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Patent US4874668A successfully refreshed from Google Patents.
US4874668A
Expired / Lapsed
US
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Magnetic powder and magnetic recording medium comprising the same
Assignee: Maxell Ltd
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Filing: 1987-07-07
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Granted: 1989-10-17
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Expires: 2007-07-07
Abstract
Abstract Magnetic powder at least a part of particles of which have surface-adjacent layers comprising an aluminium-containing oxide of the corundum structure has high hardness so that a magnetic recording medium comprising a magnetic layer containing such magnetic powder has improved durability.
Inventors
- 👤 Seiichi Asada
- 👤 Toshinobu Sueyoshi
- 👤 Akira Miyake
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-23 16:44
CPC Classifications
G; G11; G11B; G11B5/00; G11B5/62; G11B5/68; G11B5/70; G11B5/712; Y; Y10; Y10S; Y10S428/00; Y10S428/90; Y10T; Y10T428/00; Y10T428/29; Y10T428/2982; Y10T428/2991; Y10T428/2993
Claims Analysis
Total Claims: 11
Claim 1
Independent Claim
29 words
Magnetic powder particles comprising a metal powder and an aluminum-containing oxide which has a corundum structure at least in a surface region of each of said magnetic powder particles.
Claim 2
Dependent Claim
29 words
Magnetic powder particles comprising a metal powder and an aluminum-containing oxide which has a corundum structure at least in a surface region of each of said magnetic powder particles.
Claim 3
Dependent Claim
47 words
The magnetic powder particles according to claim 1, wherein said surface region of each particle comprises an aluminum-containing oxide which has the corundum structure and at least one oxide selected from the group consisting of chromium oxide, gallium oxide and vanadium oxide which have the corundum structure.
Claim 4
Dependent Claim
58 words
The magnetic powder particles according to claim 2, wherein said surface region of each powder particle comprises a laminate layer which comprises a layer of the aluminum-containing oxide of the corundum structure and a layer of at least one oxide selected from the group consisting of chromium oxide, gallium oxide and vanadium oxide which have the corundum structure.
Claim 5
Dependent Claim
54 words
The magnetic powder particles according to claim 2, wherein said surface region of each powder particle comprises a layer which comprises a mixture of the aluminum-containing oxide of the corundum structure with at least one oxide selected from the group consisting of chromium oxide, gallium oxide and vanadium oxide which have the corundum structure.
Claim 6
Dependent Claim
50 words
The magnetic powder particles according to claim 2, wherein said surface region of each powder particle comprises a layer which comprises a double oxide of aluminum of the corundum structure and at least one element selected from the group consisting of chromium, gallium and vanadium which have the corundum structure.
Claim 7
Dependent Claim
35 words
The magnetic powder particles according to claim 2, wherein said surface region of each powder particle comprises an aluminum-containing oxide which has the corundum structure and Cr 2 O 3 which has the corundum structure.
Claim 8
Dependent Claim
48 words
A magnetic recording medium comprising a substrate and at least one magnetic layer which comprises magnetic powder particles dispersed in a binder, said magnetic powder particles comprising a metal powder having an aluminum-containing oxide which has a corundum structure at least in a surface region said metal powder.
Claim 9
Dependent Claim
48 words
A magnetic recording medium comprising a substrate and at least one magnetic layer which comprises magnetic powder particles dispersed in a binder, said magnetic powder particles comprising a metal powder having an aluminum-containing oxide which has a corundum structure at least in a surface region said metal powder.
Claim 10
Dependent Claim
51 words
The magnetic recording medium according to claim 7, wherein said surface region of said magnetic powder particles comprises an aluminum-containing oxide which has the corundum structure and at least one oxide selected from the group consisting of chromium oxide, gallium oxide and vanadium oxide each of which has the corundum structure.
Claim 11
Dependent Claim
26 words
The magnetic recording medium according to claim 8, wherein said oxide is Cr 2 O 3 together with said aluminum-containing oxide, both of the corundum structure.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1992-10-16 | 1993-04-17 | 1993-10-17 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1996-10-16 | 1997-04-17 | 1997-10-17 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2000-10-16 | 2001-04-17 | 2001-10-17 | $7700.00 | Window Closed / Lapsed |