Magnetic tape

Details Magnetic tape Magnetic tape

2000-09-12

2001-11-20

Resan, Stevan A. (Department: 1773)

Stock material or miscellaneous articles

Structurally defined web or sheet

Including components having same physical characteristic in...

C428S328000, C428S329000, C428S690000, C428S690000, C428S690000, C428S690000, C428S690000, C360S134000

Reexamination Certificate

active

06319595

ABSTRACT:

TECHNICAL FIELD
The present invention relates to magnetic tape having magnetic servo tracks. More particularly, it relates to magnetic tape having magnetic servo tracks on the side opposite to the magnetic recording side.
BACKGROUND ART
The recent expanding scale of the computer network and the importance of security for data management have been increasing the demand for magnetic tape having an increased recording capacity for use as a medium for data backup. Approaches to high recording capacity are divided into improvement on recording density and extension of the tape length.
Since the tape length that can be put in a tape cartridge as wound is the upper limit of the recording capacity, extension of the tape length for increasing the recording capacity cannot be achieved but by reducing the tape thickness. Therefore, an increase in recording capacity attained by this approach is of necessity limited. With respect to the method of increasing a recording density, it is known that magnetic tape has a lower recording density than a hard disc drive. Serpentine type magnetic tape particularly has a low recording density, which is due to the low track density. On the other hand helical scan type magnetic tape is known to have a higher track density than the serpentine type magnetic tape. This is because the magnetic tape of helical scan type uses a servo tracking system called automatic track finding (ATF).
A servo tracking system has also been adopted to serpentine type magnetic tape to improve the track density. Methods that have been proposed as such a servo tracking system include an embedded servo system, in which servo signals are written on the same track as the data track on the magnetic recording surface, and a system in which a track exclusive to servo signals is provided on the magnetic recording surface. Japanese Patent Publication No. 82626/95 proposes a tracking system particularly useful where the pitch of data tracks is as small as several tens of microns, in which a dedicated track for servo information is provided on the magnetic recording surface and a plurality of servo signal reproduction heads are used to read the servo signals for tracking. According to this technique, however, the number of servo signal reproduction heads must be increased as the number of tracks increases. In order to avoid this, the servo track should be increased. Like this, conventional servo tracking systems use the same side of magnetic tape as used for data recording, which results in reduction of the data recording area. This problem is conspicuous in the servo tracking system of Japanese Patent Publn. No. 82626/95 when a track density is as high as about 30 tpmm (tracks per mm) or even more.
DISCLOSURE OF THE INVENTION
Accordingly, an object of the present invention is to provide magnetic tape which is capable of servo tracking without reducing the data area.
Another object of the present invention is to provide magnetic tape having an increased track density.
Still another object of the present invention is to provide magnetic tape having a high recording capacity.
As a result of extensive investigation, the present inventors found that servo tracking can be carried out without diminishing the data area of a magnetic layer by providing a magnetic servo track on the backcoating layer of magnetic tape, which turned out to give rise to a new problem as to various characteristics of the magnetic tape. As a result of further study, they have found that the various problems associated with a magnetic servo track formed on the backcoating layer can be solved to provide magnetic tape accomplishing the above objects by defining the coercive force and saturation flux density of the backcoating layer to be above a specific value or below a specific value, respectively, in relation to the coercive force and the saturation flux density of the whole of all the layers on the magnetic layer side.
Completed based on the above finding, the present invention has accomplished the above objects by providing magnetic tape comprising a substrate, a magnetic layer provided on one side of the substrate and a backcoating layer provided on the other side of the substrate, wherein the backcoating layer is a layer capable of magnetic recording on which three or more servo tracks have magnetically been formed in parallel with the longitudinal direction of the tape, and the backcoating layer has a higher coercive force than the coercive force of the whole of all the layers on the magnetic layer side and has a lower saturation flux density than the saturation flux density of the whole of all the layers on the magnetic layer side.


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