Stock material or miscellaneous articles – Composite – Of inorganic material
Reexamination Certificate
2001-07-24
2003-11-11
Le, H. Thi (Department: 1773)
Stock material or miscellaneous articles
Composite
Of inorganic material
C428S690000, C428S690000
Reexamination Certificate
active
06645648
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a particulate magnetic recording medium of high recording density, and more particularly, to a magnetic recording medium for high-density recording having a magnetic layer and an essentially nonmagnetic underlayer, with the magnetic layer comprising a ferromagnetic metal powder or a hexagonal ferrite powder.
RELATED ART
As minicomputers, personal computers, work stations, and other office computers have become widespread in recent years, there has been significant research into magnetic tapes (so-called “backup tapes”) for recording computer data as an external memory medium. As the magnetic tapes employed in these applications have been put to practical use, and particularly as computers have grown smaller and information processing capacity has increased, there has been strong demand for increased recording capacity to achieve high capacity and reduction in size.
In the past, magnetic recording media in which a magnetic layer comprising iron oxide, Co-modified iron oxide, CrO
2
, a ferromagnetic metal powder, or a hexagonal ferrite powder dispersed in a binder is coated on a nonmagnetic support have been widely employed. Of these, ferromagnetic metal powders and hexagonal ferrite powders are known to have good high-density recording characteristics.
To improve the characteristics of a disk magnetic recording medium, the use of vinyl chloride resin having an acid group, epoxy group, and hydroxyl group is proposed in Japanese Unexamined Patent Publication (KOKAI) Showa No. 64-84418; the use of a metal powder with an Hc equal to or higher than 80 kA/m (1,000 Oe) and a specific surface area ranging from 25 to 70 m
2
/g is proposed in Japanese Examined Patent Publication (KOKOKU) Heisei No. 3-12374; and the incorporation of an abrasive to stabilize the magnetization level and specific surface area of the magnetic material is proposed in Japanese Examined Patent Publication (KOKOKU) Heisei No. 6-28106.
To improve the durability of the magnetic recording medium, the incorporation of a nonmagnetic powder with a Mohs' hardness equal to or higher than 6 and a higher fatty acid ester is proposed in Japanese Unexamined Patent Publication (KOKAI) Showa No. 54-124716; the setting of the volume of pores in a lubricant and the setting of the surface roughness to the range of 0.005 to 0.025 &mgr;m is proposed in Japanese Examined Patent Publication (KOKOKU) Heisei No. 7-89407; the use of a low-melting-point fatty acid ester and an abrasive with a particle diameter of from one-fourth to three-fourths the thickness of the magnetic layer is proposed in Japanese Examined Patent Publication (KOKOKU) Heisei No. 7-36216; and the use of chromium oxide and a metal magnetic material comprising Al is proposed in Japanese Unexamined Patent Publication (KOKAI) Heisei No. 3-203018.
As the configuration of a magnetic recording medium having a nonmagnetic lower layer and intermediate layer, a configuration having an electrically conductive layer and a magnetic layer having a metal powder is proposed in Japanese Unexamined Patent Publication (KOKAI) Heisei No. 3-120613; a configuration having a magnetic layer equal to or lower than 1 &mgr;m and a nonmagnetic layer is proposed in Japanese Unexamined Patent Publication (KOKAI) Heisei No. 6-290446; a configuration comprising an intermediate layer of carbon and a magnetic layer containing a lubricant is proposed in Japanese Unexamined Patent Publication (KOKAI) Showa No. 62-159337; and a configuration having a nonmagnetic layer with carbon of specified size is proposed in Japanese Unexamined Patent Publication (KOKAI) Heisei No. 5-290358.
As minicomputers, personal computers, and other office computers have become widespread in recent years, there has been significant research into magnetic tapes (so-called “backup tapes”) for recording computer data as an external memory medium. As the magnetic tapes employed in these applications have been put to practical use, and particularly as computers have grown smaller and information processing capacity has increased, there has been strong demand for increased recording capacity to achieve high capacity and size reduction. Further, demand has increased for further improvement in magnetic tapes for use under a wide variety of environmental conditions (particularly conditions of sharp fluctuation in temperature and humidity) due to the varied environment in which these magnetic tapes are employed, as well as for reliable data storage, stable recording of data during high-frequency travel with repeated use at high speeds, and reliable performance in reading and the like.
Conventionally, the magnetic tapes employed in digital signal recording systems are determined by the system; there are known magnetic tapes corresponding to DLT-type, 3480, 3490, 3590, QIC, D8-type, and DDS-type systems. Irrespective of the system in which employed, a magnetic layer comprising a ferromagnetic powder, binder, and abrasive of single-layer structure with a relatively thick film thickness ranging from 2.0 to 3.0 &mgr;m is provided on one side of a nonmagnetic support, and a backcoat layer for preventing tangled winding and ensuring good running durability is provided on the other side of the magnetic tape. However, in such magnetic layers of relatively thick single-layer structure, there is generally a problem in the form of loss due to thickness resulting in decreased output.
Thinning of the magnetic layer is known to afford improvement by reducing the drop in reproduction output caused by the thickness loss of the magnetic layer. For example, Japanese Unexamined Patent Publication (KOKAI) Heisei No. 5-182178 discloses a magnetic recording medium in which a lower nonmagnetic layer comprising an inorganic powder dispersed in resin is provided on a nonmagnetic support and an upper magnetic layer equal to or less than 1.0 &mgr;m in thickness comprising a ferromagnetic powder dispersed in binder is provided over said nonmagnetic layer while said nonmagnetic layer is wet.
However, with the rapidly increasing capacity and high densification of magnetic recording media, it is difficult to achieve satisfactory characteristics with such technology. It has also been difficult to achieve durability simultaneously.
Accordingly, the object of the present invention is to provide a magnetic recording medium with improved electromagnetic characteristics, particularly improved high-density recording characteristics, combined with good durability, particularly a substantially improved C/N ratio in the high-density recording region.
The present inventors conducted extensive research into obtaining a magnetic recording medium with good electromagnetic characteristics and durability, and particularly, a markedly improved C/N ratio in the high-density recording region, resulting in the discovery that the good high-density recording characteristics and good durability targeted by the present invention were achieved by the medium set forth below; the present invention was devised on that basis.
SUMMARY OF THE INVENTION
That is, the present invention relates to a magnetic recording medium comprising a nonmagnetic lower layer and a magnetic layer provided in this order on a support wherein said magnetic layer comprises a ferromagnetic metal powder or a ferromagnetic hexagonal ferrite powder and a binder and has a coercive force equal to or higher than 143 kA/m, wherein said magnetic recording medium is a medium for recording signals having a surface recording density ranging from 0.2 to 2 Gbit/inch
2
, said support has a thickness equal to or less than 5.5 &mgr;m and a Young's modulus in the MD direction equal to or higher than 11,000 Mpa, and said support has on the reverse surface from said magnetic layer a backcoat layer, said backcoat layer having not fewer than 200 and not more than 1,000 protrusions having a height equal to or higher than 50 nm per 10,000 &mgr;m
2
.
The above-stated object of the present invention is achieved by making it possible in the magnetic recording medium of the present
Doushita Hiroaki
Matsubaguchi Satoshi
Nishida Tetsuji
Le H. Thi
Stroock & Stroock & Lavan LLP
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