GB1193843A - Process for the Production of Magnetic Tapes - Google Patents

Abstract

1,193,843. Copying magnetic tapes. AGFAGEVAERT A.G. 27 July, 1967 [29 July, 1966], No. 34602/67, Heading G5R. In a process for producing non-erasable magnetic copies of magnetic tape recordings, movable magnetizable particles are applied to the tape carrying the original magnetic information and are magnetically distributed to form an arrangement in accordance with the magnetic field of the original; the arrangement is then stripped from the original whilst maintaining the distribution. In a first method, the particles are applied to the original as a suspension in a solution of volatile and non-volatile substances and when this solidifies with the particles arranged in accordance with the original field a carrier foil is applied, by casting, coating or sticking, to the solidified magnetic layer and this is then stripped from the original. In a second method, the particles are suspended in a liquid which completely vaporizes after application to the original leaving the particles distributed in accordance with the original magnetic field. A binding agent e.g. cellulose ester is applied which after solidification is removed from the original with the arranged particles. In a third method, magnetic particles are mixed with a thermoplastic resin in a warm state. The mixture is ground on cooling and the granulate when mixed with a granulate derived from thermoplastic resin only is applied to the original and gently shaken. When the magnetic particles are arranged in accordance with the original field the granules are heated and on cooling the layer thus formed is stripped from the original. To enable the copy layer to be stripped easily from the original the surface of the original may have applied thereto vapour-coated layers of SiO 2 , Al 2 O 3 or aluminium or a layer of fat, wax or synthetic film-forming resin. The action of the original field can be intensified by subjecting the tapes to an alternating field during the copying process or by heating the copying layer to a temperature above the Curie point of its magnetic material but which must be below the Curie point of the magnetic material of the original. After copying the copied tape is subjected to a uniform unidirectional magnetic field which may be accompanied by an idealising alternating field. Since the tape is density modulated by the magnetic particles, the information can be reproduced, even if the tape is erased, by subjecting it again to a uniform field. Wavelength halving may be avoided by subjecting the tapes to a unidirectional field during the copying process. If a transparent support and binding agent is used for the copy the tape can be optically played back.