WO2020008901A1

WO2020008901A1 - Chemically strengthened glass and method for manufacturing same

Info

Publication number: WO2020008901A1
Application number: PCT/JP2019/024562
Authority: WO
Inventors: 拓実馬田; 健二今北
Original assignee: Ａｇｃ株式会社
Priority date: 2018-07-03
Filing date: 2019-06-20
Publication date: 2020-01-09
Also published as: JPWO2020008901A1; JP7255594B2; CN112399964B; CN115716714B; CN115716714A; CN112399964A

Abstract

A chemically strengthened glass having a compressive stress layer, the CS₀ thereof measured using an optical waveguiding surface stress meter being 500 MPa or greater, |x|/|y| being 0-0.8 as determined by the formula in the specification, where D is the depth from the glass surface of a position at which the compressive stress value measured using an optical waveguiding surface stress meter is 0, and CS₂is the compressive stress value at a position at a depth of (D/2) from the glass surface, and the DOL measured using a scattered light photoelastic stress meter being 50 µm or greater.

Description

Chemically tempered glass and method for producing the same

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

2. Description of the Related Art Chemically strengthened glass is used for a cover glass or the like of a portable terminal.
Chemically strengthened glass contacts glass with a molten salt containing metal ions such as alkali metal ions, causing ion exchange between the metal ions in the glass and the metal ions in the molten salt and compressing the glass surface. This is a glass on which a stress layer is formed. The strength of chemically strengthened glass strongly depends on a stress profile represented by a compressive stress value in which the depth from the glass surface is a variable.

It is considered that a cover glass of a portable terminal or the like is less likely to be cracked by bending by increasing the compressive stress value on the glass surface.
Further, it is considered that by increasing the depth of the compressive stress layer to form the compressive stress layer even in a deep portion of the glass, it is possible to prevent the glass from cracking even when subjected to a large impact.

However, when a compressive stress layer is formed on the surface of glass, a tensile stress layer is necessarily formed inside the glass. When the value of the internal tensile stress is large, when the chemically strengthened glass is broken, the glass is crushed violently and fragments are easily scattered. Therefore, a method of increasing the surface compressive stress and the compressive stress depth while reducing the internal tensile stress value has been studied.

Patent Document 1 illustrates a typical stress profile when ion exchange processing is performed twice. The profile is composed of two straight line components, a straight line representing a stress profile from the glass surface to a point X at a certain depth and a straight line representing a stress profile from the point X to a point where the stress becomes zero. (Patent Document 1, FIG. 8). It is said that by using such a stress profile, the compressive stress on the surface can be increased, the compressive stress depth can be increased, and the internal tensile stress value can be reduced.

WO 2015/127483

In a typical stress profile in the case where the ion exchange treatment is performed twice, the stress greatly changes near the glass surface even if the depth from the glass surface slightly changes.
By the way, in the process of actually manufacturing a cover glass or the like of a portable terminal, the surface of the chemically strengthened glass may be polished for the purpose of erasing scratches generated on the surface. However, in the case of chemically strengthened glass having a stress profile in which the stress changes greatly even when the depth from the glass surface slightly changes, the surface compressive stress after polishing greatly differs due to a slight difference in the polishing amount. This has led to a decrease in yield.

The present invention provides a chemically strengthened glass having high strength and a small change in characteristics even when the surface is polished after chemical strengthening.

The present invention is a chemically strengthened glass having a compressive stress layer on the glass surface, wherein the compressive stress value CS _{0 of the} glass surface measured using an optical waveguide surface stress meter is 500 MPa or more, The depth from the glass surface at a position where the compressive stress value measured using the method becomes 0 is D [unit: μm], and the depth from the glass surface measured using the optical waveguide surface stress meter is (D / 2). the compressive stress value at the position of) the CS _2, and the absolute value, the depth from the depth (D / 2) of the inclination x of the stress profile from the glass surface to be determined by the following equation to a depth of (D / 2) The ratio | x | / | y | to the absolute value of the slope y of the stress profile up to D is 0 to 0.8, and the depth DOL of the compressive stress layer measured using a scattered photoelastic stress meter is 50 μm. The present invention provides a chemically strengthened glass.
x = (CS ₂ -CS ₀ ) / ((D / 2) -0) = 2 × (CS ₂ -CS ₀ ) / D
y = (0−CS ₂ ) / (D− (D / 2)) = − 2 × CS ₂ / D

Chemically tempered glass of the present invention, from the glass surface to be determined by the following equation from the depth from the glass surface to be measured using the optical waveguide surface stress meter and compressive stress value CS ₁ at the position of 1μm the CS ₀ Metropolitan The slope z of the stress profile up to a depth of 1 μm may be -100 MPa / μm or more and less than 0.
z = (CS ₁ -CS ₀ ) / (1 μm-0 μm) = (CS ₁ -CS ₀ ) / 1 μm
Further, the plate may have a thickness of 2000 μm or less.
Further, the glass composition of the central part in the thickness direction of the chemically strengthened glass contains 50% or more of SiO ₂ and 5% or more of Al ₂ O ₃ in terms of mol% on an oxide basis, and Li ₂ O, Na ₂ the total content of O and _{K 2} O is at least 5%, and the content of Li ₂ _O, Li 2 O, the ratio of the total content of Na ₂ O and _{K 2} O 0.5 It may be the above.

Chemically tempered glass of the present invention, matrix composition of chemically tempered glass, as represented by mol% based on _{_{_{oxides, SiO 2 50 ~ 80%,}}} Al 2 O 3 5 ~ 25%, B 2 O 3 0 ~ 10%, P ₂ O ₅ 0-10%, Li ₂ O 2-20%, Na ₂ O 0.5-10%, K ₂ O 0-5%, MgO + ZnO + CaO + SrO + BaO 0-15%, ZrO ₂ + TiO ₂ 0-5%, It may be.

The method for producing a chemically strengthened glass of the present invention includes immersing a glass plate in a potassium-containing strengthening salt at 400 ° C. to 500 ° C. for 1 to 8 hours, and thereafter, bringing the glass plate to a temperature of 300 ° C. or less. The potassium-containing strengthened salt may be a method for producing chemically strengthened glass, which contains 70% by mass or more of potassium ions, with the mass of metal ions contained in the strengthened salt being 100% by mass.
In the above-described method for producing a chemically strengthened glass according to the present invention, the glass composition of the glass sheet before chemical strengthening contains 50% or more of SiO ₂ and 5% or more of Al ₂ O ₃ in terms of mol% on an oxide basis. and _is a Li 2 O, the total content of Na ₂ O and _{K 2} O is more than 5%, and the content of Li ₂ _O, containing a total of Li 2 O, Na ₂ O and _{K 2} O The ratio with the amount may be 0.5 or more.

According to the present invention, it is possible to obtain a chemically strengthened glass having a high strength, which suppresses the scattering of fragments at the time of breaking, and has a small change in characteristics even when the surface is polished after the chemical strengthening.

FIG. 1 is a diagram showing a stress profile near the surface of the chemically strengthened glass of Example 1 measured by an optical waveguide surface stress meter. FIG. 2 is a diagram showing a stress profile of the chemically strengthened glass of Example 1 measured using a scattered light photoelastic stress meter. FIG. 3 is a stress profile diagram obtained by synthesizing data of the optical waveguide surface stress meter and data of the scattered light photoelastic stress meter.

において In this specification, unless otherwise specified, “to”, which indicates a numerical range, is used to mean that the numerical values described before and after it are included as the lower limit and the upper limit.

As used herein, the term “stress profile” refers to a value representing a compressive stress value from a glass surface to a central portion, with the depth from the glass surface as a variable. The “compression stress depth (DOL)” is a depth at which the compression stress value becomes zero in the stress profile.
“Internal tensile stress (CT)” refers to a tensile stress value at a depth of の of the thickness t of the glass.

In this specification, “chemically strengthened glass” refers to glass that has been subjected to chemical strengthening treatment, and “glass for chemical strengthening” refers to glass that has not been subjected to chemical strengthening treatment.
In this specification, the glass composition of the glass for chemical strengthening may be referred to as “the mother composition of chemically strengthened glass”. Except when an extreme ion exchange treatment is performed, the glass composition at a portion deeper than the DOL of the chemically strengthened glass is the mother composition of the chemically strengthened glass.

In the present specification, the glass composition is expressed in terms of mole percentage on an oxide basis unless otherwise specified, and mol% is simply expressed as “%”.
Further, “substantially not contained” in the glass composition means that the glass composition is at or below the level of impurities contained in raw materials and the like, that is, it is not intentionally contained. Specifically, for example, it is less than 0.1%.

<Destruction of glass>
When the glass plate bends due to an impact, if the amount of the bending increases, a large tensile stress is applied to the glass surface to break the glass. In the present specification, such a fracture is referred to as “glass fracture by a bending mode”. In the chemically strengthened glass of the present invention (hereinafter sometimes referred to as “the present tempered glass”), since a large compressive stress is formed on the glass surface, glass breakage due to a bending mode is suppressed.
On the other hand, when a small and hard object collides with the glass plate, a stress is generated inside the glass plate by the impact, and the glass plate is broken from the inside. In the present specification, such a fracture is referred to as “glass fracture by an impact mode”. In the present tempered glass, since a compressive stress layer is formed up to the inside of the glass plate, glass breakage due to the impact mode is suppressed.
If the compressive stress value on the glass surface is large and the compressive stress layer is formed even inside the glass plate, both glass breakage in the bending mode and glass breakage in the impact mode are suppressed, making the glass very hard to break. Should be. However, when a compressive stress layer is formed inside a glass sheet, an internal tensile stress that cancels out the layer is generated. If the internal tensile stress is large, severe breakage occurs when the glass breaks, and fragments are scattered.
Since the stress profile of the tempered glass according to the present invention is appropriately adjusted, both the glass breakage in the bending mode and the glass breakage in the impact mode are suppressed, and the shards are less scattered even when broken.

As a method of obtaining chemically strengthened glass in which both glass breakage in the bending mode and glass breakage in the impact mode are suppressed, and there is little scattering of fragments even when broken, ion exchange treatment of lithium aluminosilicate glass and different inclinations Methods for producing two stress profiles are known.

In this case, the lithium aluminosilicate glass can be chemically strengthened by an ion exchange treatment using a strengthening salt containing sodium ions and potassium ions. Alternatively, chemical strengthening can be performed by an ion exchange treatment using a strengthening salt containing potassium ions after an ion exchange treatment using a strengthening salt containing sodium ions.
According to these methods, a relatively large compressive stress is generated in a relatively shallow region from the surface by ion exchange of sodium ions and potassium ions, and a relatively small compressive stress is generated in a deeper region by ion exchange of lithium ions and sodium ions. Stress occurs.
Sodium ions having a relatively small ionic radius have a high diffusion rate into the glass, whereas potassium ions having a relatively large ionic radius have a low diffusion rate into the glass. Therefore, in a deep region, ion exchange between lithium ions and sodium ions occurs, but ion exchange between sodium ions and potassium ions does not easily occur.

(4) In a region near the surface where ion exchange between sodium ions and potassium ions occurs, a large compressive stress is generated when potassium ions having a large ionic radius enter the glass. In a deeper region, a relatively small compressive stress is generated even in a deeper region due to ion exchange between lithium ions and sodium ions. The chemically strengthened glass obtained in this manner has a stress profile that is sharp in the vicinity of the surface and relatively gentle in a deep part and is bent in two stages. By forming such a stress profile, it is possible to obtain a chemically strengthened glass that has a high surface strength, is hardly crushed even when subjected to a strong impact, and hardly shards when broken.

However, in this stress profile, since the compressive stress value on the outermost surface becomes very large, so-called “delay chipping” tends to occur near the surface. Delayed chipping is a phenomenon in which an edge is chipped at a portion where an excessive stress is introduced by chemical strengthening with a small force. Further, when the surface of the chemically strengthened glass having such a stress profile is polished, even the slightest difference in the amount of polishing greatly changes the stress on the outermost surface.
In the tempered glass, these problems are unlikely to occur because the stress profile near the glass surface is adjusted.

<Measurement of compressive stress>
By using a combination of two types of devices, an optical waveguide surface stress meter and a scattered light photoelastic stress meter, the compressive stress in chemically strengthened glass can be accurately measured.

The reason for measuring the compressive stress using two types of devices is as follows.
A method using an optical waveguide surface stress meter is widely known as a method capable of accurately measuring the stress of a glass sample in a short time. However, in principle, this method can measure stress only when the refractive index decreases from the sample surface toward the inside.
In chemically strengthened glass, the layer in which sodium ions in the glass are replaced with potassium ions has a lower refractive index from the surface toward the inside, so that the stress can be measured using an optical waveguide surface stress meter. However, in a layer in which lithium ions in glass are replaced with sodium ions, such a refractive index distribution does not occur, so that stress cannot be measured with an optical waveguide surface stress meter.
FIG. 1 is an example of a stress profile obtained by measuring stress of the present tempered glass using an optical waveguide surface stress meter. Although the broken line portion of the graph actually causes stress due to ion exchange between lithium ions and sodium ions, the stress cannot be measured by the optical waveguide surface stress meter.

The stress measurement method using the scattered light photoelastic stress meter can measure the stress in principle without depending on the refractive index distribution. However, since the scattered light photoelastic stress meter is affected by light scattering on the glass surface, the stress near the glass surface cannot be measured correctly. FIG. 2 is an example of a stress profile obtained by measuring the stress of the present tempered glass using a scattered light photoelastic stress meter. The broken line in the graph is not reliable because it is affected by light scattering on the glass surface.
Therefore, the stress can be analyzed by measuring the stress with two types of stress meters and combining the results. This method is described in detail in WO2018 / 056121. FIG. 3 is an example of a stress profile diagram obtained by synthesis.

As the optical waveguide surface stress meter, for example, FSM-6000 manufactured by Orihara Seisakusho can be used. Using the FSM-6000 and the attached software FsmV enables highly accurate stress measurement.
For example, SLP-1000 manufactured by Orihara Seisakusho can be used as the scattered light photoelastic stress meter. When FSM-6000 is used as the optical waveguide surface stress meter and SLP-1000 is used as the scattered light photoelastic stress meter, data can be easily synthesized using dedicated software.

<Chemically tempered glass>
The present tempered glass preferably has a plate shape, and is usually a flat plate shape, but may be a curved surface shape.

The thickness of the tempered glass is preferably 400 μm or more, more preferably 600 μm or more, and even more preferably 700 μm or more. This is because the strength of the glass increases. The thickness of the tempered glass is preferably as large as possible to increase the strength, but is preferably 2000 μm or less, more preferably 1000 μm or less, to reduce the weight.

(4) In the tempered glass, it is preferable that a compressive stress is generated by ion exchange of sodium ions and potassium ions in a relatively shallow region from the surface, and a compressive stress is generated by ion exchange of lithium ions and sodium ion in a deeper region. Such chemically tempered glass has a stress profile that bends in two steps, which is steep near the surface and relatively gentle in deep parts, resulting in high surface strength and crushing even when subjected to strong impact. Because it is hard to do.

This tempered glass, compressive stress value CS ₀ in the glass surface to be measured using the optical waveguide surface stress meter is not less than 500 MPa, therefore has high strength. For example, in FIG. 1, CS value of the glass surface shown by the arrow a is CS _0. CS ₀ is more preferably 900 MPa or more, further preferably 950 MPa or more, and particularly preferably 1000 MPa or more.
This tempered glass, the compressive stress value CS ₀ in the glass surface is less than 1200 MPa, preferably since the late chipping is suppressed. CS ₀ is more preferably 1100 MPa or less, still more preferably 1050 MPa or less.

(4) It is preferable that the tempered glass has a depth D [unit: μm] at which the “compressive stress value measured by the optical waveguide surface stress meter” is zero is 3 μm or more, because it can suppress breakage in a bending mode. In order to suppress breakage due to the bending mode, D is more preferably 4 μm or more, and further preferably 5 μm or more. In order to suppress the destruction due to the bending mode, D is more preferably about 10 μm. If D is too large, the tensile stress generated in the central glass layer will increase. In order to prevent the severe destruction due to the tensile stress, D is preferably 20 μm or less, more preferably 15 μm or less, and further preferably 10 μm or less.

{For example, in FIG. 1, the depth of the “point at which the CS value becomes 0” indicated by the arrow d is D. As described above, when a strengthening layer formed by ion exchange of lithium ions and sodium ions is formed inside glass, a strengthened layer formed by ion exchange of lithium ions and sodium ions is formed near a point where the CS value becomes zero. Therefore, stress cannot be measured accurately with an optical waveguide surface stress meter. D is thought to represent the depth at which potassium ions diffused.

The tempered glass has a stress profile gradient x [unit: MPa / μm] from the glass surface measured using an optical waveguide surface stress meter to a depth of (D / 2) [unit: μm], which is −200 MPa / μm. It is preferably at least 200 MPa / μm. The gradient x is more preferably −100 MPa / μm or more and 100 MPa / μm or less, and still more preferably −70 MPa / μm or more and 70 MPa / μm or less. As the absolute value of x is smaller, the thickness of the layer having an appropriate compressive stress value increases, and excellent characteristics can be obtained even when the surface is polished.
Also, the slope x is preferably a negative value. The highest compressive stress is required for a glass surface that requires a high compressive stress to suppress fracture in a bending mode. If there is a positive part in the slope of the stress profile, there will be places where excessive stress is introduced inside the glass, which will cause delayed chipping, or the stress on the outermost surface will be insufficient, and fracture due to bending mode will occur. It is easy to occur.

For example, in FIG. 1, x is the slope of the stress profile from the glass surface indicated by arrow a to the glass surface indicated by arrow c to a depth of (D / 2).
x is the D, obtained from the compression stress value CS ₂ at a depth of a compression stress value CS ₀ and glass surfaces of the glass surface (D / 2) in the equation below.
x = (CS ₂ -CS ₀ ) / ((D / 2) -0)
= 2 × (CS ₂ −CS ₀ ) / D

This tempered glass bends when the gradient y [unit: MPa / μm] of the stress profile from depth D / 2 to depth D measured using an optical waveguide surface stress meter is −125 MPa / μm or less. This is preferable because a high compressive stress layer necessary for suppressing breakage by a mode can be formed as a thin outermost layer. The smaller the slope y, the better, but it is usually at least -500 MPa / μm.

For example, in FIG. 1, the slope of the stress profile from a point at a depth of D / 2 from the glass surface indicated by an arrow c to a point at a depth D indicated by an arrow d is y.
Where y is obtained by the equation below from the D and CS _2.
y = (0−CS ₂ ) / (D− (D / 2))
= −2 × CS ₂ / D

When the ratio | x | / | y | of the absolute value of the gradient x and the absolute value of the stress profile described above | x | / | y | is 0.8 or less, the tempered glass keeps the high compressive stress layer of the glass outermost layer thin. On the other hand, it is preferable because a stress region suitable for suppressing both the delayed chipping and the fracture caused by the bending mode can be formed thick. More preferably, it is 0.6 or less. The minimum value of | x | / | y | is 0. That is, | x | / | y | is preferably from 0 to 0.8, and more preferably from 0 to 0.6.
Further, x is preferably 0 or less, and y is preferably a negative value. Therefore, x / y is preferably from 0 to 0.8, and more preferably from 0 to 0.6. The smaller the value of x / y is, the more preferable it is.

When the gradient z of the stress profile from the glass surface to the depth of 1 μm from the glass surface measured by an optical waveguide surface stress meter is -100 MPa / μm or more, this tempered glass can suppress both delayed chipping and fracture due to bending mode. This is preferable because the thickness of a suitable stress region increases. z is more preferably −80 MPa / μm or more. z is usually 100 MPa / μm or less, preferably 0 MPa / μm or less.

For example, in FIG. 1, the slope of the stress profile from the glass surface indicated by arrow a to the point at a depth of 1 μm from the glass surface indicated by arrow b is z.
Assuming that a compressive stress value at a depth of 1 μm measured by an optical waveguide surface stress meter is CS ₁ [unit: MPa], z is obtained by the following equation.
z = (CS ₁ -CS ₀ ) / (1 μm-0 μm)
= (CS ₁ -CS ₀ ) / 1 μm

において In this tempered glass, the compressive stress depth DOL measured by a scattered light photoelastic stress meter is preferably 50 μm or more. For example, in FIG. 2, the depth of the point at which the CS value indicated by the arrow e becomes 0 is DOL. Since a typical asphalt projection may be about 50 μm, in order to prevent cracking when the glass plate collides with the asphalt, a compressive stress is formed from the surface of the glass to a depth of 50 μm from the surface layer of the glass. preferable. When the plate thickness is t μm, DOL / t is preferably 0.1 or more, more preferably 0.12 or more, and still more preferably 0.14 or more. On the other hand, if DOL is too large with respect to t, an excessive tensile stress will be generated in the center layer of the plate thickness, and severe damage will occur at the time of injury. Therefore, DOL / t is preferably 0.25 or less, more preferably 0.22 or less, and particularly preferably 0.2 or less.

There is generally a positive correlation between D and DOL, and DOL tends to increase as D increases. DOL is determined by the depth at which lithium and sodium ions are exchanged, and D is determined by the depth at which sodium and potassium ions are exchanged. Generally, the ease of ion exchange depends on the glass composition. It is.

<Glass for chemical strengthening>
The chemically strengthened glass of the present invention is obtained by chemically strengthening a glass for chemical strengthening which is a lithium aluminosilicate glass (hereinafter, referred to as “glass for strengthening”). The composition of the glass for chemical strengthening is the same as the glass composition of the central part in the thickness direction of the chemically strengthened glass, except for the case where the chemical strengthening treatment is extremely performed. The above description also applies to the composition of the central part in the thickness direction of the chemically strengthened glass.
The lithium aluminosilicate glass contains, for example, 50% or more of SiO ₂ and 5% or more of Al ₂ O ₃ in terms of mol% on an oxide basis, and has a total content of Li ₂ O, Na ₂ O and K ₂ O. is 5% or more, and the content of _{_{Li 2 O, Li 2 O,}} Na 2 O and _{K 2} O ratio of the sum of the content of _{_{_{(Li 2 O / (Li 2}}} O + Na 2 O + K 2 O)) Is 0.5 or more glass.

The present tempering glass more preferably has the following composition in terms of mole percentage on an oxide basis.
_{_{_{_{SiO 2 50 ~ 80%, Al}}}} 2 O 3 5 ~ 25%, B 2 O 3 0 ~ 10%, P 2 O 5 0 ~ 10%, Li 2 O 2 ~ 20%, Na 2 O 0.5 ~ 10 %, K ₂ O 0-5%.
The content of MgO + ZnO + CaO + SrO + BaO (total content of MgO, ZnO, CaO, SrO, and BaO) is preferably 0 to 15%, and the content of ZrO ₂ + TiO ₂ (total content of ZrO ₂ and TiO ₂ ) is 0 to 5%. Is preferred.
Such a glass tends to form a favorable stress profile by a chemical strengthening treatment. Hereinafter, this preferred glass composition will be described.

SiO ₂ is a component constituting the skeleton of glass. Further, it is a component that increases chemical durability and is a component that reduces the occurrence of cracks when the glass surface is damaged. The content of SiO ₂ is preferably at least 50%, more preferably at least 55%, even more preferably at least 58%.
Further, the content of SiO ₂ is preferably 80% or less, more preferably 75% or less, and even more preferably 70% or less, in order to enhance the melting property of the glass.

Al ₂ O ₃ is an effective component for improving the ion exchange property during chemical strengthening and increasing the surface compressive stress after strengthening, and is a component for increasing the glass transition temperature (Tg) and increasing the Young's modulus. But also. The content of Al ₂ O ₃ is preferably at least 5%, more preferably at least 7%, even more preferably at least 13%.
Further, the content of Al ₂ O ₃ is preferably 25% or less, more preferably 23% or less, and further preferably 20% or less, in order to enhance the melting property.

B ₂ O ₃ is not essential, but may be included for the purpose of improving the melting property during glass production and the like. In order to reduce the gradient of the stress profile near the surface of the chemically strengthened glass, it is preferable to contain B ₂ O ₃ , in which case the content is preferably 0.5% or more, more preferably 1% or more. More preferably, it is at least 2%.
Since B ₂ O ₃ is a component that easily causes stress relaxation after chemical strengthening, the content of B ₂ O ₃ is preferably 10% or less, more preferably, in order to prevent a decrease in surface compressive stress due to stress relaxation. Is at most 8%, more preferably at most 5%, particularly preferably at most 3%.

Li ₂ O is a component that forms a surface compressive stress by ion exchange, and is an essential component of lithium aluminosilicate glass. By chemically strengthening the lithium aluminosilicate glass, a chemically strengthened glass having a favorable stress profile can be obtained. The content of Li ₂ O is preferably 2% or more, more preferably 3% or more, and still more preferably 5% or more, in order to increase the depth DOL of the compressive stress layer.
In addition, in order to suppress the occurrence of devitrification when producing glass or performing bending, the content of Li ₂ O is preferably 20% or less, more preferably 15% or less, and still more preferably. 10% or less.

Na ₂ O is a component that forms a surface compressive stress layer by ion exchange using a molten salt containing potassium, and is a component that improves the meltability of glass. The content of Na ₂ O is preferably 0.5% or more, more preferably 1% or more, and still more preferably 1.5% or more.
Further, the content of Na ₂ O is preferably at most 10%, more preferably at most 8%, further preferably at most 6%.

K ₂ O is not essential, but may be contained in order to improve the meltability of the glass and suppress devitrification. The content of K ₂ O is preferably at least 0.1%, more preferably at least 0.5%, further preferably at least 1%.
Further, the content of K ₂ O is preferably 5% or less, more preferably 3% or less, and still more preferably 1% or less, in order to increase the compressive stress value due to ion exchange.

Alkali metal oxides such as Li ₂ O, Na ₂ O and K ₂ O are components that lower the melting temperature of glass, and are preferably contained in a total amount of 5% or more. The total content of Li ₂ O, Na ₂ O, and K ₂ O (Li ₂ O + Na ₂ O + K ₂ O) is preferably 5% or more, more preferably 7% or more, and even more preferably 8% or more.
(Li ₂ O + Na ₂ O + K ₂ O) is preferably at most 20%, more preferably at most 18%, in order to maintain the strength of the glass.

Alkaline earth metal oxides such as MgO, CaO, SrO, BaO, and ZnO are components that enhance the melting property of glass, but tend to decrease ion exchange performance.
The total content of MgO, CaO, SrO, BaO, and ZnO (MgO + CaO + SrO + BaO + ZnO) is preferably 15% or less, more preferably 10% or less, and even more preferably 5% or less.

When containing any of MgO, CaO, SrO, BaO and ZnO, it is preferable to contain MgO in order to increase the strength of the chemically strengthened glass.
When MgO is contained, the content is preferably 0.1% or more, more preferably 0.5% or more. In order to enhance ion exchange performance, the content is preferably 10% or less, more preferably 8% or less.

The content of CaO when contained is preferably 0.5% or more, more preferably 1% or more. In order to enhance ion exchange performance, the content is preferably 5% or less, more preferably 3% or less.

The content when SrO is contained is preferably 0.5% or more, more preferably 1% or more. In order to enhance ion exchange performance, the content is preferably 5% or less, more preferably 3% or less.

The content of BaO when contained is preferably 0.5% or more, more preferably 1% or more. In order to enhance ion exchange performance, the content is preferably 5% or less, more preferably 1% or less, and further preferably substantially no content.

ZnO is a component for improving the melting property of glass, and may be contained. When ZnO is contained, the content is preferably 0.2% or more, and more preferably 0.5% or more. In order to increase the weather resistance of the glass, the content of ZnO is preferably 5% or less, more preferably 3% or less.

TiO ₂ is a component that suppresses scattering of fragments when the chemically strengthened glass is broken, and may be contained. When TiO ₂ is contained, the content is preferably 0.1% or more. The content of TiO ₂ is preferably 5% or less, more preferably 1% or less, and further preferably substantially no content, in order to suppress devitrification at the time of melting.

ZrO ₂ is a component that increases the surface compressive stress due to ion exchange, and may be included. When ZrO ₂ is contained, the content is preferably 0.5% or more, and more preferably 1% or more. In order to suppress the devitrification at the time of melting, the content is preferably 5% or less, more preferably 3% or less.

The content of TiO ₂ and ZrO ₂ (TiO ₂ + ZrO ₂ ) is preferably 5% or less, more preferably 3% or less.

Y ₂ O ₃ , La ₂ O ₃ and Nb ₂ O ₅ are components that suppress the fracture of chemically strengthened glass, and may be contained. When these components are contained, the content of each component is preferably 0.5% or more, more preferably 0.5% or more, further preferably 1% or more, particularly preferably 1.5% or more, and most preferably 1.5% or more. It is preferably at least 2%.

The total content of Y ₂ O ₃ , La ₂ O ₃ and Nb ₂ O ₅ is preferably 9% or less, more preferably 8% or less. In such a case, the glass is less likely to be devitrified at the time of melting, so that the quality of the chemically strengthened glass can be prevented from lowering. The content of each of Y ₂ O ₃ , La ₂ O ₃ and Nb ₂ O ₅ is preferably at most 7%, more preferably at most 6%, further preferably at most 5%, particularly preferably at most 4%, most preferably. Is not more than 3%.

Ta ₂ O ₅ and Gd ₂ O ₃ may be contained in small amounts in order to suppress the fracture of the chemically strengthened glass. However, since the refractive index and the reflectance become high, the contents of these are each preferably 1% or less. , 0.5% or less, more preferably, substantially not contained.

P ₂ O ₅ may be contained in order to improve the ion exchange performance. When P ₂ O ₅ is contained, the content is preferably 0.5% or more, and more preferably 1% or more. In order to increase the chemical durability, the content of P ₂ O ₅ is preferably 10% or less, more preferably 5% or less, and even more preferably 3% or less.

When coloring the glass, a coloring component may be added in a range that does not hinder achievement of the desired chemical strengthening properties. As the coloring component, for example, 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 and Nd ₂ O ₃ are mentioned. These may be used alone or in combination.

The total content of the coloring components is preferably 7% or less. Thereby, devitrification of glass can be suppressed. The content of the coloring component is more preferably 5% or less, further preferably 3% or less, and particularly preferably 1% or less. When it is desired to increase the visible light transmittance of the glass, it is preferable that these components are not substantially contained.

Further, SO ₃ , chloride, fluoride, and the like may be appropriately contained as a fining agent at the time of glass melting. It is preferable that As ₂ O ₃ is not substantially contained. When Sb ₂ O ₃ is contained, the content is preferably 0.3% or less, more preferably 0.1% or less, and most preferably substantially no content.

The glass transition temperature (Tg) of the present tempering glass is preferably 480 ° C. or higher, more preferably 500 ° C. or higher, even more preferably 520 ° C. or higher, in order to suppress stress relaxation during chemical strengthening.
Tg is preferably 700 ° C. or lower because the ion diffusion rate is increased during chemical strengthening. In order to easily obtain a deep DOL, Tg is preferably 650 ° C. or lower, more preferably 600 ° C. or lower.

The tempering glass preferably has a Young's modulus of 70 GPa or more. The higher the Young's modulus, the more difficult it is for fragments to be scattered when the tempered glass breaks. Therefore, the Young's modulus is more preferably at least 75 GPa, even more preferably at least 80 GPa. On the other hand, if the Young's modulus is too high, diffusion of ions during chemical strengthening is slow, and it tends to be difficult to obtain a deep DOL. Therefore, the Young's modulus is preferably 110 GPa or less, more preferably 100 GPa or less, and even more preferably 90 GPa or less.

The Vickers hardness of the tempering glass is preferably 575 or more. The higher the Vickers hardness of the glass for chemical strengthening, the greater the Vickers hardness after chemical strengthening, and the less likely the glass when chemically strengthened falls. Therefore, the Vickers hardness of the glass for chemical strengthening is more preferably 600 or more, and further preferably 625 or more.
The Vickers hardness after chemical strengthening is preferably 600 or more, more preferably 625 or more, and even more preferably 650 or more.

(4) The larger the Vickers hardness is, the more difficult it is to be damaged. Therefore, it is preferable that the tempered glass generally has a Vickers hardness of 850 or less. Glasses having too high a Vickers hardness tend to have difficulty in obtaining sufficient ion exchangeability. Therefore, the Vickers hardness is preferably 800 or less, more preferably 750 or less.

The fracture toughness value of the present tempering glass is preferably 0.7 MPa · m ^1/2 or more. As the fracture toughness value increases, the scattering of fragments tends to be suppressed when the chemically strengthened glass is broken. The fracture toughness value is more preferably 0.75 MPa · m ^1/2 or more, and still more preferably 0.8 MPa · m ^1/2 or more.
The fracture toughness value is usually 1 MPa · m ^1/2 or less.

The average thermal expansion coefficient (α) of the tempering glass at 50 ° C. to 350 ° C. is preferably 100 × 10 ⁻⁷ / ° C. or less. If the average coefficient of expansion (α) is small, the glass is less likely to warp during molding or cooling after chemical strengthening. The average expansion coefficient (α) is more preferably not more than 95 × 10 ⁻⁷ / ° C., and further preferably not more than 90 × 10 ⁻⁷ / ° C.
In order to suppress the warpage of the chemically strengthened glass, the average coefficient of thermal expansion (α) is preferably as small as possible, but is usually 60 × 10 ⁻⁷ / ° C. or more.

In the tempering glass, the temperature (T ₂ ) at which the viscosity becomes 10 ² dPa · s is preferably 1750 ° C. or lower, more preferably 1700 ° C. or lower, and further preferably 1680 ° C. or lower. T ₂ is usually at 1400 ℃ or more.

In the present tempering glass, the temperature (T ₄ ) at which the viscosity becomes 10 ⁴ dPa · s is preferably 1350 ° C. or lower, more preferably 1300 ° C. or lower, and further preferably 1250 ° C. or lower. T ₄ is usually at 1000 ℃ or more.

<Production method of chemically strengthened glass>
The present tempered glass can be produced, for example, by chemically tempering glass having the above-mentioned composition for chemical tempering.
The glass for chemical strengthening can be manufactured using, for example, the following general glass manufacturing method. The following manufacturing method is an example of manufacturing a plate-shaped chemically strengthened glass, but the glass for chemical strengthening may have a shape other than the plate shape.

(4) The glass raw materials are appropriately prepared so that a glass having a preferable composition is obtained, and the mixture is heated and melted in a glass melting furnace. Thereafter, the glass is homogenized by bubbling, stirring, addition of a fining agent, etc., formed into a glass plate having a predetermined thickness, and gradually cooled. Alternatively, it may be formed into a plate by a method of cutting into a block, followed by slow cooling, and then cutting.

方法 Examples of the method of forming into a plate shape include a float method, a press method, a fusion method, and a downdraw method. In particular, when manufacturing a large glass plate, the float method is preferred. Further, a continuous molding method other than the float method, for example, a fusion method and a downdraw method are also preferable.

ガラス The glass ribbon obtained by molding is ground and polished as required to form a glass plate. When the glass plate is cut into a predetermined shape and size or the glass plate is chamfered, if the glass plate is cut or chamfered before performing the chemical strengthening process described later, the chemical strengthening process is performed. Thus, a compressive stress layer is also formed on the end face, which is preferable.

Then, the chemically strengthened glass is obtained by subjecting the formed glass plate to a chemical strengthening treatment, followed by washing and drying.

<Chemical strengthening treatment>
Chemical strengthening treatment involves contacting glass with a metal salt, such as by immersing the glass in a melt of a metal salt (eg, potassium nitrate) containing a metal ion having a large ionic radius (typically, sodium ion or potassium ion). Metal ions of small ionic radius in glass (typically lithium or sodium ions) and metal ions of large ionic radius in metal salts (typically sodium or potassium ions for lithium ions) This is a treatment for replacing sodium ions with potassium ions.

The method using “Li—Na exchange” in which lithium ions in glass are exchanged for sodium ions is preferred because the chemical strengthening treatment speed is high. In order to form a large compressive stress by ion exchange, a method utilizing "Na-K exchange" in which sodium ions in glass are exchanged for potassium ions is preferable.
It is more preferable to use the method of performing “Li—Na exchange” and “Na—K exchange” in combination, since a high surface compressive stress and a deep compressive stress layer can be formed in a relatively short processing time. In that case, it is more effective to perform “Na—K exchange” after performing “Li—Na exchange”.

溶融 Examples of the molten salt for performing the chemical strengthening treatment include nitrate, sulfate, carbonate, and chloride. Among these, 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, potassium carbonate and the like. Examples of the chloride 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.

More specifically, the present tempered glass can be manufactured by a tempering treatment method described below (hereinafter, referred to as “the present tempering treatment method”).
This tempering treatment method includes a step of immersing the glass plate in a potassium-containing reinforcing salt. As the potassium-containing fortifying salt, a salt containing 70% by mass or more of potassium ion is preferable, and a salt containing 90% by mass or more is more preferable, with the mass of the metal ion contained in the reinforcing salt being 100% by mass. By using such a reinforcing salt, a high compressive stress layer can be formed on the surface layer. As the potassium-containing reinforcing salt, potassium-containing nitrate is preferable from the viewpoint of easy handling such as boiling point and danger.
The strengthening salt preferably contains potassium nitrate, and as a component other than potassium nitrate, a nitrate of an alkali metal or an alkaline earth metal such as sodium nitrate or magnesium nitrate may be contained. Further, lithium at an impurity level may be contained.

In this tempering treatment method, it is preferable to immerse the glass plate in a potassium-containing tempering salt at 400 ° C. to 500 ° C. When the temperature of the potassium-containing reinforcing salt is 400 ° C. or higher, ion exchange is easy to proceed, which is preferable. Also, the occurrence of stress relaxation tends to reduce the | x | / | y | ratio in the stress profile. More preferably, the temperature is 420 ° C. or higher. Further, it is preferable that the temperature of the potassium-containing reinforcing salt is 500 ° C. or lower, since excessive stress relaxation of the surface layer can be suppressed. More preferably, it is 480 ° C or lower.

ガラス The time for immersing the glass in the potassium-containing reinforcing salt is preferably 1 hour or more because the surface compressive stress increases. Also, the occurrence of stress relaxation tends to reduce the | x | / | y | ratio in the stress profile. The immersion time is more preferably 2 hours or more, and still more preferably 3 hours or more. If the immersion time is too long, not only does the productivity decrease, but also the compressive stress may decrease due to the relaxation phenomenon. In order to increase the compressive stress, the time is preferably 8 hours or less, more preferably 6 hours or less, and further preferably 4 hours or less.

前 Before immersing the glass plate in the potassium-containing reinforcing salt, it may be immersed in another reinforcing salt. As another fortifying salt, a sodium-containing fortifying salt is preferable. The sodium-containing fortifying salt is preferably a sodium nitrate-reinforcing salt from the viewpoint of ease of handling, similarly to potassium nitrate. Further, it is preferable that 70% by mass or more of sodium ions be contained, with the mass of metal ions contained in the reinforcing salt being 100% by mass.

(4) After the glass plate is immersed in the potassium-containing reinforcing salt, the temperature is preferably maintained at 300 ° C. or lower. This is because when the temperature becomes higher than 300 ° C., the compressive stress generated by the ion exchange treatment is reduced by the relaxation phenomenon. The holding temperature after immersing the glass plate in the potassium-containing reinforcing salt is more preferably 250 ° C. or lower, and further preferably 200 ° C. or lower.

処理 The processing conditions of the chemical strengthening treatment may be appropriately selected such as time and temperature in consideration of the properties and composition of the glass and the type of the molten salt.

The chemically strengthened glass of the present invention is particularly useful as a cover glass used for mobile devices such as mobile phones and smartphones. Further, the present invention is also useful for cover glass of a display device such as a television, a personal computer, and a touch panel, an elevator wall surface, and a wall surface of a building such as a house or a building (entire display) which is not intended for carrying. It is also useful for building materials such as window glasses, table tops, interiors of automobiles and airplanes and the like, and as cover glasses for them, and for applications such as housings having a curved surface shape.

Hereinafter, the present invention will be described with reference to examples, but the present invention is not limited thereto.
Glass raw materials were prepared so as to have the compositions of glass A to glass E shown in Table 1 in terms of mole percentage on an oxide basis, and weighed to 400 g as glass. Next, the mixed raw materials were put into a platinum crucible, put into an electric furnace at 1500 to 1700 ° C., melted for about 3 hours, defoamed, and homogenized.

(4) The obtained molten glass was poured into a metal mold, kept at a temperature about 50 ° C. higher than the glass transition point for 1 hour, and then cooled to room temperature at a rate of 0.5 ° C./min to obtain a glass block. The obtained glass block was cut and ground, and finally both surfaces were mirror-polished to obtain a glass plate having a thickness of 800 μm.

化学 Using Glasses A to E, chemically strengthened glasses of the following Examples 1 to 15 were produced and evaluated. Examples 1, 2, 5, 6, 8, 11, and 14 are Examples, and Examples 3, 4, 7, 9, 10, 12, 13, and 15 are Comparative Examples.

[Chemical strengthening treatment]
(Example 1)
A glass plate made of glass A is immersed in 450% sodium nitrate 100% strengthening salt (sodium-containing strengthening salt) at 450 ° C. for 1 hour, and then immersed in 450 ° C. potassium nitrate 100% (potassium-containing strengthening salt) for 1 hour and cooled in cold water And washed.
(Examples 2 to 15)
Using the glass shown in the glass column of Table 2, the time of immersion in the sodium-containing reinforcing salt is the time (unit: hours) shown in processing time 1 of Table 2, and the time of immersing in the potassium-containing reinforcing salt is processing time 2 The chemically strengthened glasses of Examples 2 to 15 were obtained in the same manner as in Example 1 except that the time (unit: hours) shown in (1) was used.

[Measurement of stress profile]
The stress value was measured using an optical waveguide surface stress meter FSM-6000 and a scattered light photoelastic stress meter SLP-1000 manufactured by Orihara Seisakusho. Table 2 shows CS ₀ (unit: MPa), D (unit: μm), x (unit: MPa / μm), y (unit: MPa / μm), x / y, z (unit: MPa / μm), and DOL (unit: μm) is shown. FIG. 1 is a stress profile obtained by using FSM-6000 for the chemically strengthened glass of Example 1, and FIG. 2 is a stress profile obtained by using SLP-1000. FIG. 3 shows the result of the synthesis.

In Example 4 where x / y is 1, delayed chipping is apt to occur, which causes a decrease in yield during polishing. In Example 5 in which the same glass B was strengthened, the above-described problem did not occur. This may be because the reinforcement processing time is appropriate and x / y is as low as 0.19.
In both Examples 2 and 3, glass A was chemically strengthened. In Example 2, the compression stress layer was introduced as deep as 180 μm, but the processing time 2 was too long. In Example 3, since the DOL is as shallow as 27 μm, it is easily broken when dropped on sand.

Although the present invention has been described in detail with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention. This application is based on a Japanese patent application filed on Jul. 3, 2018 (Japanese Patent Application No. 2018-126894), which is incorporated by reference in its entirety. Also, all references cited herein are incorporated in their entirety.

Claims

Chemically strengthened glass having a compressive stress layer on the glass surface,
Compressive stress value CS 0 of the glass surface to be measured using the optical waveguide surface stress meter is not less than 500 MPa,
The depth from the glass surface at the position where the compressive stress value measured using the optical waveguide surface stress meter becomes 0 is D [unit: μm], and the depth from the glass surface measured using the optical waveguide surface stress meter. Saga (D / 2) a compressive stress value at the position of the CS 2, the absolute value and the depth of the inclination x of the stress profile from the glass surface to be determined by the following equation to a depth of (D / 2) (D / 2) to the depth D, the ratio | x | / | y | of the gradient y of the stress profile from 0 to 0.8 is 0 to 0.8,
A chemically strengthened glass having a compressive stress layer depth DOL measured using a scattered light photoelastic stress meter of 50 μm or more.
x = (CS 2 -CS 0 ) / ((D / 2) -0) = 2 × (CS 2 -CS 0 ) / D
y = (0−CS 2 ) / (D− (D / 2)) = − 2 × CS 2 / D
From the compressive stress value CS 1 at a position at a depth of 1 μm from the glass surface measured using an optical waveguide surface stress meter and the above-described CS 0 , the stress profile from the glass surface to a depth of 1 μm obtained from the following equation: 2. The chemically strengthened glass according to claim 1, wherein the slope z is at least -100 MPa / μm and less than 0.
z = (CS 1 -CS 0 ) / (1 μm-0 μm) = (CS 1 -CS 0 ) / 1 μm
The chemically strengthened glass according to claim 1 or 2, wherein the glass has a thickness of 2000 µm or less.
The glass composition of the central part in the thickness direction of the chemically strengthened glass contains 50% or more of SiO 2 and 5% or more of Al 2 O 3 in terms of mol% on an oxide basis,
The total content of Li 2 O, Na 2 O and K 2 O is 5% or more;
And the content of Li 2 O, the ratio of Li 2 O, the total content of Na 2 O and K 2 O is 0.5 or more, according to any one of claims 1 to 3 Chemically tempered glass.
When the mother composition of the chemically strengthened glass is 50 to 80% of SiO 2 in terms of mol% on an oxide basis,
Al 2 O 3 5 to 25%,
B 2 O 3 0-10%,
P 2 O 50 0-10%,
Li 2 O 2-20%,
Na 2 O 0.5-10%,
K 2 O 0-5%,
MgO + ZnO + CaO + SrO + BaO 0-15%,
ZrO 2 + TiO 2 0-5%,
The chemically strengthened glass according to any one of claims 1 to 4, wherein
The method for producing a chemically strengthened glass according to any one of claims 1 to 5, wherein
Immersing the glass plate in a potassium-containing reinforcing salt at 400 ° C. to 500 ° C. for 1 to 8 hours;
And thereafter bringing the glass plate to a temperature of 300 ° C. or less,
The method for producing chemically strengthened glass, wherein the potassium-containing strengthening salt contains 70% by mass or more of potassium ions, with the mass of metal ions contained in the strengthening salt being 100% by mass.
The glass composition of the glass plate before the chemical strengthening contains 50% or more of SiO 2 and 5% or more of Al 2 O 3 in terms of mol% on an oxide basis,
The total content of Li 2 O, Na 2 O and K 2 O is 5% or more;
And the content of Li 2 O, the ratio of the total content of Li 2 O, Na 2 O and K 2 O is 0.5 or more, a manufacturing method of chemically strengthened glass according to claim 6.