PURPOSE: To obtain a magnetic fluid excellent in dispersibility without causing desorption of a modifier, separation and settling of fine particles, etc., by reacting ferromagnetic substance particles with a specific monoisocyanate compound and then dispersing the resultant reaction product in a high-boiling organic solvent.
CONSTITUTION: Ferromagnetic substance particles such as magnetite having especially preferably 100-10nm particle diameter are reacted with a monoisocyanate compound expressed by the formula OCN-R (R is 1-30C alkyl, 6-30C cycloalkyl or aryl) and the resultant reaction product is then dispersed in a high-boiling organic solvent such as kerosene, n-paraffin or a polyalkylene oxide having preferably 170-500°C boiling point and 1-50cSt viscosity (at 40°C) to afford the objective magnetic fluid. Furthermore, the amount of the aforementioned organic solvent is preferably 5-200wt.% based on the magnetic substance particles.
SUZUKI AKINORI
SATO NAOTAKE
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