ACICULAR HEMATITE PARTICLE POWDER FOR NONMAGNETIC BASE LAYER AND MAGNETIC RECORDING MEDIUM HAVING NONMAGNETIC BASE LAYER USING THE ACICULAR HEMATITE PARTICLE POWDER

摘要

PROBLEM TO BE SOLVED: To obtain acicular hematite particle powder suitable for nonmagnetic particle powder of a nonmagnetic base layer of a magnetic recording medium which has small transmittance for light, smooth surface, large strength and excellent durability and which suppresses deterioration in the magnetic characteristics. ;SOLUTION: This hematite particle powder is obtd. by dissolving an aq. suspension of an acicular hematite particle powder with an acid under conditions of ≥1.0 N acid concn., ≤3.0 pH, and 20 to 100°C temp. range, then controlling the pH to ≥13, and heat treating at 80 to 103°C. The obtd. powder has 0.004 to 0.295 μm average major axial length, 35.9 to 212 m²/g BET specific surface area, ≥8 pH of the powder, ≤300 ppm soluble sodium salts amt. expressed in terms of Na, ≤150 ppm soluble sulfates amt. expressed in terms of SO₄, and 0.05 to 50 wt.% aluminum expressed in terms of Al in the particle.;COPYRIGHT: (C)1999,JPO