Stock material or miscellaneous articles – Composite – Of inorganic material
Reexamination Certificate
2001-11-09
2004-01-06
Le, H. Thi (Department: 1773)
Stock material or miscellaneous articles
Composite
Of inorganic material
C428S336000, C428S690000
Reexamination Certificate
active
06673477
ABSTRACT:
FIELD OF INVENTION
The present invention relates to a particulate type magnetic recording medium for high-density recording, which has a magnetic layer where a ferromagnetic powder is dispersed in a binder. More specifically, the invention relates to a magnetic recording medium for high-density recording, which has on each side thereof a magnetic layer and a substantially non-magnetic lower layer, and contains in each outermost layer a fine powder of ferromagnetic metal or hexagonal ferrite.
BACKGROUND OF THE INVENTION
In the field of magnetic disks, 2MB of MF-2HD floppy disks using Cobalt-modified iron oxide have become standard with personal computers. In these days of upsurge in data volume to be processed, however, it can no longer be said that such a capacity is sufficient, but it is desirable to further enlarge the capacities of floppy disks.
In order to achieve increased recording capacity and miniaturization of recording media coupled with downsizing of computers and enhancement of computers' ability to process information in particular, expansion of recording capacity and improvement of data transfer speed are intensely required.
Hitherto, magnetic recording media which each comprise a non-magnetic support coated with a magnetic layer containing iron oxide, cobalt-modified iron oxide, CrO
2
, a ferromagnetic metal powder or a hexagonal ferrite powder in a state of being dispersed in binder have been widely used. Of these magnetic substances, ferromagnetic metal powder and hexagonal ferrite powder are known to have excellent high-density recording characteristics.
In the case of disk-shaped magnetic recording media, the available large-capacity disks utilizing ferromagnetic metal powders excellent in high-density recording characteristics are 10 MB of MF-2TD and 21 MB of MF-2SD, and those utilizing hexagonal ferrite powders are 4MB of MF-2ED and 21 MB of Floptical. However, it can be said that the capacities and performances of these disks are no longer sufficient. Under these circumstances, many attempts to improve high-density recording characteristics have been made. Examples thereof are described below.
For improving characteristics of disk-shaped magnetic recording media, JP-A-64-84418 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”) proposes using vinyl chloride resin having acidic groups, epoxy groups and hydroxyl groups, JP-B-3-12374 (the term “JP-B” as used herein means an “examined Japanese patent publication”) proposes using a fine powder of metal having Hc of at least 79,600 A/m (1,000 oersted (Oe)) and a specific surface area of 25 to 70 m
2
/g, and JP-B-6-28106 proposes specifying the specific surface area and the magnetization intensity of a magnetic powder and further incorporating abrasives.
For improving durability of a disk-shaped magnetic recording medium, JP-B-7-85304 proposes using an unsaturated fatty acid ester and an ether linkage-containing fatty acid ester, JP-B-7-70045 proposes using a branched fatty acid ester and an ether linkage-containing fatty acid ester, JP-A-54-124716 proposes incorporating non-magnetic powder having a Mohs' hardness of at least 6 and a higher fatty acid ester, JP-B-7-89407 discloses controlling the volume of pores taking in a lubricant to within the specified limits and the surface roughness to the range of 0.005 to 0.025 &mgr;m, JP-A-61-294637 discloses the use of fatty acid esters having low and high melting points, JP-B-7-36216 discloses the use of an abrasive having a grain size equal to from one-fourth to three-fourth the magnetic layer thickness and a fatty acid ester having a low melting point, and JP-A-3-203018 discloses the use of an Al-containing ferromagnetic metal and chromium oxide.
As to the structures of disk-shaped magnetic recording media having non-magnetic lower or intermediate layers, JP-A-3-120613 proposes the structure made up of a conductive layer and a magnetic layer containing a fine powder of metal, JP-A-6-290446 proposes the structure made up of a magnetic layer having a thickness of 1 &mgr;m or below and a non-magnetic layer, JP-A-62-159337 proposes the structure made up of a carbon interlayer and a magnetic layer containing a lubricant, JP-A-5-290358 proposes the structure having a non-magnetic layer in which carbon particles limited in size are incorporated, and JP-A-8-249649 proposes specifying an amount of the porosity in a lower coating layer and that in an upper magnetic layer and providing a reservoir for liquid lubricant.
On the other hand, disk-shaped magnetic recording media made up of thin-layer magnetic layers and functional non-magnetic layers have been developed in recent years, and 100 MB-class floppy disks have made their debut. As to magnetic disks having these features, JP-A-5-109061 proposes the magnetic disk constituted of a magnetic layer having Hc of at least 111,440 A/m (1,400 Oe) and a thickness of at most 0.5 &mgr;m and a non-magnetic layer containing conductive particles, JP-A-5-197946 proposes the magnetic disk having a constitution that the abrasive having a size greater than the magnetic layer thickness is incorporated, JP-A-5-290354 proposes the magnetic disk having a constitution that the magnetic layer has a thickness of no greater than 0.5 &mgr;m, variations in the magnetic layer thickness is controlled to within ±15% and the surface electric resistance is adjusted to the specified range, and JP-A-6-68453 proposes the magnetic disk having a constitution that two types of abrasives differing in grain size are incorporated and the total quantity of the abrasives at the surface are controlled to the specified range.
The reliability on magnetic disk performance, such as consistent writing and reading of data, under a condition that a magnetic disk is repeatedly used and running operations at a high speed are performed over great many times, is required more intensely than ever. For instance, JP-A-6-52541 discloses the magnetic recording medium containing as an abrasive at least one powder chosen from alumina, chromium oxide or diamond powder, and reports that the addition of such a highly hard powder has improved running stability. Further, large-capacity magnetic disks have increased linear recording density and track density, and enable a sharp decrease in area per one Bit of signal. Therefore, even minute defects on the disks come to be a fatal flaw in recording and reproducing signals.
The invention relates to a large-capacity floppy disk having improved high-density recording characteristics, and aims to provide a floppy disk having high durability and a reduced rate of error increase.
From our intensive studies to provide a magnetic recording medium having excellent electromagnetic conversion characteristics, satisfactory durability and an markedly improved error rate, especially in the high-density recording area, it has been noted that an error increase phenomenon occurred during repeated reproduction of recorded signals. By a close examination of a disk surface at which such errors occurred, it has been found that part of projections on the disk surface were shaved off by the use of a head slider and the shavings of magnetic layer adhered to other areas of the disk surface to cause defects. Further, by removal of the coating from the projections on the disk surface, it has been shown that a great part of the projections on the magnetic layer was ascribed to projections on the non-magnetic support.
More specifically, even when lower non-magnetic and upper magnetic layers provided on a non-magnetic support had a thickness several times greater than the height of projections on the non-magnetic support, the projections on the non-magnetic support formed protuberances from the magnetic layer surface. The projections on a non-magnetic support, such as a polyester film, have their source in aggregates of inorganic powder as filler, such as silica particles, and polymerization residues formed upon stretch of the polyester film.
Even the projections causing no problem in the case of using magnetic m
Saito Shinji
Yamazaki Nobuo
Fuji Photo Film Co. , Ltd.
Le H. Thi
Stroock & Stroock & Lavan LLP
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