| 摘要 |
PURPOSE:To decrease the coefft. of friction and to improve durability by forming a magnetic layer in the main plane of a base, forming a back coating layer dispersed with carbon powder in a binder resin on the other main plane, and incorporating an urethane resin contg. a siloxane bond in the molecule in the binder resin. CONSTITUTION:An urethane resin having a siloxane bond in the molecule is obtd. by the reaction of polyester polyols and polysiloxanes having hydroxyl group at the terminal, for example, dimethyl siloxane and isocyanate. The content of the siloxane occupying in the molecule of the urethane resin is preferably in a 1-10% range by weight with respect to the entire part of the resin. If the content is below said range, the coefft. of friction is not improved. If the content exceeds said range, adhesiveness is decreased. The urethane resin contg. the siloxane bond is preferably used as a mixed system with other resins in order to increase the glass transition temp. Tg of the resin to >=40 deg.C. The more particularly preferable resin is nitrocellulose, and a vinyl chloride/vinyl acetate/vinylalcohol copolymer resin. The carbon powder is used to decrease the coefft. of static friction of the back coating film and to increase the strength of the film. |
