EP0206516A2 — Ferrofluid composition, method of making, and app…

Claim 1

Independent Claim 80 words

A stable ferrofluid composition which comprises: a) an organic liquid carrier; b) magnetic particles in an amount sufficient to provide magnetic properties to the ferrofluid composition; and c) a dispersing agent in an amount sufficient to disperse and stabilize the magnetic particles in the organic liquid carrier, which dispersing agent comprises: a cationic surfactant composed of a cationic positively charged portion and a long chain portion, the long chain portion being compatible with or soluble in the organic liquid carrier.

Claim 2

Dependent Claim 80 words

A stable ferrofluid composition which comprises: a) an organic liquid carrier; b) magnetic particles in an amount sufficient to provide magnetic properties to the ferrofluid composition; and c) a dispersing agent in an amount sufficient to disperse and stabilize the magnetic particles in the organic liquid carrier, which dispersing agent comprises: a cationic surfactant composed of a cationic positively charged portion and a long chain portion, the long chain portion being compatible with or soluble in the organic liquid carrier.

Claim 3

Independent Claim 49 words

A method of preparing a stable ferrofluid composition, which method comprises dispersing magnetic particles in an organic liquid carrier by employing a dispersing amount of a cationic surfactant sufficient to provide a stable, dispersed ferrofluid composition, a portion of the cationic surfactant being soluble in the organic liquid carrier.

Claim 4

Independent Claim 49 words

A method of preparing a stable ferrofluid composition, which method comprises dispersing magnetic particles in an organic liquid carrier by employing a dispersing amount of a cationic surfactant sufficient to provide a stable, dispersed ferrofluid composition, a portion of the cationic surfactant being soluble in the organic liquid carrier.

Claim 5

Independent Claim 62 words

A method of providing a ferrofluid seal about a rotating member subject to the accumulation of static charges, which method comprises: sealing the rotary member with an electrically conductive ferrofluid composition, which ferrofluid composition includes therein a dispersing and electrically conductive amount of a quaternary ammonium cationic surfactant to provide an electrically conductive path to ground for the electrically conductive ferrofluid composition.

Claim 6

Independent Claim 62 words

A method of providing a ferrofluid seal about a rotating member subject to the accumulation of static charges, which method comprises: sealing the rotary member with an electrically conductive ferrofluid composition, which ferrofluid composition includes therein a dispersing and electrically conductive amount of a quaternary ammonium cationic surfactant to provide an electrically conductive path to ground for the electrically conductive ferrofluid composition.

Claim 7

Dependent Claim 127 words

A low-viscosity, electrically conductive ferrofluid for use in a ferrofluid hydrodynamic bearing apparatus, which ferrofluid composition comprises: a) a non-volatile hydrocarbon or ester liquid carrier compound; - , b) finely-divided ferromagnetic particles in an amount sufficient to impart magnetic properties to the liquid carrier; c) up to 4% by weight of finely-divided carbon-black particles; and .. d) a cationic surfactant composed of a quaternary-ammonium salt comprising a nitrogen-positive head portion and a long-tail portion, which long-tail portion is soluble in the liquid carrier, and which cationic surfactant is present in an amount which, in combination with the carbon particles, provides for a non-thixotropic ferrofluid composition, having an electrical resistivity of about 10 +2 ohms or less, and a low-viscosity of about 25 cps at 25°C or less.

Claim 8

Dependent Claim 127 words

A low-viscosity, electrically conductive ferrofluid for use in a ferrofluid hydrodynamic bearing apparatus, which ferrofluid composition comprises: a) a non-volatile hydrocarbon or ester liquid carrier compound; - , b) finely-divided ferromagnetic particles in an amount sufficient to impart magnetic properties to the liquid carrier; c) up to 4% by weight of finely-divided carbon-black particles; and .. d) a cationic surfactant composed of a quaternary-ammonium salt comprising a nitrogen-positive head portion and a long-tail portion, which long-tail portion is soluble in the liquid carrier, and which cationic surfactant is present in an amount which, in combination with the carbon particles, provides for a non-thixotropic ferrofluid composition, having an electrical resistivity of about 10 +2 ohms or less, and a low-viscosity of about 25 cps at 25°C or less.

Claim 9

Dependent Claim 124 words

A low-viscosity, electrically conductive ferrofluid composition for use in ferrofluid hydrodynamic bearing and seal apparatuses, which composition comprises: a) a liquid carrier; b) ferromagnetic particles in an amount sufficient to impart magnetic properties to the ferrofluid composition; and c) in combination finely-divided carbon particles and a cationic surfactant, the cationic surfactant present in an amount to provide for dispersion of the carbon particles and the magnetic particles in the liquid carrier, and in combination with the carbon particles present in an amount of up to about 4% by weight of the ferrofluid composition, to provide a low-viscosity, electrically conductive ferrofluid composition which has an electrical resistivity of about 10 2 ohms or less, and a viscosity of about 50 cps at 27°C or less.

Claim 10

Dependent Claim 124 words

A low-viscosity, electrically conductive ferrofluid composition for use in ferrofluid hydrodynamic bearing and seal apparatuses, which composition comprises: a) a liquid carrier; b) ferromagnetic particles in an amount sufficient to impart magnetic properties to the ferrofluid composition; and c) in combination finely-divided carbon particles and a cationic surfactant, the cationic surfactant present in an amount to provide for dispersion of the carbon particles and the magnetic particles in the liquid carrier, and in combination with the carbon particles present in an amount of up to about 4% by weight of the ferrofluid composition, to provide a low-viscosity, electrically conductive ferrofluid composition which has an electrical resistivity of about 10 2 ohms or less, and a viscosity of about 50 cps at 27°C or less.

Claim 11

Dependent Claim 189 words

A ferrofluid bearing apparatus, which bearing apparatus comprises in combination: a) a housing characterized by a shaft-receiving cavity therein and having a one and another end, and having a radial-bearing, inner wall surface; b) a rotary shaft disposed for rotary movement within the shaft-receiving cavity, and defining with the cavity a radial-bearing cavity; c) thrust-bearing means to provide support for the longitudinal movement of the rotary shaft in the housing; d) a ferrofluid-seal-apparatus means at the one or the other or both ends of the shaft-receiving cavity, to provide a ferrofluid 0-ring-type seal about the surface of the rotary shaft; e) an electrically conductive ferrofluid composition employed as the ferrofluid in the ferrofluid seal apparatus; f) a low-viscosity, electrically conductive ferrofluid composition in the bearing cavity, the ferrofluid composition having a viscosity of less than about 50 cps at 27°C and a resistivity of about 10 2 ohms or less; and g) means to ground the bearing apparatus, thereby providing an electrically conductive bearing apparatus which conducts accumulated electrical charges from the shaft to the ground, without the need for a mechanical grounding button in contact with the shaft.

Claim 12

Dependent Claim 189 words

A ferrofluid bearing apparatus, which bearing apparatus comprises in combination: a) a housing characterized by a shaft-receiving cavity therein and having a one and another end, and having a radial-bearing, inner wall surface; b) a rotary shaft disposed for rotary movement within the shaft-receiving cavity, and defining with the cavity a radial-bearing cavity; c) thrust-bearing means to provide support for the longitudinal movement of the rotary shaft in the housing; d) a ferrofluid-seal-apparatus means at the one or the other or both ends of the shaft-receiving cavity, to provide a ferrofluid 0-ring-type seal about the surface of the rotary shaft; e) an electrically conductive ferrofluid composition employed as the ferrofluid in the ferrofluid seal apparatus; f) a low-viscosity, electrically conductive ferrofluid composition in the bearing cavity, the ferrofluid composition having a viscosity of less than about 50 cps at 27°C and a resistivity of about 10 2 ohms or less; and g) means to ground the bearing apparatus, thereby providing an electrically conductive bearing apparatus which conducts accumulated electrical charges from the shaft to the ground, without the need for a mechanical grounding button in contact with the shaft.

Claim 13

Dependent Claim 26 words

The composition of claim 1 wherein the cationic surfactant is present in a ratio by weight of surfactant to magnetic particles from about 1:1 to 20:1.

Claim 14

Dependent Claim 34 words

The composition of claim 1 wherein the cationic surfactant comprises from about 4 to 25 moles of a polyalkoxylate portion, and wherein the organic liquid carrier comprises an ester, a glycol or an esterglycol.

Claim 15

Dependent Claim 61 words

The composition of claim 1 wherein the cationic surfactant comprises a quaternary ammonium cationic surfactant having a quaternary ammonium head portion of the molecule and a long chain tail portion of the molecule, the long chain tail portion of the molecule selected from the group consisting of: a long chain hydrocarbon; a long chain fatty acid; or a poly alkoxylated chain.

Claim 16

Dependent Claim 36 words

Claim 10. The composition of claim 1 wherein the cationic surfactant is selected from a group consisting from a fatty acid quaternary imidozoline salt; a polypropoxy quaternary ammonium salt; an acylated polyamine salt; or combinations thereof.

Claim 17

Dependent Claim 70 words

Claim 11 . The composition of claim 1 wherein the cationic surfactant comprises a quaternary ammonium cationic surfactant having the structural formula: . wherein R 1 is a long chain aliphatic radical; R 2 and R 3 are hydrogen or an alkyl; and X- is an anionic-salt radical, such as C 1 -C 4 like methyl, or hydroxy C 2 -C 6 alkyl like -C 2 H 4 0H radicals.

Claim 18

Dependent Claim 57 words

Claim 12 . The composition of claim 1 wherein the cationic surfactant comprises a quaternary ammonium surfactant having the structural formula: wherein R 1 is a long chain radical; R 2 and R 3 are poly alkoxy radicals, such as polyoxypropylenated radicals; and R 4 is a lower alkyl radical; and X- is an annoinic salt radical.

Claim 19

Dependent Claim 37 words

Claim 13. The composition of claim 1 wherein the cationic surfactant comprises a quaternary ammonium cationic surfactant having the structural formula: wherein n is a number from 1 to 20; and X- is an anionic salt radical.

Claim 20

Dependent Claim 14 words

Claim 14 The composition of claim 1 which includes a nonionic or anionic surfactant.

Claim 21

Dependent Claim 45 words

Claim 15. The composition of claim 1 which includes a first dispersing agent of a long chain acid anionic surfactant and a second dispersing agent of a cationic surfactant which comprises a quaternary ammonium surfactant having a tail portion soluble in the organic liquid carrier.

Claim 22

Dependent Claim 27 words

The composition of any preceding claim which includes a first layer of an anionic surfactant in the ferromagnetic particles and a second layer of the cationic surfactant.

Claim 23

Dependent Claim 36 words

The composition of any preceding claim wherein the organic liquid carrier comprises a hydrocarbon or polyalphaolefine oil, and wherein the long chain portion of the cationic surfactant comprises a C 6 to about C 30 hydrocarbon.

Claim 24

Dependent Claim 30 words

The composition of any of claims 7 to 16 wherein the organic liquid carrier is selected from the group consisting of liquid hydrocarbons, liquid esters, liquid glycols and silicone oils.

Claim 25

Dependent Claim 26 words

The composition of any of claims 7 to 18 wherein the magnetic particles comprise ferromagnetic particles having a diameter ranging from about 20 to 500 angstroms.

Claim 26

Dependent Claim 41 words

The composition of any of claims 7 to 18 wherein the magnetic particles comprise ferromagnetic particles having a diameter of from about 20 to 200 angstroms, and wherein the cationic surfactant has a long chain portion greater than about 15 angstroms.

Claim 27

Dependent Claim 19 words

The composition of claim 1 wherein the compositin has an electrical resistivity of about 10 o hm-cm or less.

Claim 28

Dependent Claim 25 words

Claim 22. The method of claim 2 wherein the cationic surfactant comprises a quaternary ammonium cationic surfactant having a long chain hydrocarbon or alkyoxy group.

Claim 29

Dependent Claim 95 words

Claim 2 3. The method of claim 2 wherein the organic liquid character comprises a hydrocarbon or .polyalphaolefine oil, and which method comprises: dispersing the magnetic particles in the organic liquid carrier in the presence of from about 5 to 25 percent by weight of the magnetic particles of an anionic surfactant to provide a first layer of surfactants, and thereafter dispersing the anionic surfactant containing magnetic particles in the organic liquid carrier employing a cationic surfactant, whereby the ratio by weight of the cationic surfactant to magnetic particles varies from about 1:1 to 40:1.

Claim 30

Dependent Claim 25 words

Claim 24. The method of claim 23 wherein the anionic ' surfactant has more than 8 carbon atoms and contains one or more polar groups.

Claim 31

Dependent Claim 44 words

Claim 25. The method of claim 2 wherein the cationic surfactant employed as the second layer surfactant in the method of dispersing and preparing the ferrofluid composition comprises: a quaternary ammonium cationic surfactant having a C 6 -C 30 hydrocarbon or alkoxy tail portion.

Claim 32

Dependent Claim 41 words

Claim 26. The method of claim 2 wherein the cationic surfactant employed as a second layer surfactant has from about 5 to 25 moles of a polyoxyethoxylate tail portion, and wherein the organic liquid carrier comprises an ester or a glycol.

Claim 33

Dependent Claim 36 words

Claim 27. The method of claim 2 wherein the cationic surfactant is selected from a group consisting of: a fatty acid quaternary imizozoline salt; a polypropoxy quaternary ammonium salt; an acylated polyamine salt; or combinations thereof.

Claim 34

Dependent Claim 31 words

Claim 28. The method of claim 2 wherein the anionic surfactant comprises a long chain carboxylic acid anionic surfactant and wherein the cationic surfactant comprises a long chain quaternary ammonium surfactant.

Claim 35

Dependent Claim 37 words

Claim 2 9. The method of claim 28 wherein the cationic surfactant is selected from a group consisting of: a fatty acid quaternary imidozoline salt; a polypropoxy quaternary ammonium salt; an acylated polyamine salt; or combinations thereof.

Claim 36

Dependent Claim 104 words

A stable ferrofluid composition, which composition comprises: a) an organic liquid carrier, which organic liquid carrier is selected from the group consisting of hydrocarbons, esters and glycols; b) finely divided ferromagnetic particles in an amount to provide magnetic properties to the ferrofluid composition and having an average diameter ranging from about 20 to 300 angstroms; and c) a dispersing agent in an amount sufficient to disperse and stabilize the magnetic particles in the organic liquid carrier, which dispersing agent comprises a quaternary ammonium surfactant selected from a group consisting of: fatty quaternary imidozoline salts; polypropoxy quaternary ammonium salts; acylated polyamine salts; and combinations thereof.

Claim 37

Dependent Claim 104 words

A stable ferrofluid composition, which composition comprises: a) an organic liquid carrier, which organic liquid carrier is selected from the group consisting of hydrocarbons, esters and glycols; b) finely divided ferromagnetic particles in an amount to provide magnetic properties to the ferrofluid composition and having an average diameter ranging from about 20 to 300 angstroms; and c) a dispersing agent in an amount sufficient to disperse and stabilize the magnetic particles in the organic liquid carrier, which dispersing agent comprises a quaternary ammonium surfactant selected from a group consisting of: fatty quaternary imidozoline salts; polypropoxy quaternary ammonium salts; acylated polyamine salts; and combinations thereof.

Claim 38

Dependent Claim 14 words

The composition of claim 5 wherein the cationic surfactant comprises a quaternary ammonium surfactant.

Claim 39

Dependent Claim 31 words

The composition of claim 5 wherein the cationic surfactant comprises a quaternary ammonium surfactant compcund, having a nitrogen-positive head group and a long-tail portion which is soluble in the liquid carrier.

Claim 40

Dependent Claim 31 words

The composition of claim 1 or claim 31 or 32 wherein the carbon particles are present in an amount of from about 2% to 4% by weight of the ferrofluid composition.

Claim 41

Dependent Claim 42 words

The composition of claim 1 or claim 31, 32 or 33, wherein the carbon particles are finely-divided carbon particles having a particle size of less than about 200 Angstroms, and wherein the carbon particles are carbon black derived from a furnace process.

Claim 42

Dependent Claim 25 words

The composition of claim 5 or any of claims 31 to 34 wherein the carrier comprises a non- volatile hydrocarbon or ester organic liquid-carrier material.

Claim 43

Dependent Claim 29 words

The composition of claim 5 or any of claims 31 to 35 wherein the ferrofluid composition has a viscosity of about 15 cps at 27 0 C or less.

Claim 44

Dependent Claim 28 words

The composition of claim 5 or any of claims 31 to 36 wherein the ratio of the magnetic particles to cationic surfactant ranges from about 0.5:1 to 20:1.

Claim 45

Dependent Claim 39 words

The bearing apparatus of claim 6 wherein the ferrofluid 0-ring-type seal about the surface of the shaft element comprises an electrically conductive ferrofluid composition, and wherein the rotating shaft element and the housing are composed of electrically conductive materials.

Claim 46

Dependent Claim 78 words

The bearing apparatus of claim 6 or 38, which bearing apparatus comprises a first thrust-bearing means at the one end and a second thrust-bearing means at the other end of the shaft-receiving cavity, and wherein the ferrofluid-seal-apparatus means comprises a first ferrofluid-seal-apparatus means at the one end and a second ferrofluid-seal-apparatus means at the other end of the shaft-receiving cavity, to seal the surface of the rotary shaft at the one and other ends of the shaft-receiving cavity.

Claim 47

Dependent Claim 41 words

The bearing apparatus of claim 6 or claim 38 or 39 wherein the ferrofluid composition, which forms the 0-ring-type ferrofluid seal about the surface of the rotating shaft, is the same, low-viscosity, electrically conductive ferrofluid composition employed in the bearing cavity.

Claim 48

Dependent Claim 75 words

The bearing apparatus of claim 6 wherein the ferrofluid-seal-apparatus means comprises a single-stage ferrofluid-seal-apparatus means at the one and other ends of the shaft-receiving cavity, which ferrofluid-seal-apparatus means comprises an annular permanent magnet and a single pole piece, one end of the pole piece defining a radial gap about the surface of the shaft apparatus, and ferrofluid disposed in the radial gap, to form the ferrofluid seal at both the one and the other ends.

Claim 49

Dependent Claim 87 words

The bearing apparatus of claim 6 wherein the ferrofluid-seal-apparatus means comprises a first sealing means at the one end and a second sealing means at the other end of the shaft-receiving cavity, each of the ferrofluid sealing means comprising dual pole pieces and an annular magnet, the dual pole pieces forming radial gaps at the one end thereof with the surface of the rotating shaft, and a dual-stage ferrofluid seal about the surface of the shaft at the one first and the other second ferrofluid sealing means.

Claim 50

Dependent Claim 56 words

A computer-disc-drive system which-comprises: the bearing apparatus of claim 6 or any one of claims 38 to 42; a computer disc secured to the rotating shaft for rotation therewith; a magnetic head means to receive or impart information to the computer disc; and a motor means to provide for the rotary motion of the rotary shaft.

Claim 51

Dependent Claim 222 words

Claim 44. A computer-disc-drive system, which computer-disc-drive system comprises in combination: a) a magnetic head means to receive or impart information from or to a computer disc; b) a computer disc; c) a magnetically permeable rotary-shaft element, the computer disc secured to one end of the shaft for rotation therewith; d) a housing characterized by a shaft-receiving cavity and an internal wall surface, to define a bearing cavity, the shaft-receiving cavity having a one end and another end; e) an electrically conductive, low-viscosity ferrofluid composition i disposed in the bearing cavity; f) a ferrofluid-seal-apparatus means at the one and the other ends of the shaft-receiving cavity, to define a ferrofluid O-ring-type seals about the surface of the rotary-shaft element; g) thrust-bearing means at the one and the other ends of the shaft-receiving cavity, to provide for support of the longitudinal movement of the rotary-shaft element; h) a motor means to impart rotary motion to the shaft element and the computer disc; and i) means to ground the housing, so that accumulated static charges across the magnetic head means and the computer disc may be conducted through the rotating shaft element and the housing to ground, the ferrofluid in the bearing cavity having a viscosity of less than about 25 cps at 27°C, and having a resistance of less than about 50 ohms.

Claim 52

Dependent Claim 46 words

Claim 45. The computer-disc-drive system of claim 44 wherein the ferrofluid employed as the ferrofluid O-ring-type seal about the rotating shaft comprises a low-viscosity, electrically conductive ferrofluid having a resistivity of about 10 2 ohms or less and a viscosity of about 50 cps or less.

Ferrofluid composition, method of making, and apparatus and method using same

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