JPH06240280A - Electrorheological fluid - Google Patents

Abstract

(57) [Abstract] [Purpose] To prevent the aggregation and precipitation of anisotropic particles of electrorheological fluid. [Structure] A polymer is dispersed together with anisotropic particles in an insulating medium of an electrorheological fluid. The anisotropic particles preferably have a major axis length of 0.1 to 10 μm and an aspect ratio of 2 or more and are needle-shaped, rod-shaped or plate-shaped, and the polymer is an acrylic or methacrylic polymer or Copolymer having a molecular weight of 10,000 or more, 250,000
It is preferably 0 or less. [Effect] The polymer effectively prevents aggregation and precipitation of anisotropic particles, and also facilitates increase in viscosity increase rate.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrorheological fluid whose viscosity can be adjusted by applying an electric field.

[0002]

2. Description of the Related Art An electrorheological fluid is a suspension in which fine solid particles are dispersed in an insulating medium and is a fluid whose viscosity rapidly increases under the action of a sufficient electric field. In order to change the viscosity of the fluid, either an electric field of direct current or alternating current may be applied, and by changing the strength of the applied electric field, the viscosity of the fluid can be arbitrarily adjusted within a possible range. Is. This will be specifically described with reference to the drawings. Under a zero electric field in which no voltage is applied to the electrorheological fluid 1 as shown in FIG. 1, the anisotropic particles 3 dispersed in the electrical insulating medium 2 are It is distributed in random directions by Brownian motion.

However, as shown in FIG. 2, when the switch 4 is turned on and a voltage is applied to the electrorheological fluid 1 from the power source 5, dielectric polarization in the anisotropic particles 3 or anisotropic particles 3 is generated.
The anisotropic particles 3 are oriented parallel to the electric field direction due to the bias of the electric double layer at the interface between the electric insulating medium 2 and the electric insulating medium 2. Since the anisotropic particles 3 are attracted from both sides of the electrodes 6, 6, they are in the same state as when they are fixed in place, and they act as a resistance against the fluid flow 7. become. This increases the apparent viscosity of the fluid. Then, by changing the electric field strength, the attractive force with respect to the anisotropic particles and the degree of orientation of the anisotropic particles change, and it becomes possible to adjust the ability as resistance, that is, the change rate of the viscosity of the fluid.

This electrorheological fluid is under development as a mechanism for controlling a clutch, a shock absorber, an actuator, a robot arm and the like. The electrorheological fluids that have been reported so far include cellulose, starch, silica gel (JP-A-1-304189),
Carbonaceous powder (JP-A-3-157498), fine carbon powder coated with a polymer (JP-A-3-247698)
No.), spherical or granular solid particles such as sodium polymethacrylate are treated with silicone oil (JP-A-63-30519).
No. 6), hydrocarbon oil, halogenated paraffin (JP-A-1)
No. 266193) and the like, which are dispersed in an electrically insulating medium are known.

[0005]

However, in the conventional electrorheological fluid, there is a large difference in specific gravity between the solid particles and the electric insulating medium, so that the solid and liquid are dispersed even if the solid particles precipitate or do not precipitate. It is difficult to maintain a stable state for a long period of time, and there is a problem that an electrorheological fluid having a constant viscosity cannot always be obtained without applying an electric field. On the other hand, a method of improving the dispersion stability of particles by adding a surfactant to an electrorheological fluid has been devised, but when a high voltage is applied, discharge occurs, so a high electrorheological effect at high voltage is obtained. There is a problem that you can not get. Also, a method of reducing the difference in specific gravity between the insulating medium and the solid particles has been considered, but there is a problem that the manufacturing cost increases because a special insulating medium is used.

Further, in order to increase the increase rate of the viscosity of the fluid, there is a method of increasing the applied electric field strength or increasing the dispersion amount of solid particles in the fluid. To increase the electric field strength, a high voltage is applied. When applied, the voltage is high even before discharge occurs or before discharge, so that there is a problem that power consumption increases even if the current value is as small as several tens μA to several tens mA, which is not practical. Therefore, a method of increasing the dispersion amount of the solid particles in the fluid is promising, but when the dispersion amount of the solid particles is increased, the solid particles agglomerate in the liquid,
The particle size becomes large and the particles tend to precipitate, causing the same problem as precipitation due to the difference in specific gravity. Further, when particles adhere and aggregate on the electrode surface, it takes several days to redisperse the aggregate. When such agglomeration occurs, the fluid viscosity in the state where no electric field is applied differs from that before the agglomeration occurs, or the number of particles oriented during the application of the electric field changes from the viscosity before the agglomeration occurs and the electric viscosity changes. Stable performance cannot be obtained as a viscous fluid. As described above, preventing the aggregation and precipitation of anisotropic particles is a very important issue in order to secure better performance of the electrorheological fluid.
The present invention has been made in view of the above circumstances, and an object thereof is to provide an electrorheological fluid that is excellent in the effect of preventing the aggregation of anisotropic particles and that can increase the rate of increase in viscosity.

[0007]

That is, the first aspect of the present invention is an electrorheological fluid in which the viscosity of a fluid is controlled by applying an electric field. Anisotropic particles oriented by the application of
It is characterized by containing at least one polymer. The second invention is characterized in that the anisotropic particles are needle-shaped, rod-shaped, or plate-shaped having a major axis length of 0.1 to 10 μm and an aspect ratio of 2 or more. Furthermore, the third
In the invention, the polymer is an acrylic or methacrylic polymer or copolymer and has a molecular weight of 10,000.
It is characterized by being 0 or more and 250,000 or less.

[0008]

In other words, according to the present invention, it is possible to effectively prevent the solid particles from aggregating and precipitating in the insulating medium, and also to prevent the solid particles from adhering and aggregating to the electrode surface when an electric field is applied. It can be stably dispersed in an insulating medium for a long period of time. Moreover, since the dispersion amount of the solid particles can be increased without causing aggregation or precipitation of the solid particles, the rate of increase in viscosity can be easily improved.

Further, according to the second invention, excellent response performance and a large change in viscosity can be obtained. In the current particle crushing technology and shape control technology during synthesis, the long axis is 0.1μ.
It is difficult to produce particles having a size of less than m, and when the size of the particles exceeds 10 μm, the Brownian motion of the particles is hindered, which makes it difficult to stably disperse the particles in a medium, and the liquid at the time of orientation is also used. Since the resistance increases and the responsiveness to electrolysis decreases, the length of the major axis is limited in the second invention. Furthermore, for particles with an aspect ratio of less than 2,
Since the orientation ability when a voltage is applied decreases and the viscosity change becomes small, it is not possible to obtain a practical viscous fluid.
The aspect ratio was limited as was the major axis length. Furthermore, from our previous experiments, the length of the major axis is 0.3-1 μm,
More preferable results have been obtained with particles having an aspect ratio of 7 or more.

Further, according to the third aspect of the invention, the solid particles are more effectively prevented from agglomerating and precipitating. The acrylic and methacrylic polymers in the third invention are excellent in these effects. If the molecular weight is less than 10,000, the above effect is insufficient, and if it exceeds 250,000, it becomes difficult to dissolve in the dispersion medium and, on the contrary, it adversely affects the aggregation of particles. Therefore, the molecular weight is limited. Also,
In order to further improve the dispersibility of the anisotropic particles, it is also effective to add another acrylic or methacrylic polymer or a surfactant together. In addition, in the third invention, the molecular weight is defined for acrylic or methacrylic, but it is desirable to set the above molecular weight range for polymers of other types for the same reason. The amount of the polymer added in the present invention is 1 to 30% by weight.
Is desirable. This is because if it is less than 1%, the effect of addition is insufficient, and if it exceeds 30%, the amount of polymer dissolved becomes supersaturated and the dispersibility of particles is impaired. Further, for the same reason, it is more desirable to set it to 10 to 25%.

[0011]

EXAMPLES Examples of the present invention will be described below.
The viscosity measurement of the viscous fluid in these examples was performed using a double cylinder type rotational viscometer (outer cylinder 16 mm, inner cylinder 18 mm). The viscous fluid precipitation test was carried out by storing the viscous fluid in a glass tube having a diameter of 30 mm and a length of 100 mm and storing it at room temperature, observing the precipitation state of the particles and measuring the particle concentration.

Example 1 0.5 g of an iodide crystal of cinchonidine sulfate (anisotropic particles having an average major axis length of 0.3 μm and an aspect ratio of 12) and an acrylate polymer (molecular weight 4
20,000 polymer dispersant) and 20.0 g were dispersed in a fluororesin (insulating medium) to prepare 100 g of viscous fluid. The viscosity of this viscous fluid is 236 mPas when no voltage is applied. Furthermore, commercial AC voltage is 1
Frequency conversion to kHz, effective voltage 0 to 1500 Vrm
Fig. 3 shows the change in viscosity when applied in the range of s / mm.
Shown in. As is clear from the figure, this viscous fluid has a very excellent thickening rate. In the viscous fluid precipitation test, no change was observed in the appearance and particle concentration of the viscous fluid even after 400 days had passed.

(Example 2) 2,5-dimethylpyrazine iodide crystal (average major axis length 0.5 μm, aspect ratio 9)
0.5 g and methacrylate polymer (molecular weight 120,0
00) 13.5 g and 1.0 g of cetyl octanoate (surfactant) having a functional group at only one location were dispersed in mineral oil to prepare 100 g of a viscous fluid. The viscosity of this viscous fluid is 141.5 mPas when no voltage is applied, and an alternating voltage of 1 kHz produces an effective voltage of 1500 Vrms.
The viscosity increased to 9600 mPas when applied at a rate of 1 / mm.
In addition, in this viscous fluid precipitation test, no change was observed in appearance and particle concentration even after 400 days had passed.

Example 3 2.5 g of titanium oxide crystals (average major axis length 1.0 μm, aspect ratio 7) and 10.0 g of acrylate polymer (molecular weight 250,000) were dispersed in a fluororesin to obtain 100 g of viscous fluid. Was produced. The viscosity of this viscous fluid is 208.7 when no voltage is applied.
mPas, frequency 1 kHz, effective voltage 1500 V
15,400 with AC voltage of rms / mm applied
Thickened to mPas. In the precipitation test, no change was observed in appearance and particle concentration even after 400 days had passed.

Example 4 Cinchonidine sulfate iodide crystal (average major axis length 13.5 μm, aspect ratio 10)
0.5 g and acrylate polymer (molecular weight 40,000
0) 20.0 g and fluororesin dispersed in viscous fluid 1
00g was produced. The viscosity of this viscous fluid is 254.3 mPas when no voltage is applied, and the frequency is 1 kHz.
z, the viscosity was increased to 16,390 mPas in a state where an AC voltage of effective voltage 1500 Vrms / mm was applied. In this example, the major axis length of the solid particles is large, and the agglomeration prevention effect is
It is slightly inferior to the above-mentioned examples. Specifically, about 1 hour after applying a voltage, agglomeration occurred on the electrode surface, and the agglomeration grew with the lapse of time.
In addition, the fluid viscosity in the voltage application state when the voltage was applied for 4 hours passed was 15,970 mPas, and after 6 hours, it was 14,340 mPas. Further, in this viscous fluid precipitation test, after 150 days, a small amount of crystals in the fluid were precipitated at the bottom of the glass tube, and the particle concentration was reduced to 93 wt% compared to the beginning of the test.

Example 5 2,5-Dimethylpyrazine iodide crystal (average major axis length 0.5 μm, aspect ratio 9)
0.5g and methacrylate polymer (molecular weight 300,0
00) 10.0 g was dispersed in a fluororesin to prepare 100 g of a viscous fluid. The viscosity of this viscous fluid is 197.8 mPas when no voltage is applied, and is 1 kH
When the AC voltage of z was applied at an effective voltage of 1500 Vrms / mm, viscosity could not be measured because aggregation occurred on the electrode surface 10 minutes after the application. From this, it was found that even in the constitution of the present invention, if the molecular weight of the polymer is too large, it causes aggregation at the electrode. However, in the viscous fluid precipitation test, no change was observed in appearance and particle concentration even after 400 days had passed.

Example 6 Anhydrous glycine iodide crystal (average major axis length 1.0 μm, aspect ratio 1.7) 0.5
g and methacrylate polymer (molecular weight 40,000) 2
100g of viscous fluid by dispersing 0.0g with fluororesin
Was produced. The viscosity of this viscous fluid was 227.5 mPas when no voltage was applied, and increased to 6370 mPas when an alternating voltage with a frequency of 1 kHz and an effective voltage of 1500 Vrms / mm was applied. In this example, the aspect ratio of the solid particles is less than 2, and the thickening rate is slightly smaller than in the other examples. In the precipitation test, 400
The appearance and particle concentration did not change after the day.

Comparative Example 1 38.5 g of polystyrene resin (average particle size 30.0 μm) was dispersed in 61.5 g of a mixed liquid of paraffin chloride and decane chloride (mixing ratio = 2: 3) to prepare 100 g of viscous fluid. did. The viscosity of this viscous fluid is
230 mPas when no voltage is applied,
11,4 with DC voltage of 0 Vrms / mm applied
The viscosity increased to 00 mPas. Further, in the precipitation test, after 100 days, crystal precipitation was observed at the bottom of the glass tube, and the particle concentration was reduced to 94 wt% as compared with the beginning of the test.

Comparative Example 2 Carbonaceous powder (carbon content 93
34.4 g (wt%, average particle diameter: 3.0 μm) and 0.5 g of a polysiloxane modified with ethylene oxide and propylene oxide were dispersed in 65.1 g of silicon oil to prepare 100 g of a viscous fluid. The viscosity of this viscous fluid is
It is 112 mPas when no voltage is applied.
350 m with a direct current voltage of 0 Vrms / mm applied
Thickened to Pas. Further, in the precipitation test, after 50 days, precipitation of crystals was observed at the bottom of the glass tube, and the particle concentration was reduced to 93 wt% as compared with the beginning of the test.

Comparative Example 3 Carbonaceous powder (carbon content 93
34.4 g (wt%, average particle size 3.0 μm) and 0.5 g of an ethylene oxide adduct of noniphenol were dispersed in 65.1 g of silicone oil to prepare 100 g of a viscous fluid. The viscosity of this viscous fluid is 2 when no voltage is applied.
The viscosity was 42 mPas, and the viscosity was increased to 410 mPas while a direct current voltage of 1500 Vrms / mm was applied. In the precipitation test, after 50 days, crystal precipitation was observed at the bottom of the glass tube, and the particle concentration was 9% lower than that at the beginning of the test.
It was reduced to 1 wt%.

[0021]

[Effects of the Invention] That is, according to the electrorheological fluid of the present invention, by including a polymer together with anisotropic particles in the insulating medium, the dispersibility of the anisotropic particles is improved, and aggregation,
Precipitation is effectively prevented, and anisotropic particles are stably dispersed over a long period of time. In addition, the anti-aggregation effect of anisotropic particles makes it possible to increase the amount of dispersion of these particles and improve the viscosity increase rate, and the electrorheological effect under the same voltage is superior to conventional viscous fluids. There is also an effect that power consumption can be saved.

[Brief description of drawings]

FIG. 1 is a schematic view showing an operation of an electrorheological fluid and showing a state in which a voltage is not applied to anisotropic particles.

FIG. 2 is a schematic view showing the operation of an electrorheological fluid, showing a state in which a voltage is applied to anisotropic particles.

FIG. 3 is a graph showing the relationship between the applied voltage and the viscosity of a viscous fluid in Example 1.

[Explanation of symbols]

 1 electrorheological fluid 2 electrical insulating medium 3 anisotropic particles

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Claims (3)

[Claims] 1. An electrorheological fluid in which the viscosity of a fluid is controlled by applying an electric field, wherein an anisotropic particle oriented by application of an electric field and at least one polymer are contained in a medium having excellent electric insulation. Electrorheological fluid characterized by 2. The anisotropic particle has a major axis length of 0.1 to 1.
The electrorheological fluid according to claim 1, wherein the electrorheological fluid is 0 μm and has an aspect ratio of 2 or more and is needle-like, rod-like or plate-like. 3. The polymer is an acrylic or methacrylic polymer or copolymer having a molecular weight of 10,000.
It is 0 or more and 250,000 or less, The electrorheological fluid of Claim 1 or 2 characterized by the above-mentioned.