Patent ID: 8349454

Claim:
A strengthened glass substrate having a compression stress layer in the surface thereof, said glass substrate having a glass composition comprising, in terms of % by mass, 40-70% of SiO 2 , 12-25% of Al 2 O 3 , 0-10% of B 2 O 3 , 0 to less than 4% of Li 2 O, 6-15% of Na 2 O, 0-10% of K 2 O, 13-20% of Li 2 O+Na 2 O+K 2 O, 0-3.9% of MgO, 0-0.8% of CaO, 0-5% of ZnO, 0-6% of ZrO 2 , and 0-5% of SrO+BaO, the value of (MgO+ZrO 2 +ZnO)/(MgO+ZrO 2 +ZnO+Al 2 O 3 ) in terms of mass proportion being from 0.25 to 0.45.