Magnetic recording medium

Details Magnetic recording medium Magnetic recording medium

2002-03-27

2003-11-04

Resan, Stevan A. (Department: 1773)

Stock material or miscellaneous articles

Circular sheet or circular blank

Recording medium or carrier

C428S328000, C428S329000, C428S336000, C428S690000, C428S690000

Reexamination Certificate

active

06641891

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to particulate high-density magnetic recording media. More particularly, the present invention relates to a magnetic recording medium for high-density recording having a magnetic layer, an essentially nonmagnetic lower layer, and an uppermost layer comprising a ferromagnetic powder in the form of a ferromagnetic metal powder, hexagonal ferrite powder, or the like.
RELATED ART
With the widespread popularity of office computers such as minicomputers and personal computers in recent years, considerable research has been conducted into the use of magnetic tapes (so-called “backup tapes”) for recording computer data as external memory devices. In the course of the practical development of magnetic tapes for such applications, particularly when combined with size reduction and increased information processing capability in computers, there has been a strong demand for increased recording capacity to achieve high-capacity recording and size reduction. Further, there has been increasing demands for the use under the wide surrounding conditions (in particular, under the conditions in which temperature and humidity are significantly varied) with increasing environments in which magnetic tapes are used, the reliability for data storage, the stable data recording and reading on multiple running by the repeated use at even higher speeds.
With the development of a multimedia society, the need for image recording is becoming increasingly strong not only in the business world, but also in the home. There is a demand for high-capacity magnetic recording media having ample ability to respond to the functional and cost requirements as a medium for recording image other than data such as text and numbers. Further, high-capacity magnetic recording media are preferably based on particulate magnetic recording media with their proven track records, affording good long-term reliability and cost performance.
The magnetic tapes employed in digital signal recording systems have been determined by system. There are magnetic tapes corresponding to so-called models DLT, 3480, 3490, 3590, QIC, model D8, and model DDS. In the magnetic tape employed in any system, a nonmagnetic support is provided on one side with a single-layer-structure magnetic layer with a relatively thick film thickness of 2.0 to 3.0 &mgr;m comprising a ferromagnetic powder, binder, and abrasives, and on the other side with a backcoat layer to prevent winding irregularity and ensure good running durability. However, these comparatively thick, single-layer-structure magnetic layers have a problem in the form of thickness loss, where output drops off.
Thinning of the magnetic layer is known to provide improvement with regard to reproduction output drop-off due to thickness loss in the magnetic layer. For example, Japanese Unexamined Patent Publication (KOKAI) Heisei No. 5-182178 discloses a magnetic recording medium in which, on a nonmagnetic support, a lower nonmagnetic layer comprising an inorganic powder dispersed in binder is provided and an upper magnetic layer equal to or less than 1.0 &mgr;m thickness comprising a ferromagnetic powder dispersed in binder is provided while the nonmagnetic layer is still wet.
Japanese Unexamined Patent Publication (KOKAI) Showa No. 64-84418 proposes the use of a vinyl chloride resin having an acid group, epoxy group, and hydroxyl group to improve the characteristics of a disk-shaped magnetic recording medium. Japanese Examined Patent Publication (KOKOKU) Heisei No. 3-12374 discloses the use of a metal micropowder with a specific surface area of 25 to 70 m
2
/g and an Hc equal to or higher than 79.6 kA/m (1,000 Oe). And Japanese Examined Patent Publication (KOKOKU) Heisei No. 6-28106 proposes the establishment of the specific surface area and level of magnetization of the magnetic material and the incorporation of abrasives.
To improve the durability of the magnetic recording medium, Japanese Unexamined Patent Publication (KOKAI) Showa No. 54-124716 proposes the incorporation of a nonmagnetic powder with a Mohs hardness equal to or higher than 6 and a high weight fatty acid ester, Japanese Examined Patent Publication (KOKOKU) Heisei No. 7-89407 proposes restricting the volume of voids containing lubricants and setting the surface roughness thereof to 0.005 to 0.025 &mgr;m Japanese Examined Patent Publication (KOKOKU) Heisei No. 7-36216 proposes the use of abrasives with a particle diameter of one-fourth to three-fourths the thickness of the magnetic layer and low-melting-point fatty esters, and Japanese Unexamined Patent Publication (KOKAI) Heisei No. 3-203018 proposes the use of aluminum-comprising metal magnetic material and chromium oxide.
As configurations of magnetic recording media having nonmagnetic lower layers and intermediate layers, Japanese Unexamined Patent Publication (KOKAI) Heisei No. 3-120613 proposes a configuration having an electrically conductive layer and a magnetic layer comprising metal micropowder, Japanese Unexamined Patent Publication (KOKAI) Heisei No. 6-290446 proposes a configuration having a magnetic layer equal to or less than 1 &mgr;m and a nonmagnetic layer, Japanese Unexamined Patent Publication (KOKAI) Showa No. 62-159337 proposes a configuration comprising a carbon intermediate layer and a magnetic layer comprising lubricants, and Japanese Unexamined Patent Publication (KOKAI) Heisei No. 5-290358 proposes a configuration having a nonmagnetic layer having carbon of prescribed size.
Magnetic recording media having a magnetic layer in which iron oxide, Co-modified iron oxide, CrO
2
, ferromagnetic metal powder, and/or hexagonal ferrite powder is dispersed in binder that is coated on a nonmagnetic support are widely employed. Of these, ferromagnetic metal powders and hexagonal ferrite powders are known to have good high-density recording characteristics.
However, as the capacity and density of magnetic recording media have rapidly increased, it has become difficult to achieve satisfactory characteristics even with the above-cited art. It has also proved difficult to simultaneously achieve durability.
Magnetic heads with magnetic inductance as their operating principle (inductive magnetic heads) have been widely employed. However, limits have begun to appear in the use thereof in the area of higher density recording and reproduction. That is, to achieve high reproduction output, coil winding numbers must be employed in the reproduction head. However, there are problems in that inductance increases and resistance increases at high frequencies, resulting in a drop in reproduction output.
In recent years, one means of solving this problem has been proposed in the form of reproduction heads the operating principle of which is magnetoresistance (MR); their use in hard disks and the like has began. MR heads yield several times the reproduction output of inductive magnetic heads without employing inductive coils, permitting a substantial reduction in device noise such as inductance noise. Thus, it is possible to achieve high S/N ratios by using MR heads to reduce the noise of magnetic recording media.
High densities are generally achieved by reducing bit area, that is, recording at shorter wavelengths and narrowing the track width. However, since both short wavelength recording and narrow tracks cause a drop in output, it is difficult to ensure a good C/N ratio. Accordingly, the present inventors investigated how to achieve high output by using layered heads and MR heads in the most recent tape systems and what technologies are capable of ensuring a good C/N ratio when recording at short wavelengths and narrowing the track width.
In addition, further thinning of the magnetic layer and heightened dispersion of ferromagnetic powder were examined to achieve a magnetic recording medium corresponding to high density recording. As a result, it was determined that, as shortening recording wavelength, the magnetic particles aggregate and behave like a single large magnetic member (magnetic cluster), causing problems. That is, as reco

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