Magnetic viscous fluid composition

Abstract

To provide a magnetic viscous fluid composition that, when the magnetic field is turned off, exhibits excellent flowability under high shear and excellent anti-settling properties of magnetic particles over a wide temperature range.SOLUTION: A magnetic viscous fluid composition includes magnetic particles, a base oil, a dispersant, and organically modified bentonite. The organically modified bentonite includes at least one selected from the group consisting of dimethyldialkylammonium and benzyldimethylalkylammonium, and the mass loss in an ignition loss test is 35% or more relative to the total amount of the organically modified bentonite, and the content of the organically modified bentonite is 1.0 to 1.3 mass% relative to the total amount of the magnetic viscous fluid composition.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. The use of MRF has the advantage that the viscosity can be reversibly changed by applying a magnetic field, thereby widening the control range of the device.

[0003] Known magnetorheological fluids include those containing a magnetic material, a medium capable of dispersing the magnetic material, and sepiolite and bentonite as dispersants (Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2023-17481 Summary of the Invention [Problem to be solved by the invention]

[0005] Since magnetorheological fluids contain base oil and magnetic particles, the magnetic particles, which have a higher density than the base oil, tend to settle. The settling of magnetic particles makes it difficult to obtain a stress appropriate for the setting when a magnetic field is applied. Therefore, there is a need to suppress the settling of magnetic particles. 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 increasing the damping 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 also require improved fluidity compared to conventional models when subjected to high shear stresses when the magnetic field is off.

[0006] One embodiment of the present disclosure aims to provide a magnetorheological fluid composition that has excellent fluidity at high shear when the magnetic field is turned off and excellent anti-settling properties of magnetic particles over a wide temperature range. [Means for solving the problem]

[0007] The present disclosure includes the following aspects.

[0008] <1> A magnetorheological fluid composition comprising magnetic particles, a base oil, a dispersant, and organically modified bentonite, wherein the organically modified bentonite comprises at least one selected from the group consisting of dimethyldialkylammonium and benzyldimethylalkylammonium, and wherein the mass loss in an ignition loss test is 35% or more relative to the total amount of the organically modified bentonite, and the content of the organically modified bentonite is 1.0% by mass to 1.3% by mass relative to the total amount of the magnetorheological fluid composition. <2> The cumulative 50% particle size of the magnetic particles is 1 μm to 30 μm. <1> 10. The magnetorheological fluid composition according to claim 1 . <3> The organically modified bentonite contains at least one selected from the group consisting of dimethyl distearyl ammonium and benzyl dimethyl stearyl ammonium. <1> or <2> 10. The magnetorheological fluid composition according to claim 1 . <4> The base oil is a hydrocarbon lubricating base oil. <1> ~ <3> 10. The magnetorheological fluid composition according to claim 9, wherein the magnetorheological fluid composition is a magnetic material. [Effects of the Invention]

[0009] According to one embodiment of the present disclosure, it is possible to provide a magnetorheological fluid composition that has excellent flowability at high shear when the magnetic field is turned off and excellent anti-settling properties of magnetic particles over a wide temperature range. DETAILED DESCRIPTION OF THE INVENTION

[0010] 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.

[0011] 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.

[0012] In the present disclosure, "fluidity at high shear" refers to the fluidity at 20°C without applying a magnetic field to the target magnetorheological fluid composition at a shear rate of 1000 s -1 The viscosity is judged by the measured value of shear viscosity measured by applying shear stress at 1000 kJ / cm. The method and conditions for measuring shear viscosity will be described in the Examples below. In the present disclosure, "excellent fluidity at high shear" means that the shear viscosity measured by the above-mentioned measurement method and measurement conditions is 300 mPa·s or less.

[0013] In this disclosure, anti-settling properties over a wide temperature range are determined based on the test results of the sedimentation property test at room temperature (20°C) and the test results of the sedimentation property test at 80°C. The test results of the sedimentation property test are taken as the anti-settling properties. The sedimentation property test will be described in the Examples below. In the present disclosure, "excellent anti-settling properties of magnetic particles over a wide temperature range" means that the anti-settling properties at both room temperature (20°C) and 80°C are 25% or less, and preferably 15% or less.

[0014] The magnetorheological fluid composition according to the present disclosure contains magnetic particles, a base oil, a dispersant, and organically modified bentonite, the organically modified bentonite containing at least one selected from the group consisting of dimethyldialkylammonium and benzyldimethylalkylammonium, and the mass loss in an ignition loss test is 35% or more relative to the total amount of the organically modified bentonite, and the content of the organically modified bentonite is 1.0% by mass to 1.3% by mass relative to the total amount of the magnetorheological fluid composition.

[0015] The magnetorheological fluid composition according to the present disclosure exhibits excellent high shear flowability when the magnetic field is turned off, and also exhibits excellent anti-settling properties for magnetic particles over a wide temperature range, meaning that the anti-settling properties are excellent both at room temperature and at high temperatures such as 80°C.

[0016] (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.

[0017] 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.

[0018] 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.

[0019] 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.

[0020] 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.

[0021] 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.

[0022] (base oil) The magnetorheological fluid composition according to the present disclosure contains a base oil, which is preferably a hydrocarbon-based lubricating base oil. The base oil components constituting the hydrocarbon lubricating base oil are not particularly limited, and may be mineral base oil components or synthetic base oil components.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] The base oil may be used alone or in combination of two or more.

[0033] 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.

[0034] 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 preferably 5 mm 2 / s~500mm 2 / s is more preferred.

[0035] 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.

[0036] (dispersant) The magnetorheological fluid composition according to the present disclosure contains a dispersant, which is used to disperse the magnetic particles in the base oil.

[0037] The dispersant preferably has a functional group that has affinity with the magnetic particles. Specific examples of dispersants include higher fatty acids such as caproic acid, lauric acid, myristic acid, palmitic acid, stearic acid, and oleic acid, fatty acid esters, and esters such as sorbitan fatty acid esters. Other examples include fatty acid amides, fatty acid amines, polyoxyethylene derivatives, glycerin derivatives, castor oil derivatives, and ammonium salts.

[0038] The content of the dispersant is 0.20% by mass to 0.40% by mass, and preferably 0.25% by mass to 0.35% by mass, relative to the total amount of the magnetorheological fluid composition. By including a 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.

[0039] (organically modified bentonite) The magnetorheological fluid composition according to the present disclosure contains an organically modified bentonite, which functions as a rheology control agent. The rheology control agent referred to here is an additive that imparts non-Newtonian properties to the shear rate change, and imparts flow characteristics such as increasing the shear viscosity in the low shear rate range while decreasing the shear viscosity in the high shear rate range.

[0040] Organically modified bentonite is a modified product made by reacting the clay mineral bentonite with quaternary ammonium ions. Modification with organic substances is also called modification, and organically modified bentonite is also called organic bentonite or organically modified bentonite. The layered clay mineral that serves as the host of organically modified bentonite has exchangeable cations between the layers. Organically modified bentonite is produced by reacting unmodified bentonite with quaternary ammonium ions. For example, organically modified bentonite is produced by reacting Na ions present between the layers of montmorillonite, a layered clay mineral. + It is produced by an ion exchange reaction between ions and quaternary ammonium ions. The organically modified bentonite according to the present disclosure is obtained by modifying unmodified bentonite to contain at least one selected from the group consisting of dimethyldialkylammonium and benzyldimethylalkylammonium. The organically modified bentonite may contain one kind of dimethyldialkylammonium and benzyldimethylalkylammonium, or may contain a plurality of different kinds thereof.

[0041] In the organically modified bentonite according to the present disclosure, it is preferable that the dimethyldialkylammonium or benzyldimethylalkylammonium has an alkyl group having 16 to 22 carbon atoms, since these have excellent affinity with hydrocarbon lubricating base oils and provide the magnetorheological fluid composition with excellent fluidity under high shear when the magnetic field is turned off. Specific examples of the alkyl group include a stearyl group (octadecyl group, carbon number 18) and a palmityl group (hexadecyl group, carbon number 16), with the stearyl group being preferred.

[0042] The organically modified bentonite has a mass loss in an ignition loss test of 35% or more, more preferably 38% or more, based on the total mass of the organically modified bentonite. The upper limit is preferably 55% or less, and more preferably 50% or less. When the mass loss of the organically modified bentonite is within these ranges, compatibility with the base oil is improved, and better anti-settling properties of the magnetic particles are obtained. Furthermore, when the mass loss is 50.0% or less, the amount of the organically modified bentonite itself is sufficiently secured, and the flowability under high shear when the magnetic field is turned off is superior.

[0043] The loss on ignition test is a test to measure the mass of volatile substances, mainly organic matter, contained in minerals, and is calculated from the amount of mass lost after heating. In the present disclosure, the mass loss of organically modified bentonite in an ignition loss test is measured by the following method. The dried organically modified bentonite is heated at 800°C for 1 hour, and the mass is measured before and after heating. The mass loss after heating is used to calculate the percentage of mass loss.

[0044] The magnetorheological fluid composition may contain one type of organically modified bentonite, or may contain a plurality of different types of organically modified bentonite.

[0045] The content of the organically modified bentonite is 1.0 to 1.3 mass %, preferably 1.0 to 1.2 mass %, relative to the total amount of the magnetorheological fluid composition. When the content of the organically modified bentonite is within this range, the composition exhibits excellent fluidity under high shear when the magnetic field is turned off.

[0046] (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 organically modified bentonite 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.

[0047] 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.

[0048] Examples of oily agents include 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.

[0049] 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.

[0050] 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.

[0051] The magnetorheological fluid composition according to the present disclosure can be prepared, for example, by the following procedure.

[0052] <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 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 organically modified bentonite and other additives> After the magnetic particles are uniformly mixed in step 2, the organically modified bentonite and any other additives other than the oil-soluble component that are used as desired are mixed in. As in step 2, a rotation-revolution type propellerless mixer, planetary mixer, homogenizer, etc. can be used as the mixer. It is desirable to heat the materials to be mixed to around 60°C to 100°C, and pre-heated materials can 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.

[0053] <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]

[0054] 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.

[0055] 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.

[0056] <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 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, each of organically modified bentonite A to organically modified bentonite G (rheology control agents) was 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.

[0057] Details of the components used in the production of the magnetorheological fluid compositions of the Examples and Comparative Examples are as follows:

[0058] (magnetic particles) Carbonyl iron powder (magnetic particles, pyrolysis product of pentacarbonyl iron (Fe(CO)5): iron content is 99.7% by mass, cumulative 50% particle size is 6.2 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.

[0059] (base oil) Base oil A: Poly-α-olefin, kinematic viscosity at 40°C is 5.2 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

[0060] (dispersant) Oleic acid

[0061] (Organically modified bentonite (rheology control agent)) Organically modified bentonite A (manufactured by Hojun Co., Ltd., product name: Esben N400) This is an organically modified bentonite modified with dimethyl distearyl ammonium, and the organic matter content was 39.3% according to the loss on ignition test. Organically modified bentonite B (manufactured by Hojun Co., Ltd., product name: Esben NX80) The organically modified bentonite modified with dimethyl distearyl ammonium exhibited a mass loss of 49.9% in the loss on ignition test. Organically modified bentonite C (manufactured by Hojun Co., Ltd., product name: Moistnite WO) The organically modified bentonite was modified with dimethyl distearyl ammonium, and the mass loss in the loss on ignition test was 49.0%. Organically modified bentonite D (manufactured by Hojun Co., Ltd., product name: Organite) The bentonite was modified with benzyldimethylstearylammonium, and the mass loss in the loss on ignition test was 28.9%. Organically modified bentonite E (manufactured by Hojun Co., Ltd., product name: Esben NZ70) The bentonite was modified with benzyldimethylstearylammonium, and the mass loss in the loss on ignition test was 51.4%. Organically modified bentonite F (Kunimine Industries, product name: Kunibis 110) The trimethylstearylammonium-modified organically modified bentonite showed a mass loss of 36.0% in an ignition loss test. Organically modified bentonite G (Kunimine Industries, product name: Sumecton-SAN) The trimethylstearylammonium-modified organically modified bentonite showed a mass loss of 43.0% in an ignition loss test.

[0062] <Evaluation> The magnetorheological fluid compositions of the Examples and Comparative Examples were subjected to the shear viscosity test and anti-settling test when the magnetic field was off, as described below, to evaluate their fluidity and anti-settling properties at high shear.

[0063] =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.

[0064] (Test conditions) Measurement jig: φ20mm parallel plate Gap: 0.5mm ·Temperature: 20℃ Shear rate: 1000s -1 constant speed

[0065] (Judgment criteria) A shear viscosity of 300 mPa·s or less was determined to have excellent fluidity under high shear.

[0066] = Sedimentation characteristics test = (After 168 hours at room temperature) 10 ml of each of the magnetorheological fluid compositions obtained in the Examples and Comparative Examples was placed in a 10 ml glass measuring cylinder and allowed to stand at room temperature (approximately 20°C) for 168 hours. After 168 hours, the amount of oil [ml] that had separated to the top of the measuring cylinder was visually read, and this value was substituted into the following formula (1) to calculate the separation rate. The results are shown in Table 1. Separation rate (%)=(separated oil amount [ml] / 10[ml])×100 (1) The smaller the separation rate, the better the suppression of sedimentation. For practical purposes, the separation rate after 168 hours is preferably 25% or less, more preferably 20% or less, and even more preferably 10% or less.

[0067] (80℃ 5 hours later) 10 ml of each of the magnetorheological fluid compositions obtained in the Examples and Comparative Examples was placed in a 10 ml glass measuring cylinder and allowed to stand at approximately 80°C for 5 hours. After 5 hours, the amount of oil [ml] that had separated to the top of the measuring cylinder was visually read, and this value was substituted into the above formula (1) to calculate the separation rate. The results are shown in Table 1. The smaller the separation rate, the better the suppression of sedimentation. For practical purposes, the separation rate after 168 hours is preferably 25% or less, more preferably 20% or less, and even more preferably 15% or less.

[0068] [Table 1]

[0069] 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, and are superior in preventing the settling of magnetic particles over a wide temperature range, compared to the magnetorheological fluid compositions of the comparative examples.

Claims

1. The magnetic material contains magnetic particles, a base oil, a dispersant, and organically modified bentonite, the organically modified bentonite contains at least one selected from the group consisting of dimethyldialkylammonium and benzyldimethylalkylammonium, and the mass loss in an ignition loss test is 35% or more relative to the total mass of the organically modified bentonite; A magnetorheological fluid composition, wherein the content of the organically modified bentonite is 1.0% by mass to 1.3% by mass based on the total amount of the magnetorheological fluid composition.

2. 2. The magnetorheological fluid composition according to claim 1, wherein the cumulative 50% particle diameter of the magnetic particles is 1 μm to 30 μm.

3. 2. The magnetorheological fluid composition according to claim 1, wherein the dimethyldialkylammonium or the benzyldimethylalkylammonium has an alkyl group having 16 to 22 carbon atoms.

4. 2. The magnetorheological fluid composition according to claim 1, wherein the base oil is a hydrocarbon-based lubricating base oil.

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