Carbon-coated non-magnetic iron oxide particles for the substrate of multi-layered magnetic recording media

Non-magnetic particles with finer size (less than 200 nm), higher dispersibility, higher blackness and lower electrical resistance are required to produce better multi-layered magnetic tape media which have non-magnetic substrate using non-magnetic sub-layer materials. A special method to prepare acicular hematite particles, whose cross-sectional diameter is about 150 nm, coated with carbon black using a surface modification agent is reported in this paper. Transmission electron microscopy photographs of carbon-coated hematite particles indicate that all of the carbon black is firmly bound to the surface in a distinct layer. The thickness of carbon-coating layer was about 1 to 2 nm if 15% by weight of carbon black is coated onto the particle surface. Non-magnetic substrates for multi-layered magnetic recording media prepared using the carbon-coated particles exhibit improvements in both light transparency and electrical resistance, A decrease in transparency of about 30% as well as a reduction in the electrical resistance of about 1.5 orders of magnitude relative to conventionally prepared substrates was achieved. The surface smoothness and the viscosity were also improved because the dispersibility of these particles in non-magnetic lacquer became better than that of the physical mixture of uncoated hematite particles and carbon black.