JP2019068073A - Magnetic viscous fluid - Google Patents

Abstract

To provide magnetic viscous fluid capable of achieving excellent dispersion stability and re-dispersibility of magnetic particles, high exciting average torque value and short torque recovery time.SOLUTION: The magnetic viscous fluid containing magnetic particles, disperse medium, fatty amide, dispersant and dispersion assistant acquires dispersion stability and re-dispersibility of magnetic particles. The magnetic viscous fluid has high exciting average torque value and short torque recovery time; therefore, it can be suitably used to control a frictional force working between objects in various types of apparatuses such as a brake, a clutch, a vibration isolator and a damper of a vibration control device.SELECTED DRAWING: None

Description

  The present invention relates to a magnetorheological fluid. In particular, the present invention relates to a magnetorheological fluid used to control the frictional force acting between objects in various mechanical devices such as a brake, a clutch, an antivibration device, and a damper of a vibration control device.

  Generally, the magnetorheological fluid is prepared by dispersing magnetic particles, which are magnetizable metal particles, in a dispersion medium. The magnetorheological fluid functions as a fluid when no magnetic field is acting. On the other hand, when a magnetic field is applied, the magnetic particles form clusters to increase viscosity, and internal stress increases.

Due to the above-mentioned increase in internal stress, the magnetorheological fluid acts like a rigid body and exhibits drag against shear flow and pressure flow. Magneto-rheological fluid is used to control the frictional force acting between objects in various mechanical devices such as brakes, clutches, vibration control devices, dampers of vibration control devices, and the like.
For this reason, when a magnetic field is acting (during excitation), it is better for the resistance against shear flow and pressure flow (the average torque value at excitation) to be large. On the other hand, in the state where the action of the magnetic field is stopped, it is preferable that the state of the torque before the action of the magnetic field is quickly returned by the collapse of the cluster. Thus, good torque response can be obtained if the torque recovery time is short.
A material containing an abrasive in the magnetorheological fluid is also used as magneto-viscoelastic fluid polishing (MRF).

Since the magnetic particles and the dispersion medium in the magnetorheological fluid have a large difference in specific gravity, sedimentation of the magnetic particles is likely to occur. Then, due to the cohesion of the magnetic particles, a hard slurry-like precipitate is easily generated.
In this case, since application of a magnetic field leads to a decrease in internal stress of the fluid, it is required to improve the dispersion stability of the magnetic particles and to suppress the sedimentation of the magnetic particles.
In addition, when the above-mentioned mechanical device is stopped for a long time, a slurry-like precipitate may be generated. Even in such a case, when physical force is applied to the precipitate, the magnetic particles need to be dispersed uniformly in the dispersion medium instantaneously. For this reason, magnetic particles are also required to have high redispersibility.

The following is known as an example which improved these problems (for example, refer patent documents 1-2). Patent document 1 is an example using clay minerals, such as organic bentonite and organic hectorite. Patent Document 2 is an example using Neuburg silica soil.
The organic bentonite, organic hectorite and Neuburg silica earth used in Patent Document 1 and Patent Document 2 are all added as an additive. For this reason, although it is effective in terms of improvement of dispersion stability, it has not been satisfactory in terms of redispersibility.

Magnetorheological fluids are commercially available, for example, products "E-600" manufactured by Sigma High Chemical Co., "MRF-122-2ED" manufactured by Lord, "MRF-132DG", "MRF-140CG", etc. Are known.
As a result of measurement using the above-mentioned commercially available product, it was found that there is room for improvement in the average torque value at the time of excitation and the recovery time of the torque.

JP 2002-121578 A Unexamined-Japanese-Patent No. 2006-286890

  An object of the present invention is to provide a magnetorheological fluid which is excellent in dispersion stability and redispersibility of magnetic particles, has a high average torque value at excitation, and has a short recovery time of torque.

  As a result of intensive studies to solve the above problems, the present inventors find that the above problems can be solved by containing a fatty acid amide and a dispersion aid in the magnetorheological fluid, and complete the present invention. It came to

That is, the magnetorheological fluid of the present invention comprises (A) magnetic particles, (B) a dispersion medium, (C) a fatty acid amide, (D) a dispersant, and (E) a dispersion aid. It features.
The dispersion aid is preferably at least one selected from the group consisting of xylan, cyclodextrin, and hollow inorganic particles.
The hollow inorganic particles are preferably at least one selected from the group consisting of a glass balloon, a silica balloon, and a ceramic balloon.
Furthermore, when a magnetic field of direct current 0.5 T is applied to the above-mentioned magnetorheological fluid under an atmosphere of 40 ° C., the average torque value at excitation is 20,000 μN · m or more, and the torque recovery time is 1.8 It is preferable that it becomes less than second.

  According to the present invention, it is possible to provide a magnetorheological fluid which is excellent in dispersion stability and redispersibility of magnetic particles. The magnetorheological fluid of the present invention has a high excitation average torque value and a short torque recovery time.

It is a graph which shows the evaluation result of the recovery time average torque value at the time of excitation of the magnetorheological fluid of Example 5, the reference example 1, and the reference example 2, and torque.

Hereinafter, embodiments of the present invention will be described in detail.
The magnetorheological fluid of the present invention contains (A) magnetic particles, (B) a dispersion medium, (C) a fatty acid amide, (D) a dispersant, and (E) a dispersion aid.
Hereinafter, in the present specification, the magnetorheological fluid, the method of manufacturing the magnetorheological fluid, and the magnetic properties of the magnetorheological fluid will be described in order.

(Magneto-rheological fluid)
The magnetorheological fluid of the present invention is a colloidal fluid containing magnetic particles, a dispersion medium, a fatty acid amide, a dispersant, and a dispersion aid, and generally, the magnetic particles are dispersed in the dispersion medium. .

  Hereinafter, each component contained in the magnetorheological fluid will be described.

(A) Magnetic Particles The magnetic particles contained in the magnetorheological fluid of the present invention can be selected according to the target permeability. For example, ferromagnetic oxides such as magnetite, carbonyl iron, gamma iron oxide, manganese ferrite, cobalt ferrite or composite ferrites of these with zinc and nickel, barium ferrite, etc .; ferromagnetic metals such as iron, cobalt, rare earths; metal nitrides Various alloys such as Sendust (registered trademark), Permalloy (registered trademark), Supermalloy (registered trademark), and the like. Among these, carbonyl iron is preferred.
The magnetic particles may be used alone or in combination of two or more.
In the magnetorheological fluid of the present invention, when a magnetic field is applied from the outside, the dispersed magnetic particles are oriented in the direction of the magnetic field to form chain-like clusters, thereby thickening and changing their flow characteristics and yield stress. Do. The average particle size of the magnetic particles is determined to exhibit such behavior. Specifically, a range of 0.1 to 100 μm is preferable, a range of 1 to 60 μm is more preferable, and a range of 5 to 50 μm is particularly preferable. The shape of the magnetic particles is preferably spherical or nearly spherical.
The average particle size of the magnetic particles is an average primary particle size measured by a laser diffraction / scattering type particle size distribution measuring apparatus.

  The content ratio of the magnetic particles contained in the magnetorheological fluid is preferably in the range of 30 to 90% by mass, and more preferably in the range of 40 to 80% by mass, with respect to the total amount of the magnetorheological fluid.

(B) Dispersion Medium The dispersion medium contained in the magnetorheological fluid of the present invention is liquid at normal temperature (25 ° C.), and is not particularly limited as long as it can disperse magnetic particles. Examples thereof include hydrocarbon solvents such as alpha-olefin, isoparaffin, normal paraffin and halogenated hydrocarbon, ester solvents, glycol solvents and silicone solvents. As an alpha olefin, 1-hexene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene etc. are mentioned. Among these, C1-C14 alpha olefins, such as 1-octene, 1-decene, 1-dodecene, are preferable. Moreover, as a glycol solvent, polyethylene glycol, polypropylene glycol, polybutylene glycol, or ethylene oxide-propylene oxide copolymer, propylene oxide-butylene oxide copolymer, and derivatives of these may be mentioned. As long as the compatibility is good, plural kinds of dispersion media may be mixed and used.

Kinematic viscosity at 40 ° C. of dispersion medium used in the present invention is preferably in the range of 2~5000mm ² / s, more preferably in the range of 5~2000mm ² / s, the 5~1000mm ² / s More preferably, it is in the range. The kinematic viscosity is a value measured by the JIS K 2283: 2000 kinematic viscosity test method.

  The content ratio of the dispersion medium is preferably in the range of 5 to 30% by mass, and more preferably in the range of 9 to 25% by mass, based on the total amount of the magnetorheological fluid.

(C) Fatty Acid Amide As fatty acid amide contained in the magnetorheological fluid of the present invention, for example, stearic acid amide, oleic acid amide, erucic acid amide, methylenebisstearic acid amide, ethylenebisstearic acid amide and the like can be mentioned. Among these, stearic acid amide and oleic acid amide are preferable. The fatty acid amide may be used alone or in combination of two or more.

  The content ratio of the fatty acid amide is preferably in the range of 0.1 to 10% by mass, and more preferably in the range of 1 to 5% by mass with respect to the total amount of the magnetorheological fluid. When the amount is less than 0.1% by mass, the fluid can not be maintained and the magnetic particles may be precipitated. When the amount is more than 10% by mass, the viscosity may be increased and the fluidity may be lost.

(D) Dispersant The dispersant is added to improve the dispersibility of the magnetic particles in the dispersion medium. As the dispersant, known surfactants, polymer dispersants and the like may be used as appropriate. Among these, surfactants are preferable from the viewpoint of dispersibility.

As surfactant used as a dispersing agent, for example, petroleum sulfonic acid or a salt thereof, synthetic sulfonic acid or a salt thereof, eicosyl naphthalene sulfonic acid or a salt thereof, polybutene succinic acid or a salt thereof, erucic acid or a salt thereof, etc. Anionic surfactant which is a hydrocarbon compound having a polar group such as carboxyl group, hydroxyl group and sulfonic acid group; polyoxyalkylene lauryl ether, polyoxyalkylene decyl ether, polyoxyalkylene isodecyl ether, polyoxyalkylene tridecyl ester Decyl ether, polyoxyethylene lauryl ether, polyoxyethylene decyl ether, polyoxyethylene isodecyl ether, polyoxyethylene tridecyl ether, polyoxyethylene alkyl ether, polyoxyethylene ether Amphoteric surfactant together with a cationic moiety and an anionic moiety in the molecular structure, such as alkyldiaminoethylglycine; nonionic surfactants such as nonylphenyl ether and the like.
Among these, polyoxyalkylene lauryl ether and polyoxyalkylene decyl ether are preferable.

(E) Dispersion assistant The magnetorheological fluid of the present invention contains a dispersion assistant as an essential component. Examples of the dispersion aid used in the present invention include xylan, cyclodextrin, hollow inorganic particles and the like.
The shape of the dispersion aid is not particularly limited, and examples thereof include crushed, spherical, plate-like, bead-like, rod-like, fibrous, needle-like, hollow and the like.
The dispersing aid may be used alone or in combination of two or more. Below, the detail of each dispersion adjuvant is demonstrated.

(E) -1. Xylan xylan refers to a polysaccharide in which D-xylose is β-1,4 linked. Naturally, they are present as heterosaccharides with various side chains attached to the main chain of xylose, and their structures differ among plant species. For example, as xylan contained in monocotyledonous plants, arabinoxylan is known and has an arabinose residue in the side chain. Examples of monocotyledonous plants include grasses such as corn, wheat and oat straw, and conifers.
As xylan contained in dicotyledonous plants, glucuronoarabinoxylan and glucuronoxylan are known, and they have a glucuronic acid residue and an arabinose residue in the side chain. Examples of dicotyledonous plants include beech, poplar and hippo.
The water-soluble xylan refers to a molecule containing six or more xylose residues linked by β-1,4 bonds, and which dissolves in water at 20 ° C. in an amount of 6 mg / mL or more. Water-soluble xylan is a molecule in which at least a part of the hydroxyl groups of xylose is replaced with another substituent (eg, acetyl group, glucuronic acid residue, arabinose residue, etc.).
The xylan may be used alone or in combination of two or more.

(E) -2. Cyclodextrin Cyclodextrin is a generic term for oligosaccharides having a cyclic structure. The cyclodextrin is, for example, one in which 6 to 8 D-glucopyranose residues are cyclically linked by an α-1,4-glucosidic bond. Examples of cyclodextrin include α-cyclodextrin (number of glucose: 6), β-cyclodextrin (number of glucose: 7), γ-cyclodextrin (number of glucose: 8) and the like. Among these, γ-cyclodextrin is preferable. The cyclodextrin may be used alone or in combination of two or more.

(E) -3. Hollow Inorganic Particles Hollow inorganic particles are particles in which the outer shell is made of an inorganic material and the inside is hollow. Specific examples of the hollow inorganic particles include glass balloons: Shirasu balloon: ceramic balloons such as silica, alumina, zirconia and the like. Among these, a glass balloon is preferred. As a commercial product of the glass balloon, "Glass Bubbles S60SH" (manufactured by Sumitomo 3M; true density 0.6 g / cm ³ , average particle diameter 27 μm), "Glass Bubbles S60" (manufactured by Sumitomo ³ M; true density 0.6 g / Cm ³ , average particle diameter 30 μm), “Sphericel (registered trademark) 110 P 8” (manufactured by Potters Barrotini; bulk specific gravity 0.4 g / cc, average particle diameter 13 μm), and the like. The hollow inorganic particles may be used alone or in combination of two or more.

  The content ratio of the dispersion aid is preferably in the range of 1 to 8% by mass, and more preferably in the range of 2 to 6% by mass with respect to the total amount of the magnetorheological fluid. By setting it as said range, the magnetorheological fluid which was further excellent in the dispersion stability and redispersion property can be obtained.

  The compounding ratio of the fatty acid amide to the dispersing aid is preferably 1: 4 to 4: 1 by mass, more preferably 1: 3 to 3: 1, and particularly preferably 1: 2 to 2: 1. By setting it as said range, the magnetorheological fluid which was further excellent in the dispersion stability and redispersion property can be obtained.

Other components In addition to magnetic particles, dispersion media, fatty acid amides, dispersants and dispersion aids, various other components may be added to the magnetorheological fluid, as long as the effects of the present invention are not impaired. You may use together. Other components include, for example, fine magnetic particles, viscosity modifiers, pour point depressants, viscosity index improvers, extreme pressure agents, rust inhibitors, antioxidants, corrosion inhibitors, metal deactivators, antifoam agents Etc.

Although fine magnetic particles having the same material composition as the magnetic particles can be used, the average particle diameter is 5 to 50 nm, preferably 7 to 40 nm.
The average particle size of the fine magnetic particles is an average primary particle size measured by a dynamic light scattering method.

  As a viscosity regulator, hydrogenated castor oil wax, benlylidene sorbitol, metal soap, oxidized polyethylene, sulfuric acid ester type anionic surfactant and the like can be mentioned.

(Manufacturing method of magnetorheological fluid)
The method of producing the magnetorheological fluid is not particularly limited. For example, a method of mixing magnetic particles, a dispersing agent, a dispersion medium, a fatty acid amide, a dispersion aid and other components with a processing machine such as a homogenizer, a bead mill, a mechanical mixer or the like to which a high shear force is applied. In the production of the magnetorheological fluid, it may be heated or cooled as needed.

(Magnetic properties of magnetorheological fluid)
As described above, the magnetorheological fluid of the present invention has the characteristics that the excitation average torque value is high and the recovery time of torque is short. Specifically, when a magnetic field of direct current 0.5 T is applied to the magnetorheological fluid of the present invention under an atmosphere at 40 ° C., the average torque value at excitation is 20,000 μN · m or more, and the torque is recovered. The time is preferably 1.8 seconds or less.
The excitation average torque value and the torque recovery time are values measured using a rheometer under the conditions described later.
The excitation-time average torque value is more preferably 35,000 μN · m or more, and further preferably 40,000 or more. On the other hand, the recovery time of the torque is more preferably 1.5 seconds or less, further preferably 1.2 seconds or less.
Also, the ratio (hereinafter sometimes referred to as relative ratio) of the average torque value during excitation to the average torque value (hereinafter referred to as initial value) before applying the magnetic field (hereinafter referred to as initial value) is 1500 or more. Is preferable, and 2000 or more is more preferable.

Hereinafter, the present invention will be described in more detail using examples.
<Examples 1 to 8, Comparative Examples 1 to 6>
Various components were put into a beaker at a mass ratio shown in Tables 1 to 3 and heated at 80 ° C. for 10 minutes, and then stirred for 1 minute at 100 rpm using a homogenizer to produce a magnetorheological fluid. The obtained magnetorheological fluid was sampled using the sample bottle No. In 25 ml of 7 (manufactured by AS-ONE, 50 ml), dispersion stability, re-dispersibility and fluidity were evaluated, and state observation was performed.
Each evaluation method will be described later.
The following raw materials are used.
(A) Magnetic particles (a1) Carbonyl iron (spherical particles, D ₅₀ = 5.9 μm)
(B) Dispersion medium (b1) α-olefin (1-decene, dynamic viscosity 15 mm ² / s, 40 ° C.)
(B2) Polyalkylene glycol (Kinematic viscosity 30 mm ² / s, 40 ° C.)
(C) Fatty acid amide (c1) stearic acid amide (D) dispersant (d1) surfactant: polyoxyalkylene decyl ether (E) dispersing aid (E) -1 xylan (e1) corn derived xylan (β- 1,4 xylan): reagent, manufactured by Tokyo Chemical Industry Co., Ltd.
(E2) Water-soluble xylan: trade name GX1 manufactured by PS-Baiotec (e3) Beech-derived xylan: reagent Wako Pure Chemical Industries (E) -2 cyclodextrin (e4) γ-cyclodextrin (polysaccharide): reagent, Kanto Chemical Co., Ltd. (E) -3 hollow inorganic particles (e5) Glass balloon: trade name 110P8 Potters Sparotini Co., Ltd. organically modified bentonite: trade name TIXOGEL-VP BYK Co., sepiolite, saponite, hectorite: goods Name GARAMITE-1958 BYK company · Reference example 1: Magnetorheological fluid (brand name MRF-132 DG, made by Lord company)
Reference Example 2: Magnetorheological Fluid (trade name E-600, manufactured by Sigma High Chemical Co.)

<Evaluation of dispersion stability>
The magnetorheological fluid was placed in a sample bottle, and the thicknesses of the magnetic particle-containing layer and the dispersion medium layer (supernatant layer) were measured after 24 hours, 96 hours, 120 hours and 240 hours at 23 ° C. The value which represented the thickness of the dispersion-medium layer with respect to the sum total thickness of a magnetic particle content layer and a dispersion-medium layer in 100 fractions was made into the evaluation value. The obtained results are shown in Table 1.
Moreover, in Table 2 and Table 3, it represented by the following evaluation criteria.
A: The thickness of the dispersion medium layer (supernatant layer) after 240 hours has elapsed is less than 1/3 of the whole.
B: The thickness of the dispersion medium layer (supernatant layer) after 240 hours has elapsed is 1/3 or more and less than 1/2 of the whole.
C: The thickness of the dispersion medium layer (supernatant layer) after 240 hours has passed is 1/2 or more of the whole.

<Evaluation of redispersibility>
The magnetorheological fluid after 120 hours in the above-mentioned evaluation of dispersion stability was vibrated again for 10 seconds using a vibration motor (TURBIN BTP24 manufactured by EXEN) and dispersed again. After 5 minutes, the thicknesses of the magnetic particle-containing layer and the dispersion medium layer were measured. The value which represented the thickness of the dispersion-medium layer with respect to the sum total thickness of a magnetic particle content layer and a dispersion-medium layer in 100 fractions was made into the evaluation value. The obtained results are shown in Table 1. The vibration conditions are as follows.
Working pressure: 0.6MPa, frequency: 351Hz

<Evaluation of liquidity>
The magnetorheological fluid after 240 hours in the evaluation of the dispersion stability was inclined to 45 degrees to evaluate the fluidity of the magnetic fluid. Evaluation criteria are as follows.
A: Flowed by 10 mm or more when inclined for 10 seconds B: Flowed by 10 mm or more when inclined for 20 seconds (except for the sample of A evaluation)
C: less than 10 mm flowed when inclined for 20 seconds D: not flowed when inclined for 20 seconds

<State observation>
The state of the magnetorheological fluid after 240 hours in the evaluation of the dispersion stability was visually observed. Evaluation criteria are as follows.
A: No or almost no gel-like part is observed.
B: A slight gel-like part is observed.
C: Partially gel-like (except for the sample of B evaluation).
D: Gel-like or solidified as a whole

<Evaluation of average torque value at excitation, relative ratio, and recovery time of torque>
The magnetorheological fluid of Example 5 is injected into the following test plate, and a torque value (μN · m) is measured in an atmosphere of 40 ° C. using a TA Instruments Rheometer DHR equipped with this test plate, and excitation is performed. The time average torque value, relative ratio and recovery time of torque were evaluated. The conditions evaluated are as follows.
Application condition of magnetic field: A magnetic field of DC 0.5 T is applied 30 seconds after the start of measurement, and the application of the magnetic field is stopped 50 seconds after the start of measurement.
The test plate used 20 mm pararell plate.
The excitation average torque value indicates an arithmetic average of torque values in 30 seconds to 50 seconds after the start of measurement.
The recovery time of the torque indicates a time obtained by subtracting 50 from the time it takes for the torque value to return to the initial value after the action of the magnetic field is stopped (magnetic flux density 0 T). In addition, said "returning" means that the torque value after stopping the application of a magnetic field shows the value of +/- 1% of initial value. Further, under the same conditions, the average torque value at the time of excitation and the recovery time of the torque were also measured for Reference Example 1 and 2 which are commercially available magnetorheological fluids, and the relative ratio was calculated.

  As shown in Table 1, in Comparative Example 1 in which (C) fatty acid amide was not contained, sedimentation of particles was observed after 24 hours, and it was found that sufficient redispersibility could not be obtained even if vibration was given. Further, in Comparative Example 2 in which the (E) dispersion aid was not contained, both the dispersibility and the redispersibility were improved as compared with Comparative Example 1, but sufficient properties were not obtained. On the other hand, in Example 1 in which all of (A) magnetic particles, (B) dispersion medium, (C) fatty acid amide, (D) dispersant and (E) dispersion aid are contained, the dispersion stability and redispersion are achieved. The sex was also clearly improved, and the effect of the present invention was confirmed.

As shown in Table 2, in Example 2 in which the dispersion medium was changed from (b1) α-olefin of Example 1 to (b2) polyalkylene glycol, good dispersion stability was obtained even after 240 hours. In addition, in Example 2, the fluidity after 240 hours was good, and the formation of a gel was not observed, so it was confirmed that the redispersibility was also good. As described above, the effect of the present invention can be obtained also with the (b2) polyalkylene glycol which is a dispersion medium having a higher viscosity, and accordingly, in the present invention, according to the application, a dispersion medium having suitable physical properties is appropriately selected. It was confirmed that it was possible. Although not described in the table, it has been confirmed that the effects of the present invention can be obtained by mixing a plurality of dispersion media.
Furthermore, also in Example 3 and Example 4 in which the ratio of (D) dispersant and (E) dispersion aid of Example 2 was changed, the dispersibility after 240 hours was good. Further, in both of Examples 3 and 4, the fluidity after 240 hours was good, and no gel formation was observed (Example 3), but even if recognized, the amount was small (Example 4). From this, it is considered that by appropriately adjusting the ratio of the (D) dispersant to the (E) dispersion aid, it is possible to realize a magnetorheological fluid further adapted to the required characteristics.

Since both the (c1) stearic acid amide and the (d1) polyoxyalkylene decyl ether have a structure having a hydrophilic group and a hydrophobic group, it was confirmed whether the effect of the present invention can be obtained with a configuration containing either one. In Comparative Example 3 in which (d1) polyoxyalkylene decyl ether was added twice as much as (c1) no stearic acid amide, sufficient dispersion stability could not be realized. On the other hand, in Comparative Example 4 where (d1) polyoxyalkylene decyl ether was not added and twice (c1) stearic acid amide was added, the whole became gel-like after 240 hours, and fluidity was lost. From this, it is confirmed that the effect of the present invention can not be obtained on one side of (C) fatty acid amide and (D) dispersant, and it is important to use (C) fatty acid amide and (D) dispersant in combination. It was done.
In Comparative Examples 5 and 6, sepiolite saponite hectorite is regarded as a rheology control agent (see JP-A-2017-59660) in the same manner as (C) fatty acid amide in place of (C) fatty acid amide. And organically modified bentonite were added. In all of Comparative Example 5 and Comparative Example 6, after 240 hours, the whole became gel-like, fluidity was lost, and it was confirmed that the effect of the present invention could not be obtained.
As a result of the above, in order to obtain the effects of the present invention, all of (A) magnetic particles, (B) dispersion medium, (C) fatty acid amide, (D) dispersant and (E) dispersion aid are included. It became clear that it is necessary.

  As shown in Table 3, the (E) dispersing aid (e1) corn-derived xylan which is the (E) dispersing aid of Example 2 is changed to (e2) the water-soluble xylan (Example 5), (e3) the beech-derived xylan Example 6) In any of the samples using (e4) γ-cyclodextrin (Example 7) and (e5) glass balloon (Example 8), the dispersion stability is good even after 240 hours, and a gel is formed. It was found to maintain excellent liquidity without From this, it was found that cyclodextrin and hollow inorganic particles can be effectively used in addition to xylan as the (E) dispersion aid of the present invention.

  Although the mechanism in the magnetorheological fluid of the present invention has not been clarified, it can be considered, for example, as follows. The hydrophilic group of the dispersant is bonded to the surface of the magnetic particle, and a particle having the hydrophobic group facing outward is formed. In addition, the lipophilic group of fatty acid amide is bonded to the surface of the dispersion aid to form particles having the hydrophobic group facing outward. In the magnetorheological fluid of the present invention, the two types of particles whose hydrophobic groups face outward as described above float while repelling each other, and this configuration provides excellent dispersion stability of the magnetorheological fluid of the present invention. And redistribution may be realized.

FIG. 1 shows evaluation results of the average torque value at excitation and the recovery time of torque of the magnetorheological fluid of Example 5, Reference Example 1 and Reference Example 2. Here, the average torque value at excitation is shown as a relative value with the value of the fifth embodiment (average torque value at excitation / initial value) as 100. Moreover, the recovery time of torque has shown the actual value.
The measured values of the average torque values at excitation of the magnetorheological fluid of Example 5, Reference Example 1 and Reference Example 2 are 42782 N · m, 38389 N · m and 30868 N · m, respectively, and the initial value is 18.7 N · m respectively. , 16.6 N · m, 26.4 N · m.
As a result, the relative ratios were 2281, 2310, and 1169, respectively.
In Example 5, although the excitation average torque value was equivalent to the reference example 1, it was confirmed that the recovery time of torque was shortened to about 1/2 of the reference example 1. Further, it was found that the average torque value at the time of excitation of Example 5 is about twice that of Reference Example 2, and the recovery time of the torque is shortened to about 1⁄5 of Reference Example 2.
From the above results, it was confirmed that the magnetorheological fluid in which the average torque value at the time of excitation is higher and the recovery time of the torque is shorter than that of the existing product is achieved by the present invention.

Claims (4)

  A magnetorheological fluid comprising (A) magnetic particles, (B) a dispersion medium, (C) a fatty acid amide, (D) a dispersant, and (E) a dispersion aid.   The magnetorheological fluid according to claim 1, wherein the dispersion aid is at least one selected from the group consisting of xylan, cyclodextrin, and hollow inorganic particles.   The magnetorheological fluid according to claim 2, wherein the hollow inorganic particles are at least one selected from the group consisting of a glass balloon, a silica balloon, and a ceramic balloon. The average torque value at excitation is 20,000 μN · m or more when a magnetic field of DC 0.5 T is applied to the magnetorheological fluid in an atmosphere at 40 ° C., and the torque recovery time is 1.8 seconds The magnetorheological fluid according to any one of claims 1 to 3, which is as follows.