Abstract: A magnetic recording medium of the present invention comprises:

Abstract: The present invention provides particles for a non-magnetic undercoat layer of a magnetic recording medium, which comprises acicular hematite particles having an average major axial diameter of not more than 0.3 &mgr;m, a geometrical standard deviation in the major axial diameter of not more than 1.50 and a BET specific surface area of not less than 40 m2/g, and containing a total amount of sodium of not more than 50 ppm calculated as Na. The acicular hematite particles have an excellent dispersibility in a vehicle so that a non-magnetic undercoat layer containing the particles is excellent in surface smoothness and strength. A magnetic recording medium using the non-magnetic undercoat layer is excellent not only in electromagnetic performance, but in storage stability.

Abstract: High-density acicular hematite particles comprise acicular hematite particles and a coat comprising an oxide of tin or oxides of tin and antimony, formed on at least a part of surfaces of said acicular hematite particles; and have an average major axial diameter of not more than 0.3 &mgr;m, a pH value of not less than 8, a soluble sodium salt content of not more than 300 ppm, calculated as Na, and a soluble sulfate content of not more than 150 ppm, calculated as SO4. Such high-density acicular hematite particles is suitable as non-magnetic particles for a non-magnetic undercoat layer of a magnetic recording medium using magnetic particles containing iron as a main ingredient, have an excellent dispersibility in vehicle and a low volume resistivity.

Abstract: Composite particles having an average particle diameter of 0.001 to 10.

Abstract: A magnetic recording medium of the present invention comprises a non-magnetic base film; a non-magnetic undercoat layer formed on the non-magnetic base film, comprising non-magnetic acicular composite particles and a binder resin; and a magnetic recording layer formed on the non-magnetic undercoat layer, comprising magnetic particles and a binder resin,

Abstract: Non-magnetic composite particles have an average particle diameter of 0.06 to 1.

Abstract: Magnetic composite particles having an average particle diameter of 0.06 to 1.0 &mgr;m and a coercive force value of less than 39.

Abstract: The present invention provides particles for a non-magnetic undercoat layer of a magnetic recording medium, which comprises acicular hematite particles having an average major axial diameter of not more than 0.3 &mgr;m, a geometrical standard deviation in the major axial diameter of not more than 1.50 and a BET specific surface area of not less than 40 m2/g, and containing a total amount of sodium of not more than 50 ppm calculated as Na. The acicular hematite particles have an excellent dispersibility in a vehicle so that a non-magnetic undercoat layer containing the particles is excellent in surface smoothness and strength. A magnetic recording medium using the non-magnetic undercoat layer is excellent not only in electromagnetic performance, but in storage stability.

Abstract: A magnetic recording medium of the present invention comprises: a non-magnetic base film; a non-magnetic undercoat layer formed on the non-magnetic base film, comprising a binder resin and non-magnetic acicular black iron-based composite particles; and a magnetic coating film comprising a binder resin and magnetic particles, the non-magnetic acicular black iron-based composite particles comprising: acicular hematite particles or acicular iron oxide hydroxide particles (core particles) having an average major axis diameter of 0.01 to 0.3 &mgr;m; a coating layer formed on the surface of the particles, comprising a specific organosilicon compound; and a carbon black coat composed of at least two carbon black layers integrally formed on the coating layer, adhered with each other through an adhesive on the coating layer.

Abstract: High-density acicular hematite particles comprise acicular hematite particles and a coat comprising an oxide of tin or oxides of tin and antimony, formed on at least a part of surfaces of said acicular hematite particles; and have an average major axial diameter of not more than 0.3 &mgr;m, a pH value of not less than 8, a soluble sodium salt content of not more than 300 ppm, calculated as Na, and a soluble sulfate content of not more than 150 ppm, calculated as SO4. Such high-density acicular hematite particles is suitable as non-magnetic particles for a non-magnetic undercoat layer of a magnetic recording medium using magnetic particles containing iron as a main ingredient, have an excellent dispersibility in vehicle and a low volume resistivity.

Abstract: The present invention provides particles for a non-magnetic undercoat layer of a magnetic recording medium, which comprises particular hematite particles having an average major axial diameter of not more than 0.3 &mgr;m, a geometrical standard deviation in the major axial diameter of not more than 1.50 and a BET specific surface area of not less than 40 m2/g, and containing a total amount of sodium of not more than 50 ppm calculated as Na. The particular hematite particles have an excellent dispersibility in a vehicle so that a non-magnetic undercoat layer containing the particles is excellent in surface smoothness and strength. A magnetic recording medium using the non-magnetic undercoat layer is excellent not only in electromagnetic performance, but in storage stability.

Abstract: A magnetic recording medium of the present invention comprises: a non-magnetic base film; and a magnetic recording layer comprising a binder resin and black magnetic acicular composite particles having an average particle diameter of 0.051 to 0.72 &mgr;m, comprising: magnetic acicular core particles; a coating formed on surface of said magnetic acicular core 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.

Abstract: A magnetic recording medium of the present invention comprises: a non-magnetic base film; a non-magnetic undercoat layer formed on said non-magnetic base film, comprising a binder resin and non-magnetic acicular black iron-based composite particles; and a magnetic coating film comprising a binder resin and magnetic particles, said non-magnetic acicular black iron-based composite particles comprising: acicular hematite particles or acicular iron oxide hydroxide particles having an average major axis diameter of 0.02 to 0.30 &mgr;m; a coating layer formed on the surface of said acicular hematite particle or acicular iron oxide hydroxide particle, comprising a specific organosilicon compound; and a carbon black coat formed on said coating layer. Such a magnetic recording medium has a more smooth surface, a high strength and a lower light transmittance and a low electric resistance even at a small carbon black content.

Abstract: High-density acicular hematite particles comprise acicular hematite particles and a coat comprising an oxide of tin or oxides of tin and antimony, formed on at least a part of surfaces of said acicular hematite particles; and have an average major axial diameter of not more than 0.3 &mgr;m, a pH value of not less than 8, a soluble sodium salt content of not more than 300 ppm, calculated as Na, and a soluble sulfate content of not more than 150 ppm, calculated as SO4. Such high-density acicular hematite particles is suitable as non-magnetic particles for a non-magnetic undercoat layer of a magnetic recording medium using magnetic particles containing iron as a main ingredient, have an excellent dispersibility in vehicle and a low volume resistivity.

Abstract: High-density acicular hematite particles comprise acicular hematite particles and a coat comprising an oxide of tin or oxides of tin and antimony, formed on at least a part of surfaces of said acicular hematite particles; and have an average major axial diameter of not more than 0.3 &mgr;m, a pH value of not less than 8, a soluble sodium salt content of not more than 300 ppm, calculated as Na, and a soluble sulfate content of not more than 150 ppm, calculated as SO4. Such high-density acicular hematite particles is suitable as non-magnetic particles for a non-magnetic undercoat layer of a magnetic recording medium using magnetic particles containing iron as a main ingredient, have an excellent dispersibility in vehicle and a low volume resistivity.

Abstract: The present invention relates to acicular hematite particles containing aluminum of 0.05 to 50% by weight, calculated as Al, having an average major axial diameter of not more than 0.3 &mgr;m and a pH value of the particles of not less than 8, and containing soluble sodium salts of not more than 300 ppm soluble sodium, calculated as Na, and soluble sulfates of not more than 150 ppm soluble sulfate, calculated as SO4, which have an excellent dispersibility in a binder resin, and a magnetic recording medium which uses the hematite particles as non-magnetic particles for a non-magnetic undercoat layer, which has small light transmittance, smooth surface, high strength and high durability, and which is capable of suppressing the deterioration in the magnetic properties caused by a corrosion of the magnetic particles containing as a main ingredient in the magnetic recording layer.

Abstract: Acicular hematite particles of the present invention comprise an average major axis diameter of 0.004 to 0.295 &mgr;m, a geometrical standard deviation of minor axis diameter of not more than 1.35 and a pH value of not less than 8, and containing not more than 300 ppm of soluble sodium salt, calculated as Na and not more than 150 ppm of soluble sulfate, calculated as SO4. Such acicular hematite particles are suitable as non-magnetic particles for a non-magnetic undercoat layer of a magnetic recording medium which exhibits a low light transmittance, an excellent smooth surface and a high strength, and can be prevented from being deteriorated in magnetic properties due to the corrosion of magnetic acicular metal particles containing iron as a main component which are dispersed in a magnetic recording layer thereof.

Abstract: High-density acicular hematite particles comprise acicular hematite particles and a coat comprising an oxide of tin or oxides of tin and antimony, formed on at least a part of surfaces of said acicular hematite particles; and have an average major axial diameter of not more than 0.3 &mgr;m a pH value of not less than 8, a soluble sodium salt content of not more than 300 ppm, calculated as Na, and a soluble sulfate content of not more than 150 ppm, calculated as SO4. Such high-density acicular hematite particles is suitable as non-magnetic particles for a non-magnetic undercoat layer of a magnetic recording medium using magnetic particles containing iron as a main ingredient, have an excellent dispersibility in vehicle and a low volume resistivity.

Abstract: A magnetic recording medium comprising: a base film; a non-magnetic undercoat layer formed on said base film, comprising a binder resin and non-magnetic acicular particles containing iron as a main component, which particles comprise iron and zirconium of 0.05 to 30% by weight, calculated as Zr, based on the total weight of the particles, which is present within the particle; and a magnetic recording layer formed on said non-magnetic undercoat layer and comprising magnetic particles and a binder resin. Such a magnetic recording medium has a low light transmittance, an excellent smooth surface, a high mechanical strength and an excellent durability.

Abstract: Acicular hematite particles of the present invention contain zirconium of 0.05 to 30% by weight (calculated as Zr) based on the total weight of the particles, which is present within the particle, which have an average major axis diameter of not more than 0.3 .mu.m and a pH value of not less than 8, and contain not more than 300 ppm of soluble sodium salt, calculated as Na and not more than 150 ppm of soluble sulfate, calculated as SO.sub.4.Such acicular hematite particles are suitable as non-magnetic particles for a non-magnetic undercoat layer of a magnetic recording medium which exhibits a low light transmittance, an excellent smooth surface, a high strength and an excellent durability, and can be prevented from being deteriorated in magnetic properties due to the corrosion of magnetic acicular metal particles containing iron as a main component which are dispersed in a magnetic recording layer thereof.