JP2001329285A - Dispersion-stabilizing magnetorheological fluid - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a dispersion-stabilizing magnetorheological fluid having an excellent dispersion stability and magnetorheology-recovering property by using a specific dispersant. SOLUTION: The dispersion-stabilizing magnetorheological fluid is prepared by dispersing magnetic particles in polydimethylsiloxane which is a dispersing medium using a dispersant. Here, the dispersant is a copolymer of polydimethylsiloxane and a (meth)acrylic ester and/or a (meth)acrylic acid.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dispersion-stabilized magneto-rheological fluid having excellent dispersion stability and magneto-rheological property recovery properties, and having long-term performance.

[0002]

2. Description of the Related Art A magnetorheological fluid has a diameter of several μm to several tens μm.
m are dispersed in a liquid dispersion medium. In a magnetorheological fluid, when a magnetic field is applied from the outside, dispersed magnetic particles form chain-like clusters in the direction of the magnetic field, thicken or gel, and the yield stress greatly increases. For this reason, when a magnetic field does not exist, it functions as a liquid, and when a magnetic field exists, it can function like a rigid body, and can exert a drag against a shear flow and a pressure flow.

An electrorheological fluid, which is a suspension of inorganic or polymer particles dispersed in an electrically insulating liquid, has a mechanism similar to that of a magnetorheological fluid.
There is a magnetic fluid in which m magnetic particles are dispersed in a solvent.
However, the electrorheological fluid has a smaller change range of the yield stress, a narrower usable temperature range, and a slower response speed than the magnetorheological fluid. In addition, the magnetic fluid has ferromagnetic particles having a diameter of several μm to several tens of μm dispersed in a magnetic viscous fluid, whereas magnetic particles having a particle size on the order of nm are dispersed. Therefore, a larger apparatus is required to exhibit a small change in viscosity and develop a sufficient stress. As described above, the magneto-rheological fluid has characteristics distinctly different from those of the electro-rheological fluid and the magnetic fluid.

For this reason, the magnetic viscous fluid has been considered to be used for automobile members such as clutches, brakes, dampers, shock absorbers, engine mounts, members for elevating functions, etc., but it has not yet been sufficiently commercialized. Not done.

In order for a magnetic viscous fluid to exhibit the above-described characteristics, it is necessary that magnetic particles in the fluid are uniformly dispersed. However, in a magnetorheological fluid,
Since the magnetic particles have a much higher density than the liquid dispersion medium,
If left for a while, the magnetic particles may precipitate or irreversibly form aggregates, which hinders practical application. For this reason, a magnetorheological fluid having good dispersibility has been desired.

[0006] Japanese Patent Application Publication No. Hei 8-502784, Japanese Patent Application Publication No.
JP-A-502780, JP-A-8-502779 and JP-A-8-503909 describe dispersants and the like for uniformly dispersing magnetic particles. Even if a material having a stabilizing effect is used, it has been difficult to obtain remarkable dispersion stability.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances and provides a dispersion-stabilized magnetorheological fluid having excellent dispersion stability and magnetic viscosity recovery properties by using a specific dispersant. It is intended for.

[0008]

According to the present invention, there is provided a magnetic particle comprising:
What is claimed is: 1. A dispersion-stabilized magnetorheological fluid obtained by dispersing in a polydimethylsiloxane as a dispersion medium using a dispersant, wherein the dispersant is polydimethylsiloxane, and a (meth) acrylate and / or (meth) acrylate. A) A dispersion stabilized magnetic viscous fluid which is a copolymer of acrylic acid. Hereinafter, the present invention will be described in detail.

The present invention is a dispersion-stabilized magnetorheological fluid in which magnetic particles are dispersed in polydimethylsiloxane as a dispersion medium using a dispersant. The magnetic particles used in the dispersion-stabilized magnetorheological fluid of the present invention are not particularly limited, for example, iron, iron nitride, iron carbide, carbonyl iron,
Chromium dioxide, low carbon steel, nickel, cobalt; aluminum-containing iron alloy, silicon-containing iron alloy, cobalt-containing iron alloy, nickel-containing iron alloy, vanadium-containing iron alloy, molybdenum-containing iron alloy, chromium-containing iron alloy, tungsten-containing iron alloy And particles composed of iron alloys such as manganese-containing iron alloys and copper-containing iron alloys, and particles composed of a mixture thereof.

The magnetic particles have a particle size of 0.01 to 100.
It is preferably μm. If the particle size is less than 0.01 μm, the resulting dispersion-stabilized magneto-rheological fluid has a low viscosity and may not exert sufficient stress. Particle size 10
If it exceeds 0 μm, the magnetic particles tend to settle. More preferably, it is 0.5 to 20 μm.

In the dispersion-stabilized magnetorheological fluid of the present invention, polydimethylsiloxane used as a dispersion medium is obtained by polymerizing dimethylsiloxane, and is represented by the following general formula (1). When phenylsiloxane or the like is used as a dispersion medium instead of polydimethylsiloxane in the dispersion-stabilized magnetorheological fluid, the dispersion stability is impaired.

[0012]

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In the dispersion-stabilized magnetorheological fluid of the present invention, the polydimethylsiloxane as a dispersion medium preferably has a viscosity at 25 ° C. of 300 cSt or more in view of creep characteristics when a magnetic field is applied. . More preferably, the polydimethylsiloxane has a viscosity at 25 ° C. of 300 to 10,000 cSt.

In the dispersion-stabilized magnetorheological fluid of the present invention, the mixing ratio of magnetic particles to polydimethylsiloxane as a dispersion medium is (weight of magnetic particles) / (weight of polydimethylsiloxane) = 10/90 to 90. / 10 is preferred. If the blending amount of polydimethylsiloxane is less than 10% by weight, the fluidity of the obtained dispersion-stabilized magnetorheological fluid may decrease. If it exceeds 90% by weight, the viscosity of the resulting dispersion-stabilized magnetorheological fluid may be reduced. The rise may decrease.

In the dispersion-stabilized magnetorheological fluid of the present invention, polydimethylsiloxane is used as a dispersant, and
A copolymer of (meth) acrylic acid ester and / or (meth) acrylic acid is used. By using the above-mentioned polydimethylsiloxane and a copolymer of (meth) acrylate and / or (meth) acrylic acid as a dispersant, the dispersibility of the magnetic particles in the polydimethylsiloxane as a dispersion medium is improved. improves. In the dispersion-stabilized magnetorheological fluid of the present invention, the dispersant is preferably polydimethylsiloxane and a block copolymer of (meth) acrylate and / or (meth) acrylic acid. The above polydimethylsiloxane as a dispersant,
In addition, by using a block copolymer of (meth) acrylic acid ester and / or (meth) acrylic acid, the dispersibility of the magnetic particles in the dispersion medium is significantly improved. As the above-mentioned polydimethylsiloxane, the same as those used for the above-mentioned dispersion medium can be mentioned. The (meth) acrylate is not particularly limited,
For example, methyl (meth) acrylate, butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate,
Lauryl (meth) acrylate and the like can be mentioned.
These may be used alone or in combination of two or more.

The weight ratio of polydimethylsiloxane and (meth) acrylic acid ester and / or (meth) acrylic acid in the copolymer used as a dispersant is as follows: polydimethylsiloxane: (meth) acrylic acid ester and / Or (meth) acrylic acid is 90:10 to 10:90
It is preferred that If the content of polydimethylsiloxane in the dispersant is less than 10% by weight, the dispersibility may decrease, and if it exceeds 90% by weight, the dispersibility may decrease.

The dispersant used in the dispersion-stabilized magnetorheological fluid of the present invention is, for example, a polymerization initiator having a structure in which a plurality of polydimethylsiloxane segments are bonded via an azo group, for example, Wako Pure Chemical Industries, Ltd. VPS-01
51, VPS-1001, etc., by polymerizing the above (meth) acrylic acid ester and / or (meth) acrylic acid.

In the dispersion-stabilized magnetorheological fluid of the present invention, the addition amount of the above-mentioned polydimethylsiloxane as a dispersant and a copolymer of (meth) acrylic acid ester and / or (meth) acrylic acid is determined based on the amount of the magnetic particles. For example, it is preferably 0.1 to 20 parts by weight based on 100 parts by weight of the magnetic particles. If the amount of the dispersant added is less than 0.1 part by weight based on 100 parts by weight of the magnetic particles, the resulting dispersion-stabilized magnetorheological fluid may not have sufficient dispersion stability.
If the amount exceeds 0 parts by weight, the fluidity of the resulting dispersion-stabilized magnetorheological fluid may decrease.

In the dispersion-stabilized magnetorheological fluid of the present invention, as a method for dispersing magnetic particles in polydimethylsiloxane as a dispersion medium, for example, first, the above-mentioned polydimethylsiloxane as a dispersant, and (meth) acrylic The magnetic particles are immersed in a solution in which a copolymer of an acid ester and / or (meth) acrylic acid is dissolved in a solvent, and after the solvent is volatilized, poured into a polydimethylsiloxane as a dispersion medium and premixed with a spatula or the like. Then, a method of mixing with a dispersing machine such as a homogenizer, a ball mill, a sand mill, or a three-roll mill may be used.

Since the dispersion-stabilized magnetorheological fluid of the present invention has the above-described structure, it has excellent dispersion stability of magnetic particles and excellent creep characteristics. The use of the dispersion-stabilized magnetorheological fluid of the present invention is not particularly limited, and examples thereof include clutches, brakes, dampers, shock absorbers, engine mounts, members for raising and lowering functions, materials for construction, and the like.

[0021]

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

(Preparation of Magnetic Viscous Fluid) Examples 1 to 3 and Comparative Example 2 A magnetic viscous fluid having the composition shown in Table 1 was prepared. In addition,
In Examples 1 to 3 and Comparative Example 2, the magnetic particles were dissolved in THF with dispersant PAS-001 (polydimethylsiloxane-butyl methacrylate-butyl methacrylate-methacrylic acid copolymer, manufactured by Wako Pure Chemical Industries, Ltd.). It was immersed in a predetermined amount of the solution to evaporate THF, and then premixed with polydimethylsiloxane or kerosene. Thereafter, the premix was placed in a pot having an inner diameter of 90 mm and a capacity of 900 mL.
00 mL, and 1/2 inch steel ball 2
000g, 100rpm × 2 on a ball mill rotary table
After rotating for 4 hours, a magnetorheological fluid was prepared.

Comparative Example 1 and Comparative Example 3 With the composition shown in Table 1, magnetic particles, a dispersant and a dispersion medium were mixed at once to form a premix, and the premix was placed in a pot having an inner diameter of 90 mm and a capacity of 900 mL in a pot of 200 mL. Then, 2,000 g of a 1/2 inch steel ball was further charged, and the ball was rotated at 100 rpm × 24 hours on a ball mill turntable to produce a magnetic viscous fluid.

[0024]

[Table 1]

The compounds shown in Table 1 are as follows. a) Carbonyl iron powder (manufactured by EN BASF) b) Polydimethylsiloxane-butyl methacrylate-methacrylic acid copolymer (manufactured by Wako Pure Chemical Industries) c) Phosphate ester surfactant (manufactured by Toho Chemical Industry) d) Amino-modified silicone oil (Nippon Unicar) e) SH200-200cSt (Toray Dow Corning Silicone) f) SH200-200cSt and SH200-500c
G) SH200-1000cSt (manufactured by Toray Dow Corning Silicone Co., Ltd.)

With respect to the magnetic viscous fluids obtained in Examples 1 to 3 and Comparative Examples 1 to 3, the following items were evaluated. The results are shown in Table 2. (1) Initial Magnetic Viscosity Characteristics The cylinder device shown in FIG. 1 was filled with a magnetic viscous fluid immediately after fabrication, and the displacement-load was measured at a magnetic field of 0 and 900 gauss, a frequency of 1 Hz, and an amplitude of 10 mm. FIG. 2 shows a measurement example. From the ratio of the displacement-load loop area when the magnetic field was 900 gauss to the displacement-load loop area when the magnetic field was 0, the rate of increase of the loss energy when the magnetic field was 900 gauss with respect to the loss energy when the magnetic field was 0 was calculated. In each of the magnetorheological fluids, the energy lost in the third cycle became a constant value, and the energy loss in the third cycle was used to calculate the rate of increase in the energy lost.

(2) Creep characteristics The cylinder device shown in FIG. 1 is filled with a magnetorheological fluid immediately after fabrication, and a magnetic field of 900 gauss is applied. A load was applied from one direction, and the time until the 5 mm piston moved was measured.

(3) Recoverability of Magneto-Rheological Properties After measurement of the initial magneto-rheological properties, the cylinder apparatus was allowed to stand at 50 ° C. for 3 months while being filled with the magneto-rheological fluid. After a lapse of 3 months, the sample was allowed to stand at room temperature for 24 hours, and then the displacement-load at 0 magnetic field was measured, and the number of cycles until the initial loss energy value immediately after the production measured in (1) above was measured. . Immediately after reaching the initial energy loss value immediately after fabrication, 900 gauss was applied, the energy loss in the third cycle was measured, and the increase rate of the energy loss was calculated.

(4) Dispersion stability 25 mL of the magnetic viscous fluid immediately after preparation was placed in a graduated cylinder, allowed to stand at 50 ° C. for 3 months, and the volume of the supernatant layer was measured after 3 months.

[0030]

[Table 2]

From Table 2, it can be seen that the magnetic viscous fluids prepared in Examples 1 to 3 have better dispersion stability than the magnetic viscous fluids prepared in Comparative Examples 1 to 3, and have a magnetic viscous recovery characteristic and creep. It can be seen that the characteristics are also excellent.

[0032]

As described above, the dispersion-stabilized magnetorheological fluid of the present invention is excellent in recovery of the magnetorheological properties and can exhibit good dispersion stability over a long period of time by using a specific dispersant.

[Brief description of the drawings]

FIG. 1 is a schematic view of a magnetic viscosity measurement device used in an embodiment.

FIG. 2 is a diagram showing a measurement example of a magnetic viscous characteristic.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Magneto-rheological fluid 2 Cylinder 3 Piston 4 Electromagnet 5 Hydraulic servo testing machine 6 Control / measurement personal computer 7 Displacement-load loop 8 Displacement-load loop at zero magnetic field 9 Displacement-load loop at 900 gauss magnetic field

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Claims (3)

[Claims] 1. A dispersion-stabilized magneto-rheological fluid comprising magnetic particles dispersed in a polydimethylsiloxane as a dispersion medium using a dispersant, wherein the dispersant is composed of polydimethylsiloxane, (3) A dispersion-stabilized magnetic viscous particle, which is a copolymer of an acrylic ester and / or (meth) acrylic acid. 2. A dispersant comprising polydimethylsiloxane and (meth) acrylate and / or (meth)
2. The dispersion-stabilized magnetorheological granule according to claim 1, which is a block copolymer of acrylic acid. 3. The dispersion-stabilized magnetorheological fluid according to claim 1, wherein the polydimethylsiloxane serving as a dispersion medium has a viscosity at 25 ° C. of 300 cSt or more.