| 摘要 |
899,483. Magnetic structures. DU PONT DE NEMOURS & CO., E.I. Oct. 21, 1960 [Oct. 22, 1959], No. 36157/60. Class 38 (2). In making a magnetic recording tape for which the ratio of remanence in the longitudinal direction to remanence in the transverse direction is greater than 5.3 : 1 acicular magnetic particles in a binder are oriented by a magnetic field before the binder is set and are further oriented by stretching or rolling after the setting. The magnetic particles may beγFe 2 O 3 or CrO 2 and the binder may be polyvinyl butyral, polyvinyl fluoride, polyvinyl chloride, polyacrylonitrile, cellulose acetate butyrate cellulose acetate propylene. The tapes may be coated tapes in which the magnetic material may be applied by solution coating, melt coating or dispersion coating on to a tape base of one of the materials as specified above for the binder and a doctor knife or calendering may be used. Alternatively integral tapes (i.e. without a base) may be formed. Preferred materials are acicular chromium oxide of maximum length 2 Á and axial ratio 8. The chromium oxide particles are prepared by heating chromium trioxide with antimony oxide, ferric oxide and water at 400‹ C. under 600 atmospheres pressure for 3 hours. Details of milling procedures are specified. The magnetic field may be provided by a horseshoe magnet or solenoid. Specifications 686,234, 810,005 and 859,937 are referred to.
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