HEMATITE POWDER FOR NONMAGNETIC SUBSTRATE OF MAGNETIC RECORDING MEDIUM PRODUCED BY USING MAGNETIC METAL POWDER COMPOSED MAINLY OF IRON, NONMAGNETIC SUBSTRATE OF MAGNETIC RECORDING MEDIUM PRODUCED BY USING SAID HEMATITE POWDER, MAGNETIC RECORDING MEDIUM PRODUCED BY USING SAID NONMAGNETIC SUBSTRATE LAYER AND PRODUCTION OF SAID HEMATITE POWDER

摘要

PROBLEM TO BE SOLVED: To obtain hematite particle powder having low soluble sodium salt content and soluble sulfate content, low electrical resistance and improved dispersibility by heating and dehydrating acicular goethite particles coated with tin hydroxide, heating the resultant low- density acicular hematite particles, crushing the obtained slurry containing high-density acicular hematite particles and heat-treating the product under specific condition. SOLUTION: Acicular goethite particles surface-coated with tin hydroxide are dehydrated by heating and the obtained low-density acicular goethite particles are heated at =550 deg.C to obtain high-density acicular hematite particles coated with tin oxide. A slurry containing the hematite particles is crushed in wet state, adjusted to pH=13, heated at =80 deg.C, filtered, washed with water and dried to obtain hematite powder composed of high-density acicular hematite particle powder having an average major axis diameter of =0.3 m, pH of =8, a soluble sodium salt content of =300 ppm in terms of Na and a soluble sulfate content of =150 ppm in terms of SO4 and surface-coated with tin oxide and useful for a nonmagnetic substrate of a magnetic recording medium.