JP2019033222A - Magneto rheological fluid composition - Google Patents

Abstract

To provide a magneto rheological fluid composition superior in long-term stability and arranged so that the precipitation of magnetic particles can be suppressed.SOLUTION: A magneto rheological fluid composition comprises: (A) magnetic particles; (B) a lubricant base oil; and (C) a copolymer having a constituting unit originating from ethylene and a constituting unit originating from an olefin-based carbon hydride other than the ethylene.SELECTED DRAWING: None

Description

  The present invention relates to a magnetorheological fluid composition.

A magnetic fluid is a mixture of synthetic oil and magnetic particles and a surfactant, and is generally sold. Since the particle size of magnetic particles used in magnetic fluids is as small as a few nanometers, particle agglomeration can be prevented by the dispersion force of the surfactant, and usually the magnetic particles do not settle even after standing for several years.
However, since the magnetic particles used in magnetic fluids have a very small particle size, the increase in viscosity and yield stress is small even when a magnetic field is applied, and magnetic fluids can be applied to clutches, dampers, etc. It is difficult to use in applications such as magnetic seals.

In recent years, for the purpose of application to automobile dampers, a magnetic viscous fluid (Magneto-Rheological Fluid: MR) in which magnetic particles having a particle diameter much larger than that of magnetic particles used in magnetic fluids are blended in a base oil. Fluid) has been developed.
The magnetorheological fluid is a functional fluid that rapidly, continuously, and reversibly changes from a highly fluid state to a gel state having a large yield stress in accordance with the magnetic field strength applied from the outside.
A damper filled with a magnetorheological fluid is generally called an MR damper. Since the MR damper can control the magnitude of the yield stress by changing the magnetic field strength, the damping force can be adjusted in a wide range. Therefore, when applied to an automobile damper, the MR damper improves the body stability of the automobile. At the same time, it is said that an excellent ride comfort can be realized (for example, see Non-Patent Document 1 and Non-Patent Document 2).

In recent years, various applications of magnetorheological fluids to various clutches, actuators, brakes and the like have been studied in addition to MR dampers for automobiles.
Magneto-viscous fluid has recently attracted attention in the field of seismic isolation and vibration control for buildings such as high-rise buildings and ordinary detached houses, and reduces both the response acceleration and response displacement of structures against vibration. For this purpose, it is being applied to energy absorbing members such as dampers. When the MR damper is applied to this application, since the yield stress control range is wide, a damping force corresponding to the degree of shaking of the building can be generated, and the shaking of the building can be suppressed when an earthquake occurs.

  Magnetorheological fluid is a mixture of lubricating oil base oil and magnetic particles, but with only two components of lubricating oil base oil and magnetic particles, magnetic particles of much higher density are more likely to settle out earlier than base oil. It is known that once the magnetic particles settle, it is difficult to obtain an output (yield stress) corresponding to the set value when necessary.

  For example, since an MR damper installed in a building has been in a stationary state for a long time, magnetic particles settle, and, for example, a magnetic field is turned on (ie, a magnetic field is applied to a magnetorheological fluid) when an earthquake occurs. Even in such a case, the actual yield stress is small, and there is a risk that a sufficient vibration control effect cannot be obtained compared to the initial setting value.

As an attempt to suppress the sedimentation of magnetic particles by adding various additives to the magnetorheological fluid, for example, magnetorheological fluid in which fumed silica is blended with 50% by mass of glycols as a carrier fluid (lubricant base oil). Is disclosed (for example, see Patent Document 1).
Furthermore, as a magnetic viscosity agent composition excellent in stability capable of suppressing sedimentation of magnetic particles over a long period of time, a specific base oil, a specific magnetic particle having a specific average particle diameter, and a specific settling inhibitor, The magnetic viscosity agent composition to contain is disclosed (for example, refer patent document 2).

Journal of Precision Engineering, P813-816, Vol. 72, no. 7 (2006) HONDA R & D Technical Review, Vol. 19, no. 1 (April 2007)

Special table 2010-535432 gazette Japanese Unexamined Patent Publication No. 2016-213301

In the magnetorheological fluid described in Patent Document 1, although the sedimentation of iron particles is suppressed for a short period (24 hours in the example of the same document), the sedimentation suppression of magnetic particles in a short time is not effective in terms of performance. For this reason, development of a magnetorheological fluid capable of suppressing sedimentation of magnetic particles over a long period of time is desired.
Moreover, in the magnetic viscosity agent composition described in Patent Document 2, further improvement is required for long-term sedimentation suppression of magnetic particles.

  An object of the present invention is to provide a magnetorheological fluid composition that suppresses sedimentation of magnetic particles and has excellent long-term stability.

  As a result of repeated studies with the intention of achieving the above-mentioned problems, the present inventors have found that magnetic particles, lubricating base oils, structural units derived from ethylene, and structures derived from olefinic hydrocarbon monomers other than ethylene By blending a copolymer having units, a magnetorheological fluid composition in which sedimentation of magnetic particles was suppressed and excellent in stability was found, and the present invention was completed.

Means for solving the above problems include the following embodiments.
<1> Magnetic particles (A), lubricating base oil (B), a copolymer (C) having a structural unit derived from ethylene and a structural unit derived from an olefinic hydrocarbon other than ethylene. A magnetorheological fluid composition.
<2> The magnetorheological fluid according to <1>, wherein the magnetic particles (A) are metal particles containing iron, and the content of the iron is 98% by mass or more based on the total mass of the metal particles. Composition.
<3> The magnetorheological fluid composition according to <1> or <2>, wherein a cumulative 50% particle size of the magnetic particles (A) is 0.05 μm to 50 μm.
<4> The kinematic viscosity at 40 ° C. of the lubricating base oil (B) is ^{2mm 2 / s~5000mm 2 / s,} <1> ~ magnetorheological fluid composition according to any one of <3> .
<5> The magnetorheological fluid composition according to any one of <1> to <4>, wherein the copolymer (C) has a weight average molecular weight of 20,000 to 500,000.
<6> 40% by mass to 95% by mass of the magnetic particles (A) with respect to the total mass of the composition, and 0.3% by mass to 8% by mass of the copolymer with respect to the total mass of the composition ( C), and the magnetorheological fluid composition according to any one of <1> to <5>.
<7> The magnetism according to any one of <1> to <6>, including at least one selected from a detergent, a dispersant, an antioxidant, an antiwear agent, an extreme pressure agent, and a friction modifier. Viscous fluid composition.

  ADVANTAGE OF THE INVENTION According to this invention, the magnetorheological fluid composition which suppressed sedimentation of a magnetic particle and was excellent in long-term stability is provided.

Hereinafter, the magnetorheological fluid composition of the present invention will be described in detail.
In addition, in this specification, "-" showing a numerical range represents the range containing the numerical value each described as the upper limit and lower limit. In addition, when only the upper limit value is described in the numerical range, it means that the lower limit value is also in the same unit as the upper limit value.
In the numerical ranges described stepwise in this specification, the upper limit value or the lower limit value described in a numerical range may be replaced with the upper limit value or the lower limit value of another numerical range described. Further, in the numerical ranges described in this specification, the upper limit value or the lower limit value described in a certain numerical range may be replaced with the values shown in the examples.
In the present specification, the content rate or content of each component in the composition is such that when there are a plurality of substances corresponding to each component in the composition, the plurality of kinds present in the composition unless otherwise specified. It means the total content or content of substances.

<Magnetoviscous fluid composition>
The magnetorheological fluid composition of the present invention has at least magnetic particles (A), a lubricating base oil (B), a structural unit derived from ethylene, and a structural unit derived from an olefinic hydrocarbon other than ethylene. A copolymer (C) (hereinafter also referred to as “specific copolymer (C)”).
The magnetorheological fluid composition may contain other components in addition to the above components.

The magnetorheological fluid composition of the present invention contains the magnetic particles (A), the lubricating base oil (B), and the specific copolymer (C), whereby the sedimentation of the magnetic particles is suppressed, and , Tend to be excellent in long-term stability.
The reason for this is not clear, but is presumed as follows.
For example, the precipitation inhibitor described in Patent Document 2 has four amide groups in the molecule and a specific alkyl group in the side chain. Form. It is assumed that the self-organized body spreads in the base oil to form a three-dimensional network structure, thereby suppressing the sedimentation of the magnetic particles. On the other hand, since the magnetorheological fluid composition of the present invention contains the specific copolymer (C) which is a polymer compound, the polymer chains are entangled with each other, and the specific entangled structure causes the magnetic particles to settle. It is thought to suppress.
The entangled structure of polymer chains is less likely to be affected by external factors such as temperature change, moisture, vibration, and the like, and is considered to be strong and stable, compared to a network structure based on hydrogen bonds.

Therefore, it is surmised that the magnetorheological fluid composition of the present invention suppresses sedimentation of magnetic particles and is excellent in long-term stability.
Hereinafter, the detail of each component contained in the magnetorheological fluid composition of this invention is demonstrated.

<Magnetic particles (A)>
The magnetorheological fluid composition of the present invention contains magnetic particles (A).
Examples of magnetic particles include metal particles containing (preferably as a main component) at least one metal selected from iron, cobalt, and nickel, and at least one selected from iron nitride, iron carbide, ferrite, and magnetite. Examples thereof include metal compound particles containing a compound (preferably as a main component) and exhibiting ferromagnetism.
Among these, the magnetic particles are preferably at least one of metal particles containing iron as a main component and metal compound particles containing ferrite as a main component, and more preferably metal particles containing iron as a main component.
Magnetic particles may be used singly or in combination of two or more.

In the present specification, the term “metal particles” basically means particles of a single metal, particles of an alloy in which two or more metals are bonded, particles in which two or more metals are not bonded, and the like. . For example, particles containing a metal as a main component and a residual component other than the metal in the raw material, such as carbonyl iron described later, are also included. Similarly, the metal compound particles include particles containing a metal as a main component and a residual component other than the metal in the raw material.
In the present specification, the “main component” means a component having the largest mass ratio among the components constituting the magnetic particles, and preferably 50% by mass or more of the components constituting the magnetic particles, Preferably it is 70 mass% or more.

When the magnetic particles contain metal particles containing iron as the main component, the metal particles containing iron as the main component are metal particles having a higher iron content and fewer impurities from the viewpoint of increasing saturation magnetization. preferable.
In the present specification, an impurity refers to a component contained in a raw material or a component mixed in a manufacturing process and not intentionally included in a metal particle.

When the magnetic particles are metal particles containing iron, the iron content is preferably 98% by mass or more, more preferably 99% by mass or more, based on the total mass of the metal particles.
Examples of magnetic particles having an iron content within the above range include carbonyl iron. Carbonyl iron is high-purity metal particles produced by thermal decomposition of pentacarbonyl iron (Fe (Co) ₅ ).

The cumulative 50% particle size of the magnetic particles is preferably 0.05 μm to 50 μm, more preferably 0.1 μm to 30 μm, still more preferably 1.0 μm to 20 μm.
A cumulative 50% particle size of 0.05 μm or more is preferable because the yield stress when a magnetic field is applied is higher.
Further, when the cumulative 50% particle diameter is 50 μm or less, the sedimentation of the magnetic particles in the base oil can be further delayed. In addition, the wear of the apparatus members can be reduced in lubrication of the friction part of the apparatus.
In the present specification, the cumulative 50% particle diameter is the particle diameter (μm) corresponding to the cumulative value 50% of the cumulative curve when a cumulative curve is obtained such that the total volume of magnetic particles is 100%. ).
The cumulative 50% particle size can be measured by a laser diffraction / scattering particle size distribution analyzer (device name: SK Microanalyzer LMS-2000e: manufactured by Seishin Enterprise Co., Ltd.).

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 coupling agents, aluminate coupling agents, titanate coupling agents, and the like.
Examples of the resin include hydrocarbon resin, wax, polyethylene, polymethacrylate, and the like.

The content of the magnetic particles is preferably 40% by mass to 95% by mass, more preferably 50% by mass to 92% by mass, and still more preferably 60% by mass to 90% by mass with respect to the total mass of the magnetorheological fluid composition. %.
When the content of the magnetic particles is 40% by mass or more, there is a tendency that a necessary shear stress can be obtained when a magnetic field is applied. Further, when the content of magnetic particles is 95% by mass or less, the magnetorheological fluid composition tends to be a fluid, and it is easy to fill the apparatus and easily obtain a function as a magnetorheological fluid.

<Lubricant base oil (B)>
The magnetorheological fluid composition of the present invention contains a lubricating base oil (B).
The lubricating base oil serves as a dispersion medium for the magnetic particles (A) and the copolymer (C) described later in the magnetorheological fluid composition.
The base oil component constituting the lubricant base oil is not particularly limited, and may be a mineral oil base oil component, a synthetic lubricant base oil component or a vegetable oil base oil component. Good.

Examples of mineral oil base oils include, for example, solvent oil removal, solvent extraction, hydrocracking, solvent removal of lubricating oil fractions obtained by distillation under reduced pressure of atmospheric residual oil obtained by atmospheric distillation of crude oil. Examples thereof include those refined by performing at least one treatment selected from dewaxing and hydrorefining, and wax isomerized mineral oil.
As the mineral oil base oil component, a paraffin base oil and a naphthenic base oil are suitable.

  Synthetic lubricant base oil components include lubricant 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 alkylbenzene and alkylnaphthalene, synthetic lubricating base oils such as ester oils, alkylated phenyl ether oils, isoparaffin oils, polybutene oils, polyalkylene glycols, and the like.

  As a suitable production method of the poly-α-olefin base oil, an α-olefin having 6 to 18 carbon atoms is synthesized by low polymerization of ethylene or thermal decomposition of wax, and 2 to 9 units of this α-olefin are polymerized. The method of performing a hydrogenation reaction is mentioned.

  Preferable examples of ester oils include diesters produced from monohydric alcohols and dicarboxylic acids, polyol esters produced from polyols and monocarboxylic acids, or produced from polyols, monocarboxylic acids and polycarboxylic acids. And complex esters.

  Examples of the diester include esters of dibasic acids such as adipic acid, azelaic acid, sebacic acid, and dodecanedioic acid.

  As the dibasic acid, an aliphatic dibasic acid having 4 to 36 carbon atoms is preferable. The alcohol residue constituting the ester portion of the dibasic acid ester is preferably a monohydric alcohol residue having 4 to 26 carbon atoms.

  Examples of such diesters include dioctyl adipate, dioctyl sebacate, diisodecyl adipate, dioctyl azelate, and the like.

Further, as the polyol used in the polyol ester and complex ester, specifically, hindered alcohols having no β hydrogen such as trimethylolpropane, pentaerythritol, neopentyl glycol and the like are preferably used.
Moreover, as monocarboxylic acid used for polyol ester and complex ester, coconut oil fatty acid, linear saturated fatty acid such as stearic acid, linear unsaturated fatty acid such as oleic acid, branched fatty acid such as isostearic acid, etc. are preferably used. It is done.
As the polycarboxylic acid, linear saturated polycarboxylic acids such as succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid and sebacic acid are preferably used.

  Preferable examples of the alkylated phenyl ether oil include alkylated diphenyl ether and (alkylated) polyphenyl ether.

  Polyalkylene glycols include polyethylene glycol, polypropylene glycol, polybutylene glycol or ethylene oxide-propylene oxide copolymer, propylene oxide-butylene oxide copolymer, and derivatives thereof.

  Examples of vegetable oil-based lubricant base oils include soybean oil, rapeseed oil, and palm oil.

Each of these lubricating base oils may be used alone or in combination of two or more.
Further, two or more kinds of lubricating base oils selected from mineral base oils, synthetic base oils, and vegetable base oils may be mixed and used.

Kinematic viscosity at 40 ° C. of the lubricating base oil (B) ^is preferably 2mm ² / s~5000mm 2 / s, more preferably ^{3mm 2} / ^s~2000mm 2 / s, more preferably ^{3 mm} 2 / s -1000 mm < ² > / s.
Moreover, 50 or more are preferable and, as for the viscosity index of lubricating base oil (B), 80-200 are more preferable.
The kinematic viscosity and viscosity index at 40 ° C. of the lubricating base oil (B) can be determined by Japanese Standards Association JIS K2283 (2000) “Crude oil and petroleum products—Kinematic viscosity test method and viscosity index calculation method”.
When the base oil has a kinematic viscosity at 40 ° C. of 2 mm ² / s or more, the flash point tends to be high and evaporation tends to be suppressed, which is preferable as an MR fluid.
Further, when the base oil has a kinematic viscosity at 40 ° C. of 5000 mm ² / s or less, the viscosity tends to be low, and the stable dispersion of the magnetic particles in the base oil is more likely during the production of the magnetorheological fluid composition. It becomes easy.

<Copolymer (C)>
The magnetorheological fluid composition of the present invention contains a copolymer (C) (specific copolymer (C)) having at least a structural unit derived from ethylene and a structural unit derived from an olefinic hydrocarbon other than ethylene. To do.
By including the specific copolymer (C), the magnetorheological fluid composition of the present invention can suppress sedimentation of magnetic particles.

The olefinic hydrocarbon other than ethylene is not particularly limited and may be linear, cyclic or branched.
The number of carbon atoms of the olefinic hydrocarbon other than ethylene is preferably 3 to 30, more preferably 3 to 25, still more preferably 3 to 15, particularly preferably 3 to 8, most preferably. Is 3-5.

Specific examples of the olefinic hydrocarbon include n-propylene, n-butene, isobutene, cyclobutene, n-pentene, isopentene, cyclopentene, isopropylene, n-hexene, isohexene, n-heptene and isoheptene. Etc.
From the viewpoint of suppressing sedimentation of magnetic particles, the olefin hydrocarbon is preferably an olefin hydrocarbon having 3 to 15 carbon atoms, more preferably an olefin hydrocarbon having 3 to 8 carbon atoms, and an olefin having 3 to 5 carbon atoms. Series hydrocarbons are more preferable, and linear or branched olefin hydrocarbons having 3 to 5 carbon atoms are particularly preferable.

  In addition to the structural unit derived from ethylene and the structural unit derived from olefinic hydrocarbons other than ethylene, the magnetorheological fluid composition of the present invention may contain other structural units as necessary.

  The polymerization ratio of structural units derived from ethylene and structural units derived from olefinic hydrocarbons other than ethylene ((structural units derived from ethylene): (structural units derived from olefinic hydrocarbons other than ethylene)) is mol. The standard is preferably 80:20 to 20:80, more preferably 70:30 to 30:70, and still more preferably 65:35 to 35:65.

The specific copolymer (C) is a random copolymer containing a structural unit derived from ethylene and a structural unit derived from an olefinic hydrocarbon other than ethylene, an alternating copolymer containing alternating units, a copolymer containing regularly. Examples thereof include a polymer and a block copolymer contained in a block form.
As the specific copolymer (C), any one of these may be used alone, or two or more may be used in combination.

The weight average molecular weight of the specific copolymer (C) is preferably 20,000 to 500,000, more preferably 30,000 to 450,000, still more preferably 40,000 to 400,000. It is.
When the weight average molecular weight is 20,000 or more, the sedimentation of the magnetic particles can be further suppressed. When the weight average molecular weight is 500,000 or less, the copolymer (C) is easily dissolved uniformly, and a uniform dispersion state can be maintained in the magneto-rheological fluid composition.
The weight average molecular weight is a value in terms of polystyrene measured by gel permeation chromatography (GPC).

<Conditions>
Apparatus: Shodex GPC-101 (Showa Denko)
Column: Three Shodex GPC LF-804 (manufactured by Showa Denko KK) Detector: Differential refraction detector Mobile phase: THF (tetrahydrofuran)
Flow rate: 1 ml / min Sample concentration: About 1.0% by mass / vol% THF
Injection volume: 100 μL

The content of the specific copolymer (C) is preferably 0.3% by mass to 8% by mass, and more preferably 0.4% by mass to 7% by mass with respect to the total mass of the magnetorheological fluid composition. %, And more preferably 0.5% by mass to 6% by mass.
There exists a tendency which suppresses sedimentation of a magnetic particle more as content rate is 0.3 mass% or more. Further, when the content is 8% by mass or less, the specific copolymer (C) is more easily dissolved more uniformly, and a uniform dispersion state can be maintained in the magneto-rheological fluid composition.
A specific copolymer (C) may be used individually by 1 type, and may use 2 or more types together.

<Lubricant additive>
From the viewpoint of ensuring long-term stability, the magnetorheological fluid composition may further contain a general lubricating oil additive used in the lubricating oil composition.
Examples of lubricant additives include detergents, dispersants, antioxidants, antiwear agents, extreme pressure agents, friction modifiers, viscosity index improvers, pour point depressants, metal deactivators, and rust inhibitors. , Antifoaming agents, coloring agents and the like.
Among these, the magnetorheological fluid composition of the present invention contains at least one lubricating oil additive selected from detergents, dispersants, antioxidants, antiwear agents, extreme pressure agents, and friction modifiers. Is preferred.

The blending ratio of the lubricating oil additive can be appropriately set according to the use of the obtained magnetorheological fluid composition.
The total blending ratio of the lubricating oil additive is preferably 0% by mass to 10% by mass, more preferably 0% by mass to 8% by mass, and still more preferably 0% by mass with respect to the total mass of the magnetorheological fluid composition. -6 mass%.

(Cleaning agent)
Examples of the detergent include sulfonate, finate, salicylate and the like whose metal components are calcium, magnesium and the like.
The above-mentioned detergent can be suitably used for a magnetorheological fluid composition that is used particularly in an environment where the inside of the machine is at a high temperature.

(Dispersant)
Examples of the dispersant include succinimide ashless dispersant, succinamide ashless dispersant, and boronated derivatives thereof.
Examples of succinimide-based ashless dispersants include bispolypropenyl succinimide, monopropenyl succinimide, bispolybutenyl succinimide, monobutenyl succinimide, bispolypentenyl succinimide, monopentenyl succinimide, etc. And polyalkenyl succinimide.
Examples of the succinic acid amide-based ashless dispersant include polyalkenyl succinic acid amides such as polypropenyl succinic acid amide, polybutenyl succinic acid amide, and polypentenyl succinic acid amide.
Usually, the weight average molecular weight of the polyalkenyl group in these ashless dispersants is about 70 to 50000.
Examples of these boronated derivatives include ashless dispersants obtained by reacting polyalkenyl succinic anhydride with boron compounds such as boric acid, boric acid esters and borates, and polyamines.

(Antioxidant)
Examples of the antioxidant include ashless antioxidants such as phenols and amines, and metal antioxidants such as zinc, copper, and molybdenum.
Specifically, monocyclic phenols such as 2,6-di-t-butylphenol, 2,6-di-t-butyl-4-methylphenol, 2,6-di-t-butyl-4-ethylphenol, etc. 4,4′-bis (2,6-di-t-butylphenol), 4,4′-methylenebis (2,6-di-t-butylphenol), 4,4′-ethylenebis (2 , 6-di-t-butylphenol), 4,4′-butylenebis (2,6-di-t-butylphenol), 6,6′-methylenebis (2-di-t-butyl-4-methylphenol), etc. Sulfur-containing phenols such as bisphenol antioxidants, 4,4′thiobis- (2,6-di-tert-butyl-phenol), 4,4′thiobis- (2-methyl-6-tert-butyl-phenol) Antioxidants, aromatic amine compounds, Kill diphenylamine, alkyl naphthyl amine, phenyl -α- naphthylamine, amine antioxidant such as an alkyl phenyl -α- naphthylamine, alkyl phosphites, phosphorus-based antioxidants such as aryl phosphites, and the like.

(Antiwear agent)
Examples of the antiwear agent include zinc dialkyldithiophosphates, various phosphate esters, thiophosphate esters, and amine salts of various phosphate esters.

(Extreme pressure agent)
Examples of extreme pressure agents include hydrocarbon sulfides, sulfurized fats and oils, sulfurized olefins, sulfur, phosphate esters, phosphite esters, chlorinated paraffins, and chlorinated diphenyls.

(Friction modifier)
As friction modifiers, organic molybdenum compounds, polyhydric alcohol partial esters, amines, amides, sulfurized esters, phosphate esters, acidic phosphate esters or amine salts thereof, diols, oleic acid, stearic acid, higher alcohols , Amines, esters, sulfurized fats and oils, acidic phosphates, acidic phosphites and the like.

<Other ingredients>
In addition to the components described above, the magnetorheological fluid composition of the present invention includes a surfactant used for the purpose of stable dispersion of magnetic particles, if necessary, and a specific copolymer (C) for the purpose of suppressing sedimentation of the magnetic particles. It is possible to mix a precipitation inhibitor other than

As the surfactant, those having a functional group having affinity for magnetic particles are preferable.
Specific examples of the surfactant include higher fatty acids such as caproic acid, lauric acid, myristic acid, palmitic acid, stearic acid and oleic acid, and esters such as fatty acid esters and sorbitan fatty acid esters.
Moreover, fatty acid amides, fatty acid amines, polyoxyethylene derivatives, glycerin derivatives, castor oil derivatives, ammonium salts and the like can be mentioned.

  Examples of the precipitation inhibitor other than the specific copolymer (C) include fumed silica, fatty acid amide wax, bentonite and the like.

The magnetic viscous fluid composition may be prepared by appropriately mixing magnetic particles, lubricating base oil, specific copolymer (C), various lubricating oil additives, and other additives as necessary.
The mixing order of each component is not particularly limited, and a propeller type high-speed stirrer, a planetary mixer type stirrer, etc. are preferably used, and the temperature of the magnetorheological fluid composition at the time of stirring is about 50 ° C. to 100 ° C. It is preferable that

  The magnetorheological fluid composition of the present invention can be suitably used for various vehicle or industrial dampers, clutches, torque transmission devices and brakes, and earthquake-proof devices for buildings.

  Next, the present invention will be described more specifically with reference to examples. In addition, this invention is not restrict | limited at all by these examples.

In the magnetorheological fluid compositions of Examples 1 to 8 and Comparative Examples 1 to 5, the components shown below were blended in the proportions shown in Table 1 or Table 2 below, and using a propeller type high-speed stirrer, the composition was about 70 Prepared by mixing at a temperature of from 85C to 85C.
In addition, 40 degreeC kinematic viscosity, a viscosity index, and a weight average molecular weight are measured and calculated by the above-mentioned method. “-” In the table means that the component is not blended or measured.

The components used for the preparation of the magnetorheological fluid compositions of Examples and Comparative Examples are as follows.
(Magnetic particles (A))
Carbonyl iron powder: Thermal decomposition product of pentacarbonyl iron (Fe (Co) ₅ ), iron content: 99.7% by mass, cumulative 50% particle size: 6.2 μm

(Lubricant base oil (B))
Lubricating base oil A; poly-α-olefin, kinematic viscosity at 40 ° C .; 5.2 mm ² / s
Lubricating base oil B; Mineral base oil base oil; API (American Petroleum Institute) base oil category group I, 40 ° C. kinematic viscosity; 33.73 mm ² / s, viscosity index; 108
Lubricating oil base oil C; Mineral oil base oil base oil; API (American Petroleum Institute) base oil category group I, kinematic viscosity at 40 ° C. is 504.0 mm ² / s, viscosity index: 97

(Copolymer (C))
E-P copolymer; ethylene propylene copolymer, weight average molecular weight; 87,300

(Polymer other than copolymer (C))
PMA; polymethacrylate, weight average molecular weight; 275,000

(Other additives)
-Antioxidant; 2,6-di-t-butyl-4-methylphenol-Extreme pressure agent; Sulfurized olefin-Friction modifier; Sulfurized oil, fumed silica; Nihon Aerosil Co., Ltd., dimethyldichlorosilane surface treatment, Specific surface area by ET: 110 m ² / g ± 20 m ² / g, average diameter of primary particles: about 16 nm

[Evaluation]
The magnetorheological fluid compositions of Examples 1 to 8 and Comparative Examples 1 to 5 were evaluated for sedimentation characteristics by the following method.
-Sedimentation property test-
10 ml of the magnetorheological fluid composition was placed in a 10 ml glass graduated cylinder and allowed to stand at room temperature (about 20 ° C.) for 648 hours or 7296 hours. The amount of separated oil [ml] separated at the top of the graduated cylinder after 648 hours or 7296 hours was visually read, and this numerical value was substituted into the following formula (1) to obtain the separation rate. The results are shown in Table 1 or Table 2.

  Separation rate (%) = (separated oil amount [ml] / 10 [ml]) × 100 (1)

  The smaller the separation rate, the better the suppression of sedimentation, and the practical one is 25% or less, preferably 20% or less, more preferably 15% or less.

As shown in Table 1 and Table 2, the magnetic particles (A), the lubricating base oil (B), a copolymer having structural units derived from ethylene and structural units derived from olefinic hydrocarbons other than ethylene. The magnetorheological fluid compositions of Examples 1 to 8 containing the coalesced (C) were excellent in long-term stability because sedimentation of magnetic particles was suppressed.
On the other hand, the magnetorheological fluid compositions of Comparative Examples 1 to 5, which do not contain the copolymer (C), were inferior in suppressing sedimentation of magnetic particles.

  As described above, the magnetorheological fluid composition of the present invention suppresses sedimentation of magnetic particles and is excellent in long-term stability. Therefore, various vehicle or industrial dampers, clutches, torque transmission devices and brakes, and more It is extremely useful for the use of seismic devices.

Claims (7)

  Magnetic material containing magnetic particles (A), lubricating base oil (B), and a copolymer (C) having a structural unit derived from ethylene and a structural unit derived from an olefinic hydrocarbon other than ethylene. Viscous fluid composition.   The magnetorheological fluid composition according to claim 1, wherein the magnetic particles (A) are metal particles containing iron, and the content of the iron is 98 mass% or more with respect to the total mass of the metal particles.   3. The magnetorheological fluid composition according to claim 1, wherein a cumulative 50% particle diameter of the magnetic particles (A) is 0.05 μm to 50 μm. The kinematic viscosity at 40 ° C. of the lubricating base oil (B) is ^{2mm 2} / ^s~5000mm 2 / s, the magnetic fluid composition according to any one of claims 1 to 3.   The magnetorheological fluid composition according to any one of claims 1 to 4, wherein the copolymer (C) has a weight average molecular weight of 20,000 to 500,000.   40% by mass to 95% by mass of the magnetic particles (A) with respect to the total mass of the composition, and 0.3% by mass to 8% by mass of the copolymer (C) with respect to the total mass of the composition; The magnetorheological fluid composition according to claim 1, comprising:   The magnetorheological fluid composition according to any one of claims 1 to 6, comprising at least one selected from a detergent, a dispersant, an antioxidant, an antiwear agent, an extreme pressure agent, and a friction modifier. object.