DE2802494A1 - ELECTROVISCOSIS FLUID COMPOSITION - Google Patents

Description

The invention relates to electroviscous (EV) fluid compositions and represents a modification of the fluid compositions which are described in DE-OS 2 5J5O 694.

DE-OS 2 530 694 describes a normally fluid one Composition that is likely to increase the apparent To show viscosity under the influence of an electric field, and at least one polyhydric alcohol in solid Particle shape that contains acid groups and has an open structure in which a significant amount of water is adsorbed, and comprises an electrically non-conductive sl-like binder in which the solid particles are dispersed.

It has now been found that a much wider range of polymer materials than the solid medium for an electroviscous Fluid is useful, the distinguishing feature of such polymeric materials being that they contain acid groups should. It was found that polymers containing acid groups show improved behavior compared to those without acid groups. This improved behavior can be seen, for example in an increase in EV effect responsiveness up to three times

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Compared with that of fluids for which corresponding, no solids containing acid groups are used.

The invention therefore relates to an electroviscous fluid composition which has water-containing particles of a polymer material in dispersion in an electrically non-conductive oil-like binder, with the characteristic that the polymer has free or neutralized acid groups, a density of at most 1.8 and a water absorption capacity such that a sample of it, after equilibrium with humid air, loses at least 8% of its weight when heated to constant weight at a temperature which does not cause the polymer to decompose, and regains at least 40 % of this weight loss when it contains air at an ambient temperature. Relative humidity of about 60 % and a temperature of 20 ⁰ C is exposed, wherein the polymer is not a polyhydric alcohol.

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

It was found that the introduction of acid groups into a neutral solid material leads to improved electroviscous effects in fluids containing such solids. this applies both if the acid groups are in free form and if they are in neutralized form as a salt, and the improvement achieved results in EV fluids superior to those known. The use of solid phase materials, which give a better EV response typical of them, as in the fluids according to the invention, enables either the use of a lower water content in the polymer

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Maintains a good EV response, or it lets itself into the solid phase with the same water content achieve much higher EV responsiveness. In the former In this case, the use of a lower water content can be advantageous; for example, the zero field properties the fluids are improved, and in general the current flows are lower with a lower water content in the solid. It is true that, among other things, the acid groups themselves are higher Promote current flow, the advantage of lower water content diminished to a certain extent with regard to this property and that in the case where the water content is maintained for better EV response, it does so Loads of a slightly higher current flow than occurs with the corresponding neutral solid is achieved, however, the improvement in EV response is such that it readily overcompensates for these disadvantages. Put further, it is generally required to have a To compose electroviscous fluid so as to obtain optimum performance for any given application and the solids according to the invention considerably increase the area for optimization in addition to Delivery of positive, the substances own advantages over the known solids, such as. B. starch, silica or alginic acid.

The acid group or groups in the polymer can be of any type, i. H. be any group dedicated to the Increasing the concentration of hydrogen ion in a medium into which the polymer is incorporated are suitable, but are preferred Acid groups the carboxylic acid group and the sulfur-containing acid groups, e.g. B. sulfate, sulfonic or sulfonous acid groups. These groups are preferably neutralized, and

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for this purpose metal cations, e.g. B. of alkali metals, are introduced into the polymers. All or just one Part of the acid groups can be neutralized by metal cations, and one can use them as a type of cation in a given Introduce polymer material. Certain organic cations can also neutralize the polymer acid group be used.

As for the polymer skeleton, one is particularly preferred Polymer class an addition polymer which contains at least one monomer which has at least one acid group and / or has at least one group which can be converted into an acid group after polymerization of the monomer. Examples such monomers are acrylic acid, methacrylic acid, methyl acrylate and methyl methacrylate. The polymer can only contain one such monomer, or, alternatively, more than one such monomer may come together in any combination are copolymerized. In any case, these monomers with other unsaturated monomers, e.g. B. olefins or other vinyl monomers, ζ. Β. Vinyl acetate, maleic acid, maleic anhydride or N-vinylpyrrolidone.

Generally speaking, it is important that the polymer to be used in the electroviscous fluid according to the invention has at least some hydrophilic behavior in terms of water-retaining property. This is the case because it is responsible for creating an electroviscous effect it is essential that the polymer contain water. In addition, the amount of water retained by the polymer is a significant one Factor to achieve the EV properties that a polymer has shows containing fluid. Another important factor

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as far as the EV properties are concerned, the environment is of the ι water contained within the polymer. Although the Invention by the following explanation of the factors that affect the EV responsiveness of the invention Mastering fluids, is in no way restricted, it appears in principle that the function of the polymer is that to provide the right environment for the water that must be present in an electroviscous fluid. In particular, it seems it may be necessary for a certain amount of water to be in places, of a given energy in that Polymer is absorbed. The one when a water molecule is absorbed The energy generated in the polymer structure depends on the environment in which the molecule itself is located. These The relationship between water and the polymer can be expediently determined by the hydrophilic or water-retaining behavior consider the polymer.

A factor influencing the absorption space energy for a polymer in a fluid according to the invention is that Amount of charge on the polymer in the vicinity of the place. The probable " The function of acid groups in polymers is that, through their ionization, the polymer has a negative effect Assumes charge towards the water molecules absorbed in it, and as a result an electric field acts, when applied to the polymer, electro-osmosis displaces the water therefrom. The result is that, when the polymer is the solid phase of an electroviscous fluid, the shear properties of the fluid by the Application of an electric field can be changed. From this it can be deduced that the number and strength of the acid groups are important in the polymer in that they determine to a considerable extent the environment of the water present in the polymer.

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The properties of the polymer itself affect the EV response master the fluids according to the invention, can expediently together on the basis of the individual parameter the hydrophile-oleophilic balance of the polymer. As stated, the polymer needs something show hydrophilic behavior. However, it should not be so hydrophilic in nature that it is water soluble as such Materials that have disadvantages, only with difficulty from foreign materials to be freed and when used for deposition as a compact layer on the electrodes tend, which requires frequent wiping and cleaning. Such soluble solids are also very troublesome to process, as they instead of becoming tacky by absorption of atmospheric moisture and thus clogging tend to flow freely. However, it is also important that the polymer does not exhibit too oleophilic behavior, since this does so the zero field properties of any electroviscous fluid containing such a polymer due to a Swelling of the polymer in the oily binder in which it is is suspended, very deteriorated.

The water content of the polymer can be within the limit set by the water absorption capacity of the polymer can be varied widely as desired to optimize the EV properties of any given polymer-containing fluid. The water absorption capacity of the polymer is a measure of its openness to water penetration and sets an upper limit for the possible water content of the polymer. Since the optimal behavior of an electroviscous fluid according to the invention strongly depends on the water content of the solid phase, the limits of this parameter with regard to the behavior can be very high be significant, and it has been found that the water absorption

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REVISED

the capacity of the polymer should be such that after making it possible to establish an equilibrium of the polymer with moist air, a sample of the same should lose at least β% of its weight when heated to constant weight under vacuum at a temperature that does not cause its decomposition, and • if possible regain at least 40 % of this weight loss when exposed to air at an ambient relative humidity of about 60 $ and a temperature of 20 ^{° C.} The heating step is normally carried out at a temperature of about 50 to 60 ^° C., but higher temperatures can also be safely used for many polymers.

With regard to the fluid containing a polymer The EV effect shown is the effect of the actual water content this polymer following. The higher the water content, the higher the EV response (change in Yield point per applied tension unit) up to one Limit, the lower the threshold voltage and the more higher the current flow. Such a fluid also has excellent dynamic properties; H. it delays effectively a system in which the fluid is already sheared when the voltage is applied. A fluid with a high Water content also responds quickly to changes in the applied field and provides generally reproducible results. If the water content is too high, however, the zero field properties are poor, the working voltage range is reduced because arcing occurs at low field strengths, and in some cases the response is at the higher stresses poorly, so that an increase in the stress does not lead to an increase in the shear resistance. at

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In fluids of low water content, on the other hand, the currents are weak and the working voltage range large, although the threshold voltage is also high. The zero field properties are usually good. In operation, however, although such fluids have good static properties, that is, effectively lock two initially stationary components together, their dynamic properties are poor. As a result of having a higher static than dynamic yield strength, such fluids tend to suffer from hysteresis effects and the form of "stick-slip". EV fluids with a low water content also respond relatively slowly to changes in the applied field.

It can therefore be seen that in all EV fluids, water content is an important parameter in optimizing a fluid for a given use. In EV fluids according to the invention, the range of water contents over which both a good electroviscous response and an acceptable current level can be obtained is much larger than in the previously known fluids. Typically for EV fluids according to the invention, if the use is static, the water content of the polymer should be such that at 30 ⁰ C the equilibrium relative humidity (defined as the relative humidity of air in equilibrium with the solid at a known temperature ) about 1%, while more water is to be added to the polymers up to about 5 wt.% of the polymer for dynamic use cases. This increases the equilibrium relative humidity of the polymer to a maximum of about 60 #, although even higher water contents may be appropriate in certain cases.

From the point of view of the structure of the polymer, they become Properties affecting its behavior in an electroviscous fluid by such factors as the inclusion of non-ionizing hydrophilic groups, e.g. B. pyrrolidone groups, in the polymer, by crosslinking the polymer and by neutralizing the acid groups in the polymer Formation of salts influenced. All of these change factors have an effect on the energy distribution of the water absorption places in the polymer and thus, in the sense of the above discussion, bring about changes in the EV response a fluid composition containing such a modified polymer.

In addition to influencing the EV response, crosslinking of the polymer also has a profound effect on the zero field properties of the final fluid. It appears that when a polymer is not or only slightly crosslinked, the solid contains a significant amount of low molecular weight material which is soluble in the adsorbed water and therefore to some extent mobile within the polymer. Such moving material has a "flocculation" effect on the polymer particles, which leads to an increase in the zero-field flow resistance of the fluid. In connection thus it is found that these movable elements can be removed from the solid by exhaustive washing with water results in significantly improved zero field properties in the final fluid, but such washing is generally at completely uncrosslinked polymers impracticable because they are soluble. With more fully crosslinked polymers this becomes a problem avoided, and therefore the zero field properties of fluids containing such polymers are better than in the case of the others Polymer types.

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The crosslinking of the polymer can be carried out in the conventional manner by using crosslinking agents, but particular attention must be paid to the type of agent, since it should preferably be hydrophilic, which is especially true if the polymer itself is not particularly hydrophilic. Crosslinking agents, such as. B. Ν, Ν'-methyl bisacrylamide or Dlallylather are therefore generally suitable, although more hydrophobic agents such. B. diphenylbenzene, can be used when the polymer itself is highly hydrophilic, for example in the case of acrylate polymers.

Another method of crosslinking that avoids the introduction of additional materials is irradiation of the Polymers, provided they do not damage the polymer structure, and also the formation of salts with a polyvalent cation can be effective in crosslinking the polymer chains.

The formation of salts of the polymers with metal or organic base cations can be used to further improve the EV properties of the fluids containing the polymers control, and also tends to improve the stability of the polymers. The presence of cations and, accordingly, the Existence of charged groups on the polymer framework the polarity of the polymer and thus its water absorption properties affect considerably. When the cations have a high charge density, e.g. B. calcium, aluminum and Chromium cations, the charge separation is minimal, the solid does not appear to be polar and may well be too oleophilic in nature. However, such cations are used to effect crosslinking of the polymer chains useful, but the polymer should also cations to suppress the oleophilic character contain low or moderate charge density.

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to
Opposite the cations of high charge density

Ions of low charge density, e.g. B. organic base cations, relatively loose at the charged places on the polymer chains and the polymer salts obtained are very hydrophilic or even deliquescent and are for use as such unsuitable in EV fluids. In general, therefore, polymer salts combine with cations of moderate charge density the most suitable Properties of good water penetration to cargo centers, such as required for strong EV effects, with controlled water absorption. Suitable cations of this type include those of metals in Groups IA and IB of the Periodic Table, especially those of low atomic weight such as lithium, sodium, potassium and copper (II). Instead of using it easier Salts with cations of a single metal can also achieve equivalent results using mixed salts, in which two or more different metal cations are present, at least one of which has a high charge density and at least one more may be of low charge density. In this way the effect can be different Cations are balanced to produce a polymer salt with properties similar to those of a salt with a moderate cation To surrender charge. Indeed, the use of mixed salts is advantageous in that it is more accurate Control of the polymer properties by suitable selection of the various cations and their individual components in the salt enables. The use of mixed salts also means, as already indicated, that the crosslinking of the polymer chains can be achieved simultaneously using at least a portion of a polyvalent cation in the salt. Considering in all respects a mixture of mono- and trivalent cations, e.g. B. a mixture of cations of metals from groups I and III of the Jeriodic system, found suitable.

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The use of the hydrophilic-hydrophobic behavior of the polymer as a parameter of useful EV properties can with reference to, for example, a number of salts of monovalent guanidine and lithium cations and trivalent ones Aluminum and chromium cations are illustrated. Electroviscous fluids containing these salts can be used in the Arrange the order of increasing zero-field shear resistance as follows:

Lithium; Guanidine / chromium; Guanidine / aluminum lithium / chromium
Lithium / aluminum
Chromj aluminum (highest value).

This sequence runs parallel to the sequence of increasing covalent bonding of the metal cation to the polymer acid groups, d. H. increasing hydrophobicity of the polymer salt. Corresponding The zero-field viscosities also grow in this sequence increasing hydrophobicity, making the "baseline" for EV responsiveness in the case of containing such polymer salts Pluiden will be relatively high. Therefore, if the fluid does not have a great EV response, be it as Result of its own high responsiveness of the fluid composition and / or as a result of using a large volume fraction of the solid phase in the fluid, the proportional Change in viscosity on application of an electric field will be quite small and the fluid will not be very useful.

The use of mixed metal polymer salts is also advantageous because of the inclusion of at least an amount of a highly charged Cations in a salt means that there is less metal

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is present in the salt and the density of the salt is reduced so much. This is important as there is at least where a density adjustment is to be made, the use of less dense oily binders or at least a smaller proportion of a high-density oil, which is important both economically and because the high-density oils tend to be very viscous. If more dense oil is used becomes, the volume fraction of the solid phase material must be continuous be lowered in order to keep the zero field viscosity of the fluid at a usable level. If the Solid volume fraction is low, becomes the absolute level of EV response can also be quite low, and it will certainly then be necessary to use a solid with a good EV response. In practice Suitable oil-like binders with densities above 1.8 are not available and therefore the polymer or the Polymer salt do not have a density higher than 1.8: the practical lower limit is about 1.2,

As for other general properties of the polymers, they should be chemically stable and chemically stable Be resistant to attack or impairment by heat or light. The transition temperature of the polymer can be in be important in certain contexts of use and dictate the selection of the polymer in these cases.

Polymers suitable for fluid compositions according to the invention may in certain cases be commercially available or can generally by radical polymerization, if these monomers are water-soluble, or from the corresponding Ester monomers by the conventional method of suspension or emulsion polymerization in an aqueous medium

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subsequent hydrolysis of the ester groups, if at least some of the monomers are not water soluble. As this hydrolysis step, the polyester to obtain of a polymer with acid groups is difficult to carry out, but requires very strict conditions researched an easier method for obtaining acid group-containing polymers from such monomers.

Accordingly, a process for the direct production of polyacid polymers from acid group-containing monomers was developed, if these are not all soluble in water. This new manufacturing process sees suspending or Emulsification of acid group-containing monomers developed, if these are not all soluble in water. This new manufacturing process involves suspending or emulsifying acid group-containing monomers (with comonomers if required) in a perfIuorροIyäther, in which the monomers (and the obtained polymers) are insoluble, the implementation of the polymerization of the monomers and finally the separation of the formed insoluble polymers. You will find that this procedure is a very simple and straightforward route too offers the desired polyacid polymers. Because the polymer tends to entrain part of the perfused material and taking into account the considerable price of this Materials, it is most advantageous to add the polymer to a material after it has been filtered off from the polymerization medium extract, which dissolves the perfluorinated polyether and which can then be easily separated from it. A particularly suitable material for this function is trichlorotrifluoroethane.

An alternate way of performing either conventional polymerization of an ester monomer or direct

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Preparation of an acid group half polymer according to The new process described here is the application of radiation polymerization, where this does not apply to the material has a destructive effect.

Regarding the polymer salts for use as the solid phase of the EV fluids, it has been found suitable for the manufacturing route found to start from a salt of a polymer with a monovalent cation and a sufficient amount of one add trivalent metal salt to make the salt water-insoluble. In general, the salts can be based on the following Because of being made.

For metals with water-soluble hydroxides, an aqueous solution of the appropriate hydroxide can be a well-stirred solution acidic polymer solution can be added. A titration curve can be applied to find the end point. In other cases, a suitable method is to start with a salt of the above type and then adding a solution of a soluble salt of the metal, the polymer salt of which is obtained would like, whereupon the latter will precipitate out of solution. At least a stoichiometric amount of the polymer should be added with the exception of when mixed salts are to be produced. To the inclusion of spheres of soluble polymer solution To avoid the insoluble polymer inside a skin, it is advisable to use the solution while performing to homogenize this precipitate. It is also recommended that the precipitate is washed completely free of residual salts by washing with distilled water. Another method for the production of simple metal salts provides the titration of a solution of the polymer acid with a strong base Determination of the amount of base required to neutralize the acid groups in the polymer. In possession of this knowledge can

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the amount of metal salt that must be added is easily calculated will. The mixed metal salts can by double conversion from a simple metal hall:?. be formed, e.g. B. can for the lithium / chromium polymethacrylate chromium chloride of a sample of lithium polymethacrylate can be added.

In the production of the electroviscous fluids according to of the invention, the polymer is in particulate form in one dispersed oil-like binder. It has been found advantageous to avoid the use of polymer parts, which are too small (roughly below a particle size of 1 / µm), as these lead to undesirable zero-field properties in a fluid lead, and it is also preferable that the particles do not are too large in relation to the working gap of any device in which the fluid is to be used. The reason for that is that when particles larger than about 1/10 of the smallest gap in the flow circuit are used, the fluid in the gap can be inhomogeneous, which leads to anomalies in operation. So in the event that the working gap is 0.5 mm, as upper limit for particle size about 50 µm as best found authoritative. Within the given limits, the particle size of the solid phase material does not seem particularly great to be meaningful.

As for the oily binders for the EV fluids according to The invention relates, if the density of the binder is to be blended with the solid phase material, it is a mixture of 2 or more oily liquids required. The one

Density adjustment of liquid and solid phase materials relevant factors are discussed in DE-OS 2,550,694.

The viscosity of the oleaginous binder determines how much of the solid polymer in a W-fluid is suitable for any

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specific use is intended, can be used. For example, when using a binder that is a mixture of "Aroclor 1242" and "Fluorolube F8-5", a volume fraction of the solid of about 150 % gives a fluid that is still pumpable and has a viscosity of about 200 mPa.s. . For some applications, higher viscosities and thus higher volume fractions of the solid can be tolerated, while lower viscosities are required for other applications.

Some examples of the preparation of electroviscous fluids according to the invention and the results achieved therewith shall now be given are described using further explanations. Measurements of electroviscous fluid behavior are made in the following manner performed.

A concentric * cylinder apparatus is used to put an electroviscous fluid sample in the annular gap between a stationary grounded outer cylinder and a cylindrical rotor mounted therein. A field can be accessed via the Gap can be applied, and increasing torque can act on the rotor, with both tension and torque are measurable. The current flowing through the fluid sample is also measured. The whole device is during the Measurements kept at a constant temperature, since the characteristic parameters of the fluid, in particular the current, are temperature-dependent are.

As far as the characteristic parameters of a fluid are concerned, the yield point is the fourth of the

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Torque taken at which an undamped rotation is observed. In a diagram in which the yield point is plotted against the applied voltage, the curve is basically linear, but there is usually a threshold voltage, V, below which no electr3-viscous effect occurs. The mechanical behavior of an electroviscous fluid can be described by two parameters, namely the threshold voltage V and the slope of the linear part of the stretch limit / voltage curve, ie 3 Al .

For so-called "dynamic" measurements, the fluid is sheared during the measurements, and three-dimensional diagrams have to be produced in order to relate all variables δλχ .

In order to obtain further parameters which are characteristic of a given fluid, the value flowing through the fluid can be used Direct current according to and with the applied across the working gap Tension can be related. The relationship between current and voltage takes the following form:

Current / area unit = P (V) + Qi (V) ²

This relationship tends to decrease at low voltage values, and this leads to negative values of P, but for all practical purposes this law is sufficiently precise over the working range of the fluids.

The constants P and Q can easily be determined from experimental results of current and voltage by performing a linear regression of conductivity versus voltage; the slope of the regression line gives Q, and the intersection: the point on the conductivity axis gives I.

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It appears that the values of P and Q are not greatly affected by shearing the fluid. P is actually independent of temperature, however, Q has a Boltsmann temperature dependence igke it up.

The characteristic data are strongly dependent on the water content of the polymer, and this was not optimized in any event, 'v'enri the polymer used in the producible state after ds ¹ "was dried, wild the' Jsssergehalt as"Urngebungsv; found ater content ". In some cases more water has been added in the vapor phase and the amount so added is, appropriately, expressed as a weight percentage of the "dry" polymer weight, i.e., on the left, "ambient water content + XYes".

The polymers were after XugeIrühlen treatment and sieving : 'ir' Removal of particles over particle sizes of 50 µm tested.

The EV response measurements were all with ;) 0 <o vol .-, 'vol. Suspensions of solids in "Aroclor 1242"'Monsanto; carried out unless otherwise stated. The temperature was JO ⁰ C. All the results listed were obtained using the heating apparatus with a working gap of 0.5 mm.

For the zero field properties (ie yield strength and plastic viscosity) a conventional cone and plate viscometer (Haake) using a 1.89 ° cone was used. The solids were J50 fo Vol./Vol.-Suspensionen in "Aroclor 1242" (Monsanto), unless otherwise specified, and the measurements were carried out at 30 ⁰ C.

example 1

A sample of divinylbenzene crosslinked polyacrylic acid was prepared in the following manner.

142.5 ml of methyl acrylate was taken and the stabilizer was removed by washing with dilute alkali in a separatory funnel, followed by washing with water. The divinylbenzene (7.5 ml of 50-βθ % w / w in ethyl - * - vinylbenzene) was treated similarly, the monomers were then mixed, and 1.5 S benzoyl peroxide was added to the mixture. The solution was then quickly added to a well-stirred aqueous solution of 1 g of potassium stearate in 200 ml of water in the reaction vessel. This mixture was then held for 8 hours at 60 ° C. with continuous stirring under reflux and a low positive nitrogen pressure. (This serves to exclude oxygen, which hinders the polymerization). At the end of this time the mixture was cooled and the solids removed and washed with water.

The solids were then in a 5: 1 mixture of acetone and sodium hydroxide resuspended and refluxed in a water bath for about 30 hours. The solid, apparently not swollen or in appearance. . was changed, was then detected by decanting, several times by decanting with distilled water to remove

em
Washed fines and gummy material and finally filtered and washed on the filter with more distilled water. The material was then resuspended in 1 liter of 3% aqueous potassium hydroxide and refluxed with stirring for an additional 20 hours. It was recaptured and washed by decantation with distilled water; again there appeared to be no noticeable change in its physical appearance. The material was then in a k : 1 dilution of

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concentrated hydrochloric acid suspended to water and with a fresh amount of acid stirred for a further 4 h. It was finally washed carefully with distilled water and dried under vacuum. This through this sequence of steps The material produced was a white, granular material very similar in appearance to powdered sugar. When drying the water recovery was 0.9 (g water / g solids weight); as expected, the crosslinking had the water holding property of the material significantly reduced. The pesticide was milled for 3 hours and a sample was taken for density testing. By the end of that time, the material was in particle size to about twice the radius of strength, such as detected under the microscope, d. H. to about 10 / Utn particle radius scaled down. The density was 1.36, which can be compared to 1.42 for polyacrylic acid and 1.35 for polymethaeric acid should; as expected, the introduction of the hydrocarbon decreased off monomers the density. In contrast to commercially available polyacrylic acid, the crosslinked polymer was not soluble and consequently not "sticky" at all

After overnight grinding, the majority of the material was in its particle size to about 3-5 / µm (as under found under the microscope) crushed, although some coarser particles remained; the latter could by means of coarse sieving can be removed through a sieve cloth.

Static methods were applied to evaluate the EV properties to investigate the solid. A sample lot was dried to an arbitrary level and then became a series of samples rehydrated to known dimensions under vacuum and tested as fluids with 30 vol. # in "Aroclor". The measuring

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are results of the characteristic values for the fluids given in Table 1 for each sample.

Table 1

Water addition
Weight % , 3 s / v (Pa / O V O ^ + ) O , 29 0 P ¹ o, 5l C. 0.62 + 0 , 20 1 , 2 1.95 + O , 17th 1 , 68 + O , 10 0 , 66 + 0.23 3.43 + 0 , 12 3 2.14 + O , 11 O , 61 + O , 07 0 , 49 + 1.67 23.6 + 1 , 21 5 1.58 + O O , 29 , 62 +

1 The units of P and Q are A / V χ 7.87 χ 10 and A / V ² χ 7.87 x 10 ^9, respectively.

There is a clear trend in that an increase in the water content is associated with a decrease in V, an increase in the current flowing through, but only fairly small changes in S / V. Apparently, V drops to useful levels before the current becomes unacceptably high and so this solid would make practically useful fluids.

Zero field property measurements result in a yield point ?! ^e of 92 Pa and a plastic viscosity of 0.22 Pa.s.

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- 27 -

Example 2

The procedure of Example 1 was repeated, except that 135 ml of methyl acrylate with 15 ml (10%) of divinylbenzene (50-60% w. I ⁿ A'thylvinylbenzol) were used. The product had a density of 1.4 and was a white granular material. After grinding to a particle size of 3-5 / dn in order fluid in "Aroclor" (30% vol./vol) is prepared, wherein the water content of the polymer "environment" + was 6.2 wt.%. The static test data obtained were as follows:

S / V 1.38 + 0.07 Pa / V

V ₀ 0.33 kV

P 8.75 + 67.7 A / V x 7 * 87 χ 10 ^β

Q 23.56 + 100 A / V ² x 7.87 χ 10 ⁹

The zero field property values were:

Yield strength: 33 Pa

Plastic viscosity 0.26 Pa.s.

Example 3

142.5 ml of acrylic acid were mixed with divinyl benzene (7.5 ml) and benzoyl peroxide (2 g) and this mixture was added 1 kg (530 ml) "Fomblin" added to the vigorously stirred in a flanged bottle and kept at 70 ⁰ C became. (Note that it was not possible to easily remove the inhibitor (p-methoxyphenol) from the acrylic acid; it became

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therefore "floated" using a double amount of benzoyl peroxide). As usual, nitrogen was on the Surface of the reaction mixture for removing oxygen directed; the reaction vessel was fitted with a thermometer and a reflux condenser. .

After stirring the mixture for about 1 hour, it solidified. the whole mass suddenly, which stopped the stirrer (it is essential to connect the latter to the drive motor with a slip clutch to avoid breakage) . The mass was allowed to cool, lifted over the reaction vessel and allowed to drain. The material was white and crumbly. With some difficulty the polymer was removed from the stirrer, roughly. broken open and on a filter washed with trichlorotrifluorathane (TCTFE). It then became exhaustively in single amounts in a S oxhl et apparatus with extracted with the same solvent and finally dried and ground.

It should be noted that approximately one third of the "Fomblin" was entrained in the solid. After filtering it was found that less than 10 g of "Fomblin" was lost in total, which is a very satisfactory level of recovery is.

The solid was obtained as a pure white powder with a density of 1.37 (cf. the value of 1.36 for after Example 1 material produced according to conventional methods). If you put the powder in water, it showed up Appearance of sources; the initially hard particles swelled a little, became more translucent and rubbery.

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In line with the previous experiments, the solids on its EV activity was tested as 30 Joige suspension in "Aroclor" after a known amount of Peststoffes had the opportunity to record a 3.5 wt.% Of the polymer equivalent amount of water. The static test results obtained were as follows:

S / V = 1.90 Pa / V

V ₀ = 0.52 kV

P = 3.59 + 0.63 A / V χ 7.87 χ 10 ^L Q = 6.4 + 0.48 A / V ² χ 7.87 χ ΙΟ ⁹

Example 4

The procedure of Example 3 was repeated, but 148.5 ml of acrylic acid and 1.5 ml were used instead

(1 %) of the divinylbenzene solution is used. The product had a density of 1.39. Static test results were obtained for a 30% v / v solution in "Aroclor" of the product with "ambient" water content as follows:

S / V = 2.00 + 0.16 Pa / V

V ₀ = 0.48 + 0.18 kV

P = 0.44 + 0.82 A / V χ 7.87 x 10 ⁶

Q = 13.30 + 0.58 AA ² χ 7.87 χ ίο ⁹

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Example 5

Commercially available pure samples of polyacrylic and polymethacrylic acids were statically tested for EV "activity as fluids in ~ $ Q # v / v" Aroclor ". The results obtained are shown in Table 2. Zero field property data are also for polymethacrylic acid specified.

Example 6

4.1 kg lithium hydroxide (BDH Ltd) was made up in the minimum amount of distilled water (about 16 liters) and slowly with stirring 41 l of a 20% aqueous polymethacrylic acid solution (BDH Ltd) added. The pH was monitored continuously while mixing was taking place, and after an initial one rapid change, the pH shows a period of slow change followed by another sudden rapid change followed. At this point the addition of the lithium hydroxide was discontinued: the pH was about 9.

The solution was then evaporated at a temperature not exceeding 80 ^° C. using the lowest practicable vacuum. As drying progresses, it is recommended to break open the surface at intervals in order to avoid "skin formation" that delays evaporation. In order to ensure that the solid is dry through and through, it is also preferred ^{to heat it to 80 °} C. in a vacuum of about 5.26 mbar at least overnight.

After the solid obtained had been dried, it was ground in a vibrating ball mill and then before the Classification dried again to remove moisture that may have been absorbed during milling. Of the Solid was then classified, taking the proportion under

809833/0739

20 / um withheld and the larger particles to the mill (after renewed drying) for further grinding. The fine particles were then hydrated in the following manner.

The solid was kept at 30 ^° C. and a stream of controlled humidity (relative humidity for static measurements about 1 %, for dynamic measurements about 60 %) was passed through the solid until no further change in the relative humidity of the effluent was observed.

After hydration, the solid (yield 8.82 kg) was immediately mixed with the base liquid which contained 2.66 kg "Fluorolube FS-5" (Hooker Chemicals and Plastics Corporation) and 9.45 kg "Aroclor 1242" (Monsanto). The requirement to mix the hydrated solid immediately is because the solid will rapidly absorb water when exposed to the environment without the base oil.

Samples of the fluid composition were then tested for zero field properties and statically tested for EV activity and the results are shown in Table 2.

Example 7

109 g of a 20% aqueous polymethacrylic acid solution (BDH Ltd) were diluted to 200 ml with distilled water. The solution was diluted with 6.2% lithium hydroxide solution (solid supplied by BDH Ltd) titrated to pH 9.0. 186 ml of the lithium hydroxide solution was required. the Lithium polymethacrylate solution was continuously homogenized using, and in, a "Hado" homogenizer

«09833/0739

State an aqueous solution (29 % w / v) of chromium chloride (green form supplied by Hopkin & Williams Ltd) was slowly added. As the ratio

Moles of added C ^

Moles of for initial neutralization

required Li ⁺ a value of 0.294
reached, the entire solution completely gelled, and in

At this stage the addition of the chromium chloride solution was discontinued. The gel was dispersed in distilled water, filtered and washed with additional portions of distilled water, dried on a fluid bed dryer, ground and then sieved to remove particles larger than 50 µm. The dark gray-green solid obtained was then processed into a ^ O % v / v suspension in "Aroclor" and checked both for zero field properties and statically for EV activity. The results are given in the table.

Example 8

A chemically crosslinked lithium polymethacrylate polymer salt was prepared by the following procedure.

1 liter of distilled water, 100 g of methacrylic acid (Koch-Light Laboratories), 48.8 g of lithium hydroxide monohydrate (BDH Ltd) and 8.5 g of methylenebisacrylamide (Koch-Light Laboratories) were placed in a 5 liter beaker and stirred magnetically. The contents were ^{heated to 70 °} C., and when no further solution took place, 1.5 g of solid potassium persulfate were added to the solution. Heating and stirring continued,

8Q9833 / 0739

- 25 -

and after about 15 minutes the liquid gelled rapidly, with the temperature rising by about 20 ° C at the same time. (The final temperature at this point should be kept below 100 ^° C. in order to prevent the contents from being blown out of the beaker by steam pressure, or alternatively a closed reaction vessel could be used and the process carried out under pressure).

After the contents of the beaker had gelled, the beaker became removed from the direct heating and placed in a boiling water bath where it was held until the gel was sufficient was stiff to crack as it shrunk, which after about

2 h in the water bath was the case.

The white, opaque gel was removed from the beaker, cooled, and raw chopped into small pieces. Approximately

3 liters of distilled water were then added and the Suspension was in an "Ilado" homogenizer at approx 10,000 rpm homogenized. The finely divided polymer was then removed from soluble materials by passing a slow stream of distilled water upward through the in a tube about 10 cm in diameter with a glass sintered disk at the bottom of the suspension was washed free. Distilled water was added to the bottom of the tube through the disc using a peristaltic pump pumped in a throughput of about 500 ml / h. (The throughput is chosen so that the polymer in suspension neither sinks to the bottom of the tube nor is discharged from the top of the tube.) The washing was done for at least Continued for 24 h at which time the solid was filtered off

809833/0739

obtained, allowed to drain and dried in a fluidized bed dryer at 6o ⁰ C for about 3 h or to dryness. About 130 g of a white, friable powder was obtained and after vacuum drying and grinding at 30 % v / v. suspended in "Aroclor 1242". Results of static tests for this material and for another hydrated sample are given in Table 2.

Example ff

The same procedure was followed as in Example 8 except that the initial neutralization of methacrylic acid using guanidine carbonate using the procedure described in Example 6 was followed. The product was obtained as a white, friable solid which, after drying over silica gel, gave the static test results given in Table 2 when it was tested as a 50% v / v suspension in "Aroclor 1242". Two samples were further hydrated by the addition of 2.5 and 4.9 % v / water (% of polymer weight), respectively, the results of which are also shown in Table 2.

809833/0739

Table 2

Solid
No / material

density
of

polymer
ren

Water content

limit (Pa)

Plastic viscosity (mPa.s)

Polyacrylic acid

■;

Surroundings

3.63 + 0.31

0.75 + 0.19

2.33 + 0.20

Polymethacrylic acid

1.35 environment

2.13 + 0.0:

2.14 + 0.21 2.17 + Ο, ΟΕ

1.03 +0.09 1.29 +0.27

0.27 + ρ, οβ

0.45 + 0.11

2.05 + 0.81

-9.00 + 7.32

1.27 +0.05

15.98 + 0.42

2.00+ 5.4

58

330

Li t hiump ο Iy me th-l
acrylate (crosslinked) 1.47

optimum

3.6 +

0.43 +

0.52 +

110 +

Lithium / chromium polymethac iy lat

1.51

[Environment

3.92 + 0.49

0.97 ± 0.29

0.5 07 +0.075] 0.456 +0.05dj 0.6i

236

Li t hium p oly methacrylate (cross-linked
with methylene-b3 & -
acrylamide

[Environment 1.43 "+ $ 4.2

3.95 + 0.45 3.33 + 0.21

0.52 + 0.16 0.35 + 0, C

-2.50 +1.12] 20.3 +1.0
-25.7 + 8.30l277 +7.3

Guanidine polymethylene dries over « ₇ n _n ^ o

acrylate (crosslinked 1.36 / S illtegel ^ ^ji - ^{u>; ö} with methylene bis / 2.5 $ Vfesserzusa '

acrylamide) ι Nj-, 9p u

atej ^ .02 + 0.27 p2.66 + 0.13

1.49 + 0.39

0.78 + 0.14 0.38 + 0.06

about 20

39.5 + 3.46 / 16.4 + 2.0
15.2 + 10 * y 468 + 91
· "I""

1 The solids were tested in each case as 30 % vol / tvol. Suspensions in "Aroclor 1242" (Monsanto),

2 The units of P and Q are A / V x 7.87 x 10 ⁶ and A / V ² x 7.87 x 10 ^{9, respectively}

ro 00 ο

CO

3f

From the results in Table 2, it can be seen, first, that the 12% of occupied by lithium in the mixed salt Squares (example 7) are sufficient to completely reduce the zero field shear resistance to that of the simple equivalent Salt (Example 6), at least when the trivalent ion is chromium. Very similar results will be

.. when using the lithium polyacrylate salt

of the added agent N, N " ^f -ethylene bisacrylamide is crosslinked instead

obtained by means of the trivalent chromium ions. However the crosslinked polymer salt has the advantage of a lower density than the mixed salt (and also a lower than

the density of the simple uncrosslinked lithium polymethacrylate),

as the results in Table 2 show. Furthermore, the crosslinked lithium salt is lighter than the uncrosslinked salt handle as it has no tendency to absorb moisture. With a density of 1.4j3 this polymer salt would be in

a tightly fitted, oil-like, mixed "Aroclor-Fluorolube" -

Binder the presence of only $ 13 "Fluorolube" require which is the more expensive and viscous component. in the

In contrast, the uncrosslinked lithium polymethacrylate salt would a binder with 22 $ "Fluorolube" and the lithium / chromium-Mlsch.-

require salt one with J> 1% "Fluoroltibe".

The guanidine salt of Example 9 would be even less require dense fluid binder than the lithium salt of Example &, but it has been found to be somewhat less satisfactory otherwise found than the latter because of its greater sensitivity to water content. When weighing up, this is preferred Salt the lithium polymethacrylate in which the polymer is with Ν, Ν'-methylenebisacrylamide to the lowest possible extent which at the same time a solid material that is easy to wash and handle is obtained, is crosslinked.

• 01133/0731

Claims (1)

Claims 1.) Electroviscous fluid composition, the water-containing particles of a polymer material in Lispersion in an electrically non_leitendon oil-like binder, characterized in that the polymer has free or neutralized acid groups, a density of at most 1.8 and such a water absorption capacity that a sample from it after setting the equilibrium with humid. Air loses at least 8 % of its weight when heated to constant weight at a temperature that does not cause polymer degradation, and regains at least 40% of this weight loss when it is air at an ambient relative humidity of about 60 % and is exposed to a temperature of 20 ⁰ C, wherein the polymer is not a polyhydric alcohol. 2. Fluid composition according to claim 1, characterized in that the acid group or groups include carboxylic acid, sulfate, sulfonic acid or sulfine acid groups. 3. Fluid composition according to claim 1 or 2, characterized in that the polymer is an addition polymer. 5112/06) -TF 809835/0739 4. fluid composition according to claim 3 »characterized in that that the polymer is an addition polymer of one or more several monomers from the group of acrylic acid and substituted acrylic acids. 5. Fluid composition according to claim 4, characterized in that that the substituted acrylic acid is methacrylic acid. 6. Fluid composition according to claim 3, characterized in that that the addition polymer is derived from a, monomer which contains at least one group which can be converted to an acid group after polymerization of the monomer is. 7- fluid composition according to claim β, characterized in that the monomer is an alkyl acrylate, in particular Is methacrylate or ethyl acrylate. 8. Fluid composition according to one of claims 3 to 7 » characterized in that the polymer contains at least one further monomer component, for example an olefin, maleic acid, maleic anhydride, vinyl acetate or N-vinylpyrrolidone. 9. fluid composition according to any one of claims 3 to 8, characterized in that the polymer is made using divinylbenzene, diallyl ether or IJ, N'-dimethylene bisacrylamide is networked. 10. Fluid composition according to one of claims 1 to 9, characterized in that at least some of the acid groups of the polymer is neutralized to form salts. 509833/0739 11. Fluid --UiJ amme ns ot :: unc according to claim I ¹ '., Characterized in that the acid groups are represented by meta]] - or organic Cations are neutralized. 12. Fluid composition according to claim 11, characterized in that • It is evident that the metal or metals are selected from groups 2, II -; rd III of the Periodic Table, in particular from lithium, striurr., Potassium, copper, magnesium, aluminum or chromium, selected c-ind. ijj. Fluid composition according to claim 11, characterized in that äaS. the polymer is a Polymethacrylsäuresal ..:, in particular a lithium, guanidine or lAthium-Ohrom-niGchsa thereof. 1 · 'ί. A fluid composition according to claim 13, characterized in that the polymer has an equilibrium relative humidity in the range ^r v on 1 to 65 75 miles. 15 · fluid composition according to any one of claims 1 to 14, characterized in that the polymer particles are one size from 1 to 50 µm. 16. Fluid composition according to one of claims 1 to I5, characterized in that the fluid 20 to 40 fb vol./vol. of the polymer. I ?. Fluid composition according to claim 16, characterized in that it consists of lithium polymethacrylate particles with a water content such that the equilibrium relative humidity of the solid is in the range from 1 to 65 fo , 1) 09831/0739 BAD ORIGINAL in a 25 to 55 % v / v of the fluid and consists of an electrically non-conductive oily liquid having a density of 1.40 to 1.50 as the remainder of the fluid. 18. Fluid composition according to claim 17, characterized in that that the lithium polymethacrylate with N, N'-methylenebisacrylamide is cross-linked and has a density below 1.45. ORIGINAL INSPECTED 809833/0739