Electroviscous fluids containing semiconducting particles and dielectric particles

#The present invention relates to an electroviscous fluid and, more particularly, to an electroviscous fluid which has an excellent insulating property, which is usable in a high electric field and which generates an excellent electroviscous effect. The electroviscous fluid is useful for a vibration isolator and a power transmission which are electrically controllable.

#The electroviscous fluid is a fluid whose apparent viscosity rapidly and reversibly changes depending on ON and OFF (change) of an electric field applied.

#The electroviscous fluid is generally produced by dispersing polarizable particles in an electrical insulating liquid. It is considered that an electroviscous effect is produced as follows. When an electric field is applied to the electroviscous fluid, the particles dispersed in the liquid are polarized and agglomerate in the form of a chain by electrostatic attraction based on the polarization. As a result, an electroviscous effect is displayed.

#FIG. 1 is a graph showing a relation of the electroviscous effect of the electroviscous fluid in Example 1 to a voltage applied.

#The electrical insulating liquid used in the present invention is a liquid having an insulating property corresponding to a resistivity of usually not less than 10.sup.9 .OMEGA.cm, preferably not less than 10.sup.10 .OMEGA.cm. As the electrical insulating liquid, for example, silicone oils, ester oils and mineral oils can be cited. More specifically, dimethyl polysiloxane, dioctyl phthalate, dibutyl phthalate, diisononyl phthalate, trioctyl trimellitate, triisodecyl trimellitate, dibutyl adipate, butyl stearate, paraffin-based mineral oil, naphthene-based mineral oil, may be exemplified.

#The semiconducting particles used in the present invention are composed of a material having an electrical conductivity of usually 10.sup.-2 to 10.sup.-10 S.multidot.cm.sup.-1, preferably 10.sup.-4 to 10.sup.-9 S.multidot.cm.sup.-1. If the electrical conductivity is too low, it may be difficult to obtain an electroviscous effect. On the other hand, if the electrical conductivity is too high, application of an electric field may cause dielectric breakdown.

#The preferred specific gravity of the semiconducting particles depends upon the particle size and the amount of particles added, but the semiconducting particles having a specific gravity of not more than 3, more preferably 0.7 to 2.5 are preferred in order to suppress the sedimentation of the particles. As the semiconducting particles used in the present invention, particles composed of a carbonaceous material such as coke, having the above-mentioned electric conductivity and obtained by heating a hydrocarbon at a temperature of not higher than 1000.degree. C., copper phthalocyanine or polyacene quinone may be exemplified.