JP6807814B2 - Ferrofluid composition - Google Patents

Description

The present invention relates to ferrofluid compositions.

The magnetic fluid is a mixture of synthetic oil with magnetic particles and a surfactant, and is generally sold. Since the particle size of the magnetic particles used in the magnetic fluid is as small as several nanometers, the dispersion force of the surfactant can prevent the particles from agglomerating, and usually the magnetic particles do not settle even after being allowed to stand for several years.
However, since the magnetic particles used in the magnetic fluid have an extremely small particle size, the increase in viscosity and yield stress is small even when a magnetic field is applied, and the magnetic fluid can be applied to clutches, dampers, etc. It is difficult and is limited to use in applications such as magnetic seals.

In recent years, for the purpose of application to automobile dampers, a magnetic viscous fluid (Magneto-Magnetorheological Fluid: MR) in which magnetic particles having a significantly larger particle diameter than magnetic particles used in a magnetic fluid is blended in a base oil. Fluid) is being developed.
The ferrofluid is a functional fluid that rapidly, continuously, and reversibly changes from a highly fluid state to a gel state having a large yield stress according to the magnetic field strength applied from the outside.
A damper filled with ferrofluid 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 stability of the automobile body is improved. At the same time, it is said that excellent riding comfort can be realized (see, for example, Non-Patent Document 1 and Non-Patent Document 2).

In recent years, various applications of ferrofluids to not only MR dampers for automobiles but also various clutches, actuators, brakes and the like have been studied.
Recently, magnetic viscous fluid has also attracted attention in the fields of seismic isolation and vibration damping structures for buildings such as high-rise buildings and general detached houses, and reduces both the response acceleration and response displacement of the structure to 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 control range of the yield stress is wide, it is possible to generate a damping force according to the degree of shaking of the building, and it is possible to suppress the shaking of the building when an earthquake occurs.

The magnetic viscous fluid is a mixture of magnetic particles in a lubricating oil base oil, but with only two components, the lubricating oil base oil and the magnetic particles, the magnetic particles, which are much denser than the base oil, tend to settle early. It is known that once the magnetic particles settle, it is difficult to obtain an output (yield stress) commensurate with the set value when necessary.

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

As an attempt to suppress the sedimentation of magnetic particles by blending various additives with a ferrofluid, for example, a ferrofluid in which fumed silica is mixed with 50% by mass of glycols as a carrier fluid (lubricating oil base oil). Is disclosed (see, for example, Patent Document 1).
Further, as a magnetic viscous agent composition having excellent stability capable of suppressing the sedimentation of magnetic particles for a long period of time, a specific base oil, specific magnetic particles having a specific average particle size, and a specific sedimentation inhibitor are used. The magnetic viscous composition contained therein is disclosed (see, for example, Patent Document 2).

Journal of Precision Engineering, P83-816, Vol. 72, No. 7 (2006) HONDA R & D Technical Review, Vol. 19, No. 1 (April 2007)

Special Table 2010-535432 JP-A-2016-213301

The magnetically viscous fluid described in Patent Document 1 suppresses the sedimentation of iron particles for a short period of time (24 hours in the example of the same document), but the short-term suppression of the sedimentation of magnetic particles is inferior in performance. Therefore, it is desired to develop a magnetic viscous fluid capable of suppressing the sedimentation of magnetic particles for a long period of time.
Further, in the magnetic viscous 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 magnetically viscous fluid composition which suppresses sedimentation of magnetic particles and has excellent long-term stability.

As a result of repeated studies with the intention of achieving the above problems, the present inventors have conducted studies, and as a result, magnetic particles, a lubricating oil base oil, a structural unit derived from ethylene, and a configuration derived from an olefin hydrocarbon monomer other than ethylene. By blending a copolymer having a unit, a magnetically viscous fluid composition in which precipitation of magnetic particles is suppressed and excellent in stability has been found, and the present invention has been completed.

Means for solving the above problems include the following embodiments.
<1> Magnetic particles (A), a lubricating oil base oil (B), and a copolymer (C) having a structural unit derived from ethylene and a structural unit derived from an olefin hydrocarbon other than ethylene. The ferrofluid composition contained.
<2> The magnetic viscous fluid according to <1>, wherein the magnetic particles (A) are metal particles containing iron, and the iron content is 98% by mass or more with respect to the total mass of the metal particles. Composition.
<3> The magnetically viscous fluid composition according to <1> or <2>, wherein the cumulative 50% particle diameter 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 ferrofluid 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> The magnetic particles (A) in an amount of 40% by mass to 95% by mass based on the total mass of the composition, and the copolymer (0.3% by mass to 8% by mass) based on the total mass of the composition. C), and the magnetically viscous fluid composition according to any one of <1> to <5>.
<7> The magnetism according to any one of <1> to <6>, which comprises at least one selected from a cleaning agent, a dispersant, an antioxidant, an anti-wear agent, an extreme pressure agent, and a friction modifier. Viscous fluid composition.

According to the present invention, a magnetically viscous fluid composition that suppresses sedimentation of magnetic particles and has excellent long-term stability is provided.

Hereinafter, the ferrofluid composition of the present invention will be described in detail.
In addition, in this specification, "~" which represents a numerical value range represents a range including the numerical value described as the upper limit value and the lower limit value respectively. Further, when the unit is described only for the upper limit value in the numerical range, it means that the lower limit value is also the same unit as the upper limit value.
In the numerical range described stepwise in the present specification, the upper limit value or the lower limit value described in a certain numerical range may be replaced with the upper limit value or the lower limit value of another numerical range described stepwise. Further, in the numerical range described in the present specification, the upper limit value or the lower limit value described in a certain numerical range may be replaced with the value shown in the examples.
In the present specification, the content or content of each component in the composition refers to the content of each component in the composition when a plurality of substances corresponding to each component are present in the composition, unless otherwise specified. It means the total content or content of substances.

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

By containing the magnetic particles (A), the lubricating oil base oil (B), and the specific copolymer (C), the magnetic viscous fluid composition of the present invention suppresses the sedimentation of the magnetic particles and , Tends to be excellent in long-term stability.
The reason for this is not clear, but it is presumed as follows.
For example, the sedimentation inhibitor described in Patent Document 2 has four amide groups in the molecule and a specific alkyl group in the side chain, so that a micron-order self-assembling body is generated by using a hydrogen bond as a driving force. Form. It is presumed that this self-assembling body spreads in the base oil to form a three-dimensional network structure, thereby suppressing the sedimentation of magnetic particles. On the other hand, since the ferrofluid 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 precipitation of magnetic particles. It is thought to suppress it.
The entangled structure of polymer chains is considered to be stronger and more stable than the network structure by hydrogen bonds, because it is less susceptible to external factors such as temperature changes, moisture, and vibration.

Therefore, it is presumed that the ferrofluid composition of the present invention suppresses the sedimentation of magnetic particles and is excellent in long-term stability.
Hereinafter, details of each component contained in the ferrofluid composition of the present invention will be described.

<Magnetic particles (A)>
The ferrofluid composition of the present invention contains magnetic particles (A).
The magnetic particles include, for example, metal particles containing at least one metal selected from iron, cobalt and nickel (preferably as a main component), 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.
The magnetic particles may be used alone or in combination of two or more.

In the present specification, the "metal particles" basically mean particles of a single metal, particles of an alloy in which two or more kinds of metals are bonded, particles in which two or more kinds of 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 also include particles containing a metal as a main component and a residual component other than the metal in the raw material.
Further, in the present specification, the “main component” means the component having the largest mass ratio among the components constituting the magnetic particles, preferably 50% by mass or more of the components constituting the magnetic particles, and more. It is preferably 70% by mass or more.

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

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 the magnetic particles having an iron content in the above range include carbonyl iron. The carbonyl iron is a high-purity metal particle 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, and even more preferably 1.0 μm to 20 μm.
When the cumulative 50% particle diameter is 0.05 μm or more, the yield stress when a magnetic field is applied is higher, which is preferable.
Further, when the cumulative 50% particle diameter is 50 μm or less, the sedimentation of the magnetic particles in the base oil can be slowed down. Further, in the lubrication of the friction portion of the device, the wear of the device member can be further reduced.
In the present specification, the cumulative 50% particle diameter means a particle diameter (μm) corresponding to a cumulative value of 50% of the cumulative curve when a cumulative curve is obtained such that the total volume of magnetic particles is 100%. ) Means.
The cumulative 50% particle size can be measured by a laser diffraction / scattering type particle size distribution measuring device (device name: SK microanalyzer LMS-2000e: manufactured by Seishin Co., Ltd.).

The magnetic particles may be surface-treated with various coupling agents or resins, or may be untreated.
Examples of various coupling agents include silane-based coupling agents, aluminate-based coupling agents, titanate-based coupling agents, and the like.
Examples of the resin include hydrocarbon resins, waxes, polyethylenes, polymethacrylates 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 further preferably 60% by mass to 90% by mass with respect to the total mass of the magnetic viscous fluid composition. %.
When the content of the magnetic particles is 40% by mass or more, the required shear stress tends to be obtained when a magnetic field is applied. Further, when the content of the magnetic particles is 95% by mass or less, the magnetic viscous fluid composition tends to become a fluid, it is easy to fill the apparatus, and it is easy to obtain a function as a magnetic viscous fluid.

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

As the mineral oil-based lubricating oil base oil, for example, the lubricating oil distillate obtained by distilling the atmospheric residual oil obtained by atmospheric distillation of crude oil under reduced pressure is subjected to solvent removal, solvent extraction, hydrocracking, and solvent. Examples thereof include those purified by performing at least one treatment selected from dewaxing, hydrorefining and the like, and wax isomerized mineral oil and the like.
As the mineral oil-based lubricating oil base oil component, a paraffin-based lubricating oil base oil and a naphthen-based lubricating oil base oil are suitable.

As the synthetic lubricating oil base oil component, a lubricating oil base oil obtained by hydrocracking and hydroisomerizing raw materials such as wax obtained by Fisher-Tropsch synthesis, poly-α-olefin base oil, Examples thereof include aromatic synthetic oils such as alkylbenzene and alkylnaphthalene, ester oils, alkylated phenyl ether oils, isoparaffin oils, polybutene oils, and synthetic lubricating oil base oils such as polyalkylene glycols.

A suitable method for producing a poly-α-olefin base oil is to synthesize an α-olefin having 6 to 18 carbon atoms by low polymerization of ethylene or thermal decomposition of wax, and polymerize 2 to 9 units of this α-olefin. Examples thereof include a method of carrying out a hydrogenation reaction.

Preferable examples of ester oils are diesters made from monohydric alcohols and dicarboxylic acids, polyol esters made from polyols and monocarboxylic acids, or polyols made from monocarboxylic acids and polycarboxylic acids. Examples thereof include complex esters.

Examples of the diester include esters of dibasic acids such as adipic acid, azelaic acid, sebacic acid, and dodecane diic 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, and dioctyl azelate.

Further, as the polyol used for the polyol ester and the complex ester, specifically, a hindered alcohol having no β-hydrogen such as trimethylolpropane, pentaerythritol, and neopentyl glycol is preferably used.
Further, as the monocarboxylic acid used for the polyol ester and the complex ester, a linear saturated fatty acid such as coconut oil fatty acid and stearic acid, a linear unsaturated fatty acid such as oleic acid, and a branched fatty acid such as isostearic acid are preferably used. Be 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 ethers, (alkylated) polyphenyl ethers and the like.

Examples of 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 the vegetable oil-based lubricating oil base oil include soybean oil, rapeseed oil, palm oil and the like.

Each of these lubricating oil base oils may be used alone or in combination of two or more.
Further, two or more kinds of lubricating oil base oils selected from mineral oil-based lubricating oil base oils, synthetic lubricating oil base oils and vegetable oil-based lubricating oil 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.
The viscosity index of the lubricating oil base oil (B) is preferably 50 or more, more preferably 80 to 200.
The kinematic viscosity and viscosity index of the lubricating oil base oil (B) at 40 ° C. can be obtained by the Japanese Standards Association JIS K2283 (2000) "Crude oil and petroleum products-kinematic viscosity test method and viscosity index calculation method".
When the kinematic viscosity of the base oil at 40 ° C. is 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 kinematic viscosity of the base oil at 40 ° C. is 5000 mm ² / s or less, the viscosity tends to be low, and the stable dispersion of the magnetic particles in the base oil during the production of the ferrofluid composition becomes more stable. It will be easier.

<Copolymer (C)>
The ferrofluid 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 olefin hydrocarbon other than ethylene. To do.
The magnetic viscous fluid composition of the present invention can suppress the sedimentation of magnetic particles by containing the specific copolymer (C).

The olefinic hydrocarbon other than ethylene is not particularly limited and may be linear, cyclic or branched.
The carbon number of the olefin 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, and most preferably. Is 3-5.

Specific examples of olefin hydrocarbons include n-propylene, n-butene, isobutene, cyclobutene, n-pentene, isopentene, cyclopentene, isopropylene, n-hexene, isohexene, n-heptene, and isohepten. And so on.
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. System hydrocarbons are more preferred, and linear or branched olefin hydrocarbons having 3 to 5 carbon atoms are particularly preferred.

The ferrofluid fluid composition of the present invention may contain other structural units, if necessary, in addition to the structural units derived from ethylene and the structural units derived from olefin hydrocarbons other than ethylene.

The polymerization ratio of the structural unit derived from ethylene and the structural unit derived from an olefin hydrocarbon other than ethylene ((constituent unit derived from ethylene): (constituent unit derived from an olefin hydrocarbon other than ethylene)) is molar. By reference, it is preferably 80:20 to 20:80, more preferably 70:30 to 30:70, and even more preferably 65:35 to 35:65.

The specific copolymer (C) is a random copolymer randomly containing a structural unit derived from ethylene and a structural unit derived from an olefin-based hydrocarbon other than ethylene, an alternating copolymer containing alternately, and a copolymer containing regularly. Examples thereof include polymers and block copolymers contained in blocks.
As the specific copolymer (C), any one of these may be used alone, or two or more thereof 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, and even more preferably 40,000 to 400,000. 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) can be easily dissolved uniformly, and a uniform dispersed state can be maintained in the ferrofluid composition.
The weight average molecular weight is a polystyrene-equivalent value measured by gel permeation chromatography (GPC).

<Conditions>
Equipment: Shodex GPC-101 (manufactured by Showa Denko KK)
Column: Shodex GPC LF-804 (manufactured by Showa Denko KK) 3 detectors: differential refractometer mobile phase: THF (tetrahydrofuran)
Flow rate: 1 ml / min Sample concentration: Approximately 1.0 mass% / vol% THF
Injection volume: 100 μL

The content of the specific copolymer (C) is preferably 0.3% by mass to 8% by mass, more preferably 0.4% by mass to 7% by mass, based on the total mass of the ferrofluid composition. %, More preferably 0.5% by mass to 6% by mass.
When the content is 0.3% by mass or more, the sedimentation of magnetic particles tends to be further suppressed. Further, when the content is 8% by mass or less, the specific copolymer (C) is easily dissolved more uniformly, and it is possible to maintain a uniform dispersed state in the ferrofluid composition.
As the specific copolymer (C), one type may be used alone, or two or more types may be used in combination.

<Lubricating oil additive>
From the viewpoint of ensuring long-term stability, the ferrofluid composition may further contain a general lubricating oil additive used in the lubricating oil composition.
Lubricating oil additives include, for example, cleaning agents, dispersants, antioxidants, anti-wear agents, extreme pressure agents, friction modifiers, viscosity index improvers, pour point depressants, metal defoamers, and rust preventives. , Antifoaming agent, coloring agent and the like.
Among these, the ferrofluid composition of the present invention contains at least one lubricating oil additive selected from a cleaning agent, a dispersant, an antioxidant, an anti-wear agent, an extreme pressure agent, and a friction modifier. Is preferable.

The blending ratio of the lubricating oil additive can be appropriately set according to the application of the obtained ferrofluid 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 further preferably 0% by mass with respect to the total mass of the ferrofluid composition. ~ 6% by mass.

(Cleaning agent)
Examples of the cleaning agent include sulfonate, finate, salicylate and the like whose metal components are calcium, magnesium and the like.
The cleaning agent can be suitably used particularly for a ferrofluid composition used in an environment where the inside of a machine becomes hot.

(Dispersant)
Examples of the dispersant include an succinic acid imide-based ashless dispersant, a succinic acid amide-based ashless dispersant, and a boronized derivative thereof.
Examples of the succinate imide-based ashless dispersant include bispolypropenyl succinate imide, monopropenyl succinate imide, bispolybutenyl succinate imide, monobutenyl succinate imide, bispolypentenyl succinate imide, and monopentenyl succinate imide. Polyalkenyl succinate imide and the like.
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 50,000.
Examples of these boried derivatives include an ashless dispersant obtained by reacting a polyalkenyl succinic anhydride with a boron compound such as boric acid, a borate ester, or a borate, and a polyamine.

(Antioxidant)
Examples of the antioxidant include ashless antioxidants such as phenol-based and amine-based, and metal-based antioxidants such as zinc-based, copper-based and molybdenum-based.
Specifically, monocyclic phenols such as 2,6-di-t-butylphenol, 2,6-di-t-butyl-4-methylphenol, and 2,6-di-t-butyl-4-ethylphenol. Antioxidants, 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-t-butyl-phenol), 4,4'thiobis- (2-methyl-6-t-butyl-phenol) Amine-based antioxidants such as antioxidants, aromatic amine compounds, alkyldiphenylamines, alkylnaphthylamines, phenyl-α-naphthylamines, alkylphenyl-α-naphthylamines, and phosphorus-based antioxidants such as alkylphosphite and arylphosphite. Examples include agents.

(Abrasion inhibitor)
Examples of the anti-wear agent include zinc dialkyldithiophosphate, various phosphate esters, thiophosphate esters, amine salts of various phosphate esters, and the like.

(Extreme pressure agent)
Examples of extreme pressure agents include hydrocarbon sulfides, sulfide oils and fats, sulfide olefins, sulfur, phosphoric acid esters, phosphite esters, chlorinated paraffins, chlorinated diphenyls and the like.

(Friction modifier)
As the friction modifier, organic molybdenum compounds, polyhydric alcohol partial ester-based, amine-based, amide-based, sulfurized ester, phosphoric acid ester, acidic phosphoric acid ester or its amine salt, diols, oleic acid, stearic acid, higher alcohol , Amine, ester, sulfide oil and fat, acidic phosphoric acid ester, acidic subphosphate ester and the like.

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

As the surfactant, those having a functional group having an 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.
In addition, fatty acid amides, fatty acid amines, polyoxyethylene derivatives, glycerin derivatives, castor oil derivatives, ammonium salts and the like can be mentioned.

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

As a method for preparing the magnetic viscous fluid composition, magnetic particles, a lubricating oil base oil, a specific copolymer (C), various lubricating oil additives, and if necessary, other additives may be appropriately mixed.
The mixing order of each component is not particularly limited, and a propeller type high-speed stirrer, a planetary mixer type stirrer, or the like is preferably used, and the temperature of the ferrofluid composition during stirring is about 50 ° C. to 100 ° C. Is preferable.

The ferrofluid composition of the present invention can be suitably used for various vehicle or industrial dampers, clutches, torque transmission devices and brakes, and seismic devices for buildings.

Next, the present invention will be described in more detail with reference to Examples. The present invention is not limited to these examples.

In the ferrofluid compositions of Examples 1 to 8 and Comparative Examples 1 to 5, the components shown below are blended in the proportions shown in Table 1 or Table 2 below, and about 70 using a propeller type high-speed stirrer. It was prepared by mixing at ° C. to 85 ° C.
The 40 ° C. kinematic viscosity, viscosity index and weight average molecular weight are measured and calculated by the methods described above. "-" In the table means that the component is not blended or measured.

The components used in the preparation of the ferrofluid compositions of Examples and Comparative Examples are as follows.
(Magnetic particles (A))
-Muldon iron powder: pyrolyzed product of pentacarbonyl iron (Fe (Co) ₅ ), iron content; 99.7% by mass, cumulative 50% particle size; 6.2 μm

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

(Copolymer (C))
-EP 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; Olefin sulfide ・ Friction modifier; Fat and oil sulfide ・ Fumed silica; dimethyldichlorosilane surface treatment, manufactured by Nippon Aerosil Co., Ltd. Specific surface area by ET; 110 m ² / g ± 20 m ² / g, average diameter of primary particles; about 16 nm

[Evaluation]
The ferrofluid compositions of Examples 1 to 8 and Comparative Examples 1 to 5 were evaluated for sedimentation characteristics by the following method.
-Settling property test-
10 ml of the ferrofluid composition was placed in a 10 ml glass measuring cylinder and allowed to stand at room temperature (about 20 ° C.) for 648 hours or 7296 hours. The amount of separated oil [ml] separated into the upper part of the graduated cylinder after 648 hours or 7296 hours was visually read, and this 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 (%) = (separation oil amount [ml] / 10 [ml]) x 100 (1)

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

As shown in Tables 1 and 2, the coweight having magnetic particles (A), lubricating oil base oil (B), a structural unit derived from ethylene, and a structural unit derived from an olefin hydrocarbon other than ethylene. The magnetically viscous fluid compositions of Examples 1 to 8 containing the coalesced (C) were excellent in long-term stability because the settling of magnetic particles was suppressed.
On the other hand, the magnetically viscous fluid compositions of Comparative Examples 1 to 5 containing no copolymer (C) were inferior in suppressing the sedimentation of magnetic particles.

From the above, the magnetic viscous fluid composition of the present invention suppresses the sedimentation of magnetic particles and is excellent in long-term stability. Therefore, in particular, dampers, clutches, torque transmission devices and brakes for various vehicles or industries, and structures. It is extremely useful for the use of seismic devices and the like.

Claims (7)

Magnetism containing magnetic particles (A), a lubricating oil base oil (B), and a copolymer (C) having a structural unit derived from ethylene and a structural unit derived from an olefin hydrocarbon other than ethylene. Viscous fluid composition. The magnetic viscous fluid composition according to claim 1, wherein the magnetic particles (A) are metal particles containing iron, and the iron content is 98% by mass or more with respect to the total mass of the metal particles. The magnetic viscous fluid composition according to claim 1 or 2, wherein the 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 ferrofluid 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 magnetically viscous fluid composition according to any one of claims 1 to 5, which comprises. The ferrofluid composition according to any one of claims 1 to 6, which comprises at least one selected from a cleaning agent, a dispersant, an antioxidant, an anti-wear agent, an extreme pressure agent, and a friction modifier. Stuff.