Glass substrate for an information recording medium, method for manufacturing a glass substrate for an information recording medium, and an information recording medium
Provided are a glass substrate for an information recording medium, which has both high strength and high flatness and can be manufactured at low cost, a method for manufacturing such glass substrate and an information recording medium using such glass substrate. The glass substrate for the information recording medium satisfies inequalities of 0.1≦(W1−W3)/W2≦5, where, W1 is an ion concentration at the center portion in the thickness direction of the glass substrate in a chemically reinforced region at the outer circumference end surface and the inner circumference end surface of the glass substrate and is the maximum value of K + ion concentration, W2 is a Na + ion concentration at a position where the K + ion concentration is maximum, and W3 is a K + ion concentration in a glass substrate region not chemically reinforced.
1. A glass substrate for an information recording medium, the substrate comprising:
a disk shaped glass substrate having a center hole, containing at least Na 2 O as a composition thereof, and including, on an outer circumferential end face and an inner circumferential end face, regions which are chemically reinforced with a chemically-reinforcing treatment liquid containing a K + ion, wherein the following relationship is satisfied:
1≦( W 1 −W 3)/ W 2≦5
wherein:
W1 is a maximum value of a K + ion concentration at a central portion in a thickness direction of the glass substrate, in the chemically reinforced regions on the outer circumferential end face and the inner circumferential end face;
W2 is an Na + ion concentration at a position at which the K + ion concentration is the maximum value W1; and
W3 is a K + ion concentration at the central portion in a thickness direction of the glass substrate and in a not chemically-reinforced region of the glass substrate.
2. The glass substrate for an information recording medium of claim 1 , the glass substrate including Li 2 O in addition to Na 2 O as a component thereof.
3. The glass substrate for an information recording medium of claim 1 , wherein the position at which the K + ion concentration is the maximum value W1 is located inside the glass substrate and away from the outer circumferential end face and the inner circumferential end face.
4. A method for manufacturing a glass substrate for an information recording medium, the method comprising the step of:
chemically reinforcing, with a chemical reinforcement processing solution containing a K + ion, a glass substrate which is a disk-shaped glass substrate, has a center hole, and contains at least Na 2 O as a composition thereof, wherein the following relationship is satisfied:
1≦( W 1 −W 3)/ W 2≦5
wherein:
W1 is a maximum value of a K + ion concentration at a central portion in a thickness direction of the glass substrate, in chemically reinforced regions on an outer circumferential end face and an inner circumferential end face;
W2 is an Na + ion concentration at a position at which the K + ion concentration is the maximum value W1; and
W3 is a K + ion concentration at the central portion in a thickness direction of the glass substrate and in a not chemically-reinforced region of the glass substrate.
5. The method for manufacturing a glass substrate for an information recording medium of claim 4 , wherein the position at which the K + ion concentration is the maximum value W1 is located inside the glass substrate and away from the outer circumferential end face and the inner circumferential end face.
6. The method for manufacturing a glass substrate for an information recording medium of claim 4 , the glass substrate including Li 2 O in addition to Na 2 O as a component thereof.
7. An information recording medium, comprising:
a disk shaped glass substrate having a center hole, containing at least Na 2 O as a composition thereof, and including, on an outer circumferential end face and an inner circumferential end face, regions which are chemically reinforced with a chemically-reinforcing treatment liquid containing a K + ion; and
at least a recording layer provided on the glass substrate for an information recording medium,
wherein the following relationship is satisfied:
1≦( W 1 −W 3)/ W 2≦5
wherein:
W1 is a maximum value of a K + ion concentration at a central portion in a thickness direction of the glass substrate, in the chemically reinforced regions on the outer circumferential end face and the inner circumferential end face;
W2 is an Na + ion concentration at a position at which the K + ion concentration is the maximum value W1; and
W3 is a K + ion concentration at the central portion in a thickness direction of the glass substrate and in a not chemically-reinforced region of the glass substrate.
8. The information recording medium of claim 7 , wherein the recording layer includes a magnetic layer.