JP2956402B2 - Electrorheological fluid - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrorheological fluid whose viscosity can be controlled by an external voltage.

[0002]

2. Description of the Related Art An electrorheological fluid is a suspension in which dielectric solid fine particles are dispersed in an insulating fluid such as silicone oil, and is a liquid whose viscosity is reversibly increased by the action of a strong electric field. Applications for clutches, shock absorbers, etc. are being considered. Here, as the dielectric solid fine particles used for the electrorheological fluid, water-absorbing or hydrophilic solid fine particles such as cellulose, starch, silica gel, and lithium polyacrylate have been conventionally used. However, in such an electrorheological fluid using solid fine particles, the temperature dependence of the electrorheological effect is large, and the conductivity increases at high temperatures, and the amount of flowing current is large. There was a problem of becoming. At a low temperature of 0 ° C. or less, there is also a problem that the electrorheological effect becomes extremely small.

Japanese Patent Application Laid-Open No. 2-255798 discloses an electrorheological fluid using dielectric fine particles in which the surface of crystalline cellulose particles containing a polyhydric alcohol as a hydrophilic agent is coated with an electrically insulating thin film. Have been. According to this electrorheological fluid, while exhibiting a good electrorheological effect, the electric conductivity is small even at a high temperature, and the amount of flowing current can be reduced.

[0004]

However, in the electrorheological fluid disclosed in the above publication, the dielectric fine particles have such a property that the electric conductivity greatly changes depending on the thickness of the electrically insulating film. In addition, it is difficult to precisely control the thickness of the electrically insulating film, resulting in a problem that the amount of flowing current varies.

On the other hand, an electrorheological fluid using organic semiconductor particles instead of water-absorbing or hydrophilic solid fine particles has been studied. With such organic semiconductor particles, the control of the conductivity can be performed relatively easily. However, this electrorheological fluid has the characteristic that the electrorheological effect changes greatly depending on the particle size of the organic semiconductor particles, and it is difficult to control the particle size, so that sufficient characteristics have not yet been obtained. It is.

[0006] The present invention has been made in view of such circumstances, and by using novel hydrophilic solid fine particles,
An object is to prevent an increase in conductivity at high temperatures while maintaining a high electrorheological effect.

[0007]

The electrorheological fluid of the present invention for solving the above-mentioned problems is an electrorheological fluid in which solid fine particles are dispersed in an electrically insulating medium.
A matrix resin comprising a resin selected from BS resin, polyolefin, polyethylene terephthalate, and polymethyl methacrylate; and a matrix resin,
Hydrophilic selected from poly (ethylene oxide / propylene oxide) copolymer, polyethylene glycol-based polyamide, polyester amide, poly (epichlorohydrin / ethylene oxide) copolymer, polyethylene glycol methacrylate copolymer, and methacrylate copolymer containing quaternary ammonium base Consisting of a conductive resin, containing substantially no water on the surface, and having a volume specific conductivity of 1 × 10 ^−11.
２2 × 10 ⁻⁹ S / cm.

[0008] The solid fine particles are composed of a matrix resin and a hydrophilic resin contained in the matrix resin. Among these, the matrix resin serves as a substrate for solid fine particles, and is selected from ABS resin, polyolefin, polyethylene terephthalate, and polymethyl methacrylate. This matrix resin imparts heat resistance and mechanical strength to the solid fine particles, and both an insulator and a dielectric are used. However, it is selectively used depending on the compatibility with the hydrophilic resin.

The hydrophilic resin is poly (ethylene oxide /
Propylene oxide) copolymer, polyethylene glycol polyamide, polyester amide, poly (epichlorohydrin / ethylene oxide) copolymer, polyethylene glycol methacrylate copolymer, and methacrylate copolymer containing a quaternary ammonium base. Those having a ^{density of} 10 ^-9 to 10 ^-8 S / cm are desirable.
This hydrophilic resin has a volume specific conductivity of the whole solid fine particles of 1 × 10 ⁻¹¹ to 2 × 10 ^{−9 in the} matrix resin.
S / cm is contained. Volume specific conductivity is 1
If it is smaller than × 10 ⁻¹¹ S / cm, the electrorheological effect will be small, and if it is larger than 2 × 10 ⁻⁹ S / cm, the amount of current flowing at high temperature will be large. The mixing ratio thus obtained is: matrix resin / hydrophilic resin = 99 by weight.
The range of / 1/80/20 is common.

The hydrophilic resin may be in a state of being uniformly dispersed in the matrix resin, but is preferably in a state in which a continuous layer is formed in a streak or a layer. Therefore, the combination of the matrix resin and the hydrophilic resin is
It is preferable to select a combination having compatibility that easily forms such a continuous layer. In the present invention, the surface of the solid fine particles contains substantially no moisture. Such solid fine particles can be easily formed by performing a drying step after forming the solid fine particles.

[0011]

In the electrorheological fluid of the present invention, no moisture is present on the surface of the solid fine particles contained therein, and a hydrophilic resin containing moisture is contained therein. Therefore, since the conductivity of the surface of the solid fine particles is low, the amount of current flowing at a high temperature can be suppressed low. In addition, the solid fine particles have an appropriate conductivity as a whole having an intrinsic volume conductivity of 1 × 10 ⁻¹¹ to 2 × 10 ⁻⁹ S / cm, so that charge transfer is fast inside and a high yield stress is obtained. Also, the response (time from application of voltage to change in viscosity) is sufficiently high.

[0012]

The present invention will be specifically described below with reference to examples. (Example 1) While selecting an ABS resin as a matrix resin, a polyethylene glycol methacrylate copolymer left at room temperature and a humidity of 80% for one day was selected as a hydrophilic resin, and each was heated and melted at 250 ° C. The mixture was kneaded with a kneader and extruded into pellets. The mixing ratio of the two was as follows: matrix resin / hydrophilic resin = 89 in weight ratio.
/ 11.

The pelletized mixed resin was dissolved in THF (tetrahydrofuran) in which both resins were dissolved, and methanol was gradually added to reprecipitate the resin into particles. Its average particle size is 20 μm. After filtration, vacuum drying was performed at room temperature for 1 to 2 days to remove water from the surface, and the dispersion was dispersed in silicone oil having a viscosity of 20 cs to a concentration of 20% by volume to prepare an electrorheological fluid of this example. The base viscosity of the obtained electrorheological fluid was 0.2 Pas, and the volume specific conductivity of the particles was 3 × 1.
It was 0 ^-10 S / cm.

The electric field strength-yield stress characteristics of this electrorheological fluid were examined, and the results are shown in FIG. FIG. 2 shows a current density-temperature curve. Further, electrorheological fluids having various volume specific conductivities were prepared in the same manner except that the mixing ratio of the matrix resin and the hydrophilic resin was variously changed, and the relationship between the yield stress at 80 ° C and the current density was determined. It was measured. The results are shown in FIG. (Example 2) An ABS resin was selected as a matrix resin, and a polyethylene glycol methacrylate copolymer left at room temperature and a humidity of 80% for one day was selected as a hydrophilic resin, and each was heated and melted at 250 ° C. The mixture was kneaded with a kneader and extruded into pellets. The mixing ratio of the two is matrix resin / hydrophilic resin = 8 by weight ratio.
9/11.

The pelletized mixed resin is freeze-pulverized by a ball mill or a jet mill so as to have an average particle diameter of 20 μm, and vacuum-dried at room temperature for 3 hours to remove water on the surface. The electrorheological fluid of this example was prepared by dispersing so that the volume became 20% by volume. The base viscosity of the obtained electrorheological fluid is 0.2 Pas,
The volume specific conductivity of the particles was 3 × 10 ⁻¹⁰ S / cm.

The electric field strength-yield stress characteristics of this electrorheological fluid were examined, and the results are shown in FIG. FIG. 2 shows temperature-current density characteristics. (Example 3) An ABS resin was selected as a matrix resin, and a polyethylene glycol-based polyamide left for one day at room temperature and a humidity of 80% was selected as a hydrophilic resin. And extruded into pellets. The mixing ratio of both is
Matrix resin / hydrophilic resin = 90/10 by weight ratio.

The pelletized mixed resin is freeze-pulverized with a ball mill or a jet mill so as to have an average particle diameter of 30 μm, and vacuum-dried at room temperature for 3 hours to remove water on the surface. To prepare an electrorheological fluid of this example. The base viscosity of the obtained electrorheological fluid is 0.15 Pa
s, the volume specific conductivity of the particles was 2 × 10 ⁻¹⁰ S / cm.

The electric field strength-yield stress characteristics of this electrorheological fluid were examined, and the results are shown in FIG. FIG. 2 shows temperature-current density characteristics. (Example 4) Poly (ethylene oxide / propylene oxide) left for one day and night at room temperature and 80% humidity while selecting polypropylene as the matrix resin
Select copolymers as hydrophilic resins, each at 210 ° C
The mixture was heated and melted, kneaded with a kneader, and extruded into pellets. The mixing ratio of both is a matrix resin / hydrophilic resin = 85/15 by weight ratio.

The pelletized mixed resin was dissolved in THF (tetrahydrofuran) in which both resins were dissolved, and methanol was gradually added to reprecipitate the resin into particles. Its average particle size is 40 μm. After filtration, vacuum drying was performed at room temperature for 3 hours to remove water on the surface, and the dispersion was dispersed in silicone oil having a viscosity of 20 cs to 15% by volume to prepare an electrorheological fluid of this example. The base viscosity of the obtained electrorheological fluid is 0.1 Pas, and the volume specific conductivity of the particles is 5 × 10
^-10 S / cm.

The electric field strength-yield stress characteristics of this electrorheological fluid were examined, and the results are shown in FIG. FIG. 2 shows temperature-current density characteristics. (Example 5) Poly (epichlorohydrin / ethylene oxide) which was left for one day and night at a room temperature and a humidity of 80% while selecting polypropylene as a matrix resin.
Select copolymers as hydrophilic resins, each at 210 ° C
The mixture was heated and melted, kneaded with a kneader, and extruded into pellets. The mixing ratio of both is a matrix resin / hydrophilic resin = 85/15 by weight ratio.

The pelletized mixed resin was dissolved in THF (tetrahydrofuran) in which both resins were dissolved, and methanol was gradually added to reprecipitate the resin into particles. Its average particle size is 40 μm. After filtration, vacuum drying was performed at room temperature for 3 hours to remove water on the surface, and the dispersion was dispersed in silicone oil having a viscosity of 20 cs to 15% by volume to prepare an electrorheological fluid of this example. The base viscosity of the obtained electrorheological fluid is 0.11 Pas, and the volume specific conductivity of the particles is 4 × 10
^-10 S / cm.

The electric field strength-yield stress characteristics of this electrorheological fluid were examined, and the results are shown in FIG. FIG. 2 shows temperature-current density characteristics. (Example 6) Polyethylene terephthalate (PET) was selected as a matrix resin, and a humidity of 8
A quaternary ammonium salt-containing methacrylate copolymer left at 0% for one day was selected as a hydrophilic resin, and each was heated and melted at 280 ° C., kneaded with a kneader, and extruded into pellets. The mixing ratio of the two is matrix resin / hydrophilic resin = 91/9 by weight ratio.

The pelletized mixed resin is freeze-pulverized by a ball mill or a jet mill so as to have an average particle diameter of 10 μm, and vacuum-dried at room temperature for 3 hours to remove water on the surface. The electrorheological fluid of this example was prepared by dispersing so that the volume became 14% by volume. The base viscosity of the obtained electrorheological fluid is 0.09 Pa
s, the volume specific conductivity of the particles was 8 × 10 ⁻¹⁰ S / cm.

The electric field strength-yield stress characteristics of this electrorheological fluid were examined, and the results are shown in FIG. FIG. 2 shows temperature-current density characteristics. (Conventional Example) A conventional electrorheological fluid having a composition in which 20% by volume of silica powder is dispersed in the same silicone oil as that used in the examples is prepared, and its electric field strength-yield stress characteristic and current density- The temperature curves are shown in FIGS. 1 and 2, respectively. (Evaluation) It can be seen from FIG. 1 that the electrorheological fluid of the present embodiment has better electrorheological characteristics than that of the conventional example.
From FIG. 2, it is apparent that the current density of the conventional electrorheological fluid sharply increases with an increase in temperature as compared with that of the embodiment. This is due to the effect of water adsorbed on the surface of silica particles used in conventional electrorheological fluids.

FIG. 3 shows that the current density is the volume specific conductivity.
Is almost proportional to. However, the current density is 30μ
A / cm^TwoIf it exceeds, the heat resistance will decrease, so
Conductivity is 2 × 10^-9S / cm or less is practically preferable.
New On the other hand, the yield stress is 2 × 10^-9If it exceeds S / cm
Almost constant value, 1 × 10 ^-11Smaller than S / cm
Then it drops sharply. Therefore, from FIG.
Volume specific conductivity is 1 × 10^-11~ 2 × 10^-9S / cm
Obviously, a range is desirable.

[0026]

That is, according to the electrorheological fluid of the present invention, it exhibits excellent characteristics in both the yield stress and the current density at a high temperature, and has excellent electrorheological characteristics and does not require equipment for preventing dielectric breakdown. Becomes Further, since the fine particles used in the present invention have a specific gravity close to that of silicone oil or the like, problems such as precipitation hardly occur, and they are less expensive than organic semiconductor particles.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between electric field strength and yield stress.

FIG. 2 is a graph showing a relationship between temperature and current density.

FIG. 3 is a graph showing a relationship among a volume specific conductivity, a yield stress, and a current density.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ identification code FI C10M 145: 26 149: 18 145: 22) C10N 20:00 20:06 40:14 (58) Fields surveyed (Int.Cl. ⁶ , DB name) C10M 157/04 C10M 149/08-149/18 C10M 145/14-145/26 C10M 143/00 C10N 20:00 C10N 20:06 C10N 40:14 WPI / L (QUESTEL)

Claims (1)

(57) [Claims] 1. An electrorheological fluid in which solid fine particles are dispersed in an electrically insulating medium, the solid fine particles comprising: a matrix resin comprising a resin selected from ABS resin, polyolefin, polyethylene terephthalate, and polymethyl methacrylate; Poly (ethylene oxide / propylene oxide) copolymer, polyethylene glycol polyamide, polyester amide, poly (epichlorohydrin / ethylene oxide) copolymer, polyethylene glycol methacrylate copolymer, quaternary ammonium base contained in the matrix resin A hydrophilic resin selected from a methacrylate copolymer, substantially free of moisture on the surface, and having a volume specific conductivity of 1 × 10 ⁻¹¹ to 2 × 10 ⁻⁹ S / cm. Electrorheological fluid.