JP2021042116A - Crystallized glass and reinforced crystallized glass - Google Patents

Abstract

To obtain a crystallized glass and a reinforced crystallized glass, comprising a novel composition and having a high refractive index and a high hardness.SOLUTION: The crystallized glass contains, in percentages by mass in terms of oxides, 20.0% or more but less than 40.0% of an SiO2 component, over 0% and at most 20.0% of an Rn2O component (provided that Rn is one or more selected from Li, Na, and K), 7.0% to 25.0% of an Al2O3 component, 0% to 25.0% of an MgO component, 0% to 45.0% of a ZnO component, and 0% to 20.0% of a Ta2O5 component, the total amount of the MgO component, the ZnO component, and the Ta2O5 component being 10.0% or greater.SELECTED DRAWING: None

Description

The present invention relates to crystallized glass and toughened crystallized glass having a compressive stress layer.

A cover glass for protecting a display is used in a portable electronic device such as a smartphone or a tablet PC. In addition, protectors for protecting lenses are also used in in-vehicle optical devices. Further, in recent years, it has been required to be used for a housing or the like which is an exterior of an electronic device. And there is an increasing demand for materials with high hardness so that these devices can withstand harsh use.

Crystallized glass is an example of increasing the strength of glass. Crystallized glass is a glass in which crystals are precipitated, and is known to have superior mechanical strength to amorphous glass.

Further, chemical strengthening is known as a method for increasing the strength of glass. By exchanging the alkaline component existing in the surface layer of glass with the alkaline component having a larger ionic radius to form a compressive stress layer in the surface layer, it is possible to suppress the growth of cracks and increase the mechanical strength. ..

Patent Documents 1 and 2 disclose high-strength crystallized glass and crystallized glass obtained by chemically strengthening them. However, in order to further expand the application as an optical member, crystallized glass having a high refractive index in addition to hardness has been required.

JP 2011-207626 JP 2017-001937

An object of the present invention is to provide a crystallized glass having a novel composition and a high refractive index and high hardness, and a strengthened crystallized glass.

The present invention provides:
(Structure 1)
By mass% in terms of oxide,
SiO ₂ component is 20.0% or more and less than 40.0%,
Rn ₂ O component is more than 0% and 20.0% or less (however, Rn is one or more selected from Li, Na, and K).
Al ₂ O ₃ component 7.0% to 25.0%,
MgO component 0% to 25.0%,
ZnO component is 0% -45.0%,
Ta ₂ O ₅ component 0% to 20.0%,
Contains,
A crystallized glass in which the total amount of the MgO component, the ZnO component and the Ta ₂ O _{5 component is 10.0% or more.}
(Structure 2)
By mass% in terms of oxide,
TiO ₂ component from 0% to 15.0%,
CaO component 0% -15.0%,
BaO component 0% -15.0%,
The crystallized glass according to configuration 1, which contains 0% to 10.0% of the SrO component.
(Structure 3)
By mass% in terms of oxide,
ZrO ₂ component from 0% to 10.0%,
WO ₃ component from 0% to 10.0%,
La ₂ O ₃ component 0 to 10.0%,
Gd ₂ O ₃ component 0 to 15.0%,
Bi ₂ O ₃ component 0 to 15.0%,
P ₂ O ₅ component 0 to 10.0%,
Nb ₂ O ₅ component 0 to 10.0%,
The crystallized glass according to the configuration 1 or 2, which contains 0 to 5.0% of the Sb ₂ O _{3 component.}
(Structure 4)
The crystallized glass according to any one of configurations 1 to 3, wherein the total amount of the MgO component, the ZnO component and the Ta ₂ O _{5 component is 18.0% or more.}
(Structure 5)
Refractive index _{(n d)} of crystallized glass according to any one of configurations 1 is 1.55 or more 4.
(Structure 6)
The crystallized glass according to any one of configurations 1 to 5, which has a specific gravity of 3.0 or more.
(Structure 7)
A reinforced crystallized glass using the crystallized glass according to any one of configurations 1 to 6 as a base material and having a compressive stress layer on the surface.

According to the present invention, it is possible to provide a crystallized glass having a novel composition and a high refractive index and a high hardness, and a strengthened crystallized glass.

The crystallized glass or reinforced crystallized glass of the present invention can be used as a cover glass or housing of a smartphone, tablet, or PC, and as an optical application member (lens, substrate, etc.) such as a filter and a camera. Specific examples include in-vehicle lenses, short-focus projector lenses, wearable devices, ornaments (vehicles, buildings, smart keys, etc.), touch panels, and dielectric filters. The high refractive index facilitates compactness, and the high strength facilitates thin film and weight reduction.

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, and changes are appropriately made within the scope of the object of the present invention. Can be carried out.

In the present specification, the content of each component is indicated by mass% in terms of oxide unless otherwise specified. Here, "oxide conversion" is used in the crystallized glass when it is assumed that all the constituents of the crystallized glass are decomposed and changed into an oxide, and the total mass of the oxide is 100% by mass. The amount of oxide of each component contained is expressed in mass%. In the present specification, A to B% represent A% or more and B% or less. Further, 0% of 0% to C% means that the content is 0%.

The crystallized glass of the present invention
SiO ₂ component is 20.0% or more and less than 40.0%,
Rn ₂ O component is more than 0% and 20.0% or less (however, Rn is one or more selected from Li, Na, and K).
Al ₂ O ₃ component 7.0% to 25.0%,
MgO component 0% to 25.0%,
ZnO component is 0% -45.0%,
Ta ₂ O ₅ component 0% to 20.0%,
Contains,
The total amount of the MgO component, the ZnO component and the Ta ₂ O ₅ component is 10.0% or more.

Generally, when the amount of SiO ₂ component which is a glass forming component is small and the amount of crystal constituent components such as ZnO component increases, it tends to be difficult to vitrify. However, according to the present invention, crystallized glass can be obtained with the above composition.
Further, since the crystallized glass of the present invention contains a predetermined amount of a component for increasing the refractive index such as a _{ZnO component, an MgO component, and a Ta 2} O _{5 component, the refractive index becomes high.}
That is, with the above composition, a hard crystallized glass having a high refractive index can be obtained.
Furthermore, it can be chemically strengthened to further increase its hardness.

Crystallized glass is also called glass-ceramic, and is a material in which crystals are precipitated inside the glass by heat-treating the glass. Crystallized glass is a material having a crystalline phase and a glass phase, and is distinguished from an amorphous solid. Generally, the crystal phase of crystallized glass is determined by using the angle of the peak appearing in the X-ray diffraction pattern of the X-ray diffraction analysis.

The crystallized glass of the present invention has, for example, ZnAl ₂ O ₄ , Zn ₂ Ti ₃ O ₈ , Zn ₂ SiO ₄ , ZnTIO ₃ , Mg ₂ SiO ₄ , Mg ₂ Al ₄ Si ₅ O ₁₈ , NaAlSiO as the main crystal phase. _4. Contains 1 or more selected from Na ₂ Zn ₃ SiO ₄ , Na ₄ Al ₂ Si ₂ O ₉ , LaTIO _{3, and solid solutions thereof.}
The "main crystal phase" in the present specification corresponds to the crystal phase most contained in the crystallized glass, which is determined from the peak of the X-ray analysis figure.

The SiO ₂ component is a glass-forming component that forms a network structure of glass, and is an essential component. On the other hand, if the SiO ₂ component is insufficient, the chemical durability of the obtained glass is poor and the devitrification resistance is deteriorated.
Therefore, _{the upper limit of the content of the SiO 2} component can be less than 40.0%, 39.0% or less, 37.0% or less, or 35.0% or less. Further, _{the lower limit of the content of the SiO 2} component can be 20.0% or more, 23.0% or more, 25.0% or more, or 30.0% or more.

The Rn ₂ O component (Rn is one or more selected from Li, Na, and K) is a component involved in ion exchange during chemical strengthening, but if it is excessively contained, the chemical durability deteriorates and the chemical durability is lost. It is a component that deteriorates transparency.
Therefore, _{the upper limit of the content of the Rn 2} O component can be 20.0% or less, 18.0% or less, 15.0% or less, or 14.0% or less. Further, _{the lower limit of the content of the Rn 2} O component can be more than 0%, 2.0% or more, 4.0% or more, or 6.0% or more.

In particular, the Na ₂ O component is, for example, as a result of the progress of the exchange reaction between the ^{potassium component (K +} ion) having a large ionic radius in the molten salt and the ^{sodium component (Na +} ion) having a small ionic radius in the substrate. Since compressive stress is formed on the surface of the substrate, it is preferable to use it as an essential component.
Therefore, _{the upper limit of the content of the Na 2} O component can be 20.0% or less, 18.0% or less, 15.0% or less, or 14.0% or less. Further, _{the lower limit of the Na 2} O component can be more than 0%, 2.0% or more, 4.0% or more, or 6.0% or more.

The Al ₂ O ₃ component is a component suitable for improving the mechanical strength, but when it is contained in an excessive amount, the meltability and devitrification resistance are deteriorated.
Therefore, _{the upper limit of the content of the Al 2} O ₃ component can be 25.0% or less, 23.0% or less, 22.0% or less, or 20.0% or less. Further, _{the lower limit of the content of the Al 2} O ₃ component can be 7.0% or more, 9.0% or more, 10.0% or more, or 11.0% or more.

The MgO component is a component that increases the refractive index and contributes to mechanical strength, but if it is contained in an excessive amount, the devitrification resistance deteriorates.
Therefore, the upper limit of the content of the MgO component can be 25.0% or less, 22.0% or less, 20.0% or less, 18.0% or less, or 15.0% or less. Further, the lower limit of the content of the MgO component can be 0% or more, 1.0% or more, 1.5% or more, or 2.0% or more.

The ZnO component not only increases the refractive index and contributes to mechanical strength, but is also an effective component for reducing the viscosity of glass, but when it is excessively contained, the devitrification resistance deteriorates.
Therefore, the upper limit of the content of the ZnO component can be 45.0% or less, 40.0% or less, 38.0% or less, or 25.0% or less. Further, the lower limit of the content of the ZnO component can be 0% or more, 2.0% or more, 5.0% or more, or 8.0% or more, 10.0% or more.

The Ta ₂ O ₅ component is a component that increases the refractive index, but on the other hand, if it is contained in an excessive amount, the devitrification resistance deteriorates.
Therefore, _{the upper limit of the content of the Ta 2} O ₅ component can be 20.0% or less, 19.0% or less, 17.0% or less, or 15.0% or less.
Further, _{the lower limit of the content of the Ta 2} O ₅ component can be 0% or more, 1.0% or more, 3.0% or more, or 5.0% or more. Further, _{the lower limit of the content of the Ta 2} O ₅ component can be more than 5.0 mol% or 5.5 mol% or more.

A high refractive index can be obtained by adjusting the total amount of the MgO component, the ZnO component, and the Ta ₂ O ₅ component, but if it is excessively contained, the devitrification resistance of the glass deteriorates.
Therefore, the lower limit of the total amount of the MgO component, the ZnO component and the Ta ₂ O ₅ component can be preferably 10.0% or more, 15.0% or more, 18.0% or more, or 20.0% or more. Preferably, the upper limit of the total amount of the MgO component, the ZnO component and the Ta ₂ O ₅ component can be 45.0% or less, 40.0% or less, or 38.0% or less.

A high refractive index can be obtained by adjusting the total amount of the ZnO component and the Ta ₂ O _{5 component.} On the other hand, if it is contained in an excessive amount, the devitrification resistance of the glass deteriorates.
Therefore, the lower limit of the total amount of the ZnO component and the Ta ₂ O ₅ component can be preferably 5.0% or more, 8.0% or more, or 10.0% or more, and the total amount of the Zn O _{component and the Ta 2 O 5 component.} The upper limit of is preferably 35.0% or less, 30.0% or less, or 28.0% or less.

The TiO ₂ component is a crystallization nucleating agent and a component that contributes to high refractive index.
Therefore, _{the content of the TiO 2} component can be preferably 0% to 15.0%, more preferably 1.0% to 13.0%, and even more preferably 2.0% to 10.0%.

The CaO component, the BaO component, and the SrO component are components that contribute to the improvement of the refractive index and the stabilization of the glass.
Therefore, the content of the CaO component can be preferably 0% to 15.0%, more preferably 0.1% to 13.0%, and even more preferably 0.5% to 10.0%.
The content of the BaO component can be preferably 0% to 15.0%, more preferably 0% to 13.0%, still more preferably 0% to 12.0%.
The content of the SrO component can be preferably 0% to 10.0%, more preferably 0% to 8.0%, and even more preferably 0% to 7.0%.

The crystallized glass may or may not contain _{ZrO 2} component, WO ₃ component, La ₂ O ₃ component, P ₂ O ₅ component, and Nb ₂ O _{5 component, respectively.} The content of each component can be 0-10.0%, 0-8.0%, or 0-7.0%.

The crystallized glass may or may not contain _{the Gd 2} O ₃ component and the Bi ₂ O _{3 component, respectively.} The content of each component can be 0 to 15.0%, 0 to 13.0%, or 0 to 10.0%.

Further, the crystallized glass may or may not contain _{the B 2} O ₃ component, the Y ₂ O ₃ component, and the TeO _{2 component, respectively.} The content of each component can be 0% to 2.0%, 0% or more and less than 2.0%, or 0% to 1.0%.

The crystallized glass contains _{1 or more selected from Sb 2} O ₃ component, SnO ₂ component and CeO ₂ component as a fining agent from 0% to 5.0%, preferably 0.03% to 2.0%, and further. It can preferably contain 0.05% to 1.0%.

The above blending amounts can be combined as appropriate.

By adjusting the total content of SiO ₂ component, Rn ₂ O component, Al ₂ O ₃ component, Mg O component, Zn O component and Ta _{2 O 5 component, RAl 2} O ₄ , R ₂ SiO ₄ , (however, R Contains one or more selected from (one or more selected from Zn and Mg) as a crystal phase, and can be chemically strengthened by ion exchange. At the same time, it is possible to obtain a glass having excellent mechanical strength and a high refractive index.
Therefore, the lower limit of the mass sum SiO ₂ + Rn ₂ O + Al ₂ O ₃ + MgO + ZnO + Ta ₂ O ₅ can be 70.0% or more, 75.0% or more, 80.0% or more, or 85.0% or more.

The crystallized glass of the present invention has a high refractive index ( _nd ). Preferably, the lower limit of the refractive index is 1.55 or more, 1.58 or more, 1.60 or more, or 1.61 or more. Generally, the upper limit of the refractive index is 1.65 or less.

The crystallized glass of the present invention has a high Vickers hardness. Generally, the lower limit of Vickers hardness is 500 or more, preferably 600 or more, and more preferably 700 or more. Generally, the upper limit of Vickers hardness is 800 or less. Further, the crystallized glass strengthened by chemical strengthening or the like has a higher hardness, and some of them are 800 to 900.

The crystallized glass of the present invention usually has a heavy specific gravity, and the lower limit of the specific gravity is 2.95 or more, or 3.00 or more. Usually, the upper limit of specific gravity is 3.40 or less.

The crystallized glass of the present invention can be produced by the following method. That is, the raw materials are uniformly mixed and melt-molded to produce raw glass. Next, this raw glass is crystallized to produce crystallized glass. Further, a compressive stress layer may be formed and strengthened using crystallized glass as a base material.

The raw glass is heat-treated to precipitate crystals inside the glass. This heat treatment may be performed in one step or in two steps.
In the two-step heat treatment, the nucleation step is first performed by heat treatment at the first temperature, and after this nucleation step, the crystal growth step is performed by heat treatment at a second temperature higher than the nucleation step.
In the one-step heat treatment, the nucleation step and the crystal growth step are continuously performed at the one-step temperature. Usually, the temperature is raised to a predetermined heat treatment temperature, the temperature is maintained for a certain period of time after reaching the heat treatment temperature, and then the temperature is lowered.
The first temperature of the two-step 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-step 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 the heat treatment is performed at a one-step temperature, the heat treatment temperature is preferably 600 ° C. to 800 ° C., more preferably 630 ° C. to 770 ° C. The holding time at the heat treatment temperature is preferably 30 minutes to 500 minutes, more preferably 60 minutes to 300 minutes.

When the substrate is chemically strengthened, a thin plate-shaped crystallized glass is usually produced from the crystallized glass by means of grinding and polishing, for example. After that, a compressive stress layer is formed on the crystallized glass substrate by ion exchange by a chemical strengthening method.

As a method for forming the compressive stress layer, for example, a chemical strengthening method in which an alkaline component existing in the surface layer of crystallized glass is exchanged with an alkaline component having a larger ionic radius to form a compressive stress layer in the surface layer is used. is there. Further, there are a heat strengthening method in which the crystallized glass is heated and then rapidly cooled, and an ion implantation method in which ions are implanted into the surface layer of the crystallized glass.

The chemical strengthening method can be carried out, for example, in the following steps. The crystallized glass base material is contacted or immersed in a salt containing potassium or sodium, for example, potassium nitrate (KNO ₃ ), sodium nitrate (NaNO ₃ ) or a mixed salt thereof or a molten salt of a composite salt thereof. The treatment of contacting or immersing the molten salt (chemical strengthening treatment) may be performed in one step or in two steps.

For example, in the case of a two-step chemical strengthening treatment, first contact or immersion is carried out in a sodium salt heated at 350 ° C. to 550 ° C. or a mixed salt of potassium and sodium for 1-1440 minutes, preferably 90 to 800 minutes. Subsequently, it is contacted or immersed in a potassium salt or a mixed salt of potassium and sodium heated at 350 ° C. to 550 ° C. for 1 to 1440 minutes, preferably 60 to 800 minutes.
In the case of one-step chemical strengthening treatment, contact or immersion is carried out in a salt containing potassium or sodium heated at 350 ° C. to 550 ° C., or a mixed salt thereof for 1-1440 minutes, preferably 60 to 800 minutes.

The heat strengthening method is not particularly limited, but for example, the surface and the inside of the glass substrate are obtained by heating the crystallized glass base material to 300 ° C. to 600 ° C. and then performing rapid cooling such as water cooling and / or air cooling. A compressive stress layer can be formed by the temperature difference of. The compressive stress layer can be formed more effectively by combining with the above chemical treatment method.

The ion implantation method is not particularly limited, but for example, ions are implanted into the surface of the base metal by colliding arbitrary ions on the surface of the crystallized glass base material with acceleration energy and acceleration voltage that do not destroy the surface of the base material. .. After that, by performing heat treatment as necessary, a compressive stress layer can be formed on the surface in the same manner as in other methods.

Examples 1-35
1. 1. Manufacture of crystallized glass Raw materials such as oxides, hydroxides, carbonates, nitrates, fluorides, chlorides, and metaphosphate compounds corresponding to each component of crystallized glass are selected and these raw materials are shown in the table. Weighed so as to have the composition (% by mass) described in 1 to 4, and mixed uniformly.

Next, the mixed raw materials were put into a platinum crucible and melted in an electric furnace at 1300 ° C. to 1600 ° C. for 2 to 24 hours depending on the degree of difficulty in melting the glass composition. Then, the molten glass was stirred and homogenized, the temperature was lowered to 1000 ° C. to 1450 ° C., the glass was cast into a mold, and the glass was slowly cooled to prepare a raw glass. The obtained raw glass was heated at 730 ° C. to crystallize it.

The produced crystallized glass was cut and ground, and face-to-face parallel polishing was performed to a thickness of 1 mm to obtain a crystallized glass substrate. Next, using the crystallized glass substrate as a base material, it _{was immersed in a molten salt of KNO 3} at 420 ° C. for 500 minutes to obtain a strengthened crystallized glass.

2. Evaluation of Crystallized Glass The following physical properties of the obtained crystallized glass and strengthened crystallized glass were measured. The results are shown in Tables 1-4.

(1) Refractive index ( _nd )
Refractive index _{(n d)} is, JIS B 7071-2: according to the V block method specified in 2018, indicated by measured values for helium lamp d line (587.56 nm).

(2) Specific gravity (d)
It was measured by Archimedes' method.

(3) Vickers hardness (Hv)
It was determined by pushing a 136 ° diamond square weight indenter under a load of 980.7 mN for 10 seconds and dividing ^{by the surface area (mm 2) calculated from the length of the indentation.} The measurement was performed using a micro Vickers hardness tester HMV-G manufactured by Shimadzu Corporation.

(4) Stress measurement For the reinforced crystallized glass of Examples 3, 5, 6, 13, 20, the surface compressive stress value (CS) and the thickness of the compressive stress layer (stress depth DOLzero) were determined by Orihara Seisakusho. The measurement was performed using a glass surface stress meter FSM-6000LE series. As the light source of the measuring machine used in the CS measurement, a light source having a wavelength of 596 nm was selected for measurement. As the refractive index used for the CS measurement, the value of the refractive index of 596 nm was used. The value of the refractive index at a wavelength of 596 nm is secondary from the measured values of the refractive index at the wavelengths of C line, d line, F line, and g line according to the V block method defined in JIS B 7071-2: 2018. It was calculated using the approximate expression of. The central compressive stress value (CT) was determined by curve analysis.

(4) Photoelastic constant (β)
The value of the photoelastic constant as the CS measurement condition ^{β (nm / cm / 10 5} Pa) was used the values shown in Table 1-4. As the photoelastic constant used for the CS measurement, the value of the photoelastic constant at 596 nm was used.
The photoelastic constant is measured by face-to-face polishing the sample shape into a disk shape with a diameter of 25 mm and a thickness of 8 mm, and a compressive load of 0 to about 100 in the lateral direction. kgf was added, and the optical path difference generated in the center of the glass was measured and determined by the relational expression of δ = β · d · F. In the above formula, the optical path difference is expressed as δ (nm), the glass thickness is expressed as d (cm), and the stress is expressed as F (MPa).

In Examples 11, 14, 23, 24, 26 to 30, the refractive index could not be measured because the crystallization temperature was high and devitrification occurred. As shown in Tables 1 to 4, the Vickers hardness is increased by chemical strengthening, so that the compressive stress layer is formed. Example 29 shattered in a salt bath and could not be chemically fortified.

Example 36
Crystallized glass was produced in the same manner as in Example 24 except that the crystallization temperature was set to 680 ° C. The refractive index could be measured without devitrification. The refractive index was 1.63, the specific gravity was 3.16, and the Vickers hardness was 755.

Example 37
Crystallized glass was produced in the same manner as in Example 26 except that the crystallization temperature was 700 ° C. The refractive index could be measured without devitrification. The refractive index was 1.63 and the specific gravity was 3.18.

Example 38
Crystallized glass and strengthened crystallized glass were produced in the same manner as in Example 2 except that the crystallization temperature was set to 760 ° C. The refractive index of the crystallized glass was 1.60, the specific gravity was 3.05, the Vickers hardness was 682, and the Vickers hardness of the strengthened crystallized glass was 803.

Example 39
Crystallized glass and strengthened crystallized glass were produced in the same manner as in Examples 7 and 8 except that the crystallization temperature was set to 760 ° C. The specific gravity of the crystallized glass was 3.17 and 3.15, respectively, and the Vickers hardness of the strengthened crystallized glass was 815,834, respectively.

Comparative Example 1
As Comparative Example 1, the crystallized glass of Example 26 of Patent Document 2 was used and evaluated in the same manner as in Example. The results are shown in Table 4.

Claims (7)

By mass% in terms of oxide,
SiO ₂ component is 20.0% or more and less than 40.0%,
Rn ₂ O component is more than 0% and 20.0% or less (however, Rn is one or more selected from Li, Na, and K).
Al ₂ O ₃ component 7.0% to 25.0%,
MgO component 0% to 25.0%,
ZnO component is 0% -45.0%,
Ta ₂ O ₅ component 0% to 20.0%,
Contains,
A crystallized glass in which the total amount of the MgO component, the ZnO component and the Ta ₂ O _{5 component is 10.0% or more.} By mass% in terms of oxide,
TiO ₂ component from 0% to 15.0%,
CaO component 0% -15.0%,
BaO component 0% -15.0%,
The crystallized glass according to claim 1, which contains 0% to 10.0% of the SrO component. By mass% in terms of oxide,
ZrO ₂ component from 0% to 10.0%,
WO ₃ component from 0% to 10.0%,
La ₂ O ₃ component 0 to 10.0%,
Gd ₂ O ₃ component 0 to 15.0%,
Bi ₂ O ₃ component 0 to 15.0%,
P ₂ O ₅ component 0 to 10.0%,
Nb ₂ O ₅ component 0 to 10.0%,
The crystallized glass according to claim 1 or 2, which contains 0 to 5.0% of the Sb ₂ O _{3 component.} The crystallized glass according to any one of claims 1 to 3, wherein the total amount of the MgO component, the ZnO component and the Ta ₂ O _{5 component is 18.0% or more.} Refractive index (n _d) of crystallized glass according to claim 1 is 1.55 or more 4. The crystallized glass according to any one of claims 1 to 5, which has a specific gravity of 3.0 or more. A reinforced crystallized glass using the crystallized glass according to any one of claims 1 to 6 as a base material and having a compressive stress layer on the surface.