High-density acicular hematite particles, non-magnetic undercoat layer and magnetic recording medium

• US 6,350,505 B2
• Filed: 01/12/2001
• Issued: 02/26/2002
• Est. Priority Date: 03/27/1997
• Status: Expired due to Term

• Current Assignee: TODA Kogyo Corporation
• Original Assignee: TODA Kogyo Corporation
• Inventors: Tanaka, Yasuyuki, Morii, Hiroko, Hayashi, Kazuyuki, Iwasaki, Keisuke
• Primary Examiner(s): Resan, Stevan A.
• Application Number:
  US09/758,211
• Publication Number:
  US 20010016270A1
• Time in Patent Office: 410 Days
• Field of Search: 428/141, 428/329, 428/336, 428/403, 428/694.BS, 428/694.BA
• US Class Current: 428/141
• CPC Class Codes: B82Y 30/00 Nanotechnology for materials or surface science, e.g. nanocomposites
• CPC Class Codes: C01G 49/06 Ferric oxide [Fe2O3]
• CPC Class Codes: C01P 2004/10 extending in one dimension, e.g. needle-like
• CPC Class Codes: C01P 2004/54 Particles characterised by their aspect ratio, i.e. the ratio of sizes in the longest to the shortest dimension
• CPC Class Codes: C01P 2004/62 Submicrometer sized, i.e. from 0.1-1 micrometer
• CPC Class Codes: C01P 2004/64 Nanometer sized, i.e. from 1-100 nanometer
• CPC Class Codes: C01P 2004/84 one phase coated with the other
• CPC Class Codes: C01P 2006/12 Surface area
• CPC Class Codes: C01P 2006/22 Rheological behaviour as dispersion, e.g. viscosity, sedimentation stability
• CPC Class Codes: C01P 2006/40 Electric properties
• CPC Class Codes: C01P 2006/42 Magnetic properties
• CPC Class Codes: C01P 2006/80 Compositional purity
• CPC Class Codes: G11B 5/708 characterised by addition of non-magnetic particles to the layer
• 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 5/7334 Base layer characterised by composition or structure
• CPC Class Codes: Y10T 428/24355 Continuous and nonuniform or irregular surface on layer or component [e.g., roofing, etc.]
• CPC Class Codes: Y10T 428/257 Iron oxide or aluminum oxide
• CPC Class Codes: Y10T 428/265 1 mil or less
• CPC Class Codes: Y10T 428/2991 Coated

Abstract

High-density acicular hematite particles comprise acicular hematite particles and a coat comprising an oxide of tin or oxides of tin and antimony, formed on at least a part of surfaces of said acicular hematite particles; and have an average major axial diameter of not more than 0.3 μm, a pH value of not less than 8, a soluble sodium salt content of not more than 300 ppm, calculated as Na, and a soluble sulfate content of not more than 150 ppm, calculated as SO₄. Such high-density acicular hematite particles is suitable as non-magnetic particles for a non-magnetic undercoat layer of a magnetic recording medium using magnetic particles containing iron as a main ingredient, have an excellent dispersibility in vehicle and a low volume resistivity.

Claims

1. A magnetic recording medium comprising:

a non-magnetic substrate;

a non-magnetic undercoat layer formed on said magnetic substrate comprising high-density acicular hematite particles and a coat comprising an oxide of tin or oxides of tin and antimony, formed on at least a part of surfaces of said acicular hematite particles, said particles having an average major axial diameter of not more than 0.3 μ

m, a pH value of not less than 8, a soluble sodium salt content of not more than 300 ppm, calculated as Na, a soluble sulfate content of not more than 150 ppm, calculated as SO4, and a volume resistivity of 10³ to 5×

10⁷ Ω

cm and a binder resin; and

a magnetic recording layer comprising magnetic particles containing iron as a main ingredient and a binder resin, formed on said non-magnetic undercoat layer.

2. A magnetic recording medium according to claim 1, wherein said magnetic particles containing iron as a main ingredient comprise 50 to 99% by weight of iron, 0.05 to 10% by weight of aluminum, and at least one selected from the group consisting of Co, Ni, P, Si, Zn, Ti, Cu, B, Nd, La and Y.

3. A magnetic recording medium according to claim 1, wherein said magnetic particles containing iron as a main ingredient comprise 50 to 99% by weight of iron, 0.05 to 10% by weight of aluminum, and at least one rare earth metal selected from the group consisting of Nd, La and Y.

4. A magnetic recording medium according to claim 1, wherein said magnetic particles containing iron as a main ingredient have an average major axial diameter of 0.01 to 0.50 μ

m, an average minor axial diameter of 0.0007 to 0.17 μ

m, an aspect ratio of not less than 3;

1, a resin adsorptivity of not less than 65%, a coercive force of 1200 to 3200 Oe, and a saturation magnetization of 100 to 170 emu/g.

5. A magnetic recording medium according to claim 1, which further have an coercive force of 900 to 3500 Oe, a squareness of 0.85 to 0.95, a gloss of 195 to 300%, a surface roughness of not more than 11.0 nm, a linear adsorption coefficient of 1.10 to 2.00 μ

m<sup>−

1</sup>, a surface resistivity of 10⁴ to 5×

10⁸ Ω

/sq.

6. A magnetic recording medium according to claim 1, which further have a percentage of change in said coercive force of not more than 10.0%, and a percentage of change in said saturation magnetization flux of not more than 10.0%.

7. A magnetic recording medium according to claim 1, wherein said high-density acicular hematite particles further comprise a coat comprising at least one compound selected from the group consisting of a hydroxide of aluminum, an oxide of aluminum, a hydroxide of silicon and an oxide of silicon.

8. A magnetic recording medium according to claim 7, wherein the amount of said hydroxide of aluminum or said oxide of aluminum contained in said coat is 0.01 to 50% by weight, calculated as Al, based of the weight of said acicular hematite particles.

9. A magnetic recording medium according to claim 7, wherein the amount of said hydroxide of silicon or said oxide of silicon contained in said coat is 0.01 to 50% by weight, calculated as SiO₂, based of the weight of said acicular hematite particles.

10. A magnetic recording medium according to claim 1, wherein the amount of said oxide of tin is 0.5 to 500% by weight, calculated as Sn, based on the weight of said acicular hematite particles.

11. A magnetic recording medium according to claim 1, wherein the amount of said oxide of antimony when present is 0.05 to 50% by weight, calculated as Sb, based of the weight of said acicular hematite particles.

12. A magnetic recording medium according to claim 1, wherein both Sn and Sb are present in a weight ratio of tin to antimony of 20:

1 to 1;

1.

13. A magnetic recording medium according to claim 1, wherein said high-density acicular hematite particles have an aspect ratio (average major axial diameter:

average minor axial diameter) of not less than 2;

1.

14. A magnetic recording medium according to claim 1, wherein said high-density acicular hematite particles have a degree of densification (S_BET/S_TEM) of 0.5 to 2.5,

wherein S_BET represents a specific surface area measured by a BET method, and S_TEM represents a surface area calculated from values of major axial diameter and minor axial diameter obtained by measurement of particles on electron microscope photograph.

15. A magnetic recording medium according to claim 1, wherein said high-density acicular hematite particles have a particle size distribution of major axial diameter represented by a geometrical standard deviation of not more than 1.50.

16. A magnetic recording medium according to claim 1, wherein said high-density acicular hematite particles have a BET specific surface area of not less than 35 m²/g.