Nichtmagnetische Unterschicht für magnetischer Aufzeichnungsmedium, magnetisches Aufzeichnungsmedium und nichtmagnetische Teilchen

摘要

A magnetic recording medium comprises, in order: (A) a non-magnetic substrate; (B) a non-magnetic undercoat layer comprising a binder resin and non-magnetic particles selected from: (1) acicular or spindle-shaped alpha -Fe2O3 particles which are coated with from 0.01 to 20 wt% (calculated as Al, SiO2 or Al and SiO2 and based on the uncoated alpha -Fe2O3 particles) of an oxide or a hydroxide containing Al, Si or both Al and Si, which coated particles have a molecular-weight-dependent parameter alpha of not less than 0.5 wherein alpha is defined by formula (I): As = K1 . M< alpha > (I> wherein M is the number-average molecular weight of a binder, As is the saturation adsorption of the binder, and K1 is a constant dependent on the binder and the solvent used for measuring As; and (2) BaO.4.5Fe2O3 particles having an average particle diameter of not more than 0.1 mu m; and (C) a magnetic recording layer comprising magnetic particles and a binder resin.