Magnetorheological fluid and mechanical device

Abstract

Provided are: a magnetorheological fluid which has low viscosity when not excited, has good resistance when excited, and has improved lubricity; and a mechanical device. The magnetorheological fluid comprises magnetic particles and a dispersion medium, and the dispersion medium comprises base oil and double-terminal higher fatty acid ester modified silicone oil, and / or side-chain higher fatty acid ester modified silicone oil.

Description

Technical Field

[0001] This invention relates to magnetorheological fluids and mechanical devices. In particular, it relates to magnetorheological fluids and mechanical devices for controlling the frictional forces acting between objects in various mechanical devices such as brakes, clutches, vibration damping devices, and dampers for vibration reduction devices. Background Technology

[0002] Magnetorheological (MR) fluids are fluids formed by dispersing magnetic particles, such as magnetizable metal particles, in a dispersion medium. In the absence of a magnetic field, the magnetic particles in a magnetorheological fluid are randomly suspended in the dispersion medium, functioning as a fluid. However, when a magnetic field is applied, the magnetic particles form numerous clusters, increasing viscosity and internal stress.

[0003] Magnetorheological fluids function like rigid bodies by increasing internal stress, exhibiting resistance to shear and pressure flows. Due to these properties, magnetorheological fluids are used in various mechanical devices such as brakes, clutches, vibration damping devices, and dampers in vibration reduction systems to control frictional forces acting between objects.

[0004] Therefore, when no magnetic field is applied to the magnetorheological fluid (unexcited), low drag resistance (viscous resistance) is desirable, thus lower viscosity of the magnetorheological fluid is preferred. On the other hand, when a magnetic field is applied to the magnetorheological fluid (excited), higher resistance to shear flow and pressure flow (hereinafter also referred to as "excited resistance") is preferred. It should be noted that the excited resistance is evaluated by measuring torque, viscosity, or shear stress, etc. In this specification, the excited resistance is evaluated by measuring the viscosity during excitation.

[0005] Patent document 1 proposes a magnetorheological fluid containing a specified amount of magnetic particles, clay mineral-based dispersing stabilizers, and surfactants in a carrier liquid.

[0006] Existing technical documents Patent documents Patent Document 1: Japanese Patent Application Publication No. 2002-121578 Summary of the Invention

[0007] The problem that the invention aims to solve However, while the magnetorheological fluid described in Patent Document 1 has low viscosity when no magnetic field is applied, it also exhibits low resistance during excitation, which is unsatisfactory. Furthermore, if magnetic particles are added to increase the resistance during excitation, the lubricity of the magnetorheological fluid will decrease, adversely affecting its wear resistance.

[0008] This invention addresses the aforementioned problems and aims to provide a magnetorheological fluid and mechanical device with low viscosity when unexcited, good resistance when excited, and improved lubricity.

[0009] Solution for solving the problem In order to solve the above-mentioned problems, the present invention is specifically defined as [1] to [6].

[0010] [1] A magnetorheological fluid comprising magnetic particles and a dispersion medium, wherein the dispersion medium comprises a base oil and a dual-terminal type higher fatty acid ester modified silicone oil, and / or a side-chain type higher fatty acid ester modified silicone oil.

[0011] [2] According to the magnetorheological fluid described in [1], the higher fatty acids in the dual-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 with 13 to 20 carbon atoms and / or unsaturated fatty acids with 13 to 20 carbon atoms.

[0012] [3] According to the magnetorheological fluid of [1] or [2], wherein the higher fatty acid esters in the dual-terminal type higher fatty acid ester modified silicone oil and the side-chain type higher fatty acid ester modified silicone oil are fatty acid esters composed of saturated fatty acids with 13 to 20 carbon atoms and / or unsaturated fatty acids with 13 to 20 carbon atoms and methyl groups.

[0013] [4] The magnetorheological fluid according to any one of [1] to [3], wherein the total content of the dual-terminal 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 relative to the total amount of the magnetorheological fluid.

[0014] [5] The magnetorheological fluid according to any one of [1] to [4] further comprises a wear-resistant agent.

[0015] [6] A mechanical device that uses a magnetorheological fluid as described in any one of [1] to [5].

[0016] Invention Effects According to embodiments of the present invention, a magnetorheological fluid and mechanical device with low viscosity when unexcited, good resistance when excited, and improved lubricity can be provided. Detailed Implementation

[0017] The embodiments of the magnetorheological fluid and mechanical device of the present invention will be described below, but the present invention is not to be construed as limited thereto. Various changes, modifications and improvements can be made based on the knowledge of those skilled in the art without departing from the scope of the present invention.

[0018] It should be noted that in this specification, the "~" indicating a numerical range signifies a range that includes the values ​​recorded as its upper and lower limits. Furthermore, if only the upper limit unit is recorded in the numerical range, it means that the lower limit unit is also the same as the upper limit unit.

[0019] In the numerical ranges described in this specification, the upper or lower limit of a certain numerical range can be replaced with the upper or lower limit of other numerical ranges.

[0020] Furthermore, within the numerical ranges described in this specification, the upper or lower limit value within a certain numerical range can be replaced with the value shown in the embodiment.

[0021] In this specification, the content or percentage of each component in the composition, unless otherwise specified, refers to the total content or percentage of the multiple substances present in the composition when multiple substances equivalent to each component are present in the composition.

[0022] (Magnetorheological fluid) The magnetorheological fluid of this embodiment comprises magnetic particles and a dispersion medium, wherein the dispersion medium contains a base oil and a high-grade fatty acid ester modified silicone oil. With this configuration, the magnetorheological fluid of this embodiment has low viscosity when unmagnetized, good resistance when magnetized, and improved lubricity. The components contained in the magnetorheological fluid of this embodiment will be described below.

[0023] 1. Magnetic particles The magnetic particles contained in the magnetorheological fluid of this embodiment can be selected according to the target magnetic permeability. Examples include: strongly magnetic oxides such as magnetite, iron carbonyl, γ-iron oxide, manganese ferrite, cobalt ferrite, or composite ferrites of these with zinc and nickel, barium ferrite; strongly magnetic metals such as iron, cobalt, and rare earth elements; metal nitrides; and various alloys such as Sendust, Permalloy, and Supermalloy. Among these, iron carbonyl is preferred from the perspective of soft magnetic materials with low magnetic retention and high permeability. Iron carbonyl is a high-purity metal particle produced by the thermal decomposition of iron pentacarbonyl (Fe(CO)5).

[0024] It should be noted that magnetic particles can be used alone or in combination with two or more.

[0025] In the magnetorheological fluid of this embodiment, when a magnetic field is applied from the outside, the dispersed magnetic particles orient themselves along the direction of the magnetic field and form chain-like clusters, thereby increasing viscosity and changing its flow characteristics and yield stress. The average particle size of the magnetic particles is determined in a manner that demonstrates this behavior. Specifically, it is preferably in the range of 0.1 to 100 μm. The lower limit of the average particle size is more preferably 1 μm or more, and more particularly preferably 4 μm or more. The upper limit of the average particle size is more preferably 80 μm or less, further more preferably 60 μm or less, even more preferably 50 μm or less, and more particularly preferably 40 μm or less. The shape of the magnetic particles is preferably spherical or substantially spherical to facilitate dispersion.

[0026] It should be noted that the average particle size of the magnetic particles is the average primary particle size measured using a laser diffraction / scattering particle size distribution measuring device.

[0027] The content of magnetic particles relative to the total amount of magnetorheological fluid in this embodiment is preferably in the range of 30 to 90% by mass. By setting the content of magnetic particles relative to the total amount of magnetorheological fluid in this embodiment to a range of 30 to 90% by mass, the required resistance can be obtained when a magnetic field is applied, and the dispersion of magnetic particles can be maintained, thus also functioning as a fluid. The lower limit of the content of magnetic particles is more preferably 40% by mass or more, even more preferably 45% by mass or more, and even more preferably 50% by mass or more. The upper limit of the content of magnetic particles is more preferably 85% by mass or less, even more preferably 80% by mass or less, and even more preferably 75% by mass or less.

[0028] 2. Dispersion medium The magnetorheological fluid of this embodiment contains a base oil and a high-grade fatty acid ester modified silicone oil as the dispersion medium. The dispersion medium may also contain components other than the base oil and the high-grade fatty acid ester modified silicone oil (other dispersion medium components), and there are no particular limitations as long as these other dispersion medium components are liquid at room temperature (25°C) and can disperse magnetic particles.

[0029] The content of the dispersion medium is preferably in the range of 10 to 70% by mass relative to the total amount of magnetorheological fluid in this embodiment. By setting the content of the dispersion medium to 10% by mass or more, magnetic particles can be dispersed, and fluidity can also be improved. By setting the content of the dispersion medium to 70% by mass or less, the magnetic properties during excitation can be improved. The content of the dispersion medium is more preferably in the range of 10 to 40% by mass relative to the total amount of magnetorheological fluid in this embodiment, and more particularly preferably in the range of 10 to 30% by mass.

[0030] 2-1. Base Oil The base oil contained in the magnetorheological fluid of this embodiment is liquid at room temperature (25°C), and any substance can be appropriately selected from mineral oils and synthetic oils conventionally used as dispersion media for magnetic particles. A single base oil can be used, or two or more can be used in combination. As the base oil for the magnetorheological fluid of this embodiment, either mineral oil or synthetic oil can be used alone, or a combination of mineral oil and synthetic oil can be used. It should be noted that by using the base oil in the magnetorheological fluid of this embodiment, lubricity can be improved.

[0031] As synthetic oils, examples include hydrocarbon solvents such as α-olefins, polyα-olefins, isoparaffins, n-paraffins, and halogenated hydrocarbons, as well as ester solvents, ether solvents, and glycol solvents.

[0032] As a mineral oil, it can be any substance commonly used in the lubricant industry, such as cycloalkane mineral oil, alkane mineral oil, liquid paraffin, hydrodewaxed oil, etc.

[0033] Examples of α-olefins include 1-hexene, 1-octene, 1-decene, 1-dodecene, 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, and polyα-olefins are preferably polymers of these α-olefins. α-olefins and polyα-olefins can be used individually or in combination of two or more.

[0034] Examples of ester-based solvents include monoesters, polyol esters, diesters (diesters), and polyoxyalkylene glycol esters. Among these, monoesters with 12 to 30 carbon atoms are preferred, such as 2-ethylhexyl laurate, 2-ethylhexyl palmitate, and n-butyl stearate. Polyol esters refer to esters formed from polyols and straight-chain or branched saturated or unsaturated fatty acids. Hindered esters are examples of polyol esters. Ester-based solvents can be used alone or in combination of two or more.

[0035] Examples of ether-based solvents include polyethylene ethers, polyphenylene ethers, and perfluoroethers. Ether-based solvents can be used alone or in combination with two or more.

[0036] Examples of glycol-based solvents include polyethylene glycol, polypropylene glycol, polybutane glycol, or ethylene oxide-propylene oxide copolymers, propylene oxide-butyl oxide copolymers, and their derivatives. A single glycol-based solvent can be used alone, or in combination of two or more.

[0037] The preferred kinematic viscosity of the base oil at 40°C is 50.0 mm. 2 / s or less, more preferably 5.0 to 40.0 mm 2The range is defined by setting the kinematic viscosity of the base oil at 40°C to 50.0 mm². 2 Below / s, it is more preferable in terms of easily dispersing magnetic particles.

[0038] It should be noted that the kinematic viscosity is determined according to the JIS K2283:2000 kinematic viscosity test method.

[0039] The base oil content is preferably in the range of 2 to 20% by mass relative to the total amount of magnetorheological fluid in this embodiment. Setting the base oil content to 2% by mass or more improves the lubricity of the magnetorheological fluid. Setting the base oil content to 20% by mass or less prevents excessive drag resistance and improves the magnetic properties during excitation. More preferably, the base oil content is in the range of 3 to 15% by mass relative to the total amount of magnetorheological fluid in this embodiment.

[0040] 2-2. Silicone oil modified with higher fatty acid esters The magnetorheological fluid of this embodiment comprises a dual-terminal type high-fatty acid ester modified silicone oil and / or a side-chain type high-fatty acid ester modified silicone oil as a high-fatty acid ester modified silicone oil. Generally, adding organosilicon to a magnetorheological fluid reduces its viscosity, thereby reducing drag resistance. However, adding organosilicon can lead to a decrease in resistance during excitation of the magnetorheological fluid. To address this, since the magnetorheological fluid comprises dual-terminal type high-fatty acid ester modified silicone oil and / or a side-chain type high-fatty acid ester modified silicone oil, drag resistance can be reduced while maintaining good resistance during excitation. The dual-terminal type high-fatty acid ester modified silicone oil and the side-chain type high-fatty acid ester modified silicone oil can be used individually or in combination.

[0041] The magnetorheological fluid of this embodiment contains a dual-terminal type higher fatty acid ester modified silicone oil with higher fatty acid esters bonded to both ends of a dimethylsiloxane backbone. Furthermore, the magnetorheological fluid of this embodiment contains a side-chain type higher fatty acid ester modified silicone oil with higher fatty acid esters bonded to the side chains of a dimethylsiloxane backbone. The higher fatty acid is preferably a saturated fatty acid with 13 to 20 carbon atoms, and / or an unsaturated fatty acid with 13 to 20 carbon atoms.

[0042] An example of the chemical formula of a side-chain type higher fatty acid ester modified silicone oil is shown in the following formula (1). An example of the chemical formula of a dual-terminal higher fatty acid ester modified silicone oil is shown in the following formula (2). In equations (1) and (2) above, in R 1In the case of an alkyl group having 12 to 19 carbon atoms, R 2 For methylene, in R 1 In the case of methyl, R 2 It is an alkylene group with 12 to 19 carbon atoms. n is a natural number. The alkyl group and alkylene group can be straight-chain or branched. The alkyl group can be saturated or unsaturated, and the alkylene group can be saturated or unsaturated.

[0043] As based on R in equations (1) and (2) above 1 and R 2 Fatty acid esters with corresponding alkyl and alkylene groups having 12 to 19 carbon atoms, such as methyl palmitate [CH3(CH2)], can be listed as examples. 14 COOCH3], Methyl stearate [CH3(CH2)] 16 COOCH3], Methyl myristate [CH3(CH2)] 12 [COOCH3], Methyl heptadecanoate [CH3(CH2)] 15 Saturated fatty acid esters such as COOCH3, methyl octadecenoate [C 19 H 36 Unsaturated fatty acid esters such as O2], methyl palmitate [CH3(CH2)5CH=CH(CH2)7COOCH3], etc.

[0044] The viscosities of dual-terminated higher fatty acid ester modified silicone oil and side-chain-type higher fatty acid ester modified silicone oil are preferably 20–20000 mmHg at 25°C. 2 The range of / s is more preferably 20 to 15000 mm. 2 The range of / s is particularly preferred to be 20–100 mm. 2 The range of / s.

[0045] In the magnetorheological fluid of this embodiment, the combined content of the dual-terminal 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 lubricity of the magnetorheological fluid is 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, manufacturing costs can be suppressed, and the sedimentation stability of magnetic particles is improved. More preferably, the content of the higher fatty acid ester modified silicone oil in the magnetorheological fluid of this embodiment is 0.9 to 5% by mass relative to the total amount of the magnetorheological fluid. It should be noted that, regarding the above-mentioned "total content of dual-terminal high fatty acid ester modified silicone oil and side-chain high fatty acid ester modified silicone oil", when the magnetorheological fluid contains only one of dual-terminal high fatty acid ester modified silicone oil or side-chain high fatty acid ester modified silicone oil, it means the content of one type of high fatty acid ester modified silicone oil relative to the total amount of magnetorheological fluid.

[0046] In the magnetorheological fluid of this embodiment, the combined content of the dual-terminal 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, manufacturing costs can be suppressed, and the settling stability of magnetic particles is 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. It should be noted that, regarding the above-mentioned "combined content of dual-terminal type higher fatty acid ester modified silicone oil and side-chain type higher fatty acid ester modified silicone oil", when the magnetorheological fluid contains only one of the dual-terminal type higher fatty acid ester modified silicone oil or the side-chain type higher fatty acid ester modified silicone oil, it refers to the content of one type of higher fatty acid ester modified silicone oil relative to the total amount of base oil.

[0047] 3. Wear-resistant agent The magnetorheological fluid of this embodiment preferably includes a wear-resistant agent. Because the magnetorheological fluid of this embodiment contains a dual-terminal or side-chain type high-grade fatty acid ester modified silicone oil, its viscosity before excitation is lower than that of conventional magnetorheological fluids, which can reduce stirring resistance and frictional resistance. On the other hand, the lower viscosity of the magnetorheological fluid is sometimes accompanied by a decrease in lubricity (wear resistance, anti-sintering properties, fatigue life, etc.), therefore, adding a wear-resistant agent is preferred as a means to ensure lubricity. It should be noted that the wear-resistant agent is an additive added to the base oil to reduce friction or wear between metals, prevent sintering, and prevent base oil vaporization. Examples of wear-resistant agents include zinc dithiophosphate, metal dithiophosphate salts (Sb, Mo, etc.), metal dithiocarbamate salts (Zn, Sb, Mo, etc.), naphthenic acid metal salts, fatty acid metal salts, boron compounds, phosphate esters, phosphites, phosphate ester amine salts, metal phosphate salts, metal phosphate ester salts, and metal phosphite ester salts. In particular, zinc dialkyl dithiophosphate is preferred as it imparts sufficient anti-wear properties. The content of the wear-resistant agent is preferably 0.05 to 2% by mass relative to the total amount of magnetorheological fluid. When the content of the wear-resistant agent in the magnetorheological fluid is 0.05% by mass or more, it further improves the properties of reducing intermetallic friction, wear, and preventing sintering. Furthermore, when the content of the wear-resistant agent in the magnetorheological fluid is 0.05% by mass or more, it improves wear resistance. The content of the wear-resistant agent is more preferably 0.1 to 1.8% by mass relative to the total amount of magnetorheological fluid, and more particularly preferably 0.3 to 1.5% by mass.

[0048] 4. Other ingredients In addition to the components described above, the magnetorheological fluid of this embodiment may be further combined with various other components according to the purpose, without compromising the effect of this embodiment.

[0049] Other components include, for example, dispersants, surfactants, viscosity modifiers, lubrication improvers, sedimentation inhibitors, pour point depressants, extreme pressure agents, rust inhibitors, antioxidants, corrosion inhibitors, metal passivators, and defoamers.

[0050] Dispersants are added to improve the dispersibility of magnetic particles in base oils. Examples include well-known low-molecular-weight dispersants and high-molecular-weight dispersants. Specific examples of dispersants include alkylated naphthalene, oleic acid, and sulfonic acid. Dispersants can be used alone or in combination with two or more.

[0051] Examples of viscosity modifiers include: castor oil, hydrogenated castor oil, fatty acid amides, beeswax, carnauba wax, benzyl sorbitol, metal soaps, oxidized polyethylene, sulfate-based anionic surfactants, polyolefins, (meth)acrylates, polyisobutylene, ethylene-propylene copolymers, and polyalkyl styrene.

[0052] Viscosity modifiers can be used alone or in combination with two or more.

[0053] Lubrication improvers are a type of load-bearing additive, also known as oiliness agents or oiliness enhancers. Examples of lubrication improvers include dimethyl silicone oil or modified silicone oils other than those modified with higher fatty acid esters. For example, substances modified from linear silicone oils using alkyl, aralkyl, polyether, amino, epoxy, carboxyl, or alcohol groups can be used. Non-silicone oils can also be used as lubrication improvers. Examples of non-silicone oils include polybutene, polyisobutylene, and polyalkyl methacrylates. Lubrication improvers can be used alone or in combination with two or more.

[0054] <Viscosity of magnetorheological fluids> The pre-excitation viscosity of the magnetorheological fluid in this embodiment is preferably 0.4 Pa•s or less at 25°C, more preferably in the range of 0.03 to 0.3 Pa•s. By setting it to 0.4 Pa•s or less, the drag resistance can be controlled within a good range. It should be noted that the measurement conditions for the pre-excitation viscosity are as follows.

[0055] 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 at 25°C with a 100 μm gap and 20 revolutions.

[0056] The viscosity of the magnetorheological fluid in this embodiment during excitation 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.

[0057] It should be noted that the viscosity during excitation was measured as follows: using the same measuring apparatus as before excitation, a 0.8T magnetic field was applied at 25°C with a 700μm gap and 20 revolutions to measure the viscosity.

[0058] 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.

[0059] (Methods for manufacturing magnetorheological fluids) The method for manufacturing the magnetorheological fluid in this embodiment is not particularly limited. For example, a method can be described by mixing magnetic particles, a dispersion medium containing base oil and high fatty acid ester modified silicone oil, and other components added as needed, in predetermined amounts using a homogenizer, bead mill, mechanical stirrer, or other processing equipment capable of applying high shear forces. It should be noted that during the manufacturing of the magnetorheological fluid, heating or cooling can be performed as needed.

[0060] (A mechanical device that uses magnetorheological fluid) The magnetorheological fluid of this embodiment can be applied to various mechanical devices such as brakes, clutches, anti-vibration devices, and dampers used to control friction between objects.

[0061] [Example] The following are embodiments of the present invention, but these embodiments are provided to better understand the invention and its advantages and are not intended to limit the invention.

[0062] <Examples 1-11, Comparative Examples 1-6> The components shown in Tables 1 and 2 were placed in a beaker according to the recorded mass ratios, and stirred for 5 minutes at 40 Hz and room temperature using a SEIKO ADVANCE AD-MIX multi-functional vibratory stirrer to produce a magnetorheological fluid. The raw materials for each component shown in Tables 1 and 2 are shown below.

[0063] (A) Magnetic particles • Carbonyl iron (spherical, average particle size D50 = 4.0–6.0 μm).

[0064] (B) Base oil • Liquid paraffin [hydrogenated hydrocarbon, kinematic viscosity 7.827 mmHg at 40°C] 2 / s].

[0065] • Hindered ester [Trimethylolpropane trioctanoate (SP value: 9.1 (cal / cm³)] 3 ) 1 / 2 Kinematic viscosity at 40℃ is 16.0 mm. 2 / s)].

[0066] • A mixture of dimers and trimers of polyalphaolefin (1-decene) (SP value: 7.8 (cal / cm³) 3 ) 1 / 2 Kinematic viscosity at 40℃ is 5.5 mm. 2 / s)).

[0067] (C) Dispersant • Alkylnaphthalene.

[0068] (D) Silicone oil • Silicone Oil 1: (Double-terminated high-grade fatty acid ester modified silicone oil, viscosity (25℃, 30mm) 2 / s)).

[0069] • Silicone Oil 2: (Double-terminated high-grade fatty acid ester modified silicone oil, viscosity (25℃, 27mm)) 2 / s)).

[0070] • Silicone Oil 3: (Side-chain type higher fatty acid ester modified silicone oil, viscosity (25℃, 14000 mm) 2 / s)).

[0071] • Silicone Oil 4: PDMS 50J (linear silicone oil, dimethyl silicone oil) manufactured by Momentive.

[0072] • Silicone Oil 5: Momentive's TSF4700 (amino-modified silicone oil).

[0073] (E) Non-silicone oil • Polybutene: Polybutene 10N (manufactured by Nippon Oil Company, kinematic viscosity (40℃), 9000 mm 2 / s).

[0074] (F) Wear-resistant agent • Dialkyl dithiophosphate zinc.

[0075] The aforementioned "silicone oil 1" and "silicone oil 2" are respectively derived from 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 palmitate [CH3(CH2)5CH=CH(CH2)7COOCH3], and methyl heptadecanoate [CH3(CH2)] 15 [COOCH3] Modified silicone oils made from higher fatty acid esters. It should be noted that silicone oil 1 contains methyl palmitate, methyl stearate, and methyl octadecenoate as the main components, in descending order of content. Silicone oil 2 contains methyl stearate, methyl palmitate, and methyl octadecenoate as the main components, in descending order of content.

[0076] The aforementioned “silicone oil 3” is a side-chain type high fatty acid ester modified silicone oil as shown in the above formula (1), wherein the number of carbon atoms of the alkyl or alkylene groups in formula (1) is in the range of 13 to 17.

[0077] <Evaluation of viscosity before excitation (without excitation) and viscosity during excitation> Three ml of the magnetorheological fluids from Examples 1-11 and Comparative Examples 1-6 were injected into the test plate of a TA Instruments DHR-2 rheometer equipped with a magnetic measurement option. Viscosity (Pa•s) was measured at 25°C with a 100 μm gap and 20 revolutions. The viscosity before excitation (without excitation) was determined. Using the same measuring apparatus, at 25°C, a 0.8 T magnetic field was applied with a 700 μm gap and 20 revolutions to measure the viscosity during excitation. Furthermore, the change in viscosity during excitation relative to the viscosity before excitation (viscosity during excitation / viscosity before excitation) was calculated.

[0078] The above test conditions and test results are shown in Tables 1-2.

[0079] <Evaluation of Lubricity> For the magnetorheological fluids of Examples 1-11 and Comparative Examples 1-6, the stopping time of the test cup (rotating roller) was measured using a simple Timken testing machine (model: KT5820) under the following conditions. It should be noted that this measurement was performed with the magnetorheological fluids of Examples 1-11 and Comparative Examples 4-6 filled to 90% of the sample tank. The measurement was performed three times, and the average value was taken as the measured value. For Comparative Examples 1-3, lubricity evaluation was not performed because the viscosity before excitation exceeded 0.4 Pa•s at 25°C.

[0080] The results of the above test (Timken test) are shown in Tables 1-2.

[0081] (Experimental conditions) Load 400kgf / m 2 The test cup rotated at 1500 rpm.

[0082] Test cup (rotary roller) Product name: A4138, manufactured by Timken Company.

[0083] The test block (roller bearing) measures Φ9.98×13.98 and was manufactured by Timken. The magnetorheological fluids in Examples 1-11 are magnetorheological fluids containing magnetic particles and a dispersion medium, wherein the dispersion medium contains a base oil and dual-terminal type higher fatty acid ester modified silicone oil, and / or side-chain type higher fatty acid ester modified silicone oil. Therefore, it has low viscosity when unexcited and good resistance when excited.

[0084] Furthermore, regarding lubricity, the magnetorheological fluids in Examples 1-11 all resulted in the test cup stopping for more than 30 seconds, indicating good results.

[0085] Comparative Example 1 does not contain silicone oil modified with double-terminal type or side-chain type of higher fatty acid ester, and its viscosity before excitation exceeds 0.4 Pa•s, which can be understood as having high drag resistance.

[0086] The magnetorheological fluid of Comparative Example 2 is an example of the silicone oil modified with dual-terminal high fatty acid esters removed from Example 1, but its viscosity when unexcited is much greater than 0.4 Pa•s, which can be understood as having a large drag resistance.

[0087] Comparative Example 3 uses an amino-modified silicone oil instead of a dual-terminal type or a side-chain type of higher fatty acid ester modified silicone oil. However, its viscosity when unexcited exceeds 0.4 Pa•s, which explains its high drag resistance.

[0088] The magnetorheological fluid in Comparative Example 4 does not contain base oil, and the test cup stops for less than 30 seconds, which can be understood as indicating poor lubricity.

[0089] Comparative Examples 5 and 6 are examples of magnetorheological fluids that use dimethyl silicone oil and polybutene instead of dual-terminal type higher fatty acid ester modified silicone oil or side-chain type higher fatty acid ester modified silicone oil, respectively. However, the test cup stops for less than 30 seconds, which can be understood as poor lubricity.

Claims

1. A magnetorheological fluid, wherein, Contains magnetic particles and a dispersion medium. The dispersion medium comprises a base oil and a dual-terminal 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 claim 1, wherein, The higher fatty acids in the dual-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 with 13 to 20 carbon atoms and / or unsaturated fatty acids with 13 to 20 carbon atoms.

3. The magnetorheological fluid according to claim 1, wherein, The higher fatty acid esters in the dual-terminal type and side-chain type modified silicone oils are fatty acid esters composed of saturated fatty acids with 13 to 20 carbon atoms and / or unsaturated fatty acids with 13 to 20 carbon atoms and methyl groups.

4. The magnetorheological fluid according to claim 1, wherein, The combined content of the dual-terminal higher fatty acid ester modified silicone oil and the side-chain higher fatty acid ester modified silicone oil is 0.8 to 10% by mass relative to the total amount of magnetorheological fluid.

5. The magnetorheological fluid according to claim 1, wherein, The magnetorheological fluid also contains a wear-resistant agent.

6. A mechanical device that uses the magnetorheological fluid as described in any one of claims 1 to 5.

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