JP2761774B2 - Electrorheological fluid - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an electrorheological fluid capable of controlling the viscosity of a liquid by an external voltage.

2. Description of the Related Art An electrorheological fluid is a suspension in which a finely divided conductive solid is dispersed in a non-conductive oil, and very quickly under the action of a sufficiently strong electric field, and A liquid whose viscosity increases reversibly.

In order to change the viscosity, not only a DC electric field but also an AC electric field can be used, and the required electric current is very small, giving a large change in viscosity from a liquid to almost a solid state with a small amount of power, for example, Electro-rheological fluids have been studied as components for controlling devices and components such as clutches, valves, shock absorbers, vibrators, various types of vibration isolating rubber, actuators, robot arms, and damping materials.

[Problems to be Solved by the Invention] Conventionally, as solid particles which are one of the constituent elements of the electrorheological fluid, cellulose, starch, silica gel, ion exchange resin, lithium polyacrylate, etc., having water absorbed from the surface, are used. , And the other liquid phase is PCB,
Those using butyl sebacate, trans oil, spindle oil, chlorinated paraffin, silicone oil and the like are known.

However, the electrorheological fluid using the above-described water-absorbed particles has a large temperature dependence of the electrorheological effect in a low temperature region and a high temperature region, and lacks stability. In particular, when used at a high temperature, an excessive current flows and power consumption becomes extremely high. At a low temperature of 0 ° C. or lower, the electrorheological effect becomes extremely small. As described above, since the conventional electrorheological fluid is greatly affected by moisture, it cannot be applied to devices used in a wide temperature range such as automobile parts. Therefore, development of an electrorheological fluid exhibiting a high electrorheological effect even in a low temperature range and a high temperature range has been desired.

[Means for Solving the Problems] The electrorheological fluid according to the present invention comprises polyaniline or its dielectric substance obtained by oxidative polymerization, polypyrrole,
Alternatively, it is characterized by comprising an organic insulating polymer fine powder obtained by subjecting a polythiophene to an alkali treatment and a fine powder having an electric insulating layer provided on the surface and an electric insulating oil.

The conductive polymer used in the present invention is obtained by oxidative polymerization, and includes polyaniline or its dielectric, polypyrrole, and polythiophene, and among them, polyaniline or its dielectric is preferable.

However, these conductive polymers have high conductivity when oxidatively polymerized, and are not suitable as a dispersed phase of an electrorheological fluid as it is. Therefore, it is necessary to perform an alkali treatment to reduce the conductivity. The alkali treatment can most effectively reduce the conductivity of the conductive polymer by adjusting the pH.

Hereinafter, a method for producing a conductive polymer by oxidative polymerization will be described using polyaniline or its dielectric as an example, but the same applies to the other conductive polymers described above.

Polyaniline or its dielectric is an electrolytic polymerization method of electrolytically oxidizing aniline or its dielectric on an anode made of platinum, gold, carbon, stainless steel, or the like in an acidic solution,
An aniline or its dielectric substance obtained by any of the production methods of a catalytic polymerization method (chemical oxidation polymerization method) in which aniline or its dielectric substance is oxidized with an oxidizing agent such as ferric chloride or ammonium persulfate in an acidic solution is suitably used.

In the present invention, aniline or a dielectric thereof has the following structure.

[Wherein, R _{1 to} R ₉ each represent a hydrogen atom, an aryl group, an alkyl group, NO ₂ , NH ₂ , CF ₃ , (R represents an aryl group or an alkyl group) and represents the same or different groups. Here, when polyaniline or its dielectric substance is obtained by the electrolytic oxidation polymerization method, it is preferable to use an acidic aqueous solution such as hydrochloric acid, sulfuric acid, borofluoric acid, or perchloric acid, and particularly preferable to use an aqueous sulfuric acid or borofluoric acid solution. In this case, the aniline concentration is 0.05-2 mol / l, preferably 0.5-1.6 mol / l,
The acid concentration is suitably 0.1 to 4 mol / l, preferably 1 to 3.2 mol / l. The temperature of the electrolytic polymerization solution is -10 to 30 ° C,
It is particularly preferable to keep the temperature between -5 and 10C. The polymerization method may be any of a constant potential method, a cyclic method, and a pulse method, but a constant current method capable of controlling the amount of polymerization by time is preferably used.

When polyaniline or its dielectric material is obtained by the catalytic polymerization method, a polymerization liquid similar to the one used in the electrolytic oxidation polymerization method is used, while stirring vigorously, 0.01 to 5 mol / l, preferably 0.5 to 3 mol / l. Of the oxidizing agent is added. As the type of the oxidizing agent, such as ferric chloride and potassium iodate, the standard potential when used as an aqueous solution is 0.8 to 1.2 V compared to the standard hydrogen electrode.
Is preferably used. This is not preferable because the standard potential of aniline is about 0.78 V, and an oxidizing agent of 1.2 V or more causes excessive three-dimensional crosslinking due to excessive oxidation, localization of electricity occurs, and electric charge is generated.

The polyaniline or its dielectric substance thus obtained has a linear structure from the solubility in organic solvents such as N, N'-dimethylformamide, dimethylsulfoxide, and 2-methylpyrrolidone, and from the results of the infrared spectrum. You can see that. Therefore, it is distinguished from aniline black having a three-dimensional and irregular structure having a crosslinked structure.

In the case of electrolytic oxidation polymerization, the obtained polyaniline or its dielectric is separated from the electrode, dispersed in a predetermined amount of ion-exchanged water, and subjected to alkali treatment, and in the case of catalytic polymerization, solidified by filtration or centrifugation. The phase and the liquid phase are separated, dispersed in a predetermined amount of ion-exchanged water in the same manner as in the electrolytic oxidation polymerization method, and subjected to an alkali treatment. In this case, as a method of alkali treatment,
It is preferable to add an aqueous alkali solution such as sodium hydroxide, aqueous potassium, or ammonia to the dispersion of the polyaniline or a derivative thereof. The concentration of the aqueous alkali solution is 1 to 2 mol / l, and the pH of the dispersion is 5 to 5 mol / l.
9, preferably 7.2 to 7.8.

It is known that the alkali treatment increases the quinoid structure of the polyaniline structure as shown in the figure below.

The alkali-treated polyaniline or a derivative thereof is cleaned with ion-exchanged water to remove attached salts and the like.
If necessary, the treatment may be performed using an organic solvent such as acetone, acetonitrile, and alcohol. Thereafter, the mixture is separated by filtration or centrifugation, and subjected to a drying treatment until the weight becomes constant. As a drying method, a vacuum heating method, a freeze drying method, and the like are preferable. If necessary, the obtained polyaniline or a derivative thereof may be pulverized by an automatic mortar, a ball mill, or the like.

The electric conductivity of the alkali-treated polyaniline or its derivative fine powder thus obtained is 10 ⁻⁷ to 10 ⁻¹⁰ S / c.
m, it is suitable as a dispersed phase of an electrorheological fluid exhibiting an electrorheological effect due to interfacial polarization of the dispersed phase particles by electrons, and by exhibiting a high electrorheological effect by using this fine powder as a dispersed phase, An electrorheological fluid having excellent long-term stability can be obtained.

Further, as a method of maintaining the electrorheological effect to some extent and reducing only the consumption current, it is effective that the particles in the above-mentioned alkali-treated polyaniline or its derivative fine powder have an electrically insulating layer on part or all of the surface. Headlined.

Here, as the electric insulating layer, a thin layer irrespective of organic or inorganic may be formed so as to have a thickness of 1/10 or less of the particle diameter of the conductive polymer fine particles. It depends on the conductivity of the fine powder.

That is, when the conductivity of the conductive polymer fine powder is high, the insulating layer is preferably relatively thick, and conversely, when the conductivity of the fine powder is low, the insulating layer is relatively thin. It is necessary to maintain the electrorheological effect and reduce the current when applying a voltage.

Such an electrically insulating layer is coated on a powder from a polymer solution, hybridized to mix small-sized particles in a dry manner and melted on the surface of the powder, surface treatment such as silane treatment, sputtering vacuum deposition, polymerization from monomer. Formed and used as the electrically insulating material are synthetic high molecular substances such as polymethyl methacrylate, polystyrene, polyvinyl acetate, polyvinyl chloride, polyvinylidene fluoride, epoxy resin, phenol resin, methyltrimethoxysilane, phenyl Silane treating agents such as trimethoxysilane, hexamethyldisilazane, and trimethylchlorosilane; modified silicone oil or silicone surfactant having a dimethylpolysiloxane or phenylmethylpolysiloxane structure as a main chain using a carboxyl group or a hydroxyl group; silica; Na, inorganic compounds such as rutile can be mentioned as typical examples.

By using the conductive polymer fine powder having an electrically insulating layer on its surface as a dispersion phase of an electrorheological fluid, a high electrorheological effect is obtained, but the electrorheological effect with low electric consumption is obtained. A fluid can be obtained.

The preferred particle size for the dispersed phase of the electrorheological fluid is 0.01 to
It is in the range of 100 microns, preferably 0.1-20 microns, more preferably 0.5-5 microns. If it is less than 0.01 micron, 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 microns, 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.

Among these electrical insulating oils, silicone oils such as polydimethylsiloxane and polymethylphenylsiloxane are excellent in that they can be used even in a state of being in direct contact with a rubbery elastic material.

The viscosity of the electrically insulating oil at 25 ° C. is 0.65 to 1000 centistokes (cSt), preferably 5 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 fluid of the present invention is such that the content of the dispersed phase composed of the conductive polymer fine powder is 1 to 60% by weight, preferably 10 to 50% by weight. The content of the liquid phase composed of the electric insulating oil is 99 to 40% by weight, preferably 90 to 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 is significantly increased. The electrorheological fluid of the present invention may contain water and additives such as a surfactant and a dispersant within a range not to impair the effects of the present invention.

Hereinafter, the present invention will be described specifically with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples.

Comparative Example 1 A 0.5 mol / l aqueous solution of ferric chloride was added while vigorously stirring an aniline acid solution having an acid concentration of 1 mol / l and an aniline concentration of 1 mol / l. After dispersion, the dispersion is added to an aqueous sodium hydroxide solution,
The pH was adjusted to 6.5. The thus obtained alkali-treated polyaniline was washed with ion-exchanged water, separated by filtration, and vacuum-dried at 80 ° C. for 3 days. Further, the powder is pulverized in an automatic mortar to obtain a dispersed phase of an electrorheological fluid, and has an average particle diameter of about 20 μm and 0 μm, an electron spin concentration of 1.44 × 10 ¹⁹ , and a water content
A powder having 1.19% and conductivity of 2.16 × 10 ⁻¹⁰ Scm ⁻¹ was obtained. The electric resistance was measured by compacting the powder. The water content was measured from the volatile matter at 250 ° C. by the Karl Fisher method.
14.3% by weight of this powder was dispersed in 85.7% by weight of silicone oil (TSF451-10 manufactured by Toshiba Silicone Co., Ltd.) to obtain an electrorheological fluid as a suspension.

[Example 1] 23.3 g of the same powder used in Comparative Example 1 was mixed with 5% by weight of H ₂ S.
Dispersed in an O ₄ solution, 10 g of phenol and 3.7 g of formalin were added, reacted at 80 ° C. for 30 minutes, filtered, and dried at 80 ° C. for 5 days to obtain a powder having a phenol resin layer on the surface. This powder 1
1.1% by weight of silicone oil (Toshiba Silicone Co., Ltd .: TS
F451-10) 88.9% by weight to obtain an electrorheological fluid as a suspension.

The electrorheological effect of each electrorheological fluid was measured. For the electrorheological effect, the same shear rate (375se
c ^-1 ), the shear force at a temperature of 25 ° C. was evaluated, and simultaneously the current density flowing between the inner and outer cylinders was measured. (Inner cylinder radius: 34mm, outer cylinder radius: 36mm, inner cylinder height: 20mm) Table 1 Shearing force To when no electric field is applied, DC electric field 2K
The shear force To when V / mm is applied, the difference T-To, and the current density when a DC electric field of 2 KV / mm is applied are shown.

In Table 1, shear force T when electric field (2KV / 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, T-To in Table 1
Liquids exhibit large electrorheological effects. The current density (μA / cm ² ) is related to the electric power required to develop the electric field (2 KV / mm).

[Operation] In Example 1, since the powder has the electric insulating layer on the surface, the current density is lower than that in Comparative Example 1 having no electric insulating layer, and the electrorheological effect is maintained at substantially the same level. .

[Effect of the Invention] An electrorheological fluid exhibiting a high electrorheological effect can be obtained with a small current.

────────────────────────────────────────────────── ─── Continued on the front page (51) Int.Cl. ⁶ Identification symbol FI H01B 1/12 H01B 1/12 FE // C10N 40:14 60:00 (72) Inventor Tsubasa Saito Kamiarai, Tokorozawa-shi, Saitama 1265-2 (56) References JP-A-2-305895 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C10M 149/12 C10M 151/04 H01B 1/12 C10N 40: 14 C08J 3/12 C08J 3/11 C10N 60:00

Claims (1)

(57) [Claims] An electric insulating oil comprising polyaniline obtained by oxidative polymerization or a dielectric thereof, polypyrrole or polythiophene, obtained by subjecting polypyrrole or polythiophene to an alkali treatment, and an electric insulating layer provided on the surface of an organic conductive polymer fine powder; An electrorheological fluid comprising: