Stock material or miscellaneous articles – Structurally defined web or sheet – Continuous and nonuniform or irregular surface on layer or...
Reexamination Certificate
2002-05-30
2004-03-09
Resan, Stevan A. (Department: 1773)
Stock material or miscellaneous articles
Structurally defined web or sheet
Continuous and nonuniform or irregular surface on layer or...
C428S212000, C428S220000, C428S323000, C428S336000, C428S480000, C428S690000
Reexamination Certificate
active
06703107
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a magnetic tape, and particularly to a magnetic tape advantageously used for recording computer data. More particularly, the present invention relates to a magnetic tape advantageously used in a magnetic recording and reproduction system particularly using a reproducing head (MR head) of a magnetic resistance type.
BACKGROUND OF THE INVENTION
In magnetic recording and reproduction systems for recording and reproducing computer data, systems in which thin film magnetic heads are incorporated has recently come in practice. The thin film magnetic heads are easily miniaturized and processed to multi track heads, so that stationary multi track heads of the thin film magnetic heads have been frequently used, particularly in systems using magnetic tapes as recording media. The use of the thin film magnetic heads makes it possible to improve track density and recording efficiency by miniaturization to realize high-density recording, and also makes it possible to improve the transfer rate of data by the multiplication of trucks. The thin film magnetic heads can be roughly divided into induction type heads responding to changes in magnetic flux with time and magnetic resistance type heads (MR heads) utilizing a magnetic resistance effect which respond to the magnitude of magnetic flux. The induction type head has the problem that the number of turns of a head coil is small because of its planar structure, resulting in difficulty of increasing magnetomotive force to fail to obtain sufficient reproduction output. Accordingly, the MR heads which can easily obtain high reproduction output have been used for reproduction, whereas the induction type head have been used for recording. These recording and reproduction heads are usually incorporated in systems as the integral type (complex type). In the magnetic recording systems as described above, the linear recording system which can realize faster transfer of data have been employed.
As magnetic tapes for recording computer data used in the magnetic recording and reproduction systems in which the MR heads are incorporated, there are known, for example, magnetic tapes corresponding to the 3480 type, the 3490 type, the 3590 type or the 3570 type by the IBM standard. These magnetic tapes each has the basic structure that a magnetic layer of the monolayer structure having a thickness as relatively large as about 2.0 to about 3.0 &mgr;m and containing a ferromagnetic powder and a binder is provided on a support. The magnetic tapes having such magnetic layers of the monolayer structure have the problem that they can not sufficiently comply with recent needs for media which store a large amount of data.
In order to solve such a problem, for example, Japanese Patent Application (Laid-Open) No. 227517/1996 proposes a magnetic recording medium (magnetic tape) comprising a non-magnetic support, a lower non-magnetic layer provided thereon in which an inorganic non-magnetic powder is dispersed in a binder, and an upper thin magnetic layer provided thereon in which a ferromagnetic metal powder is dispersed in a binder, as a magnetic recording medium used in the magnetic recording system in which the thin film magnetic head is incorporated. A reduction in output caused by thickness loss is suppressed by thinning the upper magnetic layer (0.3 &mgr;m), and high recording density can be achieved. It becomes therefore possible to store larger amounts of data, compared to a magnetic tape having a magnetic layer of the monolayer structure. Japanese Patent Application (Laid-Open) No. 250449/1999 also discloses a magnetic tape in which a magnetic layer is similarly provided on a non-magnetic layer.
In order to realize higher recording density and larger recording capacity in the magnetic recording and reproduction systems employing the linear recording system, the recording wavelength tends to become short, and the track width in recording/reproduction of magnetic tapes tends to become narrow. The induction type heads responding to changes in magnetic flux with time, which have conventionally been used, are difficult to increase magnetomotive force, and have the problem that sufficient reproduction output can not be obtained. Accordingly, the systems in which the magnetic resistance type heads (MR heads) responding to magnetic flux and giving high reproduction output are used as the reproduction heads have spread in computer systems of the linear recording system. The MR heads are high in sensitivity compared to the induction type heads, so that the MS heads are sensitive to projections (i.e., protrusions) on the tapes. Accordingly, such projections on the magnetic layers as introduce no problem in conventional systems are liable to cause errors. It is therefore preferred that the projections on the magnetic layers of the magnetic tapes are decreased.
In large-capacity data storage tapes, not only recording and reproduction characteristics and durability but also keeping quality (i.e., storage property) is very important. There are the problems of deposition and decomposition of magnetic layer and back layer components, and deposition of oligomers in polyester supports, in storage, and the problem of cinching caused by winding squeezes of tape winding rolls. However, improvements thereof have intensively proceeded. Further, in some cases, the tapes are deformed by changes in temperature during storage. In general, such problems tend to be solved by decreasing the heat shrinkage of the magnetic tapes, but it is not sufficient yet. Further improvements have therefore been required.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a magnetic tape having high recording density and suitable for a magnetic recording and reproduction system employing the linear recording system in which a magnetic resistance type reproduction head is incorporated.
In particular, another object of the present invention is to provide a magnetic tape which is not deformed even by changes in temperature during storage, and not changed in recording and reproduction characteristics after storage.
A further object of the present invention is to provide a magnetic tape excellent in durability and having high recording density, in which errors can be decreased, and recording and reproduction can be repeated with high output and high reliability, when an MR head is used.
According to further studies of the present inventors, there can be provided a magnetic tape, preferably a magnetic tape on which a signal having an areal recording density of 10 to 100 Mbit/cm
2
is recorded, which is decreased in errors and excellent in reproduction characteristics even when the signal having an areal recording density of 10 to 100 Mbit/cm
2
is recorded, by decreasing the number of projections (i.e., protrusions) having an area (i.e., an area of a part where the projection is contact with the magnetic layer surface) of 30 &mgr;m
2
or more and a height of 40 nm or more to 16 projections/mm
2
or less.
The magnetic tape of the present invention is achieved by the following means:
(1) A magnetic tape comprising a non-magnetic support having provided on one face thereof a substantially non-magnetic layer containing a non-magnetic powder and a binder and a magnetic layer containing a ferromagnetic powder and a binder, in this order, and having provided on the other face thereof a back coat layer containing carbon black, wherein 16 projections/mm
2
or less of projections having an area of 30 &mgr;m
2
or more and a height of 40 nm or more exist on a surface of the magnetic layer;
(2) The magnetic tape as described in the above (1), wherein a ratio of the thermal expansion coefficient of the magnetic tape to that of the support in a machine direction is 3 or less;
(3) The magnetic tape as described in the above (1) or (2), on which a signal having an areal recording density of 10 to 100 Mbit/cm
2
is recorded;
(4) The magnetic tape as described in any one of the above (1) to (3), wherein the support is a polyethylene terephthalate supp
Doushita Hiroaki
Takahashi Masatoshi
Fuji Photo Film Co. , Ltd.
Resan Stevan A.
Sughrue & Mion, PLLC
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