JP2944670B2 - Electrorheological liquid - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an electrorheological liquid whose viscosity is increased by applying a voltage.

[Prior art] An electrorheological liquid is a suspension in which a finely divided hydrophilic solid is dispersed in a hydrophilic, non-conductive oil, and is extremely quickly under the action of a sufficiently strong electric field. In addition, it is a functional material that reversibly increases the viscosity of the liquid.

In order to change the viscosity, not only a DC electric field but also an AC electric field can be used, and the required current is very small, and a small amount of power gives a large viscosity change, so that, for example, a clutch, a hydraulic valve, a shock absorber,
It can be used as a component in a vibrator, anti-vibration rubber, or an electro-mechanical interface to control a system that holds the workpiece in place.

[Problems to be Solved by the Invention] Conventionally, solid particles which are one of the components of the electrorheological liquid include cellulose, starch, silica gel, ion exchange resin, polyacrylic acid, which are made fine by absorbing water from the surface. Lithium, etc., and those using PCB, butyl sebacate, trans oil, chlorinated paraffin, silicone oil, etc. as the other liquid phase are known, but they have poor practicality and have practical value An extremely viscous and highly stable electrorheological liquid does not yet exist.

The properties required for a practical electrorheological liquid include a large electrorheological effect, low power consumption when an electric field is applied, and low viscosity when the electric field is removed.

However, as described above, in the dispersed phase in which water is absorbed in order to promote the manifestation of the electrorheological effect, the current flowing between the particles increases at the same time, and thus there is a large problem in power consumption. In particular, this tendency becomes stronger as the temperature increases, and the upper limit of the operating temperature of a conventional electrorheological liquid using a dispersed phase is 70.
When used at temperatures higher than about 80 ° C, current flows excessively, resulting in extremely high power consumption and the reduction of the electrorheological effect and responsiveness due to water evaporation over time. Even when used in an atmosphere of room temperature or near room temperature,
The flow of excess current and the change in performance due to the evaporation of moisture have been obstacles to the practical use of conventional electrorheological liquids containing a dispersed phase that has absorbed moisture.

Therefore, there has been a demand for the development of an electrorheological liquid which does not cause performance degradation due to containing water, consumes less electricity, and exhibits a high electrorheological effect.

[Means for Solving the Problems] Accordingly, the present invention aims at providing an electrorheological liquid which contains little water and exhibits a high electrorheological effect but consumes less power, and is coated with an electrically insulating thin film. The dispersed carbon fine particles having an average particle size of 0.01 to 100 microns have a viscosity at room temperature of 1 to 500 centistokes (cSt).
This object is achieved by an electrorheological liquid having an electrically insulating oil as a liquid phase, wherein the carbon fine particles are carbides of mesophase carbon microbeads, coal or thermosetting resin microbeads. did.

These carbon fine particles have a carbon content of 85% by weight or more.

Here, as the electrically insulating thin film, regardless of whether it is organic or inorganic, any thin film may be formed on the surface of the carbon fine particles, but the optimum thickness of the thin film depends on the conductivity of the carbon fine particles. That is, when the conductivity of the carbon fine particles is high, it is better that the insulating thin film is relatively thick. On the contrary, when the conductivity of the fine particles is low, the insulating thin film is relatively thin. It is necessary to lower the current when applying a voltage. Further, carbon fine particles having a carbon content of 85% by weight or less have low electric conductivity and hardly exhibit an electrorheological effect.

Such an electrically insulating thin film is coated on a powder from a polymer solution, hybridized to mix small-sized particles in a dry manner and melted on the powder surface, surface treatment such as silane treatment, sputtering vacuum deposition, Formed by polymerization or the like, and used as the electrically insulating material are synthetic polymers such as polymethyl methacrylate, polystyrene, polyvinyl acetate, polyvinyl chloride, epoxy resin, and phenol resin, methyltrimethoxysilane,
Silane treating agents such as phenyltrimethoxysilane, hexamethyldisilazane, and trimethylchlorosilane; modified silicone oils having a carboxyl group or a hydroxyl group and having a dimethylpolysiloxane or phenylmethylpolysiloxane structure as a main chain; silica, alumina, rutile, etc. Inorganic compounds are typical examples.

By using the carbon fine particles coated with the electrically insulating thin film thus formed as the dispersed phase of the electrorheological liquid, it contains almost no water and has a high electrorheological effect due to the polarization action due to the conductivity of the carbonaceous material in the particles. However, it is possible to obtain an electrorheological liquid which consumes less electricity.

The preferred particle size as the dispersed phase of the electrorheological liquid is 0.01 to
It is in the range of 100 microns. If it is less than 0.05 μm, the initial viscosity becomes remarkably large in the absence of an electric field, and the change in viscosity due to the electrorheological effect is small. If it exceeds 100 μm, sufficient stability as a liquid dispersed phase cannot be obtained.

Examples of the electric insulating oil constituting the liquid phase include hydrocarbon oils, ester oils, aromatic oils, and silicone oils. These can be used alone or in combination of two or more, but it is necessary to select a combination of the electric insulating oil and the electric insulating layer so that the electric insulating oil does not dissolve the electric insulating layer.

The viscosity of the electric insulating oil is 1 to 500 centistokes (cSt) at 25 ° C., and preferably has a viscosity of 10 to 50 cSt. If the viscosity of the liquid phase is too low, the volatile content increases and the stability of the liquid phase deteriorates. If the viscosity of the liquid phase is too high, the initial viscosity in the absence of an electric field increases, and the change in viscosity due to the electrorheological effect decreases. In addition, by using a moderately low-viscosity electric insulating oil as a liquid phase, the dispersed phase can be efficiently suspended.

The proportion of the dispersed phase and the liquid phase constituting the electrorheological liquid of the present invention is such that the content of the dispersed phase composed of the carbon fine particles is 1 to 60% by weight, preferably 20 to 50% by weight, Liquid phase content of 99 to 40% by weight, preferably 80 to 50%
% By weight. If the amount of the dispersed phase is less than 1% by weight, the electrorheological effect is small, and if it exceeds 60% by weight, the initial viscosity in the absence of an electric field is significantly increased.

In the electrorheological liquid of the present invention, other additives such as a dispersed phase, a surfactant, a dispersant, and an inorganic salt can be blended within a range that does not impair the effects of the present invention.

 Hereinafter, the present invention will be described specifically with reference to examples.

Example 1 Mesophase carbon microbeads (average particle diameter 16.5 μm) using coal tar pitch as a raw material in a nitrogen stream
Heat-treated at 450 ° C, carbon fine particles with a carbon content of 93.4% by weight were dissolved in xylene solution of phenyltrimethoxysilane.
After heating and refluxing at 80 ° C. for 6 hours, the mixture was filtered to obtain a fine powder whose surface was treated with silane. 40% by weight of this fine powder is 25
It was well dispersed in 60% by weight of a silicone oil (TSF451-10, manufactured by Toshiba Silicone Co., Ltd.) having a viscosity of 10 cSt at 10 ° C. to obtain an electrorheological liquid as a suspension.

Example 2 Mesophase carbon microbeads (average particle diameter: 19.3 μm) using coal tar pitch as a raw material in a nitrogen stream
Carbon fine particles having a carbon content of 94.4% by weight were heat-treated at 600 ° C. in a xylene solution of methyltrimethoxysilane.
The mixture was filtered under heating and reflux at 6 ° C. for 6 hours to obtain a fine powder whose surface was treated with silane. 40% by weight of this fine powder was used as a liquid phase component in a silicone oil having a viscosity of 20 cSt at 25 ° C (Toshiba Silicone Co., Ltd.)
Manufactured by TSF451-20) and dispersed well in 60% by weight to obtain an electrorheological liquid as a suspension.

Example 3 Mesophase carbon microbeads (average particle diameter 14.5 μm) using coal tar pitch as a raw material in a nitrogen stream
Heat-treated at 700 ° C and added to the carbon fine particles with a carbon content of 95.5% by weight, polymethyl methacrylate spherical fine particles with an average particle diameter of 0.25μm in a weight ratio of 100: 5, and put this mixture into a hybridizer manufactured by Nara Corporation. Then, a carbon fine powder coated with a polymethyl methacrylate thin film layer was obtained. 40% by weight of this fine powder is a liquid phase component
The dispersion was well dispersed in 60% by weight of silicone oil (TSF451-20 manufactured by Toshiba Silicone Co., Ltd.) having a viscosity of 20 cSt at 25 ° C. to obtain an electrorheological liquid as a suspension.

Example 4 The carbon fine powder after silane treatment used in Example 1 was heated to 130 ° C.
For 2 hours to obtain an electrorheological liquid with the same formulation as in Example 1.

Comparative Example 1 An average of 100% by weight of lithium polyacrylate obtained by neutralizing commercially available polyacrylic acid with lithium hydroxide, containing 5% by weight of water, followed by pulverization and sizing. 40% by weight of lithium polyacrylate having a particle diameter of about 100 μm is dispersed and suspended in 60% by weight of a liquid phase component, a silicone oil having a viscosity of 20 cSt at 25 ° C. (manufactured by Toshiba Silicone Co., Ltd .: TSF451-20). A viscous liquid was obtained.

Comparative Example 2 40% by weight of carbon fine powder before coating the thin film layer used in Example 3 was used as a liquid phase component and had a viscosity at 25 ° C. of 20 cS.
t silicone oil (Toshiba Silicone Co., Ltd .: TSF451-2
0) Dispersed well to 60% by weight to obtain an electrorheological liquid as a suspension.

Comparative Example 3 The lithium polyacrylate fine powder used in Comparative Example 1
Comparative Example 1 was dried at 0 ° C. for 2 hours to obtain a water content of 0.5% by weight.
An electrorheological liquid was obtained with the same formulation as in.

The electrorheological effects of the electrorheological liquids obtained in Examples 1 to 4 and Comparative Examples 1 to 3 were measured. The electrorheological effect was evaluated at the same shear rate (375sec ^-1 ) and a shear force at a temperature of 25 ° C when a voltage was applied between the inner and outer cylinders using a double-cylinder rotary viscometer. The flowing current was measured.

Table 1 Shearing force when no voltage is applied To, voltage 1KV / mm
, The difference T-To, and the voltage 1K
It shows the current density when V / mm is applied.

[Action] In Table 1, the shear force T when an electric field (1 KV / mm) is applied
The difference T-To obtained by subtracting the shearing force To when no electric field is applied from T represents the magnitude of the electrorheological effect of the liquid. That is, the liquid having a large T-To in Table 1 shows a large electrorheological effect. At the same time, the magnitude of the current density when an electric field (1 KV / mm) is applied indicates the power consumption for developing the electrorheological effect.

As shown in Table 1, all of Examples 1 and 2 show a higher electrorheological effect than Comparative Example 1, and the power consumption is at the same level. Even when the drying becomes almost free of moisture, the electrorheological effect hardly changes as in the fourth embodiment.

On the other hand, Comparative Example 1 also shows a high electrorheological effect and consumes less power, but does not show the electrorheological effect by drying as in Comparative Example 3 because it contains moisture.

Further, when not covered with the insulating thin film as in Comparative Example 2, an excessive current flows. However, by covering with the insulating thin film as in Example 3, the power consumption can be reduced and the device operates as an electrorheological liquid.

[Effects of the Invention] An electro-rheological liquid exhibiting no electro-rheological effect with little change in performance due to a small amount of water content, low power consumption.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-63-97694 (JP, A) JP-A-2-164438 (JP, A) JP-A-2-35933 (JP, A) JP-A 64-64 6093 (JP, A) JP-A-60-51749 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) B01J 13/00 C10M 125/02

Claims (1)

(57) [Claims] An average particle size of 0.01 coated with an electrically insulating thin film.
An electro-rheological liquid having carbon fine particles of about 100 μm as a dispersed phase and an electric insulating oil having a viscosity of 1 to 500 centistokes (cSt) at room temperature as a liquid phase, wherein the carbon fine particles are mesophase carbon micro beads, coal or heat. An electrorheological fluid, which is a carbide of curable resin microbeads.