Magnetic recording medium having controlled protrusion characteristics

Patent metadata

Field	Value
Publication number	US-11250880-B2
Application number	US-201816627600-A
Country	US
Kind code	B2
Filing date	Apr 13, 2018
Priority date	Jun 30, 2017
Publication date	Feb 15, 2022
Grant date	Feb 15, 2022

Abstract

A magnetic recording medium includes: a substrate that is long in shape; and a magnetic layer containing magnetic powder and a binder. The glass transition point of the binder is not lower than 75° C. In a case where atomic force microscope observation images in a 10 μm×10 μm rectangular shape are acquired at five locations randomly selected from the surface on the side of the magnetic layer, any linear protrusion that is 3 nm to 20 nm in height, is 0.3 μm to 1.0 μm in width, and extends across two sides of the observation image does not exist in the observation images of four locations among the acquired observation images of the five locations.

First claim

The invention claimed is:

1. A magnetic recording medium comprising:
a substrate that is long in shape; and
a magnetic layer including a magnetic powder and a binder, wherein
a glass transition point of the binder is not lower than 75° C., and
in a case where atomic force microscope observation images in a 10 μm×10 μm square shape are acquired at five locations randomly selected from a surface on a side of the magnetic layer, any linear protrusion that is 3 nm to 20 nm in height, is 0.3 μm to 1.0 μm in width, and extends across two sides of an observation image does not exist in the observation images of four locations among the observation images of the five locations that are acquired.

2. The magnetic recording medium according to claim 1 , wherein an arithmetic average roughness Ra of the surface is not higher than 1.5 nm.

3. The magnetic recording medium according to claim 1 , wherein an average thickness of the magnetic recording medium is not greater than 5.0 μm.

4. The magnetic recording medium according to claim 1 , wherein an average thickness of the magnetic recording medium is not greater than 4.5 μm.

5. The magnetic recording medium according to claim 1 , further comprising
a nonmagnetic layer disposed between the substrate and the magnetic layer.

6. The magnetic recording medium according to claim 5 , wherein a sum of an average thickness of the magnetic layer and an average thickness of the nonmagnetic layer is not greater than 0.7 μm.

7. The magnetic recording medium according to claim 5 , wherein a sum of an average thickness of the magnetic layer and an average thickness of the nonmagnetic layer is not greater than 0.5 μm.

8. The magnetic recording medium according to claim 5 , wherein
the nonmagnetic layer includes acicular nonmagnetic particles, and
an average long axis length of the nonmagnetic particles is not smaller than 70 nm.

9. The magnetic recording medium according to claim 5 , wherein
the nonmagnetic layer includes carbon, and
an area ratio of the carbon in the nonmagnetic layer is not lower than 80%.

10. The magnetic recording medium according to claim 1 , wherein the magnetic powder includes particles including c iron oxide or barium ferrite.

11. The magnetic recording medium according to claim 1 , wherein a linear recording density is not lower than 520 kbpi.

12. The magnetic recording medium according to claim 1 , wherein a track pitch is not wider than 2.0 μm.

13. The magnetic recording medium according to claim 1 , wherein the magnetic recording medium is reproduced by a reproducing head having a width not greater than 1.0 μm.

14. The magnetic recording medium according to claim 1 , wherein the magnetic recording medium is reproduced by a tunnel magnetoresistive head.

15. The magnetic recording medium according to claim 1 , wherein any linear protrusion does not exist in the observation images of the five locations that are acquired.

Assignees

• Sony Corp

Inventors

• Miura Toshiaki
• Abe Satoru
• Kamoshita Yuuko
• Yoshida Riku

Classifications

• G11B5/70 Primary

  on a base layer · CPC title

• G11B5/7368

  Non-polymeric layer under the lowermost magnetic recording layer (base layers having a non-magnetic layer under a soft magnetic layer G11B5/736; magnetic recording media substrates G11B5/739) · CPC title

• G11B5/68

  comprising one or more layers of magnetisable material homogeneously mixed with a bonding agent · CPC title

• G11B5/70678

  Ferrites · CPC title

• G11B5/7334

  Base layer characterised by composition or structure · CPC title