High-density acicular hematite particles, non-magnetic undercoat layer and magnetic recording medium

摘要

High-density acicular hematite particles comprise acicular hematite particles and a coat comprising an oxide of tin or oxides of tin and antimony 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 mu 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 are 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.