Hoya Corporation

Katsuyuki Iwata

Hideki Isono

Kinobu Osakabe

Kenichiro Terada

Shinji Eda

Mikio Ikenishi

Naomi Matsumoto

A glass substrate for a magnetic disk of the invention is a disk-shaped glass substrate for a magnetic disk where the substrate has a main surface and end face and is subjected to chemical reinforcement treatment, and is characterized in that the penetration length in the uppermost-portion stress layer on the main surface is 49.1 &#x3bc;m or less, and that assuming that an angle between the main surface and compressive stress in the stress profile by a Babinet compensator method is &#x3b8;, a value y of {12&#xb7;t&#xb7;ln(tan &#x3b8;)+(49.1/t)} is the penetration length in the uppermost-portion stress layer or less.

Glass substrate for magnetic disk and manufacturing method of the same

An aspect of the present invention relates to a glass substrate for a magnetic recording medium, which is comprised of glass with a glass transition temperature of equal to or greater than 600&#xb0; C., an average coefficient of linear expansion at 100 to 300&#xb0; C. of equal to or greater than 70&#xd7;10/&#xb0; C., a Young's modulus of equal to or greater than 81 GPa, a specific modulus of elasticity of equal to or greater than 30 MNm/kg, and a fracture toughness value of equal to or greater than 0.9 MPa&#xb7;m.

Glass substrate for magnetic recording medium and its use

This invention provides a method for manufacturing a glass substrate for a magnetic disk comprising a chemical strengthening step. The method provides a glass substrate for a magnetic disk that can suppress the occurrence of very small waves in cooling a glass substrate after the chemical strengthening step, and, while preventing troubles such as head crush and thermal asperity, can realize lowered flying height of a magnetic head and high-density information recording, and is particularly suitable for application to small-size magnetic disks for portable information equipment. In the step of cooling after the chemical strengthening step, cooling treatment is carried out in which the glass substrate is brought into contact with a treatment liquid containing a melt of a material having a solidification temperature below that of a chemical strengthening salt. The temperature of the treatment liquid is regulated to be below the temperature of the chemical strengthening salt melted liquid in the chemical strengthening step.

Method for manufacturing glass substrate for magnetic disk and method for manufacturing magnetic disk

The present invention provides a method for producing a glass substrate for a magnetic disk in which the occurrence of micro-waviness on the glass substrate is prevented in a cooling step after a chemically strengthening step so that the glass substrate has a significantly smooth principal surface, and provides a method for producing a magnetic disk in which head crash, thermal asperity failures, and the like are prevented, the flying height of a magnetic head can be decreased, and high-density recording is enabled. In a method for producing a glass substrate for a magnetic disk including a chemically strengthening step in which a glass substrate is immersed in a heated chemically strengthening salt solution prepared by dissolving a chemically strengthening salt under heating, and metal ions in the glass substrate are ion-exchanged with metal ions in the chemically strengthening salt, wherein the chemically strengthening step is carried out using a chemically strengthening salt solution in which the dissolved chemically strengthening salt does not solidify until the temperature decreases to a temperature that provides hardness at which the surface shape of the glass substrate is not deformed by a force applied to the glass substrate when the chemically strengthening salt having adhered onto the glass substrate solidifies.

Growing community of inventors

Shinjuku-ku, Japan

Katsuyuki Iwata