GRANULATED SUBSTANCE FOR MAGNETIC IRON OXIDE PARTICLE FOR MAGNETIC RECORDING, PRODUCTION THEREOF AND PRODUCTION OF MAGNETIC IRON OXIDE GRANULAR POWDER FOR MAGNETIC RECORDING WITH THE USE OF THE GRANULATED SUBSTANCE

摘要

PURPOSE:To provide a granulated substance for magnetic iron oxide particle for magnetic recording composed of needle-like granulated substance of iron(III) oxide hydrate or needle-like granulated substance of iron(III) oxide and to provide a production method capable of obtaining the granulated substance on an industrial scale. CONSTITUTION:Needle-like particles of iron(III) oxide hydrate or needle-like particles of iron(III) oxide is suspended in water. Semisynthetic starch or semisynthetic cellulose, which is soluble in water or hot water, is added to a suspension in the ratio of 0.1-5.0wt.% to the needle-like particles of iron(III) oxide hydrate or the needle-like particles of iron(III) oxide. After mixing of the liquid, a cake is obtained by press-dehydration and this is granulated to obtain the granulated substance for magnetic iron oxide particles for magnetic recording. The granulated substance has an average granulated size of 1-7mm, an apparent density of >=0.3g/cm<3> and a powder ratio of <=40%. This is reduced under heating in a reducing gas to obtain needle-like magnetite particles or thereafter further oxidized to obtain needle-like maghemite particles. The objective magnetic iron oxide granular powder for magnetic recording is obtained from either of those particles, optionally after the modification with Co or Co and Fe<2+>.