Compositions – Etching or brightening compositions
Patent
1993-12-07
1995-10-31
Skane, Christine
Compositions
Etching or brightening compositions
252 73, 252 783, 252572, C10M17100, C10M16904
Patent
active
054626870
DESCRIPTION:
BRIEF SUMMARY
This invention relates to electroviscous fluids containing polymers bearing polyether and (meth)acrylate units as disperse phase.
Electroviscous fluids (EVF's) are dispersions of finely divided hydrophilic solids in hydrophobic, electrically non-conductive oils of which the viscosity may be increased very quickly and reversibly from the liquid to the plastic or solid state under the effect of a sufficiently strong electrical field. Their viscosity responds both the electrical d.c. fields and Lo a.c. fields, the current flow through the EVF being extremely low. Accordingly, electroviscous fluids may be used for any applications in which it is desired to control the transmission of powerful forces by low electric power levels, for example in clutches, hydraulic valves, shock absorbers, vibrators of systems for positioning and holding workpieces in position.
In many known electroviscous fluids, the disperse phase consists of inorganic solids. Electroviscous fluids based on silica gel are known from DE-PS 3 517 281 and 3 427 499. According to EP 265 252, zeolites are used as the disperse phase. DE-PS 3 536 934 describes the use of aluminosilicates. Electroviscous fluids based on polymer particles as the disperse phase have also been proposed. Thus, DE-PS 28 02 494 describes electroviscous fluids containing a polymer bearing free of neutralized acid groups. A polyhydric alcohol bearing acidic groups is disclosed as the disperse phase of electroviscous fluids in DE 2 530 694. JP 1 266 191 (CA 113, 1 00 684) describes electroviscous fluids based on polysiloxane particles modified with polyethylene oxide/polysiloxane block copolymers and doped with water. In the systems mentioned, the electroviscous effect is attributable to charging of the solids with water. These systems generally show favorable electroviscous effects, but often lack stability in storage and can only be used in a limited temperature range.
Anhydrous electroviscous fluids are known from EP 191 585 where electron conductors are mentioned as the disperse phase. EP 387 857 describes electroviscous fluids based on solid electrolyte particles, such as .beta.-aluminum oxide for example. The disadvantage of these systems generally lies in the extreme hardness of the disperse phase which leads to undesirable abrasiveness of the electroviscous fluids. Another disadvantage is the high density of the dispersed particles which can lead to unstable dispersion with a marked tendency towards sedimentation. The poor sedimentation stability of known anhydrous electroviscous fluids is a well-known problem. It is proposed in JP 1 172 496 to introduce bubble-like voids into the dispersed particles in order to reduce their density and to increase their sedimentation stability. In practice, however, this is a difficult objective to achieve.
Known anhydrous electroviscous fluids are not entirely satisfactory. Apart from their high abrasiveness and inadequate sedimentation stability, it is also difficult to combine a high electroviscous effect with a low basic viscosity and high shear stability.
The problem addressed by the present invention was to provide non-abrasive, sedimentation-stable, anhydrous electroviscous fluids which would be distinguished by a high electroviscous effect, a low basic viscosity and high shear stability.
According to the invention, this problem has been solved by an electroviscous fluid of a non-aqueous liquid as the dispersion medium, a particulate polymer containing polyether and (meth)acrylate units as the disperse phase and a dispersant. In a preferred embodiment, the electroviscous liquid according to the invention is characterized in that the polymer contains 50 to 99% by weight polyether units and 1 to 25% by weight (meth)acrylate units.
Non-aqueous liquids suitable as the dispersion medium are, for example, hydrocarbons, such as paraffins, olefins and aromatic hydrocarbons. Silicone oils, such as polydimethyl siloxanes and liquid methyl phenyl siloxanes, are also used. These dispersion media may be used individually or in combinations
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Bloodworth Robert
Oppermann Gunter
Podszun Wolfgang
Bayer Aktiengesellschaft
Skane Christine
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