Glass substrate for magnetic disk and magnetic disk

Patent metadata

Field	Value
Publication number	US-9595284-B2
Application number	US-201414767515-A
Country	US
Kind code	B2
Filing date	Feb 24, 2014
Priority date	Feb 22, 2013
Publication date	Mar 14, 2017
Grant date	Mar 14, 2017

Abstract

A magnetic-disk glass substrate has a circular hole at a center, and includes a pair of main surfaces and a side wall surface orthogonal to the main surfaces. A roundness of the circular hole is 1.5 μm or less. A difference between a maximum value and a minimum value of radii of three inscribed circles that are respectively derived from outlines in the circumferential direction at three positions spaced apart by 200 μm in a substrate thickness direction on the side wall surface of the circular hole is 3.5 μm or less.

First claim

The invention claimed is:

1. A magnetic-disk glass substrate having a circular hole at a center, the magnetic-disk glass substrate comprising:
a pair of main surfaces; and
a side wall surface orthogonal to the main surfaces,
a substrate thickness of the magnetic-disk glass substrate being 0.635 mm or less,
a roundness of the circular hole being 1.5 μm or less, and
a difference between a maximum value and a minimum value of radii of three inscribed circles that are respectively derived from outlines in a circumferential direction at three positions spaced apart by 100 μm in a substrate thickness direction on the side wall surface of the circular hole being 3.5 μm or less.

2. The magnetic-disk glass substrate according to claim 1 , wherein
a surface roughness Rz of the side wall surface of the circular hole is 0.2 μm or less.

3. The magnetic-disk glass substrate according to claim 1 , wherein
an average coefficient of thermal expansion from 100° C. to 300° C. is 60×10 −7 (K −1 ) or less.

4. The magnetic-disk glass substrate according to claim 1 , wherein
with regard to a surface roughness of the side wall surface of the circular hole, in a case where a maximum height in the substrate thickness direction is Rz(t) and a maximum height in the circumferential direction is Rz(c), Rz(t)/Rz(c) is 1.2 or less.

5. The magnetic-disk glass substrate according to claim 1 , wherein
when a measurement point is provided every 30 degrees in the circumferential direction referenced on the center of the magnetic-disk glass substrate, and a radius of curvature of a shape of a portion between the side wall surface and a chamfered surface of the circular hole at the measurement point is derived, a difference in the radius of curvature between adjacent measurement points is 0.01 mm or less.

6. A magnetic disk in which at least a magnetic layer is formed on a main surface of the magnetic-disk glass substrate according to claim 1 .

Assignees

• Hoya Corp

Inventors

• Tamaki Masanori
• Takahashi Takeyoshi
• Ueda Masaaki

Classifications

• G11B5/8404

  manufacturing base layers · CPC title

• G11B5/82 Primary

  Disk carriers · CPC title

• G11B5/7315 Primary

  Physics · mapped topic

• G11B5/73921

  Glass or ceramic substrates · CPC title