that of the first alkali metal ion is brought into contact with the strengthening glass, thereby introducing the second alkali metal ion into the strengthening glass. In the second ion exchange step, after the first ion exchange step, a second molten salt containing the first alkali metal ions is brought into contact with the strengthening glass, causing at least a portion of the second alkali metal ions to detach from the strengthening glass; and In the third ion exchange step, after the second ion exchange step, a third molten salt containing the second alkali metal ions is brought into contact with the strengthening glass to introduce the second alkali metal ions into the strengthening glass. In the first ion exchange step, the second alkali metal ions are introduced into the strengthening glass from its surface to a depth of at least 10.5% of its thickness T. In the second ion exchange step, at least a portion of the second alkali metal ions are removed from the strengthening glass, extending from the surface to a region shallower than 10% of its thickness T. In the third ion exchange process, the second alkali metal ions are introduced into the strengthening glass from the surface up to a region shallower than 7% of the thickness T.

12. The method for manufacturing tempered glass according to claim 11, characterized in that, The first alkali metal ion is a Na ion. The second alkali metal ion is a K ion. The first molten salt contains KNO3. The second molten salt contains NaNO3. The third molten salt contains KNO3.

13. The method for manufacturing tempered glass according to claim 11 or 12, characterized in that, The first alkali metal ion is a Na ion. The second alkali metal ion is a K ion. The first molten salt, in the presence of NaNO3 and KNO3, contains at least KNO3. The second molten salt, in the presence of NaNO3 and KNO3, at least contains NaNO3. In the first molten salt, the concentration of KNO3 is higher than that of NaNO3. In the second molten salt, the concentration of NaNO3 is higher than that of KNO3.

14. The method for manufacturing tempered glass according to claim 13, characterized in that, The concentration of KNO3 in the first molten salt is 50% by mass or more. The concentration of NaNO3 in the first molten salt is less than 50% by mass. The concentration of NaNO3 in the second molten salt is above 60% by mass. The concentration of KNO3 in the second molten salt is less than 40% by mass. The concentration of KNO3 in the third molten salt is higher than that in the first molten salt. The ion exchange treatment temperature for the first ion exchange step is 420℃~500℃. The ion exchange treatment temperature for the second ion exchange step is 420℃~500℃. The ion exchange treatment temperature in the third ion exchange step is more than 10°C lower than the ion exchange treatment temperature in the first ion exchange step. The ion exchange treatment time for the first ion exchange step is 2 hours to 40 hours. The ion exchange treatment time for the second ion exchange step is 2 hours to 40 hours. The ion exchange processing time of the third ion exchange step is shorter than that of the first and second ion exchange steps.

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