Chemically strengthened glass, and glass for chemical strengthening

1. A glass for chemical strengthening, comprising, in mole percentage on an oxide basis, 54 to 62% of SiO 2 , 16 to 20% of Al 2 O 3 , 0.5 to 5% of B 2 O 3 , 0 to 4% of P 2 O 5 , 5 to 13% of Li 2 O, 7 to 14% of Na 2 O, 0 to 2% of K 2 O, 0 to 10% of MgO, 0 to 1% of CaO, 0 to 1% of SrO, 0 to 1% of BaO, 0 to 5% of ZnO, 0 to 1% of TiO 2 , and 0 to 4% of ZrO 2 ,

wherein a value of X is at least 40,000, the value of X being calculated based on the following formula by using contents in mole percentage on an oxide basis of components of SiO 2 , Al 2 O 3 , B 2 O 3 , P 2 O 5 , Li 2 O, Na 2 O, K 2 O, MgO, CaO, SrO, BaO, and ZrO 2 :

X=SiO 2 ×329+Al 2 O 3 ×786+B 2 O 3 ×627+P 2 O 5 ×(−941)+Li 2 O×927+Na 2 O×47.5+K 2 O×(−371)+MgO×1230+CaO×1154+SrO×733+ZrO 2 ×51.8.

2. The glass for chemical strengthening according to claim 1 , wherein a value of Y is at least 0.7, the value of Y being calculated based on the following formula by using contents in mole percentage on an oxide basis of components of SiO 2 , Al 2 O 3 , B 2 O 3 , P 2 O 5 , Li 2 O, Na 2 O, K 2 O, MgO, CaO, SrO, BaO, and ZrO 2 :

Y=SiO 2 ×0.00884+Al 2 O 3 ×0.0120+B 2 O 3 ×(−0.00373)+P 2 O 5 ×0.000681+Li 2 O×0.00735+Na 2 O×(−0.00234)+K 2 O×(−0.00608)+MgO×0.0105+CaO×0.00789+SrO×0.00752+BaO×0.00472+ZrO 2 ×0.0202.

3. The glass for chemical strengthening according to claim 1 , wherein a devitrification temperature T is equal to or lower than a temperature T4 at which a viscosity reaches 10 4 dPa·s.

4. The glass for chemical strengthening according to claim 1 , having a fracture toughness value of at least 0.7 MPa·m 1/2 .

5. The glass for chemical strengthening according to claim 1 , having a Young's modulus of at least 74 GPa.

6. A chemically strengthened glass, having a surface compressive stress (CS) of at least 450 MPa,

wherein

the chemically strengthened glass has a matrix composition comprising, in mole percentage on an oxide basis, 54 to 62% of SiO 2 , 16 to 20% of Al 2 O 3 , 0.5 to 5% of B 2 O 3 , 0 to 4% of P 2 O 5 , 5 to 13% of Li 2 O, 7 to 14% of Na 2 O, 0 to 2% of K 2 O, 0 to 10% of MgO, 0 to 1% of CaO, 0 to 1% of SrO, 0 to 1% of BaO, 0 to 5% of ZnO, 0 to 1% of TiO 2 , and 0 to 4% of ZrO 2 ; and

a value of X is at least 40,000, the value of X being calculated based on the following formula by using contents in mole percentage on an oxide basis of components of SiO 2 , Al 2 O 3 , B 2 O 3 , P 2 O 5 , Li 2 O, Na 2 O, K 2 O, MgO, CaO, SrO, BaO, and ZrO 2 in the matrix composition of the chemically strengthened glass:

X=SiO 2 ×329+Al 2 O 3 ×786+B 2 O 3 ×627+P 2 O 5 ×(−941)+Li 2 O×927+Na 2 O×47.5+K 2 O×(−371)+MgO×1230+CaO×1154+SrO×733+ZrO 2 ×51.8.

7. The chemically strengthened glass according to claim 6 , having a value of ΔCS DOL-20 , in MPa/μm, of at least 0.4, the value of ΔCS DOL-20 being calculated by the following formula by using a compressive stress value CS DOL-20 at a depth of 20 μm glass surface side from a depth (DOL) from a glass surface of a portion at which stress is zero in a stress profile of the chemically strengthened glass:

Δ CS DOL-20 =CS DOL-20 /20.

8. The chemically strengthened glass according to claim 6 , wherein the value of ΔCS DOL-20 , in MPa/μm, is 4.0 or less.

9. The chemically strengthened glass according to claim 6 , wherein a compressive stress value (CS 100 ) in a portion at a depth of 100 μm from the glass surface is at least 15 MPa.

10. The chemically strengthened glass according to claim 9 , wherein a product (CS 100 ×t 2 ) of the CS 100 and a square of a sheet thickness t in mm, is 120 MPa·mm 2 or less.

11. The chemically strengthened glass according to claim 6 , having a sheet shape with a sheet thickness t of 2 mm or less.