NONMAGNETIC PARTICLE POWDER FOR NONMAGNETIC GROUND LAYER OF MAGNETIC RECORDING MEDIUM, ITS PRODUCTION AND MAGNETIC RECORDING MEDIUM

摘要

PROBLEM TO BE SOLVED: To produce a needlelike hematite particle powder suitable as a nonmagnetic particle powder for a nonmagnetic ground layer of a magnetic recording medium having a smooth surface, a high strength, excellent in durability and having suppressed deterioration of magnetic characteristics accompanying the corrosion of a needlelike metal magnetic particle powder dispersed in the magnetic recording layer and consisting essentially of iron. ;SOLUTION: This needlelike hematite particle powder comprises an aluminum-containing needlelike hematite particle powder containing aluminum in an amount of 0.05-50 wt.% expressed in terms of Al in the interior of the particle and having ≤1.50 geometrical standard deviation value of the major axial diameter, ≤1.30 geometrical standard deviation value of the minor axial diameter, 40-180 m2/g specific surface area according to the BET method, ≥8.0 powder pH value, ≤300 ppm content of soluble sodium salts expressed in terms of Na, ≤150 ppm content of soluble sulfates expressed in terms of SO4 and further 0.01-0.2 μm average major axial diameter.;COPYRIGHT: (C)2000,JPO