WO2018056168A1 - Glass capable of being chemically reinforced, and chemically reinforced glass - Google Patents

Abstract

The purpose of the present invention is to provide: a chemically reinforced glass which has high strength and undergoes the scattering of shards to a reduced extent upon breakage; and a glass capable of being chemically reinforced, which is useful for the production of the chemically reinforced glass. The present invention relates to a glass capable of being chemically reinforced, which is composed of a lithium aluminosilicate glass, wherein the liquidus temperature T_L of the lithium aluminosilicate glass is equal to or lower than a temperature T₄ at which the viscosity of the lithium aluminosilicate glass becomes 10⁴ dPa·s, and the fictive temperature of the lithium aluminosilicate glass is equal to or higher than a temperature lower by 30°C than the glass transition temperature Tg of the lithium aluminosilicate glass and is equal to or lower than a temperature higher by 25°C than the Tg.

Description

Chemically strengthened glass and chemically strengthened glass

The present invention relates to a chemically strengthened glass and a chemically strengthened glass.

As a cover glass for display devices of mobile devices such as mobile phones and smartphones, a chemically strengthened glass that is thin but high in strength is used.

In chemically strengthened glass, the strength tends to be higher as the surface compressive stress value (CS) is larger and the depth (DOL) of the compressive stress layer is larger. On the other hand, internal tensile stress (CT) is generated inside the glass so as to maintain a balance with the surface compressive stress. When a glass having a large internal tensile stress breaks, it tends to crack violently, increasing the number of fragments and causing the fragments to scatter.

Patent Document 1 discloses a calculation formula showing the allowable limit of internal tensile stress of tempered glass, and it is said that chemically strengthened glass with less debris scattering can be obtained by strengthening within that range.

Further, Patent Document 2 describes a chemically strengthened glass subjected to a two-stage ion exchange treatment as a chemically strengthened glass having high strength and less scattering of fragments.

U.S. Pat. No. 8,075,999 U.S. Pat. No. 9,487,434

However, sufficiently high strength may not be obtained within the allowable limit described in Patent Document 1. That is, the strength of the chemically strengthened glass described in Patent Document 1 and Patent Document 2 may be insufficient.
An object of the present invention is to provide a chemically strengthened glass having high strength and less scattering of fragments when broken, and a glass for chemical strengthening useful for producing the chemically strengthened glass.

From the following considerations, the present inventors considered that how to break chemically strengthened glass depends on the properties of the glass before chemical strengthening.
Chemically tempered glass breaks when a crack generated in the glass reaches a portion where tensile stress is applied inside the glass. Since the part to which the tensile stress is applied is considered to be a part that is not ion-exchanged even by the chemical strengthening treatment, it was considered that the crushing characteristics of this part depend on the characteristics of the glass before chemical strengthening.
In addition, the present inventors have studied glass that cracks are difficult to branch by paying attention to the fact that a large number of cracks are generated when the number of crack branches increases when the glass breaks. As a result, it has been found that a glass having a large mirror constant has a small number of fragments when it is broken even when chemically strengthened.
Moreover, the characteristic of glass with a large mirror constant was found.

The present invention has been made on the basis of the above findings, and is composed of a lithium aluminosilicate glass having a liquidus temperature T _L of a temperature T ₄ or less at which the viscosity is 10 ⁴ dPa · s, and the fictive temperature is a glass transition. Provided is a glass for chemical strengthening that is at least 30 ° C. below the point Tg and at most 25 ° C. below the Tg.

Furthermore, a mole percentage based on oxides, SiO ₂ 68 ~ 72%, the _{Al 2 O 3 6 ~ 10%} , 7 ~ 11% of Li ₂ O, 4 ~ 7% of Na _{2 O, K} 2 O 0 to 3%, MgO 4 to 10%, CaO 0 to 3%, SrO 0 to 2%, BaO 0 to 2%, ZnO 0 to 2%, B ₂ O ₃ 0 to 3% For chemical strengthening containing 0 to 3% of P ₂ O ₅ , 0 to ₂ % of TiO ₂ and 0 to 3% of ZrO ₂ and having a fictive temperature of 25 ° C. or lower than the glass transition point Tg Provide glass.

Further, in terms of oxide-based molar percentage, SiO ₂ is 60 to 80%, Al ₂ O ₃ is 4 to 25%, Li ₂ O is 5 to 15%, Na ₂ O is 1 to 15%, K ₂ O. 0-5%, MgO 2-25%, CaO 0-10%, SrO 0-10%, BaO 0-10%, ZnO 0-10%, B ₂ O ₃ 0-10% , P ₂ O ₅ 0-10%, TiO ₂ 0-10% and ZrO ₂ 0-8%, and the liquid phase temperature T _L is a temperature T at which the viscosity becomes 10 ⁴ dPa · s. Provided is a method for producing a glass for chemical strengthening, wherein ₄ or less glasses are melted and cooled at an average cooling rate of 10 ° C / min to 300 ° C / min.

Moreover, when the surface compressive stress layer was provided and the stress pattern near the glass surface and the stress pattern on the glass inner layer side were approximated by a linear function, the stress pattern P1 on the glass inner layer side was extended to the glass surface. The imaginary surface stress value CS1 obtained from the line is a chemically strengthened glass smaller than the surface compressive stress value CS2 obtained from the stress pattern P2 near the glass surface, and the CS1 is 200 MPa or more and the CS2 is 800 MPa. There is provided a chemically tempered glass having the above and a mirror constant A of 2.0 MPa · m ^1/2 or more.

The chemically tempered glass of the present invention is high in strength and does not break severely when it is broken. Moreover, according to a preferable aspect, devitrification hardly occurs.

FIG. 1 is a diagram schematically showing a stress profile of chemically strengthened glass, where the vertical axis represents the compressive stress value and the horizontal axis represents the depth from the glass surface. FIG. 2 is a diagram schematically showing how the cracks around the fracture starting point occur when glass without residual stress is broken by uniform tensile stress. FIG. 3 is a graph showing the relationship between the refractive index and the virtual temperature of the glass 1. FIG. 4 is a schematic diagram showing a test method for a drop-on-sand test.

In the present specification, “chemically tempered glass” refers to glass after being subjected to chemical tempering treatment. “Chemical strengthening glass” refers to glass before chemical strengthening treatment. “Chemical strengthening glass” is glass that can be chemically strengthened.
In this specification, “the mother composition of chemically strengthened glass” is a glass composition of chemically strengthened glass. In chemically strengthened glass, a compressive stress layer by ion exchange is usually formed on the glass surface portion, so that the glass composition of the portion not ion-exchanged matches the mother composition of chemically strengthened glass.

In the present specification, the glass composition is expressed in terms of a mole percentage based on an oxide, and mol% may be simply described as%.
“Substantially not contained” in the glass composition means that it is not contained except for inevitable impurities contained in raw materials and the like, that is, it is not intentionally contained. Specifically, for example, the content in the glass composition is less than 0.1 mol%.
In the present specification, the “stress profile” is a pattern representing a compressive stress value with the depth from the glass surface as a variable. A negative compressive stress value means tensile stress.
In the present specification, the “friability” of glass refers to a property in which fragments are easily scattered when glass is broken.

(Chemical tempered glass)
The chemically strengthened glass has a compressive stress layer formed on the surface by a chemical strengthening process (ion exchange process). In the ion exchange treatment, the surface of the glass is ion exchanged to form a surface layer in which compressive stress remains. Specifically, a metal ion (typically Li ion, Na ion) having a small ionic radius on the surface of the glass plate is ion-exchanged at a temperature below the glass transition point Tg (typically Li ion, Na ion). , Li ions are Na ions or K ions, and Na ions are substituted with K ions). Thereby, a compressive stress arises on the surface of glass and the intensity | strength of glass improves.

Chemically tempered glass having a large compressive stress value CS ₀ on the glass surface is hard to break even if scratches occur on the surface because the scratches are not easily spread by being pressed by the surface compressive stress. Further, since the tensile stress applied to the outside of the curved surface when the glass plate is bent is offset by the surface compressive stress, it is difficult to break even when bent. On the other hand, chemically strengthened glass having a large compressive stress depth DOL is less likely to break because the tip of a relatively deep flaw remains in the compressive stress layer.
Therefore, chemically strengthened glass is considered to be harder to break as the CS _{0 on} the glass surface is larger and the DOL is larger. However, if CS ₀ and DOL are increased simultaneously, the internal tensile stress value CT increases accordingly, and the friability tends to increase.

FIG. 1 is a graph schematically showing a stress profile of chemically strengthened glass which is one embodiment of the present invention, in which the vertical axis represents the compressive stress value and the horizontal axis represents the depth from the glass surface. The thick solid line is a line obtained by approximating the stress pattern P1 on the glass inner layer side and the stress pattern P2 near the glass surface by a linear function.
In this stress profile, the virtual surface compressive stress value CS1 obtained from the line (dotted line p1 in FIG. 1) obtained by extending the stress pattern P1 to the glass surface is smaller than the surface compressive stress value CS2 obtained from the stress pattern P2. . Note that the actual surface compressive stress value CS ₀ is approximately equal to CS2.
Further, the depth DOL2 at which the stress value becomes zero on the line obtained by extending the stress pattern P2 (dotted line p2 in FIG. 1) is smaller than the depth DOL1 at which the stress value becomes zero in the stress pattern P1. The actual compressive stress layer depth DOL is substantially equal to DOL1.

Such a stress profile is preferable because even if the compressive stress value on the glass surface is large, the internal tensile stress CT is relatively small. Such a stress profile is obtained, for example, by a two-step chemical strengthening process.
In this stress profile, CS1 is preferably 200 MPa or more. Further, CS ₀ (and CS2) is preferably 800 MPa or more.

On the other hand, CS2 is, for example, preferably 2000 MPa or less, more preferably 1500 MPa or less, and further preferably 1000 MPa or less in order to suppress crushability. When CS2 that is the surface compressive stress value is increased, the internal tensile stress value CT is increased, so that the friability is increased.

In the chemically strengthened glass of this embodiment, the virtual surface stress value CS1 obtained from a line obtained by extending the stress pattern P1 on the glass inner layer side to the glass surface is obtained from the surface compressive stress obtained from the stress pattern P2 in the portion close to the glass surface. By being smaller than the value CS2 and the mirror constant A being 2.0 MPa · m ^1/2 or more, the friability is suppressed even if both the surface compressive stress CS ₀ and the compressive stress depth DOL are increased. .

Mirror constant A of chemically tempered glass of the present invention is preferably 2.0 MPa ^{· m 1/2} or more, more preferably 2.1 MPa ^{· m 1/2} or more, more preferably 2.3 MPa ^{· m 1/2} or more. Chemically tempered glass having a large mirror constant A has a small number of fragments when it is broken, so that its friability is not large even if the internal tensile stress CT is large.

Here, in order to help understanding of the present invention, the mirror constant A will be described.
It is known that when the glass is broken, the shape of the fracture surface varies depending on the magnitude of the stress. FIG. 2 schematically shows how the glass without residual stress breaks around the fracture starting point when it is broken by uniform tensile stress (see ASTM C-1678-10). In addition, since the chemically strengthened glass has residual stress, the appearance around the fracture starting point of the chemically strengthened glass may be greatly different from that in FIG.
In FIG. 2, a smooth surface called a mirror surface is generated around the fracture starting point indicated by a black circle. In addition, a slightly rough boundary surface called a mist surface is generated around the surface, and a rough surface called a hackle is generated at the tip. In FIG. 2, when the distance from the fracture starting point indicated by the black circle to the boundary between the mirror surface and the mist surface is R, and the stress causing the fracture is σ, σ is the square root of R. It is known to be proportional to the reciprocal, and the proportionality constant is the Miller constant A. That is, the relationship is as shown in the following equation.
σ = A / R ^1/2
The mirror constant A is experimentally obtained by measuring the stress σ at the time of fracture and the distance R from the fracture starting point to the interface between the mirror surface and the mist surface.

Mirror constant A depends on glass composition and fictive temperature. The relationship between the mirror constant A and the glass composition and the relationship between the mirror constant A and the virtual temperature will be described in detail later.

The above-mentioned Patent Document 1 discloses a formula indicating the allowable limit of the internal tensile stress CT of chemically strengthened glass. When the plate thickness is t [mm], CT is −38.7 × ln (t) +48. It should be 2 [MPa] or less.
However, since the chemically strengthened glass of one embodiment of the present invention has a large Miller constant A, even if the internal tensile stress value CT is larger than −38.7 × ln (t) +48.2, fragments are not easily scattered.

As the mother composition of the chemically strengthened glass of the present invention, SiO ₂ is 60 to 80%, Al ₂ O ₃ is 4 to 25%, Li ₂ O is 5 to 15%, Na ₂ O in terms of mole percentage based on oxide. 1 to 15%, K ₂ O 0 to 5%, MgO 2 to 25%, CaO 0 to 10%, SrO 0 to 10%, BaO 0 to 10%, ZnO 0 to 10%, the _{B 2 O 3 0 ~ 10%} , the _{P 2 O 5 0 ~ 10%} , the TiO ₂ 0 ~ 10%, and it is preferred that the ZrO ₂ containing 0-8%. This preferred glass composition will be described in detail later.

(Chemical strengthening glass)
The glass for chemical strengthening of the present invention is preferably lithium aluminosilicate glass. Lithium aluminosilicate glass undergoes ion exchange between Li ions in the glass and Na ions in the molten salt by an ion exchange treatment with a sodium salt such as sodium nitrate, so that a deep surface compression layer is easily formed. Also, when ion exchange treatment with potassium salt (for example, potassium nitrate) is performed after ion exchange treatment with sodium salt, or ion exchange treatment with a mixed salt of sodium salt and potassium salt (for example, sodium nitrate-potassium nitrate mixed salt) is performed. In such a case, since ion exchange between Na ions and K ions occurs in addition to ion exchange between Li ions and Na ions, the surface compressive stress value CS ₀ is large and the internal tensile stress CT is relatively small. Tempered glass is easily obtained.

The glass for chemical strengthening of the present invention preferably generates a surface compressive stress of 200 MPa or more by an ion exchange treatment with a sodium salt. Such glass is easy to obtain high strength by chemical strengthening. For example, the surface compressive stress when treated for 1 hour in 450 ° C. sodium nitrate is preferably 200 MPa or more, more preferably 250 MPa or more, and even more preferably 300 MPa or more. For such chemically strengthened glass, when ion exchange treatment with potassium salt is performed after ion exchange treatment with sodium salt, or when ion exchange treatment with a mixed salt of sodium salt and potassium salt is performed, the surface Even if the compressive stress value CS ₀ is large, a chemically strengthened glass having a relatively small internal tensile stress value CT can be obtained.
Moreover, the glass for chemical strengthening of the present invention preferably generates a surface compressive stress of 800 MPa or more by ion exchange treatment with a potassium salt. For example, the surface compressive stress at the time of immersion in 450 ° C. potassium nitrate for 6 hours is preferably 800 MPa or more, more preferably 850 MPa or more, and further preferably 900 MPa or more. A preferred stress profile is obtained by chemically strengthening such chemically strengthened glass.

Moreover, the liquid phase temperature _TL of the glass for chemical strengthening is preferably a temperature T ₄ or less at which the viscosity becomes 10 ⁴ dPa · s. Such glass is easy to be formed into a plate shape using a float process. For molding the ease of a float process, _{T L} is more preferably 10 ° C. lower temperature _(T 4 -10 ℃) less than _{T 4,} T 4 is more preferably -30 ° C. or _less, T 4 -50 ° C. or less Is even more preferable. For ease of chemical strengthening, _TL is preferably T ₄ −150 ° C. or higher, more preferably T ₄ −125 ° C. or higher, and further preferably T ₄ −100 ° C. or higher.

The mirror constant A of the glass for chemical strengthening is preferably 2.0 MPa · m ^1/2 or more. Such a glass for chemical strengthening is less likely to splatter when broken after chemical strengthening.
Mirror constant A glass for chemical strengthening is more preferably 2.1 MPa ^{· m 1/2} or more, more preferably 2.3 MPa ^{· m 1/2} or more.

The mirror constant A tends to increase as the fictive temperature Tf of the glass decreases.
In order to increase the mirror constant A, the fictive temperature Tf of the glass for chemical strengthening is preferably near the glass transition point Tg of the glass. Specifically, a temperature of 25 ° C. higher than Tg (described as Tg + 25 ° C.) or lower is preferable, Tg + 20 ° C. or lower is more preferable, and Tg + 15 ° C. or lower is more preferable. The fictive temperature Tf is preferably as small as possible to increase the mirror constant A. However, if the fictive temperature Tf is significantly lower than Tg, cooling is performed at a very slow rate, resulting in poor glass productivity. Therefore, Tf is preferably at least 30 ° C. lower than Tg (Tg-30 ° C.), more preferably at least Tg-10 ° C., and even more preferably at least Tg.

When the glass is obtained by melting the glass raw material at a high temperature and cooling it, the fictive temperature Tf of the glass becomes lower as the cooling rate after melting is smaller. Therefore, in order to obtain glass with a very low fictive temperature, it is necessary to cool slowly over a long period of time. When glass is slowly cooled, depending on the glass composition, a devitrification phenomenon in which crystals precipitate during cooling tends to occur.
In consideration of glass production efficiency and suppression of devitrification, the fictive temperature Tf is preferably Tg-30 ° C. or higher, more preferably Tg-10 ° C. or higher, and further preferably Tg or higher, as described above.

In summary, the fictive temperature Tf is preferably Tg-30 ° C. or higher and Tg + 25 ° C. or lower, more preferably Tg−10 ° C. or higher and Tg + 20 ° C. or lower, and further preferably Tg or higher and Tg + 15 ° C. or lower.

The fictive temperature Tf of glass can be experimentally determined from the refractive index of glass. A plurality of glass pieces having the same glass composition and different fictive temperatures are prepared by a method of rapidly cooling glass held at a certain temperature from the temperature. Since the fictive temperature of these glass pieces is the temperature that was maintained before quenching, a calibration curve in which the refractive index is plotted against the fictive temperature can be created by measuring the refractive index of these glass pieces. An example is shown in FIG. Even if the cooling rate or the like is not clear, by measuring the refractive index, the virtual temperature can be obtained from the calibration curve created for the glass having the same composition.

Chemically strengthened glass of the present invention, for example, a SiO ₂ 60 ~ 80%, the _{Al 2 O 3 4 ~ 25%} , the Li ₂ O 5 ~ 15%, a _{Na 2 O 1 ~ 15%,} K 2 O 0-5%, MgO 2-25%, CaO 0-10%, SrO 0-10%, BaO 0-10%, ZnO 0-10%, B ₂ O ₃ 0-10% the _{P 2 O 5 0 ~ 10%} , Ti 2 O 0 to 10% and ZrO ₂ are those containing 0-8% preferred. Such glasses have excellent chemical strengthening properties.

The glass for chemical strengthening of the present invention is SiO ₂ 60-60%, Al ₂ O ₃ 7-30%, Li ₂ O 5-15%, Na ₂ O 1-25%, K ₂ O 0 ~ 5%, MgO 3 ~ 25%, CaO 0 ~ 10%, SrO 0 ~ 10%, BaO 0 ~ 10%, ZnO 0 ~ 10%, B ₂ O ₃ 0 ~ 5%, P the ₂ O ₅ 0 ~ 4%, it is preferable that the TiO ₂ containing 0-10%. Such glass has a large mirror constant A.

Also, SiO ₂ is 67 to 75%, Al ₂ O ₃ is 4 to 15%, Li ₂ O is 5 to 15%, Na ₂ O is 1 to 9%, K ₂ O is 0 to 5%, and MgO is 4%. ~ 15%, CaO 0 ~ 4%, SrO 0 ~ 5%, BaO 0 ~ 5%, ZnO 0 ~ 5%, B ₂ O ₃ 0 ~ 10%, P ₂ O ₅ 0 ~ 10 %, TiO ₂ 0 to 4%, and ZrO ₂ 0 to 8% are more preferable. Such glass has excellent chemical strengthening properties, little scattering of fragments at the time of breakage, and devitrification hardly occurs.

Further chemical strengthening glass of the present invention, the SiO ₂ 68 ~ 72%, the _{Al 2 O 3 6 ~ 10%} , the Li ₂ O 7 ~ 11%, a Na ₂ O 4 ~ 7%, the _{K 2} O 0-3%, MgO 4-10%, CaO 0-3%, SrO 0-2%, BaO 0-2%, ZnO 0-2%, B ₂ O ₃ 0-3%, It is preferable that P ₂ O ₅ is contained in an amount of 0 to 3%, TiO ₂ is contained in an amount of 0 to 2%, and ZrO ₂ is contained in an amount of 0 to 3%, and the fictive temperature is 25 ° C. or higher than the glass transition point Tg. Such glass has excellent chemical strengthening properties.

Each component in the glass composition will be described below.
SiO ₂ is a component constituting the skeleton of glass. Moreover, it is a component which raises chemical durability, and is a component which reduces generation | occurrence | production of the crack when a glass surface is damaged. In order to suppress the occurrence of cracks, the SiO ₂ content is preferably 60% or more, more preferably 63% or more, further preferably 65% or more, further preferably 67% or more, and particularly preferably 68% or more. On the other hand, if the SiO ₂ content is more than 80%, the meltability is remarkably lowered, so 80% or less is preferable. For ease of melting, it is more preferably 75% or less, still more preferably 72% or less, and particularly preferably 70% or less.

Al ₂ O ₃ is an effective component for improving the ion exchange performance during the chemical strengthening treatment and increasing the surface compressive stress value CS ₀ after the chemical strengthening. Moreover, it is a component which has the effect of improving the mirror constant A of glass. Moreover, it is a component which raises Tg of glass, and is also a component which raises Young's modulus. In order to enhance the chemical strengthening characteristics, the Al ₂ O ₃ content is preferably 4% or more, and more preferably 6% or more. In order to increase the mirror constant, the Al ₂ O ₃ content is preferably 7% or more, more preferably 10% or more, and further preferably 13% or more. On the other hand, if the Al ₂ O ₃ content is more than 30%, the acid resistance of the glass tends to decrease, or the devitrification temperature tends to increase. Moreover, there exists a possibility that the viscosity of glass may increase and a meltability may fall. Therefore, the Al ₂ O ₃ content is preferably 30% or less, more preferably 25% or less, still more preferably 20% or less, and particularly preferably 15% or less.

When the Al ₂ O ₃ content is large, the temperature at the time of melting the glass increases and the productivity decreases. When emphasizing the productivity of glass, the content of Al ₂ O ₃ is preferably 11% or less, more preferably 10% or less, still more preferably 9% or less, and particularly preferably 8% or less.

Li ₂ O is a component that forms a surface compressive stress layer by ion exchange during chemical strengthening treatment with Na salt.
When performing chemical strengthening treatment in which Li ions on the glass surface are exchanged with Na ions using Na salt, the Li ₂ O content is preferably 5% or more because the compressive stress generated by chemical strengthening is increased, and more Preferably it is 6% or more, More preferably, it is 7% or more. On the other hand, if the content of Li ₂ O exceeds 15%, the acid resistance of the glass is significantly reduced. It is preferably 15% or less, more preferably 13% or less. 11% or less is more preferable.

Na ₂ O is a component capable of forming a surface compressive stress layer by ion exchange during chemical strengthening treatment and improving the meltability of glass.
The content of Na ₂ O is preferably 1% or more, more preferably 3% or more, still more preferably 4% or more, and particularly preferably 6% or more. On the other hand, when the content of Na ₂ O exceeds 15%, the surface compressive stress value CS ₀ formed by ion exchange is remarkably lowered, so 15% or less is preferable. The content of Na ₂ O is more preferably 9% or less, still more preferably 6% or less, and particularly preferably 5% or less.

When Li ion and Na ion, and Na ion and K ion on the glass surface are simultaneously ion-exchanged by a method such as immersion in a mixed molten salt of potassium nitrate and sodium nitrate, the content of Na ₂ O is preferably 10 % Or less, more preferably 9% or less, further preferably 7% or less, particularly preferably 6% or less, and most preferably 5% or less. Further, the content of Na ₂ O is preferably 2% or more, more preferably 3% or more, and further preferably 4% or more.

K ₂ O may be contained to improve ion exchange performance during chemical strengthening treatment. When K ₂ O is contained, the content is preferably 0.5% or more, and more preferably 1% or more. On the other hand, if the content of K ₂ O is more than 5%, the friability of the chemically strengthened glass is lowered, so the content of K ₂ O is preferably 5% or less. The content of K ₂ O is more preferably 3% or less, and further preferably 2% or less.

MgO is preferably contained in order to increase the surface compressive stress value CS ₀ of the chemically strengthened glass. In addition, there is an effect of improving the mirror constant A. The content of MgO is preferably 2% or more, more preferably 3% or more, still more preferably 4% or more, and particularly preferably 5% or more. On the other hand, when the content of MgO is more than 25%, the glass for chemical strengthening tends to be devitrified when melted. Therefore, the content is preferably 25% or less. The content of MgO is more preferably 15% or less, and further preferably 10% or less.

CaO is a component that improves the meltability of glass, has an effect of improving the mirror constant A, and may be contained. When CaO is contained, the content is preferably 0.1% or more, more preferably 0.2% or more, still more preferably 0.3% or more, and particularly preferably 0.4% or more. Preferably it is 0.5% or more. On the other hand, if the content exceeds 14%, the ion exchange performance at the time of chemical strengthening may be lowered, so 14% or less is preferable. More preferably, it is 10% or less, More preferably, it is 8% or less, More preferably, it is 4% or less, Most preferably, it is 3% or less. 1% or less is preferable.

SrO is a component that improves the meltability of glass, has the effect of improving the mirror constant A, and may be contained. When it is contained, the content is preferably 0.1% or more, more preferably 0.2% or more, further preferably 0.3% or more, particularly preferably 0.4% or more, and most preferably 0.5% or more. On the other hand, if the content exceeds 10%, the ion exchange performance at the time of chemical strengthening treatment may be lowered, so 10% or less is preferable. The SrO content is more preferably 8% or less, further preferably 5% or less, particularly preferably 2% or less, and most preferably 1% or less.

BaO is a component that improves the meltability of glass, has an effect of improving the mirror constant A, and may be contained. When BaO is contained, the content is preferably 0.1% or more, more preferably 0.2% or more, still more preferably 0.3% or more, and particularly preferably 0.4% or more. Preferably it is 0.5% or more. On the other hand, if the BaO content exceeds 10%, the ion exchange performance at the time of chemical strengthening treatment decreases, so 10% or less is preferable. The content of BaO is more preferably 8% or less, further preferably 5% or less, particularly preferably 2% or less, and most preferably 1% or less.

ZnO is a component that improves the meltability of the glass and may be contained. Content in the case of containing ZnO becomes like this. Preferably it is 0.25% or more, More preferably, it is 0.5% or more. On the other hand, when the ZnO content exceeds 10%, the weather resistance of the glass is significantly lowered. The content of ZnO is preferably 10% or less, more preferably 7% or less, still more preferably 5% or less, still more preferably 2% or less, and particularly preferably 1% or less.

B ₂ O ₃ is a component that improves the meltability. Moreover, it is a component which improves the chipping resistance of glass. B ₂ O ₃ is not essential, but the content in the case of containing B ₂ O ₃ is preferably 0.5% or more, more preferably 1% or more, further preferably, in order to improve the meltability. 2% or more. On the other hand, when the content of B ₂ O ₃ exceeds 10%, striae are generated at the time of melting, and the quality of the chemically strengthened glass tends to be lowered, so that it is preferably 10% or less. The content of B ₂ O ₃ is more preferably 5% or less, still more preferably 3% or less, and particularly preferably 1% or less. In order to make acid resistance high, it is preferable not to contain substantially.

P ₂ O ₅ is a component that improves ion exchange performance and chipping resistance during chemical strengthening treatment. P ₂ O ₅ is not essential, but the content when P ₂ O ₅ is contained is preferably 0.5% or more, more preferably 1% or more, and further preferably 2% or more. On the other hand, if the content of P ₂ O ₅ is more than 10%, the acid resistance is remarkably lowered, so 10% or less is preferable. The content of P ₂ O ₅ is more preferably 4% or less, further preferably 3% or less, still more preferably 2% or less, and particularly preferably 1% or less. In order to make acid resistance high, it is preferable not to contain substantially.

TiO ₂ is a component that increases the surface compressive stress value CS ₀ due to ion exchange during the chemical strengthening treatment, and may be contained. When TiO ₂ is contained, the content is preferably 0.1% or more, more preferably 0.15% or more, still more preferably 0.2% or more, and most preferably 0.5% or more. On the other hand, if the content is more than 10%, devitrification tends to occur at the time of melting, and the quality of chemically strengthened glass may be deteriorated, so 10% or less is preferable. The content is more preferably 4% or less, further preferably 2% or less, and still more preferably 1% or less.

ZrO ₂ is a component that increases the surface compressive stress value CS ₀ due to ion exchange during the chemical strengthening treatment, and may be contained. When these are contained, the content is preferably 0.5% or more, more preferably 1% or more. On the other hand, if the content exceeds 8%, devitrification tends to occur during melting, and the quality of the chemically strengthened glass may be deteriorated. The content is preferably 8% or less, more preferably 4% or less, still more preferably 3% or less, and particularly preferably 2% or less.

Y ₂ O ₃ , La ₂ O ₃ , and Nb ₂ O ₅ may be included. When each of these components is contained, the content is preferably 0.5% or more, more preferably 1% or more, still more preferably 1.5% or more, particularly preferably 2% or more, most preferably Preferably it is 2.5% or more. On the other hand, if the contents of Y ₂ O ₃ , La ₂ O ₃ , and Nb ₂ O ₅ are each over 8%, the glass tends to be devitrified at the time of melting, and the quality of the chemically strengthened glass may be deteriorated. The contents of Y ₂ O ₃ , La ₂ O ₃ and Nb ₂ O ₅ are each preferably 8% or less, more preferably 6% or less, still more preferably 5% or less, and particularly preferably 4%. Or less, most preferably 3% or less.

Ta ₂ O ₅ and Gd ₂ O ₃ may be contained in a small amount in order to improve the crushability of chemically strengthened glass. However, the refractive index and the reflectance are increased, so 1% or less is preferable, and 0.5% or less. Is more preferable, and it is still more preferable not to contain.

Furthermore, when coloring and using glass, you may add a coloring component in the range in which a desired chemical strengthening characteristic is acquired. 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 , and Er _2. O ₃ , Nd ₂ O _{3 and the} like are preferable.

The content of the coloring components is preferably 7% or less in total because glass devitrification is suppressed. This content is preferably 5% or less, more preferably 3% or less, and even more preferably 1% or less. When it is desired to increase the visible light transmittance of the glass, it is more preferable that these components are not substantially contained.

As a fining agent for melting the glass, SO ₃ , chloride, fluoride and the like may be appropriately contained. It is preferable not to contain As ₂ O ₃ . When containing Sb ₂ O ₃ content _of preferably 0.3% or less, more preferably 0.1% or less, and most preferably substantially not contained.

Further, fracture toughness of the glass for chemical strengthening, preferably 0.70 MPa ^{· m 1/2} or more, more preferably 0.75 MPa ^{· m 1/2} or more, more preferably 0.77MPa ^{· m 1/2} or more, particularly preferably 0.80 MPa ^{· m 1/2} or higher, 0.82 MPa ^{· m 1/2} or more is most preferred. When the fracture toughness value is 0.70 MPa · m ^1/2 or more, the friability of the glass can be effectively suppressed.

The Young's modulus of the glass for chemical strengthening of the present invention is preferably 74 GPa or more, more preferably 78 GPa or more, and further preferably 82 GPa or more. The upper limit of the Young's modulus is not particularly limited, but is, for example, 90 GPa or less, preferably 88 GPa or less. The Young's modulus can be measured by, for example, an ultrasonic pulse method.
Moreover, the liquid phase temperature _TL of the glass for chemical strengthening of the present invention is preferably a temperature T ₄ or less at which the viscosity becomes 10 ⁴ dPa · s. In that case, it is easy to produce a glass plate by the float process. For ease of molding glass by a float method, _{T L} is preferably not more than _{T 4} from 10 ° C. lower temperature _{(T 4 -10 ℃), T} 4 , more preferably -30 ° C. or _less, T 4 -50 ° C. The following is more preferable. For ease of chemical strengthening, _TL is preferably T ₄ −150 ° C. or higher, more preferably T ₄ −125 ° C. or higher, and further preferably T ₄ −100 ° C. or higher.

(Method for producing chemically strengthened glass)
The chemically strengthened glass can be produced, for example, as follows.

First, prepare glass for chemical strengthening (chemical strengthening glass). The glass for chemical strengthening treatment is preferably the glass for chemical strengthening of the present invention. The chemical strengthening glass may be subjected to mechanical processing such as cutting, end surface processing, and drilling processing according to the application before chemical strengthening treatment is performed to obtain chemically strengthened glass. If the glass plate is cut or chamfered before the chemical strengthening treatment, a compressive stress layer is also formed on the end face by the subsequent chemical strengthening treatment, which is preferable.

The chemical strengthening treatment is performed, for example, by cutting the manufactured chemical strengthening glass into a desired size and then preheating the chemical strengthening glass to about 400 ° C., and in the molten salt, Li ions contained in the glass and the molten salt are contained in the molten salt. The glass can be strengthened by ion exchange of Na ions or Na ions contained in the glass and K ions in the molten salt.
Further, after ion exchange in a molten salt containing a specific salt, an acid treatment and an alkali treatment may be performed to obtain a chemically strengthened glass with higher strength.

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

Examples of molten salts for performing chemical strengthening treatment include nitrates, sulfates, carbonates, chloride salts and the like. Among these, examples of the nitrate include lithium nitrate, sodium nitrate, potassium nitrate, cesium nitrate, and silver nitrate. Examples of the sulfate include lithium sulfate, sodium sulfate, potassium sulfate, cesium sulfate, and the like. Examples of the carbonate include lithium carbonate, sodium carbonate, and potassium carbonate. Examples of the chloride salt 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. Further, other salts may be mixed in order to adjust the chemical strengthening characteristics.

Adjustment of surface compressive stress CS ₀ of chemically strengthened glass, for example the Na concentration in the molten potassium nitrate salt used in the ion-exchange, it is possible by adjusting the reinforced time and / or molten salt temperature.
The compression stress layer depth DOL can be adjusted by adjusting the Na concentration, the strengthening time and / or the molten salt temperature in the molten potassium nitrate salt used for ion exchange. In order to obtain a higher DOL, the temperature of the molten salt may be increased.
Adjustment of CT of chemically strengthened glass is possible by adjusting CS ₀ and DOL described above.

In the present invention, the chemical strengthening treatment may be performed only once, or multiple times of chemical strengthening treatment (multi-stage strengthening) may be performed under two or more different conditions. Here, for example, as the first-stage chemical strengthening process, after performing the chemical strengthening process under the condition that the CS is relatively low, the second-stage chemical strengthening process is performed under the condition that the CS is relatively high. Doing strengthening, while increasing the surface compressive stress CS ₀ of chemically strengthened glass, it is possible to suppress the internal tensile stress CT.

The chemically strengthened glass of the present invention can be produced by subjecting the obtained glass plate to chemical strengthening treatment, followed by washing and drying.

Chemically tempered glass can be cut after chemical tempering treatment. As a cutting method, scribing and breaking with a normal wheel tip cutter can be applied, and laser cutting is also possible. In order to maintain the strength of the glass plate, the cutting edge may be chamfered after cutting. The chamfering may be a mechanical grinding process or a method of treating with a chemical solution such as hydrofluoric acid.

The glass for chemical strengthening of the present invention is produced, for example, by appropriately preparing a glass raw material, heating and melting at about 1500 to 1700 ° C., molding and cooling. Molten glass obtained by melting a glass raw material is usually formed by homogenization by defoaming, stirring, or the like. As a forming method when the glass for chemical strengthening is formed on a plate, a well-known float method, down draw method, press method or the like is used. Or you may cast, shape | mold into a block shape, and cut | disconnect to a desired size after slow cooling.

For example, when forming into a plate shape by a float method, a down draw method, etc., high temperature molten glass is shape | molded, being cooled. In this case, the cooling rate in the molding step is preferably 300 ° C./min or less, more preferably 120 ° C./min or less, and further preferably 90 ° C./min or less in order to lower the fictive temperature.
On the other hand, when the cooling rate is slow, not only the production efficiency of the glass plate is lowered, but the glass tends to be devitrified. In particular, lithium aluminosilicate glass is liable to be devitrified because lithium aluminosilicate crystals are likely to precipitate.
The cooling rate is preferably 10 ° C./min or more in order to suppress devitrification of the glass.

The chemically strengthened glass of the present invention is subjected to a polishing process as necessary, but the main surface of the chemically strengthened glass can be treated with a fluorine agent in addition to or in place of the polishing process. Considering that the glass for chemical strengthening of the present invention is produced stably, the float process is preferable as the forming method, especially considering the production of a large glass for chemical strengthening. Then, it cut | disconnects as needed. Generally, it is cut into a rectangular shape, but other shapes such as a circular shape or a polygonal shape may be used without any problem and may be subjected to drilling.

The thickness t of the glass for chemical strengthening of the present invention is selected according to the application. For example, when used as a cover glass for a display part of a mobile phone or the like, the thickness t is preferably 2.0 mm or less, more preferably 1.0 mm or less, and 0.75 mm or less. Is more preferable. The thickness t is usually 0.1 mm or more.

Since the chemically strengthened glass of the present invention has high mechanical strength, it is suitable for use in places where impact due to dropping or contact with other substances is expected.
Specifically, it is particularly useful as a cover glass used for mobile devices such as mobile phones, smartphones, personal digital assistants (PDAs), and tablet terminals. Furthermore, non-portable products such as televisions (TVs), personal computers (PCs), cover glass for display devices such as touch panels, wall surfaces of elevators, wall surfaces of buildings such as houses and buildings (full display), and construction of window glass, etc. It is also useful for interior materials such as automobile materials, table tops, automobiles and airplanes.

EXAMPLES Hereinafter, although this invention is further demonstrated using an Example, this invention is not limited to this.
A glass material was appropriately prepared, heated and melted, homogenized by defoaming, stirring and the like, and formed into a plate shape to obtain a glass plate. The cooling rate was about 70 ° C./min. Table 1 shows the composition (mol%) of the glass used in Examples and Comparative Examples. Although not shown in the table, P ₂ O ₅ and ZnO are “0.0” (not included) in any glass. Glass 2 is the glass described in Patent Document 1. The obtained glass was evaluated for the following characteristics.

(Glass transition point Tg)
The glass transition point Tg was determined from the thermal expansion curve obtained by the method described in JIS R3102 (1995).
(Young's modulus, Poisson's ratio)
The Young's modulus and Poisson's ratio of the glass plate obtained by the above procedure were measured by the ultrasonic pulse method.

(T ₂ , T ₄ )
The temperature _{T 4} to a temperature _{T 2} and viscosity viscosity becomes ¹⁰ 2 dPa · s is ¹⁰ 4 dPa · s, it was measured using a rotational viscometer.
(Liquid phase temperature T _L , devitrification viscosity)
5 g of glass crushed so that the average particle size is about 500 μm is put in a 35 ml platinum dish, kept in an electric furnace at a predetermined temperature for 17 hours, and then taken out and observed with an optical microscope with a magnification of 10 times. The presence or absence was examined. In the temperature range of 800 ° C. to 1500 ° C., the operation for examining the presence or absence of crystal precipitation was repeated while changing the holding temperature, and the lowest temperature at which no crystal was precipitated was defined as the liquidus temperature _TL .
From the relationship between temperature and viscosity obtained with a rotational viscometer, the viscosity at the liquidus temperature was obtained and defined as devitrification viscosity.

<Influence of mirror constant>
(Adjustment of virtual temperature)
The obtained glass 1 plate is held at a temperature 30 ° C. higher than the glass transition point Tg for 1 hour, and then precisely annealed at a cooling rate of 1 ° C./min. Got. It was 535 degreeC when fictive temperature was measured by the below-mentioned method.
Moreover, the glass plate whose virtual temperature is Tg + 60 degreeC was obtained by performing the process which cools rapidly after hold | maintaining to the temperature 60 degreeC higher than a glass transition point.
Glasses 2 and 3 were produced by using a glass having a thermal history simulating a glass plate obtained in a commercial production process. Glass 2 simulates the thermal history of glass produced by the fusion method, and the fictive temperature was Tg + 50 ° C. Glass 3 simulates the thermal history of glass produced by the float process, and the fictive temperature was Tg + 30 ° C.
(Mirror constant)
The mirror constant A was measured by the following procedure. However, Example 3 and Example 4 were calculated from a sample having a fictive temperature near Tg and a mirror constant of Tg + 60 ° C.
It processed to the magnitude | size of 40x6x3 mm, and mirror-polished the front and back and the end surface (a total of 4 surfaces) of the longitudinal direction.
Using a 110 ° diamond indenter with a Vickers hardness tester, the indenter was pushed in under different loads to be injured. The indentation load was set to 0.05 kgf, 0.1 kgf, 0.3 kgf, 0.5 kgf, 0.75 kgf, 1.0 kgf, 2.0 kgf, and 3.0 kgf.
Heat treatment was performed to remove the influence of strain due to the scratch. This heat treatment was performed according to the following procedure also for adjusting the fictive temperature.
Sample having a fictive temperature near Tg: held for 1 hour at a temperature 30 ° C. higher than Tg, and gradually cooled by lowering to room temperature at 1 ° C./min.
Sample having a fictive temperature of Tg + 60 ° C .: held at a temperature 60 ° C. higher than Tg for 1 hour and rapidly cooled in air.

A four-point bending test was performed on a glass plate which was scratched with the span of the four-point bending jig set to the load side (upper): 10 mm and the support side (lower): 30 mm. Apply the adhesive tape on the opposite side of the scratched and heat-treated glass, apply the load with the scratched surface down (the surface with the adhesive tape applied up), and the load when crushed It was measured. The stress at the time of crushing was calculated | required from the measured load using the following formula | equation.
σ = (3F (Ls−Ll)) / (2wh ² )
Where σ: stress during crushing (MPa), F: load during crushing (N), Ls: distance between lower fulcrums (mm), Ll: distance between upper load points (mm), w: sample width (mm) ), H: sample thickness (mm).
Next, the fracture surface was observed using a KEYENCE digital microscope VHX-5000, and the distance R from the fracture starting point to the interface between the mirror surface and the mist surface was measured. At the time of observation, the sample and the lens of the microscope were made parallel and the observation was performed at a magnification of 20 × 150 times.
From the results obtained by the above procedure, the mirror constant A was determined using the following equation.
σ = A / R ^1/2

(Chemical strengthening properties)
Glass 1 was subjected to chemical strengthening treatment at 450 ° C. for 1 hour using sodium nitrate, glass 2 was subjected to chemical treatment at 450 ° C. for 6 hours using potassium nitrate, and glass 3 was subjected to chemical strengthening treatment at 425 ° C. for 12 hours using potassium nitrate. .
The stress of the glass after chemical strengthening treatment was measured to determine CS ₀ , DOL, and CT.
The glass used had a thickness t of 0.8 mm, and −38.7 × ln (t) +48.2 was 56.5 MPa.

(Number of crushing)
The number of glass fragments after chemical strengthening treatment was measured by the following method.
Using a HMV micro Vickers hardness tester manufactured by SHIMADZU, a regular quadrangular pyramid-shaped 60 ° (face-to-face) indenter is pushed into the glass after chemical strengthening at the following indenter load speed, load 4 kgf, and indentation time 15 sec. If the glass is not crushed as a result of the indentation, the indentation load is increased by 0.5 kgf. The number of debris when crushed is taken as the number of crushed pieces. If the number of crushing is less than 10, it can be said that it is suitable for a cover glass of mobile devices, for example.
Indenter loading speed: 260 μm / sec until touching the glass surface, 5 to 120 μm / sec after glass penetration

(Sand drop test)
About the glass after a chemical strengthening process, the drop test on sand was done with the following test methods.
FIG. 4 is a schematic diagram showing a test method of a drop-on-sand test.
First, chemically tempered glass 13 (50 mm × 50 mm × thickness 0.8 mm) and sponge double-sided tape 12 (# manufactured by Sekisui Chemical Co., Ltd.) are used on a hard nylon mock plate 11 (50 mm × 50 mm × thickness 18 mm, weight: 54 g). 2310, 50 mm × 50 mm × thickness 3 mm) to prepare a measurement sample 10. Next, 1 g of silica sand 22 (No. 5 silica sand made by Takefori Co., Ltd.) is uniformly spread on a metal plate 21 (SUS (stainless steel)) having a size of 15 cm × 15 cm, and a measurement sample is prepared. 10 was dropped from a predetermined height (falling height) onto the surface of the metal plate 21 on which the silica sand 22 was coated with the chemically strengthened glass 13 facing down. The drop test was carried out starting from a drop height of 10 mm and increasing the height by 10 mm. The height at which the glass 13 was broken was defined as the crack height (unit: mm). The drop test was carried out 5 to 10 times for each example, and the average crack height in the drop test was defined as the average crack height (unit: mm). These results are shown in Table 2.

Glasses 2 and 3 used in Examples C and D were severely crushed when a tensile stress exceeding the limit CT (56.8 MPa) shown in Patent Document 1 was applied. The glass after chemical strengthening applied with an internal tensile stress exceeding the conventional limit CT (56.8 MPa) has a large number of fractures of 10 or more, and the result of the drop-on-sand test is not good. It was confirmed that the glasses of Examples C and D had a small mirror constant.
Examples A and B using glass 1 had a mirror constant of 2.0 MPa · m ^1/2 or more. Even after chemically strengthened glass to which internal tensile stress exceeding the conventional limit CT (56.8 MPa) was applied, the number of fractures was small, and the results of a drop-on-sand test were also good.
Moreover, when Example A and Example B are compared, even if it is the same glass composition, it turns out that a mirror constant is so large that virtual temperature is low.

<Difference between cooling rate and glass composition>
About glass 1, 4, 5, 6, 7, the plate-shaped sample of 15 mm x 15 mm x 0.8 mmt was produced. For Examples 1, 2, 3, and 4, a belt furnace programmed to be held at a temperature 30 ° C. higher than the Tg of each glass for 5 minutes and then cooled to near room temperature at a cooling rate of 70 ° C./min. Heat treated. About Example 5 and Example 6, after hold | maintaining at the temperature 60 degreeC higher than Tg of each glass for 1 hour, it cooled to room temperature with the cooling rate of 0.5 degreeC / min. Example 7 was held at a temperature 60 ° C. higher than Tg for 1 hour and then cooled at 500 ° C./min.
Examples 1 to 3 are examples, and examples 4 to 7 are comparative examples.

(Virtual temperature)
Table 3 shows the results of measuring the refractive index for Examples 1 to 7 and obtaining the fictive temperature from the calibration curve prepared by the following method.
The calibration curve is created by holding glass plates of 15 mm × 15 mm × 0.8 mm thickness at a high temperature for each of the glass 1, 4, 5, 6, 7 and then rapidly cooling, each of the virtual temperatures being Tg + 50 ° C., The glass plates of Tg + 20 ° C., Tg + 5 ° C., Tg−10 ° C., and Tg−30 ° C. were adjusted, and the refractive index was measured to plot the relationship between the fictive temperature and the refractive index. FIG. 3 is a calibration curve for the glass 1. The glass whose fictive temperature was adjusted was obtained, for example, by maintaining the glass at a temperature higher by 50 ° C. than the Tg of the glass, and then quenching by putting it into water to obtain a glass plate having a fictive temperature of Tg + 50 ° C.

(Chemical strengthening properties)
Each glass of Examples 1 to 7 was subjected to chemical strengthening treatment with Na salt by immersing in sodium nitrate molten salt at 450 ° C. for 1 hour. After cooling, washing and drying, the surface compressive stress value CS1 and the compressive stress layer depth DOL1 by Na salt treatment were measured by a photoelastic scattering type stress analysis device (manufactured by Orihara Seisakusho, provisional name SLPII).
Next, it is treated with molten potassium nitrate at 450 ° C. for 6 hours, cooled, washed and dried, and then subjected to a stress analysis device (FSM6000 manufactured by Orihara Seisakusho Co., Ltd.) and the surface compressive stress value CS2 and compression after chemical strengthening with K salt. The stress layer depth DOL2 was measured.
In Example 4, since CS2 and DOL2 could not be measured, the surface was treated with a photoelastic scattering type stress analyzer (provisionally named SLPII) after treatment with a potassium nitrate molten salt at 450 ° C. for 48 hours. The compressive stress value and the compressive stress layer depth are measured, and the surface compressive stress value does not depend on the processing time, and the compressive stress layer depth is proportional to the square root of the processing time. CS2 and DOL2 when time processing was performed were calculated.

(Devitrification characteristics)
The glass of Examples 1 to 7 was put in a platinum crucible and held at 1500 ° C. for 3 hours to melt, then cooled to room temperature at a predetermined cooling rate, taken out from the platinum crucible, and visually checked for devitrification. Observed.

Examples 1-3 surface compressive stress CS ₀ higher by chemical strengthening is obtained and, devitrification was observed. Example 4, _{T L} is high glass than _{T 4,} devitrification was severe.
Comparing Example 1 and Example 5, it can be seen that even glasses having the same composition are easily devitrified when the cooling rate is very slow and the fictive temperature is low. In Example 7, which did not devitrify even when the cooling rate was very low, CS ₀ and DOL did not increase. This is because the glass composition is different.
When Example 1 and Example 7 are compared, Example 7 with a high fictive temperature even with the same glass composition has low CS2 and insufficient strength.

Although the present invention has been described in detail and 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 a Japanese patent application filed on September 21, 2016 (Japanese Patent Application No. 2016-183936), a Japanese patent application filed on October 18, 2016 (Japanese Patent Application 2016-204745), and a Japanese patent application filed on July 20, 2017. This is based on a patent application (Japanese Patent Application No. 2017-141284), the contents of which are incorporated herein by reference.

10: Measurement sample 11: Mock plate 12: Sponge double-sided tape 13: Chemically tempered glass 21: Metal plate 22: Silica sand

Claims (8)

1. The liquid phase temperature T _L is made of lithium aluminosilicate glass having a temperature T ₄ or less at which the viscosity becomes 10 ⁴ dPa · s,
   The glass for chemical strengthening whose fictive temperature is not less than a temperature 30 ° C. lower than the glass transition point Tg and not more than 25 ° C. higher than the Tg.
2. The glass for chemical strengthening according to claim 1, wherein the mirror constant A is 2.0 MPa · m ^1/2 or more.
3. Expressed in mole percentages based on oxide, SiO ₂ is 60 to 80%, Al ₂ O ₃ is 4 to 25%, Li ₂ O is 5 to 15%, Na ₂ O is 1 to 15%, and K ₂ O is 0. ~ 5%, MgO 2 ~ 25%, CaO 0 ~ 10%, SrO 0 ~ 10%, BaO 0 ~ 10%, ZnO 0 ~ 10%, B ₂ O ₃ 0 ~ 10%, P ₂ O ₅ 0 to 10% of TiO ₂ 0-10%, and chemically strengthened glass according to claim 1 or 2 ZrO ₂ contains 0 to 8%.
4. Expressed in oxide-based mole percentage, SiO ₂ is 67 to 75%, Al ₂ O ₃ is 4 to 15%, Li ₂ O is 5 to 15%, Na ₂ O is 1 to 9%, and K ₂ O is 0. ~ 5%, MgO 4 ~ 15%, CaO 0 ~ 4%, SrO 0 ~ 5%, BaO 0 ~ 5%, ZnO 0 ~ 5%, B ₂ O ₃ 0 ~ 10%, P ₂ O ₅ 0 to 10% of TiO ₂ 0 ~ 4% and chemically strengthened glass according to any one of claims 1 to 3, the ZrO ₂ contains 0 to 8%.
5. Expressed in molar percentage on oxide basis, SiO ₂ is 68-72%, Al ₂ O ₃ is 6-10%, Li ₂ O is 7-11%, Na ₂ O is 4-7%, K ₂ O is 0 ~ 3%, MgO 4 ~ 10%, CaO 0 ~ 3%, SrO 0 ~ 2%, BaO 0 ~ 2%, ZnO 0 ~ 2%, B ₂ O ₃ 0 ~ 3%, P _A glass for chemical strengthening containing 0 to 3% of ₂ O ₅ , 0 to ₂ % of TiO ₂ and 0 to 3% of ZrO ₂ and having a fictive temperature of 25 ° C. or lower than the glass transition point Tg.
6. Expressed in mole percentages based on oxide, SiO ₂ is 60 to 80%, Al ₂ O ₃ is 4 to 25%, Li ₂ O is 5 to 15%, Na ₂ O is 1 to 15%, and K ₂ O is 0. ~ 5%, MgO 2 ~ 25%, CaO 0 ~ 10%, SrO 0 ~ 10%, BaO 0 ~ 10%, ZnO 0 ~ 10%, B ₂ O ₃ 0 ~ 10%, P ₂ O ₅ 0 to 10%, TiO ₂ 0 to 10%, ZrO ₂ 0 to 8%, and the liquidus temperature T _L is a temperature T ₄ or less at which the viscosity becomes 10 ⁴ dPa · s Melting glass of
   Cool at an average cooling rate of 10 ° C / min to 300 ° C / min.
   A method for producing chemically strengthened glass.
7. Having a surface compressive stress layer,
   A virtual surface stress obtained from a line obtained by extending the stress pattern P1 on the glass inner layer side to the glass surface when the stress pattern near the glass surface and the stress pattern on the glass inner layer side are approximated by a linear function. The value CS1 is a chemically strengthened glass smaller than the surface compressive stress value CS2 obtained from the stress pattern P2 of the portion close to the glass surface,
   The CS1 is 200 MPa or more, and the CS2 is 800 MPa or more,
   And chemically strengthened glass whose mirror constant A is 2.0 Mpa * m < ^1/2 > or more.
8. As the mother composition of chemically strengthened glass, SiO ₂ is 60 to 80%, Al ₂ O ₃ is 4 to 25%, Li ₂ O is 5 to 15%, and Na ₂ O is 1 to _{2 in} terms of mole percentage based on oxide. 15%, K ₂ O 0-5%, MgO 2-25%, CaO 0-10%, SrO 0-10%, BaO 0-10%, ZnO 0-10%, B ₂ O The chemically strengthened glass according to claim 7, comprising 0 to 10% of ₃ ; 0 to 10% of P ₂ O ₅ ; 0 to 10% of TiO ₂ ; and 0 to 8% of ZrO ₂ .

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