In the field of magnetic tapes, with the widespread use of minicomputers, personal computers, workstations, and other office computers, there has been abundant research in recent years into magnetic tapes (known as “backup tapes”) for recording computer data as external memory devices. In the practical development of magnetic tapes for such applications, particularly in combination with size reduction and the increase in information processing capability in computers, there has been a strong demand for improvement in recording capacity to complement this increase in recording capacity and reduction in size.
In the past, magnetic recording media obtained by coating a magnetic layer comprised of iron oxide, Co-modified iron oxide, CrO2, a ferromagnetic metal powder, and/or a hexagonal ferrite powder dispersed in a binder on a nonmagnetic support have been widely employed. Of these, microgranular ferromagnetic alloy powders and hexagonal ferrite micropowders are known to have good high-density recording characteristics. However, when employing inductive heads that have mainly employed in systems with flexible media, these ferromagnetic powders have not provided adequate output due to their low saturation magnetization. However, the use of the magnetoresistive heads (MR heads) employed on hard disks has also begun in removable recording employing such flexible media.
It is known that due to the high sensitivity of MR heads, adequate reproduction output is achieved even when the above microgranular alloy powders and hexagonal ferrite micropowders are employed and high C/N ratios are achieved due to the low noise characterizing these microgranular powders. When employing MR heads in high-density recording, the use of these microgranular ferromagnetic powders, the smoothing of a magnetic layer surface, and the thinning of a magnetic layer have been proposed to improve resolution.
It is known that a backcoat layer with protrusions is employed to improve the running properties of a magnetic recording medium having a smooth magnetic layer. However, protrusions on a backcoat layer cause pits (called “transfer”) on a magnetic layer surface because the protrusions bite into the magnetic layer surface when the backcoat layer and the magnetic layer surface are superposed, resulting in the problem of decreased output. When the linear recording density is high and the track is narrow, this “transfer” results not only in decreased output, but also in lost signal.
As a means of preventing this transfer, Japanese Unexamined Patent Publication (KOKAI) Heisei No. 10-64041 discloses specifying the density of protrusions equal to or greater than 100 nm in height and employing highly rigid urethane in the magnetic layer to reduce the effect of back transfer in 8 mm video. Japanese Unexamined Patent Publication (KOKAI) No. 2000-40218 describes that a medium suited to a high-density digital recording, which exhibits good electromagnetic characteristics and low dropout as well as good running property and durability of a magnetic layer, can be provided when, in the surface profile of the magnetic layer measured by an atomic force microscope, recesses the cross section of which at 20 nm depth from the root mean square surface is 3 percent or less of the area of the reproduction bit are present by 3 or less in number per 100 μm2.
Japanese Unexamined Patent Publication (KOKAI) Heisei Nos. 11-213377 and 11-259851 disclose a backcoat layer comprising a granular oxide and carbon black, describing that when the adhesive strength of the backcoat to an aramid base is equal to or greater than 80 g/(8 mm width), good running durability is achieved.
However, in addition to preventing transfer of the backcoat layer to the magnetic layer, there is also a need to improve running stability, durability, and storage properties in higher-density recording.
Accordingly, it is an object of the present invention to provide a magnetic recording medium permitting the controlling of backcoat layer transfer to a magnetic layer surface, a reduction in dropout even when employing microgranular magnetic material, as well as good running stability, durability, and storage properties.