In recent years, there has been a growing tendency in magnetic recording media, especially in magnetic recording media for videorecorders required to record a short wave length signal, to use the magnetic powder having finer grain size and higher capability of magnetization.
However, when the grain size of magnetic powder is made finer and its BET value is increased, the light transmittance of the magnetic recording medium is increased and the efficiency to shield light is decreased. This causes a problem relating to the light-transmission of the recording medium. For example, in the case of a videotape, the end of the tape is detected by the variation of light transmittance. Especially in the case of VHS type videotape, the light transmittance of the videotape must be not more than 0.1%, at a wave length of 900 nm.
Recently, there has been a tendency to reduce the thickness of a videotape in order to make it possible to increase the recording time of a videotape. Accordingly, the thickness of the magnetic layer becomes thinner, which is why the magnetic layer is required to have its light-shielding power increased.
As a measure to increase the light-shielding power of a videotape, it is publicly known that carbon black is added to a magnetic layer. However, when too much carbon black is added to a magnetic layer, it causes a reduction of the dispersibility of the magnetic powder and carbon black in the paint, and furthermore it causes a reduction of the stability of the dispersion. Since the magnetic powder is reduced in quantity, the electro magnetic conversion characteristic and tape running durability are deteriorated.