Tempered glass, tempered glass, and display devices

Abstract

A tempered glass that can be bent along a predetermined band-shaped bendable portion and has a thickness t of 20-70 μm, wherein the uneven thickness Δt2, which is the difference between the maximum thickness and the minimum thickness in the bendable portion, is 8 μm or less.

Description

[Technical Field]

[0001] The present invention relates to tempered glass, tempering glass, and display devices. [Background technology]

[0002] In recent years, devices such as smartphones and tablet PCs with foldable display surfaces have been developed, and the use of chemically strengthened glass as the cover glass is being considered (for example, Patent Document 1). [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2012-78570 [Overview of the project] [Problems that the invention aims to solve]

[0004] Cover glass used in the above applications suffers from a problem in that it is prone to breakage at the bent portion due to the extremely high internal tensile stress acting on the bent area during bending. To suppress such breakage, technologies have been developed to adjust stress characteristics such as the magnitude of the compressive stress value and the depth of the compressive stress layer. However, even with adjustments to the stress characteristics, localized increases in tensile stress still occur at the bent portion, and breakage of the glass cannot always be completely suppressed. In other words, there was still room for improvement in tempered glass used in the above applications.

[0005] The present invention aims to provide tempered glass with high bending strength. [Means for solving the problem]

[0006] The tempered glass according to the first invention of the present invention is a tempered glass that can be bent along a predetermined strip-shaped bendable portion, characterized in that its thickness t is 20 to 70 μm, and the thickness variation Δt2, which is the difference between the maximum and minimum thickness in the bendable portion, is 8 μm or less.

[0007] By controlling the thickness variation in the bent portion in this way, it is possible to prevent areas with locally thin thickness, i.e., areas where tensile stress is locally high, from being located in the bent portion. This prevents damage caused by localized excessive tensile stress and improves bending strength.

[0008] In the tempered glass according to the second invention of the present invention, it is preferable that the thickness variation Δt2 in the bendable portion is 0.1 to 2.0 μm in the first invention.

[0009] In the tempered glass according to the third invention of the present invention, it is preferable that the thickness variation Δt1, which is the difference between the maximum and minimum thickness of the entire tempered glass, is 15 μm or less, in the first or second invention.

[0010] In the tempered glass according to the fourth invention of the present invention, it is preferable that the thickness variation Δt1 in the entire tempered glass is 0.2 to 1.5 μm, as in the third invention.

[0011] In the tempered glass according to the fifth invention of the present invention, it is preferable that the thickness variation Δt2 in the bendable portion is smaller than the thickness variation Δt1 in the entire tempered glass, in any of the first to fourth inventions.

[0012] In the sixth invention of the present invention, the tempered glass preferably has a Δt2 / Δt1 ≤ 0.9.

[0013] In the tempered glass according to the seventh invention of the present invention, it is preferable that the extending direction of the bendable portion is set parallel to the drawing direction during glass molding, in any of the first to sixth inventions.

[0014] The tempered glass according to the eighth invention of the present invention preferably does not break when bent at a curvature radius of 1.0 mm in the bendable portion in any of the first to seventh inventions.

[0015] The tempered glass according to the ninth invention of the present invention has a compressive stress layer on the surface in any of the first to eighth inventions, the maximum compressive stress CS in the compressive stress layer is 450 to 850 (MPa), the depth DOL of the compressive stress layer is 2 to 23 μm, and a tensile stress layer is provided at a position deeper than the compressive stress layer, and it is preferable that the maximum tensile value CT in the tensile stress layer is 120 to 1500 (MPa).

[0016] The tempered glass according to the tenth invention of the present invention preferably contains, in mass %, 45 to 80% of SiO2, 5 to 30% of Al2O3, 0 to 15% of B2O3, 1 to 25% of Na2O, and 0 to 10% of K2O as the glass composition in any of the first to ninth inventions.

[0017] The display device according to the present invention is a foldable display device including any of the above tempered glasses.

[0018] The glass for strengthening according to the present invention is an unstrengthened glass for strengthening that can be bent along a preset strip-shaped bendable portion, the thickness t is 20 to 70 μm, and the thickness unevenness Δt2, which is the difference between the maximum value and the minimum value of the thickness in the bendable portion, is 8 μm or less.

Effects of the Invention

[0019] According to the present invention, a tempered glass having a higher bending strength than the prior art and a display device including the same can be obtained.

Brief Description of the Drawings

[0020] [Figure 1] It is a perspective schematic view of the tempered glass and the glass for strengthening according to an embodiment of the present invention. [Figure 2]This is a schematic perspective view showing tempered glass and tempering glass in a bent state according to an embodiment of the present invention. [Figure 3] This figure shows an example of a method for forming tempered glass according to an embodiment of the present invention. [Modes for carrying out the invention]

[0021] The tempered glass 1a and tempering glass 1b according to embodiments of the present invention will be described below.

[0022] Tempered glass 1a is obtained by ion exchange treatment (strengthening treatment) of tempering glass 1b. In other words, tempering glass 1b is unstrengthened glass. Figures 1 and 2 are schematic diagrams of tempered glass 1a and tempering glass 1b. Since the shape and dimensions of the glass do not change significantly before and after ion exchange treatment, in Figures 1 and 2, the schematic shapes of both tempered glass 1a and tempering glass 1b are shown on the same drawing by indicating the corresponding reference numerals in parentheses.

[0023] As shown in Figure 1, tempered glass 1a and tempering glass 1b are plate-shaped or sheet-shaped glass. In this embodiment, as shown in Figures 1 and 2, we illustrate the case where tempering glass 1b and tempered glass 1a are rectangular in shape with long sides and short sides in a plan view. The length of the long side of tempering glass 1b can be arbitrarily set depending on the application, but for example, it is 50 mm or more and 500 mm or less, preferably 60 mm or more and 450 mm or less, more preferably 65 mm or more and 400 mm or less, even more preferably 70 mm or more and 300 mm or less, 75 mm or more and 200 mm or less, or 80 mm or more and 160 mm or less. The length of the short side is, for example, 40 mm or more and 400 mm or less, preferably 45 mm or more and 350 mm or less, more preferably 50 mm or more and 300 mm or less, even more preferably 55 mm or more and 120 mm or less, or 60 mm or more and 80 mm or less. If the side dimensions are too large, it becomes difficult to control the glass shape in the molding and processing processes, and uneven thickness is likely to occur. On the other hand, if the side dimensions are too small, it becomes unsuitable for applications such as foldable devices.

[0024] The tempered glass 1a and the tempering glass 1b are provided with a bendable portion 2a(2b). The bendable portion 2a(2b) is pre-set in any region of the tempered glass 1a according to the design of the device on which the tempered glass 1a is mounted, as shown in the hatching in Figure 1. The bendable portion 2a(2b) extends in a strip shape from one end to the other of the tempered glass 1a and the tempering glass 1b. In other words, the bendable portion 2a(2b) is provided to divide and connect two regions (first region S1 and second region S2) of the tempered glass 1a and the tempering glass 1b. The bendable portion 2a(2b) is provided, for example, parallel to the short side from the center of one long side to the center of the other long side. Alternatively, the bendable portion 2a(2b) may be provided parallel to the long side from the center of one short side to the center of the other short side. The tempered glass 1a and the tempering glass 1b are configured, for example, to have a shape that is symmetrical with respect to the bendable portion 2a (2b) as a reference (line of symmetry).

[0025] In this invention, "bendable" means having flexibility such that it can be bent without damage, with a bending radius of 10 mm or less.

[0026] The foldable portion 2a(2b) is set in the shape of a strip with width W centered on the planned bending line J when mounted on the device. The width W of the foldable portion 2a(2b) may be arbitrarily set according to the minimum bending radius R when mounted on the device, for example, πR. Specifically, the width W of the foldable portion 2a(2b) is 0.5 mm or more and 20 mm or less, preferably 1 mm or more and 10 mm or less, or 2 mm or more and 5 mm or less. It is preferable that the width of the foldable portion 2a(2b) is constant.

[0027] Preferably, the tempered glass 1a does not break when bent at a radius of curvature of 3.0 mm in the bendable portion 2a, more preferably at 2.0 mm, and even more preferably at 1.0 mm.

[0028] The thickness t of the tempered glass 1a and tempering glass 1b can be arbitrarily set in the range of 20 to 70 μm, preferably 25 μm to 60 μm, preferably 27 μm to 53 μm, and more preferably 30 μm to 50 μm. If the plate thickness t is too large, the tensile stress acting on the bendable portion 2a when bent at a small radius of curvature becomes extremely large, making it prone to breakage. On the other hand, if the plate thickness t is too small, the impact resistance tends to decrease.

[0029] While it is preferable that the thickness of tempered glass 1a and tempering glass 1b be constant, the actual thickness distribution varies due to production factors, etc. Therefore, the above thickness t is strictly speaking a production target value or control value. The degree of variation in glass thickness can be evaluated by the thickness variation, which is the difference between the maximum and minimum thickness of the measurement target area.

[0030] The thickness variation Δt1 in the entire tempered glass 1a and the entire tempering glass 1b is determined by measuring the thickness distribution of the entire glass and taking the difference between the maximum and minimum values ​​of the obtained thickness measurements. The thickness variation Δt1 in the entire tempered glass 1a and the entire tempering glass 1b is preferably 15 μm or less, more preferably 10 μm or less, and even more preferably 5.5 μm or less, 4.5 μm or less, 3.5 μm or less, 2.5 μm or less, 1.5 μm or less, and 1.0 μm or less. From the viewpoint of productivity, the lower limit of the thickness variation Δt1 is preferably 0.2 μm or more, and more preferably 0.25 μm or more. By controlling the thickness variation Δt1 in the entire glass in this way, it becomes easier to reduce the thickness variation Δt2 in the bendable portion 2a (2b).

[0031] The thickness variation Δt2 in the bendable portion 2a(2b) is determined by measuring the thickness distribution with only the bendable portion 2a(2b) as the measurement target, and taking the difference between the maximum and minimum values ​​of the obtained thickness measurements. The thickness variation Δt2 in the bendable portion 2a(2b) is 8 μm or less, preferably 4 μm or less, and more preferably 3 μm or less, 2 μm or less, 1.5 μm or less, 1.0 μm or less, 0.8 μm or less, and 0.5 μm or less. From the viewpoint of productivity, the lower limit of the thickness variation Δt2 is preferably 0.1 μm or more, more preferably 0.15 μm or more and 0.2 μm or more. By controlling the thickness variation Δt2 in the bendable portion 2a(2b) in this way, damage when bending can be suppressed.

[0032] The thickness variation Δt2 in the bendable portion 2a(2b) is preferably smaller than the thickness variation Δt1 in the entire tempered glass. The value of Δt2 / Δt1 is, for example, 0.9 or less, more preferably 0.8 or less, and even more preferably 0.7 or less. By suppressing the thickness variation Δt2 in the bendable portion 2a(2b) of the tempered glass 1a and tempering glass 1b to improve strength, while allowing large thickness variations in the portions other than the bendable portion 2a(2b), the productivity of the tempered glass 1a and tempering glass 1b can be improved.

[0033] The tempered glass 1a comprises a compressive stress layer having compressive stress and a tensile stress layer having tensile stress. The compressive stress layer is formed on the surface of the tempered glass 1a, and the tensile stress layer is formed deeper than the compressive stress layer, i.e., inside the tempered glass 1a. Note that the tempered glass 1b before ion exchange treatment (untempered) does not have a compressive stress layer or a tensile stress layer.

[0034] The maximum compressive stress CS in the compressive stress layer is preferably 1200 MPa or less, more preferably 850 MPa or less, and even more preferably 800 MPa or less, 750 MPa or less, and 700 MPa or less. Limiting CS prevents the tensile stress in the tensile stress layer from becoming excessive, thereby suppressing the scattering of glass fragments in the event of breakage. On the other hand, if CS is too low, the impact resistance of the tempered glass 1a decreases, so the lower limit of CS is preferably 450 MPa or more, more preferably 500 MPa or more, and even more preferably 530 MPa or more and 600 MPa or more. Note that if the thickness t of the tempered glass 1a is relatively thick, even if CS is increased, the increase in the maximum tensile stress CT of the tensile stress layer is suppressed, so CS may be set to 650 MPa or more and 680 MPa or more.

[0035] The depth DOL of the compressive stress layer is preferably 23 μm or less, more preferably 20 μm or less, and even more preferably 18 μm or less, 15 μm or less, or 13 μm or less. Limiting DOL suppresses excessive maximum tensile stress CT and reduces the scattering of glass fragments in the event of breakage. On the other hand, if DOL is too small, the impact resistance of the tempered glass 1a decreases, so the lower limit of DOL is preferably 2 μm or more, more preferably 3 μm or more, 4 μm or more, or 5 μm or more. Note that if the thickness t of the tempered glass 1a is relatively thick, the increase in maximum tensile stress CT is suppressed even if the maximum compressive stress CS is increased, so DOL may be 8 μm or more, more preferably 10 μm or more.

[0036] The maximum tensile stress CT of the tensile stress layer is preferably 1500 MPa or less, more preferably 500 MPa or less, and even more preferably 400 MPa or less, 300 MPa or less, and 200 MPa or less. By suppressing CT, the scattering of glass fragments in the event of breakage can be suppressed. On the other hand, a minimum CS and DOL are necessary to ensure the impact resistance of the tempered glass 1a, and accordingly, the lower limit of CT is preferably 50 MPa or more, more preferably 80 MPa or more, and even more preferably 120 MPa or more, 125 MPa or more, 130 MPa or more, 140 MPa or more, 150 MPa or more, and 160 MPa or more.

[0037] Furthermore, the numerical values ​​related to stress, such as the maximum compressive stress CS, the depth of the compressive stress layer DOL, and the maximum tensile stress CT in this invention, can be measured using a measuring device such as the FSM-6000 manufactured by Orihara Corporation. In addition, the maximum tensile stress CT can also be calculated from t, Δt1, CS, and DOL based on the following formula (1). CT=(CS×DOL) / (t-Δt1 / 2-2×DOL) …(1)

[0038] The tempered glass 1a and tempering glass 1b are, for example, alkali aluminosilicate glass, and preferably have the following glass composition. Note that for tempered glass 1a, this refers to the glass composition in the area where ion exchange has not occurred.

[0039] Tempered glass 1a and tempering glass 1b contain, for example, SiO2 45-80%, Al2O 35-30%, B2O 30-15%, Na2O 1-25%, and K2O 0-10% by mass. In this composition, Li2O may be substantially absent. In this invention, substantially absent means that its content is less than 0.1% by mass.

[0040] The composition of tempered glass 1a and tempering glass 1b, more specifically in mass%, contains SiO2 50%~70%, Al2O3 15%~28%, B2O 30%~10%, Na2O 5%~20%, K2O 0%~3%, Li2O 0%~4%, MgO 0%~5.5%, CaO 0%~6%, P2O 50%~15%, and SnO 20.1%~0.5%.

[0041] SiO2 is a component that forms the network of glass. The preferred lower limit range for SiO2 is 45% or more by mass, 50% or more, 55% or more, 58% or more, 59% or more, 60% or more, and especially 61% or more. If the SiO2 content is too low, it becomes difficult to vitrify, and the coefficient of thermal expansion becomes too high, which tends to reduce thermal shock resistance. On the other hand, if the SiO2 content is too high, meltability, formability, and bendability tend to decrease. Therefore, the preferred upper limit range for SiO2 is 80% or less, 75% or less, 73% or less, 70% or less, 68% or less, and especially 67% or less.

[0042] Al2O3 is a component that enhances ion exchange performance and also increases strain point and Young's modulus. If the Al2O3 content is too low, the ion exchange performance may not be fully realized. Therefore, the suitable lower limit range for Al2O3 is 5% or more, 7% or more, 8% or more, 10% or more, and 12% or more. On the other hand, if the Al2O3 content is too high, meltability, formability, and bendability tend to decrease. Furthermore, devitrified crystals tend to precipitate in the glass, making it difficult to form glass plates, especially by overflow downdrawing methods. Therefore, the suitable upper limit range for Al2O3 is 30% or less, 25% or less, 22% or less, 20% or less, 19% or less, and 18% or less.

[0043] B2O3 is a component that lowers the softening point, as well as the liquidus temperature, high-temperature viscosity, and density. The preferred lower limit range for B2O3 is 0% or more, 0.1% or more, and especially 0.2% or more by mass. If the B2O3 content is too high, the ion exchange performance and water resistance tend to decrease. Therefore, the preferred upper limit range for B2O3 is 15% or less, 10% or less, and especially 5% or less.

[0044] Na2O is an ion exchange component and also a component that reduces high-temperature viscosity, thereby improving melting and moldability. Furthermore, Na2O is a component that improves devitrification resistance and devitrification in reaction with molded refractories, especially alumina refractories. If the Na2O content is too low, melting will decrease, the coefficient of thermal expansion will decrease too much, and the ion exchange rate will tend to decrease. Therefore, the suitable lower limit range for Na2O is 1% or more by mass, 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 especially 12.5% ​​or more. On the other hand, if the Na2O content is too high, the phase separation viscosity tends to decrease. It may also decrease acid resistance, disrupt the balance of components in the glass composition, and conversely, decrease devitrification resistance. Therefore, the preferred upper limits for Na2O are 25% or less, 22% or less, 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, and especially 15% or less.

[0045] K2O is a component that reduces high-temperature viscosity, thereby improving meltability and moldability. Furthermore, it is a component that improves devitrification resistance and increases Vickers hardness. However, if the K2O content is too high, the phase separation viscosity tends to decrease. It can also reduce acid resistance and disrupt the balance of components in the glass composition, which can actually decrease devitrification resistance. Therefore, it is acceptable to substantially omit K2O from the glass composition, but the preferred lower limit range for K2O is 0% or more, 0.01% or more, 0.02% or more, 0.1% or more, and especially 0.5% or more by mass%, and the preferred upper limit range is 10% or less, 5.5% or less, 5% or less, and especially less than 4.5%.

[0046] Li2O is an ion exchange component and also a component that reduces high-temperature viscosity, thereby improving meltability and moldability. Furthermore, it is a component that increases Young's modulus. In addition, Li2O is a component that dissolves during ion exchange treatment, degrading the ion exchange solution. Therefore, as described above, Li2O may be substantially omitted from the glass composition, but if it is included, the preferred lower limit range of Li2O is 0.05% or more, 0.1% or more, 0.5% or more, 1.0% or more, 1.5% or more, 2.0% or more, and especially 2.5% or more by mass%, and the preferred upper limit range is 10% or less, 8% or less, 5% or less, 4.5% or less, 4.0% or less, and especially less than 3.5%.

[0047] MgO is a component that lowers high-temperature viscosity, improves meltability and moldability, and increases strain point and Young's modulus. Among alkaline earth metal oxides, it is a component that has a significant effect on improving ion exchange performance. However, if the MgO content is too high, the density and coefficient of thermal expansion tend to increase, and the glass becomes more prone to devitrification. Therefore, the suitable upper limit range for MgO is 12% or less, 10% or less, 8% or less, 5.5% or less, 5% or less, and especially 4% or less. When MgO is introduced into the glass composition, the suitable lower limit range for MgO is 0.1% or more, 0.5% or more, 1% or more, and especially 2% or more.

[0048] Compared to other components, CaO reduces high-temperature viscosity without compromising devitrification resistance, thereby improving meltability and moldability, and increasing strain point and Vickers hardness. However, if the CaO content is too high, it may reduce ion exchange performance or degrade the ion exchange solution during ion exchange treatment. Therefore, the preferred upper limit range for CaO is 6% or less, 5% or less, 4% or less, 3.5% or less, 3% or less, 2% or less, 1% or less, less than 1%, 0.5% or less, and especially less than 0.1%. When CaO is introduced into the glass composition, the preferred lower limit range for CaO is 0.1% or more, 0.3% or more, 0.5% or more, and especially 0.7% or more.

[0049] P2O5 is a component that enhances ion exchange performance, and in particular, increases stress depth. Furthermore, it is a component that improves acid resistance. On the other hand, if the P2O5 content is too high, the glass is prone to phase separation and water resistance is likely to decrease. Therefore, the suitable upper limits for P2O5 are 15% or less, 13% or less, 12% or less, 10.5% or less, 10% or less, 9.5% or less, and 9% or less. It is also possible to have a glass composition that is substantially free of P2O5, but when P2O5 is introduced into the glass composition, the suitable lower limits for P2O5 are 0.1% or more, 0.7% or more, 1% or more, 3% or more, 4% or more, 4.5% or more, 5% or more, 5.5% or more, 6% or more, and especially 7% or more.

[0050] SnO2 acts as a fining agent and is an ingredient that reduces bubble defects in glass. The preferred content range for SnO2 is 0-1.0%, 0-0.7%, and especially 0.05-0.6% and 0.1-0.5%.

[0051] As an example of a different glass composition, tempered glass 1a and tempering glass 1b may contain, in mass%, SiO2 50%~70%, Al2O3 15%~20%, B2O3 0%~1%, Na2O 5%~25%, K2O 0%~3%, Li2O 0%~1%, MgO 0%~5.5%, and SnO2 0.1%~0.5%.

[0052] As an example of a different glass composition, tempered glass 1a and tempering glass 1b may contain, in mass%, SiO2 40%~70%, Al2O3 10%~30%, B2O 30%~3%, Na2O 5%~25%, K2O 0%~5.5%, Li2O 0.1%~10%, MgO 0%~5.5%, and P2O 52%~10%.

[0053] As an example of another glass composition, the tempered glass 1a and the tempering glass 1b may contain, as the glass composition, in mass %, SiO2 40% to 70%, Al2O3 10% to 20%, B2O3 1.5% to 5%, Na2O 5% to 25%, K2O 0% to 3%, Li2O 0% to 1%, MgO 0% to 5.5%, and SnO2 0.1% to 0.5%. According to such a glass composition, in the tempered glass 1a and the tempering glass 1b, high chemical durability can be obtained, erosion of the glass in a cleaning process or the like can be suppressed, an increase in uneven thickness can be suppressed, and clouding defects on the glass surface can be suppressed.

[0054] The tempered glass 1a and the tempering glass 1b are made into samples with dimensions of 50 mm × 10 mm × 7 mm, immersed in 100 ml of a 5 mass% HCl aqueous solution at 80°C for 30 minutes, and when shaken, the weight loss of the glass is 30 mg / cm 2 ,

[0056] , 2 , 2 , , 2 , 2 , , 2 It is preferably as follows. The weight loss is more preferably 20 mg / cm 2 or less, 11 mg / cm 2 or less, 8 mg / cm 2 or less, 2 mg / cm 2 or less, 0.8 mg / cm 2 or less, 0.5 mg / cm 2 or less, 0.1 mg / cm 2 or less, particularly 0.05 mg / cm 2 or less.

[0055] The tempered glass 1a and the tempering glass 1b are made into samples with dimensions of 50 mm × 10 mm × 7 mm, immersed in 100 ml of a 5 mass% NaOH aqueous solution at 80°C for 30 minutes, and when shaken, the weight loss of the glass is 5.0 mg / cm 2 It is preferably as follows. The weight loss is more preferably 3.0 mg / cm 2 or less, 2.0 mg / cm 2 or less, 1.0 mg / cm​​​​​​​​​​​Tempered glass 1a is obtained by molding and processing tempering glass 1b into the shape described above, and then subjecting it to ion exchange treatment.

[0057] The tempered glass 1b is obtained by cutting and processing a plate-shaped or sheet-shaped mother glass, obtained by a molding method such as the overflow downdraw method, slot downdraw method, float method, or redraw method, into small pieces. To obtain a smooth surface, it is preferable to use the overflow downdraw method as the molding method.

[0058] For example, when forming the mother glass of tempered glass 1b using the overflow downdraw method as shown in Figure 3, the glass flowing down from the molded body 10 is pulled using tension rollers 11 and cooling rollers 12, and the mother glass can be obtained by cutting the cooled glass ribbon G. In this case, it is preferable to set the pulling speed of the glass ribbon G in the tension rollers 11 to 1 to 200 m / min, the pulling speed of the glass ribbon G in the cooling rollers 12 to 1 to 200 m / min, the temperature distribution of the heating device 13, which is arranged in the width direction (X direction in Figure 3) perpendicular to the glass ribbon drawing direction (Y direction in Figure 3), to ±0 to ±50°C, the temperature of the glass ribbon to 800 to 1500°C, the glass flow rate to 10 to 5000 kg / h, the glass flow rate fluctuation to ±0 to 60 kg / h, and the glass ribbon drawing speed to 1 to 200 m / min. With such forming conditions, the thickness variation Δt2 can be suitably reduced.

[0059] In tempered glass 1a and tempering glass 1b, it is preferable that the bendable portion 2a(2b) is formed such that its extension direction coincides with the drawing direction during molding. The drawing direction during glass molding is the flow direction of the glass ribbon G, and for example, in the overflow down-draw molding method shown in Figure 3, it is the direction of arrow Y. The extension direction of the bendable portion 2a(2b) is the direction of arrow D in Figure 1. In the molding of plate glass, variations in thickness tend to occur in the width direction (arrow X direction) perpendicular to the drawing direction (arrow Y direction), and are less likely to occur in the drawing direction (arrow Y direction). Therefore, by controlling the extension direction of the bendable portion 2a(2b) as described above, it is possible to easily reduce the thickness variation Δt2 in the bendable portion 2a(2b). The drawing direction in tempered glass 1a and tempering glass 1b can be observed, for example, by irradiating light from a light source (e.g., a xenon light) while adjusting the angle of tempered glass 1a or tempering glass 1b in a darkroom, and projecting the transmitted light onto a screen, thereby observing it as a striped pattern. Therefore, the drawing direction during molding can be determined even in the state of the glass after molding.

[0060] In tempered glass 1a and tempering glass 1b, to ensure that the extension direction of the bendable portion 2a (2b) matches the drawing direction during molding, tempering glass 1b is obtained as follows. First, a mother glass is taken from a glass ribbon G in a manner that allows for the determination of the drawing direction. For example, if the mother glass has a long side and a short side, the mother glass is cut from the glass ribbon G so that the drawing direction matches the extension direction of either the long side or the short side. The mother glass may be marked with notches, markings, or adhesive tags to indicate the drawing direction. Next, if the extension direction of the bendable portion 2b is, for example, along the long side (or short side) of the tempering glass 1b, the tempering glass 1b is cut from the mother glass so that the drawing direction indicated on the mother glass matches the direction of the long side (or short side). By this method, tempering glass 1b is obtained in which the extension direction of the bendable portion 2b matches the drawing direction during molding. Furthermore, by subjecting the obtained reinforced glass 1b to ion exchange treatment, it is possible to obtain reinforced glass 1a in which the extending direction of the bendable portion 2a coincides with the drawing direction during molding.

[0061] Furthermore, even when using other molding methods such as the slot-down draw method or the float method, the same principle applies as described above. The flow direction of the molded glass ribbon is set as the drawing direction, and the reinforced glass 1b can be obtained so that it coincides with the extending direction of the bendable portion 2b.

[0062] In the manufacturing process of the tempered glass 1b, the process may include measuring the thickness distribution of the bendable portion 2b for each of the multiple tempered glass 1b obtained by cutting the mother glass, and selecting only those in which the thickness variation Δt2 in the bendable portion 2b is below a predetermined threshold as good products. By such a process, it is possible to reliably obtain tempered glass 1a with a small thickness variation Δt2 and high bending strength.

[0063] The end faces of the tempered glass 1b are preferably treated to chamfer or improve strength by polishing, heat treatment, etching, etc. The main surface of the tempered glass 1b may be polished, but if the main surface is pre-formed to be smooth by the overflow down-draw method, for example, or if the thickness is uniform and formed with good precision, the main surface may not be polished and may remain an unpolished surface. If it is formed by the overflow down-draw method and is not polished, the main surface of the tempered glass 1b will be a forged surface. Furthermore, the tempered glass 1b may be subjected to a slimming treatment to reduce its thickness by etching. In this case, the main surface of the tempered glass 1b will be an etched surface. In this invention, the main surface refers to the front and back surfaces of a plate-like or sheet-like glass surface, excluding the end faces.

[0064] The tempered glass 1b obtained as described above is subjected to ion exchange treatment. Specifically, the tempered glass 1b is treated by immersing it in a molten salt for ion exchange treatment.

[0065] The molten salt is a salt containing components that can be ion-exchanged with the components of the strengthening glass 1b, and is typically an alkaline nitrate. Examples of alkaline nitrates include NaNO3, KNO3, and LiNO3, which can be used individually or in combination. The composition of the molten salt can be determined arbitrarily, but when ion-exchanging glass with the glass composition described above, KNO3 is essential, and for example, the composition can be 30-50% NaNO3 and 50-100% KNO3 by mass, preferably 0.1-30% NaNO3 and 70-99.9% KNO3.

[0066] 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 glass composition, molten salt composition, etc., within the range in which the above stress characteristics can be obtained. For example, the temperature of the molten salt is 350°C to 500°C, preferably 360°C to 470°C, 360°C to 450°C, 360°C to 430°C, or 360°C to 410°C. The immersion time is, for example, 3 to 300 minutes, preferably 5 to 120 minutes, more preferably 7 to 100 minutes.

[0067] As described above, tempered glass 1a can be obtained by ion exchange treatment of tempered glass 1b. Note that the above ion exchange treatment method is just one example; for example, molten salt may be applied to the surface of tempered glass 1b by spraying or the like and then the ion exchange treatment may be performed.

[0068] The obtained tempered glass 1a is preferably washed and dried, and then etched. Specifically, the entire tempered glass 1a is immersed in a liquid etching medium such as hydrofluoric acid or buffered hydrofluoric acid, and the entire surface of the tempered glass 1a is etched, making the entire surface an etched surface. This treatment removes minute scratches and other defects from the surface of the tempered glass 1a, thereby improving its strength. Furthermore, since the entire glass can be etched uniformly by immersion etching, an increase in thickness variation caused by the etching process can be suppressed. The etching temperature is preferably, for example, 10 to 30°C, and the immersion time of the tempered glass 1b is preferably, for example, 0.1 to 60 minutes. The above etching treatment may be performed only on the end face of the tempered glass 1a, with the end face being the etched surface and the main surface being the unetched surface.

[0069] After the etching process described above, the tempered glass 1a is cleaned and dried, and then protected by applying a protective film. To ensure high surface cleanliness without any adhesive residue after the protective film is removed, it is preferable to use a self-adhesive protective film or a protective film equipped with a mildly adhesive.

[0070] (modified version) In the above embodiment, the tempered glass 1a and tempering glass 1b are exemplified as having a rectangular shape with a long side and a short side, but the shapes of the tempered glass 1a and tempering glass 1b are not limited to this and can be any shape. For example, the tempered glass 1a and tempering glass 1b may be in the shape of a square plate or sheet, or they may be disc-shaped (including ellipses and perfect circles).

[0071] In the above embodiment, the example shown was that tempered glass 1a and tempering glass 1b are amorphous glass, but the tempered glass of the present invention may be a crystalline glass containing crystalline material that has been chemically strengthened.

[0072] In the above embodiment, the case where the tempered glass 1a and tempering glass 1b are flat plates was described as an example. However, the tempered glass of the present invention may be given a curved shape as a three-dimensional shape as needed, and an uneven shape may be given to some or all of the area other than the bendable portion. Furthermore, through holes, notches, etc., may be formed in the tempering glass 1b.

[0073] The entire tempered glass 1a and tempering glass 1b, or a portion of 70% or more by volume, may be set as the bendable portion 2a (2b). By setting the bendable portion 2a (2b) in this way, it becomes possible to continuously move the actual bending position, making it suitable for displays where the bending position changes, such as slide displays and rollable displays.

[0074] The tempered glass 1a can be laminated with any plate-shaped or sheet-shaped resin material or metal material via an adhesive, adhesive sheet, etc., and used as a laminate. In such a laminated state, the tempered glass 1a can be mounted on a device, for example, as cover glass for the display surface and touch panel surface of a foldable device. In addition to the tempered glass 1a, the foldable device includes, for example, a processing unit such as a CPU, a battery, an interface device, and a housing that accommodates these. [Examples]

[0075] The tempered glass and tempering glass according to the present invention will be described below based on examples. Note that the following examples are illustrative, and the present invention is not limited to these examples.

[0076] Samples were prepared as follows. First, glass raw materials were weighed and mixed to produce glass batches with glass compositions (i) to (vii) as shown in Table 1. Next, these glass batches were melted in a refractory furnace to obtain molten glass.

[0077] [Table 1]

[0078] Next, the obtained molten glass was formed into a plate using the overflow downdraw method to obtain tempered glass. Subsequently, the tempered glass was immersed in molten salt and subjected to ion exchange treatment to obtain tempered glass. The results of the property measurement and strength test of the obtained tempered glass are shown in Table 2. In Tables 2-4, Nos. 1-17 are examples of the present invention, and Nos. 18 and 19 are comparative examples.

[0079] The molding conditions for each sample were adjusted as follows: Samples No. 1-3, 5-11, and 13-17 were molded under conditions where the temperature distribution width in the width direction perpendicular to the glass ribbon drawing direction was small, and the glass flow rate fluctuation range was small. Specifically, the glass was molded by controlling the temperature distribution to be in the range of ±0-10°C and the glass flow rate to be in the range of ±0-10 kg / h. On the other hand, samples No. 4, 12, 18, and 19 were molded under conditions where the temperature distribution width was large and the glass flow rate fluctuation range was large. Specifically, the glass was molded by controlling the temperature distribution to be in the range of ±10-50°C and the glass flow rate to be in the range of ±10-60 kg / h.

[0080] The thickness t of each glass was adjusted during molding to match the thicknesses listed in Tables 2 and 3, and then cut into rectangular plates with a long side (160 mm) and a short side (100 mm) to prepare tempered glass samples.

[0081] The foldable portion was set as a strip with a width W of 3 mm, centered on the short side. The relationship between the extension direction of the foldable portion and the drawing direction during glass molding is shown in Tables 2 and 3.

[0082] The ion exchange treatment was performed by immersing the tempered glass sample in a molten salt containing 99.85% KNO3 and 0.15% NaNO3 by mass at the temperatures and times specified in Tables 2 and 3.

[0083] [Table 2]

[0084] [Table 3]

[0085] The properties of each tempered glass sample obtained as described above were measured and tested according to the following procedure.

[0086] The overall thickness variation Δt1 of the glass and the thickness variation Δt2 of the bendable portion were measured as follows: Using an automatic thickness measuring machine manufactured by Toshiba Engineering, the thickness was measured at 5 mm intervals in both the longitudinal and transverse directions along the main surface of a rectangular glass sample. The difference between the maximum and minimum values ​​among all measured values ​​was calculated and this was defined as the overall thickness variation Δt1 of the glass. In addition, only the data where the measurement position is located in the bendable portion was extracted, and the difference between the maximum and minimum values ​​among the extracted data was defined as the thickness variation Δt2 of the bendable portion.

[0087] The maximum compressive stress CS and compressive stress depth DOL were measured using a surface stress meter FSM-6000LE manufactured by Orihara Corporation. The maximum tensile stress CT was calculated based on the above equation (1).

[0088] The bending test was performed using a bending test machine. Specifically, the first region S1 and the second region S2, which are demarcated by the bendable portion of the tempered glass sample, were attached to the support plates of the bending test machine, which rotate independently, via adhesive. By rotating the support plates, the glass was bent and deformed in the bendable portion until the radius of curvature R of the glass reached a set value. When the glass broke during bending and deformation, it was evaluated as ×, and when it did not break, it was evaluated as ○. The radius of curvature R was set to 1.5 mm, 1.4 mm, and 1.0 mm, and each radius of curvature was tested individually.

[0089] The chemical durability, i.e., acid and alkali resistance, of the glass compositions (i) and (ii) shown in Table 1 was evaluated using the following method. First, glass samples with dimensions of 50 mm × 10 mm × 7 mm were prepared for each composition and their pre-test weight was measured. For the acid resistance test, the glass samples, after pre-test weight measurement, were placed in a container containing 100 ml of 5 wt% HCl as the test solution, shaken in a constant temperature shaker maintained at 80°C, and removed after 30 minutes to measure the post-test weight. For the alkali resistance test, the glass samples were treated in the same manner as for the acid resistance test, except that 5 wt% NaOH was used as the test solution, and the post-test weight was measured. Next, the weight loss (mg / cm²) was calculated from the weight change before and after each test and the surface area of ​​the glass. 2 ) was sought.

[0090] According to the results of the bending test described above, the tempered glass according to the example had a smaller thickness variation Δt2 in the bendable portion compared to the glass of the comparative example, and was confirmed to have high bending strength in the bending test.

[0091] Furthermore, it was confirmed that tempered glass in which the drawing direction during molding and the extension direction of the bendable portion are parallel tends to have a smaller and easier-to-control thickness variation Δt2 compared to glass in which these directions are perpendicular. Potential for industrial application

[0092] The tempered glass of the present invention can be used in, for example, smartphones, mobile phones, tablet computers, personal computers, digital cameras, touch panel displays, cover glass for other display devices, automotive display devices, automotive panels, and other display devices that are bendable or have a bendable portion. [Explanation of symbols]

[0093] 1a Tempered glass 1b Tempered glass 2a, 2b Bendable part S1 1st area S2 2nd area 10 Molded body 11. Tension roller 12 Cooling Rollers 13 Heating device G Glass Ribbon

Claims

1. A tempered glass that can be bent along a pre-set strip-shaped bendable portion, The thickness t is 20 to 70 μm. The difference between the maximum and minimum thickness in the bendable portion, which is the thickness variation Δt2, is 8 μm or less. Tempered glass that does not break when bent at a radius of curvature of 1.0 mm in the aforementioned bendable portion.

2. The tempered glass according to claim 1, wherein the thickness variation Δt2 in the bendable portion is 0.1 to 2.0 μm.

3. The tempered glass according to claim 1 or 2, wherein the thickness variation Δt1, which is the difference between the maximum and minimum thickness of the entire tempered glass, is 15 μm or less.

4. The tempered glass according to claim 3, wherein the thickness variation Δt1 in the entire tempered glass is 0.2 to 1.5 μm.

5. The tempered glass according to claim 1 or 2, wherein the thickness variation Δt2 in the bendable portion is smaller than the thickness variation Δt1 in the entire tempered glass.

6. The tempered glass according to claim 5, wherein Δt² / Δt¹ ≤ 0.

9.

7. The tempered glass according to claim 1 or 2, wherein the extending direction of the bendable portion is set parallel to the drawing direction during glass molding.

8. The surface is equipped with a compressive stress layer, The maximum compressive stress CS in the aforementioned compressive stress layer is 450 to 850 (MPa), The depth DOL of the compressive stress layer is 2 to 23 μm. A tensile stress layer is provided at a position deeper than the aforementioned compressive stress layer, The tempered glass according to claim 1 or 2, wherein the maximum tensile value CT in the tensile stress layer is 120 to 1500 (MPa).

9. The glass composition is SiO2 by mass%. ２ 45-80%, Al ２ O ３ 5-30%, B ２ O ３ 0-15%, Na ２ O 1-25%, K ２ A tempered glass according to claim 1 or 2, containing 0 to 10% of O.

10. A foldable display device comprising tempered glass according to claim 1 or 2.

Images