JP2023130286A - Chemically strengthened glass and method for manufacturing the same - Google Patents

Abstract

To provide a chemically strengthened glass with high strength and a method for manufacturing the same.SOLUTION: A chemically strengthened glass exhibits specific ranges for the slope (%/μm) at depths of 1 to 3 μm and the slope (%/μm) at depths of 5 to 10 μm, in a K2O concentration profile having an abscissa representing the depth (μm) from the surface and an ordinate representing the K2O concentration (%) by mole percentage in terms of oxides. A method for manufacturing the chemically strengthened glass comprises the following successive steps (1) to (3): (1) subjecting a lithium-containing glass to an ion exchange at least once with an inorganic-salt composition containing potassium; (2) subjecting the lithium-containing glass to a reverse ion exchange under specific conditions with an inorganic-salt composition including LiNO3 and NaNO3, with a mass ratio of NaNO3 to LiNO3 within a specific range; (3) subjecting the lithium-containing glass to an ion exchange at least once with an inorganic-salt composition containing potassium.SELECTED DRAWING: None

Description

The present invention relates to chemically strengthened glass and a method for manufacturing the same.

BACKGROUND ART Conventionally, cover glasses for displays of various information terminal devices and the like have been required to have excellent strength, and chemically strengthened glass has been used because it is thin but resistant to cracking. Chemically strengthened glass has a compressive stress layer formed on the surface of the glass through an ion exchange treatment in which the glass is brought into contact with a molten salt composition such as sodium nitrate or potassium nitrate.

In the ion exchange treatment, ion exchange occurs between the alkali metal ions contained in the glass and the alkali metal ions contained in the molten salt composition that have a different ionic radius, and a compressive stress layer is formed on the surface of the glass. be done. The strength of chemically strengthened glass depends on the stress profile expressed by compressive stress (hereinafter also abbreviated as CS), where the depth from the glass surface is a variable.

The cover glass of a mobile terminal or the like may break due to deformation such as when it is dropped. In order to prevent such fractures, that is, fractures due to bending, it is effective to increase the compressive stress on the glass surface. Therefore, recently, high surface compressive stress of 700 MPa or more is often formed.

Further, the cover glass of a mobile terminal or the like may break due to collision with a protrusion when the terminal falls onto asphalt or sand. In order to prevent such breakage, that is, breakage due to impact, it is effective to increase the depth of the compressive stress layer and form the compressive stress layer in a deeper part of the glass to improve the strength.

On the other hand, when a compressive stress layer is formed on the surface of a glass article, a tensile stress (hereinafter referred to as CT ) will inevitably occur. If the CT value becomes too large, the glass article will crack violently and scatter fragments when broken. When the CT value exceeds the threshold value (hereinafter also abbreviated as CT limit), the glass may self-destruct and the number of fractures during damage may increase explosively. The CT limit is a value specific to the glass composition.

Therefore, chemically strengthened glass is required to further improve its strength by increasing the compressive stress on the surface and forming a compressive stress layer in deeper parts. The total amount is designed.

On the other hand, in the manufacturing process of chemically strengthened glass, glass that does not meet the desired specifications may be produced, for example, glass that has defects below the standard or an inappropriate stress profile. Conventionally, as a reprocessing method for chemically strengthened glass that has the above-mentioned defects or an inappropriate stress profile after ion exchange, chemical strengthening is performed by ion exchange (hereinafter also referred to as reverse ion exchange) or polishing to reduce the compressive stress of the compressive stress layer. A method is used in which after removing the compressive stress layer of tempered glass, the glass is subjected to ion exchange (hereinafter also referred to as re-ion exchange) to form a compressive stress layer.

For example, Patent Document 1 describes step (1): preparing a glass plate having a compressive stress layer on the surface layer; step (2): bringing the glass plate into contact with an inorganic salt composition; A first ion exchange step, step (3), in which at least one set of ions is exchanged so as to reduce the compressive stress of the compressive stress layer: the glass plate is brought into contact with an inorganic salt composition to reduce the compressive stress of the surface layer. A method of manufacturing chemically strengthened glass is disclosed that sequentially includes a second ion exchange step, performing at least one set of ion exchanges to increase the compressive stress of the layers.

Patent Document 2 describes a process for manufacturing a reverse ion-exchanged glass article by performing reverse ion exchange on an ion-exchanged glass article in a reverse ion exchange bath containing a lithium salt, and a process for manufacturing a reverse ion-exchanged glass article in a re-ion exchange bath. A method is disclosed that includes reion-exchanging a glass article to form a reion-exchanged glass article.

Further, Patent Document 3 includes a step of performing reverse ion exchange of an ion-exchanged glass-based article with a reverse ion-exchange medium to produce a reverse-ion-exchanged glass-based article, and the reverse ion-exchange medium includes: Methods are disclosed that include lithium salts and non-ion exchangeable polyvalent metal salts.

JP 2019-194143 Publication Special Publication No. 2020-506151 Special Publication No. 2021-525208

An object of the present invention is to provide a chemically strengthened glass exhibiting excellent strength and a method for manufacturing the same.

The present inventors performed reverse ion exchange under specific conditions on a lithium-containing glass in which a compressive stress layer was formed on the surface layer through chemical strengthening including at least ion exchange with K ions, and then removed the glass surface and re-ion-exchanged the glass. The present invention was completed based on the discovery that chemically strengthened glass having a specific K ₂ O concentration profile and exhibiting excellent strength can be obtained by doing the following.

The present invention provides a K _{2 O concentration profile in which the horizontal axis is the depth from the surface (μm) and the vertical axis is the K 2 O} concentration (%) expressed as a molar percentage on an oxide basis.
The present invention relates to chemically strengthened glass having a slope (%/μm) at a depth of 1 to 3 μm of -1.9 or more and a slope (%/μm) at a depth of 5 to 10 μm of -0.001 or less.

The present invention also relates to a method for manufacturing chemically strengthened glass, which includes the following steps (1) to (3) in sequence.
(1) The lithium-containing glass is ion-exchanged at least once with an inorganic salt composition containing potassium. (2) It contains LiNO ₃ and NaNO ₃ and the mass ratio of NaNO ₃ to LiNO ₃ is 0.25. -3.0, the lithium-containing glass is brought into contact with an inorganic salt composition containing potassium at 425° C. or higher for 5 hours or more to undergo reverse ion exchange. ion exchange at least once with

Further, the present invention provides a K _{2 O concentration profile in which the horizontal axis is the depth from the surface (μm) and the vertical axis is the K 2 O} concentration (%) expressed as a molar percentage on an oxide basis. Regarding chemically strengthened glass, the slope (%/μm) at a depth of 1 to 3 μm is −1.9 or more and 0.0 or less, and the slope (%/μm) at a depth of 5 to 10 μm is −0.001 or less. .

The chemically strengthened glass of the present invention has a specific K ₂ O concentration profile and many K ions are introduced into the surface layer, so that it has excellent surface strength and can improve ball drop strength and scratch resistance.

Further, according to the method for producing chemically strengthened glass of the present invention, after a lithium-containing glass in which a compressive stress layer is formed on the surface layer by chemical strengthening including at least ion exchange with K ions is subjected to reverse ion exchange under specific conditions, the glass By removing the surface and performing reion exchange, a chemically strengthened glass with a specific K ₂ O concentration profile and excellent strength is obtained.

FIGS. 1A and 1B show stress profiles of chemically strengthened glass according to an embodiment of the present invention. FIG. 1(a) shows the stress profile of the surface layer. FIG. 1(b) shows the stress profile in the deep layer. (a) and (b) of FIG. 2 show the results of measuring the Na ₂ O concentration in chemically strengthened glass by EPMA (Example 1). FIGS. 2(c) and 2(d) show the results of measuring the K ₂ O concentration in chemically strengthened glass by EPMA (Example 1). In FIGS. 2A to 2D, the horizontal axis shows the depth (μm) from the glass surface, and the vertical axis shows the concentration (%) expressed as a molar percentage on an oxide basis. (a) and (b) of FIG. 3 show the results of measuring the Na ₂ O concentration in chemically strengthened glass by EPMA (Example 2). (c) and (d) of FIG. 3 show the results of measuring the K ₂ O concentration in chemically strengthened glass by EPMA (Example 2). In (a) to (d) of FIG. 3, the horizontal axis shows the depth (μm) from the glass surface, and the vertical axis shows the concentration (%) expressed as a molar percentage on an oxide basis. (a) and (b) of FIG. 4 show the results of measuring the Na ₂ O concentration in chemically strengthened glass by EPMA (Example 5). (c) and (d) of FIG. 4 show the results of measuring the K ₂ O concentration in chemically strengthened glass by EPMA (Example 5). In (a) to (d) of FIG. 4, the horizontal axis shows the depth (μm) from the glass surface, and the vertical axis shows the concentration (%) expressed as a molar percentage on an oxide basis.

The present invention will be described in detail below, but the present invention is not limited to the following embodiments, and can be implemented with arbitrary modifications within the scope of the gist of the present invention.

In this specification, "~" indicating a numerical range is used to include the numerical values written before and after it as a lower limit value and an upper limit value. Further, in this specification, the composition of glass (the content of each component) will be described in terms of mole percentage based on oxides, unless otherwise specified.

In the following, "chemically strengthened glass" refers to glass that has been subjected to chemical strengthening treatment, and "chemically strengthened glass" refers to glass that has not been subjected to chemical strengthening treatment.

In this specification, unless otherwise specified, the glass composition is expressed in mol% based on oxides, and mol% is simply expressed as "%".

Further, in this specification, "substantially no content" means that the content is below the level of impurities contained in raw materials, etc., that is, it is not intentionally added. Specifically, it is, for example, less than 0.1%.

In this specification, "K ₂ O concentration profile" or "Na ₂ O concentration profile" is expressed in terms of the depth (μm) from the glass surface on the horizontal axis and the mole percentage on an oxide basis on the vertical axis. It is expressed as K ₂ O concentration (%) or Na ₂ O concentration.

In this specification, the K ₂ O concentration or Na ₂ O concentration at the depth x (μm) is determined by measuring the concentration in a cross section in the thickness direction using an EPMA (Electron Probe Micro Analyzer). Specifically, EPMA measurement is performed as follows, for example.
First, a glass sample is embedded in an epoxy resin and mechanically polished in a direction perpendicular to a first main surface and a second main surface opposite to the first main surface to prepare a cross-sectional sample. A C coat is applied to the cross section after polishing, and measurement is performed using EPMA (manufactured by JEOL: JXA-8500F). The accelerating voltage was 15kV, the probe current was 30nA, and the integration time was 1000msec. A line profile of the X-ray intensity of K ₂ O or Na ₂ O is obtained at 1 μm intervals as /point. Regarding the obtained K ₂ O concentration profile or Na ₂ O concentration profile, the average count of the central part of the plate thickness (0.5 x t) ± 25 μm (the plate thickness is t μm) is taken as the bulk composition, and the count of the entire plate thickness is calculated. Calculate by proportionally converting to mol%.

In this specification, the potassium ion diffusion layer depth refers to the average K ₂ O concentration (%) at the center of the plate thickness (0.5 x t) ± 25 μm in the K ₂ O concentration profile and its variance value σ, The depth (μm) at which the K ₂ O concentration falls within the range of +2σ or less when viewed from the outermost surface side is defined as the depth of the potassium ion diffusion layer.

In this specification, the term "stress profile" refers to a compressive stress expressed using the depth from the glass surface as a variable. In the stress profile, tensile stress is expressed as negative compressive stress.

"Compressive stress (CS)" can be measured by sectioning a cross section of glass and analyzing the sectioned sample with a birefringence imaging system. Birefringence imaging system A birefringence stress meter is a device that measures the magnitude of retardation caused by stress using a polarizing microscope, liquid crystal compensator, etc. For example, there is the birefringence imaging system Abrio-IM manufactured by CRi. .

In addition, measurement may also be possible using scattered light photoelasticity. In this method, light is incident on the surface of the glass and the polarization of the scattered light is analyzed to measure CS. An example of a stress measuring instrument that uses scattered light photoelasticity is the scattered light photoelasticity stress meter SLP-2000 manufactured by Orihara Seisakusho.

In this specification, "compressive stress layer depth (DOC)" is the depth at which the compressive stress is zero. Hereinafter, the surface compressive stress may be referred to as CS ₀ and the compressive stress at a depth of 50 μm from the surface may be referred to as CS ₅₀ . Moreover, "internal tensile stress (CT)" refers to tensile stress at a depth of 1/2 of the plate thickness t.

In this specification, "4PB strength" (4-point bending strength) is measured by the following method.
Fracture obtained by performing a 4-point bending test using a 50 mm x 50 mm test piece under the conditions that the distance between the external supports of the support is 30 mm, the distance between the internal supports is 10 mm, and the crosshead speed is 5.0 mm/min. Let the stress (unit: MPa) be the four-point bending strength. The number of test pieces is, for example, ten.

<Stress measurement method>
In recent years, for cover glasses such as smartphones, the lithium ions inside the glass are exchanged with sodium ions (Li-Na exchange), and then the sodium ions inside the glass are exchanged with potassium ions (Na- Glass that has been chemically strengthened in two stages (K exchange) has become mainstream.

In order to non-destructively obtain the stress profile of such two-stage chemically strengthened glass, for example, a scattered light photoelastic stress meter (hereinafter also abbreviated as SLP) or a glass surface stress meter (film stress measurement) is used. (hereinafter also abbreviated as FSM), etc. may be used in combination.

In a method using a scattered light photoelastic stress meter (SLP), compressive stress derived from Li--Na exchange can be measured inside the glass at a distance of several tens of micrometers or more from the glass surface layer. On the other hand, in a method using a glass surface stress meter (FSM), compressive stress derived from Na-K exchange can be measured in the glass surface layer at a depth of several tens of micrometers or less from the glass surface (for example, WO 2018/056121, International Publication No. 2017/115811). Therefore, in two-stage chemically strengthened glass, a combination of SLP and FSM information is sometimes used as the stress profile in the glass surface layer and inside.

In the present invention, stress profiles mainly measured by a scattered light photoelastic stress meter (SLP) are used. Note that in this specification, when stress CS, tensile stress CT, compressive stress layer depth DOL, etc. are referred to, they mean values in the SLP stress profile.

A scattered light photoelasticity stress meter consists of a polarization phase difference variable member that changes the polarization phase difference of a laser beam by one wavelength or more with respect to the wavelength of the laser beam, and a laser beam with the changed polarization phase difference that is made of tempered glass. an image sensor that captures scattered light emitted by the incident light multiple times at predetermined time intervals to obtain a plurality of images; and a periodic brightness change of the scattered light that is measured using the plurality of images; and a calculation section that calculates a stress distribution in the depth direction from the surface of the tempered glass based on the phase change.

As a method for measuring a stress profile using a scattered light photoelasticity stress meter, the method described in International Publication No. 2018/056121 can be mentioned. Examples of the scattered light photoelasticity stress meter include SLP-1000 and SLP-2000 manufactured by Orihara Seisakusho. Highly accurate stress measurement is possible by combining these scattered light photoelasticity stress meters with the attached software SlpIV_up3 (Ver. 2019.01.10.001).

<Chemically strengthened glass>
The chemically strengthened glass of this embodiment (hereinafter also referred to as "this chemically strengthened glass") has the horizontal axis representing the depth (μm) from the surface, and the vertical axis representing the K expressed in mole percentage based on oxides. In the K ₂ O concentration profile defined as ₂ O concentration (%), the slope (%/μm) at a depth of 1 to 3 μm is -1.9 or more, and the slope (%/μm) at a depth of 5 to 10 μm is - It is characterized by being 0.001 or less.

In the K ₂ O concentration profile, the slope (%/μm) at a depth of 1 to 3 μm is -1.9 or more, and the slope (%/μm) at a depth of 5 to 10 μm is -0.001 or less. This increases the K ion concentration in the surface layer and improves the strength. Examples of the strength include bending strength, surface hardness, falling ball strength, and scratch resistance.

In the K ₂ O concentration profile, when the slope (%/μm) at a depth of 1 to 3 μm is −1.9 or more, the K ion concentration in the surface layer can be increased and the strength can be improved. In the K ₂ O concentration profile, the slope (%/μm) at a depth of 1 to 3 μm is preferably -1.80 or more, more preferably -1.70 or more, still more preferably -1.65 or more, especially Preferably it is -1.60 or more.

The slope (%/μm) at a depth of 1 to 3 μm in the K ₂ O concentration profile is preferably −1.000 or less, more preferably −1.10 or less, still more preferably −1.20 or less, and particularly preferably is -1.30 or less. In the K ₂ O concentration profile, by setting the slope (%/μm) at a depth of 1 to 3 μm to be −1.000 or less, extra stress that does not contribute to strength can be reduced. The slope (%/μm) at a depth of 1 to 3 μm in the K ₂ O concentration profile functions by having a value of 0.0 or less.

In the K ₂ O concentration profile, the slope (%/μm) at a depth of 5 to 10 μm is -0.001 or less, which means that the amount of potassium ions in the glass surface layer can be diffused to the micro-crack region on the surface, resulting in surface compression. Bending strength due to stress can be improved. The slope (%/μm) at a depth of 5 to 10 μm in the K ₂ O concentration profile is preferably −0.010 or less, more preferably −0.020 or less, still more preferably −0.030 or less, and particularly preferably is less than -0.040.

The slope (%/μm) at a depth of 5 to 10 μm in the K ₂ O concentration profile is preferably −0.200 or more, more preferably −0.180 or more, still more preferably −0.160 or more, and particularly preferably is -0.140 or more. In the K ₂ O concentration profile, since the slope (%/μm) at a depth of 5 to 10 μm is -0.200 or more, the amount of potassium ions in the glass surface layer is not too large, and inhibition of ion exchange due to re-strengthening is suppressed. , stress in deep layers can be improved.

This chemically strengthened glass has a Na ₂ O concentration profile in which the horizontal axis is the depth from the surface (μm) and the vertical axis is the Na ₂ O concentration (%) expressed as a molar percentage based on oxide. It is preferable that the slope (%/μm) at a depth of 10 to 50 μm is −0.001 or less, and the slope (%/μm) at a depth of 50 to 90 μm is −0.012 or more.

In the Na ₂ O concentration profile, the slope (%/μm) at a depth of 10 to 50 μm is -0.001 or less, and the slope (%/μm) at a depth of 50 to 90 μm is -0.012 or more. Compared to conventional chemically strengthened glass, the Na ion concentration in the surface layer portion can be lowered to further reduce the generation of extra stress that does not contribute to strength.

The slope (%/μm) at a depth of 10 to 50 μm in the Na ₂ O concentration profile is preferably −0.001 or less, more preferably −0.002 or less, still more preferably −0.003 or less, and particularly preferably − It is 0.004 or less. In the Na ₂ O concentration profile, the slope (%/μm) at a depth of 10 to 50 μm is -0.001 or less, which lowers the Na ion concentration in the surface layer compared to conventional chemically strengthened glass and increases the strength. The generation of extra stress that does not contribute to the above can be further reduced.

The slope (%/μm) at a depth of 10 to 50 μm in the Na ₂ O concentration profile is preferably −0.020 or more, more preferably −0.018 or more, still more preferably −0.016 or more, and particularly preferably − It is 0.014 or more. In the Na ₂ O concentration profile, the slope (%/μm) at a depth of 10 to 50 μm is -0.020 or more, which lowers the Na ion concentration in the surface layer compared to conventional chemically strengthened glass and increases the strength. The generation of extra stress that does not contribute to the above can be further reduced.

The slope (%/μm) of the Na ₂ O concentration profile at a depth of 50 to 90 μm is preferably −0.012 or more, more preferably −0.011 or more, still more preferably −0.010 or more, and particularly preferably − It is 0.009 or more. In the Na ₂ O concentration profile, the slope (%/μm) at a depth of 50 to 90 μm is -0.012 or more, thereby increasing the Na ion concentration in the deep layer and generating stress that contributes to drop strength. I can do it.

The slope (%/μm) of the Na ₂ O concentration profile at a depth of 50 to 90 μm is preferably −0.002 or less, more preferably −0.003 or less, still more preferably −0.004 or less, and particularly preferably − It is 0.005 or less. In the Na ₂ O concentration profile, the slope (%/μm) at a depth of 50 to 90 μm is -0.002 or less, thereby increasing the Na ion concentration in the deep layer and generating stress that contributes to drop strength. I can do it.

In the chemically strengthened glass of this embodiment, in the K ₂ O concentration profile, the absolute value of the slope (%/μm) at a depth of 5 to 10 μm divided by the slope (%/μm) at a depth of 1 to 3 μm is 0. It is preferably .005 or more and 0.10 or less. When the absolute value is within the range, the amount of potassium ions in the glass surface layer can be diffused to the micro-crack region on the surface. The absolute value is more preferably 0.010 or more, still more preferably 0.015 or more, particularly preferably 0.020 or more. The absolute value is more preferably 0.095 or less, still more preferably 0.090 or less, even more preferably 0.085 or less, particularly preferably 0.080 or less.

In the chemically strengthened glass of this embodiment, in the Na ₂ O concentration profile, the absolute value of the slope (%/μm) at a depth of 50 to 90 μm divided by the slope (%/μm) at a depth of 10 to 50 μm is 0. It is preferably .50 or more and 4.0 or less. The absolute value is more preferably 0.60 or more, still more preferably 0.70 or more, even more preferably 0.80 or more, particularly preferably 0.90 or more. The absolute value is more preferably 3.9 or less, still more preferably 3.8 or less, even more preferably 3.7 or less, particularly preferably 3.6 or less.

In the chemically strengthened glass of this embodiment, in the K ₂ O concentration profile, the absolute value of the difference between the K ₂ O concentration (%) at a depth of 15 to 25 μm and the K ₂ O concentration (%) at the center is 0. The content is preferably 20% or less, more preferably 0.16% or less, further preferably 0.12% or less, particularly preferably 0.10% or less. Since the absolute value of the difference between the K ₂ O concentration at a depth of 15 to 25 μm and the K ₂ O concentration at the center is 0.20% or less, the tensile stress that balances the compressive stress is reduced, and the tensile stress The development of scars caused by this can be suppressed. Here, the K ₂ O concentration at a depth of 15 to 25 μm refers to the average K ₂ O concentration at a depth of 15 to 25 μm. The lower limit of the absolute value of the difference is usually preferably 0.001% or more, more preferably 0.005% or more.

In the chemically strengthened glass of this embodiment, the depth of the potassium ion diffusion layer is preferably 5 μm or more, more preferably 7 μm or more, and even more preferably 20 μm or less. Further, it is usually preferably 18 μm or less, more preferably 16 μm or less. When the depth of the potassium ion diffusion layer is 5 μm or more, the K ion concentration in the surface layer can be increased and the strength can be improved.

Stress profiles in one embodiment of the present chemically strengthened glass are shown in FIGS. 1(a) and 1(b). FIG. 1(a) shows the stress profile of the surface layer. FIG. 1(b) shows the stress profile in the deep layer. In FIGS. 1A and 1B, solid lines indicate examples and dotted lines indicate comparative examples. As shown in Figure 1(a), this chemically strengthened glass has higher K ion-dependent compressive stress in the surface layer than the comparative example, and has higher compressive stress in the deeper layer as shown in Figure 1(b). The present chemically strengthened glass exhibits excellent strength because the DOC and DOC are equivalent to those of the comparative example.

The present chemically strengthened glass preferably has a surface compressive stress (CS ₀ ) of 500 MPa or more because it is difficult to break due to deformation such as bending. CS ₀ is more preferably 600 MPa or more, and even more preferably 700 MPa or more. The larger the CS ₀ , the higher the strength, but if it is too large, severe crushing may occur when cracked, so it is preferably 1200 MPa or less, more preferably 1000 MPa or less.

If the chemically strengthened glass has a compressive stress (CS ₅₀ ) of 50 MPa or more at a depth of 50 μm from the surface, the chemically strengthened glass will break when a mobile terminal, etc. equipped with the chemically strengthened glass as a cover glass is dropped. This is preferable because it makes it easier to prevent. CS ₅₀ is more preferably 60 MPa or more, and even more preferably 70 MPa or more. The larger the CS ₅₀ , the higher the strength, but if the CS 50 is too large, severe crushing may occur if it breaks, so it is preferably 180 MPa or less, more preferably 160 MPa or less.

This chemically strengthened glass has a compressive stress CS ₉₀ of 30 MPa or more at a depth of 90 μm from the surface, and when a mobile terminal, etc., having this chemically strengthened glass as a cover glass is dropped onto coarse sand, etc., this chemically strengthened glass This is preferable because it prevents cracking. CS ₉₀ is more preferably 40 MPa or more, and even more preferably 50 MPa or more. The larger the CS ₉₀ , the higher the strength, but if it is too large, severe crushing may occur if it breaks, so it is preferably 170 MPa or less, more preferably 150 MPa or less.

It is preferable that the chemically strengthened glass has a DOC of 80 μm or more because it is difficult to break even if the surface is scratched. DOC is more preferably 90 μm or more, still more preferably 100 μm or more, particularly preferably 110 μm or more. The larger the DOC, the more difficult it is to break even if a scratch occurs, but in chemically strengthened glass, tensile stress is generated internally in response to the compressive stress formed near the surface, so it cannot be made extremely large. When the thickness of DOC is t, it is preferably t/4 or less, more preferably t/5 or less. In order to shorten the time required for chemical strengthening, DOC is preferably 160 μm or less, more preferably 150 μm or less.

The CS and DOC of chemically strengthened glass can be adjusted as appropriate by adjusting the chemical strengthening conditions, glass composition, thickness, and the like.

This chemically strengthened glass exhibits excellent strength due to the large amount of K ions introduced into the glass surface layer. The chemically strengthened glass preferably has a four-point bending strength of 480 MPa or more, more preferably 500 MPa or more, and still more preferably 520 MPa or more. Strength reliability can be improved by having a four-point bending strength of 540 MPa or more.

The present chemically strengthened glass is typically a plate-shaped glass article, and may be flat or curved. Furthermore, there may be portions with different thicknesses.

When the present chemically strengthened glass is in the form of a plate, the thickness (t) is preferably 3000 μm or less, more preferably 2000 μm or less, 1600 μm or less, 1500 μm or less, 1100 μm or less, 900 μm or less, 800 μm or less, and 700 μm. It is as follows. Further, the thickness (t) is preferably 300 μm or more, more preferably 400 μm or more, and even more preferably 500 μm or more, in order to obtain sufficient strength by chemical strengthening treatment.

<<Applications>>
The present chemically strengthened glass is also useful as a cover glass for use in electronic devices such as mobile devices such as mobile phones and smartphones. Furthermore, it is useful for cover glasses of electronic devices such as televisions, personal computers, touch panels, etc. that are not intended to be portable, walls of elevators, and walls (full-scale displays) of buildings such as houses and buildings. It is also useful as building materials such as window glass, table tops, interiors of automobiles and airplanes, and cover glasses thereof, and cases having curved shapes.

<<Composition>>
In this specification, the "base composition of chemically strengthened glass" refers to the glass composition of chemically strengthened glass, which is the part deeper than the compressive stress layer depth of chemically strengthened glass, except in cases where extreme ion exchange treatment has been performed. The glass composition is almost the same as the mother composition of chemically strengthened glass.

The chemically strengthened glass of this embodiment has a mother composition expressed in mol% based on oxides,
SiO ₂ 52-75%,
8-20% Al ₂ O ₃ ,
It is preferable to contain 5 to 18% of Li ₂ O.

More preferably, the chemically strengthened glass of this embodiment has a mother composition expressed in mol% based on oxides,
SiO ₂ 52-75%,
8-20% Al ₂ O ₃ ,
5-18% Li ₂ O,
0-15% Na ₂ O,
0-5% K ₂ O,
MgO 0-20%,
CaO 0-20%,
0 to 20% SrO,
BaO 0-20%,
ZnO 0-10%,
0-1% _TiO2 ,
ZrO ₂ 0-8%,
Contains 0 to 5% of Y ₂ O ₃ .
Hereinafter, preferred glass compositions will be explained.

In the chemically strengthened glass in this embodiment, SiO ₂ is a component that forms the network structure of the glass. It is also a component that increases chemical durability. The content of SiO ₂ is preferably 52% or more, more preferably 56% or more, even more preferably 60% or more, particularly preferably 64% or more. On the other hand, in order to improve meltability, the content of SiO ₂ is preferably 75% or less, more preferably 73% or less, even more preferably 71% or less, particularly preferably 69% or less.

Al ₂ O ₃ is a component that increases surface compressive stress due to chemical strengthening and is essential. The content of Al ₂ O ₃ is preferably 8% or more, more preferably 10% or more, even more preferably 11% or more, particularly preferably 12% or more. On the other hand, the content of Al ₂ O ₃ is preferably 20% or less, more preferably 18% or less, further preferably 17% or less, 16% or less, and 15% or less in order to prevent the devitrification temperature of the glass from becoming too high. % or less is most preferable.

Li ₂ O is a component that forms surface compressive stress through ion exchange. The content of Li ₂ O is preferably 5% or more, more preferably 7% or more, still more preferably 9% or more, particularly preferably 11% or more. On the other hand, in order to stabilize the glass, the content of Li ₂ O is preferably 18% or less, more preferably 17% or less, still more preferably 16% or less, and most preferably 15% or less.

MgO is a component that stabilizes glass and is also a component that increases mechanical strength and chemical resistance, so it is preferable to include it when the Al ₂ O ₃ content is relatively low. The content of MgO is preferably 1% or more, more preferably 2% or more, still more preferably 3% or more, and particularly preferably 4% or more. On the other hand, if too much MgO is added, the viscosity of the glass decreases and devitrification or phase separation tends to occur. The content of MgO is preferably 20% or less, more preferably 19% or less, still more preferably 18% or less, particularly preferably 17% or less.

CaO, SrO, BaO, and ZnO are all components that improve the meltability of glass, and may be contained.

CaO is a component that improves the meltability of glass, and is a component that improves the breakability of chemically strengthened glass, and may be included. When CaO is contained, the content is preferably 0.5% or more, more preferably 1% or more, even more preferably 2% or more, particularly preferably 3% or more, and most preferably 5% or more. be. On the other hand, if the CaO content exceeds 20%, the ion exchange performance will be significantly reduced, so it is preferably 20% or less. The CaO content is more preferably 16% or less, and more preferably 12% or less, 10% or less, and 8% or less in stages.

SrO is a component that improves the meltability of glass, and is a component that improves the breakability of chemically strengthened glass, and may be included. When SrO is contained, the content is preferably 0.5% or more, more preferably 1% or more, even more preferably 2% or more, particularly preferably 3% or more, and most preferably 5% or more. be. On the other hand, if the SrO content exceeds 20%, the ion exchange performance will drop significantly, so it is preferably 20% or less. The SrO content is more preferably 16% or less, and more preferably 12% or less, 10% or less, and 8% or less in stages.

BaO is a component that improves the meltability of glass, and is a component that improves the breakability of chemically strengthened glass, and may be included. When BaO is contained, the content is preferably 0.5% or more, more preferably 1% or more, even more preferably 2% or more, particularly preferably 3% or more, and most preferably 5% or more. be. On the other hand, if the BaO content exceeds 20%, the ion exchange performance will drop significantly, so it is preferably 20% or less. The BaO content is more preferably 16% or less, and more preferably 12% or less, 10% or less, and 8% or less in stages.

ZnO is a component that improves the meltability of glass, and may be included. When ZnO is contained, the content is preferably 0.25% or more, more preferably 0.5% or more. On the other hand, if the ZnO content exceeds 10%, the weather resistance of the glass will be significantly reduced. The content of ZnO is preferably 10% or less, more preferably 8% or less, 6% or less, 4% or less, 2% or less, and 1% or less in steps.

Na ₂ O is a component that improves the meltability of glass. Although Na ₂ O is not essential, when it is contained, it is preferably 1% or more, more preferably 2% or more, particularly preferably 4% or more. If the amount of Na ₂ O is too large, the chemical strengthening properties will deteriorate, so the content of Na ₂ O is preferably 15% or less, more preferably 12% or less, particularly preferably 10% or less, and most preferably 8% or less.

K ₂ O, like Na ₂ O, is a component that lowers the melting temperature of glass, and may be included. When containing K ₂ O, the content is preferably 0.5% or more, more preferably 0.8% or more, even more preferably 1% or more, even more preferably 1.2% or more, particularly preferably is 1.5% or more. If the K ₂ O content is too large, the chemical strengthening properties or chemical durability will decrease, so it is preferably 5% or less, more preferably 4.8% or less, still more preferably 4.6% or less, and particularly preferably is 4.2% or less, most preferably 4.0% or less.

The total content of Na ₂ O and K ₂ O (Na ₂ O+K ₂ O) is preferably 3% or more, more preferably 5% or more, in order to improve the meltability of the glass raw material. _{In addition , it is chemical _} It is preferable because it can improve reinforcement properties and chemical durability. K ₂ O/R ₂ O is more preferably 0.15 or less, and even more preferably 0.10 or less. Note that R ₂ O is preferably 10% or more, more preferably 12% or more, and even more preferably 15% or more. Moreover, R ₂ O is preferably 20% or less, more preferably 18% or less.

ZrO ₂ is a component that increases mechanical strength and chemical durability, and is preferably included because it significantly improves CS. The content of _ZrO2 is preferably 0.5% or more, more preferably 0.7% or more, even more preferably 1.0% or more, particularly preferably 1.2% or more, and most preferably 1.0% or more. .5% or more. On the other hand, in order to suppress devitrification during melting, ZrO ₂ is preferably 8% or less, more preferably 7.5% or less, even more preferably 7% or less, and particularly preferably 6% or less. If the content of ZrO ₂ is too large, the devitrification temperature increases and the viscosity decreases. In order to suppress deterioration of moldability due to such a decrease in viscosity, when the molding viscosity is low, the ZrO ₂ content is preferably 5% or less, more preferably 4.5% or less, and 3.5% or less. More preferred.

In order to improve chemical durability, ZrO ₂ /R ₂ O is preferably 0.01 or more, more preferably 0.02 or more, even more preferably 0.04 or more, particularly preferably 0.08 or more, Most preferably 0.1 or more. ZrO ₂ /R ₂ O is preferably 0.2 or less, more preferably 0.18 or less, even more preferably 0.16 or less, and particularly preferably 0.14 or less.

Although TiO ₂ is not essential, when it is contained, it is preferably 0.05% or more, more preferably 0.1% or more. On the other hand, in order to suppress devitrification during melting, the content of TiO ₂ is preferably 1% or less, more preferably 0.5% or less, and even more preferably 0.3% or less.

Although SnO ₂ is not essential, when it is contained, it is preferably 0.5% or more, more preferably 1% or more, even more preferably 1.5% or more, particularly preferably 2% or more. On the other hand, in order to suppress devitrification during melting, the SnO ₂ content is preferably 4% or less, more preferably 3.5% or less, even more preferably 3% or less, and particularly preferably 2.5% or less.

Y ₂ O ₃ is a component that is effective in making it difficult for fragments to scatter when chemically strengthened glass is broken, and may be included. The content of Y ₂ O ₃ is preferably 0.3% or more, more preferably 0.5% or more, still more preferably 0.7% or more, particularly preferably 1.0% or more. On the other hand, in order to suppress devitrification during melting, the content of Y ₂ O ₃ is preferably 5% or less, more preferably 4% or less.

B ₂ O ₃ is a component that improves the chipping resistance of chemically strengthened glass or chemically strengthened glass and also improves the meltability, and may be contained. In order to improve meltability, the content of B ₂ O ₃ is preferably 0.5% or more, more preferably 1% or more, and still more preferably 2% or more. On the other hand, if the content of B ₂ O ₃ is too large, striae will occur during melting or phase separation will easily occur, which will likely deteriorate the quality of the chemically strengthened glass, so the content is preferably 10% or less. The content of B ₂ O ₃ is more preferably 8% or less, further preferably 6% or less, particularly preferably 4% or less.

La ₂ O ₃ , Nb ₂ O ₅ and Ta ₂ O ₅ are all components that make it difficult for fragments to scatter when chemically strengthened glass is broken, and may be included in order to increase the refractive index. When these are contained, the total content of La ₂ O ₃ , Nb ₂ O ₅ and Ta ₂ O ₅ (hereinafter referred to as La ₂ O ₃ +Nb ₂ O ₅ +Ta ₂ O ₅ ) is preferably 0.5% or more. It is more preferably 1% or more, still more preferably 1.5% or more, particularly preferably 2% or more. In addition, in order to make the glass less likely to devitrify during melting, La ₂ O ₃ + Nb ₂ O ₅ + Ta ₂ O ₅ is preferably 4% or less, more preferably 3% or less, still more preferably 2% or less, and especially Preferably it is 1% or less.

Moreover, it may contain _CeO2 . CeO ₂ may suppress discoloration by oxidizing glass. When containing CeO ₂ , the content is preferably 0.03% or more, more preferably 0.05% or more, and even more preferably 0.07% or more. The content of CeO ₂ is preferably 1.5% or less, more preferably 1.0% or less, in order to increase transparency.

When chemically strengthened glass is used in a colored manner, a coloring component may be added within a range that does not inhibit the achievement of desired chemically strengthened properties. Examples of coloring _components include _Co3O4 , _MnO2 , _Fe2O3 , NiO _, CuO _{, Cr2O3 , V2O5 , Bi2O3 , SeO2} , _Er2O3 , _{Nd2O. 3} can be mentioned.

The total content of the coloring components is preferably in a range of 1% or less. When it is desired to increase the visible light transmittance of the glass, it is preferable that these components are not substantially contained.

HfO ₂ , Nb ₂ O ₅ , and Ti ₂ O ₃ may be added to improve the weather resistance against irradiation with ultraviolet light. When added for the purpose of improving weather resistance against ultraviolet light irradiation, the total content of HfO ₂ , Nb ₂ O ₅ and Ti ₂ O ₃ is preferably 1% or less in order to suppress the influence on other properties. It is more preferably 0.5% or less, and even more preferably 0.1% or less.

Further, SO ₃ , chloride, and fluoride may be appropriately contained as a fining agent or the like during glass melting. The total content of components that function as clarifiers is preferably 2% or less, more preferably 1% or less, expressed as mass % based on oxides, since adding too much will affect the reinforcing properties. Preferably it is 0.5% or less. The lower limit is not particularly limited, but is typically 0.05% or more in total expressed as % by mass based on the oxide.

When SO ₃ is used as a clarifier, the content of SO ₃ is preferably 0.01% or more, more preferably 0.05%, expressed as mass % based on oxides, since no effect will be seen if it is too small. or more, and more preferably 0.1% or more. Further, when SO ₃ is used as a clarifier, the content of SO ₃ is preferably 1% or less, more preferably 0.8% or less, and even more preferably 0.6% by mass based on oxides. % or less.

When using Cl as a clarifier, the content of Cl is preferably 1% or less, expressed as % by mass based on oxides, and 0.8% or less, since adding too much will affect physical properties such as reinforcing properties. It is more preferably 0.6% or less. In addition, when using Cl as a clarifier, the content of Cl is preferably 0.05% or more, more preferably 0.1%, expressed as mass % based on oxides, since no effect will be seen if it is too small. or more, and more preferably 0.2% or more.

When SnO ₂ is used as a clarifier, the content of SnO ₂ is preferably 1% or less, more preferably 0.5% or less, and even more preferably 0.3% or less, expressed as mass % based on the oxide. In addition, when using SnO ₂ as a clarifier, the content of SnO ₂ is preferably 0.02% or more, more preferably 0.02% or more, expressed as mass % based on oxides, since no effect will be seen if it is too small. 0.05% or more, more preferably 0.1% or more.

It is preferable that P ₂ O ₅ is not contained. When P ₂ O ₅ is contained, it is preferably 2.0% or less, more preferably 1.0% or less, even more preferably 0.5% or less, and most preferably not contained.

It is preferable that As ₂ O ₃ is not contained. When As ₂ O ₃ is contained, it is preferably 0.3% or less, more preferably 0.1% or less, and most preferably not contained.

<Method for manufacturing chemically strengthened glass>
A method for manufacturing chemically strengthened glass (hereinafter also abbreviated as the present manufacturing method) according to an embodiment of the present invention will be described below.

The present manufacturing method is characterized in that it sequentially includes the following steps (1) to (3).
(1) Ion exchange step of ion-exchanging the lithium-containing glass at least once with an inorganic salt composition containing potassium (2) Containing LiNO ₃ and NaNO ₃ and the mass ratio of NaNO ₃ to LiNO ₃ NaNO ₃ Reverse ion exchange step ( ₃ ) in which the lithium-containing glass is brought into contact with an inorganic salt composition having a content of 0.25 to 3.0 at 425° C. or higher for 5 hours or more. Re-ion exchange step of performing ion exchange at least once with an inorganic salt composition. Each step will be explained below.

<<Step (1)>>
Step (1) is a step of ion-exchanging the lithium-containing glass at least once by bringing it into contact with the potassium-containing inorganic salt composition. The lithium-containing glass may have any composition as long as it contains lithium and can be formed by molding and chemical strengthening. Examples of the glass include aluminosilicate glass, soda lime glass, borosilicate glass, lead glass, alkali barium glass, aluminoborosilicate glass, and the like.

The preferred composition of the lithium-containing glass is the same as that described in the section <<Composition>> of <Chemically strengthened glass>. That is, it is preferable that the mother composition contains 52 to 75% of SiO ₂ , 8 to 20% of Al ₂ O ₃ , and 5 to 18% of Li ₂ O in terms of mol% based on oxides. Glass having such a preferable matrix composition has a property that potassium is difficult to diffuse into the glass due to ion exchange, but according to the present manufacturing method, many potassium ions can be introduced into the glass surface layer and the surface strength can be increased.

Chemical strengthening treatment to form a compressive stress layer on the surface layer of glass involves bringing the glass into contact with an inorganic salt composition to strengthen the metal ions in the glass and the metal ions in the inorganic salt composition with an ionic radius smaller than that of the metal ions. This process replaces large metal ions.

Methods for bringing the glass into contact with the inorganic salt composition include methods of applying a paste-like inorganic salt composition to the glass, methods of spraying an aqueous solution of the inorganic salt composition onto the glass, and methods of contacting the glass with the inorganic salt composition heated above the melting point. Examples include a method in which a glass plate is immersed in a salt bath of molten salt. Among these, from the viewpoint of improving productivity, a method of immersing glass in a molten salt of an inorganic salt composition is preferred.

Chemical strengthening treatment by immersing glass in a molten salt of an inorganic salt composition can be carried out, for example, by the following procedure. First, the glass is preheated to 100° C. or higher, and the molten salt is adjusted to a temperature for chemical strengthening. Next, after immersing the preheated glass in the molten salt for a predetermined time, the glass is pulled out of the molten salt and allowed to cool.

The salts contained in the inorganic salt composition used for ion exchange in step (1) are not particularly limited, and include, for example, sodium nitrate, sodium carbonate, sodium chloride, sodium borate, sodium sulfate, potassium nitrate, potassium carbonate, potassium chloride, Examples include potassium borate, potassium sulfate, lithium nitrate, lithium carbonate, lithium chloride, lithium borate, and lithium sulfate, and these may be added alone or in combination of multiple types. Examples of the inorganic salt composition containing potassium include, for example, preferably an inorganic salt composition containing sodium nitrate or potassium nitrate.

The contact temperature between the lithium-containing glass and the inorganic salt composition in step (1) is not particularly limited, but from the viewpoint of accelerating the ion exchange rate and improving productivity, it is preferably 310 ° C. or higher, more preferably 330 ° C. or higher, More preferably, the temperature is 350°C or higher. Further, from the viewpoint of reducing salt volatilization, the contact temperature is preferably 530°C or lower, more preferably 500°C or lower, and even more preferably 480°C or lower.

The contact time between the lithium-containing glass and the inorganic salt composition in step (1) is not particularly limited, but from the viewpoint of reducing variations in the ion exchange level due to time fluctuations, it is preferably 30 minutes or more, more preferably 45 minutes or more, More preferably one hour or more. Moreover, from the viewpoint of improving productivity, the time is preferably 20 hours or less.

The ion exchange in step (1) may be a one-stage ion exchange, as long as the ion exchange is brought into contact with the potassium-containing inorganic salt composition at least once, or it may be a multi-stage ion exchange with two or more stages. It may be an exchange.

Examples of the two or more stages of ion exchange in step (1) include the following.
- In the first stage of ion exchange, a glass plate is brought into contact with an inorganic salt composition containing preferably 20% by mass or more of NaNO ₃ to ionize Li ions in the glass and Na ions in the inorganic salt composition. After the exchange, as a second stage of ion exchange, the glass plate is brought into contact with an inorganic salt composition preferably containing 80% by mass or more of _KNO3 , so that the Na ions in the glass and the K ions in the inorganic salt composition are combined. ion exchange.
The content of NaNO ₃ in the inorganic salt composition during ion exchange in the first stage is more preferably 30% by mass or more, and even more preferably 40% by mass or more. Further, the content of KNO ₃ in the inorganic salt composition during ion exchange in the second stage is more preferably 85% by mass or more, and even more preferably 90% by mass or more.

Among the compressive stress layers formed on the surface layer of the lithium-containing glass in step (1), the compressive stress (CS) at the outermost surface is not particularly limited, but is usually preferably 600 MPa or more, more preferably 650 MPa or more, and 700 MPa or more. More preferred.

<<Step (2)>>
Step (2) is to bring the lithium-containing glass into contact with the inorganic salt composition containing LiNO ₃ and NaNO ₃ to ion-exchange the ions in the lithium-containing glass with ions having a smaller ionic radius than the ions. This is a reverse ion exchange step to reduce the compressive stress of the compressive stress layer formed in step (1). More specifically, for example, K ions in the glass and Na ions in the inorganic salt composition, and Na ions in the glass and Li ions in the inorganic salt composition are exchanged.

The inorganic salt composition used in step (2) contains LiNO ₃ and NaNO ₃ , and the mass ratio of NaNO ₃ to LiNO ₃ , NaNO ₃ /LiNO ₃ , is 0.25 or more and 3.0 or less. When the mass ratio NaNO ₃ /LiNO ₃ is 0.25 or more and 3.0 or less, the Na ion concentration in the glass surface layer can be sufficiently reduced and the reverse ion exchange efficiency can be increased. From the viewpoint of improving the efficiency of reverse ion exchange, the mass ratio NaNO ₃ /LiNO ₃ is more preferably 0.40 or more, still more preferably 0.55 or more, particularly preferably 0.75 or more. Further, it is more preferably 2.5 or less, further preferably 1.8 or less, particularly preferably 1.3 or less.

The content of LiNO ₃ contained in the inorganic salt composition used in step (2) is preferably 20% by mass or more, more preferably 30% by mass or more, and still more preferably 40% by mass or more. Moreover, the content of LiNO ₃ contained in the inorganic salt composition is preferably 75% by mass or less, more preferably 70% by mass or less, still more preferably 65% by mass or less.

In addition to LiNO ₃ and NaNO ₃ , other inorganic salts may be added to the inorganic salt composition. Examples of the other inorganic salts include sodium carbonate, sodium chloride, sodium borate, sodium sulfate, potassium nitrate, potassium carbonate, potassium chloride, potassium borate, potassium sulfate, lithium carbonate, lithium chloride, lithium borate, and lithium sulfate. can be mentioned.

Among these, KNO ₃ is preferred from the viewpoint of increasing the reverse ion exchange efficiency without increasing the LiNO ₃ content. When the inorganic salt composition contains KNO ₃ , the content of KNO ₃ in the inorganic salt composition is preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 15% by mass or more. Further, the content of KNO ₃ in the inorganic salt composition is preferably 60% by mass or less, more preferably 50% by mass or less, and even more preferably 40% by mass or less.

The contact temperature between the lithium-containing glass and the inorganic salt composition in step (2) is 425°C or higher, preferably 435°C or higher, and more preferably 445°C or higher. By setting the contact temperature to 425° C. or higher, the reverse ion exchange efficiency can be increased to sufficiently remove ions from the glass, and the reion exchange efficiency in step (3) can be increased to improve the strength. Further, expansion of the glass caused by steps (1) and (2) can be suppressed. Further, from the viewpoint of reducing salt volatilization, the contact temperature is preferably 500°C or lower, more preferably 485°C or lower, and even more preferably 470°C or lower.

The contact time between the lithium-containing glass and the inorganic salt composition in step (2) is determined from the viewpoint of improving reverse ion exchange efficiency by reducing variations in ion exchange level due to time fluctuations, and from the viewpoint of step (1) and step (2). From the viewpoint of suppressing the expansion of the glass due to step (1) and step (2), the heating time is preferably 4 hours or more, more preferably 6 hours or more, and even more preferably 8 hours or more. Further, from the viewpoint of improving productivity, the heating time is preferably 72 hours or less, more preferably 48 hours or less, and still more preferably 24 hours or less.

It is preferable that the compressive stress of the compressive stress layer reduced in step (2) is as low as possible, and it is most preferable that the compressive stress layer is completely removed. For example, the compressive stress (CS) of the compressive stress layer after the first ion exchange step is preferably 10 MPa or less, more preferably 7 MPa or less, further preferably 4 MPa or less, and most preferably 0 MPa at a depth of 50 μm from the surface. . Further, the compressive stress on the glass surface after step (2) may be 100 MPa or less, preferably 50 MPa or less, more preferably 20 MPa or less, and even more preferably 10 MPa or less.

The lithium-containing glass subjected to reverse ion exchange in step (2) has an expansion coefficient of 0.4% or less in the longitudinal direction of the glass plate relative to the lithium-containing glass before ion exchange in step (1). is preferable, more preferably 0.3% or less, still more preferably 0.2% or less. By setting the expansion coefficient to 0.1% or less, it is possible to suppress warping of the glass due to an increase in the expansion coefficient. The upper limit of the expansion rate is not particularly limited, and is preferably as close to 0% as possible, but is usually -0.05% or more.

<<Step (A)>>
This manufacturing method may include the following step (A) between the reverse ion exchange step of step (2) and the reion exchange step of step (3). (A) Step of removing 0.5 to 15 μm per side of the surface of lithium-containing glass on one or both sides

The amount of lithium-containing glass surface removed in step (A) is 0.5 μm or more per side, preferably 0.7 μm or more, more preferably 0.9 μm or more, and still more preferably 1.3 μm or more. Further, the amount removed in step (A) is 15 μm or less per side, preferably 12 μm or less, more preferably 10 μm or less, and still more preferably 8 μm or less. By setting the removal amount in step (A) within the above range, not only micro scratches (defects) on the glass surface can be removed, but also cloudiness generated by reverse ion exchange can be sufficiently removed.

The amount of removal of the lithium-containing glass surface in step (A) does not require that the amount of polishing on both sides be equal; for example, if the difference in the amount of polishing on both sides is preferably within a range of 3.0 μm or less, warping can be reduced. It is more preferably 2.0 μm or less, still more preferably 1.0 μm or less, particularly preferably 0.5 μm or less.

Means for removing the surface of the lithium-containing glass include polishing or etching the glass surface. In addition, in step (A), from the point of view of preventing warping of the glass, it is preferable to remove the same amount from the two main surfaces of the glass plate facing each other in the thickness direction, but the removal conditions in step (A) are particularly There are no restrictions, and it may be carried out under conditions that provide the desired surface roughness.

As the polishing means, for example, abrasive grains such as cerium oxide and colloidal silica can be used. The average particle diameter of the abrasive grains is preferably 0.02 to 2.0 μm, and the concentration of the abrasive grains and the specific gravity of the slurry are preferably 1.03 to 1.13. The polishing pressure is preferably 6 to 20 kPa, and the rotation speed of the surface plate of the polishing device is preferably 20 to 100 m/min at the outermost circumference. As an example, cerium oxide with an average particle size of about 1.2 μm is dispersed in water to prepare a slurry with a specific gravity of 1.07, and using a polishing pad with a nonwoven fabric or suede surface, the polishing pressure is 9.8 kPa. This can be carried out by a general method such as polishing the surface of a glass plate with a thickness of 0.5 μm or more per side. Further, in the polishing step, a polishing pad having a surface of nonwoven fabric or suede and having a Shore A hardness of 25 to 65 degrees and a sinking amount of 0.05 mm or more at 100 g/cm ² can be used. Among these, it is preferable to use a polishing pad made of non-woven fabric from the viewpoint of cost.

Examples of the removal of the glass surface by etching include etching with a chemical solution containing hydrofluoric acid.

<<Step (3)>>
Step (3) is to bring the lithium-containing glass whose compressive stress has been reduced in step (2) into contact with an inorganic salt composition to increase the compressive stress of the compressive stress layer formed on the surface layer of the glass plate. This is a re-ion exchange step in which ions are exchanged at least once with an inorganic salt composition containing potassium.

Specifically, in step (3), ions in the glass are ion-exchanged with ions having a larger ionic radius than the ions to increase the compressive stress of the compressive stress layer. More specifically, for example, Na ions in the glass and K ions in the inorganic salt composition, and Li ions in the glass and Na ions in the inorganic salt composition are exchanged.

Examples of the salts contained in the inorganic salt composition used for ion exchange in step (3) include sodium nitrate, sodium carbonate, sodium chloride, sodium borate, sodium sulfate, potassium nitrate, potassium carbonate, potassium chloride, potassium borate, Potassium sulfate is mentioned, and these may be added alone or in combination of multiple types.

The type and content of salt contained in the inorganic salt composition used for ion exchange in step (3) can be appropriately set so as to obtain desired compressive stress and compressive stress layer depth.

For example, as a method for ion-exchanging Na ions in glass and K ions in an inorganic salt composition, KNO ₃ is preferably 20% by mass or more, more preferably 30% by mass or more, and It is preferable to use an inorganic salt composition containing preferably 40% by mass or more.

The ion exchange in step (3) may be a one-stage ion exchange, as long as the ion exchange is brought into contact with the potassium-containing inorganic salt composition at least once, or it may be a multi-stage ion exchange with two or more stages. It may be an exchange.

Furthermore, examples of the two or more stages of ion exchange in step (3) include the following. - In the first stage of ion exchange, a glass plate is brought into contact with an inorganic salt composition containing preferably 20% by mass or more of NaNO ₃ to ionize Li ions in the glass and Na ions in the inorganic salt composition. After the exchange, as a second stage of ion exchange, the glass plate is brought into contact with an inorganic salt composition preferably containing 80% by mass or more of _KNO3 , so that the Na ions in the glass and the K ions in the inorganic salt composition are combined. ion exchange.
The content of NaNO ₃ in the inorganic salt composition during ion exchange in the first stage is more preferably 30% by mass or more, and even more preferably 30% by mass or more. Further, the content of KNO ₃ in the inorganic salt composition during ion exchange in the second stage is more preferably 85% by mass or more, and even more preferably 90% by mass or more.

The contact temperature between the lithium-containing glass and the inorganic salt composition in the ion exchange of step (3) is not particularly limited, but from the viewpoint of accelerating the ion exchange rate and improving productivity, it is preferably 310°C or higher, and 330°C or higher. More preferably, the temperature is 350°C or higher. Further, from the viewpoint of reducing salt volatilization, the contact temperature is preferably 530°C or lower, more preferably 500°C or lower, and even more preferably 480°C or lower.

The contact time between the lithium-containing glass and the inorganic salt composition in the ion exchange in step (3) is not particularly limited, but from the viewpoint of reducing variations in the ion exchange level due to time fluctuations, it is preferably 30 minutes or more, and 45 minutes or more. More preferably, one hour or more is even more preferable. Moreover, from the viewpoint of improving productivity, the time is preferably 20 hours or less.

When the ion exchange of step (1) and the ion exchange of step (3) each include two stages of ion exchange, the time of the first stage of ion exchange included in the ion exchange of step (3) is the same as that of step (1). It is preferable that the time is longer than the time of the first stage of ion exchange included in the ion exchange of . Thereby, the Na ions extracted in excess from the glass surface in step (2) can be sufficiently introduced into the glass surface layer.

The present manufacturing method preferably further includes a step of cleaning the glass between each step. For cleaning, industrial water, ion exchange water, etc. can be used. Washing conditions vary depending on the washing liquid, but when using ion-exchanged water, it is preferable to wash at a temperature of 0 to 100° C., since adhered salts can be completely removed. In the cleaning process, various methods can be used, such as immersing the glass in a water tank containing ion-exchanged water, exposing the glass surface to running water, and spraying a cleaning solution onto the glass surface using a shower.

The compressive stress (CS) of the compressive stress layer of the chemically strengthened glass manufactured by this manufacturing method is not particularly limited, but at a depth of 50 μm from the surface, it is preferably 50 MPa or more, more preferably 60 MPa or more, and still more preferably 70 MPa or more. preferable. Further, the compressive stress on the glass surface of the chemically strengthened glass produced by this production method is not particularly limited either, but may be 500 MPa or more, preferably 600 MPa or more, more preferably 700 MPa or more, and even more preferably 800 MPa or more.

EXAMPLES The present invention will be explained below with reference to Examples, but the present invention is not limited thereto.

<Production of chemically strengthened glass>
(Production of chemically strengthened glass)
Glass raw materials were prepared to have the following composition expressed in mole percentage based on oxides, and weighed to give 400 g of glass. Next, the mixed raw materials were placed in a platinum crucible and placed in an electric furnace at 1,500 to 1,700°C, where they were melted for about 3 hours, defoamed, and homogenized.
Glass material A: SiO ₂ 69.2%, Al ₂ O ₃ 12.4%, MgO 0.1%, CaO 0.1%, ZrO ₂ 0.3%, Y ₂ O ₃ 1.3%, Li ₂ O 10.6%, _Na2O
4.7%, _K2O 1.2%

The obtained molten glass was poured into a metal mold, held at a temperature approximately 50° C. higher than the glass transition point for 1 hour, and then cooled to room temperature at a rate of 0.5° C./min to obtain a glass block. The obtained molten glass was poured into a mold, held at a temperature near the glass transition point (714°C) for about 1 hour, and then cooled to room temperature at a rate of 0.5°C/min to obtain a glass block. A glass plate of 50 mm x 50 mm x 0.7 mm was produced from the obtained glass block.

Step (1): Ion exchange step Using the glass plate obtained above, the glass plate was immersed in an inorganic salt composition under the conditions shown in Table 1 to perform an ion exchange treatment. In Table 1, when "first stage" and "second stage" are described, the second stage ion exchange treatment was performed after the first stage ion exchange treatment. Between each ion exchange, the surface of the glass plate was cleaned and dried.

Step (2): Reverse ion exchange step After the ion exchange step, the glass plate was immersed in the inorganic salt composition under the conditions shown in Table 1 to perform ion exchange treatment, thereby performing reverse ion exchange. Thereafter, the surface of the glass plate was washed and dried.

Step (A): Removal Step As a polishing slurry, cerium oxide having an average particle diameter (d50) of 1.2 μm was dispersed in water to prepare a slurry having a specific gravity of 1.07. Next, using the obtained slurry, a glass plate was polished at a polishing pressure of 9.8 kPa using a nonwoven fabric polishing pad with a Shore A hardness of 58° and a sinking amount of 0.11 mm at 100 g/ ^cm2 . Both sides were simultaneously polished by 5 μm each.

Step (3): Re-ion exchange step After the above-mentioned removal step, the glass plate was immersed in the inorganic salt composition under the conditions shown in Table 1 to perform an ion exchange treatment and perform re-ion exchange. Thereafter, the surface of the glass plate was washed and dried.

<Evaluation>
Various evaluations in this example were performed by the methods shown below.
(EPMA)
The K ₂ O concentration or Na ₂ O concentration in the glass was measured by EPMA as follows. First, a glass sample was embedded in an epoxy resin and mechanically polished in a direction perpendicular to a first main surface and a second main surface opposite to the first main surface to prepare a cross-sectional sample. A C coat was applied to the cross section after polishing, and measurement was performed using EPMA (manufactured by JEOL: JXA-8500F). The accelerating voltage was 15kV, the probe current was 30nA, and the integration time was 1000msec. A line profile of the X-ray intensity of K ₂ O or Na ₂ O was obtained at 1 μm intervals as /point. Regarding the obtained K ₂ O concentration profile and Na ₂ O concentration profile, the average count of the central part of the plate thickness (0.5 x t) ± 25 μm (the plate thickness is t μm) is taken as the bulk composition, and the count of the entire plate thickness is calculated. was calculated by proportionally converting it into mol%, and the slope (%/μm) in each region shown in Table 2 was determined.

(stress profile)
Using a scattered light photoelastic stress meter (SLP-2000 manufactured by Orihara Seisakusho), the stress of chemically strengthened glass was measured by the method described in International Publication No. 2018/056121. In addition, the stress profile was calculated using the software [SlpV (Ver. 2019.11.07.001)] attached to the scattered light photoelastic stress meter (SLP-2000 manufactured by Orihara Seisakusho).

The function used to obtain the stress profile is σ(x)=[a ₁ ×erfc(a ₂ ×x)+a ₃ ×erfc(a ₄ ×x)+a ₅ ]. a _i ( _i =1 to 5) are fitting parameters, and erfc is a complementary error function. The complementary error function is defined by the following formula.

In the evaluation herein, fitting parameters were optimized by minimizing the sum of squared residuals between the obtained raw data and the above function. The measurement processing conditions are single shot, and the measurement area processing adjustment items are edge method for the surface, 6.0 μm for the internal surface edge, automatic for the internal left and right edges, automatic for the internal deep edge (center of sample film thickness), and phase. A fitting curve was selected, each specifying a curve extending to the center of the sample thickness.

The stress in the glass surface layer, which is several tens of μm or less from the glass surface, is measured using a glass surface stress meter (FSM6000-UV manufactured by Orihara Seisakusho) using the method described in International Publication No. 2018/056121 and International Publication No. 2017/115811. It was measured by

At the same time, the concentration distribution of alkali metal ions (sodium ions and potassium ions) in the cross-sectional direction was measured using SEM-EDX (EPMA), and it was confirmed that there was no contradiction with the obtained stress profile.

Further, from the obtained stress profile, the values of compressive stress CS ₀ , DOL, CS ₅₀ , CS ₉₀ , CTave, CT-Max, and DOC were calculated by the method described above.

(Potassium ion diffusion layer depth)
The depth of the potassium ion diffusion layer is calculated from the outermost surface side with respect to the average K ₂ O concentration (%) at the center of the plate thickness (0.5 x t) ± 25 μm in the K ₂ O concentration profile obtained by EPMA. The depth (μm) at which the K ₂ O concentration falls within the range of +2σ or less was defined as the depth of the potassium ion diffusion layer.

(Expansion rate)
The rate of change in the length of the glass plate in the longitudinal direction after the re-ion exchange step in step (3) with respect to the length in the longitudinal direction of the glass plate before ion exchange in step (1) was determined and used as the expansion rate. The length of the glass plate was measured using a digital caliper manufactured by Mitutoyo Co., Ltd.

(4PB strength)
Chemically strengthened glass was cut to 50 mm x 50 mm, and a 50 x 50 x 0.7 mm thick piece was obtained by automatic chamfering (C chamfering) using a 1000-grid whetstone (manufactured by Tokyo Diamond Tools Manufacturing Co., Ltd.). After processing in the order of steps (1), (2), (A), and (3), the distance between the external supports of the support is 30 mm, the distance between the internal supports is 10 mm, and the crosshead speed is 5.0 mm/min. A 4-point bending test was conducted under the following conditions, and the 4-point bending strength was measured. The number of test pieces was 10.

Table 2 shows the results of evaluating chemically strengthened glass. In Tables 1 and 2, Examples 1 to 4 are examples, and Example 5 is a comparative example. The stress profiles of Examples 1 and 5 are shown in FIG. Further, the K ₂ O concentration or Na ₂ O concentration profiles of Examples 1, 2, and 5 are shown in FIGS. 2 to 4, respectively.

In Table 2, each notation represents the following. "N.D." indicates that it has not been evaluated.
t [μm]: Plate thickness CS ₀ [MPa]: Compressive stress at the glass surface DOL [μm]: Compressive stress depth CS ₅₀ [MPa]: Compressive stress at a depth of 50 μm from the glass surface CS ₉₀ [MPa]: Glass Compressive stress CTave [MPa] at a depth of 90 μm from the surface: Average value of tensile stress CT-Max (MPa): Maximum tensile stress DOC [μm]: Compressive stress layer depth mK1-3 [mol%/μm]: K ₂ O concentration profile, slope at depth 1 to 3 μm mK5-10 [mol%/μm]: K ₂ O concentration profile, slope at depth 5 to 10 μm mNa10-50 [mol%/μm]: Na ₂ O Slope mNa50-90 [mol%/μm] at a depth of 10 to 50 μm in the concentration profile: Slope at a depth of 50 to 90 μm in the Na ₂ O concentration profile | mK5-10/mK1-3 |: K ₂ O concentration profile The absolute value of the slope at a depth of 5 to 10 μm divided by the slope at a depth of 1 to 3 μm | mNa50-90/mNa10-50 |: The slope at a depth of 50 to 90 μm in the Na ₂ O concentration profile is Absolute value of the difference in K _{2 O concentration between the depth 15-25 μm and the center [%]: K 2 O} concentration (%) at the depth 15-25 μm , Absolute value of the difference from the K ₂ O concentration (%) in the center 4PB Strength: Average value of 4-point bending strength measurement results performed on 10 test pieces

As shown in Table 2, Example 1, which is an example, exhibited superior 4PB strength compared to Example 5, which is a comparative example. As shown in Table 2 and FIG. 1(a), in Examples 1 and 2, which are examples, more K ions are introduced into the surface layer than in Example 5, which is a comparative example. It has high stress and exhibits excellent strength. In Example 3, which is an example, more K ions are introduced into the surface layer than in the comparative example, the surface compressive stress CS ₀ is high, and the specimen has excellent strength. In Example 4, which is an example, more K ions are introduced into the surface layer than in the comparative example, the compressive stress layer depth DOC is deep, and it has excellent strength.

Example 1, which is an example, had higher CS ₅₀ and DOC than Example 3, which is an example. From this result, it is considered that by making the first ion exchange time in step (3) longer than the first ion exchange time in step (1), it is possible to increase CS ₅₀ and DOC and further improve drop strength.

Further, in Example 3, which is an example, the expansion coefficient of the glass was lower than that in Example 4, which is an example. From this result, it is considered that the smaller the NaNO ₃ /LiNO ₃ ratio in step (2), the lower the expansion rate up to step (2), and therefore the lower the expansion rate after step (3).

Furthermore, a glass (glass material B) having a different composition from the glass (glass material A) used in the above example was prepared, and a chemically strengthened glass was produced using this glass. Glass raw materials were prepared to have the composition of glass material B shown below in terms of mole percentage based on oxides, and weighed to give 400 g of glass. Next, the mixed raw materials were placed in a platinum crucible and placed in an electric furnace at 1,500 to 1,700°C, where they were melted for about 3 hours, defoamed, and homogenized.
Glass material B: SiO ₂ 66.2%, Al ₂ O ₃ 11.2%, MgO 3.1%, CaO 0.2%, ZrO ₂ 1.3%, Y ₂ O ₃ 0.5%, Li ₂ O 10.4%, Na ₂ O 5.6%, K ₂ O 1.5%

The obtained molten glass was poured into a metal mold, held at a temperature approximately 50° C. higher than the glass transition point for 1 hour, and then cooled to room temperature at a rate of 0.5° C./min to obtain a glass block. The obtained molten glass was poured into a mold, held at a temperature near the glass transition point (714°C) for about 1 hour, and then cooled to room temperature at a rate of 100°C/min to obtain a glass block. A glass plate of 50 mm x 50 mm x 0.6 mm was produced from the obtained glass block.

Below, step (1): ion exchange step, step (2): reverse ion exchange step, step (A): removal step, and step (3): reion exchange step are chemically strengthened glass under the conditions shown in Table 3. Created.

Various evaluations of the chemically strengthened glass obtained by chemically strengthening the glass material B were conducted in the same manner as for the chemically strengthened glass obtained by chemically strengthening the glass material A described above.

Table 4 shows the results for chemically strengthened glass obtained by chemically strengthening glass material B. In Tables 3 and 4, Examples 6 to 9 are Examples, and Example 10 is a Comparative Example.

As shown in Table 4, in Examples 6 to 9, the slope mK1-3 [mol%/μm] at a depth of 1 to 3 μm is -1.9 or more, similar to Examples 1 to 4. The slope mK5-10 [mol%/μm] at a depth of 5 to 10 μm was −0.001 or less.

In addition, the following verification was conducted for Examples 6 to 9, which are examples.
In Examples 6 to 9, as in Examples 1 to 4, the slope (%/μm) at a depth of 5 to 10 μm was divided by the slope (%/μm) at a depth of 1 to 3 μm. The absolute value |mK5-10/mK1-3| was 0.005 or more and 0.10 or less.
In Examples 6 to 9, as in Examples 1 to 4, the slope (%/μm) at a depth of 50 to 90 μm is divided by the slope (%/μm) at a depth of 10 to 50 μm. The absolute value |mNa50-90/mNa10-50| was 0.50 or more and 4.0 or less.
Examples 6 to 9 are similar to Examples 1 to 4, in which the K ₂ O concentration (%) at a depth of 15 to 25 μm and the K ₂ O concentration (%) at the center of the plate thickness are determined. The absolute value of the difference was 0.20% or less.
In Examples 6 to 9, as in Examples 1 to 4, the depth of the potassium ion diffusion layer was 5 μm or more.
In Examples 6 to 9, which are examples, the slope mK1-3 [mol%/μm] at a depth of 1 to 3 μm is larger than that in Example 5, which is a comparative example in which the reverse ion exchange step is not performed. The slope mK5-10 [mol%/μm] at a depth of 5 to 10 μm showed a small value.
Examples 6 to 9, which are working examples, have more K ions introduced at a depth of 15 to 25 μm, and have high stress in the surface layer, compared to Example 10, which is a comparative example in which no reion exchange process is performed. It was found that the material had excellent strength.

As explained above, the following matters are disclosed in this specification.
1. In the K ₂ O concentration profile where the horizontal axis is the depth from the surface (μm) and the vertical axis is the K ₂ O concentration (%) expressed in mole percentage based on oxide,
Chemically strengthened glass having a slope (%/μm) at a depth of 1 to 3 μm of -1.9 or more and a slope (%/μm) at a depth of 5 to 10 μm of -0.001 or less.
2. In the Na ₂ O concentration profile where the horizontal axis is the depth from the surface (μm) and the vertical axis is the Na ₂ O concentration (%) expressed as a molar percentage on an oxide basis,
The chemically strengthened glass according to 1 above, wherein the slope (%/μm) at a depth of 10 to 50 μm is -0.001 or less, and the slope (%/μm) at a depth of 50 to 90 μm is -0.012 or more. .
3. In the above K ₂ O concentration profile, the absolute value obtained by dividing the K ₂ O concentration slope (%/μm) at a depth of 5 to 10 μm by the K ₂ O concentration slope (%/μm) at a depth of 1 to 3 μm The chemically strengthened glass according to 1 or 2 above, which has a value of 0.005 or more and 0.10 or less.
4. In the Na ₂ O concentration profile where the horizontal axis is the depth from the surface (μm) and the vertical axis is the Na ₂ O concentration (%) expressed as a molar percentage on an oxide basis,
The absolute value of the slope (%/μm) of Na ₂ O concentration at a depth of 50 to 90 μm divided by the slope (%/μm) of Na ₂ O concentration at a depth of 10 to 50 μm is 0.50 or more.4. 4. The chemically strengthened glass according to any one of 1 to 3 above, wherein the chemically strengthened glass is 0 or less.
5. In the K ₂ O concentration profile, the absolute value of the difference between the K ₂ O concentration (%) at a depth of 15 to 25 μm and the K ₂ O concentration (%) at the center of the plate thickness is 0.20% or less, 5. The chemically strengthened glass according to any one of 1 to 4 above.
6. 6. The chemically strengthened glass according to any one of 1 to 5 above, wherein the depth of the potassium ion diffusion layer is 5 μm or more.
7. 7. The chemically strengthened glass according to any one of 1 to 6 above, which is a lithium-containing glass.
8. The mother composition is expressed as a mole percentage based on oxides,
SiO ₂ 52-75%,
8-20% Al ₂ O ₃ ,
Contains 5 to 18% Li ₂ O,
8. The chemically strengthened glass according to any one of 1 to 7 above.
9. The mother composition is expressed as a mole percentage based on oxides,
SiO ₂ 52-75%,
8-20% Al ₂ O ₃ ,
5-18% Li ₂ O,
0-15% Na ₂ O,
0-5% K ₂ O,
MgO 0-20%,
CaO 0-20%,
0 to 20% SrO,
BaO 0-20%,
ZnO 0-10%,
0-1% _TiO2 ,
ZrO ₂ 0-8%,
Contains 0 to 5% of Y ₂ O ₃ ,
The chemically strengthened glass according to any one of 1 to 8 above.
10. A method for manufacturing chemically strengthened glass, which includes the following (1) to (3) in sequence.
(1) The lithium-containing glass is ion-exchanged at least once with an inorganic salt composition containing potassium. (2) It contains LiNO ₃ and NaNO ₃ and the mass ratio of NaNO ₃ to LiNO ₃ is 0.25. -3.0, the lithium-containing glass is brought into contact with an inorganic salt composition containing potassium at 425° C. or higher for 5 hours or more to undergo reverse ion exchange. 11. Perform ion exchange at least once. The lithium-containing glass is expressed as a molar percentage on an oxide basis,
SiO ₂ 52-75%,
8-20% Al ₂ O ₃ ,
11. The method for producing chemically strengthened glass as described in 10 above, containing 5 to 18% of Li ₂ O.
12. The lithium-containing glass is expressed as a molar percentage on an oxide basis,
SiO ₂ 52-75%,
8-20% Al ₂ O ₃ ,
5-18% Li ₂ O,
0-15% Na ₂ O,
0-5% K ₂ O,
MgO 0-20%,
CaO 0-20%,
0 to 20% SrO,
BaO 0-20%,
0-10% ZnO
0-1% _TiO2
12. The method for producing chemically strengthened glass as described in 10 or 11 above, containing 0 to 8% ZrO ₂ .
13. The ion exchange in the above (1) and the ion exchange in the above (3) each include two stages of ion exchange, and the time of the first stage ion exchange included in the ion exchange in the above (3) is longer than the above (3). 13. The method for producing chemically strengthened glass according to any one of 10 to 12 above, wherein the ion exchange time in the first stage included in 1) is longer.
14. 14. The method for producing chemically strengthened glass according to any one of 10 to 13 above, comprising the following (A) between the above (2) and the above (3).
(A) Step 15: removing the surface of the lithium-containing glass by 0.5 to 15 μm per side on one or both sides. 15. The method for producing chemically strengthened glass as described in 14 above, wherein in (A), the surface of the lithium-containing glass is polished within a range where the difference in polishing amount between both surfaces is 3.0 μm or less.
16. In the K ₂ O concentration profile where the horizontal axis is the depth from the surface (μm) and the vertical axis is the K ₂ O concentration (%) expressed in mole percentage based on oxide,
Chemically strengthened glass having a slope (%/μm) at a depth of 1 to 3 μm of -1.9 or more and 0.0 or less, and a slope (%/μm) at a depth of 5 to 10 μm of -0.001 or less.
17. 17. The chemically strengthened glass according to item 16, wherein the slope (%/μm) at the depth of 1 to 3 μm is −1.9 or more and −1.000 or less.
18. 17. The chemically strengthened glass according to 16 above, wherein the slope (%/μm) at the depth of 5 to 10 μm is −0.200 or more and −0.001 or less.

Claims (18)

In the K ₂ O concentration profile where the horizontal axis is the depth from the surface (μm) and the vertical axis is the K ₂ O concentration (%) expressed in mole percentage based on oxide,
Chemically strengthened glass having a slope (%/μm) at a depth of 1 to 3 μm of -1.9 or more and a slope (%/μm) at a depth of 5 to 10 μm of -0.001 or less. In the Na ₂ O concentration profile where the horizontal axis is the depth from the surface (μm) and the vertical axis is the Na ₂ O concentration (%) expressed as a molar percentage on an oxide basis,
The chemical strengthening according to claim 1, wherein the slope (%/μm) at a depth of 10 to 50 μm is -0.001 or less, and the slope (%/μm) at a depth of 50 to 90 μm is -0.012 or more. glass. In the above K ₂ O concentration profile, the absolute value obtained by dividing the K ₂ O concentration slope (%/μm) at a depth of 5 to 10 μm by the K ₂ O concentration slope (%/μm) at a depth of 1 to 3 μm The chemically strengthened glass according to claim 1, having a value of 0.005 or more and 0.10 or less. In the Na ₂ O concentration profile where the horizontal axis is the depth from the surface (μm) and the vertical axis is the Na ₂ O concentration (%) expressed as a molar percentage on an oxide basis,
The absolute value of the slope (%/μm) of Na ₂ O concentration at a depth of 50 to 90 μm divided by the slope (%/μm) of Na ₂ O concentration at a depth of 10 to 50 μm is 0.50 or more.4. The chemically strengthened glass according to claim 1, wherein the chemically strengthened glass is 0 or less. In the K ₂ O concentration profile, the absolute value of the difference between the K ₂ O concentration (%) at a depth of 15 to 25 μm and the K ₂ O concentration (%) at the center of the plate thickness is 0.20% or less, The chemically strengthened glass according to claim 1. The chemically strengthened glass according to claim 1, wherein the depth of the potassium ion diffusion layer is 5 μm or more. The chemically strengthened glass according to any one of claims 1 to 6, which is a lithium-containing glass. The mother composition is expressed as a mole percentage based on oxides,
SiO ₂ 52-75%,
8-20% Al ₂ O ₃ ,
Contains 5 to 18% Li ₂ O,
The chemically strengthened glass according to any one of claims 1 to 6. The mother composition is expressed as a mole percentage based on oxides,
SiO ₂ 52-75%,
8-20% Al ₂ O ₃ ,
5-18% Li ₂ O,
0-15% Na ₂ O,
0-5% K ₂ O,
MgO 0-20%,
CaO 0-20%,
0 to 20% SrO,
BaO 0-20%,
ZnO 0-10%,
0-1% _TiO2 ,
ZrO ₂ 0-8%,
Contains 0 to 5% of Y ₂ O ₃ ,
The chemically strengthened glass according to any one of claims 1 to 6. A method for manufacturing chemically strengthened glass, which includes the following (1) to (3) in sequence.
(1) The lithium-containing glass is ion-exchanged at least once with an inorganic salt composition containing potassium. (2) It contains LiNO ₃ and NaNO ₃ and the mass ratio of NaNO ₃ to LiNO ₃ is 0.25. -3.0, the lithium-containing glass is brought into contact with an inorganic salt composition containing potassium at 425° C. or higher for 5 hours or more to undergo reverse ion exchange. ion exchange at least once with The lithium-containing glass is expressed as a molar percentage on an oxide basis,
SiO ₂ 52-75%,
8-20% Al ₂ O ₃ ,
The method for producing chemically strengthened glass according to claim 10, which contains 5 to 18% of Li ₂ O. The lithium-containing glass is expressed as a molar percentage on an oxide basis,
SiO ₂ 52-75%,
8-20% Al ₂ O ₃ ,
5-18% Li ₂ O,
0-15% Na ₂ O,
0-5% K ₂ O,
MgO 0-20%,
CaO 0-20%,
0 to 20% SrO,
BaO 0-20%,
0-10% ZnO
0-1% _TiO2
The method for producing chemically strengthened glass according to claim 11, which contains 0 to 8% ZrO ₂ . The ion exchange in the above (1) and the ion exchange in the above (3) each include two stages of ion exchange, and the time of the first stage ion exchange included in the ion exchange in the above (3) is longer than the above (3). The method for producing chemically strengthened glass according to any one of claims 10 to 12, wherein the time for the first stage of ion exchange included in the ion exchange of 1) is longer. The method for producing chemically strengthened glass according to any one of claims 10 to 12, comprising the following (A) between said (2) and said (3).
(A) Step of removing 0.5 to 15 μm per side of the surface of the lithium-containing glass on one side or both sides 15. The method for producing chemically strengthened glass according to claim 14, wherein in (A), the surface of the lithium-containing glass is polished within a range where the difference in polishing amount between both surfaces is 3.0 μm or less. In the K ₂ O concentration profile where the horizontal axis is the depth from the surface (μm) and the vertical axis is the K ₂ O concentration (%) expressed in mole percentage based on oxide,
Chemically strengthened glass having a slope (%/μm) at a depth of 1 to 3 μm of -1.9 or more and 0.0 or less, and a slope (%/μm) at a depth of 5 to 10 μm of -0.001 or less. The chemically strengthened glass according to claim 16, wherein the slope (%/μm) of the depth of 1 to 3 μm is −1.9 or more and −1.000 or less. The chemically strengthened glass according to claim 16, wherein the slope (%/μm) at the depth of 5 to 10 μm is −0.200 or more and −0.001 or less.

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