Tempered glass

Abstract

Provided is tempered glass having a much lower thickness, higher strength, and higher safety than in the prior art. Plate-form or sheet-form tempered glass having a compressive stress layer on the surface and having a tensile stress layer toward the inside of the compressive stress layer in the direction of glass thickness, wherein there is at least one bendable thin portion having a thickness t1, thickness t1 is 105 μm or less, the depth DOC of the compressive stress layer is 9.0 μm or less, and CS / DOC≥95.

Description

[Technical Field]

[0001] The present invention relates to tempered glass, particularly to thin chemically tempered glass. [Background technology]

[0002] In recent years, chemically strengthened glass with a thickness of approximately 0.4 to 1.0 mm has been widely used as cover glass for various electronic terminals and display devices. In particular, when used in portable electronic terminals such as non-bending (so-called straight type) smartphones, it has been thought that the depth of the compressive stress layer needs to be at least 15 μm or more to ensure the strength of the cover glass (for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-102060 Summary of the Invention [Problem to be solved by the invention]

[0004] In recent years, so-called foldable devices, such as smartphones and tablet PCs, have been developed, with display surfaces that can be folded. To enable foldability, the cover glass used in these devices is being considered for thinner thicknesses than conventional devices, for example, ultrathin dimensions of 105 μm (i.e., 0.105 mm) or less. The required properties of glass for such foldable devices differ from those of glass for conventional straight-type devices. For thin glass for such applications, if a deep DOC is designed and CS is increased in order to achieve a deep tempered layer, as in conventional glass, excessive internal stress within the thin plate may result in self-destruction or explosive shattering of the glass upon fracture. In other words, there remains room for improvement in the design of stress characteristics, etc., for thin chemically tempered glass with a thickness of 105 μm or less.

[0005] An object of the present invention is to provide a tempered glass that simultaneously has an extremely thin thickness, high strength, and high safety. [Means for solving the problem]

[0006] The tempered glass of the present invention is a plate- or sheet-shaped tempered glass having a compressive stress layer on its surface and a tensile stress layer located inward of the compressive stress layer in the thickness direction of the glass, characterized in that it has a bendable thin portion having a thickness t1 in at least a portion thereof, the thickness t1 being 105 μm or less, the depth DOC of the compressive stress layer being 9.0 μm or less, and satisfying CS / DOC≧95, where CS is the maximum compressive stress in the compressive stress layer.

[0007] The tempered glass according to the present invention preferably has a thickness t1 of 20 μm or more and 95 μm or less, a maximum compressive stress CS of the compressive stress layer of 550 MPa or more and 1600 MPa or less, and a depth DOC of the compressive stress layer of 1.0 μm or more and 8.5 μm or less.

[0008] In the tempered glass according to the present invention, it is preferable that the maximum compressive stress CS in the compressive stress layer and the depth DOC of the compressive stress layer satisfy CS / DOC≧110.

[0009] The tempered glass according to the present invention preferably has a tensile stress CT of 95 MPa or less.

[0010] The tempered glass according to the present invention preferably satisfies the ratio DOC / t1 of the depth DOC to the thickness t1 of the compressive stress layer: DOC / t1≦0.09.

[0011] In the tempered glass according to the present invention, the tensile stress layer preferably includes a first region extending from a depth DOC of the compressive stress layer to a tensile stress convergence depth DCT, where the tensile stress varies in the thickness direction of the glass, and a second region extending to a region deeper than the tensile stress convergence depth DCT, where the tensile stress is constant in the thickness direction, and the tensile stress convergence depth DCT is 10.0 μm or less, and DCT / t1≦0.10 is satisfied.

[0012] The tempered glass according to the present invention preferably includes a plurality of thick portions each having a thickness t2 greater than a thickness t1 of the thin portions, the thickness t2 being 110 μm or more and 300 μm or less, and the thin portions preferably extending in a strip shape so as to connect the plurality of thick portions.

[0013] In the tempered glass according to the present invention, the thin portion preferably has a width of 3 mm or more.

[0014] The tempered glass according to the present invention is preferably entirely composed of thin portions and has a substantially uniform plate thickness.

[0015] The tempered glass according to the present invention preferably contains, in mole percent, 50 to 80% of SiO2, 5 to 20% of Al2O3, 0 to 15% of B2O3, 0 to 20% of Li2O, 1 to 20% of Na2O, and 0 to 10% of K2O as a glass composition.

[0016] The tempered glass according to the present invention preferably contains, in mole percent, 50 to 80% of SiO2, 5 to 25% of Al2O3, 0 to 1% of B2O3, 0 to 20% of Li2O, 1 to 20% of Na2O, and 0 to 10% of K2O as a glass composition.

[0017] The tempered glass according to the present invention preferably contains, in mole percent, 50 to 80% of SiO2, 5 to 25% of Al2O3, 1 to 5% of B2O3, 0 to 20% of Li2O, 1 to 20% of Na2O, and 0 to 10% of K2O as a glass composition.

[0018] The tempered glass according to the present invention preferably contains, in mole percent, 50 to 80% of SiO2, 5 to 10% of Al2O3, 1 to 5% of B2O3, 0 to 20% of Li2O, 1 to 20% of Na2O, and 0 to 10% of K2O as a glass composition.

[0019] The tempered glass according to the present invention preferably has an etched surface over the entire surface.

[0020] In another aspect, the tempered glass of the present invention is a plate- or sheet-shaped tempered glass having a compressive stress layer on a surface and a tensile stress layer on the inner side of the compressive stress layer in the thickness direction of the glass, the tempered glass having at least a bendable thin portion having a thickness t1, the thickness t1 being 105 μm or less, the depth DOC of the compressive stress layer being 9.0 μm or less, and satisfying CS / DOC≧110, where CS is the maximum compressive stress in the compressive stress layer. [Effects of the Invention]

[0021] According to the present invention, it is possible to obtain tempered glass that is extremely thin, has high strength, and is highly safe, compared to conventional techniques. [Brief explanation of the drawings]

[0022] [Figure 1] 1 is a schematic plan view of a tempered glass according to a first embodiment of the present invention, viewed in the thickness direction. [Figure 2] 1 is a schematic cross-sectional view of a tempered glass according to a first embodiment of the present invention. [Figure 3] FIG. 2 is an image diagram of stress distribution in the thickness direction of the tempered glass according to the first embodiment of the present invention. [Figure 4] FIG. 3 is a schematic cross-sectional view of a tempered glass according to a second embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0023] (First embodiment) Hereinafter, the tempered glass according to the first embodiment of the present invention will be described.

[0024] <Tempered glass> Fig. 1 is a schematic plan view of tempered glass 1 according to a first embodiment of the present invention, viewed in the thickness direction. Fig. 2 is a schematic cross-sectional view taken along line AA in Fig. 1. As shown in Figs. 1 and 2, tempered glass 1 is a plate-like or sheet-like chemically tempered glass.

[0025] In this embodiment, as shown in Fig. 1, tempered glass 1 has a rectangular (rectangular) shape having long and short sides in a plan view. The length of the long side of tempered glass 1 is, for example, 50 mm to 500 mm, preferably 60 mm to 450 mm, more preferably 65 mm to 400 mm, even more preferably 70 mm to 300 mm, 75 mm to 200 mm, or 80 mm to 160 mm. The length of the short side is, for example, 40 mm to 400 mm, preferably 45 mm to 350 mm, more preferably 50 mm to 300 mm, or even more preferably 55 mm to 120 mm, or 60 mm to 80 mm.

[0026] The tempered glass 1 has at least a bendable thin portion 11. In the present invention, bendable means having flexibility such that the minimum bending radius is 10 mm or less when bent without breakage.

[0027] The tempered glass 1 includes a thick portion 12 that is relatively thicker than the thin portion 11.

[0028] The thin portion 11 is provided to separate and interconnect the two thick portions 12. In other words, the thin portion 11 extends in a strip shape from one end to the other end of the tempered glass 1. More specifically, the thin portion 11 is provided parallel to the short sides so as to cross the main surface of the tempered glass 1 from the center of one long side to the center of the other long side.

[0029] The two thick portions 12 preferably have shapes that are line-symmetrical to each other with respect to the thin portion 11. With such a configuration, the tempered glass 1 can be folded so that the two thick portions 12b overlap, which is suitable for use in foldable devices and the like.

[0030] The thickness t1 of the thin-walled portion 11 is 105 μm or less, preferably 10 μm to 95 μm, preferably 20 μm to 85 μm, and more preferably 30 μm to 75 μm. To meet demands for even thinner walls, the thickness t1 can be set to 65 μm or less, or even 55 μm or less. On the other hand, the preferred lower limit of the thickness t1 is preferably 40 μm or more, or even 50 μm or more. If the glass is too thin, it becomes difficult to ensure sufficient strength. Furthermore, if the glass is too thin, it becomes difficult to increase the compressive stress value on the surface, which may actually impair flexibility. It is preferable that the thickness of the thin-walled portion 11 is constant; however, if the thickness is not constant, the thickness of the thinnest portion of the thin-walled portion 11 can be determined as t1.

[0031] The width W of the thin portion 11 is, for example, 3 mm or more and 50 mm or less, and preferably 5 mm or more and 30 mm or less. It is preferable that the width of the thin portion 11 is constant. By setting the width W within this range, a sufficient range of motion required for bending can be ensured.

[0032] The thickness t2 of the thick portion 12 is, for example, 110 μm or more, preferably more than 120 μm and not more than 300 μm, more preferably 150 μm or more and not more than 270 μm, and even more preferably 170 μm or more and not more than 250 μm. The thickness t2 of the thick portion 12 is preferably constant. By setting the thickness t2 of the thick portion 12 within this range, the deformability of the thick portion 12 can be appropriately suppressed, and the handleability during device assembly and manufacturing can be improved.

[0033] In this embodiment, the thin portion 11 forms a groove on one main surface of the tempered glass 1, and is composed of the remaining portion on the other main surface. The tempered glass 1 can be bent, for example, in a direction in which the groove side faces outward (the direction of arrow R in FIG. 2). By making it bendable in this direction, the flat surface without the groove can be used as the touch surface of the foldable device, and the touch surface can be protected when the foldable device is folded.

[0034] The tempered glass 1 has a compressive stress layer on the surface and a tensile stress layer on the inner side of the compressive stress layer (toward the center in the thickness direction). An example of the stress distribution in the tempered glass 1 is shown in FIG. 3. In FIG. 3, the vertical axis indicates the stress value, and the horizontal axis indicates the depth from the surface. On the vertical axis in FIG. 3, positive values ​​indicate compressive stress, and negative values ​​indicate tensile stress. In this specification, unless otherwise specified, the magnitude of each stress is indicated as an absolute value.

[0035] The stress distribution shown in FIG. 3 illustrates the case where the tempered glass 1 is glass that has been subjected to a single-stage ion exchange treatment. In the stress distribution of the tempered glass 1, the compressive stress is maximum at the surface (maximum compressive stress CS), and the stress gradually decreases with increasing depth from the surface, reaching zero at a depth DOC. In other words, DOC is synonymous with the depth of the compressive stress. A tensile stress layer having tensile stress extends in a region deeper than the depth DOC. It is preferable that the compressive stress distribution of the tempered glass 1 be symmetrical on the front and back as shown in FIG. 3.

[0036] The tensile stress layer includes a first region A1 in which the tensile stress varies in the thickness direction of the glass, and a second region A2 in which the tensile stress is constant in the thickness direction. More specifically, the first region A1 extends from the depth DOC of the compressive stress layer to the tensile stress convergence depth DCT, and is a region in which the absolute value of the tensile stress gradually increases (negative numbers in FIG. 3 indicate gradual decreases) as the depth increases. The second region A2 extends to a region deeper than the tensile stress convergence depth DCT, and is a region in which the tensile stress is constant in the thickness direction. In the present invention, "constant tensile stress" refers to a change in stress in the depth direction of 0.5 MPa / μm or less, and this change can be calculated, for example, by differential values ​​of stress sampled at 0.1 μm depth intervals.

[0037] The depth DOC of the compressive stress layer of the tempered glass 1 is 9.0 μm or less, preferably 1 μm or more and 8.5 μm or less, more preferably 2 μm or more and 8.0 μm or less, more preferably 2.5 μm or more and 7.5 μm or less, or 2.5 μm or more and 5.5 μm or less. After extensive research into the surface compressive stress value and the depth threshold of the compressive stress layer that do not result in dangerous fracture mode upon fracture, the inventors found that for thin glass of 105 μm or less as in the present invention, it is effective to set the depth of the compressive stress layer to 9.0 μm or less. This ensures sufficient strength against bending while also ensuring safety.

[0038] The maximum compressive stress CS in the compressive stress layer of the tempered glass 1 is, for example, 520 MPa or more and 2000 MPa or less, preferably 600 MPa or more and 1800 MPa or less, more preferably 650 MPa or more and 1800 MPa or less, 650 MPa or more and 1700 MPa or less, or 700 MPa or more and 1700 MPa or less. By setting CS in such a range, high bending strength can be obtained. Note that, when further improving bending strength, the maximum compressive stress CS can be more preferably 670 MPa or more and 1600 MPa or less, even more preferably 760 MPa or more and 1600 MPa or less, 820 MPa or more and 1550 MPa or less, or 700 MPa or more and 1550 MPa or less. On the other hand, when emphasis is placed on suppressing crushing upon breakage and prioritizing suppression of the maximum tensile stress CT, the upper limit of the maximum compressive stress CS can be limited to 1000 MPa or less, 900 MPa or less, 800 MPa or less, 750 MPa or less, or 740 MPa or less.

[0039] In the first region A1, the tensile stress changes linearly, and the slope of the change, CS / DOC (MPa / μm), obtained by dividing the maximum compressive stress value CS on the surface by the compressive stress layer depth DOC, satisfies the following formula (1): CS / DOC≧95 (1) The inventors conducted extensive research into the threshold values ​​of the surface compressive stress and the depth of the compressive stress layer that ensure sufficient bending strength while preventing dangerous fractures upon breakage. As a result, they found that it is effective to set the value obtained by dividing the surface compressive stress by the compressive stress layer depth to 95.0 MPa / μm or more. The lower limit of CS / DOC is 95 MPa / μm or more, preferably 97 MPa / μm or more, 100 MPa / μm or more, 105 MPa / μm or more, 110 MPa / μm or more, 120 MPa / μm or more, 130 MPa / μm or more, 140 MPa / μm or more, or 145 MPa / μm or more, while the upper limit is, for example, 300 MPa / μm or less, preferably 250 MPa / μm or less, or 200 MPa / μm or less. By setting the value within these numerical ranges, it is possible to obtain a surface compressive stress value that has sufficient strength against bending in thin glass of 105 μm or less, while controlling the depth of the compressive stress layer to ensure safety.

[0040] The depth DOC of the compressive stress layer and the thickness t1 of the thin-walled portion 11 satisfy the following formula (2). DOC / t1≦0.09 (2) By limiting the ratio of DOC to t1 within the above range, sufficient bending strength can be maintained while also ensuring safety. The upper limit of DOC / t1 is preferably 0.085 or less, more preferably 0.08 or less, and the lower limit is preferably 0.03 or more, more preferably 0.04 or more.

[0041] The tensile stress convergence depth DCT can be calculated by the following formula (3): DCT=(CS+CT) / (CS / DOC) (3)

[0042] The tensile stress convergence depth DCT and the thickness t1 of the thin-walled portion 11 satisfy the following formula (4). DCT / t1≦0.10 (4) By limiting the ratio of DCT to t1 within the above range, sufficient strength against bending can be maintained while also ensuring safety. The upper limit of DCT / t1 is preferably 0.10 or less, more preferably 0.09 or less, or 0.08 or less, and the lower limit is preferably 0.03 or more, more preferably 0.04 or more.

[0043] The upper limit of the tensile stress convergence depth DCT is, for example, 10.0 μm or less, preferably 9.5 μm or less, more preferably 9.0 μm or less or 8.5 μm or less, and the lower limit is, for example, 2.5 μm or more, preferably 3.0 μm or more, 3.5 μm or more, 4.0 μm or more.

[0044] The upper limit of the maximum tensile stress CT of the second region A2 in the thin-walled portion 11 is, for example, 1000 MPa or less, preferably 500 MPa or less, more preferably 400 MPa or less, and even more preferably 285 MPa or less, 250 MPa or less, 240 MPa or less, 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, 70 MPa or less, and the lower limit is preferably 20 MPa or more, 50 MPa or more, 55 MPa or more, more preferably 60 MPa or more. By limiting CT as described above, strength against bending can be ensured while ensuring safety by preventing dangerous fractures in the event of fracture.

[0045] In addition, the numerical values ​​related to stresses such as CS, DOC, DCT, and CT in the present invention can be derived by measuring the stress distribution of glass using a measuring device such as FSM-6000 or SLP-1000 manufactured by Orihara Seisakusho.

[0046] The Young's modulus of the tempered glass 1 is preferably 60 GPa or more, more preferably 65 GPa or more, 70 GPa or more, or 75 GPa or more to 90 GPa or less.

[0047] It is preferable that the entire surface of the tempered glass 1, i.e., both the front and back main surfaces and the end surfaces including the thin-walled portions 11, are etched. By etching the entire surface, defects are reduced over the entire surface, and the tempered glass 1 has high strength.

[0048] As a method for forming tempered glass 1 into a sheet, the overflow downdraw method is preferred from the standpoints of cost and production volume. However, the thinner the sheet, the more rapidly the glass is cooled, resulting in a lower CS and a deeper DOC. It is also known that when ion-exchanging thin glass, there is less internal glass to suppress the volume expansion of the ion-exchanged portion, making it more difficult to obtain a high CS compared to thicker glass. For thin glass such as the tempered glass of the present invention, achieving both a high CS and a shallow DOC at high levels is not simply a design issue and is not easy. In other words, the glass composition, glass forming method, and tempering conditions must be appropriately selected. Therefore, for tempered glass 1, alkali aluminosilicate glass suitable for chemical strengthening is suitable, and among alkali aluminosilicate glasses, a composition that can achieve a particularly high surface compressive stress value is suitable. Furthermore, a compositional balance that achieves a high liquidus viscosity to enable forming by the overflow downdraw method is preferable. The tempered glass 1 contains, for example, in mole percent, 50 to 80% SiO2, 5 to 25% Al2O3, 30 to 35% B2O, 0 to 20% Li2O, 1 to 20% Na2O, 1 to 20% Li2O + Na2O, and 0 to 10% K2O as a glass composition.

[0049] 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 preferred lower limit range of SiO2 is, in mole percent, 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, meltability and formability tend to decrease, and the thermal expansion coefficient becomes too low, making it difficult to match the thermal expansion coefficient of surrounding materials. Therefore, the preferred 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.

[0050] Al2O3 is a component that enhances ion exchange performance and also increases strain point, Young's modulus, fracture toughness, and Vickers hardness. Therefore, the preferred lower limit range of Al2O3 is, in mole percent, 5% or more, 8% or more, 10% or more, 11% or more, or 11.2% or more. On the other hand, if the Al2O3 content is too high, the high-temperature viscosity increases, and meltability and formability tend to decrease. In addition, devitrification crystals tend to precipitate in the glass, making it difficult to form into a plate shape by the overflow downdraw method or the like. In particular, when an alumina-based refractory is used as the formed body refractory and a glass plate is formed by the overflow downdraw method, spinel devitrification crystals tend to precipitate at the interface with the alumina-based refractory. Furthermore, acid resistance also decreases, making it difficult to apply to an acid treatment process. Therefore, the preferred 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. If the Al2O3 content, which has a large effect on ion exchange performance, is kept within the preferred range, it becomes easier to design a high CS / DOC value even in thin glass of 105 μm or less.

[0051] B2O3 is a component that reduces high-temperature viscosity and density, stabilizes glass, and reduces crystal precipitation, lowering the liquidus temperature. It also suppresses Young's modulus and increases flexural strength and crack resistance. However, excessive B2O3 content can lead to surface discoloration (known as fading) during ion exchange treatment, reduced water resistance, and a decrease in the compressive stress value of the compressive stress layer. Therefore, the preferred lower limit of B2O3, in mole percent, is 0% or more, 0.01% or more, 0.02% or more, 0.1% or more, or 0.3% or more, while the preferred upper limit is 35% or less, 30% or less, 25% or less, 22% or less, 20% or less, and particularly 15% or less. From the perspective of prioritizing high CS, the B2O3 content can be more preferably 0.2 to 5%, or 0.3 to 1%. From the viewpoint of improving chemical durability for the purpose of suppressing defects during etching, the upper limit of the B2O3 content can be preferably 1% or more, 1.5% or more, or 2% or more, and the lower limit can be 5% or less, 4.5% or less, 4% or less, or 3% or less. On the other hand, from the viewpoint of prioritizing suppression of Young's modulus, the B2O3 content can be more preferably 10 to 25%, 15 to 23%, or 18 to 22%.

[0052] Li2O is an ion-exchange component, specifically, Li ions contained in the glass and K ions in the molten salt are ion-exchanged to obtain a high surface compressive stress. Li2O also reduces high-temperature viscosity and improves meltability and formability. Therefore, the preferred lower limit of Li2O, in mole percent, is 3% or more, 4% or more, 4.2% 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 preferred upper limit of Li2O is 20% or less, 15% or less, 13% or less, 12% or less, 11.5% or less, 11% or less, 10.5% or less, or less than 10%, and particularly 9.9% or less, 9% or less, or 8.9% or less.

[0053] Na2O is an ion-exchange component and also a component that reduces high-temperature viscosity and improves meltability and formability. Na2O also improves devitrification resistance and reaction devitrification resistance with refractory molded bodies, particularly alumina refractories. If the Na2O content is too low, meltability decreases, the thermal expansion coefficient decreases too much, and the ion exchange rate tends to decrease. Therefore, the preferred lower limit range of Na2O, in mole percent, is 5% or more, 7% or more, 8% or more, 8.5% or more, 9% or more, 9.5% or more, 10% or more, 11% or more, 12% or more, and particularly 12.5% ​​or more. On the other hand, if the Na2O content is too high, the phase separation viscosity tends to decrease. Furthermore, acid resistance may decrease, and the glass composition may become unbalanced, resulting in a decrease in devitrification resistance. Therefore, the preferred upper limit range of Na2O is 20% or less, 19.5% or less, 19% or less, 18% or less, 17% or less, 16.5% or less, 16% or less, 15.5% or less, particularly 15% or less.

[0054] K2O is a component that reduces high-temperature viscosity and improves meltability and formability. It also improves devitrification resistance and increases Vickers hardness. However, if the K2O content is too high, the phase separation viscosity tends to decrease. Furthermore, acid resistance tends to decrease and the glass composition tends to be unbalanced, resulting in decreased devitrification resistance. Therefore, the preferred lower limit of K2O, in mole percent, 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, 3% or more, and particularly 3.5% or more. The preferred upper limit is 10% or less, 5.5% or less, 5% or less, and particularly less than 4.5%.

[0055] Both Li2O and Na2O undergo ion exchange with K ions in the molten salt to obtain a high surface compressive stress value, and either one is essential for the present invention. Therefore, the preferred lower limit range of Li2O + Na2O is 1% or more, 3% or more, 4% or more, 5% or more, 6% or more, 7% or more, 8% or more, 9% or more, 10% or more, 11% or more, 12% or more, 13% or more, 14% or more, 15% or more, 16% or more, 17% or more, 18% or more, and particularly 18.5% or more, in mole percent. On the other hand, if the content of Li2O + Na2O is too high, the thermal expansion coefficient becomes too high, which tends to reduce thermal shock resistance. Furthermore, the component balance of the glass composition may be disrupted, which may actually reduce devitrification resistance. Therefore, the preferred upper limit range of Li2O + Na2O is 20% or less, and particularly 19% or less.

[0056] In addition to the above components, the tempered glass 1 may contain, for example, the following components as part of its glass composition.

[0057] MgO is a component that reduces high-temperature viscosity, improves meltability and formability, and increases the strain point and Young's modulus. Among alkaline earth metal oxides, it is a component that is particularly effective in improving ion exchange performance. However, if the MgO content is too high, the density and thermal expansion coefficient tend to increase, and the glass is prone to devitrification. Therefore, the preferred upper range of MgO is 12% or less, 10% or less, 8% or less, 6% or less, and particularly 5% or less. When MgO is incorporated into the glass composition, the preferred lower limit of MgO is 0.1% or more, 0.5% or more, 1% or more, and particularly 2% or more, in mole percent.

[0058] Compared with other components, CaO has a significant effect of reducing high-temperature viscosity, improving meltability and formability, and increasing strain point and Young's modulus without reducing devitrification resistance. The CaO content is preferably 0 to 10%. However, if the CaO content is too high, the density and thermal expansion coefficient increase, and the component balance of the glass composition is lost, making the glass more susceptible to devitrification and reducing ion exchange performance. Therefore, the preferred CaO content is 0 to 5%, 0.01 to 4%, 0.1 to 3%, and particularly 1 to 2.5% by mole.

[0059] SrO is a component that reduces high-temperature viscosity, improves meltability and formability, and increases the strain point and Young's modulus without reducing devitrification resistance. However, if the SrO content is too high, the density and thermal expansion coefficient increase, the ion exchange performance decreases, and the component balance of the glass composition is lost, making the glass more susceptible to devitrification. The preferred SrO content range, in mole percent, is 0 to 5%, 0 to 3%, 0 to 1%, and particularly 0 to less than 0.1%.

[0060] BaO is a component that reduces high-temperature viscosity, improves meltability and formability, and increases strain point and Young's modulus without reducing devitrification resistance. However, if the BaO content is too high, the density and thermal expansion coefficient increase, the ion exchange performance decreases, and the component balance of the glass composition is lost, making the glass more susceptible to devitrification. The preferred BaO content range, in mole percent, is 0 to 5%, 0 to 3%, 0 to 1%, and particularly 0 to less than 0.1%.

[0061] ZnO is a component that enhances ion exchange performance, and is particularly effective in increasing compressive stress. It also reduces high-temperature viscosity without reducing low-temperature viscosity. However, if the ZnO content is too high, the glass tends to undergo phase separation, reduce devitrification resistance, increase density, and reduce the stress depth of the compressive stress layer. Therefore, the ZnO content is preferably 0 to 6%, 0 to 5%, 0 to 1%, or 0 to 0.5%, particularly preferably 0 to less than 0.1%, in mole percent.

[0062] ZrO2 is a component that significantly enhances ion exchange performance, as well as increasing viscosity near the liquidus viscosity and strain point. However, if its content is too high, there is a risk that devitrification resistance will be significantly reduced and the density will be too high. Therefore, the preferred upper range of ZrO2 is 10% or less, 8% or less, 6% or less, and particularly 5% or less, in mole percent. Furthermore, if it is desired to enhance ion exchange performance, it is preferable to incorporate ZrO2 into the glass composition. In this case, the preferred lower limit of ZrO2 is 0.001% or more, 0.01% or more, 0.5%, and particularly 1% or more.

[0063] P2O5 is a component that enhances ion exchange performance, particularly increasing the stress depth of the compressive stress layer. It also suppresses the Young's modulus. However, if the P2O5 content is too high, the glass is prone to phase separation. Therefore, the preferred upper limit of P2O5 content is 10% or less, 8% or less, 6% or less, 4% or less, 2% or less, or 1% or less, particularly less than 0.1%, by mole.

[0064] As a fining agent, one or more selected from the group consisting of As2O3, Sb2O3, SnO2, F, Cl, and SO3 (preferably the group consisting of SnO2, Cl, and SO3) may be incorporated in an amount of 0 to 30,000 ppm (3%). From the viewpoint of adequately obtaining the fining effect, the content of SnO2 + SO3 + Cl is preferably 0 to 10,000 ppm, 50 to 5,000 ppm, 80 to 4,000 ppm, 100 to 3,000 ppm, and particularly 300 to 3,000 ppm. Here, "SnO2 + SO3 + Cl" refers to the combined amount of SnO2, SO3, and Cl.

[0065] The preferred range of SnO2 content is 0 to 10,000 ppm, 0 to 7,000 ppm, and particularly 50 to 6,000 ppm, the preferred range of Cl content is 0 to 1,500 ppm, 0 to 1,200 ppm, 0 to 800 ppm, or 0 to 500 ppm, and particularly 50 to 300 ppm, and the preferred range of SO3 content is 0 to 1,000 ppm, 0 to 800 ppm, and particularly 10 to 500 ppm.

[0066] Rare earth oxides such as Nd2O3 and La2O3 are components that increase Young's modulus and can control the color of glass by decolorizing when a complementary color is added. However, the raw materials themselves are expensive, and adding large amounts can easily reduce devitrification resistance. Therefore, the content of rare earth oxides is preferably 4% or less, 3% or less, 2% or less, 1% or less, and particularly 0.5% or less.

[0067] In the present invention, from an environmental perspective, it is preferable that the glass be substantially free of As2O3, F, PbO, and Bi2O3. Here, "substantially free of As2O3" means that As2O3 is not actively added as a glass component, but is allowed to be present at the impurity level; specifically, the As2O3 content is less than 500 ppm. "Substantially free of F" means that F is not actively added as a glass component, but is allowed to be present at the impurity level; specifically, the F content is less than 500 ppm. "Substantially free of PbO" means that PbO is not actively added as a glass component, but is allowed to be present at the impurity level; specifically, the PbO content is less than 500 ppm. "Substantially free of Bi2O3" means that Bi2O3 is not actively added as a glass component, but is allowed to be present at the impurity level; specifically, the Bi2O3 content is less than 500 ppm.

[0068] For example, the tempered glass 1 may not contain B2O3 in its glass composition or may contain only a small amount of B2O3, limiting its content. That is, the tempered glass 1 may contain, in mole percent, 50-80% SiO2, 5-25% Al2O3, 0-1% B2O3, 0-20% Li2O, 1-20% Na2O, and 0-10% K2O.

[0069] As another example, the tempered glass 1 may have a glass composition containing B2O3 as an essential component, i.e., the tempered glass 1 may have a glass composition containing, in mole percent, 50-80% SiO2, 5-25% Al2O3, 1-5% B2O3, 0-20% Li2O, 1-20% Na2O, and 0-10% K2O.

[0070] Since there is a concern that the formability of the glass may be reduced if the tempered glass 1 contains B2O3 as an essential component in its glass composition, the content of other components such as Al2O3 may be limited to strike a balance. That is, the tempered glass 1 may have a glass composition containing, in mole percent, 50-80% SiO2, 5-10% Al2O3, 1-5% B2O3, 0-20% Li2O, 1-20% Na2O, and 0-10% K2O.

[0071] <Method of manufacturing tempered glass> The tempered glass 1 is obtained by subjecting glass for chemical tempering to an ion exchange treatment.

[0072] First, a glass for chemical strengthening is prepared. The glass for chemical strengthening is glass having the same shape and dimensions and glass composition as the above-mentioned strengthened glass 1.

[0073] Glass for chemical strengthening is obtained by cutting and processing plate- or sheet-shaped mother glass obtained by a forming method such as the overflow downdraw method, slot downdraw method, float method, or redraw method into small glass pieces. To obtain a smooth surface, the overflow downdraw method is preferably used as the forming method. The cut glass pieces are then processed to form grooves in order to form the thin-walled portions 11. The grooves are formed by processing such as etching or grinding.

[0074] The end faces of the chemically strengthened glass are preferably subjected to treatments such as polishing, heat treatment, and etching to chamfer or improve strength. The main surfaces of the chemically strengthened glass may be polished, but for example, if the main surfaces have been formed smoothly in advance by the overflow downdraw method or if the thickness has been formed uniformly and accurately, the main surfaces may not be polished, i.e., the non-polished surfaces may be used. Note that if the glass is formed by the overflow downdraw method and not polished, the main surfaces of the chemically strengthened glass will be fire-polished surfaces. The chemically strengthened glass may also be subjected to a slimming treatment to reduce the thickness by etching. Note that, in the present invention, the main surfaces refer to the front and back surfaces of the entire surface of the plate-shaped or sheet-shaped glass, excluding the end faces.

[0075] The glass for chemical strengthening obtained as described above is subjected to an ion exchange treatment. Specifically, the glass for chemical strengthening is treated by immersing it in a molten salt for ion exchange treatment.

[0076] The molten salt is a salt containing a component that is ion-exchangeable with the components in the chemically strengthened glass, and is typically an alkali nitrate. Examples of alkali nitrates include NaNO3, KNO3, and LiNO3, which can be used alone (at 100% by mass) or in combination. When multiple alkali nitrates are mixed, the mixing ratio can be determined arbitrarily, but can be, for example, 5 to 95% NaNO3 and 5 to 95% KNO3, preferably 30 to 80% NaNO3 and 20 to 70% KNO3, and more preferably 50 to 70% NaNO3 and 30 to 50% KNO3, by mass.

[0077] The conditions for the ion exchange treatment, such as the temperature of the molten salt and the immersion time, may be set according to the composition and the like within a range that allows the above-mentioned stress characteristics to be obtained, and the temperature of the molten salt is, for example, 350°C to 500°C, preferably 355°C to 470°C, 360°C to 450°C, 365°C to 430°C, or 370°C to 410°C. The immersion time is, for example, 3 to 300 minutes, preferably 5 to 120 minutes, and more preferably 7 to 100 minutes.

[0078] The tempered glass 1 is obtained through the above-described ion exchange treatment. After the above-described ion exchange treatment, the tempered glass 1 is preferably washed and dried. Furthermore, it is preferably protected by attaching a protective film. It is preferable to use a self-adhesive protective film or a protective film with a weak adhesive so that a high level of surface cleanliness can be achieved without leaving any adhesive residue after the protective film is peeled off.

[0079] The tempered glass 1 may be further polished after the ion exchange treatment. If the dimensions, shape, or surface condition of the tempered glass 1 change due to the ion exchange treatment, these can be corrected by polishing. On the other hand, polishing may increase unwanted microcracks, so if the tempered glass 1 is an unpolished product formed by an overflow downdraw method or the like as described above, and the main surfaces of the tempered glass 1 after the ion exchange treatment are also smooth, unpolished surfaces (fire-polished surfaces), it is preferable not to polish it. If the tempered glass 1 is formed by the overflow downdraw method, it has a forming confluence surface inside.

[0080] Furthermore, the tempered glass 1 may be subjected to an etching treatment after the ion exchange treatment. Specifically, the entire tempered glass 1 is immersed in a liquid etching medium, and the entire surface of the tempered glass 1 is wet-etched. This treatment allows the entire glass to be uniformly etched, thereby suppressing variations in thickness caused by the etching treatment. When this etching treatment is performed, the surface of the tempered glass 1 is composed of an etched surface.

[0081] The etching medium can be an acidic or alkaline aqueous solution capable of etching glass.

[0082] An example of an acidic etching medium that can be used is an acidic aqueous solution containing HF. When an aqueous solution containing HF is used, the etching rate for glass is high, and tempered glass 1 can be produced with high productivity.

[0083] The HF-containing aqueous solution may be, for example, an aqueous solution containing only HF, or a combination of HF and HCl, HF and HNO3, HF and H2SO4, or HF and NHF. The concentration of each of the HF, HCl, HNO3, H2SO4, and NHF compounds is preferably 0.1 to 30 mol / L. When etching using an HF-containing aqueous solution, fluorides containing glass components are generated as by-products, which can lead to a decrease in etching rate and defects. However, as described above, by using a mixed acid with other acids such as HCl, HNO3, or H2SO4, the by-products can be decomposed, thereby preventing a decrease in productivity. When etching is performed using an acidic aqueous solution, the temperature of the acidic aqueous solution is preferably, for example, 10 to 30°C, and the tempered glass 1 is preferably immersed for, for example, 0.1 to 60 minutes.

[0084] The alkaline etching medium can be an alkaline aqueous solution containing NaOH or KOH. The alkaline aqueous solution has a relatively low etching rate for glass compared to the HF-containing etching medium, making it easier to precisely control the amount of etching. This is particularly suitable for cases where the glass thickness and DOC must be controlled in units of several micrometers, as in the present invention.

[0085] In the aqueous solution containing NaOH or KOH, the concentration of the alkaline component is preferably 1 to 20 mol / L. When etching is performed using an alkaline aqueous solution, the temperature of the alkaline aqueous solution is, for example, 10 to 130°C, and the time for immersing the tempered glass 1 is preferably, for example, 0.5 to 120 minutes. When increasing the etching rate to improve productivity, it is preferable to heat the alkaline aqueous solution to 80°C or higher. Conversely, when it is desired to control the etching amount with higher precision, it is preferable to limit the temperature of the alkaline aqueous solution to 70°C or lower. When a high etching rate is more important, it is preferable to use an aqueous NaOH solution.

[0086] Etching is preferably performed using the above-described etching medium so that the etching amount (thickness reduction due to etching) on ​​one surface of the tempered glass 1 is 0.25 μm to 3 μm. The etching amount of the tempered glass 1 is preferably 0.4 μm to 2.7 μm, more preferably 0.6 μm to 2.5 μm, and even more preferably 0.8 μm to 2.3 μm. Setting the etching amount within this range reduces the amount of variation in the maximum compressive stress and compressive stress depth before and after etching, making them easier to control.

[0087] The above-described tempered glass 1 can simultaneously achieve high bending performance, bending strength, and suppression of shattering upon breakage by suitably controlling its stress characteristics and thickness and further reducing surface defects through etching.

[0088] In the first embodiment, the thin portion 11 is formed by a groove portion formed on one main surface of the tempered glass 1 and remaining on the other main surface. The thin portion 11 may be formed by forming grooves on both main surfaces so as to leave a central portion of the cross section of the tempered glass 1. This configuration makes it difficult for the tempered glass 1 to break when bent either toward the front or back side.

[0089] (Second embodiment) In the first embodiment, the tempered glass 1 includes the thin portion 11 and the thick portion 12. However, the tempered glass of the present invention may be entirely made up of thin portions. In the second embodiment described below, the same configurations and processes as those in the first embodiment can be applied to configurations and processes that are not specifically described, and detailed description thereof will be omitted.

[0090] Fig. 4 is a schematic cross-sectional view of tempered glass 2 according to a second embodiment of the present invention. The shape and dimensions in a plan view of tempered glass 2 are similar to those of tempered glass 1 according to the first embodiment (Fig. 1). Fig. 4 is a view showing a cross section along a long side of tempered glass 2.

[0091] As shown in FIG. 4 , tempered glass 2 according to the second embodiment is entirely composed of thin-walled portions 21 and has a substantially uniform thickness. In the present invention, "substantially uniform thickness" means that the deviation in glass thickness is within ±10%. The thickness of tempered glass 2 is the same as the thickness t1 of thin-walled portions 11 of tempered glass 1 according to the first embodiment. The stress characteristics and composition of tempered glass 2 can be configured similarly to those of tempered glass 1 according to the first embodiment.

[0092] The tempered glass 2 is obtained by subjecting glass for chemical tempering having the same dimensions and shape to the same ion exchange treatment as in the first embodiment.

[0093] The tempered glass 2 according to the second embodiment has the thin-walled portion 21 on the entire surface, allowing it to be bent at any desired location, improving the degree of freedom in device design. Furthermore, there is no need to form grooves, and tempered glass that combines high bendability and strength can be obtained with high productivity.

[0094] (Variation) In each of the above embodiments, the shape of the tempered glass is rectangular in a plan view, but the shape is not limited thereto. The shape of the tempered glass of the present invention may be, for example, a square, a circle, an ellipse, or the like.

[0095] The tempered glass of the present invention may be subjected to three-dimensional bending as necessary. Specifically, by subjecting the glass for chemical strengthening to three-dimensional bending in advance, in whole or in part, the tempered glass after the ion exchange treatment and the etching treatment can be given a three-dimensional bent shape.

[0096] In the above embodiments, the tempered glass has been subjected to a single ion exchange treatment, but the tempered glass may be subjected to two, three, or more ion exchange treatments. Heat treatment may be performed before or after the ion exchange. The heat treatment can reduce stress and promote ion diffusion, thereby controlling the depth of the compressive stress layer, etc.

[0097] The tempered glass according to each of the above embodiments can be laminated with any plate- or sheet-shaped resin material, or a transparent material such as a metal material or glass via an adhesive or the like to form a laminate. [Example]

[0098] The tempered glass according to the present invention will be described below based on examples. Note that the following examples are merely illustrative and the present invention is not limited to the following examples in any way.

[0099] The samples were prepared as follows: First, ion-exchange glasses having the glass compositions shown in Table 1 were prepared.

[0100] Specifically, glass raw materials were prepared to have the compositions shown in Table 1, and melted in a test melting furnace to obtain molten glass. The obtained molten glass was then formed by flowing down from a refractory molding using the overflow downdraw method, and cut and processed to obtain glass to be tempered with the thicknesses shown in Tables 2 to 4. The Young's modulus shown in Table 1 is a value measured by a resonance method for glass to be tempered with each composition.

[0101] In Tables 2 to 4, the glasses for which the thickness t2 of the thick portion is indicated are glasses having thick and thin portions, as in the first embodiment described above. For glasses having thick and thin portions, a plate-shaped sample with a uniform thickness in the thick portion was first prepared, and then the thin portion was formed by etching so that the band width W was 20 mm. Note that, in Tables 2 to 4, the glasses for which the thickness t2 of the thick portion is not indicated are glasses whose entire glass is made up of thin portions and has a uniform thickness t1, as in the second embodiment described above. Note that the planar dimensions of each sample were 50 × 50 mm.

[0102] Next, the glass to be tempered was immersed in a molten salt of 100% KNO3 at 390°C for the time shown in Tables 2 to 4, to obtain tempered glass.

[0103] In Tables 2 to 4, Nos. 1 to 20 and 23 to 31 are examples of the present invention, and Nos. 21 and 22 are comparative examples.

[0104] [Table 1]

[0105] [Table 2]

[0106] [Table 3] [Table 4]

[0107] The maximum compressive stress CS, compressive stress depth DOC, and tensile stress CT in Tables 2 to 4 are values ​​measured in the thin-walled portion of each sample using a surface stress meter FSM-6000LE manufactured by Orihara Manufacturing Co., Ltd. More specifically, DOC is the DOL_zero value measured using the FSM-6000LE, and CT is the CT_CV value measured using the FSM-6000LE.

[0108] A pen drop test was also conducted on each sample. Specifically, the glass sample was placed on a stone surface plate, and the tip of a ballpoint pen (BIC, Orange EG0.7) with a ball diameter of 0.7 mm and a mass of 5.4 g was dropped vertically onto the center of the glass sample. The height of the pen tip before the drop was defined as the drop height, and the initial value was set to 1 cm. If the glass sample did not break after the drop, the drop height was increased by 1 cm and the test was repeated. This process of increasing the drop height and dropping the sample was repeated until the glass sample broke. The drop height at which the glass sample broke was determined as the pen drop breakage height. The glass sample was replaced with a new one after each pen drop. The number of broken glass fragments was counted. Note that because it is difficult to count small fragments, the count was limited to samples with a maximum outer diameter of 0.1 mm or more. For glass samples with thick and thin sections, the flat surface was placed downward (with the grooved portion facing upward), and the pen tip was dropped onto the thin section.

[0109] In addition, a bending fracture test was performed on the glass sample to determine the fracture bending radius. Specifically, the glass sample was placed between two SUS plates, one above the other, in a Shimadzu Autograph AG-X precision universal testing machine, with the two shorter sides of the glass sample in contact with each other. A load was applied to the glass sample so that the center of the longer side was bent and deformed. While measuring the bending radius, the load was gradually increased until the glass sample broke. The bending radius just before the glass sample broke was determined as the fracture bending radius. The dimensions of the glass sample used in the bending fracture test were 130 × 20 mm.

[0110] According to the results of the pen drop test, it was confirmed that the glass samples according to the examples had fewer fragments and less shattering than the comparative examples. [Industrial Applicability]

[0111] The tempered glass of the present invention can be used, for example, for smartphones, mobile phones, tablet computers, personal computers, digital cameras, touch panel displays, cover glass for other display devices, in-vehicle display devices, in-vehicle panels, etc. [Explanation of symbols]

[0112] 1, 2 Tempered glass 11, 21 Thin section 12 Thick wall part

Claims

1. A plate- or sheet-shaped tempered glass having a compressive stress layer on a surface thereof and a tensile stress layer disposed on the inner side of the compressive stress layer in a thickness direction of the glass, At least a portion of the flexible thin-walled portion has a thickness t1, A plurality of thick portions each having a thickness t2 greater than the thickness t1 are provided, The thickness t1 is 105 μm or less, The depth DOC of the compressive stress layer is 9.0 μm or less, When the maximum compressive stress in the compressive stress layer is CS, CS / DOC≧95 Meet the tempered glass.

2. The thickness t1 is 20 μm or more and 95 μm or less, The maximum compressive stress CS in the compressive stress layer is 550 MPa or more and 1600 MPa or less, The tempered glass according to claim 1 , wherein the compressive stress layer has a depth DOC of 1.0 μm or more and 8.5 μm or less.

3. The maximum compressive stress CS in the compressive stress layer and the depth DOC of the compressive stress layer are CS / DOC≧110 The tempered glass according to claim 1 or 2, which satisfies the above.

4. The tempered glass according to claim 1 , wherein the maximum tensile stress CT of the tensile stress layer in the thin portion is 95 MPa or less.

5. The ratio of the depth DOC to the thickness t1 of the compressive stress layer satisfies the following: DOC / t1≦0.09 The tempered glass according to claim 1 .

6. The tensile stress layer is a first region extending from a depth DOC of the compressive stress layer to a tensile stress convergence depth DCT, in which the tensile stress varies in the thickness direction of the glass; a second region extending to a region deeper than the tensile stress convergence depth DCT, in which the tensile stress is constant in the thickness direction; The tensile stress convergence depth DCT is 10.0 μm or less, DCT / t1≦0.10 The tempered glass according to claim 1 , which satisfies the above.

7. The thickness t2 of the thick portion is 110 μm or more and 300 μm or less, The tempered glass according to claim 1 , wherein the thin portion extends in a strip shape so as to connect the plurality of thick portions.

8. The tempered glass according to claim 7 , wherein the thin-walled portion has a width of 3 mm or more.

9. The tempered glass according to claim 1 , wherein the entire glass is constituted by the thin-walled portion and has a substantially uniform thickness.

10. The glass composition is, in mol%, SiO ２ 50-80%, Al ２ O ３ 5-25%, B ２ O ３ 0-15%, Li ２ O 0-20%, Na ２ O 1-20%, K ２ The tempered glass according to any one of claims 1 to 9, containing 0 to 10% of O.

11. The glass composition is, in mol%, SiO ２ 50-80%, Al ２ O ３ 5-25%, B ２ O ３ 0-1% Li ２ O 0-20%, Na ２ O 1-20%, K ２ The tempered glass according to claim 10, containing 0 to 10% O.

12. The glass composition is, in mol%, SiO ２ 50-80%, Al ２ O ３ 5-25%, B ２ O ３ 1-5% Li ２ O 0-20%, Na ２ O 1-20%, K ２ The tempered glass according to claim 10, containing 0 to 10% O.

13. The glass composition is, in mol%, SiO ２ 50-80%, Al ２ O ３ 5-10%, B ２ O ３ 1-5% Li ２ O 0-20%, Na ２ O 1-20%, K ２ The tempered glass according to claim 12, containing 0 to 10% O.

14. 14. The tempered glass according to claim 1, wherein the entire surface is an etched surface.

15. A plate- or sheet-shaped tempered glass having a compressive stress layer on a surface thereof and a tensile stress layer disposed on the inner side of the compressive stress layer in a thickness direction of the glass, At least a portion of the flexible thin-walled portion has a thickness t1, A plurality of thick portions each having a thickness t2 greater than the thickness t1 are provided, The thickness t1 is 105 μm or less, The depth DOC of the compressive stress layer is 9.0 μm or less, CS / DOC≧110 Meet the tempered glass.

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