# US 6,720,094 B2 · Secondary agglomerates of magnetic metal particles for magnetic recording and process for producing the same

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- Number: US 6,720,094 B2
- Document ID: US6720094B2
- Status: Granted
- Kind: B2
- Application number: 09/878,184
- Filed: 2001-06-12
- Published: 2002-02-21
- Granted: 2004-04-13
- Earliest claimed: 2000-06-13
- Assignees: Toda Kogyo Corporation
- Inventors: Kenji Okinaka; Masayuki Uegami
- Web page: https://patentgrep.com/patent/US6720094B2

## CPC

- G11B 5/70621: {containing Co metal or alloys}
- B82Y 30/00: Nanotechnology for materials or surface science, e.g. nanocomposites
- C01G 49/06: Ferric oxide [Fe2O3]
- C01P 2002/60: Compounds characterised by their crystallite size
- C01P 2004/03: obtained by SEM
- C01P 2004/10: extending in one dimension, e.g. needle-like
- C01P 2004/50: Agglomerated particles
- C01P 2004/51: Particles with a specific particle size distribution
- C01P 2004/54: Particles characterised by their aspect ratio, i.e. the ratio of sizes in the longest to the shortest dimension
- C01P 2004/61: Micrometer sized, i.e. from 1-100 micrometer
- C01P 2004/62: Submicrometer sized, i.e. from 0.1-1 micrometer
- C01P 2004/64: Nanometer sized, i.e. from 1-100 nanometer
- C01P 2006/10: Solid density
- C01P 2006/11: Powder tap density
- C01P 2006/12: Surface area
- C01P 2006/22: Rheological behaviour as dispersion, e.g. viscosity, sedimentation stability
- C01P 2006/42: Magnetic properties
- Y10T 428/25: Web or sheet containing structurally defined element or component and including a second component containing structurally defined particles
- Y10T 428/26: Web or sheet containing structurally defined element or component, the element or component having a specified physical dimension
- Y10T 428/29: Coated or structually defined flake, particle, cell, strand, strand portion, rod, filament, macroscopic fiber or mass thereof
- Y10T 428/2982: Particulate matter [e.g., sphere, flake, etc.]
- G11B: INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER (recording measured values in a way that does not require playback through a transducer G01D9/00; recording or playback apparatus using mechanically marked tape, e.g. punched paper tape, or using unit records, e.g. punched or magnetically marked cards G06K; transferring data from one type of record carrier to another G06K1/18; circuits for coupling output of reproducer to radio receiver H04B1/20; gramophone pick-ups or like acoustic electromechanical transducers or circuits therefor H04R)
- B82Y: SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
- C01G: COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F (metal hydrides {monoborane, diborane or addition complexes thereof} C01B6/00; salts of oxyacids of halogens C01B11/00; peroxides, salts or peroxyacids C01B15/00; thiosulfates, dithionites, polythionates C01B17/64; compounds containing selenium, or tellurium C01B19/00; binary compounds of nitrogen with metals C01B21/06; azides C01B21/08; {compounds containing nitrogen, other non-metals and metal C01B21/082}; metal amides C01B21/092; nitrites C01B21/50; {compounds of noble gases C01B23/0005}; phosphides C01B25/08; salts of oxyacids of phosphorus C01B25/16; carbides C01B32/90; compounds containing silicon C01B33/00; compounds containing boron C01B35/00; compounds having molecular sieve properties but not having base-exchange properties C01B37/00; compounds having molecular sieve and base-exchange properties, e.g. crystalline zeolites, C01B39/00; cyanides C01C3/08; salts of cyanamide C01C3/16; thiocyanates C01C3/20)
- C01P: INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- Y10T: TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION

## Abstract

Secondary agglomerates of magnetic metal particles containing primary particles having an average major axial diameter of 0.05 to 0.25 μm, said secondary agglomerates having an average particle diameter of 300 to 800 μm, an upper limit of particle diameter of 2,000 μm and a repose angle of 38 to 45°. The secondary agglomerates exhibit not only excellent handing property due to high storage efficiency, high transport efficiency and good flowability thereof, but also excellent kneading property when kneaded with various binder resins and organic solvents in a kneader, and excellent dilution-dispersibility when diluted with an additional amount of the organic solvent, upon the production of coating-type magnetic recording media, so as to more improve a surface smoothness and squareness of a magnetic coating film obtained therefrom, and a process for producing such secondary agglomerates of magnetic metal particles for magnetic recording.

## Claims

### Claim 1

Secondary agglomerates of magnetic metal particles comprising magnetic metal primary particles having an average major axial diameter of 0.05 to 0.25 μm, said secondary agglomerates having an average particle diameter of 300 to 800 μm, an upper limit of particle diameter of 2,000 μm and a repose angle of 38 to 45°, and the amount of the secondary agglomerates having a diameter of not more than 53 μm is more than 30% by weight.

### Claim 2 (depends on 1)

Secondary agglomerates of magnetic metal particles according to claim 1, which further have a bulk density of 0.35 to 0.65 g/ml, a tap density of 0.39 to 0.75 g/ml and a compaction percentage of 10 to 15%.

### Claim 3 (depends on 1)

Secondary agglomerates of magnetic metal particles according to claim 1, wherein said primary particles of the magnetic metal particles constituting the secondary agglomerates are acicular magnetic metal particles having an average major axial diameter of 0.05 to 0.25 μm, an aspect ratio of 4:1 to 13:1 and a BET specific surface area of 35 to 65 m2/g.

### Claim 4 (depends on 1)

Secondary agglomerates of magnetic metal particles according to claim 1, wherein said primary particles of the magnetic metal particles constituting the secondary agglomerates are spindle-shaped magnetic metal particles containing iron as a main component, having an average major axial diameter of 0.05 to 0.15 μm, an aspect ratio of 5:1 to 9:1, a size distribution (standard deviation/average major axial diameter) of not more than 0.30, a crystallite size D110 of 130 to 160 Å, a Co content of from 0.5 to less than 6 atm% based on whole Fe, an Al content of from more than 10 to less than 20 atm% based on whole Fe, a rare earth content of 1.5 to 5 atm% based on whole Fe, an atomic ratio of Al to Co of from more than 2 to 4, a coercive force of 111.4 to 143.2 kA/m, an oxidation stability (Aas) of saturation magnetization of not more than 10%, and an ignition temperature of not less than 130° C.

### Claim 5 (depends on 1)

Secondary agglomerates of magnetic metal particles according to claim 1, wherein said primary particles of the magnetic metal particles constituting the secondary agglomerates are spindle-shaped magnetic metal particles containing iron as a main component, having an average major axial diameter (L) of 0.05 to 0.15 μm; a coercive force of 111.4 to 143.2 kA/m; a Co content of from 0.5 to less than 5 atm% based on whole Fe; a crystallite size of from 150 to less than 170 Å; a specific surface area (S) represented by the formula:
S<−160×L+65;
an oxidation stability (Δσs) of saturation magnetization of not more than 5%; and an ignition temperature of not less than 140° C.

### Claim 6 (depends on 1)

Secondary agglomerates of magnetic metal particles according to claim 1, wherein said primary particles of the magnetic metal particles constituting the secondary agglomerates are spindle-shaped magnetic metal particles containing iron as a main component, having a Co content of from 0.5 to less than 10 atm% based on whole Fe, an Al content of from 5 to 10 atm% based on whole Fe, a rare earth content of from 1 to 5 atm% based on whole Fe, an atomic ratio of Al to rare earth element of 1.5 to 5, calculated as atm% of the respective elements based on Fe, an average major axial length of 0.05 to 0.25 μm, a size distribution (standard deviation/major axial length) of not more than 0.26, an average minor axial length of 0.015 to 0.025 μm, an average aspect ratio of 5:1 to 9:1, a specific surface area of 30 to 60 m2/g, an ignition temperature of not less than 145° C., an oxidation stability of not more than 6%, and a coercive force of 103.5 to 143.2 kA/m.

### Claim 7 (depends on 1)

Secondary agglomerates of magnetic metal particles according to claim 1, wherein said primary particles of the magnetic metal particles constituting the secondary agglomerates are spindle-shaped magnetic metal particles containing iron as a main component, having a Co content of from 0.5 to less than 10 atm% based on whole Fe, an Al content of 5 to 10 atm% based on whole Fe, a rare earth content of 1 to 5 atm% based on whole Fe, an atomic ratio of Al to rare earth element of 1.5 to 5, calculated as atm% of the respective elements based on Fe, an average major axial length of 0.15 to 0.25 μm, a size distribution (standard deviation/major axial length) of not more than 0.30, an average minor axial length of 0.015 to 0.025 μm, an average aspect ratio of 5:1 to 9:1, a specific surface area of 30 to 60 m2/g, an ignition temperature of not less than 135° C., an oxidation stability of not more than 10%, and a coercive force of 103.5 to 143.2 kA/m.

### Claim 8

Secondary agglomerates of magnetic metal particles comprising magnetic metal primary particles having an average major axial diameter of 0.05 to 0.25 μm, said secondary agglomerates having an average particle diameter of 300 to 800 μm, an upper limit of particle diameter of 2,000 μm, a repose angle of 38 to 45° the amount of the secondary agglomerates having a diameter of not more than 53 μm is not more than 30% by weight a bulk density of 0.35 to 0.65 g/ml, a tap density of 0.39 to 0.75 g/ml and a compaction percentage of 10 to 15%.

### Claim 9

A magnetic recording medium comprising a non-magnetic substrate and a magnetic recording layer formed on the non-magnetic substrate comprising a binder resin and magnetic metal particles containing iron as a main component which are derived from secondary agglomerates of magnetic metal particles containing primary particles having an average major axial diameter of 0.05 to 0.25 μm, said secondary agglomerates having an average particle diameter of 300 to 800 μm, an upper limit of particle diameter of 2,000 μm a repose angle of 38 to 45°°, and the amount of the secondary agglomerates having a diameter of not more than 53 μm is not more than 30% by weight.

### Claim 10 (depends on 9)

A magnetic recording medium according to claim 9, which further has a coercive force value of 111.4 to 143.2 kA/m, and when the magnetic coating film is oriented by applying a magnetic field of 397.9 kA/m thereto, a squareness (Br/Bm) of not less than 0.84, an orientation property (OR) of usually not less than 2.8, a coercive force distribution (Switching Field Distribution) of not more than 0.53 and an oxidation stability (ΔBm) of not more than 8.0%.