GLASS CERAMIC, MANUFACTURING METHOD THEREOF, AND DEVICE

Abstract

Provided is a transparent glass ceramic that has sufficiently low viscosity in the melt state, allows effective chemical strengthening by ion exchange, and has high internal strength. The glass ceramic has a composition including, in mol % by oxide equivalent, SiO.sub.2: 55% or more to 70% or less; B.sub.2O.sub.3: over 0% to 10% or less; P.sub.2O.sub.5: over 0% to 5% or less; Li.sub.2O: 18% or more to 30% or less; Na.sub.2O: over 3% to 10% or less; K.sub.2O: 0% or more to 5% or less; and ZrO.sub.2: over 0% to 5% or less. The glass ceramic substantially does not include Al.sub.2O.sub.3.

Claims

1. A glass ceramic having a composition comprising: in mol % by oxide equivalent, SiO.sub.2: 55% or more to 70% or less; B.sub.2O.sub.3: over 0% to 10% or less; P.sub.2O.sub.5: over 0% to 5% or less; Li.sub.2O: 18% or more to 30% or less; Na.sub.2O: over 3% to 10% or less; K.sub.2O: 0% or more to 5% or less; and ZrO.sub.2: over 0% to 5% or less, wherein the glass ceramic substantially does not comprise Al.sub.2O.sub.3.

2. The glass ceramic according to claim 1, wherein a temperature at which viscosity of the glass ceramic in a melt state exhibits a value of 100 dPa.Math.s is 1200 C. or less.

3. The glass ceramic according to claim 1, comprising at least one of a Li.sub.2SiO.sub.3 crystalline phase and a Li.sub.2Si.sub.2O.sub.5 crystalline phase.

4. The glass ceramic according to claim 1, wherein at a thickness of 1 mm, the glass ceramic has a transmittance of 85% or more with respect to 400 nm wavelength light.

5. The glass ceramic according to claim 1, wherein Vickers hardness of the glass ceramic is 600 HV or more.

6. The glass ceramic according to claim 1, wherein a fracture toughness value of the glass ceramic is 1.00 MPa.Math.m.sup.1/2 or more.

7. The glass ceramic according to claim 1, comprising a compressive stress layer on a surface of the glass ceramic.

8. The glass ceramic according to claim 7, wherein the compressive stress layer has a surface compressive stress value of 400 MPa or more and a compressive stress depth of 50 m or more.

9. A method for manufacturing glass ceramic, the method comprising: preparing a glass composition having a composition including in mol % by oxide equivalent, SiO.sub.2: 55% or more to 70% or less, B.sub.2O.sub.3: over 0% to 10% or less, P.sub.2O.sub.5: over 0% to 5% or less, Li.sub.2O: 18% or more to 30% or less, Na.sub.2O: over 3% to 10% or less, K.sub.2O: 0% or more to 5% or less, and ZrO.sub.2: over 0% to 5% or less, the glass composition substantially not including Al.sub.2O.sub.3; and applying crystallization treatment to the glass composition to obtain a glass ceramic.

10. A device using the glass ceramic according to claim 1.

11. The glass ceramic according to claim 2, comprising at least one of a Li.sub.2SiO.sub.3 crystalline phase and a Li.sub.2Si.sub.2O.sub.5 crystalline phase.

12. The glass ceramic according to claim 2, wherein at a thickness of 1 mm, the glass ceramic has a transmittance of 85% or more with respect to 400 nm wavelength light.

13. The glass ceramic according to claim 2, wherein Vickers hardness of the glass ceramic is 600 HV or more.

14. The glass ceramic according to claim 2, wherein a fracture toughness value of the glass ceramic is 1.00 MPa.Math.m.sup.1/2 or more.

15. The glass ceramic according to claim 2, comprising a compressive stress layer on a surface of the glass ceramic.

16. The glass ceramic according to claim 15, wherein the compressive stress layer has a surface compressive stress value of 400 MPa or more and a compressive stress depth of 50 m or more.

17. A device using the glass ceramic according to claim 2.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0054] In the accompanying drawings:

[0055] FIG. 1 is a diagram illustrating the X-ray diffraction pattern of a glass ceramic in Example 1;

[0056] FIG. 2 is a diagram illustrating the X-ray diffraction pattern of a glass ceramic in Example 2;

[0057] FIG. 3 is a diagram illustrating the transmission spectrum of the glass ceramic in Example 2; and

[0058] FIG. 4 is a diagram illustrating the residual stress profile of the glass ceramic in Example 2.

DETAILED DESCRIPTION

(Glass Ceramic)

[0059] The glass ceramic of an embodiment of the present disclosure (also referred to as the glass ceramic of the present embodiment) is described below in detail. The glass ceramic of the present embodiment has a composition including, in mol % by oxide equivalent, [0060] SiO.sub.2: 55% or more to 70% or less, [0061] B.sub.2O.sub.3: over 0% to 10% or less, [0062] P.sub.2O.sub.5: over 0% to 5% or less, [0063] Li.sub.2O: 18% or more to 30% or less, [0064] Na.sub.2O: over 3% to 10% or less, [0065] K.sub.2O: 0% or more to 5% or less, and [0066] ZrO.sub.2: over 0% to 5% or less,
and the glass ceramic substantially does not include Al.sub.2O.sub.3.

[0067] The glass ceramic according to the present embodiment is a transparent glass ceramic that has sufficiently low viscosity in the melt state, allows effective chemical strengthening by ion exchange, and has high internal strength.

[0068] In the present specification, a glass ceramic refers to glass that partially contains crystals and that can be made by, for example, causing crystals to precipitate inside the glass. Glass ceramic is also referred to as crystallized glass in this field.

[0069] The glass ceramic of the present embodiment has a sufficiently low viscosity in the melt state by virtue of having the predetermined composition described above. Therefore, use of the glass ceramic of the present embodiment enables production of members with complex shapes by DP, can reduce costs, and enables mass production. In addition, the glass ceramic of the present embodiment has high ion-exchangeability due to the predetermined composition described above. Therefore, high strength can effectively be achieved by ion exchange (chemical strengthening). Furthermore, the glass ceramic of the present embodiment has transparency and high internal strength (strength of the material itself) due to the predetermined composition described above. Therefore, the glass ceramic of the present embodiment can be used as cover glass for mobile devices or the like that require transparency. As described above, the glass ceramic of the present embodiment has high adaptability as a glass-based material.

[0070] The glass ceramic of the present embodiment may contain other components (described below) other than the above-described components. However, from the viewpoint of more reliably expressing the desired characteristics, the glass ceramic of the present embodiment preferably has a composition consisting only of the above-described components (SiO.sub.2, B.sub.2O.sub.3, P.sub.2O.sub.5, Li.sub.2O, Na.sub.2O, and ZrO.sub.2 as essential components and only K.sub.2O an optional component, in oxide notation).

[0071] Here, consisting only of the above-described components includes the case of impurity components other than the aforementioned components being unavoidably mixed in, specifically when the ratio of impurity components is 0.2 mol % or less.

[0072] First, the reasons for limiting the composition of the glass ceramic in the present embodiment to the above ranges are described.

[0073] The % indication regarding components refers to mol % by oxide equivalent, unless otherwise specified.

<SiO.SUB.2.>

[0074] In the glass ceramic of the present embodiment, SiO.sub.2 is an important essential component that enables glass formation and forms the Li.sub.2SiO.sub.3 and/or Li.sub.2Si.sub.2O.sub.5 crystalline phases that are mainly precipitated during crystallization. However, if the content exceeds 70%, the viscosity of the glass melt may increase significantly. On the other hand, if the content is less than 55%, the glass-forming ability may decrease, and transparency may decrease during crystallization. Therefore, in the glass ceramic of the present embodiment, the SiO.sub.2 content is in a range of 55% or more to 70% or less. From the same perspective, the SiO.sub.2 content in the glass ceramic of the present embodiment is preferably 56% or more, more preferably 57% or more, even more preferably 58% or more, preferably 69% or less, more preferably 67% or less, and even more preferably 66% or less.

<B.sub.2O.sub.3>

[0075] In the glass ceramic of the present embodiment, B.sub.2O.sub.3 is an important essential component that enables glass formation, lowers the viscosity of the glass melt, and furthermore promotes homogeneous crystallization. However, if the content exceeds 10%, the glass-forming ability may decrease, and transparency may decrease during crystallization. On the other hand, if B.sub.2O.sub.3 is not included, the effect of lowering the viscosity of the glass melt cannot be obtained, and transparency may decrease during crystallization. Therefore, in the glass ceramic of the present embodiment, the B.sub.2O.sub.3 content is in a range of over 0% to 10% or less. From the same perspective, the B.sub.2O.sub.3 content in the glass ceramic of the present embodiment is preferably 1% or more, more preferably 2% or more, preferably 9% or less, more preferably 8% or less, and even more preferably 7% or less.

<P.sub.2O.sub.5>

[0076] In the glass ceramic of the present embodiment, P.sub.2O.sub.5 is an important essential component that promotes homogeneous crystallization. However, if the content exceeds 5%, the glass-forming ability may decrease, and transparency may decrease during crystallization. On the other hand, if P.sub.2O.sub.5 is not included, transparency may decrease during crystallization. Therefore, in the glass ceramic of the present embodiment, the P.sub.2O.sub.5 content is in a range of over 0% to 5% or less. From the same perspective, the P.sub.2O.sub.5 content in the glass ceramic of the present embodiment is preferably 0.5% or more, more preferably 1% or more, preferably 4% or less, and more preferably 3% or less.

<Li.SUB.2.O>

[0077] In the glass ceramic of the present embodiment, Li.sub.2O is an important essential component that significantly reduces the viscosity of the glass melt, forms the Li.sub.2SiO.sub.3 and/or Li.sub.2Si.sub.2O.sub.5 crystalline phases that are mainly precipitated during crystallization, and furthermore is a source of Li+ ions that are exchanged with Na+ ions in the chemical strengthening treatment using NaNO.sub.3 melt or the like. However, if the content exceeds 30%, the glass-forming ability may decrease, and transparency may decrease during crystallization. On the other hand, if the content is less than 18%, the effect of lowering the viscosity of the glass melt may be insufficient, and the strength improvement by the chemical strengthening treatment may not be sufficiently achieved. Therefore, in the glass ceramic of the present embodiment, the Li.sub.2O content is in a range of 18% or more to 30% or less. From the same perspective, the Li.sub.2O content in the glass ceramic of the present embodiment is preferably 19% or more, more preferably 20% or more, preferably 29% or less, more preferably 28% or less, and even more preferably 27% or less.

<Na.SUB.2.O>

[0078] In the glass ceramic of the present embodiment, Na.sub.2O is an important essential component that reduces the viscosity of the glass melt, increases the glass-forming ability in combination with Li.sub.2O, increases the ion-exchangeability between Na+ ions and Li+ ions in the chemical strengthening treatment using NaNO.sub.3 melt or the like, and furthermore is a source of Na+ ions that are exchanged with K+ ions in the chemical strengthening treatment using KNO.sub.3 melt or the like. However, if the content exceeds 10%, the glass-forming ability may decrease, and transparency may decrease during crystallization. On the other hand, if the content is 3% or less, the effect of lowering the viscosity of the glass melt may be insufficient, and the strength improvement by chemical strengthening treatment may not be sufficiently achieved (for example, formation of a compressive stress layer with a surface compressive stress value of 400 MPa or more may not be achieved). Therefore, in the glass ceramic of the present embodiment, the Na.sub.2O content is in a range of over 3% to 10% or less. From the same perspective, the Na.sub.2O content in the glass ceramic of the present embodiment is preferably 3.5% or more, more preferably 4% or more, even more preferably 4.5% or more, preferably 9% or less, and more preferably 8% or less.

<K.SUB.2.O>

[0079] In the glass ceramic of the present embodiment, K.sub.2O is a component that reduces the viscosity of the glass melt and enhances the ion-exchangeability between K+ and Na+ ions in the chemical strengthening treatment using KNO.sub.3 melt. However, if the content exceeds 5%, the glass-forming ability may decrease, and transmittance may decrease during crystallization. Therefore, in the glass ceramic of the present embodiment, the K.sub.2O content is in a range of 0% or more to 5% or less. From the same perspective, the K.sub.2O content in the glass ceramic of the present embodiment is preferably 0.2% or more, more preferably 0.7% or more, even more preferably 1.0% or more, preferably 4% or less, more preferably 3% or less, and even more preferably 2% or less.

<ZrO.SUB.2.>

[0080] In the glass ceramic of the present embodiment, ZrO.sub.2 is an important essential component that promotes homogeneous crystallization. However, if the content exceeds 5%, the viscosity of the glass melt may increase, and the glass-forming ability may decrease. On the other hand, if ZrO.sub.2 is not included, transparency may decrease during crystallization. Therefore, in the glass ceramic of the present embodiment, the ZrO.sub.2 content is in a range of over 0% to 5% or less. From the same perspective, the ZrO.sub.2 content in the glass ceramic of the present embodiment is preferably 1% or more, more preferably 2% or more, preferably 4.5% or less, and more preferably 4% or less.

<Al.sub.2O.sub.3>

[0081] It was discovered that even a small amount of Al.sub.2O.sub.3 in the glass ceramic of the present embodiment may significantly increase the viscosity of the glass melt. Therefore, the glass ceramic of the present embodiment substantially does not include Al.sub.2O.sub.3.

[0082] In the present disclosure, substantially does not include means not included intentionally.

Other Components

[0083] Other components other than those described above can be included in the glass ceramic of the present embodiment, as long as the components do not deviate from the purpose. Examples of other components include coloring components such as V.sub.2O.sub.5, Cr.sub.2O.sub.3, MnO, MnO.sub.2, FeO, Fe.sub.2O.sub.3, Co.sub.2O.sub.3, Co.sub.3O.sub.4, NiO, CuO, MoO.sub.3, CeO.sub.2, Pr.sub.2O.sub.3, Nd.sub.2O.sub.3, Sm.sub.2O.sub.3, Eu.sub.2O.sub.3, Tb.sub.2O.sub.3, Dy.sub.2O.sub.3, Ho.sub.2O.sub.3, Er.sub.2O.sub.3, and Tm.sub.2O.sub.3. The glass ceramic of the present embodiment can contain one or more coloring components, selected from these components, in small amounts (for example, an amount such that the total is 10 mol % or less by outer percentage). Further examples of the other components include defoaming components such as Sb.sub.2O.sub.3, and the glass ceramic of this embodiment can contain a small amount of such defoaming components (for example, an amount such that the total is 0.5 mol % or less by outer percentage).

[0084] The calculation of the composition of each component (SiO.sub.2, Li.sub.2O, and the like) in the glass ceramic of the present embodiment does not take into account the aforementioned other components.

[0085] Next, the various characteristics of the glass ceramic of the present embodiment are described.

[0086] The glass ceramic of the present embodiment has transparency, as described above. In greater detail, at a thickness of 1 mm, the glass ceramic of the present embodiment preferably has a transmittance of 85% or more with respect to 400 nm wavelength light. Therefore, the glass ceramic of the present embodiment is suitable for producing members that require transparency, such as front displays of mobile devices, for example.

[0087] The glass ceramic of the present embodiment has a sufficiently low viscosity in the melt state, as described above. In greater detail, the temperature at which the viscosity of the glass ceramic of the present embodiment in the melt state exhibits a value of 100 dPa.Math.s is preferably 1200 C. or less. The temperature at which the viscosity of the glass ceramic of the present embodiment in the melt state exhibits a value of 100 dPa.Math.s is more preferably 1180 C. or less, even more preferably 1160 C. or less.

[0088] When glass materials such as glass ceramic are in the melt state, the viscosity tends to be lower as the temperature is higher. Therefore, the temperature at which the viscosity exhibits a certain value (for example, 100 dPa.Math.s) in the melt state is uniquely measured. The temperature at which the viscosity in the melt state exhibits a value of 100 dPa.Math.s can be adjusted by, for example, adjusting the composition of the glass ceramic as appropriate.

[0089] The glass ceramic of the present embodiment has a high internal strength (strength of the material itself), as described above. In greater detail, the glass ceramic of the present embodiment preferably includes at least one of a Li.sub.2SiO.sub.3 crystalline phase and a Li.sub.2Si.sub.2O.sub.5 crystalline phase. Both of the aforementioned Li.sub.2SiO.sub.3 crystalline phase and Li.sub.2Si.sub.2O.sub.5 crystalline phase can significantly contribute to the improvement of internal strength (strength of the material itself).

[0090] The presence of the aforementioned Li.sub.2SiO.sub.3 crystalline phase and/or Li.sub.2Si.sub.2O.sub.5 crystalline phases in glass ceramic can be identified from an X-ray diffraction pattern. The above Li.sub.2SiO.sub.3 crystalline phase and/or Li.sub.2Si.sub.2O.sub.5 crystalline phase can be formed by adjusting the composition of the glass ceramic (in particular SiO.sub.2 and Li.sub.2O) and the conditions of crystallization, such as heat treatment, as appropriate.

[0091] With respect to the aforementioned internal strength, the glass ceramic of the present embodiment preferably has a Vickers hardness of 600 HV or more. The Vickers hardness of the glass ceramic of the present embodiment is more preferably 630 HV or more, and even more preferably 650 HV or more.

[0092] The Vickers hardness of the glass ceramic can, for example, be adjusted by adjusting the composition of the glass ceramic and the conditions of crystallization, such as heat treatment, as appropriate.

[0093] With respect to the aforementioned internal strength, the glass ceramic of the present embodiment preferably has a fracture toughness value of 1.00 MPa.Math.m.sup.1/2 or more. The fracture toughness value of the glass ceramic of the present embodiment is more preferably 1.10 MPa.Math.m.sup.1/2 or more, and even more preferably 1.20 MPa.Math.m.sup.1/2 or more.

[0094] The fracture toughness value of the glass ceramic can be measured in accordance with JIS R1607:2015. The fracture toughness value of the glass ceramic can, for example, be adjusted by adjusting the composition of the glass ceramic and the conditions of crystallization, such as heat treatment, as appropriate.

[0095] The glass ceramic of the present embodiment preferably includes a compressive stress layer on the surface. As described above, since the glass ceramic of the present embodiment has high ion-exchangeability, the formation of a compressive stress layer on the surface via chemical strengthening by the ion-exchange method or the like can effectively achieve higher strength in the glass ceramic.

[0096] The compressive stress layer refers to a layer with a stress value exceeding 0 MPa. The formation of a compressive stress layer on the glass ceramic surface can be achieved by, for example, applying chemical strengthening treatment to the glass ceramic by the ion-exchange method, applying strain to the surface by rapid cooling, or the like.

[0097] In a case in which the glass ceramic of the present embodiment has a compressive stress layer on the surface, the compressive stress layer preferably has a surface compressive stress value of 400 MPa or more and a compressive stress depth of 50 m or more. The surface compressive stress value of the glass ceramic of the present embodiment is more preferably 450 MPa or more, and even more preferably 500 MPa or more. Similarly, the compressive stress depth of the glass ceramic of the present embodiment is more preferably 55 m or more, and even more preferably 60 m or more.

[0098] The surface compressive stress value refers to the stress value at the outermost surface and can be measured using a surface stress meter. The compressive stress depth refers to the thickness of the layer where the stress value exceeds 0 MPa and can be measured using a scattered light photoelastic analyzer. The surface compressive stress value and compressive stress depth can be adjusted by adjusting the formation conditions of the compressive stress layer (for example, the time and temperature of the chemical strengthening treatment) as appropriate.

(Method for Manufacturing Glass Ceramic)

[0099] Next, a method for manufacturing a glass ceramic of an embodiment of the present disclosure (also referred to as the manufacturing method of the present embodiment) is described in detail. The method for manufacturing glass ceramic includes: [0100] preparing a glass composition having a composition including [0101] in mol % by oxide equivalent, [0102] SiO.sub.2: 55% or more to 70% or less; [0103] B.sub.2O.sub.3: over 0% to 10% or less; [0104] P.sub.2O.sub.5: over 0% to 5% or less; [0105] Li.sub.2O: 18% or more to 30% or less; [0106] Na.sub.2O: over 3% to 10% or less; [0107] K.sub.2O: 0% or more to 5% or less; and [0108] ZrO.sub.2: over 0% to 5% or less, [0109] the glass composition substantially not including Al.sub.2O.sub.3 (glass preparation step); and [0110] applying crystallization treatment to the glass composition to obtain a glass ceramic (crystallization step).

[0111] According to this manufacturing method, the above-described glass ceramic of the present embodiment can be manufactured. The manufacturing method of the present embodiment may also include other steps (such as a chemical strengthening step) as necessary.

<Glass Preparation Step>

[0112] The glass preparation step is a step for preparing a glass composition having a predetermined composition. In the glass preparation step, for example, oxides, hydroxides, carbonates, nitrates, phosphates, and the like are weighed in predetermined proportions and thoroughly mixed as raw materials for each component contained in the aforementioned glass composition (and hence the glass ceramic) and for other components optionally included as needed, thereby yielding a glass preparation raw material. This glass preparation raw material is then placed into a melting vessel, that does not react with raw materials or the like (for example, a precious metal crucible), and the raw material is heated to 1200 C. to 1500 C. in an electric furnace to melt the raw material. The obtained melt is stirred for an appropriate time. Next, the result is clarified and homogenized in an electric furnace, cast in a mold preheated to an appropriate temperature, and then slowly cooled in an electric furnace to remove strain, thereby yielding the glass composition.

[0113] Alternatively, the glass preparation step can be performed by formation into a member having a predetermined shape by the direct pressing (DP) method. In greater detail, the above-described glass preparation raw material is heated in an electric furnace to 1200 C. to 1500 C. and melted. The resulting glass melt is then cooled to 1200 C. or less and poured into a mold having a predetermined shape by means of an outflow pipe or the like. Then, by using a shear blade or by dropping the mold straight down, a constricted part is formed by surface tension, the glass melt flow is separated, and a glass melt body of the desired mass is formed. Subsequently, the glass melt body is cooled in the mold and pressed to obtain a glass member (glass composition) with a predetermined shape.

[0114] This type of molding by DP is particularly suitable for making relatively large and complex-shaped members, such as mobile device housings.

[0115] A specific description of the composition (by oxide equivalent) of the aforementioned glass composition is substantially the same as the above description of the composition of the glass ceramic.

<Crystallization Step>

[0116] The crystallization step is a step of applying crystallization treatment to the aforementioned glass composition to obtain a glass ceramic. In the crystallization step, for example, crystals are precipitated to obtain a glass ceramic by heat-treating the aforementioned glass composition in a temperature range that is higher than the glass transition temperature but does not melt the glass composition. From the perspective of obtaining the desired glass ceramic more reliably, the temperature of the heat treatment is preferably 400 C. to 700 C. The duration of the heat treatment is preferably from 1 to 20 hours from the perspective of more reliably causing the desired crystals to precipitate. In addition, as heat treatment in the crystallization step, it is preferable from the perspective of increasing transparency to perform multi-step heat treatment, such as heat treatment at a relatively low temperature of 400 C. to 500 C., followed by heat treatment at a relatively high temperature of 600 C. to 700 C.

[0117] In addition to the above-described heat treatment, laser annealing treatment can also be performed in the crystallization process.

[0118] Alternatively, crystallization treatment may be applied at the time of formation into a member having a predetermined shape by the direct pressing (DP) method described above as the glass preparation step. For example, in a case in which the cooling rate in the temperature range of 400 C. to 700 C. is slow during formation by DP, crystals may precipitate in the glass member (glass composition).

<Chemical Strengthening Step>

[0119] In the manufacturing method of the present embodiment, a step of applying chemical strengthening treatment using the ion-exchange method to the glass ceramic obtained in the crystallization step may be further performed (chemical strengthening step). The chemical strengthening treatment is a treatment to immerse the aforementioned glass ceramic in a heated melt of NaNO.sub.3, KNO.sub.3, or the like. As a result of this process, Li+ ions and Na+ ions near the surface of the glass ceramic are replaced by ions with larger ionic radii, thus forming a compressive stress layer on the surface of the glass ceramic.

[0120] In the chemical strengthening treatment, from the perspective of increasing the surface compressive stress value and the compressive stress depth, i.e., for further chemical strengthening, it is preferable to perform a multi-step immersion treatment in which the glass ceramic is immersed in a heated NaNO.sub.3 melt and then immersed in a heated KNO.sub.3 melt.

[0121] In the chemical strengthening treatment, from the perspective of increasing the surface compressive stress value and the compressive stress depth, i.e., for further chemical strengthening, the temperature of the melt of NaNO.sub.3, KNO.sub.3, or the like is preferably 360 C. to 440 C. From the perspective of suppressing the decrease in the surface compressive stress value, the immersion time during the chemical strengthening treatment is preferably 24 hours or less.

(Device)

[0122] A device in an embodiment of the present disclosure uses the above-described glass ceramic. In other words, the device in an embodiment of the present disclosure includes the above-described glass ceramic as a member.

[0123] The aforementioned device is typically a device that includes a member for which at least one of strength, transparency, and freedom of shape is required (for example, a protective member for a display or housing, or a protective member for a front display or optical device). Examples of the aforementioned device include electronic devices and optical devices. Electronic devices include notebook PCs, smartphones, smartwatches, tablet terminals, and the like. Optical devices include cameras, telescopes, projectors, in-vehicle cameras, in-vehicle sensors, and the like.

EXAMPLES

[0124] The present disclosure will now be described in detail based on Examples and Comparative Examples, but the present disclosure is not limited to these Examples.

(Preparation of Glass Compositions)

[0125] Oxides, hydroxides, carbonates, nitrates, phosphates, and the like corresponding to the raw materials for each of the ingredients listed in Tables 1 and 2 were weighed to become 100 g after vitrification, mixed thoroughly, placed into a platinum crucible, and melted in an electric furnace at 1200 C. to 1500 C. for 1 to 2 hours to obtain a melt.

[0126] The temperature at which the viscosity of the obtained melt exhibited a value of 100 dPa.Math.s was measured by a rotating cylinder method. Specifically, a platinum cylinder was immersed in the melt, and the temperature at which the viscosity exhibited a value of 100 dPa.Math.s was measured based on the rotational force (torque) received by the cylinder when the cylinder was rotated. The results are listed in Tables 1 and 2.

[0127] For the examples in which the aforementioned temperature exceeded 1200 C., the viscosity in the melt state was determined to be poor, and the process was terminated without proceeding to the operations and evaluations after obtaining the glass.

[0128] The aforementioned melt was then stirred for an appropriate time to homogenize and clarify the melt, which was then cast into a mold preheated to an appropriate temperature. The glass (glass composition) was then slowly cooled in an electric furnace to remove strain.

[0129] The examples that did not vitrify were determined to be of poor quality, and the process was terminated without proceeding to the subsequent operations and evaluations. (In Tables 1 and 2, the glass compositions that vitrified are designated A, and those that did not vitrify are designated B.)

(Crystallization Treatment)

[0130] The aforementioned glass was then subjected to one or multiple steps of heat treatment in an electric furnace at 700 C. or lower for 1 to 20 hours (conditions are listed in Tables 1 and 2). As a result, crystals were precipitated inside the glass, and a glass ceramic was obtained. The conditions of heat treatment in each example were determined appropriately according to various circumstances such as glass composition.

[0131] The precipitated crystalline phase of the resulting glass ceramic was identified from the X-ray diffraction pattern obtained using an X-ray diffractometer (ULTIMA4, produced by Rigaku Corporation). The results are listed in Tables 1 and 2. In general, only precipitation of the Li.sub.2SiO.sub.3 and/or Li.sub.2Si.sub.2O.sub.5 crystalline phases was confirmed in the Examples, but in some Comparative Examples, precipitation of crystalline phases other than Li.sub.2SiO.sub.3 and Li.sub.2Si.sub.2O.sub.5 crystalline phases was also confirmed. For reference, the X-ray diffraction pattern of the glass ceramic in Example 1 is illustrated in FIG. 1, and the X-ray diffraction pattern of the glass ceramic in Example 2 is illustrated in FIG. 2.

[0132] The transparency of the resulting glass ceramic was evaluated according to the following criteria by measuring the transmittance, at a thickness of 1 mm, with respect to light having a 400 nm wavelength using a spectrophotometer (U-4100, produced by Hitachi, Ltd.). The results are listed in Tables 1 and 2. [0133] A: Transmittance of 85% or more [0134] B: Transmittance of less than 85%

[0135] For reference, the transmission spectrum of the glass ceramic in Example 2, at a thickness of 1 mm, with respect to light having 200 to 800 nm wavelengths is illustrated in FIG. 3.

[0136] The examples for which the transmittance was less than 85% were determined to have poor transparency, and the process was terminated without proceeding to the subsequent operations and evaluations.

[0137] The Vickers hardness of the resulting glass ceramic was measured using a Vickers hardness tester (MMT-X3, produced by Matsuzawa Co., Ltd.). The results are listed in Tables 1 and 2. A higher value indicates higher internal strength (strength of the material itself).

[0138] The fracture toughness value of the obtained glass ceramic was measured using the IF method according to JIS R1607:2015, Testing methods for fracture toughness of fine ceramics at room temperature. The results are listed in Tables 1 and 2. A higher value indicates higher internal strength (strength of the material itself).

(Chemical Strengthening Treatment)

[0139] Next, the aforementioned glass ceramic was subjected to chemical strengthening treatment. Specifically, the glass ceramic was immersed in a melt of NaNO.sub.3 heated to 360 C. to 440 C. for 24 hours or less and then immersed in a melt of KNO.sub.3 heated to 360 C. to 440 C. for 24 hours or less (conditions are listed in Tables 1 and 2). A compressive stress layer was thereby formed on the surface of the glass ceramic. The conditions of the chemical strengthening treatment in each example were determined appropriately according to various circumstances such as the glass composition and the conditions of the heat treatment performed in the previous step.

[0140] The surface compressive stress value and the compressive stress depth were measured for the glass ceramic on which the compressive stress layer was formed. Specifically, a glass surface stress meter (FSM-6000LEUV, produced by Orihara Manufacturing Co., Ltd.) was used to measure the surface compressive stress value. A scattered light photoelastic analyzer (SLP-2000, produced by Orihara Manufacturing Co., Ltd.) was used to measure the compressive stress depth. The results are listed in Tables 1 and 2. For reference, the residual stress profiles calculated using synthesis software (Pmc, produced by Orihara Manufacturing Co., Ltd.) from the values measured by the aforementioned glass surface stress meter and the scattered light photoelastic analyzer for the glass ceramic of Example 2 are illustrated in FIG. 4.

TABLE-US-00001 TABLE 1 Exam- Exam- Exam- Exam- Exam- Exam- Exam- Exam- Exam- Exam- ple 1 ple 2 ple 3 ple 4 ple 5 ple 6 ple 7 ple 8 ple 9 ple 10 SiO.sub.2 [mol %] 64.90 60.98 64.59 62.98 62.20 57.18 61.61 60.10 60.47 67.54 B.sub.2O.sub.3 2.40 2.45 2.39 2.45 2.39 4.50 2.36 8.69 2.33 2.15 P.sub.2O.sub.5 1.92 1.78 1.91 1.89 1.91 2.01 1.90 1.80 1.85 1.40 Al.sub.2O.sub.3 0 0 0 0 0 0 0 0 0 0 Li.sub.2O 24.05 23.57 23.93 23.50 23.92 24.58 23.70 22.84 23.26 23.00 Na.sub.2O 4.81 6.62 4.78 6.13 6.79 6.55 6.73 4.76 6.60 4.25 K.sub.2O 0.96 1.41 0.96 0.00 1.34 2.03 1.33 0.94 1.30 0.81 ZrO.sub.2 0.96 3.19 1.44 3.05 1.45 3.15 2.37 0.87 4.19 0.85 Total 100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00 Melt temperature [ C.] 1178 1133 1155 1142 1135 1079 1119 1100 1154 1196 exhibiting viscosity of 100 dPa .Math. s Vitrifiability A A A A A A A A A A Heat treatment conditions 540-5 490-5, 540-5 490-4, 540-5 480-4, 480-4, 540-5 490-5, 490-15, (temperature 620-2 510-4, 590-4 505-4, 600-2 600-2 [ C.] - time [hr]) 600-4 610-4 Precipitated crystalline Li.sub.2SiO.sub.3 Li.sub.2Si.sub.2O.sub.5 Li.sub.2SiO.sub.3 Li.sub.2Si.sub.2O.sub.5 Li.sub.2SiO.sub.3 Li.sub.2SiO.sub.3, Li.sub.2Si.sub.2O.sub.5 Li.sub.2SiO.sub.3 Li.sub.2SiO.sub.3, Li.sub.2SiO.sub.3, phase Li.sub.2SiO.sub.5 Li.sub.2Si.sub.2O.sub.5 Li.sub.2Si.sub.2O.sub.5 Transparency A A A A A A A A A A Vickers hardness [HV] 686 780 741 782 735 645 851 631 814 774 Fracture toughness value 1.16 2.73 1.34 2.30 1.22 1.60 2.44 1.30 2.12 1.89 [MPa .Math. m.sup.1/2] Chemical strengthening NaNO.sub.3- NaNO.sub.3- NaNO.sub.3- NaNO.sub.3- NaNO.sub.3- NaNO.sub.3- NaNO.sub.3- NaNO.sub.3- NaNO.sub.3- NaNO.sub.3- treatment conditions 380-6, 400-16, 380-4, 400-8, 360-8, 360-8, 400-16, 380-6, 400-8, 420-8, (melt - temperature KNO.sub.3- KNO.sub.3- KNO.sub.3- KNO.sub.3- KNO.sub.3- KNO.sub.3- KNO.sub.3- KNO.sub.3- KNO.sub.3- KNO.sub.3 [ C.] - 370-4 380-6 360-2 380-6 340-4 340-4 380-8 370-6 380-6 400-4 time[hr]) Surface compressive 551 719 574 695 535 525 468 520 577 643 stress value [MPa] Compressive 123 92 110 97 131 129 114 131 94 121 stress depth [m] Exam- Exam- Exam- Exam- Exam- Exam- Exam- Exam- Exam- Exam- ple 11 ple 12 ple 13 ple 14 ple 15 ple 16 ple 17 ple 18 ple 19 ple 20 SiO.sub.2 [mol %] 64.11 61.38 63.14 63.00 66.99 62.28 63.40 64.59 61.20 64.30 B.sub.2O.sub.3 2.33 2.61 1.41 2.20 2.39 1.88 2.05 2.39 2.65 2.38 P.sub.2O.sub.5 1.10 2.13 1.91 3.77 1.91 1.64 1.88 1.91 1.92 1.90 Al.sub.2O.sub.3 0 0 0 0 0 0 0 0 0 0 LiO 24.15 23.76 24.02 23.50 21.53 28.36 22.57 19.14 23.75 23.81 Na.sub.2O 5.19 6.92 5.02 4.44 4.78 3.95 5.19 8.80 6.95 4.76 K.sub.2O 0.99 0.00 1.46 1.51 0.96 0.85 3.95 1.73 0.00 0.95 ZrO.sub.2 2.13 3.20 3.04 1.58 1.44 1.04 0.96 1.44 3.53 1.90 Total 100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00 Melt temperature [ C.] 1166 1133 1163 1140 1189 1075 1157 1170 1166 1161 exhibiting viscosity of 100 dPa .Math. s Vitrifiability A A A A A A A A A A Heat treatment conditions 500-2, 490-5, 490-4, 540-8 570-5 470-4. 560-10 570-5 490-5, 550-5 (temperature 610-2 570-5 515-4, 495-4. 600-2 [ C.] - time [hr]) 620-4 590-4 Precipitated crystalline Li.sub.2SiO.sub.5 Li.sub.2SiO.sub.3 Li.sub.2Si.sub.2O.sub.5 Li.sub.2SiO.sub.3 Li.sub.2SiO.sub.3 Li.sub.2Si.sub.2O.sub.5 Li.sub.2SiO.sub.3 Li.sub.2SiO.sub.3 Li.sub.2SiO.sub.3, Li.sub.2SiO.sub.3 phase Li.sub.2Si.sub.2O.sub.5 Transparency A A A A A A A A A A Vickers hardness [HV] 766 668 803 638 702 729 649 699 745 693 Fracture toughness value 2.09 1.56 2.22 1.29 1.23 2.11 1.66 1.47 1.99 1.25 [MPa .Math. m.sup.1/2] Chemical strengthening NaNO.sub.3- NaNO.sub.3- NaNO.sub.3- NaNO.sub.3- NaNO.sub.3- NaNO.sub.3- NaNO.sub.3- NaNO.sub.3 NaNO.sub.3- NaNO.sub.3- treatment conditions 400-8, 400-16, 400-8, 400-4, 390-12, 360-8, 400-4, 400-4, 400-16, 390-2, (melt - temperature KNO.sub.3- KNO.sub.3- KNO.sub.3- KNO.sub.3- KNO.sub.3- KNO.sub.3- KNO.sub.3- KNO.sub.3- KNO.sub.3- KNO.sub.3- [ C.] - 380-4 380-6 380-8 380-4 380-2 340-2 380-4 380-4 380-6 370-2 time[hr]) Surface compressive 644 530 623 661 581 606 683 603 606 566 stress value [MPa] Compressive 116 136 91 107 134 99 118 118 112 106 stress depth [m]

TABLE-US-00002 TABLE 2 Compar- Compar- Compar- Compar- Compar- Compar- Compar- Compar- Compar- ative ative ative ative ative ative ative ative ative Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Example 8 Example 9 SiO.sub.2 [mol %] 58.52 53.11 70.10 67.24 61.58 64.33 62.79 59.25 63.57 B.sub.2O.sub.3 11.80 7.75 0.15 0 2.22 1.84 2.41 2.04 3.08 P.sub.2O.sub.5 1.60 2.12 0.83 2.24 7.01 0 1.50 1.77 1.79 Al.sub.2O.sub.3 0 0 4.27 0 0 0 0 0 0 Li.sub.2O 20.98 25.51 21.42 21.81 23.01 23.46 22.01 31.76 24.08 Na.sub.2O 3.46 5.54 1.48 4.51 4.00 4.32 3.27 3.37 1.85 K.sub.2O 1.55 2.22 0 1.36 0.99 2.35 7.11 0.90 3.50 ZrO.sub.2 2.09 3.75 1.75 2.84 1.19 3.70 0.91 0.91 2.13 Total 100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00 Melt temperature 1055 1021 1330 1265 1147 1169 1160 1020 1186 [ C.] exhibiting viscosity of 100 dPa .Math. s Vitrifiability A A A A B A A A A Heat treatment 540-5 540-5 540-5 540-5 540-5 490-4, conditions 600-4 (temperature [ C.] - time [hr]) Precipitated crystalline Li.sub.2SiO.sub.3 Li.sub.2SiO.sub.3 Li.sub.2SiO.sub.3 Li.sub.2SiO.sub.3 Li.sub.2SiO.sub.3 Li.sub.2SiO.sub.3, phase and other and other Li.sub.2Si.sub.2O.sub.5 Transparency B B B B B A Vickers hardness [HV] 710 Fracture toughness value 1.85 [MPa .Math. m].sup.1/2 NaNO.sub.3- Chemical strengthening 400-8, treatment conditions KNO.sub.3- (melt - 380-2 temperature [ C.] - time [hr]) Surface compressive 370 stress value [MPa] Compressive 106 stress depth [m] Compar- Compar- Compar- Compar- Compar- Compar- ative ative ative ative ative ative Example 10 Example 11 Example 12 Example 13 Example 14 Example 15 SiO.sub.2 [mol %] 61.18 71.98 66.07 61.10 64.28 64.25 B.sub.2O.sub.3 1.95 1.15 3.88 2.84 3.91 1.69 P.sub.2O.sub.5 1.67 1.65 2.02 1.79 1.97 1.46 Al.sub.2O.sub.3 0 0 0 0 0 5.89 Li.sub.2O 20.22 20.64 16.12 22.28 23.69 21.22 Na.sub.2O 12.52 3.75 5.47 3.52 3.73 3.49 K.sub.2O 1.40 0 3.03 0.96 2.42 0.86 ZrO.sub.2 1.06 0.83 3.41 7.51 0 1.14 Total 100.00 100.00 100.00 100.00 100.00 100.00 Melt temperature 1109 1315 1259 1207 1129 1272 [ C.] exhibiting viscosity of 100 dPa .Math. s Vitrifiability A A A B A A Heat treatment 540-5 540-5 conditions (temperature [ C.] - time [hr]) Precipitated crystalline Li.sub.2SiO.sub.3 Li.sub.2SiO.sub.3 phase and other Transparency B B Vickers hardness [HV] Fracture toughness value [MPa .Math. m].sup.1/2 Chemical strengthening treatment conditions (melt - temperature [ C.] - time [hr]) Surface compressive stress value [MPa] Compressive stress depth [m]

[0141] It is clear from Table 1 that the glass ceramics according to Examples 1 to 20 have sufficiently low viscosity in the melt state, transparency, and high internal strength (strength of the material itself). Furthermore, on the glass ceramics according to Examples 1 to 20, a compressive stress layer with a surface compressive stress value of 400 MPa or higher can be formed by chemical strengthening, i.e., effective chemical strengthening by ion exchange is possible.

[0142] In contrast, it is clear from Table 2 that in Comparative Examples 1 to 15, either vitrification was not possible to begin with during preparation of the glass ceramic, or even if vitrification did take place, viscosity in the melt state, transparency, or effective chemical strengthening by ion exchange was not achieved.

INDUSTRIAL APPLICABILITY

[0143] According to the present disclosure, a transparent glass ceramic that has sufficiently low viscosity in the melt state, allows effective chemical strengthening by ion exchange, and has high internal strength, and a manufacturing method thereof, can be provided. According to the present disclosure, a device using the above-described glass ceramic can also be provided.