Tempered glass sheet, method for manufacturing tempered glass sheet, and glass sheet for tempering

Abstract

To provide a toughened glass plate that resists being broken when falling to a floor and the like, has high chemical stability and clarity, and prevents the occurrence of devitrification seeds during molding.SOLUTION: A toughened glass plate according to the present invention has a compression stress layer on a surface thereof, and has a glass composition containing, in mol%, SiO2 40-80%, Al2O3 6-25%, B2O3 0-10%, Li2O 3-15%, Na2O 1-21%, K2O 0-10%, MgO 0-10%, ZnO 0-10%, P2O5 0-15%, SnO2 0.001-0.30%, with ([Li2O]+[Na2O]+[K2O]) / [Al2O3]≥0.86, and ([SiO2]+[B2O3]+[P2O5]) / ((100×[SnO2])×([Al2O3]+[Li2O]+[Na2O]+[K2O]+[MgO]+[CaO]+[SrO]+[BaO]+[ZnO]))≥0.40.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a strengthened glass plate, a method for manufacturing a strengthened glass plate, and a strengthening glass plate, and particularly to a strengthened glass plate, a method for manufacturing a strengthened glass plate, and a strengthening glass plate suitable for a cover glass of a touch panel display such as a mobile phone, a digital camera, a PDA (portable terminal), etc.

Background Art

[0002] In applications such as mobile phones, digital cameras, and PDAs (portable terminals), an ion-exchanged strengthened glass plate is used as a cover glass of a touch panel display (see Patent Document 1 and Non-Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Non-Patent Documents

[0004]

Non-Patent Document 1

Disclosure of the Invention

Problems to be Solved by the Invention

[0005] By the way, if a smartphone is accidentally dropped on the road surface or the like, the cover glass may be damaged and the smartphone may become unusable. In order to avoid such a situation, it is important to increase the strength of the strengthened glass plate.

[0006] Increasing the stress depth is an effective way to increase the strength of tempered glass sheets. Specifically, when a smartphone is dropped and the cover glass collides with the road surface, protrusions and sand particles on the road surface penetrate the cover glass, reaching the tensile stress layer and causing breakage. Therefore, by increasing the stress depth of the compressive stress layer, it becomes more difficult for protrusions and sand particles on the road surface to reach the tensile stress layer, reducing the probability of breakage of the cover glass.

[0007] Lithium aluminosilicate glass is advantageous for achieving deep stress depth. In particular, by immersing a glass plate to be tempered made of lithium aluminosilicate glass in a molten salt containing NaNO3 and exchanging the Li ions in the glass for the Na ions in the molten salt, a tempered glass plate with deep stress depth can be obtained.

[0008] However, in conventional lithium aluminosilicate glass, the compressive stress value of the compressive stress layer may be too small, while designing the glass composition to increase the compressive stress value of the compressive stress layer may result in a decrease in chemical stability.

[0009] Furthermore, conventional lithium aluminosilicate glass has insufficient clarity, which can lead to bubbles remaining in the glass when it is formed into a sheet. On the other hand, when tin oxide (SnO2) is introduced into the glass composition as a fining agent to reduce bubbles, devitrification particles of SnO2 are generated, which can make it difficult to form into a sheet.

[0010] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a tempered glass sheet that is resistant to breakage when dropped, has excellent chemical stability and clarity, and is resistant to the generation of devitrification particles during forming. [Means for solving the problem]

[0011] As a result of various studies by the present inventors, it has been found that the above technical problems can be solved by restricting the glass composition within a predetermined range, and the present invention is proposed. That is, the tempered glass sheet of the present invention is a tempered glass sheet having a compressive stress layer on the surface, and as the glass composition, in mol%, SiO2 is 40 to 80%, Al2O3 is 6 to 25%, B2O3 is 0 to 10%, Li2O is 3 to 15%, Na2O is 1 to 21%, K2O is 0 to 10%, MgO is 0 to 10%, ZnO is 0 to 10%, P2O5 is 0 to 15%, and SnO2 is 0.001 to 0.30%, ([Li2O]+[Na2O]+[K2O]) / [Al2O3]≧0.86, and ([SiO2]+[B2O3]+[P2O5]) / ((100×[SnO2])×([Al2O3]+[Li2O]+[Na2O]+[K2O]+[MgO]+[CaO]+[SrO]+[BaO]+[ZnO]))≧0.40. Here, [Li2O] refers to the mol% content of Li2O. [Na2O] refers to the mol% content of Na2O. [K2O] refers to the mol% content of K2O. [Al2O3] refers to the mol% content of Al2O3. ([Li2O]+[Na2O]+[K2O]) / [Al2O3] refers to the value obtained by dividing the total content of Li2O, Na2O and K2O by the content of Al2O3. [SiO2] refers to the mol% content of SiO2. [B2O3] refers to the mol% content of B2O3. [P2O5] refers to the mol% content of P2O5. [SnO2] refers to the mol% content of SnO2. [MgO] refers to the mol% content of MgO. [CaO] refers to the mol% content of CaO. [SrO] refers to the mol% content of SrO. [BaO] refers to the mol% content of BaO. [ZnO] refers to the mol% content of ZnO. ([SiO2]+[B2O3]+[P2O5]) / ((100×[SnO2])×([Al2O3]+[Li2O]+[Na2O]+[K2O]+[MgO]+[CaO]+[SrO]+[BaO]+[ZnO])) refers to the value obtained by dividing the total content of SiO2, B2O3 and P2O5 by the value obtained by multiplying the content of 100 times of SnO2 by the total content of Al2O3, Li2O, Na2O, K2O, MgO, CaO, SrO, BaO and ZnO.

[0012] In addition, in the tempered glass sheet of the present invention, the content of B2O3 is preferably 0.1 to 3 mol%.

[0013] In addition, in the tempered glass sheet of the present invention, the content of SnO2 is preferably 0.045 mol% or less.

[0014] In addition, in the tempered glass sheet of the present invention, the content of Cl is preferably 0.02 to 0.3 mol%.

[0015] The tempered glass sheet of the present invention is a tempered glass sheet having a compressive stress layer on the surface. As the glass composition, in mol%, it contains 40 to 80% of SiO2, 6 to 25% of Al2O3, 0 to 10% of B2O3, 3 to 15% of Li2O, 1 to 21% of Na2O, 0 to 10% of K2O, 0 to 10% of MgO, 0 to 10% of ZnO, 0 to 15% of P2O5, 0.001 to 0.045% of SnO2, and 0.02 to 0.3% of Cl, and ([Li2O] + [Na2O] + [K2O]) / [Al2O3] ≥ 0.86, and ([SiO2] + [B2O3] + [P2O5]) / ((100 × [SnO2]) × ([Al2O3] + [Li2O] + [Na2O] + [K2O] + [MgO] + [CaO] + [SrO] + [BaO] + [ZnO])) ≥ 0.40.

[0016] The tempered glass sheet of the present invention is a tempered glass sheet having a compressive stress layer on the surface. As the glass composition, in mol%, it contains 40 to 80% of SiO2, 6 to 25% of Al2O3, 0.1 to 3% of B2O3, 3 to 15% of Li2O, 1 to 21% of Na2O, 0 to 10% of K2O, 0 to 10% of MgO, 0 to 10% of ZnO, 0 to 15% of P2O5, 0.001 to 0.30% of SnO2, and 0.02 to 0.3% of Cl, and ([Li2O] + [Na2O] + [K2O]) / [Al2O3] ≥ 0.86, and ([SiO2] + [B2O3] + [P2O5]) / ((100 × [SnO2]) × ([Al2O3] + [Li2O] + [Na2O] + [K2O] + [MgO] + [CaO] + [SrO] + [BaO] + [ZnO])) ≥ 0.40.

[0017] In addition, in the tempered glass plate of the present invention, the content of P2O5 is preferably 2.5 mol % or more.

[0018] In the tempered glass plate of the present invention, the Fe2O3 content is preferably 0.001 to 0.1 mol %.

[0019] In the tempered glass plate of the present invention, the content of TiO2 is preferably 0.001 to 0.1 mol %.

[0020] In addition, in the tempered glass plate of the present invention, the compressive stress value of the outermost surface of the compressive stress layer is preferably 200 to 1200 MPa. Here, the "compressive stress value of the outermost surface" and "stress depth" refer to values measured from a phase difference distribution curve observed using, for example, a scattered light photoelastic stress meter SLP-1000 (manufactured by Orihara Manufacturing Co., Ltd.). The stress depth refers to the depth at which the stress value becomes zero. In calculating the stress characteristics, the refractive index of each measurement sample is set to 1.51 and the photoelastic constant is set to 29.0 [(nm / cm) / MPa].

[0021] In the tempered glass plate of the present invention, the stress depth of the compressive stress layer is preferably 50 to 200 μm.

[0022] In addition, in the tempered glass plate of the present invention, the compressive stress value at a depth of 2.5 μm is preferably 350 MPa or more. In this way, the bending strength is increased.

[0023] In addition, the tempered glass plate of the present invention preferably has an average compressive stress value of 85 MPa or more at a depth of 30 to 45 μm, thereby increasing drop strength.

[0024] In addition, in the tempered glass sheet of the present invention, the high-temperature viscosity is 10 2.5 It is preferable that the temperature at which the viscosity reaches 10 dPa·s is less than 1650°C. 2.5 The "temperature at dPa·s" can be measured, for example, by the platinum sphere pull-up method.

[0025] Further, the tempered glass sheet of the present invention preferably has an overflow confluence surface at the central portion in the plate thickness direction. Here, the "overflow down-draw method" is a method of manufacturing a glass sheet by causing molten glass to overflow from both sides of a shaped refractory, causing the overflowed molten glass to converge at the lower end of the shaped refractory, and stretching and forming downward.

[0026] Further, the tempered glass sheet of the present invention is preferably used as a cover glass for a touch panel display.

[0027] Further, the tempered glass sheet of the present invention preferably has a stress profile in the thickness direction having at least a first peak, a second peak, a first bottom, and a second bottom.

[0028] The method for manufacturing a tempered glass sheet of the present invention comprises a preparation step of preparing a tempered glass sheet for strengthening, which contains, as a glass composition, in mol%, 40 to 80% of SiO2, 6 to 25% of Al2O3, 0 to 10% of B2O3, 3 to 15% of Li2O, 1 to 21% of Na2O, 0 to 10% of K2O, 0 to 10% of MgO, 0 to 10% of ZnO, 0 to 15% of P2O5, 0.001 to 0.30% of SnO2, ([Li2O]+[Na2O]+[K2O]) / [Al2O3]≧0.86, and ([SiO2]+[B2O3]+[P2O5]) / ((100×[SnO2])×([Al2O3]+[Li2O]+[Na2O]+[K2O]+[MgO]+[CaO]+[SrO]+[BaO]+[ZnO]))≧0.40; and an ion exchange step of performing ion exchange treatment on the tempered glass sheet for strengthening a plurality of times to obtain a tempered glass sheet having a compressive stress layer on the surface.

[0029] The glass sheet for strengthening of the present invention is an ion-exchangeable glass sheet for strengthening. As a glass composition, in mol%, it contains 40 to 80% of SiO2, 6 to 25% of Al2O3, 0 to 10% of B2O3, 3 to 15% of Li2O, 1 to 21% of Na2O, 0 to 10% of K2O, 0 to 10% of MgO, 0 to 10% of ZnO, 0 to 15% of P2O5, and 0.001 to 0.30% of SnO2, and ([Li2O] + [Na2O] + [K2O]) / [Al2O3] ≥ 0.86, and ([SiO2] + [B2O3] + [P2O5]) / ((100 × [SnO2]) × ([Al2O3] + [Li2O] + [Na2O] + [K2O] + [MgO] + [CaO] + [SrO] + [BaO] + [ZnO])) ≥ 0.40, which is characterized by this.

[0030] The glass sheet for strengthening of the present invention is an ion-exchangeable glass sheet for strengthening. As a glass composition, in mol%, it contains 40 to 80% of SiO2, 6 to 25% of Al2O3, 0 to 10% of B2O3, 3 to 15% of Li2O, 1 to 21% of Na2O, 0 to 10% of K2O, 0 to 10% of MgO, 0 to 10% of ZnO, 0 to 15% of P2O5, 0.001 to 0.045% of SnO2, and 0.02 to 0.3% of Cl, and ([Li2O] + [Na2O] + [K2O]) / [Al2O3] ≥ 0.86, and ([SiO2] + [B2O3] + [P2O5]) / ((100 × [SnO2]) × ([Al2O3] + [Li2O] + [Na2O] + [K2O] + [MgO] + [CaO] + [SrO] + [BaO] + [ZnO])) ≥ 0.40, which is characterized by this.

[0031] The glass plate to be tempered of the present invention is an ion-exchangeable glass plate to be tempered, and has a glass composition, in mole %, of SiO2 40 to 80%, Al2O3 6 to 25%, B2O3 0.1 to 3%, Li2O 3 to 15%, Na2O 1 to 21%, K2O 0 to 10%, MgO 0 to 10%, ZnO 0 to 10%, P2O 50 to 15%, SnO2 0.001 to 0.30%, Cl It is characterized by containing 0.02 to 0.3% of Li2O, ([Li2O] + [Na2O] + [K2O]) / [Al2O3] ≧ 0.86, and ([SiO2] + [B2O3] + [P2O5]) / ((100 × [SnO2]) × ([Al2O3] + [Li2O] + [Na2O] + [K2O] + [MgO] + [CaO] + [SrO] + [BaO] + [ZnO])) ≧ 0.40. [Brief explanation of the drawings]

[0032] [Figure 1] FIG. 2 is an explanatory diagram illustrating a stress profile having a first peak, a second peak, a first bottom, and a second bottom. [Figure 2] 10 is a stress profile of the strengthened glass sheet according to Example 3. [Figure 3] 10 is a stress profile of the strengthened glass sheet according to Example 3. DETAILED DESCRIPTION OF THE INVENTION

[0033] The tempered glass sheet (tempering glass sheet) of the present invention is a tempered glass sheet having a compressive stress layer on the surface. As the glass composition, in mol%, it contains 40 to 80% of SiO2, 6 to 25% of Al2O3, 0 to 10% of B2O3, 3 to 15% of Li2O, 1 to 21% of Na2O, 0 to 10% of K2O, 0 to 10% of MgO, 0 to 10% of ZnO, 0 to 15% of P2O5, and 0.001 to 0.30% of SnO2, ([Li2O]+[Na2O]+[K2O]) / [Al2O3]≧0.86, and ([SiO2]+[B2O3]+[P2O5]) / ((100×[SnO2])×([Al2O3]+[Li2O]+[Na2O]+[K2O]+[MgO]+[CaO]+[SrO]+[BaO]+[ZnO]))≧0.40. The reasons for limiting the content ranges of the respective components are shown below. In the description of the content ranges of the respective components, the % indication refers to mol% unless otherwise specified.

[0034] SiO2 is a component that forms the glass network. If the content of SiO2 is too low, it becomes difficult to vitrify, and the thermal expansion coefficient becomes too high, making the thermal shock resistance likely to decrease. Therefore, the preferred lower limit range of SiO2 is 40% or more, 45% or more, 50% or more, 55% or more, 57% or more, particularly 59% or more. On the other hand, if the content of SiO2 is too high, the meltability and formability are likely to decrease, and the thermal expansion coefficient becomes too low, making it difficult to match the thermal expansion coefficient of the surrounding materials. Therefore, the preferred upper limit range of SiO2 is 80% or less, 70% or less, 68% or less, 66% or less, 65% or less, 64.5% or less, 64% or less, 63% or less, particularly 62% or less.

[0035] 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 of Al2O3 is 6% or more, 7% or more, 8% or more, 10% or more, 12% or more, 13% or more, 14% or more, 14.4% or more, 15% or more, 15.3% or more, 15.6% or more, 16% or more, 16.5% or more, 17% or more, 17.2% or more, 17.5% or more, 17.8% or more, 18% or more, more than 18%, 18.3% or more, particularly 18.5% or more, 18.6% or more, 18.7% or more, or 18.8% or more. On the other hand, if the Al2O3 content is too high, the high-temperature viscosity increases, which tends to reduce meltability and formability. Furthermore, devitrification crystals tend to precipitate in the glass, making it difficult to form it into a plate shape using the overflow downdraw method or the like. In particular, when an alumina-based refractory is used as the formed refractory and formed into a plate by the overflow downdraw method, devitrified crystals of spinel are likely to precipitate at the interface with the alumina-based refractory. Furthermore, acid resistance is also reduced, 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. By setting the Al2O3 content, which has a significant impact on ion exchange performance, within a preferred range, it becomes easier to form a profile with a first peak, a second peak, a first bottom, and a second bottom.

[0036] B2O3 is a component that reduces the high-temperature viscosity and density, stabilizes the glass, makes it difficult for crystals to precipitate, and lowers the liquidus temperature. It also increases the binding force of oxygen electrons by cations, lowering the basicity of the glass. If the B2O3 content is too low, the stress depth due to the ion exchange between the Li ions contained in the glass and the Na ions in the molten salt becomes too deep, resulting in a decrease in the compressive stress value (CS Na) tends to be small. Also, the glass may become unstable and its devitrification resistance may decrease. Further, if the basicity of the glass becomes too high, the amount of O2 released due to the reaction of the fining agent decreases, the foaming property deteriorates, and there is a risk that bubbles will remain in the glass when it is formed into a plate shape. Therefore, a suitable lower limit range of B2O3 is 0% or more, 0.10% or more, 0.12% or more, 0.15% or more, 0.18% or more, 0.20% or more, 0.23% or more, 0.25% or more, 0.27% or more, 0.30% or more, 0.35% or more, particularly 0.4% or more. On the other hand, if the content of B2O3 is too high, there is a risk that the stress depth will become shallow. In particular, the efficiency of ion exchange between Na ions contained in the glass and K ions in the molten salt tends to decrease, and the stress depth (DOL_ZERO K ) tends to be small. Therefore, a suitable upper limit range of B2O3 is 10% or less, 5% or less, 4% or less, 3.8% or less, 3.5% or less, 3.3% or less, 3.2% or less, 3.1% or less, 3% or less, 2.9% or less, 2.8% or less, 2.5% or less, 2.0% or less, 1.5% or less, 1.0% or less, less than 1.0%, 0.8% or less, particularly 0.5% or less. If the content of B2O3 is within a suitable range, it becomes easier to form a profile having a first peak, a second peak, a first bottom, and a second bottom.

[0037] Alkali metal oxides are ion-exchange components and components that lower the high-temperature viscosity and enhance the meltability and formability. However, if the content of alkali metal oxides ([Li2O]+[Na2O]+[K2O]) is too high, there is a risk that the thermal expansion coefficient will increase. Also, there is a risk that the acid resistance will decrease. Therefore, a suitable lower limit range of alkali metal oxides ([Li2O]+[Na2O]+[K2O]) is 10% or more, 11% or more, 12% or more, 13% or more, 14% or more, 14.2% or more, 14.5% or more, 14.8% or more, 15% or more, 15.2% or more, 15.5% or more, 15.8% or more, particularly 16% or more, and a suitable upper limit range is 25% or less, 23% or less, 20% or less, 19% or less, particularly 18% or less.

[0038] Li2O is an ion-exchange component, particularly an essential component for achieving deep stress depth by ion-exchanging Li ions contained in the glass with Na ions in the molten salt. Li2O also reduces high-temperature viscosity, improving meltability and formability, and increasing Young's modulus. Therefore, the preferred lower limit of Li2O is 3% or more, 4% or more, 5% or more, 5.5% or more, 6.5% or more, 7% or more, 7.3% or more, 7.5% or more, 7.8% or more, and particularly 8% or more. Therefore, the preferred upper limit of Li2O is 15% or less, 13% or less, 12% or less, 11.5% or less, 11% or less, 10.5% or less, less than 10%, 9.9% or less, 9% or less, and particularly 8.9% or less.

[0039] Na2O is an ion-exchange component and a component that reduces high-temperature viscosity and improves meltability and formability. Na2O also improves devitrification resistance, particularly suppressing devitrification caused by reaction with alumina-based refractories. Therefore, the preferred lower limit of Na2O is 1% or more, 2% or more, 3% or more, 4% or more, 5% or more, 6% or more, 7% or more, 7.5% or more, 8% or more, 8.5% or more, 8.8% or more, and particularly 9% or more. On the other hand, if the Na2O content is too high, the thermal expansion coefficient becomes too high, which can lead to a decrease in thermal shock resistance. Furthermore, the component balance of the glass composition may be disrupted, which may actually result in a decrease in devitrification resistance. Therefore, the preferred upper limit of Na2O is 21% or less, 20% or less, 19% or less, particularly 18% or less, 15% or less, 13% or less, 11% or less, and particularly 10% or less.

[0040] K2O is a component that reduces high-temperature viscosity and improves meltability and moldability. However, if the K2O content is too high, the thermal expansion coefficient becomes too high, which tends to reduce thermal shock resistance. It also tends to reduce the compressive stress value of the outermost surface. Therefore, the preferred upper limit of K2O is 10% or less, 7% or less, 6% or less, 5% or less, 4% or less, 3% or less, 2% or less, and particularly 1.5% or less. In addition, from the perspective of increasing the stress depth, the preferred lower limit of K2O is 0% or more, 0.1% or more, 0.3% or more, and particularly 0.4% or more.

[0041] The preferred lower limit of ([LiO] + [NaO] + [KO]) / [AlO] is 0.86 or more, 0.87 or more, and particularly 0.88 or more. If ([LiO] + [NaO] + [KO]) / [AlO] is too small, the efficiency of ion exchange tends to decrease. On the other hand, if the molar ratio ([LiO] + [NaO] + [KO]) / [AlO] is too large, the efficiency of ion exchange tends to decrease. Therefore, the preferred upper limit of ([LiO] + [NaO] + [KO]) / [AlO] is preferably 2.0 or less, 1.8 or less, 1.7 or less, 1.6 or less, 1.5 or less, 1.4 or less, 1.3 or less, 1.2 or less, 1.1 or less, 1.0 or less, and particularly 0.95 or less.

[0042] ([SiO2] + [B2O3] + [P2O5]) / ((100 × [SnO2]) × ([Li2O] + [Na2O] + [K2O] + [MgO] + [CaO] + [SrO] + [BaO] + [ZnO] + [Al2O3])) is preferably 0.40 or more, 0.41 or more, 0.42 or more, 0.43 or more, 0.44 or more, 0.45 or more, 0.48 or more, 0.50 or more, 0.51 or more, 0.52 or more, 0.53 or more, 0.54 or more, particularly 0.55 or more. If the molar ratio ([SiO2] + [B2O3] + [P2O5]) / ((100 × [SnO2]) × ([Li2O] + [Na2O] + [K2O] + [MgO] + [CaO] + [SrO] + [BaO] + [ZnO] + [Al2O3])) is too small, SnO2 particles are more likely to precipitate. Also, less oxygen is released from the fining agent during melting and molding, making it more likely that bubbles will remain in the glass when it is molded into a plate. The upper limit of ([SiO2] + [B2O3] + [P2O5]) / ((100 × [SnO2]) × ([Li2O] + [Na2O] + [K2O] + [MgO] + [CaO] + [SrO] + [BaO] + [ZnO] + [Al2O3])) is not particularly limited, but in order to enhance clarity while suppressing devitrification, it is preferably 4.0 or less, 3.0 or less, 2.0 or less, 1.8 or less, 1.5 or less, 1.2 or less, 1.0 or less, 0.90 or less, 0.80 or less, and particularly 0.70 or less.

[0043] The ratio [Li2O] / ([Na2O]+[K2O]) is preferably 0.4 to 1.0, 0.5 to 0.9, and particularly 0.6 to 0.8. If the ratio [Li2O] / ([Na2O]+[K2O]) is too small, the ion exchange performance may not be fully exhibited. In particular, the efficiency of ion exchange between the Li ions contained in the glass and the Na ions in the molten salt tends to decrease. On the other hand, if the molar ratio [Li2O] / ([Na2O]+[K2O]) is too large, devitrification crystals tend to precipitate in the glass, making it difficult to form the glass into a plate shape by the overflow downdraw method or the like. Here, [Li2O] / ([Na2O]+[K2O]) refers to the value obtained by dividing the Li2O content by the combined amount of Na2O and K2O.

[0044] MgO is a component that reduces high-temperature viscosity, improves meltability and formability, and increases strain point and Vickers hardness. 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, devitrification resistance tends to decrease, and it becomes particularly difficult to suppress devitrification caused by reaction with alumina-based refractories. Therefore, the preferred MgO content is 0-10%, 0-7%, 0-5%, 0.1-3%, 0.2-2.5%, 0.3-2%, 0.4-1.5%, and particularly 0.5-1.0%.

[0045] Compared to other components, CaO reduces high-temperature viscosity, improves meltability and formability, and increases strain point and Vickers hardness without reducing devitrification resistance. However, if the CaO content is too high, ion exchange performance may be reduced and the ion exchange solution may be deteriorated during ion exchange treatment. Therefore, the preferred upper limit of CaO content 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%, 0.7% or less, 0.5% or less, 0.3% or less, 0.1% or less, 0.05% or less, and particularly 0.01% or less.

[0046] SrO and BaO are components that reduce the high-temperature viscosity, enhance the meltability and formability, or increase the strain point and Young's modulus. However, if their contents are too high, in addition to the ion exchange reaction being easily inhibited, the density and thermal expansion coefficient will become unduly high, and the glass will be prone to devitrification. Therefore, the preferred content ranges of SrO and BaO are 0 - 2%, 0 - 1.5%, 0 - 1%, 0 - 0.5%, 0 - 0.1%, especially less than 0 - 0.1% respectively.

[0047] ZnO is a component that enhances the ion exchange performance, especially a component with a large effect of increasing the compressive stress value on the outermost surface. It is also a component that reduces the high-temperature viscosity without reducing the low-temperature viscosity. The preferred lower limit range of ZnO is 0% or more, 0.1% or more, 0.3% or more, 0.5% or more, 0.7% or more, especially 1% or more. On the other hand, if the content of ZnO is too high, the glass tends to phase-separate, the devitrification resistance decreases, the density increases, and the stress depth becomes shallow. Therefore, the preferred upper limit range of ZnO is 10% or less, 6% or less, 5% or less, 4% or less, 3% or less, 2% or less, 1.5% or less, 1.3% or less, 1.2% or less, especially 1.1% or less.

[0048] P2O5 is a component that enhances the ion exchange performance, especially a component that deepens the stress depth. It further improves the acid resistance. Furthermore, it is a component that increases the binding force of oxygen electrons by cations and reduces the basicity of the glass. If the content of P2O5 is too low, there is a risk that the ion exchange performance cannot be fully exerted. In particular, the efficiency of ion exchange between Na ions contained in the glass and K ions in the molten salt tends to decrease, and the stress depth (DOL_ZERO) of the compressive stress layer K) tends to be small. Also, the glass becomes unstable and there is a risk of a decrease in devitrification resistance. Further, if the basicity of the glass becomes too high, the amount of O2 released by the reaction of the fining agent decreases, the foaming property deteriorates, and there is a risk that bubbles remain in the glass when it is formed into a plate shape. Therefore, the preferable lower limit range of P2O5 is 0% or more, 0.1% or more, 0.4% or more, 0.7% or more, 1% or more, 1.2% or more, 1.4% or more, 1.6% or more, 2% or more, 2.3% or more, 2.5% or more, 2.6% or more, 2.7% or more, 2.8% or more, 2.9% or more, 3.0% or more, 3.2% or more, 3.5% or more, 3.8% or more, 3.9% or more, 4.0% or more, 4.1% or more, 4.2% or more, 4.3% or more, 4.4% or more, 4.5% or more, particularly 4.6% or more. On the other hand, if the content of P2O5 is too high, the glass may phase-separate or the water resistance tends to decrease. Also, in the ion exchange of Li ions contained in the glass and Na ions in the molten salt, the stress depth becomes too deep, and as a result, the compression stress value (CS Na ) tends to be small. Therefore, the preferable upper limit range of P2O5 is 15% or less, 10% or less, 8% or less, 7% or less, 6% or less, 5% or less, 4.9% or less, 4.8% or less. If the content of P2O5 is within the preferable range, it becomes easier to form a non-monotonic profile.

[0049] ([SiO2] + 1.2×[P2O5]) - (3×[Al2O3] + 2×[Li2O] + 1.5×[Na2O] + [K2O] + [B2O3]) is preferably -40% or more, -30% or more, -25% or more, -24% or more, -23% or more, -22% or more, -21% or more, -20% or more, -19% or more, particularly -18% or more. If ([SiO2] + 1.2×[P2O5]) - (3×[Al2O3] + 2×[Li2O] + 1.5×[Na2O] + [K2O] + [B2O3]) is too small, the acid resistance tends to decrease. On the other hand, if ([SiO2] + 1.2×[P2O5]) - (3×[Al2O3] + 2×[Li2O] + 1.5×[Na2O] + [K2O] + [B2O3]) is too large, there is a risk that the ion exchange performance cannot be fully exerted. Therefore, ([SiO2] + 1.2×[P2O5]) - (3×[Al2O3] + 2×[Li2O] + 1.5×[Na2O] + [K2O] + [B2O3]) is preferably 30 mol% or less, 20 mol% or less, 15 mol% or less, 10 mol% or less, 5 mol% or less, particularly 0 mol% or less. Note that ([SiO2] + 1.2×[P2O5]) - (3×[Al2O3] + 2×[Li2O] + 1.5×[Na2O] + [K2O] + [B2O3]) refers to the value obtained by subtracting the total of 3 times the content of Al2O3, 2 times the content of Li2O, 1.5 times the content of Na2O, the content of K2O, and the content of B2O3 from the total of the content of SiO2 and 1.2 times the content of P2O5.

[0050] SnO2 is a fining agent and a component that enhances the ion exchange performance. However, if its content is too large, the devitrification resistance tends to decrease. Therefore, the preferable lower limit range of SnO2 is 0.001% or more, 0.002% or more, 0.005% or more, 0.007% or more, particularly 0.010% or more, and the preferable upper limit range is 0.30% or less, 0.27% or less, 0.25% or less, 0.20% or less, 0.18% or less, 0.15% or less, 0.12% or less, 0.10% or less, 0.09% or less, 0.08% or less, 0.07% or less, 0.06% or less, 0.05% or less, 0.047% or less, 0.045% or less, 0.042% or less, 0.040% or less, 0.038% or less, 0.035% or less, 0.032% or less, particularly 0.030% or less.

[0051] In addition to the above components, for example, the following components may also be added.

[0052] ZrO2 is a component that increases Vickers hardness and also a component that increases viscosity and strain point near the liquid-phase viscosity. However, if its content is too high, there is a risk of significantly reducing the devitrification resistance. Therefore, the preferred content of ZrO2 is 0 to 3%, 0 to 1.5%, 0 to 1%, particularly 0 to 0.1%.

[0053] TiO2 is a component that enhances ion-exchange performance and also a component that reduces high-temperature viscosity. However, if its content is too high, transparency and devitrification resistance are likely to decrease. Therefore, the preferred content of TiO2 is 0 to 3%, 0 to 1.5%, 0 to 1%, 0 to 0.1%, particularly 0.001 to 0.1%.

[0054] Cl is a fining agent. In particular, when used in combination with SnO2, the bubble diameter in the glass is likely to increase, and the fining effect is likely to be exerted. In this regard, if SnO2 and Cl are used in combination, the fining effect can be maintained even if the content of SnO2 is reduced. On the other hand, if the content of Cl is too high, it is a component that has an adverse effect on the environment and equipment. Therefore, the preferred lower limit range of Cl is 0% or more, 0.001% or more, 0.005% or more, 0.008% or more, 0.010% or more, 0.015% or more, 0.018% or more, 0.019% or more, 0.020% or more, 0.021% or more, 0.022% or more, 0.023% or more, 0.024% or more, 0.025% or more, 0.027% or more, 0.030% or more, 0.035% or more, 0.040% or more, 0.050% or more, 0.070% or more, 0.090% or more, particularly 0.100% or more, and the preferred upper limit range is 0.3% or less, 0.2% or less, 0.17% or less, 0.15% or less, particularly 0.12% or less.

[0055] As a fining agent, in addition to the above, 0.001 to 1% of SO3 and CeO2 may also be added.

[0056] Fe2O3 is an impurity that is inevitably mixed in from the raw materials. The preferred content of Fe2O3 is less than 1000 ppm (less than 0.1%), less than 800 ppm, less than 600 ppm, less than 400 ppm, and particularly less than 300 ppm. If the Fe2O3 content is too high, the transmittance of the cover glass is likely to decrease. On the other hand, the preferred lower limit range of Fe2O3 is 10 ppm or more, 20 ppm or more, 30 ppm or more, 50 ppm or more, 80 ppm or more, and particularly 100 ppm or more. If the Fe2O3 content is too low, the raw material cost is likely to rise due to the use of high-purity raw materials.

[0057] Rare earth oxides such as Nd2O3, La2O3, Y2O3, Nb2O5, Ta2O5, and Hf2O3 are components that increase Young's modulus. However, the raw material cost is high, and adding large amounts can easily reduce devitrification resistance. Therefore, the preferred content of rare earth oxides is 5% or less, 4% or less, 3% or less, 2% or less, 1% or less, 0.5% or less, and particularly 0.1% or less.

[0058] From an environmental perspective, the tempered glass plate (glass plate to be tempered) of the present invention preferably contains substantially no As2O3, Sb2O3, PbO, or F in its glass composition. From an environmental perspective, it also preferably contains substantially no Bi2O3. The phrase "substantially does not contain ..." means that the specified components are not actively added as glass components, but impurity-level addition is permitted, and specifically refers to a case where the content of the specified components is less than 0.05%.

[0059] The tempered glass plate (glass plate to be tempered) of the present invention preferably has the following properties.

[0060] The density is preferably 2.55 g / cm 3 Below, 2.53g / cm 3 Below 2.50g / cm 3 Below, 2.49g / cm 3 Below, 2.45g / cm 3 Below, especially 2.35 to 2.44 g / cm 3That is, the lower the density, the lighter the tempered glass sheet can be. Note that the "density" can be measured by well-known methods such as the Archimedes' method.

[0061] The coefficient of thermal expansion at 30 to 380 °C is preferably 150×10 -7 / °C or less, 100×10 -7 / °C or less, particularly 50×10 -7 ~95×10 -7 / °C. Note that the "coefficient of thermal expansion at 30 to 380 °C" refers to the value obtained by measuring the average coefficient of thermal expansion using a dilatometer.

[0062] The softening point is preferably 950 °C or less, 930 °C or less, 920 °C or less, 910 °C or less, 900 °C or less, particularly 880 to 900 °C. If the softening point is too high, bending by heat treatment becomes difficult. Note that the "softening point" refers to the value measured based on the method of ASTM C338.

[0063] The temperature at a high-temperature viscosity of 10 2.5 dPa·s is preferably 1660 °C or less, less than 1600 °C, 1590 °C or less, 1580 °C or less, 1570 °C or less, 1560 °C or less, particularly preferably 1400 to 1550 °C. If the temperature at a high-temperature viscosity of 10 2.5 dPa·s is too high, the meltability and formability decrease, and it becomes difficult to form the molten glass into a plate shape. Note that the "temperature at a high-temperature viscosity of 10 2.5 dPa·s" refers to the value measured by the platinum ball pulling-up method.

[0064] The liquid-phase viscosity is preferably 10 3.74 dPa·s or more, 10 4.5 dPa·s or more, 10 4.8 dPa·s or more, 10 4.9 dPa·s or more, 10 5.0 dPa·s or more, 10 5.1 dPa·s or more, 10 5.2 dPa·s or more, 10 5.3 dPa·s or more, 10 5.4 dPa·s or more, particularly 10 5.5It is dPa·s or higher. The higher the liquidus viscosity, the better the resistance to devitrification, and the less likely devitrification particles will occur during molding. Here, "liquidus viscosity" refers to the value of the viscosity at the liquidus temperature measured using the platinum ball pull-up method. "Liquidus temperature" is defined as the highest temperature at which devitrification (devitrification particles) is observed inside the glass when glass powder that passes through a standard 30 mesh (500 μm) sieve and remains on the 50 mesh (300 μm) sieve is placed in a platinum boat and held in a temperature gradient furnace for 24 hours, after which the platinum boat is removed and observed under a microscope.

[0065] The Young's modulus is preferably 70 GPa or more, 74 GPa or more, 75 to 100 GPa, particularly 76 to 90 GPa. If the Young's modulus is low, the cover glass will be easily bent when the plate thickness is thin. The "Young's modulus" can be calculated by the well-known resonance method.

[0066] The tempered glass sheet of the present invention has a compressive stress layer on its surface. The compressive stress value of the outermost surface is preferably 200 MPa or more, 220 MPa or more, 250 MPa or more, 280 MPa or more, 300 MPa or more, 310 MPa or more, particularly 320 MPa or more. The higher the compressive stress value of the outermost surface, the higher the Vickers hardness. On the other hand, if an extremely large compressive stress is formed on the surface, the tensile stress inherent in the tempered glass becomes extremely high, and there is a risk of large dimensional changes before and after ion exchange treatment. For this reason, the compressive stress value of the outermost surface is preferably 1200 MPa or less, 1100 MPa or less, 1000 MPa or less, 900 MPa or less, 700 MPa or less, 680 MPa or less, 650 MPa or less, particularly 600 MPa or less. Note that shortening the ion exchange time or lowering the temperature of the ion exchange solution tends to increase the compressive stress value of the outermost surface.

[0067] The stress depth is preferably 50 μm or more, 60 μm or more, 80 μm or more, 100 μm or more, 110 μm or more, 120 μm or more, 130 μm or more, particularly 140 μm or more. The deeper the stress depth, the more difficult it is for protrusions or sand grains on the road surface to reach the tensile stress layer when the smartphone is dropped, and the probability of cover glass breakage can be reduced. On the other hand, if the stress depth is too deep, there is a risk that the dimensional change will be large before and after the ion exchange treatment. Furthermore, the compressive stress value on the outermost surface tends to decrease. Therefore, the stress depth is preferably 200 μm or less, 180 μm or less, particularly 170 μm or less. Note that increasing the ion exchange time or raising the temperature of the ion exchange solution tends to deepen the stress depth.

[0068] The compressive stress value at a depth of 2.5 μm is preferably 350 MPa or more, 360 MPa or more, 370 MPa or more, 380 MPa or more, 390 MPa or more, 400 MPa or more, 410 MPa or more, 420 MPa or more, 430 MPa or more, 440 MPa or more, 450 MPa or more, 460 MPa or more, 470 MPa or more, 480 MPa or more, 490 MPa or more, 500 MPa or more, 510 MPa or more, 520 MPa or more, 530 MPa or more, 540 MPa or more, 550 MPa or more, particularly 600 MPa or more. The greater the compressive stress value at a depth of 2.5 μm, the higher the bending strength. On the other hand, if an extremely large compressive stress is formed at a depth of 2.5 μm, the tensile stress inherent in the tempered glass plate may become extremely high. Therefore, the compressive stress value at a depth of 2.5 μm is preferably 800 MPa or less, 750 MPa or less, 730 MPa or less, 700 MPa or less, 680 MPa or less, 650 MPa or less, 640 MPa or less, particularly 630 MPa or less.

[0069] The average compressive stress value at a depth of 30 to 45 μm is preferably 85 MPa or more, 86 MPa or more, 87 MPa or more, 88 MPa or more, 89 MPa or more, 90 MPa or more, 92 MPa or more, 95 MPa or more, 98 MPa or more, and particularly 100 MPa or more. The higher the average compressive stress value at a depth of 30 to 45 μm, the less likely the smartphone will crack due to protrusions or sand particles on the road surface when dropped, thereby reducing the probability of breakage of the cover glass. On the other hand, if the average compressive stress value at a depth of 30 to 45 μm becomes extremely high, the tensile stress inherent in the tempered glass sheet may become extremely high. Therefore, the average compressive stress value at a depth of 30 to 45 μm is preferably 150 MPa or less, 140 MPa or less, 130 MPa or less, 125 MPa or less, 120 MPa or less, 115 MPa or less, 110 MPa or less, and particularly 105 MPa or less.

[0070] The tempered glass sheet of the present invention preferably has a thickness of 2.0 mm or less, 1.5 mm or less, 1.3 mm or less, 1.1 mm or less, 1.0 mm or less, 0.9 mm or less, particularly 0.8 mm or less. The smaller the thickness, the lighter the tempered glass sheet can be. On the other hand, if the thickness is too thin, it becomes difficult to obtain the desired mechanical strength. Therefore, the thickness is preferably 0.3 mm or more, 0.4 mm or more, 0.5 mm or more, 0.6 mm or more, particularly 0.7 mm or more.

[0071] The method for producing a tempered glass sheet of the present invention is characterized by comprising: a preparation step of preparing a glass sheet to be tempered that is manufactured to have the above-described glass composition; and an ion exchange step of subjecting the glass sheet to be tempered to multiple ion exchange treatments to obtain a tempered glass sheet having a compressive stress layer on its surface. Note that, although the method for producing a tempered glass sheet of the present invention is characterized by performing multiple ion exchange treatments, the tempered glass sheet of the present invention also encompasses not only glass sheets that have been subjected to multiple ion exchange treatments, but also glass sheets that have been subjected to only one ion exchange treatment.

[0072] A method for producing the glass to be tempered according to the present invention is, for example, as follows. First, glass raw materials prepared to obtain a desired glass composition are charged into a continuous melting furnace, and the raw materials are heated and melted at 1400 to 1700°C. After clarification, the molten glass is preferably supplied to a forming device, formed into a plate, and cooled. After forming into a plate, a known method can be used to cut the glass into a predetermined size.

[0073] The overflow downdraw method is preferred as a method for forming molten glass into a plate. In the overflow downdraw method, the surface to become the glass plate is not in contact with the surface of the refractory molding, and is formed into a plate in a free surface state. This makes it possible to inexpensively produce a glass plate that is unpolished but has good surface quality. Furthermore, in the overflow downdraw method, an alumina-based refractory or a zirconia-based refractory is used as the refractory molding. The tempered glass plate (glass plate to be tempered) of the present invention has good compatibility with alumina-based refractories and zirconia-based refractories (particularly alumina-based refractories), and therefore has the property of being less likely to react with these refractories to generate bubbles, bumps, etc.

[0074] In addition to the overflow downdraw method, various other forming methods can be employed, such as the float method, the downdraw method (slot downdraw method, redraw method, etc.), the rollout method, and the press method.

[0075] When forming the molten glass, it is preferable to cool the temperature range between the annealing point and the strain point of the molten glass at a cooling rate of 3 ° C. / min or more and less than 1000 ° C. / min, and the lower limit of the cooling rate is preferably 10 ° C. / min or more, 20 ° C. / min or more, 30 ° C. / min or more, particularly 50 ° C. / min or more, and the upper limit is preferably less than 1000 ° C. / min, less than 500 ° C. / min, particularly less than 300 ° C. / min. If the cooling rate is too fast, the glass structure becomes coarse, making it difficult to increase the Vickers hardness after ion exchange treatment. On the other hand, if the cooling rate is too slow, the production efficiency of the glass sheet decreases.

[0076] In the method for manufacturing a tempered glass sheet of the present invention, ion exchange treatment is performed multiple times. As the multiple ion exchange treatments, it is preferable to perform an ion exchange treatment by immersing in a molten salt containing KNO3 molten salt and then perform an ion exchange treatment by immersing in a molten salt containing NaNO3 molten salt. By doing so, while ensuring a deep stress depth, the compressive stress value at the outermost surface can be increased.

[0077] In particular, in the method for manufacturing a tempered glass sheet of the present invention, after performing an ion exchange treatment (first ion exchange step) of immersing in a NaNO3 molten salt or a mixed molten salt of NaNO3 and KNO3, it is preferable to perform an ion exchange treatment (second ion exchange step) of immersing in a mixed molten salt of KNO3 and LiNO3. By doing so, a non-monotonic stress profile shown in FIG. 1, that is, a stress profile having at least a first peak, a second peak, a first bottom, and a second bottom can be formed. As a result, it becomes possible to significantly reduce the breakage probability of the cover glass when the smartphone is dropped.

[0078] In the first ion exchange step, Li ions contained in the glass and Na ions in the molten salt are ion-exchanged. When using a mixed molten salt of NaNO3 and KNO3, further, Na ions contained in the glass and K ions in the molten salt are ion-exchanged. Here, the ion exchange between Li ions contained in the glass and Na ions in the molten salt is faster and more efficient than the ion exchange between Na ions contained in the glass and K ions in the molten salt. In the second ion exchange step, Na ions in the vicinity of the glass surface (shallow region from the outermost surface to 20% of the plate thickness) and Li ions in the molten salt are ion-exchanged. In addition, Na ions in the vicinity of the glass surface (shallow region from the outermost surface to 20% of the plate thickness) and K ions in the molten salt are ion-exchanged. That is, in the second ion exchange step, while removing Na ions in the vicinity of the glass surface, K ions having a large ionic radius can be introduced. As a result, while maintaining a deep stress depth, the compressive stress value at the outermost surface can be increased.

[0079] In the first ion exchange step, the temperature of the molten salt is preferably 360 to 400 °C, and the ion exchange time is preferably 30 minutes to 6 hours. In the second ion exchange step, the temperature of the ion exchange solution is preferably 370 to 400 °C, and the ion exchange time is preferably 15 minutes to 3 hours.

[0080] In forming a non-monotonic stress profile, in the mixed molten salt of NaNO3 and KNO3 used in the first ion exchange step, the concentration of NaNO3 is preferably higher than the concentration of KNO3, and in the mixed molten salt of KNO3 and LiNO3 used in the second ion exchange step, the concentration of KNO3 is preferably higher than the concentration of LiNO3.

[0081] In the mixed molten salt of NaNO3 and KNO3 used in the first ion exchange step, the concentration of KNO3 is preferably 0 mass% or more, 0.5 mass% or more, 1 mass% or more, 5 mass% or more, 7 mass% or more, 10 mass% or more, 15 mass% or more, particularly 20 to 90 mass%. If the concentration of KNO3 is too high, there is a risk that the compressive stress value formed when Li ions contained in the glass and Na ions in the molten salt undergo ion exchange will decrease too much. On the other hand, if the concentration of KNO3 is too low, it may be difficult to measure the stress with a surface stress meter.

[0082] In the mixed molten salt of KNO3 and LiNO3 used in the second ion exchange step, the concentration of LiNO3 is preferably more than 0 to 5 mass%, more than 0 to 3 mass%, more than 0 to 2 mass%, particularly 0.1 to 1 mass%. If the concentration of LiNO3 is too low, it becomes difficult for Na ions near the glass surface to be released. On the other hand, if the concentration of LiNO3 is too high, there is a risk that the compressive stress value formed by the ion exchange of Na ions near the glass surface and K ions in the molten salt will decrease too much.

Examples

[0083] Hereinafter, the present invention will be described based on examples. Note that the following examples are merely illustrative. The present invention is not limited to the following examples at all.

[0084] Table 1 shows the glass compositions and glass properties of examples of the present invention (samples Nos. 1 to 8 and 12), and Table 2 shows the glass compositions and glass properties of comparative examples of the present invention (samples Nos. 9 to 11). In the table, "NA" means not measured, "(Li2O + Na2O + K2O) / Al2O3" means the molar ratio ([Li2O] + [Na2O] + [K2O]) / [Al2O3], and "(Si+P+B) / ((100Sn) × (Al+Li+Na+K+Mg+Ca+Sr+Ba+Zn))" means the molar ratio ([SiO2] + [B2O3] + [P2O5]) / ((100 × [SnO2]) × ([Al2O3] + [Li2O] + [Na2O] + [K2O] + [MgO] + [CaO] + [SrO] + [BaO] + [ZnO])).

[0085] [Table 1]

[0086] [Table 2]

[0087] Each sample in the table was prepared as follows. First, glass raw materials were mixed to obtain the glass composition shown in the table, and melted in a platinum pot at 1600°C for 21 hours. The resulting molten glass was then poured onto a carbon plate and formed into a flat plate. The plate was then cooled at 3°C / min through a temperature range between the annealing point and the strain point to obtain a glass plate (glass plate to be tempered). The surface of the resulting glass plate was optically polished to a thickness of 1.5 mm, and various properties were evaluated.

[0088] The density (ρ) is a value measured by the well-known Archimedes method.

[0089] Thermal expansion coefficient (α) at 30 to 380°C 30-380℃ ) is the average thermal expansion coefficient measured using a dilatometer.

[0090] High temperature viscosity 10 2.5The temperature in dPa·s (10 2.5 dPa·s) is the value measured by the platinum ball pulling-up method.

[0091] The softening point (Ts) is the value measured based on the method of ASTM C338.

[0092] The liquidus temperature (TL) is the highest temperature at which devitrification (devitrified particles) is observed inside the glass by microscopic observation after putting glass powder that passes through a standard sieve of 30 mesh (500 μm) and remains on a 50 mesh (300 μm) into a platinum boat and holding it in a temperature gradient furnace for 24 hours. The liquidus viscosity (logη at TL) is the value measured by the platinum ball pulling-up method for the viscosity at the liquidus temperature, and is expressed as logη after taking the logarithm.

[0093] For the acid resistance test, a glass sample mirror-polished on both sides to a size of 50×10×1.0 mm was used as the measurement sample. After thoroughly washing with a neutral detergent and pure water, it was immersed in a 5 mass% HCl aqueous solution heated to 80°C for 24 hours, and the mass loss per unit surface area (mg / cm 2 ) before and after immersion was calculated for evaluation.

[0094] For the alkali resistance test, a glass sample mirror-polished on both sides to a size of 50×10×1.0 mm was used as the measurement sample. After thoroughly washing with a neutral detergent and pure water, it was immersed in a 5 mass% NaOH aqueous solution heated to 80°C for 6 hours, and the mass loss per unit surface area (mg / cm 2 ) before and after immersion was calculated for evaluation.

[0095] The Young's modulus (E) was calculated by a method conforming to JIS R1602-1995 "Test Method for Elastic Modulus of Fine Ceramics".

[0096] Next, each glass plate was immersed in molten KNO3 at 430°C for 4 hours to carry out an ion exchange treatment, obtaining a tempered glass plate with a compressive stress layer on the surface. After cleaning the glass surface, the compressive stress value (CS) of the compressive stress layer on the outermost surface was determined from the number and spacing of interference fringes observed using a surface stress meter FSM-6000 (manufactured by Orihara Seisakusho Co., Ltd.). K ) and stress depth (DOL_ZERO K ) was calculated. Here, DOL_ZERO K is the depth at which the compressive stress value becomes zero. In calculating the stress characteristics, the refractive index of each sample was set to 1.51 and the optical elastic constant was set to 29.0 [(nm / cm) / MPa].

[0097] In addition, each glass plate was immersed in molten NaNO3 salt at 380°C for 1 hour to carry out an ion exchange treatment to obtain a tempered glass plate. After cleaning the glass surface, the compressive stress value (CS) of the outermost surface was determined from the phase difference distribution curve observed using a scattered light photoelastic stress meter SLP-1000 (manufactured by Orihara Seisakusho Co., Ltd.). Na ) and stress depth (DOL_ZERO Na ) was calculated. Here, DOL_ZERO Na is the depth at which the stress value becomes zero. In calculating the stress characteristics, the refractive index of each sample was set to 1.51 and the optical elastic constant was set to 29.0 [(nm / cm) / MPa].

[0098] Furthermore, each glass plate was crushed and classified to a size of 2 to 5.6 mm, and then heated to 1650°C. The molten glass was directly observed (High Temperature Observation; HTO). If no bubbles of 75 μm or more were observed, the clarity was evaluated as "Good", and if not, the clarity was evaluated as "Good".

[0099] As is clear from Table 1, samples No. 1 to No. 8 and No. 12 have a large molar ratio ([Li2O] + [Na2O] + [K2O]) / [Al2O3), so when they are ion-exchanged with KNO3 molten salt, the compressive stress value (CS K) is 1090 MPa or more, and when further ion-exchanged with NaNO3 molten salt, the compressive stress value of the compressive stress layer on the outermost surface (CS Na ) was over 279 MPa.

[0100] As is clear from Table 1, samples Nos. 1 to 8 and 12 had a molar ratio ([SiO] + [B2O3] + [P2O5]) / ((100 × [SnO2]) × ([Al2O3] + [Li2O] + [Na2O] + [K2O] + [MgO] + [CaO] + [SrO] + [BaO] + [ZnO])) of 0.40 or more, and therefore were evaluated as having good clarity.

[0101] On the other hand, as is clear from Table 2, in Samples Nos. 9 and 10, the molar ratio ([Li2O] + [Na2O] + [K2O]) / [Al2O3] was less than 0.86, and therefore the compressive stress value (CS K In addition, sample No. 11 was evaluated as poor in clarity because the molar ratio ([SiO2] + [B2O3] + [P2O5]) / ((100 × [SnO2]) × ([Al2O3] + [Li2O] + [Na2O] + [K2O] + [MgO] + [CaO] + [SrO] + [BaO] + [ZnO])) was less than 0.40. [Example]

[0102] First, glass raw materials were mixed to obtain the glass compositions of Samples No. 1 and No. 6 in Table 1, and melted in a platinum pot at 1600°C for 21 hours. The resulting molten glass was then poured onto a carbon plate and formed into a flat plate, which was then cooled at 3°C / min through a temperature range from the annealing point to the strain point to obtain a glass plate (glass plate to be tempered). The surface of the resulting glass plate was optically polished to a thickness of 0.7 mm.

[0103] The obtained strengthened glass plate was subjected to ion exchange treatment by immersing it in a NaNO3 molten salt at 380 °C (NaNO3 concentration: 100% by mass) for 3 hours, and then subjected to ion exchange treatment by immersing it in a mixed molten salt of KNO3 and LiNO3 at 380 °C (LiNO3 concentration: 2.5% by mass) for 75 minutes. Further, after washing the surface of the obtained strengthened glass plate, the stress profile of the strengthened glass plate was measured using a scattered light photoelastic stress meter SLP-1000 (manufactured by Orihara Seisakusho Co., Ltd.) and a surface stress meter FSM-6000 (manufactured by Orihara Seisakusho Co., Ltd.). As a result, in each case, a non-monotonic stress profile similar to that in Fig. 1, that is, a stress profile having a first peak, a second peak, a first bottom, and a second bottom was obtained.

Example

[0104] First, glass raw materials were prepared to have the glass compositions of Sample Nos. 6, 9, and 12 in Table 1, and melted at 1600 °C for 21 hours using a platinum pot. Subsequently, the obtained molten glass was poured onto a carbon plate and formed into a flat plate shape. Then, it was cooled at 3 °C / min in the temperature range between the strain point and the annealing point to obtain a glass plate (strengthened glass plate). The surface of the obtained glass plate was optically polished to a thickness of 0.8 mm.

[0105] The obtained strengthened glass plate was subjected to ion exchange treatment by immersing it in a mixed molten salt of KNO3 and NaNO3 at 380 °C (NaNO3 concentration: 60% by mass) for 3 hours, and then subjected to ion exchange treatment (Condition A) by immersing it in a mixed molten salt of KNO3 and LiNO3 at 380 °C (LiNO3 concentration: 1.0% by mass) for 30 minutes. Further, after washing the surface of the obtained strengthened glass plate, the stress profile of the strengthened glass plate was measured using a scattered light photoelastic stress meter SLP-1000 (manufactured by Orihara Seisakusho Co., Ltd.) and a surface stress meter FSM-6000 (manufactured by Orihara Seisakusho Co., Ltd.). As a result, in each case, the non-monotonic stress profile shown in Fig. 2 was obtained.

[0106] The resulting tempered glass sheet was subjected to an ion exchange treatment by immersing it in a mixed molten salt of KNO3 and NaNO3 (NaNO3 concentration 60 mass%) at 380°C for 3 hours, and then to an ion exchange treatment (condition B) by immersing it in a mixed molten salt of KNO3, NaNO3, and LiNO3 (NaNO3 concentration 4.0 mass%, LiNO3 concentration 1.0 mass%) at 380°C for 45 minutes. Furthermore, after cleaning the surface of the resulting tempered glass sheet, the stress profile of the tempered glass sheet was measured using a scattered light photoelastic stress meter SLP-1000 (manufactured by Orihara Corporation) and a surface stress meter FSM-6000 (manufactured by Orihara Corporation). In both cases, the non-monotonic stress profile shown in Figure 3 was obtained.

[0107] Table 3 shows the compressive stress value (CS) of the outermost surface of each sample, the stress depth (DOC), and the compressive stress value at a depth of 2.5 μm (CS 2.5 ), and the average compressive stress at a depth of 30 to 45 μm (CS 30‐45 ), which indicates

[0108] [Table 3]

[0109] As is clear from Figures 3 and 4 and Table 3, samples No. 6 and No. 12 showed CS in the stress profile after ion exchange under conditions A and B. 2.5 is 350MPa or more and CS 30‐45 On the other hand, sample No. 9 has a high bending strength and a high drop strength because the stress is 85 MPa or more. 30‐45 Since the strength is less than 85 MPa, the drop strength is considered to be low. [Industrial Applicability]

[0110] The tempered glass sheet of the present invention is suitable as a cover glass for touch panel displays such as mobile phones, digital cameras, and PDAs (portable terminals). Further, in addition to these applications, the tempered glass sheet of the present invention is also expected to be applied to applications that require high mechanical strength, such as window glass, substrates for magnetic disks, substrates for flat panel displays, substrates for flexible displays, cover glass for solar cells, cover glass for solid-state imaging devices, and cover glass for in-vehicle use.

Claims

1. In a tempered glass sheet having a compressive stress layer on the surface, as the glass composition, in mol%, SiO ２ 40 to 80%, Al ２ O ３ 16 to 25%, B ２ O ３ 0.1 to 10%, Li ２ O 3 to 15%, Na ２ O 1 to 21%, K ２ O 0 to 10%, MgO 0 to 10%, ZnO 0 to 10%, P ２ O ５ 0 to 15%, SnO ２ 0.001 to 0.30%, Cl 0.02 to 0.3% are contained, ([Li ２ O] + [Na ２ O] + [K ２ O]) / [Al ２ O ３ ≥ 0.86, and ([SiO ２ + [B ２ O ３ + [P ２ O ５ ) / ((100 × [SnO ２ ) × ([Al ２ O ３ + [Li ２ O] + [Na ２ O] + [K ２ (END]]O] + [MgO] + [CaO] + [SrO] + [BaO] + [ZnO])) ≥ 0.40, and the stress depth of the compressive stress layer is 50 to 200 μm, characterized by a tempered glass sheet.

2. B ２ O ３ The tempered glass sheet according to claim 1, characterized in that the content of is 0.1 to 3 mol%.

3. SnO ２ The strengthened glass sheet according to claim 1 or 2, characterized in that the content of ２ is 0.045 mol% or less.

4. The strengthened glass sheet according to any one of Claims 1 to 3, characterized in that the Cl content is 0.100 to 0.3 mol%.

5. In a tempered glass plate having a compressive stress layer on the surface, the glass composition contains, in mol%, SiO ２ 40-80%, Al ２ O ３ 16-25%, B ２ O ３ 0.1-10%, Li ２ O 3-15%, Na ２ O 1-21%, K ２ O 0-10%, MgO 0-10%, ZnO 0-10%, P ２ O ５ 0-15% SnO ２ 0.001 to 0.045%, Cl 0.02 to 0.3%, ([SiO ２ ]+[B ２ O ３ ]+[P ２ O ５ ]) / ((100×[SnO ２ ])×([Al ２ O ３ ] + [Li ２ O] + [Na ２ O] + [K ２ O] + [MgO] + [CaO] + [SrO] + [BaO] + [ZnO]))≧0.40, ([Li ２ O] + [Na ２ O] + [K ２ O]) / [Al ２ O ３ ]≧0.86, and the stress depth of the compressive stress layer is 50 to 200 μm.

6. In a tempered glass sheet having a compressive stress layer on its surface, in terms of mol%, the glass composition contains SiO ２ 40 to 80%, Al ２ O ３ 16 to 25%, B ２ O ３ 0.1 to 3%, Li ２ O 3 to 15%, Na ２ O 1 to 21%, K ２ O 0 to 10%, MgO 0 to 10%, ZnO 0 to 10%, P ２ O ５ 0 to 15%, SnO ２ 0.001 to 0.30%, Cl 0.02 to 0.3%, and ([Li ２ O] + [Na ２ O] + [K ２ O]) / [Al ２ O ３ ≥ 0.86, and ([SiO ２ + [B ２ O ３ + [P ２ O ５ ) / ((100 × [SnO ２ ) × ([Al ２ O ３ + [Li ２ O] + [Na ２ O] + [K ２ O] + [MgO] + [CaO] + [SrO] + [BaO] + [ZnO])) ≥ 0.40, and the stress depth of the compressive stress layer is 50 to 200 μm. A tempered glass sheet characterized by the above is provided.

7. P ２ O ５ The strengthened glass sheet according to any one of claims 1 to 6, characterized in that the content of

8. Fe ２ O ３ The strengthened glass sheet according to any one of claims 1 to 7, characterized in that the content of

9. TiO ２ The strengthened glass sheet according to any one of claims 1 to 8, characterized in that the content of ２ is 0.001 to 0.1 mol%.

10. The strengthened glass sheet according to any one of Claims 1 to 9, characterized in that the compressive stress value at the outermost surface of the compressive stress layer is 200 to 1200 MPa.

11. The strengthened glass sheet according to any one of Claims 1 to 10, characterized in that the stress depth of the compressive stress layer is 100 to 200 μm.

12. The strengthened glass sheet according to any one of Claims 1 to 11, characterized in that the compressive stress value at a depth of 2.5 μm is 350 MPa or more.

13. The strengthened glass sheet according to any one of Claims 1 to 12, characterized in that the average compressive stress value at a depth of 30 to 45 μm is 85 MPa or more.

14. High-temperature viscosity 10 ２．５ The tempered glass sheet according to any one of claims 1 to 13, characterized in that the temperature at dPa·s is less than 1650°C.

15. The strengthened glass sheet according to any one of Claims 1 to 14, characterized in that it has an overflow confluence surface at the central part in the plate thickness direction.

16. The strengthened glass sheet according to any one of Claims 1 to 15, characterized in that it is used as a cover glass for a touch panel display.

17. The strengthened glass sheet according to any one of Claims 1 to 16, characterized in that the stress profile in the thickness direction has at least a first peak, a second peak, a first bottom, and a second bottom.

18. As a glass composition, in mol%, SiO ２ 40 to 80%, Al ２ O ３ 16 to 25%, B ２ O ３ 0.1 to 10%, Li ２ O 3 to 15%, Na ２ O 1 to 21%, K ２ O 0 to 10%, MgO 0 to 10%, ZnO 0 to 10%, P ２ O ５ 0 to 15%, SnO ２ 0.001 to 0.30%, Cl 0.02 to 0.3% are contained, and ([Li ２ O] + [Na ２ O] + [K ２ O]) / [Al ２ O ３ ≥ 0.86, and (([SiO ２ + [B ２ O ３ + [P ２ O ５ ) / ((100 × [SnO ２ ) × ([Al ２ O ３ + [Li ２ O] + [Na ２ O] + [K ２ O] + [MgO] + [CaO] + [SrO] + [BaO] + [ZnO])) ≥ 0.40, a preparation step of preparing a tempered glass plate, and an ion exchange step of performing ion exchange treatment on the tempered glass plate a plurality of times to obtain a tempered glass plate having a compressive stress layer with a stress depth of 50 to 200 μm on the surface, and a method for manufacturing a tempered glass plate, characterized by comprising these steps.

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