Reinforced glass-ceramics

Abstract

Reinforced crystallized glass characterized in containing, in mol% expressed in terms of oxides, 30.0–70.0% of an SiO2 component , 8.0–25.0% of an Al2O3 component, 2.0–25.0% of an Na2O component, of 1.0–6.0% of an Li2O component, 0–25.0% of an MgO component, 0–30.0% of a ZnO component, and 0–10.0% of a TiO2 component, crystallized glass being used as the base member, a compressive stress layer being provided on the surface, and the compressive stress layer being 60 μm or more in depth (DOLzero).

Description

[Technical Field]

[0001] The present invention relates to a strengthened glass-ceramic having a compressive stress layer on its surface.

[0002] Cover glass is used to protect the displays of mobile electronic devices such as smartphones and tablet PCs. Protectors are also used to protect lenses in automotive optical devices. Furthermore, in recent years, there has been a growing demand for glass to be used in the exterior housings of electronic devices. Therefore, there is a growing demand for high-strength materials to enable these devices to withstand harsh use.

[0003] Chemically strengthened glass has traditionally been used as a material for protective components, etc. However, conventional chemically strengthened glass has been problematic because it has frequently caused breakage when mobile devices such as smartphones are dropped.

[0004] For example, Patent Document 1 discloses high-strength crystallized glass and crystallized glass obtained by chemically strengthening the same. However, in order to further expand the applications of crystallized glass as the exterior of electronic devices, there is a demand for crystallized glass with even higher strength, in particular, crystallized glass that is less likely to break when dropped on an uneven, rough surface such as asphalt. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent Publication No. 2017-001937 Summary of the Invention

[0006] An object of the present invention is to provide a tempered crystallized glass that is less likely to break when dropped on a rough surface.

[0007] The present inventors conducted extensive research to solve the above problems and discovered that chemically strengthening glass-ceramics containing a predetermined amount of lithium under specified conditions makes the glass less likely to break when dropped onto a rough surface, leading to the completion of the present invention. Patent Document 1 describes that lithium can be included as a constituent component of glass-ceramics, but because lithium is difficult to use and the inclusion of lithium makes the glass more susceptible to devitrification, lithium is not required, and instead sodium is included as a constituent component of the glass-ceramics, which is chemically strengthened in a potassium salt bath. The details of the present invention are described below.

[0008] (Configuration 1) In mole % of oxide equivalent, SiO2 content: 30.0% to 70.0% Al2O3 component 8.0% to 25.0%, Na2O content: 2.0% to 25.0% Li2O component 1.0% to 6.0%, MgO content: 0% to 25.0% ZnO content: 0% to 30.0%, and containing 0% to 10.0% of TiO2 component, The base material is crystallized glass, It has a compressive stress layer on the surface, The strengthened crystallized glass is characterized in that the depth (DOLzero) of the compressive stress layer is 60 μm or more. (Configuration 2) 2. The strengthened glass-ceramics according to configuration 1, wherein the total content of the MgO component and the ZnO component is 1.0% or more and 30.0% or less in mole % calculated as oxide. (Configuration 3) The crystallized glass contains, in mole percent in terms of oxides: B2O3 content: 0% to 25.0% P2O5 component 0% to 10.0%, K2O content: 0% to 20.0% CaO content: 0% to 10.0% BaO content: 0% to 10.0% FeO content: 0% to 8.0% ZrO2 content: 0% to 10.0% SnO2 content: 0% to 5.0% 3. The strengthened crystallized glass according to configuration 1 or 2, comprising: (Configuration 4) The crystallized glass contains, in mole percent in terms of oxides: SrO content: 0% to 10.0% La2O3 component 0% to 3.0%, Y2O3 content: 0% to 3.0% Nb2O5 component 0% to 5.0%, Ta2O5 component 0% to 5.0%, WO3 component 0% to 5.0% 4. The strengthened crystallized glass according to any one of configurations 1 to 3, comprising: (Configuration 5) 5. The strengthened crystallized glass according to any one of configurations 1 to 4, wherein the content of the B2O3 component in the crystallized glass is 0.0% or more and less than 2.0% by mass in terms of oxide. (Configuration 6) 6. The strengthened glass-ceramics according to any one of aspects 1 to 5, wherein the molar ratio of the TiO2 component to the Na2O component [TiO2 / Na2O] is 0 or more and 0.41 or less in mole % calculated as oxide. (Configuration 7) 7. The strengthened crystallized glass according to any one of configurations 1 to 6, wherein the compressive stress layer has a surface compressive stress value (CS) of 800 MPa or more.

[0009] According to the present invention, it is possible to obtain tempered crystallized glass that is resistant to breaking when dropped on a rough surface.

[0010] The tempered crystallized glass of the present invention can be used for protective materials for devices, taking advantage of its high strength. It can be used as cover glass or housing for smartphones, components for portable electronic devices such as tablet PCs and wearable devices, and components for protective protectors and head-up display substrates used in transportation vehicles such as cars and airplanes. It can also be used for other electronic devices and machinery, building components, solar panel components, projector components, and cover glass (windshields) for eyeglasses and watches. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, embodiments and examples of the present invention will be described in detail, but the present invention is not limited to the following embodiments and examples in any way, and can be practiced with appropriate modifications within the scope of the object of the present invention.

[0012] Glass-ceramics, also known as glass ceramics, are materials in which crystals are precipitated within the glass by heat treatment. The crystalline phase of glass-ceramics is generally identified by the peak angle that appears in the X-ray diffraction pattern of X-ray diffraction analysis, and, if necessary, by TEMEDX.

[0013] The strengthened crystallized glass of the present invention may contain, for example, RAl2O4, RTi2O4, RTi2O5, R2TiO4, R2SiO4, RAl2Si2O8, R2Al4Si5O as a crystalline phase. 18 , R2TiO5, RSiO3, NaAlSiO4 (where R is one or more selected from Zn, Mg, and Fe), and solid solutions thereof. Preferably, the above crystalline phase is the main crystalline phase. By having the above crystalline phase, the glass becomes one with high mechanical strength. The present invention is directed to a lithium silicate crystalline phase and a petalite crystalline phase (LiAlSiO4 10 ) may not be the predominant crystalline phase. A predominant crystalline phase is one that has a higher weight percentage than other crystalline phases.

[0014] In the description of the content of the crystallized glass constituent components, "mol% or mass% in terms of oxide" means the amount of oxide of each component contained in the crystallized glass, when the total amount of the oxide is 100mol% or 100mass%, respectively, when the crystallized glass constituent components are all decomposed and converted into oxides.In this specification, the content of each component is expressed in "mol% in terms of oxide" unless otherwise specified.

[0015] In this specification, A to B% represents A% or more and B% or less. Also, 0% in "contains 0% to C%" means that the content is 0%.

[0016] Chemical strengthening is a method of strengthening glass surfaces by exchanging alkali ions contained in the glass with other alkali ions to generate compressive stress. The inventors discovered that adding a certain amount of lithium to glass and then ion-exchanging it primarily with sodium ions and then primarily with potassium ions increases the strength of the glass when dropped on a rough surface such as asphalt. The inventors believe that this improvement in strength is achieved by focusing on the ionic radii of the alkali ions: lithium ions have 0.60 Å, sodium ions have 0.95 Å, and potassium ions have 1.33 Å. When lithium ions with a small ionic radius are present in glass, they are ion-exchanged from lithium ions to sodium ions deeper from the surface than other alkali ions. This means that a compressive stress layer can be formed deep from the surface of the glass. Furthermore, by subsequently replacing sodium ions with potassium ions with a larger ionic radius, the compressive stress at the surface of the compressive stress layer increases. It is believed that the ion exchange with potassium ions occurs near the surface of the compressive stress layer and not deep enough to reach the lithium ion-exchanged portion. Therefore, the characteristic of the components constituting the crystallized glass (crystallized glass before strengthening) that is the base material used in the present invention is that it contains at least a predetermined amount of lithium as an alkali metal component.

[0017] The composition ranges of the components constituting the glass-ceramics that serve as the base material for the strengthened glass-ceramics of the present invention will be specifically described below.

[0018] The SiO2 component is an essential component for forming the glass network structure of the crystallized glass. If the content is less than 30.0%, the resulting glass will have poor chemical durability and poor devitrification resistance. Therefore, the lower limit of the SiO2 content is preferably 30.0% or more, more preferably 40.0% or more, and most preferably 50.0% or more. On the other hand, by keeping the SiO2 content at 70.0% or less, excessive increases in viscosity and deterioration of meltability can be suppressed. Therefore, the upper limit of the SiO2 content is preferably 70.0% or less, more preferably 68.0% or less, even more preferably 66.5% or less, and most preferably 65.0% or less.

[0019] The Al2O3 component is an essential component that forms a glass network structure, similar to SiO2, and can also become a component that forms a crystalline phase when the base glass is heat-treated before crystallization. It also contributes to the stabilization of the base glass and the improvement of its chemical durability, but if its content is less than 8.0%, these effects are poor. Therefore, the lower limit of the Al2O3 content is preferably 8.0% or more, more preferably 9.0% or more, and most preferably 10.0% or more. On the other hand, if the content of the Al2O3 component exceeds 25.0%, the meltability and devitrification resistance deteriorate, so the upper limit of the content of the Al2O3 component is preferably 25.0% or less, more preferably 20.0% or less, even more preferably 17.0% or less, and most preferably 15.0% or less.

[0020] The Na2O component is involved in chemical strengthening and is an essential component for improving low-temperature melting properties and formability. On the other hand, by limiting the Na2O content to 25.0% or less, deterioration of chemical durability and an increase in the average linear expansion coefficient due to excessive Na2O content can be suppressed. Therefore, the upper limit of the Na2O content is preferably 25.0% or less, more preferably 20.0% or less, and most preferably 15.0% or less. When chemical strengthening is performed by ion exchange, the NaO component contained in the crystallized glass is used. + Ion is K +The NaO content is exchanged with ions and contributes to the formation of a compressive stress layer. The lower limit of the NaO content is preferably 2.0% or more, more preferably 4.0% or more, even more preferably 6.0% or more, even more preferably 8.0% or more, and most preferably 8.5% or more. Furthermore, the lower limit of the NaO content, in terms of oxide mass%, is preferably 7.0% or more, more preferably 9.0% or more, even more preferably more than 10.0%, and most preferably 10.1% or more.

[0021] The Li2O component is involved in chemical strengthening and is an essential component for improving the low-temperature melting property and formability of the glass. On the other hand, if the Li2O component is contained in excess, the glass becomes significantly more likely to devitrify. Therefore, the upper limit of the Li2O component content is preferably 6.0% or less, more preferably 5.0% or less, even more preferably 4.0% or less, and most preferably 3.5% or less. When chemical strengthening by ion exchange is performed, the inclusion of Li2O in the crystallized glass is effective in forming a deep compressive stress layer. Therefore, the lower limit of the Li2O content may be set to preferably 1.0% or more, more preferably 1.1% or more, even more preferably 1.2% or more, and most preferably 1.3% or more.

[0022] The MgO component is one of the components that can form a crystalline phase and is an optional component. An optional component is a component that may or may not be included. The content can be 0% or more. When the MgO component is contained in an amount greater than 0%, it has the effect of improving low-temperature melting properties. Therefore, the content of the MgO component may preferably be greater than 0%, and the lower limit may be set to more preferably 5.0% or more, and even more preferably 8.0% or more. On the other hand, by limiting the content of the MgO component to 25.0% or less, it is possible to prevent a decrease in devitrification resistance due to an excessive content of the MgO component. Therefore, the upper limit of the content of the MgO component is preferably set to 25.0% or less, more preferably 20.0% or less, and most preferably 15.0% or less.

[0023] ZnO is an optional component that can form a crystalline phase. When the ZnO content exceeds 0%, it has the effect of improving low-temperature melting properties and chemical durability. On the other hand, by keeping the ZnO content at 30.0% or less, deterioration of devitrification can be suppressed. Therefore, the upper limit of the ZnO content is preferably 30.0% or less, more preferably 15.0% or less, even more preferably 10.0% or less, and most preferably 5.0% or less.

[0024] The TiO2 component is an optional component that plays a role in forming nuclei for crystal precipitation and also contributes to lowering the viscosity of the glass-ceramics and improving its chemical durability. The TiO2 component content may be preferably more than 0%, more preferably 0.5% or more, even more preferably 1.0% or more, and most preferably 1.5% or more as the lower limit. On the other hand, by keeping the content of the TiO2 component at 10.0% or less, deterioration of devitrification can be suppressed. Therefore, the upper limit of the content of the TiO2 component is preferably set to 10.0% or less, more preferably 8.0% or less, even more preferably 6.0% or less, and most preferably 5.0% or less.

[0025] In order to achieve excellent resistance to devitrification during melting while precipitating crystals, it is preferable that the molar ratio of TiO2 to Na2O, i.e., the value of [TiO2 / Na2O], in mole percent converted to oxide, is in the range of 0 to 0.41. The lower limit of the value of [TiO2 / Na2O] is preferably 0 or more, more preferably 0.05 or more, even more preferably 0.10 or more, and most preferably 0.12 or more. Similarly, the upper limit of the value of [TiO2 / Na2O] is preferably 0.41 or less, more preferably 0.40 or less.

[0026] In the present invention, in order to obtain the above-mentioned crystalline phase while maintaining excellent meltability and moldability, the total content of the MgO and ZnO components, i.e., the value of [MgO + ZnO], in mole percent (oxide equivalent), is preferably in the range of 1.0% to 30.0%. The lower limit of the value of [MgO + ZnO] is preferably 1.0% or more, more preferably 5.0% or more, even more preferably 10.0% or more, and most preferably 12.0% or more. Similarly, the upper limit of the value of [MgO + ZnO] is preferably 30.0% or less, more preferably 20.0% or less, even more preferably 18.0% or less, even more preferably 17.0% or less, and most preferably 16.0% or less.

[0027] When the B2O3 content exceeds 0%, it contributes to lowering the viscosity of the glass and improves the meltability and formability of the glass, and therefore can be added as an optional component. On the other hand, if the B2O3 component is contained in excess, the chemical durability of the crystallized glass tends to decrease and the precipitation of crystals tends to be suppressed. Therefore, the content of the B2O3 component is preferably 25.0% or less, more preferably 10.0% or less, even more preferably 5.0% or less, and most preferably less than 2.0%. Furthermore, the content of the B2O3 component, in terms of mass% of oxide, may be 0.0% to less than 2.0% or 0.0% to 1.0%.

[0028] The P2O5 component is an optional component that contributes to improving the low-temperature melting property of the glass when the content exceeds 0%. On the other hand, excessive inclusion of the P2O5 component reduces devitrification resistance and makes the glass more susceptible to phase separation. Therefore, the upper limit of the P2O5 content is preferably 10.0% or less, more preferably 7.0% or less, more preferably 5.0% or less, even more preferably 4.0% or less, and most preferably 3.0% or less. The lower limit of the P2O5 component is 0% or more, more preferably more than 0%, and even more preferably 0.5% or more.

[0029] The K2O component is an optional component that contributes to improving the low-temperature melting property and moldability of the glass. On the other hand, excessive inclusion of the K2O component tends to deteriorate chemical durability and increase the average linear expansion coefficient. Therefore, the upper limit of the K2O component content is preferably 20.0% or less, more preferably 10.0% or less, even more preferably 5.0% or less, and most preferably less than 2.0%. The lower limit of the K2O component content is preferably 0% or more, more preferably more than 0%, more preferably 0.5% or more, even more preferably 0.8% or more, and most preferably 1.0% or more.

[0030] The CaO component is an optional component that contributes to improving the low-temperature melting property of the glass when the content exceeds 0%. On the other hand, excessive CaO content tends to reduce devitrification resistance. Therefore, the upper limit of the CaO content is preferably 10.0% or less, more preferably 7.0% or less, more preferably 5.0% or less, more preferably 4.0% or less, even more preferably 3.0% or less, even more preferably 1.2% or less, and most preferably 1.0% or less. The lower limit of the CaO content is 0% or more, more preferably more than 0%, and even more preferably 0.5% or more.

[0031] The BaO component is an optional component that contributes to improving the low-temperature melting property of the glass when the content exceeds 0%. On the other hand, excessive inclusion of BaO component tends to reduce devitrification resistance. Therefore, the upper limit of the BaO component content is preferably 10.0% or less, more preferably 5.0% or less, more preferably 4.0% or less, even more preferably 3.0% or less, and most preferably 1.0% or less. The lower limit of the BaO component content is 0% or more, more preferably more than 0%, and even more preferably 0.5% or more.

[0032] The FeO component is one of the components that can form a crystalline phase and also acts as a fining agent, so it can be optionally contained. On the other hand, excessive FeO content can cause excessive coloring and alloying with platinum used in glass melting equipment. Therefore, the upper limit of the FeO content is preferably 8.0% or less, more preferably 5.0% or less, more preferably 3.0% or less, and most preferably 1.0% or less. The lower limit of the FeO content is 0% or more, more preferably more than 0%, and even more preferably 0.5% or more.

[0033] The ZrO2 component is an optional component that can act as a nucleator for crystal precipitation and also contributes to improving the chemical durability of the glass. Therefore, the content of the ZrO2 component may be preferably 0% or more, or may be greater than 0%, more preferably 0.4% or more, even more preferably 0.8% or more, and most preferably 1.0% or more as the lower limit. On the other hand, if the ZrO2 component is contained in excess, the devitrification resistance of the glass tends to decrease. Therefore, the upper limit of the ZrO2 component content is preferably set to 10.0% or less, more preferably 4.0% or less, even more preferably 2.0% or less, and most preferably 1.5% or less.

[0034] The SnO2 component is an optional component that can act as a clarifier and as a nucleator for crystal precipitation. Therefore, the content of the SnO2 component may be preferably 0% or more, or may be greater than 0%, more preferably 0.01% or more, and most preferably 0.05% or more as the lower limit. On the other hand, if the SnO2 component is contained in excess, the devitrification resistance of the glass tends to decrease. Therefore, the upper limit of the SnO2 component content is preferably 5.0% or less, more preferably 1.0% or less, even more preferably 0.4% or less, and most preferably 0.2% or less.

[0035] The SrO component is an optional component that, when contained in an amount of more than 0%, improves the low-temperature melting property of the glass. On the other hand, if the SrO component is contained in excess, the devitrification resistance tends to decrease. The upper limit is preferably 10.0% or less, more preferably 7.0% or less, more preferably 5.0% or less, more preferably 4.0% or less, even more preferably 3.0% or less, and most preferably 1.0% or less. The lower limit is 0% or more, more preferably more than 0%, and even more preferably 0.5% or more.

[0036] The La2O3 component is an optional component that improves the mechanical strength of the glass-ceramics when the content exceeds 0%. On the other hand, excessive inclusion of the La2O3 component tends to reduce devitrification resistance. Therefore, the upper limit of the La2O3 content is preferably 3.0% or less, more preferably 2.0% or less, and most preferably 1.0% or less. The lower limit is 0% or more, more preferably more than 0%, and even more preferably 0.5% or more.

[0037] The Y2O3 component is an optional component that improves the mechanical strength of the glass-ceramics when the content exceeds 0%. On the other hand, if the Y2O3 component is contained in excess, the devitrification resistance tends to decrease. Therefore, the upper limit of the Y2O3 component content is preferably set to 3.0% or less, more preferably 2.0% or less, and most preferably 1.0% or less.

[0038] The Nb2O5 component is an optional component that improves the mechanical strength of the glass-ceramics when the content exceeds 0%. On the other hand, if the Nb2O5 component is contained in excess, the devitrification resistance tends to decrease. Therefore, the upper limit of the Nb2O5 component content is preferably 5.0% or less, more preferably 2.0% or less, and most preferably 1.0% or less.

[0039] The Ta2O5 component is an optional component that improves the mechanical strength of the glass-ceramics when contained in an amount exceeding 0%. On the other hand, if the Ta2O5 component is contained in excess, the devitrification resistance tends to decrease. Therefore, the upper limit of the Ta2O5 component content is preferably 5.0% or less, more preferably 2.0% or less, and most preferably 1.0% or less.

[0040] The WO3 component is an optional component that improves the mechanical strength of the glass-ceramics when it is contained in an amount of more than 0%. On the other hand, excessive WO3 content tends to reduce devitrification resistance, so the upper limit of the WO3 content is preferably 5.0% or less, more preferably 2.0% or less, and most preferably 1.0% or less.

[0041] The crystallized glass may contain optional components such as Gd2O3 and TeO2, with the content of each component being 0% to 2.0%, or 0.5% to 1.0%.

[0042] The crystallized glass may contain, as a fining agent, one or more selected from the group consisting of Sb2O3, SnO2 and CeO2 components in an amount of 0% to 2.0%, preferably 0.005% to 1.0%, and more preferably 0.01% to 0.5%.

[0043] Other components not mentioned above can be added to the glass-ceramics as needed, within the range that does not impair the properties of the strengthened glass-ceramics of the present invention.

[0044] In recent years, there has been a trend to reduce the use of Pb, Th, Cd, Tl, Os, Be, and Se as harmful chemical substances, so it is preferable that these components are substantially not contained.

[0045] The above blending amounts can be combined as appropriate.

[0046] The total content of the SiO2 component, Al2O3 component, Na2O component, Li2O component, MgO component, ZnO component, and TiO2 component can be 85.0% or more, 90.0% or more, 95.0% or more, or 97.0% or more.

[0047] The strengthened crystallized glass of the present invention has a compressive stress layer on its surface due to chemical strengthening. If the outermost surface is defined as having a depth of zero, the compressive stress of the outermost surface (surface compressive stress) is CS. The depth of the compressive stress layer when the compressive stress is 0 MPa is defined as DOLzero.

[0048] The surface compressive stress value (CS) of the compressive stress layer is preferably 800 MPa or more. Such a surface compressive stress value can suppress crack extension and increase mechanical strength. The compressive stress value of the surface compressive stress layer can be 800 MPa or more, 900 MPa or more, 1000 MPa or more, 1010 MPa or more, or 1140 MPa or more. On the other hand, the upper limit can be set to 1300 MPa or less, or 1280 MPa or less.

[0049] The central tensile stress (CT) is preferably 25 MPa or more. Such a central tensile stress can suppress crack extension and increase mechanical strength. The lower limit of the central tensile stress can be 25 MPa or more, 27 MPa or more, 30 MPa or more, or 32 MPa or more. On the other hand, the upper limit can be set to 80 MPa or less, 70 MPa or less, or 60 MPa or less.

[0050] The depth (DOLzero) of the compressive stress layer is preferably 60 μm or more. When the compressive stress layer has such a depth, even if deep cracks occur in the strengthened crystallized glass, the cracks can be prevented from extending or the substrate can be prevented from breaking. The lower limit of the depth of the compressive stress layer can be 60 μm or more, 70 μm or more, 75 μm or more, 80 μm or more, or 110 μm or more.

[0051] The crystallized glass of the present invention preferably has a CT / DOLzero ratio of 0.10 to 0.90, which allows the glass to maintain high mechanical strength and is less likely to break into small pieces when broken. The lower limit of the ratio of CT / DOLzero can be 0.10 or more, 0.20 or more, or 0.30 or more. On the other hand, the upper limit of the CT / DOLzero ratio can be 0.90 or less, 0.80 or less, or 0.70 or less.

[0052] The strengthened glass-ceramics of the present invention preferably has a product of CT×DOLzero of 1500 to 10000. This makes it possible to suppress the extension of cracks even if deep cracks occur in the strengthened glass-ceramics. The lower limit of the product of CT x DOLzero can be 1500 or more, 2000 or more, 2300 or more, or 2500 or more. On the other hand, the upper limit of the product of CT×DOLzero can be 10,000 or less, 8,000 or less, 7,500 or less, or 7,300 or less.

[0053] The crystallized glass of the present invention preferably has a CS / CT ratio of 10 to 50. This allows the glass to maintain high mechanical strength while being less likely to break into small pieces when broken. The lower limit of the CS / CT ratio can be 10 or more, 13 or more, or 15 or more. On the other hand, the upper limit of the CS / CT ratio can be 50 or less, 45 or less, or 40 or less.

[0054] The crystallized glass of the present invention preferably has a ratio of DOLzero / T (%) of 8.0% to 23%, where T is the thickness (mm) of the crystallized glass substrate. This makes it possible to suppress the extension of deep cracks even if they occur in the strengthened crystallized glass. The lower limit of the ratio of DOLzero / T (%) can be 8.0% or more, 9.0% or more, 10.0% or more, or 11.0% or more. On the other hand, the upper limit of the ratio of DOLzero / T (%) can be 23.0% or less, 20.0% or less, 19.0% or less, or 18.0% or less.

[0055] The lower limit of the thickness of the strengthened crystallized glass substrate is preferably 0.10 mm or more, more preferably 0.20 mm or more, more preferably 0.40 mm or more, and even more preferably 0.50 mm or more, and the upper limit of the thickness of the strengthened crystallized glass substrate is preferably 1.00 mm or less, more preferably 0.90 mm or less, more preferably 0.80 mm or less, and even more preferably 0.70 mm or less.

[0056] The height of the sandpaper drop test for the tempered crystallized glass carried out in the examples is preferably 70 cm or more, more preferably 80 cm or more, and even more preferably 90 cm. By having such impact resistance, the glass can withstand the impact of a drop when used as a protective member.

[0057] The strengthened glass-ceramics of the present invention can be produced, for example, by the following method. The raw materials are mixed uniformly, and the resulting mixture is placed in a platinum or quartz crucible. Depending on the melting difficulty of the glass composition, the mixture is melted and stirred in an electric or gas furnace at a temperature between 1300 and 1540°C to homogenize it. The mixture is then shaped and slowly cooled to produce base glass. This base glass is then crystallized to produce crystallized glass. The crystallized glass can then be used as a base material for chemical strengthening to form a compressive stress layer.

[0058] The raw glass is heat-treated to precipitate crystals inside the glass. This heat treatment can be performed at one temperature or two temperatures. In the two-stage heat treatment, a nucleation step is first performed by heat treatment at a first temperature, and after this nucleation step, a crystal growth step is performed by heat treatment at a second temperature higher than that of the nucleation step. In one-stage heat treatment, the nucleation process and the crystal growth process are carried out consecutively at a single temperature. Typically, the temperature is raised to a predetermined heat treatment temperature, and after reaching that temperature, the temperature is maintained for a certain period of time, and then the temperature is lowered. The first temperature of the two-stage heat treatment is preferably 600° C. to 750° C. The holding time at the first temperature is preferably 30 minutes to 2000 minutes, more preferably 180 minutes to 1440 minutes. The second temperature of the two-stage heat treatment is preferably 650° C. to 850° C. The holding time at the second temperature is preferably 30 minutes to 600 minutes, more preferably 60 minutes to 300 minutes. When heat treatment is performed at one temperature step, the heat treatment temperature is preferably 600 to 800° C., more preferably 630 to 770° C. The holding time at the heat treatment temperature is preferably 30 to 500 minutes, more preferably 60 to 300 minutes.

[0059] When chemically strengthening is performed, a thin-plate-shaped crystallized glass substrate is usually produced from crystallized glass by, for example, grinding and polishing, and then a compressive stress layer is formed on the crystallized glass substrate by ion exchange using a chemical strengthening method.

[0060] The crystallized glass (base material) is preferably chemically strengthened by contacting or immersing the base material in a salt bath (first salt bath) of a molten salt (single bath) of sodium salt alone or a molten salt (mixed bath) containing potassium salt and sodium salt, and then subsequently contacting or immersing the base material in a salt bath (second salt bath) of a molten salt (single bath) of potassium salt alone or a molten salt (mixed bath) containing potassium salt and sodium salt. The mixed molten salt used in the first salt bath preferably contains more sodium salt than potassium salt, and the mixed molten salt used in the second salt bath preferably contains more potassium salt than sodium salt.

[0061] Potassium nitrate (KNO3) and sodium nitrate (NaNO3), for example, can be used as the potassium salt and sodium salt. Specifically, in the first salt bath, for example, the crystallized glass base material is contacted with or immersed in sodium nitrate or a molten salt of a mixed salt or composite salt of potassium nitrate and sodium nitrate heated to 300 to 700°C (preferably 350 to 600°C, more preferably 400 to 550°C) for 100 minutes or more, for example, 200 to 900 minutes, preferably 250 to 800 minutes, and more preferably 270 to 750 minutes. The ratio of potassium salt to sodium salt can be, for example, 0 to less than 100 parts by mass, 0 to 70 parts by mass, 0 to 50 parts by mass, 0 to 30 parts by mass, or 0 to 10 parts by mass, relative to 100 parts by mass of sodium nitrate.

[0062] In the second salt bath treatment, for example, the crystallized glass base material that has been treated in the first salt bath is brought into contact with or immersed in a molten salt of potassium nitrate or a mixed salt or composite salt of potassium nitrate and sodium nitrate heated to 200 to 700°C (preferably 300 to 600°C, more preferably 350 to 550°C) for, for example, 1 minute or more, 3 to 300 minutes, 4 to 200 minutes, or 5 to 150 minutes. The ratio of potassium salt to sodium salt can be, for example, 0 to 70 parts by mass, 0 to 50 parts by mass, 0 to 30 parts by mass, 0 to 10 parts by mass, or 0 to 5 parts by mass of sodium nitrate, when the mass of potassium nitrate is taken as 100 parts by mass.

[0063] The chemical strengthening described above promotes an ion exchange reaction between components present near the surface and components contained in the molten salt, resulting in the formation of a compressive stress layer on the surface. [Example]

[0064] Examples 1 to 16, Comparative Examples 1 and 2 1. Manufacturing of crystallized glass As raw materials for each component of the crystallized glass, raw materials such as oxides, hydroxides, carbonates, nitrates, fluorides, chlorides, metaphosphate compounds, etc. were selected, and these raw materials were weighed and mixed uniformly to obtain the compositions (mol %) shown in Table 1. In Table 1, crystallized glasses A to E are glasses used in the examples, and crystallized glasses F and G are glasses used in the comparative examples.

[0065] Next, the mixed raw materials were placed in a platinum crucible and melted in an electric furnace at a temperature ranging from 1300°C to 1540°C depending on the melting difficulty of the glass composition. The molten glass was then stirred to homogenize it, poured into a mold, and slowly cooled to produce the base glass.

[0066] The obtained raw glasses were subjected to a one-stage heat treatment for glasses A to F and a two-stage heat treatment for glass G under the crystallization conditions shown in Table 1 for nucleation and crystallization, to produce the base materials glasses A to G. The obtained glasses were subjected to lattice image confirmation using electron diffraction images and analysis using EDX, confirming the presence of MgAl2O4 and MgTi2O5 crystalline phases.

[0067] 2. Chemical strengthening of glass-ceramics using sodium alone The produced crystallized glasses A to G were cut and ground, and then polished parallel to each other to a thickness of 1 mm to obtain crystallized glass substrates.

[0068] Next, the glass-ceramics substrates were immersed in a NaNO3 salt bath at 490°C for 500 minutes to perform chemical strengthening, and the surface conditions of the substrates after chemical strengthening were confirmed. The surface conditions of strengthened glass-ceramics F and G were rougher than before strengthening, and strengthened glass-ceramics F in particular was cracked. In contrast, the surface conditions of strengthened glass-ceramics A to E did not change significantly from before strengthening.

[0069] 3. Two-stage chemical strengthening of glass-ceramics Crystallized glasses B to G were cut and ground, and then polished parallel to each other to obtain the thicknesses shown in Tables 2 to 4, to obtain crystallized glass substrates. The crystallized glass substrates were then used as base materials and chemically strengthened using KNO3 and NaNO3 under the conditions shown in Tables 2 to 4. In the tables, "Na only" indicates a molten salt containing only NaNO3, "K only" indicates a molten salt containing only KNO3, and "K:Na" indicates a mixed molten salt of KNO3 and NaNO3 with a salt bath ratio of KNO3:NaNO3 (mass ratio). Specifically, for example, in Example 1, the glass substrates were immersed in a molten salt containing only NaNO3 at 490°C for 500 minutes, and then in a molten salt containing only KNO3 at 380°C for 60 minutes.

[0070] 4. Evaluation of tempered glass-ceramics The strengthened crystallized glass substrate obtained by the above two-stage chemical strengthening was subjected to the following measurements. The results are shown in Tables 2 to 4. (1) Stress measurement The surface compressive stress (CS) of the tempered crystallized glass substrate was measured using an Orihara Manufacturing Co., Ltd. FSM-6000LE series glass surface stress meter. A 596 nm wavelength light source was selected for the CS measurement. The refractive index used for CS measurement was the refractive index value at 596 nm. The refractive index value at a wavelength of 596 nm was calculated using a quadratic approximation formula from the measured refractive index values at the C-line, d-line, F-line, and g-line wavelengths in accordance with the V-block method specified in JIS B 7071-2:2018. The photoelastic constant value at 596 nm used in the CS measurement was calculated using a quadratic approximation formula from the measured values of the photoelastic constant at wavelengths of 435.8 nm, 546.1 nm, and 643.9 nm.

[0071] The depth DOLzero (μm) and central tensile stress (CT) of the compressive stress layer when the compressive stress was 0 MPa were measured using a scattered light photoelastic stress meter SLP-1000. A light source with a wavelength of 640 nm was selected for the measurement of DOLzero and CT. The refractive index used for DOLzero and CT measurements was the value at 640 nm, which was calculated using a second-order approximation formula from the measured refractive indices at the wavelengths of C-line, d-line, F-line, and g-line in accordance with the V-block method specified in JIS B 7071-2:2018.

[0072] The photoelastic constant value at 640 nm used for DOLzero and CT measurements was calculated using a quadratic approximation formula from the measured values of the photoelastic constant at wavelengths of 435.8 nm, 546.1 nm, and 643.9 nm.

[0073] (2) Sandpaper drop test A sandpaper drop test was conducted in the following manner, which simulated a drop onto asphalt. A drop test sample was prepared by attaching a glass substrate of the same dimensions to a tempered crystallized glass substrate (150 mm long x 70 mm wide). All drop test samples weighed 40 g. A layer of #80 sandpaper was placed on a stainless steel base, and the drop test sample was dropped onto the base from a height of 20 cm, with the tempered crystallized glass substrate facing downwards. If the substrate did not break after the drop, the height was increased by 5 cm, and the drop was repeated until the substrate broke. The test was performed three times (n1 to n3). The table shows the height at which the sample broke, the maximum value (Max), the minimum value (Min), and the average value (Ave).

[0074] [Table 1]

[0075] [Table 2]

[0076] [Table 3]

[0077] [Table 4]

[0078] Although several embodiments and / or examples of the present invention have been described in detail above, those skilled in the art will readily be able to make numerous modifications to these exemplary embodiments and / or examples without substantially departing from the novel teachings and advantages of the present invention, and therefore, these numerous modifications are within the scope of the present invention. The disclosures (including the specification, drawings, and claims) of the documents cited in this specification and the Japanese application specification on which the present application has Paris priority are incorporated herein in their entirety by reference.

Claims

1. In mole percent converted to oxide, SiO ２ Ingredients: 30.0% to 70.0%, Al ２ O ３ Ingredients: 8.0% to 25.0%, Na ２ O component 2.0% to 25.0%, Li ２ O component 1.0% to 6.0%, MgO content: 10.914% to 25.0% ZnO component: 0% to 30.0% and TiO ２ Contains 0% to 10.0% of the ingredient, The base material is crystallized glass, It has a compressive stress layer on the surface, The strengthened crystallized glass is characterized in that the depth (DOLzero) of the compressive stress layer is 60 μm or more.

2. 2. The strengthened crystallized glass according to claim 1, wherein the total content of said MgO component and said ZnO component is 10.914% or more and 30.0% or less in mole percent calculated as oxide.

3. The crystallized glass contains, in mole percent in terms of oxides: B ２ O ３ Ingredients: 0% to 25.0%, P ２ O ５ Ingredients: 0% to 10.0%, K ２ O component 0% to 20.0%, CaO component 0% to 10.0%, BaO component 0% to 10.0%, FeO content: 0% to 8.0% ZrO ２ Ingredients: 0% to 10.0%, SnO ２ Ingredients: 0% to 5.0% 3. The strengthened crystallized glass according to claim 1, comprising:

4. The crystallized glass contains, in mole percent in terms of oxides: SrO component 0% to 10.0%, La ２ O ３ Ingredients: 0% to 3.0%, Y ２ O ３ Ingredients: 0% to 3.0%, Nb ２ O ５ Ingredients: 0% to 5.0%, Ta ２ O ５ Ingredients: 0% to 5.0%, WO ３ Ingredients: 0% to 5.0% 4. The strengthened crystallized glass according to claim 1, comprising:

5. B of the crystallized glass ２ O ３ 5. The strengthened crystallized glass according to claim 1, wherein the content of the component is 0.0% or more and less than 2.0% by mass in terms of oxide.

6. The TiO in mole percent in terms of oxide ２ The component Na ２ Molar ratio to the O component [TiO ２ / Na ２ 6. The strengthened glass-ceramics according to claim 1, wherein the value of [O] is 0 or more and 0.41 or less.

7. 7. The strengthened crystallized glass according to claim 1, wherein the compressive stress layer has a surface compressive stress value (CS) of 800 MPa or more.

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