| 摘要 |
PROBLEM TO BE SOLVED: To obtain a dispersing agent which can give magnetic substance particles having excellent dispersibility when applied to magnetic substance particles by using a high-molecular-weight copolymer obtained by copolymerizing a specified polyoxyalkylene vinyl ether with maleic anhydride. SOLUTION: A polyoxyalkylene vinyl ether represented by the formula (A is a 2-4C alkylene; R is H or a 1-4C alkyl; and n is 1-50) is radical-copolymerized with maleic anhydride in the presence of a radical initiator (e.g. benzoyl peroxide) to produce a copolymer having a weight-average molecular weight of 500-500,000. A dispersing agent comprising the obtained copolymer is applied to the surfaces of magnetic substance particles such asγ-Fe2 O3 , Fe3 O4 or ferrite. A water-based coating material containing the obtained magnetic substance particles, an acrylic resin, water, etc., is applied to the surface of a substrate and dried to obtain a magnetic recording medium. Thus, it is possible to produce magnetic recording media having a high magnetic recording density easily and inexpensively.
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