Magnetic recording medium
View Patent ↗Multilayer magnetic recording medium which is suitable for high recording densities and the recording of digital data, has very good electromagnetic recording properties and good surface smoothness and can absorb a large amount of lubricant in the lower layer and has at least one upper magnetic recording layer less than 0.5 μm thick and at least one lower layer which contains a magnetically soft pigment.
1. A magnetic recording medium containing an upper layer, and a lower layer, said lower layer including magnetically soft pigment which is selected from γ-Fe 2 O 3 , Fe 3 O 4 , and a solid solution of these components and has a mean crystallite size of less than 10 nm, and a coercive force H c of less than 0.7 kA/m.
2. The magnetic recording medium as claimed in claim 1 , wherein the magnetically soft pigment has a mean crystallite size of less than 8 nm as a pigment in a lower layer of a magnetic recording medium.
3. The magnetic recording medium us claimed in claim 1 , wherein the lower layer has a coercive force H c of less than 0.3 kA/m.
4. The magnetic recording medium as claimed in claim 1 , wherein the isotropic magnetically soft pigment has a specific surface area determined on the basis, of BET method is more than 100 m 2 /g.
5. The magnetic recording medium as claimed in claim 4 , wherein the isotropic magnetically soft pigment has a specific surface area determined on the basis of BET method is more than 120 m 2 /g.
6. A multilayer magnetic recording medium which comprises, on a nonmagnetic substrate, at least one upper binder-containing magnetic recording layer which has a thickness of less than 0.5 μm and contains finely divided magnetic pigment having a coercive force H c of 100-250 kA/m, at least one lower binder-containing layer which contains an isotropic magnetically soft pigment which is selected from γ-Fe 2 O 3 , Fe 3 O 4 or a solid solution of these components and has a mean crystallite size of less than 10 nm, and the lower layer has a coercive force H c of less than 0.7 kA/m.
7. A magnetic recording medium as claimed in claim 6 , wherein the coercive force H c of the pigment in the upper layer is from 130 to 220 kA/m.
8. A magnetic recording medium as claimed in claim 6 , wherein the magnetic pigment in the upper layer is a metal pigment or metal alloy pigment.
9. A magnetic recording medium as claimed in claim 6 , wherein the magnetic pigment in the upper layer is a hexagonal ferrite pigment or a Co-modified γ-Fe 2 O 3 , Co-modified Fe 3 O 4 or a solid solution of these components.
10. A magnetic recording medium as claimed in claim 6 , wherein the isotropic magnetically soft pigment in the lower layer has a mean crystallite size of less than 6 nm.
11. A magnetic recording medium as claimed in claim 6 , wherein the lower layer has a coercive force H c of less than 0.3 kA/m.
12. A magnetic recording medium as claimed in claim 6 , wherein the amount of the magnetically soft pigment in the lower layer is from 25 to 85% by weight, based on the weight of all pigments in the lower layer.
13. A magnetic recording medium as claimed in claim 6 , wherein the amount of the magnetically soft pigment in the lower layer is from 35 to 78% by weight, based on the weight of all pigments in the lower layer.
14. A magnetic recording medium as claimed in claim 6 , wherein the magnetically soft pigment in the lower layer has been surface-treated with an aluminum compound or a silicon compound or a mixture of the two compounds.
15. A magnetic recording medium as claimed in claim 6 , wherein the magnetically soft pigment in the lower layer is spherical or amorphous.
16. A magnetic recording medium as claimed in claim 6 , wherein the lower layer contains at least one nonmagnetic pigment in addition to the magnetically soft pigment.
17. A magnetic recording medium as claimed in claim 16 , wherein the nonmagnetic pigment is acicular, having a mean longitudinal axis of from 5 to 200 nm, or spherical or amorphous, having a mean particle size of from 5 to 180 nm.
18. A magnetic recording medium as claimed in claim 16 , wherein the nonmagnetic pigment is α-Fe 2 O 3 .
19. A magnetic recording medium as claimed in claim 16 , wherein the nonmagnetic pigment is carbon black.
20. A magnetic recording medium as claimed in claim 16 , wherein the nonmagnetic pigment is a mixture of carbon black and α-Fe 2 O 3 .
21. The magnetic recording medium as claimed in claim 6 , wherein the isotropic magnetically soft pigment has a specific surface area determined on the basis of BET method is more than 100 m 2 /g.
22. The magnetic recording medium as claimed in claim 21 , wherein the isotropic magnetically soft pigment has a specific surface area determined on the basis of BET method is more than 120 m 2 /g.
23. A magnetic tap, magnetic card or floppy disk comprising a multilayer magnetic recording medium which comprises, on a nonmagnetic substrate, at least one upper binder-containing magnetic recording layer which has a thickness of less than 0.5 μm and contains a finely divided magnetic pigment having a coercive force H c of 100-250 kA/m, and at least one lower binder-containing layer which contains an isotropic magnetically soft pigment which is selected from γ-Fe 2 O 3 , Fe 3 O 4 , or a solid solution of these components and has a mean crystallite size of less than 10 nm, end the lower layer has a coercive force H c of less than 0.7 kA/m.
24. The magnetic recording medium as claimed in claim 23 , wherein the lower layer has a coercive force H c of less than 0.3 kA/m.