Disk-shaped glass substrate, magnetic-disk glass substrate, method for manufacturing magnetic-disk glass substrate, and magnetic disk

Patent metadata

Field	Value
Publication number	US-9697862-B2
Application number	US-201414894859-A
Country	US
Kind code	B2
Filing date	Jun 27, 2014
Priority date	Jun 27, 2013
Publication date	Jul 4, 2017
Grant date	Jul 4, 2017

Abstract

A disk-shaped glass substrate for a magnetic-disk glass substrate includes an outer circumference having a roundness of 1.3 μm or less. A first reference circle is obtained with a least squares method from a first outline corresponding to a shape of a lap around the outer circumference. A second reference circle is obtained with a least squares method from a second outline obtained by performing low-pass filtering using a period in which the number of peaks per lap is 150 as a cut-off value on the first outline. A ratio of the second peak count value defined by the number of peaks of the second outline that project outward in a radial direction from the second reference circle to the first peak count value defined by the number of peaks of the first outline that project outward in a radial direction from the first reference circle is 0.2 or less.

First claim

The invention claimed is:

1. A disk-shaped glass substrate comprising:
a pair of main surfaces, the disk-shaped glass substrate being to be made into a magnetic-disk glass substrate,
an outer circumference of the disk-shaped glass substrate having a roundness of 1.3 μm or less,
a first reference circle being obtained with a least squares method from a first outline corresponding to a shape of a lap around the outer circumference of the disk-shaped glass substrate, and the number of peaks of the first outline that project outward in a radial direction from the first reference circle being defined as a first peak count value,
a second reference circle being obtained with a least squares method from a second outline obtained by performing low-pass filtering using a period in which the number of peaks per lap is 150 as a cut-off value on the first outline, and the number of peaks of the second outline that project outward in a radial direction from the second reference circle being defined as a second peak count value, and
a ratio of the second peak count value to the first peak count value being from 0.034 to 0.2.

2. The disk-shaped glass substrate according to claim 1 , wherein
a surface roughness of an outer circumferential edge surface is set such that an arithmetic mean roughness Ra is 0.02 μm or less.

3. The disk-shaped glass substrate according to claim 2 , wherein
an outer diameter is larger than that of a 2.5-inch magnetic-disk glass substrate.

4. The disk-shaped glass substrate according to claim 3 , further comprising
a side wall surface orthogonal to the main surfaces, and
a chamfered surface connecting one of the main surfaces and the side wall surface, the side wall surface and the chamfered surface being disposed at least at an edge surface of an outer circumferential side of the disk-shaped glass substrate, wherein
a surface roughness of one of the side wall surface and the chamfered surface is set such that an arithmetic mean roughness Ra is 0.02 μm or less.

5. The disk-shaped glass substrate according to claim 2 , further comprising
a side wall surface orthogonal to the main surfaces, and
a chamfered surface connecting one of the main surfaces and the side wall surface, the side wall surface and the chamfered surface being disposed at least at an edge surface of an outer circumferential side of the disk-shaped glass substrate, wherein
a surface roughness of one of the side wall surface and the chamfered surface is set such that an arithmetic mean roughness Ra is 0.02 μm or less.

6. The disk-shaped glass substrate according to claim 1 , wherein
an outer diameter is larger than that of a 2.5-inch magnetic-disk glass substrate.

7. The disk-shaped glass substrate according to claim 6 , further comprising
a side wall surface orthogonal to the main surfaces, and
a chamfered surface connecting one of the main surfaces and the side wall surface, the side wall surface and the chamfered surface being disposed at least at an edge surface of an outer circumferential side of the disk-shaped glass substrate, wherein
a surface roughness of one of the side wall surface and the chamfered surface is set such that an arithmetic mean roughness Ra is 0.02 μm or less.

8. The disk-shaped glass substrate according to claim 1 , further comprising
a side wall surface orthogonal to the main surfaces, and
a chamfered surface connecting one of the main surfaces and the side wall surface, the side wall surface and the chamfered surface being disposed at least at an edge surface of an outer circumferential side of the disk-shaped glass substrate, wherein
a surface roughness of one of the side wall surface and the chamfered surface is set such that an arithmetic mean roughness Ra is 0.02 μm or less.

9. A magnetic-disk glass substrate comprising:
a pair of main surfaces,
an outer circumference of the glass substrate having a roundness of 1.3 μm or less,
a first reference circle being obtained with a least squares method from a first outline corresponding to a shape of a lap around the outer circumference of the glass substrate, and the number of peaks of the first outline that project outward in a radial direction from the first reference circle being defined as a first peak count value,
a second reference circle being obtained with a least squares method from a second outline obtained by performing low-pass filtering using a period in which the number of peaks per lap is 150 as a cut-off value on the first outline, and the number of peaks of the second outline that project outward in a radial direction from the second reference circle being defined as a second peak count value,
a ratio of the second peak count value to the first peak count value being from 0.034 to 0.2, and
an arithmetic mean roughness Ra of the main surfaces being 0.15 nm or less.

10. A magnetic disk obtained by forming magnetic layers on the main surfaces of the magnetic-disk glass substrate according to claim 9 .

11. The magnetic-disk glass substrate according to claim 9 , further comprising
a side wall surface orthogonal to the main surfaces, and
a chamfered surface connecting one of the main surfaces and the side wall surface, the side wall surface and the chamfered surface being disposed at least at an edge surface of an outer circumferential side of the magnetic-disk glass substrate, wherein
a surface roughness of one of the side wall surface and the chamfered surface is set such that an arithmetic mean roughness Ra is 0.02 μm or less.

12. A method for manufacturing a magnetic-disk glass substrate comprising:
polishing an outer circumferential edge surface of a disk-shaped glass substrate using a polishing brush; and
polishing main surfaces of the glass substrate while the glass substrate with the polished outer circumferential edge surface is held with a carrier,
the polishing of the outer circumferential edge surface including polishing the outer circumferential edge surface such that
an outer circumference of the disk-shaped glass substrate has a roundness of 1.3 μm or less,
a first reference circle is obtained with a least squares method from a first outline corresponding to a shape of a lap around the outer circumference of the disk-shaped glass substrate, and the number of peaks of the first outline that project outward in a radial direction from the first reference circle is defined as a first peak count value,
a second reference circle is obtained with a least squares method from a second outline obtained by performing low-pass filtering using a period in which the number of peaks per lap is 150 as a cut-off value on the first outline, and the number of peaks of the second outline that project outward in a radial direction from the second reference circle is defined as a second peak count value, and
a ratio of the second peak count value to the first peak count value is from 0.034 to 0.2.

13. A magnetic-disk substrate comprising:
a pair of main surfaces,
an outer circumference of the magnetic-disk substrate having a roundness of 1.3 μm or less,
a first reference circle being obtained with a least squares method from a first outline corresponding to a shape of a lap around the outer circumference of the disk-shaped substrate, and the number of peaks of the first outline that project outward in a radial direction from the first reference circle being defined as a first peak count value,
a second reference circle being obtained with a least squares method from a second outline obtained by performing low-pass filtering using a period in which the number of peaks per lap is 150 as a cut-off value on the first outline, and the number of peaks o

Assignees

• Kashima Ryuichi
• Hoya Corp

Inventors

• Kashima Ryuichi

Classifications

• G11B5/73

  Base layers {, i.e. all non-magnetic layers lying under a lowermost magnetic recording layer, e.g. including any non-magnetic layer in between a first magnetic recording layer and either an underlying substrate or a soft magnetic underlayer} · CPC title

• G11B5/7315

  Physics · mapped topic

• C03C19/00

  Surface treatment of glass, not in the form of fibres or filaments, by mechanical means (sand-blasting, grinding, or polishing glass B24) · CPC title

• G11B5/8404

  manufacturing base layers · CPC title

• G11B5/84

  Processes or apparatus specially adapted for manufacturing record carriers · CPC title