Magnetorheological fluid composition

Abstract

To provide a magnetorheological fluid composition more excellent in fluidity under high shear when a magnetic field is turned off, as compared with a conventional magnetorheological fluid composition.SOLUTION: The magnetorheological fluid composition includes: magnetic particles; a base oil; a dispersant represented by the following formula (1); and a rheology control agent, the content of the dispersant represented by the formula (1) being 0.30 mass% to 0.55 mass% with respect to the total amount of the magnetorheological fluid composition. In the formula (1), R1 represents an aliphatic hydrocarbon group having 14 to 22 carbon atoms, R2 represents an ethylene group or a propylene group, and n represents an integer of 1 to 12.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to magnetorheological fluid compositions. [Background technology]

[0002] Magneto-rheological fluids (also called "MRF" or "MR fluid") are functional fluids that are made by mixing magnetic particles of several micrometers to several tens of micrometers in size with hydrocarbon synthetic oils or silicone oils, and generate extremely large stresses when exposed to a magnetic field.

[0003] MRFs have the advantage of being able to reversibly change viscosity significantly using a magnetic field, thereby widening the range of control for devices. For this reason, MRFs are expected to be applied to dampers, clutches, brakes, and other devices. Reported applications of MRFs to dampers include automobile suspensions and seismic isolation dampers for buildings (see Non-Patent Document 1). MRFs have also been applied and put to practical use in the suspensions of home appliances (see Non-Patent Document 2). [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] Journal of the Robotics Society of Japan, "Applications of MRF Dampers", pp.483-485, Vol.31, No.5 (2013) [Non-patent document 2] Journal of the Robotics Society of Japan, "Application of MRF Active Suspension to Washing Machines", pp.488-489, Vol.31, No.5 (2013) Summary of the Invention [Problem to be solved by the invention]

[0005] The greatest feature of devices using MRF is that by applying a magnetic field to the MRF, the viscosity of the MRF can be significantly changed to a range that is not possible with ordinary fluids, thereby widening the control range of the device. The desired performance of an MRF is to have a lower viscosity when the magnetic field is off and to generate higher stress when the magnetic field is on. Furthermore, from the perspective of device operability, the shear viscosity characteristics of the MRF require improved fluidity compared to conventional models when subjected to high shear stresses when the magnetic field is off.

[0006] An object of one embodiment of the present disclosure is to provide a magnetorheological fluid composition that has superior fluidity at high shear when the magnetic field is turned off compared to conventional magnetorheological fluid compositions. [Means for solving the problem]

[0007] The present disclosure includes the following aspects.

[0008] <1> magnetic particles; A base oil, When expressed by the following formula (1), and a rheology control agent, A magnetorheological fluid composition, wherein the content of the dispersant represented by formula (1) is 0.30% by mass to 0.55% by mass relative to the total amount of the magnetorheological fluid composition.

[0009] [ka]

[0010] In formula (1), R 1 represents an aliphatic hydrocarbon group having 14 to 22 carbon atoms, and R 2 represents an ethylene group or a propylene group, and n represents an integer of 1 to 12.

[0011] <2> The dispersant represented by formula (1) includes a dispersant represented by the following formula (2): <1> 10. The magnetorheological fluid composition according to claim 1 .

[0012] [ka]

[0013] In formula (2), n represents an integer of 1 to 12.

[0014] <3> The cumulative 50% particle size of the magnetic particles is 1 μm to 30 μm. <1> or <2> 10. The magnetorheological fluid composition according to claim 1 . [Effects of the Invention]

[0015] According to one embodiment of the present disclosure, it is possible to provide a magnetorheological fluid composition that has superior fluidity at high shear when the magnetic field is turned off, compared to conventional magnetorheological fluid compositions. DETAILED DESCRIPTION OF THE INVENTION

[0016] Specific embodiments of the magnetorheological fluid composition according to the present disclosure are described in detail below, but the magnetorheological fluid composition according to the present disclosure is not limited to the following embodiments and can be modified as appropriate within the scope of the present disclosure.

[0017] In the present disclosure, a numerical range indicated using "to" means a range that includes the numerical values ​​before and after "to" as the minimum and maximum values, respectively. In the present disclosure, the upper or lower limit of a numerical range described in stages may be replaced with the upper or lower limit of another numerical range described in stages. Furthermore, in the present disclosure, the upper or lower limit of a numerical range described in stages may be replaced with a value shown in the examples. In the present disclosure, a combination of two or more preferred embodiments is a more preferred embodiment. In the present disclosure, "mass %" and "weight %" are synonymous. In the present disclosure, when there are multiple substances corresponding to each component, the amount of each component means the total amount of the multiple substances unless otherwise specified. In this disclosure, "JIS" is used as an abbreviation for Japanese Industrial Standards.

[0018] In the present disclosure, "fluidity at high shear" refers to the fluidity of a target magnetorheological fluid composition at a shear rate of 1000 s at 20°C. -1 The shear viscosity is determined by the measured value of shear viscosity measured by applying shear stress at 1000 kJ / min. The method and conditions for measuring shear viscosity will be described in the examples below.

[0019] The magnetorheological fluid composition according to the present disclosure contains magnetic particles, a base oil, a dispersant represented by the following formula (1), and a rheology control agent, and the content of the dispersant represented by formula (1) is 0.30 mass % to 0.55 mass % relative to the total amount of the magnetorheological fluid composition.

[0020] [ka]

[0021] In formula (1), R 1 represents an aliphatic hydrocarbon group having 14 to 22 carbon atoms, and R 2 represents an ethylene group or a propylene group, and n represents an integer of 1 to 12.

[0022] The magnetorheological fluid composition according to the present disclosure has superior fluidity under high shear when the magnetic field is turned off compared to conventional magnetorheological fluid compositions.

[0023] (magnetic particles) The magnetorheological fluid composition according to the present disclosure contains magnetic particles. Examples of magnetic particles include metal particles containing (preferably as a main component) one or more metals selected from iron, cobalt, and nickel, and metal compound particles that contain (preferably as a main component) one or more compounds selected from iron nitride, iron carbide, ferrite, and magnetite and exhibit ferromagnetism. Among these, metal particles containing iron as a main component or metal compound particles containing ferrite as a main component are preferred, and metal particles containing iron as a main component are particularly preferred. These magnetic particles may be used alone or in combination of two or more types.

[0024] Here, the term "metal particles" basically refers to particles of a single metal, particles of an alloy in which two or more metals are bonded, particles containing two or more metals without being bonded, etc. However, it also includes particles that are primarily composed of metal and contain residual components other than the metal in the raw material, such as carbonyl iron, which will be described later. The same applies to metal compound particles. Furthermore, the term "main component" refers to the component that makes up the magnetic particle with the largest mass proportion, and is preferably 50 mass % or more, and more preferably 70 mass % or more, of the components that make up the magnetic particle.

[0025] Among the preferred magnetic particles, metal particles containing iron as the main component are preferred because the higher the iron content and the fewer impurities, the higher the saturation magnetization. The iron content of metal particles containing iron as the main component is preferably 98% to 100% by mass, and particularly preferably 99% to 100% by mass. Carbonyl iron is an example of such magnetic particles. Carbonyl iron is a high-purity metal particle produced by thermal decomposition of iron pentacarbonyl.

[0026] The cumulative 50% particle diameter of the magnetic particles is preferably 0.5 μm to 50 μm, more preferably 1 μm to 30 μm, and even more preferably 2.5 μm to 20 μm. The cumulative 50% particle diameter is a particle diameter measured by laser diffraction scattering. If the cumulative 50% particle diameter is 0.5 μm or more, the shear stress increases when a magnetic field is applied, while if it is 50 μm or less, the rapid settling of the magnetic particles is further suppressed, improving stability and suppressing an increase in friction during sliding, which is preferable.

[0027] The magnetic particles may be surface-treated with various coupling agents or resins, or may be untreated. Examples of the various coupling agents include silane-based coupling agents, aluminate-based coupling agents, and titanate-based coupling agents. Examples of the resins include hydrocarbon-based resins, wax, polyethylene, polymethacrylate, etc.

[0028] If the content of magnetic particles is too low, the necessary shear stress will tend not to be obtained when a magnetic field is applied, and if the content is too high, the composition will become semi-solid rather than fluid, making it difficult to fill into a device and making it difficult to function as a magnetorheological fluid. From these perspectives, the content of magnetic particles in the magnetorheological fluid composition according to the present disclosure is preferably 60% by mass to 94% by mass, more preferably 70% by mass to 92% by mass, and even more preferably 75% by mass to 90% by mass, based on the total amount of the composition.

[0029] (base oil) The magnetorheological fluid composition according to the present disclosure contains a base oil. The base oil components constituting the base oil are not particularly limited, and may be mineral base oil components or synthetic base oil components. The base oil may be a single type or a mixture of two or more types.

[0030] Examples of mineral oil-based base oil components include solvent refined mineral oil, hydrorefined mineral oil, and hydrocracked mineral oil. Of these, hydrorefined mineral oil and hydrocracked mineral oil are preferred. The method for producing hydrorefined mineral oil and hydrocracked mineral oil is not particularly limited, but the following method is a preferred production method.

[0031] A preferred method for producing hydrorefined mineral oil is to vacuum distill the residual oil obtained by atmospheric distillation, then solvent extract the fraction obtained as a lubricating oil fraction, hydrorefining and solvent dewaxing, followed by a second hydrorefining.

[0032] A preferred method for producing hydrocracked mineral oil is to first treat the residual oil obtained by atmospheric distillation of crude oil in a vacuum distillation unit, hydrotreating and hydrocracking the resulting vacuum gas oil, then removing the light components and fuel components in a vacuum stripper to obtain a residue, which is then vacuum distilled, and the resulting lubricating oil fraction is hydrodewaxed or wax isomerized and stabilized, with wax isomerization being a more preferred method in which a high viscosity index is achieved.Furthermore, base oils obtained by hydrocracking and hydroisomerizing raw materials such as slack wax obtained by solvent dewaxing can also be used.

[0033] Examples of synthetic base oil components include base oils obtained by hydrocracking and hydroisomerization of raw materials such as wax obtained by Fischer-Tropsch synthesis, poly-α-olefin base oils, aromatic synthetic oils such as alkylbenzenes and alkylnaphthalenes, ester oils, alkylated phenyl ether oils, polyalkylene glycols, etc. A suitable method for producing poly-α-olefin base oils includes synthesizing α-olefins having 6 to 18 carbon atoms by oligomerization of ethylene or thermal cracking of wax, polymerizing 2 to 9 units of this α-olefin, and then hydrogenating the resulting α-olefins.

[0034] Suitable examples of the ester oil include monoesters produced from monohydric alcohols and monocarboxylic acids, diesters produced from monohydric alcohols and dicarboxylic acids, polyol esters produced from polyols and monocarboxylic acids, and complex esters produced from polyols, monocarboxylic acids, and polycarboxylic acids.

[0035] Examples of monoesters include those produced by a synthesis method using a monohydric alcohol having a branched structure and a monocarboxylic acid as raw materials. Specific examples of alcohols that can be used as raw materials for monoesters include 2-butyloctanol, 2-pentylnonanol, 2-hexyldecanol, 2-heptylundecanol, 2-octyldodecanol, 2-nonyltridecanol, and 2-decyltetradecanol. Specific examples of monocarboxylic acids that can be used as raw materials for monoesters include caprylic acid, capric acid, lauric acid, myristic acid, and palmitic acid. The total number of carbon atoms in the monoester is preferably 16 to 50, and more preferably 20 to 40.

[0036] Examples of diesters include esters of dibasic acids such as adipic acid, azelaic acid, sebacic acid, and dodecanedioic acid. The dibasic acid is preferably an aliphatic dibasic acid having 4 to 36 carbon atoms. The alcohol residue constituting the ester moiety is preferably a monohydric alcohol residue having 4 to 26 carbon atoms. Examples of such diesters include dioctyl adipate, dioctyl sebacate, diisodecyl adipate, and dioctyl azelate.

[0037] As the polyol used in the polyol ester or complex ester, specifically, a hindered alcohol having no β-hydrogen, such as trimethylolpropane, pentaerythritol, or neopentyl glycol, is suitable. In addition, preferred monocarboxylic acids used in polyol esters and complex esters include straight-chain saturated fatty acids such as coconut fatty acid and stearic acid, straight-chain unsaturated fatty acids such as oleic acid, and branched fatty acids such as isostearic acid. Preferred polycarboxylic acids include straight-chain saturated polycarboxylic acids such as succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, and sebacic acid.

[0038] Suitable examples of the alkylated phenyl ether oil include alkylated diphenyl ether, (alkylated) polyphenyl ether, etc. Also, examples of polyalkylene glycols include polyethylene glycol, polypropylene glycol, polybutylene glycol, ethylene oxide-propylene oxide copolymer, propylene oxide-butylene oxide copolymer, and derivatives thereof.

[0039] In the magnetorheological fluid composition according to the present disclosure, the content of the base oil is preferably 7% by mass to 50% by mass, more preferably 8% by mass to 40% by mass, and even more preferably 10% by mass to 30% by mass, based on the total amount of the magnetorheological fluid composition. A base oil content of 7% by mass or more tends to provide good fluidity and improve handleability, while a base oil content of 50% by mass or less is preferred because it increases shear stress when a magnetic field is applied.

[0040] The base oil has a kinematic viscosity of 2mm at 40°C according to the JIS K2283:2000 kinematic viscosity test method. 2 / s~1000mm 2 / s is preferred, 5mm 2 / s~700mm 2 / s is more preferable, 5mm 2 / s~500mm 2 / s is more preferred.

[0041] The kinematic viscosity of the base oil at 40°C is 2mm 2 If the kinematic viscosity of the base oil at 40°C is 1000mm / s or more, the flash point will be high, which will suppress evaporation and make it suitable for MR fluids. 2 A viscosity of 1 / s or less is preferred because it reduces the viscosity and facilitates stable dispersion of magnetic particles in the base oil during production of the magnetorheological fluid composition.

[0042] (Dispersant represented by formula (1)) The magnetorheological fluid composition according to the present disclosure contains a dispersant (hereinafter also referred to as the "specific dispersant") represented by the following formula (1). The specific dispersant is used to disperse magnetic particles in a base oil.

[0043] In the magnetorheological fluid composition according to the present disclosure, the content of the specific dispersant is 0.30% by mass to 0.55% by mass, and preferably 0.35% by mass to 0.50% by mass, relative to the total amount of the magnetorheological fluid composition.

[0044] By containing the specific dispersant in the above content range, the magnetorheological fluid composition according to the present disclosure exhibits significantly excellent fluidity at high shear when the magnetic field is turned off.

[0045] The specific dispersant may be used alone or in combination of two or more. When two or more specific dispersants are used, the total content is set to be 0.30% by mass to 0.55% by mass relative to the total amount of the magnetorheological fluid composition.

[0046] The specific dispersant will be described in more detail below.

[0047] [ka]

[0048] In formula (1), R 1 represents an aliphatic hydrocarbon group having 14 to 22 carbon atoms, and R 2 represents an ethylene group or a propylene group, and n represents an integer of 1 to 12.

[0049] In formula (1), R 1 The aliphatic hydrocarbon group having 14 to 22 carbon atoms represented by R may be saturated or unsaturated. 1 The aliphatic hydrocarbon group having 14 to 22 carbon atoms represented by the formula (I) may be a straight-chain aliphatic hydrocarbon group or a branched-chain aliphatic hydrocarbon group, but is preferably a straight-chain aliphatic hydrocarbon group.

[0050] R 1 The aliphatic hydrocarbon group represented by the formula (I) has 14 to 22 carbon atoms, preferably 16 to 20 carbon atoms, and more preferably 18 carbon atoms.

[0051] R1 Examples of the aliphatic hydrocarbon group represented by the formula (I) include a myristyl group, a palmityl group, an oleyl group, a stearyl group, and a stearyl group, with an oleyl group being preferred.

[0052] In formula (1), R 2 represents an ethylene group or a propylene group, and is preferably an ethylene group. When n is 2 or more, a plurality of R 2 may be the same or different, but are preferably the same.

[0053] In formula (1), n ​​represents an integer of 1 to 12. In one embodiment, n in formula (1) may be an integer of 3 to 10.

[0054] The dispersant represented by formula (1) preferably includes a dispersant represented by the following formula (2):

[0055] [ka]

[0056] In formula (2), n represents an integer of 1 to 12. In one embodiment, n may be an integer of 3 to 10 in formula (2).

[0057] Specific examples of the specific dispersant are shown below, but the specific dispersant is not limited to these.

[0058] [ka]

[0059] The magnetorheological fluid composition according to the present disclosure preferably contains only the specific dispersant as a dispersant.

[0060] (rheology control agent) The magnetorheological fluid composition according to the present disclosure contains a rheology control agent. Various rheology control agents can be used. The term "rheology control agent" used here refers to an additive that imparts non-Newtonian properties to the shear rate change, i.e., increases the shear viscosity in the low shear rate range while decreasing the shear viscosity in the high shear rate range.

[0061] The rheology control agent may be an inorganic compound-based rheology control agent or an organic compound-based rheology control agent. Inorganic rheology control agents include fumed silica, bentonite, mica, and kaolin. Examples of organic compound-based rheology control agents include urea-modified polymers, urethane-modified polymers, castor oil wax, polyethylene wax, polyamide wax, and fatty acid amide wax.

[0062] Among these, inorganic compound-based rheology control agents are preferred, with fumed silica and bentonite being more preferred. When fumed silica is used as the rheology control agent, it is preferable that the surface is made hydrophobic by a silane coupling agent or other surface modifier. When bentonite is used as the rheology control agent, it is preferable to use organo-bentonite which has been organically modified with a quaternary ammonium salt or other organic modifier.

[0063] In the magnetorheological fluid composition according to the present disclosure, the content of the rheology control agent is preferably 0.01% by mass to 5% by mass, more preferably 0.05% by mass to 4% by mass, and even more preferably 0.07% by mass to 3% by mass, relative to the total amount of the magnetorheological fluid composition. When the content of the rheology control agent is 0.01% by mass or more, a thickening effect can be obtained in the low shear rate range, and when the content of the rheology control agent is 5% by mass or less, an appropriate viscosity can be obtained when the magnetic field is turned off, and handling properties are also good, which is preferable. The rheology control agent may be used alone or in combination of two or more. When two or more types are used, the total content is preferably within the above range.

[0064] (Other additives) The magnetorheological fluid composition according to the present disclosure may contain other components in addition to the magnetic particles, base oil, dispersant, and rheology control agent in order to ensure various performance properties. Other components include known additives that are commonly used in magnetorheological fluid compositions, such as metal detergents, ashless detergents, oiliness agents, antiwear agents, extreme pressure agents, rust inhibitors, friction modifiers, solid lubricants, antioxidants, metal deactivators, antifoaming agents, colorants, viscosity index improvers, and pour point depressants.

[0065] Metallic detergents include sulfonates, phenates, salicylates, etc., in which the metal component is calcium or magnesium. Examples of ashless detergents include succinimide-based ashless detergents, succinamide-based ashless detergents, and boronated derivatives thereof. Examples of succinimide-based ashless detergents include polyalkenyl succinimides such as bispolypropenyl succinimide, monopropenyl succinimide, bispolybutenyl succinimide, monobutenyl succinimide, bispolypentenyl succinimide, and monopentenyl succinimide. Examples of succinamide-based ashless detergents include polyalkenyl succinamides such as polypropenyl succinamide, polybutenyl succinamide, and polypentenyl succinamide. Typically, the molecular weight (Mw) of the polyalkenyl group in these ashless detergents is about 70 to 50,000. Furthermore, examples of these boronated derivatives include ashless detergents obtained by reacting polyalkenyl succinic anhydrides with boron compounds such as boric acid, borate esters and borate salts, and polyamines.

[0066] Examples of oily agents include oleic acid, stearic acid, higher alcohols, amines, esters, sulfurized oils and fats, acid phosphates, and acid phosphites. Examples of the anti-wear agent include zinc dialkyldithiophosphate, various phosphoric acid esters, thiophosphate esters, and amine salts of various phosphoric acid esters. Examples of extreme pressure agents include hydrocarbon sulfides, sulfurized oils and fats, sulfur, phosphate esters, phosphites, chlorinated paraffins, and chlorinated diphenyls. Examples of the rust inhibitor include carboxylic acids and their amine salts, esters, sulfonates, and boron compounds. Examples of friction modifiers include organic molybdenum compounds, polyhydric alcohol partial esters, amines, amides, sulfurized esters, phosphates, acidic phosphates and their amine salts, and diols. Examples of solid lubricants include molybdenum disulfide, polytetrafluoroethylene (PTFE), graphite, calcium carbonate, boron nitride, and mica.

[0067] Examples of the antioxidant include amine-based, phenol-based, and sulfur-based antioxidants. Examples of the amine-based antioxidants include diphenylamine-based and naphthylamine-based antioxidants, and examples of the phenol-based antioxidants include hindered phenol-based antioxidants. Metal deactivators include benzotriazole, thiadiazole, alkenyl succinate, and the like. Examples of the antifoaming agent include silicone compounds such as dimethylpolysiloxane, fluorosilicone compounds, and ester compounds. Examples of pour point depressants include polyalkyl methacrylates, chlorinated paraffin-naphthalene condensates, and alkylated polystyrenes.

[0068] Examples of viscosity index improvers include polyalkyl methacrylates, polyisobutylenes, ethylene-propylene copolymers, styrene-isoprene copolymers, styrene-butadiene hydrogenated copolymers, and polyisobutylenes. The weight-average molecular weight (Mw) of the polymer used as the viscosity index improver is preferably 10,000 to 400,000, and particularly preferably 20,000 to 200,000. The amount of such viscosity index improver added is preferably 0.1% by mass to 10% by mass of the total amount of the composition.

[0069] The magnetorheological fluid composition according to the present disclosure can be prepared, for example, by the following procedure.

[0070] <Step 1: Preparation of oil for magnetorheological fluid composition> First, prepare an oil for a magnetorheological fluid composition by mixing a base oil and a specific dispersant. Mixing is carried out using a beaker and a magnetic stirrer at a temperature of about 50°C to 80°C. If oil-soluble additives such as antioxidants and viscosity index improvers are to be added, add them at this time. <Step 2: Mixing magnetic particles> The oil for the magnetorheological fluid composition prepared in step 1 is mixed with magnetic particles to allow the dispersant to be adsorbed onto the magnetic particles. As a mixer, a rotation-revolution type propellerless mixer, a planetary mixer, a homogenizer, or the like can be used. The materials to be mixed are preferably heated to about 60°C to 100°C in advance, and may be charged into the mixer after being heated. <Step 3: Mixing rheology control agent and other additives> After the magnetic particles have been uniformly mixed in step 2, the rheology control agent and any other additives other than the oil-soluble components that are used as desired are mixed in. As in step 2, the mixer that can be used may be a rotation-revolution type propellerless mixer, a planetary mixer, a homogenizer, or the like. The materials to be mixed should preferably be heated to around 60°C to 100°C, and pre-heated materials may also be added to the mixer. The magnetorheological fluid composition according to the present disclosure can be suitably obtained through the above steps 1 to 3. However, the method for producing the magnetorheological fluid composition according to the present disclosure is not limited to the above method.

[0071] <Application> The magnetorheological fluid composition according to the present disclosure is suitable for use in MR devices such as rotary and reciprocating dampers, clutches, and brakes. [Example]

[0072] Next, the magnetorheological fluid composition according to the present disclosure will be described in more detail with reference to examples, although the magnetorheological fluid composition according to the present disclosure is not limited by these examples.

[0073] In the examples and comparative examples, magnetorheological fluid compositions were prepared according to the following procedure. The performance of each of the resulting magnetorheological fluid compositions was then evaluated. The results are shown in Table 1.

[0074] <Preparation of magnetorheological fluid composition> (1) A base oil and a dispersant were placed in a beaker and mixed at 60°C using a magnetic stirrer so that the content of the components in the magnetorheological fluid composition would be the content shown in Table 1, to obtain an oil for the magnetorheological fluid composition. (2) The obtained oil for a magnetorheological fluid composition and magnetic particles were blended in the proportions shown in Table 1, heated to 80°C, and then uniformly stirred in a rotation-revolution propellerless mixer (ARE-500, manufactured by Thinky Corporation). After the magnetic particles were uniformly mixed, a rheology control agent and an antioxidant were blended in the proportions shown in Table 1, heated to 80°C, and then uniformly stirred in a rotation-revolution propellerless mixer to obtain a magnetorheological fluid composition.

[0075] Details of the components used in the production of the magnetorheological fluid compositions of the Examples and Comparative Examples are as follows:

[0076] (magnetic particles) Carbonyl iron powder (magnetic flux): Iron content is 99.7% by mass, cumulative 50% particle size is 4.5 μm The particle diameter of the magnetic particles is measured by laser diffraction scattering using a particle size measuring device (manufactured by Microtrac, product name: FRA), and is the average particle diameter of particles corresponding to 50% of the volume accumulated from the smallest diameter side of all particles.

[0077] (base oil) Base oil A: Poly-α-olefin, kinematic viscosity at 40°C is 17.1 mm 2 / s Base oil B: Monoester synthesized from capric acid and 2-hexyldecanol, carbon number 26, kinematic viscosity at 40°C 9.0mm 2 / s

[0078] (dispersant) Dispersant A: Polyoxyethylene oleyl ether phosphate (specific dispersant in formula (2) where n = 10) Dispersant B: Polyoxyethylene oleyl ether phosphate (specific dispersant in which n = 3 in formula (2)) Dispersant C: Acetoalkoxyaluminum diisopropylate Dispersant D: Oleylamine

[0079] (rheology control agent) Rheology control agent A: Bentonite treated with quaternary ammonium cations to make it lipophilic. Organized bentonite with an Al content of 5.9% by mass and a Si content of 15% by mass.

[0080] (antioxidant) Antioxidant A: Dialkylated diphenylamine Antioxidant B: 2,6-di-tert-p-cresol (DBPC) <Evaluation> The magnetorheological fluid compositions of the examples and comparative examples were subjected to the shear viscosity test when the magnetic field was off, as described below, to evaluate their fluidity at high shear.

[0081] =Shear viscosity test when magnetic field is off= The shear viscosity of the magnetorheological fluid composition was measured with an Anton Paar MCR101 rheometer under the following test conditions when the magnetic field was off.

[0082] (Test conditions) Measurement jig: φ20mm parallel plate Gap: 0.5mm ·Temperature: 20℃ Shear rate: 1000s -1 constant speed

[0083] (Judgment criteria) A shear viscosity of 700 mPa·s or less was determined to have excellent fluidity at high shear. A shear viscosity of 500 mPa·s or less is more preferable.

[0084] [Table 1]

[0085] The results shown in Table 1 show that the magnetorheological fluid compositions of the examples have superior fluidity under high shear when the magnetic field is off, compared to the magnetorheological fluid compositions of the comparative examples.

Claims

1. magnetic particles; A base oil, A dispersant represented by the following formula (1), and a rheology control agent, A magnetorheological fluid composition, wherein the content of the dispersant represented by formula (1) is 0.30% by mass to 0.55% by mass relative to the total amount of the magnetorheological fluid composition. 【Chemical 1】 In formula (1), R １ represents an aliphatic hydrocarbon group having 14 to 22 carbon atoms, and R ２ represents an ethylene group or a propylene group, and n represents an integer of 1 to 12.

2. 2. The magnetorheological fluid composition according to claim 1, wherein the dispersant represented by formula (1) includes a dispersant represented by formula (2): 【Chemistry 2】 In formula (2), n represents an integer of 1 to 12.

3. 3. The magnetorheological fluid composition according to claim 1, wherein the magnetic particles have a cumulative 50% particle size of 1 μm to 30 μm.

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