| 摘要 |
PURPOSE:To improve the dispersibility of magnetic powder and the wear resistance of a magnetic layer by making combination use of a prescribed branched polyurethane resin and hydroxyl group-contg. vinyl chloride/vinyl acetate copolymer as a binder for the magnetic powder constituting the magnetic layer on a substrate. CONSTITUTION:The branched polyurethane resin of which the number of the terminals of the main chain and branched chain is >=3 pieces average and which is introduced with a primary hydroxyl group into each terminal and the hydroxyl group-contg. vinyl chloride/vinyl acetate copolymer are used in combination as the binder for the magnetic powder constituting the magnetic layer on the substrate and the content of the branched polyurethane resin occupying the entire part is made 10-90wt%. Such branched polyurethane resin is obtd. by bringing diisocyanate into addition reaction with, for example, polyester polyol having the branched chain and, if necessary, bringing the diol into reaction thereafter.
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