Magnetic recording medium

Black magnetic acicular composite particles for a magnetic recording medium, said black magnetic acicular composite particles having an average particle diameter of 0.051 to 0.72 μm, comprising:

• magnetic acicular iron oxide particles which may contain Co, Al, Ni, P, Zn, Si or B, or may coat with cobalt or both cobalt and iron as magnetic acicular particles,
• a coating formed on surface of said magnetic acicular particles, comprising at least one organosilicon compound selected from the group consisting of:
• (1) organosilane compounds obtainable from alkoxysilane compounds,
• (2) polysiloxanes or modified polysiloxanes, and
• (3) fluoroalkyl organosilane compounds obtainable from fluoroalkylsilane compounds, and
• a carbon black coat formed on said coating layer comprising said organosilicon compound, in an amount of 0.5 to 10 parts by weight based on 100 parts by weight of said magnetic acicular particles.

Black magnetic acicular composite particles for a magietic recording medium, said black magnetic acicular composite particles having an average particle diameter of 0.051 to 0.72 μm, comprising:

• magnetic acicular metal particles containing iron as a main component which contain Co, Al, Ni, P, Zn, Si, B or rare earth elements, or magnetic acicular iron alloy particles containing Co, Al, Ni, P, Zn, Si, B or rare earth elements, as magnetic acicular particles,
• a coating formed on surface of said magnetic acicular particles, comprising at least one organosilicon compound selected from the group consisting of:
• (1) organosilane compounds obtainable from alkoxysilane compounds,
• (2) polysiloxanes or modified polysiloxanes, and
• (3) fluoroalkyl organosilane compounds obtainable from fluoroalkylsilane compounds, and
• a carbon black coat formed on said coating layer comprising said organosilicon compound, in an amount of 0.5 to 10 parts by weight based on 100 parts by weight of said magnetic acicular particles.

In a method of forming a magnetic recording medium comprising a non-magnetic base film, and a magnetic recording layer comprising a binder resin and magnetic particles, the improvement comprising using as magnetic particles black magnetic acicular composite particles having an average particle diameter of 0.051 to 0.72 μm, comprising

• magnetic acicular particles,
• a coating formed on surface of said magnetic acicular particles, comprising at least one organosilicon compound selected from the group consisting of:
• (1) organosilane compounds obtainable from alkoxysilane compounds,
• (2) polysiloxanes or modified polysiloxanes, and
• (3) fluoroalkyl organosilane compounds obtainable from fluoroalkylsilane compounds, and
• a carbon black coat formed on said coating layer comprising said organosilicon compound, in an amount of 0.5 to 10 parts by weight based on 100 parts by weight of said magnetic acicular particles.

A method of producing a magnetic recording medium, comprising forming on a non-magnetic base film a magnetic recording layer comprising a binder resin and as magnetic particles black magnetic acicular composite particles having an average particle diameter of 0.051 to 0.72 μm, comprising

• magnetic acicular particles,
• a coating formed on surface of said magnetic acicular particles, comprising at least one organosilicon compound selected from the group consisting of:
• (1) organosilane compounds obtainable from alkoxysilane compounds,
• (2) polysiloxanes or modified polysiloxanes, and
• (3) fluoroalkyl organosilane compounds obtainable from fluoroalkylsilane compounds, and
• a carbon black coat formed on said coating layer comprising said organosilicon compound, in an amount of 0.5 to 10 parts by weight based on 100 parts by weight of said magnetic acicular particles.