EP0845790B1 - Magnetorheological fluids and polymer coated magnetic particles - Google Patents

Description

The invention relates to new magnetorheological fluids, a method for their manufacture and their use as well as processes for the manufacture of with a organic polymer coated magnetizable particles.

Dispersions are called magnetorheological fluids (MRF) consist of a carrier liquid and magnetizable particles dispersed therein. These dispersions change their flow behavior when a magnetic field is applied. Possible areas of application of magnetorheological fluids are, for example Couplings, dampers and bearings.

So far, for use in magnetorheological fluids magnetizable particles paramagnetic, superparamagnetic and ferromagnetic Fabrics used.

Despite extensive research in this area, the Settling stability problem to be solved satisfactorily. The previously known methods, such as e.g. the addition of carbon fibers, according to EP-A 406 692, silica gel, according to US-A 4 992 190 or polystyrene beads, according to JP-A 419 8297, led to only minor ones Improvements.

Another problem that is also still insufficiently solved Magnetorheological fluids is the abrasiveness that is particularly critical as it is too a premature failure of the one operated with the magnetorhelical liquid Device can lead.

Even those described in US-A 5,354,488, with an insulating sheath Silicon dioxide coated magnetizable particles show no improved Abrasiveness.

US-A-5 354 488 discloses magnetorheological fluids which are a carrier, include magnetizable particles and a particulate dispersant. EP-A-0023265 discloses fine-particle solids that have a coating of polymer Have organosilicon compounds, and their use as pigments.

There is therefore a need for magnetorheological fluids that have a low abrasiveness and high settling stability.

The object of the invention is therefore to provide MRFs which are in the prior art Technology known disadvantages do not have problems.

It has now been found that magnetorheological fluids containing a contain organic polymer-coated, previously silanized, magnetizable particles, improved colloid stability, improved settling stability and decreased Have abrasiveness.

The invention therefore relates to magnetorheological liquids made of magnetizable particles coated with an organic polymer, at least one oleophilic liquid and optionally a thickener, characterized in that the magnetizable particles are such particles deals, the surface before coating with the organic polymer mentioned has been subjected to silanization.

Preferred magnetorheological liquids are 45 to 95% by weight, particularly preferably 60 to 95% by weight, very particularly preferably 75 to 95% by weight, of the magnetizable particles coated with an organic polymer, and 2 to 45% by weight an oleophilic liquid and 0 to 20 wt .-% thickener, the Sum of the% by weight results in 100% by weight.

Magnetizable particles in the sense of the invention are paramagnetic, superparamagnetic and ferromagnetic substances. Examples include: iron, iron nitride, iron carbide, steel with less than 1% carbon, nickel and cobalt. Mixtures of the substances mentioned and iron alloys with aluminum, silicon, cobalt, nickel, vanadium, molybdenum, chromium, tungsten and manganese are also suitable. Iron-nickel alloys and iron-cobalt alloys can be mentioned as well-suited alloys. Magnetic oxides of chromium and iron, such as chromium dioxide, gamma-Fe ₂ O ₃ and Fe ₃ O _4, are also suitable.

Iron and / or iron alloys are preferred magnetizable particles.

The so-called carbonyl iron, which is produced by thermal Decomposition of pentacarbonyl iron (0) is obtained.

The mean longest dimension of the invention is preferably, with an organic polymer coated magnetizable particles, based on their mass (mass average), 0.1 to 100 microns, particularly preferably 1 to 50 microns.

The shape of the magnetizable particles can also be irregular, rod-shaped or be needle-shaped. The spherical shape or a shape similar to the spherical shape is especially preferred when high fill levels are desired.

Organic polymers in the sense of the invention are natural polymers, such as e.g. Gelatin or cellulose, modified natural polymers, in particular cellulose derivatives, and synthetic polymers, with synthetic polymers being preferred.

The term gelatin includes gelatin coacervates and gelatin-like complex coacervates. Combinations of are particularly suitable as gelatin-containing complex coacervates Gelatin with synthetic polyelectrolytes preferred. Suitable synthetic polyelectrolytes are those which are obtained by homo- or copolymerization of e.g. maleic acid, Acrylic acid, methacrylic acid, acrylamide and methacrylamide emerge. The The term gelatin also includes those with conventional hardening agents such as e.g. formaldehyde or glutardialdehyde further cross-linked gelatin.

Suitable synthetic polymers are: polyester, polyurethane, in particular polyester urethanes and polyether urethanes, polycarbonates, polyester-polycarbonate copolymers, Polyureas, melamine resins, polysiloxanes, fluoropolymers and vinyl polymers. Examples of suitable vinyl polymers are called: polyvinyl chloride, polyvinyl esters, e.g. Polyvinyl acetate, polystyrene, Polyacrylic esters, such as polymethyl methacrylate, polyethylhexyl acrylate, polylauryl methacrylate, Polystearyl methacrylate or polyethylacrylate, polyvinyl acetals, such as polyvinyl butyral. Other synthetic polymers are also copolymers or terpolymers from various Vinyl and vinylidene monomers such as e.g. Polystyrene-co-acrylonitrile and copolymers from (meth) acrylic acid and (meth) acrylic esters. Particularly preferred organic Polymers are vinyl polymers, polyureas and / or polyurethanes.

The molecular weight of the polymer can be chosen arbitrarily for this application become. Usual suitable polymers have a weight average of 30,000 - 1,000,000 daltons. The polymers can also be cross-linked.

The magnetorheological liquids according to the invention contain as oleophilic Liquid (carrier liquid) preferably mineral oils, paraffin oils, hydraulic oils, oils containing chlorinated aromatics (so-called transformer oils), and chlorinated and fluorinated oils. Likewise preferred are silicone oils, fluorinated silicone oils, polyethers, fluorinated polyethers and polyether polysiloxane copolymers. The viscosity of the carrier liquid is preferably 1 to 1000 mPas, particularly preferably 3 to 800 mPas, measured at 25 ° C.

In a particularly preferred embodiment of the invention, the magnetorheological liquids as carrier liquid at least one mineral oil or at least one silicone oil.

In a further preferred embodiment of the invention contain the invention magnetorheological liquids additionally at least one thickener, which gives the magnetorheological fluid a thixotropy and increases the settling stability of the magnetizable particles. Are thickeners e.g. finely divided inorganic or organic microparticles. As such are preferred Gels, silicates such as bentonite or metal oxides such as titanium dioxide, aluminum oxide or Silicon dioxide and / or flame-hydrolytically obtained highly disperse silicas, which e.g. under the trade names Aerosil® or HDK® from Degussa AG, Germany, or Wacker Chemie GmbH, Germany, commercially available are, with all microparticles an average particle diameter of less than 1 micron exhibit.

In this preferred embodiment, the amount of thickeners is 0.1 to 20 wt .-%, preferably 0.5 to 5 wt .-%.

The magnetorheological liquids according to the invention can also contain dispersing agents contain. Examples of dispersants are lecithin, oleic acid and oleates such as iron oleate, fatty acids, alkali soaps such as lithium stearate, sodium stearate, Aluminum tristearate, sulfonates and phosphonates with lipophilic residues as well Glycerol esters such as glycerol monostearate.

The dispersants are preferably in amounts of 0.01 to 2% by weight, particularly preferably 0.1 to 0.5% by weight, based on the magnetizable particles.

The weight fraction of the coating of those coated with organic polymer magnetizable particles is 0.1 to 50% by weight, preferably 0.5 to 20 Wt .-%.

The invention also relates to a method for producing the organic polymers coated magnetizable particles, after which the organic Polymer in molten form or from a solvent by precipitation or vaporization is applied to the magnetizable particles.

The invention also relates to a further method for producing the organic polymers coated magnetizable particles, after which in the presence the magnetizable particles are organic monomer components by means of polycondensation, Polyaddition or polymerization implemented to an organic polymer become.

For the polycondensation, the organic monomer components are, for example, the Combination of aliphatic diols and aromatic or aliphatic dicarboxylic acids, dicarboxylic acid chlorides, for the polyaddition, for example, the combination of diols, polyester and / or Polyether diols with di- or triisocyanates and for the polymerization, for example, olefinically unsaturated compounds, such as Styrene, acrylic acid ester, methacrylic acid ester and / or vinyl acetate are preferred.

Common reaction conditions are for polycondensation, polyaddition or polymerization applicable.

It has been found that polymer coatings which adhere particularly well can be achieved are when the magnetizable particles silanized before the polymer coating become. Silanization means surface treatment with silanes, preferably those silanes are used which have at least one functional group, e.g. OH, Cl.

in der

R¹

ein C₁ - C₂₀-Alkylrest oder C₂ - C₂₀-Alkylenrest, der gegebenenfalls mit einer Amino-, Isocyanato- Methacryloyoxy- Acryloyloxy-, Epoxy- oder Mercaptogruppe substituiert sein und / oder durch -O-, -NH-, -COO- oder -NH-COO unterbrochen sein kann

R²

ein Phenyl, ein C₁ - C₁₈-Alkylrest oder ein C₂ - C₁₈-Alkylenrest

X

eine hydrolisierbare Gruppe bedeuten und

a

den Wert 0, 1 oder 2 annimmt, silanisiert.

In a preferred embodiment of the invention, the magnetizable particles are coated with a silane of the formula (I) before coating

in the

R ¹

a C ₁ - C ₂₀ alkyl radical or C ₂ - C ₂₀ alkylene radical which may be substituted by an amino, isocyanato, methacryloyoxy, acryloyloxy, epoxy or mercapto group and / or by -O-, -NH-, - COO- or -NH-COO can be interrupted

R ²

a phenyl, a C ₁ -C ₁₈ -alkyl radical or a C ₂ - C ₁₈ -alkylene radical

X

mean a hydrolyzable group and

a

assumes the value 0, 1 or 2, silanized.

und/oder

Examples of radicals R ¹ are methyl, ethyl, propyl, n-butyl, tert-butyl, hexyl, octyl, ethylhexyl, decyl, dodecyl, stearyl, vinyl or allyl. Examples of substituted R ¹ radicals are:

and or

R ² is preferably a phenyl or a C ₁ -C ₆ alkyl radical, such as methyl, ethyl, propyl, n-butyl, tert-butyl, pentyl or hexyl.

The hydrolyzable groups on the Si atom symbolized by X comprise, for example, halogen atoms, in particular chlorine and bromine, C ₁ -C ₆ alkoxy groups, preferably methoxy and ethoxy, and carboxylate groups, such as acetate and propionate.

Examples of particularly preferred silanes are listed in the overview below:

Of course, the silane must be matched to the following polymer coating his.

If the silanization takes place, for example, with silanes 3 or 4, a silane is also used polymerizable double bonds applied to the magnetizable particles. In In this case, the application of a polymer coating by radical Polymerization of monomers, e.g. Acrylic acid esters, creating a solid chemical bond is established between the silane and the polymer coating, prefers. Surfaces that have been modified with Silane 7 or 9 can easily with isocyanate-containing compounds, e.g. with stearyl isocyanate for reaction brought, whereby a polymer coating with urea units is formed. Silanization with silanes 3, 4, 7 and / or 9 is therefore preferred.

The implementation can be done by simply mixing the components with usual stirring or mixing devices. The temperature during the implementation is preferably in the range from 0 ° C to 100 ° C and the reaction time is preferably 0.1 h to 10 h.

The amount of silane used can be varied within wide limits; it lies preferably in the range from 0.01 to 25% by weight, particularly preferably 0.1 to 10 % By weight, based on the magnetizable particles.

The silanization is preferably carried out in the presence of at least one aprotic Solvent carried out. Suitable solvents are e.g. Acetone, butanone, Dichloromethane, trichloromethane, toluene, ethyl acetate or tetrahydrofuran.

A catalyst can also be used in the silanization. suitable Catalysts are protonic acids such as acetic acid or hydrogen chloride as well amines; such as dicyclohexylamine. The amount of the catalyst is preferably 0.01 up to 5 wt .-%, based on the silane.

The silane used in the silanization can initially with acid catalysis e.g. molar amounts of water are hydrolyzed, the hydrolyzable residues X are converted into OH groups, and then the freshly prepared OH compound reacted with the magnetizable particle in a solvent becomes.

The invention also relates to a method for producing the invention magnetorheological fluids, after which in an oleophilic fluid, optionally in the presence of a thickener, which is also according to the invention Process produced, coated with an organic polymer magnetizable particles are dispersed.

In a preferred embodiment of the invention, the carrier liquid is first with the thickener using high shear forces, i.e. preferably at dispersing energies between 50 and 500 W / l, for example with the help of an Ultraturrax®, available from IKA-Labortechnik, Germany, homogeneous mixed and then stirred in the coated magnetizable particles.

The invention also relates to the use of the nonaqueous compositions according to the invention magnetorheological fluids in couplings, dampers and / or To store.

The invention will be explained on the basis of the present examples. The invention is not limited to these examples.

embodiment example 1 Coating carbonyl iron

By mixing 200 g of gamma-methacryloxypropyltrimethoxysilane for 30 minutes, 352 g of deionized water and 2.6 g of glacial acetic acid were placed in a beaker at room temperature creates a silanization solution. In a heatable 4l three-necked flask with Glass stirrer, thermometer and intensive cooler were 1000 g of carbonyl iron Company BASF AG, Germany, with an average particle size (measured according to ASTM B 330) of 4-5 µm, the following impurities C: 0.8% by weight, N: 0.8% by weight, O: 0.3% by weight, placed in 2000 ml of butanone and mixed with the Silanization solution added. The mixture was stirred at 40 ° C for 16 h. After this After cooling, the solid is suctioned off on a suction filter, several times with butanone washed and dried at 80 ° C for 10 h.

The silanized carbonyl iron was slurried in 2000ml butanone and with 190g Stearyl methacrylate, 10 g ethylene glycol dimethacrylate and 6 g azoisobutyronitrile added. The mixture was stirred and refluxed at 70 ° C for 2 h and 2 h heated. The solid is filtered off after cooling, three times with 1500 ml each Washed butanone and dried in vacuo at 50 ° C for 12 h.

Example 2 Silanization of carbonyl iron

50 g of gamma-aminopropyltriethoxysilane was dissolved in 1000 ml of chloroform. In these The solution was 1000 g of carbonyl iron EN from BASF AG, Germany an average particle size (measured according to ASTM B 330) of 4-5 µm, the has the following impurities C: 0.8% by weight, N: 0.8% by weight, O: 0.3% by weight, Sprinkle in at room temperature and stand for 1 hour, shaking occasionally calmly. Then the coated carbonyl iron became intensive with 1000 ml Washed chloroform, 1 d at room temperature and atmospheric pressure and 18 h dried at 50 ° C in a high vacuum.

Example 3 Polyurethane coating of carbonyl iron and manufacture of a magnetorheological liquid

32 g of silanized carbonyl iron from Example 2 were octane with 0.04 g of diazabicyclo [2.2.2] in 8.0 g of a trifunctional polyethylene glycol with a Molecular weight of 1015, produced by ethoxylation of trimethylolpropane, stirred. This mixture was made into a solution using an Ultraturrax® 0.84 g of the reaction product from 40 parts of octamethylcyclotetrasiloxane with 2 Share N- (β-aminoethyl) -γ-aminopropylmethyldiethoxysilane in 13.3 g of silicone oil (Baysilone® M 5, available from Bayer AG, Germany). To this Dispersion was added under shear 2.05 g of toluene diisocyanate and 30 s further dispersed. The dispersion was then ready for use at 80 ° C. for 12 h magnetorheological fluid cured.

Claims (15)

1. Magnetorheological liquids, consisting of magnetisable particles which are coated with an organic polymer, at least one oleophilic liquid and optionally a thickener, characterised in that the magnetisable particles are particles, the surface of which has been subjected to silanisation before coating with said organic polymer.
2. Magnetorheological liquids according to claim 1, characterised in that they contain 45 to 98 % by weight of magnetisable particles coated with an organic polymer, 2 to 45 % by weight of an oleophilic liquid, and 0 to 20% by weight of a thickener, wherein the sum of the percentages by weight is 100 % by weight.
3. Magnetorheological liquids according to either one of claims 1 or 2, characterised in that the average longest dimension of the magnetisable particles which are coated with an organic polymer, with respect to the weight of the particles, is 0.1 to 100 µm.
4. Magnetorheological liquids according to one or more of claims 1 to 3, characterised in that the proportion by weight of the coating of the magnetisable particles which are coated with an organic polymer is 0.1 to 50 % by weight with respect to the magnetisable particles.
5. Magnetorheological liquids according to one or more of claims 1 to 4, characterised in that the organic polymers are vinyl polymers, polyureas and/or polyurethanes.
6. Magnetorheological liquids according to one or more of claims 1 to 5, characterised in that the magnetisable particles comprise iron and/or iron alloys.
7. Magnetorheological liquids according to one or more of claims 1 to 6, characterised in that the thickeners are gels, silicates, metal oxides and/or microdispersed hydrated silicas obtained by flame hydrolysis with an average particle diameter less than 1 µm.
8. Magnetorheological liquids according to one or more of claims 1 to 7, characterised in that the amount of thickener is 0.1 to 20 % by weight.
9. Magnetorheological liquids according to one or more of claims 1 to 8, characterised in that the oleophilic liquid is at least one mineral oil or at least one silicone oil.
10. Magnetisable particles which are coated with an organic polymer, characterised in that the magnetisable particles are particles, the surface of which has been subjected to silanisation before coating with said organic polymer.
11. Magnetisable particles according to claim 10, characterised in that silanisation of the magnetic particles is effected by reaction with a silane of formula (I)

    

    where

    R1

    is a C₁-C₂₀ alkyl radical or a C₂-C₂₀ alkylene radical which may optionally be substituted with an amino, isocyanato, methacryloyloxy, acryloyloxy, epoxy or mercapto group, and/or interrupted by -O-, -NH-, -COO- or NH-COO,

    R2

    represents a phenyl or a C₁-C₆ alkyl radical,

    X

    represents a hydrolysable group, and

    a

    assumes the value 0, 1 or 2.

12. A process for producing magnetisable particles according to claims 10 or 11, characterised in that organic monomer constituents are reacted to form an organic polymer by means of polycondensation, polyaddition or polymerisation in the presence of the magnetisable particles.
13. A process for producing magnetisable particles according to claims 10 or 11, characterised in that the organic polymer is deposited in molten form, or is precipitated from a solvent, or is deposited by evaporation of the solvent on to the silanised, magnetisable particles.
14. A process for producing magnetorheological liquids according to one or more of claims 1 to 9, characterised in that the magnetisable particles according to claims 10 or 11 are dispersed in the oleophilic liquid, optionally in the presence of a thickener.
15. Use of the magnetorheological liquids according to one or more of claims 1 to 9 in couplings, dampers and/or bearings.