CH634435A5 - Electroviscous fluid - Google Patents

Description

The present invention relates to an electroviscous (EV) in an electrically non-conductive, oil-like

Medium-dispersed liquid containing water-containing polymer particles.

A normally flowable liquid is already known which, under the influence of an electric field, has an increased viscosity and contains at least one polyhydric alcohol in the form of solid particles, which has acid groups and an open structure and in which a significant amount of water is adsorbed, the Solid particles are dispersed in an electrically non-conductive, oil-like medium.

It has now been found that a much wider range of polymer materials is suitable as solid particles in an electroviscous liquid, provided that the polymer materials have acid groups. It has been found that polymers containing acid groups perform better than those without acid groups. This better performance manifests itself in an increase in the electroviscous effect by up to 3 times in comparison to liquids which contain solid particles which, however, have no acid groups.

The present invention thus relates to the electroviscous liquid defined in claim 1.

The invention thus provides alternative polymer materials to the polyhydric alcohols mentioned.

It has been shown that the introduction of acid groups into a neutral solid polymer material leads to an increased electroviscous effect in liquids which contain such polymer particles. This is the case both when the acid groups are in free form and when they are in the neutralized form of a salt, and the improvement leads to EV liquids which are superior to those known hitherto. The solid phase in the liquid according to the invention, which results in a better EV effect, either allows the use of a lower water content in the polymer while maintaining a good EV effect or a much stronger EV effect if the water content of the solid phase remains unchanged. In the former case, the use of a lower water content can be advantageous, for example the properties of the liquid are improved without the action of an electric field, and in general the electrical current flow in polymer particles with a lower water content is lower. Since the acid groups themselves result in a higher current flow, the advantage of a lower water content in relation to this property is somewhat canceled out, and if the water content is kept unchanged in order to achieve a better EV effect, this will be at the expense of a somewhat higher current flow compared to a corresponding neutral polymer, but the improvement of the EV effect outweighs these disadvantages. Generally speaking, it is desirable to produce an EV liquid with optimal performance for any intended use, the polymer particles described greatly expanding the possibilities for optimization and also having various other advantages over previously known solids for such uses, such as starch, silicon dioxide or alginic acid.

The polymer of the polymer particles described can have any acid groups which are capable of increasing the hydrogen ion concentration in the medium in which the polymer particles are dispersed. Preferred acid groups are carboxylic acid groups and sulfur-containing acid groups, such as sulfate, sulfonic and sulfonic acid groups. The acid groups are preferably neutralized, expediently with cations of metals, for example of alkali metals. All or only some of the acid groups can be neutralized with metal cations, and the polymer can contain several different types of cations. For

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The neutralization of the acid groups in the polymer can also be used with certain organic cations.

With regard to the polymer backbone, a particularly preferred class of polymers are the addition polymers which contain at least one monomer which has at least one acid group and / or at least one group which can be converted into an acid group after the polymerization of the monomer. Such monomers are, for example, acrylic and methacrylic acid, methyl acrylate and methacrylate. The polymer may comprise only one such monomer, or multiple such monomers may be copolymerized with one another in any combination. In any case, such monomers can be copolymerized with further unsaturated monomers, for example with olefins or vinyl monomers, such as vinyl acetate, maleic acid or anhydride, N-vinylpyrrolidone.

In general, it is expedient that the polymer of the polymer particles of the liquid according to the invention is at least somewhat hydrophilic, i.e. water-retentive, since it is essential for achieving an electroviscous effect,

that the polymer contains water. In addition, the water content of the polymer is an important factor in achieving the EV properties of a liquid which contains the polymer in question. Another important factor with regard to the EV properties is the environment of the water contained in the polymer. Although the invention is not intended to be limited in any way by the explanations below regarding the factors which determine the EV effect of the liquid according to the invention, it basically appears that the function of the polymer is to create the right environment for the water which must be present in an electroviscous liquid. More specifically, it seems necessary that a certain amount of water be adsorbed at the starting points of a certain energy in the polymer. The energy generated by the adsorption of a water molecule in the polymer structure depends on the environment in which the molecule is located. This ratio of water to the polymer is appropriately considered to be the hydrophilic or water-retentive character of the polymer.

A factor influencing the adsorption batch energy of a polymer in the liquid according to the invention is the extent of the charge of the polymer in the vicinity of this batch site. The likely function of acid groups in the polymer is that their ionization causes the polymer to assume a negative charge with respect to the water molecules adsorbed therein, so that the polymer shifts the water by electro-osmosis under the action of an electric field. As a result, the polymer, when it is the solid state phase of an electroviscous liquid, changes the shear properties of the liquid under the action of an electric field. This shows that the number and strength of the acid groups in the polymer are important and determine the environment of the water contained in the polymer to a considerable extent.

The properties of the polymer itself, which control the EV effect of the liquid according to the invention, are expediently considered as the only parameter of the hydrophilic / olephilic balance of the polymer. As already mentioned, the polymer must expediently be at least somewhat hydrophilic, but is preferably not hydrophilic in such a way that it is water-soluble, since such materials have the disadvantages of being difficult to keep free from dirt and, in use, tend to be on the electrodes as compact layer, which requires frequent cleaning. Such water-soluble polymers are also very laborious to process, since when moisture is adsorbed from the atmosphere they tend to become sticky and thus to clump together instead of flowing freely. However, it is

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It is also important that the polymer is not too olephilic, since as a result the properties of an electroviscous liquid which contains such polymer are very poor without the action of an electric field due to swelling of the polymer in the oil-like dispersion medium.

The water content of the polymer can be varied as desired within the limits set by the water adsorption capacity of the polymer in order to achieve the optimum EV properties of a liquid containing the polymer in question. The water adsorption capacity of the polymer is a measure of its openness to the penetration of water and places an upper limit on the possible water content of the polymer. Since the optimal performance of the electroviscous liquid according to the invention is strongly dependent on the water content of the solid phase, the limits of this parameter can be very significant with regard to the performance, and it has been found that the water adsorption of the polymer must correspond to the definition given in claim 1, wherein the heat treatment usually takes place in a temperature range of 50-60 ° C, but for many polymers it can also be carried out safely at a higher temperature.

With regard to the EV effect of a liquid containing dispersed polymer particles, the water content of this polymer has the following effect:

The higher the water content, the higher the EV effect, i.e. the change in the yield point per applied voltage unit, up to an upper limit, the lower the threshold voltage and the higher the current flow. In addition, such a liquid shows excellent dynamic properties, i.e. it will effectively retard a system in which the liquid is sheared as soon as a voltage is applied. A liquid with a higher water content of the polymer also responds more quickly to changes in the applied electric field and generally gives reproducible results. If the water content is too high, however, the liquid exhibits poor properties without the influence of an electric field, the usable voltage range is reduced because arcing occurs even at low field strengths, and in certain cases the effect is deteriorated at higher voltages, so that an increase in the voltage does not increase the shear strength results. On the other hand, with liquids with a low water content of the polymer, the current flow becomes low and the usable voltage range becomes wide, although the threshold voltage is also high. The properties without exposure to an electric field are usually good, but the dynamic properties in use are poor, although such liquids have good static properties, i.e. effectively combine two originally stationary components. As a result of a higher static than dynamic flow limit, such liquids tend to have a hysteresis effect and form of sluggish sliding. EV liquids with a low water content in the polymer particles also respond relatively slowly to changes in the electrical field.

It is thus evident that the water content of the polymer particles in all EV liquids is an important parameter with regard to the optimization of a liquid for a particular use. With embodiments of the liquid according to the invention, the range of water content in which both good EV effect and an acceptable current flow can be achieved is much broader than in previously known liquids of this type. In embodiments of the EV liquid according to the invention, the water content of the polymer should expediently be such that, for static use of the liquid, the polymer at a predetermined temperature 30 ° C. with the ambient air at 1%. Humidity is in a state of equilibrium with moisture,

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while for dynamic application of the liquid, the water content of the polymer should be increased to approximately 5% by weight, whereby this moisture equilibrium state of the polymer with the ambient air tends to approximately 60%. Humidity increases, although in certain cases the water content of the polymer can be even higher.

With regard to the structural structure of the polymer, those properties which influence its behavior in an electroviscous liquid can be modified by introducing non-ionizing hydrophilic groups, for example pyrrolidone groups, by crosslinking the polymer and by neutralizing the acid groups in the polymer with salt formation. All of these modifying factors have an effect on the energy distribution of the water adsorption sites in the polymer and thus bring about changes in the EV effect of a liquid containing such modified polymer in the sense of the preceding explanations.

In addition to influencing the EV effect, crosslinking of the polymer also has a significant impact on the properties of the final liquid in the absence of an electrical field. It appears that a polymer which is not or only slightly crosslinked contains a significant amount of low molecular weight substance which is soluble in the adsorbed water and is to a certain extent movable within the polymer. Such a mobile substance has a flocculating effect on the polymer particles, which leads to an increase in the flow resistance of the liquid in the absence of an electric field. In connection with this, it has been found that removal of this mobile substance from the solid by exhaustive washing out with water leads to greatly improved properties of the final liquid in the absence of an electric field, but such washing out with completely uncrosslinked polymers is generally not practicable, since these polymers are water-soluble are. With more cross-linked polymers this problem is avoided, so that the properties of liquids containing such polymers are better in the absence of an electric field than liquids with other types of polymers.

The polymer can be crosslinked in a known manner using crosslinking agents, although it should be noted that the crosslinking agent should preferably be hydrophilic, in particular if the polymer itself is not particularly hydrophilic. Crosslinking agents such as N, N'-methyl-bis-acrylamide or diallyl ether are generally suitable, although more hydrophobic agents, for example divinylbenzene, can also be used if the polymer itself is highly hydrophilic, such as polyacrylates.

Another method of crosslinking while avoiding the introduction of further substances is irradiation of the polymer, provided that this does not damage the polymer backbone, and salt formation with a polyvalent cation can also be effective for crosslinking the polymer chains.

Salt formation of the polymers with metal or organic cations can be used for the further regulation of the EV properties of liquids containing such polymers and also tends to improve the stability of the polymers. The presence of cations and, accordingly, of charged groups in the polymer skeleton can significantly influence the polarity of the polymer and thus its water adsorption properties. If the cations have a high density of the charge, such as calcium, aluminum and chromium cations, the separation of the charge is minimal and the solid appears non-polar and can be too oleophilic. However, such cations are useful for crosslinking the polymer chains, however, to reduce the oleophilic character, the polymer should also contain cations of low or moderate charge density.

As an opposite extreme to the cations with a high density charge, those with a low density charge, such as organic base cations, are held relatively loosely at the charged attachment points of the polymer chains and the resulting polymer salts are very hydrophilic or even deliquescent and therefore unsuitable for use in EV liquids . In general, therefore, polymer salts with cations of moderate charge density appropriately combine the properties of good water penetration against the centers of the charge, as is necessary for a strong EV effect, with regulated water adsorption. Suitable such cations are those of metals from groups Ia and Ib of the Periodic Table of the Elements, especially those with low atomic weight, such as lithium, sodium, potassium and copper (II). Instead of single salts with cations of a single metal, similar results can be achieved by using mixed salts with two or more different metal cations, of which at least one can have a high density charge and at least one further low density charge. In this way, the different cations give an average and a polymer salt with properties similar to a salt with a cation of moderate charge density. In fact, the use of mixed salts is advantageous, since this enables more precise regulation of the polymer properties by appropriate selection of the different cations and their respective proportions in the salt. As already mentioned, the use of mixed salts also enables simultaneous crosslinking of the polymer chains by using at least some of the cations in the form of a polyvalent cation in the salt. The use of a mixture of mono- and trivalent cations, for example a mixture of cations of metals from groups I and III of the Periodic Table of the Elements, has proven expedient from every point of view.

The use of the hydrophilic-hydrophobic characteristics of the polymer as an indication of useful EV properties can be explained, for example, with respect to a number of salts of polymethacrylic acid with monovalent guanidinium and lithium cations and trivalent aluminum and chromium cations. Electroviscous liquids containing these salts can be arranged in the order of increasing shear strength in the absence of an electric field as follows:

Lithium; Guanidinium / chromium; Guanidinium / aluminum

Lithium / chrome

Lithium / aluminum

Chrome; Aluminum (highest).

This arrangement runs in parallel with the order of increasing covalent bonding of the metal cation to the acid groups of the polymer, i.e. increasing hydrophobicity of the polymer salt. According to this sequence, the viscosity also increases with increasing hydrophobicity in the absence of an electric field, so that the baseline for the EV effect of liquids containing such polymer salts is relatively high. Thus, if the liquid does not have a high EV effectiveness, either due to the high effectiveness of the liquid itself and / or due to a high proportion of the solid phase, the corresponding change in viscosity under the action of an electric field will be rather small and the liquid will not be very useful.

The use of mixed metal salts of the polymer is also advantageous since the addition of a salt with at least some of the cations in the form of a high charge cation means that less salt is present in the salt

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and thus the density of the salt is reduced to a minimum. This is important because, at least where density compensation is to be achieved, the use of less dense oil-like media enables at least a lower proportion of a high-density oil, which is important from an economic point of view and therefore also that high-density oils also tend to be highly viscous. If a larger proportion of a high-density oil is used as the medium, the volumetric proportion of the solid phase must be progressively reduced in order to keep the viscosity of the liquid at an acceptably low level in the absence of an electrical field, but the EV effectiveness is likewise correspondingly low, and it will certainly be necessary to use a solid with good EV effectiveness. In practice, suitable oil-like media with a density above 1.8 g / cm 3 are not available, and thus the density of the polymer or polymer salt should not be higher either, the lower limit of the density being approximately 1.2 g / cm 3.

With regard to other general properties of the polymers, they should be chemically stable and resistant to chemical attack or degradation by exposure to heat or light. The transition temperature of the polymer can be important for certain uses and thus determine the choice of the polymer.

Polymers suitable for the liquid according to the invention are in some cases commercially available or can generally be obtained by radical polymerization processes if the monomers are water-soluble or from the corresponding ester monomers by known suspension or emulsion polymerization processes in an aqueous medium and subsequent hydrolysis of the ester groups, if at least some of the monomers are not water soluble. Because the hydrolysis of polyesters to produce an acid group-containing polymer is difficult to carry out and requires very rigorous conditions, an easier to carry out production process for acid group-containing polymers from such monomers has been sought.

A possibility was found for the direct production of the polyacid polymers from monomers containing acid groups, not all of which are water-soluble. This new manufacturing process involves suspending or emulsifying monomers containing acid groups, optionally together with comonomers, in a perfluoropolyether in which the monomers and the resulting polymer are insoluble, polymerizing the monomers and separating the insoluble polymer formed. It should be noted that this method is a very simple and direct method for producing the desired polyacid polymers. Since the polymer tends to carry over some perfluorinated material and in view of the considerably high cost of this material, it is highly advantageous to extract the polymer after filtering it out of the polymerization medium with a material which dissolves the perfluorinated polyether and then easily from it this can be separated. A particularly suitable material for this is tri-chlorotrifluoroethane.

Another way of either conventional polymerization of an ester monomer or direct production of an acid group-containing polymer by the new process described above is by radiation polymerization if it is not detrimental to the material.

With regard to the production of polymer salts suitable as a solid phase for the EV liquid described, it has been found expedient to start from a salt of a polymer with a monovalent cation and to add a sufficient amount of a trivalent metal to this, in order to render the salt water-insoluble. In general

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such salts can be prepared as follows:

For metals with water-soluble hydroxides, an aqueous solution of the corresponding hydroxide can be added to a solution of a polymeric acid with thorough stirring, it being possible to record a titration curve to determine the end point. In other cases, it is appropriate to first prepare a salt of the above type and then to add a solution of a soluble salt of the metal whose polymer salt is to be produced, the latter salt being precipitated from the solution. At least a stoichiometric proportion of the polymer should be added, except for the preparation of mixed salts. In order to avoid the inclusion of droplets of solution of the soluble polymer in a skin of the insoluble polymer, it is advisable to homogenize the solution during the precipitation. It is also recommended that the precipitate be washed completely free of residual salts using distilled water. Another method for producing simple metal salts is titration of a solution of the polymeric acid with a strong base to determine the proportion of the base required for the neutralization of the acid groups in the polymer, from which it is easy to calculate how much metal salt has to be added. Mixed salts can be produced by double decomposition from a simple metal salt, for example lithium / chromium polymethacrylate by adding chromium chloride to lithium polymethacrylate.

For the production of the electroviscous liquid according to the invention, the particulate polymer can be dispersed in an oil-like medium. It has been found advantageous to use polymer particles that are too small, i. with an average particle size below 1 µm, since these lead to undesirable properties of the liquid in the absence of an electric field, and it is also advantageous to determine the particle size in relation to the electrode spacing in the apparatus in which the liquid is to be used not to choose too big. The reason for this latter requirement is that with an average particle size of more than Vw of the smallest passage opening in the flow system of the apparatus, the liquid in this passage opening could be inhomogeneous and could lead to malfunctions. With a passage opening of 0.5 mm, an upper limit of the average particle size of about 50 | i, m has proven to be expedient. Within the specified limits, the average particle size of the polymer particles of the solid phase does not appear to be of particular importance.

With regard to the oil-like media used for the EV liquid according to the invention, it should be noted that if the density of the medium is to be adapted to that of the solid phase, a mixture of two or more oil-like liquids is required. The procedure for adapting the densities of the medium and solid phase in this way has already been explained in detail elsewhere.

The viscosity of the oil-like medium is decisive for the proportion of polymer particles in each EV liquid intended for a specific purpose. For example, the use of a mixture of "Aroclor" 1242 and "Fluorolube" FS-5 with a proportion of 30 vol.% Polymer particles as the solid phase results in a still pumpable liquid with a viscosity of approximately 200 mPas. For certain uses, higher viscosities and thus higher volume fractions of the solid phase are permissible, while lower viscosities are required for other uses.

The following explains, for example, the production of embodiments of the electroviscous liquid according to the invention and the results obtained therewith. The behavior of an EV liquid is determined as follows

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gender:

A device with two concentric cylinders creates an annular space for receiving an EV liquid with a fixed, grounded outer cylinder and an inner cylindrical rotor. An electric field can be applied across the annular space and increasing torque can be applied to the rotor, whereby voltage and torque as well as the current flow can be measured through the test pattern of the liquid located in the annular space. The entire device is kept at a constant temperature during the test, since the characteristic parameters of the liquid, in particular the current flow, are temperature-dependent.

With regard to the important parameters of a liquid, the yield point is used as the value of the torque at which continuous rotation is observed. In a diagrammatic record of the yield point against the applied voltage, the curve is basically linear, but usually a threshold voltage Vo occurs below which there is no electroviscous effect. The mechanical behavior of an electroviscous liquid can be represented by two parameters, namely the threshold voltage Vo and the slope of the linear part of the yield stress curve, which is referred to as "S / Y".

For so-called “dynamic” measurements, the liquid is subjected to a shear force during the measurement, and three-dimensional recordings are necessary to record all variables.

To determine further characteristic parameters, the current flow through the liquid can be measured and related to the voltage applied across the annular space. The ratio of current flow and voltage corresponds to the formula:

Voltage / unit area = P (V) + Q (V) 2.

This ratio tends to collapse at low voltage values, which leads to negative values for P; however, the formula is sufficient for all practical applications in the field of liquids.

The constants P and Q can be easily determined from experimental results of current flow and voltage by linear regression of conductivity against voltage, the inclination of the regression line Q and the intersection on the conductivity axis P.

It appears that the P and Q values are not significantly affected by shear on the liquid. P is almost independent of temperature, however Q shows Boltzmann temperature dependence.

The characteristic data strongly depend on the water content of the respective polymer, and this was not optimized in every case. When the polymer is used in the form it was obtained after it was manufactured and dried, its water content is referred to as “ambient moisture”. In some cases, water was additionally added in the vapor phase, and the water content added in this way is given in the corresponding cases in% by weight, based on the weight of the polymer dried after production, and as “ambient moisture + X% by weight”. designated.

Before the experiments, the polymers were ball milled and sieved to remove particles with an average particle size greater than 50 µm.

Unless otherwise stated, all measurements of the EV effect were carried out with suspensions of 30% by volume of the respective polymer particles in “Aroclor” 1242 from Monsanto at 30 ° C. All the results mentioned were determined with the measuring device described above with a width of the annular slot of 0.5 mm.

For the determination of the properties without the influence of the electrical field, i.e. Yield point and plastic viscosity, a conventional cone-plate viscometer according to Haake with a 1.89 ° cone was used. The measurements were also carried out at 30 ° C. with the test suspensions described above.

example 1

Polyacrylic acid crosslinked with divinylbenzene was produced as follows:

142.5 ml of methyl acrylate were freed from stabilizer by washing with dilute alkali solution and then with water in a separating funnel. In the same way, 7.5 ml of a solution of 50-60% by weight of divinylbenzene in ethylvinylbenzene was treated, and then the monomers were mixed and mixed with 1.5 g of benzoyl peroxide. The solution obtained was quickly added to a solution of 1 g of potassium stearate in 200 ml of water with good stirring and the mixture was refluxed for 8 hours with constant stirring and a slight excess pressure of nitrogen to exclude oxygen which prevents the polymerization kept at 60 ° C. The mixture was then cooled, the solid was separated off and washed with water.

The solid obtained was then resuspended in a 5: 1 mixture of acetone and sodium hydroxide solution and kept in a water bath at the reflux temperature for about 30 hours. The solid, which was not visibly swollen or changed in appearance, was then obtained by decanting, several times by decanting with dist. Washed water to remove fine particles and rubbery constituents, filtered off and on the filter with further dest. Washed water. The material obtained was then suspended in 1 liter of a 3% by weight aqueous potassium hydroxide solution and stirred at reflux temperature for 20 h, then recovered by decanting and distilled with distilled water. Washed water, after which there was still no physical change. The material obtained was concentrated in a hydrochloric acid diluted 4: 1 with water. suspended, with further acid addition stirred for 4 h, then thoroughly with distilled water. Washed water and dried under reduced pressure. A white, granular material with a sugar-like appearance was obtained. After drying, the material took up 0.9 g water / g solid weight. As expected, the water retention of the material was greatly reduced by the crosslinking. The solid obtained was ground for 3 h and then a sample was taken for the density determination. After this treatment, the particle size, as viewed under the microscope, was approximately twice the radius of starch particles, i.e. reduced to approximately 10 | in particle radius. The density of the material was 1.36 g / cm3 compared to 1.42 g / cm3 for polyacrylic acid and 1.35 g / cm3 for polymethacrylic acid, so that, as expected, the introduction of the hydrocarbon monomer had reduced the density. Unlike commercially available polyacrylic acid, the cross-linked polymer was not soluble and, consequently, was not sticky at all.

After grinding overnight, the bulk of the material, as viewed under the microscope, was reduced to an average particle size of 3-5 µm, although some coarser particles remained, which could be removed by coarse sieving through a bag filter.

Static test methods were used to clarify the EV properties of the solid. A swatch was dried to an arbitrary extent, and then a series of swatches were rewet under reduced pressure to known water levels and as liquids in

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Form of a dispersion of 30 vol .-% of the polymer particles tested in «Aroclor». The water contents of three different polymers and the measurement results obtained with the corresponding liquids are summarized in Table 1.

Table 1

Water content S / V (Pa / V)

Vo (KV)

P *

Q *

% By weight

1.3 1.95 ± 0.17

1.68 ± 0.29

0.66 ± 0.51

0.62 ± 0.20

3.2 2.14 ± 0.11

0.61 ± 0.10

0.49 ± 0.23

3.43 ± 0.12

5 1.58 ± 0.08

0.29 ± 0.07

0.62 ± 1.67

23.6 ± 1.21

* The units for P and Q are A / Vx 7.87 x 106 or A / V2x 7.87x10 '.

There is a clear tendency that as the water content of the polymer increases, the threshold voltage Vo decreases, the current passage increases and there are only slight changes in the yield point-voltage curve S / V, and that Vo drops to usable values before the current passage becomes unacceptable achieved so that the solid in question results in practically usable liquids.

Measurements of the properties without the influence of an electric field showed a yield point of 92 Pa and a plastic viscosity of 0.22 Pa * s.

Example 2

The procedure described in Example 1 was repeated using 135 ml of methyl acrylate and 15 ml of the divinylbenzene solution. The product obtained in the form of a white granular material showed a density of 1.34 g / cm 3. After grinding to an average particle size of 3-5 μm, a 30 vol.% Dispersion of the polymer particles with a water content of ambient moisture + 6.2 wt.% Was produced and tested in "Aroclor". The following static test results were obtained:

S / V = 1.38 ± 0.07 Pa / V Vo = 0.33 KV

P = 8.75 ± 67.7 A / VX7.87X106 Q = 23.56 ± 100 A / V2x 7.87x10®

The measurement of the properties without exposure to an electric field showed a yield point of 33 Pa and a plastic viscosity of 0.26 Pa * s.

Example 3

142.5 ml of acrylic acid were mixed with 7.5 ml of divinylbenzene and 2 g of benzoyl peroxide, added to 1 kg and 530 ml of «Fomblin» from Montecatini Edison, respectively, and kept in a buckling bottle at 70 ° C and stirred vigorously. It should be noted that it was not possible to easily remove the inhibitor p-methoxyphenol from acrylic acid, so that it was flooded using twice the amount of benzoyl peroxide. As usual, the reaction was carried out to remove oxygen under a stream of nitrogen and the reaction vessel was equipped with a thermometer and a reflux condenser.

After stirring the mixture for about 1 h, the mass suddenly solidified with the stirrer stopped, so it is important to connect it to the drive motor via a slip clutch in order to prevent it from breaking. The mass was allowed to cool, lifted from the reaction vessel and drained over it. The white, brittle polymer obtained was removed with some difficulty from the stirrer, roughly dismembered and washed on a filter with trichlorotrifluoroethane (TCTFE), then exhaustively extracted in a Soxhlet apparatus with the same solvent, finally dried and ground. It should be noted that about% of the «Fomblin» was carried into the solid mass. After filtration, it was found that less than 10 g of «Fomblin» were lost in total, which is a very satisfactory recovery rate.

The solid obtained was a pure white powder with a density of 1.37 g / cm3 compared to the density of 1.36 g / cm3 for the product prepared according to Example 1 by the conventional method. Slight swelling occurred in water, with the originally hard particles swelling slightly, becoming more translucent and rubbery.

An EV liquid was prepared and tested as described in Example 1 using the polymer particles obtained with a water content of ambient moisture + 3.5% by weight. The test results obtained are listed below:

S / V = 1.90 Pa / V

Vo = 0.52 KV

P = 3.59 + 0.63 A / Vx7.87xl06 Q = 6.4 ± 0.48 A / V2x7.87xl09

Example 4

Example 3 was repeated with the exceptions that 148.5 ml of acrylic acid and 1.5 ml of the divinylbenzene solution were used and the EV liquid was prepared with the polymer obtained at ambient humidity. The test results obtained are listed below:

S / V = 2.00 ± 0.16 Pa / V Vo = 0.48 ± 0.18 KV P = 0.44 ± 0.82 A / Vx7.87xl06 Q = 13.30 ± 0.58 A / V2X7 , 87x10 '

Example 5

In the same way as described above, commercially available pure polyacrylic and polymethacrylic acid in particle form was used to produce 30 vol.% Dispersions in "Aroclor" and tested statically for EV effects. The results obtained are shown in Table 2, which also contains information about the properties of the liquid containing polymethacrylic acid without the action of an electric field.

Example 6

4.1 kg of lithium hydroxide from BDH Limited was used with the smallest possible amount of about 161 dest. Water was mixed and then slowly added to 411 a 20% by weight aqueous solution of polymethacrylic acid from BDH Limited, with stirring, the pH being monitored continuously, which after an initial rapid change over a period of time followed by a slow one and then another showed sudden rapid change. At that moment, the addition of lithium hydroxide was stopped, after which the pH of the mixture was about 9.

The liquid obtained was then evaporated at a temperature of at most 80 ° C under the greatest possible pressure reduction. When drying, it is recommended to break up the surface at intervals to prevent skin formation, which delays evaporation. To ensure complete drying of the solid, the heat treatment is continued at 80 ° C. under a pressure of approximately 4 mm Hg, preferably at least overnight.

The dried solid obtained was ground in a vibrating ball mill and dried again before sieving in order to remove any moisture adsorbed during the grinding. Then the ground solid was sieved to a fraction of an average particle size below 20 p.m, and larger particles became

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which is returned to the grinding process after drying. The fine particles obtained were then moistened as follows:

The solid particles were kept at 30 ° C and a stream of air with regulated humidity of about 1% was obtained. Moisture for static and about 60% clean. Moisture for dynamic measurements was blown through the solid particles until there was no change in the rei. Moisture of the escaping air flow could be determined more.

After moistening the yield of 8.82 kg of polymer particles, these were immediately mixed with the liquid medium in the form of a mixture of 2.66 kg of "Fluorolube" FS-5 from Hooker Chemicals and Plastics Corporation and 9.45 kg of "Aroclor" 1242 from Monsanto mixed. The need for direct mixing is based on the fact that the solid particles in the unmixed state absorb water very quickly with the medium.

The liquid obtained was then tested for properties without exposure to an electric field and statically for EV effectiveness as described above, and the test results obtained are shown in Table 2.

Example 7

109 g of a 20% by weight aqueous solution of polymethacrylic acid from BDH Limited were mixed with dist. Diluted water to 200 ml and adjusted to a pH of 9.0 with a 6.2 wt% aqueous solution of lithium hydroxide from BDH Limited, which required 186 ml of the lithium hydroxide solution. The solution of lithium polymethacrylate obtained was homogenized continuously using an “Ilado” homogenizer and slowly with a 29% by weight aqueous solution of chromium (III) chloride in green form from Hopkin & Williams Ltd. transferred. After the molar ratio of Cr3 + added to Li + required for the initial neutralization reached 0.294, the solution gelled completely and the addition of the chromium chloride solution was stopped at that moment. The gel was in dist. Dispersed water, filtered off and further dist. Washed water, dried in a fluid bed dryer, ground and then sieved to remove particles with an average particle size of more than 50 (in. After that, a 30 vol.% Dispersion in "Aroclor" was prepared with the dark gray-green solid particles obtained, and this as Tested above for properties without the action of an electric field and statically for EV action The results obtained are shown in Table 2.

Example 8

A chemically cross-linked lithium polymethacrylate salt was prepared as follows:

1 liter of dist. Water, 100 g methacrylic acid from Koch-Light Laboratories, 48.8 g lithium hydroxide monohydrate from BDH

Limited and 35.8 g of methylene bis-acrylamide from Koch-Light Laboratories were placed in a 5-1 beaker and stirred at 70 ° C using a magnetic stirrer. After nothing went into solution, 1.5 g of solid potassium persulfate were added, and stirring was continued at the same temperature, the liquid gelling rapidly after about 15 minutes and the temperature simultaneously increasing by about 20 ° C. The final temperature should be kept below 100 ° C at this point to prevent the contents of the cup from being blown out by vapor pressure, or alternatively a closed reactor could be used and the process carried out under pressure.

After gelling the contents of the beaker, the beaker was removed from the direct heat source and placed in a boiling water bath 9S0'0 + 9Çfr'0 nge until the gel was sufficiently stiff to form cracks when shrinking, which was approximately 2 hours in the water bath needed.

The white, opaque gel was removed from the cup, cooled and roughly crushed into small pieces. Then about 31 dest. Water was added and the suspension was homogenized in an “Ilado” homogenizer at about 10,000 rpm. The finely divided polymer was then purified by passing a slow stream of dist. Wash the water from the bottom upwards through the suspension in a tube of about 10 cm inside diameter with a sintered glass pane at the bottom of soluble components. The distilled water was pumped through the sintered disk in the bottom of the tube using a peristaltic pump at a rate of approximately 500 ml / h, the pumping rate being chosen so that the polymer in suspension neither sank to the bottom of the tube nor from the top of the pipe flows out. Flushing with water was continued for at least 24 hours, after which the solid particles were filtered off, drained and then dried to dryness in a fluidized bed dryer at 60 ° C. for about 3 hours. About 130 g of a white, crumbly powder was obtained, which after drying under reduced pressure and grinding, as described in Example 1, was processed into an EV liquid and tested. The test results obtained for this and another similar liquid with additionally wetted polymer particles are listed in Table 2.

Example 9

Example 8 was repeated with the exception that the initial neutralization of the methacrylic acid was carried out according to the procedure described in Example 6 using guanidinium carbonate. A white, crumbly powder was obtained which was dried over silica gel and processed into an EV liquid as described in Example 1 and this was tested. The test results obtained therewith and with other liquids obtained in the same way with the same polymer particles, but whose water content had been increased to ambient humidity + 2.5% by weight or ambient humidity + 4.9% by weight, are shown in the table 2 listed.

8th

5

10th

15

20th

25th

30th

35

40

45

50

9 634 435

Table 2

At

polymer

density

Water content

S / V (Pa / V)

Vo (KV)

P

Q

Flows plastic game

of

Polymer g / cm3

% By weight

limit Pa

Viscosity mPa-s

5

Polyacrylic acid

Ambient humidity

3.63 ± 0.31

0.75 ± 0.19

2.33 ± 0.20

1.89 ± 0.10

5

Polymethacrylic acid 1.35

Ambient humidity

2.13 ± 0.02

1.03 ± 0.09

0.45 ± 0.11

1.27 ± 0.05

58

330

action

Ambient humidity

2.14 ± 0.21

1.29 ± 0.27

-2.05 ± 0.81

15.98 ± 0.42

activity + 2.2%

Ambient humidity

2.17 ± 0.08

0.27 ± 0.06

-9.00 ± 7.32

2.00 ± 5.4

activity + 3.7%

6

unconnected

1.47

optimum

3.6 ±

0.43 ±

0.52 ±

110 ±

Lithium polymeth

acrylate

7

Lithium / chrome polymethacrylate

1.51

Ambient humidity

3.92 ± 0.49

0.97 ± 0.29

0.507 ± 0.075

0.456 ± 0.56

0.65

236

8th

With

Methylene bisacryl amide

1.43

Ambient humidity

3.95 ± 0.45

0.52 ± 0.16

-2.50 ± 1.12

20.3 ± 1.0

networked lithium

Ambient humidity

3.33 ± 0.21

0.35 ± 0.08

-25.7 ± 8.30

277 ± 7.3

polymethacrylate

activity + 4.2%

9

mixed with methylene-bis-acrylamide

1.36

dried over silica gel

2.78 ± 0.38

1.49 ± 0.39

approx. 20

0

networked guanidi

Ambient humidity

4.02 ± 0.27

0.78 ± 0.14

39.5 ± 3.46

16.4 ± 2.0

nium polymeth

activity + 2.5%

acrylate

Ambient humidity + 4.9%

2.66 ± 0.13

0.38 ± 0.06

15.2 ± 10.3

468 ± 91

Table 2 primarily shows that the 12% of "Aroclor" and "Fluorolube" as an oil-like medium only 13

35% by weight of the more expensive and more viscous component "fluoro attachment points sufficient for lithium in the mixed salt according to Example 6 are sufficient to demand the shear strength without indentation", in contrast to the uncrosslinked lithium effect of an electric field completely on that with polymethacrylate, the to reduce a proportion of 22% by weight “fluo-a simple equivalent salt according to example 5 minerolube” and the lithium chromium mixed salt even when the trivalent ion is chromium. of 31% by weight «Fluorolube» in mixed media require very similar results if the lithium Po 40 would.

lymethacrylate rather using N, N'-methylene-bis- The guanidinium salt according to Example 9 would even be an acrylamide rather than being crosslinked by means of trivalent chromium ions. require even less dense medium than the lithium salt. However, the crosslinked polymer salt has the advantage of a low density according to Example 8, but has otherwise been found to be somewhat less dense than the mixed salt and also to be simpler, less satisfactory than the latter, since it relates to What-not cross-linked lithium polymethacrylate, as shown in Table 2, is much more sensitive. This is the case with regard to compensation. In addition, the crosslinked lithium salt is easier to lithium polymethacrylate, which handle with N, N '-methylene-bis-acrylamide than the uncrosslinked salt has been crosslinked to the least possible extent without tendency to moisture, with slight activity adsorption. At a density of 1.43 g / cm 3, the washable and manageable solid particles would receive this polymer salt in a mixture adapted to its density, the preferred salt.

G

Claims (11)

634435 PATENT CLAIMS 1. Electroviscous liquid containing aqueous homopolymer or copolymer particles dispersed in an electrically non-conductive, oil-like medium, characterized in that the polymer contains free and / or neutralized acid groups, a density of at most 1.8 g / cm 3 and Such a water adsorption has that a sample of the polymer after reaching equilibrium in moist air with heat treatment to constant weight at a temperature that does not lead to decomposition of the polymer loses at least 8% of its weight and in air of 20 ° C and a rei . Moisture of 60% recovers at least 40% of the lost weight, whereby the polymer is not a polyhydric alcohol. 2. Electroviscous liquid according to claim 1, characterized in that the acid groups of the polymer comprise carbon, sulfone, sulfine or sulfate acid groups. 3. Electroviscous liquid according to claim 1 or 2, characterized in that the polymer is an addition, homo- or copolymer. 4. Electroviscous liquid according to claim 3, characterized in that the addition polymer is composed of one or more monomers) selected from the group consisting of acrylic acid and substituted acrylic acids, preferably methacrylic acid. 5. Electroviscous liquid according to claim 3, characterized in that the addition polymer is a polyacid derived from a monomer, preferably from an alkyl acrylate, in particular methyl or ethyl acrylate. 6. Electroviscous liquid according to one of claims 3-5, characterized in that the addition polymer contains at least one further monomer component, for example an olefin, maleic acid or anhydride, vinyl acetate or N-vinylpyrrolidone. 7. Electroviscous liquid according to one of claims 3-6, characterized in that the polymer is crosslinked by means of divinyl benzene, diallyl ether or N, N'-dimethylene-bis-acrylamide. 8. Electroviscous liquid according to claim 1, characterized in that at least part of the acid groups of the polymer is neutralized with salt formation, preferably by means of metal or organic cations, in particular with cations of metals, selected from groups I, II and III of the periodic table Elements, preferably of lithium, sodium, potassium, copper, magnesium, aluminum or chromium. 9. electroviscous liquid according to claim 8, characterized in that the polymer is a polymethacrylic acid salt, in particular a lithium or guanidinium salt or a lithium-chromium mixed salt. 10. Electroviscous liquid according to claim 9, characterized in that it contains water-containing particles of lithium polymethacrylate in a proportion of 25-35 wt .-%, based on the total weight of the liquid, wherein the water content of the polymer particles is such that the polymer particles with the ambient air at a clean. Humidity of 1-65% are in the moisture equilibrium state. 11. Electroviscous liquid according to claim 10, characterized in that the lithium polymethacrylate is crosslinked with N, N'-methylene-bis-acrylamide and has a density of at most 1.45 g / cm3.