Cover glass and method for producing same
A cover glass having a compressive-stress layer on the principal surfaces thereof, and having a glass composition containing 50% to 70% by mole of SiO 2 , 3% to 20% by mole of Al 2 O 3 , 5% to 25% by mole of Na 2 O, more than 0% by mole and less than or equal to 2.5% by mole of Li 2 O, 0% to 5.5% by mole of K 2 O, and 0% to less than 3% by mole of B 2 O 3 . Also disclosed is a method for producing a cover glass which includes: (i) preparing molten glass by melting a glass raw material; (ii) forming the prepared molten glass into a plate-like shape by a down-draw process and thereby obtaining a glass substrate; and (iii) forming a compressive-stress layer on the surface of the glass substrate.
1. A cover glass comprising a compressive-stress layer on principal surfaces thereof, the cover glass having a glass composition containing
50% to 70% by mole of SiO 2 ,
3% to 20% by mole of Al 2 O 3 ,
5% to 25% by mole of Na 2 O,
more than 0% by mole and less than or equal to 2.5% by mole of Li 2 O,
0% to 5.5% by mole of K 2 O,
0% to less than 3% by mole of B 2 O 3 , and
more than or equal to 0.11% by mole of MgO/(Li 2 O+Na 2 O+K 2 O),
wherein the glass composition does not substantially contain As 2 O 3 and Sb 2 O 3 .
2. The cover glass according to claim 1 , further containing 3% to 15% by mole of MgO.
3. The cover glass according to claim 1 , containing 15.5% to 30% by mole of Na 2 O+Li 2 O+K 2 O.
4. The cover glass according to claim 1 , containing more than 12% by mole of Na 2 O.
5. The cover glass according to claim 1 , wherein Li 2 O/(Na 2 O+Li 2 O+K 2 O) is greater than 0 and less than or equal to 0.2 in mole fraction.
6. The cover glass according to claim 1 , in which the glass composition does not contain SrO, BaO and ZnO.
7. The cover glass according to claim 1 , in which the glass composition contains more than 0% by mole and less than or equal to 0.2% by mole of Li 2 O/(Na 2 O+Li 2 O+K 2 O).
8. The cover glass according to claim 1 , in which the glass composition does not substantially contain CaO.
9. The cover glass according to claim 1 , wherein the amount of MgO is larger than the amount of CaO in the glass composition.
10. A strengthened glass comprising a compressive-stress layer on principal surfaces thereof, the strengthened glass having a glass composition containing
50% to 70% by mole of SiO 2 ,
3% to 20% by mole of Al 2 O 3 ,
5% to 25% by mole of Na 2 O,
more than 0% by mole and less than or equal to 2.5% by mole of Li 2 O,
0% to 5.5% by mole of K 2 O,
0% to less than 3% by mole of B 2 O 3 , and
more than or equal to 0.11% by mole of MgO/(Li 2 O+Na 2 O+K 2 O),
wherein the glass composition does not substantially contain As 2 O 3 and Sb 2 O 3 .
11. The strengthened glass according to claim 10 , in which the glass composition does not substantially contain CaO.
12. The cover glass according to claim 10 , wherein the amount of MgO is larger than the amount of CaO in the glass composition.
13. A cover glass comprising a compressive-stress layer on principal surfaces thereof, the cover glass having a glass composition containing
45% to 70% by mass of SiO 2 ,
5% to 25% by mass of Al 2 O 3 ,
9% to 25% by mass of Na 2 O,
more than 0% by mass and less than or equal to 2.5% by mass of Li 2 O,
0% to 3% by mass of B 2 O 3 ,
more than 0% by mass and less than or equal to 10% by mass of MgO, and
more than or equal to 0.11% by mole of MgO/(Li 2 O+Na 2 O+K 2 O),
wherein the compressive-stress layer has a surface stress depth of 30 μm or greater, and wherein the glass composition does not substantially contain As 2 O 3 and Sb 2 O 3 .
14. The cover glass according to claim 13 , further containing 0% to 15% by mass of K 2 O.
15. The cover glass according to claim 13 , further containing 0% to 5% by mass of ZrO 2 .
16. The cover glass according to claim 13 , containing 0% to 15% by mass of K 2 O,
wherein Li 2 O+Na 2 O+K 2 O is 30% by mass or less.
17. The cover glass according to claim 13 , wherein SiO 2 -(½Al 2 O 3 ) is 57.5% by mass or less.
18. The cover glass according to claim 13 , wherein the compressive-stress layer has a compressive stress of 400 MPa or greater and a surface stress depth of layer of 20 μm or greater.
19. The cover glass according to claim 13 , containing more than 0% by mass and less than or equal to 10% by mass of K 2 O.
20. The cover glass according to claim 13 , in which the glass composition does not substantially contain SrO, BaO and ZnO.
21. The cover glass according to claim 13 , in which the glass composition contains 0.15% or less by mass of Li 2 O/(Na 2 O+Li 2 O+K 2 O).
22. The cover glass according to claim 13 , in which the glass composition does not substantially contain CaO.
23. The cover glass according to claim 13 , wherein the amount of MgO is larger than the amount of CaO in the glass composition.
24. A method for producing the cover glass as claimed in claim 1 , comprising:
(i) preparing molten glass by melting a glass raw material;
(ii) forming the prepared molten glass into a plate-like shape by a down-draw process and thereby obtaining a glass substrate having a glass composition containing
50% to 70% by mole of SiO 2 ,
3% to 20% by mole of Al 2 O 3 ,
5% to 25% by mole of Na 2 O,
more than 0% by mole and less than or equal to 2.5% by mole of Li 2 O,
0% to 5.5% by mole of K 2 O,
0% to less than 3% by mole of B 2 O 3 , and
more than or equal to 0.11% by mole of MgO/(Li 2 O+Na 2 O+K 2 O; and
(iii) forming a compressive-stress layer on the surface of the glass substrate,
wherein the glass composition does not substantially contain As 2 O 3 and Sb 2 O 3 .