CN115385571B - Chemically strengthened glass and glass for chemical strengthening - Google Patents

Abstract

The present invention relates to chemically strengthened glass and chemically strengthened glass. The purpose of the present invention is to provide a chemically strengthened glass having improved strength and scratch resistance. The present invention relates to a chemically strengthened glass comprising: 38% -75% of SiO ₂, 1% -30% of Al ₂O₃, 3% -20% of MgO, more than 0% and less than or equal to 20% of Li ₂ O, more than 0% and less than or equal to 20% of Y ₂O₃, 0% -5% of B ₂O₃, 0% -6% of P ₂O₅, 0% -8% of Na ₂ O, 0% -10% of K ₂ O, 0% -20% of CaO, 0% -20% of SrO, 0% -15% of BaO, 0% -10% of ZnO, 0% -1% of TiO ₂ and 0% -8% of ZrO ₂, and the chemically strengthened glass has Young's modulus, vickers hardness, CS and CS ₅₀ above specified values.

Description

Chemically strengthened glass and glass for chemical strengthening

This application is a divisional application of the Chinese patent application with application date of April 23, 2018 and application number 201880027496.8.

Technical Field

The present invention relates to chemically strengthened glass and glass for chemical strengthening.

Background technique

In recent years, cover glass including chemically strengthened glass has been used to protect display devices of mobile devices such as mobile phones, smart phones, personal digital assistants (PDAs), and tablet terminals and to improve their appearance.

In chemically strengthened glass (so-called chemically strengthened glass), the higher the surface compressive stress (value) (CS) and the depth of the compressive stress layer (DOL), the higher the strength tends to be. On the other hand, in order to maintain a balance with the surface compressive stress, internal tensile stress (CT) is generated inside the glass. Therefore, the larger the CS and DOL, the larger the CT. When glass with a large CT breaks, it becomes a violent breakage mode with a large number of fragments, and the fragments are easy to fly.

Therefore, for example, Patent Document 1 discloses the formula (10) representing the allowable limit of the internal tensile stress of chemically strengthened glass, and by adjusting the following CT', even if the strength of the chemically strengthened glass is increased, a chemically strengthened glass with less scattering of fragments can be obtained. The internal tensile stress CT' described in Patent Document 1 is derived by the following formula (11) using the measured values of CS and DOL'.

CT’≤-38.7×ln(t)+48.2 (10)

CS×DOL’＝(t-2×DOL’)×CT’ (11)

Here, DOL' corresponds to the depth of the ion exchange layer.

Prior art literature

Patent Literature

Patent Document 1: U.S. Patent No. 8075999

Summary of the invention

Problems to be solved by the invention

However, in the method described in Patent Document 1, the strength of chemically strengthened glass may be insufficient. The reasons are believed to be that the influence of glass composition is not fully considered; the stress distribution is linearly approximated in the above formula for calculating CT'; the point where the stress is zero is assumed to be equal to the depth of the ion diffusion layer, etc. In addition, the method described in Patent Document 1 only mentions the strength against cracking of chemically strengthened glass, and the countermeasure for scratch resistance, which is important in actual use, is insufficient.

Therefore, an object of the present invention is to provide a chemically strengthened glass and a glass for chemical strengthening having improved strength and scratch resistance.

Means used to solve problems

The present inventors have conducted intensive studies and have found that the above-mentioned problems can be solved by limiting the glass composition and physical properties, thereby completing the present invention.

That is, the present invention relates to the following <1> to <5>.

<1> A chemically strengthened glass, wherein the chemically strengthened glass comprises, expressed in terms of molar percentage based on oxides:

38%～75% SiO ₂ ,

1% to 30% Al ₂ O ₃ ,

3% to 20% MgO,

Greater than 0% and less than or equal to 20% Li ₂ O,

Y ₂ O ₃ greater than 0% and less than or equal to 20%,

0% to 5% B ₂ O ₃ ,

0%～6% P ₂ O ₅ ,

0% to 8% _Na2O ,

0%～10% K ₂ O,

0%～20%CaO,

0%～20% SrO,

0%～15%BaO,

0%～10% ZnO,

0% to 1% TiO ₂ , and

0% to 8% ZrO ₂ , and

The chemically strengthened glass has a Young's modulus of 90 GPa or more and a Vickers hardness of 650 kgf/mm ² or more.

<2> A chemically strengthened glass, wherein, expressed in terms of molar percentage based on oxides, the chemically strengthened glass comprises:

38%～75% SiO ₂ ,

1% to 30% Al ₂ O ₃ ,

3% to 20% MgO,

Greater than 0% and less than or equal to 20% Li ₂ O,

Y ₂ O ₃ greater than 0% and less than or equal to 20%,

0% to 5% B ₂ O ₃ ,

0%～6% P ₂ O ₅ ,

0% to 8% _Na2O ,

0%～10% K ₂ O,

0%～20%CaO,

0%～20% SrO,

0%～15%BaO,

0%～10% ZnO,

0% to 1% TiO ₂ , and

0% to 8% ZrO ₂ , and

The chemically strengthened glass has a Young's modulus of 90 GPa or more and a Vickers hardness of 700 kgf/ ^mm2 or more, and

The chemically strengthened glass has a surface compressive stress (CS) of 300 MPa or more, and a compressive stress value (CS ₅₀ ) of 30 MPa or more at a depth of 50 μm from the glass surface.

<3> The chemically strengthened glass according to <2> above, wherein a compressive stress value (CS ₉₀ ) of a portion of the chemically strengthened glass at a depth of 90 μm from a glass surface is 25 MPa or more.

<4> The chemically strengthened glass according to <2> or <3>, wherein the relationship between the surface compressive stress and the compressive stress value (CS ₅₀ ) is represented by at least two different functions.

<5> The chemically strengthened glass as described in <4> above, wherein the two different functions are a linear function representing the first region and a linear function representing the second region in a first region from the glass surface to a specified depth and a second region from the first region to a depth where the surface compressive stress is 0, and the slope of the linear function representing the first region is greater than the slope of the linear function representing the second region.

Effects of the Invention

According to the present invention, it is possible to provide a chemically strengthened glass and a glass for chemical strengthening having improved strength and scratch resistance.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing the results of a scratch test of the present invention.

Detailed ways

Hereinafter, the chemically strengthened glass and the glass for chemical strengthening of the present invention will be described in detail, but the present invention is not limited to the following embodiments and can be implemented with arbitrary modifications within the scope of the present invention.

In this specification, the glass composition of the chemically strengthened glass may be referred to as the basic composition of the chemically strengthened glass. In addition, "to" indicating a numerical range is used to mean that the numerical values described before and after it are included as the lower limit and the upper limit.

<Glass Composition>

When the thickness of the chemically strengthened glass is sufficiently large, the portion of the chemically strengthened glass having tensile stress (hereinafter also referred to as the tensile stress portion) is not ion-exchanged, and thus the tensile stress portion of the chemically strengthened glass has the same composition as the glass before chemical strengthening. In this case, the composition of the tensile stress portion of the chemically strengthened glass can be regarded as the basic composition of the chemically strengthened glass.

The composition of the glass can be measured by a wet analysis method such as ICP emission analysis, etc. In addition, except when a large amount of a component that is particularly easy to volatilize during melting is contained, the composition of the glass can be obtained by calculation from the blending amount of the glass raw materials used.

In addition, the content of each component is shown as a molar percentage based on an oxide unless otherwise specified.

The chemically strengthened glass of the present invention contains, in terms of molar percentage based on oxides, 38% to 75% of _SiO2 , 1% to 30% of _{Al2O3 ,} 3% to 20% of MgO, more than 0% and less than 20% of _Li2O , more than 0% and less than 20% of _{Y2O3 ,} 0% to 5% of _{B2O3 ,} 0% to 6% of _P2O5 , 0% to 8% of _Na2O , 0% to 10% of _K2O , 0% to 20% of CaO, 0% to 20% of SrO, 0% to 15% of BaO, 0% to 10% of ZnO, 0% to 1% of _{TiO2 ,} and 0% to 8% of _ZrO2 , and the chemically strengthened glass has a Young's modulus of 90 GPa or more and a Vickers hardness of 700 kgf/mm ² or more, and the surface compressive stress (CS) of the chemically strengthened glass is 300 MPa or more, and the compressive stress value (CS ₅₀ ) at a depth of 50 μm from the glass surface is 30 MPa or more.

The composition of the chemically strengthened glass of the present invention (the basic composition of the chemically strengthened glass of the present invention) comprises, in terms of molar percentages based on oxides, 38% to 75% of SiO ₂ , 1% to 30% of Al ₂ O ₃ , 3% to 20% of MgO, more than 0% to 20% of Li ₂ O, more than 0% to 20% of Y ₂ O ₃ , 0% to 5% of B ₂ O ₃ , 0% to 6% of P ₂ O ₅ , 0% to 8% of Na ₂ O, 0% to 10% of K ₂ O, 0% to 20% of CaO, 0% to 20% of SrO, 0% to 15% of BaO, 0% to 10% of ZnO, 0% to 1% of TiO ₂ , and 0% to 8% of ZrO ₂ , and the chemically strengthened glass has a Young's modulus of 90 GPa or more and a Vickers hardness of 650 kgf/mm ² or more.

Hereinafter, each composition of the chemically strengthened glass and the glass for chemical strengthening of the present invention will be described.

SiO ₂ is a component constituting the skeleton of glass and is a component that improves chemical durability. In addition, in order to reduce the generation of cracks when scratches (indentations) are generated on the glass surface, the content of SiO ₂ is preferably 38% or more. The content of SiO ₂ is more preferably as follows: 42% or more, 46% or more, 50% or more, 54% or more, 58% or more, and 62% or more.

On the other hand, in order to improve the solubility of the glass, the SiO ₂ content is 75% or less, more preferably 72% or less, further preferably 70% or less, particularly preferably 68% or less, and most preferably 66% or less.

_Al2O3 is a component _that reduces the number of fragments when chemically strengthened glass breaks and suppresses the scattering of fragments. In order to improve the ion exchange performance during chemical strengthening and increase the surface compressive stress after strengthening, the content _{of Al2O3} is 1% or more, preferably 3% or more, 5% or more, 7% or more, 8% or more, 9% or more, 10% or more, 11% or more, 12% or more, and 13% or more.

On the other hand, in order to improve the acid resistance of the glass or lower the devitrification temperature, the Al ₂ O ₃ content is preferably 30% or less, more preferably 25% or less, further preferably 20% or less, particularly preferably 18% or less, and most preferably 15% or less. When the Al ₂ O ₃ content is high, the melting temperature of the glass increases and the productivity decreases. In order to improve productivity, the Al ₂ O ₃ content is preferably 11% or less, preferably 10% or less, 9% or less, 8% or less, and 7% or less.

MgO is a component that increases the surface compressive stress of chemically strengthened glass. In order to reduce the number of fragments when chemically strengthened glass breaks and suppress the scattering of fragments, the content of MgO is preferably 3% or more, and more preferably the following: 4% or more, 5% or more, 6% or more, 7% or more, and 8% or more.

On the other hand, in order to suppress devitrification during glass melting, the MgO content is preferably 20% or less, and more preferably is as follows: 18% or less, 15% or less, 14% or less, 13% or less, 12% or less, 11% or less, and 10% or less.

_Li2O is a component that forms a surface compressive stress layer by ion exchange, and is a component that reduces the number of fragments when chemically strengthened glass breaks and suppresses the scattering of fragments. When Li ions on the glass surface are exchanged for Na ions and chemical strengthening treatment is performed so that the above-mentioned _CS90 reaches 30 MPa or more, the content of _Li2O is preferably greater than 0%, more preferably 4% or more, further preferably 5% or more, further preferably 6% or more, and particularly preferably 7% or more.

On the other hand, in order to maintain the acid resistance of the glass, the Li ₂ O content is preferably 20% or less, more preferably 18% or less, further preferably 16% or less, particularly preferably 15% or less, and most preferably 13% or less.

_Y2O3 is a component that increases Young _{'s modulus and chipping resistance without excessively increasing density. The content of Y2O3 is greater} than 0%, preferably 1% or more, more preferably 1.5% or more, further preferably 3% or more, particularly preferably 5% or more, and most preferably 7.5% or more.

On the other hand, if the content _{of Y2O3} is excessive, the acid resistance of the glass decreases or the devitrification temperature increases, so it is preferably 20% or less, more preferably 15% or less, further preferably 12% or less, and particularly preferably 9% or less.

_B2O3 is a component _that improves the chipping resistance of chemically strengthened glass and improves its solubility _{. B2O3} is _not an essential component, but when _B2O3 is contained, the content of _B2O3 is preferably 0.5% or more, more preferably 1% or more, and even more preferably 2% or more in order to _improve solubility.

On the other hand, in order to maintain the acid resistance of the glass, _{the B2O3} content is preferably 5% or less. _{The B2O3 content} is more preferably 4% or less, further preferably 3% or less, and particularly preferably 1% or less. In order to prevent the generation of striae during melting, it is preferred that substantially _{no B2O3} is contained.

_P2O5 is a component that improves _{ion exchange performance and chipping resistance. P2O5 may not} be contained, but when _P2O5 is contained, _{the content of P2O5 is preferably} 0.5% or more, more preferably 1% or more, and even more preferably 2% or more.

On the other hand, in order to reduce the number of fragments when the chemically strengthened glass breaks and to suppress the scattering of the fragments, the content _{of P2O5} is 6% or less, preferably 4% or less, more preferably 3% or less, further preferably 2% or less, and particularly preferably 1% or less. In order to prevent the generation of striae (grains) during melting, it is preferred _{that P2O5} is substantially not contained.

_Na2O is a component that forms a surface compressive stress layer by ion exchange and improves the solubility of glass. _{Na2O may not be contained, but when Na2O} is contained by exchanging Li ions on the glass surface with Na ions, the content of _Na2O is preferably 1% or more. The content of _Na2O is more preferably 2% or more, _and further preferably 3% or more.

On the other hand, when the content of _Na2O is excessive, the surface compressive stress formed by ion exchange is significantly reduced. The content of _Na2O is preferably 8% or less, more preferably 7% or less, further preferably 6% or less, particularly preferably 5% or less, and most preferably 4% or less.

When the Li ions on the glass surface are exchanged with Na ions, and the Na ions on the glass surface are exchanged with K ions simultaneously by immersion in a mixed molten salt of potassium nitrate and sodium nitrate, the Na ₂ O content is more preferably 7% or less, particularly preferably 6% or less, and most preferably 5% or less. In addition, the Na ₂ O content is preferably 2% or more, more preferably 3% or more, and even more preferably 4% or more.

K ₂ O may be contained in order to improve ion exchange performance, etc. When K ₂ O is contained, the content of K ₂ O is preferably 0.5% or more, more preferably 1% or more, further preferably 2% or more, particularly preferably 3% or more.

On the other hand, when the content of _K2O is excessive, a violent fracture mode with a large number of fragments may occur, and the fragments are likely to fly. In order to reduce the number of fragments when the chemically strengthened glass is fractured and suppress the scattering of fragments, the content of _K2O is preferably 10% or less. The content of _K2O is more preferably 8% or less, further preferably 6% or less, particularly preferably 4% or less, and most preferably 2% or less.

CaO is a component that improves the meltability of glass, and is a component that reduces the number of fragments when chemically strengthened glass breaks and suppresses the scattering of fragments, and CaO may be contained. When CaO is contained, the content of CaO is preferably 0.5% or more, more preferably 1% or more, further preferably 2% or more, particularly preferably 3% or more, and most preferably 5% or more.

On the other hand, in order to improve the ion exchange performance, it is preferably 20% or less. The CaO content is more preferably 14% or less, and further preferably 10% or less, 8% or less, 6% or less, 3% or less, and 1% or less.

SrO is a component that improves the meltability of glass, and is a component that reduces the number of fragments when chemically strengthened glass breaks and suppresses the scattering of fragments, and SrO may be contained. When SrO is contained, the content of SrO is preferably 0.5% or more, more preferably 1% or more, further preferably 2% or more, particularly preferably 3% or more, and most preferably 5% or more.

On the other hand, in order to improve the ion exchange performance, it is preferably 20% or less. The SrO content is more preferably 14% or less, and further preferably 10% or less, 8% or less, 6% or less, 3% or less, and 1% or less.

BaO is a component that improves the solubility of chemically strengthened glass, and is a component that reduces the number of fragments when chemically strengthened glass breaks and suppresses the scattering of fragments, and BaO may be contained. When BaO is contained, the content of BaO is preferably 0.5% or more, more preferably 1% or more, further preferably 2% or more, particularly preferably 3% or more, and most preferably 5% or more.

On the other hand, in order to improve the ion exchange performance, the BaO content is preferably 15% or less, more preferably 10% or less, 8% or less, 6% or less, 3% or less, and 1% or less. In order to improve the chipping resistance, it is preferred not to contain BaO.

ZnO is a component that improves the solubility of glass, and ZnO may be contained. When ZnO is contained, the content of ZnO is preferably 0.25% or more, and more preferably 0.5% or more.

On the other hand, in order to maintain the weather resistance of glass, the ZnO content is preferably 10% or less, more preferably 7% or less, further preferably 5% or less, particularly preferably 2% or less, and most preferably 1% or less.

TiO ₂ is a component _{that reduces the number of fragments when chemically strengthened glass breaks and suppresses the scattering of fragments, and may be contained. When TiO 2 is contained, the content of TiO 2 is preferably} 0.1% or more, more preferably 0.15% or more, and further preferably 0.2% or more.

On the other hand, in order to suppress devitrification during melting, the content of TiO ₂ is preferably 1% or less, more preferably 0.5% or less, and even more preferably 0.25% or less.

ZrO ₂ is a component that increases surface compressive stress by ion exchange, and has the effect of reducing the number of fragments when chemically strengthened glass breaks and suppressing the scattering of fragments. ZrO ₂ may be contained. When ZrO ₂ is contained, the content of ZrO ₂ is preferably 0.5% or more, more preferably 1% or more.

On the other hand, in order to prevent devitrification during melting, the ZrO ₂ content is preferably 8% or less, more preferably 6% or less, further preferably 4% or less, particularly preferably 2% or less, and most preferably 1.2% or less.

_{La2O3 and Nb2O5 are} components that reduce the number of fragments when chemically strengthened glass breaks and suppress _{the scattering of fragments, and La2O3 and Nb2O5 may be contained} . When these components are contained, the content of each is preferably _0.5 % or more, more preferably 1% or more, further preferably 1.5% or more, particularly preferably 2% or more, and most preferably 2.5% or more.

On the other hand, when the contents _{of La2O3} and _Nb2O5 are excessive _, the glass may be easily devitrified during melting, _{and the quality of the chemically strengthened glass may be reduced. The contents of La2O3 and Nb2O5 are} preferably 8% or less, more preferably 6% or less, further preferably 5% or less, particularly preferably 4% or less, and most preferably 3% or less.

In order to reduce the number of fragments when chemically strengthened glass breaks and suppress scattering of fragments, a small amount of _{Ta2O5 or Gd2O3} may be contained. However, since the refractive index and reflectivity _are increased, 1% or less is preferred, _0.5 % or less is more preferred, and no _{Ta2O5 or Gd2O3} is further preferred.

_Fe2O3 is a component _{that improves the meltability of glass. Since Fe2O3 is} a component that absorbs heat rays _, it has the effects of promoting thermal convection of molten glass to increase the homogeneity of glass, and preventing the temperature of the bottom bricks of the melting furnace from _{rising to extend the life of the furnace. In the melting process of plate glass using a large furnace, it is preferred to include Fe2O3 in the composition. The content of Fe2O3 is preferably 0.002} % or more, more preferably 0.006% or more, further preferably 0.01% or more, and particularly preferably 0.02% or more.

On the other hand, when _Fe2O3 is contained in excess, coloration due to _Fe2O3 becomes a problem. It is known _{that Fe2O3 in} an oxidized state causes _yellow coloration, and FeO in a reduced state causes blue coloration, _{and it is known that the glass is colored green in a balance between the two. The content of Fe2O3 is preferably} 0.3% or less, more preferably 0.04% or less, further preferably 0.03% or less, and particularly preferably 0.025% or less.

When the glass is colored, a coloring component may be added within a range that does not hinder the achievement of desired chemical strengthening characteristics. Examples of suitable coloring components include Co ₃ O ₄ , MnO ₂ , Fe ₂ O ₃ , NiO, CuO, Cr ₂ O ₃ , V ₂ O ₅ , Bi ₂ O ₃ , SeO ₂ , TiO ₂ , CeO ₂ , Er ₂ O ₃ , and Nd ₂ O ₃ .

The content of the coloring components is preferably within a range of 7% or less in total, expressed as a molar percentage based on the oxide. When it is greater than 7%, the glass is prone to devitrification, which is not preferred. The content is preferably 5% or less, more preferably 3% or less, and further preferably 1% or less. In the case where the visible light transmittance of the glass is given priority, it is preferred that these components are substantially not contained.

SO ₃ , chloride, fluoride, etc. may be appropriately contained as a clarifier during glass melting. As ₂ O ₃ is preferably _not contained. When Sb ₂ O ₃ is contained, _it is preferably 0.3% or less, more preferably 0.1% or less, and most preferably not contained.

Furthermore, the chemically strengthened glass or the glass for chemical strengthening of the present invention has silver ions on the surface, and thus can be provided with antimicrobial properties.

The fracture toughness value (K1c) of the chemically strengthened glass or chemically strengthened glass of the present invention is preferably 0.7 MPa·m ^1/2 or more, more preferably 0.75 MPa·m ^1/2 or more, further preferably 0.77 MPa·m ^1/2 or more, particularly preferably 0.80 MPa·m ^1/2 or more, and most preferably 0.82 MPa·m ^1/2 or more. When the fracture toughness value (K1c) is ^{0.7 MPa·m 1/2 or} more, the number of fragments generated when the glass breaks can be suppressed.

It should be noted that the fracture toughness value (K1c) in this specification is the fracture toughness value obtained by measuring the K1-v curve using the DCDC method (double cleavagedrilled compression) and taking the form of the stress expansion coefficient K1 (MPa·m ^1/2 ) when the crack growth rate v reaches 10 ^{- 1} m/sec.

In the present invention, it is preferred that the Young's modulus of the chemically strengthened glass is 70 GPa or more, and the difference between the compressive stress value (CS) of the outermost surface of the chemically strengthened glass and the compressive stress value (CS ₁ ) of the portion with a depth of 1 μm from the glass surface is 50 MPa or less. This is preferred because warping is less likely to occur when the glass surface is polished after the chemical strengthening treatment.

The Young's modulus (E) of the chemically strengthened glass or chemically strengthened glass is more preferably 90 GPa or more, particularly preferably 95 GPa or more, and further preferably 100 GPa or more. The upper limit of the Young's modulus is not particularly limited, but in consideration of the acid resistance and devitrification characteristics of the glass, it is, for example, 150 GPa or less, preferably 145 GPa or less, further preferably 135 GPa or less, particularly preferably 125 GPa or less, and most preferably 118 GPa or less. The Young's modulus can be measured, for example, by an ultrasonic pulse method.

In order to reduce the weight of the product and improve the chipping resistance, the density (ρ) of the chemically strengthened glass is preferably 3.2 g/cm ³ or less, more preferably 3.1 g/cm ³ or less, and further preferably 3.0 g/cm ³ or less. The lower limit of the density is not particularly limited, but in order to maintain chemical resistance such as acid resistance, it is, for example, 2.3 g/cm ³ or more, preferably 2.5 g/cm ³ or more, and further preferably 2.7 g/cm ³ or more.

In order to reduce warpage after chemical strengthening, the average linear thermal expansion coefficient (linear expansion coefficient α) of the chemically strengthened glass at 50°C to 350°C is preferably 120×10 ^-7 /°C or less, more preferably 100×10 ^-7 /°C or less, further preferably 90×10 ^-7 /°C or less, and particularly preferably 80×10 ^-7 /°C or less. The linear expansion coefficient is, for example, 45×10 ^-7 /°C or more, preferably 55×10 ^-7 /°C or more.

In order to reduce the warpage after chemical strengthening, the glass transition temperature (Tg) of the chemically strengthened glass is preferably 550°C or higher, more preferably 570°C or higher, and further preferably 590°C or higher. On the other hand, when the glass transition temperature is higher than 750°C, the components that can be used in sheet forming such as float forming are limited. It is preferably 750°C or lower, more preferably 720°C or lower, further preferably 700°C or lower, and particularly preferably 660°C or lower.

The Vickers hardness (Hv) of the chemically strengthened glass is preferably 650 kgf/mm ² or more, more preferably 700 kgf/mm ² or more. The upper limit of the Vickers hardness (Hv) of the chemically strengthened glass is not particularly limited, but in consideration of the manufacturing characteristics of the glass, it is, for example, 1000 kgf/mm ² or less, preferably 900 kgf/mm ² or less, and more preferably 800 kgf/mm ² or less.

The Vickers hardness (Hvct or Hv) of the chemically strengthened glass is preferably 700 kgf/mm ² or more, more preferably 750 kgf/mm ² or more, and further preferably 800 kgf/mm ² or more. The upper limit of the Vickers hardness (Hvct) of the chemically strengthened glass is not particularly limited, but in consideration of the manufacturing characteristics of the glass, it is, for example, 1100 kgf/mm ² or less, preferably 1000 kgf/mm ² or less, and more preferably 900 kgf/mm ² or less.

The surface compressive stress value (CS ₀ ) of the chemically strengthened glass of the present invention (hereinafter, sometimes referred to as "surface compressive stress value" or simply "CS") is preferably 300 MPa or more, more preferably 350 MPa or more, and further preferably 400 MPa or more. On the other hand, the upper limit of CS ₀ is not particularly limited, and is, for example, 1200 MPa or less, preferably 1000 MPa or less, and further preferably 800 MPa or less.

The compressive stress layer depth (DOL) of the chemically strengthened glass of the present invention is preferably 50 μm or more, more preferably 70 μm or more, further preferably 90 μm or more, and particularly preferably 110 μm or more. On the other hand, when the DOL is greater than 200 μm, there is a risk that the CT becomes larger and fragments may be scattered when broken. The DOL is preferably 200 μm or less, more preferably 160 μm or less.

The compressive stress value (CS ₅₀ ) of the chemically strengthened glass of the present invention at a depth of 50 μm from the glass surface is preferably 30 MPa or more, more preferably 40 MPa or more, further preferably 50 MPa or more, and particularly preferably 60 MPa or more.

The compressive stress value (CS ₉₀ ) of the chemically strengthened glass of the present invention at a depth of 90 μm from the glass surface is preferably 25 MPa or more, more preferably 30 MPa or more, further preferably 40 MPa or more, and particularly preferably 50 MPa or more.

It is preferred that the relationship between the surface compressive stress (CS) and the compressive stress value (CS ₅₀ ) is represented by at least two different functions. For example, the two different functions are a function representing the first region and a function representing the second region in a first region from the glass surface to a predetermined depth and a second region from the first region to a depth at which the surface compressive stress is 0. In this case, the function representing the first region and the function representing the second region are both linear functions, and it is preferred that the slope of the linear function representing the first region is greater than the slope of the linear function representing the second region.

The chemically strengthened glass of the present invention can be produced, for example, as follows.

First, glass for chemical strengthening is prepared. The glass for chemical strengthening is preferably the chemically strengthened glass of the present invention. The glass for chemical strengthening can be manufactured by a common method. For example, raw materials of each component of the glass are mixed and heated and melted in a glass melting furnace. Thereafter, the glass is homogenized by a known method, formed into a desired shape such as a glass plate, and slowly cooled.

As the forming method of the glass sheet, for example, there can be mentioned: float process, press process, fusion process and down-draw process. The float process suitable for mass production is particularly preferred. In addition, continuous forming methods other than the float process, namely, fusion process and down-draw process are also preferred.

Afterwards, the formed glass is ground and polished as needed to form a glass substrate. It should be noted that when the glass substrate is cut into a specified shape and size, or chamfered, if the glass substrate is cut and chamfered before the chemical strengthening treatment described later is performed, a compressive stress layer is also formed on the end face by the subsequent chemical strengthening treatment, so it is preferred.

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

The chemical strengthening treatment can be performed by a conventionally known method. In the chemical strengthening treatment, the glass sheet is contacted with a melt of a metal salt (e.g., potassium nitrate) containing a metal ion with a large ionic radius (typically K ion) by immersion, etc., so that the metal ions with a small ionic radius (typically Na ions and Li ions) in the glass sheet are replaced with metal ions with a large ionic radius (typically, K ions for Na ions and Na ions or K ions for Li ions).

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

As for the molten salt for chemical strengthening treatment, nitrate, sulfate, carbonate, chloride etc. can be listed. Among them, as nitrate, lithium nitrate, sodium nitrate, potassium nitrate, cesium nitrate, silver nitrate etc. can be listed. As sulfate, lithium sulfate, sodium sulfate, potassium sulfate, cesium sulfate, silver sulfate etc. can be listed. As carbonate, lithium carbonate, sodium carbonate, potassium carbonate etc. can be listed. As chloride, lithium chloride, sodium chloride, potassium chloride, cesium chloride, silver chloride etc. can be listed. These molten salts can be used alone or in combination.

In the present invention, the treatment conditions of the chemical strengthening treatment can be appropriately selected by taking into account the properties and composition of the glass, the type of molten salt, and the desired chemical strengthening properties of the final chemically strengthened glass, such as the surface compressive stress (CS) and the depth of the compressive stress layer (DOL).

In addition, in the present invention, the chemical strengthening treatment may be performed only once, or a plurality of chemical strengthening treatments may be performed under two or more different conditions (multi-stage strengthening). Here, for example, when the chemical strengthening treatment is performed under relatively low CS conditions as the first stage of chemical strengthening treatment, and then the chemical strengthening treatment is performed under relatively high CS conditions as the second stage of chemical strengthening treatment, the internal tensile stress area (St) can be suppressed while increasing the CS of the outermost surface of the chemically strengthened glass, and as a result, the reduction of the internal tensile stress (CT) can be suppressed.

The chemically strengthened glass of the present invention is particularly useful as a cover glass used in mobile devices such as mobile phones, smart phones, portable information terminals (PDAs), and tablet terminals. In addition, it is useful as a cover glass for display devices such as televisions (TVs), personal computers (PCs), and touch panels that are not intended to be portable, building materials such as elevator walls, walls of buildings such as houses or buildings (full-screen displays), window glass, etc., desktops, interiors of cars or airplanes, etc., or their cover glass, and housings having a curved shape other than a flat plate by bending and processing.

The chemically strengthened glass of the present invention preferably has a devitrification temperature T of not more than T4, the temperature at which the viscosity reaches 10 ⁴ dPa·s. This is because when the devitrification temperature T is higher than T4, quality degradation due to devitrification is likely to occur during glass sheet forming by a float process or the like.

The chemically strengthened glass of the present invention preferably has a surface compressive stress value (CS _g ) of 300 MPa or more, more preferably 350 MPa or more, and even more preferably 400 MPa or more, after chemically strengthening the glass having a plate thickness of 0.8 mm at 100% NaNO ₃ at 500° C. for 15 hours. On the other hand, the upper limit of CS _g is not particularly limited, but is, for example, 1200 MPa or less, preferably 1000 MPa or less, and even more preferably 800 MPa or less.

In the chemically strengthened glass of the present invention, the compressive stress layer depth (DOL _g ) after chemical strengthening of a glass having a thickness of 0.8 mm at 100% NaNO ₃ at 500° C. for 15 hours is preferably 30 μm or more, more preferably 40 μm or more, further preferably 50 μm or more, and particularly preferably 60 μm or more.

When the chemically strengthened glass of the present invention is in the form of a plate (glass plate), in order to enhance the effect of chemical strengthening, the plate thickness (t) is, for example, 2 mm or less, preferably 1.5 mm or less, more preferably 1 mm or less, further preferably 0.9 mm or less, particularly preferably 0.8 mm or less, and most preferably 0.7 mm or less. In addition, from the viewpoint of obtaining a sufficient effect of strength improvement by chemical strengthening treatment, the plate thickness is, for example, 0.1 mm or more, preferably 0.2 mm or more, more preferably 0.4 mm or more, and further preferably 0.5 mm or more.

The chemically strengthened glass of the present invention may be in a shape other than a plate shape depending on the product to which it is applied, the purpose, etc. In addition, the glass plate may also have a frame shape with different peripheral thicknesses, etc. In addition, the above-mentioned glass plate may also have two main surfaces and end surfaces adjacent to them to form the plate thickness, and the two main surfaces form flat surfaces parallel to each other. However, the shape of the glass plate is not limited to this, for example, the two main surfaces may not be parallel to each other, and in addition, all or part of one or both of the two main surfaces may be a curved surface. More specifically, the glass plate may be, for example, a flat glass plate without warping, or a curved glass plate with a curved surface.

Example

The present invention will be described below by way of examples, but the present invention is not limited thereto. It should be noted that, for each measurement result in the table, a blank column indicates that the measurement was not performed.

(Production of chemically strengthened glass)

A glass plate was produced by melting in a platinum crucible in such a manner that each glass composition is expressed as a molar percentage based on the oxide shown in the table. Commonly used glass raw materials such as oxides, hydroxides, carbonates or nitrates were appropriately selected and weighed in such a manner that the glass reached 1000 g. Next, the mixed raw materials were loaded into a platinum crucible and placed in a resistance heating electric furnace at 1500°C to 1700°C, melted for about 3 hours, degassed and homogenized. The obtained molten glass was poured into a mold material, kept at a temperature of glass transition temperature + 50°C for 1 hour, and then cooled to room temperature at a rate of 0.5°C/min to obtain a glass block. The obtained glass block was cut and ground, and finally both sides were processed into mirror surfaces to obtain a plate-shaped glass (chemically strengthened glass) with a length of ₂₀ mm × a width of 20 mm × a thickness of 0.8 (mm). The _Fe2O3 content in the glass is 0.0125%.

Next, each glass was subjected to chemical strengthening treatment to obtain chemically strengthened glass. In order to obtain CS _g and DOL _g , the glasses of Examples 1 to 7 were subjected to chemical strengthening treatment under the conditions of plate thickness 0.8 mm, NaNO ₃ : 100%, 500° C., and 15 hours. The results are shown in Table 1. It should be noted that the values of CS _g and DOL _g of Examples 1 and 7 are calculated values.

In addition, as for the glass used in the scratch test, the glass of Example 1 was treated in two kinds of molten salts, and the conditions were: plate thickness 0.8 mm, (first time) NaNO ₃ : 100%, 450°C, 4 hours; (second time) KNO ₃ : 100%, 450°C, 6 hours. The glasses of Examples 2 to 6 were chemically strengthened using one kind of molten salt, and the conditions were: plate thickness 0.8 mm, NaNO ₃ : 100%, 500°C, 15 hours. The glass of Example 7 was treated in two kinds of molten salts, and the conditions were: plate thickness 0.8 mm, (first time) NaNO ₃ : 100%, 450°C, 3 hours; (second time) KNO ₃ : 100%, 450°C, 1.5 hours.

<Density (ρ)>

Density measurement was performed by immersion weighing method (JISZ 8807:2012, Methods for measuring density and specific gravity of solids). The unit is g/cm ³ .

<Young's modulus (E)>

The Young's modulus E (unit: GPa) of the glass before chemical strengthening was measured by an ultrasonic pulse method (JIS R1602: 1995).

<Vickers hardness (Hv)>

The Vickers hardness Hv (unit: kgf/mm ² ) of the glass before and after chemical strengthening was measured at a load of 100 gf in accordance with JIS Z2244:2009 “Vickers hardness test-test method”.

<Glass transition temperature (Tg)>

The glass transition temperature Tg (unit: °C) of the glass before chemical strengthening was measured using a thermomechanical analyzer (TMA) in accordance with the method specified in JIS R3103-3:2001.

<Linear expansion coefficient α>

Linear Expansion Coefficient α and Glass Transition Temperature Tg The average linear thermal expansion coefficient (α ^50-350 ) at 50° C. to 350° C. (unit: /° C.) was measured in accordance with JIS R 3102:1995 “Test method for average linear expansion coefficient of glass”.

<CS, DOL>

The surface compressive stress CS (unit: MPa) was measured using a surface stress meter FSM-6000 manufactured by Orihara Seisakusho Co., Ltd. The thickness of the compressive stress layer DOL (unit: μm), CS ₅₀ , CS ₉₀ , CS _g , and DOL _g were measured by a method using Abrio-IM and a thin sheet sample for the glasses of Examples 1 and 2, and by a measuring instrument SLP1000 manufactured by Orihara Seisakusho Co., Ltd. using scattered light photoelasticity for the glasses of Examples 3 to 7.

<Scratch test>

#80 garnet sandpaper was cut into approximately 1 cm squares, mounted on a friction and wear tester manufactured by Shinto Scientific Co., Ltd., rubbed with a load of 300 gf, and the appearance of the scratches generated was observed.

Table 1

Table 2

The above results show that Examples 1 to 6 have a Vickers hardness Hv of 700 (kgf/mm ² ) or more after chemical strengthening, and thus have excellent scratch resistance. Examples 1 and 3 to 6 have a Vickers hardness Hv of 700 (kgf/mm ² ) or more, and a DOL _g of 30 μm or more, and thus have excellent scratch resistance and excellent bending fracture resistance.

The present invention is described in detail and with reference to specific embodiments, but various changes and modifications can be implemented without departing from the spirit and scope of the present invention, which is obvious to those skilled in the art. This application is based on Japanese patent application (Japanese patent application 2017-089984) filed on April 28, 2017, and its contents are incorporated herein by reference.

Claims (10)

1. A glass for chemical strengthening, wherein the glass for chemical strengthening comprises, in mole percent based on oxides:

62 to 75 percent of SiO ₂,

10 To 15 percent of Al ₂O₃, but not 10 percent,

3-20% MgO,

More than 8% and less than or equal to 20% of Li ₂ O,

More than 0% and less than or equal to 20% of Y ₂O₃,

0 To 1 percent of B ₂O₃,

0 To 2 percent of P ₂O₅,

1 To 6 percent of Na ₂ O,

0.5 To 2 percent of K ₂ O, but not including 2 percent,

0 To 0.5 percent of CaO, but not 0.5 percent,

0 To 20 percent of SrO,

0 To 15 percent of BaO,

0 To 10 percent of ZnO,

0% To 1% TiO ₂, but not including 1%, and

0.5% To 2% ZrO ₂, but excluding 0.5%, and

The Young's modulus of the glass for chemical strengthening is 90GPa or more and the Vickers hardness is 650kgf/mm ² or more.

2. A chemically strengthened glass, wherein the chemically strengthened glass comprises, in mole percent on an oxide basis:

62 to 75 percent of SiO ₂,

10 To 15 percent of Al ₂O₃, but not 10 percent,

3-20% MgO,

More than 8% and less than or equal to 20% of Li ₂ O,

More than 0% and less than or equal to 20% of Y ₂O₃,

0 To 1 percent of B ₂O₃,

0 To 2 percent of P ₂O₅,

1 To 6 percent of Na ₂ O,

0.5 To 2 percent of K ₂ O, but not including 2 percent,

0 To 0.5 percent of CaO, but not 0.5 percent,

0 To 20 percent of SrO,

0 To 15 percent of BaO,

0 To 10 percent of ZnO,

0% To 1% TiO ₂, but not including 1%, and

0.5% To 2% ZrO ₂, but excluding 0.5%, and

The chemically strengthened glass has a Young's modulus of 90GPa or more, a Vickers hardness of 700kgf/mm ² or more, and

The chemically strengthened glass has a surface compressive stress CS ₀ of 300MPa or more and a compressive stress CS ₅₀ of 30MPa or more in a portion having a depth of 50 [ mu ] m from the surface of the glass.

3. The chemically strengthened glass according to claim 2, wherein a compressive stress value CS ₉₀ of a portion of the chemically strengthened glass having a depth of 90 μm from a surface of the glass is 25MPa or more.

4. A chemically strengthened glass according to claim 2 or 3, wherein the relationship between the surface compressive stress CS ₀ and the compressive stress value CS ₅₀ is represented by 2 different functions,

Wherein the 2 different functions are a first order function indicating the 1 st area and a second order function indicating the 2 nd area in a1 st area from a glass surface to a predetermined depth and a2 nd area from the 1 st area to a depth where the surface compressive stress is 0, and a slope of the first order function indicating the 1 st area is larger than a slope of the first order function indicating the 2 nd area.

5. The glass for chemical strengthening according to claim 1, wherein the glass for chemical strengthening contains 3 to 6% of MgO.

6. A chemically strengthened glass according to claim 2 or claim 3, wherein the chemically strengthened glass comprises 3% to 6% MgO.

7. The chemically strengthened glass according to claim 1 or 5, wherein the chemically strengthened glass contains 0% to 1% of TiO ₂, but does not contain 0% and 1%.

8. A chemically strengthened glass according to claim 2 or claim 3, wherein the chemically strengthened glass comprises 0% to 1% TiO ₂, but does not comprise 0% and 1%.

9. The glass for chemical strengthening according to claim 1 or 5, wherein the glass for chemical strengthening has a fracture toughness value K1c of 0.75MPa m ^1/2 or more.

10. The chemically strengthened glass according to claim 2 or 3, wherein the chemically strengthened glass has a fracture toughness value K1c of 0.75 MPa-m ^1/2 or more.