JPH06240281A - Production of electroviscous fluid - Google Patents

Abstract

PURPOSE:To facilitate the formation of an electroviscous fluid having desired viscosity. CONSTITUTION:Anisotropic particles which can orient upon the application of an electric field together with at least one polymeric dispersant are added to an electrical insulating medium to obtain an electroviscous fluid having an adjusted viscosity. Thus, the polymeric dispersant added can facilitate the formation of an electroviscous fluid of desired extensively adjustable viscosity without detriment to the properties of the fluid.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an electrorheological fluid in which the viscosity of the fluid 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 electrorheological fluid is being developed 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 composed of sodium polymethacrylate, etc.
5196), hydrocarbon oil, halogenated paraffin (JP-A-1-266193), and the like, which are dispersed in an electrically insulating medium. The desirable viscosity of this electrorheological fluid varies depending on the above-mentioned application, and there are cases where it is desired to appropriately select and change the viscosity in a state where no electric field is applied. Conventionally, in such a case, the content of the solid particles dispersed in the medium is increased or decreased, or the viscosity of the insulating medium itself is changed.

[0004]

However, it is known that changing the viscosity of the fluid by the conventional method causes the following problems. That is, regarding the increase / decrease of solid particles, when the solid particles are reduced for the purpose of lowering the viscosity of the fluid, the density of cross-linking of particles formed between electrodes becomes small,
The binding force is weakened and the electrorheological effect is reduced. On the contrary, if the amount of solid particles is increased in order to increase the viscosity of the fluid, the frequency of contact of the solid particles with the electrode due to the flow of the fluid increases and the electrode is easily damaged or worn. There is a problem that a functional disorder occurs. In addition, the increased solid particles are likely to impair the uniform dispersibility, and may aggregate or settle.

Further, the method of changing the viscosity of the insulating medium has a narrow range of selectable viscosities and cannot cover a sufficiently wide range of viscosities. Further, when a medium having a high viscosity is selected, there is a problem that the dispersion state of solid particles becomes unstable. As described above, in the method of increasing / decreasing the solid particles or selecting the viscosity of the medium, other problems may occur along with the change of the viscosity of the fluid, and the range of change in the viscosity of the fluid that can be selected is not so wide. , 0.0
The limit is about 5 Pas to 0.7 Pas. The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for producing an electrorheological fluid that can sufficiently change the viscosity of the fluid without impairing the properties of the fluid.

[0006]

[Means for Solving the Problems] In order to solve these problems, as a result of intensive research, as a result, an adjusting method in which the viscosity can be arbitrarily set by changing the addition amount and / or the molecular weight of a polymer used as a dispersant Invented The structure of the present invention is as follows. That is, the present invention is a method for producing an electrorheological fluid in which the viscosity of a fluid is controlled by applying an electric field, in which anisotropic particles oriented by the application of an electric field are dispersed in a medium having excellent electrical insulation properties. At the same time, the second invention is characterized by containing at least one polymer dispersant to adjust the viscosity of the fluid, and the polymer dispersant is contained in the medium in an amount of 1 to 30% by weight. To do. Further, the third invention is characterized in that the polymer dispersant has a molecular weight of 10,000 or more and 250,000 or less, and the fourth invention is that the polymer dispersant is an acrylic or methacrylic polymer or It is characterized by comprising a copolymer.

The anisotropic particles of the electrorheological fluid used in the present application are preferably needle-shaped, rod-shaped or plate-shaped particles having a major axis length of 0.1 to 10 μm and an aspect ratio of 2 or more. This is because it is difficult to produce particles whose major axis is less than 0.1 μm by the current particle crushing technology and shape control technology at the time of synthesis. Moreover, when the particle size exceeds 10 μm, Brownian motion of the particles occurs. Therefore, it is difficult to stably disperse in the medium, and the liquid resistance at the time of orientation becomes large, and the response to the electric field decreases, so the length of the major axis is desirable. Furthermore, in the case of particles having an aspect ratio of less than 2, the orientation ability when a voltage is applied decreases,
The above aspect ratio is desirable because the change in viscosity becomes small and a viscous fluid that is practical cannot be obtained. Furthermore, from our previous experiments, the length of the long axis is 0.3-1μ.
More preferable results are obtained with m and particles having an aspect ratio of 7 or more.

[0008]

That is, according to the present invention, since the polymer dispersant is added to the medium together with the anisotropic particles, by selecting the type, molecular weight and addition amount of the polymer dispersant,
The viscosity of the viscous fluid can be changed within a wide range. As a result, the fluid viscosity is 0.003 when no electric field is applied.
It is possible to easily obtain a fluid having a low viscosity of Pas and a fluid having a higher viscosity. Further, according to the present invention,
Addition of the polymer dispersant can also prevent the aggregation of anisotropic particles and increase the thickening effect. The operation will be described below.

The polymer dissolved in the dispersion medium is adsorbed on the anisotropic particles and suppresses the aggregation and sedimentation of the particles, and plays a role of maintaining a stable dispersed state. This polymer dispersant also has a role of suppressing particles from adsorbing and aggregating on the electrode surface in a state where an electric field is applied to the electrorheological fluid.
When many polymer dispersants are added to this electrorheological fluid, it dissolves in the electrically insulating medium, increasing the viscosity of the entire fluid. When the strength of the electric field applied to the electrorheological fluid is increased, the electric thickening effect also increases along with the increase in the electric field strength. In the state where an electric field is applied, + -electrons of the electric double layer are biased to the electrodes on the surface of the anisotropic particles,
Orient. When this movement is repeated, the thickness of the electric double layer around the particles is reduced, the attractive force received from the electric field is reduced, and the electrorheological effect is reduced. However, when the viscosity of the dispersion medium is high, peeling of the electric double layer during orientation is suppressed. As a result, in an electrorheological fluid with a large amount of polymer dispersant added and a high fluid viscosity, the attractive force received by the electric field of anisotropic particles is greater than that with a low polymer dispersant content, and the anisotropic particles It is considered that because the force of orienting to the electric field becomes stronger, the resistance of the particles to the fluid flowing perpendicularly to the electric field direction becomes larger and the thickening effect becomes larger.

The addition amount of the polymer dispersant in the present invention is preferably 1 to 30% by weight. If it is less than 1%, the effect of addition is insufficient,
If it exceeds, the amount of the polymer dissolved will be supersaturated and the dispersion stability of the particles will be impaired. For the same reason, 10
It is more desirable to be 25%. The molecular weight of the polymer dispersant is preferably 10,000 or more and 250,000 or less. It has a molecular weight of 10,0.
If it is less than 00, the above effect is insufficient, and if
If it exceeds 000, the solubility is lowered and precipitation tends to occur, so the above range is desirable. Furthermore, acrylic and methacrylic polymers are excellent in these effects. 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.

[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). In each of the following examples, the solid particles were stably dispersed, and neither aggregation nor sedimentation occurred.

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
10,000 polymer dispersants) 3.0, 7.0, 13.
5, 18.0 or 20.0 g was dispersed in a fluororesin (insulating medium) to prepare 100 g of viscous fluid (test liquids 1-1 to 1-5). With respect to the viscosities of these viscous fluids, the viscosities were measured in a state where no voltage was applied and when an effective voltage of 1500 V / mm was applied at 1 kHz, and the results are shown in Table 1 and FIG. as a result,
It was possible to change the viscosity of the fluid in a wide range by changing the addition amount of the polymer dispersant, and the viscosity at the time of application had a sufficiently high value.

Example 2 0.5 g of cinchonidine sulfate iodide crystal (anisotropic particles having an average major axis length of 0.3 μm and an aspect ratio of 12) and methacrylate polymer (polymer dispersant having a molecular weight of 120,000) 3 0.0 g was dispersed in a fluororesin (insulating medium) to prepare 100 g of viscous fluid (Test liquid 2). The viscosity of this viscous fluid was determined as in Example 1.
The measurement was carried out in the same manner as above, and the results are shown in Table 1 and FIG.
It was shown to. As a result, it is understood that the viscosity range can be easily changed by changing the type and molecular weight of the polymer dispersant.

(Example 3) 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) 10.0 or 20.0 g, and dispersed in mineral oil to prepare 100 g of viscous fluid (test liquids 3-1 and 3-2,
The viscosity was measured in the same manner as in Example 1. The results are shown in Table 1.
And, as shown in FIG. 1, the viscosity can be changed in a wide range.

Example 4 2.5 g of titanium oxide crystals (average major axis length 1.0 μm, aspect ratio 7) and 10.0 g or 1 of acrylate polymer (molecular weight 250,000)
Disperse 5.0g and fluororesin 100g viscous fluid
(Test liquids 4-1 and 4-2) were prepared and the viscosity was measured in the same manner as in Example 1. As a result, as shown in Table 1 and FIG. 1, the viscosity can be changed to a high viscosity side by a relatively large molecular weight, and the viscosity can be changed in a wider range by changing the addition amount.

Comparative 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) was dispersed in a fluororesin (insulating medium) to obtain 100 g of a viscous fluid. (Test liquid 5) was prepared. The viscosity of this viscous fluid was measured in the same manner as in Example 1, and the results are shown in Table 1 and FIG. In order to reduce the viscosity of this viscous fluid, when the amount of iodide crystals dispersed was reduced (0.18 g), the clay decreased to 0.0028 Pas when no electric field was applied. The viscosity is 0.015 Pas, and the thickening effect is significantly reduced. Further, when the amount of iodide crystals dispersed was increased to increase the viscosity (2.5 g), precipitation of anisotropic particles occurred early and the particles could not be used.

[0017]

[Table 1]

[0018]

That is, according to the method for producing an electrorheological fluid of the present invention, anisotropic particles oriented by application of an electric field are dispersed in a medium having excellent electric insulation and at least one polymer is used. Since the viscosity of the fluid is adjusted by containing the dispersant, a viscous fluid having a desired viscosity can be easily obtained without impairing its properties. Moreover, the obtained viscous fluid has excellent dispersibility of anisotropic particles, and has an effect of effectively preventing aggregation and sedimentation.

[Brief description of drawings]

FIG. 1 is a graph showing a viscosity range when a voltage is not applied and a viscosity range when a voltage is applied to the viscous fluids of Examples and Comparative Examples.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location C10M 135: 10) C10N 10:08 20:04 20:06 Z 8217-4H 30:00 D 8217- 4H 30:04 40:14 70:00

Claims (4)

[Claims] 1. A method for producing an electrorheological fluid in which the viscosity of a fluid is controlled by applying an electric field, in which anisotropic particles oriented by the application of an electric field are dispersed in a medium having excellent electrical insulation properties. And a method for producing an electrorheological fluid, characterized in that the viscosity of the fluid is adjusted by containing at least one polymer dispersant. 2. The polymer dispersant is 1% by weight in the medium.
The method for producing an electrorheological fluid according to claim 1, characterized in that the content is -30%. 3. The polymer dispersant has a molecular weight of 10,000.
It is 0 or more and 250,000 or less, The manufacturing method of the electrorheological fluid of Claim 1 or 2 characterized by the above-mentioned. 4. The electrorheological fluid according to claim 3, wherein the polymer dispersant is made of an acrylic or methacrylic polymer or copolymer.