| 摘要 |
PURPOSE:To improve the viscosity and stability of a magnetic paint and to improve the workability in a coating stage, etc. by using a specific hydroxyl group-contg. acrylic copolymer and polyisocyanate as a binder component for a magnetic recording medium. CONSTITUTION:The binder contains the hydroxyl group-contg. polymer which is obtd. by polymerizing a monomer compsn. consisting of 60-95wt% the copolymerizable alkyl (meth)acrylate expressed by the formula, 5-40wt% hydroxyl group-contg. vinyl monomer and 0-40wt% other copolymerizable monomer and has 600-20,000 number average mol. wt. and the low mol. wt. polyisocyanate having >=2 isocyanate groups. The number average mol. wt. of the hydroxyl group-contg. copolymer to be used is more preferably 2,000-12,000. The elasticity of the resulted acryl urethane resin is poor if said mol. wt. is <=600. The dispersibility of the magnetic powder and the stability of the paint viscosity are poor at >=20,000 and therefore the number average mol. wt. above said value is undesirable. The tough magnetic coated film is obtd. by the above-mentioned binder coupled with the network urethane bond by the reaction between the hydroxyl group and isocyanate group and the allophanate bond by the reaction of the urethane bond and the isocyanate.
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