JP2006193686A - Magnetic viscous fluid - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic viscous fluid in which magnetic particles can stably be dispersed for a long time and which can be produced with excellent productivity. <P>SOLUTION: The magnetic viscous fluid comprises a non-clay type inorganic whisker having an aspect ratio of 2 or more and a true specific gravity of 5 or lower, a dispersion medium and magnetic particles. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

The present invention relates to a magnetorheological fluid.

Non-patent document 1 describes a liquid composition that changes its fluid characteristics in response to a magnetic field called a magnetorheological fluid, magnetic fluid, or magnetorheological material. In Patent Document 1, iron oleate or the like is used as a dispersant. In addition, the technique is disclosed also in patent documents 2-5 grade | etc.,. In any of these magnetorheological fluids, the contained magnetic particles (average particle size: several tens of nanometers to several tens of micrometers) are aligned by an externally applied magnetic field to form chain clusters, thereby increasing the viscosity or It gels and its flow characteristics and yield stress change significantly.

Magnetorheological fluids have been used in bearings, sealing materials, centering devices, speakers, clutches, brakes, dampers, shock absorbers, engine mounts, members for elevating functions, building vibration control devices, and the like. Among these, in applications such as clutches, brakes, dampers, shock absorbers, etc., not only does the magnetorheological fluid exhibit stable characteristics during operation of the device, but also sedimentation of magnetic particles in the non-operating state (stationary state). There is a demand to stably disperse it in a dispersion medium without causing it.

Normally, the true specific gravity of the magnetic particles constituting the magnetorheological fluid is significantly larger than the true specific gravity of the dispersion medium, so it is extremely difficult to prevent sedimentation of the magnetic particles and maintain stable dispersibility over a long period of time. is there. In general, it is effective to use a high-viscosity dispersion medium in order to prevent sedimentation of magnetic particles in a magnetorheological fluid.

However, the use of a high-viscosity dispersion medium results in an increase in the viscosity of the magnetorheological fluid itself, which makes it difficult to inject and operate the magnetorheological fluid for application to the device. However, there is a problem that the rate of change in the viscosity of the magnetorheological fluid at the time of non-application becomes small, and it becomes impossible to construct a device that can exhibit sufficient performance.

On the other hand, as another measure for preventing sedimentation of magnetic particles, there is a method of blending a thixotropic agent (thixotropic agent). As a result, a physical network structure derived from the hydrogen bonding force or van der Waals force of the thixotropic agent is formed in the magnetorheological fluid, and the apparent viscosity of the fluid rises in the stationary state to prevent sedimentation of the magnetic particles. be able to. When a mechanical stimulus is applied to the magnetorheological fluid, the physical network structure by the thixotropic agent is destroyed, and the magnetorheological fluid behaves as a low viscosity fluid. Since the formation and destruction of the physical network structure by the thixotropic agent is reversible, the apparent viscosity increases and the sedimentation of the magnetic particles can be prevented if the magnetorheological fluid is allowed to stand again.

As thixotropic agents that exhibit such effects, swellable clay minerals are usually used, and such techniques are disclosed in Patent Documents 6 to 9. Swellable clay minerals swell in the dispersion medium and form hydrogen bonds to form a physical network structure to express thixotropic properties. To achieve this effect, higher alcohol, water, propylene carbonate, etc. It is necessary to add a polar additive (glue agent), and in a low temperature environment such as −30 to −40 ° C., the viscosity of the magnetorheological fluid is greatly increased due to the increase in viscosity of the polar additive (glue agent). There was a problem that.

In general, clay minerals are highly hydrophilic and do not swell sufficiently in mineral oils, synthetic oils, and silicon oils. Therefore, when these oils are used as dispersion media, clay minerals are hydrophobic organic compounds such as long-chain fatty acids. It was necessary to perform a denaturing treatment with the above. Furthermore, since it takes time to swell the clay mineral in the dispersion medium, it is necessary to knead the dispersion medium and the clay mineral for a long time until stable thixotropic properties are obtained. It was a factor that hindered productivity improvement.

US Pat. No. 2,661,596 US Patent No. 3006656 US Pat. No. 4,604,229 Japanese Patent Laid-Open No. 51-13995 JP 51-44579 A US Pat. No. 5,599,474 US Pat. No. 6,203,717 US Pat. No. 6,547,986 US Patent Application Publication No. 2004/84651 AIEE Transactions, “Magnetic Fluid Properties”, February 1955, p. 149-152 (JD Coolidge Jr. and RW Hallberg paper 55-170)

An object of the present invention is to provide a magnetorheological fluid in which magnetic particles are stably dispersed over a long period of time and have excellent productivity.

The present invention is a magnetorheological fluid comprising a non-clay mineral-based inorganic whisker having an aspect ratio of 2 or more and a true specific gravity of 5 or less, a dispersion medium, and magnetic particles (first magnetorheological fluid) .
In the first magnetorheological fluid, the content of the inorganic whiskers is preferably 0.05 to 15% by mass in 100% by mass of the magnetorheological fluid.

The present invention is a magnetorheological fluid characterized by containing basic magnesium sulfate whiskers and / or calcium silicate whiskers, a dispersion medium, and magnetic particles (second magnetorheological fluid).
In the second magnetorheological fluid, the content of the basic magnesium sulfate whisker and / or the calcium silicate whisker is preferably 0.05 to 15% by mass in 100% by mass of the magnetorheological fluid. .
Hereinafter, the present invention will be described in detail.

The first magnetorheological fluid of the present invention contains a non-clay mineral-based inorganic whisker having an aspect ratio of 2 or more and a true specific gravity of 5 or less, a dispersion medium, and magnetic particles. That is, the above-mentioned magnetorheological fluid contains non-clay mineral-based inorganic whiskers (hereinafter also simply referred to as “inorganic whiskers”) having a specific aspect ratio and true specific gravity, so that sufficient thixotropic properties are imparted to the dispersion medium. As a result, the magnetic particles contained in the stationary magnetorheological fluid can be stably dispersed for a long period of time, and sedimentation of the magnetic particles can be prevented.

Since the first magnetorheological fluid contains the inorganic whisker, it exhibits thixotropic properties without adding a polar additive (glue agent) such as higher alcohol, water or propylene carbonate as an essential component. It is something that can be done. For this reason, in a low temperature environment of −30 to −40 ° C., an increase in the viscosity of the magnetorheological fluid due to an increase in the viscosity of the polar additive can be prevented.

In a magnetorheological fluid, when a swellable clay mineral is used as a thixotropic agent and an oil is used as a dispersion medium, the swellable clay mineral needs to be modified with a hydrophobic organic compound or the like in order to impart thixotropic properties. On the other hand, since the first magnetorheological fluid contains the inorganic whisker, thixotropic properties can be sufficiently imparted without applying such a modification treatment to the inorganic whisker. Since the apparent clay of the fluid can be raised in the stationary state of the magnetorheological fluid, sedimentation of the magnetic particles can be prevented.

In the case of using a swellable clay mineral as a thixotropic agent in a magnetorheological fluid, it is necessary to knead the dispersion medium and the swellable clay mineral for a long time in order to impart stable thixotropic properties. Since the magnetorheological fluid contains the inorganic whisker, stable thixotropic properties can be easily imparted without kneading the inorganic whisker and the dispersion medium for a long time. For this reason, the first magnetorheological fluid can be easily produced.

The first magnetorheological fluid contains non-clay mineral-based inorganic whiskers. The whisker is an extremely thin needle-like crystal called a so-called beard-like crystal, and the inorganic whisker means a whisker made of an inorganic compound. By using the inorganic whisker, thixotropic property can be imparted to the magnetorheological fluid, and therefore, the magnetic particles can be stably dispersed for a long period of time in the static fluid.

The inorganic whisker has an aspect ratio of 2 or more. If it is less than 2, the ability to form a physical network structure derived from hydrogen bonding force or van der Waals force is lowered, and sufficient thixotropic property cannot be imparted to the dispersion medium, and the magnetic particles in the magnetorheological fluid May cause a problem of separation and sedimentation at an early stage. The aspect ratio is preferably 2 to 200, and more preferably 2 to 100.

The value of the aspect ratio (major axis / minor axis) is a value obtained by a conventionally known measuring method used for measuring inorganic whiskers, for example, randomly on an electron micrograph taken of the inorganic whiskers. It is a measured value obtained from 20 inorganic whisker particles present on the drawn straight line.

The inorganic whisker preferably has an average length of 50 μm or less. When it exceeds 50 μm, there is a possibility that sufficient thixotropic property cannot be imparted to the dispersion medium. 0.1-40 micrometers is more preferable.

The inorganic whisker has a true specific gravity of 5 or less (g / cm ³ ). If it exceeds 5, the specific gravity difference between the inorganic whisker and the dispersion medium becomes too large, and the inorganic whisker is separated from the dispersion medium or precipitates, so that sufficient thixotropic properties cannot be imparted to the dispersion medium. There is a fear. The true specific gravity is preferably 0.2 to 5, and more preferably 0.8 to 4. The value of true specific gravity is a value obtained by a conventionally known measuring method used for measuring inorganic whiskers and the like.

The inorganic whisker is not particularly limited. For example, potassium titanate whisker, silicone carbide whisker, carbon graphite whisker, silicon nitride whisker, α-alumina whisker, zinc oxide whisker, aluminum borate whisker, calcium carbonate whisker, water Examples include magnesium oxide whisker, basic magnesium sulfate whisker [magnesium oxysulfate whisker MgSO ₄ .5Mg (OH) ₂ .3H ₂ O], calcium silicate whisker, and the like.

Among the inorganic whiskers, basic magnesium sulfate whiskers and calcium silicate whiskers are preferable. When using basic magnesium sulfate whisker or calcium silicate whisker having the specific aspect ratio and true specific gravity described above, thixotropic properties can be particularly preferably imparted, so that the magnetic particles can be more stably dispersed. it can. These inorganic whiskers may be used alone or in combination of two or more.

The inorganic whisker can be provided with sufficient thixotropic properties even if it is not subjected to a surface treatment.
The surface treatment can be performed with a coupling agent such as silane or titanate. Examples of the coupling agent include vinyltriethoxysilane, vinyl-tris (β-methoxyethoxy) -silane, vinyltriacetoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-aminopropyltrimethoxysilane, γ- (β -Aminoethyl) aminopropyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-mercaptopropyltrimethoxysilane, β- (3,4-epoxy-cyclohexylethyltrimethoxysilane, γ-chloropropyltri Examples include silane coupling agents such as methoxysilane; titanate coupling agents such as diisostearolylethylene titanate.

The surface treatment with the coupling agent can be performed by a dry method. The coupling agent is preferably added in an amount of 0.1 to 2 parts by mass (solid content part by mass), more preferably 0.5 to 1 part by mass with respect to 100 parts by mass of the inorganic whisker.

In the first magnetorheological fluid, the content of the inorganic whiskers is preferably 0.05 to 15% by mass in 100% by mass of the magnetorheological fluid. If the amount is less than 0.05% by mass, sufficient thixotropic properties may not be exhibited, and magnetic particles may settle and a magnetorheological fluid having excellent dispersion stability may not be obtained. When the content exceeds 15% by mass, the sedimentation of the magnetic particles can be suppressed, but the magnetorheological fluid completely loses the fluidity and may not be able to exhibit sufficient performance when applied to a device. More preferably, it is 0.1-8 mass%.

The first magnetorheological fluid contains a dispersion medium.
The dispersion medium is not particularly limited as long as it is a substance capable of dispersing thixotropic agents and magnetic particles, for example, organic solvents such as toluene, xylene, hexane, etc .; mineral oils composed of petroleum hydrocarbons; Synthetic oils such as alkylbenzene, polyphenyl ether, alkylphenyl ether, polybutene, silicone oil and fluorine oil; animal oil such as fish oil, pork oil and cow oil; soybean oil, rapeseed oil, corn oil, palm oil, palm oil Vegetable oils such as cottonseed oil, sunflower oil, castor oil; water and glycol derivatives; ionicity represented by ethylmethylimidazolium salt, 1-butyl-3-methylimidazolium salt, 1-methylpyrazolium salt, etc. Examples thereof include liquids (room temperature molten salts). These may be used alone or in combination of two or more.

The first magnetorheological fluid contains magnetic particles.
The magnetic particle is not particularly limited as long as it is a substance having magnetism. For example, iron, iron nitride, iron carbide, carbonyl iron, chromium dioxide, low carbon steel, nickel, cobalt, aluminum-containing iron alloy, silicon-containing iron alloy , Cobalt-containing iron alloys, nickel-containing iron alloys, vanadium-containing iron alloys, molybdenum-containing iron alloys, chromium-containing iron alloys, tungsten-containing iron alloys, manganese-containing iron alloys, copper-containing iron alloys, etc., gadolinium, gadolinium organic derivatives Paramagnetic, superparamagnetic, or ferromagnetic compound particles made of, and particles made of a mixture thereof. These magnetic particles may be used alone or in combination of two or more.

Among the above magnetic particles, carbonyl iron is preferable from the viewpoint of expressing a large stress even with a small magnetic field.
The magnetic particles may be those obtained by subjecting the surface of these magnetic particles to a dispersion treatment. By subjecting the surface to a dispersion treatment, the dispersibility of the magnetic particles is improved, and a magnetorheological fluid having excellent responsiveness can be obtained. Examples of the magnetic particles (surface-treated magnetic particles) whose surface has been subjected to a dispersion treatment include those obtained by treating the surface of the magnetic particles with a silane coupling agent.

Examples of the surface-treated magnetic particles include those obtained by treating the surface of magnetic particles with a silane coupling agent containing an epoxy group or an amino group. The silane coupling agent containing an epoxy group or amino group is not particularly limited as long as it is a silane coupling agent containing at least one epoxy group or amino group in one molecule, but is represented by the following formula (1). The compound to be used is preferably used.

X- (Y) -SiR _3-b L _b (1)
In the formula, X represents an epoxy group, a cyclic epoxy group or an amino group. Y represents (CH ₂ ) _k or a hydrocarbon group containing an ether bond, an ester bond or a ketone bond. k represents an integer of 1 to 4. R represents an alkyl group such as a methyl group, an ethyl group, a propyl group, or a butyl group. L represents an alkoxyl group such as a halogen atom, a hydroxyl group, a methoxyl group, an ethoxyl group, a propoxyl group, or a butoxyl group, or an acyloxyl group such as a formyl group, an acetoxyl group, a propionyloxyl group, or a butyryloxyl group. b represents an integer of 1 to 3.

As a method for treating the surface of the magnetic particles with a silane coupling agent containing an epoxy group or an amino group, for example, a solution in which the silane coupling agent containing the epoxy group or amino group is dissolved in a solvent such as alcohol In addition, the magnetic particles may be immersed, or the silane coupling agent solution may be sprayed onto the magnetic particles and then the solvent is volatilized. Furthermore, after volatilizing the solvent, heat treatment may be performed at 40 to 150 ° C. for 5 minutes to 24 hours. The surface-treated magnetic particles are much more excellent in dispersion stability than untreated magnetic particles.

The amount of the silane coupling agent containing the epoxy group or amino group can be appropriately adjusted depending on the specific surface area of the magnetic particles. For example, 0.05 to 10 parts per 100 parts by mass of the magnetic particles. It is preferable that it is a mass part.

The magnetic particles preferably have a particle size of 0.01 to 100 μm. If it is less than 0.01 μm, since the particle size is too small, the rate of increase in the viscosity of the magnetorheological fluid at the time of applying a magnetic force becomes small, and there is a possibility that sufficient performance cannot be exhibited when applied to a device. If it exceeds 100 μm, the magnetic particles are likely to aggregate and settle, and it is difficult to obtain a magnetorheological fluid having excellent dispersion stability. More preferably, it is 0.5-20 micrometers.

In the first magnetorheological fluid, the content of the magnetic particles is preferably 10 to 95% by mass in 100% by mass of the magnetorheological fluid. If it is less than 10% by mass, the viscosity of the magnetorheological fluid does not sufficiently increase when magnetism is applied, and there is a possibility that sufficient performance cannot be exhibited when applied to a device. If it exceeds 95% by mass, the viscosity of the magnetorheological fluid will increase so much that it will not function as a fluid, and may not be able to exhibit sufficient performance when applied to a device. More preferably, it is 50-85 mass%.

The first magnetorheological fluid is an oil-based improver, extreme pressure additive, solid lubricant, cleaning dispersant, viscosity index improver, pour point depressor, as long as the properties of the magnetorheological fluid, particularly thixotropic properties, are not impaired. It may contain additives such as an agent, an antioxidant, a rust inhibitor, and an antifoaming agent. These may be used alone or in combination of two or more.

Examples of the oiliness improver include higher fatty acids, higher alcohols, aliphatic amines, aliphatic amides and esters.
Examples of the extreme pressure additive include olefin polysulfide, dibenzyl disulfide, alkyl phosphate ester, allyl phosphate ester, amine salt of phosphate ester, thiophosphate ester and its amine salt, naphthenate, chlorinated paraffin, etc. Can be mentioned.

Examples of the solid lubricant include graphite, fullerene, and carbon nanotube.
Examples of the washing dispersant include metal sulfonate, metal phosphonate, metal carboxylate, metal phenate, succinimide, succinate ester, benzylamine, alkylphenolamines and the like.

Examples of the viscosity index improver include polymethacrylic acid ester, polyacrylic acid ester, polyisobutylene, olefin copolymer, polyalkylstyrene, ethylene-propylene copolymer, hydrogenated styrene-diene copolymer, and the like. Can do.

Examples of the pour point depressant include low molecular weight polymethacrylic acid esters and polyacrylic acid esters, chlorinated paraffin-naphthalene condensates, chlorinated paraffin-phenol condensates, and polyalkylstyrenes.

Examples of the antioxidant include phenol derivatives, amines, benzotriazole, zinc phosphate derivatives, metal phenates, and organic nitrogen compounds. Examples of the rust inhibitor include amine salts of metal soaps, succinic acid derivatives, metal sulfonate salts, oleic acid derivatives, alkylamines, and phosphate esters.

Examples of the antifoaming agent include silicon compounds, aliphatic alcohols, metal exploration, succinic acid derivatives, polyacrylic acid esters and the like. In the present invention, it is preferable to use a nonionic surfactant based on propylene carbonate or polyethylene glycol as the additive.

The magnetorheological fluid of the present invention does not need to use a polar additive (glue agent) such as higher alcohol, water or propylene carbonate as an essential component as described above. For this reason, when using the said polar additive, it is preferable that content of the said polar additive is 0.05 mass% or less in 100 mass% of the said magnetorheological fluid.

Said 1st magnetorheological fluid can be manufactured by kneading | mixing an inorganic whisker, a dispersion medium, a magnetic particle, and another additive as needed. As a kneading procedure, it is possible to knead all the components of the measured magnetorheological fluid at one time. However, according to this method, it takes time to uniformly disperse, and inorganic kneading is performed during kneading. Whisker and magnetic particles are easily crushed. Therefore, it is desirable to perform two-stage kneading in which materials other than magnetic particles are preliminarily kneaded and dispersed, and magnetic particles are added thereto and kneaded again. The means for kneading / dispersing is not particularly limited, and examples thereof include a sand mill, a bead mill, a ball mill, a roll mill, a kneader, a planetary mixer, a high speed mixer, a universal mixer, and a homogenizer. In order to improve kneading / dispersibility, a heating device, an ultrasonic bath, or the like can be used in combination.

Since the second magnetorheological fluid of the present invention contains basic magnesium sulfate whiskers and / or calcium silicate whiskers, a dispersion medium, and magnetic particles, it is described in the first magnetorheological fluid described above. An effect similar to the effect can be obtained.

In the second magnetorheological fluid, the content of the basic magnesium sulfate whisker and / or the calcium silicate whisker is preferably 0.05 to 15% by mass in 100% by mass of the magnetorheological fluid. . When the amount is less than 0.05% by mass or more than 15% by mass, the same problem as described in the content of the inorganic whisker in the first magnetorheological fluid may occur. More preferably, it is 0.1-8 mass%. In addition, content of the said basic magnesium sulfate whisker and / or the said calcium silicate whisker is these total amounts.

In the second magnetorheological fluid, examples of the dispersion medium and the magnetic particles include those described in the first magnetorheological fluid. The preferable content of the magnetic particles is also the same. Furthermore, the second magnetorheological fluid may include the same additive as described in the first magnetorheological fluid. The second magnetorheological fluid can be produced by the same method as the first magnetorheological fluid described above.

The first magnetorheological fluid of the present invention contains a non-clay mineral-based inorganic whisker having an aspect ratio of 2 or more and a true specific gravity of 5 or less, a dispersion medium, and magnetic particles. The second magnetorheological fluid contains basic magnesium sulfate whiskers and / or calcium silicate whiskers, a dispersion medium, and magnetic particles. Therefore, since the first and second magnetorheological fluids can provide sufficient thixotropic properties, the magnetic particles contained in the stationary magnetorheological fluid can be stably dispersed for a long period of time. The sedimentation of the magnetic particles can be prevented. The first and second magnetorheological fluids can be easily manufactured. Therefore, the first and second magnetorheological fluids can satisfactorily control the generated stress by applying a magnetic force, and are suitably applied to stress control devices such as dampers, shock absorbers, brakes, and clutches. be able to.

Since the magnetorheological fluid of the present invention exhibits high thixotropic properties, it has excellent ability to prevent sedimentation of magnetic particles and can maintain stable performance for a long period of time.

Example 1 Production of Magnetorheological Fluid The constituent materials of the magnetorheological fluid were weighed so that the total amount was 430 g with the composition ratio shown in Table 1. Synthetic oil (Neosk-OIL 1300, manufactured by Soken Chemical Co., Ltd.) and basic magnesium sulfate whisker (Musheidi, Ube Materials, aspect ratio: 10-60, true specific gravity: 2.3, average length: 15 μm) The mixture was stirred with a homogenizer at 7600 rpm for 10 minutes to obtain a premix having a thixotropic property. To this is added magnetic carbonyl iron powder (BASF carbonyl iron powder CM, particle size D ₅₀ ≈7 μm), and the mixture is kneaded for 1.5 hours in a ball mill using a 1/4 inch steel ball as a medium. Was made.

Example 2
A magnetorheological fluid was prepared in the same manner as in Example 1 except that a polyethylene glycol-based nonionic surfactant was added and the composition ratio was changed to those shown in Table 1. The nonionic surfactant was added before premixing.

Example 3
Calcium silicate whisker (Uno Materials Zonoheiji, aspect ratio: 2-50, true specific gravity: 2.5, average length: 4 μm) was used in place of basic magnesium sulfate whisker, and the composition ratio shown in Table 1 A magnetorheological fluid was produced in the same manner as in Example 1 except that the above was changed.

Comparative Example 1
The constituent materials of the magnetorheological fluid were weighed so that the total amount was 430 g at the composition ratio shown in Table 1. Synthetic oil as a dispersion medium (Neosk-OIL 1300 manufactured by Soken Chemical Co., Ltd.), organic bentonite as a thixotropic agent (BENTONE 57, clay mineral) as an additive and propylene carbonate as an additive are stirred for 10 minutes at 7600 rpm with a homogenizer. did. This was kneaded in a ball mill using 1/4 inch steel balls as a medium for 24 hours to obtain a premix having thixotropic properties. To this, carbonyl iron powder (BASF carbonyl iron powder CM) as magnetic particles was added and kneaded again in a ball mill for 1.5 hours to prepare a magnetorheological fluid.

Comparative Example 2
The same method as in Comparative Example 1 was used except that organic colloidal calcium carbonate (particle size 0.15 μm sphere, true specific gravity: 2.5) was used as the thixotropic agent, and the composition ratio was changed to the composition ratio shown in Table 1. Although a premix was obtained, the magnetorheological fluid could not be prepared because the organic colloidal calcium carbonate precipitated at this stage and did not show any thixotropic properties.

[Evaluation of magnetorheological fluid]
The sedimentation stability and viscosity of the magnetorheological fluids obtained in Examples and Comparative Examples were evaluated by the following methods.

(Evaluation of sedimentation stability)
50 ml of magnetorheological fluid was placed in a 50 ml measuring cylinder with a stopper, stoppered, and allowed to stand in a 25 ° C. atmosphere. Measure the volume of supernatant produced in the magnetorheological fluid 3 days after standing and 3 months later, and evaluate the volume fraction (vol%) [volume of supernatant (ml) x 100/50 (ml)] did.

(Viscosity evaluation)
The viscosity (Pa · s) of the magnetorheological fluid at 25 ° C. and shear rates of 1 (1 / s) and 500 (1 / s) was evaluated using a stress rheometer RC20-CPS manufactured by Viscotec.

From Table 1, the magnetorheological fluids obtained in the examples have excellent sedimentation stability and behave as suitable low-viscosity fluids at shear rates of 1 (1 / s) and 500 (1 / s). It was to show. On the other hand, the product obtained in Comparative Example 1 was inferior in sedimentation stability and required a long time of kneading. Also, in Comparative Example 2 using spherical organic colloidal calcium carbonate, a magnetorheological fluid could not be produced.

The magnetorheological fluid of the present invention can be suitably applied to stress control devices such as dampers, shock absorbers, brakes and clutches.

Claims (4)

A magnetorheological fluid comprising a non-clay mineral-based inorganic whisker having an aspect ratio of 2 or more and a true specific gravity of 5 or less, a dispersion medium, and magnetic particles. 2. The magnetorheological fluid according to claim 1, wherein the content of the inorganic whisker is 0.05 to 15% by mass in 100% by mass of the magnetorheological fluid. A magnetorheological fluid comprising basic magnesium sulfate whiskers and / or calcium silicate whiskers, a dispersion medium, and magnetic particles. The magnetorheological fluid according to claim 3, wherein the content of the basic magnesium sulfate whisker and / or the calcium silicate whisker is 0.05 to 15% by mass in 100% by mass of the magnetorheological fluid.