| 摘要 |
PURPOSE:To shorten the half-value period of the charges in a magnetic recording medium by coating magnetic powders with a surface active agent such as fourth grade ammonium salt in advance when a binder containing a special copolymer is used. CONSTITUTION:An aqueous solution of at least one kind of a surface active agent of alkyl ether and betaine types as well as fourth grade ammonium salt and alkyl amine salt is mixed with magnetic powders. After that, the surface active agent adsorbed in the surfaces of the magnetic powders is heated and dried. The magnetic powders thus coated with the surface active agent and treated to be antistatic are dispersed in a ball mill together with nitrile butadiene rubber, copolymer of vinyl chrolide and vinyl acetate and a solvent, and the dispersion is applied to a suitable substrate. As a result, the electric resistance itself is not reduced so much, but the half-value period of the charges is reduced so that the catch of dusts can be reduced. |
