JPH04275398A - Electroviscous fluid - Google Patents

Abstract

PURPOSE:To provide the title fluid capable of generating high shear stress, excellent in current characteristics, stability with time, dispersion stability and redispersibility. CONSTITUTION:The objective fluid excellent in good balance among various performances, comprising (A) disperse phase consisting of organic polymer particles with cation exchange ability, (B) dispersion medium consisting of electrical insulating liquid and (C) 0.01-20 pts.wt., based on 100 pts.wt. of the component A, of an additive, i.e., fine particles 0.05-0.1mum in average size consisting of a metallic oxide. The present electric viscous fluid can be applied to various kinds of device such as clutches, dampers, brakes, shock absorbers, actuators, valves and engine mounts.

Description

[Detailed description of the invention]

0001

FIELD OF THE INVENTION This invention relates to electrorheological fluids. More specifically, it has excellent current characteristics in that it generates large shear stress even by applying a relatively weak electric field, and the current density that flows at that time is small, and it has excellent stability over time of the generated shear stress and current density. Dispersion stability (the ability to maintain an electrorheological fluid in a homogeneous state for a long time without causing the dispersed phase to settle or float) and redispersibility (the ability to maintain non-uniformity due to the dispersed phase settling or floating) when no electric field is applied This relates to electrorheological fluids that are particularly excellent in their ability to reproduce the original dispersion state with a simple external force.

0002

[Prior Art] An electrorheological fluid is a fluid obtained by dispersing or suspending solid particles in an insulating dispersion medium, and its rheological or flow properties can be changed to viscoplastic by applying an electric field change. It is a fluid whose properties change depending on the mold, and is generally known as a fluid exhibiting the so-called Winslow effect, in which the viscosity increases significantly and a large shear stress is induced when an external electric field is applied. Since the Winslow effect is characterized by quick response, attempts have been made to apply electrorheological fluids to clutches, dampers, brakes, shock absorbers, actuators, valves, and the like.

Conventionally, known electrorheological fluids include solid particles such as cellulose, starch, soybean casein, and silica gel dispersed in insulating oil such as silicone oil, diphenyl chloride, and transformer oil. . However, those using cellulose, starch, soybean casein, silica gel, etc. have a problem in that the shear stress generated is small.

On the other hand, electrorheological fluids that generate high shear stress include, for example, powdered ion exchange resins suspended in higher alkyl esters of aromatic carboxylic acids (Japanese Unexamined Patent Publication No. 50-92278), A composition comprising a crystalline material, a dielectric liquid, and a steric stabilizer that conducts current along only one of the crystal axes (Japanese Patent Application Laid-open No. 1-170693) has been proposed. However, these electrorheological fluids have poor dispersion stability when no electric field is applied, poor redispersibility after settling or floating, and when the concentration of the dispersed phase is increased to prevent separation of the dispersed phase. had the problem of poor liquidity.

[0005] Therefore, the present inventors have searched and studied various additives in order to improve the dispersion stability of electrorheological fluids without deteriorating the shear stress characteristics and current characteristics. As a result, it was found that the use of a specific polymeric dispersant as an additive improves the dispersion stability of electrorheological fluids (Japanese Patent Application No. 2-107427). However, electrorheological fluids containing polymeric dispersants as additives have a problem with redispersibility after the dispersed phase has settled, and have not been able to achieve both dispersion stability and redispersibility.

[0006]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems of conventional electrorheological fluids.

Therefore, an object of the present invention is to generate a large shear stress even by applying a relatively weak electric field, and to have excellent current characteristics such that the current density flowing at that time is small, and to reduce the generated shear stress and current density. It has excellent stability over time, and has excellent dispersion stability (ability to maintain the electrorheological fluid in a homogeneous state for a long time without causing the dispersed phase to settle or float) and redispersibility (the ability to maintain the dispersed phase in a uniform state without an applied electric field). The object of the present invention is to provide an electrorheological fluid that is particularly excellent in its ability to reproduce the original dispersion state by a simple external force after becoming uneven due to sedimentation or floating.

[0008]

[Means for Solving the Problems] The present invention provides an electrorheological fluid comprising a dispersed phase made of organic polymer particles having cation exchange ability, a dispersion medium made of an insulating liquid, and an additive, As an additive, the average particle size is 0.005μ
Fine particles made of metal oxide with a diameter of 0.1 μm are dispersed in the dispersed phase 1.
The present invention relates to an electrorheological fluid characterized in that it is used in an amount of 0.01 to 20 parts by weight per 00 parts by weight.

[0009]

[Operation] The fine particles that can be used as an additive in the present invention must have an average particle diameter in the range of 0.005 μm to 0.1 μm. If the average particle diameter is outside this range, the effect of improving dispersion stability and redispersibility will be insufficient. The fine particles used as additives are metal oxides, and the metal oxides in the present invention are compounds consisting of one or more of alkaline earth metals, transition metals, and silicon and oxygen. Alkali metals, if necessary
It may also contain other elements such as halogen and hydrogen. Examples of these metal oxides include MgO, CaO, Al
2O3, TiO2, MnO2, Fe2O3, Fe3O4
, FeO, CoO, Co3O4, NiO, CuO, Cu
2O, ZnO, SiO2, SiO2-TiO2, TiO
2-ZrO2, Fe2O3-ZnO, SiO2-ZnO
, MgO.SiO2, CaO.SiO2, etc., and one or more of these can be used.

The method for obtaining the additive used in the present invention is not particularly limited, and commercially available additives (for example, powdered anhydrous silica manufactured by Nippon Aerosil Co., Ltd.) can be used. Also,
A dry method in which metal hydroxides, chlorides, carbonates, alkoxides, etc. constituting the above metal oxides are heated at high temperature and calcined or decomposed, a wet method in which they are heated or pH adjusted in a solution, and a sol with a predetermined composition. The resulting hydrogel may be synthesized by a known method such as a sol-gel method in which the resulting hydrogel is dried, or a gas phase hydrolysis method in which chloride is hydrolyzed at high temperature, and if necessary, pulverization, heat treatment, modification treatment with a reagent, etc. You can go and use it.

The organic polymer particles having cation exchange ability constituting the dispersed phase in the electrorheological fluid of the present invention include functional groups that dissociate cations and become anions themselves in the presence of a polar solvent such as water. There are no particular limitations on the particles as long as they are particles of a polymer having the following, and examples thereof include particles of organic polymers having ionic dissociative groups such as sulfonic acid groups, carboxylic acid groups, and phosphoric acid groups in the molecule. Among these, organic polymer particles having sulfonic acid groups are preferable, and particles made of polystyrene polymers containing sulfonic acid groups are particularly preferable because they provide an electrorheological fluid with excellent shear stress and current density.

There are no particular restrictions on the type of cations that the organic polymer particles dissociate in the polar solvent, such as hydrogen cations; lithium ions, sodium ions, potassium ions, calcium ions, aluminum ions, cuprous ions. , metal cations such as cupric ions; ammonium ions; organic cations such as tetramethylammonium ions and pyridinium ions.

In order to obtain organic polymer particles having cation exchange ability that can be used as a dispersed phase in the present invention, for example, a vinyl compound having a sulfonic acid group or a carboxylic acid group may be used alone or, if necessary, in combination with other A monomer mixture to which a vinyl monomer has been added may be polymerized by a known method and pulverized to a predetermined particle size if necessary, or an ionic dissociative group such as a sulfonic acid group may be introduced into the polymer by a known method. Alternatively, an ion dissociative group may be introduced by hydrolyzing a polymer having an ester group or the like by a known method. Furthermore, a commercially available cation exchange resin pulverized to an appropriate particle size may be used.

In the present invention, the average particle diameter of the organic polymer particles constituting the dispersed phase is preferably in the range of 0.5 μm to 30 μm. The average particle diameter of the organic polymer particles is 0
．． If it is less than 5 μm, a large shear stress may not be obtained when an electric field is applied to the prepared electrorheological fluid. Furthermore, if the average particle diameter of the organic polymer particles exceeds 30 μm, an electrorheological fluid with excellent dispersion stability in the absence of an applied electric field may not be obtained.

The insulating liquid constituting the dispersion medium in the electrorheological fluid of the present invention is not particularly limited as long as it is an oily substance that exhibits electrical insulation, and examples include aliphatic hydrocarbons such as dodecane, hexadecane, and octadecane; benzene, naphthalene, Aromatic hydrocarbons such as anthracene and phenanthrene;
Alkyl-substituted aromatic hydrocarbons such as toluene, ethylbenzene, propylbenzene, butylbenzene, pentylbenzene, octylbenzene, dodecylbenzene, xylene, trimethylbenzene; THERM-S (registered trademark) 30
0, THERM-S (registered trademark) 700, THERM-S (registered trademark) 800, THERM-S (registered trademark) 900 (manufactured by Nippon Steel Chemical Co., Ltd.), and Nisseki Hysol (registered trademark) S
Hydrocarbon heating medium such as AS-296 (manufactured by Nippon Petrochemical Co., Ltd.); Higher alkyl esters of aromatic polycarboxylic acids such as didecyl phthalate and trioctyl trimellitate; benzene fluoride, benzene chloride, benzene bromide , halogenated hydrocarbons such as fluorinated naphthalene, chlorinated naphthalene, brominated naphthalene, and chlorinated diphenyl; silicone oils such as polydimethylsiloxane and polydiphenylsiloxane; and liquid paraffin. Two or more types can be used.

The electrorheological fluid of the present invention is obtained by mixing and dispersing the specific dispersed phase described above in a dispersion medium in the presence of additives.

The ratio of the dispersed phase to the dispersion medium in the electrorheological fluid of the present invention is 100 parts by weight of the former to 50 to 5 parts by weight of the latter.
The amount is preferably in the range of 0.00 parts by weight. If the amount of the dispersion medium exceeds 500 parts by weight, the shear stress obtained when an electric field is applied to the prepared electrorheological fluid may not be sufficiently large. Furthermore, if the amount of the dispersion medium is less than 50 parts by weight, the fluidity of the prepared electrorheological fluid itself may decrease, making it difficult to use it as an electrorheological fluid.

Further, the amount of fine particles made of metal oxide as an additive in the electrorheological fluid of the present invention is in the range of 0.01 to 20 parts by weight based on 100 parts by weight of the dispersed phase. If the amount of the additive is less than 0.01 part by weight, an electrorheological fluid with excellent dispersion stability and redispersibility in the absence of an applied electric field cannot be obtained. Furthermore, if the amount of additive exceeds 20 parts by weight, not only will the dispersion stability not improve commensurately with the increase in the amount added, but also the shear stress characteristics and current characteristics will deteriorate, making it difficult to use as an electrorheological fluid. becomes difficult.

The electrorheological fluid of the present invention may contain, for example, a surfactant, in order to adjust its viscosity or improve its shear stress.
Various conventionally known additives such as polymeric dispersants and polymeric thickeners can be added.

[0020]

Effects of the Invention The electrorheological fluid of the present invention generates large shear stress even when a relatively weak electric field is applied, and has excellent current characteristics such that the current density flowing at that time is small, and the generated shear stress and current Excellent density stability over time, and dispersion stability when no electric field is applied (
The ability to maintain the electrorheological fluid in a homogeneous state for a long time without causing the dispersed phase to settle or float) and redispersibility (the ability to restore the original uniform state by a simple external force after the dispersed phase settles or floats and becomes non-uniform) Because it is particularly excellent in reproducing performance), it is suitable for clutches, dampers, brakes, shock absorbers,
It can be effectively used for actuators, valves, engine mounts, etc.

[0021]

[Examples] The present invention will be explained below with reference to Examples, but the scope of the present invention is not limited to these Examples.

[0022]

[Example 1] 1200 g of ion-exchanged water and 16.0 g of polyvinyl alcohol (Kuraray Poval PVA-205 manufactured by Kuraray Co., Ltd.) were placed in a 3000 ml four-necked flask equipped with a stirrer, reflux condenser, thermometer, and nitrogen inlet tube. After addition and dissolution, a mixture consisting of 250 g of styrene, 50 g of industrial divinylbenzene (manufactured by Wako Pure Chemical Industries, Ltd., a mixture of 55% by weight of divinylbenzene, 35% by weight of ethylstyrene, etc.) and 5g of benzoyl peroxide was added. added. Thereafter, the contents of the flask were dispersed using a disperser (rotation speed: 6000 rpm) and heated at 70° C. for 8 hours. The obtained solid was filtered, thoroughly washed with acetone and water, and then dried at 80° C. for 12 hours using a hot air drier to obtain a polymerized crosslinked product (hereinafter referred to as polymerized crosslinked product (1)). ) 293g was obtained.

Next, 100 g of this polymerized crosslinked product (1) was placed in a 1000 ml container equipped with a stirrer, a reflux condenser, and a thermometer.
into a three-necked flask, add 98% by weight sulfuric acid 5 under ice cooling.
00g was added dropwise and heated at 80°C for 24 hours with stirring to carry out a sulfonation reaction. Thereafter, the contents of the flask were poured into 0°C water, filtered and washed with water.

The obtained solid was neutralized with 390 ml of a 10% by weight aqueous sodium hydroxide solution, and then thoroughly washed with water. Thereafter, the organic polymer particles (hereinafter referred to as dispersed phase particles (1)) having an average particle diameter of 6.1 μm were dried at 80° C. for 10 hours using a vacuum dryer. }184g was obtained. In addition, the anionic dissociative group density of the dispersed phase particles (1) is 4.4 m
g equivalent/g.

After drying 30 g of dispersed phase particles (1) at 150° C. for 3 hours, the particles were left in a room at a temperature of 20° C. and a relative humidity of 60% for 30 minutes to absorb moisture. (AEROSI manufactured by Nippon Aerosil Co., Ltd.)
1.4 g of L (registered trademark) 380) was added to silicone oil (Shin-Etsu Silicone (registered trademark) KF manufactured by Shin-Etsu Chemical Co., Ltd.).
The electrorheological fluid (1) of the present invention was obtained by uniformly dispersing it in a dispersion medium obtained by adding it to 68.6 g of 96-20cs).

[0026]

[Example 2] Powdered silica in Example 1 (AEROSIL (registered trademark) 380 manufactured by Nippon Aerosil Co., Ltd.)
Powdered silica with an average particle size of 0.012 μm (
AEROSIL (registered trademark) manufactured by Nippon Aerosil Co., Ltd.
Electrorheological fluid (2) of the present invention was obtained in the same manner as in Example 1 except that 0.03 g of R805) was used and the amount of silicone oil used was changed to 69.97 g.

[0027]

[Example 3] Powdered silica in Example 1 (AEROSIL (registered trademark) 380 manufactured by Nippon Aerosil Co., Ltd.)
Powdered silica with an average particle size of 0.012 μm (
AEROSIL (registered trademark) manufactured by Nippon Aerosil Co., Ltd.
Using 2g of R974), the amount of silicone oil used was 6
Electrorheological fluid (3) of the present invention was obtained in the same manner as in Example 1 except that the amount was changed to 8 g.

[0028]

[Example 4] Powdered silica in Example 1 (AEROSIL (registered trademark) 380 manufactured by Nippon Aerosil Co., Ltd.)
The electrorheological fluid (4) of the present invention was obtained in the same manner as in Example 1, except that 4 g of powdered titanium oxide with an average particle size of 0.08 μm was used instead of 1, and the amount of silicone oil used was changed to 66 g. Ta.

[0029]

[Example 5] Powdered silica in Example 1 (AEROSIL (registered trademark) 380 manufactured by Nippon Aerosil Co., Ltd.)
Powdered silica with an average particle size of 0.016 μm (
AEROSIL (registered trademark) manufactured by Nippon Aerosil Co., Ltd.
This product was prepared in the same manner as in Example 1, except that 0.7 g of R972) was used and 69.3 g of hydrogenated triphenyl (Therm-S (registered trademark) 900 manufactured by Nippon Steel Chemical Co., Ltd.) was used instead of silicone oil. Electrorheological fluid of the invention (5
) was obtained.

[0030]

[Example 6] 1200 g of ion-exchanged water and 20.0 g of polyvinyl alcohol (Kuraray Poval PVA-205 manufactured by Kuraray Co., Ltd.) were placed in a 3000 ml four-necked flask equipped with a stirrer, reflux condenser, thermometer, and nitrogen inlet tube. After addition and dissolution, a mixture consisting of 250 g of styrene, 50 g of industrial divinylbenzene (manufactured by Wako Pure Chemical Industries, Ltd., a mixture of 55% by weight of divinylbenzene, 35% by weight of ethylstyrene, etc.) and 5g of benzoyl peroxide was added. added. After that, disperser (rotation speed: 22000 rpm)
The contents of the flask were dispersed using a water bottle and heated at 70°C for 8 hours. The obtained solid was filtered, thoroughly washed with acetone and water, and then dried at 80° C. for 12 hours using a hot air drier to obtain a polymerized crosslinked product (hereinafter referred to as polymerized crosslinked product (2)). ) 261g was obtained.

Next, 100 g of this polymerized crosslinked product (2) was poured into a 1000 ml container equipped with a stirrer, a reflux condenser, and a thermometer.
into a three-necked flask, add 98% by weight sulfuric acid 5 under ice cooling.
00g was added dropwise and heated at 80°C for 24 hours with stirring to carry out a sulfonation reaction. Thereafter, the contents of the flask were poured into 0°C water, filtered and washed with water.

The obtained solid was neutralized with 400 ml of a 10% by weight aqueous sodium hydroxide solution, and then thoroughly washed with water. Thereafter, the organic polymer particles (hereinafter referred to as dispersed phase particles (2)) having an average particle diameter of 1.5 μm were dried at 80° C. for 10 hours using a vacuum dryer. }168g was obtained. In addition, the anionic dissociative group density of the dispersed phase particles (2) is 4.5 m
g equivalent/g.

After drying 30 g of dispersed phase particles (2) at 150° C. for 3 hours, the particles were left in a room at a temperature of 20° C. and a relative humidity of 60% for 25 minutes to absorb moisture. (AEROSI manufactured by Nippon Aerosil Co., Ltd.)
1.2 g of L (registered trademark) 380) was added to silicone oil (Shin-Etsu Silicone (registered trademark) KF manufactured by Shin-Etsu Chemical Co., Ltd.).
The electrorheological fluid (6) of the present invention was obtained by uniformly dispersing it in a dispersion medium obtained by adding it to 68.8 g of 96-10cs).

[0034]

[Example 7] 1200 g of ion-exchanged water and 16.0 g of polyvinyl alcohol (Kuraray Poval PVA-205 manufactured by Kuraray Co., Ltd.) were placed in a 3000 ml four-necked flask equipped with a stirrer, reflux condenser, thermometer and nitrogen inlet tube. After addition and dissolution, a mixture consisting of 250 g of styrene, 50 g of industrial divinylbenzene (manufactured by Wako Pure Chemical Industries, Ltd., a mixture of 55% by weight of divinylbenzene, 35% by weight of ethylstyrene, etc.) and 5g of benzoyl peroxide was added. added. Thereafter, the contents of the flask were dispersed using a disperser (rotation speed: 4000 rpm) and heated at 70° C. for 8 hours. The obtained solid was filtered, thoroughly washed with acetone and water, and then dried at 80° C. for 12 hours using a hot air drier to obtain a polymerized crosslinked product (hereinafter referred to as polymerized crosslinked product (3)). ) 292g was obtained.

Next, 100 g of this polymerized crosslinked product (3) was poured into a 1000 ml container equipped with a stirrer, a reflux condenser, and a thermometer.
into a three-necked flask, add 98% by weight sulfuric acid 5 under ice cooling.
00g was added dropwise and heated at 80°C for 24 hours with stirring to carry out a sulfonation reaction. Thereafter, the contents of the flask were poured into 0°C water, filtered and washed with water.

The obtained solid was neutralized with 400 ml of a 10% by weight aqueous sodium hydroxide solution, and then thoroughly washed with water. Thereafter, the organic polymer particles (hereinafter referred to as dispersed phase particles (3)) having an average particle diameter of 14 μm were dried at 80° C. for 10 hours using a vacuum dryer. }187g was obtained. In addition,
The anionic dissociative group density of the dispersed phase particles (3) is 4.4 mg
equivalent/g.

After drying 30 g of dispersed phase particles (3) at 150° C. for 3 hours, the particles were left in a room at a temperature of 20° C. and a relative humidity of 60% for 40 minutes to absorb moisture. (AEROSI manufactured by Nippon Aerosil Co., Ltd.)
L (registered trademark) R974) 0.6g with silicone oil (
Shin-Etsu Silicone (registered trademark) K manufactured by Shin-Etsu Chemical Co., Ltd.
The electrorheological fluid (7) of the present invention was obtained by uniformly dispersing it in a dispersion medium obtained by adding it to 69.4 g of F96-20cs).

[0038]

[Comparative Example 1] 30 g of dispersed phase particles (1) in Example 1
After drying at 150℃ for 3 hours, the temperature was 20℃ and the relative humidity was 60℃.
% for 30 minutes to absorb moisture, and then mixed and dispersed in 70 g of silicone oil (Shin-Etsu Silicone (registered trademark) KF96-20cs, manufactured by Shin-Etsu Chemical Co., Ltd.), and mixed with a comparative electrorheological fluid (see below). , this is called comparison fluid (1). } was obtained.

[0039]

[Comparative Example 2] 30 g of dispersed phase particles (1) in Example 1
After drying at 150℃ for 3 hours, the temperature was 20℃ and the relative humidity was 60℃.
% in a room for 30 minutes to absorb moisture, then add 70 g of triphenyl hydride (Therm-S manufactured by Nippon Steel Chemical Co., Ltd.).
(Registered Trademark) 900) and mixed and dispersed into a comparative electrorheological fluid (hereinafter referred to as comparative fluid (2)). } was obtained.

[0040]

[Comparative Example 3] A 500ml four-necked flask equipped with a stirrer, reflux condenser, thermometer and nitrogen inlet tube was filled with xylene.
50g, methoxypolyethylene glycol methacrylate (NK ester M-230G manufactured by Shin-Nakamura Chemical Co., Ltd.;
Weight average molecular weight super system controller GP
1 g of C data processing device (manufactured by Tosoh Corporation) was 1,400) and 149 g of dodecyl methacrylate, 0.7 g of azobisisobutyronitrile was added thereto, and nitrogen was introduced. 30 minutes at room temperature while
The mixture was stirred for a minute. Thereafter, the mixture was heated at 70°C for 10 hours and then further heated at 90°C for 2 hours to perform polymerization.

The solid content of the resulting xylene solution of the polymer (hereinafter referred to as polymer solution (1)) was 50% by weight. When the polymerization rate was measured from the residual rate of the monomer, the polymerization rate of dodecyl methacrylate was 100%. The weight average molecular weight of the polymer was measured using a Super System Controller GPC data processing device (manufactured by Tosoh Corporation) and was found to be 29.0.
It was 00.

In Example 1, 5 g of polymer solution (1) was used instead of powdered silica, and 65 g of hydrogenated triphenyl (Therm-S (registered trademark) 900 manufactured by Nippon Steel Chemical Co., Ltd.) was used instead of silicone oil. A comparative electrorheological fluid (hereinafter referred to as comparative fluid (3)) was prepared in the same manner as in Example 1 except for the following steps. } was obtained.

[0043]

[Comparative Example 4] 30 g of dispersed phase particles (3) in Example 7
After drying at 150℃ for 3 hours, the temperature was 20℃ and the relative humidity was 60℃.
% for 40 minutes to absorb moisture, then mixed and dispersed in 70 g of silicone oil (Shin-Etsu Silicone (registered trademark) KF96-20cs, manufactured by Shin-Etsu Chemical Co., Ltd.), and mixed with electrorheological fluid for comparison (see below). , this is called comparison fluid (4). } was obtained.

[0044]

[Comparative Example 5] Powdered silica used as an additive in Example 1 (AEROSIL manufactured by Nippon Aerosil Co., Ltd.)
After drying 1.4 g of (registered trademark) 380 at 150°C for 3 hours, and leaving it in a room at a temperature of 20°C and relative humidity of 60% for 30 minutes, 68.6 g of silicone oil (Shin-Etsu Chemical Co., Ltd.
Shin-Etsu Silicone (registered trademark) KF96-20c manufactured by Co., Ltd.
s) and mixed and dispersed into a comparative electrorheological fluid (hereinafter referred to as comparative fluid (5)). } was obtained.

[0045]

[Comparative Example 6] Powdered silica used as an additive in Example 1 (AEROSIL manufactured by Nippon Aerosil Co., Ltd.)
After drying 30g of (registered trademark) 380 at 150℃ for 3 hours, leave it in a room at 20℃ and 60% relative humidity for 30 minutes to absorb moisture. Shin-Etsu Silicone (registered trademark) KF96-2
0 cs), but it was not uniformly dispersed and a uniform fluid could not be obtained.

[0046]

[Example 8] Each of the electrorheological fluids (1) to (7) and comparative fluids (1) to (5) of the present invention obtained in Examples 1 to 7 and Comparative Examples 1 to 5 was heated to a height of 150 mm. , diameter 15m
The test tube was filled to a depth of 100 mm from the bottom and sealed. After that, we tracked the sedimentation speed of the dispersed phase particles at room temperature, measured the time (in days) required for the dispersed phase particles to settle 5 mm from the liquid level of the electrorheological fluid filled in the test tube, and determined the dispersion stability. was evaluated. The results are shown in Table 1. In addition, the electrorheological fluid that had settled after being left standing for one week was redispersed using a test dispersion machine (manufactured by Toyo Seiki Seisakusho Co., Ltd.).
: Disperses quickly, △: Takes several minutes to disperse, ×
: Redispersibility was evaluated in three stages: difficult to disperse. The results are shown in Table 1.

Each of the electrorheological fluids was placed in a double cylindrical rotational viscometer with a coaxial electric field, and the inner/outer cylinder gap was 1.0 mm.
The shear stress value (initial value) and the current density (initial value) flowing at that time were measured when an AC external electric field of 4000 V/mm (frequency: 50 Hz) was applied at a shear rate of 400 s 1 and a temperature of 25°C. Furthermore, 4000V/m
The shear stress value (value after 3 days) and current density (value after 3 days) after continuous operation of the viscometer at 25°C for 3 days with an external electric field of m Stability was investigated. The results are shown in Table 1.

[0048]

[Table 1]

As is clear from Table 1, comparative fluid (1)
and (2), a large shear stress was obtained by applying a relatively weak electric field, but the dispersion stability was poor when no electric field was applied. Comparative fluid (3) obtained a large shear stress by applying a relatively weak electric field and had excellent dispersion stability when no electric field was applied, but had poor redispersibility.

On the other hand, the electrorheological fluids (1) to (5) of the present invention
) generates large shear stress even when a relatively weak electric field is applied, and has excellent current characteristics such that the current density flowing at that time is small. The dispersion stability and redispersibility were excellent even in the absence of application.

Furthermore, the electrorheological fluid (7) of the present invention exhibits a higher level of dispersion stability than the corresponding comparative fluid (4), and has excellent shear stress, current characteristics, stability over time, and redispersibility. It was excellent.

Comparative fluid (5) was found to generate almost no shear stress and was of no value as an electrorheological fluid.

Claims (1)

[Claims] 1. An electrorheological fluid comprising a dispersed phase made of organic polymer particles having cation exchange ability, a dispersion medium made of an insulating liquid, and an additive, the additive having an average particle diameter of 0.005 μm to 0.1 μm fine particles made of metal oxide per 100 parts by weight of the dispersed phase.
An electrorheological fluid characterized in that 01 to 20 parts by weight are used.