Magnetorheological fluids and mechanical devices

Abstract

A magnetorheological fluid comprises: magnetic particles; at least one selected from ester synthetic oil, ether synthetic oil, and alkylnaphthalene having an alkyl group with 10 to 20 carbon atoms; an inorganic cation exchanger having a siloxane bond; and silicone oil.

Description

Technical Field

[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 isolation devices, and dampers of vibration reduction devices. Background Art

[0002] Magnetorheological (MR) fluids are composed of magnetizable metal particles, or magnetic particles, dispersed in a dispersion medium. In the absence of a magnetic field, MR fluids function as a fluid by randomly suspending the magnetic particles in the dispersion medium. However, when a magnetic field is applied, the magnetic particles cluster, increasing the viscosity and increasing internal stress.

[0003] Magnetorheological fluids, due to the aforementioned increase in internal stress, function like a rigid body, offering resistance to shear and pressure flows. Due to these properties, magnetorheological fluids are used to control frictional forces acting between objects in various mechanical devices, such as brakes, clutches, and dampers for vibration isolation and vibration reduction systems.

[0004] Therefore, it is preferable for a magnetorheological fluid to exhibit a high resistance to shear flow and pressure flow when subjected to a magnetic field (during excitation) (hereinafter referred to as "resistance during excitation"). It should be noted that resistance during excitation is evaluated by measuring torque, viscosity, shear stress, etc. In this specification, resistance during excitation is evaluated by measuring viscosity during excitation.

[0005] Furthermore, in various mechanical devices such as brakes, clutches, vibration isolators, and dampers of vibration reduction devices, the frictional force acting between objects is stable, and thus the temporal stability of the resistance during excitation is excellent.

[0006] Patent Document 1 proposes a magnetorheological fluid comprising a carrier fluid containing predetermined amounts of magnetic particles, a clay mineral-based dispersion stabilizer, and a surfactant.

[0007] Prior art literature

[0008] Patent Literature

[0009] Patent Document 1: Japanese Patent Application Laid-Open No. 2002-121578 Summary of the Invention

[0010] Problems to be solved by the invention

[0011] The magnetorheological fluid described in Patent Document 1 has a low resistance during magnetization, which is unsatisfactory. Furthermore, the temporal stability of the resistance during magnetization is also unsatisfactory. Therefore, the development of a magnetorheological fluid with excellent resistance during magnetization and temporal stability of the resistance is desired.

[0012] The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide a magnetorheological fluid and a mechanical device having good resistance during excitation and temporal stability of the resistance.

[0013] Solutions for solving problems

[0014] In order to solve the above-mentioned problems, the present invention is specifically as follows [1] to [8].

[0015] [1] A magnetorheological fluid comprising: magnetic particles; at least one selected from ester synthetic oil, ether synthetic oil, and alkylnaphthalene having an alkyl group with 10 to 20 carbon atoms; an inorganic cation exchanger having a siloxane bond; and silicone oil.

[0016] [2] The magnetorheological fluid according to [1], wherein the ester-based synthetic oil is at least one selected from polyol esters and dibasic acid esters.

[0017] [3] The magnetorheological fluid according to [2], wherein the polyol ester is a hindered ester.

[0018] [4] The magnetorheological fluid according to [2], wherein the dibasic acid ester is an aliphatic dibasic acid ester.

[0019] [5] The magnetorheological fluid according to [4], wherein the aliphatic dibasic acid ester is an ester of an aliphatic dicarboxylic acid having 2 to 10 carbon atoms and an alcohol having 1 to 10 carbon atoms.

[0020] [6] The magnetorheological fluid according to [1], wherein the ether-based synthetic oil is a polyalkylene glycol.

[0021] [7] The magnetorheological fluid according to [6], wherein the polyalkylene glycol is at least one selected from the group consisting of compounds represented by the following formula (1).

[0022] R 1 -O-(R 2 -O) n -R 3 ……(1)

[0023] [In formula (1), R 1 and R 3 are optionally the same or different, each representing a hydrogen atom or an alkyl group having 1 to 18 carbon atoms, R 2represents an alkylene group having 2 to 4 carbon atoms, and n represents an integer of 2 to 30.]

[0024] [8] A mechanical device using the magnetorheological fluid described in any one of [1] to [7].

[0025] Effects of the Invention

[0026] According to the embodiments of the present invention, a magnetorheological fluid and a mechanical device having excellent resistance during excitation and temporal stability of resistance can be provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is an electron micrograph of the magnetorheological fluid of Example 1 taken using a scanning electron microscope (magnification: 15,000 times).

[0028] Figure 2 This is a schematic diagram showing an enlarged portion of magnetic particles in the magnetorheological fluid of Example 1.

[0029] Figure 3 This is a graph showing the relationship between the elapsed time and the viscosity in Example 2, Comparative Example 1, and Comparative Example 2.

[0030] Figure 4 This is a graph showing the relationship between the elapsed time and the viscosity in Example 2, Example 11, Example 13, and Comparative Example 4. DETAILED DESCRIPTION

[0031] The following describes embodiments of the magnetorheological fluid and mechanical device of the present invention. However, the present invention is not limited thereto and 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.

[0032] It should be noted that, in this specification, " to " indicating a numerical range means a range including the numerical values ​​recorded as the upper limit and lower limit, respectively. In addition, when only the upper limit is recorded with a unit in a numerical range, it means that the lower limit is also in the same unit as the upper limit.

[0033] In the numerical ranges described in stages in this specification, the upper limit value or the lower limit value described in a certain numerical range may be replaced with the upper limit value or the lower limit value of another numerical range described in stages.

[0034] Furthermore, in the numerical ranges described in this specification, the upper limit value or the lower limit value described in a certain numerical range may be replaced with the value shown in the Examples.

[0035] In this specification, when there are multiple substances corresponding to each component in the composition, the content rate or content of each component in the composition refers to the total content rate or content of the multiple substances present in the composition unless otherwise specified.

[0036] (Magnetorheological fluid)

[0037] The magnetorheological fluid of this embodiment contains magnetic particles, a specific base oil, an inorganic cation exchanger with siloxane bonds, and silicone oil. This composition allows the magnetorheological fluid of this embodiment to exhibit excellent resistance during excitation and resistance stability over time. The reasons for this are explained below using hindered esters, a type of ester-based synthetic oil, and dimethyl silicone oil, a type of silicone oil, as examples.

[0038] Magnetic particles 1 are dispersed in hindered ester 2 (refer to Figure 1 ). Furthermore, it is speculated that the surface of the magnetic particle 1 is in the state described below. That is, the magnetic particle 1 has cationic properties, and therefore adsorbs the inorganic cation exchanger 3 having a siloxane bond. In addition, the surface energy of the dimethyl silicone oil 4 is small, and it does not dissolve but disperses in the hindered ester 2 having a large solubility parameter. Moreover, the inorganic cation exchanger 3 having a siloxane bond and the dimethyl silicone oil 4 both have siloxane bonds, and therefore have high affinity. It is speculated that the dimethyl silicone oil 4 exists in a state surrounding the magnetic particle 1 adsorbed with the inorganic cation exchanger 3 having a siloxane bond (refer to Figure 2 ).

[0039] When a magnetic field is applied in this state, the magnetic particles 1 surrounded by the dimethyl silicone oil 4 rapidly combine with each other and form clusters. The presence of the dimethyl silicone oil 4 around the magnetic particles 1 suppresses excessive aggregation of the magnetic particles 1. Therefore, it is speculated that when a magnetic field is applied to measure the resistance (viscosity), although shear force is generated, the clusters do not disintegrate, and the resistance is highly stable. This allows the production of a magnetorheological fluid with high resistance during excitation and good temporal stability of resistance.

[0040] Hereinafter, each component contained in the magnetorheological fluid of this embodiment will be described.

[0041] 1. Magnetic particles

[0042] The magnetic particles contained in the magnetorheological fluid of this embodiment can be selected according to the target magnetic permeability. For example, there can be listed: magnetite, carbonyl iron, gamma iron oxide, manganese ferrite, cobalt ferrite, or composite ferrites of these with zinc and nickel, barium ferrite and other ferromagnetic oxides; 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). Among them, carbonyl iron is preferred from the perspective of soft magnetic materials with low coercive force and high magnetic permeability. Carbonyl iron is a high-purity metal particle produced by thermal decomposition of pentacarbonyl iron (Fe(CO)5).

[0043] In addition, the magnetic particles may be used alone or in combination of two or more.

[0044] In the magnetorheological fluid of the present embodiment, when a magnetic field is applied from the outside, the dispersed magnetic particles are oriented in the direction of the magnetic field to form chain-like clusters, thereby increasing the viscosity and changing the flow characteristics and yield stress thereof. The average particle size of the magnetic particles is determined in a manner that shows such behavior. Specifically, it is preferably in the range of 0.1 to 100 μm. The lower limit value of the average particle size of the magnetic particles is more preferably 1 μm or more, further preferably 5 μm or more, further preferably 10 μm or more. The upper limit value of the average particle size of the magnetic particles is more preferably 80 μm or less, further preferably 60 μm or less, further preferably 50 μm or less, further preferably 40 μm or less. The shape of the magnetic particles is preferably spherical or approximately spherical so as to be easily dispersed.

[0045] The average particle size of the magnetic particles is an average primary particle size measured using a laser diffraction / scattering particle size distribution analyzer.

[0046] The content of magnetic particles is preferably in the range of 30 to 90 mass% relative to the total amount of the magnetorheological fluid of this embodiment. By setting the content of magnetic particles in the range of 30 to 90 mass% relative to the total amount of the magnetorheological fluid of this embodiment, the desired resistance can be obtained when a magnetic field is applied, and the dispersibility of the magnetic particles can be maintained, thereby also functioning as a fluid. The lower limit of the content of magnetic particles is more preferably 40 mass% or more, more preferably 45 mass% or more, and even more preferably 50 mass% or more. The upper limit of the content of magnetic particles is more preferably 85 mass% or less, more preferably 80 mass% or less, and even more preferably 75 mass% or less.

[0047] 2. Base oil

[0048] The base oil contained in the magnetorheological fluid of this embodiment is at least one selected from ester synthetic oils, ether synthetic oils, and alkylnaphthalenes having an alkyl group with 10 to 20 carbon atoms. Hereinafter, unless otherwise specified, "base oil" refers solely to any of these. These base oils may be used alone or in combination of two or more.

[0049] 2-1. Ester synthetic oil

[0050] Examples of ester-based synthetic oils include monoesters, polyol esters, dibasic acid esters (diesters), and polyoxyalkylene glycol esters. Among these, monoesters preferably have 12 to 30 carbon atoms, such as 2-ethylhexyl laurate, 2-ethylhexyl palmitate, and n-butyl stearate. Polyol esters refer to esters of polyols (polyols) and linear or branched saturated or unsaturated fatty acids. Examples of polyol esters include hindered esters. Ester-based synthetic oils may be used alone or in combination of two or more.

[0051] <Hindered ester>

[0052] Hereinafter, hindered ester, which is a type of ester-based synthetic oil contained in the magnetorheological fluid of the present embodiment, will be described in detail.

[0053] Hindered esters are esters of hindered polyols and aliphatic monocarboxylic acids. These hindered polyols have one or more quaternary carbon atoms in the molecule, with one to four hydroxymethyl groups bonded to at least one of these carbon atoms. Hindered esters can be used alone or in combination of two or more.

[0054] Examples of hindered polyols include trimethylolpropane (TMP), pentaerythritol (PE), dipentaerythritol (DPE), neopentyl glycol (NPG), and 2-methyl-2-propyl-1,3-propanediol (MPPD). Among these hindered polyols, trimethylolpropane, pentaerythritol, and dipentaerythritol are preferred because the resulting hindered esters have higher flash points, while trimethylolpropane is more preferred because the resulting hindered esters have lower pour points.

[0055] The aliphatic monocarboxylic acid is preferably an aliphatic monocarboxylic acid having 5 to 15 carbon atoms. The acyl group of the aliphatic monocarboxylic acid may be linear or branched. The aliphatic group of the aliphatic monocarboxylic acid may be an aliphatic saturated hydrocarbon group (alkyl group) or an aliphatic unsaturated hydrocarbon group. Examples of aliphatic monocarboxylic acids include saturated aliphatic carboxylic acids such as pentanoic acid, hexanoic acid, heptane acid, octanoic acid, nonanoic acid, decanoic acid, undecanoic acid, lauric acid (dodecanoic acid), tridecanoic acid, myristic acid (tetradecanoic acid), and pentadecanoic acid; and unsaturated aliphatic carboxylic acids such as pentenoic acid, hexenoic acid, heptenoic acid, octenic acid, nonenoic acid, decenoic acid, undecenoic acid, dodecenoic acid, tridecenoic acid, tetradecenoic acid, pentadecenoic acid, physeteric acid, 10-undecenoic acid, 5-dodecenoic acid, and sorbic acid. These aliphatic monocarboxylic acids may be used alone or in combination of two or more. The number of carbon atoms in the aliphatic monocarboxylic acid is more preferably 6 or more. When the number of carbon atoms in the aliphatic monocarboxylic acid is 5 or more, the flash point of the resulting hindered ester becomes higher, which is preferred. When the number of carbon atoms in the aliphatic monocarboxylic acid is 12 or less, it is more preferred. When the number of carbon atoms in the aliphatic monocarboxylic acid is 10 or less, it is particularly preferred. When the number of carbon atoms in the aliphatic monocarboxylic acid is 15 or less, it is preferred from the perspective of increasing the solubility parameter of the resulting hindered ester.

[0056] It should be noted that, unless otherwise specified, in the present invention, the number of carbon atoms in an aliphatic monocarboxylic acid also includes the carbon atoms in the carboxyl group (—COOH) of the aliphatic monocarboxylic acid.

[0057] <Dibasic acid esters>

[0058] Hereinafter, the dibasic acid ester which is a type of ester-based synthetic oil contained in the magnetorheological fluid of the present embodiment will be described in detail.

[0059] Examples of the dibasic acid ester include esters of dicarboxylic acids having 2 to 10 carbon atoms and alcohols having 1 to 10 carbon atoms.

[0060] Examples of the dicarboxylic acid having 2 to 10 carbon atoms include aliphatic dicarboxylic acids such as oxalic acid, malonic acid, succinic acid, glutaric acid, 2-methylglutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, and sebacic acid; and aromatic dicarboxylic acids such as phthalic acid, isophthalic acid, and terephthalic acid.

[0061] Examples of the alcohol having 1 to 10 carbon atoms include methanol, ethanol, propanol, isopropanol, butanol, isobutanol, hexanol, octanol, 2-ethylhexanol, isononanol, decanol, and isodecanol.

[0062] More specific examples include diisobutyl adipate, di(2-ethylhexyl) adipate, diisodecyl adipate, diisobutyl sebacate, di(2-ethylhexyl) sebacate, diisodecyl sebacate, diisobutyl phthalate, di(2-ethylhexyl) phthalate, and diisodecyl phthalate.

[0063] Among them, aliphatic dibasic acid esters, which are esters of an aliphatic dicarboxylic acid having 2 to 10 carbon atoms and an alcohol having 1 to 10 carbon atoms, are preferred because they further improve the temporal stability of the resistance during excitation.

[0064] Among the above-mentioned aliphatic dibasic acid esters, preferred are dibasic acid esters of aliphatic dicarboxylic acids having 6 to 10 carbon atoms and alcohols having 4 to 10 carbon atoms, such as diisobutyl adipate, di(2-ethylhexyl) adipate, diisodecyl adipate, and di(2-ethylhexyl) sebacate. Particularly preferred are dibasic acid esters of aliphatic dicarboxylic acids having 6 to 10 carbon atoms and alcohols having 4 to 8 carbon atoms, such as diisobutyl adipate, di(2-ethylhexyl) adipate, and di(2-ethylhexyl) sebacate. These dicarboxylic acids and alcohols may be used alone or in combination for esterification.

[0065] It should be noted that, unless otherwise specified, the number of carbon atoms in an aliphatic dicarboxylic acid in the present invention also includes the carbon atoms in the carboxyl group (—COOH) of the aliphatic dicarboxylic acid. Furthermore, unless otherwise specified, the number of carbon atoms in an aromatic carboxylic acid in the present invention also includes the carbon atoms in the aromatic ring of the aromatic carboxylic acid. A dibasic acid ester may be used alone or in combination of two or more.

[0066] 2-2. Ether-based synthetic oil

[0067] Examples of the ether-based synthetic oils include polyvinyl ethers, polyalkylene glycols, polyphenylene ethers, and perfluoroethers. The ether-based synthetic oils may be used alone or in combination of two or more.

[0068] <Polyalkylene glycols>

[0069] Hereinafter, polyalkylene glycols, which are one type of ether-based synthetic oil contained in the magnetorheological fluid of the present embodiment, will be described in detail.

[0070] The polyalkylene glycol is preferably at least one selected from the group consisting of compounds represented by the following formula (1).

[0071] R1 -O-(R 2 -O) n -R 3 ……(1)

[0072] In formula (1), R 1 and R 3 Optionally the same or different, R 1 and R 3 Each represents a hydrogen atom or an alkyl group having 1 to 18 carbon atoms. 2 represents an alkylene group having 2 to 4 carbon atoms. n represents an integer of 2 to 30.

[0073] It should be noted that in formula (1) R 1 and R 3 When both of them are hydrogen atoms, the compound represented by the above formula (1) is a polyalkylene glycol. 1 or R 3 When one of R is a hydrogen atom, the compound represented by formula (1) is a monoether of polyalkylene glycol. 1 and R 3 When both of these groups are alkyl groups, the compound represented by formula (1) is a diether product of a polyalkylene glycol.

[0074] In formula (1), R 1 and R 3 When one or both of them is an alkyl group, the number of carbon atoms of the alkyl group is preferably 5 to 18, more preferably 6 to 15, and particularly preferably 8 to 14.

[0075] When the number of carbon atoms of the alkyl group is 5 or more, the group has polarity, and thus, it is expected that the viscosity will be improved during excitation.

[0076] From the perspective of easy availability, the number of carbon atoms in the alkyl group is preferably 18 or less. The alkyl group may be linear or branched. Specifically, examples include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, and octadecyl.

[0077] R in formula (1) 2The number of carbon atoms in the alkylene group is preferably 2 to 4. When the number of carbon atoms in the alkylene group is 2 to 4, the viscosity before excitation can be reduced. Specific examples of the alkylene group having 2 to 4 carbon atoms include ethylene, propylene (including 1-methylethylene and 2-methylethylene), trimethylene, butylene (including 1-ethylethylene and 2-ethylethylene), 1,2-dimethylethylene, 2,2-dimethylethylene, 1-methyltrimethylene, 2-methyltrimethylene, 3-methyltrimethylene, and tetramethylene.

[0078] It should be noted that the compound represented by formula (1) can be R 2 It can be a homopolymer of R 2 Furthermore, when the compound represented by formula (1) is a copolymer, the monomer ratio and arrangement of the monomers constituting the copolymer are not particularly limited, and the copolymer may be any of a random copolymer, an alternating copolymer, and a block copolymer.

[0079] In the formula (1), n ​​is preferably an integer in the range of 2-30, more preferably an integer in the range of 5-30, and particularly preferably an integer in the range of 7-15.

[0080] 2-3. Alkylnaphthalene having an alkyl group having 10 to 20 carbon atoms

[0081] Examples of alkylnaphthalenes having an alkyl group with 10 to 20 carbon atoms include decylnaphthalene, undecylnaphthalene, dodecylnaphthalene, tridecylnaphthalene, tetradecylnaphthalene, pentadecylnaphthalene, hexadecylnaphthalene, heptadecylnaphthalene, octadecylnaphthalene, nonadecylnaphthalene, eicosylnaphthalene, didecylnaphthalene, diundecylnaphthalene, didodecylnaphthalene, ditridecylnaphthalene, ditetradecylnaphthalene, dipentadecylnaphthalene, dihexadecylnaphthalene, diheptadecylnaphthalene, dioctadecylnaphthalene, dinonadecylnaphthalene, and dieicosylnaphthalene. All isomers thereof are also exemplified. Alkylnaphthalenes having an alkyl group with 10 to 20 carbon atoms may be used alone or in combination of two or more.

[0082] The lower limit of the solubility parameter of the base oil is preferably 8.5 (cal / cm 3 ) 1 / 2 , more preferably 8.8 (cal / cm 3 ) 1 / 2 , particularly preferably 9.0 (cal / cm 3 ) 1 / 2 The upper limit of the solubility parameter of the base oil is preferably 12.0 (cal / cm 3 ) 1 / 2 , more preferably 11.0 (cal / cm3 ) 1 / 2 , particularly preferably 10.0 (cal / cm 3 ) 1 / 2 By setting the solubility parameter to 8.5 (cal / cm 3 ) 1 / 2 The above is more preferable from the viewpoint of making the base oil incompatible with the silicone oil described later.

[0083] If the solubility parameter is set to 12.0 (cal / cm 3 ) 1 / 2 The following are more preferable from the viewpoint of improving the heat resistance of the base oil.

[0084] It should be noted that the solubility parameter (SP value) can be calculated according to the method proposed by Fedors et al. "Polymer Engineering and Science, 14, 147-154 (1974)".

[0085] That is, it can be calculated based on the following formula.

[0086] SP value δ=(ΣΔe / ΣΔv) 1 / 2

[0087] (In the above formula, Δe is the evaporation energy of each atom or atomic group at 25°C, and Δv is the molar volume of each atom or atomic group at the same temperature.)

[0088] The kinematic viscosity of the base oil at 40°C is preferably 50.0 mm 2 / s or less, more preferably 5.0 to 40.0 mm 2 By setting the kinematic viscosity of the base oil at 40°C to 50.0 mm 2 / s or less is more preferable from the viewpoint of facilitating dispersion of the magnetic particles.

[0089] In addition, the kinematic viscosity is a kinematic viscosity measured by the kinematic viscosity test method of JIS K2283:2000.

[0090] The flash point of the base oil is preferably 200°C or higher, more preferably 250°C or higher.

[0091] A base oil with a flash point of 200°C or higher is classified as a Class III or IV petroleum oil under the Fire Services Act, making it more preferable from the perspective of increasing the amount of hazardous materials handled (specified quantity). Note that the flash point is measured according to JIS K2265-4:2007 (Cleveland open-cup (COC) method).

[0092] The pour point of the base oil is preferably -10°C or lower, more preferably -20°C or lower, particularly preferably -30°C or lower, and most preferably -50°C or lower. A pour point of -10°C or lower is more preferred due to excellent low-temperature fluidity. The pour point is measured in accordance with JIS K2269:1987.

[0093] The lower limit of the base oil content is preferably 10% by mass or greater, and more preferably 20% by mass or greater, relative to the total amount of the magnetorheological fluid of this embodiment. Setting the base oil content to 10% by mass or greater allows for dispersion of the magnetic particles and improves fluidity. The upper limit of the base oil content is preferably 70% by mass or less, and more preferably 60% by mass or less, relative to the total amount of the magnetorheological fluid of this embodiment. Setting the base oil content to 70% by mass or less further improves magnetic properties during excitation.

[0094] The magnetorheological fluid of this embodiment may contain base oils other than ester synthetic oils, ether synthetic oils, and alkylnaphthalenes having an alkyl group with 10 to 20 carbon atoms, such as mineral oils, poly-α-olefins, and α-olefins, within a range that does not impair the effects of the present invention.

[0095] 3. Inorganic cation exchangers with siloxane bonds

[0096] The magnetorheological fluid of this embodiment contains an inorganic cation exchanger having a siloxane bond and silicone oil described later. Therefore, the resistance of the magnetorheological fluid during excitation is increased, and the temporal stability of the resistance is also improved.

[0097] More specifically, the magnetic particles are dispersed in the base oil. Because the magnetic particles are cationic, they adsorb the inorganic cation exchanger with siloxane bonds. Furthermore, silicone oil has a low surface energy and does not dissolve in the base oil, which has a high solubility parameter. Furthermore, since both the inorganic cation exchanger with siloxane bonds and the silicone oil contain silicon, they have a high affinity for silicon. It is speculated that the silicone oil surrounds the magnetic particles adsorbed with the inorganic cation exchanger with siloxane bonds.

[0098] If a magnetic field is applied in this state, the magnetic particles surrounded by silicone oil quickly combine with each other and cluster. The presence of silicone oil around the magnetic particles suppresses excessive aggregation of the magnetic particles. Therefore, it is speculated that when a magnetic field is applied to measure resistance (viscosity), although shear force is generated, the clusters do not disintegrate, and their resistance is highly stable, thereby obtaining a magnetorheological fluid with high resistance during excitation and good stability of resistance over time.

[0099] <Inorganic cation exchangers with siloxane bonds>

[0100] Examples of inorganic cation exchangers having siloxane bonds include zeolite, silica, and layered silicates. Zeolite is preferred, considering wear resistance. Inorganic cation exchangers having siloxane bonds may be used alone or in combination of two or more. Both natural and synthetic products may be used.

[0101] Zeolite consists of a crystalline, porous aluminosilicate framework with anionic properties and a cationic metal element M adsorbed within the framework. More specifically, it has a structure in which tetrahedral SiO₄ and AlO₄ basic structural units are three-dimensionally linked to form a crystal with pores (voids), within which crystal water and the cationic metal element M are adsorbed. Zeolite's crystal structure is not particularly limited; specific examples include zeolite A, zeolite X, zeolite Y, zeolite L, zeolite β, ZSM-5, ZSM-11, silicalite, ferrierite, mordenite, clinoptilolite, and bohlinite.

[0102] Layered silicates are silicate compounds with a crystal structure consisting of layers of surfaces weakly bonded together by ionic bonds. Layered silicates often have a negative charge throughout the layer, with large cations intercalating between the layers to neutralize the negative charge. Because the layer charge is small, these cations can exchange with cations in solution, resulting in cation exchange properties. Examples of the layered silicate include smectites (bentonite, montmorillonite, beidellite, nontronite, saponite, hectorite, and stevensite), vermiculite, kaolinites (kaolinite, halloysite, chrysotile, and magnesia), mica (muscovite, biotite, ankerite, phlogopite, lepidolite, paragonite, siderophyllite, eastonite, lepidolite, lepidolite, nacreous mica, illite, and glauconite), talc, palygorskite, sepiolite, magadiite, kanemite, kenyaite, and synthetic fluorine mica. Among these, smectites, vermiculite, and synthetic fluorine mica are preferred from the perspective of ion exchange capacity.

[0103] The cation exchange capacity of the inorganic cation exchanger having a siloxane bond is preferably 30 meq / 100 g or more, more preferably 60 meq / 100 g or more, and particularly preferably 150 meq / 100 g or more.

[0104] The cation exchange capacity of the inorganic cation exchanger having a siloxane bond is preferably 400 meq / 100 g or less, more preferably 350 meq / 100 g or less, and particularly preferably 300 meq / 100 g or less.

[0105] The cation exchange capacity of inorganic cation exchangers having siloxane bonds is 260 meq / 100 g for mordenite, 120 meq / 100 g for synthetic fluorine mica, 60 to 150 meq / 100 g for smectites, 80 to 150 meq / 100 g for montmorillonite, and 100 to 150 meq / 100 g for vermiculite.

[0106] The lower limit of the content of the inorganic cation exchanger having siloxane bonds is preferably 0.8% by mass or greater, more preferably 1.0% by mass or greater, and particularly preferably 1.3% by mass or greater, relative to the total amount of the magnetorheological fluid of this embodiment. A content of 0.8% by mass or greater is more preferable from the perspective of suppressing aggregation of magnetic particles when no magnetic field is applied.

[0107] The upper limit of the content of the inorganic cation exchanger having siloxane bonds is preferably 4.0% by mass or less, more preferably 3.5% by mass or less, and even more preferably 3.0% by mass or less, relative to the total amount of the magnetorheological fluid of this embodiment. A content of 4.0% by mass or less is more preferable from the perspective of enabling appropriate formation of magnetic particle clusters when a magnetic field is applied.

[0108] 4. Silicone oil

[0109] Silicone oil can be used without particular limitation as long as it is incompatible with the base oil. Silicone oil is roughly divided into ordinary silicone oil (straight silicone oil) and modified silicone oil. As ordinary silicone oil, dimethyl silicone oil, methylphenyl silicone oil, methyl hydrogen silicone oil can be listed. As modified silicone oil, reactive silicone oil and non-reactive silicone oil can be listed. Reactive silicone oil, for example, can be listed: amino-modified silicone oil, epoxy-modified silicone oil, carboxyl-modified silicone oil, methanol-modified silicone oil, methacryloyl-modified silicone oil, mercapto-modified silicone oil, phenol-modified silicone oil and the like. Non-reactive silicone oil can be listed: polyether-modified silicone oil, methylstyrene-modified silicone oil, alkyl-modified silicone oil, higher fatty acid ester-modified silicone oil, hydrophilic special modified silicone oil, higher fatty acid-containing silicone oil, fluorine-modified silicone oil and the like. Among them, dimethyl silicone oil and fluorine-modified silicone oil are preferred because of their small surface energy. If the ease of acquisition is considered, dimethyl silicone oil is more preferred.

[0110] The lower limit of the silicone oil content is preferably 0.5% by mass or greater, and more preferably 1.0% by mass or greater, relative to the total amount of the magnetorheological fluid of this embodiment. A content of 0.5% by mass or greater is more preferable from the perspective of being able to surround the magnetic particles to which the inorganic cation exchanger having siloxane bonds is attached.

[0111] The upper limit of the silicone oil content is preferably 3.0% by mass or less, and more preferably 2.5% by mass or less, relative to the total amount of the magnetorheological fluid of this embodiment. Setting the content to 3.0% by mass or less is more preferable from the perspective of preventing a decrease in the dispersibility of the magnetic particles.

[0112] The mixing ratio of the inorganic cation exchanger having a siloxane bond to the silicone oil is preferably in the range of 2:8 to 8:2, and more preferably in the range of 3:7 to 7:3, in terms of mass ratio.

[0113] The range of 2:8 to 8:2 is more preferable from the viewpoint of improving the temporal stability of the resistance during excitation.

[0114] The absolute value of the difference in solubility parameter between the base oil and the silicone oil is preferably 1.3 (cal / cm 3 ) 1 / 2 More preferably, 1.5 (cal / cm 3 ) 1 / 2 Above, particularly preferably 1.8 (cal / cm 3 ) 1 / 2 If the absolute value of the difference between the solubility parameters of the base oil and the silicone oil is 1.3 (cal / cm 3 ) 1 / 2 The above is more preferable from the viewpoint of increasing the incompatibility between the base oil and the silicone oil.

[0115] 5. Other ingredients

[0116] The magnetorheological fluid of the present embodiment may contain various other components in addition to the above-mentioned components according to the purpose, within a range that does not impair the effects of the present invention.

[0117] Examples of other components include anti-wear agents, dispersants, surfactants, viscosity modifiers, flow improvers, sedimentation inhibitors, pour point depressants, extreme pressure agents, rust inhibitors, antioxidants, corrosion inhibitors, metal deactivators, and defoaming agents.

[0118] Examples of anti-wear 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.

[0119] The anti-wear agents may be used alone or in combination of two or more.

[0120] The dispersant is added to improve the dispersibility of the magnetic particles in the base oil, and examples thereof include known low-molecular-weight dispersants and high-molecular-weight dispersants. The dispersants may be used alone or in combination of two or more.

[0121] Examples of the viscosity modifier include castor oil, hydrogenated castor oil, fatty acid amide, beeswax, carnauba wax, benzylidene sorbitol, metal soap, polyethylene oxide, sulfate-based anionic surfactants, polyolefins, (meth)acrylates, polyisobutylene, ethylene-propylene copolymers, and polyalkylstyrenes.

[0122] The viscosity modifiers may be used alone or in combination of two or more.

[0123] Examples of fluidity improvers include modified silicone oils. Examples include conventional silicone oils modified with alkyl groups, aralkyl groups, polyethers, higher fatty acid esters, amino groups, epoxy groups, carboxyl groups, alcohols, and the like. It should be noted that modified silicone oils may also be compatible with base oils. One fluidity improver may be used alone, or two or more may be used in combination.

[0124] <Viscosity of Magnetorheological Fluid>

[0125] The viscosity of the magnetorheological fluid of this embodiment before excitation is preferably in the range of 0.03 to 1.0 Pa·s, more preferably in the range of 0.03 to 0.6 Pa·s at 40° C. The measurement conditions of the viscosity before excitation are as follows.

[0126] 3 ml of magnetorheological fluid was injected into a test plate of a TA Instruments DHR-2 rheometer equipped with a magnetic measurement option, and the viscosity (Pa·s) was measured at 40° C., a gap of 100 μm, and 20 revolutions.

[0127] Magnetic Properties of Magnetorheological Fluids

[0128] The magnetorheological fluid of this embodiment has the characteristics of high resistance during excitation (good resistance during excitation) and good temporal stability of resistance. High resistance during excitation means that, in the magnetorheological fluid of this embodiment of the invention, when the magnetic particle content is 2 / 3 by mass, the maximum viscosity during excitation under the following conditions is 230 Pa·s or greater. Furthermore, the maximum viscosity during excitation is preferably 230 Pa·s or greater, more preferably 240 Pa·s or greater. The minimum viscosity during excitation is preferably 200 Pa·s or greater, more preferably 210 Pa·s or greater.

[0129] Furthermore, since the composition contains an inorganic cation exchanger having siloxane bonds and silicone oil, excellent temporal stability of resistance during excitation (viscosity stability over time) can be achieved. Excellent temporal stability of resistance during excitation (viscosity stability over time) means that the stabilization rate C, described below, is 90% or higher. Furthermore, a stabilization rate C of 90% or higher is preferred, a stabilization rate B of 80% or higher is more preferred, a stabilization rate A of 80% or higher is even more preferred, and a stabilization rate A of 90% or higher is particularly preferred.

[0130] The viscosity during excitation refers to the viscosity during the 210 seconds of application of the magnetic field, in which a DC magnetic field of 0.8 T is applied 5 seconds after the start of measurement and the application of the magnetic field is stopped 215 seconds after the start of measurement, using the same measuring apparatus as that used to measure the viscosity before excitation, under the same temperature environment.

[0131] Stabilization rates A to C (%) were calculated based on the following formulas.

[0132] Stabilization rate A (%) = (stabilization time A / total application time) × 100

[0133] In addition, the stabilization time A represents the application time corresponding to 97 to 100% of the maximum value of the viscosity during excitation.

[0134] The stabilization rate B (%) was calculated based on the following formula.

[0135] Stabilization rate B (%) = (stabilization time B / total application time) × 100

[0136] In addition, the stabilization time B represents the application time corresponding to 95 to 100% of the maximum value of the viscosity during excitation.

[0137] The stabilization rate C (%) was calculated based on the following formula.

[0138] Stabilization rate C (%) = (stabilization time C / total application time) × 100

[0139] The stabilization time C refers to the application time corresponding to 90% to 100% of the maximum value of the viscosity during excitation.

[0140] (Method for producing magnetorheological fluid)

[0141] The method for producing the magnetorheological fluid of this embodiment is not particularly limited. For example, the following method can be used: magnetic particles, a specific base oil, an inorganic cation exchanger having siloxane bonds, silicone oil, and other desired ingredients are mixed in predetermined amounts using a homogenizer, bead mill, mechanical mixer, or other processing equipment capable of applying high shear forces. It should be noted that heating or cooling may be performed as needed during the production of the magnetorheological fluid.

[0142] (Mechanical device using magnetorheological fluid)

[0143] The magnetorheological fluid of this embodiment has excellent resistance during excitation and stability over time. Therefore, it can be used in various mechanical devices such as brakes, clutches, vibration isolation devices, and dampers for vibration reduction devices that control friction between objects.

[0144] Example

[0145] Examples of the present invention are shown below. However, these examples are provided for better understanding of the present invention and its advantages and are not intended to limit the present invention.

[0146] <Examples 1 to 14, Comparative Examples 1 to 6>

[0147] The components listed in Tables 1 to 3 were added to a beaker based on the listed mass ratios and stirred at 40 Hz for 5 minutes at room temperature using a universal vibration mixer AD-MIX manufactured by Seiko Advance Co., Ltd. to produce a magnetorheological fluid. The raw materials for the components listed in Tables 1 to 3 are shown below.

[0148] (A) Magnetic particles

[0149] (a1) Carbonyl iron (average particle size D50 = 6.0 μm).

[0150] (B) Base oil

[0151] <Hindered ester>

[0152] (b1) Trimethylolpropane trioctanoate (SP value: 9.1 (cal / cm 3 ) 1 / 2 , kinematic viscosity at 40°C 16.0 mm 2 / s, flash point 260℃, pour point -57℃).

[0153] (b2) A mixture of pentaerythritol tetra-n-hexanoate and pentaerythritol tetra-n-octanoate (SP value: 9.4 (cal / cm 3 ) 1 / 2 , kinematic viscosity at 40°C 24.8mm 2 / s, flash point 266℃, pour point -57℃).

[0154] <Dibasic acid esters>

[0155] (b3) Diisodecyl adipate (SP value: 8.9 (cal / cm 3 ) 1 / 2 , kinematic viscosity at 40°C 14.2mm 2 / s, flash point 232℃, pour point -63℃).

[0156] (b4) Di(2-ethylhexyl) adipate (SP value: 8.9 (cal / cm 3 ) 1 / 2 , kinematic viscosity at 40°C 7.8mm 2 / s, flash point 205℃, pour point -68℃).

[0157] (b5) Di(2-ethylhexyl) phthalate (SP value: 9.5 (cal / cm 3 ) 1 / 2 , kinematic viscosity at 40°C 27.0 mm 2 / s, flash point 218℃, pour point -55℃).

[0158] <Polyalkylene glycols>

[0159] (b6) Polyoxyethylene lauryl ether (SP value: 9.5 (cal / cm 3 ) 1 / 2 , kinematic viscosity at 40°C 27.0 mm 2 / s, flash point 218℃, pour point -55℃).

[0160] <Alkylnaphthalene having an alkyl group having 10 to 20 carbon atoms>

[0161] (b7) Hexadecylnaphthalene (SP value: 9.2 (cal / cm 3 ) 1 / 2 , kinematic viscosity at 40°C: 29.0mm 2 / s, flash point 222℃, pour point -39℃).

[0162] (C) Base oil not equivalent to (B) above

[0163] (c1) Poly-α-olefin (SP value: 7.9 (cal / cm) which is a trimer of 1-decene 3 ) 1 / 2 , kinematic viscosity at 40°C: 17.2mm 2 / s, flash point 222℃, pour point -68℃).

[0164] (c2) 1-Tetradecene (SP value: 8.0 (cal / cm 3 ) 1 / 2 , flash point 113℃).

[0165] (c3) Liquid paraffin (SP value: 7.9 (cal / cm 3 ) 1 / 2 , kinematic viscosity at 40℃: 7.8mm 2 / s, flash point 162℃, pour point -10.0℃).

[0166] (D) Inorganic cation exchanger with siloxane bond

[0167] (d1) Layered silicate (mineral type: smectite family, cation exchange capacity: 70 meq / 100 g).

[0168] (d2) Zeolite (crystal structure: mordenite system, cation exchange capacity: 160 to 190 meq / 100 g).

[0169] (d3) Talc (cation exchange capacity: 40 meq / 100 g).

[0170] (E) Silicone oil

[0171] (e1) Dimethyl silicone oil (SP value: 7.2 (cal / cm 3 ) 1 / 2 , kinematic viscosity at 40°C: 37.8mm 2 / s).

[0172] <Evaluation of viscosity before excitation and during excitation>

[0173] 3 ml of the magnetorheological fluids from Examples and Comparative Examples 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 at 40°C, with a 100 μm gap and 20 revolutions. The viscosity before excitation was measured. The viscosity during excitation was also measured using the same measurement equipment at 40°C under the following measurement conditions.

[0174] Magnetic field excitation conditions: a DC magnetic field of 0.8 T was applied 5 seconds after the start of measurement, and the application of the magnetic field was stopped 215 seconds after the start of measurement.

[0175] Temporal stability was evaluated based on stabilization rates A (%), B (%), and C (%) calculated using the following formulas. Temporal stability was evaluated when the minimum viscosity during excitation was 200 Pa·s or greater.

[0176] Stabilization rate A (%) = (stabilization time A / total application time) × 100

[0177] In addition, the stabilization time A represents the application time corresponding to 97 to 100% of the maximum value of the viscosity during excitation.

[0178] Stabilization rate B (%) = (stabilization time B / total application time) × 100

[0179] In addition, the stabilization time B represents the application time corresponding to 95 to 100% of the maximum value of the viscosity during excitation.

[0180] Stabilization rate C (%) = (stabilization time C / total application time) × 100

[0181] The stabilization time C refers to the application time corresponding to 90% to 100% of the maximum value of the viscosity during excitation.

[0182] The test conditions and test results are shown in Tables 1 to 3.

[0183] [Table 1]

[0184]

[0185] [Table 2]

[0186]

[0187] [Table 3]

[0188]

[0189] The magnetorheological fluids of Examples 1 to 14 all contain magnetic particles; at least one selected from ester-based synthetic oils, ether-based synthetic oils, and alkylnaphthalenes having an alkyl group containing 10 to 20 carbon atoms; an inorganic cation exchanger having siloxane bonds; and silicone oil. Consequently, the maximum viscosity during excitation is 230 Pa·s or greater, and the stabilization rate C is 90% or greater, demonstrating excellent resistance during excitation and the stability of resistance over time.

[0190] On the other hand, the magnetorheological fluid of Comparative Example 1 does not contain silicone oil, the magnetorheological fluid of Comparative Example 2 does not contain an inorganic cation exchanger having a siloxane bond, and the magnetorheological fluid of Comparative Example 3 contains neither silicone oil nor an inorganic cation exchanger, and the stabilization rates C are all less than 90%.

[0191] Furthermore, the magnetorheological fluids of Comparative Examples 4 to 6 did not contain at least one selected from ester-based synthetic oils, ether-based synthetic oils, and alkylnaphthalenes having an alkyl group with 10 to 20 carbon atoms. Therefore, the minimum viscosity during excitation was lower than that of the Examples, being less than 200 Pa·s. Therefore, the stabilization rates of Comparative Examples 4 to 6 were not evaluated.

[0192] Figure 3 This is a graph showing the relationship between the elapsed time and the viscosity of the magnetorheological fluids of Example 2, Comparative Example 1, and Comparative Example 2. Figure 3 From the curve graph, it can be seen that compared with Comparative Examples 1 and 2, Example 2 has excellent temporal stability of resistance.

[0193] Figure 4 This is a graph showing the relationship between the elapsed time and the viscosity of the magnetorheological fluids of Example 2, Example 11, Example 13, and Comparative Example 4. Figure 4 From the curve graph, it can be seen that compared with Comparative Example 4, the maximum value of the resistance of Example 2, Example 11, and Example 13 is large, and the temporal stability is also excellent.

[0194] Description of Reference Numerals

[0195] 1: Magnetic particles; 2: Hindered ester; 3: Inorganic cation exchanger with siloxane bonds; 4: Dimethyl silicone oil.

Claims

1. A magnetorheological fluid comprising: magnetic particles; At least one base oil selected from ester synthetic oils, ether synthetic oils, and alkylnaphthalenes having an alkyl group having 10 to 20 carbon atoms; an inorganic cation exchanger having a siloxane bond; and Silicone oil, In the magnetorheological fluid, The ester synthetic oil is selected from at least one of polyol esters and dibasic acid esters. The ether-based synthetic oil is a polyalkylene glycol. The content of the silicone oil is 3.0% by mass or less relative to the total amount of the magnetorheological fluid. The mixing ratio of the inorganic cation exchanger having a siloxane bond to the silicone oil is in the range of 2:8 to 8:2 by mass ratio. The inorganic cation exchanger having a siloxane bond is zeolite, bentonite, montmorillonite, beidellite, nontronite, hectorite, stevensite, kaolinite or a combination thereof.

2. The magnetorheological fluid according to claim 1, wherein The polyol esters are hindered esters.

3. The magnetorheological fluid according to claim 1, wherein The dibasic acid ester is an aliphatic dibasic acid ester.

4. The magnetorheological fluid according to claim 3, wherein The aliphatic dibasic acid ester is an ester of an aliphatic dicarboxylic acid having 2 to 10 carbon atoms and an alcohol having 1 to 10 carbon atoms.

5. The magnetorheological fluid according to claim 1, wherein The polyalkylene glycol is at least one selected from the group consisting of compounds represented by the following formula (1): R 1 -O-(R 2 -O) n -R 3 ……(1) In formula (1), R 1 and R 3 are optionally the same or different, each representing a hydrogen atom or an alkyl group having 1 to 18 carbon atoms, R 2 represents an alkylene group having 2 to 4 carbon atoms, and n represents an integer of 2 to 30.

6. A mechanical device using the magnetorheological fluid according to any one of claims 1 to 5.

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