Compositions – Heat-exchange – low-freezing or pour point – or high boiling... – Organic components
Patent
1994-03-11
1996-04-02
Lieberman, Paul
Compositions
Heat-exchange, low-freezing or pour point, or high boiling...
Organic components
252 783, 252572, 252570, C09K 300, H01B 318
Patent
active
055037631
DESCRIPTION:
BRIEF SUMMARY
This invention relates to electroviscous liquids containing, as disperse phase, polymer particles or polymer-coated particles with small particle diameters and narrow particle diameter distribution.
Electroviscous liquids (EVF) are dispersions of finely divided solids in hydrophobic, electrically non-conductive oils whose viscosity changes very rapidly and reversibly from the liquid to a highly viscous, plastic or solid state under the influence of a sufficiently powerful electric field. The viscosity reacts both to electric DC fields and electric AC fields but the flow of current through the EVF should be very low. Electroviscous liquids may be used wherever large forces are required to be transmitted with little electric power, e.g. in clutches, hydraulic valves, shock absorbers, vibrators or devices for positioning and fixing workpieces.
In many known electroviscous liquids, the disperse phase consists of inorganic solids. EVF's based on silica gel are known from German Patent Specifications DE 3 517 281 and DE 3 427 499. Zeolites are used as disperse phase in EP 265 252. DE 3 536 934 describes the use of aluminosilicates. Spherical particles obtained by the hydrolysis and condensation of metal alkoxides, for example tetraethoxysilane, may also be used as disperse phase (EP 0 341 737). The use of "Organo Silica Sol" is described in JP 01 304 189 (CA 112 142 616). In the known systems, the electroviscous effect is due to the solids being charged with water. These systems generally produce advantageous electroviscous effects but they have a poor dispersion stability and unfavourable abrasive properties due to the high density and great hardness of the inorganic solids.
Electroviscous liquids based on polymer particles as disperse phase have also been proposed. Thus DE 2 820 494 proposes EVF's having a polymer containing free or neutralised acid groups. Substituted silicone resin as disperse phase is disclosed in DE 3 912 888. Surface treated polyalkylsiloxane powders are described in JP 01 266 191. JP 01 180 240 (CA 112 23 759) mentions composite particles obtained by the condensation of ionic polymer particles and special silicon compounds.
The electroviscous liquids hitherto known, based on polymer particles, are not able to meet all the requirements. In particular, it is difficult to obtain a high electroviscous effect combined with low basic viscosity, high dispersion stability and high shearing stability.
It is an object of the present invention to provide non-abrasive, sedimentation stable, electroviscous liquids which are distinguished by a high electroviscous effect, a low basic viscosity of below 100 mPa.s and a high shearing stability as well as good response times.
It was found that the average particle diameter and the particle distribution have an important influence on the electroviscous effect. Organic polymers as disperse phase have advantageous properties with regard to the abrasiveness.
The present invention thus relates to electrorheological liquids consisting of an organic polymer as polarizable disperse phase, an electrically non-conductive, non-aqueous continuous phase and a dispersing agent, the disperse phase having an average particle diameter of from 0.2 to 30 .mu.m and a particle diameter distribution having a relative half width value below 0.8. The half width value is the quotient of the absolute half width value and the average particle diameter.
The average particle diameter is preferably from 0.5 to 20 .mu.m, most preferably from 1 to 10 .mu.m. Preferred particle size distributions of the disperse phase have relative half width values below 0.5, most preferably below 0.3.
Since many organic polymers suitable for the formation of the disperse phase have only a low electric polarizability, the phase according to the invention preferably contains a polar substance in solution. The use of such electrolytes to increase the magnitude of the electroviscous effect in polymer dispersions has been described in EP-A 0 472 991.
The polar substance used may be water and/or other electro
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Bloodworth Robert
Oppermann Gunter
Podszun Wolfgang
Bayer Aktiengesellschaft
Delcotto Gregory R.
Lieberman Paul
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