Magnetic viscous fluid and mechanical device

Abstract

Provided are: a magnetic viscous fluid that has a low viscosity during non-excitation, has good drag during excitation, and also has improved lubricity; and a mechanical device. The present invention provides a magnetic viscous fluid containing magnetic particles and a dispersion medium, wherein the dispersion medium contains a base oil and a dual end-type higher fatty acid ester-modified silicone oil and / or a side chain-type higher fatty acid ester-modified silicone oil.

Description

Magnetorheological fluids and mechanical devices

[0001] The present invention relates to a magnetorheological fluid and a mechanical device, and more particularly to a magnetorheological fluid and a mechanical device used to control frictional forces acting between objects in various mechanical devices such as brakes, clutches, vibration isolators, and dampers for vibration suppression devices.

[0002] A magnetorheological (MR) fluid is a fluid in which magnetic particles, such as magnetizable metal particles, are dispersed in a dispersion medium. In a magnetorheological fluid, the magnetic particles are randomly suspended in the dispersion medium when no magnetic field is applied, and the fluid functions as a fluid. On the other hand, when a magnetic field is applied, the magnetic particles form numerous clusters, increasing viscosity and internal stress.

[0003] The increased internal stress causes magnetorheological fluids to function like rigid bodies, resisting shear and pressure flows. Because of these properties, magnetorheological fluids are used to control the frictional forces acting between objects in various mechanical devices, such as brakes, clutches, vibration isolation devices, and dampers for vibration control devices.

[0004] For this reason, when a magnetic field is not applied to a magnetorheological fluid (when not magnetized), a small drag resistance (viscous resistance) is required, and therefore a small viscosity of the magnetorheological fluid is preferable. On the other hand, when a magnetic field is applied to the magnetorheological fluid (when excited), a large resistance to shear flow and pressure flow (hereinafter also referred to as "resistance during magnetization") is preferable. The resistance during magnetization is evaluated by measuring the torque value, viscosity, shear stress, etc. In this specification, the resistance during magnetization is evaluated by measuring the viscosity during magnetization.

[0005] Patent Document 1 proposes a magnetorheological fluid in which magnetic particles, a clay mineral-based dispersion stabilizer, and a surfactant are contained in a carrier fluid in predetermined amounts.

[0006] Japanese Patent Application Laid-Open No. 2002-121578

[0007] However, the magnetorheological fluid described in Patent Document 1 has a low viscosity when no magnetic field is applied, but has a low resistance when magnetized, which is unsatisfactory. Furthermore, if the number of magnetic particles is increased to increase the resistance when magnetized, the lubricity of the magnetorheological fluid decreases, which adversely affects the wear resistance.

[0008] The present invention has been made with the above points in mind, and aims to provide a magnetorheological fluid and a mechanical device that have low viscosity when not magnetized, good resistance when magnetized, and improved lubrication.

[0009] In order to solve the above problems, the present invention is specified as follows: [1] to [6]. [1] A magnetorheological fluid comprising magnetic particles and a dispersion medium, wherein the dispersion medium comprises a base oil and a both-end-type higher fatty acid ester-modified silicone oil and / or a side-chain type higher fatty acid ester-modified silicone oil. [2] The magnetorheological fluid according to [1] above, wherein the higher fatty acid in the both-end-type higher fatty acid ester-modified silicone oil and the side-chain type higher fatty acid ester-modified silicone oil is a saturated fatty acid having 13 to 20 carbon atoms and / or an unsaturated fatty acid having 13 to 20 carbon atoms. [3] The magnetorheological fluid according to [1] or [2] above, wherein the higher fatty acid ester in the both-end-type higher fatty acid ester-modified silicone oil and the side-chain type higher fatty acid ester-modified silicone oil is a fatty acid ester consisting of a saturated fatty acid having 13 to 20 carbon atoms and / or an unsaturated fatty acid having 13 to 20 carbon atoms and a methyl group. [4] The magnetorheological fluid according to any one of [1] to [3], wherein the total content of the both-end type higher fatty acid ester-modified silicone oil and the side-chain type higher fatty acid ester-modified silicone oil is 0.8 to 10 mass% relative to the total amount of the magnetorheological fluid. [5] The magnetorheological fluid according to any one of [1] to [4], further comprising an anti-wear agent. [6] A mechanical device using the magnetorheological fluid according to any one of [1] to [5].

[0010] According to the embodiments of the present invention, it is possible to provide a magnetorheological fluid and a mechanical device that have low viscosity when not magnetized, good resistance when magnetized, and improved lubricity.

[0011] Below, we will explain embodiments of the magnetorheological fluid and mechanical device of the present invention, but the present invention should not be construed as being limited to these, and various changes, modifications, and improvements can be made based on the knowledge of those skilled in the art as long as they do not deviate from the scope of the present invention.

[0012] In this specification, the term "to" representing a numerical range indicates a range that includes the numerical values ​​recited as the upper and lower limits. Furthermore, when a unit is recited for only the upper limit of a numerical range, this means that the lower limit is also expressed in the same unit as the upper limit. In the numerical ranges described in stages in this specification, the upper or lower limit described in a certain numerical range may be replaced with the upper or lower limit of another numerical range described in stages. Furthermore, in the numerical ranges described in this specification, the upper or lower limit described in a certain numerical range may be replaced with a value shown in the examples. In this specification, when multiple substances corresponding to each component are present in the composition, the content or amount of each component in the composition refers to the total content or amount of the multiple substances present in the composition, unless otherwise specified.

[0013] (Magnetic Rheological Fluid) The magnetic rheological fluid according to this embodiment includes magnetic particles and a dispersion medium, and the dispersion medium contains a base oil and a higher fatty acid ester-modified silicone oil. With this configuration, the magnetic rheological fluid according to this embodiment has a low viscosity when not magnetized, a good drag force when magnetized, and improved lubricity. Below, each component included in the magnetic rheological fluid according to this embodiment will be described.

[0014] 1. Magnetic Particles The magnetic particles contained in the magnetorheological fluid according to the present embodiment can be selected depending on the desired magnetic permeability. Examples include ferromagnetic oxides such as magnetite, carbonyl iron, gamma iron oxide, manganese ferrite, cobalt ferrite, or composite ferrites of these with zinc or nickel, or barium ferrite; ferromagnetic metals such as iron, cobalt, and rare earth elements; metal nitrides; and various alloys such as Sendust (registered trademark), Permalloy (registered trademark), and Supermalloy (registered trademark). Among these, carbonyl iron is preferred because it is a soft magnetic material with low coercive force and high magnetic permeability. Carbonyl iron is a high-purity metal particle produced by the thermal decomposition of pentacarbonyl iron (Fe(CO)5). Note that one type of magnetic particle may be used alone, or two or more types may be used in combination. In the magnetorheological fluid according to the present embodiment, when an external magnetic field is applied, the dispersed magnetic particles align in the direction of the magnetic field to form chain-like clusters, thereby increasing viscosity and changing the flow characteristics and yield stress. The average particle size of the magnetic particles is determined so as to exhibit this behavior. Specifically, it is preferably in the range of 0.1 to 100 μm. The lower limit of the average particle size of the magnetic particles is more preferably 1 μm or more, and particularly preferably 4 μm or more. The upper limit of the average particle size 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 particularly preferably 40 μm or less. The shape of the magnetic particles is preferably spherical or nearly spherical, as this facilitates dispersion. The average particle size of the magnetic particles is the average primary particle size measured using a laser diffraction / scattering particle size distribution analyzer.

[0015] The content of magnetic particles is preferably in the range of 30 to 90% by mass relative to the total amount of the magnetorheological fluid according to this embodiment. By setting the content of magnetic particles in the range of 30 to 90% by mass relative to the total amount of the magnetorheological 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 the fluid also functions. The lower limit of the content of the magnetic particles is more preferably 40% by mass or more, even more preferably 45% by mass or more, and particularly preferably 50% by mass or more. The upper limit of the content of the magnetic particles is more preferably 85% by mass or less, even more preferably 80% by mass or less, and particularly preferably 75% by mass or less.

[0016] 2. Dispersion Medium The dispersion medium contained in the magnetorheological fluid according to this embodiment contains a base oil and a higher fatty acid ester-modified silicone oil. The dispersion medium may contain components (other dispersion medium components) other than the base oil and the higher fatty acid ester-modified silicone oil. There are no particular restrictions on the other dispersion medium components, as long as they are liquid at room temperature (25°C) and capable of dispersing magnetic particles.

[0017] The content of the dispersion medium is preferably in the range of 10 to 70 mass % with respect to the total amount of the magnetorheological fluid according to this embodiment. By making the content of the dispersion medium 10 mass % or more, it is possible to disperse the magnetic particles and improve fluidity. By making the content of the dispersion medium 70 mass % or less, it is possible to improve the magnetic properties during excitation. The content of the dispersion medium is more preferably in the range of 10 to 40 mass % with respect to the total amount of the magnetorheological fluid according to this embodiment, and even more preferably in the range of 10 to 30 mass %.

[0018] 2-1. Base Oil The base oil contained in the magnetorheological fluid according to this embodiment is liquid at room temperature (25°C) and can be selected from mineral oils and synthetic oils that have traditionally been used as dispersion media for magnetic particles. One type of base oil may be used alone, or two or more types may be used in combination. The base oil used in the magnetorheological fluid according to this embodiment may be either a mineral oil or a synthetic oil, or a combination of a mineral oil and a synthetic oil. The use of a base oil in the magnetorheological fluid according to this embodiment can improve lubricity.

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

[0020] As the mineral oil, any of those usually used in the field of lubricating oils, such as naphthenic mineral oil, paraffinic mineral oil, liquid paraffin, and hydrodewaxed oil, can be used.

[0021] Examples of α-olefins include 1-hexene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, and 1-octadecene. Among these, α-olefins having 8 to 14 carbon atoms such as 1-octene, 1-decene, and 1-dodecene are preferred, and the polyα-olefins are preferably polymers of these α-olefins. The α-olefins and polyα-olefins may be used alone or in combination of two or more.

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

[0023] Examples of the ether-based solvent include polyvinyl ethers, polyphenyl ethers, perfluoroethers, etc. The ether-based solvents may be used alone or in combination of two or more.

[0024] Examples of glycol-based solvents include polyethylene glycol, polypropylene glycol, polybutylene glycol, ethylene oxide-propylene oxide copolymer, propylene oxide-butylene oxide copolymer, and derivatives thereof. The glycol-based solvents may be used alone or in combination of two or more.

[0025] The kinematic viscosity of the base oil at 40°C is 50.0 mm 2 / s or less, and 5.0 to 40.0 mm 2 It is more preferable that the kinematic viscosity of the base oil at 40°C is in the range of 50.0 mm / s. 2 / s or less is more preferable in that it makes it easier to disperse the magnetic particles. Note that the kinematic viscosity is the kinematic viscosity measured in accordance with JIS K2283:2000 kinematic viscosity testing method.

[0026] The base oil content is preferably in the range of 2 to 20 mass% with respect to the total amount of the magnetorheological fluid according to this embodiment. By making the base oil content 2 mass% or more, the lubricity of the magnetorheological fluid can be improved. By making the base oil content 20 mass% or less, it is possible to prevent an excessive increase in drag resistance and improve the magnetic properties during excitation. The base oil content is more preferably in the range of 3 to 15 mass% with respect to the total amount of the magnetorheological fluid according to this embodiment.

[0027] 2-2. Higher Fatty Acid Ester-Modified Silicone Oil The magnetorheological fluid according to this embodiment includes a both-end type higher fatty acid ester-modified silicone oil and / or a side-chain type higher fatty acid ester-modified silicone oil as the higher fatty acid ester-modified silicone oil. Generally, adding silicone to a magnetorheological fluid reduces the viscosity of the magnetorheological fluid, thereby reducing drag resistance. However, adding silicone can cause a problem of reducing the drag force of the magnetorheological fluid when magnetized. In contrast, by including a both-end type higher fatty acid ester-modified silicone oil and / or a side-chain type higher fatty acid ester-modified silicone oil in the magnetorheological fluid, drag resistance can be reduced and good drag force can be maintained when magnetized. The both-end type higher fatty acid ester-modified silicone oil and the side-chain type higher fatty acid ester-modified silicone oil may each be used alone or in combination in the magnetorheological fluid.

[0028] The dual-end type higher fatty acid ester-modified silicone oil contained in the magnetorheological fluid according to this embodiment has a structure in which higher fatty acid esters are bonded to both ends of a dimethyl silicone skeleton. The side-chain type higher fatty acid ester-modified silicone oil contained in the magnetorheological fluid according to this embodiment has a structure in which higher fatty acid esters are bonded to the side chains of a dimethyl silicone skeleton. The higher fatty acids are preferably saturated fatty acids having 13 to 20 carbon atoms and / or unsaturated fatty acids having 13 to 20 carbon atoms.

[0029] An example of the chemical formula of the side chain type higher fatty acid ester modified silicone oil is shown in the following formula (1).

[0030]

[0031] An example of the chemical formula of the both-end type higher fatty acid ester modified silicone oil is shown in the following formula (2).

[0032]

[0033] In the above formulas (1) and (2), R 1 is an alkyl group having 12 to 19 carbon atoms, R 2 is a methylene group, and R 1 is a methyl group, R 2 is an alkylene group having 12 to 19 carbon atoms. n is a natural number. The alkyl group and alkylene group may each be linear or branched. The alkyl group may each be either a saturated alkyl group or an unsaturated alkyl group, and the alkylene group may each be either a saturated alkylene group or an unsaturated alkylene group.

[0034] R in the above formulas (1) and (2) 1 and R 2 Examples of fatty acid esters based on alkyl groups having 12 to 19 carbon atoms and alkylene groups having 12 to 19 carbon atoms corresponding to the above formula include methyl palmitate [CH3(CH2) 14 COOCH3], methyl stearate [CH3(CH2) 16 COOCH3], methyl myristate [CH3(CH2) 12 COOCH3], methyl margarate [CH3(CH2) 15 COOCH3] and other saturated fatty acid esters, methyl octadecenoate [C 19 H 36 O2], methyl palmitoleate [CH3(CH2)5CH=CH(CH2)7COOCH3], and other unsaturated fatty acid esters.

[0035] The viscosity of the both-end type higher fatty acid ester modified silicone oil and the side chain type higher fatty acid ester modified silicone oil is 20 to 20,000 mm at 25°C. 2 / s, and 20 to 15,000 mm 2 / s, and more preferably in the range of 20 to 100 mm 2 It is particularly preferable that the range is / s.

[0036] In the magnetorheological fluid according to this embodiment, the total content of the both-end type higher fatty acid ester-modified silicone oil and the side-chain type higher fatty acid ester-modified silicone oil is preferably 0.8 to 10% by mass relative to the total amount of the magnetorheological fluid. When the content of the higher fatty acid ester-modified silicone oil relative to the total amount of the magnetorheological fluid is 0.8% by mass or more, the lubrication properties of the magnetorheological fluid are further improved. Furthermore, when the content of the higher fatty acid ester-modified silicone oil relative to the total amount of the magnetorheological fluid is 10% by mass or less, production costs can be reduced and the sedimentation stability of the magnetic particles is improved. The content of the higher fatty acid ester-modified silicone oil contained in the magnetorheological fluid according to this embodiment is more preferably 0.9 to 5% by mass relative to the total amount of the magnetorheological fluid. In addition, when the magnetorheological fluid contains only one of the two-end type higher fatty acid ester modified silicone oil and the side-chain type higher fatty acid ester modified silicone oil, the above-mentioned "total content of the both-end type higher fatty acid ester modified silicone oil and the side-chain type higher fatty acid ester modified silicone oil" indicates the content of the one higher fatty acid ester modified silicone oil relative to the total amount of the magnetorheological fluid.

[0037] In the magnetorheological fluid according to this embodiment, the combined content of the dual-end type higher fatty acid ester-modified silicone oil and the side-chain type higher fatty acid ester-modified silicone oil is preferably 3 to 500% by mass relative to the total amount of base oil. When the content of the higher fatty acid ester-modified silicone oil relative to the total amount of base oil is 3% by mass or more, the drag resistance of the magnetorheological fluid can be reduced. Furthermore, when the content of the higher fatty acid ester-modified silicone oil relative to the total amount of base oil is 500% by mass or less, production costs can be reduced and the sedimentation stability of magnetic particles can be improved. The content of the higher fatty acid ester-modified silicone oil relative to the total amount of base oil is more preferably 5 to 300% by mass, and particularly preferably 7 to 300% by mass. In addition, when the magnetorheological fluid contains only one of the two-end type higher fatty acid ester modified silicone oil and the side-chain type higher fatty acid ester modified silicone oil, the above-mentioned "total content of the both-end type higher fatty acid ester modified silicone oil" indicates the content of the one higher fatty acid ester modified silicone oil relative to the total amount of the base oil.

[0038] 3. Anti-Wear Agent The magnetorheological fluid according to this embodiment preferably contains an anti-wear agent. Because the magnetorheological fluid according to this embodiment contains a dual-end or side-chain type higher fatty acid ester-modified silicone oil, its viscosity before magnetization is lower than that of conventional magnetorheological fluids, thereby reducing stirring resistance and frictional resistance. However, lowering the viscosity of the magnetorheological fluid may result in a decrease in lubricity (wear resistance, anti-seizure properties, fatigue life, etc.). Therefore, adding an anti-wear agent is preferable as a means of ensuring lubricity. Anti-wear agents are additives added to base oils to reduce friction or wear between two metal surfaces, prevent seizure, and prevent gasification of the base oil. Examples of anti-wear agents include zinc dithiophosphate, metal dithiophosphates (e.g., Sb, Mo), metal dithiocarbamates (e.g., Zn, Sb, Mo), metal naphthenates, fatty acid metal salts, boron compounds, phosphate esters, phosphites, amine phosphate ester salts, metal phosphates, metal phosphate esters, and metal phosphites. In particular, zinc dialkyldithiophosphate is preferred because it can impart sufficient anti-wear performance. The content of the anti-wear agent is preferably 0.05 to 2 mass% based on the total amount of the magnetorheological fluid. When the content of the anti-wear agent in the magnetorheological fluid is 0.05 mass% or more, properties such as reduction of friction and wear between two metal surfaces and prevention of seizure are improved. Furthermore, when the content of the anti-wear agent in the magnetorheological fluid is 0.05 mass% or more, wear resistance can be improved. The content of the anti-wear agent is more preferably 0.1 to 1.8 mass% based on the total amount of the magnetorheological fluid, and even more preferably 0.3 to 1.5 mass%.

[0039] 4. Other Components In addition to the components described above, the magnetorheological fluid according to this embodiment may further contain various other components depending on the purpose, provided that the effects of this embodiment are not impaired. Examples of other components include dispersants, surfactants, viscosity modifiers, lubricity improvers, settling inhibitors, pour point depressants, extreme pressure agents, rust inhibitors, antioxidants, corrosion inhibitors, metal deactivators, and antifoaming agents.

[0040] Dispersants are added to improve the dispersibility of magnetic particles in the base oil, and include known low-molecular-weight dispersants and polymer-based dispersants. Specific examples of dispersants include alkylated naphthalene, oleic acid, and sulfonic acid. One type of dispersant may be used alone, or two or more types may be used in combination.

[0041] Examples of viscosity modifiers include castor oil, hydrogenated castor oil, fatty acid amides, beeswax, carnauba wax, benzylidene sorbitol, metal soaps, polyethylene oxide, sulfate ester-based anionic surfactants, polyolefins, (meth)acrylic acid esters, polyisobutylene, ethylene-propylene copolymers, polyalkylstyrenes, etc. One type of viscosity modifier may be used alone, or two or more types may be used in combination.

[0042] Lubricity improvers are a type of load-bearing additive and are also called oiliness agents or oiliness improvers. Examples of lubricity improvers include dimethyl silicone oil and modified silicone oils other than the above-mentioned higher fatty acid ester-modified silicone oils. For example, straight silicone oils modified with alkyl, aralkyl, polyether, amino, epoxy, carboxyl, alcohol, etc. may be used. Non-silicone oils may also be used as lubricity improvers. Examples of non-silicone oils include polybutene, polyisobutylene, and polyalkyl methacrylate. One type of lubricity improver may be used alone, or two or more types may be used in combination.

[0043] <Viscosity of Magnetorheological Fluid> The viscosity of the magnetorheological fluid according to this embodiment before magnetization is preferably 0.4 Pa·s or less at 25°C, and more preferably in the range of 0.03 to 0.3 Pa·s. By setting the viscosity to 0.4 Pa·s or less, the drag resistance can be kept within a favorable range. The conditions for measuring the viscosity before magnetization are as follows: 3 ml of the magnetorheological fluid is poured into the test plate of a TA Instruments DHR-2 rheometer equipped with a magnetic measurement option, and the viscosity (Pa·s) is measured at 25°C with a 100 μm gap and 20 rotations. The viscosity of the magnetorheological fluid according to this embodiment during magnetization is preferably 5000 Pa·s or more, and more preferably 6000 Pa·s or more, when a magnetic field of 0.8 T is applied at 25°C. The viscosity during magnetization is measured as follows. That is, using the same measuring device as used to measure the viscosity before excitation, the viscosity is measured by applying a magnetic field of 0.8 T with a 700 μm gap and 20 rotations in an atmosphere of 25° C. The change in viscosity during excitation relative to the viscosity before excitation (viscosity during excitation / viscosity before excitation) is preferably 20,000 or more, more preferably 30,000 or more, even more preferably 40,000 or more, and particularly preferably 60,000 or more.

[0044] (Method for Producing 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 predetermined amounts of magnetic particles, a dispersion medium containing a base oil and a higher fatty acid ester-modified silicone oil, and other components added as desired, are mixed in a processing machine that applies high shear force, such as a homogenizer, a bead mill, or a mechanical mixer. In producing the magnetorheological fluid, heating or cooling may be performed as necessary.

[0045] (Mechanical devices using magnetorheological fluid) The magnetorheological fluid according to this embodiment can be applied to various mechanical devices such as brakes, clutches, vibration isolation devices, and dampers in vibration control devices, which are used to control the frictional force acting between objects.

[0046] Examples of the present invention are given below, but these examples are provided for a better understanding of the present invention and its advantages, and are not intended to limit the invention.

[0047] Examples 1 to 11, Comparative Examples 1 to 6 The components shown in Tables 1 and 2 were placed in a beaker in the mass ratios shown therein, and stirred at 40 Hz at room temperature for 5 minutes using a Seiko Advance Corporation universal vibration mixer AD-MIX to produce magnetorheological fluids. The raw materials for the components shown in Tables 1 and 2 are as follows: (A) Magnetic particles - Carbonyl iron (spherical, average particle size D50 = 4.0 to 6.0 μm) (B) Base oil - Liquid paraffin [hydrogenated hydrocarbon, kinematic viscosity at 40°C 7.827 mm 2 / s] Hindered ester [trimethylolpropane trioctanoate (SP value: 9.1 (cal / cm 3 ) 1 / 2 , kinematic viscosity at 40 ° C. 16.0 mm 2 / s)] Polyα-olefin (mixture of 1-decene dimer and trimer (SP value: 7.8 (cal / cm 3 ) 1 / 2 , kinematic viscosity at 40 ° C. 5.5 mm 2 (C) Dispersant: Alkyl naphthalene (D) Silicone oil: Silicone oil 1: (double-ended higher fatty acid ester-modified silicone oil, viscosity (25°C, 30 mm 2 Silicone oil 2: (double-ended higher fatty acid ester-modified silicone oil, viscosity (25°C, 27 mm 2 Silicone oil 3: (side-chain type higher fatty acid ester modified silicone oil, viscosity (25°C, 14000 mm 2 / s) Silicone oil 4: PDMS50J (straight silicone oil, dimethyl silicone oil) manufactured by Momentive Corporation Silicone oil 5: TSF4700 (amino-modified silicone oil) manufactured by Momentive Corporation (E) Non-silicone oil Polybutene: Polybutene 10N (manufactured by NOF Corporation, kinematic viscosity (40°C), 9000 mm 2 / s) (F) Anti-wear agent Zinc dialkyldithiophosphate

[0048] The above-mentioned "silicone oil 1" and "silicone oil 2" are each methyl palmitate [CH3(CH2) 14 COOCH3], methyl octadecenoate [C 19 H 36 O2], methyl stearate [CH3(CH2) 16 COOCH3], methyl myristate [CH3(CH2) 12 COOCH3], methyl palmitoleate [CH3(CH2)5CH=CH(CH2)7COOCH3], and methyl margarate [CH3(CH2) 15 The silicone oils are higher fatty acid ester-modified silicone oils modified with methyl palmitate, methyl stearate, and methyl octadecenoate. Silicone oil 1 contains, in descending order of content, methyl palmitate, methyl octadecenoate as the main components. Silicone oil 2 contains, in descending order of content, methyl stearate, methyl palmitate, and methyl octadecenoate as the main components.

[0049] The above-mentioned "silicone oil 3" is a side-chain type higher fatty acid ester-modified silicone oil shown in the above formula (1), in which the number of carbon atoms in the alkyl group or alkylene group is in the range of 13 to 17.

[0050] <Evaluation of Viscosity Before Magnetization (Unmagnetized) and During Magnetization> 3 ml of each of the magnetorheological fluids of Examples 1 to 11 and Comparative Examples 1 to 6 was poured into the test plate of a TA Instruments DHR-2 rheometer equipped with a magnetic measurement option, and the viscosity (Pa s) was measured at 20 revolutions with a 100 μm gap in an atmosphere of 25°C. The viscosity before magnetization (when unmagnetized) was measured. Using the same measuring device, a magnetic field of 0.8 T was applied at 20 revolutions with a 700 μm gap in an atmosphere of 25°C, and the viscosity during magnetization was measured. The change in viscosity during magnetization relative to the viscosity before magnetization (viscosity during magnetization / viscosity before magnetization) was also calculated. The test conditions and results are shown in Tables 1 and 2.

[0051] <Evaluation of Lubricity> For the magnetorheological fluids of Examples 1 to 11 and Comparative Examples 1 to 6, a simple Timken tester (model number: KT5820) was used to measure the time it took for the test cup (rotating roller) to stop under the following conditions. This measurement was performed with the magnetorheological fluids of Examples 1 to 11 and Comparative Examples 4 to 6 each filled to 90% of the sample vessel. The measurement was performed three times, and the average value was taken as the measured value. For Comparative Examples 1 to 3, the viscosity before excitation exceeded 0.4 Pa·s at 25°C, so lubricity was not evaluated. The results of the above test (Timken test) are shown in Tables 1 and 2. (Test conditions) Load 400 kgf / m 2 Test cup rotation speed: 1500 rpm Test cup (rotating roller) Product name: A4138, manufactured by Timken Test block (roller bearing) Size: Φ9.98 x 13.98, manufactured by Timken

[0052]

[0053]

[0054] The magnetorheological fluids of Examples 1 to 11 contained magnetic particles and a dispersion medium, and the dispersion medium contained a base oil and a both-end type higher fatty acid ester-modified silicone oil and / or a side-chain type higher fatty acid ester-modified silicone oil. Therefore, they had low viscosity when not magnetized and good drag when magnetized. Furthermore, with regard to lubricity, the magnetorheological fluids of Examples 1 to 11 all had a test cup stop time of 30 seconds or more, which was a good result.

[0055] Comparative Example 1 does not contain both-end-type higher fatty acid ester-modified silicone oil or side-chain-type higher fatty acid ester-modified silicone oil, and its viscosity before magnetization exceeds 0.4 Pa·s, indicating that the drag resistance is large. The magnetorheological fluid of Comparative Example 2 is an example in which the both-end-type higher fatty acid ester-modified silicone oil is omitted from Example 1, and its viscosity when not magnetized is significantly greater than 0.4 Pa·s, indicating that the drag resistance is large. The magnetorheological fluid of Comparative Example 3 is an example in which amino-modified silicone oil is used instead of both-end-type higher fatty acid ester-modified silicone oil or side-chain-type higher fatty acid ester-modified silicone oil, and its viscosity when not magnetized is greater than 0.4 Pa·s, indicating that the drag resistance is large. The magnetorheological fluid of Comparative Example 4 does not contain base oil, and the time until the test cup stops is less than 30 seconds, indicating that the lubricity is poor. The magnetorheological fluids of Comparative Examples 5 and 6 are examples in which dimethyl silicone oil and polybutene are used instead of both-end type higher fatty acid ester modified silicone oil and side-chain type higher fatty acid ester modified silicone oil, respectively. The time until the test cup stopped was less than 30 seconds, which shows that the lubrication was poor.

Claims

1. It comprises magnetic particles and a dispersion medium. The dispersion medium comprises a base oil, a double-ended higher fatty acid ester-modified silicone oil, and / or a side-chain higher fatty acid ester-modified silicone oil. A magnetorheological fluid in which the higher fatty acid ester in the double-ended higher fatty acid ester modified silicone oil and the side-chain higher fatty acid ester modified silicone oil is a fatty acid ester consisting of a saturated fatty acid having 13 to 20 carbon atoms and / or an unsaturated fatty acid having 13 to 20 carbon atoms and a methyl group.

2. The magnetorheological fluid according to claim 1, wherein the higher fatty acids in the terminal-type higher fatty acid ester-modified silicone oil and the side-chain type higher fatty acid ester-modified silicone oil are saturated fatty acids having 13 to 20 carbon atoms and / or unsaturated fatty acids having 13 to 20 carbon atoms.

3. The magnetoviscous fluid according to claim 1, wherein the total content of the end-type higher fatty acid ester modified silicone oil and the side-chain type higher fatty acid ester modified silicone oil is 0.8 to 10% by mass with respect to the total amount of the magnetoviscous fluid.

4. Furthermore, the magnetorheological fluid according to claim 1, further comprising an anti-wear agent.

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