Glass substrate for an information recording medium, method for manufacturing a glass substrate for an information recording medium, and an information recording medium

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 Na2O as a composition thereof, wherein the following relationship is satisfied:
• 1≦(W1−W3)/W2≦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.

An information recording medium, comprising:

• a disk shaped glass substrate having a center hole, containing at least Na2O 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≦(W1−W3)/W2≦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.