Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Including a second component containing structurally defined...
Reexamination Certificate
2000-12-01
2003-04-15
Resan, Stevan A. (Department: 1773)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Including a second component containing structurally defined...
C428S336000, C428S690000, C428S690000
Reexamination Certificate
active
06548160
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to magnetic recording media capable of high-density recording with excellent preservability and running durability. The present invention also relates to magnetic recording media capable of high-density recording with low noise at high output and excellent running durability.
2. Description of Related Art
With the recent trend toward higher recording densities, recording wavelengths tend to be shorter to aggravate the problem of self-degaussing loss leading to output loss in thick magnetic layers during recording. Thus, attempts have been made to make magnetic layers thinner, but the surfaces of magnetic layers of 2 &mgr;m or less directly applied on a substrate may be roughened to deteriorate electromagnetic characteristics or to cause dropout under the influence of additives such as abrasives or carbon blacks and aggregated magnetic powders in the magnetic layers as well as the nonmagnetic substrate.
A possible solution to this problem was to apply an underlying nonmagnetic layer and a thin layer of a concentrated magnetic coating liquid thereon by simultaneous multilayer coating (see JP-A Nos. 191315/88 and 187418/88). Such simultaneous multilayer coating allowed good electromagnetic characteristics even in particulate magnetic recording media having a thin magnetic layer. This type of magnetic recording media can assign the nonmagnetic layer underlying the magnetic layer to serve as a reservoir for lubricants to limit the friction coefficient of the magnetic layer even after repeated running, so that running performance can be improved.
In recent consumer digital VCR systems or DDS-4 systems or the like, there are increasing demands for further higher recording densities. In order to satisfy these demands, attempts have been made to further smoothen the surfaces of magnetic layers to improve output by reducing spacing loss or to reduce noise by controlling spacing variation. However, these attempts to smoothen the surfaces of magnetic layers led to another problem of increased magnetic coefficient of the magnetic layers and lowered running durability. Under these circumstances, it has become necessary to provide means for combining high recording densities and running durability at a high level.
It is known that lubricants such as fatty acids can be used to ensure running performance (or lower friction coefficient) in particulate magnetic recording media. Although magnetic recording media are required to have good preservability, such fatty acids used as lubricants may form salts in the presence of impurities derived from raw materials such as powder or manufacturing processes to greatly lower preservability in environments at high temperature and high humidity (see JP-A No. 296366/95).
Thus, it is a first object of this invention to provide a magnetic recording medium capable of high-density recording with excellent running durability and preservability.
In particulate tapes for consumer digital VCR systems or DDS-4 systems, high-&sgr;s metal alloy powders are used to attain high output. However, metal alloy powders having a high &sgr;s are highly cohesive so that magnetic particles aggregate in some regions while hollows are formed by additives such as abrasives or carbon blacks in other regions (hollows are formed for lack or scanty of magnetic particles) during application of these powders. This unevenness becomes more apparent if the magnetic layer is thin, e.g. 0.3 &mgr;m or less or if the lower nonmagnetic layer is thin, e.g. 0.8 &mgr;m or less.
The unevenness is further emphasized by calendering, which strongly crushes aggregated magnetic particles while hollows are not crushed. Thus, the surface of the magnetic layer is roughened to increase noise. If the magnetic layer is thin, the packing density of the magnetic layer may be lowered.
Therefore, it is a second object of the present invention to provide a magnetic recording medium capable of high-density recording with low noise even at high output and excellent running durability.
SUMMARY OF THE INVENTION
We carefully studied to achieve the first object. As a result, we accomplished the present invention on the basis of the finding that the first object can be achieved by further adding a zirconia powder into a magnetic layer containing a ferromagnetic powder and a binder provided on a nonmagnetic flexible substrate.
Accordingly, the present invention relates to a magnetic recording medium comprising a magnetic layer containing a ferromagnetic powder and a binder provided on a flexible nonmagnetic substrate or a magnetic recording medium comprising a nonmagnetic layer containing a nonmagnetic powder and a binder and a magnetic layer containing a ferromagnetic powder and a binder provided in this order on a nonmagnetic flexible substrate wherein said magnetic layer further contains a zirconia powder (hereinafter referred to as magnetic recording medium (1)).
Preferred embodiments of magnetic recording medium (1) of the present invention are as follows.
(1) Said zirconia powder preferably has an average primary particle diameter in the range of 0.005-0.2 &mgr;m from the viewpoint that the dispersibility of magnetic solutions during preparation can be improved to reduce surface roughening of the magnetic layer while inhibiting orientational disorder.
(2) Said zirconia powder is preferably at least one member selected from the group consisting of stabilized zirconia, partially stabilized zirconia and zirconia-reinforced ceramics from the viewpoint that the compressive strength of the zirconia powder itself is increased to improve the effect of reinforcing the magnetic layer film and to improve running durability.
(3) Said zirconia powder is preferably prepared by a liquid-phase (wet) process or a gas-phase process from the viewpoint that a finely granulated homogeneous powder with low content of impurities can be formed while improving preservability in environments at high temperature and high humidity.
(4) A nonmagnetic layer is advantageously inserted between said magnetic layer and said substrate to further smoothen the surface of said magnetic layer, thereby improving output and lowering the friction coefficient of said magnetic layer.
(5) Said binder present in said magnetic layer preferably contains a polar group from the viewpoint that adsorption to zirconia powder can be enhanced to reduce separation of zirconia powder during repeated running.
(6) Said magnetic layer preferably contains a fatty acid from the viewpoint that the friction coefficient of said magnetic layer can be lowered.
We carefully studied to achieve the second object. As a result, we accomplished the present invention on the basis of the finding that the second object can be achieved by providing a magnetic recording medium comprising a nonmagnetic layer containing a nonmagnetic powder and a binder and a magnetic layer containing a ferromagnetic powder and a binder provided in this order on a nonmagnetic flexible substrate wherein said magnetic layer has an average thickness in the range of 0.04-0.3 &mgr;m, said ferromagnetic powder is a metal alloy powder having a &sgr;s of 130 A.m
2
/kg or more, and said magnetic layer contains a granulated powder having an average primary particle diameter of 0.005-0.2 &mgr;m and a specific gravity of 5 or more (hereinafter referred to as magnetic recording medium (2)).
Preferred embodiments of magnetic recording medium (2) of the present invention are as follows.
(1) Said granulated powder is preferably a zirconia powder from the viewpoint that it has a specific gravity close to that of the ferromagnetic powder so that additives-mediated surface roughening can be controlled and the strength as a powder can be readily ensured.
(2) Said granulated powder present in said magnetic layer preferably represents 0.5-10 parts by weight per 100 parts by weight of said metal alloy powder from the viewpoint that the packing density of the magnetic material is ensured while improving dispersibility.
(3) Said binder present in said m
Ejiri Kiyomi
Naoe Koji
Fuji Photo Film Co. , Ltd.
Resan Stevan A.
Stroock & Stroock & Lavan LLP
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