CN115231820B

CN115231820B - Chemically strengthened glass and chemically strengthened glass

Info

Publication number: CN115231820B
Application number: CN202210674176.XA
Authority: CN
Inventors: 今北健二; 小野円佳; 村山优; 小野和孝
Original assignee: Asahi Glass Co Ltd
Current assignee: AGC Inc
Priority date: 2016-09-21
Filing date: 2017-09-14
Publication date: 2023-06-23
Anticipated expiration: 2037-09-14
Also published as: CN109715573B; CN115231820A; CN109715573A; WO2018056168A1

Abstract

The purpose of the present invention is to provide a chemically strengthened glass having high strength and less scattering of fragments during breakage, and a glass for chemical strengthening that is useful for producing the chemically strengthened glass. The invention relates to a glass for chemical strengthening, which is prepared from a liquid phase temperature T _L At a temperature T ₄ The following lithium aluminosilicate glass is composed, the temperature T ₄ Is of viscosity up to 10 ⁴ dPa.s, the fictive temperature being a temperature 30 ℃ below the glass transition temperature Tg to a temperature 25 ℃ above the Tg.

Description

Chemically strengthened glass and chemically strengthened glass

The present application is a divisional application of the invention application with the application number 201780057539.2, the application date 2017, 9, 14, and the name "glass for chemical strengthening" and chemical strengthening glass.

Technical Field

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

Background

As cover glass for display devices of mobile devices such as mobile phones and smart phones, chemically strengthened glass having high strength even when thin is used.

For chemically strengthened glass, the greater the surface compressive stress value (CS) and the greater the depth of layer of compressive stress (DOL), the greater the strength tends to be. On the other hand, an internal tensile stress (CT) is generated inside the glass to maintain equilibrium with the surface compressive stress. When a glass having a large internal tensile stress is broken, the number of fragments increases due to severe breakage, and the fragments tend to scatter.

Patent document 1 discloses a calculation formula showing an allowable limit of an internal tensile stress of a tempered glass, and by tempering in this range, a chemically tempered glass with less scattering of fragments can be obtained.

Patent document 2 describes a chemically strengthened glass obtained by performing two-step ion exchange treatment as a chemically strengthened glass having high strength and less scattering of fragments.

Prior art literature

Patent literature

Patent document 1: U.S. Pat. No. 8075999 Specification

Patent document 2: U.S. Pat. No. 9487434 Specification

Disclosure of Invention

However, within the allowable limits as described in patent document 1, a sufficiently high strength may not be obtained. That is, the chemically strengthened glass described in patent document 1 and patent document 2 may have insufficient strength.

The purpose of the present invention is to provide a chemically strengthened glass having high strength and less scattering of fragments during breakage, and a glass for chemical strengthening that is useful for producing the chemically strengthened glass.

Based on the following examination, the present inventors considered that the breaking mode of chemically strengthened glass depends on the characteristics of glass before chemical strengthening.

The chemically strengthened glass is broken when a crack generated in the glass reaches a portion where a tensile stress is applied to the inside of the glass. Since the portion to which the tensile stress is applied is considered to be a portion to which ion exchange is not performed even by the chemical strengthening treatment, it is considered that the breaking property of the portion depends on the property of the glass before the chemical strengthening.

The present inventors have also focused on the fact that if there are a large number of branches of cracks when breaking occurs in glass, a large number of fragments are generated, and studied on glass in which cracks are not easily branched. As a result, it was found that glass having a large mirror constant had a small number of fragments at the time of fracture even when chemically strengthened.

In addition, it was found that glass having a large mirror constant is characterized by

The present invention has been made in view of the above-described circumstances, and an object thereof is to provide a glass for chemical strengthening, which is produced from a liquid phase temperature T _L At a temperature T ₄ The following lithium aluminosilicate glass is composed, the temperature T ₄ Is of viscosity up to 10 ⁴ dPa.s, the fictive temperature being a temperature 30 ℃ below the glass transition temperature Tg to a temperature 25 ℃ above the Tg.

Further, there is provided a glass for chemical strengthening, comprising 68 to 72% of SiO in terms of mole percent based on oxide ₂ 6 to 10 percent of Al ₂ O ₃ 7 to 11 percent of Li ₂ O, na 4-7% ₂ O, 0-3% of K ₂ O, 4-10% MgO, 0-3% CaO, 0-2% SrO, 0-2% BaO, 0-2% ZnO and 0-3% B ₂ O ₃ 0 to 3 percent of P ₂ O ₅ 0 to 2 percent of TiO ₂ ZrO 0-3% ₂ And the fictive temperature is a temperature 25 ℃ or lower higher than the glass transition temperature Tg.

Further, a method for producing a chemically strengthened glass is provided, wherein the glass contains 60 to 80% of SiO in terms of mole percentage based on oxides ₂ 4 to 25 percent of Al ₂ O ₃ 5 to 15 percent of Li ₂ O, na 1-15% ₂ O, 0-5% of K ₂ O, mgO 2-25%, caO 0-10%, srO 0-10%, baO 0-10%, znO 0-10% and B0-10% ₂

O

₃ 0 to 10 percent of P ₂ O ₅ 0 to 10 percent of TiO ₂ ZrO 0-8% ₂ And liquid phase temperature T _L To a viscosity of 10 ⁴ dPa·Temperature T of s ₄ The glass to be melted is cooled at an average cooling rate of 10 to 300 ℃ per minute.

Further, there is provided a chemically strengthened glass having a surface compressive stress layer, wherein when a stress pattern of a portion near a glass surface and a stress pattern of a glass inner layer side are approximated by a linear function, a virtual surface stress value CS1 obtained from a line extending the stress pattern P1 of the glass inner layer side to the glass surface is smaller than a surface compressive stress value CS2 obtained from a stress pattern P2 of a portion near the glass surface, wherein CS1 is 200MPa or more and CS2 is 800MPa or more, and a mirror constant A is 2.0 MPa.m ^1/2 The above.

The chemically strengthened glass of the present invention has high strength and does not undergo strong damage even when broken. In addition, according to the preferred embodiment, devitrification is less likely to occur.

Drawings

Fig. 1 is a diagram schematically showing a stress distribution diagram of chemically strengthened glass, wherein the vertical axis represents a compressive stress value and the horizontal axis represents a depth from the glass surface.

Fig. 2 is a diagram schematically showing a fracture mode around a fracture origin when a glass having no residual stress therein is broken by a uniform tensile stress.

Fig. 3 is a graph showing the relationship between the refractive index of the glass 1 and the virtual temperature.

Fig. 4 is a schematic diagram showing a test method of the sand falling test.

Detailed Description

In the present specification, "chemically strengthened glass" means glass after being subjected to a chemical strengthening treatment. The "glass for chemical strengthening" refers to glass before the chemical strengthening treatment is performed. "glass for chemical strengthening" is glass that can be chemically strengthened.

In the present specification, the "mother composition of chemically strengthened glass" refers to the glass composition of chemically strengthened glass. In chemically strengthened glass, since a compressive stress layer formed by ion exchange is generally formed in a glass surface portion, the glass composition of a portion where ion exchange is not performed coincides with the parent composition of chemically strengthened glass.

In the present specification, the glass composition is expressed as mole percent based on oxides, and mole percent is sometimes abbreviated as%.

The phrase "substantially free of" in the glass composition means that it is not contained, i.e., not intentionally contained, except for unavoidable impurities contained in raw materials and the like. Specifically, for example, the content in the glass composition is less than 0.1 mol%.

In the present specification, the "stress distribution diagram" is a diagram showing a compressive stress value using a depth from a glass surface as a variable. Negative compressive stress values refer to tensile stress.

In the present specification, "fragility" of glass means a property that fragments are easily scattered when the glass is broken.

(chemically strengthened glass)

The chemically strengthened glass has a compressive stress layer formed by a chemical strengthening treatment (ion exchange treatment) on the surface. For ion exchange treatment, the surface of the glass is ion exchanged to form a surface layer of residual compressive stress. Specifically, at a temperature equal to or lower than the glass transition temperature Tg, metal ions (typically, li ions and Na ions) having a small ion radius on the surface of the glass plate are replaced with ions having a larger ion radius (typically, na ions or K ions relative to the Li ions and K ions relative to the Na ions) by ion exchange. Thereby, compressive stress is generated on the surface of the glass, and the strength of the glass is improved.

Compressive stress value CS of glass surface ₀ Even if damage occurs on the surface of a large chemically strengthened glass, the damage is not easily expanded due to the compression stress on the surface, and therefore, the glass is not easily broken. In addition, since tensile stress applied to the outer side of the curved surface is offset by surface compressive stress when bending the glass sheet, breakage is not easily caused even in bending. On the other hand, chemically strengthened glass having a large depth of compressive stress DOL is not easily broken because the front end of the deep damage remains in the compressive stress layer.

Thus, CS is considered to chemically strengthen the glass surface of glass ₀ The larger the DOL is, the bigger the DOL is, the less easy the damage is. However, if CS is increased at the same time ₀ And DOL, there is a tendency that the internal tensile stress value CT becomes larger and the fracture becomes larger accordingly.

Fig. 1 is a graph schematically showing a stress distribution diagram of chemically strengthened glass according to an embodiment of the present invention, wherein the vertical axis represents a compressive stress value and the horizontal axis represents a 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 on the portion near the glass surface by a linear function, respectively.

In the stress distribution diagram, a virtual surface compression stress value CS1 obtained from a line (a broken line P1 in fig. 1) extending the stress pattern P1 to the glass surface is smaller than a surface compression stress value CS2 obtained from the stress pattern P2. Actual surface compressive stress value CS ₀ Approximately equal to CS 2.

In addition, the depth DOL2 at which the stress value is zero on the line (the broken line P2 in fig. 1) extending the stress pattern P2 is smaller than the depth DOL1 at which the stress value is zero in the stress pattern P1. The actual compressive stress layer depths DOL and DOL1 are approximately equal.

In such a stress distribution pattern, the internal tensile stress CT is preferably smaller even if the compressive stress value of the glass surface is large. Such a stress profile can be obtained, for example, by a two-step chemical strengthening treatment.

In the stress distribution diagram, CS1 is preferably 200MPa or more. In addition, CS ₀ (and CS 2) is preferably 800MPa or more.

On the other hand, in order to suppress the crushing property, CS2 is preferably 2000MPa or less, more preferably 1500MPa or less, and further preferably 1000MPa or less, for example. If CS2, which is a surface compressive stress value, is increased, the internal tensile stress value CT becomes large, so that the crushability increases.

The chemically strengthened glass of the present embodiment has a mirror constant A of 2.0 MPa.m and a surface compressive stress value CS1 calculated from a line extending a stress pattern P1 on the inner layer side of the glass to the glass surface, which is smaller than a surface compressive stress value CS2 calculated from a stress pattern P2 of a portion near the glass surface ^1/2 Above, even the surface compressive stress CS ₀ And an increase in the depth of compressive stress DOLThe crushability can also be suppressed.

The chemically strengthened glass of the present invention preferably has a mirror constant A of 2.0 MPa.m ^1/2 The above, more preferably 2.1 MPa.m ^1/2 The above is more preferably 2.3 MPa.m ^1/2 The above. Since the chemically strengthened glass having a large mirror constant a has a small number of fragments at the time of breakage, the breakage is not large even if the internal tensile stress CT is large.

Here, the mirror constant a will be described to assist understanding of the present invention.

It is known that when glass breaks, the shape of the broken surface varies according to the magnitude of stress. FIG. 2 schematically shows a fracture mode around the fracture origin when the glass having no residual stress inside is broken by a uniform tensile stress (see ASTM C-1678-10). Since the chemically strengthened glass has residual stress, the appearance of the vicinity of the fracture origin of the chemically strengthened glass may be significantly different from that of fig. 2.

In fig. 2, a smooth surface called a mirror (mirror) surface is generated around the breaking start point shown by the black dot. Further, a slightly rough boundary surface called a mist (lost) surface is generated around the surface, and a rough surface called a comb (hash) is generated at the tip end. In fig. 2, if the distance from the failure start point shown by the black point to the boundary between the mirror (mirror) surface and the fog (best) surface is R and the stress causing the failure is σ, it is known that σ is proportional to the inverse of the square root of R, and the proportionality constant thereof is the mirror constant a. That is, the relationship shown in the following formula is obtained.

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 start point to the interface between the mirror surface and the haze.

The specular constant A depends on the glass composition and the 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.

Patent document 1 discloses a formula showing the allowable limit of the internal tensile stress CT of chemically strengthened glass, and it is considered that CT should be-38.7×ln (t) +48.2 mpa or less when the plate thickness is t [ mm ].

However, since the chemically strengthened glass according to one embodiment of the present invention has a large mirror constant a, fragments are less likely to scatter even when the internal tensile stress value CT is greater than-38.7×ln (t) +48.2.

As the parent composition of the chemically strengthened glass of the present invention, it is preferable that the chemically strengthened glass contains 60 to 80% of SiO in terms of mole percentage based on oxides ₂ 4 to 25 percent of Al ₂ O ₃ 5 to 15 percent of Li ₂ O, na 1-15% ₂ O, 0-5% of K ₂ O, mgO 2-25%, caO 0-10%, srO 0-10%, baO 0-10%, znO 0-10% and B0-10% ₂ O ₃ 0 to 10 percent of P ₂ O ₅ 0 to 10 percent of TiO ₂ ZrO 0-8% ₂ . The preferred glass composition will be described in detail later.

(glass for chemical strengthening)

The glass for chemical strengthening of the present invention is preferably lithium aluminosilicate glass. Lithium aluminosilicate glass is easily formed into a deep surface compression layer by ion exchange treatment with sodium salts such as sodium nitrate to cause ion exchange between Li ions in the glass and Na ions in the molten salt. In addition, when ion exchange treatment with a potassium salt (for example, potassium nitrate) is performed after ion exchange treatment with a sodium salt, or ion exchange treatment with a mixed salt of a sodium salt and a potassium salt (for example, a sodium nitrate-potassium nitrate mixed salt) is performed, ion exchange between a Li ion and a Na ion is generated in addition to ion exchange between a Na ion and a K ion, and therefore, the surface compression stress value CS is easily obtained ₀ Chemically strengthened glass having a high internal tensile stress CT.

The chemically strengthened glass of the present invention preferably has a surface compressive stress of 200MPa or more generated by ion exchange treatment with a sodium salt. Such glass is easily strengthened chemically to obtain high strength. For example, the surface compressive stress at the time of immersing in sodium nitrate at 450 ℃ for 1 hour is preferably 200MPa or more, more preferably 250MPa or more, and still more preferably 300MPa or more. For such chemically strengthened glass, ion exchange treatment with sodium salt is performed After that, when ion exchange treatment with potassium salt is performed, or ion exchange treatment with a mixed salt of sodium salt and potassium salt is performed, the surface compressive stress value CS is also obtained ₀ The chemically strengthened glass having a small internal tensile stress value CT can be obtained.

In addition, the chemically strengthened glass of the present invention preferably has a surface compressive stress of 800MPa or more generated by ion exchange treatment with a potassium salt. For example, the surface compressive stress at the time of immersing in potassium nitrate at 450 ℃ for 6 hours is preferably 800MPa or more, more preferably 850MPa or more, and still more preferably 900MPa or more. The glass for chemical strengthening is chemically strengthened to obtain a preferable stress distribution pattern.

In addition, the liquidus temperature T of the glass for chemical strengthening _L Preferably the viscosity reaches 10 ⁴ dPa.s temperature T ₄ The following is given. Such glass is easily formed into a plate shape by a float process. T for ease of molding by float process _L More preferably than T ₄ A temperature (T) lower by 10 DEG C ₄ At-10 ℃ or lower, T is further preferred ₄ T is more preferably at a temperature of-30℃or lower ₄ Below-50 ℃. For the sake of chemical strengthening easiness, T _L Preferably T ₄ -150 ℃ or higher, more preferably T ₄ At a temperature of 125 ℃ below zero or higher, T is further preferred ₄ Above-100 ℃.

The glass for chemical strengthening preferably has a mirror constant A of 2.0MPa m ^1/2 The above. Such a chemically strengthened glass is less likely to scatter fragments when broken after chemical strengthening.

The mirror constant A of the chemically strengthened glass is more preferably 2.1MPa m ^1/2 The above is more preferably 2.3 MPa.m ^1/2 The above.

There is a tendency that the lower the fictive temperature Tf of the glass is, the larger the specular constant a is.

In order to increase the mirror constant a, the virtual temperature Tf of the chemically strengthened glass is preferably in the vicinity of the glass transition temperature Tg of the glass. Specifically, the temperature is preferably 25℃or lower higher than Tg (referred to as Tg+25℃), more preferably not higher than Tg+20℃, and still more preferably not higher than Tg+15℃. The smaller the virtual temperature Tf is, the more preferable is to increase the mirror constant a, but the slower the cooling is to be performed at a very slow rate so as to be significantly lower than Tg, and the productivity of the glass is deteriorated. Accordingly, tf is preferably a temperature 30℃or higher (Tg-30 ℃) lower than Tg, more preferably a temperature of Tg-10℃or higher, and still more preferably a temperature of Tg or higher.

When glass is obtained by a method in which a glass raw material is melted and cooled at a high temperature, the smaller the cooling rate after melting, the lower the virtual temperature Tf of the glass becomes. Therefore, in order to obtain a glass having a very low virtual temperature, it is necessary to cool slowly for a long period of time. When the glass is cooled slowly, a devitrification phenomenon in which crystals are precipitated during cooling is liable to occur depending on the glass composition.

In view of the productivity of glass and suppression of devitrification, the fictive temperature Tf is preferably Tg-30℃or higher, more preferably Tg-10℃or higher, and even more preferably Tg or higher, as described above.

If they are combined, the fictive temperature Tf is preferably Tg-30 to Tg+25℃, more preferably Tg-10 to Tg+20℃, still more preferably Tg-15 ℃.

The fictive temperature Tf of glass can be experimentally determined from the refractive index of glass. By a method of quenching glass held at a constant temperature from that temperature, a plurality of glass sheets having the same glass composition and having different virtual temperatures are produced in advance. Since the virtual temperatures of the glass sheets are temperatures that are maintained before quenching, a standard curve can be produced by measuring the refractive indices of the glass sheets, which is obtained by plotting the refractive indices against the virtual temperatures. An example is shown in fig. 3. Even for a glass whose cooling rate is unknown, the virtual temperature can be obtained from a standard curve prepared for a glass having the same composition by measuring the refractive index.

The glass for chemical strengthening of the present invention preferably contains, for example, 60 to 80% of SiO ₂ 4 to 25 percent of Al ₂ O ₃ 5 to 15 percent of Li ₂ O, na 1-15% ₂ O, 0-5% of K ₂ O, mgO 2-25%, caO 0-10%, srO 0-10%, baO 0-10%, znO 0-10% and B0-10% ₂ O ₃ 0 to 10 percent of P ₂ O ₅ 0 to 10 percent of Ti ₂ O and OZrO 0-8% ₂ . Such glass is excellent in chemical strengthening characteristics.

The glass for chemical strengthening of the present invention preferably contains 60 to 80% of SiO ₂ 7 to 30 percent of Al ₂ O ₃ 5 to 15 percent of Li ₂ O, na 1-25% ₂ O, 0-5% of K ₂ O, mgO 3-25%, caO 0-10%, srO 0-10%, baO 0-10%, znO 0-10% and B0-5% ₂ O ₃ 0 to 4 percent of P ₂ O ₅ 0 to 10 percent of TiO ₂ . The mirror constant a of such glass is large.

Further, it is more preferable to contain 67 to 75% of SiO ₂ 4 to 15 percent of Al ₂ O ₃ 5 to 15 percent of Li ₂ O, na 1-9% ₂ O, 0-5% of K ₂ O, mgO 4-15%, caO 0-4%, srO 0-5%, baO 0-5%, znO 0-5% and B0-10% ₂ O ₃ 0 to 10 percent of P ₂ O ₅ 0 to 4 percent of TiO ₂ ZrO 0-8% ₂ . Such glass has excellent chemical strengthening properties, and is less likely to cause devitrification due to scattering of fragments during breakage.

The chemically strengthened glass of the present invention further preferably contains 68 to 72% of SiO ₂ 6 to 10 percent of Al ₂ O ₃ 7 to 11 percent of Li ₂ O, na 4-7% ₂ O, 0-3% of K ₂ O, 4-10% MgO, 0-3% CaO, 0-2% SrO, 0-2% BaO, 0-2% ZnO and 0-3% B ₂ O ₃ 0 to 3 percent of P ₂ O ₅ 0 to 2 percent of TiO ₂ ZrO 0-3% ₂ And the fictive temperature is 25 ℃ or lower higher than the glass transition temperature Tg. Such glass is excellent in chemical strengthening characteristics.

The components in the glass composition are described below.

SiO ₂ Is a component constituting the skeleton of glass. In addition, the composition is a component for improving chemical durability, and is a component for reducing the occurrence of cracks when scratches are generated on the surface of glass. To suppress the generation of cracks, siO ₂ The content is preferably above 60%More preferably 63% or more, still more preferably 65% or more, still more preferably 67% or more, and particularly preferably 68% or more. On the other hand, if SiO ₂ When the content exceeds 80%, the meltability is significantly reduced, and therefore 80% or less is preferable. For ease of melting, it is more preferably 75% or less, still more preferably 72% or less, particularly preferably 70% or less.

Al ₂ O ₃ In order to improve ion exchange performance in chemical strengthening treatment and increase surface compressive stress value CS after chemical strengthening ₀ Is effective in the composition. In addition, the glass is an active ingredient for improving the mirror constant A of the glass. In addition, the glass is a component that increases Tg and Young's modulus. To improve the chemical strengthening characteristics, al ₂ O ₃ The content is preferably 4% or more, more preferably 6% or more. In addition, to increase the mirror constant, al ₂ O ₃ The content is preferably 7% or more, more preferably 10% or more, and still more preferably 13% or more. On the other hand, if Al ₂ O ₃ If the content exceeds 30%, the acid resistance of the glass decreases or the devitrification temperature tends to increase. In addition, there is a possibility that the viscosity of the glass increases and the meltability decreases. Thus, al ₂ O ₃ The content of (2) is preferably 30% or less, more preferably 25% or less, still more preferably 20% or less, particularly preferably 15% or less.

Al ₂ O ₃ When the content is large, the temperature at the time of glass melting becomes large, and productivity decreases. When importance is attached to the productivity of glass, al ₂ O ₃ The content of (2) is preferably 11% or less, more preferably 10% or less, still more preferably 9% or less, particularly preferably 8% or less.

Li ₂ O is a component that forms a surface compressive stress layer by ion exchange in the chemical strengthening treatment with Na salt.

When a chemical strengthening treatment for exchanging Li ions on the surface of a glass for Na ions is performed using Na salts, if Li ₂ Since the content of O is 5% or more, the compressive stress generated by chemical strengthening increases, it is preferably 6% or more, and more preferably 7% or more. Li, on the other hand ₂ When the content of O exceeds 15%, the acid resistance of the glass is remarkably reduced. Preferably 15% or less, more preferably 13% or less. Further, the content is 11% or less.

Na ₂ O is a component capable of forming a surface compressive stress layer by ion exchange during the chemical strengthening treatment and improving the meltability of the glass.

Na ₂ The content of O is preferably 1% or more, more preferably 3% or more, further preferably 4% or more, and particularly preferably 6% or more. On the other hand, na ₂ When the O content exceeds 15%, the surface compressive stress value CS formed by ion exchange ₀ Significantly reduced, and therefore, preferably 15% or less. Na (Na) ₂ The content of O is more preferably 9% or less, still more preferably 6% or less, and particularly preferably 5% or less.

When Li ions and Na ions, na ions and K ions on the surface of the glass are simultaneously ion-exchanged by immersing in a mixed molten salt of potassium nitrate and sodium nitrate or the like, na ₂ The content of 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. In addition, na ₂ The content of O is preferably 2% or more, more preferably 3% or more, and still more preferably 4% or more.

K ₂ O may be contained in order to improve ion exchange performance and the like at the time of the chemical strengthening treatment. Containing K ₂ The content of O is preferably 0.5% or more, more preferably 1% or more. On the other hand, if K ₂ When the O content exceeds 5%, the glass is reduced in shatter property, and thus K ₂ The content of O is preferably 5% or less. K (K) ₂ The content of O is more preferably 3% or less, and still more preferably 2% or less.

MgO is preferable for increasing the surface compressive stress value CS of the chemically strengthened glass ₀ But contains. In addition, the effect of improving the mirror constant a is obtained. The MgO content is preferably 2% or more, more preferably 3% or more, further preferably 4% or more, and particularly preferably 5% or more. On the other hand, if the MgO content exceeds 25%, the chemically strengthened glass becomes easily devitrified at the time of melting, so that it is preferableLess than 25%. The MgO content is more preferably 15% or less, and still more preferably 10% or less.

CaO is a component for improving the meltability of the glass, has an effect of improving the mirror constant A, and may be contained. The content of CaO is preferably 0.1% or more, more preferably 0.2% or more, still more 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 14%, the ion exchange performance at the time of the chemical strengthening treatment may be lowered, and therefore, 14% or less is preferable. More preferably 10% or less, still more preferably 8% or less, still more preferably 4% or less, and particularly preferably 3% or less. Preferably 1% or less.

SrO is a component for improving the meltability of glass, has an effect of improving the mirror constant A, and may be contained. The content in the case of being contained is preferably 0.1% or more, more preferably 0.2% or more, still more 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 the chemical strengthening treatment may be lowered, and therefore, 10% or less is preferable. The content of SrO is more preferably 8% or less, still more preferably 5% or less, particularly preferably 2% or less, and most preferably 1% or less.

BaO is a component for improving the meltability of glass, has an effect of improving the mirror constant A, and may be contained. The content of BaO 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 BaO content exceeds 10%, the ion exchange performance at the time of the chemical strengthening treatment is lowered, and therefore, 10% or less is preferable. The content of BaO is more preferably 8% or less, still more preferably 5% or less, particularly preferably 2% or less, and most preferably 1% or less.

ZnO is a component for improving the meltability of glass, and may be contained. The content of ZnO is preferably 0.25% or more, more preferably 0.5% or more. On the other hand, if the ZnO content exceeds 10%, the weatherability of the glass is significantly reduced. The ZnO content is preferably 10% or less, more preferably 7% or less, further preferably 5% or less, still more preferably 2% or less, and particularly preferably 1% or less.

B ₂ O ₃ Is a component for improving the meltability. In addition, the glass is a component for improving shatter resistance of the glass. B (B) ₂ O ₃ Is not necessary but is preferred for containing B ₂ O ₃ The content is preferably 0.5% or more, more preferably 1% or more, and even more preferably 2% or more, in order to improve the meltability. On the other hand, if B ₂ O ₃ If the content exceeds 10%, striae occur during melting, and the quality of the chemically strengthened glass tends to be lowered, so that 10% or less is preferable. B (B) ₂ O ₃ The content of (2) is more preferably 5% or less, still more preferably 3% or less, and particularly preferably 1% or less. In order to improve acid resistance, it is preferable that the composition is substantially not contained.

P ₂ O ₅ Is a component for improving ion exchange performance and shatter resistance during chemical strengthening treatment. P (P) ₂ O ₅ Is not essential but contains P ₂ O ₅ The content is preferably 0.5% or more, more preferably 1% or more, and even more preferably 2% or more. On the other hand, P ₂ O ₅ When the content exceeds 10%, the acid resistance is significantly reduced, and therefore, 10% or less is preferable. P (P) ₂ O ₅ The content of (2) is more preferably 4% or less, still more preferably 3% or less, still more preferably 2% or less, and particularly preferably 1% or less. In order to improve acid resistance, it is preferable that the composition is substantially not contained.

TiO ₂ Is to increase the surface compressive stress value CS based on ion exchange during chemical strengthening treatment ₀ May contain the components of (a). Containing TiO ₂ 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 exceeds 10%, devitrification is likely to occur during melting, and the quality of the chemically strengthened glass may be lowered, so that 10% or less is preferable. The content thereof is more preferably 4% or less, still more preferably 2% or less, still more preferably 1% or less.

ZrO ₂ Is based on ion exchange during chemical strengthening treatmentSurface compression stress value CS of the change ₀ May contain the components of (a). Containing ZrO ₂ The content is preferably 0.5% or more, more preferably 1% or more. On the other hand, if the content exceeds 8%, devitrification is likely to occur during melting, and there is a possibility that the quality of the chemically strengthened glass may be lowered. The content thereof is preferably 8% or less, more preferably 4% or less, still more preferably 3% or less, particularly preferably 2% or less.

May contain Y ₂ O ₃ 、La ₂ O ₃ 、Nb ₂ O ₅ . The content of each of these components is preferably 0.5% or more, more preferably 1% or more, further preferably 1.5% or more, particularly preferably 2% or more, and most preferably 2.5% or more. On the other hand, if Y ₂ O ₃ 、La ₂ O ₃ 、Nb ₂ O ₅ If the content of (2) exceeds 8%, the glass tends to devitrify during melting, and the quality of the chemically strengthened glass may be lowered. Y is Y ₂ O ₃ 、La ₂ O ₃ 、Nb ₂ O ₅ The content of (c) is preferably 8% or less, more preferably 6% or less, still more preferably 5% or less, particularly preferably 4% or less, and most preferably 3% or less, respectively.

Ta ₂ O ₅ 、Gd ₂ O ₃ Although a small amount of the glass may be contained in order to improve the breakage of the chemically strengthened glass, the refractive index and the reflectance are high, and therefore, the content is preferably 1% or less, more preferably 0.5% or less, and even more preferably no content.

Further, when the glass is colored and used, a coloring component may be added within a range where desired chemical strengthening properties are obtained. Examples of the coloring component include Co ₃ O ₄ 、MnO ₂ 、Fe ₂ O ₃ 、NiO、CuO、Cr ₂ O ₃ 、V ₂ O ₅ 、Bi ₂ O ₃ 、SeO ₂ 、TiO ₂ 、CeO ₂ 、Er ₂ O ₃ 、Nd ₂ O ₃ And the like as a preferable coloring component.

If the total content of the coloring components is 7% or less, devitrification of the glass is suppressed, and thus it is preferable. The content is preferably 5% or less, more preferably 3% or less, and even more preferably 1% or less. When the visible light transmittance of the glass is to be improved, these components are more preferably substantially not contained.

As a fining agent for glass melting, SO may be suitably contained ₃ Chlorides, fluorides, etc. Preferably without As ₂ O ₃ . Containing Sb ₂ O ₃ In this case, the content is preferably 0.3% or less, more preferably 0.1% or less, and most preferably substantially no content.

Further, the fracture toughness value of the glass for chemical strengthening is preferably 0.70 MPa.m ^1/2 More preferably 0.75 MPa.m ¹ ^/2 The above is more preferably 0.77 MPa.m ^1/2 The above is particularly preferably 0.80 MPa.m ^1/2 The above, most preferably 0.82 MPa.m ^1/2 The above. If the fracture toughness value is 0.70 MPa.m ^1/2 As described above, the glass breakage can be effectively suppressed.

The Young's modulus of the chemically strengthened glass of the present invention is preferably 74GPa or more, more preferably 78GPa or more, and still more preferably 82GPa or more. The upper limit of Young's modulus is not particularly limited, and is, for example, 90GPa or less, preferably 88GPa or less. Young's modulus can be determined, for example, by ultrasonic pulse method.

In addition, the glass for chemical strengthening of the present invention has a liquidus temperature T _L Preferably the viscosity reaches 10 ⁴ dPa.s temperature T ₄ The following is given. In this case, the glass sheet is easily manufactured by the float process. T for easy glass forming by float process _L Preference ratio T ₄ A temperature (T) lower by 10 DEG C ₄ At-10 ℃ or lower, more preferably T ₄ T is further preferred at a temperature of-30 ℃ or lower ₄ Below-50 ℃. For the sake of chemical strengthening easiness, T _L Preferably T ₄ -150 ℃ or higher, more preferably T ₄ At a temperature of 125 ℃ below zero or higher, T is further preferred ₄ Above-100 ℃.

(method for producing chemically strengthened glass)

The chemically strengthened glass can be produced, for example, as follows.

First, glass to be subjected to chemical strengthening treatment (glass for chemical strengthening) is prepared. The glass to be subjected to the chemical strengthening treatment is preferably the glass for chemical strengthening of the present invention. The chemically strengthened glass is preferably subjected to shape processing according to the application, such as machining such as cutting, end face processing, and hole forming, before being subjected to chemical strengthening treatment to produce chemically strengthened glass. If the glass plate is cut and chamfered before the chemical strengthening treatment, a compressive stress layer is preferably formed on the end face by the chemical strengthening treatment after that.

The chemical strengthening treatment may be performed, for example, by cutting the produced glass for chemical strengthening to a desired size, preheating the glass for chemical strengthening to about 400 ℃, and ion-exchanging Li ions contained in the glass with Na ions contained in the molten salt or Na ions contained in the glass with K ions contained in the molten salt.

Further, a chemically strengthened glass having further high strength can be produced by ion-exchanging a molten salt containing a specific salt and then subjecting the molten salt to an acid treatment and an alkali treatment.

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

Examples of the molten salt used for the chemical strengthening treatment include nitrate, sulfate, carbonate, and chloride salts. 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, and silver chloride. These molten salts may be used alone or in combination of two or more. In addition, other salts may be mixed for adjusting the chemical strengthening property.

Chemical chemistrySurface compressive stress CS of tempered glass ₀ The adjustment of (c) may be performed by adjusting, for example, na concentration, strengthening time, and/or molten salt temperature in the molten potassium nitrate salt used in ion exchange.

The depth of compressive stress layer DOL can also be adjusted by adjusting Na concentration, strengthening time and/or molten salt temperature in the molten potassium nitrate salt used in ion exchange. In order to obtain higher DOL, the temperature of the molten salt may also be increased.

CT adjustment of chemically strengthened glass can be achieved by adjusting CS as described above ₀ DOL.

In the present invention, the chemical strengthening treatment may be performed only once, or may be performed a plurality of times under different conditions of 2 or more (multi-step strengthening). Here, for example, if the chemical strengthening treatment is performed under a condition in which CS is relatively low as the chemical strengthening treatment of the step 1, and then the chemical strengthening treatment is performed under a condition in which CS is relatively high as the chemical strengthening treatment of the step 2, the surface compressive stress CS of the chemically strengthened glass can be improved ₀ And suppresses the internal tensile stress CT.

The chemically strengthened glass of the present invention can be produced by subjecting the obtained glass sheet to a chemical strengthening treatment and then washing and drying.

The chemically strengthened glass may be cut after the chemical strengthening treatment. The dicing method may be performed by scribing and breaking with a conventional wheel cutter, or may be performed by laser dicing. In order to maintain the strength of the glass sheet, chamfering of the cut edge may be performed after cutting. The chamfering may be performed mechanically, or may be performed by a method of treating with a chemical solution such as hydrofluoric acid.

The glass for chemical strengthening of the present invention is produced by, for example, appropriately preparing a glass raw material, heating to about 1500 to 1700 ℃ and melting, and then molding and cooling. The molten glass obtained by melting the glass raw material is generally molded by homogenizing by defoaming, stirring, or the like. As a molding method for molding the chemically strengthened glass on the sheet, a known float method, a downdraw method, a press method, or the like can be used. Alternatively, the material may be cast to be formed into a block shape, and then cut into a desired size after slow cooling.

For example, when formed into a plate shape by a float method, a downdraw method, or the like, a high-temperature molten glass is formed while being cooled. In this case, the cooling rate in the molding step is preferably 300℃per minute or less, more preferably 120℃per minute or less, and still more preferably 90℃per minute or less, in order to reduce the fictive temperature.

On the other hand, when the cooling rate is low, not only the production efficiency of the glass sheet is lowered, but also the glass tends to be easily devitrified. In particular, in the case of lithium aluminosilicate glass, lithium aluminosilicate crystals are likely to precipitate and devitrify.

In order to suppress devitrification of the glass, the cooling rate is preferably 10 ℃ per minute or more.

The chemically strengthened glass of the present invention may be polished as needed, but the principal surface of the chemically strengthened glass may be treated with a fluorine agent in addition to or instead of polishing. If it is considered to stably produce the glass for chemical strengthening of the present invention, particularly if it is considered to produce a large-sized glass for chemical strengthening, the forming method is preferably a float method. Then, cutting is performed as needed. Generally, the cutting is rectangular, but there is no problem even in other shapes such as a circle or a polygon, and the punching may be performed.

The thickness t of the glass for chemical strengthening of the present invention can be selected as required. For example, when used as a cover glass for a display portion of a mobile phone or the like, the thickness t is preferably 2.0mm or less, more preferably 1.0mm or less, and still more preferably 0.75mm or less. The thickness t is usually 0.1mm or more.

The chemically strengthened glass of the present invention has high mechanical strength, and is therefore preferably used for predicting the position where impact due to dropping and contact with other substances occur.

Specifically, the cover glass is particularly useful as a cover glass used for mobile devices such as mobile phones, smart phones, portable information terminals (PDAs), tablet terminals, and the like. Further, the present invention is useful for a cover glass of a display device such as a Television (TV), a Personal Computer (PC), or a touch panel, a wall surface (entire display) of a building such as an elevator, a house, or a building such as a building, a building material such as a window glass, a table, or an interior of an automobile, an airplane, or the like, which are not intended for portability.

Examples

The present invention will be further described below with reference to examples, but the present invention is not limited thereto.

Glass raw materials are suitably prepared, heated and melted, homogenized by defoaming, stirring, etc., and formed into a plate shape to obtain a glass plate. The cooling rate was set at about 70℃per minute. The compositions (mol%) of the glasses used in the examples and comparative examples are shown in table 1. Although not shown in the table, P ₂ O ₅ And ZnO was "0.0" (not contained) in any glass. The glass 2 is described in patent document 1. The following characteristics were evaluated for the obtained glass.

(glass transition temperature Tg)

The glass transition temperature Tg was obtained from the thermal expansion curve obtained by the method described in JIS R3102 (1995).

(Young's modulus, poisson's ratio)

Young's modulus and Poisson's ratio of the glass plate obtained by the above steps were measured by an ultrasonic pulse method.

(T ₂ 、T ₄ )

Viscosity measured using a rotational viscometer to 10 ² dPa.s temperature T ₂ And a viscosity of up to 10 ⁴ dPa.s temperature T ₄ 。

(liquidus temperature T) _L Devitrification viscosity)

5g of glass having been pulverized to an average particle size of about 500 μm was placed in a 35ml platinum dish, kept in an electric furnace at a predetermined temperature for 17 hours, and then taken out and observed with an optical microscope having a magnification of 10 times to examine the presence or absence of crystal deposition. The operation of examining the presence or absence of crystallization while changing the temperature to be maintained is repeatedly performed in a temperature range of 800 to 1500 ℃, and the minimum temperature at which crystallization does not occur is set to be the liquid phase temperature T _L 。

The viscosity at the liquid phase temperature was determined from the relationship between the temperature and the viscosity obtained by the rotational viscometer, and the obtained product was referred to as devitrification viscosity.

TABLE 1

< influence of mirror constant >

(adjustment of virtual temperature)

The obtained glass 1 sheet was held at a temperature 30 ℃ higher than the glass transition temperature Tg for 1 hour, and then subjected to precision slow cooling at a cooling rate of 1 ℃/min, whereby a glass sheet having a virtual temperature of not higher than the glass transition temperature Tg was obtained. If the fictive temperature is measured by the method described later, it is 535 ℃.

Further, a glass plate having a fictive temperature of Tg+60℃wasobtained by performing a treatment of maintaining the glass plate at a temperature 60 ℃ higher than the glass transition temperature and quenching the glass plate.

Glasses 2 and 3 were used to produce glasses having thermal histories that simulate those of glass plates obtained in commercial production processes. Glass 2 simulates the thermal history of glass produced by the fusion process, assuming a temperature of Tg+50℃. Glass 3 simulates the thermal history of glass produced by the float process, assuming a temperature of tg+30℃.

(mirror constant)

The specular constant A was determined by the following procedure. Among them, examples 3 and 4 were obtained by calculation from a sample having a virtual temperature around Tg and a specular constant of Tg+60℃.

The surface was polished to a size of 40X 6X 3mm, and the back surface and the end surfaces in the longitudinal direction (total 4 surfaces) were mirror polished.

Scratches were applied using a vickers hardness tester and using a 110 ° diamond indenter, which was pressed in with different loads. The pressing load was set to 0.05kgf, 0.1kgf, 0.3kgf, 0.5kgf, 0.75kgf, 1.0kgf, 2.0kgf, 3.0kgf.

The heat treatment is performed to remove the influence of the strain due to the scratch application. This heat treatment is also performed as a pseudo temperature adjustment by the following steps.

Samples with fictive temperature around Tg: the temperature was kept at 30℃higher than Tg for 1 hour, and the temperature was lowered to room temperature at 1℃per minute to effect slow cooling.

Samples with fictive temperature Tg+60℃: maintained at a temperature 60℃above Tg for 1 hour, quenched in air.

The span of the 4-point bending jig was set as the load side (upper): 10mm, support side (lower): 30mm, a 4-point bending test was performed on the scratched glass plate. An adhesive tape was attached to the surface opposite to the surface to which the scratch was applied and the surface to which the heat-treated glass was applied, and the load was applied while the surface to which the adhesive tape was attached was facing down (the surface to which the adhesive tape was attached was facing up), and the load at the time of breaking was measured. The stress at the time of crushing was determined from the measured load using the following equation.

σ＝(3F(Ls－Ll))/(2wh ² )

Here, σ is stress (MPa) at the time of crushing, F is load (N) at the time of crushing, ls is distance (mm) between lower support points, ll is distance (mm) between upper load points, w is sample width (mm), and h is sample thickness (mm).

Then, the fracture surface was observed using KEYENCE Digital Microscope VHX to 5000, and the distance R from the fracture origin to the interface between the mirror surface and the hazy surface was measured. In the observation, the sample was parallel to the lens of the microscope, and the observation was performed at a magnification of 20×150.

From the results obtained by the above steps, the mirror constant a was obtained using the following formula.

σ＝A/R ^1/2

(chemical strengthening Property)

Glass 1 was chemically strengthened with sodium nitrate at 450 ℃ for 1 hour, glass 2 was chemically strengthened with potassium nitrate at 450 ℃ for 6 hours, and glass 3 was chemically strengthened with potassium nitrate at 425 ℃ for 12 hours.

Measuring stress of glass after chemical strengthening treatment to obtain CS ₀ 、DOL、CT。

The thickness t of the glass used was 0.8mm, -38.7Xln (t) +48.2 was 56.5MPa.

(number of breaks)

The number of broken glass pieces after the chemical strengthening treatment was measured by the following method.

The chemically strengthened glass was press-fitted using an HMV micro vickers hardness tester manufactured by SHIMADZU corporation, with a regular quadrangular pyramid-shaped 60 ° (apex angle) press head at the following press head load speed, load of 4kgf, and press-fitting time of 15 sec. As a result of press-fitting, the press-fitting load was increased by 0.5kgf each time as long as the glass was not broken. The number of fragments at the time of crushing was set as the crushing number. If the number of breaks is less than 10, it can be said that the cover glass is suitable for, for example, a mobile device.

Pressure head load speed: 260 μm/sec before contact with the glass surface, 5 to 120 μm/sec after penetration into the glass

(test for falling on Sand)

The glass after the chemical strengthening treatment was subjected to a sand falling test by the following test method.

Fig. 4 shows a schematic diagram showing a test method of the sand drop test.

First, a chemically strengthened glass 13 (50 mm. Times.50 mm. Times.0.8 mm in thickness) was bonded to a hard nylon-made dummy plate 11 (50 mm. Times.50 mm. Times.18 mm in thickness, weight: 54 g) via a sponge double-sided tape 12 (# 2310, 50 mm. Times.50 mm. Times.3 mm in thickness, manufactured by water-accumulating chemical Co., ltd.) to prepare a measurement sample 10. Next, 1g of silica sand 22 (silica sand No. 5 manufactured by bamboo folding company) was uniformly spread on a 15cm×15 cm-sized metal plate 21 (made of SUS), and the manufactured measurement sample 10 was dropped from a predetermined height (drop height) to the surface of the metal plate 21 on which the silica sand 22 was spread so that the chemically strengthened glass 13 faced downward. The drop test was performed by raising the height of the glass 13 by 10mm each time from the drop height of 10mm, and the height of breakage (unit mm) was set as the breakage height. For each example, 5 to 10 dropping tests were performed, and the average value of the fracture heights in the dropping tests was set as the average fracture height (unit: mm). These results are shown in table 2.

TABLE 2

The glasses 2 and 3 used in example C, D were severely crushed if tensile stress exceeding the limit CT (56.8 MPa) shown in patent document 1 was applied. The number of glass fragments after chemical strengthening, to which an internal tensile stress exceeding the conventional limit CT (56.8 MPa) was applied, was as large as 10 or more, and the results of the sand falling test were also poor. The glass of example C, D was found to have a small mirror constant.

Example A, B using glass 1 had a mirror constant of 2.0 MPa.m ^1/2 The above. Even after the chemical strengthening, which applied internal tensile stress exceeding the conventional limit CT (56.8 MPa), the glass had a small number of broken pieces, and the sand falling test was good.

In addition, when example a and example B were compared, it was found that the mirror constant was increased as the virtual temperature was lower even though the glass composition was the same.

< difference in cooling speed and glass composition >

For glasses 1, 4, 5, 6, and 7, plate-like samples of 15 mm. Times.15 mm. Times.0.8 mmt were prepared. For examples 1, 2, 3 and 4, the heating treatment was performed using a belt furnace programmed to be cooled to a temperature around room temperature at a cooling rate of 70 ℃/min after being kept at a temperature of 30 ℃ or higher than the Tg of each glass for 5 minutes. For examples 5 and 6, the glass was kept at a temperature 60℃higher than the Tg of each glass for 1 hour, and then cooled to room temperature at a cooling rate of 0.5℃per minute. Example 7 after maintaining a temperature 60 c above Tg for 1 hour, cooling was performed at 500 c/min.

Examples 1 to 3 are examples, and examples 4 to 7 are comparative examples.

(fictive temperature)

The refractive indices were measured in examples 1 to 7, and table 3 shows the results of obtaining the virtual temperatures from the standard curves prepared by the following methods.

The standard curves were prepared by preparing glass plates having a virtual temperature of Tg+50℃, tg+20℃, tg+5℃, tg-10 ℃ and Tg-30 ℃ by holding glass plates having a thickness of 15mm×15mm×0.8mm at a high temperature and quenching the glass plates, and measuring the refractive indices of the glass plates and plotting the relationship between the virtual temperature and the refractive index. Fig. 3 is a standard curve for glass 1. The glass having the virtual temperature adjusted is, for example, kept at a temperature 50 ℃ higher than the Tg of the glass, and then quenched by immersing in water to obtain a glass plate having a virtual temperature of tg+50℃.

(chemical strengthening Property)

For each of the glasses of examples 1 to 7, a chemical strengthening treatment with Na salt was performed by immersing in a molten sodium nitrate salt at 450 ℃ for 1 hour. After cooling, washing and drying, the surface compressive stress value CS1 and the depth of compressive stress layer DOL1 by Na salt treatment were measured by a photoelastic scattering stress analyzer (SLPII, temporary name).

Then, after cooling, washing and drying the resultant mixture in a molten potassium nitrate salt at 450℃for 6 hours, the surface compressive stress value CS2 and the depth of layer DOL2 of the K-salt after chemical strengthening were measured by a stress analyzer (FSM 6000 manufactured by the folding original manufacturer).

In example 4, since CS2 and DOL2 could not be measured, after 48 hours of treatment in a molten potassium nitrate salt at 450 ℃, the surface compressive stress value and the compressive stress layer depth were measured by a photoelastic scattering stress analyzer (SLPII, temporarily) and, assuming that the surface compressive stress value was independent of the treatment time, the compressive stress layer depth was proportional to the square root of the treatment time, CS2 and DOL2 were calculated when 6 hours of treatment were performed in a molten potassium nitrate salt at 450 ℃.

(devitrification Property)

The glasses of examples 1 to 7 were placed in a platinum crucible, and after being kept at 1500 ℃ for 3 hours to be molten, the glass was cooled to room temperature at a predetermined cooling rate, taken out of the platinum crucible, and the presence or absence of devitrification was visually observed.

TABLE 3

TABLE 3 Table 3

	Example 1	Example 2	Example 3	Example 4	Example 5	Example 6	Example 7
								Glass composition	Glass 1	Glass 4	Glass 5	Glass 6	Glass 1	Glass 7	Glass 5
Cooling rate (. Degree. C./min)	70	70	70	70	0.5	0.5	500
								Fictive temperature (. Degree. C.)	Tg+14	Tg+15	Tg+8	Tg-6	Tg-32	Tg-47	Tg+61
Mirror constant (MPa.m) ^1/2 )	2.4	2.1	2.1	2.7	2.7	2.1
								CS1(MPa)	400	320	250	645	440	240	230
DOL1(DOL)(μm)	123	120	110	85	110	95	110
								CS2(CS ₀ )(MPa)	936	865	870	840	960	690	810
DOL2(μm)	13	12	12	14	11	15	13
								Devitrification of	Without any means for	Without any means for	Without any means for	There are (Duoduo)	There are (few)	Without any means for	Without any means for

Examples 1 to 3 high surface compressive stress CS obtained by chemical strengthening ₀ And no devitrification was confirmed. Example 4 is T _L Ratio T ₄ High glass, severe devitrification.

Comparing examples 1 and 5, it was found that even when the glass had the same composition, the glass was easily devitrified due to a very low cooling rate and a low virtual temperature. In addition, for example 7 in which the cooling rate was very low and devitrification was not observed, CS ₀ The DOL does not become large. This is because glass compositions are different.

When comparing examples 1 and 7, it was found that even with the same glass composition, CS2 was low and strength was insufficient in example 7 having a high fictive temperature.

While the present invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof. The present application is based on Japanese patent application (Japanese patent application 2016-183936) filed on the year 2016, japanese patent application (Japanese patent application 2016-204745) filed on the year 2016, month 10, month 18, and Japanese patent application (Japanese patent application 2017-141284) filed on the year 2017, month 7, month 20, the contents of which are incorporated herein by reference.

Symbol description

10: measurement sample

11: simulation board

12: sponge double-sided adhesive tape

13: chemically strengthened glass

21: metal plate

22: silica sand

Claims

1. A chemically strengthened glass is prepared from glass phase at liquid-phase temperature T _L At a temperature T ₄ The following lithium aluminosilicate glass is composed, the temperature T ₄ Is of viscosity up to 10 ⁴ The temperature of dPa.s is set,

contains 65 to 72% of SiO in terms of mole percent based on oxide ₂ 7 to 15 percent of Al ₂ O ₃ 7 to 11 percent of Li ₂ O, na 1-9% ₂ O, 0.5-2% K ₂ O, mgO 0-10%, caO 0-1%, srO 0-1%, baO 0-1%, znO 0-1% and B0-1% ₂ O ₃ 0 to 1 percent of P ₂ O ₅ 0 to 1 percent of TiO ₂ ZrO 0.5-2% ₂ 0 to 8 percent of Y ₂ O ₃ ，

The fictive temperature is a temperature 30 ℃ lower than the glass transition temperature Tg to a temperature 25 ℃ higher than the Tg,

the mirror constant A is 2.0 MPa.m ^1/2 The above method wherein the mirror constant A is obtained by measuring stress sigma at the time of fracture and the distance from the fracture origin to the mirror and the hazeThe distance R to the interface is obtained based on the following formula,

σ＝A/R ^1/2 。

2. the glass for chemical strengthening according to claim 1, wherein the fracture toughness value is 0.75 MPa-m ^1/2 The above.

3. The chemically strengthened glass according to claim 1, wherein the Young's modulus is 74 to 90GPa.

4. The chemically strengthened glass according to claim 1, wherein the glass contains 65 to 72% by mole percentage of SiO based on the oxide ₂ 7 to 15 percent of Al ₂ O ₃ 7 to 11 percent of Li ₂ O, na 4-9% ₂ O, 0.5-2% K ₂ O, mgO 2-10%, caO 0-1%, srO 0-1%, baO 0-1%, znO 0-1% and B0-1% ₂ O ₃ 0 to 1 percent of P ₂ O ₅ 0 to 1 percent of TiO ₂ ZrO 0.5-2% ₂ 0 to 8 percent of Y ₂ O ₃ 。

5. The chemically strengthened glass according to claim 4, wherein the fracture toughness value is 0.75 MPa-m ^1/2 The above.

6. The chemically strengthened glass according to claim 4, wherein the Young's modulus is 74 to 90GPa.

7. A method for producing a glass for chemical strengthening, comprising melting a glass having a mirror constant A of 2.0MPa m and cooling the glass at an average cooling rate of 10 ℃ per minute to 300 ℃ per minute ^1/2 The above-mentioned mirror constant A is obtained by measuring the stress sigma at the time of fracture and the distance R from the fracture origin to the interface between the mirror and the fog surface based on the following formula,

σ＝A/R ^1/2 ，

the glassThe glass contains 65 to 72 percent of SiO in terms of mole percent based on oxide ₂ 7 to 15 percent of Al ₂ O ₃ 7 to 11 percent of Li ₂ O, na 1-9% ₂ O, 0.5-2% K ₂ O, mgO 0-10%, caO 0-1%, srO 0-1%, baO 0-1%, znO 0-1% and B0-1% ₂ O ₃ 0 to 1 percent of P ₂ O ₅ 0 to 1 percent of TiO ₂ ZrO 0.5-2% ₂ 0 to 8 percent of Y ₂ O ₃ And a liquid phase temperature T _L At a temperature T ₄ The temperature T is as follows ₄ To a viscosity of 10 ⁴ dPa.s temperature.