Nok Corporation

Hirokazu Nagato

Takao Kanno

Yutaka Koda

Yutaka Kouda

Takahiro Ishizuka

Yasuki Karita

A magnetic fluid is produced by adding a solution of N-polyalkylenepolyamine-substituted alkenylsuccinimide in a hydrocarbon solvent to an aqueous suspension of fine particles of ferrites, thereby adsorbing the N-polyalkylenepolyamine-substituted alkenylsuccinimide onto the fine particles of ferrites, distilling off water and the hydrocarbon solvent therefrom, and dispersing the fine particles of N-polyalkylenepolyamine-substituted alkenylsuccinimide-adsorbed magnetites as residues into a base oil of low vapor pressure having a vapor pressure of not more than 0.1 mmHg at 25.degree. C.

Process for producing magnetic fluid

A magnetic fluid containing fine particles of ferrite stably dispersed in a carrier liquid is prepared by adding carrier liquid and a dispersing agent selected from N-polyalkylenepolyamine-substituted alkenylsuccinimide, an oxyalkylene-substituted phosphoric acid ester and a nonionic surfactant, and, if required, hydrocarbon solvent having a low boiling point to particles of ferrite which is coated with water-soluble surfactant and subjecting the resulting mixture to a dispersion treatment and, if required, removal of the hydrocarbon solvent.

Process for preparing a magnetic fluid

A magnetic fluid containing fine particles of ferrite stably dispersed in a low vapor pressure base oil is prepared by adding N-polyalkylenepolyamine-substituted alkenylsuccinimide (and a low vapor pressure base oil) to a suspension of fine particles of surfactant-adsorbed ferrite dispersed in a low boiling point hydrocarbon solvent, heating the resulting mixture, separating the hydrocarbon solvent therefrom, adding a low vapor pressure base oil and a specific dispersing agent to the fine particles of N-polyalkylenepolyamine-substituted alkenylsuccinimide-coated ferrite as the residues and subjecting the resulting mixture to a dispersion treatment.

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Fujisawa, Japan

Hirokazu Nagato