Stock material or miscellaneous articles – Composite – Of inorganic material
Reexamination Certificate
2001-10-09
2003-08-26
Le, H. Thi (Department: 1773)
Stock material or miscellaneous articles
Composite
Of inorganic material
C428S690000, C428S900000
Reexamination Certificate
active
06610426
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a magnetic recording medium for high-density recording comprising a ferromagnetic powder in a magnetic layer.
RELATED ART
In recent years, magnetic recording media in which a magnetic layer comprising a ferromagnetic powder dispersed in resin is provided on a nonmagnetic support have been employed as audio tapes, video tapes, floppy disks, and other magnetic recording media. A variety of characteristics are required of such magnetic recording media, such as electromagnetic characteristics, running durability, and running performance. To achieve good running durability, abrasives and lubricants are commonly added to the magnetic layer.
The magnetic recording medium comes into sliding contact with a magnetic head in the apparatus employed. Thus, the low-molecular-weight component in the binder employed in the magnetic recording medium rises up near the surface of the magnetic layer and adheres to the magnetic head. This is problematic in that the magnetic head is then dirtied. Dirtying of the magnetic head causes deterioration in electromagnetic characteristics. In particular, in high-density recording apparatuses, the magnetic heads rotate at high rpm. Even in home-use digital video tape recorders, the magnetic head rotates at 9,600 rpm. This is quite high relative to the 1,800 rpm of popular analog video recorders and the 5,000 rpms employed in industry. The sliding speed of the magnetic recording medium and the magnetic head becomes quite rapid and compact magnetic heads such as thin-film heads are employed. Thus, there is a need for improvement with regard to dirtying of the magnetic head by components produced by the magnetic recording medium. In particular, in the magnetic recording media employed for high-density recording employed in place of floppy disks, there is also a need for increased strength, improvement with regard to head dirtying, and high reliability.
In common, widely employed magnetic recording media, a thermoplastic resin such as vinyl acetate resin, vinyl chloride—vinylidene chloride resin, cellulose resin, acetal resin, urethane resin, or acrylonitrile butadiene resin is employed singly or in combination as the binder. However, magnetic layers employing these binders have drawbacks in the form of poor abrasion resistance and dirtying of the magnetic tape running path. The use of thermosetting resin such as phenol/formaldehyde resin, urea resin as the binder is known, as are binders that can be crosslinked by chemical reaction in which an isocyanate compound, epoxy compound, or the like, is added to the thermosetting resin. However, when a thermally cross-linking binder is employed, there are drawbacks in that the storage stability of the resin solution in which the magnetic powder is dispersed deteriorates, and the uniformity of magnetic coating liquid properties, and thus the homogeneity of the magnetic tape, are not maintained.
By contrast, Japanese Examined Patent Publication (KOKOKU) Heisei Nos. 3-6573 and 4-58650 disclose magnetic recording media employing binders that are crosslinked by irradiation with an electron beam employing compounds having a trifunctional urethane acrylic resin or (meth)acryloyl group. Because the crosslinking agent undergoes crosslinking when exposed to radiation, the problems caused by lack of storage stability in the above-described thermally crosslinking binder are not present and a magnetic recording medium with good electromagnetic characteristics and good durability can be obtained.
However, since the magnetic recording media described in Japanese Examined Patent Publication (KOKOKU) Heisei Nos. 3-6573 and 4-58650 are magnetic tapes with magnetic layers of single-layer structure, they are problematic in that they cannot adequately respond to current needs for the storage of large quantities of data. In light of such problems, for example, a magnetic recording medium (magnetic tape) provided with a lower nonmagnetic layer in which an inorganic nonmagnetic powder is dispersed in binder on a nonmagnetic support and a thin upper magnetic layer in which a ferromagnetic metal powder is dispersed in binder on the nonmagnetic layer has been proposed as a magnetic recording medium employed in a magnetic recording system with a built-in thin-film magnetic head (Japanese Unexamined Patent Publication (KOKAI) Heisei No. 8-227517). The upper magnetic layer is made thin to inhibit output dropoff due to thickness losses. Further, since a high recording density can be achieved, it is possible to store a greater quantity of data than on magnetic tapes having a single-layer structure magnetic layer.
However, the demands placed on high density magnetic recording media are continuously increasing, and there is a need for a magnetic recording medium having much greater durability than in the past as well as good electromagnetic characteristics. The achievement of high durability and good electromagnetic characteristics is being demanded of tapes such as video system tapes with extremely high recording densities such as DVC and DVC-PRO tapes, as well as computer backup tapes capable of the rapid transfer of large quantities of data such as DDS4 and LTO systems, and of disk systems in recording systems with recording and reproduction heads rotating at speeds of 700 rpm or greater, such as Zip and Zip250 systems.
To achieve such high level electromagnetic characteristics, these magnetic recording media are required to have an extremely thin magnetic layer of, for example, 0.05 to 0.2 &mgr;m, and extremely smooth surface roughness. Not only thin thickness, but also a high degree of uniformity is required for a magnetic layer because inadequate uniformity of thickness results in noise. As a particulate magnetic recording medium with such a magnetic layer, Japanese Unexamined Patent Publication (KOKAI) Heisei No. 10-222838 proposes a medium in which a thin magnetic layer is provided on a nonmagnetic layer and an isocyanate curing agent is employed in a nonmagnetic layer and a thin magnetic layer.
However, the characteristics of the magnetic recording medium described in Japanese Unexamined Patent Publication (KOKAI) Heisei No. 10-222838 are still inadequate in the recording systems requiring high durability and electromagnetic characteristics, as set forth above. That is, there is a demand for a magnetic recording medium achieving higher durability, a high degree of smoothness, a magnetic layer of uniform thickness, and extremely good electromagnetic characteristics.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide a magnetic recording medium achieving higher durability, a higher degree of smoothness, and a magnetic layer of more uniform thickness, and having substantially better electromagnetic characteristics than the magnetic recording medium described in Japanese Unexamined Patent Publication (KOKAI) Heisei No. 10-222838.
DETAILED EXPLANATION OF THE INVENTION
The first mode of the present invention relates to a magnetic recording medium comprising a nonmagnetic layer comprising a nonmagnetic powder and at least one magnetic layer comprising a ferromagnetic powder and binder provided on a support in this order,
wherein the binder contained in the magnetic layer comprises at least a trifunctional or greater aliphatic acrylate compound having a molecular weight ranging from 250 to 1,000 or a trifunctional or greater aliphatic methacrylate compound having a molecular weight ranging from 250 to 1,000 that has been cured by exposure to radiation, and said compound being employed in a ratio of 5 to 30 mass parts per 100 mass parts of ferromagnetic powder.
In addition, the second mode of the present invention relates to a magnetic recording medium comprising a nonmagnetic layer comprising a nonmagnetic powder and at least one magnetic layer comprising a ferromagnetic powder and binder provided on a support in this order,
wherein the binder contained in the magnetic layer comprises at least a trifunctional or greater aliphatic acrylate compound having a mo
Hashimoto Hiroshi
Murayama Yuichiro
Le H. Thi
Stroock & Stroock & Lavan LLP
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