JP7136947B2 - crystallized glass substrate - Google Patents

Description

TECHNICAL FIELD The present invention relates to a crystallized glass substrate having a compressive stress layer on its surface.

Portable electronic devices such as smart phones and tablet PCs use cover glasses to protect displays. Protectors for protecting lenses are also used in optical equipment for vehicles. Furthermore, in recent years, there is also a demand for use in housings that serve as exteriors of electronic devices. And there is an increasing demand for materials with higher hardness so that these devices can withstand more severe use.

BACKGROUND ART Conventionally, chemically strengthened glass has been used as a material for applications such as protective members. However, conventional chemically strengthened glass is very vulnerable to cracks that enter vertically from the glass surface, so there are many accidents that breakage occurs when mobile devices are dropped, which is a problem. Furthermore, when it breaks, if it is crushed into pieces and scattered, it is dangerous because there is a risk of injury. It is required to form large fragments when broken.

Patent Document 1 discloses a crystallized glass substrate for an information recording medium. When this crystallized glass substrate was chemically strengthened, a sufficient compressive stress value could not be obtained.

Japanese Unexamined Patent Application Publication No. 2014-114200

The present invention has been made in view of the above problems. An object of the present invention is to obtain a crystallized glass substrate that is hard and hard to crack.

As a result of extensive research to solve the above problems, the present inventors have found that by chemically strengthening with a mixed acid, the surface compressive stress of the compressive stress layer can be increased while the central tensile stress can be decreased, resulting in improved impact resistance. The inventors have found that it is possible to obtain a crystallized glass substrate that does not easily break into small pieces (explosive breakage) even if it is broken by impact, and have completed the present invention. Specifically, the present invention provides the following.

(Configuration 1)
A crystallized glass substrate having a compressive stress layer on its surface,
When the depth when the surface compressive stress of the compressive stress layer is 0 MPa is the stress depth DOLzero,
In the compressive stress layer, the surface compressive stress gradient A at a depth of 6 μm from the outermost surface is 50.0 to 110.0 MPa / μm,
The gradient B of the surface compressive stress from the depth (the stress depth DOLzero-10 μm) to the stress depth DOLzero is 2.5 to 15.0 MPa / μm,
The crystallized glass substrate having a hardness of 7.50 to 9.50 GPa at an indentation depth of 20 nm on the outermost surface.
(Configuration 2)
A crystallized glass substrate having a compressive stress layer on its surface,
When the depth when the surface compressive stress of the compressive stress layer is 0 MPa is the stress depth DOLzero,
In the compressive stress layer, the surface compressive stress gradient A at a depth of 6 μm from the outermost surface is 50.0 to 110.0 MPa / μm,
The gradient B of the surface compressive stress from the depth (the stress depth DOLzero-10 μm) to the stress depth DOLzero is 2.5 to 15.0 MPa / μm,
The crystallized glass substrate having a hardness of 8.00 to 9.50 GPa at an indentation depth of 100 nm on the outermost surface.
(Composition 3)
A crystallized glass substrate having a compressive stress layer on its surface,
When the depth when the surface compressive stress of the compressive stress layer is 0 MPa is the stress depth DOLzero,
In the compressive stress layer, the surface compressive stress gradient A at a depth of 6 μm from the outermost surface is 50.0 to 110.0 MPa / μm,
The gradient B of the surface compressive stress from the depth (the stress depth DOLzero-10 μm) to the stress depth DOLzero is 2.5 to 15.0 MPa / μm,
A crystallized glass substrate, wherein the surface compressive stress CS of the outermost surface of the compressive stress layer is 900.0 to 1200.0 MPa.
(Composition 4)
The stress depth DOLzero is 30.0 to 70.0 μm,
The surface compressive stress CS of the outermost surface of the compressive stress layer is 870.0 to 1150.0 MPa,
The crystallized glass substrate according to Structure 1 or 2, having a central tensile stress CT of 35.0 to 70.0 MPa.
(Composition 5)
% by weight in terms of oxides,
SiO ₂ component 40.0% to 70.0%,
Al ₂ O ₃ component 11.0% to 25.0%,
Na ₂ O component 5.0% to 19.0%,
a K ₂ O component of 0% to 9.0%;
1.0% to 18.0% of one or more selected from MgO components and ZnO components,
CaO component from 0% to 3.0% and TiO ₂ component from 0.5% to 12.0%,
The crystallized glass substrate according to any one of Structures 1 to 4, containing
(Composition 6)
The crystallized glass substrate according to any one of Structures 1 to 5, wherein the crystallized glass substrate has a thickness of 0.1 to 1.0 mm.

According to the present invention, a crystallized glass substrate that is hard and hard to break can be obtained.

The crystallized glass substrate of the present invention can be used as covers for displays and lenses of electronic devices, lens protectors for optical devices for vehicles, outer frame members or housings, optical lens materials, and various other members.

FIG. 4 is a diagram showing an example of changes in compressive stress with respect to depth from the outermost surface of the crystallized glass substrate of the present invention.

Hereinafter, embodiments and examples of the crystallized glass substrate of the present invention will be described in detail. , can be implemented with appropriate modifications.

[Crystalized glass substrate]
The crystallized glass substrate of the present invention uses crystallized glass as a base material (also referred to as a crystallized glass base material) and has a compressive stress layer on the surface. The compressive stress layer can be formed by subjecting the crystallized glass base material to ion exchange treatment. The compressive stress layer is formed with a predetermined thickness inward from the outermost surface of the substrate, and the compressive stress is highest at the outermost surface and decreases inward to zero.

FIG. 1 is a diagram showing an example of changes in compressive stress (MPa) with respect to depth (μm) from the outermost surface of the compressive stress layer on the surface portion of the crystallized glass substrate of the present invention. A depth of zero represents the topmost surface. CS represents the compressive stress of the outermost surface (also referred to as the outermost surface compressive stress), and DOLzero represents the depth of the compressive stress layer when the compressive stress is 0 MPa (also referred to as the stress depth). In FIG. 1, the compressive stress decreases rapidly (with a large slope) from the outermost surface to the inside, and then gradually decreases (with a small slope).

Specifically, the compressive stress gradient A at a depth of 6 μm from the outermost surface is 50.0 to 110.0 MPa/μm, preferably 60.0 to 105.0 MPa/μm, or 70.0 to 100 0 MPa/μm. The compressive stress gradient B from the depth of (stress depth DOLzero−10 μm) to the stress depth DOLzero is 2.5 to 15.0 MPa/μm, preferably 3.0 to 13.0 MPa/μm, or 3 .5 to 12.0 MPa/μm. In FIG. 1, when the compressive stress at a depth of 6 μm from the outermost surface is CS1, the gradient A is obtained by (CS-CS1)/6. Assuming that the compressive stress at a portion 10 μm shallower than the stress depth DOLzero is CS2, the gradient B is obtained by CS2/10.

The compressive stress CS of the outermost surface of the compressive stress layer is usually 870.0 to 1200.0 MPa, for example, 900.0 to 1200.0 MPa, 930.0 to 1150.0 MPa, 950.0 to 1100.0 MPa, or It can be 960.0 to 1050.0 MPa.

The compression depth DOLzero determined by curve analysis may be 30.0-70.0 μm, such as 35.0-60.0 μm, or 38.0-58.0 μm.

The compression depth DOL determined by linear analysis may be 40.0-80.0 μm, such as 45.0-75.0 μm, or 50.0-70.0 μm.

The central stress CT determined by curve analysis may be 35.0-70.0 MPa, for example, 38.0-65.0 MPa, or 40.0-60.0 MPa.

The hardness of the crystallized glass substrate at an indentation depth of 20 nm is preferably 7.50 to 9.50 GPa, more preferably 7.80 to 9.30 GPa, still more preferably 8.00 to 9.10 GPa. be.
The hardness when the crystallized glass substrate is pushed to a depth of 50 nm from the outermost surface (hardness at a pushing depth of 50 nm) is preferably 7.50 to 9.50 GPa, more preferably 7.80 to 9.0 GPa. It is 30 GPa, more preferably 8.00 to 9.10 GPa.
The hardness of the crystallized glass substrate at an indentation depth of 100 nm is preferably 8.00 to 9.50 GPa, more preferably 8.30 to 9.30 GPa, still more preferably 8.50 to 9.10 GPa. be.
The hardness of the crystallized glass substrate at an indentation depth of 20 nm is preferably 8.00 to 9.50 GPa, more preferably 8.30 to 9.30 GPa, still more preferably 8.50 to 9.10 GPa. be.
The above hardness can be determined by the method described in Examples.

When the compressive stress layer has the above stress gradients A and B, and hardness and/or outermost surface compressive stress CS, the substrate becomes difficult to break. The stress depth, stress gradient, hardness, outermost compressive stress and central stress can be adjusted by adjusting the composition, substrate thickness, and chemical strengthening conditions.

The lower limit of the thickness of the crystallized glass substrate is preferably 0.10 mm or more, more preferably 0.30 mm or more, more preferably 0.40 mm or more, still more preferably 0.50 mm or more. The upper limit of the thickness is preferably 1.00 mm or less, more preferably 0.90 mm or less, more preferably 0.70 mm or less, and even more preferably 0.60 mm or less.

Crystallized glasses are materials that have a crystalline phase and a glassy phase, as distinguished from amorphous solids. In general, the crystalline phase of crystallized glass is determined using the angles of peaks appearing in the X-ray diffraction pattern of X-ray diffraction analysis and, if necessary, TEMEDX.

_{The crystallized} glass has, for _example , _MgAl2O4 , _MgTi2O4 , _{MgTi2O5 , Mg2TiO4 , Mg2SiO4 , MgAl2Si2O8 , Mg2Al4Si5O18} as a _{crystal phase .} , Mg ₂ TiO ₅ , MgSiO ₃ , NaAlSiO ₄ , FeAl ₂ O ₄ and solid solutions thereof.

The average crystal diameter in crystallized glass is, for example, 4 to 15 nm, and can be 5 to 13 nm or 6 to 10 nm. If the average crystal diameter is small, the surface roughness Ra after polishing can be smoothly processed to a level of several angstroms. Also, the transmittance increases.

The composition range of each component constituting the crystallized glass is described below. In this specification, unless otherwise specified, the content of each component is indicated by weight % in terms of oxide. Here, the term "oxide conversion" refers to the amount of The amount of oxide of each component contained is expressed in weight %.

The crystallized glass as the base material is preferably, in terms of oxide weight %,
SiO ₂ component 40.0% to 70.0%,
Al ₂ O ₃ component 11.0% to 25.0%,
Na ₂ O component 5.0% to 19.0%,
a K ₂ O component of 0% to 9.0%;
1.0% to 18.0% of one or more selected from MgO components and ZnO components,
0% to 3.0% CaO component,
0.5% to 12.0% TiO ₂ component,
contains

The SiO ₂ component is more preferably 45.0% to 65.0%, still more preferably 50.0% to 60.0%.
The Al ₂ O ₃ component is more preferably contained in an amount of 13.0% to 23.0%.
The Na ₂ O component is more preferably contained at 8.0% to 16.0%. It may be 9.0% or more or 10.5% or more.
The K ₂ O component is more preferably contained between 0.1% and 7.0%, more preferably between 1.0% and 5.0%.
One or more selected from MgO component and ZnO component is more preferably 2.0% to 15.0%, still more preferably 3.0% to 13.0%, and particularly preferably 5.0% to 11.0%. %included. One or more selected from the MgO component and the ZnO component may be the MgO component alone, the ZnO component alone, or both, but preferably the MgO component alone.
The CaO component is more preferably 0.01% to 3.0%, still more preferably 0.1% to 2.0%.
The TiO ₂ component is more preferably 1.0% to 10.0%, still more preferably 2.0% to 8.0%.
Crystallized glass contains 0.01% to _3.0 % ₍ preferably 0.03% to _2.0 %, _more preferably 0.05% to 1.0%).
The above compounding amounts can be appropriately combined.

1 or more selected from SiO ₂ component, Al ₂ O ₃ component, Na ₂ O component, MgO component and ZnO component, TiO ₂ component combined 90% or more, preferably 95% or more, more preferably 98% or more, More preferably, it can be 98.5% or more.
one or more selected from SiO ₂ component, Al ₂ O ₃ component, Na ₂ O component, K ₂ O component, MgO component and ZnO component, CaO component, TiO ₂ component, and Sb ₂ O ₃ component, SnO ₂ component and The total content of one or more selected from _two CeO components can be 90% or more, preferably 95% or more, more preferably 98% or more, and still more preferably 99% or more. These components may occupy 100%.

_The crystallized glass may or may not contain a ZrO2 component as long as the effect of the present invention is not impaired. The blending amount can be 0-5.0%, 0-3.0% or 0-2.0%.
Further, the crystallized glass contains _{three B2O} components, _{five P2O} components, a BaO component, an FeO component, _two SnO components, a _Li2O component, an SrO component, and a _La2O component within a range that does not impair the effects of the present invention. ₃ components, ₃ Y ₂ O components, ₅ Nb ₂ O components, ₅ Ta ₂ O components, ₃ WO components, ₂ TeO components, and ₃ Bi ₂ O components may or may not be included. The blending amount can be 0 to 2.0%, 0 to less than 2.0%, or 0 to 1.0%.

In the crystallized glass of the present invention, as a refining agent, in addition to _three Sb ₂ O components, _two SnO components, _two CeO components, _three As ₂ O components, and one or more selected from the group of F, Cl, NOx, and SOx Two or more types may be included, or not included. However, the upper limit of the content of the clarifier is preferably 0.5% or less, more preferably 0.2% or less, and most preferably 0.1% or less.

In addition, the crystallized glass as the base material is preferably mol % in terms of oxide,
43.0 mol % to 73.0 mol % of _SiO2 component,
4.0 mol % to 18.0 mol % of the Al ₂ O ₃ component,
5.0 mol % to 19.0 mol % of the Na ₂ O component,
0 mol % to 9.0 mol % of the K ₂ O component,
2.0 mol % to 22.0 mol % of one or more selected from MgO components and ZnO components,
0 mol% to 3.0 mol% of the CaO component,
0.5 mol % to 11.0 mol % of the TiO ₂ component,
contains
1 or more selected from SiO ₂ component, Al ₂ O ₃ component, Na ₂ O component, MgO component and ZnO component, and TiO ₂ component combined 90 mol% or more, preferably 95 mol% or more, more preferably 98 mol % or more, more preferably 99 mol % or more.

Other components not mentioned above can be added to the crystallized glass of the present invention, if necessary, as long as the properties of the crystallized glass of the present invention are not impaired. For example, the crystallized glass (and substrate) of the present invention may be colorless and transparent, but the glass can be colored within a range that does not impair the characteristics of the crystallized glass.

Furthermore, Pb, Th, Tl, Os, Be, and Se, which are harmful chemical substances in recent years, have tended to be used sparingly.

[Production method]
The crystallized glass substrate of the present invention can be produced by the following method. That is, raw materials are uniformly mixed and melt-molded to produce raw glass. Next, this raw glass is crystallized to produce a crystallized glass base material. Further, the crystallized glass base material is chemically strengthened.

The raw glass is heat-treated to precipitate crystals inside the glass. This heat treatment may be performed in one stage or in two stages of temperature.
In the two-step heat treatment, the nucleation step is first performed by heat treatment at a 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 performed continuously at one step of temperature. Usually, the temperature is raised to a predetermined heat treatment temperature, and after reaching the heat treatment temperature, the temperature is maintained for a certain period of time, 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.degree. C. to 850.degree. The retention 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 one stage of 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.

A thin plate-like crystallized glass base material can be produced from the crystallized glass base material by using, for example, grinding and polishing means.

Thereafter, a compressive stress layer is formed in the crystallized glass base material by ion exchange using a chemical strengthening method.

A crystallized glass base material is chemically strengthened with a mixed molten salt (mixed bath) of potassium salt and sodium salt, and further chemically strengthened with a single molten salt of potassium salt (single bath) following the mixed bath. Specifically, for example, the crystallized glass base material is heated to ₃₅₀ to 600° C. ₍ preferably 380 to 570° C., more preferably 400 to 500° C., still more preferably 430 to 490° C.) for 100 minutes or more, for example, 200 minutes to 800 minutes, preferably 300 minutes to 700 minutes, more preferably Contact or soak for 450-550 minutes. The mixing ratio of potassium salt and sodium salt is, for example, 1:1 to 50:1, 1.5:1 to 30:1, 2:1 to 20:1 or 3:1 to 15:1 by weight. and Furthermore, preferably, a potassium-containing salt such as potassium nitrate (KNO ₃ ) is subsequently heated to 380 to 550° C. (more preferably 400 to 500° C., still more preferably 430 to 490° C.) to form a molten salt. Contact or soak for a period of time, such as 1 minute or more, 3 minutes to 40 minutes, 4 minutes to 30 minutes, or 5 minutes to 20 minutes. Such chemical strengthening promotes an ion exchange reaction between the components present near the surface and the components contained in the molten salt. As a result, a compressive stress layer is formed on the surface.

Examples 1 and 2
Materials such as oxides, hydroxides, carbonates, nitrates, fluorides, chlorides, and metaphosphoric compounds corresponding to each component of crystallized glass are selected, and these materials are mixed in the following proportions. It was weighed and mixed uniformly.
(% by weight in terms of oxide)
54% _SiO2 component _, 18% _Al2O3 component, 12% _Na2O component, ₂ % K2O component, 8% MgO component, 1% CaO component, 5% _TiO2 component , Sb ₂ O ₃ component 0.1%

Next, the mixed raw materials were put into a platinum crucible and melted. Thereafter, the molten glass was stirred and homogenized, cast into a mold, and slowly cooled to prepare a raw glass.

The raw glass thus obtained was subjected to a one-step heat treatment (650 to 730° C., 5 hours) for nucleation and crystallization to prepare crystallized glass as a base material. The obtained crystallized glass was analyzed by a 200 kV field emission transmission electron microscope FE-TEM (JEM2100F manufactured by JEOL Ltd.), and precipitated crystals with an average crystal diameter of 6 to 9 nm were observed. Furthermore, the crystal phases of MgAl ₂ O ₄ and MgTi ₂ O ₄ were confirmed by confirming the lattice image with an electron diffraction image and analyzing with EDX. The average crystal diameter was determined by using a transmission electron microscope to determine the crystal diameters of crystal particles within the range of 180×180 nm ² and calculating the average value.

The crystallized glass preforms thus produced were cut and ground, and then face-to-face parallel polishing was performed to obtain substrates having thicknesses of 0.61 mm and 0.54 mm. The crystallized glass base material was colorless and transparent.

A crystallized glass substrate was obtained by chemically strengthening the crystallized glass base material which had been subjected to face-to-face parallel polishing. Specifically, in Example 1, after immersing in a mixed molten salt of KNO ₃ and NaNO ₃ at a mixing ratio of KNO ₃ :NaNO ₃ =3:1 (weight ratio) at 460° C. for 500 minutes, KNO ₃ It was immersed in molten salt of chisel at 460° C. for 15 minutes. In Example 2, chemical strengthening was carried out in the same manner as in Example 1, except that the mixing ratio of KNO ₃ and NaNO ₃ was changed to KNO ₃ :NaNO ₃ =10:1 (weight ratio).

The obtained substrates were evaluated as follows.
(1) The thickness of the compressive stress layer (stress depth DOLzero) of the crystallized glass substrate and the surface compressive stress value from the outermost surface of the compressive stress layer to DOLzero were measured using a glass surface stress meter FSM-6000LE manufactured by Orihara Seisakusho. was measured using It was calculated with a sample refractive index of 1.54 and an optical elastic constant of 29.658 [(nm/cm)/MPa]. The surface compressive stress gradient A (MPa/μm) from the outermost surface to a depth of 6 μm, and the surface compressive stress gradient B (MPa/μm) from the depth (stress depth DOLzero-10 μm) to the stress depth DOLzero ). A central tensile stress value (CT) was determined by curve analysis. Furthermore, the thickness of the compressive stress layer (stress depth DOL) was obtained also by linear analysis. Table 1 shows the results.

(2) Bruker nanoindentation system (TI
Premier) was used to measure the hardness when the substrate was pressed into depths of 20 nm, 50 nm, 100 nm, and 200 nm from the outermost surface. Table 1 shows the results.

(3) The crystallized glass substrate was subjected to a falling ball test using sandpaper by the following method. This drop ball test simulates a drop onto asphalt.
Sandpaper with a roughness of #180 was laid on a marble base, and a crystallized glass substrate (15 cm long×7 cm wide) was placed. Then, a 16.5 g SUS steel ball was dropped onto the substrate from a height of 10 mm (1 cm) from the substrate. After dropping, if the substrate did not break, the height was increased by 10 mm (1 cm) and the same test was continued until it broke. After breaking, the condition of the fragments was observed. Table 2 shows the results. When not broken, it is indicated by ○, and when it is broken, it is indicated by ×.

The state of the fragments was evaluated according to the following criteria. Table 2 shows the results.
A: 4 or more pieces of 1 cm ² or more, or 1 or more pieces of 10 cm ² or more B: 1 to 3 pieces of 1 cm ² or more C: 0 pieces of 1 cm ² or more (all less than 1 cm ² small pieces)
From Table 2, it can be seen that the substrate of the present invention is hard and not easily broken, and even if it is broken, it is unlikely to become fine dust.

Comparative Examples 1 and 2
Comparative Examples 1 and 2 used amorphous glass.
Materials such as oxides, hydroxides, carbonates, nitrates, fluorides, chlorides, and metaphosphoric compounds corresponding to each component of the glass are selected, and these materials are mixed so as to have the following composition ratio. and mixed uniformly.
(% by weight in terms of oxide in Comparative Example 1)
62.4% _SiO2 component, 21% _Al2O3 component, ₁₂ % _Na2O component _{, 0.1% K2O component, 1.5% MgO component, and 3 B2O component} . 2.9%, Sb ₂ O ₃ component 0.1%
(% by weight in terms of oxide in Comparative Example 2)
_SiO2 component 62.2% _{, Al2O3} component 16%, _Na2O component 8.3%, _K2O component 5.7%, MgO component 4.8% _{, B2O3} component 2.9%, Sb ₂ O ₃ component 0.1%

Next, the mixed raw materials were put into a platinum crucible and melted. Thereafter, the molten glass was stirred and homogenized, cast into a mold, and slowly cooled to prepare a raw glass.

Annealing treatment was performed on the obtained raw glass to remove the strain remaining in the glass. The amorphous glass base material thus produced was cut and ground, and then parallel-polished to a thickness of 0.66 mm. The amorphous glass base material was colorless and transparent.

An amorphous glass substrate was obtained by chemically strengthening the amorphous glass base material which had been subjected to face-to-face parallel polishing. Specifically, in Comparative Example 1, after immersing in a mixed molten salt of KNO ₃ and NaNO ₃ at a mixing ratio of KNO ₃ :NaNO ₃ =2:1 (weight ratio) at 450° C. for 300 minutes, KNO ₃ It was immersed in a molten salt of chisel at 450° C. for 15 minutes. In Comparative Example 2, after being immersed in a mixed molten salt of KNO ₃ and NaNO ₃ with a mixing ratio of KNO ₃ :NaNO ₃ =1:1 (weight ratio) at 450 ° C. for 500 minutes, it was immersed in a molten salt of only KNO ₃ was immersed at 410° C. for 15 minutes.

The obtained substrates were evaluated as follows.
(1) The thickness of the compressive stress layer (stress depth DOLzero) of the amorphous glass substrate and the surface compressive stress value from the outermost surface of the compressive stress layer to DOLzero are measured using a glass surface stress meter FSM-6000LE manufactured by Orihara Seisakusho. measured by In Comparative Example 1, the refractive index of the sample was 1.50 and the optical elastic constant was 30.3 [(nm/cm)/MPa]. In Comparative Example 2, the refractive index of the sample was 1.51 and the optical elastic constant was 28.2 [(nm/cm)/MPa]. The surface compressive stress gradient A (MPa/μm) from the outermost surface to a depth of 6 μm, and the surface compressive stress gradient B (MPa/μm) from the depth (stress depth DOLzero-10 μm) to the stress depth DOLzero ). A central tensile stress value (CT) was determined by curve analysis. Furthermore, the thickness of the compressive stress layer (stress depth DOL) was obtained also by linear analysis. Table 1 shows the results.

(2) Indentation hardness was measured in the same manner as in Examples 1 and 2. Table 1 shows the results.

(3) A falling ball test was performed in the same manner as in Examples 1 and 2. Table 2 shows the results.

Although several embodiments and/or examples of the present invention have been described above in detail, those of ordinary skill in the art may modify these exemplary embodiments and/or examples without departing substantially from the novel teachings and advantages of the present invention. It is easy to make many modifications to the examples. Accordingly, many of these variations are included within the scope of the present invention.
The entire contents of the documents mentioned in this specification are hereby incorporated by reference.

Claims (6)

A crystallized glass substrate having a compressive stress layer on its surface,
When the depth when the surface compressive stress of the compressive stress layer is 0 MPa is the stress depth DOLzero,
In the compressive stress layer, the surface compressive stress gradient A at a depth of 6 μm from the outermost surface is 50.0 to 110.0 MPa / μm,
The gradient B of the surface compressive stress from the depth (the stress depth DOLzero-10 μm) to the stress depth DOLzero is 2.5 to 15.0 MPa / μm,
The surface compressive stress CS of the outermost surface of the compressive stress layer is 870.0 to 1200.0 MPa ,
A crystallized glass substrate having a central tensile stress CT of 35.0 to 70.0 MPa . 2. The crystallized glass substrate according to claim 1 , wherein the hardness of said outermost surface at an indentation depth of 20 nm is 7.50 to 9.50 GPa. 3. The crystallized glass substrate according to claim 1 , wherein the hardness of said outermost surface at an indentation depth of 100 nm is 8.00 to 9.50 GPa. 4. The crystallized glass substrate according to claim 1 , wherein said stress depth DOLzero is 30.0-70.0 μm. % by weight in terms of oxides,
SiO ₂ component 40.0% to 70.0%,
Al ₂ O ₃ component 11.0% to 25.0%,
Na ₂ O component 5.0% to 19.0%,
a K ₂ O component of 0% to 9.0%;
1.0% to 18.0% of one or more selected from MgO components and ZnO components,
CaO component from 0% to 3.0% and TiO ₂ component from 0.5% to 12.0%,
The crystallized glass substrate according to any one of claims 1 to 4, containing The crystallized glass substrate according to any one of claims 1 to 5, wherein the crystallized glass substrate has a thickness of 0.1 to 1.0 mm.

Images