Patent ID: 7396788

Claim:
A glass composition comprising the following glass ingredients: 45 to 75% by weight of SiO 2 ; 10.1 to 14.6% by weight of Al 2 O 3 ; 1.2 to 5.7% by weight of B 2 O 3 ; SiO 2 +Al 2 O 3 +B 2 O 3 accounting for 65 to 90% by weight; a total of 7 to 12.8% by weight of R 2 O compounds, where R=Li, Na, and K; and a total of 0% by weight of R′O compounds, where R′=Mg, Ca, Sr, Ba, and Zn; and a total of 0 to 7.1% by weight, zero inclusive, of TiO 2 +ZrO 2 +Ln x O y , where Ln x O y represents at least one compound selected from the group consisting of lanthanoid metal oxides, Y 2 O 3 , Nb 2 O 5 and Ta 2 O 5 , wherein the following conditions are fulfilled: Al 2 O 3 /B 2 O 3 ≧1.0; and 7.78≧(SiO 2 +Al 2 O 3 +B 2 O 3 )/(the total of R 2 O compounds ≧3.