Magnetic recording medium and method of manufacturing the same

• US 8,535,817 B2
• Filed: 08/26/2010
• Issued: 09/17/2013
• Est. Priority Date: 08/27/2009
• Status: Active Grant

• Current Assignee: Fujifilm Corporation (Fujifilm Holdings Corporation)
• Original Assignee: Fujifilm Corporation (Fujifilm Holdings Corporation)
• Inventors: Imaoka, Noriko
• Primary Examiner(s): BERNATZ, KEVIN M
• Application Number:
  US12/869,301
• Publication Number:
  US 20110052908A1
• Time in Patent Office: 1,118 Days
• Field of Search: None
• US Class Current: 428/844
• CPC Class Codes: G11B 5/70 on a base layer
• CPC Class Codes: G11B 5/7085 non-magnetic abrasive particles
• CPC Class Codes: Y10T 428/265 1 mil or less

Abstract

An aspect of the present invention relates to a magnetic recording medium comprising a nonmagnetic layer containing a nonmagnetic powder and a binder and a magnetic layer containing a ferromagnetic powder and a binder in this order on a nonmagnetic support, wherein

• the magnetic layer comprises a nonmagnetic powder of which coefficient of variation CV of a particle size distribution as denoted by the following formula (1):
  CV(%)=σ/φ×100  (1)
  is less than 20 percent, and
• the magnetic layer has a thickness being equal to or less than 0.1 μm and falling within a range of 1.1≦φ/t≦8.0, wherein σ denotes a standard deviation of a particle diameter, φ denotes an average particle diameter of the nonmagnetic powder comprised in the magnetic layer being expressed in μm, and t denotes a thickness of the magnetic layer being expressed in μm.

Claims

1. A magnetic recording medium comprising a nonmagnetic layer containing a nonmagnetic powder and a binder and a magnetic layer containing a ferromagnetic powder and a binder in this order on a nonmagnetic support, wherein

the magnetic layer comprises a nonmagnetic powder of which coefficient of variation CV of a particle size distribution as denoted by the following formula (1):

CV(%)=σ

/φ

×

100 

 

(1)

is less than 20 percent,

the nonmagnetic powder contained in the magnetic layer is silica powder,

the magnetic layer further comprises an inorganic powder other than the silica powder, with a Mohs'"'"' hardness of equal to or higher than 6,

the magnetic layer contains no carbon black, and

the magnetic layer has a thickness being equal to or less than 0.1 μ

m and falling within a range of 1.1≦

φ

/t≦

8.0, wherein σ

denotes the standard deviation of the particle diameter, φ

denotes the average particle diameter of the nonmagnetic powder comprised in the magnetic layer expressed in μ

m, and t denotes the thickness of the magnetic layer expressed in μ

m.

2. The magnetic recording medium according to claim 1, wherein the silica powder comprised in the magnetic layer is composed of silica colloidal particles.

3. The magnetic recording medium according to claim 1, wherein

the average particle diameter φ

of the nonmagnetic powder comprised in the magnetic layer ranges from 0.10 to 0.20 μ

m, and

the magnetic layer comprises the nonmagnetic powder in a quantity ranging from 1.5 to 3.5 weight parts, per 100 weight parts of the ferromagnetic powder.

4. The magnetic recording medium according to claim 1, wherein the density of protrusions on the surface of the magnetic layer, as measured by an atomic force microscope, satisfies the following equation (3):

Density of protrusions equal to or higher than 25 nm in height/density of protrusions equal to or higher than 15 nm in height <

0.1 (3).

5. The magnetic recording medium according to claim 1, wherein the maximum particle diameter of the nonmagnetic powder comprised in the magnetic layer satisfies the following equation (2):

Maximum particle diameter being expressed in μ

m<

φ

+10σ

 

 

(2).

6. The magnetic recording medium according to claim 1, wherein the average degree of circularity of the nonmagnetic powder comprised in the magnetic layer is greater than 0.8 but equal to or less than 1.0.

7. The magnetic recording medium according to claim 1, wherein the nonmagnetic layer is a radiation-cured layer.

8. A method of manufacturing a magnetic recording medium, wherein

the magnetic recording medium is the magnetic recording medium according to claim 1, and

the method comprises forming a magnetic layer with a magnetic layer coating liquid comprising a ferromagnetic powder, a binder, and a nonmagnetic powder of which coefficient of variation CV of a particle size distribution as denoted by the following formula (1) is less than 20 percent:

CV(%)=σ

/φ

×

100 

 

(1)

wherein σ

denotes a standard deviation of a particle diameter, and φ

denotes an average particle diameter of the nonmagnetic powder comprised in the magnetic layer coating liquid being expressed in μ

m.

9. The method of manufacturing a magnetic recording medium according to claim 8, which comprises preparing the magnetic layer coating liquid by mixing a first liquid comprising a ferromagnetic powder, a binder, and an organic solvent with a second liquid comprising the nonmagnetic powder and an organic solvent.

10. The method of manufacturing a magnetic recording medium according to claim 9, wherein the second liquid is a colloidal liquid.

11. The method of manufacturing a magnetic recording medium according to claim 10, wherein the colloidal liquid is a silica sol.

12. The method of manufacturing a magnetic recording medium according to claim 9, wherein the organic solvent comprised in the first liquid has a compatibility with the organic solvent comprised in the second liquid.

13. The method of manufacturing a magnetic recording medium according to claim 12, wherein the organic solvent comprised in the first liquid and the organic solvent comprised in the second liquid are respectively selected from the group consisting of methyl ethyl ketone, cyclohexanone, and mixed solvents thereof.

14. The method of manufacturing a magnetic recording medium according to claim 8, which comprises preparing the magnetic layer coating liquid by adding the nonmagnetic powder to a first liquid comprising a ferromagnetic powder, a binder, and an organic solvent.

15. The method of manufacturing a magnetic recording medium according to claim 14, wherein the nonmagnetic powder is dispersible in the organic solvent comprised in the first liquid.

16. The method of manufacturing a magnetic recording medium according to claim 8, which comprises:

coating a nonmagnetic layer coating liquid comprising a nonmagnetic powder and a binder on a nonmagnetic support to form a coating layer;

subjecting the coating layer to a curing treatment to form a nonmagnetic layer; and

then

coating the magnetic layer coating liquid on the nonmagnetic layer formed.

17. The method of manufacturing a magnetic recording medium according to claim 16, wherein the binder comprised in the nonmagnetic layer coating liquid comprises a radiation-curable resin.