JP7255594B2 - Chemically strengthened glass and its manufacturing method - Google Patents

Description

The present invention relates to chemically strengthened glass and its manufacturing method.

Chemically strengthened glass is used for the cover glass of mobile terminals and the like.
Chemically strengthened glass is made by contacting 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 to the surface of the glass. It is glass with a stress layer. The strength of chemically strengthened glass strongly depends on the stress profile represented by the compressive stress value with the depth from the glass surface as a variable.

It is believed that a cover glass for a mobile terminal or the like is less likely to crack due to bending by increasing the compressive stress value on the glass surface.
In addition, it is thought that by increasing the depth of the compressive stress layer and forming the compressive stress layer even in the deep part of the glass, it is possible to prevent cracking even when receiving a large impact.

However, when a compressive stress layer is formed on the surface of glass, a tensile stress layer is inevitably formed inside the glass. If the value of the internal tensile stress is large, when the chemically strengthened glass is broken, it is likely to be violently crushed and the fragments are likely to scatter. Therefore, a method of increasing the surface compressive stress and the compressive stress depth while decreasing the internal tensile stress value is being studied.

Patent Literature 1 shows a typical stress profile when ion exchange treatment is performed twice. The profile is composed of two linear components: a straight line representing the stress profile from the glass surface to a point X at a certain depth, and a straight line representing the stress profile from the point X to the point where the stress becomes zero. (Patent Document 1, FIG. 8). By using such a stress profile, it is possible to increase the surface compressive stress, increase the compressive stress depth, and reduce the internal tensile stress value.

WO2015/127483

In a typical stress profile when the ion exchange treatment is performed twice, the stress in the vicinity of the glass surface changes greatly with even a small change in the depth from the glass surface.
By the way, in the process of actually manufacturing a cover glass or the like for a mobile terminal, the surface of the chemically strengthened glass may be polished for the purpose of erasing scratches on the surface. However, in chemically strengthened glass having a stress profile in which a small change in depth from the glass surface causes a large change in stress, a slight difference in the amount of polishing causes a large difference in surface compressive stress after polishing. This has caused a decrease in yield.

The present invention provides a chemically strengthened glass that has high strength and shows little change in properties 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, and the optical waveguide surface stress meter is D [unit: μm] is the depth from the glass surface at the position where the compressive stress value measured using the optical waveguide surface stress meter is 0, and the depth from the glass surface measured using the optical waveguide surface stress meter is (D / 2 ) is the compressive stress value at the position of CS ₂ , the absolute value of the slope x of the stress profile from the glass surface to the depth of (D / 2) obtained by the following formula, and the depth from the depth (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 compressive stress layer depth DOL measured using a scattered light photoelastic stress meter is 50 μm. Provided is a chemically strengthened glass that is the above.
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

The chemically strengthened glass of the present invention is obtained by the following formula from the compressive stress value CS ₁ and CS ₀ at a position at a depth of 1 μm from the glass surface measured using an optical waveguide surface stress meter. 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
It may also be plate-shaped with a thickness of 2000 μm or less.
Further, the glass composition of the central portion 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% based on oxides, Li ₂ O, Na ₂ The total content of O and K ₂ O is 5% or more, and the ratio of the content of Li ₂ O to the total content of Li ₂ O, Na ₂ O and K ₂ O is 0.5 or more.

In the chemically strengthened glass of the present invention, the base composition of the chemically strengthened glass is SiO ₂ 50 to 80%, Al ₂ O ₃ 5 to 25%, B ₂ O ₃ 0 to 10%, in mol% display based on oxides. 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%, can be

The method for producing 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 then bringing the glass plate to a temperature of 300 ° C. or less. Alternatively, the potassium-containing strengthening salt may contain 70% by mass or more of potassium ions based on 100% by mass of metal ions contained in the strengthening salt.
Further, in the above method for producing chemically strengthened glass of the present invention, the glass composition before chemical strengthening of the glass plate contains 50% or more SiO ₂ and 5% or more Al ₂ O ₃ in terms of mol% based on oxides. and 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 and the total content of Li ₂ O, Na ₂ O and K ₂ O Amount ratio may be 0.5 or more.

According to the present invention, it is possible to obtain chemically strengthened glass that has high strength, suppresses the scattering of fragments when broken, and has small changes in properties even when the surface is polished after chemical strengthening.

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

In this specification, unless otherwise specified, the term "to" used to indicate a numerical range includes the numerical values before and after it as lower and upper limits.

As used herein, the term "stress profile" refers to compressive stress values from the surface of the glass to the center, expressed with the depth from the surface of the glass as a variable. Also, the "compressive stress depth (DOL)" is the depth at which the compressive stress value is zero in the stress profile.
"Internal tensile stress (CT)" refers to the tensile stress value at a depth of half the plate thickness t of the glass.

As used herein, "chemically strengthened glass" refers to glass after chemical strengthening treatment, and "chemically strengthened glass" refers to glass before chemical strengthening treatment.
In this specification, the glass composition of the chemically strengthened glass is sometimes referred to as the "base composition of the chemically strengthened glass". The glass composition of the portion deeper than the DOL of the chemically strengthened glass is the mother composition of the chemically strengthened glass, except for the case of extreme ion exchange treatment.

In this specification, unless otherwise specified, the glass composition is expressed in terms of mol percentage based on oxide, and mol% is simply expressed as "%".
In addition, the phrase "substantially does not contain" with respect to the glass composition means that it is below the level of impurities contained in the raw materials and the like, that is, it is not intentionally contained. Specifically, it is less than 0.1%, for example.

<Glass destruction>
When a glass plate receives an impact and bends, if the amount of bending increases, a large tensile stress is applied to the glass surface, causing the glass to break. In this specification, such failure is called "glass failure due to bending mode". In the chemically strengthened glass of the present invention (hereinafter sometimes referred to as "this strengthened glass"), a large compressive stress is formed on the surface of the glass, so glass breakage due to bending mode is suppressed.
On the other hand, when a small and hard object collides with the glass plate, stress due to the impact is generated inside the glass plate, thereby breaking the glass plate from the inside. In this specification, such breakage is referred to as "impact mode glass breakage". In this tempered glass, since a compressive stress layer is formed even inside the glass plate, glass breakage due to impact mode is suppressed.
If the compressive stress value on the glass surface is large and a compressive stress layer is formed even inside the glass plate, both glass breakage due to bending mode and impact mode will be suppressed, making the glass extremely difficult to break. should be. However, when a compressive stress layer is formed inside the glass plate, internal tensile stress is generated to offset it. If the internal tensile stress is large, severe breakage occurs when the glass breaks, and the fragments scatter.
In this tempered glass, the stress profile inside the glass is appropriately adjusted, so that both the glass breakage due to bending mode and the glass breakage due to impact mode are suppressed, and when broken, the scattering of fragments is small.

As a method of obtaining chemically strengthened glass that suppresses both glass breakage due to bending mode and glass breakage due to impact mode and that scatters less fragments when broken, lithium aluminosilicate glass is ion-exchanged to give different tilts. Methods are known to produce two stress profiles.

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, after ion exchange treatment using a strengthening salt containing sodium ions, chemical strengthening can be performed by ion exchange treatment using a strengthening salt containing potassium ions.
According to these methods, a relatively large compressive stress is generated in a region relatively shallow from the surface due to ion exchange of sodium ions and potassium ions, and a relatively small compression stress is generated in a deeper region due to ion exchange of lithium ions and sodium ions. stress occurs.
Sodium ions with a relatively small ionic radius diffuse rapidly into the glass, whereas potassium ions with a relatively large ionic radius diffuse slowly into the glass. Therefore, ion exchange between sodium ions and potassium ions is difficult to occur even if ion exchange between lithium ions and sodium ions occurs in a deep region.

In the region near the surface where ion exchange between sodium ions and potassium ions occurs, potassium ions with a large ionic radius enter the glass, causing a large compressive stress. At greater depths, ion exchange between lithium ions and sodium ions produces relatively small compressive stresses in the deeper regions. The chemically strengthened glass obtained in this way has a stress profile that is steep in the vicinity of the surface and relatively gentle in the deep portion, bending 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 less likely to shatter when subjected to a strong impact, and is less likely to scatter into fragments when broken.

However, with this stress profile, the compressive stress value on the outermost surface becomes extremely large, so that so-called "delayed chipping" tends to occur near the surface. Delayed chipping is a phenomenon in which the edge of a portion where excessive stress has been introduced by chemical strengthening is chipped when a slight force is applied. Further, when the surface of chemically strengthened glass having such a stress profile is polished, even a slight difference in the amount of polishing causes a large difference in the stress on the outermost surface.
Since the tempered glass has an adjusted stress profile near the glass surface, these problems are less likely to occur.

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

The reasons for measuring the compressive stress using two types of devices are 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, a layer in which sodium ions in the glass are substituted with potassium ions has a lower refractive index from the surface toward the inside, so stress can be measured using an optical waveguide surface stress meter. However, a layer in which sodium ions are substituted for lithium ions in the glass does not produce such a refractive index distribution, so stress cannot be measured by the optical waveguide surface stress meter.
FIG. 1 is an example of a stress profile obtained by measuring the stress of this tempered glass using an optical waveguide surface stress meter. The dotted line portion of the graph actually has stress due to ion exchange between lithium ions and sodium ions, but the stress cannot be measured by the optical waveguide surface stress meter.

A stress measurement method using a scattered light photoelastic stress meter can theoretically measure stress without depending on the refractive index distribution. However, since the scattered light photoelastic stress meter is affected by light scattering on the glass surface, it cannot accurately measure the stress near the glass surface. FIG. 2 is an example of a stress profile obtained by measuring the stress of the tempered glass using a scattered light photoelastic stress meter. The dashed portion of the graph is unreliable 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 synthesizing 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, FSM-6000 manufactured by Orihara Seisakusho, for example, can be used. Using FSM-6000 and accompanying software FsmV enables highly accurate stress measurements.
As the scattered light photoelastic stress meter, for example, SLP-1000 manufactured by Orihara Seisakusho Co., Ltd. can be used. When FSM-6000 is used as an optical waveguide surface stress meter and SLP-1000 is used as a scattered light photoelastic stress meter, data can be easily synthesized using dedicated software.

<Chemical strengthened glass>
The tempered glass is preferably plate-like and usually flat, but may be curved.

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 in order to increase strength, but is preferably 2000 μm or less, more preferably 1000 μm or less, in order to reduce weight.

It is preferable that this tempered glass has compressive stress due to ion exchange between sodium ions and potassium ions in a relatively shallow region from the surface, and compressive stress due to ion exchange between lithium ions and sodium ions in a deeper region. Such chemically strengthened glass has a stress profile that bends in two stages, with a steep surface near the surface and a relatively gentle deep portion. This is because it is difficult to

This tempered glass has a compressive stress value _CS0 of 500 MPa or more on the glass surface measured using an optical waveguide surface stress meter, and therefore has a high strength. For example, in FIG. 1, the CS value of the glass surface indicated by arrow a is _CS0 . CS ₀ is more preferably 900 MPa or higher, still more preferably 950 MPa or higher, and particularly preferably 1000 MPa or higher.
It is preferable that the present tempered glass has a compressive stress value _CS0 of 1200 MPa or less on the surface of the glass, since delayed chipping is suppressed. CS ₀ is more preferably 1100 MPa or less, more preferably 1050 MPa or less.

The tempered glass preferably has a depth D [unit: μm] of 3 μm or more at which the “compressive stress value measured with an optical waveguide surface stress meter” becomes zero, since breakage due to bending mode can be suppressed. In order to suppress fracture due to bending mode, D is more preferably 4 μm or more, further preferably 5 μm or more. In order to suppress the fracture due to bending mode, it is better if D is about 10 μm. If D is too large, the tensile stress occurring in the glass center layer will increase. In order to prevent severe breakage due to this tensile stress, D is preferably 20 μm or less, more preferably 15 μm or less, and even more preferably 10 μm or less.

For example, in FIG. 1, D is the depth of "the point where the CS value becomes 0" indicated by the arrow d. As described above, when a reinforced layer formed by ion exchange of lithium ions and sodium ions is formed inside the glass, a reinforced layer formed by ion exchange of lithium ions and sodium ions is formed near the point where the CS value becomes 0. Therefore, the optical waveguide surface stress meter cannot measure the stress accurately. D is considered to represent the depth to which potassium ions have diffused.

This tempered glass has a stress profile slope x [unit: MPa / μm] from the glass surface to a depth of (D / 2) [unit: μm] measured using an optical waveguide surface stress meter is -200 MPa / μm. It is preferable in it being more than 200 MPa/micrometer or less. The slope x is more preferably −100 MPa/μm or more and 100 MPa/μm or less, and more preferably −70 MPa/μm or more and 70 MPa/μm or less. The smaller the absolute value of x, the thicker the layer with the appropriate compressive stress value and the better the properties when the surface is polished.
Also, the slope x is preferably a negative value. The highest compressive stress is required for the glass surface, which requires high compressive stress to suppress fracture due to bending mode. If there is a positive portion in the slope of the stress profile, there will be places where excessive stress is introduced inside the glass, making it easier for delayed chipping to occur. more likely 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 depth of (D/2) from the glass surface indicated by arrow c.
x is determined by the following formula from D, the compressive stress value _CS0 of the glass surface, and the compressive stress value _CS2 at a depth of (D/2) from the glass surface.
x=(CS ₂ -CS ₀ )/((D/2)-0)
=2×(CS ₂ −CS ₀ )/D

In this tempered glass, if the slope 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, bending This is preferable because a thin layer of high compressive stress, which is necessary for suppressing modal destruction, can be formed as the outermost layer. The smaller the slope y, the better, but it is usually -500 MPa/μm or more.

For example, in FIG. 1, y is the slope of the stress profile from a point at a depth D/2 from the glass surface indicated by arrow c to a point at depth D indicated by arrow d.
Here, y is obtained from the above D and _CS2 by the following formula.
y=(0−CS ₂ )/(D−(D/2))
=−2×CS ₂ /D

In this tempered glass, when the ratio |x|/|y| In addition, it is preferable because it is possible to form a thick stress region suitable for suppressing both delayed chipping and fracture due to bending mode. More preferably, it is 0.6 or less. The minimum value of |x|/|y| is zero. That is, |x|/|y| is preferably 0 to 0.8, more preferably 0 to 0.6.
Also, x is preferably 0 or less, and y is preferably a negative value, so x/y is preferably 0 to 0.8, more preferably 0 to 0.6. If x/y is a positive value, the smaller the better.

When the slope z of the stress profile from the glass surface to a depth of 1 μm measured by an optical waveguide surface stress meter is -100 MPa/μm or more, this tempered glass suppresses both delayed chipping and fracture due to bending mode. This is preferable because it increases the thickness of the suitable stress area. 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, z is the slope of the stress profile from the glass surface indicated by arrow a to the point 1 μm deep from the glass surface indicated by arrow b.
Assuming that the 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 formula.
z=(CS ₁ -CS ₀ )/(1 μm-0 μm)
= (CS ₁ -CS ₀ )/1 μm

In this tempered glass, the compressive stress depth DOL measured with a scattered light photoelastic stress meter is preferably 50 μm or more. For example, in FIG. 2, the depth at which the CS value becomes 0 indicated by arrow e is DOL. A typical asphalt protrusion is about 50 μm in size, so in order to prevent cracking when the glass plate collides with the asphalt, it is recommended that compressive stress is formed to a depth of 50 μm from the surface layer of the glass. preferable. DOL/t is preferably 0.1 or more, more preferably 0.12 or more, and still more preferably 0.14 or more when the plate thickness is t μm. On the other hand, if the DOL is too large with respect to t, an excessive tensile stress is generated in the sheet thickness center layer, and severe breakage occurs during scratching. 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 ions and sodium ions are exchanged, and D is determined by the depth at which sodium ions and potassium ions are exchanged. 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 lithium aluminosilicate glass (hereinafter referred to as "this glass for strengthening"). Except for the case where extreme chemical strengthening treatment is applied, the composition of the chemically strengthened glass is the same as the glass composition of the central portion in the thickness direction of the chemically strengthened glass, that is, the following composition of the chemically strengthened glass The description also applies to the composition of the central portion in the thickness direction of the chemically strengthened glass.
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 % based on oxides, and the total content of Li ₂ O, Na ₂ O and K ₂ O is 5% or more, and the ratio of the content of Li ₂ O to the total content of Li ₂ O, Na ₂ O and K ₂ O (Li ₂ O/(Li ₂ O + Na ₂ O + K ₂ O)) is 0.5 or more.

The tempering glass more preferably has the following composition expressed in terms of mol percentage based on oxides.
_SiO2 50-80%, _{Al2O3 5-25} %, _B2O3 0-10%, _{P2O5 0-10 %} , _Li2O 2-20%, _Na2O 0.5-10 %, K ₂ O 0-5%.
In addition, MgO + ZnO + CaO + SrO + BaO (total content of MgO, ZnO, CaO, SrO, and BaO) is preferably 0 to 15%, and ZrO ₂ +TiO ₂ (total content of ZrO ₂ and TiO ₂ ) is 0 to 5%. is preferred.
Such glasses tend to form favorable stress profiles through chemical strengthening treatments. This preferred glass composition will be described below.

_SiO2 is a component that constitutes the skeleton of glass. It is also a component that increases chemical durability and reduces the occurrence of cracks when the glass surface is scratched. The content of SiO ₂ is preferably 50% or more, more preferably 55% or more, even more preferably 58% or more.
In order to improve the meltability of the glass, the content of SiO ₂ is preferably 80% or less, more preferably 75% or less, even more preferably 70% or less.

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

Although B ₂ O ₃ is not essential, it may be contained in order to improve meltability during glass production. In order to reduce the slope of the stress profile near the surface of the chemically strengthened glass, it is preferable to contain B ₂ O ₃ , and in that case the content is preferably 0.5% or more, more preferably 1% or more, More preferably, it is 2% or more.
Since B ₂ O ₃ is a component that facilitates stress relaxation after chemical strengthening, the content of B ₂ O ₃ is preferably 10% or less, more preferably 10% or less, in order to prevent a decrease in surface compressive stress due to stress relaxation. is 8% or less, more preferably 5% or less, particularly preferably 3% or less.

Li ₂ O is a component that forms surface compressive stress by ion exchange, and is an essential component of lithium aluminosilicate glass. Chemically strengthening the lithium aluminosilicate glass results in a chemically strengthened glass with a favorable stress profile. 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 compressive stress layer depth DOL.
In order to suppress the occurrence of devitrification during glass production or bending, the Li ₂ O content 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 molten salt containing potassium, and is a component that improves the meltability of the glass. The content of Na ₂ O is preferably 0.5% or more, more preferably 1% or more, and even more preferably 1.5% or more.
Also, the content of Na ₂ O is preferably 10% or less, more preferably 8% or less, still more preferably 6% or less.

K ₂ O is not essential, but may be contained in order to improve the meltability of the glass and suppress devitrification. The K ₂ O content is preferably 0.1% or more, more preferably 0.5% or more, and still more preferably 1% or more.
Also, the content of K ₂ O is preferably 5% or less, more preferably 3% or less, 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 all components that lower the melting temperature of the glass, and the total content is preferably 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 20% or less, more preferably 18% or less, in order to maintain the strength of the glass.

Alkaline earth metal oxides such as MgO, CaO, SrO, BaO, and ZnO are all components that increase the meltability of glass, but they tend to reduce 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 any one of MgO, CaO, SrO, BaO, and ZnO is contained, 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 improve the ion exchange performance, it is preferably 10% or less, more preferably 8% or less.

When CaO is contained, the content is preferably 0.5% or more, more preferably 1% or more. In order to improve the ion exchange performance, it is preferably 5% or less, more preferably 3% or less.

When SrO is included, the content is preferably 0.5% or more, more preferably 1% or more. In order to improve the ion exchange performance, it is preferably 5% or less, more preferably 3% or less.

When BaO is included, the content is preferably 0.5% or more, more preferably 1% or more. In order to improve the ion exchange performance, it is preferably 5% or less, more preferably 1% or less, and even more preferably not substantially contained.

ZnO is a component that improves the meltability of glass and may be contained. When ZnO is contained, the content is preferably 0.2% or more, more preferably 0.5% or more. In order to increase the weather resistance of the glass, the ZnO content 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 included, the content is preferably 0.1% or more. In order to suppress devitrification during melting, the content of TiO ₂ is preferably 5% or less, more preferably 1% or less, and further preferably substantially free.

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

Also, 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 breakage of chemically strengthened glass and may be contained. When these components are contained, the content of each is preferably 0.5% or more, more preferably 0.5% or more, still more preferably 1% or more, particularly preferably 1.5% or more, and most preferably 1% or more. Preferably it is 2% or more.

Also, 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 devitrify during melting, and deterioration of the quality of the chemically strengthened glass can be prevented. The contents of Y ₂ O ₃ , La ₂ O ₃ and Nb ₂ O ₅ are each preferably 7% or less, more preferably 6% or less, even more preferably 5% or less, particularly preferably 4% or less, most preferably is 3% or less.

Ta ₂ O ₅ and Gd ₂ O ₃ may be contained in small amounts in order to suppress breakage of the chemically strengthened glass, but since the refractive index and reflectance increase, the content of each of these is preferably 1% or less. , is more preferably 0.5% or less, and it is even more preferable that it is substantially free.

P ₂ O ₅ may be included to improve ion exchange performance. When P ₂ O ₅ is included, the content is preferably 0.5% or more, more preferably 1% or more. In order to improve 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 within a range that does not impede the achievement of the desired chemical strengthening properties. Examples of coloring components include _Co3O4 , _MnO2 , _Fe2O3 , NiO, CuO, _{Cr2O3 , V2O5 , Bi2O3 , SeO2} , _{TiO2 , CeO2 ,} Er2 _. O ₃ and Nd ₂ O ₃ are mentioned. These may be used alone or in combination.

The total content of coloring components is preferably 7% or less. Thereby, devitrification of the glass can be suppressed. The content of the coloring component is more preferably 5% or less, still more 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 preferred that these components are not substantially contained.

In addition, SO ₃ , chlorides, fluorides, and the like may be appropriately contained as clarifiers during glass melting. As ₂ O ₃ is preferably not substantially 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 substantially contained.

The glass transition temperature (Tg) of the 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.
Moreover, Tg is preferably 700° C. or less because the ion diffusion rate increases during chemical strengthening. The Tg is more preferably 650° C. or lower, still more preferably 600° C. or lower, in order to easily obtain a deep DOL.

The Young's modulus of the tempering glass is preferably 70 GPa or more. The higher the Young's modulus, the more difficult it is for the fragments to scatter when the tempered glass is broken. Therefore, the Young's modulus is more preferably 75 GPa or more, more preferably 80 GPa or more. On the other hand, if the Young's modulus is too high, diffusion of ions during chemical strengthening tends to be slow, making it 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 higher. The higher the Vickers hardness of the glass for chemical strengthening, the higher the Vickers hardness after chemical strengthening tends to be, and the chemically strengthened glass is less likely to be damaged when dropped. Therefore, the Vickers hardness of the glass for chemical strengthening is more preferably 600 or higher, more preferably 625 or higher.
The Vickers hardness after chemical strengthening is preferably 600 or higher, more preferably 625 or higher, and even more preferably 650 or higher.

The higher the Vickers hardness, the more difficult it is to be scratched, which is preferable. A glass with too high a Vickers hardness tends to be difficult to obtain sufficient ion exchangeability. Therefore, the Vickers hardness is preferably 800 or less, more preferably 750 or less.

The fracture toughness value of the tempering glass is preferably 0.7 MPa·m ^1/2 or more. The greater the fracture toughness value, the more likely it is that the chemically strengthened glass will be less likely to scatter when broken. The fracture toughness value is more preferably 0.75 MPa·m ^1/2 or more, 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 coefficient of thermal expansion (α) of the tempering glass at 50° C. to 350° C. is preferably 100×10 ⁻⁷ /° C. or less. When the average expansion coefficient (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 95×10 ⁻⁷ /° C. or less, more preferably 90×10 ⁻⁷ /° C. or less.
In order to suppress warping of chemically strengthened glass, the smaller the average coefficient of thermal expansion (α) is, the better, but it is usually 60×10 ⁻⁷ /° C. or higher.

In the tempering glass, the temperature (T ₂ ) at which the viscosity becomes 10 ² dPa·s is preferably 1750° C. or less, more preferably 1700° C. or less, and even more preferably 1680° C. or less. _T2 is typically 1400° C. or higher.

In the 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 even more preferably 1250°C or lower. _T4 is usually above 1000°C.

<Method for manufacturing chemically strengthened glass>
The tempered glass can be produced, for example, by subjecting the glass for chemical strengthening having the composition described above to chemical strengthening treatment.
Chemically strengthened glass can be produced, for example, using the following general glass production method. The following manufacturing method is an example of manufacturing plate-shaped chemically strengthened glass, but the glass for chemical strengthening may have a shape other than a plate-like shape.

In order to obtain a glass having a preferable composition, glass raw materials are appropriately mixed and heated and melted in a glass melting furnace. Thereafter, the glass is homogenized by bubbling, stirring, addition of a clarifier, or the like, formed into a glass plate having a predetermined thickness, and slowly cooled. Alternatively, it may be molded into a plate by a method of molding into a block, slowly cooling it, and then cutting it.

Examples of methods for forming a plate include a float method, a press method, a fusion method, and a down-draw method. In particular, the float method is preferable when manufacturing a large glass plate. Continuous molding methods other than the float method, such as the fusion method and the down-draw method, are also preferred.

The glass ribbon obtained by molding is ground and polished as necessary to form a glass plate. In addition, when cutting the glass plate into a predetermined shape and size or chamfering the glass plate, if the glass plate is cut or chamfered before the chemical strengthening treatment described later, the chemical strengthening treatment can be performed. is preferable because a compressive stress layer is also formed on the end face by .

Then, chemically strengthened glass is obtained by washing and drying the formed glass plate after performing chemical strengthening treatment.

<Chemical strengthening treatment>
In the chemical strengthening treatment, the glass is brought into contact with a metal salt by a method such as immersion in a melt of a metal salt (such as potassium nitrate) containing metal ions with a large ionic radius (typically sodium ions or potassium ions). , small ionic radius metal ions in glasses (typically lithium or sodium ions) and large ionic radius metal ions in metal salts (typically sodium or potassium ions for lithium ions and potassium ions for sodium ions).

A method utilizing “Li—Na exchange” in which lithium ions in the glass are exchanged for sodium ions is preferable because the chemical strengthening processing speed is high. Further, in order to form a large compressive stress by ion exchange, a method using "Na--K exchange" in which sodium ions in the glass are exchanged for potassium ions is preferable.
It is more preferable to combine the methods of performing "Li--Na exchange" and "Na--K exchange" because 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 “Li—Na exchange”.

Molten salts for chemical strengthening include nitrates, sulfates, carbonates, chlorides, and the like. Examples of nitrates include lithium nitrate, sodium nitrate, potassium nitrate, cesium nitrate, and silver nitrate. Sulfates include, for example, lithium sulfate, sodium sulfate, potassium sulfate, cesium sulfate, and silver sulfate. Carbonates include, for example, lithium carbonate, sodium carbonate, potassium carbonate and the like. Chlorides include, for example, lithium chloride, sodium chloride, potassium chloride, cesium chloride, and silver chloride. These molten salts may be used alone, or may be used in combination.

More specifically, the present tempered glass can be produced by the tempering method described below (hereinafter referred to as "the present tempering method").
This strengthening treatment method has a step of immersing a glass sheet in a potassium-containing strengthening salt. The potassium-containing strengthening salt is preferably a salt containing 70% by mass or more of potassium ions, more preferably 90% by mass or more, based on the mass of metal ions contained in the strengthening salt being 100% by mass. A high compressive stress layer can be formed on the surface layer by using such a strengthening salt. As the potassium-containing strengthening salt, a potassium-containing nitrate is preferable from the viewpoint of ease of handling such as boiling point and danger.
The strengthening salt preferably contains potassium nitrate, and may contain nitrates of alkali metals and alkaline earth metals such as sodium nitrate and magnesium nitrate as components other than potassium nitrate. In addition, impurity levels of lithium may be contained.

In this strengthening treatment method, the glass plate is preferably immersed in a potassium-containing strengthening salt at 400°C to 500°C. It is preferable that the temperature of the potassium-containing strengthening salt is 400° C. or higher because ion exchange proceeds easily. In addition, stress relaxation tends to reduce the |x|/|y| ratio in the stress profile. More preferably, it is 420° C. or higher. Moreover, it is preferable that the temperature of the potassium-containing strengthening salt is 500° C. or less, since excessive stress relaxation of the surface layer can be suppressed. More preferably, it is 480° C. or less.

Further, the time for which the glass is immersed in the potassium-containing strengthening salt is preferably 1 hour or more because the surface compressive stress increases. In addition, stress relaxation tends to reduce the |x|/|y| ratio in the stress profile. The immersion time is more preferably 2 hours or longer, and still more preferably 3 hours or longer. If the immersion time is too long, not only the productivity is lowered, but also the compressive stress may be lowered 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 even more preferably 4 hours or less.

Before the glass plate is immersed in the potassium-containing strengthening salt, it may be immersed in another strengthening salt. Other fortifying salts are preferably sodium-containing fortifying salts. The sodium-containing strengthening salt is preferably sodium nitrate-strengthening salt from the viewpoint of ease of handling, like potassium nitrate. Moreover, it is preferable to contain 70% by mass or more of sodium ions, with the mass of metal ions contained in the strengthening salt being 100% by mass.

After the glass plate is immersed in the potassium-containing strengthening salt, it is preferably kept at a temperature of 300° C. or less. This is because when the temperature exceeds 300° C., the compressive stress generated by the ion exchange treatment is reduced due to the relaxation phenomenon. The holding temperature after the glass plate is immersed in the potassium-containing strengthening salt is more preferably 250° C. or lower, still more preferably 200° C. or lower.

As for the treatment conditions of the chemical strengthening treatment, time, temperature, and the like may be appropriately selected in consideration of the properties and composition of the glass, the type of molten salt, and the like.

The chemically strengthened glass of the present invention is particularly useful as a cover glass for mobile devices such as mobile phones and smart phones. Furthermore, it is also useful for cover glass of display devices such as televisions, personal computers, touch panels, etc., walls of elevators, walls of buildings such as houses and buildings (full-surface displays), which are not intended for portable use. It is also useful as building materials such as window glass, table tops, interiors of automobiles, airplanes, etc., and cover glass for them, as well as applications such as housings having curved surfaces.

EXAMPLES The present invention will be described below with reference to Examples, but the present invention is not limited to these Examples.
Glass raw materials were mixed so as to have the compositions of glass A to glass E shown in Table 1 in terms of molar percentages based on oxides, and weighed to give 400 g of glass. Then, the mixed raw material was placed in a platinum crucible and placed in an electric furnace at 1500 to 1700° C., melted for about 3 hours, degassed and homogenized.

The resulting molten glass was poured into a metal mold, held 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.

Using glasses A to E, chemically strengthened glasses of Examples 1 to 15 below 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 was immersed in 100% sodium nitrate strengthening salt (strengthening salt containing sodium) at 450°C for 1 hour, then immersed in 100% potassium nitrate (strengthening salt containing potassium) at 450°C for 1 hour, and immersed in cold water. was washed.
(Examples 2-15)
Using the glass shown in the glass column of Table 2, the time of immersion in the sodium-containing strengthening salt is the time (unit: hour) shown in treatment time 1 in Table 2, and the time of immersion in the potassium-containing strengthening salt is treatment time 2. Chemically strengthened glasses of Examples 2 to 15 were obtained in the same manner as in Example 1, except that the time (unit: hour) shown in .

[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 the stress profile obtained with FSM-6000 and FIG. 2 is the stress profile obtained with SLP-1000 for the chemically strengthened glass of Example 1. FIG. FIG. 3 shows the synthesized result.

Example 4, in which x/y is 1, tends to cause delayed chipping, resulting in a decrease in yield during polishing. Example 5, in which the same glass B is tempered, does not suffer from the above problem. This may be due to the appropriate tempering time and low x/y of 0.19.
In both Examples 2 and 3, the glass A was chemically strengthened, but in Example 2, the compressive stress layer was introduced to a depth of 180 μm with a DOL, whereas the treatment time 2 was too long. Since Example 3 has a shallow DOL of 27 μm, it easily cracks 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 (Japanese Patent Application No. 2018-126894) filed on July 3, 2018, the entirety of which is incorporated by reference. Also, all references cited herein are incorporated in their entirety.

Claims (7)

A chemically strengthened glass having a compressive stress layer on the glass surface,
The base composition of the chemically strengthened glass is represented by mol% based on oxides
SiO ₂ 50-80%,
Al ₂ O ₃ 13-25%,
B2O3 0.5-10 % _{, _}
P2O5 0-10 % _{, _}
Li ₂ O 2-20%,
Na ₂ O 0.5-10%,
K2O 0-5% _,
MgO+ZnO+CaO+SrO+BaO 0-15%,
ZrO ₂ +TiO ₂ 0-5%,
and
The compressive stress value _CS0 of the glass surface measured using an optical waveguide surface stress meter is 500 MPa or more,
D [unit: μm] is the depth from the glass surface at the position where the compressive stress value measured using the optical waveguide surface stress meter becomes 0, and the depth from the glass surface measured using the optical waveguide surface stress meter Assuming that the compressive stress value at the position of Saga (D / 2) is CS ₂ , the absolute value of the slope x of the stress profile from the glass surface to the depth of (D / 2) obtained by the following formula, and the depth (D / 2) to the absolute value of the slope y of the stress profile from the depth D |x|/|y| is 0 to 0.8,
Chemically strengthened glass having a compressive stress layer depth DOL of 50 μm or more measured using a scattered light photoelastic stress meter.
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 Stress profile from the glass surface to a depth of 1 μm obtained by the following formula from the compressive stress value CS ₁ and CS ₀ at a position 1 μm deep from the glass surface measured using an optical waveguide surface stress meter. The chemically strengthened glass according to claim 1, wherein the slope z is −100 MPa/μm or more 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, which has a plate shape with a thickness of 2000 µm or less. The glass composition of the central portion in the thickness direction of the chemically strengthened glass is represented by mol% based on oxides
the total content of Li ₂ O, Na ₂ O and K ₂ O is 5% or more;
and the ratio of the content of Li ₂ O to the total content of Li ₂ O, Na ₂ O and K ₂ O is 0.5 or more. Chemically strengthened glass. The base composition of the chemically strengthened glass is represented by mol% based on oxides,
MgO + ZnO + CaO + SrO + BaO 0-5%,
The chemically strengthened glass according to any one of claims 1 to 4. A method for producing a chemically strengthened glass according to any one of claims 1 to 5,
immersing the glass plate in a potassium-containing strengthening salt at 400° C. to 500° C. for 1 to 8 hours;
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 based on 100% by mass of metal ions contained in the strengthening salt. The glass composition before chemical strengthening of the glass plate is represented by mol% based on oxides.
the total content of Li ₂ O, Na ₂ O and K ₂ O is 5% or more;
The method for producing chemically strengthened glass according to claim 6, wherein the ratio of the content of _Li2O to the total content of _Li2O , _Na2O and _K2O is 0.5 or more.

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