JPH06220476A - Electroviscous fluid - Google Patents

Abstract

PURPOSE:To obtain the subject fluid which has a high yield stress and a low current density even at high temperatures. CONSTITUTION:The objective fluid is prepared by dispersing fine solid particles in an electrical insulating medium. The solid fine particles are made from a matrix resin comprising a resin selected from among ABS resin, polyolefin, polyethylene terephthalate and polymethyl methacrylate and a hydrophilic resin contained in the matrix resin and selected from among poly(ethylene oxide/ propylene oxide) copolymer, polyethylene glycol polyamide, polyesteramide, poly(epichlorohydrin/ethylene oxide) copolymer, polyethylene glycol methacrylate copolymer and methacrylate copolymer having quat. ammonium salt groups, are substantially free from water, and have a volume specific conductivity of 1X10<-11> to 2X10<-9>S/cm.

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 reversibly increases under the action of a strong electric field. It is being considered for use in clutches and shock absorbers. 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, lithium polyacrylate, etc. have been conventionally used. However, in an electrorheological fluid using such solid fine particles, the temperature dependence of the electrorheological effect is large, and the electric current becomes large at a high temperature to flow a large amount of current, and a means for preventing dielectric breakdown is required. There was a problem that became. There is also a problem that the electrorheological effect becomes extremely small at a low temperature of 0 ° C or lower.

Therefore, JP-A-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 covered with an electrically insulating thin film. Has been done. According to this electrorheological fluid, a good electrorheological effect is exhibited, the conductivity is small even at 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 the property that the electrical conductivity greatly changes depending on the thickness of the electrically insulating coating. Moreover, it is difficult to precisely control the thickness of the electrically insulating coating, and as a result, the amount of current flowing varies.

On the other hand, electrorheological fluids using organic semiconductor particles instead of water-absorbing or hydrophilic solid particles have been investigated. With such organic semiconductor particles, the conductivity can be controlled relatively easily. However, this electrorheological fluid has the property that the electrorheological effect greatly changes depending on the particle size of the organic semiconductor particles, and it is difficult to control the particle size, so sufficient properties have not been obtained at present. Is.

The present invention has been made in view of such circumstances, and by using novel hydrophilic solid fine particles,
The purpose is to prevent an increase in conductivity at high temperature 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 made of a resin selected from BS resin, polyolefin, polyethylene terephthalate and polymethylmethacrylate, and contained in the matrix resin,
Hydrophilicity selected from poly (ethylene oxide / propylene oxide) copolymer, polyethylene glycol-based polyamide, polyesteramide, poly (epichlorohydrin / ethylene oxide) copolymer, polyethylene glycol methacrylate copolymer, and quaternary ammonium salt group-containing methacrylate copolymer It has a volume specific conductivity of 1 × 10 ^{−11, which} is composed of a conductive resin and does not substantially contain water on the surface.
It is characterized in that it is ˜2 × 10 ⁻⁹ S / cm.

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

The hydrophilic resin is poly (ethylene oxide /
Propylene oxide) copolymer, polyethylene glycol-based polyamide, polyester amide, poly (epichlorohydrin / ethylene oxide) copolymer, polyethylene glycol methacrylate copolymer, quaternary ammonium salt group-containing methacrylate copolymer, and generally has conductivity. It is preferably 10 ^-9 to 10 ^-8 S / cm.
This hydrophilic resin has a volume specific electric conductivity of the whole solid fine particles of 1 × 10 ⁻¹¹ to 2 × 10 ^{−9 in the} matrix resin.
It is contained so as to be S / cm. Volume specific conductivity is 1
If it is less than × 10 ^-11 S / cm, the electrorheological effect is small, and if it is more than 2 × 10 ^-9 S / cm, the amount of current flowing at high temperature becomes large. The mixing ratio thus obtained is, by weight ratio, matrix resin / hydrophilic resin = 99.
The range of / 1 to 80/20 is common.

The hydrophilic resin may be in a state of being uniformly dispersed in the matrix resin, but it is preferably in a state of forming a continuous layer in the form of streaks or layers. Therefore, the combination of matrix resin and hydrophilic resin is
It is preferable to select a combination that has compatibility to easily form such a continuous layer. In the present invention, the surface of the solid fine particles does not substantially contain water. 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, water does not exist on the surface of the solid fine particles contained therein, and the hydrophilic resin containing water is contained inside. Therefore, since the electric conductivity of the surface of the solid fine particles is low, the amount of current flowing at high temperature can be suppressed low. In addition, since the solid fine particles as a whole have a moderate volume conductivity of 1 × 10 ⁻¹¹ to 2 × 10 ⁻⁹ S / cm, which is an appropriate conductivity, the charge transfer is fast inside and a high yield stress can be obtained. The responsiveness (time from application of voltage to change in viscosity) is also sufficiently high.

[0012]

EXAMPLES 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 is, by weight, matrix resin / hydrophilic resin = 89.
/ 11.

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

The electric field strength-yield stress characteristics of this electrorheological fluid were investigated, and the results are shown in FIG. The current density-temperature curve is shown in FIG. Further, except that the mixing ratio of the matrix resin and the hydrophilic resin was changed variously, electrorheological fluids having various volume specific conductivities were prepared in the same manner, and the relationship between the yield stress and the current density at 80 ° C. was calculated. It was measured. The results are shown in Fig. 3. (Example 2) 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 is, by weight, matrix resin / hydrophilic resin = 8.
It is 9/11.

The pelletized mixed resin is frozen and pulverized by a ball mill or a jet mill so that the average particle diameter is 20 μm, vacuum-dried at room temperature for 3 hours to remove surface water, and then in a silicone oil having a viscosity of 20 cs. Was dispersed in 20% by volume to prepare an electrorheological fluid of this example. The base viscosity of the obtained electrorheological fluid is 0.2 Pas,
The volume specific electric conductivity of the particles was 3 × 10 ⁻¹⁰ S / cm.

The electric field strength-yield stress characteristics of this electrorheological fluid were investigated, and the results are shown in FIG. The temperature-current density characteristics are shown in FIG. (Example 3) In addition to selecting ABS resin as a matrix resin, polyethylene glycol-based polyamide left at room temperature and humidity of 80% for one day was selected as a hydrophilic resin, and each was heated and melted at 260 ° C. to be kneaded. It was kneaded and extruded into pellets. The mixing ratio of the two is
The weight ratio is matrix resin / hydrophilic resin = 90/10.

The pelletized mixed resin is frozen and pulverized by a ball mill or a jet mill so that the average particle diameter is 30 μm, and vacuum dried at room temperature for 3 hours to remove surface water, and then in a silicone oil having a viscosity of 20 cs. Was dispersed to 18% by volume to prepare an electrorheological fluid of this example. The obtained electrorheological fluid has a base viscosity of 0.15 Pa.
s, the volume specific electric conductivity of the particles was 2 × 10 ⁻¹⁰ S / cm.

The electric field strength-yield stress characteristics of this electrorheological fluid were investigated, and the results are shown in FIG. The temperature-current density characteristics are shown in FIG. (Example 4) Poly (ethylene oxide / propylene oxide) was left for one day at room temperature and humidity of 80% while polypropylene was selected as the matrix resin.
Choose the copolymer as the hydrophilic resin, 210 ℃ for each
Was melted by heating, kneaded with a kneader, and extruded into pellets. The mixing ratio of the two is, by weight, matrix resin / hydrophilic resin = 85/15.

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

The electric field strength-yield stress characteristics of this electrorheological fluid were investigated, and the results are shown in FIG. The temperature-current density characteristics are shown in FIG. (Example 5) Polypropylene selected as a matrix resin and left for one day at room temperature and a humidity of 80% (epichlorohydrin / ethylene oxide)
Choose the copolymer as the hydrophilic resin, 210 ℃ for each
Was melted by heating, kneaded with a kneader, and extruded into pellets. The mixing ratio of the two is, by weight, matrix resin / hydrophilic resin = 85/15.

The pelletized mixed resin was dissolved in THF (tetrahydrofuran) in which both resins were dissolved, and methanol was gradually added to reprecipitate it into particles. Its average particle size is 40 μm. After filtration, vacuum drying was performed at room temperature for 3 hours to remove surface water, and the dispersion was dispersed in silicone oil having a viscosity of 20 cs to be 15% by volume to prepare an electrorheological fluid of this example. The obtained electrorheological fluid has a base viscosity of 0.11 Pas, and the particles have a volume intrinsic conductivity of 4 × 10 5.
It was ^-10 S / cm.

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

The pelletized mixed resin is pulverized by a ball mill or a jet mill so as to have an average particle size of 10 μm, and vacuum-dried at room temperature for 3 hours to remove surface water, and then in a silicone oil having a viscosity of 20 cs. To 14% by volume to prepare an electrorheological fluid of this example. The obtained electrorheological fluid has a base viscosity of 0.09 Pa.
s, the volume specific electric conductivity of the particles was 8 × 10 ⁻¹⁰ S / cm.

The electric field strength-yield stress characteristics of this electrorheological fluid were investigated, and the results are shown in FIG. The temperature-current density characteristics are shown in FIG. (Conventional example) An electrorheological fluid of a conventional example having a composition in which 20% by volume of silica powder is dispersed in the same silicone oil as that used in the example 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) From FIG. 1, it can be seen that the electrorheological fluid of this example is superior in electrorheological characteristics to that of the conventional example.
It is clear from FIG. 2 that the current density of the conventional electrorheological fluid sharply increases as the temperature rises as compared with that of the embodiment. This is an effect of water adsorbed on the surface of silica particles used in the conventional electrorheological fluid.

Further, from FIG. 3, the current density is the volume specific conductivity.
Is almost proportional to. However, the current density is 30μ
A / cm²If it exceeds, the heat resistance will drop, so it is peculiar to the volume.
Conductivity is 2 × 10^-9Practically preferred to be S / cm or less
Good On the other hand, the yield stress is 2 × 10^-9When 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 x 10^-9S / cm
Clearly, a range is desirable.

[0026]

According to the electrorheological fluid of the present invention, it exhibits excellent characteristics in terms of both yield stress and current density at high temperature, has excellent electrorheological characteristics, and requires no 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 are less likely to occur, and they are cheaper than organic semiconductor particles and the like.

[Brief description of drawings]

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

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

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

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Office reference number FI technical display location C10M 145: 26 149: 18 145: 22) C10N 20:00 Z 8217-4H 20:06 Z 8217- 4H 40:14

Claims (1)

[Claims] 1. An electrorheological fluid obtained by dispersing solid fine particles in an electrically insulating medium, wherein the solid fine particles are a matrix resin made of a resin selected from ABS resin, polyolefin, polyethylene terephthalate, and polymethylmethacrylate. Contained in the matrix resin, containing poly (ethylene oxide / propylene oxide) copolymer, polyethylene glycol-based polyamide, polyesteramide, poly (epichlorohydrin / ethylene oxide) copolymer, polyethylene glycol methacrylate copolymer, quaternary ammonium salt group A hydrophilic resin selected from a methacrylate copolymer, which is substantially free of water on the surface and has a volume specific electric conductivity of 1 × 10 ⁻¹¹ to 2 × 10 ⁻⁹ S / cm. An electrorheological fluid.