Magnetorheological fluid and brake device

Abstract

Provided are: a magnetorheological fluid which is capable of achieving both high reliability and high excitation stress even when used at low temperatures or high temperatures; and a brake device which is provided with the magnetorheological fluid. The magnetorheological fluid includes: metal magnetic particles, the surface of which is modified at an ionic liquid modification site including a first cation group and a first anion group; and an ionic liquid dispersion medium containing a second cation group and a second anion group, the first cation group and the second cation group being cations of the same kind and being selected from the group consisting of quaternary ammonium ions, imidazolium ions, pyridinium ions, and phosphonium ions, the first anion group and the second anion group are selected from the group consisting of tetrafluoroboric acid ions, hexafluorophosphoric acid ions, tris (pentafluoroethyl) trifluorophosphoric acid ions, bis (trifluoromethylsulfonyl) amide ions, hydrogen phthalate ions, and bis (fluorosulfonyl) imide ions.

Description

TECHNICAL FIELD

[0001] The present application relates to a magnetorheological fluid and a brake device. BACKGROUND

[0002] A magnetorheological fluid (MR fluid) is a fluid in which magnetic particles are dispersed in a dispersion medium such as mineral oil or silicone oil. If a magnetic field is applied to the magnetorheological fluid, the metal magnetic particles are magnetized and aligned in the direction of the magnetic field to form chain-like clusters. As a result, the viscosity of the magnetorheological fluid increases, and the yield stress becomes high.

[0003] Research is being conducted on the application of such a magnetorheological fluid to various fields such as control devices such as dampers, brake devices such as brakes or clutches, and the like.

[0004] In these applications, as the temperature range in which the magnetorheological fluid is used, a range of -10°C to 100°C is assumed. Therefore, it is required that the magnetorheological fluid maintain the physical properties not only at normal temperature but also at low temperature or high temperature.

[0005] In Patent Literature 1, a magnetorheological fluid is assumed to be used at a high temperature of 200°C, and as a solution to suppress evaporation of the magnetorheological fluid, an ionic liquid is used in the dispersion medium.

[0006] PRIOR ART DOCUMENTS

[0007] PATENT LITERATURE

[0008] Patent Literature 1: Japanese Patent Application Laid-Open No. 2010-504635

[0009] From the viewpoint of further expanding the range of use of the magnetorheological fluid, it is required that, even in the case of use at low temperature or high temperature, high reliability is ensured while suppressing the aggregation and sedimentation of the magnetic particles, and a high magnetic excitation stress (excitation stress) is exhibited. SUMMARY

[0010] The magnetorheological fluid according to an application example of the present application contains:

[0011] metal magnetic particles, the surface of which is modified at an ionic liquid modification site having a first cationic group and a first anionic group; and

[0012] an ionic liquid dispersion medium having a second cationic group and a second anionic group,

[0013] the first cationic group and the second cationic group are the same kind of cation as each other, and are selected from the group consisting of a quaternary ammonium ion, an imidazolium ion, a pyridinium ion, and a phosphonium ion,

[0014] The first anion group and the second anion group are each selected from the group consisting of tetrafluoroborate ion, hexafluorophosphate ion, tris(pentafluoroethyl)trifluorophosphate ion, bis(trifluoromethylsulfonyl)amide ion, hydrogen phthalate ion, and bisfluorosulfonylimide ion.

[0015] The application example of the present application relates to a brake device provided with:

[0016] a fixed portion;

[0017] a movable portion movable with respect to the fixed portion;

[0018] magnetorheological fluid of claim 1 or 2 held between the fixed portion and the movable portion; and

[0019] a magnetic field generating portion that applies a magnetic field to the magnetorheological fluid. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 is a schematic view showing a magnetorheological fluid relating to the embodiments.

[0021] Figure 2 is a longitudinal sectional view showing a brake device relating to the embodiments.

[0022] Figure 3 is Table 1 showing a production condition of a magnetorheological fluid and an evaluation result.

[0023] Figure 4 is Table 2 showing a production condition of a magnetorheological fluid and an evaluation result.

[0024] Figure 5 is Table 3 showing a production condition of a magnetorheological fluid and an evaluation result.

[0025] Figure 6 is Table 4 showing a production condition of a magnetorheological fluid and an evaluation result.

[0026] Figure 7 is Table 5 showing a production condition of a magnetorheological fluid and an evaluation result.

[0027] Figure 8 is Table 6 showing a production condition of a magnetorheological fluid and an evaluation result.

[0028] EXPLANATION OF REFERENCE NUMERALS

[0029] 1: magnetorheological fluid, 2: metal magnetic particle, 3: non-magnetic particle, 4: ionic liquid dispersion medium, 100: brake device, 110: fixed disk, 120: movable disk, AX: rotation axis, H: magnetic field. DETAILED DESCRIPTION

[0030] Next, the magnetorheological fluid and the brake device according to the present application will be described in detail based on the embodiments shown in the drawings.

[0031] 1. Magnetorheological fluid

[0032] First, the magnetorheological fluid according to the embodiments will be described.

[0033] The magnetorheological fluid is a fluid that acts like a liquid when no magnetic field is applied and acts like a semi-solid when a magnetic field is applied. By utilizing such a change in viscosity, the stress of the magnetorheological fluid can be controlled. Therefore, the magnetorheological fluid can be used in various devices and the like that utilize a change in stress to exert various functions.

[0034] Figure 1 is a schematic view showing a magnetorheological fluid 1 according to the embodiments. Figure 1 The magnetorheological fluid 1 shown includes metal magnetic particles 2, non-magnetic particles 3, and an ionic liquid dispersion medium 4. The metal magnetic particles 2 and the non-magnetic particles 3 are dispersed substances dispersed in the ionic liquid dispersion medium 4. The non-magnetic particles 3 are provided as needed, and can be omitted.

[0035] The surface of the metal magnetic particles 2 is modified at an ionic liquid modification site having a first cationic group and a first anionic group.

[0036] The ionic liquid dispersion medium 4 has a second cationic group and a second anionic group.

[0037] The first cationic group possessed by the metal magnetic particles 2 and the second cationic group possessed by the ionic liquid dispersion medium 4 are the same kind of cation as each other, and are selected from the group consisting of a quaternary ammonium ion, an imidazolium ion, a pyridinium ion, and a phosphonium ion.

[0038] The first anionic group possessed by the metal magnetic particles 2 and the second anionic group possessed by the ionic liquid dispersion medium 4 are respectively selected from the group consisting of a tetrafluoroborate ion, a hexafluorophosphate ion, a tris(pentafluoroethyl)trifluorophosphate ion, a bis(trifluoromethylsulfonyl)amide ion, a hydrogen phthalate ion, and a bisfluorosulfonylimide ion.

[0039] According to such a configuration, good affinity of the metal magnetic particles 2 and the ionic liquid dispersion medium 4 can be maintained even at low temperatures or high temperatures. That is, in the magnetorheological fluid 1 in which the metal magnetic particles 2 modified at the ionic liquid modification site are dispersed in the ionic liquid dispersion medium 4, even in a severe environment, the settling or uneven distribution and the like of the metal magnetic particles 2 can be suppressed. As a result, a magnetorheological fluid 1 that maintains a good dispersed state of the dispersed substance regardless of the environment and exhibits a high magnetic excitation stress can be realized.

[0040] 1.1. Metal magnetic particles

[0041] The metal magnetic particle 2 has a particle main body made of a metal-based magnetic material and a surface modification film provided on the surface of the particle main body.

[0042] As the metal-based magnetic material, Fe-based metal materials, Ni-based metal materials, Co-based metal materials, and the like can be given, and one or two or more of them or a composite material thereof can be used. In addition, a composite material of these metal-based magnetic materials and an oxide-based magnetic material can also be used. Among them, from the viewpoint of high saturation magnetization, the metal-based magnetic material is preferably an Fe-based metal material.

[0043] The Fe-based metal material is a metal material in which Fe is a main component. The main component means that the content of Fe in the Fe-based metal material is 50% or more in terms of atomic ratio. Such an Fe-based metal material has high saturation magnetization, high toughness, and high strength as compared with ferrite and the like. Therefore, the Fe-based metal material is useful as a metal-based magnetic material.

[0044] The Fe-based metal material can contain an element that alone exhibits ferromagnetism such as Ni or Co in addition to Fe, and can contain at least one selected from the group consisting of Cr, Nb, Cu, Al, Mn, Mo, Si, Sn, B, C, P, Ti, and Zr depending on the characteristics targeted. In addition, the Fe-based metal material can contain unavoidable impurities within a range that does not impair the effects of the embodiments. The unavoidable impurities mean impurities that are unintentionally mixed in the raw material or during the manufacturing. As the unavoidable impurities, all elements other than the above-described elements can be given, and O, N, S, Na, Mg, K, and the like can be particularly given.

[0045] As such an Fe-based metal material, there is no particular limitation, and for example, in addition to pure iron, carbonyl iron, Fe-Si-Al-based alloys such as Fe-Si-Al-based alloys, Fe-Ni-based alloys, Fe-Co-based alloys, Fe-Ni-Co-based alloys, Fe-Si-B-based alloys, Fe-Si-Cr-B-based alloys, Fe-Si-B-C-based alloys, Fe-Si-B-Cr-C-based alloys, Fe-Si-Cr-based alloys, Fe-B-based alloys, Fe-P-C-based alloys, Fe-Co-Si-B-based alloys, Fe-Si-B-Nb-based alloys, Fe-Si-B-Nb-Cu-based alloys, Fe-Zr-B-based alloys, Fe-Cr-based alloys, Fe-Cr-Al-based alloys, and the like can be given.

[0046] Further, the metal-based magnetic material can be an amorphous metal material, a crystalline metal material, or a microcrystalline (nanocrystalline) metal material. Among them, the amorphous metal material or the microcrystalline metal material is preferably used. They contribute to sufficiently reducing the coercive force of the metal magnetic particle 2 and improving the redispersibility. Further, they have high toughness and strength compared to, for example, metal oxides, and thus can effectively suppress abrasion, damage, and the like of the metal magnetic particle 2. As a result, the magnetorheological fluid 1 in which the excitation stress is stable can be realized. Furthermore, the amorphous metal material and the microcrystalline metal material do not have grain boundaries or are micro, and thus corrosion starting from the grain boundaries is less likely to occur. Therefore, the corrosion resistance of the metal magnetic particle 2 is particularly improved. In addition, the microcrystalline metal material refers to a metal material in which microcrystals (nanocrystals) having a crystal grain diameter of 100 nm or less are present.

[0047] As the amorphous metal material, for example, an Fe-based amorphous alloy of a binary or multinary system such as Fe-Si-B system, Fe-Si-Cr-B system, Fe-Si-B-C system, Fe-Si-B-Cr-C system, Fe-Si-Cr system, Fe-B system, Fe-B-C system, Fe-P-C system, Fe-Co-Si-B system, Fe-Si-B-Nb system, Fe-Zr-B system, a Ni-based amorphous alloy such as Ni-Si-B system, Ni-P-B system, a Co-based amorphous alloy such as Co-Si-B system, and the like can be given.

[0048] As the microcrystalline metal material, for example, an Fe-based nanocrystalline alloy such as Fe-Si-B-Nb-Cu system, Fe-Zr-B system, Fe-Hf-B system, Fe-Nb-B system, Fe-Zr-B-Co system, Fe-Hf-B-Co system, Fe-Nb-B-Co system, Fe-Si-B-P-Cu system, and the like can be given.

[0049] The metal magnetic particle 2 can also be a particle manufactured by any method. As examples of the manufacturing method, in addition to various atomization methods such as water atomization method, gas atomization method, and rotary water stream atomization method, a pulverization method, a carbonyl method, and the like can be given. Among them, according to the atomization method, a particle shape closer to a true sphere is obtained. Such a particle is less likely to agglomerate.

[0050] The metal magnetic particle 2 can also include an oxide film provided between the particle main body and the surface modification film. The oxide film improves the adhesion of the surface modification film to the particle main body. Further, the oxide film can suppress agglomeration while protecting the particle main body, and can improve the moisture absorption resistance and rust resistance of the particle main body. In addition, the oxide film preferably covers the entire surface of the particle main body, but can be provided only on a part of the surface.

[0051] As a material constituting the oxide film, for example, silicon oxide, aluminum oxide, titanium oxide, vanadium oxide, niobium oxide, chromium oxide, manganese oxide, tin oxide, zinc oxide, and the like can be given, and one or a mixture or a composite of two or more of them can be given.

[0052] Among them, silicon oxide is preferably used. Silicon oxide is an oxide represented by the composition formula SiO x (0 < x < 2) is preferably SiO2.

[0053] The surface modification film includes an ionic liquid modification site having a first cationic group and a first anionic group. The ionic liquid modification site is bound to the substrate, for example, via a binding site from a coupling agent, a surfactant, a polymerization film of a polymer, or the like. The surface modification film preferably covers the entire surface of the oxide film or the particle body, but can be provided only on a part of the surface. In addition, the first cationic group and the first anionic group are described in detail later.

[0054] A compound from a coupling agent is preferably used for the binding site. By using a coupling agent, an ionic liquid structure can be introduced at a high density and stably on the surface of the oxide film or the surface of the particle body. Thereby, even in a severe environment, the aggregation of the metal magnetic particles 2 to each other can be suppressed, and the dispersibility of the metal magnetic particles 2 in the ionic liquid dispersion medium 4 can be further improved. Thereby, the metal magnetic particles 2 having excellent followability to a change in a magnetic field and capable of being uniformly dispersed even at a high concentration with respect to the ionic liquid dispersion medium 4 can be realized.

[0055] Further, the surface modification film is also effective in improving the moisture resistance, rust resistance, and the like of the metal magnetic particles 2. By improving the moisture resistance and the rust resistance, the deterioration of the metal magnetic particles 2 due to moisture absorption and rusting can be suppressed.

[0056] The average particle diameter of the metal magnetic particles 2 is preferably 0.5 μm or more and 15 μm or less, more preferably 2 μm or more and 12 μm or less, and further preferably 4 μm or more and 10 μm or less. If the average particle diameter of the metal magnetic particles 2 is within the range, the magnetic field responsiveness of the metal magnetic particles 2 can be sufficiently increased. Further, the sedimentation of the metal magnetic particles 2 can be suppressed. Thereby, the excitation stress of the magnetorheological fluid 1 can be increased. In addition, if the average particle diameter of the metal magnetic particles 2 is less than the lower limit value, the magnetic field responsiveness of the metal magnetic particles 2 becomes small, and thus the excitation stress of the magnetorheological fluid 1 can become small. On the other hand, if the average particle diameter of the metal magnetic particles 2 exceeds the upper limit value, the metal magnetic particles 2 can become easily sedimented. If the metal magnetic particles 2 are sedimented, the desired excitation stress can not be obtained.

[0057] The average particle diameter of the metal magnetic particles 2 can be found by a laser diffraction / dispersion method, based on the particle size distribution on a volume basis. Specifically, the median particle diameter in the particle size distribution is taken as the average particle diameter. As a device for measuring the particle size distribution by a laser diffraction / dispersion method, for example, the MT3300 series manufactured by Microtrac BEL Co., Ltd. or the like can be given.

[0058] The content ratio of the metal magnetic particles 2 in the magnetorheological fluid 1 is preferably 40% by mass or more and 95% by mass or less, more preferably 50% by mass or more and 90% by mass or less, and further preferably 60% by mass or more and 85% by mass or less. Thereby, the viscosity of the magnetorheological fluid 1 can be optimized. In addition, the excitation stress in the magnetorheological fluid 1 can be sufficiently increased.

[0059] The particle shape of the metal magnetic particles 2 is not particularly limited, and can be a regular sphere, an oval sphere, a polyhedron, or another shape. As another shape, for example, a needle shape, a fiber shape, a plate shape, a scale shape, a hollow shape, or the like can be given.

[0060] 1.2. Non-magnetic particles

[0061] The non-magnetic particles 3 are composed of a non-magnetic material, and are particles having a smaller average particle diameter than the metal magnetic particles 2. Such non-magnetic particles 3 are dispersed into the ionic liquid dispersion medium 4 by random Brownian motion. The non-magnetic particles 3 that perform Brownian motion generate a diffusion force that is larger than a sedimentation force generated by gravity, and also contribute to suppression of the sedimentation of the metal magnetic particles 2 while floating by themselves. Therefore, by using the non-magnetic particles 3, a good dispersion state of the metal magnetic particles 2 can be maintained. In addition, the average particle diameter of the non-magnetic particles is preferably around 0.1% or more and 1% or less of the average particle diameter of the metal magnetic particles 2.

[0062] The average particle diameter of the non-magnetic particles 3 is preferably 10 nm or more and 800 nm or less, more preferably 12 nm or more and 600 nm or less, and further preferably 14 nm or more and 550 nm or less. If the average particle diameter of the non-magnetic particles 3 is within the range, the enhancement effect by the Brownian motion of the non-magnetic particles 3 is sufficiently obtained. In addition, if the average particle diameter of the non-magnetic particles 3 is less than the lower limit value, the surface area of the non-magnetic particles 3 becomes small, and thus it can be difficult to obtain a sufficient enhancement effect even if the non-magnetic particles 3 perform Brownian motion. On the other hand, if the average particle diameter of the non-magnetic particles 3 exceeds the upper limit value, the Brownian motion of the non-magnetic particles 3 decreases, and thus the enhancement effect can become small.

[0063] The average particle diameter of the non-magnetic particles 3 can be found by a laser diffraction / dispersion method, based on the particle size distribution on a volume basis. Specifically, the median particle diameter in the particle size distribution is taken as the average particle diameter. As a device for measuring the particle size distribution by the laser diffraction / dispersion method, for example, the MT3300 series manufactured by Microtrac BEL Co., Ltd. or the like can be given.

[0064] As the constituent material of the non-magnetic particles 3, for example, a non-magnetic inorganic material, a thermoplastic resin, a thermosetting resin, or the like can be given.

[0065] As the non-magnetic inorganic material, for example, a non-magnetic metal such as gold, silver, copper, palladium, platinum, a metal oxide, a metal nitride, a metal carbide, a metal carbonate, a metal halide, a metal phosphate, a metal sulfide, a carbon-based material such as carbon black, graphite, or the like can be given. By using such an inorganic material, it is easy to improve the durability of the non-magnetic particles 3.

[0066] As the metal oxide, for example, alumina, silica, titanium oxide, zinc oxide, calcium oxide, magnesium oxide, tin dioxide, silica, non-magnetic chromium oxide, cerium oxide, non-magnetic iron oxide, or the like can be given. As the metal nitride, for example, boron nitride, silicon nitride, or the like can be given. As the metal carbide, for example, silicon carbide, molybdenum carbide, boron carbide, tungsten carbide, titanium carbide, or the like can be given. As the metal carbonate, for example, magnesium carbonate, calcium carbonate, or the like can be given. As the metal halide, for example, calcium fluoride, sodium fluoride, potassium fluoride, cesium fluoride, lithium chloride, or the like can be given. As the metal sulfide, for example, barium sulfate, calcium sulfate, or the like can be given.

[0067] As the thermoplastic resin, for example, an acrylic resin, a polystyrene resin, a polyvinyl acetate resin, a vinyl resin such as a polyvinyl chloride resin, a polyester resin, an ABS resin, an AS resin, or the like can be given.

[0068] As the thermosetting resin, for example, a phenol resin, an epoxy resin, a melamine resin, a urea resin, an unsaturated polyester resin, an alkyd resin, or the like can be given.

[0069] The content ratio of the non-magnetic particles 3 in the magnetorheological fluid 1 is preferably 0.01 mass% or more and 5 mass% or less, more preferably 0.1 mass% or more and 3 mass% or less, and further preferably 0.5 mass% or more and 2 mass% or less. Thereby, it is possible to suppress the sedimentation of the metal magnetic particles 2 with good effect while maintaining the dispersion state of the non-magnetic particles 3 well. In addition, if the content ratio of the non-magnetic particles 3 is less than the lower limit value, the effect of improvement can be small. On the other hand, if the content ratio of the non-magnetic particles 3 exceeds the upper limit value, the aggregation of the non-magnetic particles 3 or the like is likely to occur, and the dispersion state of the non-magnetic particles 3 can become poor.

[0070] Various additives can also be added to the magnetorheological fluid 1. Examples of additives include detergents, dispersants, antioxidants, anti-wear agents, extreme pressure agents, friction modifiers, surfactants, thixotropic agents (thickeners), dethickening agents, etc., and one or a mixture of two or more of them can be used.

[0071] Examples of dispersants include oleates, naphthenates, sulfonates, phosphates, stearic acid, stearates, glyceryl monooleate, sorbitan sesquioleate, lauric acid, fatty acids, and fatty alcohols.

[0072] Examples of anti-wear agents include organomolybdenum compounds such as molybdenum dialkyldithiocarbamate and molybdenum dialkyldithiophosphate, and organozinc compounds such as zinc dialkyldithiocarbamate and zinc dialkyldithiophosphate.

[0073] Furthermore, the total content of additives is preferably 10% or less by mass of the magnetorheological fluid 1, more preferably 8% or less by mass, and even more preferably 6% or less by mass. This prevents the additives from hindering the functions of the metallic magnetic particles 2 and the non-magnetic particles 3.

[0074] 1.3. Ionic Liquid Dispersion Media

[0075] The ionic liquid dispersion medium 4 has a second cation group and a second anion group. The second cation group and the second anion group will be described in detail later.

[0076] The content of the ionic liquid dispersion medium 4 in the magnetorheological fluid 1 is preferably 5% by mass or more and 60% by mass or less, more preferably 10% by mass or more and 50% by mass or less, and even more preferably 10% by mass or more and 30% by mass or less. This allows for the good maintenance of the dispersion state of the dispersed phase. Furthermore, it enables the optimization of the viscosity of the magnetorheological fluid 1.

[0077] Furthermore, to the extent that the effect of the ionic liquid dispersion medium 4 is not impaired, the magnetorheological fluid 1 may also contain liquid components (dispersion media) other than the ionic liquid dispersion medium 4, and may also contain additives. Examples of such additives include thixotropic agents, surfactants, viscoplastic media, and water-in-oil emulsions.

[0078] 1.4. Cation groups and anion groups

[0079] As described above, the ionic liquid modification site of the metallic magnetic particles 2 has a first cation group and a first anion group. Furthermore, the ionic liquid dispersion medium 4 has a second cation group and a second anion group.

[0080] The first and second cation groups are cations of the same type, selected from the group consisting of quaternary ammonium ions, imidazolium ions, pyridinium ions, and phosphonium ions.

[0081] The first anionic group and the second anionic group are respectively selected from the group consisting of tetrafluoroborate ion, hexafluorophosphate ion, tris(pentafluoroethyl)trifluorophosphate ion, bis(trifluoromethanesulfonyl)amide ion, phthalate hydrogen ion and bisfluorosulfonylimide ion.

[0082] The aforementioned specific cations and anions are both large ions with high ionic strength. By using ions with high ionic strength as the first cation group and the first anion group, respectively, the ionic liquid-modified site maintains good affinity with the ionic liquid dispersion medium 4 even under harsh environments. Furthermore, by using ions with high ionic strength as the second cation group and the second anion group, an ionic liquid dispersion medium 4 is obtained that remains liquid even at low temperatures below 0°C and does not easily evaporate even at high temperatures above 250°C. Thus, the ionic liquid dispersion medium 4 can exist without solidification or evaporation even at low or high temperatures, and maintains good affinity with the ionic liquid-modified site even under harsh environments.

[0083] Furthermore, by selecting cations of the same type as the first and second cation groups, the metallic magnetic particles 2 with ionic liquid modification sites can maintain a good dispersion state relative to the ionic liquid dispersion medium 4. As a result, a magnetorheological fluid 1 that exhibits high excitation stress independent of the environment can be realized.

[0084] Furthermore, "cations of the same kind" refers to cations with the same main skeleton. That is, in this specification, two cations that have the same main skeleton but different molecular structures, i.e., if specific examples are given, two cations with different numbers of carbon atoms in the alkyl groups bonded to the main skeleton, are considered to be cations of the same kind.

[0085] Furthermore, among the alkyl groups bonded to the main backbone of the first cation group, the alkyl group with the most carbon atoms is designated as the first long-chain alkyl group. Similarly, among the alkyl groups bonded to the main backbone of the second cation group, the alkyl group with the most carbon atoms is designated as the second long-chain alkyl group. In this case, it is preferable that the number of carbon atoms in the first long-chain alkyl group is the same as that in the second long-chain alkyl group. That is, it is preferable that the first and second cation groups are cations of the same type, and that the number of carbon atoms in each of the first and second long-chain alkyl groups is also the same. This significantly improves the dispersibility of the metallic magnetic particles 2 relative to the ionic liquid dispersion medium 4. As a result, a magnetorheological fluid 1 exhibiting higher excitation stress can be achieved even under harsh environments.

[0086] 1.4.1. Cationic group

[0087] In this embodiment, the first and second cation groups are selected from the group consisting of quaternary ammonium ions, imidazolium ions, pyridinium ions, and phosphonium ions, respectively.

[0088] 1.4.1.1. Quaternary ammonium ions

[0089] As a quaternary ammonium ion, a cation represented by the following formula (A) can be cited. The main framework of this cation is a nitrogen atom.

[0090] [Chemical Formula 1]

[0091]

[0092] In formula (A), R 11 ~R 14 Each is independently a straight-chain or branched alkyl group having 1 or more but less than 20 carbon atoms. R 11 ~R 14 They can also bond together to form a ring.

[0093] R 11 ~R 14 Quaternary ammonium ions, whether linear or branched alkyl groups, are also specifically referred to as aliphatic quaternary ammonium ions. Furthermore, R... 11 ~R 14 Quaternary ammonium ions that bond together to form a ring are also specifically called alicyclic quaternary ammonium ions.

[0094] As R 11 ~R 14 The linear alkyl group, for example, includes alkyl groups with 1 or more carbon atoms and less than 20 carbon atoms. Specifically, examples include methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecanyl, octadecyl, nonadecanyl, eicosyl, etc.

[0095] As R 11 ~R 14 Branched alkyl groups, for example, alkyl groups having 3 or more but less than 20 carbon atoms. Specifically, examples include 1-methylethyl, 1-methylpropyl, 2-methylpropyl, 1-methylbutyl, 2-methylbutyl, 3-methylbutyl, 1-ethylbutyl, 2-ethylbutyl, 1-methylpentyl, 2-methylpentyl, 3-methylpentyl, 4-methylpentyl, etc.

[0096] In R 11 ~R 14When the two groups bond together to form a ring, examples of the rings formed include cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, cyclodecyl, and cyclododecyl.

[0097] Specific examples of quaternary ammonium ions include tetraethylammonium, tetramethylammonium, tetrapropylammonium, tetrabutylammonium, and tetrapentylammonium.

[0098] As a quaternary ammonium ion, a cation represented by (A)-1 or (A)-2 is more preferred.

[0099] [Chemical Formula 2]

[0100]

[0101] In equation (A)-1, R 15 It is an alkyl group with 1 or more but less than 2 carbon atoms, R 16 It is an alkyl group having 1 or more but less than 8 carbon atoms. Furthermore, in formula (A)-2, R... 17 It is an alkyl group with 1 or more but less than 2 carbon atoms, R 18 It is an alkyl group having 1 or more but less than 8 carbon atoms.

[0102] As the quaternary ammonium ion, cations represented by (A)-3 or (A)-4 are further preferred. This enables the realization of a magnetorheological fluid 1 that maintains good dispersion of the metallic magnetic particles 2 even at high temperatures above 300°C. Furthermore, in this case, tetrafluoroborate ions are particularly preferred as the anionic group.

[0103] [Chemical Formula 3]

[0104]

[0105] In equation (A)-3, R 51 It is an alkyl group with 2 carbon atoms, R 52 It is an alkyl group having 1 or more but less than 2 carbon atoms. Furthermore, in formula (A)-4, R... 53 It is an alkyl group with 2 carbon atoms, R 54 It is an alkyl group having 1 or more but less than 2 carbon atoms.

[0106] 1.4.1.2. Imidazolium ion

[0107] As an imidazolium ion, a cation represented by the following formula (B) can be cited. The main framework of this cation is a five-membered ring structure composed of carbon and nitrogen atoms.

[0108] [Chemical Formula 4]

[0109]

[0110] In formula (B), R 21 and R 22 Each is independently a straight-chain or branched alkyl group having 1 or more but less than 20 carbon atoms.

[0111] Regarding R in equation (B) 21 and R 22 The description of the alkyl group and the R in the above formula (A) are related. 11 ~R 14 The description of alkyl groups is the same.

[0112] As R 21 and R 22 Preferably, the alkyl group has 1 or more and 10 or less carbon atoms, and more preferably, it has 1 or more and 8 or less carbon atoms.

[0113] As R 21 and R 22 Examples include n-butyl, sec-butyl, isobutyl, tert-butyl, pentyl, hexyl, heptyl, octyl, etc.

[0114] As the imidazolium ion, a cation represented by the following formula (B)-1 is more preferred. This enables the realization of a magnetorheological fluid 1 that maintains good dispersion of the metallic magnetic particles 2 even at high temperatures above 300°C. Furthermore, in this case, tetrafluoroborate ions are particularly preferred as the anionic group.

[0115] [Chemical Formula 5]

[0116]

[0117] In equation (B)-1, R 23 It is an alkyl group with 2 carbon atoms, R 24 It is an alkyl group having 1 or more but less than 2 carbon atoms.

[0118] 1.4.1.3. Pyridium ion

[0119] Examples of pyridinium ions include cations represented by the following formula (C). The backbone of this cation is a six-membered ring structure composed of carbon and nitrogen atoms.

[0120] [Chemical Formula 6]

[0121]

[0122] In formula (C), R 30 It is a straight-chain or branched alkyl group having 1 or more but less than 20 carbon atoms.

[0123] Regarding R in equation (C) 30The description of the alkyl group and the R in the above formula (A) are related. 11 ~R 14 The description of alkyl groups is the same.

[0124] As R 30 Preferably, the alkyl group has 1 or more and 10 or less carbon atoms, and more preferably, it has 1 or more and 8 or less carbon atoms.

[0125] As R 30 Examples include n-butyl, sec-butyl, isobutyl, tert-butyl, pentyl, and hexyl.

[0126] As the pyridinium ion, a cation represented by the following formula (C)-1 is more preferred. This enables the realization of a magnetorheological fluid 1 that maintains good dispersion of the metallic magnetic particles 2 even at high temperatures above 300°C. Furthermore, in this case, tetrafluoroborate ions are particularly preferred as the anionic group.

[0127] [Chemical Formula 7]

[0128]

[0129] In equation (C)-1, R 31 It is an alkyl group having 1 or more but less than 2 carbon atoms.

[0130] 1.4.1.4. Phosphorus ions

[0131] Examples of phosphonium ions include cations represented by the following formula (D). The main framework of this cation is phosphorus.

[0132] [Chemical Formula 8]

[0133]

[0134] In formula (D), R 41 ~R 44 Each is independently a straight-chain or branched alkyl group having 1 or more but less than 20 carbon atoms. R 41 ~R 44 They can also bond together to form a ring.

[0135] Regarding R in equation (D) 41 ~R 44 The description of the alkyl group and the R in the above formula (A) are related. 11 ~R 14 The description of alkyl groups is the same.

[0136] As R 41 ~R 44 Preferably, the alkyl group has 2 or more and 18 or fewer carbon atoms, and more preferably, it has 4 or more and 16 or fewer carbon atoms.

[0137] Specific examples of phosphonium ions include tetrabutylphosphonium, tetrapropylphosphonium, tetraethylphosphonium, tetramethylphosphonium, and hexadecyltributylphosphonium.

[0138] 1.4.2. Anionic group

[0139] In this embodiment, the first anionic group and the second anionic group are selected from the group consisting of tetrafluoroborate ion, hexafluorophosphate ion, tris(pentafluoroethyl)trifluorophosphate ion, bis(trifluoromethanesulfonyl)amide ion, phthalate hydrogen ion and bisfluorosulfonylimide ion, respectively.

[0140] These anions are all large ions. Therefore, by using the listed anions as the first and second anion groups, it is possible to achieve a magnetorheological fluid 1 that can maintain a good dispersion state of the dispersed phase even at low or high temperatures.

[0141] Furthermore, the first anionic group and the second anionic group are preferably anions selected from the group consisting of tetrafluoroborate ion, hexafluorophosphate ion, tris(pentafluoroethyl)trifluorophosphate ion, and bis(trifluoromethanesulfonyl)amide ion. Therefore, the above-mentioned effects are more significant.

[0142] Furthermore, the first anionic group and the second anionic group are more preferably tetrafluoroborate ions. Thus, a magnetorheological fluid 1 can be achieved that maintains a good dispersion state of the metallic magnetic particles 2 even after heating at a high temperature such as 300°C.

[0143] Furthermore, the first and second anion groups can be selected from different types of anions, but it is preferable to select anions of the same type. As a result, the metallic magnetic particles 2 with ionic liquid-modified sites can maintain a better dispersion state relative to the ionic liquid dispersion medium 4. Consequently, a magnetorheological fluid 1 exhibiting high excitation stress independent of the environment can be realized.

[0144] 1.4.3. Ionic strength

[0145] The ionic strength of the ionic liquid modification site having the first cation group and the first anion group is set as μ1. Furthermore, the ionic strength of the ionic liquid dispersion medium 4 having the second cation group and the second anion group is set as μ2. In this case, the overall ionic strength of the magnetorheological fluid 1 can be evaluated using the average value μA of the ionic strengths μ1 and μ2. The average value μA of the ionic strength is preferably 5.00 mol / L or more and 14.00 mol / L or less, more preferably 10.00 mol / L or more and 13.00 mol / L or less. In this case, the ionic liquids with relatively high ionic strengths interact with each other. Therefore, even at high temperatures, the metallic magnetic particles 2 can maintain a better dispersion state in the ionic liquid dispersion medium 4.

[0146] Furthermore, if the average value μA is below the lower limit, the ionic bonds between molecules in the ionic liquid may weaken. In this case, the dispersibility of the metallic magnetic particles 2 at high temperatures may decrease. On the other hand, if the average value μA exceeds the upper limit, the selection of ions may become difficult.

[0147] Furthermore, the ionic strength μ1 of the ionic liquid-modified site is preferably 5.00 mol / L or more and 14.00 mol / L or less, more preferably 10.00 mol / L or more and 13.00 mol / L or less. In this case, the ionic bonds in the ionic liquid-modified site become sufficiently strong.

[0148] Furthermore, the ionic strength μ2 of the ionic liquid dispersion medium 4 is preferably 5.00 mol / L or more and 14.00 mol / L or less, more preferably 10.00 mol / L or more and 13.00 mol / L or less. In this case, the ionic bonds of the ionic liquid dispersion medium 4 become sufficiently strong.

[0149] In addition, ionic strength is obtained by adding the product of the molar concentration of the ion and the square of the atomic valence of the ion to all ion species and then multiplying it by 1 / 2.

[0150] 1.3. Physical Properties of Magnetorheological Fluids

[0151] The excitation stress of the magnetorheological fluid 1 can be evaluated as the yield stress when a magnetic field with a magnetic flux density of 1.0 [T] is applied. This excitation stress is preferably 10 [kPa] or more, more preferably 15 [kPa] or more. Thus, a magnetorheological fluid 1 exhibiting sufficient excitation stress is obtained. Such a magnetorheological fluid 1 is useful in various applications.

[0152] The excitation stress of magnetorheological fluid 1 was determined in the following manner.

[0153] First, a magnetic field with a magnetic flux density of 1.0 [T] is applied to the magnetorheological fluid 1 at a specified temperature. Then, under this condition, a shear rate of 333 [ / s] is provided, and the shear stress is measured. For example, an Anton Paar rheometer MCR102 can be used to measure the shear stress. Furthermore, the measured shear stress is taken as the yield stress.

[0154] Furthermore, the aforementioned excitation stress is preferably within the range described above, regardless of temperature. For example, the excitation stress of the magnetorheological fluid 1 after being placed in an environment at 300°C for 1 hour is preferably 10 kPa or more, more preferably 15 kPa or more. Thus, a magnetorheological fluid 1 exhibiting sufficient excitation stress even at high temperatures is obtained. Such a magnetorheological fluid 1 can maintain the same properties as at room temperature even under harsh temperature conditions.

[0155] The boiling point of the magnetorheological fluid 1 is preferably 250°C or higher, more preferably 300°C or higher, and even more preferably 350°C or higher. Thus, a magnetorheological fluid 1 with sufficient heat resistance is obtained.

[0156] The boiling point of magnetorheological fluid 1 was determined as follows.

[0157] First, 2 mL of magnetorheological fluid 1 was heated using a hot plate. Then, the temperature of magnetorheological fluid 1 when white smoke was produced was measured, and the measured value was taken as the boiling point.

[0158] The freezing point of the magnetorheological fluid 1 is preferably below 0°C, more preferably below -10°C, and even more preferably below -20°C. Thus, a magnetorheological fluid 1 with sufficient cold resistance is obtained.

[0159] The freezing point of magnetorheological fluid 1 was determined as follows.

[0160] First, 2 mL of magnetorheological fluid 1 was cooled using a freezer. Then, the temperature at which the magnetorheological fluid 1 solidified was measured, and the measured value was taken as the freezing point.

[0161] 1.4. Examples of applications of magnetorheological fluids

[0162] As applications of magnetorheological fluid 1, various devices and equipment that utilize the difference in excitation stress when switching applied magnetic fields can be cited. Examples of such devices and equipment include, for instance, linear dampers, rotary dampers, shock absorbers and other vibration damping devices, brakes and other braking devices, clutches and other power transmission devices, the muscle parts of robots, end effectors, valves for fluid flow control, tactile sensing devices, audio devices, medical / welfare robotic arms, nursing arms, personal mobility devices, etc.

[0163] 1.5. Manufacturing Method of Magnetorheological Fluid

[0164] An example of a method for manufacturing magnetorheological fluid 1 will be described. In the method for manufacturing magnetorheological fluid 1, firstly, a surface modification film is formed on the surface of a metallic magnetic material particle substrate. In forming the surface modification film, for example, a coupling agent (ionic liquid coupling agent) having ionic liquid modification sites as functional groups is used. The ionic liquid coupling agent is a compound having ionic liquid modification sites and hydrolyzable groups. It is preferred to use this compound because it introduces ionic liquid modification sites onto the surface of the metallic magnetic material particle or oxide film through hydrolysis and condensation reactions. Specifically, the ionic liquid coupling agent is dissolved in a solvent to prepare a solution. The obtained solution is subjected to ultrasonic treatment and manual stirring. This causes the ionic liquid coupling agent to react with the surface of the particle substrate. The particle substrate after magnetic separation is recovered and then subjected to heat treatment. Examples of heating conditions include a heating temperature of 50°C or higher and 150°C or lower, and a heating time of 30 minutes or higher and 180 minutes or lower. This forms a surface modification film, resulting in metallic magnetic particles 2.

[0165] Furthermore, after the surface-modified film is formed, its formation state can be confirmed through surface elemental analysis. For example, ESCA (Extreme Electron Photoelectron Spectroscopy) can be used in surface elemental analysis. Then, by confirming the presence or absence of elements characteristic of cations (such as nitrogen) and elements characteristic of anions (such as boron, fluorine, and sulfur), the formation state of the surface-modified film can be determined.

[0166] Next, the metallic magnetic particles 2, non-magnetic particles 3, and ionic liquid dispersion medium 4 are mixed and stirred. Examples of stirring methods include stirring using a scraper, a vortex mixer, a high-shear mixer, and a low-frequency acoustic resonance mixer. The stirring time is set appropriately according to the stirring method, but is preferably 5 minutes or more and 4 hours or less. The stirring temperature is set appropriately according to the stirring method, but is preferably 15°C or more and 70°C or less.

[0167] 2. Braking device

[0168] Next, the braking device involved in the embodiment will be described.

[0169] Figure 2 This is a longitudinal sectional view showing the braking device 100 according to the embodiment.

[0170] Figure 2 The braking device 100 shown includes a fixed disk 110 (fixed part), a movable disk 120 (movable part), and a magnetorheological fluid 1. The movable disk 120 is rotatable relative to the fixed disk 110 about a rotation axis AX. The magnetorheological fluid 1 is held between the fixed disk 110 and the movable disk 120. Furthermore, the braking device 100 includes a magnetic field generating unit (not shown). This magnetic field generating unit applies a magnetic field to the magnetorheological fluid 1.

[0171] In the braking device 100, by switching the magnetic field applied to the magnetorheological fluid 1, the excitation stress of the magnetorheological fluid can be changed. This, in turn, changes the resistance to the rotation of the movable disc 120 relative to the fixed disc 110. As a result, in the braking device 100, this resistance is used as a braking force for braking vehicles, etc.

[0172] The fixed plate 110 is connected to the side of the vehicle body, for example, and the movable plate 120 is connected to the side of the vehicle wheel, for example.

[0173] When no magnetic field H is applied to the magnetorheological fluid 1 (H=0), the metallic magnetic particles 2 and non-magnetic particles 3 are in a dispersed state within the magnetorheological fluid 1. In this case, the excitation stress of the magnetorheological fluid 1 is sufficiently small to generate almost no braking force.

[0174] When a magnetic field H is applied to the magnetorheological fluid 1 (0 < H), metallic magnetic particles 2 form clusters within the fluid. In this case, the excitation stress of the magnetorheological fluid 1 increases, generating a braking force.

[0175] The magnetorheological fluid 1 described in the above embodiments can maintain both high reliability and high excitation stress even when used at low or high temperatures. Therefore, the braking device 100 described in the embodiments does not experience a decrease in braking force even in harsh environments, and thus exhibits high reliability.

[0176] Furthermore, the structure of the braking device 100 is not limited to the structure described above. For example, the braking device of the present invention may also include three or more discs.

[0177] 3. The effects achieved by the described implementation method

[0178] As described above, the magnetorheological fluid 1 involved in the embodiment comprises metallic magnetic particles 2 and an ionic liquid dispersion medium 4. The metallic magnetic particles 2 modify the surface of the ionic liquid-modified sites having first cation groups and first anion groups. The ionic liquid dispersion medium 4 has second cation groups and second anion groups.

[0179] The first and second cation groups are cations of the same type, selected from the group consisting of quaternary ammonium ions, imidazolium ions, pyridinium ions, and phosphonium ions. The first and second anionic groups are selected from the group consisting of tetrafluoroborate ions, hexafluorophosphate ions, tris(pentafluoroethyl)trifluorophosphate ions, bis(trifluoromethanesulfonyl)amide ions, phthalate hydrogen ions, and bis(fluorosulfonyl)imide ions, respectively.

[0180] Based on this configuration, a magnetorheological fluid 1 is obtained that can maintain both high reliability and high excitation stress even when used at low or high temperatures.

[0181] In the magnetorheological fluid 1 of the embodiment, the first cation group and the second cation group are preferably cations represented by the following formulas (A)-3, (A)-4, (B)-1 and (C)-1.

[0182] [Chemical Formula 9]

[0183]

[0184] In equation (A)-3, R 51 It is an alkyl group with 2 carbon atoms, R 52 It is an alkyl group with 1 or more but less than 2 carbon atoms. In formula (A)-4, R 53 It is an alkyl group with 2 carbon atoms, R 54 It is an alkyl group with 1 or more but less than 2 carbon atoms. In formula (B)-1, R 23 It is an alkyl group with 2 carbon atoms, R 24 It is an alkyl group having 1 or more but less than 2 carbon atoms. In formula (C)-1, R 31 It is an alkyl group having 1 or more but less than 2 carbon atoms.

[0185] Based on this configuration, a magnetorheological fluid 1 can be achieved that maintains a good dispersion state of metallic magnetic particles 2 even at high temperatures above 300°C.

[0186] In the magnetorheological fluid 1 described in the above embodiment, the first cation group and the second cation group may each have an alkyl group. Among the alkyl groups in the first cation group, the alkyl group with the most carbon atoms is designated as the first long-chain alkyl group, and among the alkyl groups in the second cation group, the alkyl group with the most carbon atoms is designated as the second long-chain alkyl group. In this case, the number of carbon atoms in the first long-chain alkyl group and the number of carbon atoms in the second long-chain alkyl group may also be the same.

[0187] This configuration significantly improves the dispersibility of the metallic magnetic particles 2 relative to the ionic liquid dispersion medium 4. As a result, a magnetorheological fluid 1 exhibiting higher excitation stress can be achieved even under harsh environments.

[0188] In the magnetorheological fluid 1 described in the embodiment, the first anion group and the second anion group may also be tetrafluoroborate ions.

[0189] Based on this configuration, a magnetorheological fluid 1 can be achieved that maintains a good dispersion state of the metallic magnetic particles 2 even after heating at a high temperature such as 300°C.

[0190] In the magnetorheological fluid 1 described in the embodiment, the average particle size of the metallic magnetic particles 2 may be 0.5 μm or more and 15 μm or less.

[0191] With this configuration, the magnetic field responsiveness of the metallic magnetic particles 2 can be significantly increased. Furthermore, the sedimentation of the metallic magnetic particles 2 can be suppressed. Therefore, the excitation stress of the magnetorheological fluid 1 can be increased.

[0192] In the magnetorheological fluid 1 described in the above embodiment, the average value μA of the ionic strength μ1 of the ionic liquid modified site and the ionic strength μ2 of the ionic liquid dispersion medium can also be 5.00 mol / L or more and 14.00 mol / L or less.

[0193] Due to this composition, the ionic liquids with relatively high ionic strength interact with each other. Therefore, even at high temperatures, the metallic magnetic particles 2 can maintain a better dispersion state in the ionic liquid dispersion medium 4.

[0194] In the magnetorheological fluid 1 described in the embodiment, non-magnetic particles 3 with an average particle size smaller than that of the metallic magnetic particles 2 may also be included.

[0195] Based on this configuration, the non-magnetic particles 3 undergo Brownian motion, generating a diffusion force greater than the settling force caused by gravity. While floating on their own, they also help to suppress the settling of the metallic magnetic particles 2. Therefore, by using the non-magnetic particles 3, it is possible to maintain a good dispersion state of the metallic magnetic particles 2.

[0196] In the magnetorheological fluid 1 described in the above embodiment, the constituent material of the non-magnetic particles 3 may also be an inorganic material.

[0197] Based on this configuration, it is easy to improve the durability of the non-magnetic particles 3.

[0198] In the magnetorheological fluid 1 described in the above embodiment, the content of non-magnetic particles 3 may be 0.01% by mass or more and 5% by mass or less.

[0199] Based on this configuration, it is possible to maintain the dispersion of non-magnetic particles 3 while effectively suppressing the sedimentation of metallic magnetic particles 2 by enhancing the effect.

[0200] In the magnetorheological fluid 1 according to the embodiment, after being placed in an environment at a temperature of 300°C for 1 hour, the yield stress when a magnetic field of 1.0 [T] is applied is preferably 15 [kPa] or more.

[0201] Based on this configuration, a magnetorheological fluid 1 exhibiting sufficient excitation stress even at high temperatures is obtained. This magnetorheological fluid 1 can maintain the same properties as at room temperature even under harsh temperature conditions.

[0202] In the magnetorheological fluid 1 described in the embodiment, the first anion base and the second anion base may also be anions of the same kind.

[0203] Based on this configuration, the metallic magnetic particles 2 with ionic liquid-modified sites can maintain a better dispersion state relative to the ionic liquid dispersion medium 4. As a result, a magnetorheological fluid 1 that exhibits high excitation stress independent of the environment can be realized.

[0204] The braking device 100 according to the embodiment includes a fixed disk 110 (fixed part), a movable disk 120 (movable part), a magnetorheological fluid 1 according to the embodiment, and a magnetic field generating part. The movable disk 120 is movable relative to the fixed disk 110. The magnetorheological fluid 1 is held between the fixed disk 110 and the movable disk 120. The magnetic field generating part applies a magnetic field to the magnetorheological fluid 1.

[0205] Based on this configuration, a highly reliable braking device 100 can be achieved without a decrease in braking force, even in harsh environments.

[0206] The magnetorheological fluid and braking device of the present invention have been described above based on preferred embodiments, but the present invention is not limited thereto.

[0207] For example, the magnetorheological fluid and braking device of the present invention can also be equipped with arbitrary structures in the described embodiments. Furthermore, the structures of various parts of the braking device involved in the described embodiments can also be replaced by structures having the same functions as described above.

[0208] Example

[0209] Next, specific embodiments of the present invention will be described.

[0210] 4. Fabrication of magnetorheological fluids

[0211] Figures 3 to 8 Tables 1 to 6 show the fabrication conditions and evaluation results of magnetorheological fluids.

[0212] Magnetorheological fluids are fabricated in the following manner.

[0213] First, Table 1 ( Figure 3 Table 6 Figure 8The mixture shown represents a mixture of magnetic metallic particles, non-magnetic particles, and an ionic liquid dispersion medium. The average particle size of the magnetic metallic particles is 8 μm, and the average particle size of the non-magnetic particles is 40 nm. Furthermore, the content of each type of magnetic metallic particle and non-magnetic particle, as well as the ionic strength (mol / L) of the ionic liquid, are shown in Tables 1 to 6. The remaining portion represents the ionic liquid dispersion medium.

[0214] Next, the resulting mixture was stirred. A high-shear mixer (Silverson, L5M-A) was used as the stirring device. The stirring conditions were 3000 rpm and 30 minutes. Thus, magnetorheological fluids of Examples 1-15 and Comparative Examples 1-7 were prepared.

[0215] In addition, the comparative examples are the following magnetorheological fluids.

[0216] Comparative Example 1: Using mineral oil as the dispersion medium

[0217] Comparative Example 2: Surface modification based on ionic liquid modification sites omitted.

[0218] Comparative Example 3: The first cationic group and the second cationic group are of different types.

[0219] Comparative Example 4: The first anion group and the second anion group are not specific ions.

[0220] Comparative Example 5: The first anion group and the second anion group are not specific ions.

[0221] Comparative Example 6: The first anion group and the second anion group are not specific ions.

[0222] Comparative Example 7: The first anion group and the second anion group are not specific ions.

[0223] In addition, “C chain of cationic group” in Tables 1 to 6 refers to alkyl groups bonded to the main skeleton of the cationic group.

[0224] 5. Evaluation of magnetorheological fluids

[0225] For the magnetorheological fluids of each embodiment and each comparative example, viscosity, dispersion stability and excitation stress were evaluated at room temperature and high temperature, respectively.

[0226] 5.1. Viscosity

[0227] For the magnetorheological fluids of each embodiment and each comparative example, the viscosity was measured under non-magnetic field conditions (magnetic flux density 0 [T]). Anton Paar MCR102 rheometer was used for the viscosity measurement. The shear rate during measurement was 0.033 [ / s].

[0228] The viscosity of the magnetorheological fluid was measured under the above conditions after being placed at 25°C for 1 day, and the measured value was taken as "viscosity (placed at room temperature for 1 day)". Similarly, the viscosity of the magnetorheological fluid was measured after being heated at 300°C for 1 hour, and the measured value was taken as "viscosity (placed at 300°C for 1 hour)".

[0229] The viscosity was then evaluated according to the following evaluation criteria. The evaluation results are shown in Tables 1 to 6.

[0230] A: Viscosity less than 10000 mPa·s

[0231] B: Viscosity above 10000 mPa·s and below 100000 mPa·s

[0232] C: Viscosity above 100,000 mPa·s

[0233] 6.2. Dispersion stability

[0234] The dispersion stability of the magnetorheological fluids in each embodiment and comparative example was evaluated by the following method.

[0235] First, 1 mL of magnetorheological fluid was placed in a 1.5 mL sample vial. After standing at 25°C for 24 hours, the thickness tA of the metal magnetic particle layer (precipitate layer) and the thickness tB of the ionic liquid dispersion medium layer (supernatant layer) after phase separation were measured. The thickness of the metal magnetic particle layer is the thickness of the layer composed of precipitated metal magnetic particles, and the thickness of the ionic liquid dispersion medium layer is the thickness from the top of the metal magnetic particle layer to the liquid surface.

[0236] Next, the supernatant ratio tB / (tA+tB) is calculated based on the thicknesses tA and tB.

[0237] Then, using the above calculation method, the supernatant of the magnetorheological fluid after being placed at 25°C for 30 days was calculated, and the result was taken as the "dispersion stability (placed at room temperature for 30 days)". In addition, using the above calculation method, the supernatant of the magnetorheological fluid after being heated at 300°C for 1 hour was calculated, and the result was taken as the "dispersion stability (placed at 300°C for 1 hour)".

[0238] Next, the dispersion stability of the magnetorheological fluid was evaluated by comparing the calculated supernatant ratio with the following evaluation criteria.

[0239] The evaluation results are shown in Tables 1 to 6. Furthermore, a lower supernatant ratio indicates higher dispersion stability of magnetic metal particles in the magnetorheological fluid.

[0240] AA: Cleansing rate less than 10%

[0241] A: The cleansing rate is above 10% and less than 30%.

[0242] B: The cleansing rate is above 30%.

[0243] C: Due to gelation, the supernatant rate cannot be calculated.

[0244] 5.3. Excitation Stress

[0245] For the magnetorheological fluids of each embodiment and each comparative example, the excitation stress was measured by the above method.

[0246] The excitation stress of the magnetorheological fluid after being placed at 25°C for 1 day was measured, and the result was taken as "excitation stress (placed at room temperature for 1 day)". In addition, the excitation stress of the magnetorheological fluid after being heated at 300°C for 1 hour was measured, and the result was taken as "excitation stress (placed at 300°C for 1 hour)".

[0247] The measured excitation stress was then evaluated according to the following evaluation criteria. The evaluation results are shown in Tables 1 to 6.

[0248] AA: Excitation stress is above 20 kPa

[0249] A: The excitation stress is above 15 kPa and less than 20 kPa.

[0250] B: The excitation stress is above 10 kPa and less than 15 kPa.

[0251] C: Excitation stress is less than 10 kPa.

[0252] As shown in Tables 1 to 6, in the magnetorheological fluids of each embodiment, the evaluation results for viscosity, dispersion stability, and excitation stress are all B or above, which are good results. Furthermore, the boiling points of the magnetorheological fluids in each embodiment are all above 250°C, and the freezing points are all below 0°C.

[0253] On the other hand, in the magnetorheological fluids of each comparative example, all evaluation results were unsatisfactory.

[0254] In addition, the average particle size of the metallic magnetic particles was changed to 5 μm, 12 μm, and 15 μm, and the same experiments as above were conducted, yielding the same evaluation results of the same tendency.

[0255] Furthermore, a magnetorheological fluid was prepared by omitting non-magnetic particles from the magnetorheological fluid of Example 9, and the same experiment as above was conducted. The evaluation results were the same as those of Example 9, except that the evaluation results for dispersion stability and excitation stress were A.

[0256] The results above demonstrate that, according to the present invention, a magnetorheological fluid that can achieve both high reliability and high excitation stress even when used at low or high temperatures is possible.

Claims

1. A magnetorheological fluid, characterized in that, Include: Metallic magnetic particles are used to modify the surface of an ionic liquid-modified site having a first cation group and a first anion group; and An ionic liquid dispersion medium having a second cation group and a second anion group. The first cationic group and the second cationic group are cations of the same type, selected from the group consisting of quaternary ammonium ions, imidazolium ions, pyridinium ions, and phosphonium ions. The first anionic group and the second anionic group are respectively selected from the group consisting of tetrafluoroborate ion, hexafluorophosphate ion, tris(pentafluoroethyl)trifluorophosphate ion, bis(trifluoromethanesulfonyl)amide ion, phthalate hydrogen ion and bisfluorosulfonylimide ion.

2. The magnetorheological fluid according to claim 1, wherein, The first cationic group and the second cationic group are cationic groups represented by the following formulas (A)-3, (A)-4, (B)-1 and (C)-1. In equation (A)-3, R 51 It is an alkyl group with 2 carbon atoms, R 52 It is an alkyl group having 1 or more but less than 2 carbon atoms; in formula (A)-4, R 53 It is an alkyl group with 2 carbon atoms, R 54 It is an alkyl group having 1 or more but less than 2 carbon atoms; in formula (B)-1, R 23 It is an alkyl group with 2 carbon atoms, R 24 It is an alkyl group having 1 or more but less than 2 carbon atoms; in formula (C)-1, R 31 It is an alkyl group having 1 or more but less than 2 carbon atoms.

3. The magnetorheological fluid according to claim 1 or 2, wherein, The first cationic group and the second cationic group have alkyl groups bonded to their respective main backbones. Of the alkyl groups bonded to the main backbone of the first cationic group, the alkyl group with the most carbon atoms is designated as the first long-chain alkyl group, and When the alkyl group with the main backbone bonded to the second cationic group is selected as the second long-chain alkyl group, the alkyl group with the most carbon atoms is selected as the second long-chain alkyl group. The first long-chain alkyl group has the same number of carbon atoms as the second long-chain alkyl group.

4. The magnetorheological fluid according to claim 1 or 2, wherein, The first anion group and the second anion group are tetrafluoroborate ions.

5. The magnetorheological fluid according to claim 1 or 2, wherein, The average particle size of the metallic magnetic particles is greater than 0.5 μm and less than 15 μm.

6. The magnetorheological fluid according to claim 1 or 2, wherein, The average ionic strength of the ionic liquid-modified site and the ionic strength of the ionic liquid dispersion medium is above 5.00 mol / L and below 14.00 mol / L.

7. The magnetorheological fluid according to claim 1 or 2, wherein, The magnetorheological fluid contains non-magnetic particles with an average particle size smaller than the metallic magnetic particles.

8. The magnetorheological fluid according to claim 7, wherein, The non-magnetic particles are composed of inorganic materials.

9. The magnetorheological fluid according to claim 7, wherein, The content of the non-magnetic particles is more than 0.01% by mass and less than 5% by mass.

10. The magnetorheological fluid according to claim 1 or 2, wherein, After being placed in an environment with a temperature of 300℃ for 1 hour, the yield stress when a magnetic field of 1.0T is applied is above 15kPa.

11. The magnetorheological fluid according to claim 1 or 2, wherein, The first anion group and the second anion group are anions of the same kind.

12. A braking device, characterized in that, have: Fixing part; The movable part is movable relative to the fixed part; The magnetorheological fluid of claim 1 or 2 is held between the fixed part and the movable part; and The magnetic field generating unit applies a magnetic field to the magnetorheological fluid.

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