JP2006253239A - Magnetic viscous fluid - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic viscous fluid in which magnetic particle distributes stably over a long period of time, and which is excellent in productivity. <P>SOLUTION: The magnetic viscous fluid contains urea series grease, a dispersion medium and the magnetic particle. <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.

Further, Patent Document 8 discloses a magnetorheological grease composition comprising magnetically responsive particles, a carrier fluid, and a thickener, and polyurea is disclosed as an example of the thickener. However, the polyurea and carrier fluid used are not discussed in detail here. Further, the stability of the magnetic particles is not yet sufficient, and further improvement has been desired.

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 containing a urea grease, a dispersion medium, and magnetic particles.
The urea grease preferably contains an alkyl-substituted diphenyl ether and a urea compound.

The alkyl-substituted product of the diphenyl ether is represented by the following formula (1);

(Wherein, R ¹ and R ² are the same or different and represent a hydrocarbon group having 1 to 24 carbon atoms. M and n represent an integer of 0 or more satisfying 1 ≦ m + n ≦ 4). It is preferable that it is a compound.

The content of the urea grease is preferably 0.1 to 25% by mass in 100% by mass of the magnetorheological fluid.
Hereinafter, the present invention will be described in detail.

The magnetorheological fluid of the present invention contains urea grease, a dispersion medium, and magnetic particles. In general, urea grease increases organic compounds having two or more urea groups (—NH—CO—NH—), such as aromatic diurea, aliphatic diurea, alicyclic diurea, triurea, tetraurea, polyurea, and the like. It is a non-soap semi-solid to solid lubricant prepared by dispersing it in a base oil such as mineral oil or synthetic oil. This urea grease exhibits thixotropic properties because it has a structure in which a needle-like urea compound forms a pseudo network three-dimensionally and includes a base oil.

Accordingly, since the magnetorheological fluid of the present invention contains the urea grease, it can impart thixotropic properties 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.

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 viscous fluid uses urea grease, stable thixotropic properties can be easily imparted without kneading the urea grease and the dispersion medium for a long time. For this reason, the magnetorheological fluid of the present invention can be easily produced.

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, in the magnetorheological fluid of the present invention, since the urea grease is used, thixotropic properties can be sufficiently imparted without performing such modification treatment. For this reason, since the apparent viscosity of the fluid can be increased in the stationary state of the magnetic viscous fluid, the sedimentation of the magnetic particles can be prevented.

Since the magnetorheological fluid of the present invention uses the above-mentioned urea grease, thixotropic properties can be obtained without adding a polar additive (glue agent) such as higher alcohol, water or propylene carbonate as an essential component. It can be expressed. 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.

As said urea-type grease, the thing containing a base oil, the urea compound used as a thickener, and an additive as needed can be mentioned, for example.
As said base oil, a conventionally well-known thing can be used as a base oil of grease, for example, mineral oil and / or synthetic oil etc. can be mentioned.

As the mineral oil, those obtained by a method usually used in a process for producing a lubricating oil in the oil refining industry can be used. For example, a lubricating oil fraction obtained by subjecting crude oil to atmospheric distillation and vacuum distillation. Examples thereof include those obtained by removing the solvent from the solvent, purifying it by performing one or more treatments such as solvent extraction, hydrocracking, solvent dewaxing, catalytic dewaxing, hydrorefining, sulfuric acid washing, and clay treatment.

Examples of the synthetic oil include poly α-olefins such as polybutene, 1-octene oligomer, 1-decene oligomer, or hydrides thereof; ditridecyl glutarate, di-2-ethylhexyl adipate, diisodecyl adipate, ditridecyl adipate, dithiol Diesters such as 3-ethylhexyl sebacate; polyol esters such as trimethylolpropane caprylate, trimethylolpropane pelargonate, pentaerythritol 2-ethylhexanoate, pentaerythritol pelargonate; alkylnaphthalenes; alkylbenzenes, polyoxyalkylene glycols; poly Examples include phenyl ethers; alkyl-substituted products of diphenyl ethers such as dialkyldiphenyl ethers; silicone oils; and mixtures thereof. .

Among the above base oils, it is preferable to use an alkyl-substituted product of diphenyl ether. Among the urea-based greases, when a urea-based grease containing an alkyl-substituted diphenyl ether as a base oil and a urea compound as a thickener is used, high thixotropic properties can be imparted to the dispersion medium. . For this reason, the magnetic particles contained in the magnetorheological fluid in a stationary state can be stably dispersed for a longer period of time, and sedimentation of the magnetic particles can be more effectively prevented.

The alkyl-substituted product of the diphenyl ether is preferably a compound represented by the above formula (1). By using the compound represented by the above formula (1), the effects of the present invention as described above can be obtained more remarkably.

In the above formula (1), said ^{R 1} and said ^{R 2} are the same or different and each represents a hydrocarbon group having 1 to 24 carbon atoms. As said C1-C24 hydrocarbon group, a linear or branched alkyl group can be mentioned. When carbon number exceeds 24, there exists a possibility that a pour point may become high. Especially, it is preferable that it is a C8-24 hydrocarbon group from the point from which the effect of this invention is acquired, and it is more preferable that it is a C10-20 alkyl group.

Examples of the alkyl group having 10 to 20 carbon atoms include a decyl group, an undecyl group, a dodecyl group, a tridecyl group, a tetradecyl group, a pentadecyl group, a hexadecyl group, a heptadecyl group, an octadecyl group, a nonadecyl group, and an eicosyl group. Can do. The alkyl group may be linear or branched. In particular, an alkyl group having 12 to 18 carbon atoms is preferable.

In the above formula (1), m and n represent an integer of 0 or more that satisfies 1 ≦ m + n ≦ 4. If m + n> 4, the oxidation stability may decrease. The m and n may be the same or different. In the compound represented by the above formula (1), the substituted hydrocarbon group may be bonded to any position of any aromatic ring of diphenyl ether having two aromatic rings.

Kinematic viscosity at 100 ° C. of the base oil is preferably 2 to 40 mm ² / s, more preferably 3 to 20 mm ² / s. Further, the viscosity index of the base oil is preferably 90 or more, and preferably 100 or more. Thereby, since thixotropic property can be imparted particularly preferably, the magnetic particles can be more stably dispersed.

In the present invention, as the alkyl-substituted product of the diphenyl ether, for example, a well-known alkylated diphenyl ether oil having a chemical structure represented by the above formula (1) in which an aromatic ring is bonded with an oxygen atom can be used.

Examples of the urea compound include organic compounds having two or more urea groups (—NH—CO—NH—) (aromatic diurea, aliphatic diurea, alicyclic diurea, triurea, tetraurea, polyurea, etc.). . Especially, it is preferable to use a diurea compound from the point which can acquire the effect of this invention effectively, following formula (2)
^{A-CONH-R 3 -NHCO-} B (2)
(In the formula, R ³ represents a divalent hydrocarbon group. A and B are the same or different and represent NHR ⁴ or NR ⁵ R ^6. R ⁴ , R ⁵ and R ⁶ are the same or different. , Which represents a hydrocarbon group having 6 to 20 carbon atoms.) It is more preferable to use one or more of the compounds represented by

Examples of the divalent hydrocarbon group represented by R ³ include a linear or branched alkylene group, a linear or branched alkenylene group, a cycloalkylene group, and an aromatic group. it can. Especially, it is preferable that it is a C6-C20 hydrocarbon group from the point which can acquire the effect of this invention effectively, and it is more preferable that it is a C6-C15 hydrocarbon group. Specific examples include an ethylene group, 2,2-dimethyl-4-methylhexylene group, and groups represented by the following formulas (3) to (11). Particularly, the following formulas (4) and (6 ) Is preferred.

As R ⁴ , R ⁵ , R ⁶ , a linear or branched alkyl group, a linear or branched alkenyl group, a cycloalkyl group, an alkylcycloalkyl group, an aryl group, an alkylaryl group, An arylalkyl group etc. can be mentioned. Specifically, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl, nonadecyl, eicosyl, etc. A linear or branched alkyl group of hexenyl, heptenyl, octenyl, nonenyl, decenyl, undecenyl, dodecenyl, tridecenyl, tetradecenyl, pentadecenyl, hexadecenyl, heptadecenyl, octadecenyl Straight chain or branched alkenyl groups such as nonadecenyl group, eicocenyl group; cyclohexyl group; methylcyclohexyl group, dimethylcyclohexyl group, ethylcyclohexyl group, diethylcyclohexyl group, propylcyclohexyl group, isopyl group Pyrucyclohexyl group, 1-methyl-3-propylcyclohexyl group, butylcyclohexyl group, amylcyclohexyl group, amylmethylcyclohexyl group, hexylcyclohexyl group, heptylcyclohexyl group, octylcyclohexyl group, nonylcyclohexyl group, decylcyclohexyl group, undecylcyclohexyl group Group, alkyl cycloalkyl group such as dodecylcyclohexyl group, tridecylcyclohexyl group, tetradecylcyclohexyl group; aryl group such as phenyl group, naphthyl group; toluyl group, ethylphenyl group, xylyl group, propylphenyl group, cumenyl group, methyl group Alkylaryl groups such as naphthyl group, ethylnaphthyl group, dimethylnaphthyl group, propylnaphthyl group; benzyl group, methylbenzyl group, ethylbenzyl group It can be mentioned an aryl alkyl group or the like. Of these, a cyclohexyl group, an octadecyl group, and a toluyl group are preferable from the viewpoint of obtaining the effects of the present invention.

The diurea compounds, for example, a diisocyanate represented by the general formula ^OCN-R 3 -NCO, and a general formula _NH 2 ^R 4, ^NHR 5 a compound represented by ^{R 6} or mixtures thereof in the base oil 10 It can manufacture by making it react at -200 degreeC. ^Here, R ^4, R 5, ^{R 6} are the same as ^{R 4,} R 5, ^{R 6} in the formula (2).

The content of the urea compound is preferably 2 to 30% by mass in 100% by mass of the urea grease. If it is less than 2% by mass, the effect as a thickener is small, and there is a possibility that it will not become a sufficient grease. When it exceeds 30% by mass, the urea-based grease becomes excessively hard, and there is a possibility that sufficient performance cannot be exhibited. More preferably, it is 5-20 mass%.

The content of the urea grease is preferably 0.1 to 25% by mass in 100% by mass of the magnetorheological fluid. If the amount is less than 0 and 1% by mass, sufficient thixotropic properties cannot be exhibited, and magnetic particles may settle and a magnetorheological fluid having excellent dispersion stability may not be obtained. If it exceeds 25% by mass, the sedimentation of the magnetic particles can be suppressed, but the fluidity of the magnetorheological fluid is lowered, and there is a possibility that sufficient performance cannot be exhibited when applied to a device. More preferably, it is 1-20 mass%. When the components such as the base oil and additives in the urea grease and the components such as the dispersion medium and additives in the magnetorheological fluid are the same, the content of the urea grease includes the above The amount of dispersion medium and additives in the magnetorheological fluid is not included.

As the above additives, known antiwear agents, extreme pressure additives, antioxidants, viscosity index improvers, pour point depressants, corrosion inhibitors, rust inhibitors (rust inhibitors) conventionally used in greases Etc. Here, examples of the extreme pressure additive, the antioxidant, the viscosity index improver, the pour point depressant, and the rust inhibitor include those described below.

The urea grease preferably has a penetration of 250 to 350, more preferably 300 to 330. By being within the above range, the dispersion stability of the magnetic particles can be improved. The test method of the above-mentioned penetration is to obtain the penetration immediately after mixing the grease in a specified mixer, keeping it at 25 ° C., and further mixing 60 times according to JIS K2220.

The urea grease preferably has an oil separation degree (100 ° C., 30 hours) of 0 to 3% by mass, and more preferably 0 to 1.5% by mass. By being within the above range, the dispersion stability of the magnetic particles can be improved. The test method of the oil separation degree (100 ° C., 30 hours) is to obtain the mass ratio of oil separated after 30 hours from a sample kept at 100 ° C. in a conical wire mesh filter according to JIS K2220. .

The urea grease has an oil separation degree (150 ° C., 30 hours) of preferably 0 to 4% by mass, and more preferably 0 to 2.5% by mass. By being within the above range, the dispersion stability of the magnetic particles can be improved. The test method of the oil separation degree (150 ° C., 30 hours) is to obtain the mass ratio of oil separated after 30 hours from a sample kept at 150 ° C. in a conical wire mesh filter according to JIS K2220. .

The urea grease preferably has an evaporation amount of 0 to 1.0% by mass, and more preferably 0 to 0.5% by mass. By being within the above range, the dispersion stability of the magnetic particles can be improved. The evaporation amount test method is based on JIS K2220, in which a sample is kept at a specified temperature (98.9 ° C.) and heated air is passed through the sample surface for 22 hours to determine the sample weight loss.

The urea grease preferably has a dropping point of 200 ° C. or higher, and more preferably 250 ° C. or higher. Thereby, the dispersion stability of magnetic particles can be improved. The dropping point test method is to determine the temperature at which the first drop falls from semi-solid to liquid when the sample is heated with a specified apparatus under a specified condition according to JIS K2220.

The magnetorheological fluid of the present invention contains a dispersion medium.
The dispersion medium is not particularly limited as long as it is a substance that can disperse urea-based grease and magnetic particles, for example, an organic solvent 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 oils such as fish oil, pork oil and cow oil; soybean oil, rapeseed oil, corn oil, palm oil, palm Vegetable oils such as oil, cottonseed oil, sunflower oil, castor oil; water and glycol derivatives; ions represented by ethylmethylimidazolium salt, 1-butyl-3-methylimidazolium salt, 1-methylpyrazolium salt, etc. Liquids (room temperature molten salts) and the like. These may be used alone or in combination of two or more.

As the dispersion medium, it is preferable to use oils (especially synthetic oils) having the same structure as the base oil of the urea-based grease from the viewpoint that magnetic particles can be stably dispersed. In particular, it is more preferable to use an alkyl-substituted diphenyl ether as the base oil of the urea grease and the dispersion medium, and it is particularly preferable to use a compound represented by the above formula (1). Thereby, the effect of the present invention can be obtained more effectively.

The 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 (12). The compound to be used is preferably used.

X- (Y) -SiR _3-b L _b (12)
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 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 above magnetorheological fluid is an oil improver, extreme pressure additive, solid lubricant, cleaning dispersant, viscosity index improver, pour point depressant, oxidation, as long as the properties of the magnetorheological fluid, especially thixotropic properties are not impaired. It may contain additives such as an inhibitor, a rust inhibitor, and an antifoaming agent. In addition, these additives may be previously blended in the urea-based grease. 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.

The magnetorheological fluid of the present invention preferably has a viscosity of 3 to 20 Pa · s, more preferably 7 to 16 Pa · s at 25 ° C. and a shear rate of 1 (1 / s). Further, the viscosity at 25 ° C. and a shear rate of 500 (1 / s) is preferably 0.1 to 1.0 Pa · s, and more preferably 0.1 to 0.6 Pa · s. In this case, the magnetorheological fluid of the present invention has good characteristics. In addition, the said viscosity is a value measured from the stress rheometer RC20-CPS (apparatus used for a viscosity measurement) by Bisco Tech.

The magnetorheological fluid of the present invention can be produced by kneading urea-based grease, a dispersion medium, magnetic particles, and other additives as required. Here, the procedure of kneading / dispersing is not particularly limited. Even in the method of kneading / dispersing all the measured components of the magnetorheological fluid at one time, materials other than magnetic particles are pre-kneaded / dispersed in advance. Alternatively, a multistage kneading / dispersing method in which magnetic particles are added and kneading / dispersing again may be used. The kneading / dispersing means 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. Moreover, in order to improve kneading | mixing and dispersibility, it is also possible to use a heating apparatus, an ultrasonic bath, etc. together.

The magnetorheological fluid of the present invention contains urea grease, a dispersion medium, and magnetic particles. For this reason, the magnetorheological fluid can impart sufficient thixotropic properties, so that the magnetic particles contained in the magnetorheological fluid in a stationary state can be stably dispersed for a long period of time. Can be prevented. Moreover, the said magnetorheological fluid can be manufactured simply. Therefore, the above-mentioned magnetorheological fluid can satisfactorily control the generated stress by applying a magnetic force, and can be suitably applied to stress control devices such as dampers, shock absorbers, brakes, and clutches.

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 ("Moresco High Lube LB-15", alkyl-substituted diphenyl ether, manufactured by Matsumura Oil Research) and urea grease ("Moresco High Grease UM-1", manufactured by Matsumura Oil Research), base oil alkyl Substituted diphenyl ether, thickener (urea compound) was stirred with a homogenizer at 7600 rpm for 10 minutes to obtain a premix showing thixotropic properties. 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
Magnetic properties were obtained in the same manner as in Example 1 except that the amounts of urea-based grease (“Moresco High Grease UM-1” manufactured by Matsumura Oil Research Institute), synthetic oil, and magnetic particles were changed as shown in Table 1. A viscous fluid was prepared.

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 (“Morseco High Lube LB-15” manufactured by Matsumura Oil Research Institute, alkyl-substituted diphenyl ether) and organic bentonite (“Elements 34” manufactured by Elements Specialties) as a thixotropic agent and a polar additive (1) (Propylene carbonate) was stirred with a homogenizer at 7600 rpm for 10 minutes. 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 constituent materials of the magnetorheological fluid were weighed so that the total amount was 430 g at the composition ratio shown in Table 1. A hydrocarbon mineral oil as a dispersion medium and an organic bentonite (Elements Specialties "BENTONE 34") and a polar additive (2) (a mixture of methanol and water at a volume ratio of 90:10) are mixed at 7600 rpm by a homogenizer. For 10 minutes. 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. Dispersant I (polyoxyethylene octylphenyl ether) and carbonyl iron powder (BASF carbonyl iron powder CM) as magnetic particles were added thereto, and kneaded again with a ball mill for 1.5 hours to prepare a magnetorheological fluid. .

Comparative Example 3
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. Silicon oil as a dispersion medium and gel type silica as a thixotropic agent were stirred at 7600 rpm for 10 minutes by a homogenizer. This was kneaded for 1 hour in a ball mill using a 1/4 inch steel ball as a medium to obtain a premix having thixotropic properties. Dispersant II (amino-modified silicone oil) and carbonyl iron powder (BASF carbonyl iron powder CM) as magnetic particles were added thereto and kneaded again in a ball mill for 1 hour to prepare a magnetorheological fluid.

In addition, the urea-based grease “Molesco High Grease UM-1” used in the Examples has a blending degree of 313, an oil separation degree (100 ° C., 30 hours) of 1.4% by mass, and an oil separation degree (150 ° C., 30 Time) 2.0% by mass, evaporation amount 0.35% by mass, dropping point 260 ° C. or more. These physical property values are values obtained by the measurement method described above.
Further, the kinematic viscosity at 100 ° C. of the base oil contained in “Molesco High Grease UM-1” was 13.2 mm ² / s, and the viscosity index 124 of the base oil.

[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, what was obtained by the comparative example was inferior to sedimentation stability, and comparative examples 1 and 2 required kneading | mixing for a long time for preparation. Moreover, what was obtained in Comparative Example 3 showed a relatively high viscosity.

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 urea-based grease, a dispersion medium, and magnetic particles. 2. The magnetorheological fluid according to claim 1, wherein the urea-based grease contains an alkyl-substituted product of diphenyl ether and a urea compound. The alkyl-substituted product of diphenyl ether has the following formula (1):

(Wherein, ^{R 1} and ^{R 2} are the same or different, .m representing a hydrocarbon group having 1 to 24 carbon atoms, n is an integer of 0 or more satisfying 1 ≦ m + n ≦ 4. )
The magnetorheological fluid according to claim 2, which is a compound represented by the formula: The magnetorheological fluid according to claim 1, 2 or 3, wherein the urea grease content is 0.1 to 25% by mass in 100% by mass of the magnetorheological fluid.