JPH04100897A - Electroviscous fluid - Google Patents

Abstract

PURPOSE:To increase the shearing force when an external voltage is applied at high temp. and reduce the consumption of electricity by dispersing fine particles of a specified dielectric in an electrically insulating oily liq. CONSTITUTION:A particulate dielectric is prepd, by coating the surface of a spherical or ellipsoidal polymeric substance having ionically dissociating groups, a particle size of 1-200mum and a water content of 0.05-20wt.% (e.g. strongly acidic ion exchange resin of styrene-divinylbenzene-sulfonic acid type) with an electrically insulating thin film having a volume resistivity or surface resistivity of 10<6> OMEGA.cm or above and a thickness of 2mum or below. Then, 1-60vol.% this dielectric is dispersed in 99-40vol.% electrically insulating oily liq. (e.g. chlorodiphenyl).

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to an electrorheological fluid whose viscosity is increased by application of an external voltage to induce a large shear core force.

(Prior Art) An electrorheological fluid is a suspension in which solid particles are dispersed in an insulating oily liquid, and whose viscosity increases significantly by an external electric field, that is, a suspension that causes the Winslow effect.

This electrorheological fluid greatly increases the viscosity of the fluid with a small amount of electric power, and its response is extremely fast. Applications to clutches, damper brakes, shock absorber actuators, etc. are being attempted.

Conventionally, known electrorheological fluids include those in which cellulose, starch, silica gel, ion exchange resin, etc. with water adsorbed on the surface are dispersed in an insulating oil such as chlorinated oil or chlorinated dipheninope trans oil.

One of the important properties required when applying electrorheological fluids
One of the advantages is that it produces a large electrorheological effect with low power consumption when an electric field is applied.

Among the electrorheological fluids that have been proposed in the past, it is known that in systems in which powders such as starch, cellulose, and silica gel are dispersed in insulating oil, large electrorheological effects are generally obtained when there is a large amount of adsorbed water. (Raijibe Hayashi, Yoshio Oishi, Applied Physics 42°1107 (1973)).

However, a large amount of water causes a rapid increase in current value, which not only increases power consumption but also makes it easier for discharge to occur in the liquid, making it difficult to utilize the characteristics of an electrorheological fluid.

As a solution to these problems, a method has been proposed in which the surface of these particles containing water or a highly polar aqueous solution is coated with a polymeric substance that is stable in the dispersion medium (Japanese Patent Application Laid-open No. 17674/1983). ) However, the electrorheological effect obtained with this method is very small.

Also, among the electrorheological fluids that have been proposed so far, those that utilize the movement of free ions based on the so-called electric double layer theory,
For example, fine particles of a hydrated strongly acidic or strongly basic ion exchange resin are dispersed in a higher alkyl ester of an aromatic carboxylic acid (Japanese Patent Publication No. 30274/1983), a halogenated diaryl compound, or a silicone oil. It is known that materials in which hydrophilic solid fine particles containing water are dispersed (Japanese Patent Application Laid-open No. 58-501178) exhibit excellent electrorheological effects with less water than cellulose, silica gel, and the like.

However, the electrorheological fluid using these water-containing particles is
When used in high-temperature environments exceeding 0°C or at high shear speeds that generate large amounts of frictional heat, an excessive amount of current flows, posing a major problem in terms of power consumption.

As a solution to these problems, a method of dispersing fine chelate resin powder in electrical insulating oil (Japanese Patent Laid-Open No. 1-2998
No. 94) has been proposed.

However, although this method exhibits an electrorheological effect with low power consumption at high temperatures, it has the drawback that it hardly exhibits an electrorheological effect near room temperature.

As another solution, an attempt has been proposed to utilize the movement of electrons and holes instead of the movement of free ions.

For example, a method in which organic semiconductors are dispersed in insulating oil (Japanese Patent Laid-Open No. 61-216202), or a method in which conductive particles coated with insulation are dispersed in insulating oil (Japanese Patent Laid-Open No. 64-1989)
6093).

However, although these methods show a stable electrorheological effect when used in high-temperature environments or at high shear speeds that generate large amounts of frictional heat, they are not as effective as those using ion movement. However, the Winslow effect is small and there is a problem in practical use.

(Problems to be Solved by the Invention) The purpose of the present invention is to exhibit a high Winslow effect when an external voltage is applied, and to be used in high-temperature environments or under high shear speeds that generate large frictional heat. It is an object of the present invention to provide an electrorheological fluid that exhibits a stable electrorheological effect even under certain conditions and consumes less power.

(Means for Solving the Problems) In order to solve the above problems, the inventors of the present invention have conducted intensive research and have found that the surfaces of dielectric fine particles made of a substance having an ionic dissociative group are coated with an electrically insulating thin film. As a result, the present invention was completed by discovering that a stable electrorheological effect was exhibited with a low current density.

That is, the present invention provides an electrorheological fluid in which dielectric fine particles are dispersed in an electrically insulating oily liquid, in which the dielectric fine particles are a substance having an ionic dissociative group, and the surface thereof is coated with an electrically insulating thin film. It is an electrorheological fluid characterized by

The ionic dissociative group contained in the dielectric fine particles used in the present invention may be any type of group as long as it can become an ion when dissociated, but especially amine groups, quaternary ammonium bases, free Alternatively, a neutralized carboxylic acid group, a free or neutralized sulfuric acid group (eg, a sulfuric acid group, a sulfonic acid group, a sulfinic acid group), a free or neutralized aluminosilicate group, etc. are preferable.

The dielectric fine particles may be of any type as long as they have an ionic dissociative group, but polymeric substances are particularly preferred.

The shape of these fine particles is preferably as round as possible, spherical or ellipsoidal. Particle size is 1-200
μm is preferable, and in particular, the smaller the particle size, the greater the Winslow effect tends to be.

Regarding the particle size distribution, particles that are as close to monodisperse as possible tend to exhibit a stable Winslow effect.

In addition, the water contained in these fine particles is
It is preferable that it is 0.05 to 20 parts by weight per 0 parts by weight. If the amount is less than 0.05 parts by weight, the electrorheological effect that occurs may become small. Further, if the amount is 20 parts by weight or more, an excessive current may flow.

The insulating material used as the electrically insulating thin film for covering the substance having an ionic dissociative group of the present invention preferably has as high dielectric breakdown strength and dielectric constant as possible. For volume resistivity or surface resistivity, 106
(Ω・cm or Ω) or more is preferable, and 1o1
Particularly preferred are those with a resistance of G (Ω·cm or Ω) or more. Further, the thickness of the electrically insulating thin film is preferably as thin as possible, particularly preferably 2 μm or less.

Examples of these insulating materials used in the present invention include polyethylene, polypropylene, polystyrene, polymethyl methacrylate, polyacrylonitrile, polyamide,
Examples include organic synthetic polymers such as polyimide and polyvinylidene fluoride, organic natural polymers such as fest, asphalt, and wax, and inorganic compounds such as silica, alumina, aluminum hydroxide, and barium titanate.

Known coating methods such as solution or powder coating, surface polymerization, vapor deposition, and surface reaction can be applied to form the electrically insulating thin film. The electrically insulating thin film preferably covers the entire surface of the particles with a uniform thickness. During coating, it is important to prevent the generation of secondary particles as much as possible.

The oily liquid used in the present invention includes diphenyl chloride, dibutyl sepatate, aromatic polycarboxylic acid higher alkyl ester, halophenyl alkyl ether, trans oil, chlorinated paraffin, and fluorine-based liquids that have been used in conventional electrorheological fluids. In addition to oils and silicone oils, basically any material can be used as long as it has high electrical insulation properties and electrical breakdown strength, is chemically stable, and does not have an extremely large difference in specific gravity from the dispersed fine particles.

The mixing volume ratio of the dielectric fine particles of the present invention with the oily liquid is 1
The ratio is selected in the range of 99 to 60 to 40, preferably 95 to 50 to 50 to 50.

Additives may be used in the mixed electrorheological fluid for purposes such as stabilizing dispersion, as long as the electrical insulation properties are not significantly reduced.

(Effects of the Invention) The electrorheological fluid of the present invention can obtain a large shearing force when an external voltage is applied at high temperatures, and has low power consumption, so it can be used in clutches, damper brakes, shock absorber actuators, etc. Can be applied effectively.

(Example) The electrorheological fluid of the present invention will be specifically explained by giving Examples and Comparative Examples, but the present invention is not limited to the following Examples unless the gist thereof is exceeded.

The electrorheological properties in this example were measured by filling the space between the inner and outer cylinders of a coaxial double-cylinder rotational viscometer (inner cylinder outer diameter 20 mm, length 50 mm, outer cylinder inner diameter 22 mm) with a sample fluid. After setting the temperature to , an AC voltage of 4 KV was applied between the inner and outer cylinders and shear was applied at a rate of 1 sec-', and the evaluation was performed using a method of measuring the shear core force and current density generated.

Example 1 Styrene/divinylbenzene/sulfonic acid type strongly acidic cation exchange resin (manufactured by The Dow Chemical Kanhoney, TOWEX 50WX8.200-400 mesh,
Sodium salt 1 of (hereinafter referred to as strongly acidic cation exchange resin)
00 parts by weight, and polymethyl methacrylate (PMMA)
Fine powder (manufactured by Soken Kagaku ■, MP-1000, hereinafter PMMA)
(referred to as fine powder) were mixed and stirred to adhere the PMMA fine powder to the surface of the ion exchange resin. Next, using a Honkawa Micron ■ mechano-furniture system AM-15F type (hereinafter referred to as AM-15F type), 230 Orpm was used.
After the ion exchange resin was coated with PMMA, it was dried at 120° C. for 5 hours under reduced pressure. This is referred to as fine particle 1. The moisture content of fine particles 1 measured by Karl Fischer method was 2.4%. This fine particle 1
was mixed and dispersed in trioctyl trimellitate (Monocizer W-700, manufactured by Dainippon Ink & Chemicals, hereinafter referred to as W-700) to give an electrorheological fluid of 15% by weight.

Example 2 Chlor salt 100 of a styrene-divinylbenzene copolymer type strongly basic ion exchange resin having trimethylbenzylammonium and M as an exchange group (The Dow Chemical Company, Towex IX 8.200-400 mesh) parts by weight and 3 parts by weight of PMMA fine powder were mixed and stirred to adhere the PMMA fine powder to the surface of the ion exchange resin. Next, treatment was performed for 30 minutes at 230 rpm using AM-15F type, and the ion exchange resin was coated with PMMA, followed by drying at 120° C. under reduced pressure for 5 hours. This is referred to as fine particle 2. Fine particles measured by Karl Fischer method 2
The water content was 4.0%. This fine particle 2 is
700 to give an electrorheological fluid of 15% by weight.

Example 3 Lithium methacrylate 5.0 gS N,N-methylenebisacrylamide 0.7 g, dimethylformamide 20 ml. t-Butylperoxy 2-ethylhexanoate (organic peroxide barbutyl O manufactured by NOF ■) 0.
] g in a degassed, melt-sealed tube at 70°C.
The reaction was allowed to proceed for 124 hours. After pulverizing and classifying the obtained cured product, it was dried at 120°C under reduced pressure for 5 hours to reduce the average particle size to 5.
Lithium methacrylate copolymer fine particles of 0 μm were obtained.

Next, the lithium methacrylate copolymer fine particles 100
parts by weight and 3 parts by weight of PMMA fine powder were mixed and stirred to adhere the PMMA fine powder to the surface of the lithium methacrylate copolymer fine particles. Next, using the AM-15F type, 230
Or pm for 30 minutes, the lithium methacrylate copolymer fine particles were coated with PMMA, and then dried at 120°C under reduced pressure for 5 hours. This is referred to as fine particle 3. The moisture content of the fine particles 3 measured by Karl Fischer method was 1.3%. Add 3 of these fine particles to 1 part of W-700.
They were mixed and dispersed to a concentration of 5% by weight to form an electrorheological fluid.

Comparative Example 1 A sodium salt of a strongly acidic cation exchange resin was heated under reduced pressure for 13 min.
It was dried at 0°C for 5 hours. This will be referred to as fine particles 4. The water content of the fine particles 4 measured by the Karl Fischer method is 0.
．． It was 9%. The fine particles 4 were mixed and dispersed in W-700 at a concentration of 15% by weight to form an electrorheological fluid.

Comparative Example 2 Microcrystalline cellulose for thin layer chromatography was prepared under reduced pressure 1
25°C relative humidity 70% after drying at 30°C for 5 hours
Moisture was absorbed under these conditions. This is referred to as fine particle 5. The moisture content of fine particles 5 measured by Karl Fischer method is 4.0
%Met. 15% by weight of this fine particle 5 was added to W-700.
They were mixed and dispersed to form an electrorheological fluid.

Comparative Example 3 PMMA dissolved in toluene was coated on the surface of microcrystalline cellulose for thin layer chromatography using a fluidized air bed method. Next, the coated particles were dried at 130°C under reduced pressure for 5 hours, and then allowed to absorb moisture at 25°C and a relative humidity of 70%. This will be referred to as fine particles 6.

The water content of the fine particles 6 measured by the Karl Fischer method is
It was 4.0%. The fine particles 6 were mixed and dispersed in W-700 at a concentration of 15% by weight to form an electrorheological fluid.

Comparative Example 4 Styrene/divinylbenzene copolymer type chelate resin having an iminodiacetate group as a reactive group (Muromasoku A-1, 200-400 mesh manufactured by Muromachi Chemical Industry Co., Ltd.)
The copper (divalent) salt was dried at 130°C under reduced pressure for 5 hours. This is referred to as fine particle 7. The moisture content of fine particles 7 measured by the Karl Fischer method was 0.8%. The fine particles 7 were mixed and dispersed in W-700 at a concentration of 15% by weight to form an electrorheological fluid.

Table 1 *: An excessive current flowed and measurement was impossible.

Next, fine particles 1 obtained in Examples 1 to 3 and Comparative Examples 1 to 4
The electrorheological properties of ~7 were measured.

Table 1 shows the measurement results of the temperature of the mixed liquid, the generated shear path force, and the current density at the time of measurement.

For fine particles 1 to 3, a stable Winslow effect was obtained from room temperature to 110° C., and the current value was also small, resulting in low power consumption. On the other hand, fine particles 4 are 110°
In C, it was impossible to measure the Winslow effect because an excessive current flowed. In fine particles 5, the Winslow effect disappeared at 110'C due to a decrease in water content. Fine particles 6 showed the Winslow effect, but the value was small, and like fine particles 2, the Winslow effect disappeared at 110° C. due to a decrease in water content. The fine particles 7 are
Although the current value was small and showed a stable Winslow effect at 80°C and 110°C, almost no Winslow effect was shown at room temperature.

Agent Patent Attorney Katsutoshi Takahashi

Claims (1)

[Scope of Claims] 1. In an electrorheological fluid formed by dispersing dielectric particles in an electrically insulating oily liquid, the dielectric particles are a substance having an ionic dissociative group, and the surface thereof is electrically insulating. An electrorheological fluid characterized by being coated with a thin film. 2. The electrorheological fluid according to claim 1, wherein the substance having an ionic dissociative group is a polymeric substance.