Magnetic recording medium

Stock material or miscellaneous articles – Composite – Of polyamide

Reexamination Certificate

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C428S474700, C428S428000, C428S428000, C428S900000

Reexamination Certificate

active

06395400

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a magnetic recording medium which comprises a nonmagnetic support having thereon a magnetic layer comprising a ferromagnetic powder dispersed in a binder, wherein the nonmagnetic support is made of an aromatic polyamide resin and, more particularly, to a magnetic recording medium hardly sustaining improper tape winding or edge damages.
2. Description of Prior Art
Magnetic recording media are required to satisfy various characteristics. For example, a magnetic recording tape used for an audio tape for reproduction of music recordings requires high original sound reproduction capability, while a magnetic recording tape used for a videotape requires high original picture reproduction capability. In addition to such electromagnetic characteristics, the magnetic recording tape requires good running performance and running durability. Recently, such a magnetic recording tape requires to record signals with high density. For media for computer storage, particularly, for compact backup system tapes as represented by the D8 and the DDS, the media are required to have a thinner total tape thickness for a large capacity.
To response various demands as above, various improvements are added to respective structural elements of the magnetic recording media. The magnetic recording medium generally has a magnetic layer on one side of the nonmagnetic support (optionally, a nonmagnetic undercoating layer may be formed when necessary) and a back-coating layer on the other side of a nonmagnetic support. To cope with downsizing and higher density recording, not only the magnetic layer but also the entire layers constituting the magnetic recording medium are required to be thinner. To make the thickness of the magnetic recording tape thinner, conventionally, the nonmagnetic support was made thinner, or the nonmagnetic layer formed between the nonmagnetic support and the magnetic layer was made thinner. If the nonmagnetic support is made thinner below a certain range, however, the medium loses the running durability. If the nonmagnetic layer is made thinner, the medium suffers from lowered outputs, increased error rates, and increased dropouts. Therefore, for the magnetic recording tapes for the DDS-2 and DDS-3 formats, aramid based supports (see, Japanese Patent No. 2,724,581) came to be used as a nonmagnetic support for improving the electromagnetic characteristics and the running durability, instead of polyester based supports such as polyethyleneterephthalate (PET) and polyethylenenaphthalate (PEN), which are used conventionally. Particularly, when the tape thickness is made thinner, it becomes difficult to keep strong contact of the head with the tape surface, and it is therefore desirable to use a support having a high module of elasticity. Consequently, aromatic polyamide (aramid) came to be used these days.
However, we have discovered that when the aromatic polyamide is used as the nonmagnetic support, tape edges of the magnetic recording tape become thicker as the tape runs more frequently, thereby creating an improper winding or thereby sustaining edge damages that the tape edges are worn out. This would cause the tape to be unable to run. This tendency is remarkable in a videotape for business use in which cueing, reviewing, and so on are frequently used.
Thus, in magnetic recording media using an aromatic polyamide as a nonmagnetic support, occurrences of improper windings and edge damages raise serious problems. Therefore, it is an object of the invention to provide a magnetic recording medium using an aromatic polyamide film as a nonmagnetic support and hardly sustaining improper windings and edge damages.
SUMMARY OF THE INVENTION
The inventors have diligently researched magnetic recording media to accomplish the above object. Consequently, the inventors have found out that the problems of sustaining improper windings and edge damages could be solved by selection of an aromatic polyamide having a loss tangent satisfying prescribed conditions for a magnetic recording medium even where an aromatic polyamide is used for nonmagnetic support, and reaches the completion of the invention.
According to the invention, a magnetic recording medium comprises a nonmagnetic support made of aromatic polyamide resin, and a magnetic layer formed on the nonmagnetic support containing ferromagnetic powders dispersed in a binder, wherein the magnetic recording medium has a loss tangent at the temperature of 40° C. is 0.7 or higher with respect to a loss tangent at the temperature of 100° C.
In the above magnetic recording medium, the loss tangent at the temperature of 40° C. is preferably 1 or higher with respect to a loss tangent at the temperature of 100° C., and the loss tangent at the temperature of 100° C. is preferably 0.05 or lower.
In another aspect of the invention, a magnetic recording medium comprises a nonmagnetic support made of aromatic polyamide resin, and a magnetic layer formed on the nonmagnetic support containing ferromagnetic powders dispersed in a binder, wherein the magnetic recording medium has a loss tangent at the temperature of 100° C. of 0.05 or lower. In this magnetic recording medium, the loss tangent at the temperature of 100° C. is preferably 0.01 or higher.
In any magnetic recording medium according to the invention, a nonmagnetic layer mainly containing nonmagnetic inorganic powders and a binder may be formed on the nonmagnetic support, and the magnetic layer containing the ferromagnetic powders and the binder and having a thickness of 0.05 &mgr;m or larger and 1.0 &mgr;m or lower may be formed on the nonmagnetic layer.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The magnetic recording medium according to the invention comprises a nonmagnetic support and a magnetic layer formed on the nonmagnetic support containing ferromagnetic powders dispersed in a binder, and is characterized in using an aromatic polyamide resin as the nonmagnetic support and having a loss tangent at the temperature of 40° C. of 0.7 or higher with respect to a loss tangent at the temperature of 100° C. In this magnetic recording medium according to the invention, the above problems can be solved by selecting an aromatic polyamide resin having a loss tangent at the temperature of 40° C. of 0.7 or higher with respect to a loss tangent at the temperature of 100° C. [0.7≦tan&dgr; (40° C.)/tan&dgr; (100° C.)]. Preferably, 0.7≦tan&dgr; (40° C.)/tan&dgr; (100° C.)≦2, and more preferably, 0.8≦tan&dgr; (40° C.)/tan&dgr; (100° C.)≦1.5.
To raise the capability of editing in a videotape for business use, the tape should be run in various running styles. During cueing mode or reviewing mode, the tape is made to run at a high speed even though a short period of time, and the tape becomes a high temperature because the tape is subject to high speed contacts, and conversely, during a normal play mode, the tape receives contacts for a long period of time, though the tape is subject to weak contacts and a relatively lower temperature. Running of the tape at a high temperature largely influences viscoelasticity of the tape but the property at a relatively low temperature is also important. To make stable the tape running at a high temperature though a short period of time and the tape running at a relatively low temperature for a long period of time, it is preferable to set the loss tangent indicating the viscoelasticity of the magnetic recording medium constant notwithstanding the temperature or frequency. The above problem can be solved by rendering the magnetic recording medium satisfy the above condition of 0.7≦tan&dgr; (40° C.)/tan&dgr; (100° C.).
Generally, a loss tangent of a magnetic recording medium is relatively low at 40° C. or around room temperature, although the loss tangent has tendency to increase as temperature increases. Accordingly, in the magnetic recording medium of the invention, in addition to the rate of tan&dgr; (40° C.)/tan&dgr; (100° C.), the loss tangent (absolute value) at the temperature

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