Magnetic recording medium

Abstract

A magnetic recording medium including: a back coat layer; a nonmagnetic support; and coated layers including: a nonmagnetic layer containing nonmagnetic powder and a binder; and a magnetic layer containing ferromagnetic powder and a binder, so that the back coat layer, the nonmagnetic support, the nonmagnetic layer and the magnetic layer are provided in this order, wherein the ferromagnetic powder is ferromagnetic hexagonal ferrite powder having an average tabular size of less than 30 nm, and a central plane surface roughness Ra of the magnetic layer, a central plane surface roughness Ra of the back coat layer, a glass transition point of the coated layers, a glass transition point of the back coat layer and a ratio of a Young's modulus of the magnetic layer to a Young's modulus of the back coat layer are defined herein.

Description

Claims

1. A magnetic recording medium comprising: a back coat layer;a nonmagnetic support; andcoated layers including: a nonmagnetic layer containing nonmagnetic powder and a binder; and a magnetic layer containing ferromagnetic powder and a binder, so that the back coat layer, the nonmagnetic support, the nonmagnetic layer and the magnetic layer are provided in this order,wherein the ferromagnetic powder is ferromagnetic hexagonal ferrite powder having an average tabular size of less than 30 nm, the magnetic layer has a central plane surface roughness Ra of from 1.0 to 2.5 nm, the back coat layer has a central plane surface roughness Ra of from 2.0 to 4.0 nm, the coated layers has a glass transition point of from 75 to 100° C., the back coat layer has a glass transition point of from 75 to 100° C., and a ratio of a Young's modulus of the magnetic layer to a Young's modulus of the back coat layer is from 0.8 to 1.20.

2. The magnetic recording medium as claimed in claim 1, wherein the ferromagnetic hexagonal ferrite powder has an average tabular size of from 10 to 29 nm.

3. The magnetic recording medium as claimed in claim 1, wherein the ferromagnetic hexagonal ferrite powder has an average tabular size of from 15 to 25 nm.

4. The magnetic recording medium as claimed in claim 1, wherein the magnetic layer has a central plane surface roughness Ra of from 1.2 to 2.3 nm.

5. The magnetic recording medium as claimed in claim 1, wherein the magnetic layer has a central plane surface roughness Ra of from 1.4 to 2.2 nm.

6. The magnetic recording medium as claimed in claim 1, wherein the back coat layer has a central plane surface roughness Ra of from 2.5 to 4.0 nm.

7. The magnetic recording medium as claimed in claim 1, wherein the back coat layer has a central plane surface roughness Ra of from 3.0 to 3.6 nm.

8. The magnetic recording medium as claimed in claim 1, wherein the coated layers has a glass transition point of from 80 to 95° C.

9. The magnetic recording medium as claimed in claim 1, wherein the coated layers has a glass transition point of from 85 to 95° C.

10. The magnetic recording medium as claimed in claim 1, wherein the back coat layer has a glass transition point of from 80 to 95° C.

11. The magnetic recording medium as claimed in claim 1, wherein the back coat layer has a glass transition point of from 85 to 95° C.

12. The magnetic recording medium as claimed in claim 1, wherein the ratio of a Young's modulus of the magnetic layer to a Young's modulus of the back coat layer is from 0.85 to 1.15.

13. The magnetic recording medium as claimed in claim 1, wherein the ratio of a Young's modulus of the magnetic layer to a Young's modulus of the back coat layer is from 0.90 to 1.10.

14. The magnetic recording medium as claimed in claim 1, wherein the back coat layer contains carbon black and inorganic powder.

15. The magnetic recording medium as claimed in claim 1, wherein the back coat layer has a thickness of 0.9 μm or less.

16. The magnetic recording medium as claimed in claim 1, wherein the back coat layer has a thickness of from 0.1 to 0.7 μm.

17. The magnetic recording medium as claimed in claim 1, wherein the nonmagnetic support contains polyester.

18. The magnetic recording medium as claimed in claim 1, wherein the nonmagnetic support has a thickness of from 3 to 80 μm.