NON-MAGNETIC GRANULAR POWDER, ITS PRODUCTION AND SUBSTRATE LAYER FOR MAGNETIC RECORDING MEDIUM USING THE SAME

摘要

PURPOSE:To obtain the subject antiseismic substrate excellent in surface smoothness and mechanical strength by using granular non-magnetic BaO.4.5Fe2O3 powder. CONSTITUTION:This antiseismic non-magnetic substrate having the above- mentioned advantages is obtained by using non-magnetic granular powder consisting of BaO.4.5Fe2O3 non-magnetic granules prepared by sticking Al and/or Si hydroxide or oxide having both these elements onto the granule surface >=0.50 in the molecular weight-dependent parameter alpha in the relationship between polymer molecular weight (M) and saturated absorption (As): As=K1M [(a) means the molecular weight-dependent parameter alpha]. Specifically, the above non-magnetic powder is produced by the following processes: an aqueous alkaline solution is added to an aqueous suspension containing BaO.4.5Fe2O3 non- magnetic granules to bring the pH level of the suspension to >=10 followed by adding Al and/or Si compound(s) to the suspension to adjust its pH level to about 7 to rapidly precipitate Al and/or Si hydroxide or oxide, and this precipitate is washed and dried and then subjected to consolidated grinding.