| 摘要 |
PURPOSE:To obtain a magnetic recording medium having a high squareness ratio and superior scratch resistance by using polyurethane resin consisting of silicone oil having groups each contg. active hydrogen, a compound having a specified spiro ring, specified polyol and polyisocyanate as a binder. CONSTITUTION:Polyurethane resin C consisting of a low molecular multi-functional compound A2 contg. active hydrogen, high molecular polyol A1 and polyisocyanate B is manufactured. The compound A2 has groups each contg. active hydrogen such as OH, NH2, NH and SH and has 30<250 equiv. per said one group. The polyol A1 has 250-5,000 equiv. When the resin C is manufactured, modified silicone oil (a) having groups each contg. active hydrogen and a compound (b) having a spiro ring represented by formula I such as a compound represented by formula II (where X is a spiro ring represented by the formula I ) are contained as the compound A2. The resulting polyurethane C having 5,000- 100,000 number average mol.wt. is used as a binder for magnetic powder. The magnetic powder is well dispersed, and a magnetic recording material having a high squareness ratio and superior adhesive strength is obtd.
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