METHOD OF MANUFACTURING HEXAGONAL FERRITE MAGNETIC POWDER, MAGNETIC RECORDING MEDIUM AND METHOD OF MANUFACTURING THE SAME

• US 20120244387A1
• Filed: 03/22/2012
• Published: 09/27/2012
• Est. Priority Date: 03/25/2011
• Status: Active Grant

• Current Assignee: Fujifilm Corporation (Fujifilm Holdings Corporation)
• Original Assignee: Fujifilm Corporation (Fujifilm Holdings Corporation)
• Inventors: MORI, Masahiko, SUZUKI, Hiroyuki
• Granted Patent: US 8,840,802 B2
• Time in Patent Office: Days
• US Class Current: 428/842.8
• CPC Class Codes: G11B 5/70678 Ferrites
• CPC Class Codes: G11B 5/842 Coating a support with a liquid magnetic dispersion
• CPC Class Codes: H01F 1/11 in the form of particles for magnetic record carriers G11B5/70626

Abstract

An aspect of the present invention relates to a method of manufacturing hexagonal ferrite magnetic powder. The method of manufacturing hexagonal ferrite magnetic powder comprises wet processing hexagonal ferrite magnetic particles obtained following acid treatment in a water-based solvent to prepare an aqueous magnetic liquid satisfying relation (1) relative to an isoelectric point of the hexagonal ferrite magnetic particles: pH0−pH*≧2.5, wherein, pH0 denotes the isoelectric point of the hexagonal ferrite magnetic particles and pH* denotes a pH of the aqueous magnetic liquid, which is a value of equal to or greater than 2.0, adding a surface-modifying agent comprising an alkyl group and a functional group that becomes an anionic group in the aqueous magnetic liquid to the aqueous magnetic liquid to subject the hexagonal ferrite magnetic particles to a surface-modifying treatment, and removing the water-based solvent following the surface-modifying treatment to obtain hexagonal ferrite magnetic particles.

Claims

1. A method of manufacturing hexagonal ferrite magnetic powder, which comprises:

preparing a melt by melting a starting material mixture comprising a hexagonal ferrite-forming component and a glass-forming component and rapidly cooling the melt to obtain a solidified product,

heating the solidified product to precipitate hexagonal ferrite magnetic particles and crystallized glass components in the solidified product,

subjecting the solidified product to an acid treatment following the heating to remove the glass components by dissolution,

wet processing the hexagonal ferrite magnetic particles obtained following the acid treatment in a water-based solvent to prepare an aqueous magnetic liquid satisfying relation (1) relative to an isoelectric point of the hexagonal ferrite magnetic particles;

pH0−

pH*≧

2.5 

 

(1)

where in relation (1), pH0 denotes the isoelectric point of the hexagonal ferrite magnetic particles and pH* denotes a pH of the aqueous magnetic liquid, which is a value of equal to or greater than 2.0,

adding a surface-modifying agent comprising an alkyl group and a functional group that becomes an anionic group in the aqueous magnetic liquid to the aqueous magnetic liquid to subject the hexagonal ferrite magnetic particles to a surface-modifying treatment, and

removing the water-based solvent following the surface-modifying treatment to obtain hexagonal ferrite magnetic particles.

2. The method of manufacturing hexagonal ferrite magnetic powder according to claim 1, wherein the starting material mixture comprises Al.

3. The method of manufacturing hexagonal ferrite magnetic powder according to claim 1, wherein the starting material mixture comprises 1.0 to 10.0 mole percent of Al, based on Al₂O₃ conversion, relative to a total of the starting material mixture based on oxide conversion.

4. The method of manufacturing hexagonal ferrite magnetic powder according to claim 1, wherein the surface-modifying agent is selected from the group consisting of a compound denoted by general formula (I) and a compound denoted by general formula (II):

5. The method of manufacturing hexagonal ferrite magnetic powder according to claim 1, wherein the wet processing comprises pH adjustment with addition of acid.

6. The method of manufacturing hexagonal ferrite magnetic powder according to claim 1, wherein a functional group that becomes an anionic group in the magnetic liquid is a sulfonic acid group or a sulfonate group.

7. The method of manufacturing hexagonal ferrite magnetic powder according to claim 1;

wherein, in general formula (I), either X¹ or X² denotes the functional group that becomes an anionic group in the magnetic liquid, and the other denotes a hydrogen atom.

8. Hexagonal ferrite magnetic powder manufactured by the manufacturing method according to claim 1.

9. A method of manufacturing a magnetic recording medium, which comprises:

manufacturing hexagonal ferrite magnetic powder by the method according to claim 1,

dispersing the hexagonal ferrite magnetic powder together with an organic solvent and a binder to prepare a magnetic coating material, and

forming a magnetic layer with the magnetic coating material that has been prepared.

10. The method of manufacturing a magnetic recording medium according to claim 9, wherein the organic solvent comprises a ketone solvent.

11. A magnetic recording medium manufactured by the manufacturing method according to claim 9.