JPWO2020008901A1 - Chemically tempered glass and its manufacturing method - Google Patents

Abstract

Depth from the glass surface at a position where it has a compressive stress layer, CS0 measured using an optical waveguide surface stress meter is 500 MPa or more, and the compressive stress value measured using an optical waveguide surface stress meter becomes 0. The compressive stress value at the position where the depth from the glass surface is (D / 2) is CS2, and | x | / | y | obtained by the formula in the specification is 0 to 0.8. Chemically tempered glass having a DOL of 50 μm or more as measured using a scattered photoelastic stress meter.

Description

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

Chemically tempered glass is used for the cover glass of mobile terminals.
In chemically strengthened glass, glass is brought into contact with a molten salt containing metal ions such as alkali metal ions to cause ion exchange between the metal ions in the glass and the metal ions in the molten salt, and the glass is compressed on the glass surface. It is a glass on which a stress layer is formed. The strength of chemically strengthened glass strongly depends on the stress profile expressed by the compressive stress value with the depth from the glass surface as a variable.

It is considered that the cover glass of a mobile terminal or the like is less likely to be cracked due to 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 and forming the compressive stress layer even in the deep part of the glass, it is possible to prevent the cracking even when a large impact is applied.

However, when a compressive stress layer is formed on the surface of the 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 breaks, it is crushed violently and the fragments are likely to scatter. Therefore, a method of increasing the surface compressive stress and the compressive stress depth while reducing the internal tensile stress value is being studied.

Patent Document 1 illustrates a typical stress profile when the 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 the 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 said that the compressive stress on the surface can be increased, the compressive stress depth can be increased, and the internal tensile stress value can be decreased.

International Publication No. 2015/1278483

In a typical stress profile when the ion exchange treatment is performed twice, the stress changes significantly in the vicinity of the glass surface even if the depth from the glass surface changes slightly.
By the way, in the process of actually manufacturing a cover glass or the like of 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 the stress changes significantly even if the depth from the glass surface changes slightly, the surface compressive stress after polishing will differ greatly depending on the slight difference in the amount of polishing. 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 being chemically strengthened.

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 by using an optical waveguide surface stress meter is 500 MPa or more, and the optical waveguide surface stress meter is used. The depth from the glass surface at the position where the compressive stress value measured using is 0 is D [unit: μm], and the depth from the glass surface measured using an optical waveguide surface stress meter is (D / 2). The absolute value of the inclination 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), where the compressive stress value at the position of) is CS _2. The ratio of the inclination y of the stress profile up to D to the absolute value | x | / | y | is 0 to 0.8, and the compressive stress layer depth DOL measured using a scattered photoelastic stress meter is 50 μm. The above-mentioned chemically strengthened glass is provided.
x = (CS _{2 -CS 0} ) / ((D / 2) -0) = 2 × (CS _{2- CS 0} ) / D
y = (0-CS ₂ ) / (D- (D / 2)) = -2 x CS ₂ / D

The chemically strengthened glass of the present invention is obtained from the glass surface obtained by the following formula from the _{compressive stress value CS 1} and the CS _{0 at} a position where the depth from the glass surface is 1 μm measured by using an optical waveguide surface stress meter. The inclination 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, it may be in the shape of a plate having a thickness of 2000 μm or less.
Further, the glass composition of the central portion of the chemically strengthened glass in the thickness direction contains _{50% or more of SiO 2} and 5% or more of Al ₂ O ₃ in terms of oxide-based mol%, and Li ₂ O and 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.

In the chemically strengthened glass of the present invention, the matrix composition of the chemically strengthened glass is expressed in mol% based on oxide, SiO ₂ 50 to 80%, Al ₂ O _{3 to} 25%, B ₂ O _{30 to} 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%, May be.

The method for producing chemically tempered glass of the present invention includes immersing a glass plate in a potassium-containing tempered 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 lower. The potassium-containing tempered salt may be a method for producing chemically strengthened glass containing 70% by mass or more of potassium ions, with the mass of metal ions contained in the tempered salt being 100% by mass.
Further, in the above-mentioned method for producing chemically strengthened glass of the present invention, the glass composition before chemically strengthening the glass plate contains _{50% or more of SiO 2} and 5% or more of Al ₂ O _{3 in terms of oxide-based mol%.} 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 to the amount may be 0.5 or more.

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

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

Unless otherwise specified in the present specification, "~" indicating a numerical range is used to mean that the numerical values described before and after the numerical range are included as the lower limit value and the upper limit value.

In the present specification, the "stress profile" refers to the compressive stress value from the glass surface to the central portion expressed as a variable of the depth from the glass surface. The "compressive stress depth (DOL)" is the depth at which the compressive stress value becomes zero in the stress profile.
"Internal tensile stress (CT)" refers to the tensile stress value at a depth of 1/2 of the glass plate thickness t.

In the present specification, "chemically strengthened glass" refers to glass after being chemically strengthened, and "chemically strengthened glass" refers to glass before being chemically strengthened.
In the present specification, the glass composition of the chemically strengthened glass may be referred to as "the mother 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 when an extreme ion exchange treatment is performed.

In the present specification, the glass composition is expressed as an oxide-based molar percentage notation unless otherwise specified, and molar% is simply expressed as "%".
Further, "substantially not contained" in the glass composition means that the glass composition is 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%.

<Break of glass>
When a glass plate is bent by an impact, if the amount of bending becomes large, a large tensile stress is applied to the glass surface and the glass breaks. In the present specification, such fracture is referred to as "glass fracture by bending mode". Since the chemically strengthened glass of the present invention (hereinafter, sometimes referred to as "this tempered glass") has a large compressive stress formed on the glass surface, glass breakage due to the 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, which causes the glass plate to break from the inside. In the present specification, such fracture is referred to as "glass fracture by impact mode". In this tempered glass, since the compressive stress layer is formed even inside 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 inside the glass plate, both glass breakage in the bending mode and glass breakage in the impact mode are suppressed, so the glass is extremely difficult to break. Should be. However, when a compressive stress layer is formed inside the glass plate, an internal tensile stress that cancels it is generated. If the internal tensile stress is large, when the glass breaks, severe fracture occurs and the fragments scatter.
Since the stress profile inside the glass is appropriately adjusted in this tempered glass, both glass breakage in the bending mode and glass breakage in the impact mode are suppressed, and fragments 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 fragments are less scattered even when broken, lithium aluminosilicate glass is ion-exchanged to have different inclinations. There are known methods of producing 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, it can be chemically fortified by an ion exchange treatment using a fortified salt containing sodium ions and then an ion exchange treatment using a fortified salt containing potassium ions.
According to these methods, a relatively large compressive stress is generated by ion exchange of sodium ion and potassium ion in a region relatively shallow from the surface, and a relatively small compression is generated in a deeper region by ion exchange of lithium ion and sodium ion. Stress is generated.
Sodium ions, which have a relatively small ionic radius, have a high diffusion rate inside the glass, whereas potassium ions, which have a relatively large ionic radius, have a slow diffusion rate inside the glass. Therefore, in the deep region, even if ion exchange between lithium ion and sodium ion occurs, ion exchange between sodium ion and potassium ion is unlikely to occur.

In the region near the surface where ion exchange between sodium ions and potassium ions occurs, a large compressive stress is generated by entering potassium ions having a large ionic radius into the glass. In deeper regions, ion exchange of lithium and sodium ions produces relatively small compressive stresses deeper. The chemically strengthened glass thus obtained has a stress profile in which the vicinity of the surface is steep and the deep portion is relatively gentle and bends in two stages. By forming such a stress profile, it is possible to obtain chemically strengthened glass having high surface strength, which is hard to be crushed even when it receives a strong impact, and which is hard to scatter fragments when it is broken.

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

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

The reason for measuring compressive stress using two types of devices is as follows.
The 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 the stress only when the refractive index decreases from the sample surface to the inside.
In chemically strengthened glass, the layer in which sodium ions are replaced with potassium ions in the glass has a lower refractive index from the surface to the inside, so that the stress can be measured using an optical waveguide surface stress meter. However, since such a refractive index distribution does not occur in the layer in which lithium ions are replaced with sodium ions in the glass, the 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. In the broken line part of the graph, stress is actually generated by ion exchange between lithium ion and sodium ion, but the stress cannot be measured by the optical waveguide surface stress meter.

In principle, the stress measurement method using a scattered light photoelastic stress meter can measure stress without depending on the refractive index distribution. However, since the scattered 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 this tempered glass using a scattered light photoelastic stress meter. The broken line part of the graph is unreliable because it is affected by light scattering on the glass surface.
Therefore, stress can be measured with two types of stress meters, and the results can be combined to analyze the stress. This method is described in detail in WO 2018/056121. 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. Highly accurate stress measurement is possible using FSM-6000 and the attached software FsmV.
As the scattered light photoelastic stress meter, for example, SLP-1000 manufactured by Orihara Seisakusho can be used. When FSM-6000 is used as the optical waveguide surface stress meter and SLP-1000 is used as the scattered photoelastic stressometer, data can be easily synthesized by using dedicated software.

<Chemically tempered glass>
The tempered glass is preferably plate-shaped, and is usually flat plate-shaped, but may be curved.

The thickness of the tempered glass is preferably 400 μm or more, more preferably 600 μm or more, still more preferably 700 μm or more. This is because the strength of the glass increases. The thickness of the tempered glass may be larger in order to increase the strength, but is preferably 2000 μm or less, more preferably 1000 μm or less in order to reduce the weight.

In this tempered glass, it is preferable that compressive stress is generated by ion exchange of sodium ion and potassium ion in a region relatively shallow from the surface, and compressive stress is generated by ion exchange of lithium ion and sodium ion in a deeper region. Such chemically strengthened glass has a stress profile that bends in two stages, which is steep near the surface and relatively gentle in the deep part, and as a result, the surface is strong and crushes even when subjected to a strong impact. This is because it is difficult to do.

_{This tempered glass has a compressive stress value CS 0} on the glass surface measured using an optical waveguide surface stress meter of 500 MPa or more, and therefore has high strength. For example, in FIG. 1, the CS value of the glass surface indicated 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.
In this tempered glass, when the compressive stress value CS _{0 on the} glass surface is 1200 MPa or less, delayed chipping is suppressed, which is preferable. CS ₀ is more preferably 1100 MPa or less, still more preferably 1050 MPa or less.

This tempered glass is preferable when the depth D [unit: μm] at which the “compressive stress value measured by the optical waveguide surface stress meter” becomes zero is 3 μm or more because fracture due to the bending mode can be suppressed. In order to suppress fracture due to the bending mode, D is more preferably 4 μm or more, still more preferably 5 μm or more. In order to suppress fracture due to the bending mode, D may be more preferably about 10 μm. If D is too large, the tensile stress generated in the glass center layer will increase. In order to prevent severe fracture due to this tensile stress, D is preferably 20 μm or less, more preferably 15 μm or less, still more preferably 10 μm or less.

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

This tempered glass has a stress profile inclination x [unit: MPa / μm] of -200 MPa / μm from the glass surface to a depth of (D / 2) [unit: μm] measured using an optical waveguide surface stress meter. It is preferably 200 MPa / μm or more. The inclination x is more preferably −100 MPa / μm or more and 100 MPa / μm or less, and further preferably −70 MPa / μm or more and 70 MPa / μm or less. The smaller the absolute value of x, the thicker the layer having an appropriate compressive stress value, and excellent properties can be obtained even when the surface is polished.
Further, the slope x is preferably a negative value. The highest compressive stress is required on glass surfaces that require high compressive stress to suppress fracture in the bending mode. If there is a positive part in the inclination of the stress profile, there will be a place where more stress than necessary is introduced inside the glass, and delayed chipping is likely to occur, or the stress value 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, the slope of the stress profile from the glass surface indicated by the arrow a to the depth (D / 2) from the glass surface indicated by the arrow c is x.
x is obtained from the above formulas D, the compressive stress value CS _{0 on the glass surface, and the compressive stress value CS 2} at a depth of (D / 2) from the glass surface.
x = (CS _{2 -CS 0} ) / ((D / 2) -0)
= 2 × (CS _{2- CS 0} ) / D

This tempered glass bends when the inclination 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. It is preferable because the high compressive stress layer required for fracture suppression by the mode can be formed thinly on the outermost layer. The smaller the inclination y, the better, but usually it is −500 MPa / μm or more.

For example, in FIG. 1, the slope of the stress profile from the point at the depth of D / 2 from the glass surface indicated by the arrow c to the point at the depth D indicated by the arrow d is y.
Here, y is _{obtained from the above D and CS 2} by the following equation.
y = (0-CS ₂ ) / (D- (D / 2))
= -2 x CS ₂ / D

In this tempered glass, when the ratio | x | / | y | of the absolute value of the inclination x of the above-mentioned stress profile to the absolute value of y is 0.8 or less, the highly compressive stress layer on the outermost layer of the glass is kept thin. On the other hand, it is preferable because a thick stress region suitable for suppressing both delayed chipping and fracture due to the bending mode can be formed. More preferably, it is 0.6 or less. Further, the minimum value of | x | / | y | is 0. That is, | x | / | y | is preferably 0 to 0.8, and more preferably 0 to 0.6.
Further, x is preferably 0 or less, and y is preferably a negative value, so x / y is preferably 0 to 0.8, and more preferably 0 to 0.6. As long as x / y is a positive value, the smaller it is, the more preferable.

When the inclination 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 can suppress both delayed chipping and fracture due to bending mode. This is preferable because the thickness of the 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 the arrow a to the point at a depth of 1 μm from the glass surface indicated by the arrow b is z.
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 can be obtained by the following equation.
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 by a scattered light photoelastic stress meter is preferably 50 μm or more. For example, in FIG. 2, the depth of the point where the CS value indicated by the arrow e becomes 0 is DOL. Since the protrusions of general asphalt may be about 50 μm, compressive stress must be formed to a depth of 50 μm from the surface layer of the glass in order to prevent cracking when the glass plate collides with the asphalt. preferable. When the plate thickness is tμm, DOL / t is preferably 0.1 or more, more preferably 0.12 or more, and further preferably 0.14 or more. On the other hand, if the DOL is too large with respect to t, an excessive tensile stress is generated in the central layer of the plate thickness, and severe fracture occurs 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 a generally positive correlation between D and DOL, and the larger D tends to be, the larger DOL tends to be. 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. Generally, the ease of ion exchange depends on the composition of the glass. Is.

<Chemical strengthening glass>
The chemically strengthened glass of the present invention is obtained by chemically strengthening a chemically strengthened glass (hereinafter referred to as "this strengthening glass") which is a lithium aluminosilicate glass. 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 composition of the following chemically strengthened glass, except when an extreme chemical strengthening treatment is applied. The description also applies to the composition of the central portion of the chemically strengthened glass in the thickness direction.
Lithium aluminosilicate glass contains, for example _{, 50% or more of SiO 2} and 5% or more of Al ₂ O ₃ in terms of oxide-based mol%, and the total content of _{Li 2} O, Na ₂ O and K _{2 O is high.} 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 a glass of 0.5 or more.

It is more preferable that the reinforcing glass has the following composition in terms of molar percentage 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%.
Further, 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 preferable.
Such glasses are prone to form favorable stress profiles by chemical strengthening. Hereinafter, this preferable glass composition will be described.

SiO ₂ is a component constituting the skeleton of glass. In addition, it is 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, still more preferably 58% or more.
Further, in order to increase the meltability of the glass, _{the content of SiO 2} is preferably 80% or less, more preferably 75% or less, still more preferably 70% or less.

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

Although B ₂ O ₃ is not essential, it may be contained in order to improve the meltability during glass production and the like. In order to reduce the inclination of the stress profile near the surface of the chemically strengthened glass, _{it is preferable to contain B 2} O _3, and the content in that case 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, and 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. By chemically strengthening the lithium aluminosilicate glass, a chemically strengthened glass having a preferable stress profile can be obtained. The content of Li ₂ O is preferably 2% or more, more preferably 3% or more, still more preferably 5% or more in order to increase the compressive stress layer depth DOL.
Further, in order to suppress the occurrence of devitrification during the production of glass or the bending process, the Li ₂ O content is preferably 20% or less, more preferably 15% or less, still more preferably. It is 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, still more preferably 1.5% or more.
The Na ₂ O content 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 included 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, more preferably 1% or more.
The K ₂ O content 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 glass, and are preferably contained in a total 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, still 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 tend to reduce the 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, still 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. Further, in order to improve the ion exchange performance, 10% or less is preferable, and 8% or less is more preferable.

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, 5% or less is preferable, and 3% or less is more preferable.

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

When BaO is contained, the content is preferably 0.5% or more, more preferably 1% or more. In order to improve the ion exchange performance, 5% or less is preferable, 1% or less is more preferable, and it is further preferable that the ion exchange performance is substantially not 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 the scattering of debris 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 even more preferably substantially absent, in order to suppress devitrification during melting.

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

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 crushing of the 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, further preferably 1% or more, particularly preferably 1.5% or more, most. It is preferably 2% or more.

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. If this is the case, it is possible to prevent the glass from being devitrified during melting and to prevent the quality of the chemically strengthened glass from deteriorating. The contents of Y ₂ O ₃ , La ₂ O ₃ and Nb ₂ O ₅ are preferably 7% or less, more preferably 6% or less, still more preferably 5% or less, and particularly preferably 4% or less, respectively. Is less than 3%.

Ta ₂ O ₅ and Gd ₂ O ₃ may be contained in a small amount in order to suppress the crushing of the chemically strengthened glass, but since the refractive index and the reflectance are high, the respective contents are preferably 1% or less. , 0.5% or less is more preferable, and it is further preferable that the content is 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, 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, still more preferably 3% or less.

When coloring glass, a coloring component may be added as long as it does not hinder the achievement of desired chemical strengthening properties. Examples of the coloring component include Co ₃ O ₄ , MnO ₂ , Fe ₂ O ₃ , NiO, CuO, Cr ₂ O ₃ , V ₂ O ₅ , Bi ₂ O ₃ , SeO ₂ , TIO ₂ , CeO ₂ , Er _2. Examples thereof include O ₃ and Nd ₂ O _3. These may be used alone or in combination.

The total content of the coloring components is preferably 7% or less. Thereby, the devitrification of the 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. If 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 clarifying agent at the time of glass melting. It is preferable that As ₂ O ₃ is substantially not contained. When Sb ₂ O ₃ is contained, it is preferably 0.3% or less, more preferably 0.1% or less, and most preferably substantially not contained.

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

The Young's modulus of the reinforcing glass is preferably 70 GPa or more. The higher Young's modulus, the less likely it is that debris will scatter when the tempered glass breaks. Therefore, Young's modulus is more preferably 75 GPa or more, and even more preferably 80 GPa or more. On the other hand, if the Young's modulus is too high, the diffusion of ions at the time of chemical strengthening is slow, and it tends to be difficult to obtain a deep DOL. Therefore, 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 reinforcing glass is preferably 575 or more. The larger the Vickers hardness of the chemically strengthened glass, the easier it is for the Vickers hardness after the chemical strengthening to increase, and the more the chemically strengthened glass falls, the less likely it is to be scratched. Therefore, the Vickers hardness of the chemically strengthened glass is more preferably 600 or more, still more 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.

The larger the Vickers hardness, the less likely it is to be scratched, which is preferable. However, the Vickers hardness of the reinforcing glass is usually 850 or less. Glass with too high Vickers hardness tends to be difficult to obtain sufficient ion exchange. Therefore, the Vickers hardness is preferably 800 or less, more preferably 750 or less.

The fracture toughness value of the reinforcing glass ^{is preferably 0.7 MPa · m 1/2} or more. The larger the fracture toughness value, the more the scattering of debris 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, 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 strengthening glass from 50 ° C. to 350 ° ^{C. is preferably 100 × 10-7} / ° C. or less. When the average coefficient of expansion (α) is small, the glass is less likely to warp during molding or cooling after chemical strengthening. The average coefficient of expansion (α) is ^{more preferably 95 × 10 -7} / ° C. or lower, and even more preferably 90 × 10 ^-7 / ° C. or lower.
In order to suppress the warp of the chemically strengthened glass, the smaller the average coefficient of thermal expansion (α) is, the ^{more preferable it is, but it is usually 60 × 10 -7} / ° C. or higher.

In the reinforced glass, the temperature at which the viscosity becomes _{^{10 2 dPa · s (T 2}} ) is preferably 1750 ° C. or less, more preferably 1700 ° C. or less, more preferably 1680 ° C. or less. T ₂ is usually 1400 ° C. or higher.

In the reinforced glass, the temperature _{(T 4)} at which the viscosity becomes ¹⁰ 4 dPa · s is preferably 1350 ° C. or less, more preferably 1300 ° C. or less, more preferably 1250 ° C. or less. T ₄ is usually 1000 ° C. or higher.

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

The glass raw materials are appropriately mixed and heated and melted in a glass melting kiln so that a glass having a preferable composition can be obtained. Then, the glass is homogenized by bubbling, stirring, addition of a clarifying agent, etc., formed into a glass plate having a predetermined thickness, and slowly cooled. Alternatively, it may be formed into a plate shape by a method of forming it into a block shape, slowly cooling it, and then cutting it.

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

The glass ribbon obtained by molding is ground and polished as necessary to form a glass plate. When cutting the glass plate to 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 is performed. This is preferable because a compressive stress layer is also formed on the end face.

Then, the formed glass plate is subjected to a chemical tempering treatment, and then washed and dried to obtain a chemically strengthened glass.

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

The method of utilizing "Li-Na exchange" in which lithium ions in glass are exchanged with sodium ions is preferable because the chemical strengthening treatment 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 glass are exchanged with potassium ions is preferable.
It is more preferable to use the methods of performing "Li-Na exchange" and "Na-K exchange" together because a high surface compressive stress and a deep compressive stress layer can be formed in a relatively short treatment time. In that case, it is more effective to perform "Na-K exchange" after performing "Li-Na exchange".

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

More specifically, the tempered glass can be produced by the tempering treatment method described below (hereinafter, referred to as "the tempered treatment method").
This strengthening treatment method includes a step of immersing the glass plate in a potassium-containing strengthening salt. As the potassium-containing fortified salt, a salt containing 70% by mass or more of potassium ions is preferable, and a salt containing 90% by mass or more is more preferable, with the mass of the metal ions contained in the fortifying 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 fortified salt, a potassium-containing nitrate is preferable from the viewpoint of ease of handling such as boiling point and danger.
The fortified 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. It may also contain impurity levels of lithium.

In this strengthening treatment method, it is preferable to immerse the glass plate in a potassium-containing strengthening salt at 400 ° C. to 500 ° C. When the temperature of the potassium-containing fortified salt is 400 ° C. or higher, ion exchange easily proceeds, which is preferable. Further, due to stress relaxation, the | x | / | y | ratio in the stress profile tends to be small. More preferably, it is 420 ° C. or higher. Further, it is preferable that the temperature of the potassium-containing fortified salt is 500 ° C. or lower because excessive stress relaxation of the surface layer can be suppressed. More preferably, it is 480 ° C. or lower.

Further, it is preferable that the time for immersing the glass in the potassium-containing fortified salt is 1 hour or more because the surface compressive stress increases. Further, due to stress relaxation, the | x | / | y | ratio in the stress profile tends to be small. The immersion time is more preferably 2 hours or more, still more preferably 3 hours or more. 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, it is preferably 8 hours or less, more preferably 6 hours or less, and further preferably 4 hours or less.

The glass plate may be immersed in another fortified salt before being immersed in the potassium-containing fortified salt. As the other fortified salt, a sodium-containing fortified salt is preferable. As the sodium-containing fortified salt, a sodium nitrate fortified salt is preferable from the viewpoint of ease of handling like potassium nitrate. Further, it is preferable that the fortified salt contains 70% by mass or more of sodium ions, with the mass of metal ions being 100% by mass.

After immersing the glass plate in the potassium-containing fortified salt, it is preferable to keep the temperature 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 decreases due to the relaxation phenomenon. The holding temperature after immersing the glass plate in the potassium-containing fortified salt is more preferably 250 ° C. or lower, still more preferably 200 ° C. or lower.

As the treatment conditions for the chemical strengthening treatment, the time, temperature, etc. may be appropriately selected in consideration of the characteristics 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 used for mobile devices such as mobile phones and smartphones. Further, it is also useful for cover glass of display devices such as televisions, personal computers and touch panels, wall surfaces of elevators, and walls of buildings such as houses and buildings (full-scale display), which are not intended to be carried. It is also useful as a building material such as a window glass, a table top, an interior of an automobile or an airplane, a cover glass thereof, or a housing having a curved surface shape.

Hereinafter, the present invention will be described by way of examples, but the present invention is not limited thereto.
The glass raw materials were prepared 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 400 g as glass. Then, 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.

The obtained 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 sides were mirror-polished to obtain a glass plate having a thickness of 800 μm.

Using the glasses A to E, the following chemically strengthened glasses of Examples 1 to 15 were prepared 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 100% sodium nitrate fortified salt (sodium-containing fortified salt) at 450 ° C. for 1 hour, then immersed in 100% potassium nitrate (potassium-containing fortified salt) at 450 ° C. for 1 hour, and then immersed 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 tempered salt was defined as the time (unit: time) shown in the treatment time 1 of Table 2, and the time of immersion in the potassium-containing tempered salt was defined as the treatment time 2. The chemically strengthened glass of Examples 2 to 15 was obtained in the same manner as in Example 1 except that the time (unit: time) shown in 1 was set.

[Measurement of stress profile]
The stress value was measured using an optical waveguide surface stress meter FSM-6000 and a scattered 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 Indicates DOL (unit: μm). FIG. 1 is a stress profile obtained with FSM-6000 for the chemically strengthened glass of Example 1, and FIG. 2 is a stress profile obtained with SLP-1000. FIG. 3 shows the combined results.

In Example 4 in which x / y is 1, delayed chipping is likely to occur, resulting in a decrease in yield during polishing. In Example 5 in which the same glass B is strengthened, the above problem does not occur. This is probably because the strengthening treatment time is appropriate and x / y is as low as 0.19.
Further, in both Examples 2 and 3, the glass A is chemically strengthened, but in Example 2, the compressive stress layer is introduced to a depth of 180 μm, whereas the treatment time 2 is too long. In Example 3, since the DOL is as shallow as 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 modifications 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, and the entire application is incorporated by reference. Also, all references cited here are taken in as a whole.

Claims (7)

A chemically strengthened glass having a compressive stress layer on the glass surface.
_{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 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. _{Let CS 2 be the} compressive stress value at the position of (D / 2), and the absolute value of the inclination x of the stress profile from the glass surface to the depth of (D / 2) calculated by the following formula and the depth (D). The ratio of the inclination y of the stress profile from / 2) to the depth D to the absolute value | x | / | y | is 0 to 0.8.
Chemically tempered glass having a compressive stress layer depth DOL of 50 μm or more as 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 x CS ₂ / D The stress profile from the glass surface to the depth of 1 μm obtained by the following formula from the _{compressive stress value CS 1} and CS _{0 at} the position where the depth from the glass surface is 1 μm measured using an optical waveguide surface stress meter. The chemically strengthened glass according to claim 1, wherein the inclination 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 having a thickness of 2000 μm or less. The glass composition of the central portion of the chemically strengthened glass in the thickness direction contains _{50% or more of SiO 2} and 5% or more of Al ₂ O ₃ in terms of molar% based on oxides.
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. The matrix composition of the chemically strengthened glass is SiO ₂ 50 to 80% in molar% representation based on oxides.
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%,
The chemically strengthened glass according to any one of claims 1 to 4. The method for producing chemically strengthened glass according to any one of claims 1 to 5.
Immersing the glass plate in a potassium-containing fortified salt at 400 ° C to 500 ° C for 1 to 8 hours and
After that, the temperature of the glass plate is set to 300 ° C. or lower, including
The potassium-containing tempered salt is a method for producing chemically strengthened glass, which comprises 70% by mass or more of potassium ions, with the mass of metal ions contained in the tempered salt being 100% by mass. The glass composition of the glass plate before chemical strengthening contains _{50% or more of SiO 2} and 5% or more of Al ₂ O ₃ in terms of molar% based on oxides.
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.

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