JP4851772B2 - Conductive magnetic fluid and its use - Google Patents

Description

  The present invention relates to a conductive magnetic fluid and its use. More specifically, the present invention relates to a conductive magnetic fluid obtained by adding a specific fine conductive carbon fiber to a magnetic fluid sensitive to a magnetic field, and a seal device and an actuator using the same.

  The magnetic fluid is a colloidal solution in which ferromagnetic particles are uniformly dispersed in a solvent, and when the magnet is brought closer, the entire liquid is attracted to the magnet, and the entire liquid behaves like a magnet. Furthermore, the magnetic fluid has a feature that a large force can be induced from the magnetic fluid by applying a magnetic field. Taking advantage of this feature, magnetic fluids are used for rotating shaft seals, and are expected to be applied to dampers, actuators, specific gravity sorting, ink jet printers, and the like. As a typical method for producing a magnetic fluid, there is a method described in JP-A-51-44579. In this method, a surfactant is added to a magnetite water slurry prepared from a ferrous sulfate aqueous solution and a ferric sulfate aqueous solution, washed with water, dried, and then dispersed in an organic solvent to produce a magnetic fluid. .

In general, a magnetic fluid has a high electric resistance value. Therefore, when used in a sealing mechanism of a magnetic disk device, for example, an earth mechanism is used to remove static electricity accumulated in the magnetic disk device (hereinafter referred to as a charged body). It was necessary to provide. If conductivity is imparted to the magnetic fluid itself, charging can be prevented without providing a ground mechanism.
In magnetic field control energy conversion MHD (Magneto Hydrodynamics) power generation, an electromotive force generated by a conductive working fluid crossing a magnetic field is taken out by two electrodes. The use of a conductive magnetic fluid as the working fluid has been studied.

As such a conductive magnetic fluid, Patent Document 1 proposes a magnetic fluid using ferromagnetic particles having a surface coated with a layer of a cationic surfactant such as a quaternary ammonium salt. Patent Document 2 proposes a magnetic fluid using a solvent imparted with conductivity by dissolving a conductivity-imparting material in which a tertiary amine and a fatty acid are combined in a solvent. Patent Document 3 proposes a magnetic fluid using an organic acid quaternary phosphonium salt as the conductivity-imparting substance.
Further, Patent Document 4 discloses a magnetic fluid in which a ferromagnetic powder such as a magnetite powder, a nickel powder, or a cobalt powder and a conductive powder such as a gold powder are dispersed in an organic liquid.

  However, the magnetic fluid has the following problems. That is, the magnetic permeability that is a measure of responsiveness is low, and a high response speed cannot be obtained. Moreover, when using as a seal | sticker, the sealing force is also mentioned small. These problems are obstacles to the spread of applications.

Japanese Patent Laid-Open No. 61-274737 JP-A-1-231302 JP-A-5-255686 Japanese Patent Laid-Open No. 5-267035

  An object of the present invention is to provide a conductive magnetic fluid that can obtain a high response speed and a large torque and induce a larger sealing force. A further object of the present invention is to provide a sealing device and an actuator using the above-described conductive magnetic fluid, which has a high response speed, a high torque and an excellent sealing force.

  In view of the above problems, the present inventors have conducted intensive research on magnetic fluid, and as a result, the conductive carbon fiber having a specific shape is added to the fluid to develop the conductive network in the fluid. Based on this finding, the present invention has been completed.

That is, according to the present invention,
(1) A conductive magnetic fluid comprising at least one solvent, at least one ferromagnetic particle, and at least one carbon-based conductive particle,
Provided is a conductive magnetic fluid, wherein the at least one carbon-based conductive particle is a carbon fiber having an average fiber diameter of 10 to 500 nm and an average aspect ratio of 30 to 200.

As a preferred embodiment, (2) the carbon fiber has a C0 value in X-rays of 0.65 nm to 0.68 nm and a specific resistance when the bulk density is compressed to 0.5 g / cm ^3. The conductive magnetic fluid according to (1), which is 0.015 Ωcm or less.
(3) The conductive magnetic fluid according to (1) or (2), wherein the surface of the carbon fiber is hydrophilic.
(4) The at least one ferromagnetic particle is a ferromagnetic metal simple substance, a ferromagnetic metal alloy, a ferromagnetic oxide and / or a ferromagnetic nitride fine particle according to any one of (1) to (3) Conductive magnetic fluid.
(5) At least one type of ferromagnetic particles
Simple metal of iron, nickel or cobalt;
Alloys containing iron, nickel and / or cobalt;
The oxide according to any one of (1) to (4), characterized in that it is an oxide containing iron, nickel and / or cobalt; and / or a nitride fine particle containing iron, nickel and / or cobalt. Magnetic fluid.
(6) The conductive magnetic fluid according to any one of (1) to (5), wherein the at least one ferromagnetic particle is a Ni—Fe alloy, iron, or magnetite.
(7) The solvent according to any one of (1) to (6), wherein the at least one solvent is a hydrocarbon solvent, ester oil, ether oil, silicone oil, and / or fluorine oil. Conductive magnetic fluid.

(8) The at least one solvent is mineral oil, alkylnaphthalene, polyalphaolefin; butyl phthalate, butyl sebacate; oligophenylene oxide; silicone oil; and / or fluorine oil (1) Conductive magnetic fluid according to any one of to (7).
(9) The conductive magnetic fluid according to any one of (1) to (8), wherein the carbon fiber is contained in the conductive magnetic fluid in an amount of 0.1% by mass to 30% by mass.
(10) The conductive magnetic fluid according to any one of (1) to (9), wherein the ferromagnetic particles are contained in the conductive magnetic fluid in an amount of 3% by mass to 80% by mass.
(11) The conductive magnetic fluid according to any one of (1) to (10), which has a viscosity of 100 mPa · sec to 100000 mPa · sec at 25 ° C. and no magnetic field.
(12) The conductivity in the direction of the magnetic field when a magnetic field of 1,500 oersted is applied at 25 ° C. is 10 ⁻² S / cm or more, according to any one of (1) to (11) Conductive magnetic fluid.
Is provided.

Furthermore, according to the present invention,
(13) A sealing device using the conductive magnetic fluid.
(14) An actuator using the conductive magnetic fluid.
Is provided.

  The conductive magnetic fluid of the present invention uses a fine carbon fiber as the conductive carbon particles, whereby a fast response speed and a large torque are obtained with respect to a magnetic field, thereby inducing a large sealing force. Furthermore, by using this conductive magnetic fluid, a sealing device and an actuator having a high response speed, a high torque and an excellent sealing force were obtained.

  The conductive magnetic fluid of the present invention contains at least one solvent, at least one ferromagnetic particle, and at least one carbon-based conductive particle. And this invention is an electroconductive magnetic fluid in which the said at least 1 type of carbon type electroconductive particle contains carbon fiber with an average fiber diameter of 10-500 nm, and an average aspect-ratio of 30-200.

(Carbon-based conductive particles)
The carbon-based conductive particles constituting the conductive magnetic fluid of the present invention are carbon fibers.
This carbon fiber has an average fiber diameter of 10 to 500 nm, preferably 20 to 140 nm. The carbon fiber is preferably one having little variation in the fiber diameter. The variation in fiber diameter is preferably included in the range of ± 20% of the average fiber diameter by 65% (number basis) or more of all fibers, more preferably 70% (number basis) or more, and 75% or more (number) It is particularly preferred that it be included. For example, when the average fiber diameter is 100 nm, this definition indicates that the number of carbon fibers having a fiber diameter of 80 to 120 nm is 65% or more of the total number of carbon fibers.
The carbon fibers used in the present invention further have an average aspect ratio in the range of 30 to 200.

Carbon fiber used in the present invention, the bulk density is preferably at 0.030 g / cm ³ or less, more preferably 0.010 g / cm ³ or less. Carbon fibers having a bulk density of more than 0.030 g / cm ³ tend to reduce the conductivity improvement effect of the magnetic fluid.
The bulk density was determined by heating the carbon fiber at 1000 ° C. for 15 minutes in an argon atmosphere, crushing it with a mixer (National MX-X62) for 1 minute, placing the crushed material in a graduated cylinder and weighing it. This is a value obtained from a weighed value and an apparent volume by oscillating for 1 minute with a machine (Yamato test tube touch mixer MT-31), measuring the apparent volume of the crushed material.

The carbon fiber used in the present invention preferably has a specific resistance of 0.015 Ωcm or less. When a carbon fiber having a specific resistance of 0.015 Ωcm or less is used, the electrical conductivity is improved by adding about 2% by mass in the composite with the resin at the time of preparing the paste. In addition, specific resistance is the value measured about the compacted body when carbon fiber is compacted by the bulk density of 0.5 g / cm < ³ >.

  The carbon fiber used in the present invention is not particularly limited by its production method, but it can be obtained by vaporizing a transition metal compound and a carbon source, and injecting the carbon fiber into a reactor to cause a thermal decomposition reaction, so-called vapor phase carbon. Fiber is preferred.

  Any carbon source (organic compound) that can be used as a raw material for carbon fiber can be used as long as it vaporizes, but it is desirable that the carbon source vaporizes at a lower temperature. Specifically, aromatic compounds such as benzene, toluene and xylene; linear hydrocarbons such as hexane and heptane; cyclic hydrocarbons such as cyclohexane; alcohols such as methanol and methanol; volatile oil and kerosene Etc. Of these, aromatic compounds are desirable, and benzene is most desirable. These carbon sources may be used individually by 1 type, and 2 or more types may be mixed and used for them.

  As the transition metal compound serving as a catalyst, an organometallic compound or an inorganic compound containing a Group 4-10 transition metal is suitable. Among these, an organometallic compound having a transition metal selected from the group consisting of Fe, Ni, and Co is preferable. In the present invention, since the reaction is performed in a vaporized state, it is preferable to use one having a high vapor pressure, specifically, a vapor pressure at 150 ° C. of 133 Pa (1 mmHg) or more. Examples of those having a high vapor pressure include ferrocene and nickelocene.

  By adjusting the concentration of the transition metal compound, it is possible to control the diameter, length, and particle content of the produced fiber. For example, in order to produce a fiber having a fiber diameter of 80 nm or more, the ferrocene concentration is preferably 1 to 5% by mass of the carbon source, and more preferably 2 to 4% by mass. If the concentration is within this range, the fiber diameter and the like can be easily controlled. In addition, productivity can be further improved by adding a sulfur source to the raw material. Any sulfur source can be used as long as it vaporizes, but a high vapor pressure is desirable, and a vapor pressure at 50 ° C. of 10 mmHg or more is desirable. Examples thereof include organic sulfur compounds such as thiophene and inorganic sulfur compounds such as hydrogen sulfide, and thiophene is particularly desirable. These sulfur sources may be used individually by 1 type, and may mix and use 2 or more types.

In the present invention, the above carbon source, transition metal compound, and sulfur source as an optional component are vaporized into a reactor and reacted. At this time, it is possible to vaporize and mix the carbon source, transition metal compound and sulfur source separately, and then inject into the reactor, but prepare a raw material liquid consisting of the carbon source, transition metal compound and sulfur source. A method of vaporizing this and injecting it into the reactor is preferred.
By injecting the vaporized raw material into the reactor, the heating efficiency is increased, the thermal decomposition of the raw material is promoted, and the yield of carbon fiber is improved. Also, carbon fibers having a small variation in fiber diameter can be obtained.

FIG. 1 shows a flow of a method for producing vapor grown carbon fiber suitable for the present invention.
The raw material liquid (1) is introduced into the vaporizer (3) by a liquid feed pump (not shown) to be a raw material gas. In order to stabilize the composition of the raw material gas, it is desirable to vaporize the entire amount of the raw material liquid. The vaporizer is heated so that the raw material is completely evaporated as long as the raw material liquid is not decomposed. The temperature of the vaporizer is preferably 200 to 700 ° C, more preferably 350 to 550 ° C. When the raw material liquid is sprayed onto the vaporizer wall by the spray nozzle, the raw material is efficiently vaporized. The carrier gas (2a) can be introduced into the vaporizer in order to adjust the feed rate of the raw material gas, but it is preferable that the carrier gas flow rate be as small as possible because the burden on the heater of the vaporizer is small.

  The carrier gas (2b) is mixed with the raw material gas exiting the vaporizer. The carrier gas preferably contains a reducing gas such as hydrogen gas. By using a reducing gas, the catalytic activity of the transition metal compound is increased and it is difficult to deactivate. The amount of the carrier gas is suitably 1 to 100 mol with respect to 1.0 mol of the organic compound as the carbon source. The source gas and the carrier gas are uniformly mixed by a mixer (static mixer (STP)) (4). By uniformly mixing, a carbon fiber with good dispersibility can be produced.

  A mixed gas of the source gas and the carrier gas is injected into the reactor (5). As a result, the raw material gas is thermally decomposed to produce carbon fibers. The temperature in the reactor is 800 to 1300 ° C, preferably 900 to 1250 ° C. The reactor can be made of a material that can withstand the heat of reaction at 1300 ° C., such as alumina, zirconia, magnesia, silicon nitride, silicon carbide and the like. A tubular reactor is preferable. The tubular reactor (reaction tube) is heated by installing a heater on the outside of the tube. The yield is improved by increasing the residence time of the raw material until the raw material is sufficiently decomposed. Specifically, it is desirable that the temperature is 1250 ° C. for 2 to 10 seconds, preferably 4 to 6 seconds.

  The carbon fiber obtained by the pyrolysis reaction can be used as it is, but it is heated at about 800 to 2000 ° C. to remove impurities, or heated at 2000 ° C. or higher to improve crystallinity and graphitize. You can also. In the present invention, it is preferable to use graphitized carbon fiber by heat treatment at 2000 ° C. or higher because it becomes highly conductive, has few impurities, and increases stability. The graphitized carbon fiber preferably has a graphitization degree represented by a C0 value obtained by X-ray diffraction measurement of 0.65 to 0.68 nm.

  Further, the carbon fiber is preferably one having a modified surface to show hydrophilicity in order to improve wettability to the matrix, dispersibility in the matrix, and enhance interfacial strength. A surface oxidation method is preferred as the surface modification method. The surface oxidation method can be performed by, for example, a method of heating in the presence of carbon fiber and an oxidizing gas, or a method of immersing the carbon fiber in an oxidizing liquid and heating in an immersed state as necessary. Among these surface oxidation methods, a method of heating carbon fibers at 300 to 800 ° C. in air is desirable because it is simple.

  As the carbon-based conductive particles that can be used in the conductive magnetic fluid of the present invention, other conductive particles may be added instead of the carbon fiber alone. The carbon fiber can exhibit a sufficiently high conductivity even with a relatively low addition amount, but it is difficult to increase the addition amount because the carbon fiber is bulky even if higher conductivity is desired. Therefore, higher conductivity can be expressed by using other low-bulk massive or spherical carbon-based conductive particles in combination. The combined use of carbon fibers and massive or spherical conductive particles is preferable because sedimentation in the case of using massive or spherical conductive particles at a high concentration can be suppressed, and the characteristics of both are effectively exhibited.

  In the present invention, the massive or spherical carbon-based conductive particles that can be used in combination with the carbon fiber are not particularly limited, and examples thereof include carbon particles such as carbon black, natural graphite particles, and artificial graphite particles. The average particle size of these massive or spherical carbon-based conductive particles is preferably 0.1 to 10 μm, and more preferably 0.2 to 3 μm in consideration of dispersion, viscosity, and workability. The average particle diameter can be measured with a laser scattering type flow distribution measuring device or the like.

  When the carbon fiber and other massive or spherical carbon-based conductive particles are used in combination, the ratio is not particularly limited, but the carbon fiber is 100 mass parts of the massive or spherical carbon-based conductive particles in mass ratio. Is preferably 100 to 500 parts by mass, more preferably 200 to 400 parts by mass.

In producing the conductive magnetic fluid of the present invention, a dispersant or a coupling agent may be added and used to improve the dispersibility of carbon fibers and / or other carbon-based conductive particles.
Although a dispersing agent is not specifically limited, For example, high carbon number saturated fatty acids, such as palmitic acid and a stearic acid, and its metal salt; High carbon number unsaturated fatty acids, such as oleic acid and linolenic acid, and its metal salt are mentioned. The blending amount of these dispersants is generally 1 to 100 parts by mass with respect to 100 parts by mass of the carbon-based conductive particles. If the blending amount of the dispersant is less than 1 part by mass, the dispersibility of the carbon fibers and / or other conductive particles is less effective, and if it exceeds 100 parts by mass, the stability of the conductive magnetic fluid is impaired. There is.

  Examples of the coupling agent include silane coupling agents such as vinylmethoxysilane, vinyltriethoxysilane, and vinyltris (β-methoxyethoxy) silane, titanate coupling agents, and aluminate coupling agents. The amount of these coupling agents added is preferably 30 parts by mass or less with respect to 100 parts by mass of the carbon-based conductive particles. If the amount added is too large, the stability of the conductive magnetic fluid may be impaired as in the case of the dispersant.

(Ferromagnetic particles)
Examples of the ferromagnetic particles constituting the conductive magnetic fluid of the present invention include fine particles of a ferromagnetic metal alone, a ferromagnetic metal alloy, a ferromagnetic oxide and / or a ferromagnetic nitride. Specifically, fine particles of simple metal such as iron, nickel or cobalt; fine particles of alloy containing iron, nickel and / or cobalt; fine particles of oxide containing iron, nickel and / or cobalt; and / or iron, nickel and / or Or the nitride fine particle containing cobalt is mentioned. Furthermore, the magnetic particle containing rare earth metals, such as samarium, neodymium, and cerium, can be mentioned. Among these, metal magnetic particles such as iron, cobalt, nickel, and Ni—Fe alloy and metal oxide magnetic particles such as ferrite and magnetite are preferable from the viewpoint of relatively large magnetism and easy handling. In the present invention, magnetism means to be sensitive to a magnetic field, for example, to be attracted to a magnet.

  The ferromagnetic particles used in the present invention preferably have a particle size of 0.003 to 200 μm. When the particle size is less than 0.003 μm, the magnetism tends to be weakened, and when it exceeds 200 μm, the dispersibility in the fluid tends to decrease. The ferromagnetic particles used in the present invention include hard magnetic particles and soft magnetic particles. 0.003 to 0.5 μm is preferably used for hard magnetic particles, and 0.1 to 200 μm is preferably used for soft magnetic particles. When trying to obtain a very large force, soft magnetic particles having a particle diameter of 1 to 100 μm are preferably used.

(solvent)
Although the solvent which comprises the electroconductive magnetic fluid of this invention is not specifically limited, What is stable in air | atmosphere, low temperature and high temperature is preferable. The solvent suitable for the present invention has a boiling point of preferably 150 to 700 ° C. (normal pressure), more preferably 200 to 650 ° C. (normal pressure), and a viscosity of preferably 10 to 5000 mPa · S (40 ° C.), More preferably, the liquid is 50 to 3000 mPa · S (40 ° C.). Examples of the solvent include hydrocarbon solvents such as mineral oil, alkylnaphthalene and polyalphaolefin; ester oils such as butyl phthalate and butyl sebacate; ether oils such as oligophenylene oxide; silicone oils and fluorine oils.

(Conductive magnetic fluid)
The conductive ferrofluid of the present invention is a fluid viscous liquid in the absence of a magnetic field. A preferred viscosity in the absence of a magnetic field is 100 mPa · sec or more and 100000 mPa · sec or less at 25 ° C. When the viscosity is low, particles are easily separated in the absence of a magnetic field. Conversely, if the viscosity is high, handling tends to be difficult and responsiveness tends to be low.

The conductive magnetic fluid of the present invention preferably has a conductivity in the magnetic field direction of 10 ⁻² S / cm or more when a magnetic field of 1,500 oersted is applied at 25 ° C. If it is lower than 10 ⁻² S / cm, the orientation of the carbon fibers is insufficient, and the effect of improving the response speed tends to be difficult to obtain.

  In the conductive magnetic fluid of the present invention, the mass ratio of the ferromagnetic particles to the solvent is preferably 1/99 to 90/10, more preferably 5/95 to 60/40. When there is little solvent, the viscosity of a magnetic fluid will increase and it will become the tendency for the function as a fluid to be impaired. On the other hand, when the amount of the solvent is large, the magnetic effect tends to be lowered. Moreover, you may mix | blend additives, such as surfactant, in the range which does not impair the effect of this invention.

  In the conductive magnetic fluid of the present invention, the amount of carbon fibers in the conductive magnetic fluid is preferably 0.1% by mass to 30% by mass, more preferably 0.1% by mass to 20% by mass, and particularly preferably. It is 0.5 mass% or more and 15 mass% or less. If the amount of carbon fiber is small, the conductivity tends to decrease, and conversely if it is large, the viscosity of the magnetic fluid tends to increase. The ferromagnetic particles are preferably contained in the conductive magnetic fluid in an amount of 3% by mass to 80% by mass.

(Use)
The conductive magnetic fluid of the present invention includes an engine mount, a damping device such as a shock absorber, a clutch, a torque converter, a brake system, a valve, a damper, a suspension, an actuator, a vibrator, an inkjet printer, a seal, a specific gravity selection, a bearing, a polishing, It can be used for applications such as packing, control valves, and vibration isolation materials.

  In particular, by using the conductive magnetic fluid having high conductivity and large magnetism according to the present invention, it is possible to obtain a high-torque, excellent sealing property, and a stable sealing device used for a hard disk drive or the like. Further, since the conductive magnetic fluid of the present invention can operate at a high response speed, it is also suitable for various actuators.

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.
Production example (production of vapor grown carbon fiber)
Vapor grown carbon fiber was produced using the apparatus shown in the flow in FIG.
As the reaction tube (5), a vertical heating furnace (inner diameter: 370 mm, length: 2000 mm) having a source gas supply nozzle attached to the top was used.
A raw material solution was prepared by dissolving 0.5 kg of ferrocene and 0.13 kg of thiophene in 14 kg of benzene. The proportion of ferrocene in the raw material liquid was 3.5% by mass, and the proportion of thiophene was 0.9% by mass.

The vaporizer (3) was brought to a temperature of 500 ° C. Then, nitrogen gas was circulated in the vaporizer to expel oxygen gas. Subsequently, hydrogen gas was circulated and replaced with a hydrogen gas atmosphere.
The temperature of the reaction tube (5) was increased to 1250 ° C. The raw material liquid was supplied to the vaporizer with a pump at 30 g / min and vaporized to obtain a raw material gas. The source gas was discharged from the vaporizer with 50 L / min of hydrogen gas supplied as the carrier gas (2a). 400 L / min hydrogen gas was supplied to the source gas as a carrier gas (2b), and mixed uniformly by a static mixer (4). This mixed gas was injected into the reaction tube (5) and reacted for a residence time of 1 hour. The reaction product was heated at 2800 ° C. for 30 minutes in an argon atmosphere to obtain carbon fibers.

The bulk density of the carbon fiber was 0.012 g / min. The specific resistance when compressed to a bulk density of 0.5 g / cm ³ was 0.007 Ωcm. Further, when the average of 100 fibers was observed by scanning electron microscope observation, the average fiber diameter was 96.9 nm, the standard deviation of the fiber diameter was 23.4 nm, and the average fiber length was 13 μm (average aspect ratio = 130). ). FIG. 2 shows the fiber diameter distribution. The range of ± 20% of the average fiber diameter included 75% (based on the number) of all fibers. The carbonization recovery rate (= mass of obtained carbon fiber / mass of supplied benzene) was 50%.

(Measurement of BET specific surface area and pore volume)
Using NOVA1200 manufactured by Quantachrome, an adsorption isotherm of nitrogen at a liquid nitrogen temperature was determined, and calculated using the BET method and the BJH method.

Example 1
Disperse 30 g of permalloy (Ni-Fe alloy) powder with an average particle size of 10 μm and 3 g of vapor grown carbon fiber obtained in the production example in 70 g of silicone oil (KF-96 manufactured by Shin-Etsu Silicone) with a viscosity of 200 mPa · S (25 ° C.). The magnetic fluid (A) was prepared. The magnetic fluid (A) had a saturation magnetization of 40 gauss and was attracted when the magnet was brought closer.
A measuring device with an electromagnet attached on both electrodes of a cell where two electrodes with an area of 400 mm ² face each other with a clearance of 1 mm is installed horizontally, and the cell is filled with magnetic fluid (A), and the magnetic properties are measured. evaluated. The torque at this time was measured by displacing the upper electrode in the horizontal direction. The response speed was obtained by measuring the delay of the torque following the application of the magnetic field using an oscillograph.
The viscosity at 25 ° C. of the magnetic fluid (A) when no magnetic field was applied was 3530 mPa · sec. The conductivity in the magnetic field direction when a magnetic field of 25 ° C. and 1,500 oersted was applied was 3.5 × 10 ⁻¹ S / cm.
The torque of the magnetic fluid (A) when no magnetic field was applied was 24 gf · cm. When a magnetic field of 1,500 oersted was applied to the magnetic fluid (A), the torque was 240 gf · cm, and the response speed was 0.10 seconds.

Example 2:
Except for changing the amount of vapor grown carbon fiber used in Example 1 to 2.0 g and adding 1.0 g of artificial graphite fine powder (UFG10: Showa Denko, average particle size 5 μm), the same as in Example 1 Thus, a magnetic fluid (B) was prepared. The magnetic fluid (B) had a saturation magnetization of 560 gauss, and was attracted when the magnet was brought closer. A measuring device with an electromagnet attached on both electrodes of a cell where two electrodes with an area of 400 mm ² face each other with a clearance of 1 mm is installed horizontally, and the cell is filled with magnetic fluid (B) to provide magnetic properties. evaluated. The torque at this time was measured by displacing the upper electrode in the horizontal direction. The response speed was obtained by measuring the delay of the torque following the application of the magnetic field using an oscillograph.
The viscosity at 25 ° C. of the magnetic fluid (B) when no magnetic field was applied was 4280 mPa · sec. Moreover, the electrical conductivity in the magnetic field direction when applying a magnetic field of 1,500 oersted at 25 ° C. was 2.5 × 10 ⁻¹ S / cm.
The torque of the magnetic fluid (B) when no magnetic field was applied was 20 gf · cm. When a magnetic field of 1,500 oersted was applied to the magnetic fluid (B), the torque was 280 gf · cm, and the response speed was 0.15 seconds.

Comparative Example 1
A magnetic fluid (C) was prepared in the same manner as in Example 1 except that 3 g of vapor grown carbon fiber was not added. The magnetic fluid (C) had a saturation magnetization of 430 gauss and was attracted when the magnet was brought closer. Further, the magnetic properties were examined in the same manner as in Example 1.
The viscosity at 25 ° C. of the magnetic fluid (C) when no magnetic field was applied was 2730 mPa · sec. The conductivity in the magnetic field direction when a magnetic field of 25 ° C. and 1,500 oersted was applied was 3.5 × 10 ⁻³ S / cm.
The torque of the magnetic fluid (C) when no magnetic field was applied was 18 gf · cm. The torque of the magnetic fluid (C) when a 1,500 oersted magnetic field was applied was 188 gf · cm, and the response speed was 3.50 seconds.

Example 3
A magnetic fluid (D) was prepared in the same manner as in Example 2 except that iron powder having an average particle size of 0.4 μm was used instead of permalloy powder. The magnetic fluid (D) had a saturation magnetization of 380 gauss and was attracted when the magnet was brought closer. Further, the magnetic characteristics were examined in the same manner as in Example 2.
The viscosity at 25 ° C. of the magnetic fluid (D) when no magnetic field was applied was 4830 mPa · sec. The conductivity in the magnetic field direction when applying a magnetic field of 25 ° C. and 1,500 oersteds was 8.1 × 10 ⁻¹ S / cm.
The torque of the magnetic fluid (D) when no magnetic field was applied was 35 gf · cm. When a magnetic field of 1,500 oersted magnetic fluid (D) was applied, the torque was 215 gf · cm, and the response speed was 0.06 seconds.

Comparative Example 2
A magnetic fluid (E) was prepared in the same manner as in Comparative Example 1 except that iron powder having an average particle size of 0.4 μm was used instead of permalloy powder. The magnetic fluid (E) had a saturation magnetization of 380 gauss and was attracted when the magnet was brought closer. Further, the magnetic characteristics were examined by the same method as in Comparative Example 1.
The viscosity at 25 ° C. of the magnetic fluid (E) when no magnetic field was applied was 3180 mPa · sec. The conductivity in the magnetic field direction when applying a magnetic field of 25 ° C. and 1,500 oersteds was 7.2 × 10 ⁻³ S / cm.
The torque of the magnetic fluid (E) when no magnetic field was applied was 28 gf · cm. The torque of the magnetic fluid (E) when a 1,500 oersted magnetic field was applied was 159 gf · cm, and the response speed was 0.30 seconds.

Example 4
A magnetic fluid (F) was prepared in the same manner as in Example 2 except that magnetite powder having an average particle size of 1.0 μm was used instead of permalloy powder. The magnetic fluid (F) had a saturation magnetization of 380 gauss and was attracted when the magnet was brought closer. Further, the magnetic characteristics were examined in the same manner as in Example 2.
The viscosity of the magnetic fluid (F) at 25 ° C. when no magnetic field was applied was 3830 mPa · sec. The conductivity in the magnetic field direction when a magnetic field of 25 ° C. and 1,500 oersted was applied was 1.5 × 10 ⁻¹ S / cm.
The torque of the magnetic fluid (F) when no magnetic field was applied was 35 gf · cm. When a magnetic field of 1,500 oersted magnetic fluid (F) was applied, the torque was 215 gf · cm, and the response speed was 0.06 seconds.

The apparatus flow figure for manufacturing the vapor grown carbon fiber of the present invention. The figure which shows the fiber diameter distribution of the carbon fiber obtained in Example 1. FIG.

Explanation of symbols

1 Raw material 2a, 2b Carrier gas 3 Vaporizer 4 Stirrer 5 Reaction tube

Claims (15)

A conductive magnetic fluid comprising at least one solvent, at least one ferromagnetic particle, and at least one carbon-based conductive particle,
A conductive magnetic fluid, wherein at least one carbon-based conductive particle is a carbon fiber having an average fiber diameter of 10 to 500 nm and an average aspect ratio of 30 to 200, which is heat-treated at a temperature of 2000 ° C. or higher . The conductive magnetic fluid according to claim 1, wherein the carbon-based conductive particles include massive or spherical carbon-based conductive particles. The carbon fiber has a CO value of 0.65 nm to 0.68 nm in X-ray and a specific resistance of 0.015 Ωcm or less when the bulk density is compressed to 0.5 g / cm ^3. Or the electroconductive magnetic fluid of 2. The conductive magnetic fluid according to any one of claims 1 to 3, wherein the surface of the carbon fiber is hydrophilic. The conductive magnetism according to any one of claims 1 to 4 , wherein the at least one ferromagnetic particle is a ferromagnetic metal simple substance, a ferromagnetic metal alloy, a ferromagnetic oxide and / or a ferromagnetic nitride fine particle. fluid. At least one type of ferromagnetic particle
Simple metal of iron, nickel or cobalt;
Alloys containing iron, nickel and / or cobalt;
Iron oxide containing nickel and / or cobalt; and / or iron, electrically conductive according to any one of claims 1 to 4, characterized in that fine particles of nitrides containing nickel and / or cobalt Magnetic fluid. At least one of the ferromagnetic particles, Ni-Fe alloy, iron, or conductive magnetic fluid according to any one of claims 1-4, characterized in that the magnetite. The conductive magnetism according to any one of claims 1 to 7 , wherein the at least one solvent is a hydrocarbon solvent, an ester oil, an ether oil, a silicone oil, and / or a fluorine oil. fluid. At least one solvent, a mineral oil, alkyl naphthalene, poly-alpha-olefins; butyl phthalate, butyl sebacic acid; claims 1-7, characterized in that a and / or fluorine-containing oil; oligophenylene oxide; silicone oil The electroconductive magnetic fluid as described in any one . Carbon fibers, conductive conductive magnetic fluid according to any one of claims 1 to 9, wherein the magnetic fluid that contained 0.1% by weight to 30% by weight. Ferromagnetic particles are conductive electrically conductive magnetic fluid according to any one of claims 1 to 10, characterized in that contained 80 wt% or less 3 wt% or more in the magnetic fluid. The conductive magnetic fluid according to any one of claims 1 to 11 , which has a viscosity of 100 mPa · sec or more and 100000 mPa · sec or less at 25 ° C and no magnetic field. The conductive magnetism according to any one of claims 1 to 12 , wherein a conductivity in a magnetic field direction when a magnetic field of 1,500 oersted is applied at 25 ° C is 10 ^-2 S / cm or more. fluid. Sealing device using a conductive magnetic fluid according to any one of claims 1 to 13. The actuator using the electroconductive magnetic fluid as described in any one of Claims 1-13.

Images