JP2005113045A - Magnetic viscous fluid - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic viscous fluid capable of suppressing sedimentation of magnetic particles over a long period, excellent in disperse stability and containing magnetic particles in large amounts. <P>SOLUTION: The magnetic viscous fluid capable of suppressing sedimentation of magnetic particles over a long period and excellent in disperse stability comprises magnetic particles and a dispersion medium. The magnetic viscous fluid further comprises oxidized polyethylene in an amount of 0.5-5 wt.% based on the magnetic particles as a viscosity adjuster and as necessary, at least one additive selected from a group consisting of hydrogenated castor oil, amide wax, montmorillonite and bentonite. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a magnetorheological fluid, and more particularly to a magnetorheological fluid having excellent dispersion stability.

  A magnetorheological fluid containing magnetic particles and a dispersion medium has the property that its viscosity changes when an external magnetic field is applied, and is useful as a working fluid for clutches, brakes, dampers, actuators, shock absorbers, etc. It is.

As an example of the above-mentioned magnetorheological fluid, a magnetorheological fluid to which various surfactants, organic bentonite, hydrogenated castor oil and the like are added has been proposed.
JP 2002-121578 A Japanese Patent No. 3275212

  However, the above-mentioned magnetorheological fluid cannot be said to sufficiently suppress sedimentation of magnetic particles over a long period of time, and as a result, it is difficult to say that the magnetorheological fluid is excellent in dispersion stability.

  The present invention has been made in view of the above circumstances, and its object is to provide a magnetorheological fluid in which sedimentation of magnetic particles is suppressed over a long period of time, excellent in dispersion stability, and high in magnetic particle content. It is in.

  As a result of various studies, the inventor has surprisingly found that a magnetorheological fluid in which a specific amount of polyethylene oxide is blended with a dispersion medium in which magnetic particles are dispersed has suppressed sedimentation of the magnetic particles over a long period of time. It was found that the dispersion stability is excellent.

  The present invention has been completed based on the above findings. The gist of the present invention is that, in a magnetorheological fluid comprising magnetic particles and a dispersion medium, polyethylene oxide as a viscosity modifier is 0.5 to It exists in the magnetorheological fluid characterized by containing 5weight%.

  According to the present invention, since sedimentation of magnetic particles can be suppressed over a long period of time, a magnetorheological fluid having a good dispersion stability for a long period of time and a high magnetic particle content is provided. The industrial value is remarkable.

  The present invention will be described below. The magnetic particles used are iron particles, iron nitride particles, iron carbide particles, carbonyl iron particles, ferrite particles, magnetite particles, cobalt particles, nickel particles and at least two selected from the group of iron, cobalt and nickel. And at least one particle selected from the group of alloy particles. Preferred magnetic particles are iron particles, carbonyl iron particles, and ferrite particles such as Mn—Zn based ferrite particles and Mn—Mg—Zn based ferrite particles.

    The particle size of the magnetic particles is usually 0.1 to 50 μm, preferably 0.3 to 10 μm. When the particle size exceeds 50 μm, the dispersion stability of the obtained magnetorheological fluid deteriorates. On the other hand, when the particle size is less than 0.1 μm, the change in viscosity of the magnetorheological fluid due to the presence or absence of application of a magnetic field is small, and the magnetorheological effect cannot be said to be sufficient.

    The content of the magnetic particles in the dispersion medium is usually 15 to 40% by volume, preferably 20 to 35% by volume. When the content of the magnetic particles exceeds 40% by volume, the viscosity of the obtained magnetorheological fluid becomes too high and the fluidity deteriorates. On the other hand, if it is less than 15% by volume, a sufficient magnetic viscosity change cannot be obtained due to insufficient magnetic force.

  Examples of the dispersion medium include hydrocarbon solvents, glycol solvents, and silicone solvents. These may be used alone or in combination of two or more as required. Examples of the hydrocarbon solvent include normal paraffin, isoparaffin, and paraffin lubricating oil, examples of the glycol solvent include diethylene glycol monoethylene ethyl ether, and examples of the silicone solvent include silicone oil such as polydimethylsiloxane. Etc.

  Polyethylene oxide as a viscosity modifier is obtained by oxidizing polyethylene to introduce a polar group, and its acid value is usually 1.0 to 70 mgKOH / g, preferably 5.0 to 50 mgKOH / g. . When the acid value is less than 1.0, the dispersion stability of the obtained magnetorheological fluid may be inferior, and when the acid value exceeds 70, the viscosity of the magnetorheological fluid becomes too high and the fluidity is low. May get worse. And the number average molecular weight of a polyethylene oxide is 1000-5000 normally, Preferably, it is 1500-4000. When the molecular weight is less than 1000, the effect of preventing sedimentation of the magnetic particles may be inferior, and when the molecular weight exceeds 5000, the viscosity of the magnetorheological fluid may become too high and the fluidity may deteriorate.

  The blending amount of the oxidized polyethylene is 0.5 to 5% by weight, preferably 0.7 to 2% by weight, based on the magnetic particles. When the blending amount is less than 0.5% by weight, the dispersion stability of the obtained magnetorheological fluid is inferior, that is, sedimentation of magnetic particles may occur over time. Moreover, when a compounding quantity exceeds 5 weight%, the viscosity of a magnetorheological fluid becomes high too much and fluidity | liquidity may deteriorate.

    In the present invention, for the purpose of further improving the dispersion stability and fluidity of the magnetorheological fluid, the following additives may be added to the magnetorheological fluid having the above-described component composition. The compounding amount of the additive is usually 5% by weight or less, preferably 0.1 to 5% by weight, more preferably 0.5 to 3% by weight with respect to the magnetic particles. When the blending amount exceeds 5% by weight, the viscosity of the magnetorheological fluid becomes too high, and the fluidity may deteriorate.

  Additives include (1) hydrogenated castor oil obtained by adding hydrogen to castor oil, (2) amide wax synthesized from vegetable oil fatty acid and amine, (3) quaternary clay mineral montmorillonite and / or its crystal surface. Examples thereof include bentonite treated with ammonium salt or organic amine salt. These may be used alone or in combination of two or more as required.

  Further, a surfactant or a higher fatty acid may be further added for the purpose of further improving the fluidity of the magnetorheological fluid. Examples of the surfactant include those having a functional group having an affinity for the dispersion medium, and specific examples include alkali metal salts or ammonium salts of higher fatty acids, sorbitan fatty acid esters, and the like. Examples of higher fatty acids include caproic acid, lauric acid, myristic acid, palmitic acid, stearic acid, and oleic acid. The compounding amount of the surfactant or higher fatty acid is usually 5% by weight or less, preferably 0.1 to 5% by weight, more preferably 0.5 to 3% by weight with respect to the magnetic particles. If it exceeds 5% by weight, the fluidity of the magnetorheological fluid may deteriorate.

  The method for producing the magnetorheological fluid of the present invention is not particularly limited. For example, there is a method in which magnetic particles, a viscosity modifier, and a dispersion medium are mixed with a processing machine capable of giving high resilience such as a homogenizer, a ball mill, and a mechanical mixer. Can be mentioned. By sufficiently dispersing the viscosity modifier using these processors, the viscosity modifier acts effectively, and a magnetic viscous fluid in which magnetic particles are stably dispersed can be obtained.

The magnetorheological fluid of the present invention has an E-type viscometer with a viscosity (shear rate of 100 sec ⁻¹ ) of usually 50 to 250 mPa · s, preferably 60 to 200 mPa · s, and a thixotropic index of usually 5 to 15, preferably 6. ˜13, the sedimentation degree which is an index of dispersibility is usually 0 to 5 ml, preferably 0 to 3 ml.

  A magnetorheological fluid having the above-described characteristics is useful as a viscous fluid for clutches, dampers, actuators, and the like because sedimentation of magnetic particles is suppressed for a long period of time and is excellent in dispersion stability.

  EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited to a following example, unless the summary is exceeded. The viscosity, thixotropy index, and sedimentation degree were measured by the following methods.

  The viscosity was measured at 25 ° C. using an E-type viscometer (TV-30; manufactured by Toki Sangyo Co., Ltd.).

Thixotropy index was expressed as the ratio of the viscosity shear rate 3.83Sec ^-1 for viscosities in shear rate 38.3Sec ^-1 as measured using the E type viscometer.

  The sedimentation degree was expressed as the volume (ml) of the supernatant layer after one month after putting 50 ml of magnetorheological fluid in a 100 ml graduated cylinder and leaving it at a temperature of 60 ° C. for one month.

Examples 1-5, Comparative Examples 1-4:
Each component was mixed with the homomixer by the mixing | blending prescription shown in Tables 1-3, and the magnetorheological fluid was manufactured. The viscosity, thixotropy index, sedimentation degree and magnetic properties of the obtained magnetorheological fluid were measured by the above-described methods. The results are shown in Tables 1-3.

  In the table, “SN-NP (trade name)” manufactured by Nikko Petrochemical Co., Ltd. as normal paraffin, “Super Oil M22 (trade name)” manufactured by Nippon Oil Co., Ltd. as paraffinic lubricant, carbonyl iron (1) “S3700 (trade name) average particle diameter: 2.6 μm” manufactured by ISP, and “S3000 (trade name) average particle diameter: 1.9 μm” manufactured by ISP as carbonyl iron (2) 3) “S-1651 (trade name) average particle size: 5.1 μm” manufactured by ISP, and “High Wax 4052E (trade name)” (acid value: 20 mgKOH) manufactured by Mitsubishi Chemical as polyethylene oxide (1). / G, number average molecular weight: 3200) as “polyethylene oxide (2)” “High Wax 4051E (trade name)” manufactured by Mitsubishi Chemical Corporation (acid value: 12 mg KOH / g, number average molecular weight: 200) as polyethylene oxide (3), “Disparon TP-203 (trade name)” (acid value: 12 mgKOH / g, number average molecular weight: 3000) manufactured by Enomoto Kasei Co., Ltd., and Mitsubishi Chemical Corporation as polyethylene oxide (4) "Hywax 2203A (trade name)" (acid value: 30 mgKOH / g, number average molecular weight: 2700) manufactured by Benidonite (1), "Hydrocol ONZ (trade name)" manufactured by Allied Colloid, “Esben W (trade name)” manufactured by Hojun Co. as 2), “Esven N-400 (trade name)” manufactured by Hojung Co. as bentonite (3), and Sannopco Co., Ltd. as hydrogenated castor oil (1) “SN thickener 4040 (trade name)” is used as hydrogenated castor oil (2), “Dispalon 305 (trade name) manufactured by Enomoto Kasei Co., Ltd. ", Which was used" SN thickener 4030 (trade name) "manufactured by San Nopco Limited as amide wax.

  From the above results, it is clear that the magnetorheological fluid of the present invention has a low sedimentation degree and excellent dispersion stability.

Claims (5)

  A magnetorheological fluid comprising a magnetic particle and a dispersion medium, wherein the magnetorheological fluid contains 0.5 to 5% by weight of polyethylene oxide as a viscosity modifier with respect to the magnetic particles.   The magnetorheological fluid according to claim 1, comprising at least one selected from the group of hydrogenated castor oil, amide wax, montmorillonite, and bentonite as an additive.   The magnetic particles are iron particles, iron nitride particles, iron carbide particles, carbonyl iron particles, ferrite particles, magnetite particles, cobalt particles, nickel particles and alloy particles comprising at least two selected from the group of iron, cobalt and nickel. 3. The magnetorheological fluid according to claim 1, wherein the magnetorheological fluid is at least one kind of particles selected from the group.   The magnetorheological fluid according to any one of claims 1 to 3, wherein the dispersion medium is a hydrocarbon solvent, a glycol solvent, or a silicone solvent.   5. The magnetorheological fluid according to claim 1, wherein the thixotropy index is 5 or more.