| 摘要 |
PURPOSE:To obtain a recording medium having a high S/N by using a urethane resin which is a mixture composed of the resin having one COOM (M is H or Na, etc.) in polyester skeleton and the resin having no COOM, has reactive double bonds and has the mol.wt. within a specific range as a binder for magnetic powder. CONSTITUTION:Polyester is so synthesized as to have one COOH in one molecule by adjusting the molar ratio of glycol, triol and dibasic acid such as adipic acid, terephthalic acid or the like. Since the molar ratio is so adjusted that one COOH exists in the same molecule as a whole, the presence of a small quantity of the molecules having no COOH is equally satisfactory. The polyester is then treated with the hydroxide of Li, Na, K to convert the COOH into the salt thereof. The presence of the non-converted COOH is of no problem. Diisocyanate is then brought into reaction with the polyester and further 2-hydroxy (meth) acrylate or the like is brought into reaction therewith, by which the resin having 1,000-100,000mol.wt. and <=56.1X10<3> acid value in terms of COOH X mol.wt. is obtd. Such resin is used for the binder of the magnetic powder, by which the dispersibility of the magnetic powder is improved and the recording medium having excellent electromagnetic transducing characteristics, etc. is obtd.
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