JP7136100B2 - tempered glass - Google Patents

Description

The present invention relates to tempered glass. More specifically, it relates to tempered glass used as window glass for buildings.

As shown in Patent Document 1, there is a movement to replace ordinary glass windows with tempered glass for safety (preventing broken glass from falling) in the event of natural disasters such as earthquakes, typhoons, and tornadoes. However, when tempered glass is used as a window, the tensile stress inside the glass is strong, so there is a danger that the glass will shatter and fall when it breaks. For this reason, tempered glass windows are replaced with laminated glass windows to prevent them from falling, but in the case of laminated glass, the thickness of the glass is too large to fit in the existing sash, so it is not possible to replace the window glass alone. There is no need to replace the entire sash.

FIG. 1 is a diagram showing an example of glass with many broken pieces, and FIG. 2 is a diagram showing an example of glass with few broken pieces. As is clear from the comparison of FIGS. 1 and 2, even if the glass is made of glass that produces few fragments when broken, the fragments are large and the glass is supported by the sash, so that broken glass can be prevented from falling.

Japanese special table 2011-530470

SUMMARY OF THE INVENTION In order to solve the problems of the prior art, it is an object of the present invention to provide a tempered glass that has high strength due to its surface having compressive stress, but that produces few fragments when broken.

In order to achieve the above object, the present invention provides tempered glass having a mirror constant A of 2.2 MPa·m ^0.5 or more, a surface compressive stress (CS) of 10 MPa or more, and a plate thickness t of 1.2 mm or more and 50 mm or less. .

The tempered glass of the present invention is highly resistant to wind pressure and impact objects, and if broken, produces few fragments, and is therefore suitable as window glass for buildings.

FIG. 1 is a diagram showing an example of glass with many broken pieces. FIG. 2 is a diagram showing an example of glass with few broken pieces. FIG. 3 is a diagram schematically showing how a glass having no residual stress inside is broken by a uniform tensile stress, and how it breaks around the starting point of breakage.

Hereinafter, embodiments of the tempered glass of the present invention will be described.
The method for tempering the tempered glass of the present invention is not particularly limited, and the tempered glass may be air-cooled tempered glass or chemically tempered glass.
However, when it is used as window glass for buildings, it is preferable to use air-cooled tempered glass in consideration of the size of the glass, which can be easily tempered, and the cost.

It is known that when glass breaks, the shape of the fracture surface varies depending on the magnitude of the stress. FIG. 3 schematically shows how glass with no residual stress inside, that is, glass that has not been tempered is broken by a uniform tensile stress.
In FIG. 3, a smooth surface called a mirror surface is generated around the starting point of fracture indicated by a black circle. In addition, a slightly rough boundary surface called mist is generated around it, and a rough surface called hackle is generated beyond it. In FIG. 3, the distance from the fracture starting point indicated by the black circle to the boundary between the mirror surface and the mist surface is R (unit: m), and the stress that caused the fracture is σ (unit: MPa ), it is known that σ is proportional to the reciprocal of the square root of R, and the constant of proportionality is Miller's constant A (unit: MPa·m ^0.5 ). That is, the relationship shown in the following formula is obtained.
σ = A/R ^1/2
The Miller constant A can be obtained experimentally by measuring the stress σ at breakage and the distance R from the breakage starting point to the interface between the mirror surface and the mist.

Also, glass with a large Miller constant A has a small number of fragments when broken. How tempered glass breaks depends on the properties of the glass before tempering. Therefore, glass (tempered glass) obtained by tempering glass having a large Miller constant A before tempering treatment has a small number of fragments even when broken, so the fragments are less likely to scatter and are highly safe.
Since the mirror constant A does not change before and after the tempering process, hereinafter, the mirror constant A obtained for the glass before the tempering process is replaced by the mirror constant A for the tempered glass (tempered glass). and

The tempered glass of the present invention has a Miller constant A of 2.2 MPa·m ^0.5 or more. This reduces the number of fragments when broken. Therefore, even if it is destroyed, the fragments are less likely to scatter and the safety is high.
The tempered glass of the present invention preferably has a Miller constant A of 2.3 MPa·m ^0.5 or more, more preferably 2.35 MPa·m ^0.5 or more, and further preferably 2.4 MPa·m ^0.5 or more. It is preferably 2.45 MPa·m ^0.5 or more, particularly preferably 2.5 MPa·m ^0.5 or more, most preferably 2.5 MPa·m 0.5 or more. Although the upper limit of the Miller constant A is not particularly limited, it is preferably 5 MPa·m ^0.5 or less in order to maintain the glass structure.

The tempered glass of the present invention can increase the surface compressive stress CS and/or the depth DOL of the compressive stress layer due to the properties described above.
If the surface compressive stress CS and/or the depth DOL of the compressive stress layer are increased in order to increase the strength, the internal tensile stress CT increases, and the density of the fragments when the glass breaks increases, increasing the danger. said to increase.
Here, Patent Document 1 discloses a formula (1) that indicates the allowable limit of the internal tensile stress of tempered glass, and by adjusting the following CT' to a low value, even if the strength of the chemically strengthened glass is increased, the crushed fragment density It was said that chemically strengthened glass with small cracks and little scattering of fragments can be obtained. As described in Patent Document 1, the internal tensile stress CT' uses the values of CS and DOL' and has the relationship of the following formula (2).
CT′≦−38.7×ln(t)+48.2 (1)
CS×DOL′=(t−2×DOL′)×CT′ (2)
Equation (2) may be rewritten as Equation (3).
CT' = CS x DOL'/(t-2 x DOL') (3)
Here, DOL' corresponds to the depth of the ion exchange layer.
DOL and DOL' often match, but the values may differ depending on the thermal history after ion exchange. Since the tempered glass of the present invention has a low fragment density when broken, it can be tempered to exceed the maximum value of CT' represented by formula (1). Since CT' has the relationship of expression (2) with CS and DOL', when CT' increases, either CS or DOL' can be increased, and the intensity increases. Tempered glass with a large CS is less likely to break even if the surface is scratched because the surface compressive stress narrows the scratch. In addition, when the glass plate is bent, the tensile stress applied to the outside of the curved surface is canceled by the surface compressive stress, so the glass plate is less likely to break when bent. If the DOL is large, the strength of resistance to collision with flying objects can be increased.

The tempered glass of the present invention can have a surface compressive stress (CS) of 10 MPa or more for the reasons described above. The tempered glass of the present invention preferably has a surface compressive stress (CS) of 15 MPa or more, more preferably 50 MPa or more, more preferably 60 MPa or more, more preferably 70 MPa or more, and 80 MPa. It is more preferably 90 MPa or more, particularly preferably 90 MPa or more, and most preferably 100 MPa or more. The upper limit of the surface compressive stress (CS) is not particularly limited, but it is known that excessive compression causes local tensile stress around microcracks and leads to overall fracture, so 2500 MPa or less is preferable.
In the tempered glass of the present invention, the product (CS×A) of surface compressive stress (CS) and Miller constant A is preferably 22 (MPa) ² ·m ^0.5 or more, and 50 (MPa) ² ·m ^0.5 or more. more preferably 100 (MPa) ² ·m ^0.5 or more, more preferably 150 (MPa) ² ·m ^0.5 or more, and 200 (MPa) ² ·m ^0.5 or more is particularly preferred.

Since the tempered glass of the present invention is used as window glass for buildings, the plate thickness t is 1.2 mm or more and 50 mm or less. If the sheet thickness t is 1.2 mm or more, a temperature difference between the surface and the inside is likely to occur, and physical strengthening treatment (also referred to as air-cooling strengthening treatment; the same applies hereinafter) can be easily performed. If the plate thickness t is 50 mm or less, the weight of the glass as a whole is light and it is easy to use as a window.
The tempered glass of the present invention preferably has a plate thickness t of 1.3 mm or more, more preferably 1.5 mm or more, more preferably 1.7 mm or more, more preferably 1.9 mm or more, and 2.0 mm or more. It is more preferably 2.1 mm or more, particularly preferably 2.3 mm or more, and most preferably 2.3 mm or more. The plate thickness t is preferably 45 mm or less, more preferably 40 mm or less, more preferably 35 mm or less, even more preferably 30 mm or less, particularly preferably 25 mm or less, and most preferably 20 mm or less.

Focusing on the relationship between the physical properties of unstrengthened glass and the Miller constant A, the Miller constant A tends to increase as the fictive temperature of unstrengthened glass decreases. Fragmentation of glass proceeds at the portion where the tensile stress of the glass is maximum. Since such a portion with the maximum tensile stress is the central portion of the glass in the thickness t direction, it is the Miller constant at the central portion of the glass in the thickness t direction that causes the breakage of the entire glass.
In addition, in this specification, the center part of the plate|board thickness t direction of glass means the following. Let t be the distance in the normal direction from one main surface of the glass plate to the other main surface, and this normal direction is defined as the t direction. The position t/2 in the t direction from the main surface is the central portion of the glass in the thickness t direction. Normally, when both surfaces of the glass are strengthened in the same way, the tensile stress is maximized at the position t/2 in the t direction from the main surface. Become.
The fictive temperature of the tempered glass, especially the fictive temperature of the central portion in the thickness direction t, is affected by the fictive temperature of the glass before tempering. If the tempering treatment is performed under appropriate conditions, the fictive temperature at the central portion in the plate thickness t direction does not substantially differ between before and after the tempering treatment.
In the tempered glass of the present invention, the fictive temperature at the center in the direction of the thickness t of the glass is not higher than the glass transition point Tg + 60 ° C., and the mirror constant A of the glass is not lower than 2.2 MPa·m ^0.5 . It is preferable.
The tempered glass of the present invention preferably has a fictive temperature of Tg+50° C. or less at the center in the thickness t direction of the glass, more preferably Tg+40° C. or less.
In addition, the fictive temperature T _f in the present invention means a numerical value obtained by the refractive index method shown below. The fictive temperature T _f can be measured by polishing the cross section of the glass and measuring the refractive index n.
T _f =a×n+b (4)
can be expressed as Here, a and b are constants unique to the type of glass.
A specific method of obtaining the fictive temperature T _f by the refractive index method is as follows. First, i (i ≥ 2) test pieces were prepared from the glass sample whose fictive temperature was to be measured, and held at different cooling start temperatures until the refractive index reached an equilibrium state. Cool over min. Here, if the cooling start temperature is lower than the glass transition temperature, a sufficiently long holding time is required. The refractive index nd is measured at a specific wavelength (for example the _d -line of He lamp, 587.6 nm) for the glass cooled under these conditions. Plot the refractive index n _di of the glass quenched from the cooling start temperature against each cooling start temperature T _i , determine the constants a and b in equation (4) by linear regression, and create a calibration curve. Next, the refractive index n _dS of a polished specimen cut from the glass whose fictive temperature T _f is to be measured can be measured, and the fictive temperature T _f of the glass can be determined using a calibration curve.

The fictive temperature of the glass before tempering can be adjusted by the following procedure.
When manufacturing tempered glass, glass raw materials having a predetermined composition are prepared and melted, and then formed into sheet glass. By adjusting the cooling temperature profile during molding, the fictive temperature of the glass can be adjusted. When the fictive temperature of the glass is lowered, for example, cooling is performed after holding the glass near the glass transition temperature for several hours, or the cooling rate near the glass transition point (for example, the temperature between the annealing point and the strain point) is decreased. Specifically, it can be achieved by setting the temperature to 200° C./min or less.
Alternatively, the fictive temperature of the glass can be adjusted by the following procedure.
After preparing and melting glass raw materials having a predetermined composition, the mixture is formed into plate glass by a known method for forming plate glass (for example, the float method, the fusion method, or the roll-out method). After molding, the glass is heated to a predetermined cooling start temperature and held at that temperature. The fictive temperature of the glass can then be adjusted by adjusting the cooling rate. To lower the fictive temperature of the glass, the cooling start temperature should be lowered. In this case, the faster the cooling rate, the closer the value of the fictive temperature to the cooling start temperature, which is preferable. The required holding time varies depending on the cooling start temperature, but is preferably 500/(cooling start temperature−T _g ) minutes or more, more preferably 1000/(cooling start temperature−T _g ) minutes or more.
The cooling start temperature is preferably Tg+100° C. or lower. If the temperature is Tg+100° C. or less, the fictive temperature can be easily lowered even with a short-time heat treatment. The cooling start temperature is more preferably Tg+60° C. or lower, still more preferably Tg+30° C. or lower, and particularly preferably Tg+20° C. or lower. When the fictive temperature is adjusted by this procedure, the cooling rate is preferably 100° C./min or higher, more preferably 200° C./min or higher, and even more preferably 300° C./min or higher.

After cooling, the glass is tempered under predetermined conditions. In the case of air cooling strengthening, the sheet is placed in a heating furnace at Tg + 60 ° C. to Tg + 110 ° C. for a short time (eg, within 7 minutes) and rapidly cooled (eg, cooling rate of 500 ° C./min or more) to the center of the plate thickness t direction. There is substantially no difference in the fictive temperature of the part before and after the tempering treatment.

As described above, since the tempered glass of the present invention has a small number of fragments when broken, it can be tempered to exceed the maximum value of CT′ represented by formula (1), and CS and DOL can be increased. can do.

In the tempered glass of the present invention, the product (CT×A) of the tensile stress CT at the central portion in the thickness t direction and the Miller constant A is preferably 11 (MPa) ² ·m ^0.5 or more, and 15 (MPa). It is more preferably ² ·m ^0.5 or more, and even more preferably 20 (MPa) ² ·m ^0.5 or more.

Since the tempered glass of the present invention has a small number of fragments when broken, it is possible to increase the compressive stress layer depth DOL by performing a tempering process that exceeds the allowable limit of the internal tensile stress CT'.
Tempered glass with a large DOL is hard to break because even when a deep scratch occurs, the tip of the scratch stays in the compressive stress layer.
The tempered glass of the present invention preferably has a compressive stress layer depth DOL of (1/10) × t mm or more, and (1/8) × t mm or more when the plate thickness is t (unit: mm). is more preferably, (1/7)×t mm or more is more preferable, and (1/6.5)×t mm or more is particularly preferable. However, DOL is preferably (1/4) x tmm or less, more preferably (1/4.2) x tmm or less, and (1/4.5) x tmm or less. More preferred. If the DOL is (1/4) × tmm or less, the area where the tensile stress occurs is (1/2) × tmm or less of the plate thickness, the tensile stress CT can be lowered, and when the tempered glass breaks, many fragments less likely to scatter.

Tempered glass with a large DOL is hard to break because even when a deep scratch occurs, the tip of the scratch stays in the compressive stress layer.
The tempered glass of the present invention preferably has a compressive stress layer depth DOL of 0.150 mm or more, more preferably 0.200 mm or more, and even more preferably 0.300 mm or more. However, the compressive stress layer depth DOL is preferably 10 mm or less, more preferably 8 mm or less, more preferably 6 mm or less, even more preferably 5 mm or less, particularly preferably 4.5 mm or less, and most preferably 4 mm or less.

Tempered glass with a large DOL' is hard to break because even when a deep scratch occurs, the tip of the scratch stays in the compressive stress layer.
The tempered glass of the present invention preferably has a compressive stress layer depth DOL' of 0.150 mm or more, more preferably 0.200 mm or more, and even more preferably 0.300 mm or more. The compressive stress layer depth DOL' is preferably 10 mm or less, more preferably 8 mm or less, more preferably 6 mm or less, even more preferably 5 mm or less, particularly preferably 4.5 mm or less, and most preferably 4 mm or less.

The applicant of the present application has obtained the following findings regarding the relationship between the mirror constant A of glass and the physical properties of glass or the composition of glass.

In the case of a glass composition containing substantially no B ₂ O ₃ (1) The higher the Poisson's ratio ν of the glass, the smaller the mirror constant A of the glass. Therefore, it is preferable that the Poisson's ratio of the glass is low. Specifically, the Poisson's ratio ν of the glass is preferably 0.28 or less, more preferably 0.26 or less, and even more preferably 0.24 or less. The lower limit of the Poisson's ratio ν of the glass is not particularly limited, but is preferably 0.1 or more because a certain range of elastic deformation upon impact is required.
There are the following means for lowering the Poisson's ratio ν of the glass. By increasing the content of SiO ₂ , Al ₂ O ₃ , and P ₂ O ₅ , which are network formers, in the glass composition, the network in the glass develops and the glass has more voids. . In this case, glass having a low Poisson's ratio can easily be obtained because the glass has a space that shrinks by compression. In addition to the above network formers, MgO, ZrO ₂ and the like are preferably used because they work as network forming factors without significantly increasing Tg. On the other hand, alkali metal oxides such as R ₂ O, CaO, and SrO cut the network, increase the packing density of the glass (the ratio of the sum of the ionic radii of the elements constituting the glass to the total volume of the glass), and increase the Poisson's ratio. tends to rise. The addition of rare earth elements also tends to increase the number of bonds and raise the Poisson's ratio, but at the same time, the Young's modulus increases, so the Miller constant A tends to increase. Here, the alkali metal oxide R ₂ O is a generic term for Li ₂ O, Na ₂ O, K ₂ O and Rb ₂ O (hereinafter the same throughout the specification). Further, "substantially free of B ₂ O ₃ " means that it does not contain B ₂ O ₃ except when it is mixed as an unavoidable impurity (hereinafter the same in this specification).
(2) The higher the Young's modulus E of the glass, the larger the mirror constant A of the glass. In order to increase the Young's modulus of the glass, it is effective to increase the Al ₂ O ₃ content in the glass. In general, when the SiO ₂ content in the glass is high, the network structure of the glass is relatively strong and the Young's modulus of the glass is high. If the SiO ₂ content in the glass is low, the Young's modulus can be increased by increasing the Al ₂ O ₃ content and repairing the broken network structure. Increasing the content of alkaline earth metal oxides (RO) in the glass is also effective in increasing the Young's modulus of the glass. Also, when the glass contains NiO, TiO ₂ , ZrO ₂ , HfO ₂ , ThO ₂ or the like, the Young's modulus of the glass increases. Here, the alkaline earth metal oxide (RO) is a generic term for MgO, CaO, SrO and BaO (hereinafter the same throughout the specification).
Although it does not affect the mirror constant A of the glass, P ₂ O ₅ tends to cause phase separation and devitrification, so it is preferable not to add a large amount to the glass.

Based on the above knowledge, the glass composition contains 30 to 85% of SiO ₂ , 0 to 40% of Al ₂ O ₃ , 0 to 10% of P ₂ O ₅ and an alkaline It preferably contains 8 to 40% total metal oxide (R ₂ O), 0 to 40% total alkaline earth metal oxide (RO), and substantially no B ₂ O ₃ .
In addition, it contains 30 to 85% of SiO ₂ , 0 to 30% of Al ₂ O ₃ and 0 to 10% of P ₂ O ₅ in terms of molar percentages based on oxides, and an alkali metal oxide (R ₂ O ) in a total amount of 10 to 40%, an alkaline earth metal oxide (RO) in a total amount of 0 to 40%, and substantially free of B ₂ O ₃ .
In addition, SiO ₂ is 35 to 55%, the ratio of Al ₂ O ₃ to SiO ₂ (Al ₂ O ₃ /SiO ₂ ) is 0.3 to 0.6, and P ₂ is expressed as a molar percentage based on oxides. 0 to 5% O ₅ , 20 to 40% total alkali metal oxide (R ₂ O), 0 to 15% total alkaline earth metal oxide (RO), B ₂ O Those substantially free of ₃ are more preferred.
In addition, SiO ₂ is 40 to 50%, the ratio of Al ₂ O ₃ to SiO ₂ (Al ₂ O ₃ /SiO ₂ ) is 0.5 to 0.6, and P ₂ is expressed as a molar percentage based on oxides. 0-1% O ₅ , 20-30% total alkali metal oxide (R ₂ O), 5-15% total alkaline earth metal oxide (RO), B ₂ O Those substantially free of ₃ are particularly preferred.
With the above glass composition, the Young's modulus E of the glass is 68 GPa or higher, preferably 70 GPa or higher, more preferably 75 GPa or higher, and still more preferably 80 GPa or higher. Although the upper limit of Young's modulus of glass is not particularly limited, it is generally 180 GPa or less.
Each component in the case of a glass composition substantially free of B ₂ O ₃ will be described below.

_SiO2 is the main component of glass.
If the content of _SiO2 is 30% or more, the weather resistance is good. The content of SiO ₂ is more preferably 35% or more, still more preferably 38% or more, and particularly preferably 40% or more. If the content of _SiO2 is 85% or less, it is difficult to devitrify. The content of SiO ₂ is more preferably 55% or less, even more preferably 50% or less, and particularly preferably 47% or less.

Al ₂ O ₃ is a component that improves weather resistance.
The content of Al ₂ O ₃ is 0% or more. When Al ₂ O ₃ is contained, the weather resistance is improved. The content of Al ₂ O ₃ is more preferably 1% or more, still more preferably 3% or more, and particularly preferably 5% or more. If the content of Al ₂ O ₃ is 40% or less, the solubility is good. The content of Al ₂ O ₃ is more preferably 35% or less, still more preferably 32% or less, and particularly preferably 30% or less.

If the ratio of Al ₂ O ₃ to SiO ₂ (Al ₂ O ₃ /SiO ₂ ) is 0.3 or more, the number of bonds increases and the structure becomes stronger. Al ₂ O ₃ /SiO ₂ is more preferably 0.35 or more, still more preferably 0.4 or more. More preferably, it is 0.5 or more. If the ratio of Al ₂ O ₃ to SiO ₂ (Al ₂ O ₃ /SiO ₂ ) is 0.6 or less, the viscosity of the glass is less likely to increase at high temperatures, which is preferable. Al ₂ O ₃ /SiO ₂ is more preferably 0.55 or less, still more preferably 0.52 or less.

P ₂ O ₅ is likely to cause phase separation and devitrification, so it is preferable not to substantially contain it, but it may be contained in an amount of 10% or less in order to increase the DOL. The content of P ₂ O ₅ may be 5% or less, or 1% or less.

If the total amount of alkali metal oxides (R ₂ O) is 8% or more, the viscosity of the glass tends to decrease when the glass is heated to a high temperature, making the glass easy to melt. The total amount of R ₂ O is preferably 10% or more, more preferably 12% or more, and particularly preferably 20% or more. Also, if the total amount of R ₂ O is 40% or less, the Young's modulus is less likely to decrease. The total amount of R ₂ O is more preferably 35% or less, more preferably 30% or less.

Li ₂ O is an alkali metal oxide component that has the effect of lowering the viscosity of glass at high temperatures and does not cause a decrease in Young's modulus at room temperature. When the content of Li ₂ O is 0.01% or more, the above effect appears. The content of Li ₂ O is more preferably 2% or more, more preferably 4% or more. If Li ₂ O is 20% or less, the network in the glass structure can be maintained. In addition, since the price of Li ₂ O is high, the price of the resulting glass does not rise. The content of Li ₂ O is more preferably 15% or less, even more preferably 10% or less.

Na ₂ O, like Li ₂ O, is a component that has the effect of lowering the viscosity of glass at high temperatures. If the content of Na ₂ O is 5% or more, the above effects are obtained. The content of Na ₂ O is more preferably 10% or more, more preferably 15% or more. If the content of Na ₂ O is 40% or less, the network in the glass structure can be maintained. The content of Na ₂ O is more preferably 30% or less, more preferably 20% or less.

K ₂ O, like Li ₂ O and Na ₂ O, is a component that has the effect of lowering the viscosity of glass at high temperatures. If the K ₂ O content is 2% or more, the effect of lowering the viscosity becomes stronger. The content of K ₂ O is more preferably 3% or more, more preferably 5% or more. If the K ₂ O content is 20% or less, the deliquescence of the glass can be lowered to some extent. The content of K ₂ O is more preferably 15% or less, even more preferably 10% or less.

Rb ₂ O, like Li ₂ O, Na ₂ O and K ₂ O, is a component that has the effect of lowering the viscosity of glass at high temperatures. If the content of Rb ₂ O is 1% or more, it is possible to improve the energy absorption effect when breaking the glass due to the mixed alkali effect. The content of Rb ₂ O is more preferably 1% or more, more preferably 2% or more. If the content of Rb ₂ O is 10% or less, excessive increase in the weight of the glass can be prevented. The content of Rb ₂ O is more preferably 5% or less, more preferably 4% or less.

Alkaline earth metal oxide (RO) is a component that increases the Miller constant, so it may be contained in both the physically strengthened glass and the chemically strengthened glass. If the total amount of RO is 3% or more, it leads to an increase in Miller's constant. The total amount of RO may be 5% or more. Also, if the total RO content is 40% or less, devitrification is less likely to occur. The total amount of RO is more preferably 30% or less, more preferably 25% or less, and particularly preferably 20% or less.
On the other hand, especially in the case of chemically strengthened glass, among the alkaline earth metal oxides (RO), if the alkaline earth metal oxide component (CaO + SrO + BaO) excluding MgO is small, the ion exchange capacity is improved and a large DOL can be obtained. (CaO+SrO+BaO) is preferably 5% or less in total. The total amount of (CaO+SrO+BaO) is more preferably 4% or less, still more preferably 3% or less, and particularly preferably 1% or less. In addition, (CaO + SrO + BaO) reduces the devitrification property of the glass and makes it possible to obtain a stable glass. More preferably, 1% or more is even more preferable.

MgO is a component that increases the mirror radius by increasing the Young's modulus of the glass. In both cases of physically strengthened glass and chemically strengthened glass, when the content of MgO is 3% or more, the effect of increasing the Young's modulus becomes remarkable. The content of MgO is more preferably 5% or more, more preferably 10% or more. If the content of MgO is 35% or less, problems such as susceptibility to devitrification can be avoided. The content of MgO is more preferably 30% or less, even more preferably 25% or less.

CaO is a component for improving meltability at high temperatures or making devitrification less likely to occur. Therefore, in both cases of physically strengthened glass and chemically strengthened glass, if the content of CaO is 0.1% or more, devitrification can be suppressed. The content of CaO is more preferably 0.5% or more, more preferably 1% or more. If the content of CaO is 15% or less, both effects of improving the meltability and increasing the Young's modulus of the glass can be obtained. The content of CaO is more preferably 10% or less, even more preferably 5% or less. Especially in the case of chemically strengthened glass, the effect of increasing the DOL can be obtained by reducing the CaO content, so the CaO content is preferably 5% or less. The content of CaO is more preferably 3% or less, and even more preferably 2% or less.

SrO is a component for improving meltability at high temperatures or making devitrification less likely to occur. Therefore, in both cases of physically strengthened glass and chemically strengthened glass, if the content of SrO is 0.1% or more, it is effective in preventing devitrification. The content of SrO is more preferably 0.2% or more, more preferably 0.3% or more. If the SrO content is 15% or less, the weight increase of the glass does not pose a problem. The content of SrO is more preferably 10% or less, more preferably 5% or less. Especially in the case of chemically strengthened glass, the effect of increasing the DOL can be obtained by reducing the SrO content, so the SrO content is preferably 5% or less. The content of SrO is more preferably 3% or less, still more preferably 1% or less.

BaO is a component for improving meltability at high temperatures or making devitrification less likely to occur. In the case of physically strengthened glass, when the content of BaO is 0.1% or more, energy dissipation tends to occur easily due to the mixing effect of alkaline earth elements. In the case of physically strengthened glass, the content of BaO is more preferably 0.2% or more, more preferably 1% or more. In the case of physically strengthened glass, if the content of BaO is 20% or less, the weight increase of the glass does not pose a problem. In the case of physically strengthened glass, the content of BaO is more preferably 15% or less, and even more preferably 10% or less. In the case of chemically strengthened glass, the effect of increasing the DOL can be obtained by reducing the content of BaO. Therefore, in the case of chemically strengthened glass, the content of BaO is preferably 5% or less. The BaO content is more preferably 3% or less, still more preferably 1% or less, and particularly preferably 0.1% or less.

Based on the above knowledge, when the tempered glass of the present invention does not substantially contain B ₂ O ₃ , G represented by the following formula (7) is preferably 0 or more.
G=E×0.013+ν×(−6.6)+[Al ₂ O ₃ ]×0.023+ΣRO×0.013 (7)
(wherein E is the Young's modulus of the glass (GPa), ν is the Poisson's ratio of the glass, [Al ₂ O ₃ ] is the content of Al ₂ O ₃ in the glass (mol% based on oxide), ΣRO is the glass It is the total content of alkaline earth metal oxides in (mole% based on oxides).)
When G is 0 or more, the Miller constant tends to increase. G is more preferably 0.05 or more, still more preferably 0.1 or more, and particularly preferably 0.2 or more. Although the upper limit of G is not particularly limited, it may be 10 or less.

Moreover, when the tempered glass of the present invention does not substantially contain B ₂ O ₃ , I represented by the following formula (9) is preferably 0.45 or more.
I=[Al ₂ O ₃ ]×0.03+ΣRO×0.014 (9)
(In the formula, [Al ₂ O ₃ ] is the Al ₂ O ₃ content in the glass (mol% based on oxides), ΣRO is the total content of alkaline earth metal oxides in the glass (moles based on oxides) %).)
When I is 0.45 or more, the Miller constant tends to increase. I is more preferably 0.5 or more, still more preferably 0.6 or more, and particularly preferably 0.7 or more. The upper limit of I is not particularly limited, but considering the amount of Al ₂ O ₃ and RO that can be contained in the glass, I is preferably 2 or less.

In the case of the glass composition containing B ₂ O ₃ (1) When the glass is fractured, cracks propagate in the glass, but stress increases at the crack tip, leading to new crack propagation. On the other hand, in a glass containing three-coordinated boron, this stress converts three-coordinated boron into four-coordinated boron, and this change in coordination number consumes the crushing energy. This energy consumption suppresses the energy distributed to crack propagation. As a result, the formation of crushed surfaces is suppressed. When the formation of the fractured surface is suppressed, the mirror surface continues for a long time and the mist surface is less likely to form, resulting in a glass with a large mirror constant. That is, the higher the content of three-coordinated boron in the glass, the higher the mirror constant A of the glass, which is preferable.
On the other hand, the addition of Al ₂ O ₃ is not preferable because it significantly lowers the mirror constant A of the glass.
Although the alkaline earth metal oxide RO does not significantly change the rigidity of the glass as a whole, it tends to make boron tetracoordinate, so it is better not to add too much alkaline earth metal oxide RO.
Alkali metal oxide R ₂ O lowers the rigidity of the glass as a whole and tends to make boron tetra-coordinated, so it is better not to add too much. However, since it has the effect of increasing α _LT and α _HT , which will be described later, it is added in an appropriate amount.

(2) The higher the Young's modulus E of the glass, the larger the mirror constant A of the glass. The component that increases the Young's modulus E of the glass is the same as in the case of the glass composition that does not substantially contain B ₂ O ₃ . However, the relationship between Young's modulus E and Miller's constant A of glass is lower than the relationship with three-coordinated boron described above.
The addition of alkaline earth metal oxides RO increases the Young's modulus E of the glass, but tends to tetracoordinate boron and lowers the Miller constant A of the glass. Therefore, in the case of a glass composition containing B ₂ O ₃ , it is preferable not to increase the content of alkaline earth metal oxide RO. Since the addition of Al ₂ O ₃ increases the Young's modulus E of the glass, the higher the Al 2 O 3 content, the better.

Although it does not affect the mirror constant A of the glass, P ₂ O ₅ tends to cause phase separation and devitrification, so it is preferable not to add a large amount to the glass.

The glass composition based on the above knowledge is 0.01 to 40% of B ₂ O ₃ , 40 to 75% of SiO ₂ , 0 to 20% of Al ₂ O ₃ and P ₂ in terms of molar percentages based on oxides. It preferably contains 0 to 10% O ₅ , a total alkali metal oxide (R ₂ O) content of 8 to 40%, and an alkaline earth metal oxide (RO) content of 0 to 40% total content.
In addition, it contains 5 to 25% of B ₂ O ₃ , 40 to 73% of SiO ₂ , 0 to 20% of Al ₂ O ₃ and 0 to 10% of P ₂ O ₅ in terms of molar percentages based on oxides. and containing 10 to 20% in total of alkali metal oxides (R ₂ O) and 0 to 30% in total of alkaline earth metal oxides (RO).
In terms of molar percentages based on oxides, 5 to 25% of B ₂ O ₃ , 43 to 55% of SiO ₂ , 0 to 15% of Al ₂ O ₃ , the sum of B ₂ O ₃ and R ₂ O and ratio (B ₂ O ₃ /ΣR ₂ O) of 0.8 to 2.5, P ₂ O ₅ content of 0 to 5%, and alkali metal oxide (R ₂ O) content of 10 to 20% in total. and alkaline earth metal oxides (RO) in a total amount of 1 to 25%.
In terms of molar percentages based on oxides, B ₂ O ₃ is 5 to 25%, SiO ₂ is 46 to 50%, Al ₂ O ₃ is 0 to 5%, and the sum of B ₂ O ₃ and R ₂ O is A ratio (B ₂ O ₃ /ΣR ₂ O) of 1.0 to 2.0, containing 0 to 1% of P ₂ O ₅ and a total amount of alkali metal oxide (R ₂ O) of 15 to 20%, Those containing 1 to 15% total alkaline earth metal oxides (RO) are particularly preferred.
With the above glass composition, the Young's modulus E of the glass is 70 GPa or more, preferably 75 GPa or more, and still more preferably 80 GPa or more. Although the upper limit of Young's modulus of glass is not particularly limited, it is generally 180 GPa or less.
Each component of the glass composition containing B ₂ O ₃ will be described below.

_SiO2 is the main component of glass.
If the content of _SiO2 is 40% or more, the weather resistance is good. The content of SiO ₂ is more preferably 43% or more, more preferably 46% or more. If the content of _SiO2 is 75% or less, it is difficult to devitrify. The content of SiO ₂ is more preferably 70% or less, even more preferably 65% or less, even more preferably 63% or less, particularly preferably 55% or less, most preferably 50% or less.

Al ₂ O ₃ is a component that improves weather resistance.
The content of Al ₂ O ₃ is 0% or more. When Al ₂ O ₃ is contained, the weather resistance is improved. The content of Al ₂ O ₃ is more preferably 0.1% or more, still more preferably 0.3% or more, and particularly preferably 0.5% or more. If the content of Al ₂ O ₃ is 20% or less, the solubility is good. However, if Al ₂ O ₃ is included, the Miller constant decreases sharply, so the content is more preferably 15% or less, even more preferably 10% or less, and particularly preferably 5% or less.

If the ratio of Al ₂ O ₃ to SiO ₂ (Al ₂ O ₃ /SiO ₂ ) is 0.01 or more, the bond cut by the alkali metal is repaired, the network structure of the glass is strengthened, and the hardness is improved. do. Al ₂ O ₃ /SiO ₂ is more preferably 0.02 or more, still more preferably 0.03 or more. If the ratio of Al ₂ O ₃ to SiO ₂ (Al ₂ O ₃ /SiO ₂ ) is 0.5 or less, it is possible to prevent the Miller constant from decreasing. Al ₂ O ₃ /SiO ₂ is more preferably 0.3 or less, still more preferably 0.1 or less.

Since P ₂ O ₅ is likely to cause phase separation and devitrification, it is preferable not to substantially contain it. good too. The content of P ₂ O ₅ may be 5% or less, or 1% or less.

B ₂ O ₃ is highly effective as a component that increases the Miller constant, and is preferably contained in an amount of 0.01% or more. The B ₂ O ₃ content is more preferably 1% or more, still more preferably 5% or more, particularly preferably 10% or more, and most preferably 15% or more. If the content of B ₂ O ₃ is 40% or less, a decrease in Young's modulus can be prevented. The B ₂ O ₃ content is more preferably 35% or less, still more preferably 30% or less, even more preferably 25% or less, particularly preferably 23% or less, and most preferably 20% or less.

If the ratio of the sum of B ₂ O ₃ and R ₂ O (B ₂ O ₃ /ΣR ₂ O) is 0.8 or more, a large amount of tricoordinated boron is present, resulting in a glass with a large Miller constant. Cheap. B ₂ O ₃ /ΣR ₂ O is more preferably 1.0 or more, still more preferably 1.2 or more, and particularly preferably 1.3 or more. If B ₂ O ₃ /ΣR ₂ O is 2.5 or less, the Tg does not become too high and is easy to handle. B ₂ O ₃ /ΣR ₂ O is more preferably 2.0 or less, even more preferably 1.8 or less.

If the total amount of alkali metal oxides (R ₂ O) is 8% or more, the viscosity of the glass tends to decrease when heated to a high temperature, resulting in a highly meltable glass. The total amount of R ₂ O is more preferably 10% or more, more preferably 12% or more, and particularly preferably 15% or less. Also, if the total amount of R ₂ O is 40% or less, a sudden drop in Young's modulus can be prevented. The total amount of R ₂ O is more preferably 35% or less, more preferably 30% or less.

Li ₂ O is an alkali metal oxide component that has the effect of lowering the viscosity of glass at high temperatures and does not cause a decrease in Young's modulus at room temperature. When the content of Li ₂ O is 0.01% or more, the above effect appears. The content of Li ₂ O is more preferably 2% or more, more preferably 4% or more. If the content of Li ₂ O is 20% or less, the network in the glass structure can be maintained. In addition, since the price of Li ₂ O is high, the price of the resulting glass does not rise. The content of Li ₂ O is more preferably 15% or less, even more preferably 10% or less.

Na ₂ O, like Li ₂ O, is a component that has the effect of lowering the viscosity of glass at high temperatures. If the content of Na ₂ O is 0.01% or more, the above effects are obtained. The content of Na ₂ O is more preferably 1% or more, more preferably 5% or more. If the content of Na ₂ O is 40% or less, the network in the glass structure can be maintained. The content of Na ₂ O is more preferably 35% or less, more preferably 30% or less.

K ₂ O, like Li ₂ O and Na ₂ O, is a component that has the effect of lowering the viscosity of glass at high temperatures. If the content of K ₂ O is 0.01% or more, the effect of lowering the viscosity becomes stronger. K ₂ O is more preferably 2% or more, and even more preferably 4% or more. If the K ₂ O content is 20% or less, the deliquescence of the glass can be lowered to some extent. The content of K ₂ O is more preferably 15% or less, even more preferably 10% or less.

Rb ₂ O, like Li ₂ O, Na ₂ O and K ₂ O, is a component that has the effect of lowering the viscosity of glass at high temperatures. When the content of Rb ₂ O is 0.01% or more, it is possible to improve the energy absorption effect when breaking the glass due to the mixed alkali effect. The content of Rb ₂ O is more preferably 2% or more, more preferably 3% or more. If the content of Rb ₂ O is 10% or less, excessive increase in the weight of the glass can be prevented. The content of Rb ₂ O is more preferably 5% or less, more preferably 4% or less.

Alkaline earth metal oxide (RO) is a component that increases the Miller constant, and thus may be contained. In both cases of physically strengthened glass and chemically strengthened glass, if the total amount of RO is 1% or more, it leads to an increase in Miller constant. The total amount of RO is preferably 3% or more, more preferably 5% or more. Further, if the total RO is 40% or less, the effect of devitrification is small. The total amount of RO is more preferably 35% or less, more preferably 30% or less, particularly preferably 25% or less, and most preferably 15% or less.
On the other hand, especially in the case of chemically strengthened glass, among the alkaline earth metal oxides (RO), when the alkaline earth metal oxide components excluding MgO, (CaO + SrO + BaO) are small, the ion exchange capacity is improved and a large DOL can be obtained. (CaO+SrO+BaO) is preferably 20% or less in total. The total content of (CaO+SrO+BaO) is more preferably 15% or less, more preferably 10% or less, and particularly preferably 5% or less. On the other hand, (CaO + SrO + BaO) reduces the devitrification property of the glass and makes it possible to obtain a stable glass. More preferably, 1% or more is even more preferable.

MgO is a component that increases the mirror radius by increasing the Young's modulus of the glass. In both cases of physically strengthened glass and chemically strengthened glass, when the content of MgO is 1% or more, the effect of increasing the Young's modulus becomes remarkable. The content of MgO is more preferably 3% or more, more preferably 10% or more. If the MgO content is 35% or less, problems such as susceptibility to devitrification can be avoided. The content of MgO is more preferably 35% or less, even more preferably 33% or less. On the other hand, in the case of chemically strengthened glass, the content of MgO is preferably 8% or less because the DOL can be easily increased. The content of MgO is more preferably 5% or less, still more preferably 4% or less.

CaO is a component for improving meltability at high temperatures or making devitrification less likely to occur. Therefore, in both physically strengthened glass and chemically strengthened glass, if the content of CaO is 0.1% or more, devitrification can be suppressed. The content of CaO is more preferably 0.5% or more, more preferably 1% or more. If the content of CaO is 15% or less, both effects of improving the meltability and increasing the Young's modulus of the glass can be obtained. The content of CaO is more preferably 10% or less, even more preferably 5% or less. Especially in the case of chemically strengthened glass, the content of CaO is preferably 8% or less because the DOL can be easily increased. 5% or less is more preferable, 3% or less is still more preferable, and 2% or less is particularly preferable.

SrO is a component for improving meltability at high temperatures or making devitrification less likely to occur. Therefore, in both physically strengthened glass and chemically strengthened glass, if the content of SrO is 0.1% or more, it is effective in preventing devitrification. The content of SrO is more preferably 0.2% or more, more preferably 0.3% or more. If the SrO content is 5% or less, the weight increase of the glass does not pose a problem. The content of SrO is more preferably 3% or less, still more preferably 1% or less.

BaO is a component for improving meltability at high temperatures or making devitrification less likely to occur. In the case of physically strengthened glass, when the content of BaO is 1% or more, energy dissipation tends to occur easily due to the mixing effect of alkaline earth elements. The content of BaO is more preferably 2% or more, more preferably 2.5% or more. In addition, when the content of BaO is 20% or less, the viscosity does not become too high, the meltability is improved, and the specific gravity becomes small, which makes it possible to reduce the weight, which is preferable. 15% or less is more preferable, 13% or less is still more preferable, and 10% or less is particularly preferable. On the other hand, particularly in the case of chemically strengthened glass, the effect of increasing the DOL can be obtained by reducing the content of BaO, so the content is preferably 5% or less. It is more preferably 3% or less, still more preferably 1% or less, and most preferably not substantially contained.

Based on the above findings, when the tempered glass of the present invention contains B ₂ O ₃ , H represented by the following formula (8) is preferably 0.4 or more.
H=B ₂ O ₃ (three-coordinate)×0.039+E×0.036+ΣRO×(−0.030)−2.3 (8)
(wherein B ₂ O ₃ (three-coordinated) is the content of three-coordinated boron in the glass (mol % based on oxide), E is the Young's modulus of the glass (GPa), and ΣRO is the alkaline earth element in the glass. It is the total content of metal oxides (mol% based on oxides).)
When H is 0.4 or more, the Miller constant tends to increase. H is more preferably 0.45 or more, still more preferably 0.50 or more, and particularly preferably 0.55 or more. The upper limit of H is not particularly limited, but since there is a limit to the fraction of B atoms that can be three-coordinated in the total B ₂ O ₃ content, it is preferably 2 or less, more preferably 1.5 or less. preferable.

Based on the above knowledge, when the tempered glass of the present invention contains B ₂ O ₃ , J represented by the following formula (10) is preferably 0.45 or more.
J=[B ₂ O ₃ ]×0.031−0.026×[K ₂ O] (10)
(In the formula, [B ₂ O ₃ ] is the B ₂ O ₃ content in the glass (mol% based on oxide), [K ₂ O] is the K ₂ O content in the glass (mol% based on oxide ).)
When J is 0.45 or more, the Miller constant tends to increase. J is more preferably 0.50 or more, even more preferably 0.55 or more. The upper limit of J is not particularly limited, but if the content of B ₂ O ₃ and the content of alkali metal oxide are too large, deliquescence occurs, and surface deterioration becomes remarkable especially in outdoor use, so it is 1 or less. is preferred, and 0.8 or less is more preferred.

As mentioned above, the addition of alkaline earth metal oxides RO to the glass increases the Young's modulus E of the glass. The effect of increasing the Young's modulus of glass is higher for alkaline earth metal oxides than for alkali metal oxides, and among alkaline earth metal oxides, CaO is more effective than other alkaline earth metal oxides. The content of CaO is preferably 0.5% or more, more preferably 1.0% or more, expressed as a molar percentage based on oxides.

In the case of the alkali metal oxide R ₂ O, addition of the alkali metal oxide R ₂ O having a small atomic weight of the alkali metal prevents the glass network structure from being cut, so that the fracture surface is less likely to be formed. Therefore, the Miller constant A tends to increase. Therefore, as the alkali metal oxide R2O added to the glass, _Na2O is preferable to _K2O , and _Li2O is _more preferable. This tendency is particularly noticeable in glasses containing no B ₂ O ₃ .
The tempered glass of the present invention preferably has <M _R2O > represented by the following formula (11) of 30 or less.
<M _R2O >=Σ(Mi×Ri)/ΣRi (11)
Here, Mi is the atomic weight of the alkali metal, Ri is the content of the alkali metal oxide contained in the glass (mol% based on the oxide), and <M R _O > is correlated with the atomic weight of the alkali metal in the glass. value. The smaller <M _R2O > suggests that the alkali metal oxides contained in the glass are lighter elements, and the networks of glasses containing light element alkali metal oxides tend to be denser, so the Young's modulus tends to be high and the Miller constant is large. <M _R2O > is more preferably 20 or less, even more preferably 15 or less.

The tempered glass of the present invention preferably contains substantially no lanthanoids. Here, "substantially free of lanthanoids" means that lanthanoids are not contained except when lanthanoids are mixed as unavoidable impurities. By substantially not containing lanthanides, the weight of the glass can be reduced. In addition, when sunlight hits the glass, no phosphorescence or light emission occurs.

Moreover, it is preferable that the tempered glass of the present invention does not substantially contain F. Here, "substantially free of F" means not containing F except when it is mixed as an unavoidable impurity. By not containing F substantially, the composition hardly changes even if the glass is heat-treated.

Glass sheets according to embodiments of the present invention may contain _SO3 . SO ₃ is mainly derived from Glauber's salt (Na ₂ SO ₄ ) used as a fining agent.
In the glass plate according to the embodiment of the present invention, the content of SO ₃ is preferably 0.001% to 0.2% in terms of % by mass based on oxides. If the content of SO ₃ is 0.001% or more, the fining effect during melting of the glass is good and bubbles are reduced. The SO ₃ content is preferably 0.003% or more, more preferably 0.01% or more, and even more preferably 0.02% or more. If the content of SO ₃ is 0.2% or less, the gas component of SO ₂ is less likely to remain in the glass as bubbles. The SO ₃ content is preferably 0.1% or less, more preferably 0.05% or less, and even more preferably 0.03% or less.

Glass sheets according to embodiments of the present invention may contain _SnO2 . _SnO2 acts as a refining agent.
In the glass plate according to the embodiment of the present invention, the SnO ₂ content is preferably 0 to 1% in terms of % by mass based on oxides. When SnO ₂ is contained, the refining effect is good and bubbles are reduced when the glass is melted. The SnO ₂ content may be 0.1% or more, 0.2% or more, or 0.3% or more. Also, if the SnO ₂ content is 1% or less, raw material costs can be suppressed, and volatilization in the production line is small. The SnO ₂ content is more preferably 0.7% or less, even more preferably 0.5% or less, and particularly preferably 0.4% or less.

_The glass plate according to the embodiment of the present invention contains _Fe2O3 , _TiO2 , _CeO2 , CoO, Se, _MnO2 , MnO, _Cr2O3 , _{V2O5 , NiO} , _Er2O as a coloring component, for example. ₃ , but may contain no coloring component. The glass sheets of the embodiments of the present invention _are preferably substantially free of _MnO2 , MnO _{, Cr2O3} , _{V2O5 ,} NiO, _Er2O3 .

When the tempered glass of the present invention is air-cooled tempered glass, it preferably satisfies the following low-temperature thermal expansion coefficient α _LT and high-temperature thermal expansion coefficient α _HT from the viewpoint of ease of air-cooling tempering.
In the air-cooling tempering treatment, the glass to be tempered is heated to a temperature near the softening point or yield point, and then cooled rapidly by spraying a cooling medium on the surface to impart residual stress.
The easiness of air-cooling strengthening in this specification means that residual stress can be easily imparted when the air-cooling strengthening treatment is carried out according to the procedure described above.

In this specification, the average thermal expansion coefficient at 50 to 350° C. is defined as the low-temperature thermal expansion coefficient α _LT .
The tempered glass of the present invention preferably has a low-temperature coefficient of thermal expansion α _LT of 60×10 ⁻⁷ ·K ⁻¹ or more from the viewpoint of imparting residual stress.
The tempered glass of the present invention more preferably has a low-temperature thermal expansion coefficient α _LT of 70×10 ⁻⁷ ·K ⁻¹ or more, more preferably 80×10 ⁻⁷ ·K ⁻¹ or more.

In this specification, in the thermal expansion curve obtained by applying a load of 10 g to a sample with a diameter of 5 mm and a length of 20 mm and measuring at a heating rate of 5 ° C./min, between the glass transition point and the yield point The maximum value of the coefficient of thermal expansion at is assumed to be the coefficient of thermal expansion at high temperature _αHT .
There is usually a correlation between the low-temperature thermal expansion coefficient α _LT and the high-temperature thermal expansion coefficient α _HT , and the higher the low-temperature thermal expansion coefficient α _LT , the higher the high-temperature thermal expansion coefficient α _HT . If the low-temperature coefficient of thermal expansion α _LT is close to that of conventional glass, but the high-temperature coefficient of thermal expansion α _HT is greater than that of conventional glass, conventional equipment can be used for molding the glass. Furthermore, it is possible to make the glass to which residual stress is easily imparted when air-cooling tempering treatment is carried out.
From this point of view, the tempered glass of the present invention preferably has a ratio α _HT /α _LT of the high-temperature thermal expansion coefficient α _HT to the low-temperature thermal expansion coefficient α _LT of 2 or more, more preferably 3 or more. It is more preferably 4 or more, more preferably 5 or more, still more preferably 6 or more, particularly preferably 7 or more, and most preferably 8 or more.

The residual stress imparted to the glass by the air-cooling tempering treatment is determined by the product α _LT ×E of the low-temperature thermal expansion coefficient α _LT and the Young's modulus E of the glass. Therefore, a glass having a larger value of α _LT ×E is preferable as an air-cooled tempered glass.
In the tempered glass of the present invention, the product α _LT ×E of the coefficient of low-temperature thermal expansion α _LT and Young's modulus E is preferably 4×10 ⁵ Pa·K ⁻¹ or more, more preferably 5×10 ⁵ Pa·K ⁻¹ . It is more preferably 6×10 ⁵ Pa·K ⁻¹ or more, more preferably 6×10 5 Pa·K −1 or more, and particularly preferably 7×10 ⁵ Pa·K ⁻¹ or more.

The present invention will be further described below using examples.
Examples 1 to 14 are examples, and Examples 15 to 27 are comparative examples.
Glass raw materials were appropriately prepared, heated and melted, homogenized by defoaming, stirring, etc., and molded by the float method to obtain a glass sheet (thickness: 2.2 mm). Tables 1 to 3 show the compositions (mol% based on oxide) of glasses used in Examples and Comparative Examples.
In Examples 7 to 14 and Examples 23 to 27 containing B ₂ O ₃ , the content of three-coordinated boron (B (three-coordinated) (mol %)) is determined by the following formulas (12) and (13). identified.
When the total amount of alkali metal oxides (ΣR ₂ O) is greater than the content of Al ₂ O ₃ (ΣR ₂ O>[Al ₂ O ₃ ]): [B (tri-coordinate)]=[B ₂ O ₃ ]-(ΣR ₂ O-[Al ₂ O ₃ ]) (12)
When the total amount of alkali metal oxides (ΣR ₂ O) is equal to or less than the content of Al ₂ O ₃ (ΣR ₂ O ≤ [Al ₂ O ₃ ]): [B (triple coordination)] = [B ₂ O ₃ ] (13)
In the formula, [B (three-coordinated)] is the content of three-coordinated boron in the glass (mol %), [B ₂ O ₃ ] is the content of B ₂ O ₃ in the glass (moles based on oxide %), [Al ₂ O ₃ ] is the content of Al ₂ O ₃ in the glass (mol % based on oxide), and ΣR ₂ O is the total content of alkali metal oxides in the glass (mol % based on oxide). %).
For Examples 1 to 6 and Examples 15 to 22 containing no B ₂ O ₃ , I represented by the following formula (9) was obtained.
I=[Al ₂ O ₃ ]×0.03+ΣRO×0.014 (9)
In the formula, [Al ₂ O ₃ ] is the Al ₂ O ₃ content in the glass (mol% based on oxides), and ΣRO is the total content of alkaline earth metal oxides in the glass (mol% based on oxides). ).
For Examples 7 to 14 and Examples 23 to 27 containing B ₂ O ₃ , J represented by the following formula (10) was obtained.
J=[B ₂ O ₃ ]×0.031−0.026×[K ₂ O] (10)
In the formula, [B ₂ O ₃ ] is the content of B ₂ O ₃ in the glass (mol% based on oxide), and [K ₂ O] is the content of K ₂ O in the glass (mol % based on oxide). %).

<Specific gravity>
The glass plate obtained by the above procedure is processed into a rectangular parallelepiped, the length of the long side and short side of the glass plate is measured with a micrometer with an error of ±0.01 mm, and the weight of the glass plate is measured with an error of ±0.02 g. It was measured and the specific gravity was determined.
<Young's modulus E, Poisson's ratio ν>
The Young's modulus E and Poisson's ratio ν of the glass plate obtained by the above procedure were measured by the ultrasonic pulse method.
For Examples 1 to 6 and Examples 15 to 22 containing no B ₂ O ₃ , G represented by the following formula (7) was obtained.
G=E×0.013+ν×(−6.6)+[Al ₂ O ₃ ]×0.023+ΣRO×0.013 (7)
In the formula, E is the Young's modulus of the glass (GPa), ν is the Poisson's ratio of the glass, [Al ₂ O ₃ ] is the Al ₂ O ₃ content in the glass (mol% based on oxide), ΣRO is the It is the total content of alkaline earth metal oxides (mole % based on oxides).
For Examples 7 to 14 and Examples 23 to 27 containing B ₂ O ₃ , H represented by the following formula (8) was obtained.
H=B ₂ O ₃ (three-coordinate)×0.039+E×0.036+ΣRO×(−0.030)−2.3 (8)
In the formula, B ₂ O ₃ (three-coordinated) is the content of three-coordinated boron in the glass (mol% based on oxide), E is the Young's modulus of the glass (GPa), and ΣRO is the alkaline earth metal in the glass. Total content of oxides (mole % based on oxides).

<Low temperature thermal expansion coefficient α _LT , high temperature thermal expansion coefficient α _HT , glass transition point Tg, yield point>
A glass rod having a diameter of 5 mm and a length of 20 mm was produced by processing the glass plate obtained by the above procedure. Using a thermal expansion meter (TD5010SA, manufactured by Bruker AXS), a load of 10 g was applied to the glass rod and the linear expansion curve was measured at a heating rate of 5 ° C./min, and the glass transition point Tg (unit: ° C. ), yield point (unit: °C), low-temperature coefficient of thermal expansion _αLT (unit: × ^10-7 /°C), and high-temperature coefficient of thermal expansion _αHT (unit: × ^10-7 /°C) were determined. In Tables 1 to 3, values shown in parentheses are calculated values.
<virtual temperature>
The fictive temperature of the glass was measured by the following procedure.
First, glasses with different fictive temperatures were produced by the following procedure. Glass raw materials having a predetermined composition were prepared and melted, and then formed into sheet glass. After molding, the glasses were held at the cooling start temperatures shown in Tables 2 and 3, respectively. The fictive temperature of the glass was then adjusted by adjusting the cooling rate. Next, the fictive temperature of the glass was determined as follows. For each composition of glass, three plate-shaped glasses were prepared and suspended in a platinum crucible using a platinum wire and a ceramic rod so as not to come into contact with the wall surface. It was placed in a holding electric furnace. Here, the cooling start temperature and holding time are Tg + 50 ° C. for 5 minutes, Tg + 30 ° C. for 20 minutes, and Tg + 10 ° C. for 2 hours. was cooled at a cooling rate of 1000° C./min or more. Next, the refractive index nd of these glasses at the _d -line is measured using a refractometer ( _KPR2000 ; manufactured by Shimadzu Device Manufacturing Co., Ltd.). Constants a and b were determined by linear regression. Next, the refractive index n _d was measured for a glass of unknown T _f , and the fictive temperature T _f was determined using the relationship T _f =a×n _d +b in equation (4).

<Miller constant>
The Miller constant was measured by carrying out glass processing, scratching, heat treatment, bending test, and observation of the fracture surface according to the following procedures.
(processing)
The glass plates obtained by the above procedure were processed into a size of 40 mm×6 mm×3 mm, and 8 glass plates were produced by mirror-polishing the front, back, and longitudinal end surfaces (four surfaces in total).
(injury)
Using a Vickers hardness tester (HMV-2; manufactured by Shimadzu Corporation) and using a diamond indenter with a facing angle of 110°, eight glass plates were indented with different loads to give scratches. The indentation loads were 0.05 kgf, 0.1 kgf, 0.3 kgf, 0.5 kgf, 0.75 kgf, 1.0 kgf, 2.0 kgf and 3.0 kgf.
(Heat treatment)
Heat treatment was performed to remove the effects of strain due to scratching. The heat treatment was carried out by holding for 1 hour at the cooling start temperature shown in Tables 1-3 and cooling to room temperature at the cooling rate shown in Tables 1-3.
(bending test)
The span of the four-point bending jig used was 10 mm on the load side (upper) and 30 mm on the support side (lower). After the glass was scratched and heat-treated, a tape was attached to the surface opposite to the scratched surface, a load was applied with the scratched surface facing downward (the taped surface facing upward), and the load when the glass was crushed was measured. . Using the following formula (14), the stress at the time of crushing was obtained from the measured load.
σ=(3F(Ls−Ll))/(2wh ² ) (14)
Here, σ: stress during crushing (MPa), F: load during crushing (N), Ls: distance between lower fulcrums (mm), Ll: distance between upper load points (mm), w: sample width (mm ), h: sample thickness (mm).
(Fracture surface observation)
The fracture surface was observed using a digital microscope (VHX-5000; manufactured by KEYENCE), and the distance R from the fracture origin to the interface between the mirror surface and the mist surface was measured. During observation, the broken surface of the sample was perpendicular to the optical axis of the lens of the microscope, and observation was performed at a magnification of 20×150.
From the results obtained by the above procedure, the Miller constant A was determined using the following formula.
σ = A/R ^1/2

<Strengthening treatment>
The glasses of Examples 1, 3 and 5 were immersed in molten potassium nitrate at 450° C. for 3 hours for chemical strengthening treatment.
The glasses of Examples 2, 4, 6, 7 to 27 were heated in an electric furnace at a temperature at which the viscosity became log η = 9 (approximately Tg + 110 to 130 ° C.), and immediately after the glass surface reached this temperature, the electric furnace was removed. The glass was taken out and quenched to perform air-cooling tempering treatment.

<CS, DOL>
The surface compressive stress (CS) and compressive stress layer depth (DOL) of the tempered glass were calculated by the following procedures.
The glasses of Examples 1, 3, and 5 subjected to the chemical strengthening treatment were measured using a surface stress meter (FSM6000; manufactured by Orihara Seisakusho Co., Ltd.). The glasses of Examples 2, 4, 6, 7 to 27 subjected to the physical strengthening treatment were measured using a scattered light photoelastic analyzer (SLP-1000; manufactured by Orihara Seisakusho Co., Ltd.).

<Number of crushed pieces>
For the glasses of Examples 2, 4, and 6 to 27, the number of fractures of the glass after tempering treatment was measured by the following procedure.
For the glass sample (10 cm square) after tempering treatment, an auto punch (automatic punch with carbide tip M type; manufactured by Niigata Seiki Co., Ltd.) was used to place an angle of 120 ° at a distance of 10 mm from one corner of the sample. It was crushed by applying an impact with an indenter. The number of crushed glass fragments was defined as the number of crushed pieces. In addition, when the glass was not crushed, the number of crushed was defined as 0.
For the glasses of Examples 1, 3, and 5, the number of fractures of the glass after tempering treatment was measured by the following procedure.
Using a micro Vickers hardness tester (HMV-2; manufactured by Shimadzu Corporation), a regular quadrangular pyramid-shaped 60° (facing angle) diamond indenter was indented at the following indenter load rate, load of 4 kgf, and indentation time of 15 sec. The number was defined as the crushing number. In addition, when the glass was not crushed, the number of crushed was defined as 0.
Indenter loading speed: 260 μm/sec until touching the glass surface, 5 to 120 μm/sec after penetrating the glass

The tempered glasses of Examples 1 to 14, which had a Miller constant A of 2.2 MPa·m ^0.5 or more, had fewer than 10 broken pieces and few broken pieces. On the other hand, the tempered glasses of Examples 15 to 27, in which Miller's constant A was less than 2.2 MPa·m ^0.5 , had 38 or more broken pieces, and many broken pieces.

Although the present invention has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention.
This application is based on Japanese Patent Application No. 2017-138853 filed on July 18, 2017, the contents of which are incorporated herein by reference.

The tempered glass of the present invention is suitable for use as, for example, window glass for vehicles, window glass for buildings, outer walls, solar battery cover glass, and particularly window glass for buildings.

Claims (22)

Tempered glass having a Miller constant A of 2.2 MPa·m ^0.5 or more, a surface compressive stress (CS) of 10 MPa or more, and a plate thickness t of 1.2 mm or more and 50 mm or less. The tempered glass according to claim 1, wherein the fictive temperature of the central portion in the thickness direction t is the glass transition point Tg + 60°C or less. The tempered glass according to claim 1 or 2, wherein the product (CS×A) of the surface compressive stress (CS) and the Miller constant A is 22 (MPa) ² ·m ^0.5 or more. The tempered glass according to any one of claims 1 to 3, wherein the compressive stress layer depth DOL is (1/10) × t mm or more, where t (unit: mm) is the plate thickness. 30 to 85% of SiO ₂ , 0 to 40% of Al ₂ O ₃ , 0 to 10% of P ₂ O ₅ in terms of molar percentages based on oxides, and an alkali metal oxide (R ₂ O) 5. The composition according to claim 1, containing 8-40% in total, 0-40% in total alkaline earth metal oxides (RO) and substantially free of B ₂ O ₃ . Tempered glass. The tempered glass according to claim 5, having a Young's modulus E of 68 GPa or more. The tempered glass according to claim 5 or 6, wherein G represented by the following formula is 0 or more.
G=E×0.013+ν×(−6.6)+[Al ₂ O ₃ ]×0.023+ΣRO×0.013
(Wherein, E is the Young's modulus of the glass (GPa), ν is the Poisson's ratio of the glass, [Al ₂ O ₃ ] is the content of Al ₂ O ₃ in the glass (mol% based on oxide), ΣRO is the glass It is the total content of alkaline earth metal oxides in (mole% based on oxides).) The tempered glass according to any one of claims 5 to 7, wherein I represented by the following formula is 0.45 or more.
I=[Al ₂ O ₃ ]×0.03+ΣRO×0.014
(In the formula, [Al ₂ O ₃ ] is the Al ₂ O ₃ content in the glass (mol% based on oxide), ΣRO is the total content of alkaline earth metal oxides in the glass (mol %).) Al ₂ O. ₃ and SiO ₂ ratio (Al ₂ O. ₃ /SiO ₂ ) is 0.3 to 0.6, the tempered glass according to any one of claims 5 to 8. Li ₂ 0-20% O, Na ₂ 0 to 40% O, K ₂ 0-15% O, 0-35% MgO, 0-15% CaO, 0-15% SrO, 0-20% BaO, according to any one of claims 5-9 Tempered glass. It contains 0.01 to 40% of B ₂ O ₃ , 40 to 75% of SiO ₂ , 0 to 20% of Al ₂ O ₃ and 0 to 10% of P ₂ O ₅ in terms of molar percentages based on oxides. , and containing 8 to 40% in total of alkali metal oxides (R ₂ O) and 0 to 40% in total of alkaline earth metal oxides (RO). tempered glass. The tempered glass according to claim 11 , having a Young's modulus E of 70 GPa or more. The tempered glass according to claim 11 or 12 , wherein H represented by the following formula is 0.4 or more.
H=B ₂ O ₃ (three-coordinate)×0.039+E×0.036+ΣRO×(−0.030)−2.3
(Wherein, B ₂ O ₃ (three-coordinated) is the content of three-coordinated boron in the glass (mol% based on oxide), E is the Young's modulus of the glass (GPa), ΣRO is the alkaline earth in the glass It is the total content of metal oxides (mol% based on oxides).) The tempered glass according to any one of claims 11 to 13 , wherein J represented by the following formula is 0.45 or more.
J=[B ₂ O ₃ ]×0.031−0.026×[K ₂ O]
(In the formula, [B ₂ O ₃ ] is the B ₂ O ₃ content in the glass (mol% based on the oxide), [K ₂ O] is the K ₂ O content in the glass (mol% based on the oxide ).) Al ₂ O. ₃ and SiO ₂ ratio (Al ₂ O. ₃ /SiO ₂ ) is 0.01 to 0.5, the tempered glass according to any one of claims 11 to 14. Li ₂ 0-20% O, Na ₂ 0 to 40% O, K ₂ 0-20% O, 0-35% MgO, 0-15% CaO, 0-5% SrO, 0-20% BaO, according to any one of claims 11-15 Tempered glass. B. ₂ O. ₃ and R ₂ ratio to the sum of O (B ₂ O. ₃ /ΣR ₂ The tempered glass according to any one of claims 11 to 16, wherein O) is from 0.8 to 2.5. <M _R2O > is 30 or less, the tempered glass according to any one of claims 11 to 17.
<M _R2O >=Σ(Mi×Ri)/ΣRi
(In the formula, Mi is the atomic weight of the alkali metal, and Ri is the content of the alkali metal oxide contained in the glass (mol % based on the oxide).) The low-temperature thermal expansion coefficient α _LT is 60× 10 ⁻⁷ ·K ⁻¹ or more, where the average thermal expansion coefficient at 50 to 350° C. is defined as the low-temperature thermal expansion coefficient α _LT . 1. Tempered glass according to item 1. When the maximum value of the thermal expansion coefficient between the glass transition point and the yield point is defined as the high temperature thermal expansion coefficient α _HT , the ratio α _HT /α _LT between the high temperature thermal expansion coefficient α _HT and the low temperature thermal expansion coefficient α _LT 20. The tempered glass of claim 19 , wherein is 2 or more. 21. The tempered glass according to claim 19 or 20 , wherein the product α _LT ×E of the low-temperature thermal expansion coefficient α _LT and Young 's modulus E is 4×10 ⁵ Pa·K ⁻¹ or more. The tempered glass according to any one of claims 1 to 21 , which is air-cooled tempered glass.

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