JP6222390B2 - Glass for chemical strengthening - Google Patents

Description

  The present invention relates to a glass for chemical strengthening suitable for a cover glass of a mobile device such as a mobile phone and a personal digital assistant (PDA), a large thin TV such as a large liquid crystal television and a large plasma television, and a display device such as a touch panel.

In recent years, for display devices such as mobile devices, liquid crystal televisions, and touch panels, a cover glass (protective glass) for protecting the display and enhancing aesthetics is often used.
Such a display device is required to be lightweight and thin in order to differentiate by a thin design and to reduce a burden for movement. Therefore, the cover glass used for display protection is also required to be thin. However, as the thickness of the cover glass decreases, the strength decreases.In the case of a stationary type, the cover glass itself is affected by the impact of flying or dropping of an object. There is a problem that the original function of protecting the display device cannot be achieved due to cracking.

In order to solve the above problem, it is conceivable to increase the strength of the cover glass, and as a method therefor, a method of forming a compressive stress layer on the glass surface is generally known.
As a method for forming a compressive stress layer on the glass surface, an air cooling strengthening method (physical strengthening method) in which the glass plate surface heated to near the softening point is rapidly cooled by air cooling or the like, and ions at a temperature below the glass transition point. A chemical strengthening method in which an alkali metal ion (typically Li ion or Na ion) having a small ionic radius on the glass plate surface is exchanged for an alkali ion (typically K ion) having a larger ionic radius by exchange. is there.

  As described above, the cover glass is required to be thin. However, when the air-cooling strengthening method is applied to a thin glass plate that is required as a cover glass and has a thickness of less than 2 mm, it is difficult to form a compressive stress layer because the temperature difference between the surface and the inside is difficult to occur. Therefore, the desired high strength characteristic cannot be obtained. Therefore, a cover glass reinforced by the latter chemical strengthening method is usually used.

As such a cover glass, a soda-lime glass that has been chemically strengthened is widely used (see, for example, Patent Document 1).
Soda lime glass is inexpensive and has a feature that the surface compressive stress S of the compressive stress layer formed on the glass surface by chemical strengthening can be increased to 200 MPa or more, but the thickness t of the compressive stress layer can be easily increased to 30 μm or more. There was a problem that was not.

Accordingly, (see for example Patent Document 2) in which different _{SiO 2 -Al 2 O 3 -Na 2} O -based glass obtained by chemically strengthening has been proposed as such a cover glass is a soda-lime glass.
The SiO ₂ —Al ₂ O ₃ —Na ₂ O glass has a feature that not only the S can be set to 200 MPa or more, but the t can be set to 30 μm or more.

JP 2007-11210 A US Patent Application Publication No. 2008/0286548

In applications such as those described above, ion exchange treatment for chemical strengthening is usually performed by immersing glass containing sodium (Na) in molten potassium salt, and the potassium salt may be potassium nitrate or potassium nitrate and nitric acid. A mixed salt of sodium is used.
In the ion exchange treatment, ion exchange between Na in the glass and potassium (K) in the molten salt is performed. Therefore, when the ion exchange treatment is repeated while continuing to use the same molten salt, the concentration of Na in the molten salt increases.

As the Na concentration in the molten salt increases, the surface compressive stress S of the chemically strengthened glass decreases, so the Na concentration in the molten salt is strictly controlled so that the S of the chemically strengthened glass does not fall below the desired value. There was a problem that it was necessary to frequently exchange the molten salt.
It is required to reduce the frequency of such molten salt exchange as much as possible, and the present invention aims to provide a glass for chemical strengthening that can solve such a problem.

The present invention, in a molar percentage based on the following oxides, the _{SiO 2 61~77%, Al 2 O} 3 7 to 18% of MgO 3 to 15% 0 to 5% of CaO, a ZrO ₂ 0 to 4% Na ₂ O of 8 to 18% _{K 2} O and containing from 0 to 1.9%, the total content of SiO ₂ and _Al 2 _{O 3} is at most 85%, containing MgO and CaO Chemical strengthening glass having a total amount of 3 to 15% and R calculated by the following formula using the content of each component is 0.66 or more (hereinafter sometimes referred to as the first invention). .)I will provide a. Incidentally, it referred to as the first glass of the present invention the glass used herein, also for example SiO ₂ in the formula is a mole percentage display content of SiO _2.
R = 0.029 × SiO ₂ + 0.021 × Al ₂ O ₃ + 0.016 × MgO−0.004 × CaO + 0.016 × ZrO ₂ + 0.029 × Na ₂ O + 0 × K ₂ O−2.002.
The total content of SiO ₂ , Al ₂ O ₃ , MgO, CaO, ZrO ₂ , Na ₂ O and K ₂ O of the first glass of the present invention is typically 98.5% or more.

In addition, in terms of the mole percentage based on the following oxide, SiO ₂ is 61 to 77%, Al ₂ O ₃ is 9.1 to 18%, MgO is ₃ to 15%, CaO is 0 to 5%, and ZrO ₂ is 0. 4% 8 to 18% of Na ₂ O, containing any one or more components of the _{K 2} O 0-6% and _B 2 _O 3, SrO and BaO, the content of SiO ₂ and _Al 2 _{O 3} Is 85% or less, the total content of MgO and CaO is 3 to 15%, and R ′ calculated by the following formula using the content of each component is 0.66 or more. A glass for chemical strengthening (hereinafter sometimes referred to as a second invention) is provided. In addition, the glass used here is called 2nd glass of this invention.
R ′ = 0.029 × SiO ₂ + 0.021 × Al ₂ O ₃ + 0.016 × MgO−0.004 × CaO + 0.016 × ZrO ₂ + 0.029 × Na ₂ O + 0 × K ₂ O + 0.028 × B ₂ O ₃ + 0.012 × SrO + 0.026 × BaO−2.002.
The total content of SiO ₂ , Al ₂ O ₃ , MgO, CaO, ZrO ₂ , Na ₂ O, K ₂ O, B ₂ O ₃ , SrO and BaO in the second glass of the present invention is typically 98. .5% or more.

In addition, in terms of a molar percentage based on the following oxide, SiO ₂ is 61 to 77%, Al ₂ O ₃ is 1 to 18%, MgO is ₃ to 15%, CaO is 0 to 5%, ZrO ₂ is 0 to 4%. %, Na ₂ O 8-18%, K ₂ O 0-1.9% and any one or more of B ₂ O ₃ , SrO, BaO, ZnO and SnO ₂ are contained, and Li ₂ O is included. The total content of SiO ₂ and Al ₂ O ₃ is 65 to 85%, the total content of MgO and CaO is 3 to 15%, and the content of each component is used to calculate the following formula The glass for chemical strengthening (hereinafter sometimes referred to as the third invention) having R ″ of 0.66 or more is provided. The glass used here is referred to as the third glass of the present invention.
R ″ = 0.029 × SiO ₂ + 0.021 × Al ₂ O ₃ + 0.016 × MgO−0.004 × CaO + 0.016 × ZrO ₂ + 0.029 × Na ₂ O + 0 × K ₂ O + 0.028 × B ₂ O _{3 + 0.012 × SrO + 0.026 ×} BaO + 0.019 × ZnO + 0.033 × Li 2 O + 0.032 × SnO 2 -2.002.
Inclusion of SiO ₂ , Al ₂ O ₃ , MgO, CaO, ZrO ₂ , Na ₂ O, K ₂ O, B ₂ O ₃ , SrO, BaO, ZnO, Li ₂ O and SnO ₂ in the third glass of the present invention The total amount is typically greater than 98.5%.

In addition, in terms of a molar percentage based on the following oxide, SiO ₂ is 62 to 77%, Al ₂ O ₃ is 7 to 18%, MgO is ₃ to 15%, CaO is 0 to 5%, ZrO ₂ is 0 to 4%. %, Na ₂ O 8 to 18%, the total content of SiO ₂ and Al ₂ O ₃ is 85% or less, the total content of MgO and CaO is 3 to 15%, Li ₂ Provided is a glass for chemical strengthening that does not contain O and K ₂ O (hereinafter sometimes referred to as a fourth invention). Incidentally, it referred to as a fourth glass of the present invention the glass not containing K 2 _O, the first present invention, the second, collectively referred to as the glass of the present invention the third and fourth glass.

  The present inventor increased the Na concentration in the molten potassium salt by immersing the Na-containing glass in the molten potassium salt and repeatedly performing ion exchange to obtain the chemically strengthened glass, along with the surface compressive stress of the chemically strengthened glass. Considering that there is a relationship between the phenomenon of decreasing and the composition of Na-containing glass, the following experiment was conducted.

First, 29 types of glass plates having the compositions shown in mol% in Tables 1 to 3, having a thickness of 1.5 mm, a size of 20 mm × 20 mm, and mirror-polished on both sides with cerium oxide were prepared.
The glass transition point Tg (unit: ° C.) and Young's modulus E (unit: GPa) of these glasses are shown in the same table.
In addition, what attached | subjected * is calculated | required from the composition.
Tg was measured as follows. That is, using a differential thermal dilatometer, the elongation of the glass was measured up to the yield point when the temperature was raised from room temperature at a rate of 5 ° C./minute using quartz glass as a reference sample, and the bending point in the obtained thermal expansion curve. The temperature corresponding to was taken as the glass transition point.
E was measured by an ultrasonic pulse method on a glass plate having a thickness of 5 to 10 mm and a size of 3 cm × 3 cm.
These 29 kinds of glass plates were subjected to ion exchange immersed in molten potassium salt having a KNO ₃ content ratio of 100% and a temperature of 400 ° C. for 10 hours to obtain chemically strengthened glass plates, and their surface compressive stress CS1 (unit: : MPa). Glass A27 is used for a cover glass of a mobile device.
These 29 kinds of glass plates were chemically strengthened by ion exchange by immersing them in molten potassium salt having a KNO ₃ content of 95%, a NaNO ₃ content of 5% and a temperature of 400 ° C. for 10 hours. It was set as the glass plate and the surface compressive stress CS2 (unit: MPa) was measured. CS1 and CS2 were measured with a surface stress meter FSM-6000 manufactured by Orihara Seisakusho.
CS1 and CS2 are shown in the corresponding columns of Tables 1 to 3 together with their ratio r = CS2 / CS1.

From these results, it was found that there is a high correlation between R (described in Tables 1 to 3) calculated by the above formula and r. FIG. 1 is a scatter diagram in which the horizontal axis is R and the vertical axis is r in order to clarify this point, and the straight line in the figure is r = 1.033 × R−0.0043, phase relationship. The number is 0.97.
The values of R ′ and R ″ are also shown below the R column in Tables 1-3.

From the correlation found by the present inventors, the following can be understood. That is, in order to reduce the exchange frequency of the molten salt as much as possible, a glass with a small reduction rate of the surface compressive stress S due to an increase in Na concentration in the molten salt, that is, a glass with a large r may be used. It can be seen that R should be increased.
In addition, since r of the conventionally used glass A27 is 0.65, by setting R to 0.66 or more, r becomes approximately 0.68 or more and becomes clearly larger than the glass A27. The frequency of replacement is significantly reduced, or the management of molten salt can be greatly relaxed.

  The strength of the chemically strengthened glass strongly depends on the surface compressive stress. The smaller the surface compressive stress, the lower the strength of the chemically strengthened glass. For this reason, it is necessary that the surface compressive stress obtained by the chemical strengthening treatment is 68% or more, that is, r is 0.68 or more as compared with the surface compressive stress when the Na concentration in the molten salt is 0%. From this, when the Na concentration in the molten salt is C, the usable C range is a range satisfying the following formula.

0.68 ≦ (r−1) × C / 5 + 1
That is, C ≦ 1.6 / (1-r).

  When r is less than 0.68, the reduction rate of the surface compressive stress S of the chemically strengthened glass due to the increase of Na concentration in the molten salt is large, so the Na concentration can be used only in a narrow range of less than 5.0%. Increases frequency. When r is 0.75, 0.79 and 0.81, the Na concentration can be used in a wide range of Na concentrations of 6.4% or less, 7.6% or less and 8.4% or less, respectively. Can be suppressed to 78%, 66%, and 59% when r is 0.75, 0.79, and 0.81, respectively, compared to when r is 0.68. Therefore, r is preferably 0.70 or more, more preferably 0.75 or more, further preferably 0.79 or more, and particularly preferably 0.81 or more.

  If r is less than 0.68, the surface compressive stress S of the chemically strengthened glass is greatly changed due to the Na concentration change in the molten salt. Therefore, it becomes difficult to adjust the surface compressive stress, and the management of the Na concentration in the molten salt is severe. Become.

Further, the glass 1 and the glass 2 having the largest r among the 29 kinds of glasses are common in that they do not contain K ₂ O when compared with the other 27 kinds of glasses. On the other hand, the coefficient relating to K ₂ O in the above formula for calculating R is 0, which is significantly smaller than the coefficient 0.029 relating to Na ₂ O which is the same alkali metal oxide. Is possible.
The present invention has been conceived based on such circumstances.

According to the present invention, the rate of decrease in the surface compressive stress S of chemically strengthened glass due to an increase in Na concentration in the molten salt can be reduced. be able to.
Moreover, the decreasing rate of S of the chemically strengthened glass immediately before the molten salt exchange with respect to S of the chemically strengthened glass obtained by the first ion exchange treatment is reduced, and variation between S lots can be reduced.

It is a figure which shows the relationship between R calculated | required from glass composition, and the fall rate r of the surface compressive stress by Na density | concentration increase in molten potassium salt. It is a figure which shows the relationship between R 'calculated by calculating from a glass composition, and the decreasing rate r of the surface compressive stress by the Na concentration increase in molten potassium salt. The straight line in the figure is r = 1.04 8 × R′−0.0135, and the correlation coefficient is 0.98. In addition, the glass used for preparation of this figure is 29 types of glasses of Tables 1-3, 20 types of glasses of Tables 4 and 5 described later, 7 types of glasses 23 to 29 of Table 6 described later, and a table described below. No. 7, 5 types of glass 36 to 40, 6 types of glass 41 to 46 of Table 8 described later, and a total of 67 types of glass. It is a figure which shows the relationship between R "calculated | required from glass composition, and the fall rate r of the surface compressive stress by the Na density | concentration increase in molten potassium salt. The straight line in a figure is r = 1.014xR". +0.0074, correlation coefficient is 0.95. In addition, the glass used for preparation of this figure is 29 types of glasses of Tables 1-3, 20 types of glasses of Tables 4 and 5 described later, 7 types of glasses 23 to 29 of Table 6 described later, and a table described below. 5 glass 36-40 of No. 7, 6 types of glass 41-46 of Table 8 described later, 8 types of glass 49, 51-55, 57, 58 of Table 9 described later, 8 types of Table 10 described later A total of 94 glasses, including 59 to 64, 66 and 68, 5 types of glass 69, 73, 74, 77 and 78 in Table 11 described later, and 6 types of glass 79 to 82, 84 and 85 in Table 12 described later. It is.

  The surface compressive stress S of the chemically tempered glass produced by the production method of the present invention (hereinafter sometimes referred to as the chemically tempered glass of the present invention) is typically 200 MPa or more, but is 400 MPa or more in a cover glass or the like. More preferably, it is 550 MPa or more, and particularly preferably more than 700 MPa. Typically, S is 1200 MPa or less. The compressive stress layer thickness t of the chemically tempered glass of the present invention is typically 10 μm or more, preferably 30 μm or more, more preferably more than 40 μm. Typically, t is 70 μm or less.

Molten salt in the present invention is not particularly limited as long as the K in Na and molten salt of the glass surface layer can be ion-exchanged include, for example, molten potassium nitrate (KNO _3).
The molten salt must be a K-containing molten salt so that the ion exchange can be performed, but there is no other limitation as long as the object of the present invention is not impaired. As the molten salt, the above-mentioned molten KNO ₃ is usually used, but one containing about 5% or less of NaNO ₃ in addition to KNO ₃ is also common. The ratio of K ions in the molten salt containing K in the cation is typically 0.7 or more in terms of molar ratio.
Ion exchange treatment conditions for forming a chemically strengthened layer (compressive stress layer) having a desired surface compressive stress on glass vary depending on the thickness of the glass plate, but 2 for molten KNO ₃ at 350 to 550 ° C. It is typical to immerse the glass substrate for ~ 20 hours. From an economical viewpoint, it is preferable to immerse on the conditions of 350-500 degreeC and 2 to 16 hours, and a more preferable immersion time is 2 to 10 hours.
In the production method of the present invention, typically, an ion exchange treatment in which glass is immersed in a molten salt is performed to obtain a chemically strengthened glass, and then the chemically strengthened glass is taken out from the molten salt, and then another glass is melted. The ion exchange treatment is repeated so that the chemically strengthened glass is taken out from the molten salt after being immersed in the glass.

  The thickness t of the compressive stress layer is preferably 30 μm or more and the surface compressive stress S is preferably 550 MPa or more, although the thickness is 0.4 to 1.2 mm and the glass plate made of the glass of the present invention is chemically strengthened. T is 40 to 60 μm, and S is 650 to 820 MPa.

The glass plate for a display device of the present invention is usually obtained by chemically strengthening a glass plate obtained by processing the glass plate made of the glass of the present invention by cutting, drilling or polishing.
The thickness of the glass plate for a display device of the present invention is typically from 0.3 to 2 mm, and usually from 0.4 to 1.2 mm.
The glass plate for a display device of the present invention is typically a cover glass.

  The manufacturing method of the glass plate made of the glass of the present invention is not particularly limited. For example, various raw materials are prepared in appropriate amounts, heated to about 1400 to 1700 ° C. and melted, and then homogenized by defoaming, stirring, etc. It is manufactured by forming into a plate shape by a float method, a downdraw method, a press method, etc., and after slow cooling, it is cut into a desired size.

  The glass transition point Tg of the glass of the present invention is preferably 400 ° C. or higher. If it is less than 400 ° C., the surface compressive stress is relaxed during ion exchange, and there is a possibility that sufficient stress cannot be obtained. It is typically 570 ° C or higher.

  The Young's modulus E of the glass of the present invention is preferably 66 MPa or more. If it is less than 66 MPa, the fracture toughness value becomes low and the glass tends to break. When used for producing the glass plate for a display device of the present invention, E of the glass of the present invention is preferably 67 MPa or more, more preferably 68 MPa or more, further preferably 69 MPa or more, particularly preferably 70 MPa or more. .

Next, the composition of the glass of the present invention will be described using the mol% display content unless otherwise specified.
SiO ₂ is a component constituting the skeleton of glass and essential. If it is less than 61%, the change in the surface compressive stress due to the NaNO ₃ concentration in the KNO ₃ molten salt increases, cracks are likely to occur when the glass surface is scratched, the weather resistance decreases, the specific gravity increases, Or liquidus temperature rises and glass becomes unstable. Preferably it is 62% or more, typically 63% or more. In the fourth glass of the present invention, SiO ₂ is 62% or more.
If the SiO ₂ content exceeds 77%, the temperature T2 at which the viscosity becomes 10 ² dPa · s or the temperature T4 at which the viscosity becomes 10 ⁴ dPa · s increases, so that it becomes difficult to melt or mold the glass, or the weather resistance decreases. Preferably it is 76% or less, More preferably, it is 75% or less, More preferably, it is 74% or less, Most preferably, it is 73% or less.

Al ₂ O ₃ is a component that improves ion exchange performance and weather resistance and is essential. If it is less than 1%, the desired surface compressive stress S and compressive stress layer thickness t cannot be obtained by ion exchange, or the weather resistance decreases. It is preferably 3% or more, more preferably 4% or more, further preferably 5% or more, particularly preferably 6% or more, and typically 7% or more. If it exceeds 18%, the change in the surface compressive stress due to the NaNO ₃ concentration in the KNO ₃ molten salt becomes large, T2 or T4 rises, and it becomes difficult to melt or mold the glass, or the liquid phase temperature becomes high and devitrification occurs. It becomes easy. It is preferably 12% or less, more preferably 11% or less, further preferably 10% or less, particularly preferably 9% or less, and typically 8% or less.
When it is desired to particularly reduce the change in the surface compressive stress due to the NaNO ₃ concentration in the KNO ₃ molten salt, the Al ₂ O ₃ content is preferably less than 6%.
The total content of SiO ₂ and Al ₂ O ₃ is typically 66-83%.

MgO is a component that improves the meltability and is essential. If it is less than 3%, the meltability or Young's modulus decreases. Preferably it is 4% or more, More preferably, it is 5% or more, More preferably, it is 6% or more. When it is particularly desired to improve the meltability, MgO is preferably more than 7%.
If MgO exceeds 15%, the change in the surface compressive stress due to the NaNO ₃ concentration in the KNO ₃ molten salt increases, the liquidus temperature rises and the glass becomes easy to devitrify, or the ion exchange rate decreases. It is preferably 12% or less, more preferably 11% or less, still more preferably 10% or less, particularly preferably 8% or less, and typically 7% or less.

CaO may be contained up to 5% in order to improve the meltability at high temperature or to prevent devitrification, but the change in surface compressive stress due to the concentration of NaNO ₃ in the KNO ₃ molten salt increases, or There is a possibility that the resistance to ion exchange rate or crack generation may be reduced. When CaO is contained, its content is preferably 3% or less, more preferably 2% or less, further preferably 1.5% or less, particularly preferably 1% or less, most preferably 0.5% or less, Does not contain CaO.

When CaO is contained, the total content of MgO and CaO is preferably 15% or less. If it exceeds 15%, the change in surface compressive stress due to the concentration of NaNO ₃ in the KNO ₃ molten salt may be increased, or the resistance to ion exchange rate or crack generation may be reduced. Preferably it is 14% or less, More preferably, it is 13% or less, More preferably, it is 12% or less, Most preferably, it is 11% or less.

Na ₂ O is a component that reduces the change in surface compressive stress due to the NaNO ₃ concentration in the KNO ₃ molten salt, forms a surface compressive stress layer by ion exchange, or improves the meltability of glass, and is essential. If it is less than 8%, it becomes difficult to form a desired surface compressive stress layer by ion exchange, or T2 or T4 rises and it becomes difficult to melt or form glass. Preferably it is 9% or more, More preferably, it is 10% or more, More preferably, it is 11% or more, Most preferably, it is 12% or more. If Na ₂ O exceeds 18%, the weather resistance is lowered, or cracks are likely to occur from the indentation. Preferably it is 17% or less, More preferably, it is 16% or less, More preferably, it is 15% or less, Most preferably, it is 14% or less.

K ₂ O is not essential, but is a component that increases the ion exchange rate, and may be contained up to 6%. If it exceeds 6%, the change in the surface compressive stress due to the NaNO ₃ concentration in the KNO ₃ molten salt becomes large, cracks are likely to occur from the indentation, or the weather resistance is lowered. Preferably it is 4% or less, more preferably 3% or less, even more preferably 1.9% or less, particularly preferably 1% or less, and typically does not contain K ₂ O. The fourth of the glass of the present invention does not contain K _{2 O.}

The total content _{R 2} O of when Na ₂ O and _{K 2} O containing K ₂ O is preferably a 8.5 to 20%. If it exceeds 20%, the weather resistance is lowered, or cracks are likely to occur from the indentation. Preferably it is 19% or less, More preferably, it is 18% or less, More preferably, it is 17% or less, Most preferably, it is 16 or less. Further, _{R 2} O is reduced meltability of the glass is less than 8.5%. Preferably it is 9% or more, More preferably, it is 10% or more, More preferably, it is 11% or less, Most preferably, it is 12% or more.

ZrO ₂ is not an essential component, but may be contained up to 4% in order to increase the surface compressive stress or improve the weather resistance. If it exceeds 4%, the change in surface compressive stress due to the concentration of NaNO ₃ in the KNO ₃ molten salt becomes large, or the resistance to cracking is reduced. Preferably 2.5% or less, 2% or more preferably less, more preferably 1% or less, particularly preferably 0.5% or less, typically do not contain ZrO _2.

  The glass of the present invention consists essentially of the components described above, but may contain other components as long as the object of the present invention is not impaired. When such components are contained, the total content of these components is preferably 5% or less, more preferably 3% or less, particularly preferably 2% or less, and typically less than 1.5%. is there. Hereinafter, such components will be exemplarily described.

SrO may be included in order to improve the meltability at high temperature or to prevent devitrification, but the change in surface compressive stress due to the concentration of NaNO ₃ in the KNO ₃ molten salt increases, or ion exchange There is a risk that the resistance to speed or cracking may be reduced. The SrO content is preferably 1% or less, more preferably 0.5% or less, and typically does not contain SrO.

BaO may be contained in order to improve the meltability at high temperature or to make devitrification less likely to occur. However, the change in surface compressive stress due to the NaNO ₃ concentration in the KNO ₃ molten salt increases, or the ion exchange rate. Or there exists a possibility that the tolerance with respect to crack generation may fall. The BaO content is preferably 1% or less, more preferably 0.5% or less, and typically does not contain BaO.

The total RO of the contents of MgO, CaO, SrO and BaO is preferably 15% or less. If it exceeds 15%, the change in surface compressive stress due to the concentration of NaNO ₃ in the KNO ₃ molten salt may be increased, or the resistance to ion exchange rate or crack generation may be reduced. Preferably it is 14% or less, More preferably, it is 13% or less, More preferably, it is 12% or less, Most preferably, it is 11% or less.

  ZnO may be contained in order to improve the melting property of the glass at a high temperature, but the content in that case is preferably 1% or less. When manufacturing by a float process, it is preferable to make it 0.5% or less. If it exceeds 0.5%, it may be reduced during float molding, resulting in a product defect. Typically no ZnO is contained.

B ₂ O ₃ is preferably 5% or less for improving the meltability. If it exceeds 5%, it is difficult to obtain homogeneous glass, and it may be difficult to mold the glass. Preferably it is 4% or less, more preferably 3% or less, still more preferably 1.7% or less, even more preferably 1% or less, particularly preferably 0.5% or less, and typically does not contain B ₂ O ₃ .
When SrO, BaO or B ₂ O ₃ is contained, the R ′ is preferably 0.66 or more.
The second glass of the present invention contains one or more components of B ₂ O ₃ , SrO and BaO.

Since TiO ₂ coexists with Fe ions present in the glass, the visible light transmittance is lowered and the glass may be colored brown, so even if it is contained, it is preferably 1% or less. Does not contain.

Li ₂ O is a component that lowers the strain point and easily causes stress relaxation, and as a result, makes it impossible to obtain a stable surface compressive stress layer. Therefore, it is preferably 4.3% or less. More preferably 3% or less, still more preferably 2% or less, particularly preferably 1% or less, and typically does not contain Li ₂ O.

SnO ₂ may be contained for the purpose of improving weather resistance, but even in that case, the content is preferably 3% or less. More preferably, it is 2% or less, more preferably 1% or less, particularly preferably 0.5% or less, and typically does not contain SnO ₂ .
The third glass of the present invention is _{B 2 O 3, SrO, BaO} , ZnO, containing any one or more components of Li ₂ O and SnO _2.

As a fining agent for melting the glass, SO ₃ , chloride, fluoride and the like may be appropriately contained. However, in order to increase the visibility of a display device such as a touch panel, it is preferable to reduce as much as possible the components that are mixed as impurities in the raw material such as Fe ₂ O ₃ , NiO, Cr ₂ O ₃ having absorption in the visible region, Each of them is preferably 0.15% or less, more preferably 0.1% or less, and particularly preferably 0.05% or less in terms of mass percentage.

In the first glass of the present invention, the R is 0.66 or more, but when any one or more of B ₂ O ₃ , SrO, BaO, ZnO, Li ₂ O and SnO ₂ is contained, these The total content of the components is preferably 5 mol% or less. More preferably 4% or less, still more preferably 3% or less, particularly preferably 2% or less, and typically less than 1.5%.

In the second glass of the present invention, R ′ is set to 0.66 or more, but when any one or more of ZnO, Li ₂ O and SnO ₂ is contained, the total content of these components is 5 It is preferable that it is below mol%. More preferably 4% or less, still more preferably 3% or less, particularly preferably 2% or less, and typically less than 1.5%.

In the third glass of the present invention, the R ″ is 0.66 or more, but SiO ₂ , Al ₂ O ₃ , MgO, CaO, ZrO ₂ , Na ₂ O, K ₂ O, B ₂ O ₃ , SrO. The total content of BaO, ZnO, Li ₂ O and SnO ₂ is preferably more than 95 mol%, more preferably more than 96%, still more preferably more than 97%, particularly preferably more than 98%. Typically, it is 98.5% or more.

In the present invention, the method for repeating the ion exchange treatment of the glass is not particularly limited, but for example, it is carried out as follows. That is, 100 glass plates each having a size of 150 to 600 cm ² are placed one by one in the gaps between the slits of the scissors with slits so that the glass plates do not contact each other. The soot is immersed for 8 hours in a 100000 cm ³ tank filled with 400 ° C. molten potassium salt, and then the soot is taken out. Then, the ion exchange process is repeated by immersing the basket containing another glass plate in the tank.

Glasses 1 and 2 in Table 1 and glass A21 in Table 3 are examples of the glass of the present invention, and were prepared as follows. That is, the raw materials of each component were prepared so as to have a composition represented by mol% in the columns from SiO ₂ to K ₂ O in the table, and dissolved at a temperature of 1550 to 1650 ° C. for 3 to 5 hours using a platinum crucible. did. In melting, a platinum stirrer was inserted into the molten glass and stirred for 2 hours to homogenize the glass. Next, the molten glass was poured out and formed into a plate shape, which was gradually cooled to room temperature at a cooling rate of 1 ° C. per minute.

Moreover, columns of Examples 3 to 29 and 36 to 46 having compositions shown in mol% in the columns of SiO ₂ to K ₂ O in Tables 4 to 8 and columns of SiO ₂ to SnO _{2 in} Tables 9 to 12 Glasses of Examples 49 to 82, 84 and 85 having the compositions shown in mol% were produced in the same manner as the glasses 1, 2 and A21 were produced.

  The Tg (unit: ° C.), Young's modulus E (unit: MPa), R, R ′, R ″, CS1 (unit: MPa), CS2 (unit: MPa), and r of these glasses are shown in the table. Tg of 13-17, 36-38, 41-46, 61, 63, 75, 77-82, 84 and Examples 13-18, 20, 23-25, 28, 36-40, 43-46, 79-82 E is calculated or estimated from the composition, and for Examples 50, 56, 65, 67, 70 to 72, 75, and 76, CS1, CS2, and r cannot be measured accurately and calculated or estimated from the composition. The glass of Examples 41 and 42 is not the glass of the present invention, but MgO is less than 3%, the Young's modulus is low, and the fracture strength may be small.

  The glasses of Examples 30 to 35 in Tables 6 and 7, Examples 47 and 48 in Table 8, and Example 83 in Table 12 were not melted as described above, and Tg, E, CS1, and CS2 shown in these tables were not used. , R was calculated or estimated from the composition.

Examples 53 and 62 are examples of the present invention. Examples 31, 37 to 40, 43 to 46, 48 , 82 and 83 are comparative examples of the present invention, Examples 1 to 30, 32 to 36, 41 , 42, 47, 49 to 52, 54 to 61, 63 to Reference numerals 81, 84, and 85 are reference examples.

  It can be used as a cover glass for display devices. Moreover, it can utilize also for a solar cell board | substrate, an aircraft window glass, etc.

Claims (10)

The following oxide-based molar percentage displays, SiO ₂ 66.6 to 73%, Al ₂ O ₃ 10.2 to 16.7%, MgO 7% or less, CaO 0 to 0.5%, ZrO ₂ to 0 to 4%, Na ₂ O to 11 to 14.6 %, K ₂ O to 0 to 1.9%, and any one or more of B ₂ O ₃ , SrO and BaO, and B ₂ O ₃ is 4.2 % or less, the total content of SiO ₂ and Al ₂ O ₃ is 83 % or less, and R ′ calculated by the following formula using the content of each component is 0.00. A glass for chemical strengthening which is 66 or more.
R ′ = 0.029 × SiO ₂ + 0.021 × Al ₂ O ₃ + 0.016 × MgO−0.004 × CaO + 0.016 × ZrO ₂ + 0.029 × Na ₂ O + 0 × K ₂ O + 0.028 × B ₂ O ₃ + 0.012 × SrO + 0.026 × BaO−2.002 The glass for chemical strengthening according to claim 1, which contains Fe ₂ O ₃ in a percentage by mass of 0.15% or less. The glass for chemical strengthening according to claim 1 or 2 , wherein SrO is 0.5% or less. The glass for chemical strengthening according to any one of claims 1 to 3 , wherein ZnO is 0.5% or less. _{SiO 2, Al 2 O 3,} MgO, CaO, of _{ZrO 2, Na 2 O, K} 2 O, B 2 O 3, a total of SrO and BaO content is 98.5% or more claims 1-4 The glass for chemical strengthening according to any one of the above. Chemically strengthened glass according to any one of claims 1 to 5 containing no li 2 _O. Chemically strengthened glass according to any one of claims 1 to 6, not containing ZrO _2. The glass for chemical strengthening according to any one of claims 1 to 7 , which has a thickness of 0.4 to 1.2 mm. SO _3, chlorides, chemically strengthened glass according to any one of claims 1 to 8 containing 0.15% or less in each mass percentage fluoride. The glass for chemical strengthening according to any one of claims 1 to 9 , which is used for a cover glass of a display device.

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