Magnetic powder for magnetic recording medium

Patent metadata

Field	Value
Publication number	US-11894171-B2
Application number	US-201916683301-A
Country	US
Kind code	B2
Filing date	Nov 14, 2019
Priority date	Nov 16, 2018
Publication date	Feb 6, 2024
Grant date	Feb 6, 2024

Abstract

Provided is an Al-containing hexagonal ferrite magnetic powder which produces an excellent durability-improving effect on a magnetic recording medium, wherein uniform pulverization of the magnetic powder can be easily achieved by dispersion treatment in preparation of a magnetic coating material even in cases where the magnetic powder has a small primary particle size or has a composition which is likely to produce hard secondary particles. The magnetic powder for a magnetic recording medium is an Al-containing hexagonal ferrite magnetic powder having an Al/Fe molar ratio of 0.030 to 0.200, and has a particle size distribution in which the volume ratio of particles having a particle size of 30 μm or more as measured by a laser diffraction particle size distribution analyzer with a dispersion pressure of 100 kPa is 5.0% or less, and an activation volume Vact of 1800 nm3 or less.

First claim

What is claimed is:

1. Magnetic powder for a magnetic recording medium, which is an Al-containing hexagonal ferrite magnetic powder having an Al/Fe molar ratio of 0.030 to 0.200, and which has a particle size distribution in which the volume ratio of particles having a particle size of 30 μm or more as measured by a laser diffraction particle size distribution analyzer with a dispersion pressure of 100 kPa is 5.0% or less, and an activation volume Vact of 1800 nm 3 or less,
wherein a BET specific surface area according to the BET single-point method is from 50 to 130 m 2 /g,
wherein D90 (500) is 7.0 μm or more and 11.4 μm or less,
wherein D90 (100) is 7.6 μm or more and 20.0 μm or less, and
wherein D90 (100) represents the cumulative 90% particle size (μm) on a volume basis as measured with a dispersion pressure of 100 kPa, and D90 (500) represents the cumulative 90% particle size (μm) on a volume basis as measured with a dispersion pressure of 500 kPa.

2. The magnetic powder for a magnetic recording medium according to claim 1 , whose particle size distribution further satisfies the following Formula (1):
D 90 (100) /D 90 (500) <1.30  (1).

3. The magnetic powder for a magnetic recording medium according to claim 1 , wherein the activation volume Vact is 1100 to 1800 nm 3 .

Assignees

• Dowa Electronics Materials Co Ltd
• Fujifilm Corp

Inventors

• Omoto Hirohisa
• Kaneda Shuji
• Shiki Satoshi
• Suzuki Hiroyuki
• Tada Toshio

Classifications

• H01F1/348 Primary

  Hexaferrites with decreased hardness or anisotropy, i.e. with increased permeability in the microwave (GHz) range, e.g. having a hexagonal crystallographic structure · CPC title

• C09C1/24 Primary

  Oxides of iron · CPC title

• H01F1/11

  in the form of particles {(for magnetic record carriers G11B5/70626)} · CPC title

• C01P2002/76

  by a space-group or by other symmetry indications · CPC title

• C01P2004/51

  Particles with a specific particle size distribution · CPC title