JPH03247698A - Electro viscous fluid - Google Patents

Abstract

PURPOSE:To provide a non-aqueous electro viscous fluid having excellent heat and cold resistance and high electro viscous effect and requiring only a low consumption electric power by dispersing specific carbonaceous fine particles in an electrically insulating oil, the surfaces of the carbonaceous fine powder being covered with the thin film layers of a high molecular polymer. CONSTITUTION:The objective electro viscous fluid is prepared by dispersing fine particles in an electrically insulating oil, the fine particles being prepared by covering the surfaces of carbonaceous fine particles having aC/H ratio of 2.4-3.0 with the thin film layers of a polymer such as poly methyl methacrylate, PS, PVAc, PVC, poly vinylidene fluoride, epoxy resin, phenolic resin or silicone polymer. The carbonaceous fine particles are preferably those prepared by separating from a pitch component optically isotropic small spheres produced by the thermal treatment of coal tar.

Description

Detailed Description of the Invention 10 Objects of the Invention [Field of Industrial Application] The present invention relates to an electrorheological fluid whose viscosity is increased by the application of voltage.

[Prior Art] An electrorheological fluid is a suspension of finely divided dielectric solids dispersed in a non-conductive oil, which rapidly and rapidly transforms under the action of a sufficiently strong electric field. It is a fluid whose viscosity changes reversibly.

In order to change the viscosity, not only a direct current electric field but also an alternating current electric field can be used, and the required current is very small (
, it causes a large change in viscosity from a liquid to an almost solid state with a small amount of electric power, so it can be used for devices and parts such as clutches, valves, shock absorbers, pie breaks, various anti-vibration rubbers, actuators, robot arms, vibration damping materials, etc. Electrorheological fluids have been considered as a component for controlling.

Conventionally, solid particles that are one of the components of electrorheological fluids include, for example, U.S. Pat.
No. 47507, No. 3397147, No. 39705
No. 73, Publication No. 4129513, or Japanese Publication No. 60-31211, or West German Published Patent No. 34274
As disclosed in No. 99, etc., water is absorbed from the surface and finely divided cellulose, starch, silica gel, ion exchange resin, lithium polyacrylate, etc. are used as other liquid phase components. Although it is known that halogenated diphenyl, butyl sebacate, hydrocarbon oil, chlorinated paraffin, silicone oil, etc. Viscous fluids do not yet exist.

The properties required of a practical electrorheological fluid are that it exhibits a large electrorheological effect over a wide temperature range, consumes little power when an electric field is applied, has low viscosity when the electric field is removed, and has a dispersed phase. The goal is to maintain stable properties over a long period of time without settling.

However, in the case of a dispersed phase in which water is absorbed in order to promote the development of the electrorheological effect as described above, the electric current flowing between the particles increases at the same time, resulting in a major problem in power consumption. In particular, this tendency becomes stronger as the temperature increases, and the upper limit of the operating temperature of electrorheological fluids using conventional dispersed phases is 7.
If used at temperatures above 0 to 80 degrees Celsius, excessive current will flow, resulting in extremely high power consumption, as well as a decline in the electrorheological effect and response over time. It was impossible to apply it to devices and parts used in high-temperature atmospheres.

Furthermore, an aqueous electrorheological fluid containing a dispersed phase that has absorbed water as described above does not exhibit an electrorheological effect at low temperatures of 0° C. or lower due to coagulation of water.

Water-based electrorheological fluids, which require the dispersed phase to contain water in order to function as electrorheological fluids, have inherent problems in the temperature range and durability associated with water evaporation.
For a long time, these were the reasons why electrorheological fluids were not put into practical use.

Therefore, the emergence of a practically applicable non-aqueous electrorheological fluid that does not require water in the dispersed phase has been awaited.

Recently, as such a non-aqueous fluid, US Pat. No. 4,687
No. 589, or Japanese Publication No. 63-97694,
Liquids that essentially do not contain water and fluids that have a multilayer structure of dispersed phases have been proposed, as disclosed in No. 193 of 1982, but they have a small electrorheological effect, high power consumption, and alternating current. There are also problems such as the fact that it only functions in an electric field, and so far it cannot be said that a practical electrorheological fluid with sufficient properties has been developed.

One of the mechanisms by which such non-aqueous electrorheological fluids develop is that when an electric field is applied, interfacial polarization occurs due to the movement of electrons or holes in the dispersed phase particles, and the dispersed phase particles attract each other.
It is thought that the particles form bridges and increase the viscosity. Based on this, the inventors filed a patent application in 1986.
As disclosed in the specification of No. 2615, we focused on so-called low-temperature treated carbon materials, which are stable and have a high concentration of radicals (unpaired electrons) necessary for interfacial polarization due to the movement of electrons or holes, and developed dispersion of non-aqueous electrorheological fluids. We considered using it as a phase. As a result, it exhibits high electrorheological effects over a wide temperature range by applying DC and AC electric fields, but consumes less power.
We have developed an electrorheological fluid with carbonaceous fine powder as a dispersed phase that can maintain the electrorheological effect for a long time.

[Problems to be Solved by the Invention] The electrorheological fluid containing the above carbonaceous fine powder as a dispersed phase has excellent heat and cold resistance, and when silicone oil made of polydimethylsiloxane is used as a dispersion medium, it does not swell into rubber. It has low properties and is suitable for applications such as anti-vibration rubber, but even higher electrorheological effects are required for applications in clutches and shock absorbers. On the other hand, in order to obtain a high electrorheological effect with an electrorheological fluid containing carbonaceous fine powder as a dispersed phase, it is necessary to increase the conductivity of the carbonaceous fine powder, which may lead to increased power consumption. Ta.

An object of the present invention is to provide a nonaqueous electrorheological fluid that exhibits a high electrorheological effect upon application of a DC or AC electric field and that requires low power consumption.

Structure of the Invention [Means for Solving the Problem] As a result of study, the present inventors have discovered an electrorheological fluid in which carbonaceous fine powder is dispersed in electrical insulating oil, the carbonaceous fine powder dispersing on the surface of the electrorheological fluid. is composed of carbonaceous fine particles coated with a thin film layer made of a polymer, and the carbonaceous fine particles have a ratio of the number of carbon atoms to hydrogen atoms (C/H) of 2.4 to 3.0. This objective was achieved by an electrorheological fluid characterized by a range of

The carbonaceous fine powder used as the dispersed phase of the electrorheological fluid in the present invention has a ratio of carbon atoms to hydrogen atoms (C/H) in the range of 2.4 to 3.0. An electrorheological fluid using carbonaceous fine powder having a C/H value within this range as a dispersed phase exhibits an electrorheological effect as it is, but the current value flowing when a voltage is applied is large.

The present inventors have discovered that the carbonaceous fine particles having a C/H value in the range of 2.4 to 3.0 are covered with a thin film layer made of a high molecular weight polymer. It has been found that the electrorheological effect increases and the current when voltage is applied can be reduced compared to the case without coating with a thin film layer. C/H value is 2.
If it is less than 4, the electric resistance of the carbonaceous fine powder is too high, and the thin film layer reduces the current, but at the same time the electrorheological effect also decreases. - If the 10,000C/H value is 3.0 or more, the electrical resistance of the carbonaceous fine powder is too low, so even if it is coated with a thin film layer, dielectric breakdown is likely to occur when high voltage is applied, and when direct current is applied, the electrical resistance of the dispersed phase Due to electrophoresis, it no longer exhibits a large reversible electrorheological effect.

Specific examples of carbonaceous fine powder having the above C/H value include:
Coal tar pitch, petroleum pitch, pitch obtained by thermally decomposing polyvinyl chloride, or fine powder consisting of various menphases obtained by heat treatment of tar components, that is, optically anisotropic small spheres formed by heating. Fine powder obtained by dissolving pitch components (spherulites or mesophase small spheres) with a solvent and separating them, finely pulverized products, bulk mesophase (e.g., Japanese Patent Publication No. 1983-1999- (See No. 308887)
So-called low-temperature-treated fine carbon powders, such as finely pulverized ones, finely pulverized pitches that have been partially refined, and carbonized thermosetting resins such as phenolic resins at low temperatures, and their heat-treated products. is exemplified. Among these, it is particularly preferable to use carbonaceous fine powder obtained by separating optically anisotropic small spheres produced by heat-treating coal tar pitch from pitch components.

To explain in more detail, coal tar pitch is 350
When heat treated at ~500°C, spherical optically anisotropic spherules (spherulites or mesophase spherules) grow from the coal tar pitch components.

(J, D, Brooks and G, H, Ta
ylor, Carbon 3.185) The size of this mesophase spherule is determined by the heating temperature and heating time, but when the desired size is reached, heating is stopped,
The mesophase spherules can be separated by dissolving the remaining coal tar pitch in a solvent such as quinoline or tar oil and filtering it. The mesophase microspheres have a liquid crystal-like structure and are spherical carbonaceous fine powders.

On the other hand, the C/H value of these carbonaceous fine powders changes by changing the calcination temperature, etc., and the conductivity changes. That is, as the C/H value increases, the electrorheological effect increases, and at the same time, the current consumption also increases.

As a polymer thin film, it is sufficient to form a thin film exhibiting electrical insulation properties with an electrical resistance of 109 Ω・cm or more on the surface of carbonaceous fine particles to an average thickness of one-tenth or less of the particle diameter. The average thickness depends on the conductivity of the carbonaceous fine powder. In other words, when the conductivity of the carbonaceous fine powder is high, a relatively thick insulating thin film is better; conversely, when the conductivity of the fine powder is low, a relatively thin insulating thin film is better for high electrical conductivity. This is necessary to maintain the viscous effect and lower the current when applying electricity.

The thin film layer made of a high molecular weight polymer may cover the entire surface of the carbonaceous fine particles or may partially cover the surface of the carbonaceous fine particles.

Such thin polymer films are formed by coating powder from a polymer solution, hybridization in which small particles are mixed dry and melted on the surface of the powder, spray drying, polymerization from monomers, etc. Examples of the polymers used include polymethyl methacrylate, polystyrene, polyvinyl acetate, polyvinyl chloride, polyvinylidene fluoride, epoxy resins, phenolic resins, and silicone polymers, and the dielectric constant of the polymers is Higher is preferable.

These high molecular weight polymers may be fixed to the surface of carbonaceous fine particles by physical adsorption, but they are more firmly fixed when they react with surface functional groups or radicals on the surface of carbonaceous fine particles and form chemical bonds. Hard to cause destruction.

The thus-prepared carbonaceous fine particles have a thin film layer made of a high molecular weight polymer on the surface, and have a ratio of carbon atoms to hydrogen atoms (C/H) of 2.4 to 3.0. By using a carbonaceous fine powder having a range of 1 to 2 as the dispersed phase of an electrorheological fluid, it is possible to obtain an electrorheological fluid that exhibits a high electrorheological effect but consumes less electricity.

The preferred particle size for the dispersed phase of the electrorheological fluid is 0.01
- 100 microns, preferably 0.1 to 20 microns,
More preferably, it is in the range of 0.5 to 5 microns. 0
．． Below 0.01 micron, the initial viscosity becomes significantly large in the absence of an electric field, and the viscosity change due to the electrorheological effect is small (
, and if it exceeds 100 microns, sufficient stability as a dispersed phase of the fluid cannot be obtained.

The particle size of the Menphase small spheres can be controlled by the heating time and heating temperature of the coal tar pitch.
Even finer particles can be obtained by pulverization using a jet mill or the like.

The electrical insulating oil constituting the liquid phase preferably has a volume resistivity of 1010 Ω·cm or more at 80°C, particularly 1012
It is preferable that the resistance is Ω·cm or more. Specifically, hydrocarbon oils, ester oils, aromatic oils, silicone oils, etc. can be exemplified. These can be used alone or in combination of two or more.

The viscosity of electrical insulating oil is 0.65 to 1000 at 25℃
centistokes (cSt), preferably 5-200c
St, more preferably one having a viscosity of 10 to 50 cSt is used. If the viscosity of the liquid phase is too low, the volatile content will increase and the stability of the liquid phase will deteriorate. If the viscosity of the liquid phase is too high, the initial viscosity in the absence of an electric field will be high and the viscosity change due to the electrorheological effect will be small. The dispersed phase can be efficiently (suspended) by using appropriately low-viscosity electrical insulating oil as the liquid phase.

The ratio of the dispersed phase and liquid phase constituting the electrorheological fluid of the present invention is such that the content of the dispersed phase consisting of the carbonaceous fine powder is 1 to 60%.
The content of the liquid phase consisting of the electrical insulating oil is 99-40% by weight, preferably 80-50% by weight. When the amount of the dispersed phase is less than 1% by weight, the electrorheological effect is small, and when it exceeds 60% by weight, the initial viscosity in the absence of an electric field becomes significantly large.

The electrorheological fluid of the present invention may be combined with or blended with other dispersed phases, surfactants, dispersants, inorganic salts, and other additives within a range that does not significantly impair the effects of the present invention.

EXAMPLES Hereinafter, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to the following Examples.

[Example 1] Coal tar pitch was heat-treated at 450°C to grow menphase spherules, and then extraction with oil in tar and filtration were repeated to remove pitch components, followed by heat treatment again at 510°C in a nitrogen stream ( C/ consisting of mesophase spherules
A carbonaceous fine powder with an H value of 2.46 was obtained. After pulverizing this carbonaceous fine powder with a jet pulverizer, it was air classified and the average particle size was 4.
A carbonaceous fine powder of 3 microns was obtained. This carbonaceous fine powder 1
400 mi of a 1% by weight cyclohexane solution of polystyrene with a molecular weight of 5,000 to 10,000 that has been modified at the end of 00g!
After the reaction, the remaining polystyrene solution was separated, and the carbonaceous fine powder was sufficiently dried to remove the solvent.

36% by weight of the carbonaceous fine powder coated with this polystyrene has a viscosity of 0. An electrorheological fluid was obtained by dispersing it in 64% by weight IP (Boyce) polydimethylsiloxane oil in an automatic mortar for 30 minutes. Furthermore, an electrorheological fluid was similarly prepared using the carbonaceous fine powder before being coated with polystyrene.

[Example 2] Carbonaceous fine powder with a C/H value of 2.44 and an average particle size of 3.8 microns, obtained in the same manner as in Example 2 except that the calcination temperature was 490°C, was dissolved in water by a spray drying method. An electrorheological fluid was obtained in the same manner as in Example 1. Furthermore, an electrorheological fluid was similarly prepared using the carbonaceous fine powder before being coated with the phenol resin.

[Comparative Example 1] Carbonaceous fine powder with a C/H value of 2.28 and an average particle size of 3.4 microns obtained in the same manner as in Example 1 except that the calcination temperature was 450°C was used in the same manner as in Example 1. An electrorheological fluid was obtained in the same manner as in Example 1 by coating with polystyrene. Furthermore, an electrorheological fluid was similarly prepared using the carbonaceous fine powder before being coated with polystyrene.

[Comparative Example 2] Carbonaceous fine powder with a C/H value of 3.1 and an average particle size of 4.1 microns obtained in the same manner as in Example 1 except that the calcination temperature was 600°C was used in the same manner as in Example 1. coated with polystyrene,
An electrorheological fluid was obtained in the same manner as in Example 1. Furthermore, an electrorheological fluid was similarly prepared using the carbonaceous fine powder before being coated with polystyrene.

The electrorheological effect of each electrorheological fluid obtained in Examples 1 and 2 and Comparative Examples 1 and 2 was measured. The electrorheological effect was determined by using a double cylindrical rotational viscometer to determine the apparent viscosity at room temperature at a shear rate of 366 sec-' when a DC voltage was applied between the inner and outer cylinders, and at the same time measuring the current density flowing between the inner and outer cylinders. Table 1 shows the measurement results.

Table 1 [Effect] As shown in Table 1, in both Examples 1 and 2, the carbonaceous particles coated with a high molecular weight polymer showed an increase in viscosity change before and after voltage application, and a decrease in current density. ing.

On the other hand, in Comparative Example 1, although the current density was reduced by the coating, the change in viscosity before and after voltage application was also reduced.

Further, in Comparative Example 2, dielectric breakdown occurred due to the coating.

In Example 1.2, almost no electrophoresis was observed when direct current was applied.

C2 Effects of the Invention The electrorheological fluid of the present invention exhibits a high electrorheological effect upon application of direct current or alternating current, and functions with low power consumption.

Claims (1)

[Claims] An electrorheological fluid in which carbonaceous fine powder is dispersed in electrical insulating oil, the carbonaceous fine powder is composed of carbonaceous fine particles whose surface is coated with a thin film layer made of a high molecular weight polymer, An electrorheological fluid having a ratio of the number of carbon atoms to hydrogen atoms (C/H) in the range of 2.4 to 3.0.