1. Field of the Invention
The present invention relates to a magnetic recording medium having a coating type magnetic recording layer wherein ferromagnetic particles are perpendicularly oriented. More particularly, the present invention relates to a magnetic recording medium which has a feature in the composition of an undercoating layer beneath the magnetic recording layer.
2. Description of the Prior Art
Magnetic recording media are now widely used in the fields of audio and video recording, computers, magnetic discs, etc., and they are expected to be used in the fields of video floppies, etc. Accordingly, the amount of information to be recorded on magnetic recording media increases year after year, and there is an increasing demand for the improvement of the recording density of magnetic recording media.
With respect to the magnetic recording media such as magnetic tapes, it has been common to improve the magnetic characteristics by e.g. orienting acicular magnetic particles in a magnetic recording layer in a longitudinal direction. However, those with acicular magnetic particles oriented in a longitudinal direction are not suitable for a high density recording although they are capable of obtaining a high output in a low frequency region.
For this reason, it has been recently proposed to use a magnetic recording medium wherein a plate crystal barium ferrite magnetic powder having an easily magnetizable axis in a perpendicular direction, is used for a magnetic recording layer (Japanese Unexamined Patent Publication No. 195328/1982).
However, such a medium wherein the barium ferrite magnetic powder is used, has a difficulty that erase characteristics are inferior although it is excellent in the short wavelength recording characteristics. Besides, barium ferrite has by itself an electric resistance of as high as at least 10.sup.16 .OMEGA./cm.sup.2, and accordingly, in the case where no conductive substance such as carbon black is used in combination with barium ferrite, the magnetic recording medium is likely to adhere to the head, or is likely to adhere to guide rollers, calender rollers, etc. during the production process such as a coating process. In an extreme case, an electric discharge noise will be generated. Under the circumstances, it is natural to consider the use of a conductive substance in combination with the magnetic powder, and it has been proposed to incorporate carbon black into the magnetic recording layer to reduce the electric resistance. However, if the amount of the incorporation is substantial, it is inevitable that the magnetic density lowers. Therefore, it is necessary to reduce the amount of carbon black in order to attain a high density. However, if the amount of carbon black is reduced, the generation of the discharge noise is inevitable.
USPTO Backgrounds
USPTO Backgrounds