Magnetoviscous fluid and mechanical device

Abstract

Provided is a magnetic viscous fluid and a mechanical device that improve both the excitation time resistance and the rubber resistance. The magnetic viscous fluid of the present invention contains magnetic particles and a base oil, and the base oil contains an ester-based base oil and a nonpolar base oil, and the nonpolarity index of the base oil is in the range of 10 to 45.

Description

Technical Field

[0001] This invention relates to a magnetic viscous fluid and a mechanical device. In particular, it relates to a magnetic viscous fluid for controlling frictional forces between objects acting on a mechanical device, and a mechanical device using the magnetic viscous fluid. Examples of mechanical devices include brakes, clutches, vibration damping devices, and dampers for vibration reduction devices. Background Technology

[0002] Magneto-viscosity (MR) fluids are fluids formed by dispersing magnetized metallic particles, i.e., magnetic particles, in the absence of a magnetic field, the magnetic particles are randomly suspended in the dispersion medium, functioning as a fluid. However, under the influence of a magnetic field, the magnetic particles in the MR fluid form numerous clusters, increasing viscosity and thus increasing internal stress.

[0003] Magnetoviscous fluids function like rigid bodies due to the increased internal stress described above, exhibiting resistance to shear and pressure flows. Because of these properties, magnetoviscous fluids are used in various mechanical devices such as brakes, clutches, vibration damping devices, and dampers in vibration reduction systems to control frictional forces acting between objects.

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

[0005] Magnetoviscous fluids possess various characteristics, primarily the resistance to excitation mentioned above. In recent years, a technique has been developed that enhances the various properties of magnetoviscous fluids by preparing a dispersion medium for them. As such a technique, Patent Document 1 discloses a magnetoviscous fluid composition formulated with a monoester, magnetic particles, a dispersant, and a rheology control agent. Furthermore, it describes that this composition provides a magnetoviscous fluid composition that exhibits low viscosity in the absence of a magnetic field, suppressed evaporation, and excellent flowability at low temperatures.

[0006] Furthermore, Patent Document 2 discloses a magnetic viscous fluid, which is formed by controlling the specific gravity and kinematic viscosity of the dispersion medium within a specific range, and controlling the average primary particle size, density, and mass ratio of the magnetic particles within a specific range. It also states that, based on this configuration, a magnetic viscous fluid can be provided that can significantly suppress the sedimentation of magnetic particles without changing the kinematic viscosity of the dispersion medium.

[0007] Existing technical documents

[0008] Patent documents

[0009] Patent Document 1: Japanese Patent Application Publication No. 2017-92119

[0010] Patent Document 2: Japanese Patent Application Publication No. 2021-163969 Summary of the Invention

[0011] The problem that the invention aims to solve

[0012] In various mechanical devices that utilize magnetic viscous fluids, such as brakes, clutches, vibration damping devices, and dampers, rubber is used as a sealing material for O-rings, oil seals, and gaskets. In this process, the rubber comes into contact with the magnetic viscous fluid, and the rubber deteriorates from this contact point due to the dispersion medium contained in the fluid. Deterioration of the rubber used for sealing O-rings, oil seals, and gaskets can lead to malfunctions in the mechanical devices.

[0013] Therefore, magnetoviscous fluids are required not only to increase resistance during excitation but also to possess properties that inhibit rubber degradation (hereinafter also referred to as rubber resistance). However, there has been no technology that can simultaneously improve resistance during excitation and rubber resistance.

[0014] This invention was made with regard to the above aspects, and its purpose is to provide a magnetic viscous fluid and mechanical device that takes into account both the improvement of resistance during excitation and the improvement of rubber resistance.

[0015] Solution for solving the problem

[0016] In order to solve the above problems, the present invention specifically includes the following (1) to (5).

[0017] (1) A magnetic viscous fluid comprising magnetic particles and a base oil, wherein the base oil comprises an ester-based base oil and a non-polar base oil, the non-polarity index of the base oil being in the range of 10 to 45.

[0018] (2) The magnetic viscous fluid according to (1), wherein the ester base oil is at least one selected from hindered ester and diester.

[0019] (3) The magnetic viscous fluid according to (1) or (2) further comprises: an alkylbenzene having an alkyl group having 10 to 24 carbon atoms, and / or an alkylnaphthalene having an alkyl group having 10 to 24 carbon atoms.

[0020] (4) The magnetic viscous fluid according to any one of (1) to (3) further comprises: an inorganic cation exchanger having siloxane bonds and silicone oil.

[0021] (5) A mechanical device that uses the magnetic viscous fluid described in any one of (1) to (4).

[0022] Invention Effects

[0023] According to embodiments of the present invention, a magnetoviscous fluid and mechanical device can be provided that simultaneously improves resistance during excitation and enhances rubber resistance. Attached Figure Description

[0024] Figure 1 These are graphs showing the relationship between the nonpolarity index and the hardness change rate of NBR in Tables 1 and 2 of Examples 1-4, 7-14, and Comparative Examples 1-3. Detailed Implementation

[0025] The following describes embodiments of the magnetic viscous fluid and mechanical device of the present invention. However, the present invention is not limited thereto and can be interpreted in various ways without departing from the scope of the present invention, based on the knowledge of those skilled in the art.

[0026] It should be noted that in this specification, the "~" indicating a numerical range means a range that includes both the upper and lower limits. Furthermore, if only the upper limit of a numerical range is specified with a unit, it means that the unit of the lower limit is the same as the unit of the upper limit.

[0027] In the numerical ranges described in this specification, the upper or lower limit of a certain numerical range may be replaced by the upper or lower limit of other numerical ranges described in different periods.

[0028] Furthermore, within the numerical range described in this specification, the upper or lower limit value described in a certain numerical range may also be replaced with the value shown in the embodiment.

[0029] Regarding the content or percentage of each component in the composition described in this specification, if there are multiple substances in the composition that are equivalent to each component, unless otherwise specified, it refers to the total content or percentage of the multiple substances present in the composition.

[0030] (Magneviscous fluid)

[0031] The magnetic viscous fluid of this embodiment is a colloidal fluid containing magnetic particles and a base oil, with the magnetic particles dispersed in the base oil. The base oil comprises an ester-based base oil and a non-polar base oil. The magnetic particles in the magnetic viscous fluid float in the base oil before excitation and cluster along the magnetic field when a magnetic field (excitation) is applied. The base oil acts as a resistance to this clustering. Ester-based base oils are synthetic oils with a fixed molecular structure compared to mineral oils, thus reducing the physical resistance between the magnetic particles and the ester-based base oil when a magnetic field is applied. As a result, ideal clusters can be formed, increasing the magnetic properties. However, considering the sedimentation stability of the magnetic particles, the ester-based base oil needs to be polar, but almost all polar ester-based base oils tend to cause rubber swelling. In this regard, the magnetic viscous fluid of this embodiment, since the magnetic particles are dispersed in the base oil, and this base oil contains both an ester-based base oil and a non-polar base oil with properties that cause rubber shrinkage, can achieve both increased resistance during excitation and improved rubber resistance.

[0032] The base oil contained in the magnetic viscous fluid of this embodiment includes ester-based base oil and non-polar base oil. Ester-based base oil has the property of swelling rubber, while non-polar base oil has the property of shrinking rubber. By mixing these ester-based base oils and non-polar base oils with opposite properties, the non-polarity index formed by the ester-based base oil and non-polar base oil contained in the magnetic viscous fluid can be adjusted to a specific range, thereby effectively suppressing the deterioration of rubber in contact with the magnetic viscous fluid.

[0033] It should be noted that the nonpolarity index is calculated according to the following formula (A).

[0034] Nonpolarity index = {(number of carbon atoms × molecular weight) / (number of ester groups × 100)} × {(content of ester base oil) / (content of ester base oil + content of nonpolar base oil)} ... (A)

[0035] (In the above formula (A), "number of carbon atoms" represents the number of carbon atoms that make up the ester base oil, "molecular weight" represents the molecular weight of the ester base oil, and "number of ester groups" represents the number of ester groups in one molecule of ester.)

[0036] Here, in this invention, "deterioration of rubber" means that the absolute value of the rate of change of rubber hardness increases by more than 5% due to contact with the magnetoviscous fluid for a specific period of time. In the magnetoviscous fluid of this embodiment, the nonpolarity index is in the range of 10 to 45, preferably in the range of 15 to 40, and more preferably in the range of 20 to 40. By setting the nonpolarity index to 45 or less, rubber deterioration can be suppressed; by setting the nonpolarity index to 10 or more, the sedimentation suppression effect of magnetic particles can be improved, and the resistance during excitation can be increased. It should be noted that the method for calculating the rate of change of rubber hardness is as described below.

[0037] Furthermore, the rubber that can suppress deterioration in this invention is not particularly limited, but examples include: acrylonitrile butadiene rubber (hereinafter also referred to as "NBR"), styrene butadiene rubber (SBR), chloroprene rubber (CR), silicone rubber, polyurethane rubber, etc. Among them, NBR is a rubber that is particularly suitable for use as a sealing material for O-rings, oil seals, gaskets, etc. in various mechanical devices such as brakes, clutches, vibration damping devices, and dampers of vibration reduction devices, and it particularly well demonstrates the rubber-resistant properties of the magnetic viscous fluid of this invention.

[0038] The components contained in the magnetic viscous fluid of this embodiment will be described below.

[0039] 1. Magnetic particles

[0040] The magnetic particles contained in the magnetic viscous fluid of this embodiment can be selected according to the target permeability. Examples include: strongly magnetic oxides such as magnetite, iron carbonyl, γ-iron oxide, manganese ferrite, cobalt ferrite, or composite ferrites of these with zinc and nickel, barium ferrite; strongly magnetic metals such as iron, cobalt, and rare earth elements; metal nitrides; and various alloys such as Sendust, Permalloy, and Supermalloy. Among these, iron carbonyl is preferred from the perspective of soft magnetic materials with low magnetic retention and high permeability. Iron carbonyl is a high-purity metal particle produced by the thermal decomposition of iron pentacarbonyl (Fe(CO)5).

[0041] It should be noted that magnetic particles can be used alone or in combination with two or more.

[0042] In the magnetoviscous fluid of this embodiment, when a magnetic field is applied from the outside, the dispersed magnetic particles orient themselves along the direction of the magnetic field and form chain-like clusters, thereby increasing viscosity and changing their flow characteristics and yield stress. The average particle size of the magnetic particles is determined in a manner that exhibits this behavior. Specifically, it is preferably in the range of 0.1 to 100 μm, more preferably in the range of 1 to 80 μm, further preferably in the range of 5 to 60 μm, even more preferably in the range of 10 to 50 μm, and most preferably in the range of 10 to 40 μm. Regarding the shape of the magnetic particles, they are preferably spherical or substantially spherical to facilitate dispersion.

[0043] It should be noted that the average particle size of the magnetic particles is the average primary particle size measured using a laser diffraction / scattering particle size distribution measuring device.

[0044] The content of magnetic particles relative to the total amount of the magnetic viscous fluid in this embodiment is preferably in the range of 30 to 90% by mass. By setting the content of magnetic particles relative to the total amount of the magnetic viscous fluid in this embodiment to a range of 30 to 90% by mass, the required resistance can be obtained when the magnetic field is applied, and the dispersion of the magnetic particles can be maintained, thus also functioning as a fluid. The content of magnetic particles is more preferably in the range of 40 to 85% by mass, further preferably in the range of 45 to 80% by mass, and most preferably in the range of 50 to 75% by mass.

[0045] 2. Base oil

[0046] The base oil contained in the magnetic viscous fluid of this embodiment comprises ester-based base oil, non-polar base oil, and specific alkylbenzene and alkylnaphthalene base oils added as needed. The ester-based base oil, non-polar base oil, and specific alkylbenzene and alkylnaphthalene are described below.

[0047] 2-1. Ester-based base oils

[0048] The ester-based base oil contained in the magnetic viscous fluid of this embodiment is a polar base oil, and the ester-based base oil is an ester-containing compound having an ester group (-C(=O)-O-). Examples of ester-based base oils include: monoesters, polyol esters, diesters (diesters), polyoxyalkylene glycol esters, etc. These ester-based base oils can be used alone or in combination of two or more.

[0049] Among these, monoesters are preferably monoesters with 12 to 30 carbon atoms, such as 2-ethylhexyl laurate, 2-ethylhexyl palmitate, and n-butyl stearate. Polyol esters refer to esters of polyols with straight-chain or branched saturated or unsaturated fatty acids. Hindered esters are examples of polyol esters.

[0050] 2-1-1. Hindered esters

[0051] As the ester-based base oil contained in the magnetic viscous fluid of this embodiment, hindered esters will be used as an example for detailed explanation. A hindered ester is an ester of a hindered polyol and an aliphatic monocarboxylic acid, which has one or more quaternary carbons in the molecule and 1 to 4 hydroxymethyl groups bonded to at least one of the quaternary carbons.

[0052] Examples of hindered polyols include: trimethylolpropane (TMP), pentaerythritol (PE), dipentaerythritol (DPE), neopentyl glycol (NPG), and 2-methyl-2-propyl-1,3-propanediol (MPPD).

[0053] 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 flow points.

[0054] The preferred aliphatic monocarboxylic acid is one with 5 to 15 carbon atoms. The acyl group of this monocarboxylic acid can be either linear or branched. Examples of aliphatic monocarboxylic acids include: valeric acid, hexanoic acid, octanoic acid, heptanoic acid, nonanoic acid, decanoic acid, undecanoic acid, lauric acid, myristic acid, undecenoic acid, linderic acid, tsuzuic acid, physeteric acid, myristoleic acid, sorbic acid, and sabinic acid. These aliphatic monocarboxylic acids can be used individually or in combination during esterification. The number of carbon atoms in the aliphatic monocarboxylic acid is more preferably in the range of 5 to 12. If the number of carbon atoms in the aliphatic monocarboxylic acid is 5 or more, the flash point of the resulting hindered ester is higher, which is therefore more preferable. If the number of carbon atoms in the aliphatic monocarboxylic acid is 15 or less, the solubility parameter of the resulting hindered ester can be improved, which is also more preferable in this respect. The number of carbon atoms in the aliphatic monocarboxylic acid is further preferably in the range of 6 to 10, and most preferably in the range of 7 to 9.

[0055] It should be noted that the carbon atom number of the fatty acids mentioned above also includes the carbon atom of the carboxyl group (-COOH) present in the fatty acid.

[0056] 2-1-2. Dicarboxylate

[0057] The ester-based base oil contained in the magnetic viscous fluid of this embodiment will be described in detail using a dicarboxylic acid ester as an example.

[0058] Examples of esters include dicarboxylic acids with 2 to 10 carbon atoms and esters of alcohols with 1 to 10 carbon atoms.

[0059] Examples of dicarboxylic acids with 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, octanoic acid, azelaic acid, and sebacic acid; and aromatic dicarboxylic acids such as phthalic acid, isophthalic acid, and terephthalic acid.

[0060] Examples of alcohols with 1 to 10 carbon atoms include methanol, ethanol, propanol, isopropanol, butanol, isobutanol, hexanol, octanol, 2-ethylhexanol, isononol, decanol, and isodecanol. Among the aforementioned diesters, diisobutyl adipate, di(2-ethylhexyl) adipate (DOA), diisodecyl adipate (DIDA), diisononyl adipate (DINA), bis(2-ethylhexyl) azelaate (DOZ), and di(2-ethylhexyl) sebacate (DOS) are preferred diesters of dicarboxylic acids with 6 to 10 carbon atoms and alcohols with 4 to 10 carbon atoms. Each of these dicarboxylic acids and alcohols can be used individually or in combination during esterification.

[0061] It should be noted that, unless otherwise specified, in this invention, the carbon atom number of aliphatic dicarboxylic acids also includes the carbon atom of the carboxyl group (-COOH) present in the aliphatic dicarboxylic acid. Dicarboxylic acid esters can be used alone or in combination with two or more.

[0062] The kinematic viscosity of the ester-based base oil contained in the magnetic viscous fluid of this embodiment is preferably 50.0 mm at 40°C. 2 / s or less, more preferably 10.0 to 50.0 mm 2 The range of / s is preferably 10.0 to 40.0 mm. 2 The range is defined by setting the kinematic viscosity of the ester-based base oil at 40°C to 50.0 mm². 2 Below / s, it is easier to disperse magnetic particles, and in this respect, it is more preferable.

[0063] It should be noted that the kinematic viscosity is measured according to JIS K2283:2000 (kinematic viscosity test method).

[0064] The flash point of the ester-based base oil contained in the magnetic viscous fluid of this embodiment is preferably 200°C or higher, and more preferably 250°C or higher.

[0065] If the flash point of the base oil is above 200°C, the base oil composition is classified as a Group III to Group IV petroleum product under the Fire Protection Act, thus allowing for an increase in the permitted quantity of hazardous materials used (specified quantity), which is preferable in this respect. It should be noted that the flash point is determined according to JIS K2265-4:2007 (Cleveland open-cup method).

[0066] The pour point of the ester-based base oil contained in the magnetic viscous fluid of this embodiment is preferably below -10°C, more preferably below -20°C, particularly preferably below -30°C, and most preferably below -50°C. A pour point of below -10°C results in excellent low-temperature fluidity, which is even more desirable in this respect. It should be noted that the pour point is the pour point measured according to JIS K2269:1987.

[0067] The preferred solubility parameter for ester-based base oils is 8.5–12.0 (cal / cm³). 3 ) 1 / 2 The range is more preferably 8.8–11.0 (cal / cm³). 3 ) 1 / 2 The optimal range is 9.0–10.0 (cal / cm³). 3 ) 1 / 2 The range. By setting the solubility parameter to 8.5 (cal / cm³). 3 ) 1 / 2 The above allows for incompatibility between ester-based base oils and the silicone oils described later, which is preferable in this respect. If the solubility parameter is 12.0 (cal / cm³),... 3 ) 1 / 2 The following can improve the heat resistance of ester-based base oils, and are therefore preferred in this respect.

[0068] 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)". That is, it can be calculated based on the following formula (B).

[0069] SP value δ=(Σ△e / Σ△v) 1 / 2 ……(B)

[0070] (In the above formula (B), Δe is the evaporation energy of each atom or group of atoms at 25℃, and Δv is the molar volume of each atom or group of atoms at the same temperature.)

[0071] 2-2. Non-polar base oils

[0072] The non-polar base oil contained in the magnetic viscous fluid of this embodiment is a non-polar oiling agent composed only of carbon and hydrogen. Examples include: paraffinic mineral oils, naphthenic mineral oils, polyalphaolefins (PAO), alpha-olefins, synthetic naphthenic oils, polybutene oils, etc. Among them, polyalphaolefins have excellent heat resistance and a high viscosity index, and are therefore preferred. These non-polar base oils can be used alone or in combination of two or more.

[0073] Among them, cycloalkane mineral oils preferably include compounds having rings selected from cyclohexane, bicycloheptane, and bicyclooctane rings.

[0074] Polyalphaolefins are polyalphaolefins or their hydrides obtained by polymerizing at least one alpha olefin in the range of degree of polymerization 2 to 10.

[0075] Polyalphaolefins can be homopolymers of alphaolefins, copolymers of two or more alphaolefins, or hydrides of them.

[0076] The α-olefin used as a raw material can be straight-chain or branched, but straight-chain is preferred. The number of carbon atoms in the α-olefin is not particularly limited, but is preferably 8 to 12, and more preferably 10. Examples of straight-chain α-olefins with 8 to 12 carbon atoms include: 1-octene (8 carbon atoms), 1-nonene (9 carbon atoms), 1-decene (10 carbon atoms), 1-undecene (11 carbon atoms), and 1-dodecene (12 carbon atoms). If the α-olefin used as a raw material has 8 to 12 carbon atoms, the resulting polyα-olefin has a higher flash point and excellent flowability in the low-temperature region, which is therefore preferred.

[0077] The content of nonpolar base oil in the magnetic viscous fluid of this embodiment is controlled with an upper and lower limit such that the nonpolarity index of the base oil is in the range of 10 to 45. The content of this nonpolar base oil can typically be appropriately set from 3 to 20% by mass, preferably 4 to 15% by mass, and more preferably 4 to 10% by mass.

[0078] In this embodiment, the kinematic viscosity of the non-polar base oil contained in the magnetic viscous fluid is preferably 50.0 mm at 40°C. 2 / s or less, more preferably 10.0 to 50.0 mm 2 The range of / s is preferably 10.0 to 40.0 mm. 2 The range is defined by setting the kinematic viscosity of the non-polar base oil at 40°C to 50.0 mm². 2 Below / s, it is easier to disperse magnetic particles, and in this respect, it is more preferable.

[0079] It should be noted that the kinematic viscosity is measured using the same method as that for ester-based base oils.

[0080] The flash point of the non-polar base oil contained in the magnetic viscous fluid of this embodiment is preferably 200°C or higher, and more preferably 250°C or higher.

[0081] If the flash point of the base oil is above 200°C, the base oil composition is classified as a Group III to Group IV petroleum product under the Fire Protection Law, thus allowing for an increase in the permitted quantity of hazardous materials used (specified quantity), which is preferable in this respect. It should be noted that the flash point is determined using the same method as for ester-based base oils.

[0082] The pour point of the nonpolar base oil contained in the magnetic viscous fluid of this embodiment is preferably below -10°C, more preferably below -20°C, particularly preferably below -30°C, and most preferably below -50°C. A pour point of below -10°C results in excellent low-temperature fluidity, which is even more desirable in this respect. It should be noted that the pour point is determined using the same method as for ester-based base oils.

[0083] Without impairing the effects of the present invention, the magnetic viscous fluid of the present invention may further contain other base oils besides ester-based base oils and non-polar base oils. Examples of base oils other than ester-based and non-polar base oils include: higher fatty acids, higher alcohols, polyols, ether-based base oils, etc.

[0084] 2-3. Alkylbenzenes having alkyl groups with 10 to 24 carbon atoms, and alkylnaphthalenes having alkyl groups with 10 to 24 carbon atoms.

[0085] The magnetic viscous fluid of this embodiment is preferably an alkylbenzene having an alkyl group having 10 to 24 carbon atoms, and / or an alkylnaphthalene having an alkyl group having 10 to 24 carbon atoms. Alkylbenzene and alkylnaphthalene can be used individually or in combination. Alkylbenzene and alkylnaphthalene function as lubricating aids to enhance the lubricity of the magnetic viscous fluid. Furthermore, both alkylbenzene and alkylnaphthalene are polar and readily compatible with ester-based base oils.

[0086] Alkylbenzenes having an alkyl group having 10 to 24 carbon atoms are aromatic hydrocarbons having an alkyl group having 10 to 24 carbon atoms bonded to a benzene ring. This alkyl group can be straight-chain or branched. Furthermore, a single alkyl group or multiple alkyl groups can be bonded to the benzene ring. Examples of alkylbenzenes include monoalkylbenzenes, dialkylbenzenes, trialkylbenzenes, and tetraalkylbenzenes. The alkyl group in the alkylbenzene preferably has 10 to 20 carbon atoms, more preferably 12 to 18 carbon atoms, and even more preferably 13 to 18 carbon atoms.

[0087] The alkylbenzene is preferably formed by bonding 1 to 4 alkyl groups to a benzene ring. Furthermore, the alkylbenzene is preferably an alkylbenzene in which the total number of carbon atoms of the alkyl groups bonded to the benzene ring is 10 to 40, more preferably an alkylbenzene in which the total number of carbon atoms of the alkyl groups is 10 to 30, and even more preferably an alkylbenzene in which the total number of carbon atoms of the alkyl groups is 10 to 20.

[0088] Examples of such alkyl groups include: decyl, undecyl, dodecyl, tridecyl, tetradecyl, heptadecanyl, octadecyl, nonadecanyl, eicosyl, dodecyl, tridecyl, tetradecyl, etc.

[0089] Alkylbenzenes having 10 to 24 carbon atoms can be used alone or in combination with two or more.

[0090] As a specific example of an alkylbenzene having an alkyl group having 10 to 24 carbon atoms in the magnetic viscous fluid used in this embodiment, there is no particular limitation as long as the alkylbenzene functions as a lubricating aid as described above. Examples include: decylbenzene, undecylbenzene, dodecylbenzene, tridecylbenzene, tetradecylbenzene, hexadecylbenzene, heptadecanylbenzene, octadecylbenzene, nonadecanylbenzene, eicosylbenzene, dodecylbenzene, dodecylbenzene, tridecylbenzene, tetradecylbenzene, etc.

[0091] Alkylnaphthalenes having an alkyl group having 10 to 24 carbon atoms are aromatic hydrocarbons having an alkyl group bonded to a naphthalene ring. Examples of such alkyl groups include those bonded to the alkylbenzenes described above. The naphthalene ring may have one or more alkyl groups having 10 to 24 carbon atoms bonded to it.

[0092] The alkyl group in the alkyl naphthalene preferably has 10 to 24 carbon atoms, more preferably 12 to 18 carbon atoms, and even more preferably 13 to 18 carbon atoms. As an alkyl naphthalene, it is preferably an alkyl naphthalene formed by bonding 1 to 4 alkyl groups having 10 to 24 carbon atoms to a naphthalene ring.

[0093] Alkyl naphthalenes having 10 to 24 carbon atoms can be used alone or in combination with two or more.

[0094] As a specific example of alkylnaphthalene used in the magnetic viscous fluid of this embodiment, there is no particular limitation as long as the alkylnaphthalene functions as a lubricating aid as described above. Examples include: decylnaphthalene, undecylnaphthalene, dodecylnaphthalene, tridecylnaphthalene, tetradecylnaphthalene, heptadecanylnaphthalene, hexadecylnaphthalene, octadecylnaphthalene, nonadecanylnaphthalene, eicosylnaphthalene, dodecylnaphthalene, dodecylnaphthalene, tridecylnaphthalene, tetradecylnaphthalene, etc.

[0095] Regarding the lower limit of the content of alkylbenzene having an alkyl group having 10 to 24 carbon atoms or alkylnaphthalene having an alkyl group having 10 to 24 carbon atoms, or the content of their combined amount when both alkylbenzene and alkylnaphthalene are included, relative to the total amount of the base oil of the magnetic viscous fluid of this embodiment, it is preferably 5% by mass or more, more preferably in the range of 5 to 25% by mass, further preferably in the range of 10 to 25% by mass, and most preferably in the range of 10 to 20% by mass. By setting this content to 5% by mass or more, the lubricity of the magnetic viscous fluid can be further improved, and thus the polarity of the magnetic viscous fluid can be further improved. By setting this content to 25% by mass or less, excessive reduction in the content of the ester base oil can be prevented, and the reduction in the sedimentation inhibition effect of magnetic particles can be prevented.

[0096] In this embodiment, the kinematic viscosity of the base oil contained in the magnetic viscous fluid is preferably 50.0 mm at 40°C. 2 / s or less, more preferably 10.0 to 40.0 mm 2 The range is defined by setting the kinematic viscosity of the base oil at 40°C to 50.0 mm². 2 Below / s, it is easier to disperse magnetic particles, and in this respect, it is more preferable.

[0097] It should be noted that the kinematic viscosity is measured using the same method as that for ester-based base oils.

[0098] The flash point of the base oil contained in the magnetic viscous fluid of this embodiment is preferably 200°C or higher, and more preferably 250°C or higher.

[0099] If the flash point of the base oil is above 200°C, the base oil composition is classified as a Group III to Group IV petroleum product under the Fire Protection Law, thus allowing for an increase in the permitted quantity of hazardous materials used (specified quantity), which is preferable in this respect. It should be noted that the flash point is determined using the same method as for ester-based base oils.

[0100] The base oil contained in the magnetic viscous fluid of this embodiment includes ester-based base oil, non-polar base oil, and specific alkylbenzenes and alkylnaphthalenes added as needed. In this case, the flash point refers to the flash point calculated based on the Flash-Point Blending Index (FPI). Hereinafter, when referred to simply as "flash point," this flash point will be used.

[0101] The flash point mixing index used to calculate the flash point is determined according to the flash point mixing index table described in Hydrocarbon Processing & Petroleum Refiner, June 1963, Vol. 42, No. 6. For example, the flash point of the mixture when oil A with a flash point of 190℉ (87.8℃) and oil B with a flash point of 330℉ (165.6℃) are mixed in a volume ratio of 30:70 is calculated as follows. Based on the flash point mixing index table described in the above literature, the FPI of oil A is 30 and the FPI of oil B is 1.0. If the FPI of the mixture is calculated based on the FPI of each oil, then "the FPI of the mixture = (30 / 100) × (30) + (70 / 100) × (1.0) = 9.7". If this FPI of 9.7 is applied to the flash point mixing index, the estimated flash point corresponding to FPI 9.7 is approximately 230℉ (110℃).

[0102] The pour point of the base oil contained in the magnetic viscous fluid of this embodiment is preferably below -10°C, more preferably below -20°C, particularly preferably below -30°C, and most preferably below -50°C. A pour point below -10°C results in excellent low-temperature fluidity, which is even more desirable in this respect. It should be noted that the pour point is determined using the same method as for ester-based base oils.

[0103] In this embodiment, the base oil content in the magnetic viscous fluid is preferably 10% by mass or more relative to the total amount of the magnetic viscous fluid, more preferably in the range of 10% to 70% by mass, further preferably in the range of 20% to 70% by mass, and most preferably in the range of 20% to 60% by mass. Setting the base oil content to 10% by mass or more allows for the dispersion of magnetic particles and improves fluidity. Setting the base oil content to 70% by mass or less improves the magnetic properties during excitation, which is more preferable in this respect.

[0104] 3. Inorganic cation exchangers with siloxane bonds, silicone oil

[0105] The magnetic viscous fluid in this embodiment preferably further contains an inorganic cation exchanger having siloxane bonds and silicone oil. With this configuration, the magnetic viscous fluid exhibits increased resistance during excitation.

[0106] More specifically, the magnetic particles are dispersed in the base oil. Because the magnetic particles are cationic, they adsorb inorganic cation exchangers with siloxane bonds. Furthermore, silicone oil has a low surface energy and is insoluble in ester-based base oils with high solubility parameters, thus dispersing in these oils. Moreover, since both the inorganic cation exchangers with siloxane bonds and the silicone oil contain silicon (Si), they have a high affinity, suggesting that the silicone oil exists in a state where it surrounds the magnetic particles adsorbed with the inorganic cation exchangers with siloxane bonds.

[0107] If a magnetic field is applied under these conditions, the magnetic particles surrounded by silicone oil rapidly combine and cluster together. The presence of silicone oil around the magnetic particles suppresses excessive aggregation. Therefore, it is hypothesized that when a magnetic field is applied and the resistance (viscosity) is measured, shear force is generated, but the clusters do not disintegrate, and the resistance remains stable.

[0108] <Inorganic cation exchangers with siloxane bonds>

[0109] Examples of inorganic cation exchangers containing siloxane bonds include zeolites, silica, and layered silicates. Zeolites are preferred if wear resistance is a consideration. One type of inorganic cation exchanger containing siloxane bonds can be used alone, or two or more can be used in combination. Both natural and synthetic products can be used.

[0110] Zeolites consist of an anionic, crystalline, porous aluminosilicate framework and cationic metal elements M adsorbed onto this framework. More specifically, the zeolite has the following structure: using tetrahedral SiO4 and AlO4 as basic structural units, they are three-dimensionally linked to form a porous (void) crystal, in which water of crystallization and cationic metal elements M are adsorbed. The crystal structure of zeolites is not particularly limited; examples include: type A zeolites, type X zeolites, type Y zeolites, type L zeolites, type β zeolites, ZSM-5, ZSM-11, silica zeolites, magnesium alkali zeolites, mordenite, clinoptilolite, and paulingite, etc.

[0111] Layered silicates are silicate compounds with a crystal structure formed by the weak bonding of layers composed of ionic bonds. Most layered silicates carry a negative charge throughout their layers, with large cations entering the interlayer spaces to neutralize this negative charge. Due to the small layer charge, these cations can exchange with cations in solution, exhibiting cation exchange properties. Examples of layered silicates include: smectite (bentonite, montmorillonite, beidellite, chlorite, soapstone, lithium montmorillonite, magnesium-rich montmorillonite), vermiculite, kaolinite (kaolinite, halloysite, fibrous serpentine, magnesium chlorite), mica (mica, biotite, ferromica, phlogopite, silicomica, sodium mica, sideerophyllite, magnesium-rich biotite, polysiliconized lepidolite, lithium muscovite, lepidolite, lepidolite, pearlite, illite, rimstone), talc, palygorskite, sepiolite, magadiite, hygroscopic sodium silicate, kenyaite, and synthetic fluoromica. From the perspective of ion exchange capacity, smectite, vermiculite, and synthetic fluoromica are preferred.

[0112] The cation exchange capacity of the inorganic cation exchanger with siloxane bonds is preferably 30 meq / 100g or more, more preferably in the range of 30 to 400 meq / 100g, even more preferably in the range of 60 to 350 meq / 100g, even more preferably in the range of 60 to 300 meq / 100g, and most preferably in the range of 60 to 150 meq / 100g.

[0113] As inorganic cation exchangers with siloxane bonds, the cation exchange capacity is as follows: mordenite is 260 meq / 100g, synthetic fluoromica is 120 meq / 100g, montmorillonite is 60–150 meq / 100g, montmorillonite is 80–150 meq / 100g, and vermiculite is 100–150 meq / 100g.

[0114] The content of the inorganic cation exchanger with siloxane bonds is preferably 0.8% by mass or more relative to the total amount of the magnetic viscous fluid in this embodiment, more preferably in the range of 0.8 to 4.0% by mass, even more preferably in the range of 1.0 to 3.5% by mass, and most preferably in the range of 1.3 to 3.0% by mass. Setting the content to 0.8% by mass or more can suppress the aggregation of magnetic particles even without the application of a magnetic field, which is more preferable in this respect. Setting the content to 4.0% by mass or less can appropriately form clusters of magnetic particles when a magnetic field is applied, which is more preferable in this respect.

[0115] Silicone oil

[0116] Silicone oils can be used without particular restrictions as long as they are incompatible with ester-based base oils. Silicone oils are broadly classified into pure silicone oils and modified silicone oils. Examples of pure silicone oils include dimethyl silicone oil, methylphenyl silicone oil, and methylhydrosilicone oil. Examples of modified silicone oils include reactive silicone oils and non-reactive silicone oils. Reactive silicone oils include various types such as amino-modified, epoxy-modified, carboxyl-modified, methanol-modified, methacrylic-modified, mercapto-modified, and phenol-modified silicone oils. Non-reactive silicone oils include polyether-modified, methylstyrene-modified, alkyl-modified, higher fatty acid ester-modified, hydrophilic special-modified, higher fatty acid-containing, and fluorine-modified silicone oils. Among these, dimethyl silicone oil and fluorine-modified silicone oils are preferred due to their low surface energy; however, dimethyl silicone oil is more preferred considering its availability.

[0117] The lower limit of the silicone oil content relative to the total amount of the magnetoviscous fluid in this embodiment is preferably 0.5% by mass or more, more preferably 0.5 to 3.0% by mass, and most preferably 1.0 to 2.5% by mass. Setting the content to 0.5% by mass or more allows for the encapsulation of magnetic particles with attached inorganic cation exchangers having siloxane bonds, which is more preferable in this respect. Setting the content to 3.0% by mass or less prevents a decrease in the dispersibility of the magnetic particles, which is more preferable in this respect.

[0118] The ratio of the inorganic cation exchanger with siloxane bonds to the silicone oil is preferably in the range of 2:8 to 8:2 by mass, and more preferably in the range of 3:7 to 7:3.

[0119] If the ratio is in the range of 2:8 to 8:2, the stability of the resistance during excitation can be improved over time, which is even better in this respect.

[0120] The absolute value of the difference in solubility parameters between ester-based base oils and silicone oils is preferably 1.3 (cal / cm³). 3 ) 1 / 2 The above, more preferably 1.5 (cal / cm) 3 ) 1 / 2 The above, especially preferred, is 1.8 (cal / cm). 3 ) 1 / 2 The above. If the absolute value of the difference in solubility parameters between ester-based base oils and silicone oils is 1.3 (cal / cm³), then... 3 ) 1 / 2 The above can improve the incompatibility between ester-based base oils and silicone oils, and is therefore a better option in this respect.

[0121] <Other Ingredients>

[0122] Without impairing the effects of the invention, in addition to the components described herein, the magnetic viscous fluid of this embodiment may be combined with various other components depending on the purpose.

[0123] Other components include, for example: wear-resistant agents, dispersants, surfactants, viscosity modifiers, flowability enhancers, sedimentation inhibitors, pour point depressants, extreme pressure additives, rust inhibitors, antioxidants, corrosion inhibitors, metal deactivators, defoamers, etc.

[0124] Examples of wear-resistant agents include: sulfur compounds such as sulfides, sulfoxides, sulfones, and thiophosphates; halogen compounds such as chlorinated hydrocarbons; and organometallic compounds such as molybdenum dithiophosphate (MoDTP), molybdenum dithiocarbamate (MoDTC), and tricresyl phosphate.

[0125] Abrasion-resistant agents can be used alone or in combination with two or more.

[0126] Dispersants are added to improve the dispersibility of magnetic particles in base oils. Examples include well-known low-molecular-weight dispersants and high-molecular-weight dispersants. A single dispersant can be used, or two or more can be used in combination.

[0127] Examples of viscosity modifiers include: castor oil, hydrogenated castor oil, fatty acid amides, beeswax, carnauba wax, benzyl sorbitol, metal soaps, oxidized polyethylene, sulfate-based anionic surfactants, polyolefins, (meth)acrylates, polyisobutylene, ethylene-propylene copolymers, and polyalkyl styrene.

[0128] Viscosity modifiers can be used alone or in combination with two or more.

[0129] Modified silicone oils can be used as flow improvers. Examples include modified silicone oils obtained by modifying pure silicone oil with alkyl groups, aralkyl groups, polyethers, higher fatty acid esters, amino groups, epoxy groups, carboxyl groups, alcohols, etc. It should be noted that modified silicone oils can be compatible with ester-based base oils. Flow improvers can be used alone or in combination with two or more.

[0130] <Viscosity of Magnetoviscous Fluids>

[0131] The pre-excitation viscosity of the magnetic viscous fluid in this embodiment is preferably in the range of 0.02 to 1.0 Pa·s at 40°C, and more preferably in the range of 0.03 to 0.6 Pa·s. It should be noted that the measurement conditions for the pre-excitation viscosity are as follows.

[0132] 3 ml of magnetic viscous fluid was injected into the test plate of a TA Instruments DHR-2 rheometer equipped with a magnetic measurement option, and the viscosity (Pa·s) was measured at 40°C with a 100 μm gap and 20 revolutions.

[0133] <Magnetic Properties of Magnetoviscous Fluids>

[0134] As described above, the magnetic viscous fluid of this embodiment has the characteristic of high resistance during excitation. High resistance during excitation means that, in the magnetic viscous fluid of the present invention, the maximum viscosity during excitation is 230 Pa·s or more under the following conditions when the content of magnetic particles in the total amount of magnetic viscous fluid is 64-67% by mass. Furthermore, the maximum viscosity during excitation is preferably 230 Pa·s or more, and more preferably 240 Pa·s or more.

[0135] Furthermore, as described above, by further including an inorganic cation exchanger with siloxane bonds and silicone oil, excellent long-term stability of the excitation resistance (viscosity long-term stability) can be obtained. Excellent long-term stability of the excitation resistance (viscosity long-term stability) means that the stabilization rate B, described later, is 80% or more. Furthermore, the stabilization rate A is preferably 70% or more, more preferably 80% or more, and particularly preferably 90% or more.

[0136] Viscosity during excitation refers to the viscosity measured using the same measuring device as the viscosity measured before excitation, under the same temperature environment, with a DC magnetic field of 0.8T applied 5 seconds after the start of the measurement, and the application of the magnetic field stopped 215 seconds after the start of the measurement, for a period of 210 seconds after the magnetic field is applied.

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

[0138] Stabilization rate A (%) = (Stabilization time A / Total application time) × 100

[0139] It should be noted that the stabilization time A represents the application time equivalent to 95-100% of the maximum viscosity during excitation.

[0140] The stabilization rate B (%) is calculated based on the following formula.

[0141] Stabilization rate B (%) = (Stabilization time B / Total application time) × 100

[0142] It should be noted that the stabilization time B represents the application time equivalent to 90-100% of the maximum viscosity during excitation.

[0143] (Method for manufacturing magnetic viscous fluids)

[0144] The method for manufacturing the magnetic viscous fluid in this embodiment is not particularly limited. For example, a method can be described as follows: magnetic particles, ester-based base oil, non-polar base oil, further, if necessary, alkyl naphthalene, an inorganic cation exchanger having siloxane bonds, silicone oil, and other components added as needed are mixed in predetermined amounts using a homogenizer, bead mill, mechanical mixer, or other processing equipment capable of imparting high shear force. In this case, the ester-based base oil and non-polar base oil are mixed such that the non-polarity index formed by the ester-based base oil and non-polar base oil is within a specific range. It should be noted that heating or cooling can be performed as needed during the manufacturing of the magnetic viscous fluid.

[0145] (Mechanical devices using magnetic viscous fluid)

[0146] The magnetic viscous fluid of this embodiment can be applied to various mechanical devices such as brakes, clutches, vibration damping devices, and dampers used to control friction between objects. With this configuration, the magnetic viscous fluid exhibits good resistance during excitation in various mechanical devices and effectively suppresses the deterioration of rubber in contact with the magnetic viscous fluid.

[0147] [Example]

[0148] The following are embodiments of the invention, but these embodiments are provided to better understand the invention and its advantages and are not intended to limit the invention.

[0149] <Examples 1-14, Comparative Examples 1-3>

[0150] The components shown in Tables 1-3 were placed in beakers according to the recorded mass ratios, and stirred at 40 Hz for 5 minutes at room temperature using a Seiko Advance AD-MIX universal vibratory stirrer to produce a magnetoviscous fluid. The raw materials for the components shown in Tables 1-3 are as follows.

[0151] (A) Magnetic particles

[0152] (a1) Carbonyl iron (average particle size D50 = 6.0 μm).

[0153] (B) Ester-based base oils

[0154] <Hindered Ester>

[0155] (b1) Trimethylolpropane trioctanoate (SP value: 9.1 (cal / cm) 3 ) 1 / 2 The kinematic viscosity at 40°C is 16.0 mm. 2 / s, flash point 260℃, pour point -57℃).

[0156] <Dice Ester>

[0157] (b2) Di(2-ethylhexyl) sebacate (SP value: 8.9 (cal / cm) 3 ) 1 / 2 The kinematic viscosity at 40℃ is 11.3 mm. 2 / s, flash point 228℃, pour point -66℃).

[0158] (b3) Di(2-ethylhexyl) adipic acid (SP value: 8.9 (cal / cm) 3 ) 1 / 2 The kinematic viscosity at 40℃ is 7.8 mm. 2 / s, flash point 205℃, pour point -68℃).

[0159] (b4) Diisodecyl adipate (SP value: 8.9 (cal / cm) 3 ) 1 / 2 The kinematic viscosity at 40℃ is 14.2 mm. 2 / s, flash point 232℃, pour point -63℃).

[0160] (C) Non-polar base oil

[0161] (c1) Trimer of polyalphaolefin (1-decene), kinematic viscosity at 40°C: 17.2 mm. 2 / s, flash point 222℃, pour point -68℃).

[0162] (D) Alkylnaphthalene

[0163] (d1) Monoalkyl naphthalenes having alkyl groups with 16-18 carbon atoms (kinematic viscosity at 40°C: 37.0 mm) 2 / s, flash point 221℃, pour point below -25℃).

[0164] (E) Inorganic cation exchangers with siloxane bonds

[0165] (e1) Zeolite (crystal structure: mordenite system, cation exchange capacity: 160-190 meq / 100g).

[0166] (F) Silicone oil

[0167] (f1) Dimethyl silicone oil (SP value: 7.2 (cal / cm) 3 ) 1 / 2 Kinematic viscosity at 40℃: 37.8 mm 2 / s).

[0168] <Evaluation of Rubber Resistance Properties>

[0169] In the magnetic viscous fluids of Examples 1-14 and Comparative Examples 1-3, solutions with magnetic particles removed were prepared as solutions for evaluating rubber resistance properties. 300 ml of each solution was placed in a 500 cc beaker. Furthermore, NBR manufactured by AS-ONE was separately cut into short strips with a width × length × thickness of 10 mm × 60 mm × 5 mm.

[0170] Next, the solutions for evaluating rubber resistance properties were placed in a convection oven (Advantest DRF633TA) heated to 100°C and left for 24 hours. Then, the short strips of NBR were placed in the beakers to serve as test subjects.

[0171] After the test subject was placed in the convection oven for 480 hours, the beaker was removed, and the NBR immersed in the magnetoviscous fluid was taken out. Oil on the surface of the NBR was removed using Kimwipe (registered trademark) S200 manufactured by NIPPON PAPER CRECIA. Then, the hardness (hardness after heating) of the NBR was measured using the method described later. Furthermore, the hardness (initial hardness) of the short strip-shaped NBR before being placed in the beaker was also measured using the same method.

[0172] • Hardness determination: The hardness was determined using the DUROMETER ADM-E manufactured by Niigata Seiki Co., Ltd., according to JISK 6253.

[0173] For the test subjects of Examples 1-14 and Comparative Examples 1-3, three samples were prepared for each, and the above-described evaluation of rubber resistance properties was performed on all samples under the same conditions. The average of the hardness measurement results of NBR in these three samples was calculated. The calculation results are shown in Tables 1 and 2.

[0174] Next, the hardness change rate is calculated using the formula described later. The calculation results are shown in Tables 1 and 2.

[0175] • Hardness change rate = {(Hardness after heating - Initial hardness) / Initial hardness} × 100 (%)

[0176] It should be noted that in Tables 1 and 2, "-" indicates shrinkage and "+" indicates swelling in the hardness change rate.

[0177] <Evaluation of viscosity before and during excitation>

[0178] Three ml of the magnetic viscous fluids from Examples 1-7 and Comparative Examples 1-2 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 measuring apparatus at 40°C under the following conditions.

[0179] Excitation conditions for the magnetic field: Apply a DC magnetic field of 0.8T 5 seconds after the start of the measurement, and stop applying the magnetic field 215 seconds after the start of the measurement.

[0180] Regarding the magnetoviscous fluids of Examples 1-7 and Comparative Examples 1-2, as described above, three samples were prepared respectively, and the above-described evaluations of pre-excitation viscosity and viscosity during excitation were performed on all samples under the same conditions. The average of the measured results of the pre-excitation viscosity and viscosity during excitation of the NBR in these three samples was calculated. The calculation results are shown in Table 3.

[0181] The stability over time was evaluated based on the stabilization rates A (%) and B (%) calculated using the following formula. The calculation results are shown in Table 3.

[0182] Stabilization rate A (%) = (Stabilization time A / Total application time) × 100

[0183] It should be noted that the stabilization time A represents the application time equivalent to 95-100% of the maximum viscosity during excitation.

[0184] Stabilization rate B (%) = (Stabilization time B / Total application time) × 100

[0185] It should be noted that the stabilization time B represents the application time equivalent to 90-100% of the maximum viscosity during excitation.

[0186] [Table 1]

[0187]

[0188] [Table 2]

[0189]

[0190] [Table 3]

[0191]

[0192] Examples 1-14 are all magnetoviscous fluids containing magnetic particles and base oil. The base oil includes ester-based base oil and non-polar base oil, with a non-polarity index ranging from 10 to 45. Therefore, in Examples 1-7, the maximum viscosity during excitation is above 230 Pa·s, indicating good resistance during excitation. Furthermore, in Examples 1-14, the absolute value of the hardness change rate of the NBR is less than 5%, demonstrating good rubber resistance.

[0193] Furthermore, in Examples 1 to 7, the stabilization rate B is above 80%, exhibiting good long-term stability of the excitation resistance.

[0194] On the other hand, since the magnetic viscous fluids in Comparative Examples 1 to 3 do not contain non-polar base oils, the hardness change rate of NBR is more than 9%, resulting in poor rubber resistance.

[0195] Figure 1 These are graphs showing the relationship between the nonpolarity index and the rate of change in hardness of NBR in Examples 1-4, 7-14, and Comparative Examples 1-3, as presented in Tables 1 and 2. Figure 1 The chart shows that if the nonpolarity index of the base oil is in the range of 10 to 45, the hardness change rate is less than 5%, indicating good rubber resistance.

Claims

1. A magnetically viscous fluid comprising magnetic particles and a base oil, wherein, The base oil comprises ester-based base oils and non-polar base oils. The ester-based base oil is selected from at least one of hindered esters and diesters. The nonpolar base oil contained in the magnetic viscous fluid accounts for 3-20% by mass. The base oil has a nonpolarity index in the range of 10 to 45.

2. The magnetic viscous fluid according to claim 1, further comprising: Alkylbenzene having an alkyl group having 10 to 24 carbon atoms, and / or alkylnaphthalene having an alkyl group having 10 to 24 carbon atoms.

3. The magnetic viscous fluid according to claim 1, further comprising: Inorganic cation exchangers and silicone oils containing siloxane bonds.

4. A mechanical device that uses the magnetic viscous fluid as described in any one of claims 1 to 3.

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