Process for producing a ferrofluid, and a composition thereof

Claim 2

A process for producing an improved ferrofluid, which comprises: controlling pH of an aqueous suspension of ferromagnetic fine particles to less than an equipotential point; adding a surface-active agent and an organic solvent having a low boiling point to said ferromagnetic fine particles to coat each surface of said fine particles with said surface-active agent; dispersing said thus coated fine particles in said organic solvent to form an intermediate particulate material; separating ferromagnetic fine particles of bad dispersion from said intermediate particulate material; mixing a dispersing medium selected from the group of an oil group, an ester group or an ether group with said intermediate particulate material to form a mixture thereof; and heating said mixture to evaporate said organic solvent to form said improved ferrofluid.

Claim 3

The process for producing an improved ferrofluid as claimed in claim 1, wherein said intermediate particulate material is obtained by adding said surface-active agent to said ferromagnetic fine particles to coat each surface of said first particles with said surface-active agent prior to adding said organic solvent to said thus coated fine particles.

Claim 4

The process for producing an improved ferrofluid as claimed in claim 1, wherein said intermediate particulate material is obtained by adding said organic solvent having a low boiling point so said ferromagnetic fine particles to form a suspension and adding said surface-active agent to said suspension.

Claim 5

The process for producing an improved ferrofluid as claimed in claim 1, wherein said intermediate particulate material is obtained by adding a mixture of said surface-active agent and said organic agent to said ferromagnetic fine particles.

Claim 6

The process for producing an improved ferrofluid as claimed in claim 1, wherein said surface-active agent is a compound having more than 10 carbon atoms and one or more polar groups selected from the COOH group, OH group, SO 3 H group and is any one of an acid, salt or lactone of said compound.

Claim 7

The process for producing an improved novel ferrofluid as claimed in claim 1, wherein when said ferromagnetic fine particles are coated in an aqueous suspension, and wherein a quantity of said surface-active agent added to said aqueous suspension is limited to an enabling formation of a monomolecular layer on each surface of said fine particles.

Claim 8

The process for producing an improved ferrofluid as claimed in claim 1, wherein said dispersing medium selected is provided with a nonionic surface-active agent.

Claim 9

A process for producing an improved ferrofluid, which comprises: (a) controlling pH of an aqueous suspension of ferromagnetic fine particles to less than an equipotential point; (b) adding a surface-active agent and an organic solvent having a low boiling point to said ferromagnetic fine particles to coat each surface of said fine particles with said surface-active agent; (c) dispersing said thus coated fine particles in said organic solvent to form an intermediate particulate material; (d) separating ferromagnetic fine particles of bad dispersion from said intermediate particulate material: (e) heating said intermediate particulate material to evaporate said organic solvent; and (f) subsequently adding a dispersion agent selected fron an oil group, an ester group or an ether group to said material of step (e) to from said improved ferrofluid.

Claim 10

A process for producing an improved ferrofluid, which comprises: (a) controlling pH of an aqueous suspension of ferromagnetic fine particles to less than an equipotential point; (b) adding a surface-active agent and an organic solvent having a low boiling point to said ferromagnetic fine particles to coat each surface of said fine particles with said surface-active agent; (c) dispersing said thus coated fine particles in said organic solvent to form an intermediate particulate material; (d) separating ferromagnetic fine particles of bad dispersion from said intermediate particulate material: (e) heating said intermediate particulate material to evaporate said organic solvent; and (f) subsequently adding a dispersion agent selected fron an oil group, an ester group or an ether group to said material of step (e) to from said improved ferrofluid.

Claim 11

A ferrofluid composition comprising: a poly-α-olefin oil as a dispersing medium having an oligomer of from 25 to 45 carbon atoms; ferromagnetic fine particles dispersed in said poly-α-olefin oil in an amount of from 1 to 20 volume percent, said ferromagnetic particles having a particle size of from 20 to 500 Å; a first surface-active agent and a second surface-active agent each of which is adsorbed on said ferromagnetic fine particles; and an oxidation inhibitor in an amount of from 0.1 to 10 weight percent of said poly-α-olefin oil.

Claim 12

A ferrofluid composition comprising: a poly-α-olefin oil as a dispersing medium having an oligomer of from 25 to 45 carbon atoms; ferromagnetic fine particles dispersed in said poly-α-olefin oil in an amount of from 1 to 20 volume percent, said ferromagnetic particles having a particle size of from 20 to 500 Å; a first surface-active agent and a second surface-active agent each of which is adsorbed on said ferromagnetic fine particles; and an oxidation inhibitor in an amount of from 0.1 to 10 weight percent of said poly-α-olefin oil.

Claim 13

The ferrofluid composition as claimed in claim 9, wherein said first surface-active agent in an unsaturated fatty acid salt having more than .[.8.]. .Iadd.10 .Iaddend.carbon atoms.

Claim 14

The ferrofluid composition as claimed in claim 9, wherein said second surface-active agent is a saturated fatty acid .[.salt.]. having more than 18 carbon atoms.

Claim 15

A process for producing an improved ferrofluid, which comprises: adding a first surface-active agent and an organic solvent having a low boiling point to ferromagnetic fine particles to coat each surface of said fine particles with said first surface-active agent; dispersing said thus coated fine particles in said organic solvent to form an intermediate particulate material; separating some ferromagnetic fine particles of bad dispersion from said intermediate particulate material; adding a poly-α-olefin oil, a saturated fatty acid as a second surface-active agent having more than 18 carbon atoms and an oxidation inhibitor to said intermediate particulate material, to prepare a mixture thereof; and heating said mixture to evaporate organic solvent.

Claim 16

A process for producing an improved ferrofluid, which comprises: adding a first surface-active agent and an organic solvent having a low boiling point to ferromagnetic fine particles to coat each surface of said fine particles with said first surface-active agent; dispersing said thus coated fine particles in said organic solvent to form an intermediate particulate material; separating some ferromagnetic fine particles of bad dispersion from said intermediate particulate material; adding a poly-α-olefin oil, a saturated fatty acid as a second surface-active agent having more than 18 carbon atoms and an oxidation inhibitor to said intermediate particulate material, to prepare a mixture thereof; and heating said mixture to evaporate organic solvent.

Claim 17

A process for producing an improved ferrofluid, which comprises: (a) adding a first surface-active agent and an organic solvent having a low boiling point to ferromagnetic fine particles to coat each surface of said fine particles with said first surface-active agent; (b) dispersing said thus coated fine particles in said organic solvent to form an intermediate particulate material; (c) separating some ferrogmagnetic fine particles of bad dispersion from said intermediate particulate material; .[.(d) adding a poly-α-olefin oil to said intermediate particulate material;.]. .[.(e).]. .Iadd.(d) .Iaddend.heating said intermediate particulate material to evaporate organic solvent; and .[.(f).]. .Iadd.(e) .Iaddend.adding a poly-α-olefin oil, a saturated fatty acid as a second surface-active agent having more than 18 carbon atoms and an oxidation inhibitor to the produce of step .[.(e).]..Iadd.(d).Iaddend..

Claim 18

A process for producing an improved ferrofluid, which comprises: (a) adding a first surface-active agent and an organic solvent having a low boiling point to ferromagnetic fine particles to coat each surface of said fine particles with said first surface-active agent; (b) dispersing said thus coated fine particles in said organic solvent to form an intermediate particulate material; (c) separating some ferrogmagnetic fine particles of bad dispersion from said intermediate particulate material; .[.(d) adding a poly-α-olefin oil to said intermediate particulate material;.]. .[.(e).]. .Iadd.(d) .Iaddend.heating said intermediate particulate material to evaporate organic solvent; and .[.(f).]. .Iadd.(e) .Iaddend.adding a poly-α-olefin oil, a saturated fatty acid as a second surface-active agent having more than 18 carbon atoms and an oxidation inhibitor to the produce of step .[.(e).]..Iadd.(d).Iaddend..