Crystallized glass

Abstract

In addition to high strength, we provide crystallized glass with high light transmittance and impact resistance. [Solution] A crystallized glass is provided, with a composition of 50-80% SiO2, 0-3.8% Al2O3, 0.2-15% P2O5, 1.5-30% Li2O, 0-15% Na2O, 1.5-10% ZrO2, and 0-15% Y2O3 in molar percentages.

Description

[Technical Field]

[0001] This invention relates to crystallized glass, and more particularly to crystallized glass suitable for cover glass in mobile phones, digital cameras, PDAs (personal digital assistants), and touch panel displays. [Background technology]

[0002] Mobile phones (especially smartphones), digital cameras, PDAs, touch panel displays, large-screen televisions, and contactless power supply devices are becoming increasingly widespread. Ion-exchange treated chemically strengthened glass is used in these applications. Furthermore, in recent years, the use of chemically strengthened glass in exterior components of digital signage, mice, and smartphones has been increasing. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] International Publication No. 2013 / 088856 [Patent Document 2] International Publication No. 2019 / 230889 [Disclosure of the Invention] [Problems that the invention aims to solve]

[0004] Cover glass, especially that used in smartphones, is often used while moving, making it susceptible to breakage when dropped on the ground. Therefore, it is important to increase the strength of cover glass against drops on the ground for its intended use.

[0005] Chemically strengthened glass possesses high strength. This is because the presence of a compressive stress layer on its surface suppresses the formation and propagation of cracks on the surface. Furthermore, it is believed that the strength of strengthened glass can be improved by adjusting the stress state of the compressive stress layer (see, for example, Patent Document 1).

[0006] Crystallized glass is glass in which crystals have been precipitated inside, meaning it contains crystals within the glass, and is known for its high strength. Patent Document 2 discloses chemically strengthened crystallized glass, but it has low transmittance, which reduces the visibility of the display when used as cover glass. Furthermore, there is still room for improvement in terms of impact resistance.

[0007] The present invention aims to create a crystallized glass that, in addition to having high strength, also possesses high transmittance and impact resistance. [Means for solving the problem]

[0008] The present inventors, after conducting various studies, have found that the above technical problems can be solved by strictly controlling the composition, and propose this as the present invention. Specifically, the crystallized glass according to the first aspect of the present invention is a crystallized glass having a compressive stress layer due to ion exchange, and its composition contains, in molar percent, SiO2 50-80%, Al2O 30-4.8%, P2O 50.2-15%, Li2O 1.5-30%, Na2O 0-15%, and ZrO2 1.5-10%, and is characterized in that the crystallized glass has a portion in which the Na ion concentration decreases from the surface side to the interior side of the glass. Here, the "Na ion concentration" can be confirmed by methods such as measuring the cross-section of the sample with SEM-EDX. In this way, a crystallized glass with high transmittance and high impact resistance can be obtained.

[0009] Furthermore, in the second aspect of the present invention, the crystallized glass preferably has a plate shape in the first aspect, and the stress depth of the compressive stress layer is preferably 13% or more of the plate thickness. This increases the resistance to crack penetration and tends to improve impact resistance.

[0010] Furthermore, in the crystallized glass according to the third aspect of the present invention, it is preferable that at least one of lithium disilicate and lithium metasilicate is precipitated in either the first or second aspect. This makes it easier to increase the transmittance.

[0011] Furthermore, in the fourth aspect of the present invention, it is preferable that the crystallized glass has a full width at half maximum (FWHM) of 0.120° or more at the maximum peak of the X-ray diffraction spectrum in any of the first to third aspects. This tends to increase the transmittance. Here, the "full width at half maximum (FWHM) at the maximum peak of the X-ray diffraction spectrum" can be evaluated using a powder method with an X-ray diffractometer (for example, Aeris manufactured by Malvern Panalytical).

[0012] Furthermore, in the fifth aspect of the present invention, it is preferable that the compressive stress value of the compressive stress layer of the crystallized glass is 100 MPa or more in any of the first to fourth aspects. This increases the resistance to crack penetration and tends to improve impact resistance.

[0013] Furthermore, in any of the first to fifth embodiments, the crystallized glass according to the sixth aspect of the present invention preferably has a plate shape and a plate thickness of 1.5 mm or less. This makes it possible to reduce the weight of the crystallized glass.

[0014] Furthermore, the crystallized glass according to the seventh aspect of the present invention is a crystallized glass having a compressive stress layer due to ion exchange, wherein at least one of lithium disilicate and lithium metasilicate is precipitated, and the crystallized glass has a portion in which the Na ion concentration decreases from the surface side to the interior side of the glass.

[0015] Furthermore, the crystallized glass according to the eighth aspect of the present invention is a crystallized glass having a compressive stress layer due to ion exchange, characterized in that its composition contains, in molar percent, SiO2 50-80%, Al2O 30-4.8%, P2O 50.2-15%, Li2O 1.5-30%, Na2O + K2O (total amount of Na2O and K2O) 0-3.8%, Na2O 0-3.8%, K2O 0-3.8%, and ZrO2 1.5-10%. This makes it possible to achieve a high level of both strength, transmittance, and impact resistance.

[0016] Also, the crystalline glass according to the ninth aspect of the present invention contains, as a glass composition, in mol%, 50 to 80% of SiO2, 0 to 4.8% of Al2O3, 0.2 to 15% of P2O5, 1.5 to 30% of Li2O, less than 0 to 3.8% of Na2O + K2O, less than 0 to 3.8% of Na2O, less than 0 to 3.8% of K2O, and 1.5 to 10% of ZrO2.

[0017] Also, the crystalline glass according to the tenth aspect of the present invention contains, as a glass composition, in mol%, 50 to 80% of SiO2, 0 to 4.8% of Al2O3, 0.2 to 15% of P2O5, 1.5 to 30% of Li2O, 0 to 15% of Na2O, and 1.5 to 10% of ZrO2.

Brief Description of Drawings

[0018] [Figure 1] It is a diagram showing the X-ray diffraction spectrum of the crystallized glass of Example 52 in Table 12.

Modes for Carrying Out the Invention

[0019] The crystallized glass (crystalline glass) of the present invention contains, as a composition, in mol%, 50 to 80% of SiO2, 0 to 4.8% of Al2O3, 0.2 to 15% of P2O5, 1.5 to 30% of Li2O, 0 to 15% of Na2O, and 1.5 to 10% of ZrO2. The reasons for limiting the content of each component as described above are shown below. In the description of the content of each component, the % indication represents mol% unless otherwise specified. In this specification, the numerical range indicated by using "~" means a range including the numerical values described before and after "~" as the minimum value and the maximum value, respectively.

[0020] SiO₂ is a component that forms the glass network and is also a component for precipitating crystals such as lithium disilicate and lithium metasilicate. The content of SiO₂ is preferably 50-80%, 55-75%, 60-73%, 60-70%, particularly 65-70%. If the content of SiO₂ is too low, it becomes difficult to vitrify, and the Young's modulus and weather resistance are likely to decrease, and it also becomes difficult to precipitate lithium disilicate and lithium metasilicate. 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. Also, the transmittance is likely to decrease due to the precipitation of heterogeneous crystals (unintended crystals).

[0021] Al₂O₃ is a component that adjusts the precipitated crystals and the compressive stress. The upper limit range of Al₂O₃ is preferably 4.8% or less, 4.7% or less, 4.5% or less, 4.4% or less, 4.3% or less, 4.2% or less, 4.0% or less, 3.8% or less, 3.5% or less, 3.3% or less, 3.0% or less, 2.8% or less, 2.5% or less, 2.2% or less, 2.1% or less, particularly 2.0% or less. If the content of Al₂O₃ is too high, there is a risk that the compressive stress value of the crystallized glass will decrease. On the other hand, if the content of Al₂O₃ is too low, there is a risk that the transmittance and devitrification resistance will be likely to decrease. Therefore, the lower limit range of the content of Al₂O₃ is preferably 0% or more, 0.1% or more, 0.2% or more, 0.3% or more, 0.4% or more, 0.5% or more, 0.7% or more, 1.0% or more, particularly 1.5% or more.

[0022] P₂O₅ is a component for generating crystal nuclei. However, if a large amount of P₂O₅ is introduced, the glass is likely to phase-separate. Therefore, the content of P₂O₅ is preferably 0.2-15%, 0.2-10%, 0.2-8%, 0.2-5%, 0.2-3%, particularly 0.5-3%.

[0023] Li2O is a component used to precipitate crystals such as lithium disilicate and lithium metasilicate, and also enhances ion exchange performance. However, if the Li2O content is too high, weather resistance tends to decrease. Therefore, the upper limit of Li2O is preferably 30% or less, 29% or less, 28% or less, 26% or less, and especially 25% or less, and the lower limit is preferably 1.5% or more, 2% or more, 3% or more, 4% or more, 4.5% or more, 5% or more, 5.5% or more, 6% or more, 6.3% or more, 6.5% or more, 6.6% or more, 8% or more, 10% or more, 12% or more, 15% or more, 18% or more, 20% or more, 21% or more, 22% or more, 22.5% or more, 23% or more, 23.5% or more, 24% or more, and especially 24.5% or more.

[0024] Na2O is a component that lowers high-temperature viscosity and significantly increases meltability. It is also a component that contributes to the initial melting of glass raw materials. However, if the Na2O content is too high, the crystallite size tends to become coarser and the weather resistance tends to decrease. Therefore, the upper limit range for Na2O is preferably 15% or less, 12% or less, 10% or less, 9.8% or less, 9.5% or less, 9.3% or less, 9.1% or less, 9% or less, 8.7% or less, especially 7% or less, 6% or less, 5% or less, 4% or less, 3% or less, less than 2.4%, 2.2% or less, 2% or less, 1.8% or less, 1.5% or less, and if weather resistance is important, 1% or less, especially less than 1%. The lower limit range is preferably 0% or more, 0.1% or more, 0.3% or more, 0.5% or more, 0.8% or more, 1% or more, especially 2% or more.

[0025] ZrO2 is a component used to generate crystal nuclei. However, if a large amount of ZrO2 is introduced, the glass becomes prone to devitrification, and because the introduced raw material is poorly soluble, there is a risk that unmelted foreign matter may be mixed into the glass. Therefore, the upper limit range for ZrO2 is preferably 10% or less, 9% or less, 8% or less, 7% or less, 6.5% or less, and especially 6% or less, and the lower limit range is preferably 1.5% or more, 1.7% or more, 1.9% or more, 2% or more, 2.1% or more, 2.3% or more, 2.5% or more, 2.7% or more, 3% or more, 3.3% or more, 3.5% or more, and especially 4% or more.

[0026] The molar ratio of Al2O3 / SiO2 is preferably 0.07 or less, 0.06 or less, 0.05 or less, 0.045 or less, 0.043 or less, 0.04 or less, 0.038 or less, 0.035 or less, 0.033 or less, 0.03 or less, 0.028 or less, and particularly 0 to 0.025. If the molar ratio of Al2O3 / SiO2 is too high, it may become difficult to vitrify, or the compressive stress value of the crystallized glass may decrease.

[0027] The molar ratio of Al2O3 / Li2O is preferably 0.2 or less, 0.15 or less, 0.14 or less, 0.13 or less, 0.12 or less, 0.11 or less, 0.1 or less, 0.09 or less, 0.08 or less, 0.07 or less, and particularly 0 to 0.065. If the molar ratio of Al2O3 / Li2O is too high, crystals such as lithium disilicate and lithium metasilicate may not precipitate easily, crystals such as petalite may precipitate easily, and the compressive stress value of the crystallized glass may decrease.

[0028] The molar ratio Al2O3 / (SiO2+Li2O) is preferably 0.06 or less, 0.055 or less, 0.05 or less, 0.047 or less, 0.045 or less, 0.043 or less, 0.04 or less, 0.038 or less, 0.035 or less, 0.033 or less, and especially 0 to 0.03. If the molar ratio Al2O3 / (SiO2+Li2O) is too high, crystals such as lithium disilicate and lithium metasilicate may not precipitate easily, crystals such as petalite may precipitate easily, and the compressive stress value of the crystallized glass may decrease.

[0029] In addition to the above-mentioned components, other components may be introduced as optional components.

[0030] K2O is a component that enhances ion exchange performance and also lowers high-temperature viscosity, thereby improving melting properties. However, if the K2O content is too high, the crystallite size tends to become coarser. Therefore, the K2O content is preferably 0-7%, 0-5%, 0-3%, 0-2%, 0-1.5%, 0-1.2%, less than 0-1%, and particularly 0-0.8%.

[0031] The combined amount of Na2O and K2O, known as Na2O+K2O, is preferably 0-8%, 0-7%, 0-5%, less than 0-3.8%, 0-3.5%, 0-3%, 0-2.5%, and particularly preferably 0-2%. If the Na2O+K2O content is too high, the crystallite size tends to become coarser.

[0032] The molar ratio (Na2O+K2O) / (Li2O+Na2O+K2O) is preferably less than 1.50, 1.40 or less, 1.30 or less, 1.20 or less, 1.10 or less, 1.00 or less, 0.05 to 0.90, and particularly 0.10 to 0.80. If the molar ratio (Na2O+K2O) / (Li2O+Na2O+K2O) is too large, the ion exchange performance by the NaNO3 molten salt decreases, making it difficult to form a region in the crystallized glass where the Na ion concentration decreases from the surface to the interior of the glass, i.e., a compressive stress layer based on Na ions. Note that "(Na2O+K2O) / (Li2O+Na2O+K2O)" is the value obtained by dividing the total amount of Na2O and K2O by the total amount of Li2O, Na2O, and K2O.

[0033] B2O3 is a component that enhances meltable properties and resistance to devitrification. However, if the B2O3 content is too high, weather resistance tends to decrease. Therefore, the B2O3 content is preferably 0-10%, 0-7%, 0-5%, 0-3%, and especially less than 0-1%.

[0034] MgO is a component that enhances Young's modulus and ion exchange performance, as well as lowering high-temperature viscosity and improving meltability. However, if the MgO content is too high, the glass is prone to devitrification during molding. Therefore, the MgO content is preferably 0-10%, 0-7%, 0-4%, 0-2%, 0-1%, and particularly 0-0.1%.

[0035] CaO is a component that lowers high-temperature viscosity and increases meltability. Furthermore, among alkaline earth metal oxides, its raw material is relatively inexpensive, thus reducing batch costs. However, if the CaO content is too high, the glass is prone to devitrification during molding. Therefore, the CaO content is preferably 0-5%, 0-3%, 0-1%, and particularly 0-0.5%.

[0036] SrO is a component that suppresses phase separation and also suppresses the coarsening of crystallite size. However, if the content is too high, it becomes difficult to precipitate crystals by heat treatment. Therefore, the SrO content is preferably 0-5%, 0-3%, 0-2%, and particularly 0-1%.

[0037] BaO is a component that suppresses the coarsening of crystallite size, but if its content is too high, it becomes difficult to precipitate crystals by heat treatment. Therefore, the BaO content is preferably 0-5%, 0-3%, 0-2%, and especially 0-1%.

[0038] ZnO is a component that significantly increases meltability by lowering high-temperature viscosity, and also suppresses the coarsening of crystallite size. However, if the ZnO content is too high, the glass is prone to devitrification during molding. Therefore, the ZnO content is preferably 0-5%, 0-3%, 0-2%, and particularly 0-1%.

[0039] TiO2 is a component that generates crystal nuclei and also improves weather resistance. However, if a large amount of TiO2 is introduced, the glass tends to become discolored and its transmittance decreases. Therefore, the TiO2 content is preferably 0-5%, 0-3%, and especially less than 0-1%.

[0040] SnO2 is a component that enhances ion exchange performance, but if its content is too high, the resistance to devitrification tends to decrease. Therefore, the SnO2 content is preferably 0-3%, 0.01-3%, 0.05-3%, 0.1-3%, and particularly 0.2-3%.

[0041] Depending on the high-temperature viscosity, an effective clarifying agent can be added. As a clarifying agent, one or more selected from the group of Cl, SO3, CeO2, and Sb2O3 (preferably from the group of Cl and SO3) may be added in an amount of 0.001 to 1%.

[0042] The preferred Fe2O3 content is less than 1000 ppm (less than 0.1 mass%), less than 800 ppm, less than 600 ppm, less than 400 ppm, and especially less than 300 ppm. Furthermore, it is preferable to restrict the Fe2O3 content to the above range and then restrict the molar ratio SnO2 / (Fe2O3+SnO2) to 0.8 or higher, 0.9 or higher, and especially 0.95 or higher. Doing so makes it easier to improve the total light transmittance in the wavelength range of 400 to 770 nm.

[0043] Y2O3 is a component that increases the strength of glass. However, the raw material for Y2O3 is expensive, and adding large amounts tends to reduce its resistance to devitrification. Therefore, the Y2O3 content is preferably 0-15%, 0-12%, 0-10%, and especially 0.1-1%.

[0044] Gd2O3, Nb2O5, La2O3, Ta2O5, and HfO2 are components that increase the strength of glass. However, the raw materials themselves are expensive, and adding large amounts tends to reduce devitrification resistance. The combined amount and individual content of Gd2O3, Nb2O5, La2O3, Ta2O5, and HfO2 are preferably 0-15%, 0-10%, 0-5%, and especially 0-3%.

[0045] From an environmental perspective, the crystallized glass of the present invention is preferably substantially free of As2O3, PbO, F, etc., in its composition. Furthermore, from an environmental perspective, it is also preferably substantially free of Bi2O3. "Substantially free of ~" means that the explicitly stated components are not actively added as glass components, but the addition at impurity levels is permitted, and specifically refers to cases where the content of the explicitly stated components is less than 0.05%.

[0046] In the crystallized glass of the present invention, it is possible to combine suitable content ranges of each component as appropriate to obtain a suitable glass composition range. Among these, the following composition ranges (1) to (3) are preferred because they can achieve a high level of balance between strength, transmittance, and impact resistance. (1) Contains, in mol%, SiO2 50-80%, Al2O 30-4.8%, P2O 50.2-15%, Li2O 1.5-30%, Na2O + K2O 0-3.8%, Na2O 0-3.8%, K2O 0-3.8%, and ZrO2 1.5-10%. (2) Contains, in mol%, SiO2 50-80%, Al2O 30-4.8%, P2O 50.2-15%, Li2O 1.5-30%, Na2O + K2O 0-3.5%, Na2O 0-2%, K2O 0-1.2%, and ZrO2 1.5-10%. (3) It contains, in mol%, SiO2 50-80%, Al2O 30-4.8%, P2O 50.2-15%, Li2O 1.5-30%, Na2O + K2O 0-3.8%, Na2O 0-3.8%, K2O 0-3.8%, and ZrO2 1.5-10%, with a molar ratio of (Na2O + K2O) / (Li2O + Na2O + K2O) of 1.20 or less.

[0047] The crystallized glass of the present invention preferably has the following properties.

[0048] In the crystallized glass of the present invention, it is preferable that lithium disilicate, lithium metasilicate, β-quartz, β-spodumene, trilithium phosphate, or petalite are precipitated in order to increase transmittance, and it is particularly preferable that lithium disilicate, lithium metasilicate, or trilithium phosphate are precipitated. Furthermore, it is preferable that lithium disilicate or lithium metasilicate is precipitated as the main crystal (the crystal with the largest precipitate amount).

[0049] Furthermore, in the crystallized glass of the present invention, it is preferable that petalite is not precipitated in order to increase the compressive stress value of the compressive stress layer. Here, "no petalite precipitated" means that in the spectrum obtained by X-ray diffraction, the ratio I2 / I1 of the diffraction intensity I2 of the diffraction peak located at a diffraction angle of 2θ = 34.9 ± 0.3° to the diffraction intensity I1 of the diffraction peak located at a diffraction angle of 2θ = 24.7 ± 0.3° is 0.03 or less.

[0050] The full width at half maximum FWHM at the maximum peak of the X-ray diffraction spectrum is preferably 0.120° or more, 0.121° or more, 0.122° or more, 0.123° or more, 0.125° or more, 0.130° or more, 0.135° or more, 0.140° or more, particularly preferably 0.150° or more. If the full width at half maximum FWHM at the maximum peak of the X-ray diffraction spectrum is too small, the transmittance tends to decrease.

[0051] The fracture toughness K before the ion exchange treatment 1C is preferably 0.7 MPa·m 0.5 or more, 0.8 MPa·m 0.5 or more, 1.0 MPa·m 0.5 or more, 1.2 MPa·m 0.5 or more, particularly 1.5 - 3.5 MPa·m 0.5 is. If the fracture toughness K 1C is too small, the strength tends to be low. Here, "the fracture toughness K 1C " is measured using the pre-crack introduction fracture test method (SEPB method: Single-Edge-Precracked-Beam method) based on JIS R1607 "Test Method for Fracture Toughness of Fine Ceramics". The SEPB method measures the maximum load until the test piece breaks by a three-point bending fracture test of the pre-crack introduction test piece, and calculates the plane strain fracture toughness K 1C from the maximum load, pre-crack length, test piece dimensions, and bending fulcrum distance. The measured value of the fracture toughness K 1C of each glass is the average value of 5 measurements.

[0052] The Young's modulus before the ion exchange treatment is preferably 70 GPa or more, 72 GPa or more, 73 GPa or more, 74 GPa or more, 75 GPa or more, 76 GPa or more, 77 GPa or more, 78 GPa or more, 79 GPa or more, 80 GPa or more, 83 GPa or more, 85 GPa or more, 87 GPa or more, 90 GPa or more, particularly 100 - 150 GPa. If the Young's modulus is low, when the plate thickness is thin, the crystallized glass tends to bend. The "Young's modulus" can be measured by the well-known resonance method.

[0053] The Vickers hardness before ion exchange treatment is preferably 500 or higher, 550 or higher, 580 or higher, and particularly 600 to 2500. If the Vickers hardness is too low, it will be easily scratched. Note that "Vickers hardness" is a value measured by pressing a Vickers indenter with a load of 100 gf using a Vickers hardness tester.

[0054] The transmittance in the thickness direction at a wavelength of 400 nm is preferably 75% or higher, 76% or higher, 77% or higher, 78% or higher, 79% or higher, 81% or higher, 83% or higher, 85% or higher, 88% or higher, and particularly 89% or higher. Note that "transmittance" is measured as the linear transmittance in the thickness direction using a spectrophotometer (Shimadzu UV-3100).

[0055] The crystallized glass of the present invention preferably has the following properties after ion exchange treatment.

[0056] The crystallized glass of the present invention has a region in the crystallized glass where the Na ion concentration decreases from the surface to the interior of the glass, or in other words, a region where the Na ion concentration increases from the interior to the surface of the glass. This increases the resistance to crack penetration from the glass surface and makes it easier to achieve high impact resistance. When an ion exchange treatment is performed to introduce Na ions into the glass using a molten NaNO3 salt, the Na ion concentration at the glass surface becomes relatively higher, making it possible to form a region where the Na ion concentration decreases from the surface to the interior of the glass. Furthermore, when Na ions in the molten NaNO3 salt and Li ions in the glass are exchanged, in contrast to the above Na ion concentration, the crystallized glass will have a region where the Li ion concentration increases from the surface to the interior of the glass, that is, a region where the Li ion concentration decreases from the interior to the surface of the glass.

[0057] The crystallized glass of the present invention has a compressive stress layer on its surface due to ion exchange, and the compressive stress value of the compressive stress layer is preferably 100 MPa or more, 110 MPa or more, 120 MPa or more, 130 MPa or more, 140 MPa or more, 150 MPa or more, 170 MPa or more, and particularly 200 MPa or more. If the compressive stress value is low, the resistance to crack penetration will be low and the impact resistance will be low. However, if the compressive stress value is too high, the tensile stress value in the center will be excessive, resulting in many fragments when broken, which is dangerous. Therefore, the compressive stress value is preferably 1000 MPa or less, 900 MPa or less, 800 MPa or less, 700 MPa or less, 600 MPa or less, 500 MPa or less, and particularly 450 MPa or less.

[0058] The stress depth of the compressive stress layer in the case of a plate shape is preferably 13% or more, 14% or more, 15% or more, 16% or more, 17% or more, 17.5% or more, 18% or more, 18.5% or more, and especially 19% or more of the plate thickness. If the stress depth is small, the resistance to crack penetration will be small and the impact resistance will tend to be low.

[0059] The internal tensile stress value is preferably 180 MPa or less, 150 PMa or less, 120 MPa or less, and particularly 110 MPa or less. If the internal tensile stress value is too high, the crystallized glass is prone to self-fracture due to hard scratching. On the other hand, if the internal tensile stress value is too low, it becomes difficult to ensure the strength of the crystallized glass. The internal tensile stress value is preferably 35 MPa or more, 45 MPa or more, 55 MPa or more, and particularly 70 MPa or more. The internal tensile stress value can be measured, for example, using the scattered light photoelastic stress meter SLP-2000 from Orihara Manufacturing Co., Ltd.

[0060] The P180 damage strength is an indicator of impact resistance, and is preferably 250 MPa or higher, 270 MPa or higher, 290 MPa or higher, and particularly 300 MPa or higher. While there is no particular upper limit to the P180 damage strength, in practice it is 800 MPa or lower. The P180 damage strength can be measured by the method described later.

[0061] The crystallized glass of the present invention is preferably in the form of a plate, and its thickness is preferably 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, and particularly 0.9 mm or less. The smaller the plate thickness, the lighter the crystallized glass can be. On the other hand, if the plate thickness is too thin, it becomes difficult to obtain the desired strength. Therefore, the plate thickness is preferably 0.3 mm or more, 0.4 mm or more, 0.5 mm or more, 0.6 mm or more, and particularly 0.7 mm or more.

[0062] The method for producing crystallized glass according to the present invention will be explained using the case of forming it into a plate shape as an example. First, glass raw materials, which have been blended to achieve the desired glass composition, are placed in a continuous melting furnace and heated and melted at 1200 to 1700°C. After clarification, the molten glass is supplied to a molding device, formed into a plate shape, and cooled to obtain a glass plate (crystalline glass plate). Crystalline glass refers to glass that is capable of precipitating crystals before crystal precipitation occurs, and does not necessarily contain crystals. After forming it into a plate shape, a well-known method can be used for cutting it to a predetermined size.

[0063] As a method for forming molten glass into a sheet shape, the overflow downdraw method is preferable. The overflow downdraw method is a method that can produce a large quantity of high-quality glass sheets. Here, the "overflow downdraw method" is a method in which molten glass is allowed to overflow from both sides of the molded refractory body, and the overflowed molten glass is drawn downwards while being brought together at the lower end of the molded refractory body, forming a sheet-shaped glass ribbon. In the overflow downdraw method, the surface that would become the surface does not come into contact with the surface of the molded refractory body, and is formed into a sheet shape. For this reason, crystalline glass with good surface quality without polishing can be manufactured at low cost.

[0064] When forming using the overflow downdraw method, it is preferable to include a cooling step in which one surface of the formed glass ribbon is brought into contact with a cooling roll to cool it. This way, the glass can be formed using a method that reduces liquidus viscosity (for example, a glass with a liquidus viscosity of 10%). 4.2 Less than dPa·s, especially when the liquid phase viscosity is 10 3.8Even with glass that has a viscosity of less than dPa·s, it becomes easier to prevent the occurrence of devitrified defects during molding. Furthermore, it is preferable to provide a heating step in which a heater is placed below the cooling roll on the surface side that is in contact with the cooling roll, thereby heating the surface that is in contact with the cooling roll. In this way, the temperature difference between the two surfaces of the glass ribbon is reduced, and it becomes possible to mitigate the warping of the glass ribbon.

[0065] In addition to the overflow downdraw method, various other molding methods can be employed. For example, the float method, downdraw method (slot downdraw method, redraw method, etc.), rollout method, and press method can be used.

[0066] Next, it is preferable to obtain a crystallized glass plate by heat-treating the glass plate. The heat treatment process preferably includes a phase formation step to generate phases in the glass matrix, a crystal nucleation step to generate crystal nuclei, and a crystal growth step to grow the generated crystal nuclei. The heat treatment temperature for the phase formation step is preferably 400 to 600°C, particularly 480 to 570°C, and the heat treatment time is preferably 10 minutes to 24 hours, particularly 30 minutes to 12 hours. The heat treatment temperature for the crystal nucleation step is preferably 500 to 700°C, particularly 520 to 650°C, and the heat treatment time is preferably 10 minutes to 24 hours, particularly 30 minutes to 12 hours. By appropriately adjusting the temperature, the phase formation step and the crystal nucleation step may be performed simultaneously. The heat treatment temperature for the crystal growth step is preferably 730 to 920°C, particularly 750 to 830°C, and the heat treatment time is preferably 10 minutes to 5 hours, particularly 30 minutes to 3 hours. Furthermore, the heating rate is preferably 1°C / min to 30°C / min, and particularly preferably 1°C / min to 10°C / min. If the heat treatment temperature, heat treatment time, and heating rate are outside the above range, the crystallite size may become coarser or the degree of crystallinity may decrease.

[0067] Next, the crystallized glass plate is subjected to ion exchange treatment to form a compressive stress layer on the surface due to ion exchange. Since ion exchange treatment forms a compressive stress layer on the surface, its strength can be increased. In the compressive stress layer formed by ion exchange, the concentration of the components subjected to ion exchange, such as alkali metal components, changes in the depth direction of the compressive stress layer. The conditions for the ion exchange treatment are not particularly limited; the optimal conditions should be selected considering the viscosity characteristics of the glass, thickness, internal tensile stress, dimensional changes, etc. In particular, it is preferable to exchange Na ions in a NaNO3 molten salt or a mixed molten salt of KNO3 and NaNO3 with Li components in the glass. Ion exchange between Na ions and Li components is faster than ion exchange between K ions and Na components, allowing for more efficient ion exchange treatment. The ion exchange solution temperature is preferably 380-500°C, and the ion exchange time is preferably 1-15 hours, 2-10 hours, 3-9 hours, and particularly 4-8 hours. [Examples]

[0068] The present invention will be described below based on the following examples. Note that the following examples are merely illustrative. The present invention is not limited in any way to the following examples.

[0069] Tables 1-6 show the glass composition of crystalline glass plates (samples No. 1-55) and amorphous glass plate (sample No. 56). Note that R2O represents the total amount of Li2O, Na2O, and K2O.

[0070] [Table 1]

[0071] [Table 2]

[0072] [Table 3]

[0073] [Table 4]

[0074] [Table 5]

[0075] [Table 6]

[0076] First, glass raw materials were mixed to achieve the glass compositions shown in Tables 1-6, and melted at 1500°C for 8 hours using a platinum pot. Next, the resulting molten glass was poured onto a carbon plate and shaped into a flat plate to obtain a glass plate. The surface of the obtained glass plate was optically polished to a thickness of 0.6 mm, and then various properties were evaluated.

[0077] Next, the obtained crystalline glass plates (samples No. 1 to 55) were heat-treated in an electric furnace under the heat treatment conditions shown in Tables 7 to 13 to precipitate and grow crystals in the glass matrix. Afterward, they were cooled to room temperature to obtain crystallized glass plates. The amorphous glass plate (sample No. 56) was not subjected to any special heat treatment. The properties of the obtained glass plates were evaluated as follows. The results are shown in Tables 7 to 13.

[0078] [Table 7]

[0079] [Table 8]

[0080] [Table 9]

[0081] [Table 10]

[0082] [Table 11]

[0083] [Table 12]

[0084] [Table 13]

[0085] The main crystal was evaluated by powder X-ray diffraction using an X-ray diffractometer (Aeris, Malvern Panalytical). The measurement range was set to 2θ = 10 to 60°. From the obtained X-ray diffraction spectrum, the background and amorphous regions (halo peaks) were removed, and peak fitting was performed on the peak with the highest intensity to derive the full width at half maximum (FWHM).

[0086] The transmittance was measured using a spectrophotometer (Shimadzu UV-3100) to obtain the linear transmittance in the thickness direction of the plate.

[0087] Next, each glass plate was subjected to ion exchange treatment under the conditions described in the table to form a compressive stress layer on its surface, thereby obtaining Examples 1 to 67 and Comparative Examples 1 and 2.

[0088] The compressive stress values ​​and stress depths were measured using Orihara Manufacturing Co., Ltd.'s scattered light photoelastic stress meter SLP-2000 or surface stress meter FSM-6000LE. For the measurements, the photoelastic constant was set to 27.0 and the refractive index to 1.55 for Examples 1 to 67 and Comparative Example 1, while the photoelastic constant was set to 30.5 and the refractive index to 1.51 for Comparative Example 2.

[0089] The injury strength was determined by first placing P180 sandpaper on the sample and pressing a 9mm diameter iron indenter against it with a 100N load for 1 second. After removing the load, a three-point bending test was performed on the injured area of ​​the sample, and the stress at fracture was defined as the injury strength.

[0090] As is clear from Tables 7-13, Examples 1-67 are considered to have high strength, high transmittance, and high impact resistance. On the other hand, Comparative Example 1 is considered to have insufficient impact resistance because it has a small stress depth (DOC) due to ion exchange using a KNO3 molten salt, and does not have a region where the Na ion concentration decreases from the surface to the interior of the glass. Comparative Example 2 is considered to have insufficient strength because it is not crystallized.

[0091] Furthermore, Figure 1 shows the X-ray diffraction spectrum of the crystallized glass of Example 52 in Table 12. As is clear from Figure 1, it was found that in Example 52, lithium disilicate precipitated, but petalite did not, resulting in a high compressive stress value in the compressive stress layer.

Claims

1. A crystallized glass having a compressive stress layer due to ion exchange, wherein the composition is SiO2 in mol%. ２ 50-80%, Al ２ O ３ 0-4.8%, P ２ O ５ 0.2-15%, Li ２ O 1.5-30%, Na ２ O 0-15%, ZrO ２ A crystallized glass characterized by containing 1.5 to 10% of a substance, and having a portion in the crystallized glass in which the concentration of Na ions decreases from the surface side to the interior side of the glass.

2. The crystallized glass according to claim 1, having a plate shape and having a stress depth of 13% or more of the plate thickness in the compressive stress layer.

3. The crystallized glass according to claim 1 or 2, wherein at least one of lithium disilicate and lithium metasilicate is precipitated.

4. The crystallized glass according to claim 1 or 2, wherein the full width at half maximum (FWHM) of the maximum peak in the X-ray diffraction spectrum is 0.120° or greater.

5. The crystallized glass according to claim 1 or 2, wherein the compressive stress value of the compressive stress layer is 100 MPa or more.

6. The crystallized glass according to claim 1 or 2, having a plate shape and a plate thickness of 1.5 mm or less.

7. A crystallized glass having a compressive stress layer due to ion exchange, characterized in that at least one of lithium disilicate and lithium metasilicate is precipitated, and there is a portion in which the Na ion concentration decreases from the surface side to the interior side of the glass.

8. A crystallized glass having a compressive stress layer by ion exchange, with a composition in mol% of SiO ２ 50 to 80%, Al ２ O ３ 0 to 4.8%, P ２ O ５ 0.2 to 15%, Li ２ O 1.5 to 30%, Na ２ O + K ２ O less than 0 to 3.8%, Na ２ O less than 0 to 3.8%, K ２ O less than 0 to 3.8%, ZrO ２ 1.5 to 10%, characterized by the crystallized glass containing the same.

9. The glass composition is SiO in mol%. ２ 50-80%, Al ２ O ３ 0-4.8%, P ２ O ５ 0.2-15%, Li ２ O 1.5-30%, Na ２ O+K ２ O 0-3.8%, Na ２ O 0-3.8%, K ２ O 0-3.8%, ZrO ２ 1. Crystalline glass characterized by containing 1.5 to 10% of a certain substance.

10. The glass composition is SiO2 in mol%. ２ 50-80%, Al ２ O ３ 0-4.8%, P ２ O ５ 0.2-15%, Li ２ O 1.5-30%, Na ２ O 0-15%, ZrO ２ 1. Crystalline glass characterized by containing 1.5 to 10% of a certain substance.

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