Strengthened glass plate and glass plate for strengthening

Abstract

To create a strengthened glass plate and a glass plate for strengthening, each having satisfactory acid resistance and being capable of achieving both a low Young's modulus and a high compressive stress value on an outermost surface thereof.SOLUTION: A strengthened glass plate of the present invention is a strengthened glass plate having a compressive stress layer on a surface thereof, wherein the strengthened glass plate comprises as a glass composition, in terms of mol%, SiO2 of 50-75%, Al2O3 of 1-20%, B2O3 of 5-30%, Li2O of 0-15%, Na2O of 1-25%, K2O of 0-10%, and P2O5 of 0-15%, wherein the strengthened glass plate has a molar ratio [Al2O3] / [Na2O] of from 0.1 to 2.5, and satisfies the following relationship: [SiO2]-3×[Al2O3]-[B2O3]-2×[Li2O]-1.5×[Na2O]-[K2O]+1.2×[P2O5]≥-20%.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a strengthened glass plate and a strengthening glass plate, and particularly to a strengthened glass plate and a strengthening glass plate suitable for a cover glass such as a foldable display.

Background Art

[0002] In recent years, foldable displays that can be bent have appeared on the market, and in order to protect the display, the use of cover glass has been considered.

[0003] Generally, ion-exchanged strengthened glass is used for cover glass (see Patent Documents 1 and 2, and Non-Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Non-Patent Documents

[0005]

Non-Patent Document 1

Disclosure of the Invention

Problems to be Solved by the Invention

[0006] The cover glass of a foldable display is required to have a low Young's modulus and a high compressive stress value on the outermost surface. When the Young's modulus is low, the tensile stress generated at the bent portion of the cover glass can be reduced when the flexible display is bent. Also, when the compressive stress value on the outermost surface is high, it becomes easier to prevent damage caused by the tensile stress generated at the bent portion of the cover glass when the flexible display is bent. As a result, when both a low Young's modulus and a high compressive stress value on the outermost surface are achieved, the cover glass is less likely to be damaged when the flexible display is bent.

[0007] In addition, in the manufacturing process of a flexible display, there is an acid treatment process for the cover glass. If the acid resistance of the cover glass is low, the cover glass becomes cloudy and the visibility decreases.

[0008] The present invention has been made in view of the above circumstances, and its technical problem is to create a tempered glass plate and a glass plate for strengthening that have good acid resistance and can achieve both a low Young's modulus and a high compressive stress value on the outermost surface.

Means for Solving the Problem

[0009] As a result of various studies, the present inventors have found that the above technical problems can be solved by strictly regulating the glass composition, 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%, it contains 50 to 75% of SiO2, 1 to 20% of Al2O3, 5 to 30% of B2O3, 0 to 15% of Li2O, 1 to 25% of Na2O, 0 to 10% of K2O, and 0 to 15% of P2O5, the molar ratio [Al2O3] / [Na2O] is 0.1 to 2.5, and the relationship of [SiO2] - 3×[Al2O3] - [B2O3] - 2×[Li2O] - 1.5×[Na2O] - [K2O] + 1.2×[P2O5] ≧ -20% is satisfied. Here, [SiO2] represents the content (mol%) of SiO2, [Al2O3] represents the content (mol%) of Al2O3, [B2O3] represents the content (mol%) of B2O3, [Li2O] represents the content (mol%) of Li2O, [Na2O] represents the content (mol%) of Na2O, [K2O] represents the content (mol%) of K2O, and [P2O5] represents the content (mol%) of P2O5, respectively.

[0010] Further, in the tempered glass sheet of the present invention, as the glass composition, in mol%, it contains 50 to 75% of SiO2, 11.7 to 13.5% of Al2O3, 5 to 30% of B2O3, 0 to 15% of Li2O, 13 to 16% of Na2O, 0 to 10% of K2O, and 0 to 15% of P2O5, the molar ratio [Al2O3] / [Na2O] is 0.8 to 1.2, and it is preferable to satisfy the relationship of [SiO2] - 3×[Al2O3] - [B2O3] - 2×[Li2O] - 1.5×[Na2O] - [K2O] + 1.2×[P2O5] ≧ -2.5%.

[0011] Further, in the tempered glass sheet of the present invention, as the glass composition, in mol%, it contains 62 to 67% of SiO2, 11.7 to 13.5% of Al2O3, 8 to 10% of B2O3, 0 to 15% of Li2O, 13 to 16% of Na2O, 0 to 10% of K2O, and 0 to 15% of P2O5, the molar ratio [Al2O3] / [Na2O] is 0.8 to 1.2, and it preferably satisfies the relationship of [SiO2] - 3×[Al2O3] - [B2O3] - 2×[Li2O] - 1.5×[Na2O] - [K2O] + 1.2×[P2O5] ≧ -2.5%.

[0012] Further, in the tempered glass sheet of the present invention, the content of P2O5 is preferably 0.1 to 15 mol%.

[0013] Further, in the tempered glass sheet of the present invention, the content of Li2O is preferably 0.1 to 15 mol%.

[0014] Further, in the tempered glass sheet of the present invention, the softening point is preferably 950 °C or lower. Here, the "softening point" refers to the value measured based on the method of ASTM C338.

[0015] Further, in the tempered glass sheet of the present invention, the temperature at a high-temperature viscosity of 10 2.5 dPa·s is preferably less than 1650 °C. Here, 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.

[0016] Further, in the tempered glass sheet of the present invention, the sheet thickness is preferably 100 μm or less.

[0017] Further, in the tempered glass sheet of the present invention, the size is preferably □100 mm or more.

[0018] Further, in the tempered glass sheet of the present invention, the compressive stress value on the outermost surface of the compressive stress layer is preferably 200 to 1100 MPa.

[0019] Further, in the tempered glass sheet of the present invention, the stress depth of the compressive stress layer is preferably 10 to 15% of the sheet thickness.

[0020] In addition, in the tempered glass sheet of the present invention, it preferably has an overflow confluence surface at the central portion in the plate thickness direction, that is, it is preferably formed by the overflow down-draw method.

[0021] In addition, the tempered glass sheet of the present invention is preferably used as a cover glass for a flexible display.

[0022] The tempered glass sheet of the present invention contains, as a glass composition, in mol%, 50 to 75% of SiO2, 1 to 20% of Al2O3, 5 to 30% of B2O3, 0 to 15% of Li2O, 1 to 25% of Na2O, 0 to 10% of K2O, and 0 to 15% of P2O5, and the molar ratio [Al2O3] / [Na2O] is 0.1 to 2.5, and satisfies the relationship of [SiO2] - 3×[Al2O3] - [B2O3] - 2×[Li2O] - 1.5×[Na2O] - [K2O] + 1.2×[P2O5] ≧ -20%.

[0023] The tempered glass sheet of the present invention contains, as a glass composition, in mol%, 50 to 75% of SiO2, 1 to 20% of Al2O3, 5 to 30% of B2O3, 1 to 25% of Na2O, 0 to 10% of K2O, and 0 to 15% of P2O5, and the molar ratio [Al2O3] / [Na2O] is 0.1 to 2.5, satisfies the relationship of [SiO2] - 3×[Al2O3] - [B2O3] - 2×[Li2O] - 1.5×[Na2O] - [K2O] + 1.2×[P2O5] ≧ -20%, and is characterized in that the plate thickness is less than 100 μm.

Embodiments for Carrying Out the Invention

[0024] The tempered glass sheet (tempering glass sheet) of the present invention contains, as a glass composition, in mol%, 50 to 75% of SiO2, 1 to 20% of Al2O3, 5 to 30% of B2O3, 0 to 15% of Li2O, 1 to 25% of Na2O, 0 to 10% of K2O, and 0 to 15% of P2O5, and the molar ratio [Al2O3] / [Na2O] is 0.1 to 2.5, and it satisfies the relationship of [SiO2] - 3×[Al2O3] - [B2O3] - 2×[Li2O] - 1.5×[Na2O] - [K2O] + 1.2×[P2O5] ≧ -20%. In the tempered glass sheet (tempering glass sheet) of the present invention, 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.

[0025] SiO2 is a component that forms the glass network. If the content of SiO2 is too small, it becomes difficult to vitrify and the acid resistance tends to decrease. Therefore, a suitable lower limit range of SiO2 is 50% or more, 52% or more, 54% or more, 55% or more, 57% or more, 59% or more, 60% or more, 61% or more, 62% or more, 63% or more, particularly 64% or more. On the other hand, if the content of SiO2 is too large, the meltability and formability tend to decrease, and the thermal expansion coefficient becomes too low, making it difficult to match the thermal expansion coefficient of the surrounding materials. Therefore, a suitable upper limit range of SiO2 is 75% or less, 73% or less, 71% or less, 70% or less, 69% or less, 68% or less, 67% or less, 66% or less, particularly 65% or less.

[0026] Al2O3 is a component that increases the ion exchange rate. The content of Al2O3 is 10 - 30%. If the content of Al2O3 is too low, the ion exchange rate tends to decrease. Therefore, the preferable lower limit range of Al2O3 is 1% or more, 3% or more, 4% or more, 5% or more, 6% or more, 7% or more, 8% or more, 9% or more, 10% or more, 11% or more, particularly 11.7% or more. On the other hand, if the content of Al2O3 is too high, devitrified crystals tend to precipitate in the glass, making it difficult to form into plates by the overflow down-draw method or the like. In particular, when using alumina refractories as the formed body refractories and forming into plates by the overflow down-draw method, devitrified crystals of spinel tend to precipitate at the interface with the alumina refractories. Also, the acid resistance decreases, making it difficult to apply in the acid treatment process. Furthermore, the Young's modulus becomes too high. Therefore, the preferable upper limit range of Al2O3 is 20% or less, 19% or less, 18% or less, 17% or less, 16% or less, 15% or less, 13.5% or less, 13% or less, particularly 12% or less.

[0027] B2O3 is a component that decreases the Young's modulus, high-temperature viscosity, and density, and increases the devitrification resistance. However, if the content of B2O3 is too high, the ion exchange rate (particularly the stress depth) tends to decrease. Also, due to ion exchange, coloring of the glass surface called "burn" may occur, and the acid resistance and water resistance tend to decrease. Therefore, the preferable lower limit range of B2O3 is 5% or more, 6% or more, 7% or more, 8% or more, 9% or more, particularly 10% or more. Also, the preferable upper limit range of B2O3 is 30% or less, 25% or less, 22% or less, 20% or less, 18% or less, 16% or less, 13% or less, 12% or less, 11% or less, 10.5% or less, particularly 10% or less.

[0028] Li2O is a component effective for ion exchange, particularly for obtaining a deep stress depth, and is also a component that reduces the high-temperature viscosity and enhances the meltability and formability. On the other hand, Li2O is a component that elutes during the ion exchange process and deteriorates the ion exchange solution. Furthermore, it is a component that increases the Young's modulus. Therefore, the preferred content of Li2O is 0 to 15%, 0 to 10%, 0 to 7%, 0 to 5%, less than 0 to 3%, 0 to 2%, particularly 0 to 1%. When adding Li2O, the preferred lower limit range of Li2O is 0.01% or more, 0.1% or more, 0.5% or more, particularly 1% or more.

[0029] Na2O is an ion exchange component and is also a component that reduces the high-temperature viscosity and enhances the meltability and formability. In addition, Na2O is also a component that improves the devitrification resistance and the reaction devitrification resistance with the shaped refractory, particularly the alumina refractory. If the content of Na2O is too low, the meltability may decrease, the coefficient of thermal expansion may decrease too much, and the ion exchange rate may easily decrease. Therefore, the preferred lower limit range of Na2O is 1% or more, 5% or more, 6% or more, 7% or more, 8% or more, 9% or more, 10% or more, 11% or more, 12% or more, particularly 13% or more. On the other hand, if the content of Na2O is too high, the Young's modulus may increase, the acid resistance may decrease, the component balance of the glass composition may be lacking, and instead the devitrification resistance may decrease. Therefore, the preferred upper limit range of Na2O is 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, particularly 15% or less.

[0030] K2O is a component that reduces the high-temperature viscosity and enhances the meltability and formability. Furthermore, it is also a component that improves the devitrification resistance. However, if the content of K2O is too high, the acid resistance may decrease, the component balance of the glass composition may be lacking, and instead the devitrification resistance may tend to decrease. Therefore, the preferred upper limit range is 10% or less, 8% or less, 6% or less, 4% or less, 3% or less, 2% or less, 1% or less, 0.1% or less, particularly less than 0.1%.

[0031] P2O5 is a component that increases the ion exchange rate while maintaining the compressive stress value. It is also a component that decreases the Young's modulus. Furthermore, it is a component that decreases the high-temperature viscosity and enhances the meltability and formability. However, if the content of P2O5 is too high, phase separation-induced cloudiness may occur in the glass, and the acid resistance tends to decrease. Therefore, the preferred upper limit range of P2O5 is 15% or less, 12% or less, 10% or less, 8% or less, 6% or less, 5% or less, 4% or less, 3% or less, 2% or less, 1% or less, 0.5% or less, particularly 0.1% or less. When adding P2O5, the preferred lower limit range of P2O5 is 0.1% or more, 0.5% or more, 1% or more, 2% or more, particularly 3% or more.

[0032] The molar ratio [Al2O3] / [Na2O] is 0.1 - 2.5, and [SiO2] - 3×[Al2O3] - [B2O3] - 2×[Li2O] - 1.5×[Na2O] - [K2O] + 1.2×[P2O5] is preferably -20% or more, -15% or more, -10% or more, -5% or more, -2.5% or more, -1% or more, particularly 0 - 35%. When the molar ratio [Al2O3] / [Na2O] is 0.1 - 2.5 and [SiO2] - 3×[Al2O3] - [B2O3] - 2×[Li2O] - 1.5×[Na2O] - [K2O] + 1.2×[P2O5] is too large, the acid resistance decreases, making it difficult to apply in the acid treatment process.

[0033] The molar ratio [Al2O3] / [Na2O] is preferably 0.1 - 2.5, 0.2 - 2.2, 0.3 - 1.8, 0.4 - 1.5, 0.5 - 1.2, 0.6 - 1.1, 0.7 - 1.0, particularly 0.8 - 0.9. If the molar ratio [Al2O3] / [Na2O] is too large, the Young's modulus becomes too high. Also, the devitrification resistance tends to decrease. On the other hand, if the molar ratio [Al2O3] / [Na2O] is too small, the Young's modulus becomes too high. Also, the compressive stress value on the outermost surface tends to decrease.

[0034] In addition to the above components, for example, the following components may be added.

[0035] MgO is a component that reduces the high-temperature viscosity, enhances the meltability and formability, and also increases the acid resistance. However, if the content of MgO is too high, the Young's modulus tends to increase, the ion exchange rate decreases, and the glass tends to devitrify. In particular, when using alumina refractories as the shaped refractory and forming into plates by the overflow down-draw method, devitrified crystals of spinel tend to precipitate at the interface with the alumina refractory. Therefore, the preferred upper limit range of MgO is 6% or less, 4.5% or less, 3% or less, 2% or less, 1% or less, especially 0.1% or less.

[0036] Compared with other components, CaO is a component that has a great effect of reducing the high-temperature viscosity, enhancing the meltability and formability, and increasing the strain point without accompanying a decrease in devitrification resistance. However, if the content of CaO is too high, the Young's modulus tends to increase, the ion exchange rate decreases, and the ion exchange solution tends to deteriorate. Therefore, the preferred content of CaO is 0 - 6%, 0 - 5%, 0 - 4%, 0 - 3.5%, 0 - 3%, 0 - 2%, 0 - 1%, especially 0 - 0.5%.

[0037] SrO and BaO are components that reduce the high-temperature viscosity, enhance the meltability and formability, and increase the strain point. However, if their contents are too high, the Young's modulus tends to increase, the ion exchange rate decreases, the density and thermal expansion coefficient increase, and the glass tends to devitrify. Therefore, the preferred content of SrO and BaO is 0 - 2%, 0 - 1.5%, 0 - 1%, 0 - 0.5%, 0 - 0.1%, especially less than 0 - 0.1% respectively.

[0038] The total content of CaO, SrO, and BaO is preferably 0 - 5%, 0 - 2.5%, 0 - 2%, 0 - 1.5%, 0 - 1%, 0 - 0.5%, 0 - 0.1%, especially less than 0 - 0.1%. If the total content of CaO, SrO, and BaO is too high, the Young's modulus tends to increase easily, and the ion exchange rate tends to decrease easily.

[0039] ZnO is a component that increases the ion exchange rate and has a particularly large effect on increasing the compressive stress value. It is also a component that reduces the high-temperature viscosity without reducing the low-temperature viscosity. However, if the ZnO content is too high, the glass tends to phase-separate, the devitrification resistance decreases, the density increases, and the stress depth becomes small. Therefore, the preferred ZnO content is 0 to 6%, 0 to 3%, particularly 0 to 1%.

[0040] TiO2 is a component that increases the ion exchange rate and also reduces the high-temperature viscosity. However, if its content is too high, the glass will be colored and prone to devitrification. Therefore, the TiO2 content is preferably 0 to 4.5%, less than 0 to 1%, 0 to 0.5%, particularly 0 to 0.3%.

[0041] ZrO2 is a component that significantly increases the ion exchange rate and also increases the viscosity and strain point near the liquid-phase viscosity. However, if its content is too high, there is a risk that the devitrification resistance will be significantly reduced, and there is also a risk that the density will become too high. Therefore, the preferred ZrO2 content is 0 to 5%, 0 to 4%, 0 to 3%, 0 to 2%, particularly less than 0 to 1%.

[0042] As a clarifying agent, it is preferable to introduce one or more selected from the group of SnO2, SO3, Cl, CeO2 (preferably the group of SnO2, SO3, Cl). The preferred content of SnO2 + SO3 + Cl is 0.01 to 3%, 0.05 to 3%, 0.1 to 3%, particularly 0.2 to 3%. Note that "SnO2 + SO3 + Cl" is the total amount of SnO2, SO3, and Cl.

[0043] Fe2O3 is an impurity component from the raw materials, but it is a component that absorbs ultraviolet light that has an adverse effect on the human eye. However, if the Fe2O3 content is too high, the coloring of the glass will be enhanced. Therefore, the preferred Fe2O3 content is less than 1000 ppm (0.1%), less than 800 ppm, less than 600 ppm, less than 400 ppm, less than 300 ppm, less than 250 ppm, less than 200 ppm, less than 150 ppm, particularly less than 100 ppm.

[0044] Rare earth oxides such as Nd2O3 and La2O3 are components that increase the Young's modulus. However, the cost of the raw materials themselves is high, and when added in large amounts, the devitrification resistance tends to decrease. Therefore, the suitable content of rare earth oxides is 3% or less, 2% or less, 1% or less, 0.5% or less, and particularly 0.1% or less.

[0045] From an environmental consideration, it is preferable that the glass composition does not substantially contain As2O3, Sb2O3, PbO, F, and Bi2O3. "Does not substantially contain ~" means that although no explicit components are actively added as glass components, the inclusion of impurity levels is tolerated, specifically referring to the case where the content of the explicit components is less than 0.05%.

[0046] The tempered glass sheet (tempering glass sheet) of the present invention preferably has, for example, the following characteristics.

[0047] The softening point is preferably 950 °C or less, 900 °C or less, 880 °C or less, 860 °C or less, and particularly 700 to 850 °C. The lower the softening point, the better the hot workability, and the burden on glass manufacturing equipment such as hot work equipment is reduced. Therefore, the lower the softening point, the easier it is to reduce the manufacturing cost of tempered glass.

[0048] The temperature at 10 2.5 dPa·s is preferably less than 1650 °C, 1630 °C or less, 1620 °C or less, and particularly 1610 °C or less. The lower the temperature at 10 2.5 dPa·s, the more possible low-temperature melting becomes, the burden on glass manufacturing equipment such as melting furnaces is reduced, and the bubble quality is easily improved. Therefore, the lower the temperature at 10 2.5 dPa·s, the easier it is to reduce the manufacturing cost of tempered glass.

[0049] The Young's modulus is preferably 70 GPa or less, 67 GPa or less, 65 GPa or less, 64 GPa or less, and particularly 50 to 63 GPa. If the Young's modulus is too high, when the flexible display is bent, the tensile stress generated at the bent portion of the cover glass becomes large.

[0050] When immersed in a 5% by mass HCl aqueous solution heated to 80°C for 24 hours, the mass reduction per unit surface area of the glass is preferably 30 mg / cm 2 or less, preferably 25 mg / cm 2 or less, preferably 20 mg / cm 2 or less, preferably 15 mg / cm 2 or less, particularly preferably 10 mg / cm 2 or less. If the above mass reduction is too large, the glass is likely to become cloudy in the acid treatment step.

[0051] The liquid-phase viscosity is preferably 4.0 dPa·s or more, 4.3 dPa·s or more, 4.5 dPa·s or more, 4.8 dPa·s or more, 5.1 dPa·s or more, 5.3 dPa·s or more, particularly preferably 5.5 dPa·s or more in terms of Logρ. If the liquid-phase viscosity is too low, the devitrification resistance decreases, making it difficult to produce a strengthened glass plate, particularly a strengthened glass plate with a small plate thickness, by the overflow down-draw method or the like.

[0052] The strengthened glass plate of the present invention has a compressive stress layer on the surface. The compressive stress value at the outermost surface is preferably 200 MPa or more, 300 MPa or more, 400 MPa or more, 500 MPa or more, particularly preferably 600 MPa or more. The larger the compressive stress value at the outermost surface, the easier it is to prevent breakage caused by the tensile stress generated at the bent portion of the cover glass when the flexible display is bent. On the other hand, if an extremely large compressive stress is formed on the surface, the tensile stress inherent in the strengthened glass plate becomes extremely high, and there is a risk that the dimensional change before and after the ion exchange treatment becomes large. Therefore, the compressive stress value at the outermost surface is preferably 1300 MPa or less, 1100 MPa or less, 900 MPa or less, particularly preferably 800 MPa or less.

[0053] The stress depth is preferably 1 μm or more, 3 μm or more, 5 μm or more, 7 μm or more, 8 μm or more, 9 μm or more, particularly 10 μm or more, and is 8 to 17%, 10 to 15%, 11 to 14%, particularly 12 to 13% of the plate thickness. The greater the stress depth, the less likely the tempered glass is to crack even if it is deeply scratched, and the smaller the variation in mechanical strength. On the other hand, the greater the stress depth, the greater the dimensional change before and after the ion exchange treatment tends to be. Therefore, the stress depth is preferably 20 μm or less, 15 μm or less, particularly 10 μm or less.

[0054] The internal tensile stress value is preferably 250 MPa or less, 220 MPa or less, 200 MPa or less, 180 MPa or less, particularly 170 MPa or less. If the internal tensile stress value is too high, the tempered glass plate is likely to self-destruct due to physical impact or the like. On the other hand, if the internal tensile stress value is too low, it becomes difficult to ensure the mechanical strength of the tempered glass plate. The internal tensile stress value is preferably 60 MPa or more, 80 MPa or more, 100 MPa or more, 125 MPa or more, 140 MPa or more, particularly 150 MPa or more. The internal tensile stress can be calculated by the following formula (1).

[0055] [Formula 1] Internal tensile stress value = (compressive stress value at the outermost surface × stress depth) / (plate thickness - 2 × stress depth)

[0056] In the tempered glass plate (tempering glass plate) of the present invention, the plate thickness is preferably 200 μm or less, 150 μm or less, 100 μm or less, 80 μm or less, 60 μm or less, 1 to 50 μm, 5 to 40 μm, particularly 10 to 30 μm. The smaller the plate thickness, the better the flexibility of the cover glass, and the easier it is to apply to a flexible display. Also, the allowable curvature radius when the cover glass is bent becomes smaller. Furthermore, it becomes easier to wind it into a roll shape.

[0057] The size is preferably □100 mm or more, □120 mm or more, □150 mm or more, particularly □200 to 2000 mm. As the size increases, it becomes easier to apply to a large flexible display.

[0058] The toughened glass sheet of the present invention contains, as a glass composition, in mol%, 50 to 75% of SiO₂, 1 to 20% of Al₂O₃, 5 to 30% of B₂O₃, 1 to 25% of Na₂O, 0 to 10% of K₂O, and 0 to 15% of P₂O₅, has a molar ratio [Al₂O₃] / [Na₂O] of 0.1 to 2.5, and satisfies the relationship of [SiO₂] - 3×[Al₂O₃] - [B₂O₃] - 2×[Li₂O] - 1.5×[Na₂O] - [K₂O] + 1.2×[P₂O₅] ≥ -20%. Further, the toughened glass sheet of the present invention contains, as a glass composition, in mol%, 50 to 75% of SiO₂, 1 to 20% of Al₂O₃, 5 to 30% of B₂O₃, 1 to 25% of Na₂O, 0 to 10% of K₂O, and 0 to 15% of P₂O₅, has a molar ratio [Al₂O₃] / [Na₂O] of 0.1 to 2.5, satisfies the relationship of [SiO₂] - 3×[Al₂O₃] - [B₂O₃] - 2×[Li₂O] - 1.5×[Na₂O] - [K₂O] + 1.2×[P₂O₅] ≥ -20%, and is characterized by having a plate thickness of less than 100 μm. The technical features of the toughened glass sheet of the present invention are common to those of the toughened glass sheet of the present invention, and detailed description thereof is omitted here.

[0059] The toughened glass sheet of the present invention can be produced as follows. First, glass raw materials prepared to have a desired glass composition are charged into a continuous melting furnace, heated and melted at 1500 to 1700 °C, clarified, and then the molten glass is supplied to a forming device and formed into a plate shape and cooled. After being formed into a plate shape, a method of cutting to a predetermined dimension can employ a well-known method, but for the end face to be smooth, it is preferable to perform cutting by laser cutting.

[0060] 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. The cooling rate is preferably 10 °C / min or more, 40 °C / min or more, 60 °C / min or more, particularly 100 °C / min or more, and preferably less than 1000 °C / min, 800 °C / min or less, particularly less than 500 °C / min. If the cooling rate is too slow, it becomes difficult to reduce the plate thickness. On the other hand, if the cooling rate is too fast, the glass structure becomes coarse and the hardness of the glass tends to decrease.

[0061] As a method of forming molten glass into a plate shape, it is preferable to adopt the overflow down-draw method. The overflow down-draw method is a method capable of producing a large amount of high-quality glass plates and easily producing thin glass plates. Furthermore, in the overflow down-draw method, alumina or zirconia is used as the forming refractory, but the reinforcing glass plate of the present invention has good compatibility with alumina, zirconia, especially alumina, so it is difficult to react with these formed bodies to generate bubbles, bumps, etc.

[0062] In addition to the overflow down-draw method, various forming methods can be adopted. For example, forming methods such as the float method, the down-draw method (slot down-draw method, lid draw method, etc.), the roll-out method, and the press method can be adopted.

[0063] The reinforced glass plate of the present invention is produced by subjecting the reinforcing glass plate to ion exchange treatment. The conditions of the ion exchange treatment are not particularly limited, and optimal conditions may be selected in consideration of the viscosity characteristics of the glass, the use, the thickness, the internal tensile stress, the dimensional change, etc. In particular, when K ions in the KNO3 molten salt are ion-exchanged with the Na component in the glass, a compressive stress layer on the surface can be efficiently formed.

[0064] The number of times of the ion exchange treatment is not particularly limited, and it may be carried out only once or a plurality of times. If the number of times of the ion exchange treatment is one, the cost of the cover glass can be reduced. When the ion exchange treatment is carried out a plurality of times, the number of times of the ion exchange treatment is preferably two. In this way, while increasing the stress depth, the total amount of tensile stress accumulated inside the glass can be reduced.

Examples

[0065] 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.

[0066] Tables 1 to 8 show Examples (Sample Nos. 1 to 76) and Comparative Examples (Sample Nos. 77 and 78) of the present invention. In the table, the acid resistance index is [SiO2] - 3×[Al2O3] - [B2O3] - 2×[Li2O] - 1.5×[Na2O] - [K2O] + 1.2×[P2O5]. Also, N.A. indicates unmeasured.

[0067] Each sample in the table was prepared as follows. First, glass raw materials were formulated to have the glass composition in the table and melted at 1580°C for 8 hours using a platinum pot. Then, the obtained molten glass was poured onto a carbon plate, formed into a flat plate shape, and gradually cooled. Various properties of the obtained strengthened glass plate were evaluated. The results are shown in Tables 1 to 8.

[0068] [Table 1]

[0069] [Table 2]

[0070] [Table 3]

[0071] [Table 4]

[0072] [Table 5]

[0073] [Table 6]

[0074] [Table 7]

[0075]

Table 8

[0076] The Young's modulus refers to the value measured by the well-known resonance method.

[0077] The strain point Ps and the slow-cooling point Ta refer to the values measured by the well-known fiber elongation method. The softening point Ts refers to the value measured by the method of ASTM C338.

[0078] High-temperature viscosity 10 2.5 The temperature at 10 dPa·s refers to the value measured by the platinum ball pulling-up method.

[0079] The liquid-phase viscosity 1ogη at TL is the value obtained by measuring the viscosity of the glass at the liquid-phase temperature using the platinum ball pulling-up method. The liquid-phase temperature is the temperature at which crystals precipitate after putting glass powder that passes through a standard sieve of 30 mesh (500 μm) and remains on a 50-mesh (300 μm) sieve into a platinum boat and holding it in a temperature-gradient furnace for 24 hours.

[0080] For the acid resistance test, as the measurement sample, a sample with both sides mirror-polished to dimensions of 50 mm × 10 mm × 1.0 mm thickness is used. After thoroughly washing with a neutral detergent and pure water, it is immersed in a 5 mass% HCl aqueous solution heated to 80°C for 24 hours, and the mass reduction per unit surface area (mg / cm 2 ) before and after immersion is calculated for evaluation.

[0081] Next, both surfaces of each sample were optically polished to a plate thickness of 1.5 mm, and then ion exchange treatment was performed by immersing them in a KNO₃ molten salt at 430 °C for 4 hours. After the ion exchange treatment, the surfaces of the samples were washed. Subsequently, the surface compression stress value and stress depth of the outermost surface were calculated from the number and interval of interference fringes observed using a surface stress meter (FSM-6000 manufactured by Orihara Seisakusho). In the calculation, the refractive index of each sample was set to 1.51 and the photoelastic constant was set to 37.2 [(nm / cm) / MPa]. Although the glass composition in the surface layer of the glass was microscopically different before and after the ion exchange treatment, the glass composition was substantially the same when viewed as a whole glass.

[0082] As is clear from the table, Samples No. 1 to 76 had a low Young's modulus and high acid resistance. On the other hand, Sample No. 77 had a large Al₂O₃ content, a large molar ratio of Al₂O₃ / Na₂O, and a small acid resistance index, so it had a high Young's modulus, low acid resistance, and low liquid-phase viscosity. Sample No. 78 had a small molar ratio of Al₂O₃ / Na₂O, so it had a high Young's modulus and a low compression stress value.

Example

[0083] A glass batch having the glass composition of Sample No. 41 described in the table was melted in a test melting furnace to obtain molten glass, and then a reinforced glass plate with a thickness of 50 μm was formed by the overflow down-draw method. When forming the reinforced glass plate, the thickness of the reinforced glass plate was adjusted by appropriately adjusting the speed of the pulling roller, the speed of the cooling roller, the temperature distribution of the heating device, the temperature of the molten glass, the flow rate of the molten glass, the plate drawing speed, the rotation speed of the stirring stirrer, etc. Next, after cutting the obtained reinforced glass plate into a predetermined size, ion exchange treatment was performed by immersing it in a KNO₃ molten salt at 430 °C for 4 hours or in a KNO₃ molten salt at 390 °C for 2.5 hours to obtain reinforced glass plates respectively.

Example

[0084] The glass batch with the glass composition of Sample No. 41 described in the table was melted in a test melting furnace to obtain molten glass respectively. After that, a toughening glass plate with a thickness of 100 μm was formed by the overflow down-draw method. When forming the toughening glass plate, the thickness of the toughening glass plate was adjusted by appropriately adjusting the speed of the pulling roller, the speed of the cooling roller, the temperature distribution of the heating device, the temperature of the molten glass, the flow rate of the molten glass, the plate drawing speed, the rotation speed of the stirring stirrer, etc. Next, after cutting the obtained toughening glass plate into a predetermined size, ion exchange treatment was carried out by immersing it in a KNO₃ molten salt at 430 °C for 4 hours or in a KNO₃ molten salt at 390 °C for 2.5 hours to obtain toughened glass plates respectively.

Example

[0085] The glass batch with the glass composition of Sample No. 41 described in the table was melted in a test melting furnace to obtain molten glass respectively. After that, a toughening glass plate with a thickness of 30 μm was formed by the overflow down-draw method. When forming the toughening glass plate, the thickness of the toughening glass plate was adjusted by appropriately adjusting the speed of the pulling roller, the speed of the cooling roller, the temperature distribution of the heating device, the temperature of the molten glass, the flow rate of the molten glass, the plate drawing speed, the rotation speed of the stirring stirrer, etc. Next, after cutting the obtained toughening glass plate into a predetermined size, ion exchange treatment was carried out by immersing it in a KNO₃ molten salt at 430 °C for 4 hours or in a KNO₃ molten salt at 390 °C for 2.5 hours to obtain toughened glass plates respectively.

Example

[0086] Glass raw materials were prepared to have the glass composition of Sample No. 41 described in the table, and melted at 1580 °C for 8 hours using a platinum pot. Then, the obtained molten glass was poured onto a carbon plate, formed into a flat plate shape, and gradually cooled. After obtaining a plate-shaped glass with a thickness of 0.5 mm through grinding and polishing from the obtained flat plate-shaped glass, a strengthened glass plate with a thickness of 75 μm was obtained through slimming by an etching process using hydrofluoric acid. Next, after cutting the obtained strengthened glass plate into a predetermined size, ion exchange treatment was performed by immersing it in a KNO3 molten salt at 390 °C for two and a half hours to obtain strengthened glass plates respectively. The compressive stress value was 763 MPa and the compressive stress layer depth was 15.6 μm. When a strength test was conducted by a two-point bending test, it broke at a bending radius R of 2.3 mm. In the two-point bending test, a sample with a size of 20 × 130 mm was used as the measurement sample, and the bending radius R was decreased until it was bent and broken in the long axis direction. The measurement results for 15 samples were recorded, and their average value was used as the evaluation result.

Example

[0087] Glass raw materials were prepared to have the glass composition of Sample No. 76 described in the table, and melted at 1580 °C for 8 hours using a platinum pot. Then, the obtained molten glass was poured onto a carbon plate, formed into a flat plate shape, and gradually cooled. After obtaining a plate-shaped glass with a thickness of 0.5 mm through grinding and polishing from the obtained flat plate-shaped glass, a strengthened glass plate with a thickness of 55 μm was obtained through slimming by an etching process using hydrofluoric acid. Next, after cutting the obtained strengthened glass plate into a predetermined size, ion exchange treatment was performed by immersing it in a KNO3 molten salt at 390 °C for 15 minutes to obtain strengthened glass plates respectively. The compressive stress value was 832 MPa and the compressive stress layer depth was 10.3 μm. When a strength test was conducted by a two-point bending test, it broke at a bending radius R of 1.8 mm. In the two-point bending test, a sample with a size of 20 × 130 mm was used as the measurement sample, and the bending radius R was decreased until it was bent and broken in the long axis direction. The measurement results for 15 samples were recorded, and their average value was used as the evaluation result.

Industrial Applicability

[0088] The tempered glass sheet and the glass sheet for tempering of the present invention are suitable for cover glass such as foldable displays, but are also suitable as cover glass for mobile phones, digital cameras, PDAs, etc., or as glass substrates for touch panel displays, etc.

Claims

Claim 1 In a toughened glass sheet having a compressive stress layer on the surface, as the glass composition, in mol%, SiO ２ 50 to 75%, Al ２ O ３ 1 to 20%, B ２ O ３ 5 to 30%, Li ２ O 0 to 15%, Na ２ O 1 to 25%, K ２ O 0 to 10%, P ２ O ５ 0 to 15% is contained, and the molar ratio [Al ２ O ３ / [Na ２ O] is 0.1 to 2.5, and [SiO ２ - 3×[Al ２ O ３ - [B ２ O ３ - 2×[Li ２ O] - 1.5×[Na ２ O] - [K ２ O] + 1.2×[P ２ O ５ ≧ -20% is satisfied. A toughened glass sheet characterized by this. Claim 2 In a tempered glass sheet having a compressive stress layer on the surface, as the glass composition, in mol%, SiO ２ 50 to 75%, Al ２ O ３ 11.7 to 13.5%, B ２ O ３ 5 to 30%, Li ２ O 0 to 15%, Na ２ O 13 to 16%, K ２ O 0 to 10%, P ２ O ５ 0 to 15% is contained, and the molar ratio [Al ２ O ３ / [Na ２ O] is 0.8 to 1.2, and [SiO ２ -3×[Al ２ O ３ -[B ２ O ３ -2×[Li ２ O]-1.5×[Na ２ O]-[K ２ O]+1.2×[P ２ O ５ ≧ -2.5% is satisfied, and the tempered glass sheet according to claim 1 is characterized in that. Claim 3 In a tempered glass sheet having a compressive stress layer on the surface, as the glass composition, in mol%, SiO ２ 62 to 67%, Al ２ O ３ 11.7 to 13.5%, B ２ O ３ 8 to 10%, Li ２ O 0 to 15%, Na ２ O 13 to 16%, K ２ O 0 to 10%, P ２ O ５ 0 to 15% is contained, the molar ratio [Al ２ O ３ / [Na ２ O] is 0.8 to 1.2, and [SiO ２ - 3×[Al ２ O ３ - [B ２ O ３ - 2×[Li ２ O] - 1.5×[Na ２ O] - [K ２ O] + 1.2×[P ２ O ５ ≥ -2.5% is satisfied, and the tempered glass sheet according to claim 1 or 2 is characterized in that. Claim 4 P ２ O ５ The strengthened glass sheet according to any one of claims 1 to 3, characterized in that the content of Claim 5 Li ２ The strengthened glass sheet according to any one of claims 1 to 4, characterized in that the content of O is 0.1 to 15 mol%. Claim 6 The tempered glass sheet according to any one of Claims 1 to 5, characterized in that the softening point is 950 °C or lower. Claim 7 High-temperature viscosity 10 ２．５ The tempered glass sheet according to any one of claims 1 to 6, characterized in that the temperature at dPa·s is less than 1650°C. Claim 8 The tempered glass sheet according to any one of Claims 1 to 7, characterized in that the plate thickness is 100 μm or less. Claim 9 The tempered glass sheet according to any one of Claims 1 to 8, characterized in that the dimension is □100 mm or more. Claim 10 The tempered glass sheet according to any one of Claims 1 to 10, characterized in that the compressive stress value at the outermost surface of the compressive stress layer is 200 to 1100 MPa. Claim 11 The tempered glass sheet according to any one of Claims 1 to 11, characterized in that the stress depth of the compressive stress layer is 10 to 15% of the plate thickness. Claim 12 The tempered glass sheet according to any one of Claims 1 to 12, characterized in that it has an overflow confluence surface at the central portion in the plate thickness direction. Claim 13 The tempered glass sheet according to any one of Claims 1 to 13, characterized in that it is used for the cover glass of a flexible display. Claim 14 As a glass composition, in mol%, SiO ２ 50 to 75%, Al ２ O ３ 1 to 20%, B ２ O ３ 5 to 30%, Na ２ O 1 to 25%, K ２ O 0 to 10%, P ２ O ５ containing 0 to 15%, and the molar ratio [Al ２ O ３ / [Na ２ O] is 0.1 to 2.5, and [SiO ２ - 3 × [Al ２ O ３ - [B ２ O ３ - 2 × [Li ２ O] - 1.5 × [Na ２ O] - [K ２ O] + 1.2 × [P ２ O ５ ≥ -20% is satisfied, and the tempered glass plate is characterized by this. Claim 15 As a glass composition, in mol%, SiO ２ 50 to 75%, Al ２ O ３ 1 to 20%, B ２ O ３ 5 to 30%, Na ２ O 1 to 25%, K ２ O 0 to 10%, P ２ O ５ 0 to 15%, with the molar ratio [Al ２ O ３ / [Na ２ O] being 0.1 to 2.5, and [SiO ２ - 3×[Al ２ O ３ - [B ２ O ３ - 2×[Li ２ O] - 1.5×[Na ２ O] - [K ２ O] + 1.2×[P ２ O ５ ≥ -20%, and the plate thickness is less than 100 μm, characterized by a toughened glass plate.

Images