Abstract: A flexible magnetic disk sheet having a central circular hole is described, through which an apparatus for reading and writing is engaged, and enclosed in an jacket having a larger central circular hole exposing the hole of the disk sheet within the hole of the jacket, wherein a reinforcing plastic ring containing a solid lubricating agent is provided on the region of the flexible magnetic disk sheet immediately surrounding the central circular hole thereof.

Abstract: A flexible disk comprises a flexible disk jacket having a central opening and a disk-like magnetic recording medium having a central opening smaller than the central opening of the flexible disk jacket in diameter. The recording medium is accommodated for rotation in the flexible disk jacket so that their central openings are concentrically positioned and the portion of the recording medium surrounding the central opening is exposed through the central opening of the jacket, thereby giving access thereto. The portion of the recording medium surrounding the central opening is provided with a protective layer on one side thereof and a reinforcement ring on the other side thereof. The protective layer is formed of a composition which contains a compound with at least one unsaturated bond per molecule that is polymerizable by ultraviolet rays, and which has been cured by exposure to ultraviolet rays.

Abstract: In a method of and apparatus for making a magnetic recording medium, a plurality of rod-like orientation magnets are positioned in spaced relation in the movement direction of a non-magnetic substrate so that the magnetic pole facing the non-magnetic substrate is different between adjacent orientation magnets and the orientation magnets are oblique with respect to the substrate movement direction and alternately point reversely. The spaces between the orientation magnets are adjusted so that the intensity of the magnetic field generated in the substrate movement direction between adjacent orientation magnets is 50 Oe or less. A magnetic coating composition is applied onto the non-magnetic substrate, and magnetic grains contained in the composition are randomly orientated by the orientation magnets.

Abstract: A method for forming protective layer on a surface portion surrounding the edge of a central aperture of a flexible magnetic disc sheet is described, comprising providing a radiation polymerizable composition on a surface portion surrounding the edge of the central aperture of the flexible magnetic disc sheet by screen printing, and hardening the composition by exposure to radiation; a flexible magnetic disc is also described, wherein a protective layer by the foregoing method is provided, with said protective layer having an inner diameter larger than the diameter of the aperture of the disc sheet and an outer diameter smaller than the diameter of the aperture of a jacket enclosing the disc sheet.

Abstract: A flexible magnetic disc comprising a magnetic sheet having on at least a part thereof a protective layer comprising (a) a straight or branched chain compound having an acrylic or methacrylic acid ester moiety on the end of at least one of the principal chain and the side chain, (b) an aromatic ketone, and (c) a silicone lubricant, said layer being hardenable by photopolymerization.

Abstract: A flexible magnetic disk sheet is described, including a central circular hole therein, having a protecting layer formed thereon using (a) a compound including one or more atomic group providing lubricity at at least one end of a main chain or a side chain of molecular of the compound and one or more ester bonds of acrylic acid or methacrylic acid at at least one end of a main chain or a side chain of molecule of the compound, and (b) an aromatic ketone, wherein said protective layer is formed on a surface portion surrounding the edge of the central circular hole of a flexible magnetic disk sheet.

Abstract: A process for preparing a magnetic recording medium comprised of a non-magnetic support having a magnetic layer coated thereon is disclosed. The process involves continuously travelling an undried magnetic layer on a support through a means for magnetic orientation. The means is comprised of at least 5 magnets which are installed at intervals from each other over the undried magnetic layer or under the support. The magnets are positioned in such a manner that each adjacent pole of the magnets facing the magnetic layer or the reverse surface of the support has a different polarity and that the strength of the magnetic field of each adjacent magnet is gradually reduced toward the travelling direction of the magnetic layer. Further the magnets are positioned in such a manner that the line of direction of the magnetic force between adjacent magnets is parallel to the magnetic layer and in opposite directions, whereby the ferromagnetic fine particles in the magnetic layer are randomly oriented.