| 摘要 |
PURPOSE:To obtain a high reproduced output and high durability by using pulverous ferromagnetic iron oxide powder having a specific surface area and a binder consisting of a polyurethane resin having SO3M groups. CONSTITUTION:The pulverous ferromagnetic iron oxide powder has <=30m<2>/g specific surface area and the binder is the polyurethane resin having >=1 SO3M groups (where M is H, Li, Na or K) for each 1mol. The pulverous ferromagnetic iron oxide powder is enumerated by mixed crystals composed of r-Fe2O3, r-Fe2O3 and Fe3O4 or these magnetic materials deposited or doped with Co, etc. The pulverous ferromagnetic iron oxide powder having the specific surface area larger than 30m<2>/g is relatively highly rugged in magnetic particle surface and is susceptible to damage by the friction with a magnetic head and therefore there is a problem in terms of durability. The successful dispersion of the powder into the urethane resin is not possible and eventually the high reproduced output and high durability are not obtainable. The number average mol. wt. of the polyurethane resin is preferably 5,000-50,000.
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