Glass substrate for magnetic disk and magnetic disk

Patent metadata

Field	Value
Publication number	US-9595283-B2
Application number	US-201314652365-A
Country	US
Kind code	B2
Filing date	Dec 27, 2013
Priority date	Dec 29, 2012
Publication date	Mar 14, 2017
Grant date	Mar 14, 2017

Abstract

A magnetic-disk glass substrate capable of suppressing turbulence of air flow in a vicinity of an outer circumferential side edge portion of the magnetic disk and suppressing disk flutter is provided. This magnetic-disk glass substrate includes a pair of main surfaces, a side wall surface formed on an outer circumferential side edge surface, and chamfered surfaces interposed between the side wall surface and the main surfaces, respectively. The side wall surface has a roundness of 1.5 μm or less. A difference in radius between an inscribed circle and a circumcircle of a plurality of outlines of the side wall surface at a plurality of positions that include a central position of the magnetic-disk glass substrate in a thickness direction and are different from each other in the thickness direction is 5 μm or less.

First claim

The invention claimed is:

1. A magnetic-disk glass substrate comprising:
a pair of main surfaces;
a side wall surface formed at an outer circumferential side edge portion; and
chamfered surfaces interposed between the side wall surface and the main surfaces, respectively,
a thickness of the magnetic-disk glass substrate being 0.635 mm or less,
the side wall surface having a roundness of 1.5 μm or less, and
a difference in radius between an inscribed circle and a circumcircle of at least three outlines of the side wall surface at at least three positions that include a central position of the magnetic-disk glass substrate in a thickness direction and are different from each other in the thickness direction being 5 μm or less.

2. The magnetic-disk glass substrate according to claim 1 ,
wherein outlines in the circumferential direction are obtained at two positions on the side wall surface on an outer circumferential side spaced apart by 200 μm in the thickness direction, and a middle point between centers of two least square circles determined from the outlines is referred to as middle point A,
outlines in the circumferential direction are obtained at positions that are located at centers of the two chamfered surfaces on the outer circumferential side in the thickness direction, and among centers of least square circles determined from the outlines, a center determined from one chamfered surface is referred to as center B, and a center determined from the other chamfered surface is referred to as center C, and
a sum of a distance between the middle point A and the center B and a distance between the middle point A and the center C is 1 μm or less.

3. The magnetic-disk glass substrate according to claim 1 ,
wherein the thickness of the magnetic-disk glass substrate is 0.5 mm or less.

4. A magnetic disk in which magnetic layers are formed on the main surfaces of the magnetic-disk glass substrate according to claim 1 .

5. The magnetic-disk glass substrate according to claim 2 ,
wherein the thickness of the magnetic-disk glass substrate is 0.5 mm or less.

6. A magnetic disk in which magnetic layers are formed on the main surfaces of the magnetic-disk glass substrate according to claim 2 .

7. A magnetic disk in which magnetic layers are formed on the main surfaces of the magnetic-disk glass substrate according to claim 3 .

8. A magnetic disk in which magnetic layers are formed on the main surfaces of the magnetic-disk glass substrate according to claim 5 .

Assignees

• Tamaki Masanori
• Hoya Corp

Inventors

• Tamaki Masanori

Classifications

• G11B5/82

  Disk carriers · CPC title

• G11B5/8404 Primary

  manufacturing base layers · CPC title

• G11B5/7315 Primary

  Physics · mapped topic

• G11B5/73921

  Glass or ceramic substrates · CPC title