Glass substrate for an information recording medium and information recording medium employing it
A chemically strengthened glass substrate for use as the substrate of an information recording medium such as a magnetic disk, magneto-optical disk, DVD, or MD, wherein a strengthened formed by chemical strengthening exists on the outer edge surface and on the inner edge surface but substantially not on a surface on which an information recording layer is formed.
1. A chemically strengthened glass substrate for an information recording medium, wherein a strengthened layer formed by chemical strengthening exists on an outer edge surface and on an inner edge surface but substantially not on a surface on which an information recording layer is formed,
wherein, on the surface on which the information recording layer is formed, the glass substrate comprises the following glass ingredients:
60 to 75% by weight of SiO 2 ;
3 to 20% by weight of Al 2 O 3 ;
0 to 8% by weight, zero inclusive, of B 2 O 3 ;
a total of 5 to 15% by weight of R 2 O compounds, where R= Li, Na, and K;
SiO 2 +Al 2 O 3 accounting for 63 to 90% by weight;
a total of 0 to 20% by weight, zero inclusive, of R′O compounds, where R′═Mg, Ca, Sr, Ba, and Zn; and
a total of 0 to 15% 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 , and
wherein the following condition is fulfilled:
1.5<Al 2 O 3 /B 2 O 3 , or B 2 O 3 =0%.
2. A glass substrate for an information recording medium as claimed in claim 1 ,
wherein the glass substrate has a specific elastic modulus E/ρ of 30 or higher.
3. A glass substrate for an information recording medium as claimed in claim 1 ,
wherein the glass substrate has a Vickers hardness Hv in a range of from 450 to 650.
4. A glass substrate for an information recording medium as claimed in claim 1 ,
wherein the glass substrate has alkali elution A of 350 ppb or lower per 2.5-inch disk.
5. A glass substrate for an information recording medium as claimed in claim 1 ,
wherein the glass substrate has Si elution S of 500 ppb or lower per 2.5-inch disk.
6. A glass substrate for an information recording medium as claimed in claim 1 ,
wherein the glass substrate has a fracture toughness Kc of 0.80 MPa/m 1/2 or greater.
7. An information recording medium comprising:
a glass substrate as claimed in claim 1 ; and
an information recording layer formed on at least one side surface of the glass substrate.
8. An information recording medium as claimed in claim 7 ,
wherein the glass substrate has a specific elastic modulus E/ρ of 30 or higher.
9. An information recording medium as claimed in claim 7 ,
wherein the glass substrate has a Vickers hardness Hv in a range of from 450 to 650.
10. An information recording medium as claimed in claim 7 ,
wherein the glass substrate has alkali elution A of 350 ppb or lower per 2.5-inch disk.
11. An information recording medium as claimed in claim 7 ,
wherein the glass substrate has Si elution S of 500 ppb or lower per 2.5-inch disk.
12. An information recording medium as claimed in claim 7 ,
wherein the glass substrate has a fracture toughness Kc of 0.80 MPa/m 1/2 or greater.
13. A chemically strengthened glass substrate as claimed in claim 1 , wherein a lower limit of the content of K 2 O is 0.5% by weight.
14. A chemically strengthened glass substrate as claimed in claim 1 wherein a lower limit of the content of B 2 O 3 is 1.0% by weight.
15. A chemically strengthened glass substrate as claimed in claim 1 , wherein the content of TiO 2 +ZrO 2 +Ln x O y is a total of 0.5% to 13% by weight.