CN113372017A

CN113372017A - Chemically strengthened glass and method for producing same

Info

Publication number: CN113372017A
Application number: CN202110259353.3A
Authority: CN
Inventors: 马田拓实; 大原盛辉
Original assignee: Asahi Glass Co Ltd
Current assignee: AGC Inc
Priority date: 2020-03-10
Filing date: 2021-03-10
Publication date: 2021-09-10
Anticipated expiration: 2041-03-10
Also published as: JP7404942B2; JP2021143079A

Abstract

The present invention relates to a chemically strengthened glass and a method for producing the same. The present invention relates to a chemically strengthened glass having a surface compressive stress value of 400MPa or more, wherein the absolute value of the refractive index distribution from the surface to the center of the sheet thickness is 0.002 or less.

Description

Chemically strengthened glass and method for producing same

Technical Field

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

Background

Chemically strengthened glass is used for cover glass of electronic devices such as mobile terminals. In recent years, the display of electronic devices such as mobile terminals has become high-definition. The chemically strengthened glass is, for example, a glass in which a compressive stress layer is formed on the surface of the glass by bringing the glass into contact with a molten salt containing alkali metal ions and causing ion exchange between the alkali metal ions in the glass and the alkali metal ions in the molten salt.

Generally, a refractive index change is generated on the surface of chemically strengthened glass by ion exchange treatment. For example, chemically strengthened glass obtained by chemically strengthening a glass containing Na ions with a molten salt containing K ions has a high refractive index of light in a region after the chemical strengthening. In chemically strengthened glass in which the surface layer of the glass is ion-exchanged, the refractive index of light in the surface layer changes and gradually approaches the refractive index of bulk glass from the surface layer to the inside (patent document 1).

Documents of the prior art

Patent document

Patent document 1: japanese patent No. 5556724

Disclosure of Invention

Problems to be solved by the invention

As described above, in recent years, the display of electronic devices such as mobile terminals has been made high-definition, but when chemically strengthened glass having a refractive index that changes by ion exchange is used as a protective glass for electronic devices, distortion may occur in an image on a display screen after the high-definition.

Accordingly, an object of the present invention is to solve the above-described problems and to provide a chemically strengthened glass which is less likely to cause distortion of an image on a display panel after high definition.

Means for solving the problems

The present inventors found that distortion of an image in a high-resolution display screen in the case of using a chemically strengthened glass for a cover glass is due to: the composition of the surface layer portion of the glass becomes uneven due to the unevenness of chemical strengthening or the like, and the refractive index locally changes at the surface layer portion of the glass, and light is refracted. Further, the inventors have found that, by setting the refractive index distribution, which is the amount of change in the refractive index of the surface layer of the chemically strengthened glass, to a specific range, even if the chemical strengthening unevenness occurs, the distortion of the image can be reduced, and have completed the present invention.

Namely, the present invention is as follows.

1. A chemically strengthened glass having a surface compressive stress value of 400MPa or more, wherein,

the absolute value of the refractive index distribution from the surface to the center of the sheet thickness is 0.002 or less.

2. The chemically strengthened glass according to claim 1, wherein the chemically strengthened glass satisfies the following formula.

-(△K₂O+△Na₂O)≤-1

In the above formula,. DELTA.K₂O and DELTA Na₂O is as follows.

△K₂O: the difference between the K ion concentration at a depth of 10 μm from the surface layer and the K ion concentration at the center of the sheet thickness in the K ion concentration distribution in the sheet thickness direction of the chemically strengthened glass measured by EPMA was converted into K₂The value obtained for O (mol%),

△Na₂o: in the distribution of Na ion concentration in the thickness direction of the chemically strengthened glass measured by EPMA, the difference between the Na ion concentration at a depth of 10 μm from the surface layer and the Na ion concentration at the center of the thickness is converted into Na₂O (mol%) value.

3. The chemically strengthened glass according to claim 1 or 2, wherein the chemically strengthened glass contains 15 mol% or more of Li in terms of mol% based on oxides₂O。

4. The chemically strengthened glass according to claim 1 or 2, wherein the chemically strengthened glass is a crystallized glass having a visible light transmittance of 85% or more in terms of a thickness of 0.7mm and a haze value of 0.5% or less in terms of a thickness of 0.7 mm.

5. The chemically strengthened glass according to claim 4, wherein the crystallized glass contains lithium silicate crystals or lithium aluminosilicate crystals.

6. The chemically strengthened glass according to any one of the above 1 to 5, wherein the chemically strengthened glass contains 30 to 70% of SiO in mol% based on an oxide₂2 to 25 percent of Al₂O₃And 15% to 40% Li₂O。

7. A method for producing a chemically strengthened glass, comprising: a chemically strengthened glass is obtained by strengthening a crystallized glass containing 30 to 70% of SiO in terms of mol% based on oxides, with a salt containing 80 mass% or more of potassium nitrate₂2% to 25%Al₂O₃And 15% to 40% of Li₂And O, and the crystallized glass contains lithium silicate crystals or lithium aluminosilicate crystals.

Effects of the invention

Since the chemically strengthened glass of the present invention can suppress the refraction of light at the surface layer portion of the glass by setting the refractive index distribution from the surface to the center of the sheet thickness to a specific range, even if the chemical strengthening unevenness occurs, the distortion of an image on a display screen after high definition does not easily occur in the case of a cover glass used for an electronic device.

Drawings

FIG. 1 shows a method for preparing a glass sample for refractive index profile determination in a two-beam interferometer.

Fig. 2(a) to (c) are diagrams showing refractive index distributions measured by a two-beam interferometer. Fig. 2(a) shows the results of example 2 of the example, fig. 2(b) shows the results of example 4, and fig. 2(c) shows the results of example 5.

FIG. 3(a) shows the composition distribution of example 2 of the example. Fig. 3(b) shows the composition distribution of example 4.

Fig. 4(a) shows a composition difference distribution based on the center of the sheet thickness in example 2. Fig. 4(b) shows a composition difference distribution based on the center of the sheet thickness in example 4.

Detailed Description

The present invention is not limited to the following embodiments, and various modifications and substitutions may be made to the following embodiments without departing from the scope of the present invention.

In the present specification, "chemically strengthened glass" refers to glass that has been subjected to a chemical strengthening treatment. In chemically strengthened glass, since a compressive stress layer is generally formed by ion exchange in a surface portion of the glass, a glass composition of a portion not subjected to ion exchange corresponds to a basic composition of the glass before chemical strengthening.

In the present specification, the glass composition is shown in terms of mole percentage based on oxides, and mole% may be abbreviated as%. "to" indicating a numerical range is used to include numerical values described before and after the range as the lower limit value and the upper limit value.

< refractive index Profile >

The chemically strengthened glass of the present invention has an absolute value of a refractive index distribution from the surface to the center of the sheet thickness of 0.002 or less, preferably 0.0015 or less, more preferably 0.0010 or less, and still more preferably 0.0005 or less. The lower limit of the absolute value of the refractive index distribution is not particularly limited, and is typically 0.0001 or more.

Since chemical strengthening is usually performed by immersing the glass substrate in a treatment liquid melted at a high temperature for a certain period of time, there is a case where chemical strengthening unevenness occurs due to temperature unevenness caused by convection of the treatment liquid or the like. Since the internal stress applied to the glass plate due to the chemical strengthening unevenness varies, conventionally, when the glass plate is used for protecting glass, in order to suppress image distortion in a display panel after high definition (hereinafter, also simply referred to as image distortion in the display panel), the chemical strengthening unevenness is evaluated by evaluating the stress of the chemical strengthening glass, and chemical strengthening glass in which the chemical strengthening unevenness does not occur is used. Under such circumstances, the present inventors have found that even in a chemically strengthened glass in which unevenness of chemical strengthening occurs, by suppressing a change in refractive index from the surface to the center of the thickness of the glass, and setting the absolute value of the refractive index distribution to 0.002 or less, it is possible to suppress refraction of light at the surface layer portion of the glass, and to suppress distortion of an image on a display panel.

Examples of the method for measuring the refractive index distribution of glass include: a method of measuring the deflection angle by the minimum deflection angle method or the like to obtain the refractive index, a method of constituting an interferometer to measure the transmission wavefront to obtain the refractive index distribution, and the like. In addition, the refractive index distribution can be obtained by a schlieren method.

In order to measure the refractive index distribution in a minute region existing in the thickness direction of the glass plate, it is preferable to measure the refractive index distribution by using a two-beam interferometer which can vertically enter the object to be measured and has two functions of a microscope and an interferometer.

As a method for producing a glass sample for refractive index distribution measurement by a two-beam interferometer, specifically, for example, it is preferable that glass is mirror-ground to a thickness of 0.5mm so that the cross-sectional direction can be observed by cutting the glass. A specific example of the sample preparation method is shown in fig. 1.

The refractive index distribution was measured by the two-beam interferometer according to the following principle. When light emitted from the same light source is split into two beams and passed through respective optical paths and then superimposed, if there is a phase shift in the respective optical paths, interference occurs and bright and dark fringes are displayed.

By disposing a transparent object to be detected (glass) on one optical path, the shift of the phase of light is observed by the movement of the interference fringe, and it is obtained as the product of the refractive index and the distance. Since one fringe corresponds to the wavelength of light, quantitative measurement of the density distribution can be performed by observing the amount of movement of the interference fringe or the equal-density interference fringe.

Since the optical path length (travel distance of light converted in vacuum) is an integral value of the propagation distance × the refractive index, the optical path length reflects the refractive index distribution when the thickness of the object to be measured is the same. The phase shift of light is "2 π × optical path length difference/wavelength of light", and the refractive index distribution is the phase shift of light and is reflected in the interference fringes.

< surface compressive stress value >

The chemically strengthened glass of the present invention has a surface compressive stress value of 400MPa or more, preferably 500MPa or more, more preferably 600MPa or more, still more preferably 700MPa or more, and particularly preferably 800MPa or more. The basic glass composition of the chemically strengthened glass is the same as the glass composition of the glass described later.

In the present specification, the "stress distribution" is a graph showing a value of compressive stress as a variable of a depth from a glass surface. The negative compressive stress value is referred to as tensile stress. In the present specification, the measurement of the "stress distribution" can be performed by a method using an optical waveguide surface stress meter and a scattered light photoelastic stress meter in combination.

An optical waveguide surface stress meter is known that can accurately measure the stress of glass in a short time. As the optical waveguide surface stress meter, for example, FSM-6000 manufactured by flexography can be listed. However, the optical waveguide surface stress meter can measure the stress only in a case where the refractive index is lowered from the surface of the sample to the inside thereof in principle. In the chemically strengthened glass, the refractive index of a layer obtained by replacing sodium ions in the glass with external potassium ions is lowered from the surface of a sample to the inside, and therefore the stress can be measured by an optical waveguide surface stress meter. However, the stress of the layer obtained by replacing lithium ions in the glass with external sodium ions cannot be accurately measured by an optical waveguide surface stress meter.

The method using the scattered light photoelastic stress meter can measure the stress regardless of the refractive index distribution. The scattered light photoelastic strain gauge may be, for example, SLP2000 manufactured by the original manufacturer. However, the scattered light photoelastic strain gauge is susceptible to surface scattering, and may not be able to accurately measure the stress near the surface. By using two types of measuring devices in combination, accurate stress measurement can be performed.

< composition distribution >

The chemically strengthened glass of the present invention is preferably represented by the formula- (. DELTA.K)₂O+△Na₂O) is-1 or less, more preferably-2 or less, and still more preferably-4 or less.

In the above formula,. DELTA.K₂O and DELTA Na₂O is as follows.

△K₂O: the difference between the K ion concentration at a depth of 10 μm from the surface layer and the K ion concentration at the center of the sheet thickness in the K ion concentration distribution in the sheet thickness direction of the chemically strengthened glass measured by EPMA (Electron Probe microanalyzer) was converted into K₂The value obtained for O (mol%),

In the present invention, the "concentration at a depth of 10 μm from the surface layer" means the concentration at a position at a depth of 10 μm from the glass surface in the plate thickness direction.

The present inventors have found that, for example, when a lithium-containing glass is chemically strengthened using a molten salt containing potassium, a change in refractive index due to ion exchange can be suppressed by performing ion exchange with both lithium ions and sodium ions in the glass. From the above formula- (. DELTA.K)₂O+△Na₂O) corresponds to lithium ions (Li) ion-exchanged with potassium ions in the molten salt by chemical strengthening₂O) amount. By reacting₂O+△Na₂O) is-1 or less, and Na in the glass₂O and Li₂Both O ions are exchanged by chemical strengthening treatment, so that a change in refractive index due to ion exchange can be suppressed, refraction of light at the surface layer portion of the glass can be suppressed, and distortion of an image on a display panel can be suppressed.

< basic composition of chemically strengthened glass >

The composition of the chemically strengthened glass can be easily determined by a semi-quantitative analysis by a fluorescent X-ray method, and more accurately, can be measured by a wet analysis method such as ICP emission analysis. Unless otherwise specified, the content of each component is expressed as a molar percentage based on the oxide.

SiO₂Is a component constituting the skeleton of the glass. In addition, SiO₂Is a component for improving chemical durability, SiO₂SiO is a component for reducing the generation of cracks when a scratch (indentation) is formed on the surface of glass₂The content of (b) is preferably 30% or more. SiO 2₂The content of (b) is more preferably 40% or more, 50% or more, 54% or more, 58% or more, 60% or more, 63% or more, 66% or more, and 68% or more in the following steps. On the other hand, SiO₂When the content of (b) is more than 80%, the meltability is remarkably reduced. SiO 2₂The content of (b) is preferably 75% or less, more preferably 74% or less, still more preferably 73% or less, still more preferably 72% or less, particularly preferably 71% or less, and most preferably 70% or less.

By containing Al₂O₃Can increase the number of protrusions on the etched surface and inhibit glareLight (ぎらつき) and improved cleaning ability. From the viewpoint of improving the characteristics of the etched surface such as an increase in the number of protrusions, Al₂O₃The content of (b) is preferably 0.1% or more, and more preferably 0.3% or more, 0.5% or more, 0.7% or more, 0.8% or more, 0.9% or more, 1% or more, 2% or more, 5% or more in the following steps.

On the other hand, Al₂O₃When the content of (b) is 25% or less, the acid resistance of the glass can be improved or the devitrification temperature can be suppressed from increasing. In addition, Al₂O₃When the content of (b) is 25% or less, the viscosity of the glass increases and the meltability decreases. Al (Al)₂O₃The content of (b) is preferably 25% or less, more preferably 20% or less, further preferably 18% or less, particularly preferably 16% or less, and most preferably 14% or less.

Y₂O₃Is a component for improving the shatterability of the chemically strengthened glass, and may contain Y₂O₃. In the presence of Y₂O₃In case of (2) Y₂O₃The content of (b) is preferably 0.5% or more, more preferably 1% or more, still more preferably 1.5% or more, particularly preferably 2% or more, and most preferably 2.5% or more. Y is₂O₃When the content of (b) is 5% or less, devitrification of the glass during melting can be suppressed. Y is₂O₃The content of (b) is preferably 5% or less, more preferably 4% or less, and further preferably 3% or less.

MgO is a component for increasing the surface compressive stress of the chemically strengthened glass when chemically strengthened, and MgO is a component for improving the breakage property, and MgO is preferably contained. When MgO is contained, the content of MgO is preferably 3% or more, and more preferably 4% or more, 5% or more, 6% or more, 7% or more, and 8% or more in the following manner. On the other hand, when the content of MgO is 20% or less, the glass is less likely to devitrify during melting. The content of MgO is preferably 20% or less, more preferably 15% or less, and further preferably gradually becomes 14% or less, 13% or less, 12% or less, 11% or less, and 10% or less as follows.

CaO is a component for improving the meltability of the glass, and CaO is a component for improving the crushability of the chemically strengthened glass when chemically strengthened, and may be contained. When CaO is contained, the content of CaO is preferably 0.5% or more, more preferably 1% or more, further preferably 2% or more, particularly preferably 3% or more, and most preferably 5% or more. On the other hand, when the content of CaO is 15% or less, the ion exchange performance can be improved, so that it is preferable to set the content of CaO to 15% or less. The content of CaO is more preferably 10% or less, still more preferably 9% or less, and particularly preferably 8% or less.

Li₂O is a component for forming a surface compressive stress by ion exchange, and Li₂O is a component for improving the shatterability of the chemically strengthened glass. When chemical strengthening treatment is performed to exchange Li ions on the glass surface for Na ions, Li ions₂The content of O is preferably 15% or more, more preferably 18% or more, further preferably 20% or more, and particularly preferably 25% or more. On the other hand, Li₂When the content of O is 40% or less, the decrease in acid resistance of the glass can be suppressed. Li₂The content of O is preferably 40% or less, more preferably 38% or less, further preferably 36% or less, particularly preferably 34% or less, and most preferably 32% or less.

By containing Na₂O, the number of protrusions on the etched surface can be increased, glare can be suppressed, and the cleaning performance can be improved. In addition, Na₂O is a component for improving the meltability of the glass, and forms a surface compressive stress layer when ion-exchanged. From the viewpoint of improving the characteristics of the etched surface such as the increase in the number of protrusions, Na₂The content of O is preferably 1% or more, more preferably 2% or more, and further preferably 3% or more. On the other hand, Na₂When the content of O is 25% or less, the decrease in acid resistance of the glass can be suppressed. From the viewpoint of acid resistance, Na₂The content of O is preferably 25% or less, more preferably 20% or less, further preferably 18% or less, particularly preferably 16% or less, and most preferably 14% or less.

By containing K₂O, the number of protrusions on the etched surface can be increased, glare can be suppressed, and the cleaning performance can be improved. In addition, by containing K₂O, can improve ion exchange propertyCan be used. From the viewpoint of improving the characteristics of the etched surface such as the increase in the number of protrusions, K is₂The content of O is preferably 0.1% or more, more preferably 0.5% or more, further preferably 1% or more, particularly preferably 2% or more, and most preferably 3% or more. On the other hand, K₂When the content of O is 20% or less, the characteristics of the etched surface can be improved, so that K is₂The content of O is preferably 20% or less. K₂The content of O is more preferably 15% or less, more preferably 12% or less, still more preferably 10% or less, particularly preferably 8% or less, and most preferably 6% or less.

Na₂O、K₂O and Li₂Total of O content (Na)₂O+K₂O+Li₂O) is preferably 30% or less, more preferably 28% or less, still more preferably 26% or less, and particularly preferably 25% or less. By reacting Na₂O+K₂O+Li₂O is 30% or less, and the cleaning property can be improved.

TiO₂Is a component for improving the shatterability of the chemically strengthened glass when chemically strengthened, and may contain TiO₂. In the presence of TiO₂In the case of (2) TiO₂The content of (b) is preferably 0.1% or more, more preferably 0.15% or more, and further preferably 0.2% or more. On the other hand, TiO₂When the content of (b) is 1% or less, devitrification is less likely to occur during melting, and the quality of the chemically strengthened glass can be improved. TiO 2₂The content of (b) is preferably 1% or less, more preferably 0.8% or less, still more preferably 0.5% or less, and particularly preferably 0.25% or less.

ZrO₂Is a component for increasing the surface compressive stress generated by ion exchange, has the effect of improving the crushability of the glass, and may contain ZrO₂. In the presence of ZrO₂In the case of (2)₂The content of (b) is preferably 0.5% or more, more preferably 1% or more. On the other hand, ZrO₂When the content of (b) is 2% or less, devitrification is less likely to occur during melting, and the quality of the chemically strengthened glass can be improved. ZrO (ZrO)₂The content of (b) is preferably 2% or less, more preferably 1.8% or less, still more preferably 1.6% or less, particularly preferably 1.4% or less, and most preferably 1.2% or less.

B₂O₃Is a component for improving the chipping resistance and the meltability of the glass. B is₂O₃B is not an essential component but is contained in order to improve the meltability₂O₃In case of (B)₂O₃The content of (b) is preferably 0.5% or more, more preferably 1% or more, and further preferably 2% or more. On the other hand, by making B₂O₃The content of (B) is 5% or less, and the occurrence of striae (pulse) during melting is suppressed, and the quality of the glass is less likely to be lowered, so that B₂O₃The content of (b) is preferably 5% or less. B is₂O₃The content of (b) is more preferably 4% or less, still more preferably 3% or less, and particularly preferably 1% or less. In order to improve acid resistance, it is preferable not to contain B₂O₃。

P₂O₅Is a component for improving ion exchange performance and chipping resistance. May not contain P₂O₅But in the presence of P₂O₅In case of (2) P₂O₅The content of (b) is preferably 0.5% or more, more preferably 1% or more, and further preferably 2% or more. On the other hand, by making P₂O₅The content of (A) is 4% or less, and the breakage resistance and acid resistance of the chemically strengthened glass are improved. P₂O₅The content of (b) is preferably 4% or less, more preferably 3% or less, still more preferably 2% or less, and particularly preferably 1% or less. In order to improve acid resistance, it is preferable not to contain P₂O₅。

SrO is a component for improving the meltability of the chemically strengthened glass, and SrO is a component for improving the crushability of the chemically strengthened glass, and may be contained. When SrO is contained, the SrO content is preferably 0.5% or more, more preferably 1% or more, further preferably 2% or more, particularly preferably 3% or more, and most preferably 5% or more. On the other hand, when the SrO content is 20% or less, the ion exchange performance is improved, and therefore, the SrO content is preferably 20% or less. The SrO content is more preferably 14% or less, and more preferably 10% or less, 8% or less, 6% or less, 3% or less, and 1% or less in the following steps.

BaO is a component for improving the meltability of the glass for chemical strengthening, and BaO is a component for improving the crushability of the glass for chemical strengthening, and BaO may be contained. When BaO is contained, the content of BaO is preferably 0.5% or more, more preferably 1% or more, further preferably 2% or more, particularly preferably 3% or more, and most preferably 5% or more. On the other hand, when the content of BaO is 15% or less, the ion exchange performance is improved. The content of BaO is preferably 15% or less, and more preferably 10% or less, 8% or less, 6% or less, 3% or less, and 1% or less in the following steps.

ZnO is a component for improving the meltability of the glass, and may contain ZnO. When ZnO is contained, the content of ZnO is preferably 0.25% or more, and more preferably 0.5% or more. On the other hand, when the content of ZnO is 10% or less, the weather resistance of the glass is improved. The content of ZnO is preferably 10% or less, more preferably 7% or less, further preferably 5% or less, particularly preferably 2% or less, and most preferably 1% or less.

La₂O₃、Nb₂O₅Is a component for improving the shatterability of the glass, and may contain La₂O₃、Nb₂O₅. When these components are contained, the content of each component is preferably 0.5% or more, more preferably 1% or more, further preferably 1.5% or more, particularly preferably 2% or more, and most preferably 2.5% or more. On the other hand, La₂O₃、Nb₂O₅When the content of (b) is 8% or less, the glass is less likely to devitrify during melting, and the quality of the glass can be improved. La₂O₃、Nb₂O₅The content of (b) is preferably 8% or less, more preferably 6% or less, still more preferably 5% or less, particularly preferably 4% or less, and most preferably 3% or less, respectively.

In order to improve the shatterability of the glass, a small amount of Ta may be contained₂O₅、Gd₂O₃However, since the refractive index and the reflectance are high, the content is preferably 1% or less, more preferably 0.5% or less, and further preferably Ta is not contained₂O₅、Gd₂O₃。

In addition, the method is carried out on the glassIn the case of coloring, a coloring component may be added within a range not hindering achievement of the desired chemical strengthening property. Examples of the coloring component include: co₃O₄、MnO₂、Fe₂O₃、NiO、CuO、Cr₂O₃、V₂O₅、Bi₂O₃、SeO₂、TiO₂、CeO₂、Er₂O₃、Nd₂O₃And the like as appropriate components.

The content of the coloring component is preferably in a range of 7% or less in total as represented by a mole percentage based on the oxide. When the content of the coloring component is 7% or less, the glass is less likely to devitrify, and therefore, it is preferable. The content is preferably 5% or less, more preferably 3% or less, and further preferably 1% or less. When priority is given to the visible light transmittance of the glass, it is preferable that these components are not substantially contained.

In the present specification, "substantially not containing" means not containing other than inevitable impurities contained in raw materials and the like, that is, means not intentionally containing. Specifically, the content is less than 0.1 mol% in the glass composition.

May suitably contain SO₃Chlorides and fluorides as fining agents in glass melting. Preferably not containing As₂O₃. In the presence of Sb₂O₃In the case of (3), the content is preferably 0.3% or less, more preferably 0.1% or less, and most preferably no Sb is contained₂O₃。

< crystallized glass >

The chemically strengthened glass of the present invention may be crystallized glass. When the chemically strengthened glass of the present invention is a crystallized glass, it is preferable that the visible light transmittance when converted to a thickness of 0.7mm is 85% or more, because the screen of a display is easily visible when used as a cover glass for a portable display. The visible light transmittance when converted to a thickness of 0.7mm is more preferably 88% or more, and still more preferably 90% or more.

Visible light transmittance was measured according to JIS R3106: 2019 for measurement. In the present specification, "light transmittance" refers to the average transmittance of light having a wavelength of 380nm to 780 nm.

When the chemically strengthened glass of the present invention is a crystallized glass, the haze value in terms of a thickness of 0.7mm is preferably 0.5% or less, more preferably 0.4% or less, and still more preferably 0.3% or less. When the haze value is 0.5% or less, visibility of a screen of a display is improved when the haze value is used for a cover glass or the like of a portable display. Haze value using C light source and according to JIS K3761: 2000 the assay was performed.

When the chemically strengthened glass of the present invention is a crystallized glass, it is preferably a crystallized glass containing one or more crystals selected from the group consisting of lithium metasilicate crystals, lithium aluminosilicate crystals, lithium phosphate crystals and β -spodumene crystals. Among them, lithium metasilicate crystals and lithium aluminosilicate crystals are more preferable from the viewpoint that severe fracture (fracture bad) is hardly generated even when a large compressive stress is formed.

In order to improve the mechanical strength, the crystallization ratio of the crystallized glass is preferably 10% or more, more preferably 15% or more, further preferably 20% or more, and particularly preferably 25% or more. In order to improve transparency, the crystallization ratio of the crystallized glass is preferably 70% or less, more preferably 60% or less, and particularly preferably 50% or less. The small crystallization rate is excellent from the viewpoint of facilitating the heating and bending molding.

The crystallization rate can be calculated from the X-ray diffraction intensity by the Reed-Bode method (リートベルト method). The Reed-Burd method is described in the Crystal analysis Manual edited by the edit Committee of the Japan Crystal society, Crystal analysis Manual (Co-published 1999 journal, pages 492 to 499).

In order to improve the transparency, the average particle size of the precipitated crystals of the crystallized glass is preferably 300nm or less, more preferably 200nm or less, still more preferably 150nm or less, and particularly preferably 100nm or less. The average particle diameter of the precipitated crystals can be determined from an image obtained by a Transmission Electron Microscope (TEM). In addition, it can be estimated from an image of a Scanning Electron Microscope (SEM).

When the chemically strengthened glass is a crystallized glass, particularly, a crystallized glass containing lithium silicate crystals or lithium aluminosilicate crystals, a glass obtained by heat treatment of a glass composition described later is preferable. The glass composition is a glass composition crystallized by appropriate heat treatment. The heat treatment in this case is preferably performed by a two-step heat treatment as follows: raising the temperature from room temperature to a first treatment temperature for a certain time, and then maintaining the temperature at a second treatment temperature higher than the first treatment temperature for a certain time.

In the case of being performed by the two-step heating treatment, the first treatment temperature is preferably a temperature range in which the crystal nucleation rate increases in the glass composition, and the second treatment temperature is preferably a temperature range in which the crystal growth rate increases in the glass composition. In addition, as for the holding time at the first treatment temperature, it is preferable to hold for a long time so that a sufficient number of crystal nuclei are generated. By forming a large number of crystal nuclei, the size of each crystal becomes small, and a crystallized glass having high transparency is obtained.

The first treatment temperature is, for example, 550 to 800 ℃ and the second treatment temperature is, for example, 850 to 1000 ℃, and the temperature is maintained at the first treatment temperature for 2 to 10 hours and then at the second treatment temperature for 2 to 10 hours.

When the chemically strengthened glass is a crystallized glass containing lithium silicate crystals or lithium aluminosilicate crystals, the chemically strengthened glass preferably contains 30 to 70% of SiO, expressed in mol% based on oxides₂2 to 25 percent of Al₂O₃And 15% to 40% Li₂O。

The composition of the above glass will be explained below.

SiO₂Is a component forming the network structure of the glass. In addition, SiO₂Is a component for improving chemical durability. SiO 2₂The content of (b) is preferably 30% or more, preferably 35% or more, more preferably 40% or more, and further preferably 45% or more. SiO 2₂The content of (b) is more preferably 60% or more, and still more preferably 64% or more. On the other hand, SiO is used for improving the melting property₂The content of (a) is preferably 70% or less,more preferably 68% or less, and still more preferably 66% or less.

Al₂O₃Al is an effective component for increasing the surface compressive stress generated by chemical strengthening₂O₃The content of (b) is preferably 1% or more. Al (Al)₂O₃The content of (b) is more preferably 2% or more, still more preferably 4% or more, particularly preferably 6% or more, and extremely preferably 8% or more. On the other hand, Al is added so that the devitrification temperature of the glass does not become too high₂O₃The content of (b) is preferably 25% or less, more preferably 20% or less, still more preferably 18% or less, and particularly preferably 15% or less.

Li₂O is a component for forming a surface compressive stress by ion exchange, Li₂O is a constituent of a beta-spodumene crystal, a lithium metasilicate crystal, and a lithium phosphate crystal. Li₂The content of O is preferably 10% or more, more preferably 15% or more. In the crystallized glass containing lithium metasilicate or lithium phosphate, Li₂The content of O is preferably 10% or more, more preferably 14% or more, 16% or more, or 18% or more. On the other hand, to improve the stability of the glass, Li₂The content of O is preferably 40% or less, more preferably 35% or less, and further preferably 30% or less.

< method for producing chemically strengthened glass >

The chemically strengthened glass of the present invention can be produced by subjecting a glass plate to a chemical strengthening treatment, followed by cleaning and drying. The chemical strengthening treatment can be performed by a known method. In the chemical strengthening treatment, a glass plate is brought into contact with a melt containing a metal salt (e.g., potassium nitrate) of metal ions having a large ionic radius (typically K ions) by immersion or the like. Thus, metal ions having a small ion radius (typically Na ions or Li ions) in the glass plate are replaced with metal ions having a large ion radius (typically K ions for Na ions; Na ions for Li ions).

The chemical strengthening treatment (ion exchange treatment) can be performed by, for example, immersing the glass plate in a molten salt such as potassium nitrate heated to 360 to 600 ℃ for 0.1 to 500 hours. The heating temperature of the molten salt is preferably 375 to 500 ℃, and the time for immersing the glass plate in the molten salt is preferably 0.3 to 200 hours.

Examples of the molten salt used for the chemical strengthening treatment include nitrates, sulfates, carbonates, chlorides, and the like. Among them, examples of the nitrate include lithium nitrate, sodium nitrate, potassium nitrate, cesium nitrate, and silver nitrate. Examples of the sulfate include lithium sulfate, sodium sulfate, potassium sulfate, cesium sulfate, and silver sulfate. Examples of the carbonate include lithium carbonate, sodium carbonate, and potassium carbonate. Examples of the chloride include lithium chloride, sodium chloride, potassium chloride, cesium chloride, and silver chloride. These molten salts may be used alone or in combination of two or more.

The conditions for the chemical strengthening treatment may be selected as appropriate in consideration of the characteristics and composition of the glass, the type of molten salt, and the chemical strengthening characteristics such as the surface Compressive Stress (CS) and the depth of the compressive stress layer (DOL) desired for the chemically strengthened glass to be finally obtained.

The chemical strengthening treatment may be performed only once, or may be performed a plurality of times under two or more different conditions (multi-stage strengthening). Here, for example, as the chemical strengthening treatment in the first stage, the chemical strengthening treatment is performed under conditions in which DOL is large and CS is relatively low. Then, as the chemical strengthening treatment of the second stage, when the chemical strengthening treatment is performed under conditions where DOL is small and CS is relatively high, the CS of the outermost surface of the chemically strengthened glass can be increased while the internal tensile stress area (St) can be suppressed, and the internal tensile stress (CT) can be suppressed to be low.

As one embodiment of the method for producing a chemically strengthened glass of the present invention, there is, for example, a production method including: a chemically strengthened glass is obtained by strengthening a crystallized glass containing 30 to 70% of SiO in terms of mol% based on oxides, with a salt containing 80 mass% or more of potassium nitrate₂2 to 25 percent of Al₂O₃And 15% to 40% Li₂O and the crystallizationThe glass contains lithium silicate crystals or lithium aluminosilicate crystals. By setting the potassium nitrate content in the salt to 80 mass% or more, high compressive stress can be introduced. The potassium nitrate content in the salt is preferably 90 mass% or more, and more preferably 95 mass% or more.

In the case where the chemically strengthened glass of the present invention is in a plate shape (glass plate), the plate thickness (t) is, for example, 2mm or less, preferably 1.5mm or less, more preferably 1mm or less, still more preferably 0.9mm or less, particularly preferably 0.8mm or less, and most preferably 0.7mm or less, from the viewpoint of enhancing the effect of chemical strengthening. The thickness is, for example, 0.1mm or more, preferably 0.2mm or more, more preferably 0.4mm or more, and further preferably 0.5mm or more, from the viewpoint of obtaining a sufficient strength improvement effect by the chemical strengthening treatment.

The shape of the chemically strengthened glass of the present invention may be other than a plate shape depending on the product, application, and the like to which it is applied. The glass plate may have a frame shape with different thicknesses on the outer periphery. The form of the glass plate is not limited to this, and for example, the two main surfaces may not be parallel to each other, and one or both of the two main surfaces may be entirely or partially curved. More specifically, the glass plate may be, for example, a flat glass plate without warp, or a curved glass plate having a curved surface.

The chemically strengthened glass of the present invention is particularly useful as a cover glass for use in mobile devices such as mobile phones, smart phones, Personal Digital Assistants (PDAs), and tablet terminals. Further, the present invention is useful for applications such as protective glass for display devices such as Television Sets (TVs), Personal Computers (PCs), and touch panels which are not intended to be portable, wall surfaces of elevators, wall surfaces of buildings such as houses and buildings (full-screen displays), building materials such as window glasses, interior materials of desktops, automobiles, airplanes, and the like, or protective glass for these, and housings which are bent or formed to have curved surfaces other than plate shapes.

[ examples ]

Hereinafter, examples of the present invention will be specifically described, but the present invention is not limited thereto.

[ preparation of sample ]

(1) Production of glass

Glass raw materials were prepared so as to have a glass composition described in table 1 as expressed in terms of mole percentage based on oxides, and were melted and polished to produce glass plates. As the glass raw material, a usual glass raw material such as an oxide, a hydroxide, a carbonate is appropriately selected and weighed so that 900g in glass is obtained. The mixed glass raw materials are put into a platinum crucible, melted and defoamed at 1700 ℃. The glass was poured onto a carbon plate to obtain a glass block.

(2) Production of crystallized glass

The obtained glass block was processed into 50mm × 50mm × 1.5mm, and then subjected to heat treatment under the conditions shown in table 2, thereby obtaining crystallized glass. In the column of crystallization conditions in the table, the upper stage is nucleation treatment conditions and the lower stage is crystal growth treatment conditions, and for example, in the case where the upper stage is 550-2 and the lower stage is 730-2, the conditions mean that the glass is maintained at 550 ℃ for 2 hours and then at 730 ℃ for 2 hours. It was confirmed by powder X-ray diffraction that a part of the obtained crystallized glass contained lithium metasilicate.

(3) Preparation of samples

The glass obtained in (1) or (2) was processed and mirror-polished to obtain a glass plate having a thickness t of 0.7 mm. For the crystallized glass, a part of the remaining crystallized glass was pulverized and analyzed for precipitated crystals.

The above glass plate was preheated at 350 ℃ for 10 minutes and then subjected to ion exchange treatment under the conditions shown in Table 2, thereby obtaining a chemically strengthened glass. The results of evaluation of the obtained samples are shown in table 2. Examples 1 to 3 are examples, and examples 4 and 5 are comparative examples. "-" indicates not evaluated.

[ evaluation method ]

(visible light transmittance)

The light transmittance of the crystallized glass plate at a wavelength of 380nm to 780nm was measured by using an integrating sphere unit (150mm InGaAs int. Spter) as a detector in a spectrophotometer (manufactured by Perkin Elmer, Inc.; LAMBDA 950). The average transmittance, which is the arithmetic average of the light transmittances, is taken as the visible light transmittance [ unit: % ].

(haze value)

The haze value under a C light source [ unit: % ].

(stress distribution)

The stress value was measured using a measuring machine SLP-2000 manufactured by kindling, and the compressive stress value [ unit: MPa ] and depth of compressive stress layer DOL [ unit: μ m ].

(refractive index distribution)

The chemically strengthened glass obtained as shown in FIG. 1 was mirror-polished to 0.5mm so that the cross-sectional direction could be observed by cutting the chemically strengthened glass, and the refractive index distribution from the surface to the center of the plate thickness was measured by a two-beam interferometer (Mach-Zehnder interferometer, manufactured by Tokyo Seiki optical industries, Ltd.).

(EPMA surface K and Na concentration)

The K and Na concentrations of the glass surface were measured using EPMA (JXA-8500F manufactured by JEOL). The samples were chemically strengthened and then embedded in resin for mirror grinding. Since it is not easy to accurately measure the concentration of the outermost surface, it is assumed that the signal intensity of K or Na at a position where the signal intensity of Si with almost no content change is half the signal intensity at the center of the sheet thickness corresponds to the K concentration or Na concentration of the outermost surface, and the signal intensity at the center of the sheet thickness is taken as the signal intensity corresponding to the glass composition before strengthening, thereby calculating the K concentration or Na concentration of the outermost surface.

The composition distribution obtained by the EPMA measurement is shown in fig. 3(a) and (b). Fig. 3(a) shows the results of example 2, and fig. 3(b) shows the results of example 4. Based on the measurement results by EPMA, K is added₂O and Na₂The distribution of the compositional difference of O in terms of oxide is shown in fig. 4(a) and (b). Fig. 4(a) shows the results of example 2, and fig. 4(b) shows the results of example 4.

TABLE 1

Mol% of	Glass A	Glass B	Glass C
				SiO₂	50.0	64.4	64.0
Al₂O₃	5.0	6.0	13.0
				P₂O₅	2.3
Li₂O	34.1		16.0
				Na₂O	1.8	12.0	4.0
K₂O	1.2	4.0
				MgO		11.0	2.0
CaO		0.1
				SrO		0.1
Y₂O₃	1.0
				ZrO₂	4.5	2.5	1.0

TABLE 2

As shown in table 2 and fig. 2(a), it is considered that in examples 1 to 3 as examples, since the absolute value of the refractive index distribution from the surface to the center of the sheet thickness is small and 0.002 or less, even if the chemical strengthening unevenness occurs, the distortion of the image in the display screen can be suppressed to be small.

On the other hand, as shown in table 2 and fig. 2(b), it is considered that in example 4 as a comparative example, since the refractive index of the glass surface is higher than that of the inside by 0.0061, when the chemical strengthening unevenness occurs, the distortion of the image occurs in the display screen. As shown in table 2 and fig. 2(c), in example 5 as a comparative example, it is considered that since the refractive index of the glass surface is smaller than that of the inside by 0.0051, when chemical strengthening unevenness occurs, image distortion occurs in the display screen.

In example 2 as an example, as shown in FIG. 4(a), the- (. DELTA.K) of the glass surface₂O+△Na₂O) has a negative value. - (. DELTA.K)₂O+△Na₂O) corresponds to Δ Li₂O due to Na₂O and Li₂Both O ions are exchanged, and as shown in fig. 2(a), it is considered that the refractive index change is suppressed by the ion exchange. On the other hand, as shown in FIG. 4(b), in example 4 as a comparative example, (. DELTA.K) of the glass surface₂O+△Na₂O) is almost zero, and as shown in fig. 2(b), the change in refractive index due to ion exchange is large.

This application is based on japanese patent application 2020-.

Claims

2. The chemically strengthened glass according to claim 1, wherein the chemically strengthened glass satisfies the following formula,

-(△K₂O+△Na₂O)≤-1

in the above formula,. DELTA.K₂O and DELTA Na₂O is as follows:

3. The chemically strengthened glass according to claim 1 or 2, wherein the chemically strengthened glass contains 15 mol% or more of Li in mol% based on an oxide₂O。

4. The chemically strengthened glass according to claim 1 or 2, wherein the chemically strengthened glass is

A visible light transmittance of 85% or more in terms of a thickness of 0.7mm, and

a crystallized glass having a haze value of 0.5% or less in terms of a thickness of 0.7 mm.

6. The chemically strengthened glass according to any one of claims 1 to 5, wherein the chemically strengthened glass contains, in mol% on an oxide basis:

30 to 70 percent of SiO₂、

2 to 25 percent of Al₂O₃And, and

15% -40% of Li₂O。

7. A method for producing a chemically strengthened glass, comprising: a chemically strengthened glass is obtained by strengthening a crystallized glass with a salt containing 80 mass% or more of potassium nitrate,

the crystallized glass contains 30 to 70% of SiO in mol% based on the oxide₂2 to 25 percent of Al₂O₃And 15% to 40% of Li₂O, and

the crystallized glass contains lithium silicate crystals or lithium aluminosilicate crystals.