Magnetic viscous fluid composition

Abstract

To provide a magnetic viscous fluid composition that has excellent flowability when the magnetic field is turned off and also has excellent wear resistance.SOLUTION: A magnetic viscous fluid composition includes magnetic particles, a base oil, a dispersant, and at least one selected from a sulfurized ester and a sulfurized olefin, and the total content of the sulfurized ester and the sulfurized olefin is 0.15 mass% to 0.45 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.

[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 the like. Applications of MRFs to dampers have been reported, including 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). Non-Patent Document 3 also reports on the lubrication properties of MRFs. [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) [Non-patent document 3] Tribology Conference 2014 Spring Tokyo Proceedings, "The Role of Iron Particles on the Lubricity of Magnetorheological Fluids," pp. 217-218 (2014) 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 changed significantly to a range that is not possible with ordinary fluids, thereby widening the control range of the device. The desirable performance of the MRF is that it has a lower viscosity when the magnetic field is off and generates higher stress when the magnetic field is applied. Furthermore, since the MRF is used in the moving parts of the device, it is also required to be wear-resistant.

[0006] An object of one embodiment of the present disclosure is to provide a magnetorheological fluid composition that has excellent fluidity when the magnetic field is turned off and excellent wear resistance. [Means for solving the problem]

[0007] The present disclosure includes the following aspects.

[0008] <1> The lubricant contains magnetic particles, a base oil, a dispersant, and at least one selected from a sulfurized ester and a sulfurized olefin, the total content of the sulfurized ester and the sulfurized olefin is 0.15% by mass to 0.45% by mass relative to the total amount of the magnetorheological fluid composition; Magnetorheological fluid compositions. <2> The dispersant comprises a compound having two or more polar functional groups; <1> 10. The magnetorheological fluid composition according to claim 1 . <3> The compound having two or more polar functional groups is a fatty acid vinyl polymer. <2> 10. The magnetorheological fluid composition according to claim 1 . <4> The cumulative 50% particle size of the magnetic particles is 1 μm to 30 μm. <1> ~ <4> 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 fluidity when the magnetic field is turned off and excellent wear resistance. 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, whether or not a magnetorheological fluid composition has flowability is determined by visually observing the appearance of the magnetorheological fluid composition. Specifically, the presence or absence of flowability is determined by the method described in the Examples below.

[0013] In this disclosure, wear resistance is determined based on the results of a block-on-ring wear test at room temperature (20°C). The results of the block-on-ring wear test are taken as the wear resistance. The block-on-ring wear test will be described in the Examples section below.

[0014] The magnetorheological fluid composition according to the present disclosure contains magnetic particles, a base oil, a dispersant, and at least one selected from a sulfurized ester and a sulfurized olefin, and the total content of the sulfurized ester and the sulfurized olefin is 0.15 mass % to 0.45 mass % relative to the total amount of the magnetorheological fluid composition.

[0015] The magnetorheological fluid composition according to the present disclosure has excellent fluidity when the magnetic field is turned off, and also has excellent wear resistance.

[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 accounts for the largest proportion by mass of the components that make up the magnetic particles, and is preferably 50% by mass or more, and more preferably 70% by mass or more, of the components that make up the magnetic particles.

[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 preferable, 5mm 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 is preferably a compound having a functional group that has affinity for the magnetic particles, and more preferably a compound having two or more polar functional groups (hereinafter also referred to as a "specific dispersant"). The magnetorheological fluid composition according to the present disclosure contains the specific dispersant and a predetermined amount of at least one selected from a sulfurized ester and a sulfurized olefin, thereby exhibiting significantly excellent fluidity and wear resistance when the magnetic field is turned off.

[0038] The polar functional group contained in the specific dispersant may be a polar functional group such as a hydroxyl group, a carboxyl group, a carbonyl group, an ester group, an ether group, a nitrile group, an amino group, an amide group, an imide group, a sulfonic acid group, a thiol group, a sulfide group, a phosphate group, or a metal salt or metal complex thereof. In one embodiment, the polar functional group contained in the specific dispersant preferably includes a carboxyl group.

[0039] The specific dispersant is preferably a fatty acid oligomer compound. In the present disclosure, the oligomer compound means a compound having a molecular weight of more than 1,000 and not more than 10,000.

[0040] Examples of the fatty acid oligomer compound that is the specific dispersant include compounds selected from fatty acid vinyl polymers and polymers of hydroxyl group-containing fatty acid monomers.

[0041] = Fatty acid vinyl polymer = Among fatty acid oligomer compounds, examples of fatty acid vinyl polymers include compounds represented by the following formula (1).

[0042] [ka]

[0043] In formula (1), R 1 represents a hydrocarbon group having 1 to 24 carbon atoms, and n is an integer of 2 to 100.

[0044] The compound represented by formula (1) includes R 1 is preferably a hydrocarbon group having 2 to 18 carbon atoms.

[0045] The fatty acid vinyl polymer is preferably an oligomer. The fatty acid vinyl polymer may be a homo-oligomer of a fatty acid vinyl monomer alone, or may be a cooligomer (copolymer) with a monomer other than the fatty acid vinyl monomer. Examples of the monomer other than the fatty acid vinyl monomer used in synthesizing the cooligomer include olefin monomers. Specific examples of the olefin monomer include ethylene monomer, propylene monomer, and butene monomer.

[0046] When synthesizing a cooligomer of a fatty acid vinyl monomer and an olefin monomer, the molar ratio of the fatty acid vinyl monomer to the olefin monomer is preferably 1:30 to 30:1, more preferably 1:20 to 20:1. Furthermore, in the cooligomer of a fatty acid vinyl monomer and an olefin monomer, the molar ratio of the constituent units derived from the fatty acid vinyl to the constituent units derived from the olefin is preferably 1:30 to 30:1, more preferably 1:20 to 20:1.

[0047] =Polymer of hydroxyl group-containing fatty acid monomer= Among fatty acid oligomer compounds, polymers of hydroxyl group-containing fatty acid monomers include compounds represented by the following formula (2).

[0048] [ka]

[0049] In formula (2), R 2 and R 3 each independently represents a divalent hydrocarbon group having 1 to 36 carbon atoms and having a straight or branched chain, m is an integer of 2 to 15, X and Y are each independently any one selected from a carboxyl group, a hydroxyl group, and a hydrogen atom, and at least one of X and Y is a carboxyl group or a hydroxyl group. When m is 2 to 15, the copolymer moiety (-R 3 -COO-)m is R 3 Two or more structural units (-R 3 -COO-).

[0050] In formula (2), X and Y are each independently any one selected from a carboxyl group, a hydroxyl group, and a hydrogen atom, and at least one of X and Y is a carboxyl group or a hydroxyl group. X and Y preferably have one carboxyl group and one hydroxyl group. Most preferably, X is a carboxyl group and Y is a hydroxyl group.

[0051] The compound represented by formula (2) can be obtained, for example, by polymerizing a hydroxycarboxylic acid having 2 to 37 carbon atoms as a monomer. Here, hydroxycarboxylic acid refers to a compound having both a hydroxyl group and a carboxyl group in the same molecule. Examples of such hydroxycarboxylic acids include 3-hydroxylauric acid, 3-hydroxypaltimic acid, 3-hydroxystearic acid, 3-hydroxyarachidic acid, 8-hydroxypaltimic acid, 12-hydroxystearic acid, 12-hydroxylauric acid, 12-hydroxypalmitoleic acid, 12-hydroxyoleic acid, and 16-hydroxypaltimic acid.

[0052] Those in which Y is a carboxyl group can be obtained by ester-bonding a dicarboxylic acid having 2 to 36 carbon atoms to the above-mentioned polymer of hydroxycarboxylic acid, and those in which X is a hydroxyl group can be obtained by ester-bonding a dihydric alcohol having 1 to 36 carbon atoms to the above-mentioned polymer of hydroxycarboxylic acid.

[0053] The specific dispersant is preferably at least one selected from a fatty acid vinyl polymer, a polymer of a hydroxyl group-containing fatty acid monomer, a partial ester of a polyhydric alcohol, and a polyhydric alcohol ether, and more preferably a fatty acid vinyl polymer.

[0054] The specific dispersant may have an acid value, a hydroxyl value, or an amine value derived from a polar functional group. When the specific dispersant has an acid value, the acid value is preferably 1 mgKOH / g to 150 mgKOH / g, and more preferably 5 mgKOH / g to 120 mgKOH / g. When the specific dispersant has a hydroxyl value, the hydroxyl value is preferably 50 mgKOH / g to 500 mgKOH / g, and more preferably 100 mgKOH / g to 450 mgKOH / g. Furthermore, the specific dispersant may be mixed with a fatty acid and / or an alcohol and used as a dispersant having an acid value and / or a hydroxyl value.

[0055] From the viewpoint of achieving both fluidity and wear resistance when the magnetic field is turned off, the content of the dispersant is preferably 0.05 mass % to 0.35 mass %, and more preferably 0.1 mass % to 0.3 mass %, relative to the total amount of the magnetorheological fluid composition.

[0056] The dispersant may be used alone or in combination of two or more. When two or more dispersants are used, the total content is preferably within the above range. When a mixture of a specific dispersant and a fatty acid and / or an alcohol is used as the dispersant, the content of the mixture is included in the content of the dispersant.

[0057] (Sulfurized esters and sulfurized olefins) The magnetorheological fluid composition according to the present disclosure contains at least one selected from a sulfurized ester and a sulfurized olefin, and the total content of the sulfurized ester and the sulfurized olefin is 0.15 mass % to 0.45 mass % based on the total amount of the magnetorheological fluid composition. The sulfurized ester and the sulfurized olefin function as an anti-wear agent.

[0058] The total content of the sulfurized ester and sulfurized olefin is 0.15 mass % to 0.45 mass % relative to the total amount of the magnetorheological fluid composition, from the viewpoint of achieving both fluidity and wear resistance when the magnetic field is turned off, and is more preferably 0.2 mass % to 0.4 mass % from the viewpoint of achieving excellent fluidity when the magnetic field is turned off and further improving wear resistance.

[0059] The magnetorheological fluid composition according to the present disclosure may contain either a sulfurized ester or a sulfurized olefin, or may contain both a sulfurized ester and a sulfurized olefin. In some embodiments, the magnetorheological fluid composition according to the present disclosure preferably contains a sulfurized ester from the viewpoint of further improving wear resistance.

[0060] Sulfurized esters are products obtained by sulfurizing fatty acid esters obtained by reacting fats and oils with various alcohols. Examples of fats and oils include animal and vegetable fats such as lard, beef tallow, whale oil, palm oil, coconut oil, and rapeseed oil. This product is not a single substance but a mixture of various substances, and its chemical structure is unclear.

[0061] Examples of sulfurized olefins include those obtained by sulfurizing olefins such as polyisobutylene and terpenes with sulfur or other sulfurizing agents.

[0062] The sulfur content of the sulfurized olefin is preferably 20% by mass or more, more preferably 25% by mass or more, on a mass basis.

[0063] The sulfur content of the sulfurized ester is preferably 5% by mass or more, more preferably 8% by mass or more, on a mass basis.

[0064] The component contained as an antiwear agent in the magnetorheological fluid composition according to the present disclosure is preferably at least one selected from sulfurized esters and sulfurized olefins.

[0065] (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., it imparts flow characteristics such as increasing the shear viscosity in the low shear rate range and decreasing the shear viscosity in the high shear rate range.

[0066] The rheology control agent may be an inorganic compound-based rheology control agent or an organic compound-based rheology control agent. Inorganic compound-based 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.

[0067] 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.

[0068] 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.

[0069] 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.

[0070] (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 commonly used in magnetorheological fluid compositions, such as metal detergents, ashless detergents, oiliness agents, rust inhibitors, solid lubricants, antioxidants, metal deactivators, antifoaming agents, colorants, viscosity index improvers, and pour point depressants.

[0071] 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.

[0072] Examples of oily agents include higher alcohols, amines, esters, sulfurized oils and fats, acid phosphates, and acid phosphites. Examples of the rust inhibitor include carboxylic acids and their amine salts, esters, sulfonates, and boron compounds. Examples of solid lubricants include molybdenum disulfide, polytetrafluoroethylene (PTFE), graphite, calcium carbonate, boron nitride, and mica.

[0073] 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.

[0074] 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.

[0075] The magnetorheological fluid composition according to the present disclosure can be prepared, for example, by the following procedure.

[0076] <Step 1: Preparation of oil for magnetorheological fluid composition> An oil for a magnetorheological fluid composition is prepared in advance by mixing a base oil, a dispersant, and a sulfurized ester and / or a sulfurized olefin. 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, they are added 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, etc. 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 other additives> After the magnetic particles have been uniformly mixed in step 2, any 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, or the like can be used as the mixer. It is desirable to heat the materials to be mixed to about 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.

[0077] <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]

[0078] 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.

[0079] 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.

[0080] <Preparation of magnetorheological fluid composition> (1) A base oil, a dispersant, and an anti-wear agent (sulfurized ester and / or sulfurized olefin, or a comparative compound) were placed in a beaker and mixed at 60°C using a magnetic stirrer so that the contents of the components in the magnetorheological fluid composition would be those shown in Table 1, to obtain an oil for a 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 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.

[0081] Details of the components used in the production of the magnetorheological fluid compositions of the Examples and Comparative Examples are as follows:

[0082] (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.

[0083] (base oil) Base oil A: Highly refined mineral oil, kinematic viscosity at 40°C is 12.9mm 2 / s Base oil B: Poly-α-olefin, kinematic viscosity at 40°C is 5.2 mm 2 / s Base oil C: 2-ethylhexyl laurate, kinematic viscosity at 40°C is 5.1mm 2 / s

[0084] (dispersant) Dispersant A: a mixture of a copolymer of vinyl butanoate monomer (a) and ethylene monomer (b) (the molar ratio of a to b is 1:12, the weight average molecular weight (Mw) is 5580) and butanoic acid (the acid value is 28 mg KOH / g, and the content of the copolymer relative to the total mass of Dispersant A is 97% by mass)

[0085] (Sulfurized ester (anti-wear agent)) Anti-wear agent A: sulfur content 11% by mass

[0086] (Sulfurized olefin (anti-wear agent)) Anti-wear agent B: sulfur content 36% by mass

[0087] (Comparative anti-wear agent) Anti-wear agent C: alkyldithiothiadiazole, sulfur content 46.5% by mass Anti-wear agent D: Amine molybdate Anti-wear agent E: Zinc dialkyldithiophosphate (ZnDTP) Anti-wear agent F: tricresyl phosphate,

[0088] (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.

[0089] <Evaluation> The magnetorheological fluid compositions of the examples and comparative examples were checked for fluidity and subjected to a block-on-ring wear test when the magnetic field was off to evaluate their fluidity and wear resistance.

[0090] =Liquidity= The presence or absence of fluidity was evaluated according to the following evaluation method and criteria.

[0091] -Judgment method- A 30 mL container (transparent glass bottle) was filled with 15 mL of the prepared magnetorheological fluid composition and sealed to prepare a test sample, which was then stored at room temperature (20°C) for two weeks. After two weeks had passed, the test sample was placed on a test stand, and the container was tilted until the angle between the side of the container and the surface of the test stand was approximately 45°. For each of the evaluation samples, the appearance of the magnetorheological fluid composition was visually observed while the container was tilted, and evaluated based on the following criteria.

[0092] -Judgment criteria- Fluidity "Yes": The magnetorheological fluid composition in the container flowed. "No" fluidity: The magnetorheological fluid composition in the container did not flow.

[0093] =Block-on-ring wear test= The magnetorheological fluid composition was subjected to an abrasion test under the following test conditions using a block-on-ring tester "LFW-1" manufactured by Falex, and the maximum abrasion width was measured.

[0094] (Test conditions) Rotation speed: 600 rpm (revolutions per minute) Load: 178N ·Temperature: Room temperature (20℃) Block material: SAE01 Ring material: SAE4620

[0095] (Judgment criteria) A maximum wear width of 2000 μm or less was determined to be excellent in wear resistance. The smaller the maximum wear width, the better the wear resistance.

[0096] [Table 1]

[0097] The results shown in Table 1 show that the magnetorheological fluid compositions of the examples have superior fluidity when the magnetic field is turned off and superior wear resistance compared to the magnetorheological fluid compositions of the comparative examples.

Claims

1. The lubricant contains magnetic particles, a base oil, a dispersant, and at least one selected from a sulfurized ester and a sulfurized olefin, the total content of the sulfurized ester and the sulfurized olefin is 0.15% by mass to 0.45% by mass based on the total amount of the magnetorheological fluid composition; Magnetorheological fluid compositions.

2. The magnetorheological fluid composition of claim 1 , wherein the dispersant comprises a compound having two or more polar functional groups.

3. 3. The magnetorheological fluid composition according to claim 2, wherein the compound having two or more polar functional groups is a fatty acid vinyl polymer.

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

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