Magnetic recording medium

• US 5,645,917 A
• Filed: 04/24/1992
• Issued: 07/08/1997
• Est. Priority Date: 04/25/1991
• Status: Expired due to Term

• Current Assignee: Fujifilm Corporation (Fujifilm Holdings Corporation)
• Original Assignee: Fuji Photo Film Co Limited (Fujifilm Holdings Corporation)
• Inventors: Saito, Shinji, Hayakawa, Satoru, Ejiri, Kiyomi, Inaba, Hiroo
• Primary Examiner(s): KILIMAN, LESZEK B
• Application Number:
  US07/873,201
• Time in Patent Office: 1,901 Days
• Field of Search: 428/141, 428/473.5, 428/694, 428/900, 428/323, 428/336, 428/329, 428/694 B, 428/694 BS, 428/694 BR, 428/694 BN, 428/694 BA, 428/694 BH , 428/694 BM
• US Class Current: 428/141
• CPC Class Codes: G11B 5/70 on a base layer
• CPC Class Codes: G11B 5/716 characterised by two or more magnetic layers
• CPC Class Codes: G11B 5/733 characterised by the addition of non-magnetic particles base layers having a non-magnetic layer under a soft magnetic layer G11B5/736; magnetic recording media substrates G11B5/739
• CPC Class Codes: G11B 5/842 Coating a support with a liquid magnetic dispersion
• CPC Class Codes: G11B 5/848 Coating a support with a magnetic layer by extrusion
• CPC Class Codes: Y10S 428/90 Magnetic feature
• CPC Class Codes: Y10T 428/12472 Microscopic interfacial wave or roughness
• CPC Class Codes: Y10T 428/24355 Continuous and nonuniform or irregular surface on layer or component [e.g., roofing, etc.]
• CPC Class Codes: Y10T 428/24942 including components having same physical characteristic in differing degree
• CPC Class Codes: Y10T 428/25 Web or sheet containing structurally defined element or component and including a second component containing structurally defined particles
• CPC Class Codes: Y10T 428/253 Cellulosic [e.g., wood, paper, cork, rayon, etc.]
• CPC Class Codes: Y10T 428/256 Heavy metal or aluminum or compound thereof
• CPC Class Codes: Y10T 428/257 Iron oxide or aluminum oxide
• CPC Class Codes: Y10T 428/258 Alkali metal or alkaline earth metal or compound thereof
• CPC Class Codes: Y10T 428/259 Silicic material
• CPC Class Codes: Y10T 428/265 1 mil or less
• CPC Class Codes: Y10T 428/269 including synthetic resin or polymer layer or component
• CPC Class Codes: Y10T 428/31551 Of polyamidoester [polyurethane, polyisocyanate, polycarbamate, etc.]
• CPC Class Codes: Y10T 428/31721 Of polyimide
• CPC Class Codes: Y10T 428/31855 Of addition polymer from unsaturated monomers

Abstract

A magnetic recording medium is disclosed comprising a non-magnetic support having provided thereon at least a lower non-magnetic layer comprising a binder having dispersed therein a non-magnetic powder and an upper magnetic layer comprising a binder having dispersed therein a ferromagnetic powder which has been coated on said lower non-magnetic layer while the lower non-magnetic layer is wet, wherein the upper magnetic layer has an average dry thickness (d) of not more than 1.0 μm and an average thickness variation (.sup.Δ d) at the interface between the upper magnetic layer and lower non-magnetic layer is not more than d/2. The magnetic recording medium exhibits excellent electromagnetic characteristics, running properties, and durability.

Claims

1. A magnetic recording medium comprising a non-magnetic support having provided thereon at least one lower non-magnetic layer comprising a binder having dispersed therein a non-magnetic powder and at least one upper magnetic layer comprising a binder having dispersed therein a ferromagnetic powder which is coated while said lower non-magnetic layer is wet, wherein said upper magnetic layer has an average dry thickness (d) of not more than 1.0 μ

m, and an average thickness variation (.sup.Δ

d) at the interface between said upper magnetic layer and lower non-magnetic layer is not more than d/2.

2. A magnetic recording medium as claimed in claim 1, wherein said upper magnetic layer has an average dry thickness (d) of from λ

/4 to 3λ

, wherein λ

is a shortest recording wavelength, and a surface roughness (Ra) of not more than λ

/50.

3. A magnetic recording medium as claimed in claim 1, wherein said upper magnetic layer has a squared average surface roughness R_rms, as measured with a scanning tunnel microscope, satisfying a relationship:

30≦

d/R_rms, wherein d is an average dry thickness of the upper magnetic layer.

4. A magnetic recording medium as claimed in claim 1, wherein said medium has a percent thermal shrinkage of not more than 0.4% after storage at 70°

C. for 48 hours.

5. A magnetic recording medium as claimed in claim 4, wherein said lower non-magnetic layer has a dry thickness 1 to 30 times that of said upper magnetic layer, and a difference determined by subtracting a powder volume ratio of said upper magnetic layer from that of said lower non-magnetic layer is within a range of from -5% to +20%.

6. A magnetic recording medium as claimed in claim 1, wherein said medium has a ratio of stiffness in coating direction (machine direction) (SMD) to stiffness in width direction (transverse direction) (STD), SMD/STD, of from 1.0 to 1.9.

7. A magnetic recording medium as claimed in claim 6, wherein said non-magnetic powder in said lower non-magnetic layer contains a spherical polyhedral inorganic powder having a Mohs hardness of 6 or higher and an average primary particle size of not more than 0.15 μ

m.

8. A magnetic recording medium as claimed in claim 1, wherein said non-magnetic powder in said lower non-magnetic layer is an inorganic powder having a Mohs hardness of not less than 3 and an average particle size ranging from 1/2 to 4 times the crystallite size of an acicular ferromagnetic powder in said upper magnetic layer.

9. A magnetic recording medium as claimed in claim 1, wherein said non-magnetic powder in said lower non-magnetic layer is an inorganic powder having a Mohs hardness of not less than 3 and an average particle size of not more than 1/3 the major axis length of an acicular ferromagnetic powder in said upper magnetic layer.

10. A magnetic recording medium as claimed in claim 1, wherein said upper magnetic layer satisfies at least one of conditions that a surface roughness (Ra) is from 1 to 5 nm, a squared average surface roughness R_rms is from 1.3 to 6 nm, and a P-V value is not more than 80 nm, as measured with an interference surface roughness testor 3d-MIRAU.

11. A magnetic recording medium as claimed in claim 1, wherein said medium has a stiffness in flexure (loop stiffness) of from 40 to 300 mg with its total thickenss being more than 11.5 μ

m, or of from 20 to 90 mg with its total thickness being 10.5±

1 μ

m, or of from 10 to 70 mg with its total thickness being thinner than 9.5 μ

m.

12. A magnetic recording medium as claimed in claim 1, wherein said magnetic layer has an elongation at cracking of not more than 20%.

13. A magnetic recording medium as claimed in claim 1, wherein said upper magnetic layer has a surface Cl/Fe ESCA spectrum α

of from 0.3 to 0.6, and an N/Fe spectrum β

of from 0.03 to 0.12.

14. A magnetic recording medium as claimed in claim 1, wherein the surface of said upper magnetic layer has a wearability with a steel ball of from 0.7×

10^-5 to 5×

10^-5 mm³ as measured at 23°

C. and 70% RH.

15. A magnetic recording medium as claimed in claim 1, wherein a surface of said upper magnetic layer has not less than 0.1 abrasive grain per μ

m² as visually observed under a scanning electron microscope at a magnification of 50000 as an average of five micrographs.

16. A magnetic recording medium as claimed in claim 1, wherein said medium does not develop more than 5 continuous black or white lines per 5 mm width as observed under a differential interference microscope (×

10) when information is recorded thereon at a short wavelength of 1 MHz and developed by magnetic development with Ferricolloid.

17. A magnetic recording medium as claimed in claim 1, wherein said upper magnetic layer has a squareness ratio of not less than 0.7 in an in-plane direction and not less than 0.6 in the vertical direction.