JP2021143079A - Chemically strengthened glass and method for producing the same - Google Patents

Abstract

To provide a chemically strengthened glass that prevents distortion of an image on a high-definition display screen.SOLUTION: A chemically strengthened glass has a surface compression stress of 400 MPa or more, and has an absolute value of refractive index distribution from the surface to the center across the thickness of 0.002 or less.SELECTED DRAWING: Figure 4

Description

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

Chemically tempered glass is used for the 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. In chemically strengthened glass, for example, glass is brought into contact with a molten salt containing alkali metal ions to cause ion exchange between the alkali metal ions in the glass and the alkali metal ions in the molten salt, and compressive stress is applied to the glass surface. It is a layer.

Generally, the surface of chemically strengthened glass undergoes a change in refractive index due to ion exchange treatment. For example, a chemically strengthened glass obtained by chemically strengthening glass containing Na ions with a molten salt containing K ions increases the refractive index of light in the chemically strengthened region. In chemically strengthened glass in which the surface layer of glass is ion-exchanged, the refractive index of light in the surface layer changes and approaches the refractive index of bulk glass as it goes from the surface layer to the inside (Patent Document 1).

Japanese Patent No. 5556724

As described above, in recent years, the display of electronic devices such as mobile terminals has been improved in definition, but when chemically strengthened glass whose refractive index changes due to ion exchange is used as the cover glass of the electronic device, the definition is improved. The image on the display screen may be distorted.

Therefore, the present invention aims to solve the above problems, and an object of the present invention is to provide chemically strengthened glass that is less likely to cause image distortion on a high-definition display screen.

When the chemically strengthened glass is used as the cover glass, the present inventors have distorted the image on the high-definition display screen because the composition of the glass surface layer portion becomes non-uniform due to unevenness of the chemical strengthening and the like. It was found that this is because the refractive index changes locally and the light is refracted. Then, they found that by setting the refractive index distribution, which is the amount of change in the refractive index on the surface layer of the chemically strengthened glass, within a specific range, distortion of the image can be reduced even if unevenness of the chemically strengthened glass occurs, and the present invention is completed. I let you.

That is, the present invention is as follows.
1. 1. Chemically tempered glass with a surface compressive stress value of 400 MPa or more.
Chemically tempered glass in which the absolute value of the refractive index distribution from the surface to the center of the plate thickness is 0.002 or less.
2. The chemically strengthened glass according to 1 above, which satisfies the following formula.
− (ΔK ₂ O + ΔNa ₂ O) ≦ -1
In the above formula, ΔK ₂ O and ΔNa ₂ O are as follows.
ΔK ₂ O: In the K ion concentration profile in the plate thickness direction of the chemically strengthened glass measured by EPMA, the difference between the concentration at a depth of 10 μm from the surface layer and the concentration at the center of the plate thickness _{is converted into K 2} O (mol%). ΔNa ₂ O: The difference between the concentration at a depth of 10 μm from the surface layer and the concentration at the center of the plate thickness in the Na ion concentration profile in the plate thickness direction of the chemically strengthened glass measured by EPMA is Na ₂ O (mol%). Value converted to 3. The chemically strengthened glass according to 1 or 2 above, which contains 15 mol% or more of _{Li 2} O in terms of oxide-based mol%.
4. The chemically strengthened glass according to 1 or 2 above, which is a crystallized glass having a visible light transmittance of 85% or more in terms of a thickness of 0.7 mm 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 4 above, wherein the crystallized glass contains a lithium silicate crystal or a lithium aluminosilicate crystal.
6. In molar% display based on oxides,
SiO ₂ 30-70%,
Al ₂ O ₃ 2-25%,
The chemically strengthened glass according to any one of 1 to 5 above, which contains 15 to 40% of Li _{2 O.}
7. In molar% display based on oxides,
SiO ₂ 30-70%,
Al ₂ O ₃ 2-25%,
Li 2 _O and containing 15% to 40%, and comprising a crystallized glass containing lithium silicate crystals or lithium aluminosilicate crystals, to obtain a chemically strengthened glass and reinforced with salts containing potassium nitrate least 80 wt% , How to make chemically strengthened glass.

In the chemically strengthened glass of the present invention, since the refractive index distribution from the surface to the center of the plate thickness is within a specific range, the refraction of light on the glass surface layer is suppressed, so that even if uneven chemical strengthening occurs. When used as a cover glass for electronic devices, image distortion on a high-definition display screen is unlikely to occur.

FIG. 1 shows a method of preparing a glass sample to be subjected to a refractive index distribution in a two-luminous flux interferometer. 2 (a) to 2 (c) are diagrams showing the refractive index distribution measured by a two-luminous flux interferometer. 2 (a) shows the results of Example 2, FIG. 2 (b) shows the results of Example 4, and FIG. 2 (c) shows the results of Example 5. FIG. 3A shows the composition profile of Example 2. FIG. 3B shows the composition profile of Example 4. FIG. 4A shows a composition difference profile based on the plate thickness center of Example 2. FIG. 4B shows a composition difference profile based on the plate thickness center of Example 4.

Hereinafter, embodiments for carrying out the present invention will be described, but the present invention is not limited to the following embodiments, and various modifications and variations to the following embodiments are made without departing from the scope of the present invention. Substitutions can be added.

As used herein, the term "chemically tempered glass" refers to glass that has been chemically strengthened. In chemically strengthened glass, a compressive stress layer is usually formed on the glass surface portion by ion exchange, so that the glass composition of the non-ion exchanged portion matches the matrix composition of the pre-chemically tempered glass.

In the present specification, the glass composition is indicated by an oxide-based molar percentage representation, and mol% may be simply referred to as%. In addition, "~" indicating a numerical range is used to mean that the numerical values described before and after the numerical range are included as the lower limit value and the upper limit value.

<Refractive index distribution>
The chemically strengthened glass of the present invention has an absolute value of the refractive value distribution from the surface to the center of the plate thickness of 0.002 or less, preferably 0.0015 or less, more preferably 0.0010 or less, and further preferably 0.0005. It is as follows. The lower limit of the absolute value of the refractive index distribution is not particularly limited, but is typically 0.0001 or more.

Since the chemical strengthening is generally performed by immersing the glass substrate in the treatment liquid melted at a high temperature for a certain period of time, unevenness in the chemical strengthening may occur due to temperature unevenness due to convection of the treatment liquid or the like. Since the internal stress of the glass plate applied due to uneven chemical strengthening varies, the image is distorted on the high-definition display screen when it is used for the cover glass (hereinafter, simply the image on the display screen). In order to suppress strain (also abbreviated as strain)), the unevenness of chemical strengthening was evaluated by evaluating the stress of the chemically strengthened glass, and the one in which the unevenness of chemical strengthening did not occur was used. In such a situation, the present inventors suppress the change in the refractive index from the surface to the center of the plate thickness even in the chemically strengthened glass having uneven chemical strengthening, and set the absolute value of the refractive index distribution to 0.002 or less. By doing so, it has been found that the refraction of light on the glass surface layer can be suppressed and the distortion of the image on the display screen can be suppressed.

As a method of measuring the refractive index distribution of glass, for example, a method of measuring the refractive index by measuring the refractive index by the minimum deviation method or the like, and a method of constructing an interferometer and measuring the transmitted wavefront to obtain the refractive index distribution. And so on. In addition, the refractive index distribution can be obtained by the Schlieren method.

In order to measure the refractive index distribution of a minute region existing in the thickness direction of the glass plate, it is preferable to measure with a two-luminous flux interferometer that can be vertically incident on the object to be measured and has both functions of a microscope and an interferometer. ..

As a method for preparing a glass sample to be used for the refractive index distribution in a two-luminous flux interferometer, specifically, for example, it is preferable to cut the glass and mirror-polish it to a thickness of 0.5 mm so that the cross-sectional direction can be observed. .. A specific example of the sample preparation method is shown in FIG.

The two-luminous flux interferometer measures the refractive index distribution according to the following principle. When light emitted from the same light source is divided into two and passed through different optical paths and then superposed, if there is a phase shift in each optical path, interference occurs and it appears as bright and dark stripes.

By setting a transparent test object (glass) in one of the optical paths, the phase shift of light is observed by the movement of the interference fringes, and the product of the refractive index and the distance is obtained. Since one fringe corresponds to the wavelength of light, it is possible to quantitatively measure the density distribution by observing the movement amount of the interference fringes or the equal density interference fringes.

Since the optical path length (distance traveled by light when converted in vacuum) is the integral value of the propagating distance x refractive index, the optical path length should reflect the refractive index profile when the thickness of the object to be measured is uniform. become. The phase shift of light is "2π x optical path length difference / wavelength of light", and the refractive index profile becomes a 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 400 MPa or more, preferably 500 MPa or more, more preferably 600 MPa or more, still more preferably 700 MPa or more, and particularly preferably 800 MPa or more. The composition of the mother glass of this chemically strengthened glass is equal to the glass composition of the above-mentioned glass.

In the present specification, the "stress profile" is a pattern expressing the compressive stress value with the depth from the glass surface as a variable. A negative compressive stress value means tensile stress. In the present specification, the measurement of the "stress profile" can be performed by a method using a combination of an optical waveguide surface stress meter and a scattered light photoelastic stress meter.

It is known that the optical waveguide surface stress meter can accurately measure the stress of glass in a short time. As an optical waveguide surface stress meter, for example, there is FSM-6000 manufactured by Orihara Seisakusho. However, in principle, the optical waveguide surface stress meter can measure the stress only when the refractive index decreases from the sample surface to the inside. In chemically strengthened glass, the layer obtained by substituting sodium ions inside the glass with potassium ions outside has a lower refractive index from the sample surface toward the inside, so that the stress can be measured with an optical waveguide surface stress meter. However, the stress of the layer obtained by substituting the lithium ion inside the glass with the sodium ion outside cannot be measured correctly by the optical waveguide surface stress meter.

The method using a scattered light photoelastic stress meter can measure stress regardless of the refractive index distribution. As a scattered light photoelastic stress meter, for example, there is SLP2000 manufactured by Orihara Seisakusho. However, the scattered photoelastic stress meter is easily affected by surface scattering, and may not be able to accurately measure the stress near the surface. Accurate stress measurement is possible by using two types of measuring devices in combination.

<Composition profile>
The chemically strengthened glass of the present invention _{preferably has a value represented by the formula − (ΔK 2} O + ΔNa ₂ O) of -1 or less, more preferably -2 or less, and further preferably -4 or less.

In the above formula, ΔK ₂ O and ΔNa ₂ O are as follows.
ΔK ₂ O: The difference between the concentration at a depth of 10 μm from the surface layer and the concentration at the center of the plate thickness in the K ion concentration profile in the plate thickness direction of the chemically strengthened glass measured by EPMA (electron probe microanalyzer) is K ₂ O. Value converted to (mol%) ΔNa ₂ O: The difference between the concentration at a depth of 10 μm from the surface layer and the concentration at the center of the plate thickness in the Na ion concentration profile in the plate thickness direction of the chemically strengthened glass measured by EPMA is Na. _{Value converted to 2} O (mol%)

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

The present inventors, for example, when chemically strengthening a lithium-containing glass using a molten salt containing potassium, the refractive index due to ion exchange is caused by ion exchange of both lithium ions and sodium ions in the glass. We found that change can be suppressed. The value represented by the formula − (ΔK ₂ O + ΔNa ₂ O) corresponds to the amount of _{lithium ions (Li 2} O) ion-exchanged with potassium ions in the molten salt by chemical strengthening. When the value represented by the formula − (ΔK ₂ O + ΔNa ₂ O) is -1 or less, _{both Na 2} O and Li ₂ O in the glass are ion-exchanged by the chemical strengthening treatment, and the ions are exchanged. The change in the refractive index due to exchange can be suppressed, the refraction of light on the glass surface layer can be suppressed, and the distortion of the image on the display screen can be suppressed.

<Mother composition of chemically strengthened glass>
The composition of the chemically strengthened glass can be simply determined by semi-quantitative analysis by the fluorescence X-ray method, but more accurately, it can be measured by a wet analysis method such as ICP emission spectrometry. Unless otherwise specified, the content of each component shall be expressed as an oxide-based molar percentage.

SiO ₂ is a component constituting the skeleton of glass. Further, it is a component that increases chemical durability and reduces the occurrence of cracks when scratches (indentations) are made on the glass surface, and _{the content of SiO 2} is preferably 30% or more. The content of SiO ₂ is more preferably 40% or more, 50% or more, 54% or more, 58% or more, 60% or more, 63% or more, 66% or more, 68% or more in a stepwise manner. .. On the other hand, if _{the content of SiO 2} is more than 80%, the meltability is remarkably lowered. The content of SiO ₂ is preferably 75% or less, more preferably 74% or less, further preferably 73% or less, still more preferably 72% or less, particularly preferably 71% or less, and most preferably 70% or less. be.

By containing Al ₂ O ₃ , the number of protrusions on the etching surface can be increased, glare can be suppressed, and detergency can be improved. From the viewpoint of improving the characteristics of the etched surface such as an increase in the number of protrusions, _{the content of Al 2} O ₃ is preferably 0.1% or more, more preferably 0.3% or more stepwise. 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.

On the other hand, when _{the content of Al 2} O ₃ is 25% or less, the acid resistance of the glass can be improved or the devitrification temperature can be suppressed from increasing. In addition, the viscosity of the glass increases and the meltability decreases. The content of Al ₂ O ₃ is preferably 25% or less, more preferably 20% or less, still more preferably 18% or less, particularly preferably 16% or less, and most preferably 14% or less.

Y ₂ O ₃ is a component that improves the crushability of chemically tempered glass, and may be contained. When Y ₂ O ₃ is contained, the content 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. Is 2.5% or more. When _{the content of Y 2} O ₃ is 5% or less, devitrification of the glass at the time of melting can be suppressed. The content of Y ₂ O ₃ is preferably 5% or less, more preferably 4% or less, still more preferably 3% or less.

MgO is a component that increases the surface compressive stress of the chemically strengthened glass when chemically strengthened, and is a component that improves crushability, and is preferably contained. When MgO is contained, the content is preferably 3% or more, and more preferably 4% or more, 5% or more, 6% or more, 7% or more, 8% or more in stages. On the other hand, when the MgO content is 20% or less, the glass is less likely to be devitrified when melted. The content of MgO is preferably 20% or less, more preferably 15% or less, and more preferably 14% or less, 13% or less, 12% or less, 11% or less, 10% in stages. It is as follows.

CaO is a component that improves the meltability of the glass, and is a component that improves the crushability of the chemical glass when chemically strengthened, and may be contained. When CaO is contained, the 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. be. On the other hand, when the CaO content is 15% or less, the ion exchange performance can be improved, so it is preferably 15% or less. The CaO content is more preferably 10% or less, further preferably 9% or less, and particularly preferably 8% or less.

Li ₂ O is also a component that forms surface compressive stress by ion exchange, and is a component that improves the crushability of chemically strengthened glass. When the chemical strengthening treatment for exchanging Li ions on the glass surface with Na ions is performed, the Li ₂ O content is preferably 15% or more, more preferably 18% or more, still more preferably 20% or more, and particularly preferably. Is 25% or more. On the other hand, when _{the content of Li 2} O is 40% or less, the decrease in acid resistance of the glass can be suppressed. The content of Li ₂ 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 Na ₂ O, the number of protrusions on the etching surface can be increased, glare can be suppressed, and detergency can be improved. In addition, it is a component that improves the meltability of glass, and forms a surface compressive stress layer when ion exchange is performed. _{The Na 2} O content is preferably 1% or more, more preferably 2% or more, still more preferably 3% or more, from the viewpoint of improving the characteristics of the etched surface such as an increase in the number of protrusions. On the other hand, when the Na ₂ O content is 25% or less, the decrease in acid resistance of the glass can be suppressed. From the viewpoint of acid resistance, the Na ₂ O content is preferably 25% or less, more preferably 20% or less, still more preferably 18% or less, particularly preferably 16% or less, and most preferably 14% or less. ..

By containing K ₂ O, the number of protrusions on the etching surface can be increased, glare can be suppressed, and detergency can be improved. Further, the ion exchange performance can be improved by containing _{K 2 O.} From the viewpoint of improving the characteristics of the etched surface, such as an increase in the number of projections, the content of K 2 _O is preferably 0.1% or more, more preferably 0.5% or more, more preferably 1% As mentioned above, it is particularly preferably 2% or more, and most preferably 3% or more. On the other hand, when _{the content of K 2} O is 20% or less, the characteristics of the etched surface can be improved, so that _{the content of K 2} O is preferably 20% or less. The K 2 _O content is more preferably 15% or less, 12% and more preferably less, more preferably 10% or less, particularly preferably not more than 8%, and most preferably not more than 6%.

The total content of Na ₂ O, K ₂ O and Li _{2 O (Na 2} O + K ₂ O + Li ₂ O) is preferably 30% or less, more preferably 28% or less, still more preferably 26% or less, in particular. It is preferably 25% or less. When Na ₂ O + K ₂ O + Li ₂ O is 30% or less, detergency can be improved.

TiO ₂ is a component that improves the crushability of chemically strengthened glass when chemically strengthened, and may be contained. When TiO ₂ is contained, the content is preferably 0.1% or more, more preferably 0.15% or more, still more preferably 0.2% or more. On the other hand, when _{the content of TiO 2} is 1% or less, devitrification is less likely to occur at the time of melting, and the quality of chemically strengthened glass can be improved. The content of TiO ₂ 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.

ZrO ₂ is a component that increases the surface compressive stress due to ion exchange, has the effect of improving the crushability of glass, and may be contained. When ZrO ₂ is contained, the content is preferably 0.5% or more, more preferably 1% or more. On the other hand, when _{the content of ZrO 2} is 2% or less, devitrification is less likely to occur at the time of melting, and the quality of chemically strengthened glass can be improved. The content of ZrO ₂ 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%. It is as follows.

B ₂ O ₃ is a component that improves the chipping resistance of glass and also improves the meltability. Although B ₂ O ₃ is not essential, _{the content when B 2} O ₃ is contained is preferably 0.5% or more, more preferably 1% or more, still more preferably 1% or more in order to improve the meltability. 2% or more. On the other hand, when _{the content of B 2} O ₃ is 5% or less, the occurrence of veins at the time of melting is suppressed and the quality of the glass is not easily deteriorated, so 5% or less is preferable. The content of B ₂ O ₃ is more preferably 4% or less, further preferably 3% or less, and particularly preferably 1% or less. It is preferably not contained in order to increase acid resistance.

P ₂ O ₅ is a component that improves ion exchange performance and chipping resistance. P ₂ O ₅ may not be contained, but the content of the case of containing a P ₂ O ₅ is preferably 0.5% or more, more preferably 1% or more, more preferably 2% or more be. On the other hand, when _{the content of P 2} O ₅ is 4% or less, the crushability and acid resistance of the chemically strengthened glass are improved, and _{the content of P 2} O ₅ is preferably 4% or less, more preferably 3%. Below, it is more preferably 2% or less, and particularly preferably 1% or less. It is preferably not contained in order to increase acid resistance.

SrO is a component that improves the meltability of the chemically strengthened glass, and is a component that improves the crushability of the chemically strengthened glass, and may be contained. When SrO is contained, the 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. be. On the other hand, when the SrO content is 20% or less, the ion exchange performance is improved, so 20% or less is preferable. The content of SrO is more preferably 14% or less, and further preferably 10% or less, 8% or less, 6% or less, 3% or less, 1% or less in a stepwise manner.

BaO is a component that improves the meltability of the chemically strengthened glass, and is a component that improves the crushability of the chemically strengthened glass, and may be contained. When BaO is contained, the 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. be. On the other hand, when the BaO content is 15% or less, the ion exchange performance is improved. The content of BaO is preferably 15% or less, more preferably 10% or less, 8% or less, 6% or less, 3% or less, 1% or less in stages.

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

La ₂ O ₃ and Nb ₂ O ₅ are components that improve the crushability of glass and may be contained. When these components are contained, the content of each is preferably 0.5% or more, more preferably 1% or more, further preferably 1.5% or more, particularly preferably 2% or more, most preferably. It is preferably 2.5% or more. On the other hand, when _{the contents of La 2} O ₃ and Nb ₂ O ₅ are 8% or less, the glass is less likely to be devitrified at the time of melting, and the quality of the glass can be improved. The contents of La ₂ O ₃ and Nb ₂ O ₅ are each preferably 8% or less, more preferably 6% or less, still more preferably 5% or less, particularly preferably 4% or less, and most preferably. It is 3% or less.

Ta ₂ O ₅ and Gd ₂ O ₃ may be contained in a small amount in order to improve the crushability of the glass, but 1% or less is preferable, and 0.5% or less is more preferable because the refractive index and reflectance are high. It is preferable, and it is more preferable that it is not contained.

Further, when the glass is colored and used, a coloring component may be added within a range that does not hinder the achievement of the desired chemical strengthening properties. Examples of the coloring component include Co ₃ O ₄ , MnO ₂ , Fe ₂ O ₃ , NiO, CuO, Cr ₂ O ₃ , V ₂ O ₅ , Bi ₂ O ₃ , SeO ₂ , TIO ₂ , CeO ₂ , Er _2. O ₃ , Nd ₂ O _{3, and the} like are preferable.

The content of the coloring component is preferably in the range of 7% or less in total in terms of molar percentage display based on oxides. When it is 7% or less, the glass is less likely to be devitrified, which is preferable. This content is preferably 5% or less, more preferably 3% or less, still more preferably 1% or less. When giving priority to the visible light transmittance of glass, it is preferable that these components are not substantially contained.

In addition, in this specification, "substantially not contained" means that it is not contained except for unavoidable impurities contained in raw materials and the like, that is, it is not intentionally contained. Specifically, it means that the content in the glass composition is less than 0.1 mol%.

_{SO 3} , chloride, fluoride and the like may be appropriately contained as a clarifying agent when melting the glass. It is preferable that As ₂ O _{3 is not contained.} When Sb ₂ O ₃ is contained, it is preferably 0.3% or less, more preferably 0.1% or less, and most preferably not contained.

<Crystallized glass>
The chemically strengthened glass of the present invention may be crystallized glass. When the chemically strengthened glass of the present invention is crystallized glass, it is preferable that the visible light transmittance is 85% or more because the screen of the display is easily visible when used as the cover glass of a portable display. The visible light transmittance is more preferably 88% or more, further preferably 90% or more.

Visible light transmittance is measured according to JIS R 3106: 2019. As used herein, the term "light transmittance" refers to the average transmittance of light having a wavelength of 380 nm to 780 nm.

When the chemically strengthened glass of the present invention is crystallized glass, the haze value in terms of thickness of 0.7 mm is preferably 0.5% or less, more preferably 0.4% or less, still more preferably 0. It is 0.3% or less. When the haze value is 0.5% or less, the visibility of the screen of the display is improved when it is used as a cover glass of a portable display or the like. The haze value is measured according to JIS K3761: 2000 using a C light source.

In the case of crystallized glass, crystallized glass containing one or more crystals selected from the group consisting of lithium metasilicate crystal, lithium aluminosilicate crystal, lithium phosphate crystal and β-spodium crystal is preferable. Among these, lithium metasilicate crystals or lithium aluminosilicate crystals are more preferable because severe fracture is unlikely to occur even if a large compressive stress is formed.

The crystallization rate 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 increase the mechanical strength. Further, in order to increase the transparency, 70% or less is preferable, 60% or less is more preferable, and 50% or less is particularly preferable. The low crystallization rate is also excellent in that it can be easily bent and molded by heating.

The crystallization rate can be calculated by the Rietveld method from the X-ray diffraction intensity. The Rietveld method is described in the "Crystal Analysis Handbook" (Kyoritsu Publishing 1999, pp. 492-499), edited by the editorial committee of the "Crystal Analysis Handbook" of the Crystallographic Society of Japan.

The average particle size of the precipitated crystals of the crystallized glass is preferably 300 nm or less, more preferably 200 nm or less, further preferably 150 nm or less, and particularly preferably 100 nm or less in order to increase transparency. The average particle size of the precipitated crystals can be determined from a transmission electron microscope (TEM) image. It can also be estimated from a scanning electron microscope (SEM) image.

When the chemically strengthened glass is a crystallized glass, particularly a crystallized glass containing a lithium silicate crystal or a lithium aluminosilicate crystal, a glass obtained by heat-treating the glass composition described later is preferable. The glass composition is a glass composition that crystallizes by an appropriate heat treatment. In that case, the heat treatment is a two-step heat treatment in which the temperature is raised from room temperature to the first treatment temperature and held for a certain period of time, and then the temperature is held at a second treatment temperature, which is higher than the first treatment temperature, for a certain period of time. Is preferable.

In the case of two-step heat treatment, the first treatment temperature is preferably a temperature range in which the crystal nucleation rate is high in the glass composition, and the second treatment temperature is a temperature range in which the crystal growth rate is high in the glass composition. Is preferable. Further, the holding time at the first treatment temperature is preferably held long so that a sufficient number of crystal nuclei are formed. By forming a large number of crystal nuclei, the size of each crystal becomes smaller, and a highly transparent crystallized glass can be obtained.

The first treatment temperature is, for example, 550 ° C. to 800 ° C., the second treatment temperature is, for example, 850 ° C. to 1000 ° C., and after holding at the first treatment temperature for 2 to 10 hours, the second treatment temperature. Hold for 2 to 10 hours.

If the chemically strengthened glass is a crystallized glass containing lithium silicate crystals or lithium aluminosilicate crystals, it is displayed in terms of mass% based on oxides.
SiO ₂ 30-70%,
Al ₂ O ₃ 2-25%,
It preferably contains 15-40% Li _{2 O.}
Hereinafter, the composition of the glass will be described.

SiO ₂ is a component that forms a network structure of glass. It is also a component that increases chemical durability. The content of SiO ₂ is preferably 30% or more, preferably 35% or more, more preferably 40% or more, still more preferably 45% or more. The content of SiO ₂ is more preferably 60% or more, still more preferably 64% or more. On the other hand, in order to improve the meltability, _{the content of SiO 2} is preferably 70% or less, more preferably 68% or less, still more preferably 66% or less.

Al ₂ O ₃ is an effective component for increasing the surface compressive stress due to chemical strengthening, and is preferably 1% or more. The content of Al ₂ O ₃ is more preferably 2% or more, further preferably 4% or more, particularly preferably 6% or more, and extremely preferably 8% or more. _{On the other hand, the content of Al 2} O ₃ is preferably 25% or less, more preferably 20% or less, further preferably 18% or less, and particularly preferably 15% or less so that the devitrification temperature of the glass does not become too high.

Li ₂ O is a component that forms surface compressive stress by ion exchange, and is a component of β-spojumen crystal, lithium metasilicate crystal, and lithium phosphate crystal. The content of Li ₂ O is preferably 10% or more, more preferably 15% or more. In the crystallized glass containing lithium metasilicate or lithium phosphate, 10% or more is preferable, and 14% or more, 16% or more, and 18% or more are more preferable. On the other hand, in order to improve the stability of the glass, the Li ₂ O content is preferably 40% or less, more preferably 35% or less, still more preferably 30% or less.

<Manufacturing method of chemically strengthened glass>
The chemically strengthened glass of the present invention can be produced by subjecting a glass plate to a chemically strengthened treatment, and then washing 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 of a metal salt (for example, potassium nitrate) containing a metal ion (typically K ion) having a large ionic radius by immersion or the like. As a result, metal ions having a small ionic radius (typically Na ions or Li ions) in the glass plate become metal ions having a large ionic radius (typically, K ions and Li ions for Na ions). On the other hand, it is replaced with Na ion).

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

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

The treatment conditions for the chemically strengthened glass include the characteristics and composition of the glass, the type of molten salt, and the chemically strengthened properties such as the surface compressive stress and the depth of the compressive stress layer desired for the finally obtained chemically strengthened glass. Appropriate conditions may be selected in consideration.

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

As one aspect of the method for producing chemically strengthened glass of the present invention, for example, SiO ₂ is 30 to 70%, Al ₂ O ₃ is 2 to 25%, and Li ₂ O is 15 to 15 to 70% in terms of oxide standard. Examples of the production method include obtaining chemically strengthened glass by strengthening crystallized glass containing 40%, and containing lithium silicate crystals or lithium aluminosilicate crystals with a salt containing 80% by mass or more of potassium nitrate. Be done. A high compressive stress can be applied by setting the content of potassium nitrate in the salt to 80% by mass or more. The content of potassium nitrate in the salt is preferably 90% by mass or more, more preferably 95% by mass or more.

When the chemically strengthened glass of the present invention has a plate shape (glass plate), its plate thickness (t) is, for example, 2 mm or less, preferably 1.5 mm or less, from the viewpoint of enhancing the effect of chemical strengthening. It is more preferably 1 mm or less, further preferably 0.9 mm or less, particularly preferably 0.8 mm or less, and most preferably 0.7 mm or less. Further, the plate thickness is, for example, 0.1 mm or more, preferably 0.2 mm or more, more preferably 0.4 mm or more, from the viewpoint of obtaining the effect of sufficient strength improvement by the chemical strengthening treatment. More preferably, it is 0.5 mm or more.

The shape of the chemically strengthened glass of the present invention may be a shape other than a plate shape, depending on the product to which it is applied, the application, and the like. Further, the glass plate may have a edging shape or the like having a different outer peripheral thickness. Further, the form of the glass plate is not limited to this, for example, the two main surfaces may not be parallel to each other, and one or both of the two main surfaces may be a curved surface in whole or in part. More specifically, the glass plate may be, for example, a flat glass plate having no 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 used in mobile devices such as mobile phones, smartphones, personal digital assistants (PDAs), and tablet terminals. Furthermore, non-portable construction such as cover glass for display devices such as televisions (TVs), personal computers (PCs), and touch panels, wall surfaces of elevators, walls of buildings such as houses and buildings (full-scale display), and window glass. It is also useful as materials for materials, table tops, interiors of automobiles and airplanes, and as cover glass for them, and also for applications such as housings having a curved shape that is not plate-shaped due to bending or molding.

Examples of the present invention will be specifically described below, but the present invention is not limited thereto.

[Preparation of sample]
(1) Preparation of Glass A glass plate was prepared by mixing glass raw materials so as to have the glass composition described in the molar percentage display based on oxides in Table 1. As the glass raw material, a general glass raw material such as an oxide, a hydroxide, and a carbonate was appropriately selected, and the amount of the glass was weighed to 900 g. The mixed glass raw material was placed in a platinum crucible, melted at 1700 ° C., and defoamed. The glass was poured onto a carbon board to obtain a glass block.

(2) Preparation of Crystallized Glass The obtained glass block was processed into 50 mm × 50 mm × 1.5 mm and then heat-treated under the conditions shown in Table 2 to obtain crystallized glass. In the crystallization condition column of the table, the upper row is the nucleation treatment condition and the lower row is the crystal growth treatment condition. For example, when 550-2 is described in the upper row and 730-2 is described in the lower row, after holding at 550 ° C. for 2 hours. , 730 ° C. for 2 hours. Using a part of the obtained crystallized glass, it was confirmed by powder X-ray diffraction that lithium metasilicate was contained.

(3) Preparation of Sample 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. As for the crystallized glass, a part of the remaining crystallized glass was crushed and used for the analysis of precipitated crystals.

The glass plate was preheated at 350 ° C. for 10 minutes and then subjected to ion exchange treatment under the conditions shown in Table 2 to obtain chemically tempered glass. The results of evaluating the obtained samples are shown in Table 2. Examples 1 to 3 are Examples, and Examples 4 and 5 are Comparative Examples. "-" Indicates unevaluated.

[Evaluation method]
(Visible light transmittance)
The light transmission rate of the crystallized glass plate at a wavelength of 380 to 780 nm was measured by using an integrating sphere unit (150 mm InGaAs Int. Sptere) as a detector in a spectrophotometer (manufactured by PerkinElmer; LAMBDA950). The average transmittance, which is the arithmetic mean value of the light transmittance, was defined as the visible light transmittance [unit:%].

(Haze value)
A hertz value [unit:%] was measured with a C light source using a hertz meter (manufactured by Suga Test Instruments Co., Ltd .; HZ-V3).

(Stress profile)
The stress value was measured using a measuring machine SLP-2000 manufactured by Orihara Seisakusho, and the compressive stress value [unit: MPa] on the glass surface and the compressive stress layer depth DOL [unit: μm] were read.

(Refractive index distribution)
The chemically strengthened glass obtained as shown in FIG. 1 is cut and mirror-polished to 0.5 mm so that the cross-sectional direction can be observed. , The refractive index distribution from the surface to the center of the plate thickness was measured.

(EPMA surface K and Na concentration)
The K and Na concentrations on the glass surface were measured using EPMA (JXA-8500F manufactured by JEOL). After chemically strengthening the sample, it was embedded in a resin and mirror-polished. Since it is difficult to measure the concentration on the outermost surface accurately, the signal strength of K at the position where the signal strength of Si, which is considered to have almost no change in content, is half the signal strength at the center of the plate thickness, is the K concentration on the outermost surface. The K concentration on the outermost surface was calculated assuming that the signal intensity at the center of the plate thickness corresponds to the glass composition before strengthening.

The composition profile obtained by the measurement by EPMA is shown in FIGS. 3 (a) and 3 (b). FIG. 3 (a) shows the results of Example 2, and FIG. 3 (b) shows the results of Example 4. From the measurement result by the EPMA, shows a composition profile in terms oxides of _{K 2} O and Na ₂ O in FIG. 4 (a) and 4 (b). FIG. 4 (a) shows the results of Example 2, and FIG. 4 (b) shows the results of Example 4.

As shown in Table 2 and FIG. 2A, in Examples 1 to 3 of Examples, the absolute value of the refractive index distribution from the surface to the center of the plate thickness was as small as 0.002 or less, and uneven chemical strengthening occurred. Even so, it is considered that the distortion of the image on the display screen can be suppressed to a small extent.

On the other hand, as shown in Table 2 and FIG. 2 (b), in Example 4 as a comparative example, the refractive index of the glass surface is 0.0061 higher than that of the inside, and the display screen is displayed when uneven chemical strengthening occurs. It is considered that the image is distorted in. Further, as shown in Table 2 and FIG. 2 (c), in Example 5 as a comparative example, the refractive index of the glass surface is 0.0051 smaller than that of the inside, and it is displayed when uneven chemical strengthening occurs. It is considered that the image is distorted on the screen.

Further, as shown in FIG. 4A, in Example 2 which is an example, _{the value of − (ΔK 2} O + ΔNa ₂ O) on the glass surface was a negative value. _{- (ΔK 2 O + ΔNa 2} O) corresponds to Li ₂ O, as shown in FIG. 2 (a) by both of Na ₂ O and Li ₂ O is ion-exchanged, the refractive index change by ion exchange It is considered to be suppressed. On the other hand, as shown in FIG. 4 (b), in Example 4 which is a comparative example, _{the value of − (ΔK 2} O + ΔNa ₂ O) on the glass surface is almost zero, and as shown in FIG. 2 (b). , It is considered that the change in refractive index due to ion exchange is large.

Claims (7)

Chemically tempered glass with a surface compressive stress value of 400 MPa or more.
Chemically tempered glass in which the absolute value of the refractive index distribution from the surface to the center of the plate thickness is 0.002 or less. The chemically strengthened glass according to claim 1, which satisfies the following formula.
− (ΔK ₂ O + ΔNa ₂ O) ≦ -1
In the above formula, ΔK ₂ O and ΔNa ₂ O are as follows.
ΔK ₂ O: In the K ion concentration profile in the plate thickness direction of the chemically strengthened glass measured by EPMA, the difference between the concentration at a depth of 10 μm from the surface layer and the concentration at the center of the plate thickness _{is converted into K 2} O (mol%). ΔNa ₂ O: The difference between the concentration at a depth of 10 μm from the surface layer and the concentration at the center of the plate thickness in the Na ion concentration profile in the plate thickness direction of the chemically strengthened glass measured by EPMA is Na ₂ O (mol%). Value converted to The chemically strengthened glass according to claim 1 or 2, which contains 15 mol% or more of _{Li 2} O in terms of oxide-based mol%. The chemically strengthened glass according to claim 1 or 2, which is a crystallized glass having a visible light transmittance of 85% or more in terms of thickness of 0.7 mm and a haze value of 0.5% or less in terms of thickness of 0.7 mm. .. The chemically strengthened glass according to claim 4, wherein the crystallized glass contains a lithium silicate crystal or a lithium aluminosilicate crystal. In molar% display based on oxides,
SiO ₂ 30-70%,
Al ₂ O ₃ 2-25%,
The chemically strengthened glass according to any one of claims 1 to 5, which contains 15 to 40% of Li _{2 O.} In molar% display based on oxides,
SiO ₂ 30-70%,
Al ₂ O ₃ 2-25%,
Li 2 _O and containing 15% to 40%, and comprising a crystallized glass containing lithium silicate crystals or lithium aluminosilicate crystals, to obtain a chemically strengthened glass and reinforced with salts containing potassium nitrate least 80 wt% , How to make chemically strengthened glass.

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