Magnetoviscous fluids and mechanical devices

Abstract

Provided are: a magnetic viscous fluid having suitable resistance during excitation and excellent dispersion stability of magnetic particles; and a mechanical device. The magnetic viscous fluid contains magnetic particles, a base oil, and a polyether-modified silicone. The value obtained by subtracting the solubility parameter (SP value) of the base oil from the HLB value of the polyether-modified silicone is 2.5 or more.

Description

[Technical Field]

[0001] This invention relates to magnetorheological fluids and mechanical devices. More particularly, it relates to magnetorheological fluids and mechanical devices used to control frictional forces acting between objects in various mechanical devices such as brakes, clutches, vibration isolation devices, and dampers for vibration damping devices. [Background technology]

[0002] Magneto-rheological (MR) fluids are fluids in which magnetic particles, such as magnetizable metal particles, are dispersed in a dispersion medium. When no magnetic field is present, the magnetic particles in a magneto-rheological fluid float randomly in the dispersion medium and function as a fluid. However, when a magnetic field is applied, the magnetic particles form numerous clusters, increasing viscosity and increasing internal stress.

[0003] Magnetorheological fluids behave like rigid bodies due to the increase in internal stress mentioned above, exhibiting resistance to shear and pressure flows. Because of these properties, magnetorheological fluids are used in various mechanical devices such as brakes, clutches, vibration dampers, and dampers to control frictional forces between objects.

[0004] Therefore, it is preferable for the resistance force against shear flow and pressure flow when a magnetic field is applied to a magnetorheological fluid (during excitation) to be large (hereinafter also referred to as "drag force during excitation"). The drag force during excitation is evaluated by measuring the torque value, viscosity, or shear stress, etc. In this specification, the drag force during excitation is evaluated by measuring the viscosity during excitation.

[0005] To increase the drag force during excitation, the amount of magnetic particles in the magnetorheological fluid should be increased. However, because there is a large difference in specific gravity between the magnetic particles in the magnetorheological fluid and the dispersion medium, sedimentation of the magnetic particles is likely to occur. Furthermore, the cohesive force of the magnetic particles tends to generate a hard, slurry-like precipitate.

[0006] Patent Document 1 proposes a magnetorheological fluid in which a predetermined amount of magnetic particles, a clay mineral-based dispersion stabilizer, and a surfactant are contained in a carrier fluid. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2002-121578 [Overview of the project] [Problems that the invention aims to solve]

[0008] However, the magnetoviscous fluid described in Patent Document 1 is unsatisfactory because it has low drag force during excitation. Furthermore, it is insufficient in terms of the dispersion stability of magnetic particles. Dampers for buildings, in particular, are left stationary for long periods of time, so they need to have excellent dispersion stability of magnetic particles.

[0009] Furthermore, while magnetorheological fluids contain additives such as dispersants and lubricity enhancers in addition to magnetic particles and base oil, securing these additives makes it difficult to increase the amount of magnetic particles, resulting in difficulty in improving the drag force during excitation.

[0010] This invention was made in view of the above points, and aims to provide a magnetoviscous fluid and mechanical device that exhibits good drag force during excitation as well as excellent dispersion stability of magnetic particles. [Means for solving the problem]

[0011] To solve the above problems, the present invention is specified as follows: [1] to [5]. [1] A magnetorheological fluid containing magnetic particles, a base oil, and a polyether-modified silicone, wherein the value obtained by subtracting the solubility parameter of the base oil from the HLB value of the polyether-modified silicone is 2.5 or more. [2] The magnetoviscous fluid according to [1], wherein the content of the magnetic particles is 75 to 90% by mass with respect to the total amount of the magnetoviscous fluid. [3] The magnetorheological fluid according to [1] or [2], wherein the base oil is an α-olefin, a polyα-olefin, or a mineral oil. [4] The magnetorheological fluid according to any one of [1] to [3], wherein the polyether-modified silicone is a side-chain type polyether-modified silicone. [5] A mechanical device using a magnetorheological fluid as described in any of [1] to [4] above. [Effects of the Invention]

[0012] According to embodiments of the present invention, it is possible to provide a magnetorheological fluid and a mechanical device that exhibit good drag force during excitation and excellent dispersion stability of magnetic particles. [Modes for carrying out the invention]

[0013] The embodiments of the magnetorheological fluid and mechanical apparatus of the present invention will be described below, but the present invention shall not be construed as being limited thereto, and various changes, modifications, and improvements may be made based on the knowledge of those skilled in the art, without departing from the scope of the present invention.

[0014] In this specification, the symbol "~" indicating a numerical range represents the range that includes the numerical values ​​specified as the upper and lower limits, respectively. Furthermore, if only the upper limit of a numerical range has a unit specified, it means that the lower limit also has the same unit as the upper limit. In the numerical ranges described in stages in this specification, the upper or lower limit of one numerical range may be replaced with the upper or lower limit of another numerical range described in stages. Furthermore, within the numerical ranges described herein, any upper or lower limit specified within a given range may be replaced with the values ​​shown in the examples. In this specification, the content rate or content amount of each component in a composition means the total content rate or content amount of the plurality of substances corresponding to each component in the composition, unless otherwise specified when there are multiple substances corresponding to each component in the composition.

[0015] (Magnetorheological fluid) The magnetorheological fluid according to this embodiment contains magnetic particles, a base oil, and a polyether-modified silicone, and has a configuration in which the value obtained by subtracting the solubility parameter of the base oil from the HLB value of the polyether-modified silicone is 2.5 or more. With such a configuration, the magnetorheological fluid according to this embodiment has good resistance during excitation and can have excellent dispersion stability of magnetic particles. Hereinafter, each component included in the magnetorheological fluid according to this embodiment will be described.

[0016] 1. Magnetic particles The magnetic particles included in the magnetorheological fluid according to this embodiment can be selected according to the target magnetic permeability. For example, ferromagnetic oxides such as magnetite, carbonyl iron, γ-iron oxide, manganese ferrite, cobalt ferrite, or composite ferrites of these with zinc or nickel, and barium ferrite; ferromagnetic metals such as iron, cobalt, and rare earths; metal nitrides; various alloys such as Sendust (registered trademark), Permalloy (registered trademark), and Supermalloy (registered trademark), etc. Among these, carbonyl iron is preferable in that it is a soft magnetic material with a small coercive force and a large magnetic permeability. Carbonyl iron is high-purity metal particles produced by thermal decomposition of pentacarbonyl iron (Fe(CO)5). Note that the magnetic particles may be used alone or in combination of two or more kinds. In the magnetorheological fluid according to this embodiment, when an external magnetic field is applied, the dispersed magnetic particles orient themselves in the direction of the magnetic field to form chain-like clusters, thereby increasing viscosity and changing its flow properties and yield stress. The average particle diameter of the magnetic particles is determined so as to exhibit such behavior. Specifically, it is preferably in the range of 0.1 to 100 μm. The lower limit of the average particle diameter of the magnetic particles is more preferably 1 μm or more, and even more preferably 4 μm or more. The upper limit of the average particle diameter of the magnetic particles is more preferably 80 μm or less, even more preferably 60 μm or less, even more preferably 50 μm or less, and even more preferably 40 μm or less. From the above viewpoint, it is more preferably 1 to 80 μm, even more preferably 4 μm to 60 μm, and even more preferably 4 to 50 μm. The shape of the magnetic particles is preferably spherical or nearly spherical because it facilitates dispersion. The average particle diameter of magnetic particles is the average primary particle diameter measured by a laser diffraction / scattering particle size distribution analyzer.

[0017] The magnetic particle content is preferably in the range of 75 to 90 mass% relative to the total amount of magnetoviscous fluid according to this embodiment. By setting the magnetic particle content in the range of 75 to 90 mass% relative to the total amount of magnetoviscous fluid according to this embodiment, the necessary drag force can be obtained when a magnetic field is applied, and the dispersibility of the magnetic particles can be maintained, so that it can also function as a fluid. The lower limit of the magnetic particle content is more preferably 80 mass% or more. The upper limit of the magnetic particle content is more preferably 88 mass% or less, and even more preferably 85 mass% or less. From the above viewpoint, it is more preferably 80 to 88 mass%, and even more preferably 80 to 85 mass%.

[0018] 2. Base oil The magnetorheological fluid according to this embodiment contains a base oil. The base oil can be any of the mineral oils and synthetic oils conventionally used as dispersion media for magnetic particles, provided that it satisfies the relationship where the difference between the HLB value of the polyether-modified silicone (described later) and the solubility parameter (SP value) of the base oil is 2.5 or greater. Among these, α-olefins, polyα-olefins, or mineral oils are preferred because they are easy to adjust to the relationship where the difference between the HLB value of the ether-modified silicone and the solubility parameter (SP value) of the base oil is 2.5 or greater. The base oil may be used alone or in combination of two or more types. The base oil used in the magnetorheological fluid according to this embodiment may be either mineral oil or synthetic oil, or a combination of mineral oil and synthetic oil. The numbers in parentheses for each base oil represent the SP value ((cal / cm²) of each base oil. 3 ) 1 / 2 This indicates that...

[0019] Examples of synthetic oils include α-olefins, poly-α-olefins, isoparaffins, n-paraffins, hydrocarbon solvents such as halogenated hydrocarbons, ester solvents, ether solvents, glycol solvents, and silicone solvents.

[0020] As for mineral oils, any of those commonly used in the field of lubricants can be used, such as naphthenic mineral oil, paraffinic mineral oil, liquid paraffin, and hydrolyzed dewaxing oil.

[0021] Examples of α-olefins include 1-hexene (7.5), 1-octene (7.6), 1-decene (7.8), 1-dodecene (7.9), 1-tetradecene, 1-hexadecene, and 1-octadecene. Among these, α-olefins with 8 to 14 carbon atoms, such as 1-octene, 1-decene, and 1-dodecene, are preferred. Poly-αolefin is a polymer of the α-olefin. More preferably, the poly-αolefin is a polymer of an α-olefin having 8 to 14 carbon atoms, such as 1-octene, 1-decene, or 1-dodecene. The α-olefin and poly-αolefin may be used individually or in combination of two or more.

[0022] Examples of ester solvents include monoesters, polyol esters, dibasic acid esters (diesters), and polyoxyalkylene glycol esters. Of these, monoesters with 12 to 30 carbon atoms are preferred, such as 2-ethylhexyl laurate, 2-ethylhexyl palmitate, and n-butyl stearate. Polyol esters are esters of polyhydric alcohols (polyols) and linear or branched saturated or unsaturated fatty acids. Examples of polyol esters include hindered esters. Ester solvents may be used individually or in combination of two or more.

[0023] Examples of ether-based solvents include polyvinyl ethers, polyphenyl ethers, and perfluoroethers. Examples of polyvinyl ethers include homopolymers of methyl vinyl ether (8.7) and homopolymers of ethyl vinyl ether (8.6). One type of ether-based solvent may be used alone, or two or more types may be used in combination.

[0024] Examples of glycol-based solvents include polyethylene glycol (9.4), polypropylene glycol (8.7), polybutylene glycol (8.6), or ethylene oxide-propylene oxide copolymer, propylene oxide-butylene oxide copolymer, and derivatives thereof. Glycol-based solvents may be used individually or in combination of two or more.

[0025] The kinematic viscosity of the base oil at 40°C is 50.0 mm². 2 Preferably, the interval is 5.0 to 40.0 mm / s or less. 2It is more preferable that the kinematic viscosity of the base oil at 40°C be in the range of / s. 2 Setting the rate to less than / s is more preferable because it makes it easier to disperse the magnetic particles. The kinematic viscosity is measured according to the kinematic viscosity test method specified in JIS K2283:2000.

[0026] The base oil content is preferably in the range of 10 to 25% by mass, and more preferably in the range of 12 to 20% by mass, relative to the total amount of the magnetorheological fluid according to this embodiment. By setting the base oil content to 10% by mass or more, magnetic particles can be dispersed and fluidity can be improved. By setting the base oil content to 25% by mass or less, the magnetic properties during excitation can be improved.

[0027] The solubility parameter (SP value) of the base oil can be calculated according to the method proposed by Fedors et al. (see Polymer Engineering and Science, 14, 147-154 (1974)). In other words, it can be calculated based on the following formula. SP value δ = (Σ△e / Σ△v) 1 / 2 (In the above equation, △e is the evaporation energy of each atom or group of atoms at 25°C, and △v is the molar volume of each atom or group of atoms at the same temperature.)

[0028] 3. Polyether-modified silicone The magnetorheological fluid according to this embodiment contains polyether-modified silicone. A magnetorheological fluid containing polyether-modified silicone becomes paste-like before excitation and exhibits high thixotropy. Therefore, even when the magnetic particle content is increased, the dispersion of magnetic particles remains stable, improving the drag force during excitation. The polyether-modified silicone content in the magnetorheological fluid according to this embodiment is preferably 0.1 to 3% by mass relative to the total amount of the magnetorheological fluid. A polyether-modified silicone content of 0.1% by mass or more yields a greater drag force during excitation. Furthermore, a polyether-modified silicone content of 3% by mass or less ensures thixotropy and suppresses an increase in viscosity. The polyether-modified silicone content in the magnetorheological fluid according to this embodiment is more preferably 0.3 to 2.5% by mass, and even more preferably 0.5 to 1.5% by mass, relative to the total amount of the magnetorheological fluid.

[0029] Furthermore, as described above, the magnetorheological fluid according to this embodiment contains polyether-modified silicone, which has an extremely high dispersion stability effect for magnetic particles. Therefore, the content of magnetic particles can be increased further, and the drag force during excitation can be further improved. In addition, when the magnetorheological fluid is used in equipment, etc., liquid phase separation of the magnetorheological fluid can be suppressed, and the seepage of the base oil can be suppressed. For example, in cases where the magnetic particles were conventionally included up to about 80% by mass to maintain the fluidity of the magnetorheological fluid, they can be included up to about 87% by mass, and the seepage of the base oil can be suppressed more effectively.

[0030] Furthermore, as described above, the magnetorheological fluid according to this embodiment contains polyether-modified silicone, which has an extremely high dispersion stability effect on magnetic particles. Therefore, even when magnetic particles are densely packed, the magnetic particles are less likely to settle, and the dispersion stability of the magnetic particles is maintained over a long period of time. For this reason, the magnetorheological fluid according to this embodiment has good drag force during excitation and can maintain the dispersion stability of magnetic particles over a long period of time. Thus, the magnetorheological fluid according to this embodiment is ideal for applications such as dampers in buildings that remain stationary for long periods of time.

[0031] Examples of polyether-modified silicones included in the magnetorheological fluid according to this embodiment include polyalkylsiloxanes having a polyether structure. The polyether structure is preferably present in the side chains of the molecular chain. Hereinafter, polyalkylsiloxanes having a polyether structure in the side chains of the molecular chain may be referred to as side-chain type polyether-modified silicones, or simply as "side-chain type". The number of carbon atoms in the alkyl group of the polyalkylsiloxane is preferably 1 to 3.

[0032] The HLB value (hydrophilic-lipophilic balance value) of polyether-modified silicone is preferably in the range of 10 to 16, and more preferably in the range of 10.5 to 15. The HLB value is defined by the following formula (Griffin method). HLB value = 20 × (sum of molecular weights of hydrophilic parts / molecular weight)

[0033] From the viewpoint of easily balancing hydrophilicity and hydrophobicity, it is preferable that the polyether structure contains a polyoxyalkylene structure (a repeating structure of oxyalkylene units).

[0034] In the polyoxyalkylene structure, the number of repeating oxyalkylene groups (oxyalkylene units) is preferably 2 to 20, more preferably 2 to 16, and particularly preferably 2 to 10, whichever is appropriately selected so that the HLB value of the modified silicone falls within the above range.

[0035] In the polyoxyalkylene structure, the number of carbon atoms in the alkylene is preferably 1 to 6, more preferably 2 to 6, even more preferably 2 to 4, and most preferably 2 to 3.

[0036] The ends of the polyoxyalkylene structure are preferably hydroxyl groups. Within the limits that do not impair the effects of this embodiment, the ends of the polyoxyalkylene structure may be capped with alkyl groups such as methyl groups.

[0037] The ratio of the total number of oxyethylene units to the total number of oxyalkylene units in the polyether-modified silicone (EO ratio) is, for example, 40% or more, and preferably 50% or more. The EO ratio is 100% or less. Therefore, 40-100% is preferred, and 50-100% is more preferred. Note that the total number of oxyalkylene units refers to the number of moles of oxyalkylene units contained in one molecule of polyether-modified silicone. The total number of oxyethylene units refers to the number of moles of oxyethylene units contained in one molecule of polyether-modified silicone. Polyether-modified silicone containing only oxyethylene units as oxyalkylene units (EO ratio = 100%) may also be used.

[0038] Examples of polyether-modified silicones having the above-mentioned EO ratio include TSF4440 (HLB: 14) and TSF4452 (HLB: 11, moles of oxyethylene units / moles of oxypropylene units (=EO / PO) = 50 / 50 (EO ratio 50%)) manufactured by Momentive Performance Materials. All of these polyether-modified silicones are side-chain type.

[0039] In this embodiment, the magnetorheological fluid has a value of 2.5 or higher obtained by subtracting the solubility parameter of the base oil from the HLB value of the polyether-modified silicone. With this configuration, the polyether-modified silicone and the base oil are not miscible, and intermolecular hydrogen bonds are formed between the terminal hydroxyl groups of the polyether portion in the polyether-modified silicone, forming a thixotropic gel. Therefore, it is presumed that the dispersion stability of magnetic particles contained in the magnetorheological fluid is improved. Furthermore, side-chain type polyether-modified silicone is more preferable because it is easier to form a three-dimensional structure.

[0040] 4. Other ingredients In this embodiment, the magnetorheological fluid may, in addition to the components described above, contain various other components depending on the purpose, as long as the effects of this embodiment are not impaired. Other components include, for example, anti-wear agents, dispersants, surfactants, viscosity modifiers, fluidity improvers, sedimentation inhibitors, pour point depressants, extreme pressure agents, rust inhibitors, antioxidants, corrosion inhibitors, metal deactivators, and defoamers.

[0041] Examples of wear-resistant agents include sulfur compounds such as sulfides, sulfoxides, sulfones, and thiophosphinates; halogen compounds such as chlorinated hydrocarbons; and organometallic compounds such as molybdenum dithiophosphate (MoDTP), molybdenum dithiocarbamate (MoDTC), and tricresyl phosphate. Abrasion-resistant agents may be used individually or in combination of two or more types.

[0042] Dispersants are added to improve the dispersibility of magnetic particles in the base oil, and examples include known low-molecular-weight dispersants and high-molecular-weight dispersants. Dispersants may be used individually or in combination of two or more types.

[0043] Examples of viscosity modifiers include castor oil, hydrogenated castor oil, fatty acid amides, beeswax, carnauba wax, benlydidenol sorbitol, metallic soaps, polyethylene oxide, sulfate ester anionic surfactants, polyolefins, (meth)acrylic acid esters, polyisobutylene, ethylene-propylene copolymers, and polyalkylstyrene. Viscosity modifiers may be used individually or in combination of two or more types.

[0044] Examples of fluidity improvers include modified silicone oils obtained by modifying straight silicone oil with alkyl, aralkyl, higher fatty acid esters, amino, epoxy, carboxyl, alcohol, etc. Note that polyether-modified silicones are not included in these fluidity improvers. A single fluidity improver may be used alone, or two or more may be used in combination.

[0045] <Viscosity of magnetorheological fluids> The viscosity of the magnetorheological fluid before excitation according to this embodiment is preferably in the range of 0.5 to 5.0 Pa·s at 25°C, and more preferably in the range of 0.8 to 4.5 Pa·s. The measurement conditions for the viscosity before excitation are as follows. 3 ml of magnetorheological fluid was injected into the test plate of a TA Instruments DHR-2 rheometer equipped with a magnetic measurement option, and the viscosity (Pa·s) was measured under a 25°C atmosphere with a 100 μm gap for 20 rotations. The viscosity of the magnetorheological fluid according to this embodiment when excited is preferably 5000 Pa·s or more, more preferably 6000 Pa·s or more, even more preferably 8000 Pa·s or more, particularly preferably 9000 Pa·s or more, and most preferably 14000 Pa·s or more, when a magnetic field of 0.8 T is applied at 25°C. The viscosity during excitation is measured as follows: Using the same measuring device as when measuring the viscosity before excitation, a magnetic field of 0.8T is applied to a 700μm gap over 20 rotations in a 25°C atmosphere, and the viscosity is measured.

[0046] (Method for manufacturing magnetorheological fluid) The method for producing the magnetorheological fluid according to this embodiment is not particularly limited. For example, a method may be used in which magnetic particles, a base oil, a polyether-modified silicone, and other components to be added as desired are mixed in predetermined amounts using a processing machine that applies high shear force, such as a homogenizer, bead mill, or mechanical mixer. In addition, heating or cooling may be applied as necessary during the production of the magnetorheological fluid.

[0047] (Mechanical devices using magnetorheological fluids) The magnetoviscous fluid according to this embodiment can be applied to various mechanical devices such as brakes, clutches, vibration isolation devices, and dampers in vibration damping devices, which are used to control the frictional force acting between objects. In particular, the magnetoviscous fluid according to this embodiment, which has excellent dispersion stability of magnetic particles, is ideal for dampers in buildings that remain stationary for long periods of time. [Examples]

[0048] Examples of the present invention are shown below. These examples are provided to better understand the present invention and its advantages, and are not intended to limit the invention.

[0049] <Examples 1 to 7, Comparative Examples 1 to 8> Each component shown in Table 1 was placed in a beaker based on the mass ratio described therein, and stirred at room temperature for 20 minutes at 40 Hz using a universal vibration stirrer AD-MIX manufactured by Seiko Advance Co., Ltd. to produce a magnetorheological fluid. The raw materials of each component shown in Table 1 are shown below. (A) Magnetic particles · Carbonyl iron (spherical, average particle diameter D50 = 4.0 to 6.0 μm) (B) Base oil · Mineral oil 1 [liquid paraffin, kinematic viscosity at 40°C 7.827 mm 2 / s, SP value 7.9 (cal / cm 3 ) 1 / 2 · Mineral oil 2 [liquid paraffin, kinematic viscosity at 40°C 28.65 mm 2 / s, SP value 8.0 (cal / cm 3 ) 1 / 2 · Ester-based solvent [hindered ester, kinematic viscosity at 40°C 16.0 mm 2 / s, SP value 9.1 (cal / cm 3 ) 1 / 2 · Hydrocarbon-based solvent [polyalphaolefin, mixture of dimers and trimers of 1-decene, kinematic viscosity at 40°C 5.5 mm 2 / s, SP value 7.8 (cal / cm 3 ) 1 / 2 (C) Dispersant · Alkyl naphthalene (D) Lubricity improver · Polyether-modified silicone 1 (side chain type, EO ratio = 100%, HLB = 14, product name: TSF4440, manufactured by Momentive Performance Materials Inc.) ​​​​• Polyether-modified silicone 2 (side-chain type, EO ratio = 50%, HLB = 11, product name: TSF4452, manufactured by Momentive Performance Materials) • Polyether-modified silicone 3 (side-chain type, EO ratio = 0%, HLB = 1, product name: TSF4460, manufactured by Momentive Performance Materials) • Amino-modified silicone (Product name: TSF4470, manufactured by Momentive Performance Materials) • Unmodified silicone (dimethyl silicone, product name: Element 14PDMS50J, manufactured by Momentive Performance Materials) • Polybutene (Product name: Polybutene-0N, manufactured by NOF Corporation) (E) Extreme pressure agent • Zinc dithiophosphate (Zn-DTP) (Product name: Kikurube Z-112, manufactured by ADEKA Corporation)

[0050] <Evaluation of viscosity before and during excitation> 3 ml of the magnetorheological fluids from Examples 1-7 and Comparative Examples 1-8 were injected into the test plate of a TA Instruments DHR-2 rheometer equipped with a magnetic measurement option. The viscosity (Pa·s) was measured under a 25°C atmosphere with a 100 μm gap for 20 rotations to determine the viscosity before excitation. Using the same measuring apparatus, the viscosity during excitation was measured under a 25°C atmosphere with a 0.8 T magnetic field applied with a 700 μm gap for 20 rotations. The test conditions and test results described above are shown in Table 1.

[0051] <Evaluation of Dispersion Stability> The dispersion stability of the magnetorheological fluids from Examples 1-7 and Comparative Examples 1-8 was evaluated. A magnetorheological fluid was placed in a sample vial, and the thicknesses of the magnetic particle-containing layer and the dispersion medium layer (supernatant) were measured after 1, 10, 20, 30, 60, and 90 days at 23°C. The separation rate, expressed as a percentage of the total thickness of the magnetic particle-containing layer and the dispersion medium layer, was used as the evaluation value. The results are shown in Table 1. The separation rate is preferably 5% or less, more preferably 3% or less, and particularly preferably 1% or less.

[0052] [Table 1]

[0053] The magnetorheological fluids of Examples 1 to 7 all contained magnetic particles, a base oil, and a polyether-modified silicone, and the value obtained by subtracting the solubility parameter of the base oil from the HLB value of the polyether-modified silicone was 2.5 or higher. As a result, they showed high viscosity values ​​of 5000 Pa·s or higher when energized. Among these, Examples 1 to 5 and 7 showed even higher viscosity values ​​of 6000 Pa·s or higher when energized. Furthermore, Examples 1 to 3 and 7 showed even higher viscosity values ​​of 8000 Pa·s or higher when energized. Example 7 showed an extremely high viscosity value of 14000 Pa·s or higher when energized. In addition, the magnetorheological fluids of Examples 1 to 7 all showed excellent dispersion stability even after 90 days.

[0054] In Comparative Examples 1-3, the magnetorheological fluids all had a value less than 2.5 obtained by subtracting the solubility parameter of the base oil from the HLB value of the polyether-modified silicone. Consequently, their dispersion stability was poor, with separation rates of 30-40% after one day.

[0055] The magnetorheological fluids of Comparative Examples 4-8 did not contain polyether-modified silicone, and therefore exhibited inferior dispersion stability, with separation rates of 10-35% after one day.

Claims

1. A magnetorheological fluid containing magnetic particles, a base oil, and a polyether-modified silicone, A magnetorheological fluid in which the value obtained by subtracting the solubility parameter of the base oil from the HLB value of the polyether-modified silicone, as defined by the formula HLB value = 20 × (sum of the formula weights of the hydrophilic portion / molecular weight), is 2.5 or greater.

2. The magnetoviscous fluid according to claim 1, wherein the content of the magnetic particles is 75 to 90% by mass with respect to the total amount of the magnetoviscous fluid.

3. The magnetorheological fluid according to claim 1, wherein the base oil is an α-olefin, a polyα-olefin, or a mineral oil.

4. The magnetorheological fluid according to claim 1, wherein the polyether-modified silicone is a side-chain type polyether-modified silicone.

5. A mechanical device using a magnetorheological fluid according to any one of claims 1 to 4.

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