Acicular hematite particles having a low sodium content and their use in a magnetic recording medium

摘要

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 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.