Magnetorheological fluids and mechanical devices

Abstract

A magnetorheological fluid comprises magnetic particles, a base oil, an inorganic cation exchanger having a siloxane bond, and silicone oil, wherein the difference A-B between the solubility parameter A of the base oil and the solubility parameter B of the silicone oil is 1.3 (cal / cm 3 ) 1 / 2 above.

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 for controlling frictional force acting between objects in various mechanical devices such as brakes, clutches, vibration-proof devices, and dampers of vibration-reducing devices. Background Art

[0002] Magnetorheological (MR) fluid is a fluid in which magnetizable metal particles, i.e. magnetic particles, are dispersed in a dispersion medium. In the absence of a magnetic field, the magnetic particles randomly suspend in the dispersion medium and function as a fluid. On the other hand, when a magnetic field is applied, the magnetic particles form many clusters and increase viscosity, thereby increasing internal stress.

[0003] The magnetorheological fluid functions like a rigid body due to the increase in internal stress, and exhibits resistance to shear flow and pressure flow. Due to such characteristics, the magnetorheological fluid is used to control the friction force acting between objects in various mechanical devices such as brakes, clutches, vibration isolation devices, and dampers of vibration reduction devices.

[0004] Therefore, it is preferred that the resistance of the magnetorheological fluid to shear flow and pressure flow (hereinafter also referred to as "resistance during excitation") is large when the magnetorheological fluid is subjected to the action of a magnetic field (during excitation). It should be noted that the resistance during excitation is evaluated by measuring the torque value, viscosity or shear stress, etc. In this specification, the resistance during excitation is evaluated by measuring the viscosity during excitation.

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

[0006] Patent Document 1 proposes a magnetorheological fluid in which a carrier fluid contains 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 Publication 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 excitation, which is not satisfactory. In addition, the magnetorheological fluid is also not satisfactory in terms of the temporal stability of the resistance during excitation. Thus, it is expected to develop a magnetorheological fluid having good resistance during excitation and temporal stability of the resistance.

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

[0013] Solutions for solving problems

[0014] In order to solve the above-mentioned problems, the present invention specifies the following [1] to [7].

[0015] [1] A magnetorheological fluid comprising magnetic particles, a base oil, an inorganic cation exchanger having a siloxane bond, and a silicone oil, wherein the difference A-B between the solubility parameter A of the base oil and the solubility parameter B of the silicone oil is 1.3 (cal / cm 3 ) 1 / 2 above.

[0016] [2] The magnetorheological fluid according to [1], wherein the base oil is at least one selected from ester synthetic oil, ether synthetic oil, and alkyl naphthalene.

[0017] [3] The magnetorheological fluid according to [2], wherein the ester-based synthetic oil is at least one selected from polyol esters and dibasic acid esters.

[0018] [4] The magnetorheological fluid according to [3], wherein the polyol ester is a hindered ester.

[0019] [5] The magnetorheological fluid according to [3], wherein the dibasic acid ester is an aliphatic dibasic acid ester.

[0020] [6] The magnetorheological fluid according to [2], wherein the ether-based synthetic oil is a polyalkylene glycol.

[0021] [7] A mechanical device using the magnetorheological fluid described in any one of [1] to [6].

[0022] Effects of the Invention

[0023] According to the embodiments of the present invention, a magnetorheological fluid and a mechanical device having good resistance during excitation and stability of resistance over time can be provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1This is an electron micrograph of the magnetorheological fluid of Example 1 taken using a scanning electron microscope (magnification: 15,000 times).

[0025] Figure 2 This is a schematic diagram of an enlarged portion of magnetic particles in the magnetorheological fluid of Example 1.

[0026] 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.

[0027] Figure 4 It is a graph showing the relationship between the elapsed time and the viscosity in Example 2, Example 10, Example 12, and Comparative Example 4. DETAILED DESCRIPTION

[0028] Hereinafter, embodiments of the magnetorheological fluid and mechanical device of the present invention will be described, but the present invention is not limited thereto and can be variously changed, modified, and improved based on the knowledge of those skilled in the art without departing from the scope of the present invention.

[0029] 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 the lower limit, respectively. In addition, when only the upper limit in the numerical range is recorded with a unit, it means that the lower limit is also in the same unit as the upper limit.

[0030] In the numerical ranges described in stages in the present 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.

[0031] Furthermore, in the numerical range described in the present 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.

[0032] In this specification, when there are plural substances corresponding to each component in the composition, the content rate or content of each component in the composition means the total content rate or content of the plural substances present in the composition unless otherwise specified.

[0033] (Magnetorheological fluid)

[0034] The magnetorheological fluid of this embodiment contains magnetic particles, base oil, an inorganic cation exchanger having a siloxane bond, and silicone oil. The difference A-B between the solubility parameter A of the base oil and the solubility parameter B of the silicone oil is 1.3 (cal / cm 3 ) 1 / 2The above. With such a structure, the magnetorheological fluid of this embodiment has good resistance during excitation and stability of resistance over time. Regarding this reason, the hindered ester as a kind of base oil and dimethyl silicone oil as a kind of silicone oil are taken as the above solubility parameter difference A-B of 1.3 (cal / cm 3 ) 1 / 2 The above examples of base oil and silicone oil are described below.

[0035] Magnetic particles 1 are dispersed in hindered ester 2 (refer to Figure 1 ). In addition, it is inferred that the surface of the magnetic particle 1 is in the state described below. That is, the magnetic particle 1 has cationicity, 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 inferred 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 ).

[0036] If a magnetic field is applied in this state, the magnetic particles 1 surrounded by the dimethyl silicone oil 4 quickly combine with each other and cluster. 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 a shear force is generated, the clusters will not collapse, and the resistance is highly stable, thereby obtaining a magnetorheological fluid with a large resistance during excitation and good stability of the resistance over time.

[0037] Hereinafter, each component contained in the magnetorheological fluid of this embodiment will be described.

[0038] 1. Magnetic particles

[0039] 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).

[0040] In addition, the magnetic particles may be used alone or in combination of two or more.

[0041] 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 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 shows such 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 greater than 1 μm, more preferably greater than 5 μm, and more preferably greater than 10 μm. The upper limit of the average particle size of the magnetic particles is more preferably less than 80 μm, more preferably less than 60 μm, more preferably less than 50 μm, and more preferably less than 40 μm. The shape of the magnetic particles is preferably spherical or roughly spherical for easy dispersion.

[0042] In addition, the average particle size of magnetic particles is an average primary particle size measured by a laser diffraction / scattering particle size distribution measuring device.

[0043] The content of the magnetic particles is preferably in the range of 30 to 90% by mass relative to the total amount of the magnetorheological fluid of the present embodiment. By setting the content of the magnetic particles to a range of 30 to 90% by mass relative to the total amount of the magnetorheological fluid of the present embodiment, the desired resistance can be obtained when the magnetic field is applied, and the dispersibility of the magnetic particles can be maintained, so that it also functions as a fluid. The lower limit of the content of the magnetic particles is more preferably 40% by mass or more, further preferably 45% by mass or more, and further preferably 50% by mass or more. The upper limit of the content of the magnetic particles is more preferably 85% by mass or less, further preferably 80% by mass or less, and further preferably 75% by mass or less.

[0044] 2. Base oil

[0045] The magnetorheological fluid of this embodiment includes a base oil. The base oil is selected from at least one of ester synthetic oil, ether synthetic oil, and alkyl naphthalene, all of which have polarity, and it is easy to adjust the difference A-B between the solubility parameter A of the base oil and the solubility parameter B of the silicone oil to 1.3 (cal / cm 3 ) 1 / 2 The base oil may be used alone or in combination of two or more.

[0046] 2-1. Ester synthetic oil

[0047] Examples of ester synthetic oils include monoesters, polyol esters, dibasic acid esters (diesters), polyoxyalkylene glycol esters, and the like. Among them, monoesters having 12 to 30 carbon atoms are preferred, and examples thereof include 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 synthetic oils may be used alone or in combination of two or more.

[0048] <Hindered ester>

[0049] 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.

[0050] The hindered ester is an ester of a hindered polyol and an aliphatic monocarboxylic acid, wherein the hindered polyol has one or more quaternary carbons in the molecule, and 1 to 4 hydroxymethyl groups are bonded to at least one of the quaternary carbons. The hindered ester may be used alone or in combination of two or more.

[0051] Examples of hindered polyols include trimethylolpropane (TMP), pentaerythritol (PE), dipentaerythritol (DPE), neopentyl glycol (NPG), 2-methyl-2-propyl-1,3-propanediol (MPPD), etc. Among these hindered polyols, trimethylolpropane, pentaerythritol, and dipentaerythritol are preferred because the flash points of the obtained hindered esters are high, and trimethylolpropane is more preferred because the pour point of the obtained hindered esters is low.

[0052] 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 either linear or branched. The aliphatic group of the aliphatic monocarboxylic acid may be either an aliphatic saturated hydrocarbon group (alkyl group) or an aliphatic unsaturated hydrocarbon group. As aliphatic monocarboxylic acids, for example, 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 can be listed; unsaturated aliphatic carboxylic acids such as pentenoic acid, hexenoic acid, heptenoic acid, octenoic 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 can be used. These aliphatic monocarboxylic acids can 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. If the carbon number of the aliphatic monocarboxylic acid is set to 5 or more, the flash point of the obtained hindered ester becomes high, so it is preferred. If the carbon number of the aliphatic monocarboxylic acid is set to 12 or less, it is more preferred. If the carbon number of the aliphatic monocarboxylic acid is set to 10 or less, it is particularly preferred. If the carbon number of the aliphatic monocarboxylic acid is set to 15 or less, it is preferred from the aspect of being able to improve the solubility parameter of the obtained hindered ester.

[0053] 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 a carboxyl group (—COOH) of the aliphatic monocarboxylic acid.

[0054] <Dibasic acid ester>

[0055] Hereinafter, the dibasic acid ester which is one kind of the ester-based synthetic oil contained in the magnetorheological fluid of the present embodiment will be described in detail.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] More specifically, diisobutyl adipate, di(2-ethylhexyl) adipate, diisodecyl adipate, diisobutyl sebacate, di(2-ethylhexyl) sebacate, diisodecyl sebacate, diisobutyl phthalate, di(2-ethylhexyl) phthalate, diisodecyl phthalate, and the like are exemplified.

[0060] Among them, aliphatic dibasic acid esters which are esters of aliphatic dicarboxylic acids having 2 to 10 carbon atoms and alcohols having 1 to 10 carbon atoms are preferred because they further improve the temporal stability of the resistance during excitation.

[0061] Among the above-mentioned aliphatic dibasic acid esters, dibasic acid esters of 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, are preferred. Dibasic acid esters of 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, are particularly preferred. These dicarboxylic acids and alcohols may be used alone or in combination of two or more in the esterification.

[0062] It should be noted that, unless otherwise specified, in the present invention, the number of carbon atoms of an aliphatic dicarboxylic acid also includes the carbon atoms of the carboxyl group (-COOH) possessed by the aliphatic dicarboxylic acid. In addition, unless otherwise specified, in the present invention, the number of carbon atoms of an aromatic carboxylic acid also includes the carbon atoms of the aromatic ring possessed by the aromatic carboxylic acid. A dibasic acid ester may be used alone or in combination of two or more.

[0063] 2-2. Ether synthetic oil

[0064] 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.

[0065] <Polyalkylene glycols>

[0066] 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.

[0067] The polyalkylene glycol is preferably at least one selected from the group consisting of compounds represented by the following formula (1).

[0068] R1 -O-(R 2 -O) n -R 3 ……(1)

[0069] 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.

[0070] 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 a polyalkylene glycol. 1 and R 3 When both of these groups are alkyl groups, the compound represented by formula (1) is a dietherified product of a polyalkylene glycol.

[0071] In formula (1), R 1 and R 3 When one or both of them are alkyl groups, the alkyl group preferably has 5 to 18 carbon atoms, more preferably 6 to 15 carbon atoms, and particularly preferably 8 to 14 carbon atoms.

[0072] When the number of carbon atoms of the alkyl group is 5 or more, the group has polarity and thus can be expected to have an increase in viscosity during excitation.

[0073] From the viewpoint of easy availability, the number of carbon atoms in the alkyl group is preferably set to 18 or less. The alkyl group may be linear or branched. Specifically, 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 may be mentioned.

[0074] R in formula (1) 2The number of carbon atoms of the alkylene group shown is preferably 2 to 4. When the number of carbon atoms of 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.

[0075] It should be noted that the compound represented by formula (1) may 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 may be any of a random copolymer, an alternating copolymer and a block copolymer.

[0076] 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.

[0077] 2-3. Alkyl naphthalene

[0078] The alkylnaphthalene is preferably an alkylnaphthalene having an alkyl group with 10 to 20 carbon atoms. When the number of carbon atoms is 10 or more, the polarity becomes large and it is easy to adjust the difference in solubility parameter with silicone oil to 1.3 (cal / cm 3 ) 1 / 2 More than, therefore preferred. If the number of carbon atoms is 20 or less, it is preferred from the perspective of easy acquisition and cost. As alkylnaphthalene having an alkyl group with 10 to 20 carbon atoms, for example, decylnaphthalene, undecylnaphthalene, dodecylnaphthalene, tridecylnaphthalene, tetradecylnaphthalene, pentadecylnaphthalene, hexadecylnaphthalene, heptadecylnaphthalene, octadecylnaphthalene, nonadecylnaphthalene, eicosylnaphthalene, di(decyl)naphthalene, di(undecyl)naphthalene, di(dodecyl)naphthalene, di(tridecyl)naphthalene, di(tetradecyl)naphthalene, di(pentadecyl)naphthalene, di(hexadecyl)naphthalene, di(heptadecyl)naphthalene, di(octadecyl)naphthalene, di(nonadecyl)naphthalene, di(eicosyl)naphthalene. In addition, all their isomers can also be listed. Alkylnaphthalene having an alkyl group with 10 to 20 carbon atoms can be used alone or in combination of two or more.

[0079] 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 2By 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 the dispersion of the magnetic particles.

[0080] In addition, the kinematic viscosity is a kinematic viscosity measured by the kinematic viscosity test method of JIS K2283:2000.

[0081] The flash point of the base oil is preferably 200°C or higher, more preferably 250°C or higher.

[0082] If the flash point of the base oil is 200°C or higher, it is classified as Class III to Class IV petroleum in the Fire Protection Act, and is therefore more preferred from the perspective of increasing the amount of hazardous materials handled (specified amount). The flash point is a flash point measured in accordance with JIS K2265-4:2007 (Cleveland open cup (COC) method).

[0083] 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 from the perspective of excellent low-temperature fluidity. The pour point is a pour point measured in accordance with JIS K2269:1987.

[0084] The lower limit of the content of the base oil is preferably 10% by mass or more, and more preferably 20% by mass or more, relative to the total amount of the magnetorheological fluid of the present embodiment. By setting the content of the base oil to 10% by mass or more, the magnetic particles can be dispersed and the fluidity can be improved. The upper limit of the content of the base oil 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 the present embodiment. By setting the content of the base oil to 70% by mass or less, it is more preferable from the aspect of being able to improve the magnetic properties during excitation.

[0085] The magnetorheological fluid of the present embodiment may contain base oils other than ester synthetic oils, ether synthetic oils, and alkylnaphthalene, such as mineral oils, poly-α-olefins, and α-olefins, within a range that does not impair the effects of the present invention.

[0086] 3. Inorganic cation exchangers with siloxane bonds

[0087] Since the magnetorheological fluid of the present embodiment contains an inorganic cation exchanger having a siloxane bond and silicone oil described later, the resistance of the magnetorheological fluid during excitation becomes large and the stability of the resistance over time is also improved.

[0088] More specifically, the magnetic particles are dispersed in the base oil. The magnetic particles are cationic, so the inorganic cation exchanger with a siloxane bond is adsorbed. In addition, the surface energy of silicone oil is small, and it does not dissolve but disperses in the base oil with a large solubility parameter. Moreover, both the inorganic cation exchanger with a siloxane bond and the silicone oil have Si, so the affinity is high. It is speculated that the silicone oil exists in a state of surrounding the magnetic particles adsorbed with the inorganic cation exchanger with a siloxane bond.

[0089] 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 will not disintegrate, and their resistance is highly stable, thereby obtaining a magnetorheological fluid with large resistance during excitation and good stability of resistance over time.

[0090] <Inorganic cation exchanger having siloxane bond>

[0091] As the inorganic cation exchanger having a siloxane bond, for example, zeolite, silicon dioxide, layered silicate, etc. can be listed. Among them, if abrasion resistance is considered, zeolite is preferred. The inorganic cation exchanger having a siloxane bond can be used alone or in combination of two or more. Both natural products and synthetic products can be used.

[0092] Zeolite is composed of a crystalline porous aluminosilicate skeleton having anionicity and a cationic metal element M adsorbed on the skeleton. More specifically, it has a structure in which SiO4 and AlO4 having a tetrahedral structure are three-dimensionally linked to form a crystal having pores (voids), and crystal water and a cationic metal element M are adsorbed in the voids. The crystal structure of zeolite is not particularly limited, and specifically, zeolite A, zeolite X, zeolite Y, zeolite L, zeolite β, ZSM-5, ZSM-11, silicalite, ferrierite, mordenite, clinoptilolite, and bohlinite can be cited.

[0093] Layered silicates are silicate compounds with the following crystal structure: the crystal structure is formed by stacking the planes formed by ionic bonds with weak bonding forces into layers. Most layered silicates have a negative charge throughout the layer, and large cations enter between the layers to neutralize the negative charge. Since the layer charge is small, the cations can be exchanged with cations in the solution, and have cation exchange properties. Examples of the layered silicate include smectite (bentonite, montmorillonite, beidellite, nontronite, saponite, hectorite, stevensite), vermiculite, kaolinite (kaolinite, halloysite, chrysotile, magnesia chlorite), mica (muscovite, biotite, ankerite, phlogopite, lepidolite, sodium mica, siderophyllite, eastonite, polysilicon lithium mica, lithium white mica, lithium mica, nacreous mica, illite, glauconite), talc, palygorskite, sepiolite, magadiite, kanemite, kenyaite, synthetic fluorine mica, etc. Among them, smectite, vermiculite, and synthetic fluorine mica are preferred from the viewpoint of the size of the ion exchange capacity.

[0094] 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, particularly preferably 150 meq / 100 g or more.

[0095] 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, particularly preferably 300 meq / 100 g or less.

[0096] 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.

[0097] The lower limit of the content of the inorganic cation exchanger having a siloxane bond is preferably 0.8% by mass or more, more preferably 1.0% by mass or more, and particularly preferably 1.3% by mass or more relative to the total amount of the magnetorheological fluid of the present embodiment. Setting the content to 0.8% by mass or more is more preferable from the perspective of being able to suppress the aggregation of magnetic particles in a state where no magnetic field is applied.

[0098] The upper limit of the content of the inorganic cation exchanger having a siloxane bond is preferably 4.0% by mass or less, more preferably 3.5% by mass or less, and further preferably 3.0% by mass or less relative to the total amount of the magnetorheological fluid of the present embodiment. Setting the content to 4.0% by mass or less is more preferred from the perspective of being able to appropriately form clusters of magnetic particles when a magnetic field is applied.

[0099] 4. Silicone oil

[0100] Silicone oil can be used without particular restrictions 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: various silicone oils such as amino-modified, epoxy-modified, carboxyl-modified, methanol-modified, methacryl-modified, mercapto-modified, phenol-modified, etc. Non-reactive silicone oil can be listed: polyether-modified, methylstyrene-modified, alkyl-modified, higher fatty acid ester-modified, hydrophilic special modified, containing higher fatty acid, fluorine-modified, etc. 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.

[0101] The lower limit of the content of silicone oil is preferably 0.5% by mass or more, and more preferably 1.0% by mass or more relative to the total amount of the magnetorheological fluid of this embodiment. By setting the content to 0.5% by mass or more, it is more preferable from the aspect of being able to surround the magnetic particles to which the inorganic cation exchanger having a siloxane bond is attached.

[0102] The upper limit of the content of silicone oil is preferably 3.0 mass % or less, more preferably 2.5 mass % or less, relative to the total amount of the magnetorheological fluid of this embodiment. Setting the content to 3.0 mass % or less is more preferable from the perspective of preventing the dispersibility of the magnetic particles from being reduced.

[0103] The blending 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.

[0104] The range of 2:8 to 8:2 is more preferable from the viewpoint of improving the temporal stability of the resistance during excitation.

[0105] The difference A-B between the solubility parameter A of the base oil of the magnetorheological fluid of this embodiment and the solubility parameter B of the silicone oil is 1.3 (cal / cm 3 ) 1 / 2The above. According to such a structure, the incompatibility between the base oil and the silicone oil is improved, and the silicone oil with a small surface energy can be well dispersed in the base oil with a large solubility parameter without being dissolved, and surround the magnetic particles. Therefore, when a magnetic field is applied, the excessive aggregation of the magnetic particles is suppressed, and their resistance is highly stable. It can be considered that as a result, a magnetorheological fluid with a large resistance during excitation and good stability of resistance over time can be obtained. The difference A-B between the solubility parameter A of the base oil and the solubility parameter B of the silicone oil is more preferably 1.5 (cal / cm 3 ) 1 / 2 More preferably, 1.8 (cal / cm 3 ) 1 / 2 above.

[0106] 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 / cm 3 ) 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 that the base oil and the silicone oil described later can be made incompatible.

[0107] 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.

[0108] It should be noted that the solubility parameter (SP value) can be calculated according to the method proposed by Fedors et al. "Refer to Polymer Engineering and Science, 14, 147-154 (1974)".

[0109] That is, it can be calculated based on the following formula.

[0110] SP value δ=(ΣΔe / ΣΔv) 1 / 2

[0111] (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.)

[0112] 5. Other ingredients

[0113] The magnetorheological fluid of the present embodiment may contain various other components in addition to the above-mentioned components according to the purpose, within the range not impairing the effects of the present invention.

[0114] Examples of other components include anti-wear agents, dispersants, surfactants, viscosity modifiers, fluidity improvers, sedimentation inhibitors, pour point depressants, extreme pressure agents, rust inhibitors, antioxidants, corrosion inhibitors, metal deactivators, and defoamers.

[0115] Examples of the anti-wear agent 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.

[0116] The anti-wear agents may be used alone or in combination of two or more.

[0117] 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, polymer-weight dispersants, etc. The dispersants may be used alone or in combination of two or more.

[0118] 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 anion active agents, polyolefins, (meth)acrylates, polyisobutylene, ethylene-propylene copolymers, and polyalkylstyrene.

[0119] The viscosity modifier may be used alone or in combination of two or more.

[0120] As the fluidity improver, modified silicone oil can be cited. For example, modified silicone oil obtained by modifying ordinary silicone oil with alkyl, aralkyl, polyether, higher fatty acid ester, amino, epoxy, carboxyl, alcohol, etc. can be cited. It should be noted that the modified silicone oil can also be compatible with the base oil. The fluidity improver can be used alone or in combination of two or more.

[0121] <Viscosity of Magnetorheological Fluid>

[0122] The viscosity before magnetization of the magnetorheological fluid of the present embodiment 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 magnetization are as follows.

[0123] 3 ml of the magnetorheological fluid was injected into a test plate of a rheometer DHR-2 manufactured by TA Instruments equipped with a magnetic measurement option, and the viscosity (Pa·s) was measured at 40° C., with a gap of 100 μm and 20 revolutions.

[0124] <Magnetic properties of magnetorheological fluid>

[0125] The magnetorheological fluid of this embodiment has the characteristics of large resistance during excitation (good resistance during excitation) and good stability of resistance over time. Large resistance during excitation means that in the magnetorheological fluid of the invention of this embodiment, when the content ratio of magnetic particles is 2 / 3 by mass ratio, the maximum value of viscosity during excitation under the following conditions is 230Pa·s or more. In addition, the maximum value of viscosity during excitation is preferably 230Pa·s or more, and more preferably 240Pa·s or more. The minimum value of viscosity during excitation is preferably 200Pa·s or more, and more preferably 210Pa·s or more.

[0126] In addition, since the inorganic cation exchanger and silicone oil having a siloxane bond are included, excellent temporal stability of resistance during excitation (viscosity temporal stability) can be obtained. Excellent temporal stability of resistance during excitation (viscosity temporal stability) means that the stabilization rate B described later is 80% or more. In addition, preferably the stabilization rate B is 80% or more, more preferably the stabilization rate B is 90% or more, further preferably the stabilization rate A is 80% or more, and particularly preferably the stabilization rate A is 90% or more.

[0127] The viscosity during excitation refers to the viscosity during the 210 seconds when the magnetic field is applied, using the same measuring device as the device for measuring the viscosity before excitation, under the same temperature environment, applying a DC 0.8T magnetic field 5 seconds after the start of measurement, and stopping the application of the magnetic field 215 seconds after the start of measurement.

[0128] The stabilization rates A and B (%) were calculated based on the following formulas.

[0129] Stabilization rate A (%) = (stabilization time A / total application time) × 100

[0130] In addition, the stabilization time A represents the application time corresponding to 97 to 100% of the maximum value of the viscosity during excitation.

[0131] The stabilization rate B (%) was calculated based on the following formula.

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

[0133] In addition, the stabilization time B represents the application time corresponding to 95 to 100% of the maximum value of the viscosity during excitation.

[0134] (Method for producing magnetorheological fluid)

[0135] The method for manufacturing the magnetorheological fluid of the present embodiment is not particularly limited. For example, the following method can be cited: using a homogenizer, a bead mill, a mechanical mixer or other processing machine that can apply high shear force to mix magnetic particles, a specific base oil, an inorganic cation exchanger having a siloxane bond, silicone oil, and other components added as desired in predetermined amounts. It should be noted that heating or cooling can also be performed as required during the manufacture of the magnetorheological fluid.

[0136] (Mechanical device using magnetorheological fluid)

[0137] The magnetorheological fluid of this embodiment has good resistance during excitation and stability over time, and can therefore be applied to various mechanical devices such as brakes, clutches, vibration isolators, and dampers of vibration reduction devices for controlling friction between objects.

[0138] Example

[0139] 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.

[0140] <Examples 1 to 13, Comparative Examples 1 to 6>

[0141] The components shown in Tables 1 to 3 were added to a beaker based on the mass ratios listed therein, and stirred at 40 Hz for 5 minutes at room temperature using a universal vibration stirrer AD-MIX manufactured by Seiko Advance Co., Ltd. to produce a magnetorheological fluid. The raw materials of the components shown in Tables 1 to 3 are shown below.

[0142] (A) Magnetic particles

[0143] (a1) Carbonyl iron (average particle size D50 = 6.0 μm).

[0144] (B) Base oil

[0145] <Hindered ester>

[0146] (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℃).

[0147] <Dibasic acid ester>

[0148] (b2) Di(2-ethylhexyl) sebacate (SP value: 8.9 (cal / cm 3 ) 1 / 2 , kinematic viscosity at 40°C 11.3 mm 2 / s, flash point 228℃, pour point -66℃).

[0149] (b3) diisodecyl adipate (SP value: 8.9 (cal / cm 3 ) 1 / 2 , kinematic viscosity at 40°C 14.2 mm 2 / s, flash point 232℃, pour point -63℃).

[0150] (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℃).

[0151] (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℃).

[0152] <Polyalkylene glycols>

[0153] (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℃).

[0154] <Alkylated naphthalene>

[0155] (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℃).

[0156] (C) Base oil not equivalent to (B) above

[0157] (c1) Poly-α-olefin (SP value: 7.9 (cal / cm) which is a trimer of 1-decene3 ) 1 / 2 , Kinematic viscosity at 40°C: 17.2mm 2 / s, flash point 222℃, pour point -68℃).

[0158] (c2) 1-Tetradecene (SP value: 8.0 (cal / cm 3 ) 1 / 2 , flash point 113°C).

[0159] (c3) Liquid paraffin (SP value: 7.9 (cal / cm 3 ) 1 / 2 , Kinematic viscosity at 40°C: 7.8mm 2 / s, flash point 162℃, pour point -10.0℃).

[0160] (D) Inorganic cation exchanger having siloxane bonds

[0161] (d1) Layered silicate (mineral type: montmorillonite family, cation exchange capacity: 70 meq / 100 g).

[0162] (d2) Zeolite (crystal structure: mordenite system, cation exchange capacity: 160 to 190 meq / 100 g).

[0163] (d3) Talc (cation exchange capacity: 40 meq / 100 g).

[0164] (E) Silicone oil

[0165] (e1) Dimethyl silicone oil (SP value: 7.2 (cal / cm 3 ) 1 / 2 , Kinematic viscosity at 40°C: 37.8mm 2 / s).

[0166] <Evaluation of viscosity before excitation and viscosity during excitation>

[0167] 3 ml of the magnetorheological fluid of the embodiment and the comparative example was injected into the test plate of the rheometer DHR-2 manufactured by TA Instruments equipped with a magnetic measurement option, and the viscosity (Pa·s) was measured at 100 μm gap and 20 revolutions at 40°C to measure the viscosity before excitation. The viscosity during excitation was also measured using the same measuring device at 40°C based on the following measurement conditions.

[0168] Excitation conditions of the magnetic field: a direct current magnetic field of 0.8 T was applied 5 seconds after the start of the measurement, and the application of the magnetic field was stopped 215 seconds after the start of the measurement.

[0169] The temporal stability was evaluated based on the stabilization rate A (%) and the stabilization rate B (%) calculated based on the following formula. The temporal stability was evaluated when the minimum value of the viscosity during excitation was 200 Pa·s or more.

[0170] Stabilization rate A (%) = (stabilization time A / total application time) × 100

[0171] In addition, the stabilization time A represents the application time corresponding to 97 to 100% of the maximum value of the viscosity during excitation.

[0172] Stabilization rate B (%) = (stabilization time B / total application time) × 100

[0173] In addition, the stabilization time B represents the application time corresponding to 95 to 100% of the maximum value of the viscosity during excitation.

[0174] Furthermore, based on the solubility parameters (SP values) A ​​and B of the base oil and silicone oil used in each of Examples 1 to 13 and Comparative Examples 1 to 6, the difference (A-B) therebetween was calculated.

[0175] It should be noted that the solubility parameter (SP value) is calculated according to the method proposed by Fedors et al. "Referring to Polymer Engineering and Science, 14, 147-154 (1974)".

[0176] That is, it is calculated based on the following formula.

[0177] SP value δ=(ΣΔe / ΣΔv) 1 / 2

[0178] (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.)

[0179] The test conditions and test results are shown in Tables 1 to 3.

[0180] [Table 1]

[0181]

[0182] [Table 2]

[0183]

[0184] [Table 3]

[0185]

[0186] The magnetorheological fluids of Examples 1 to 13 are all magnetorheological fluids as follows: containing magnetic particles, base oil, an inorganic cation exchanger having a siloxane bond, and silicone oil, wherein the difference A-B between the solubility parameter A of the base oil and the solubility parameter B of the silicone oil is 1.3 (cal / cm 3 ) 1 / 2 Therefore, the maximum value of the viscosity during excitation is 230 Pa·s or more, and the stabilization rate B is 80% or more, both of which have good resistance during excitation and stability of resistance over time.

[0187] 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 does not contain silicone oil and an inorganic cation exchanger, and the stabilization rate B is less than 80%.

[0188] In addition, the difference A-B between the solubility parameter A of the base oil of the magnetorheological fluid of Comparative Examples 4 to 6 and the solubility parameter B of the silicone oil is less than 1.3 (cal / cm 3 ) 1 / 2 , so the stabilization rate B is less than 80%. The reason is inferred as follows: the base oil and silicone oil are compatible, and as a result, the silicone oil cannot surround the magnetic particles in a dispersed state in the base oil, so when the magnetic field is applied, the magnetic particles are excessively aggregated, and the resistance is unstable during excitation.

[0189] Figure 3 Graph showing the relationship between the elapsed time and the viscosity in 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.

[0190] Figure 4 Graph showing the relationship between the elapsed time and the viscosity in the magnetorheological fluids of Example 2, Example 10, Example 12, and Comparative Example 4. Figure 4 From the curve graph, it can be seen that compared with Comparative Example 4, the maximum values ​​of the resistance of Example 2, Example 10, and Example 12 are large, and the stability over time is also excellent.

[0191] Description of Reference Numerals

[0192] 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, a base oil, an inorganic cation exchanger having a siloxane bond, and silicone oil, in, The base oil is selected from at least one of ester synthetic oil, ether synthetic oil and alkyl naphthalene. 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 difference A-B between the solubility parameter A of the base oil and the solubility parameter B of the silicone oil is 1.3 (cal / cm 3 ) 1 / 2 above, The content of the silicone oil is 3.0 mass % or less relative to the total amount of the magnetorheological fluid.

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

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

4. A mechanical device using the magnetorheological fluid according to any one of claims 1 to 3.

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