PURPOSE: To reduce the hydrophobicity rate and precipitation speed of magnetic powder and improve the dispersibility by a method wherein the surface-treated magnetic powder is transferred into a non-polar solvent layer under the existance of salt.
CONSTITUTION: When magnetic powder is subjected to surface-treatment, the magnetic powder is dispersed in a polar solvent such as a hydrophilic solvent or water. 50W200ml of the polar solvent is necessary for 100gr of the magnetic powder. When it is dispersed, a pH control agent is added to the polar solvent, if necessary, to control the pH value of the solvent in accordance with the equipotential point of the magnetic powder. NaOH, KOH, Na3PO4 and the like are used as the pH control agent to charge the powder surface negative and HCl, H2SO4, H3PO4 and the like are used as the pH control agent to charge the powder surface positive. When the magnetic powder is transferred into a non- polar solvent layer, an anion system or a cation system surface active agent composed of salt is applied and the hydrophobicity rate and precipitation speed of the magnetic powder is reduced and the dispersibility is improved.
YOSHIDA SHIGEKI
MURATA HIDENORI
MATSUMOTO KAZUMASA
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