JP2017092119A - Magnetic viscous fluid composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic viscous fluid composition which is low in viscosity, but reduced in quantity of vaporization on condition that a magnetic field is in an off state, and which is superior in fluidity at a low temperature.SOLUTION: A magnetic viscous fluid composition comprises: monoester as a base oil; metal particles including iron as a primary component, or metal compound particles including ferrite as a primary component; magnetic particles; a dispersant having a part which exhibits lipophilicity and a functional group which is adsorbed by the magnetic particles; and a rheology control agent as an additive agent which imparts such a rheological property that a shear viscosity becomes high in a low shearing rate region and the shear viscosity becomes low in a high shearing rate region.SELECTED DRAWING: None

Description

  The present invention relates to a magnetorheological fluid composition used for dampers, clutches, brakes, and the like of buildings, automobiles, construction machines, and industrial machines.

  Magneto-Rheological Fluid (MRF, hereinafter also referred to as “MRF” or “MR fluid”) is a mixture of hydrocarbon synthetic oil, silicone oil, etc. with magnetic particles of several μm to several tens of μm. It is a functional fluid that generates a very large stress by a magnetic field. Since the viscosity can be reversibly changed by a magnetic field when MRF is used, there is an advantage that the control range of the equipment can be increased. Therefore, it is expected to be applied to dampers, clutches, brakes, etc. It has been put to practical use as an MR apparatus such as a suspension for automobiles, a seismic isolation damper for buildings (see Non-Patent Document 1), or a suspension for home appliances (see Non-Patent Document 2).

  Further, for example, for the purpose of improving thermal stability, dispersion stability, etc., MRF is greased with a specific base oil and a specific thickener, and a magnetic viscous grease having high heat resistance is proposed (Patent Document 1). reference).

Journal of the Robotics Society of Japan, “Application Examples of MRF Damper”, PP483-485, Vol. 31, no. 5 (2013) Journal of the Robotics Society of Japan, “Application of MRF active suspension to washing machine”, PP488-489, Vol. 31, no. 5 (2013)

JP 2013-104037 A

In order to enable torque control in a wider range using MRF, it is necessary to increase the stress generated when a magnetic field is applied and simultaneously reduce the viscosity when the magnetic field is off. However, when a low-viscosity base oil is used to lower the viscosity when the magnetic field is off, the base oil vapor pressure increases due to frictional heat when used in an MR device because the vapor pressure of the base oil increases and heat resistance is poor. There is a concern that the pressure inside the apparatus increases or the MRF becomes highly viscous due to the deterioration of the oil content.
For example, there has been no report on MRF that suppresses evaporation while maintaining a fluid state.
On the other hand, when a high-viscosity base oil is used to increase the heat resistance of the MRF, there is a concern that the viscosity when the magnetic field is off increases and the fluidity at low temperatures decreases.

  Therefore, the present invention provides a magnetorheological fluid composition that is low in viscosity when the magnetic field is off, has a reduced amount of evaporation, and has excellent fluidity at low temperatures (hereinafter sometimes referred to as low temperature fluidity). For the purpose.

As a result of intensive studies to solve the above problems, the present inventors have found that the above problems can be solved by blending a monoester, magnetic particles, a dispersant, and a rheology control agent. The magnetic viscous fluid composition of the present invention has been completed.
That is, the magnetorheological fluid composition of the present invention contains (1) a monoester, (2) magnetic particles, (3) a dispersant, and (4) a rheology control agent.

  According to the present invention, it is possible to provide a magnetorheological fluid composition that has a low viscosity when the magnetic field is turned off, has a reduced evaporation amount, and is excellent in low-temperature fluidity. Therefore, the magnetorheological fluid composition of the present invention is also suitably used for MR devices such as rotary / reciprocating dampers, clutches and brakes.

  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 of the upper limit and the minimum.

  The magnetorheological fluid composition of the present invention contains (1) a monoester, (2) magnetic particles, (3) a dispersant, and (4) a rheology control agent.

(1) Monoester The magnetorheological fluid composition of the present invention contains a monoester as a base oil. A monoester is a compound containing one ester bond in the molecule, and is a liquid at room temperature. The monoester used in the present invention may be obtained by synthesis or may be obtained from nature.
The monoester obtained by synthesis can be obtained, for example, by subjecting a compound having a hydroxyl group and a compound having a carboxyl group as raw materials to an esterification reaction.
The monoester used in the present invention is preferably those having 16 to 50 carbon atoms, more preferably 18 to 48, and particularly preferably 20 to 40, from the viewpoint of synthesizing a monoester having a carbon number in the above preferred range. . A carbon number of 16 or more is preferable because the amount of evaporation is easily suppressed, and a carbon number of 50 or less is preferable because the viscosity of MRF tends to be more appropriate.
The monoester may have a linear structure or a branched structure, but from the viewpoint of low-temperature fluidity, a monoester having a branched structure is preferable. It is preferable to have one. Furthermore, from the viewpoint of the viscosity index, it is preferable that the branching is in the residue part of the compound having a hydroxyl group, that is, in the R site in the monoester structure represented by R′—C (═O) OR.
The monoester may be saturated or unsaturated, but is preferably saturated from the viewpoint of heat resistance.
Further, as the monoester, one kind may be used alone, or two or more kinds may be mixed and used.

As the compound having a hydroxyl group used as a raw material for the above monoester, phosphoric acid and alcohol can be used, and alcohol is particularly preferable. The alcohol is not particularly limited as long as it is a monovalent alcohol, and examples thereof include aromatic alcohols, alicyclic alcohols, and aliphatic alcohols (excluding alicyclic alcohols). Of these, aliphatic alcohols are preferred.
As the aliphatic alcohol, those having 3 to 40 carbon atoms are preferable, and 6 to 36 are more preferable. It is preferable that the aliphatic alcohol that is the raw material of the monoester has 3 or more carbon atoms because the evaporation amount of the monoester is easily suppressed, and that the carbon number is 40 or less is preferable because the viscosity can be easily reduced.
In addition, the aliphatic alcohol may have a linear structure or a branched structure, but from the viewpoint of low temperature fluidity, those having a branched structure are preferable. From the viewpoint of the index, it is preferable to have one branch. The aliphatic alcohol may be saturated or unsaturated, but is preferably saturated from the viewpoint of heat resistance.
Furthermore, as alcohol, 1 type may be used independently and 2 or more types may be mixed and used.

  Specific examples of the preferred alcohol include 2-butyloctanol, 2-pentylnonanol, 2-hexyldecanol, 2-heptylundecanol, 2-octyldodecanol, 2-nonyltridecanol and 2-decyltetradecane. Examples thereof include 2-pentylnonanol, 2-hexyldecanol, and 2-heptylundecanol.

Examples of the compound having a carboxyl group used as a raw material for the above monoester include monovalent carboxylic acids such as aromatic carboxylic acids, naphthenic acids and fatty acids, among which fatty acids are preferred. From the viewpoint of synthesizing a monoester having a carbon number in the above preferred range, the fatty acid preferably has 3 to 40 carbon atoms, and more preferably 6 to 36. The monocarboxylic acid that is the raw material of the monoester has 3 or more carbon atoms, which is preferable because the evaporation amount of the monoester is easily suppressed. The carbon number of 40 or less is preferable because the viscosity can be suppressed low.
Further, the fatty acid may have a linear structure or a branched structure, but those having a linear structure are preferred from the viewpoint of viscosity index.
The fatty acid may be a saturated fatty acid or an unsaturated fatty acid, but a saturated fatty acid is preferred from the viewpoint of heat resistance.
Furthermore, as the compound having a carboxyl group, one kind may be used alone, or two or more kinds may be mixed and used.

  Specific examples of the preferable fatty acid include caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid and the like. Among these, capric acid, lauric acid and myristic acid are preferable.

(Base oil other than monoester)
The magneto-rheological fluid composition of the present invention is mixed with the monoester, for example, a mineral base oil or a synthetic base oil other than the monoester as a base oil, as long as the effects of the present invention are achieved. May be used. Examples of the mineral base oil include base oil obtained by refining a lubricating oil fraction of crude oil by appropriately combining solvent refining, hydrorefining, and the like. Examples of synthetic base oils include poly-α-olefins, polyol esters, alkylbenzenes, polyglycols, and phenyl ethers. However, in order to obtain a magnetorheological fluid composition having a low viscosity and capable of suppressing the evaporation amount, the monoester is preferably contained in an amount of 5% by mass to 100% by mass with respect to the total amount of the base oil. The content is more preferably 10% by mass to 90% by mass, and particularly preferably 15% by mass to 80% by mass.

When a base oil other than a monoester is used by mixing with the monoester, it is preferable to use a poly-α-olefin. As a suitable method for producing a poly-α-olefin, for example, 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. The kinematic viscosity of the resulting poly -α- olefins in this manner is more preferably a is preferably from ^{4mm 2} / ^s~50mm 2 / s at ^{40 ℃, 8mm 2 / s~40mm 2} / s . Since the kinematic viscosity at 40 ° C. of the poly-α-olefin is 4 mm ² / s or more, the amount of evaporation can be further suppressed, and it is preferably 50 mm ² / s or less. This is preferable because the viscosity can be kept low. One type of poly-α-olefin may be mixed alone with a monoester, or two or more types may be mixed and used.

  The content of the base oil containing a monoester in the magnetorheological fluid composition of the present invention is preferably 6% by mass to 50% by mass, and 8% by mass to 40% by mass with respect to the total amount of the magnetorheological fluid composition. More preferably, 10% by mass to 30% by mass is most preferable. When the base oil content is 6% by mass or more, the fluidity is improved, so that the handling property is further improved, and when it is 50% by mass or less, the shear stress at the time of applying a magnetic field can be further increased.

In the base oil used in the present invention, JIS K2283: kinematic viscosity at 40 ° C. by 2000 kinematic viscosity test ^method, preferably 2mm ² / s~1000mm 2 / s, more preferably ^{5mm 2} / ^s~700mm 2 / s, particularly preferably ^{5mm 2} / ^s~500mm 2 / s.
When the base oil has a kinematic viscosity at 40 ° C. of 2 mm ² / s or higher, the flash point becomes high, and thus evaporation is suppressed, which is preferable as an MR fluid. In addition, when the kinematic viscosity at 40 ° C. of the base oil is 1000 mm ² / s or less, the viscosity becomes low, and stable dispersion of the magnetic particles in the base oil becomes easy at the time of producing the magnetorheological fluid composition.

(2) Magnetic particles Examples of the magnetic particles contained in the magnetorheological fluid composition of the present invention include metal particles containing one or more metals selected from iron, cobalt and nickel (preferably as a main component), and nitriding. Examples thereof include one or more magnetic particles selected from metal compound particles that include one or more compounds selected from iron, iron carbide, ferrite, and magnetite (preferably as a main component) and exhibit ferromagnetism. Among these, metal particles having iron as a main component or metal compound particles having ferrite as a main component are preferable, and metal particles having iron as a main component are particularly preferable.
Here, the metal particle basically means a single metal particle, an alloy particle in which two or more kinds of metals are bonded, a particle in which two or more kinds of metals are not bonded, and the like. As in the case of carbonyl iron, particles containing a metal as a main component and containing residual components other than the metal in the raw material are also included. The same applies to the metal compound particles.
Further, the “main component” means a component having the largest mass ratio among the components constituting the magnetic particles, preferably 50% by mass or more, more preferably 70% by mass of the components constituting the magnetic particles. That's it.

  Among the preferred magnetic particles used in the present invention, the metal particles containing iron as a main component are preferable because the iron content is high, and the smaller the impurities, the higher the saturation magnetization. The preferable iron content of the metal particles containing iron as a main component is 98% by mass to 100% by mass, and particularly preferably 99% by mass to 100% by mass. An example of such magnetic particles is carbonyl iron. Carbonyl iron is a high-purity metal particle produced by thermal decomposition of iron pentacarbonyl.

The cumulative 50% particle diameter of the magnetic particles used in the present invention is preferably 0.5 μm to 50 μm, more preferably 1 μm to 30 μm, and further preferably 2.5 μm to 20 μm.
The cumulative 50% particle diameter is a particle diameter measured by a laser diffraction scattering method. When the cumulative 50% particle diameter is 0.5 μm or more, the shear stress at the time of applying a magnetic field is increased, and when it is 50 μm or less, the sedimentation of the magnetic particles is further suppressed, thereby improving the stability. This is preferable because it prevents an increase in friction during sliding.

  The magnetic particles used in the present invention 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, and titanate coupling agents. Examples of the resin include hydrocarbon resins, waxes, polyethylene, polymethacrylate, and the like.

  If the content of magnetic particles is too small, the shear stress required when applying a magnetic field cannot be obtained, and if it is too large, it becomes a semi-solid rather than a fluid, making it difficult to fill the device and functioning as a magnetorheological fluid. Is difficult to obtain. From this viewpoint, the preferable content ratio of the magnetic particles in the magnetorheological fluid composition of the present invention is 60% by mass to 94% by mass, more preferably 70% by mass to 92% by mass, particularly preferably the total amount of the composition. Is 75% by mass to 90% by mass.

(3) Dispersant As the dispersant used in the magnetorheological fluid composition of the present invention, various dispersants can be used, and those having a lipophilic part and a functional group that adsorbs to magnetic particles are preferably used. Such dispersants include anionic and cationic surfactants, nonionic surfactants, amphoteric surfactants, polymeric surfactants, pigment dispersants, alcohols, fatty acids, amines, amides, imides Metal soap, fatty acid oligomer compound, silane coupling agent, titanate coupling agent, aluminate coupling agent, fluorine-based surfactant, and boron-based surfactant. Among these, those strongly adsorbing to magnetic particles and having high lipophilicity are preferable, and nonionic surfactants, amphoteric surfactants, polymer surfactants, pigment dispersants, fatty acids, amines, amides, imides Metal soap, fatty acid oligomer compound, silane coupling agent, titanate coupling agent, and aluminate coupling agent are preferably used. More preferred are nonionic surfactants, fatty acids, amines, amides, and fatty acid oligomer compounds.

The content of the dispersant in the magnetorheological fluid composition of the present invention is preferably 0.001% by mass to 3% by mass, more preferably 0.01% by mass to 2% by mass with respect to the total amount of the magnetorheological fluid composition. 0.1% by mass to 1.5% by mass is most preferable. When the content of the dispersant is 0.001% by mass or more, the dispersibility of the magnetic particles and the like is improved, the redispersibility after settling is improved, and the content of the dispersant is 3% by mass or less. This is preferable because the effect of the rheology control agent is not inhibited and good sedimentation properties can be obtained.
Moreover, these dispersing agents may be used individually by 1 type, and may use 2 or more types. When using by 2 or more types, it is preferable that total content is in the said range.

(4) Rheology control agent As the rheology control agent used in the magnetorheological fluid composition of the present invention, various rheology control agents can be used. The rheology control agent here refers to the one that gives non-Newtonian property to the change in shear rate, and imparts flow characteristics that increase the shear viscosity in the low shear rate region while decreasing the shear viscosity in the high shear rate region. Additive.
Examples of such rheology control agents include fumed silica, bentonite, mica and kaolin in the case of inorganic compounds. Examples of organic compounds include urea-modified polymers, urethane-modified polymers, castor oil wax, polyethylene wax, polyamide wax, and fatty acid amide wax. Among these, inorganic compound-based rheology control agents are preferable, and fumed silica and bentonite are particularly preferable. When fumed silica is used, it is preferable to use a silane coupling agent or other surface modifier to make the surface hydrophobic. When bentonite is used, an organic bentonite modified with a quaternary ammonium salt or other organic modifier is preferably used.

The content of the rheology control agent in the magnetorheological fluid composition of the present invention is preferably 0.01% by mass to 5% by mass, more preferably 0.05% by mass to 4% by mass, based on the total amount of the composition. 0.07% by mass to 3% by mass is most preferable. When the content of the rheology control agent is 0.01% by mass or more, a high thickening effect is obtained even at a low shear rate range, and when the content of the rheology control agent is 5% by mass or less, an appropriate viscosity is obtained. In addition, the handling property is also good, which is preferable.
Moreover, these rheology control agents may be used individually by 1 type, and may use 2 or more types. When using by 2 or more types, it is preferable that total content is in the said range.

(5) Other additives In order to ensure various performances of the magnetorheological fluid composition, known additives generally used in lubricants, such as metal-type detergent dispersants and ashless detergent dispersants, are used. , Oiliness agent, antiwear agent, extreme pressure agent, rust inhibitor, friction modifier, solid lubricant, antioxidant, metal deactivator, antifoaming agent, colorant, viscosity index improver, pour point depressant Etc. can also be added.

Examples of the metal detergent / dispersant include sulfonates, finates, salicylates and the like whose metal components are calcium and magnesium.
Examples of the ashless dispersant include succinimide ashless dispersants, succinamide ashless dispersants, 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 molecular weight (Mw) 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. .

Examples of oil agents include oleic acid, stearic acid, higher alcohols, amines, esters, sulfurized fats and oils, acidic phosphate esters, and acidic phosphite esters.
Examples of the antiwear agent include zinc dialkyldithiophosphates, various phosphate esters, thiophosphate esters, and amine salts of various phosphate esters.
Examples of extreme pressure agents include hydrocarbon sulfides, sulfurized fats and oils, sulfur, phosphate esters, phosphite esters, chlorinated paraffins, and chlorinated diphenyls.
Examples of the rust inhibitor include carboxylic acid and its amine salt, ester, sulfonate, boron compound and the like.
Examples of the friction modifier include organic molybdenum compounds, polyhydric alcohol partial esters, amines, amides, sulfurized esters, phosphate esters, acidic phosphate esters and amine salts thereof, diols, and the like.
Examples of the solid lubricant include molybdenum disulfide, polytetrafluoroethylene (PTFE), graphite, calcium carbonate, boron nitride, mica (mica), and the like.

Examples of the antioxidant include amine-based, phenol-based, and sulfur-based antioxidants. Examples of the amine type include diphenylamine type and naphthylamine type antioxidants, and examples of the phenol type include hindered phenol type antioxidants.
Examples of the metal deactivator include benzotriazole, thiadiazole, alkenyl succinate and the like.
Examples of the antifoaming agent include silicone compounds such as dimethylpolysiloxane, fluorosilicone compounds, and ester series.
Examples of the pour point depressant include polyalkyl methacrylate, chlorinated paraffin-naphthalene condensate, and alkylated polystyrene.

Examples of the viscosity index improver include polyalkyl methacrylate, polyisobutylene, ethylene-propylene copolymer, styrene-isoprene copolymer, styrene-butadiene hydrogenated copolymer, polyisobutylene. The polymer used as the viscosity index improver has a weight average molecular weight (Mw) (in terms of polystyrene) of preferably 10,000 to 400,000, particularly preferably 20,000 to 200,000. The addition amount of such a viscosity index improver is preferably 0.1% by mass to 10% by mass with respect to the total amount of the composition. In addition, the weight average molecular weight (Mw) in this invention is standard polystyrene conversion for molecular weight calculation measured by the gel permeation chromatography (GPC) on the following conditions.
<Conditions>
Apparatus: Shodex GPC-101 (manufactured by Showa Denko KK), column: three Shodex GPC LF-804 (manufactured by Showa Denko KK), detector: differential refractometer, mobile phase: THF (tetrahydrofuran), Flow rate: 1 ml / min, sample concentration: about 1.0 mass% / vol% THF, injection amount: 100 μL

The method for preparing the magnetorheological fluid composition of the present invention is performed, for example, by the following procedure.
<Procedure 1: Preparation of oil for magnetorheological fluid composition>
First, (1) monoester and (3) dispersant are mixed to prepare an oil for a magnetorheological fluid composition. Mixing is performed using a beaker and a magnetic stirrer at a temperature of about 50 ° C to 80 ° C. When adding oil-soluble additives such as antioxidants and viscosity index improvers, add them at this time.

<Procedure 2: Mixing magnetic particles>
The magnetorheological fluid composition oil prepared by the procedure 1 and (2) magnetic particles are mixed, and the dispersant in the magnetorheological fluid composition oil is adsorbed on the magnetic particles. As the mixer, a rotation / revolution type propellerless mixer, a planetary mixer, a homogenizer, or the like can be used. The material to be mixed is desirably heated to about 60 ° C. to 100 ° C., and a previously heated material may be charged into the mixer.

<Procedure 3: Mixing of rheology control agent and other additives>
After the magnetic particles are uniformly mixed in the procedure 2, (4) a rheology control agent and (5) other additives (for example, a solid lubricant) are mixed. As in procedure 2, a rotating / revolving propellerless mixer, a planetary mixer, a homogenizer, or the like can be used as the mixer. The materials to be mixed are desirably heated to about 60 ° C. to 100 ° C., and those previously heated may be charged into the mixer.
Through the above procedures 1 to 3, the magnetorheological fluid composition of the present invention can be suitably obtained. In addition, the manufacturing method of the magnetorheological fluid composition of this invention is not limited to the said method.

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 Examples and Comparative Examples, magnetorheological fluid compositions were prepared according to the following procedure, and the respective performances were evaluated. The results are shown in the table.

<Formulation method>
(1) Magnetorheological fluid composition oil was prepared so as to have the components shown in Tables 1 and 2, and mixed at 60 ° C. using a beaker and a magnetic stirrer.
(2) The above oil for magnetic viscous fluid composition and magnetic particles are blended so as to have the contents shown in Tables 1 and 2, heated to 80 ° C., and then rotated and revolved propellerless mixer ((Co., Ltd.). ) It was uniformly stirred with ARE-500 manufactured by Shinky Corporation. After the magnetic particles are uniformly mixed, the other components are blended in the proportions shown in Tables 1 and 2, heated to 80 ° C., and then uniformly stirred with a rotation / revolution propeller-less mixer. A fluid composition was formulated.

  Each component used for the preparation of the magnetorheological fluid compositions of Examples and Comparative Examples is as follows.

<Oil for magnetorheological fluid composition>
Monoester A: Monoester prepared using capric acid and 2-hexyldecanol as raw materials, having 26 carbon atoms and a kinematic viscosity at 40 ° C. of 9.0 mm ² / s.
Diester A: Dioctyl adipate, 40 ° C. kinematic viscosity of 7.8 mm ² / s.
Diester B: Dioctyl sebacate, 40 ° C. kinematic viscosity of 11.5 mm ² / s.
Polyol ester: ester of pentaerythritol and a mixture of fatty acids having 8 and 10 carbon atoms, having a kinematic viscosity at 40 ° C. of 32.4 mm ² / s.
Hydrocarbon synthetic oil A: Poly-α-olefin having a kinematic viscosity at 40 ° C. of 17.1 mm ² / s.
Hydrocarbon synthetic oil B: Poly-α-olefin having a kinematic viscosity at 40 ° C. of 5.1 mm ² / s.
-Dispersant: erucic acid-Antioxidant: Dialkylated diphenylamine-Viscosity index improver: Non-dispersed PMA (polymethacrylate), weight average molecular weight (Mw) of 100,000 (styrene conversion value measured by the method described above) , Dilution oil: 27% by mass.

<Magneous viscous fluid composition (MRF)>
-Oil for magnetorheological fluid composition: Oil for magnetorheological fluid composition prepared above-Carbonyl iron powder (magnetic particles): Iron content: 99.7 mass%, cumulative 50% Particle size: 4.5 µm
Organized bentonite (rheology control agent): Bentonite is oleophilicized with quaternary ammonium cations, Al content: 5.9% by mass, Si content: 15% by mass
Hydrophobic fumed silica (rheology control agent): fumed silica surface-treated with dimethyldichlorosilane, BET specific surface area: 110 ± 20 m ² / g, primary particle average particle size: 16 nm
The particle size of the magnetic particles is a value measured by a laser diffraction scattering method using a particle size measuring device (trade name: FRA, manufactured by Microtrack Co.).

  The magnetorheological fluid compositions of Examples and Comparative Examples were evaluated by the following methods.

(1) Evaporation test 5 ml of the magnetorheological fluid composition prepared above is placed in a glass test vessel having an inner diameter of 53 mm as defined in JIS K2540: 2000 Petroleum Products-Lubricant-Thermal Stability Test Method, and the mixture is heated at 120 ° C. for 24 hours. Then, it was allowed to stand in a thermostatic bath, and the weight change before and after being left in the thermostatic bath was measured.
In this test, it shows that heat resistance is so favorable that the ratio (%) with respect to the total mass of the magnetorheological fluid composition before standing in the thermostat of the said mass changed, ie, a weight decreasing rate, is small.

(2) Shear viscosity test when the magnetic field is off With the rheometer “MCR101” manufactured by Anton Paar, the shear viscosity when the magnetic field is off at 20 ° C. and −30 ° C. is measured under the following test conditions to evaluate the fluidity. It was used as an index. Further, the ratio of the shear viscosity when the magnetic field was off at −30 ° C. to the shear viscosity when the magnetic field was off at 20 ° C. (shear viscosity ratio) was determined from the measured value.

(Test conditions)
・ Measurement jig: φ20mm parallel plate ・ GAP: 0.5mm
・ Temperature: 20 ℃, -30 ℃
-Shear rate: 1000 s ^-1 (constant)

  In this test, the smaller the shear viscosity when the magnetic field is off at 20 ° C., the better, and the ratio of the shear viscosity when the magnetic field is off at −30 ° C. to the shear viscosity when the magnetic field is off at 20 ° C. (shear viscosity ratio, It shows that low temperature fluidity is so favorable that (-30 degreeC / 20 degreeC) is small.

(3) Shear stress test during application of magnetic field An "MCR101" manufactured by Anton Paar is equipped with a "magnetic viscoelasticity measurement cell" manufactured by the same company, and the shear stress (kPa) during application of a magnetic field is measured under the following test conditions. did.

(Test conditions)
・ Measurement jig: φ20mm parallel plate ・ GAP: 0.5mm
・ Temperature: 20 ℃
-Shear rate: 100 s ^-1 (constant)
Magnetic flux density: 0.2T, 0.4T. 0.6T, 0.8T
In this test, a material having a high shear viscosity in a wide region from a region where the magnetic flux density is low to a region where the magnetic flux density is high is preferable because the generated stress when a magnetic field is applied is high.

  The magnetorheological fluid composition of the present invention, as shown in the examples, is excellent in heat resistance, excellent in low viscosity and low temperature fluidity when the magnetic field is off, and can secure high shear viscosity when applying a magnetic field, It is useful for various dampers, torque transmission devices, clutches, brakes, vibration absorbers and the like.

Claims (1)

(1) monoester,
(2) magnetic particles;
(3) a dispersant;
(4) a rheology control agent;
A magnetorheological fluid composition comprising: