Magnetic recording medium

• US 20080057351A1
• Filed: 03/29/2007
• Published: 03/06/2008
• Est. Priority Date: 03/29/2006
• Status: Abandoned Application

• Current Assignee: Fujifilm Corporation (Fujifilm Holdings Corporation)
• Original Assignee: Fujifilm Corporation (Fujifilm Holdings Corporation)
• Inventors: Takahashi, Masatoshi, Meguro, Katsuhiko, Harasawa, Takeshi
• Application Number:
  US11/730,176
• Publication Number:
  US 20080057351A1
• Time in Patent Office: Days
• US Class Current: 428/840
• CPC Class Codes: G11B 5/70678 Ferrites
• CPC Class Codes: G11B 5/714 characterised by the dimension of the magnetic particles
• CPC Class Codes: G11B 5/735 characterised by the back layer magnetic recording media substrates G11B5/739
• CPC Class Codes: G11B 5/7356 comprising non-magnetic particles in the back layer, e.g. particles of TiO2, ZnO or SiO2

Abstract

A magnetic recording medium, which comprises: a backcoat layer; a nonmagnetic support; a nonmagnetic layer; and a magnetic layer, in this order, wherein the backcoat layer has Tg of from 65 to 95° C., and the binder constituting the backcoat layer satisfies the following requirements: (1) the binder comprises a vinyl chloride-based resin (PVC) and a polyurethane resin (PU); (2) PVC has a solubility parameter of from 9 to 11 (cal·cm³)^1/2, Tg of from 65 to 95° C. and Mw of from 5000 to 25000; (3) a ratio of PVC to the total mass of PVC and PU is from 10 to 60% by mass; (4) PU has a solubility parameter of from 9.5 to 11.5 (cal·cm⁻³)^1/2, Tg of from 80 to 110° C. and Mw of from 20000 to 60000; and (5) a ratio of PU to the total mass of PVC and PU is from 90 to 30% by mass.

Claims

1. A magnetic recording medium, which comprises:

a backcoat layer comprising a first binder;

a nonmagnetic support;

a nonmagnetic layer comprising a nonmagnetic powder and a second binder; and

a magnetic layer comprising a ferromagnetic powder and a third binder, in this order,

wherein the backcoat layer has a glass transition temperature of from 65 to 95°

C., and

the first binder satisfies all of the following requirements (1) to (5);

(1) the first binder comprises a vinyl chloride-based resin and a polyurethane resin as main components;

(2) the vinyl chloride-based resin has a solubility parameter of from 9 to 11 (cal·

cm<sup>−

3</sup>)^1/2, a glass transition temperature of from 65 to 95°

C. and a weight-average molecular weight of from 5000 to 25000;

(3) a ratio of the vinyl chloride-based resin to the total mass of the vinyl chloride-based resin and the polyurethane resin is from 10 to 60% by mass;

(4) the polyurethane resin has a solubility parameter of from 9.5 to 11.5 (cal·

cm<sup>−

3</sup>)^1/2, a glass transition temperature of from 80 to 110°

C. and a weight-average molecular weight of from 20000 to 60000; and

(5) a ratio of the polyurethane resin to the total mass of the vinyl chloride-based resin and the polyurethane resin is from 90 to 30% by mass.

2. The magnetic recording medium according to claim 1,

wherein the ferromagnetic powder is a ferromagnetic hexagonal ferrite powder having an average tabular diameter of from 10 to 50 nm, an iron nitride powder having an average particle diameter of from 5 to 25 nm or a ferromagnetic metal powder having an average major axis length of from 10 to 100 nm.

3. The magnetic recording medium according to claim 1,

wherein the backcoat layer further comprises at least one of a carbon black and an inorganic powder.

4. The magnetic recording medium according to claim 1,

wherein the backcoat layer has a thickness of from 0.1 to 1.0 μ

m.

5. The magnetic recording medium according to claim 1,

wherein the backcoat layer has a glass transition temperature of from 70 to 90°

C.

6. The magnetic recording medium according to claim 1,

wherein the vinyl chloride-based resin has a solubility parameter of from 9.5 to 10.5 (cal·

cm<sup>−

1</sup>)^1/2.

7. The magnetic recording medium according to claim 1,

wherein the vinyl chloride-based resin has a glass transition temperature of from 70 to 90°

C.

8. The magnetic recording medium according to claim 1,

wherein the vinyl chloride-based resin has a weight-average molecular weight of from 10000 to 20000.

9. The magnetic recording medium according to claim 1,

wherein the polyurethane resin has a solubility parameter of from 10.0 to 11.0 (cal·

cm<sup>−

3</sup>)^1/2.

10. The magnetic recording medium according to claim 1,

wherein the polyurethane resin has a glass transition temperature of from 80 to 95°

C.

11. The magnetic recording medium according to claim 1,

wherein the vinyl chloride-based resin contains at least one of:

from 2 to 7 eq/ton of at least one polar group selected from the group consisting of —

SO₃M, —

OSO₃M, —

PO(OM)₂, —

OPO(OM)₂ and —

COOM, wherein M represents a hydrogen atom, an alkaline metal or an ammonium salt; and

from 5 to 50 eq/ton of at least one polar group selected from the group consisting of —

CONR₁R₂, —

NR₁R₂ and —

NR₁R₂R₃⁺, wherein R₁, R₂ and R₃ each independently represents a hydrogen atom or an alkyl group.

12. The magnetic recording medium according to claim 1,

wherein the polyurethane resin contains at least one of:

from 2 to 7 eq/ton of at least one polar group selected from the group consisting of —

SO₃M, —

OSO₃M, —

PO(OM)₂, —

OPO(OM)₂ and —

COOM, wherein M represents a hydrogen atom, an alkaline metal or an ammonium salt; and

from 5 to 50 eq/ton of at least one polar group selected from the group consisting of —

CONR₁R₂, —

NR₁R₂ and —

NR₁R₂R₃⁺, wherein R₁, R₂ and R₃ each independently represents a hydrogen atom or an alkyl group.

13. The magnetic recording medium according to claim 1,

wherein the polyurethane resin contains 2 to 40 OH—

groups per molecule.