DE10261406A1 - Process for the production of surface-coated nanoscale particles and suspensions containing them - Google Patents

Abstract

The present invention relates to a method for producing a suspension which contains nanoscale particles suspended in a continuous phase and which have a coating on at least part of their surface. The invention further relates to a method for producing such nanoscale particles.

Description

The present invention relates to a method of making a suspension in a continuous Contains suspended nanoscale particles on at least one Part of their surface have a coating. The invention further relates to a Process for the production of such nanoscale particles.

Preparations of particles with particle sizes in the nanometer range (nanoscale particles) are used in many areas of technology found. They serve, for example, in the field of electrical engineering as dielectrics for miniaturized multilayer capacitors, as catalysts, as additions for colors and cosmetics, as additives to plastics, for example against thermal or photochemical Stabilize decomposition or its dielectric and / or magnetic Changing properties and as a polishing agent. Special applications exist for suspensions, the particles with magnetic, ferroelectric or piezoelectric Properties included, and which are for example for magneto-optical Applications, as sensor materials or as magnetic fluids. Such dispersions of nanoscale particles that are capable of under the influence of magnetic, electrical or electromagnetic Warm alternating fields to be used, for example, the production of adhesive and Sealants that result from the application of magnetic, electrical or curing alternating electromagnetic fields induced heating or an existing adhesive bond is separated.

In order to obtain a Agglomeration or coalescence of the particles essentially to prevent and / or to ensure good dispersibility of the particulate phase in the coherent Phase of preparations to ensure the particles used are usually surface modified or surface coated. For this purpose, the particles have a uniform surface on at least part of their surface. or multilayer coating on the at least one connection with ionogenic, ionic and / or non-ionic surface-active Contains groups.

The DE-A-19923625 describes a process for the production of redispersible metal oxides or metal hydroxides with a volume-weighted average crystallite size between 1 and 20 nm, the precipitation of the particles taking place in the presence of polymeric carboxylic acids which coat the metal oxide or metal hydroxide particles.

WO 01/27945 describes a magnetic fluid composition, which contains nanoscale magnetic particles with at least one surfactants Substance and a fluorocarbon silane surface modifier coated are.

WO 01/31662 describes a ferrofluid composition based on magnetic particles that have an internal coating layer based on a silane-containing surface coating agent and a external Have a coating based on a surface-active substance.

The DE-A-19726282 describes nanoscale particles with an iron oxide-containing core surrounded by at least two shells. The innermost shell can be, for example, aminosilanes. The outer shells are formed, for example, by naturally occurring substances such as biopolymers.

The DE-A-19955816 describes a modified nano-titanium dioxide, wherein the titanium dioxide particles are surface-modified with at least one silane coupling reagent.

None of the aforementioned documents teaches in the production of suspensions based on surface-modified use nanoscale particles ultrasound.

The US 5,718,907 describes nanoscale organophilic metal oxide particles that are surface-modified with alkoxysilanes. To produce them, an aqueous-alcoholic suspension of the metal oxide particles is reacted with an anhydrous alcoholic solution of at least one alkoxysilane, the alkoxysilanes hydrolyzing and condensing on the surface of the particles. The surface-modified particle dispersions thus obtained can be mechanically redispersed in order to maintain an optimal dispersion. It is generally described that ultrasound can be used for this redispersion.

• 1) Bereitstellung einer wässrigen Suspension von nanoskaligen Eisenoxidteilchen, die teilweise oder vollständig in Form von Agglomeraten vorliegen,
• 2) Zugabe eines Trialkoxysilans und eines mit Wasser mischbaren polaren organischen Lösungsmittels, dessen Siedepunkt mindestens 10°C höher ist als derjenige von Wasser,
• 3) Behandlung der resultierenden Suspension mit Ultraschall,
• 4) destillative Entfernung des Wassers unter Ultraschalleinwirkung und
• 5) Abtrennung der nicht aufgebrochenen Agglomerate.

WO 97/38058 describes a method for producing an agglomerate-free suspension of stably coated nanoscale iron oxide particles. This includes the following steps:

• 1) provision of an aqueous suspension of nanoscale iron oxide particles, some or all of which are in the form of agglomerates,
• 2) adding a trialkoxysilane and a water-miscible polar organic solvent whose boiling point is at least 10 ° C. higher than that of water,
• 3) treatment of the resulting suspension with ultrasound,
• 4) removal of the water by ultrasound and distillation
• 5) Separation of the unbroken agglomerates.

This document expressly teaches that an ultrasound treatment before adding the silane component and / or of the organic solvent is disadvantageous because in the absence of these components a reagglomeration can take place (page 8, lines 18-23). For ultrasound generation The device used is evident from the exemplary embodiments a conventional ultrasonic bath. The required response time for one Batch on a 500 ml scale is with 72 hours and for indicated a 15 l batch with about 10 days. Through this extremely long response times such a process can hardly be implemented economically. In addition, surface modification no alkoxysilanes are used, the less than three to the Si-bonded alkoxy groups. The use of more hydrophobic Dispersants are therefore excluded.

The present invention lies the task of an improved process for the production of Suspensions of surface modified nanoscale particles available to deliver. This should be possible, in particular, through one little time required for surface modification distinguished. It should preferably continue for one Use of a large Range of different surface modifiers, such as mono- and dialkoxy-substituted silanes.

Surprisingly it has now been found that this problem is solved by a method where you put a nanoscale particle suspension before contact with the surface treatment agent treated with ultrasound of sufficiently high energy.

• a) nanoskalige Teilchen bereitstellt und in einer die kontinuierliche Phase bildenden Flüssigkeit suspendiert,
• b) die in Schritt a) erhaltene Suspension mit Ultraschall behandelt, wobei der Energieeintrag pro 1 g dispergierter Teilchen und 1 Minute mindestens 100 J beträgt,
• c) wenigstens ein Beschichtungsmittel zugibt und in innigen Kontakt mit den suspendierten Teilchen bringt.

The invention therefore relates to a process for producing a suspension comprising nanoscale particles suspended in a continuous phase and having a coating on at least part of their surface, in which

• a) providing nanoscale particles and suspending them in a liquid forming the continuous phase,
• b) the suspension obtained in step a) is treated with ultrasound, the energy input per 1 g of dispersed particles and 1 minute being at least 100 J,
• c) adding at least one coating agent and bringing it into intimate contact with the suspended particles.

"Nanoscale particles" in the sense of the present Registration are particles with a volume-average particle diameter of at most 100 nm. A preferred particle size range is 4 to 50 nm, in particular 5 to 30 nm and particularly preferably 6 to 15 nm. Such particles are characterized by a high level of uniformity in terms of their size, size distribution and morphology. The particle size is preferably based on the UPA method (Ultrafine Particle Analyzer) determined, e.g. B. after the laser light back scattering method. The used according to the invention nanoscale particles and the preparations containing them in a preferred embodiment ferromagnetic, ferrimagnetic or piezoelectric properties on. They are particularly superparamagnetic.

The nanoparticles preferably have at least one element selected from Fe, Co, Ni, Cr, Mo, W, V, Nb, Ta, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, mixtures, alloys of two or more of the above Elements, oxides and mixed oxides from two or more of the above Elements.

For example, the nanoparticles can contain magnetite, macchiemite, goethite or a ferrite of the general formula MeOFe ₂ O ₃ , where Me is an element selected from Mn, Co, Ni, Cu, Zn, Mg or Cd, or Me is a mixture of two or means several of these elements. These include, for example, cobalt ferrite and NiZn ferrite.

A list of suitable nanoparticles can be found, for example, in the DE-A-19954960 , to which reference is made in full here.

Also suitable as nanoscale particles are metal mixed oxides of the general formula M ^II M ^III O ₄ , in which M ^{II stands} for a first metal component which comprises at least two different divalent metals and M ^{III stands} for a further metal component which comprises at least one trivalent metal. These are preferably double oxides of the spinel type, such as. B. ferrites of the formula M ^II Fe ₂ O ₄ . One of the divalent metals is preferably selected from Mn, Fe, Co and Ni. At least one further is preferably selected from Zn and Cd.

It is preferably for suspending of the nanoscale particles used in step a) selected from Water, water-miscible organic solvents and mixtures from that. Suitable water-miscible organic solvents are e.g. B. alcohols, such as methanol, ethanol, n-propanol, isopropanol and n-butanol.

Preferably, the in step a) suspension obtained has a solids content of at most 15% by weight, particularly preferably at most 10% by weight.

The continuous phase of the suspension can be more solved Contain components, for example from the manufacturing process to provide the nanoscale particles. A separation of this Components are not required as long as the surface modification the nanoscale particles with at least one coating agent do not interfere. Such components are e.g. B. of inorganic and organic acids and bases, oxidants, etc. derived ions.

Suitable processes for the production of nanoscale particles, e.g. B. of superparamagnetic nanoscale particles are known in principle. They are based, for example, on precipitation from aqueous solutions of metal salts by raising or lowering the pH with a suitable base or acid. The DE-A-196 14 136 describes a process for producing agglomerate-free nanoscale particles using the example of iron oxide particles. The DE-A-199 23 625 describes a process for producing nanoscale redispersible metal oxides and hydroxides. The disclosure of these documents is hereby fully referred to. A suitable method for producing superparamagnetic nanoscale particles which can be used according to the invention consists in the precipitation from acidic aqueous metal salt solutions by adding a base. For this purpose, if appropriate, heated, aqueous hydrochloric acid solutions of metal chlorides can be mixed with a suitable amount of a heated base for precipitation. It has proven to be advantageous to maintain a certain temperature range during the precipitation of superparamagnetic particles in order to achieve particles with the desired high magnetic field or microwave absorption capacity. The temperature during the alkaline precipitation is preferably in a range from 20 to 100 ° C., particularly preferably 25 to 95 ° C. and in particular 60 to 90 ° C.

Before contacting the Surface treatment agent becomes the nanoscale particle suspension obtained in step a) treated with ultrasound, the energy input per 1 g dispersed Particles and 1 min is at least 100 J.

The energy input in step b) is preferably in a range from 200 to 700, particularly preferably from 300 to 600 J / g ^-1 min ^-1 .

The ultrasound power density achieved in step b) is preferably at least 100 W / cm ³ , particularly preferably at least 150 W / cm ³ and in particular at least 200 W / cm ³ .

Suitable ultrasound transmission means with a correspondingly high output are known in principle. These include ultrasonic homogenizers, which are preferably designed as a sonotrode immersed in the reaction space. Such homogenizers with high power density are commercially available and are sold for example by the company. Bandelin electronic GmbH & Co. KG under the name Sonopuls ^® -Ultrasound homogenizers. For illustrative purposes only, the performance data of a 200 W sonotrode and a conventional 200 W ultrasonic bath are compared in the following table.

The one to produce one essentially agglomerate-free suspension required ultrasound treatment time is preferably at most 2 hours, particularly preferably at most 1 hour and especially at most 30 minutes.

The one after the ultrasound treatment Suspension obtained in step b) is preferably within at the most 1 hour, particularly preferably within a maximum of 30 minutes, especially within at most 10 minutes and especially immediately after the ultrasound treatment mixed with at least one coating agent and intimate Contacted (step c)).

To substantially prevent agglomeration or coalescence of the nanoscale particles and / or to ensure good dispersibility of the particulate phase in the coherent phase, the particles used are surface-modified or surface-coated in step c). According to this, the particles have a single- or multi-layer coating on at least part of their surface, which has at least one compound with ionogenic, ionic and / or nonionic surface-active Contains groups. The compounds with surface-active groups are preferably selected from the salts of strong inorganic acids, e.g. B. nitrates and perchlorates, saturated and unsaturated fatty acids such as palmitic acid, margaric acid, stearic acid, isostearic acid, nonadecanoic acid, lignoceric acid, palmitoleic acid, oleic acid, linoleic acid, linolenic acid and elaosteric acid, quaternary ammonium compounds such as tetraalkylammonium hydroxides, e.g. B. tetramethylammonium hydroxide, silanes and mixtures thereof.

The coating agent used in step c) preferably comprises at least one silane. Suitable silanes are for example in the DE-A-19955816 , the US 5,718,907 , WO 98/22536, WO 01/27945, WO 01/31662 and WO 97/38058, to which full reference is made here.

The coating composition preferably comprises at least one silane of the general formula I. SiR ^' _x R ² _4-X (I) wherein
the radicals R ¹ independently of one another represent groups which cannot be split off hydrolytically, it being possible for two radicals R ¹ which are bonded to two different silanes of the formula (I) to also jointly represent a group bridging these silanes,
the radicals R ² independently of one another represent hydroxyl groups or hydrolytically removable groups, and
x represents an integer from 0 to 3.

The hydrolytically non-removable R ¹ radicals are preferably selected from alkyl, in particular C ₁ -C ₂₀ alkyl, such as methyl, ethyl, propyl, butyl, pentyl, hexyl, decyl, undecyl, dodecyl, octadecyl etc., alkenyl, in particular C ₁ -C _{2 0} -alkenyl, such as vinyl, 1-propenyl, 2-propenyl etc., alkynyl, in particular C ₁ -C _{2 0} -alkynyl, such as acetylenyl and propargyl, cycloalkyl, preferably C ₅ - to C ₈ -cycloalkyl, such as Cyclopentyl and cyclohexyl, aryl, preferably C _{6 to} C ₁₀ aryl, such as. As phenyl and naphthyl, and the corresponding alkaryl and arylalkyl groups. Suitable longer-chain alkyl and alkenyl radicals are also the radicals derived from natural fatty acids, the alkenyl radicals also being able to be unsaturated two or more times. The aforementioned radicals may have at least one substituent, which is preferably selected from amino, acyl, carboxyl, epoxy, mercapto, cyano, halogen. The aforementioned alkyl, alkenyl, alkynyl and cycloalkyl groups can be interrupted by one or more non-adjacent heteroatoms and / or heteroatom-containing groups, which are preferably selected from O and NR ³ , where R ^{3 is} hydrogen or alkyl.

Examples of hydrolytically removable groups R ² are hydrogen, halogen, such as F, Cl, Br and I, in particular Cl and Br, alkoxy, preferably C ₁ -C ₄ alkoxy, such as, for. B. methoxy, ethoxy, n-propoxy, isopropoxy and butoxy, aryloxy, preferably C ₆ -C ₁₀ aryloxy, such as phenoxy, alkaryloxy, such as benzyloxy, acyloxy, preferably C ₁ -C ₄ acyloxy, such as acetoxy and propionyloxy and acyl such as acetyl and propionyl. Other suitable groups R ² are amino groups, where the amine nitrogen can additionally have one or two alkyl, cycloalkyl or aryl radicals, amide groups such as benzamido and aldoxime or ketoxime groups. Two radicals R ² which are bonded to different silanes of the formula I can also represent a group bridging these silanes. Such groups derive z. B. formally from diols, such as 1,2-ethanediol, 1,3-propanediol or from diamines, such as 1,2-diaminoethane, by splitting off one hydrogen atom each from the terminal hydroxyl or amino groups. Particularly preferred radicals R ² are C ₁ to C ₄ alkoxy groups, in particular methoxy and ethoxy.

Silanes of the formula I which have one, two or three radicals R ² which stand for alkoxy are particularly preferred.

Specific examples of surface modifiers suitable silanes are e.g. B. methyltriethoxysilane, 3-aminopropyltriethoxysilane, N- (2-aminoethyl) -3-aminopropyltrimethoxysilane, trimethoxysilylpropyldiethylenetriamine, N- (6-aminohexyl) -3-aminopropyltrimethoxysilane, benzoyloxypropyltrimethoxysilane, Bis (N-methylbenzamido) ethoxymethylsilane etc.

This advantageously enables inventive method the use of a large Range of different surface modifiers and in particular also mono- and dialkoxy-substituted silanes. Consequently the hydrophilicity / hydrophobicity properties of the suspended nanoscale particles to a variety of suspending agents with different polarities to adjust. For the preparation of suspensions in water, water-miscible organic solvents or mixtures thereof, silanes are preferably used which in addition to alkoxy groups have polar groups, for example Contain amino groups and / or carboxyl groups as residues. For the production of suspensions in non-polar media, such as. B. alkanes preferably monosiloxane and / or dialkoxysilanes used in addition to Alkoxy groups polar groups, such as long-chain alkyl, alkenyl, Alkynyl, cycloalkyl or aryl groups bound to the silicon atom exhibit.

The proportion of the coating composition is generally 1 to 50% by weight, preferably 2 to 40 % By weight, based on the weight of the nanoscale particles used.

The addition of the coating agent can in a solvent take place that corresponds to that forming the continuous phase or differs from it. A water-miscible is preferred organic solvent, such as B. the aforementioned alcohols used. Suitable is also the use of a water-miscible polar organic Solvent, whose boiling point is above that of water. Are preferred such solvents selected among diols and polyols, such as ethylene glycol, propylene glycol, glycerol, Trimethylolpropane and diethylene glycol.

At least as a coating agent an aminosilane is used, the pH of the suspension is preferably in an acidic range, preferably in a range from 1 to 5, in particular from 2 to 4. For inorganic purposes soluble in the continuous phase are suitable for this purpose and organic acids, such as B. hydrochloric acid, sulfuric acid and acetic acid. The use of glacial acetic acid is preferred.

• d1) Abtrennen wenigstens eines Teils der die kontinuierliche Phase bildenden Flüssigkeit,
• d2) Abtrennen wenigstens einer zusätzlich zu den Oberflächen-beschichteten nanoskaligen Teilchen in der kontinuierlichen Phase enthaltenen Komponente,
• d3) Zugabe wenigstens eines Suspendiermittels und, falls erforderlich, Resuspendieren der nanoskaligen Teilchen, und Kombinationen davon.

In the nanoparticulate preparations obtained by the process according to the invention, comprising the steps a) to c) described above, the particles are virtually dispersed as primary particles, so that the resulting suspensions are extremely stable and have no tendency to agglomerate therein for long periods of time show contained nanoscale particles. Without further processing, they are suitable for a large number of the uses mentioned at the beginning. In a further embodiment, however, the method according to the invention can also include further work-up steps. This may be necessary, for example, if a different dispersant than that used to prepare the suspensions in step a) is to be used for the intended use of the suspensions. Furthermore, it may be necessary for certain purposes of use to separate components contained in the nanoscale suspensions, for example from the production of the nanoscale particles or from the surface modification. In a further embodiment, the method according to the invention therefore additionally comprises at least one workup step d) which is selected from

• d1) separating off at least part of the liquid forming the continuous phase,
• d2) separating off at least one component contained in the continuous phase in addition to the surface-coated nanoscale particles,
• d3) adding at least one suspending agent and, if necessary, resuspending the nanoscale particles, and combinations thereof.

The separation of at least one part the liquid forming the continuous phase takes place in step d1) according to usual, processes known to the person skilled in the art, e.g. B. at least by evaporation part of the liquid at elevated Temperatures and / or in negative pressure, for example when used a rotary evaporator.

The rheological properties of the Suspensions can advantageously be dependent of the type and amount of the suspending agent in a wide range to adjust. Depending on the desired application form, preparations can thus be made produce a liquid to gel-shaped Have consistency. "Gel-shaped consistency" means that a higher one viscosity as liquids have, and which are self-supporting, d. H. the one bestowed upon them Keep shape without a stabilizing cover. The viscosity of such Preparations are, for example, in a range from about 1 to 60000 mPas.

The preparations are usually redispersible, d. H. the dispersed particles can be dried of the preparation and subsequently can be dispersed again, essentially without reducing the dispersibility and especially with magnetic particles without the absorbency across from magnetic and electromagnetic alternating fields deteriorated.

For certain areas of application, for example in pharmacy, the Cosmetics or for the production of adhesives as a result of the creation of alternating magnetic, electrical or electromagnetic fields induced warming Harden or separating an existing adhesive bond, it may be necessary be one or more in addition to the surface-coated nanoscale particles contained in the continuous phase Separate components in a step d2). With those to be separated Components can be, for example, ionic impurities from the production of the nanoscale particles to excess coating agent or act as aids used in the coating. Becomes for example in surface coating a water-miscible solvent with a boiling point above that of water, so can this is exchanged for water in step d2) by dialysis.

The method according to the invention allows the provision of suspensions of nanoscale particles, which in dependence of the surface coating agent (s) can be suspended in a variety of different media. The suspending agent used in step d) is preferably selected under water, organic solvents, polymerizable monomers, polymers and mixtures thereof.

Suitable organic suspending agents are selected, for example, from oils, fats, waxes, esters of C ₆ -C ₃₀ monocarboxylic acids with mono-, di- or trihydric alcohols, saturated acyclic and cyclic hydrocarbons, fatty acids, low molecular weight alcohols, fatty alcohols and mixtures from that. These include, for example, paraffin and paraffin oils, mineral oils, linear saturated hydrocarbons with generally more than 8 carbon atoms, such as tetradecane, hexadecane, octadecane etc., cyclic hydrocarbons such as cyclohexane and decahydronaphthalene, waxes, esters of fatty acids, silicone oils etc. , B. linear and cyclic hydrocarbons and alcohols.

In a preferred embodiment the preparations are an adhesive composition. The coherent Phase of adhesive compositions includes at least one for use polymer suitable in adhesives and / or at least one polymerizable Monomer.

In principle, all polymers suitable for adhesives can be used as the coherent phase (binder matrix) for the adhesives. Examples for the thermoplastic softenable adhesives are the hot melt adhesives based on ethylene-vinyl acetate copolymers, polybutenes, styrene-isoprene-styrene or styrene-butadiene-styrene copolymers, thermoplastic elastomers, amorphous polyolefins, linear, thermoplastic polyurethanes, copolyesters, polyamide resins, polyamide / EVA copolymers, polyaminoamides based on dimer fatty acids, polyesteramides or polyetheramides. In addition, the known reaction adhesives based on one- or two-component polyurethanes, one- or two-component polyepoxides, silicone polymers (one- or two-component), silane-modified polymers, as described, for example, by G. habenicht, are also suitable in principle. Applications ", 3rd edition, 1997 in Chapter 2.3.4.4. The (meth) acrylate-functional reactive adhesives based on peroxidic hardeners, anaerobic hardening mechanisms, aerobic hardening mechanisms or UV hardening mechanisms are also suitable as an adhesive matrix. Specific examples of the incorporation of thermally labile groups in reactive adhesives for the purpose of later breaking these bonds are the adhesives according to WO 99/07774, in which at least one structural component contains di- or polysulfide bonds. In a particularly preferred embodiment, these adhesives can also contain solid cleavage reagents in crystalline, encapsulated, chemically blocked, topologically or sterically inactivated or kinetically inhibited, finely dispersed form, as they are in the as yet unpublished form DE-A-199 04 835 on pages 14 to 16. Another possibility is the use of polyurethane adhesives, which act as a cleavage agent in the DE-A-198 32 629 disclosed amine derivatives included. The cleavage agents disclosed in the two aforementioned documents are expressly part of the present invention.

The coherent phase can be activated thermally chemically reacting adhesives generally contain one or several components that are accessible to a polyreaction. These include, for example Adhesives, the polyisocyanates with capped thermally activated Isocyanate groups and a component with reactive towards isocyanate groups Groups such as B. contain a polyol.

The according to the inventive method available surface-coated Nanoscale particles and their suspensions are suitable for a large number the one mentioned at the beginning Uses. This is especially true for Suspensions containing particles with magnetic, ferroelectric or contain piezoelectric properties and which can be affected alternating magnetic, electrical or electromagnetic fields heat to let. These are advantageously suitable for production of adhesives and sealants, which are caused by the application of magnetic, electrical or electromagnetic alternating fields induced warming Harden or where an existing adhesive bond is separated.

Are particularly advantageous for this uses superparamagnetic nanoscale particle suspensions. After this method according to the invention enable obtained superparamagnetic, nanoscale particles due to their uniformity in particle size distribution and morphology that in the preparations a sharp resonance frequency is achieved, so that such preparations significantly improved Energy use versus have those using methods from the prior art be preserved.

• a) eine Suspension nanoskaliger Teilchen bereitstellt,
• b) die Suspension mit Ultraschall behandelt, wobei der Energieeintrag pro 1g dispergierter Teilchchen und 1 Minute mindestens 100 J beträgt,
• c) wenigstens ein Beschichtungsmittel zugibt und in innigem Kontakt mit dem suspendierten Teilchen bringt,
• d) gegebenenfalls nach einer Aufarbeitung das Suspendiermittel entfernt.

The invention also relates to a method for producing nanoscale particles which have a coating on at least part of their surface, in which

• a) provides a suspension of nanoscale particles,
• b) the suspension is treated with ultrasound, the energy input per 1 g of dispersed particles and 1 minute being at least 100 J,
• c) adding at least one coating agent and bringing it into intimate contact with the suspended particle,
• d) the suspending agent is optionally removed after working up.

Regarding more preferred and suitable embodiments of the particles used, suspending agents and process measures reference is made to what was said before.

The invention is based on the following, not restrictive Examples closer explained.

To produce dispersions according to the invention, a Sonopuls ^® Ultra is used as the ultrasound device Sound homogenizer HD 2200 from Bandelin electronic GmbH & Co. KG with a cone tip 76 made of titanium and a titanium plate TT 13.

Example 1:

Making one with Zinc-doped nano-nickel ferrite

Surface modification with a monoalkoxysilane

10.15 g of Fe ₂ (SO ₄ ) ₃ .7H ₂ O are dissolved in 10 ml of H ₂ O and heated to 80 ° C. 2.10 g NiSO ₄ · 6H ₂ O and 3.45 g ZnSO ₄ · 7H ₂ O are dissolved in 2.5 ml H ₂ O and also heated to 80 ° C. 8 g NaOH are dissolved in 100 ml H ₂ O and heated to 80 ° C. The metal salt solutions are combined shortly before the precipitation. Added to the NaOH solution with vigorous stirring and stirred at 80 ° C. for 30 min. After sedimentation over a permanent magnet, the precipitate is washed several times with water and then twice with 400 ml of 2-propanol. To produce a 10% by weight nanoscale dispersion in 2-propanol, treatment is carried out for 10 minutes with an ultrasound homogenizer, as described at the beginning. 3 ml of bis (N-methylbenzamido) ethoxymethylsilane are dissolved in 80 ml of dry ethanol and added dropwise to the suspension with vigorous stirring. The mixture is then boiled under reflux for 5 h and then the solvent is removed on a rotary evaporator and the ferrite obtained which has been surface-modified with a monoalkoxysilane is dried.

The 1 shows the microwave absorption on a dispersion of particles from Example 1. The microwave frequency was 1.4 GHz. To carry out the measurement shown, about 200 mg of solution were placed in a plastic bowl on a microstrip waveguide which carried microwaves of frequency F = 1.4 GHz. The percentage change in the microwave level on this line was measured as a function of the magnetic field strength (B = 0 to 20 mT), which was supplied to the sample by an additional electromagnet.

1 shows two sharply defined minima of the microwave signal for the dispersion according to the invention. This proves that the nanoparticulate preparation obtained by the process according to the invention is essentially agglomerate-free and is well suited for energy input by a high-frequency alternating magnetic field, as is required, for example, in the alternating-field-induced heating of adhesive compositions with the aim of modifying the adhesive properties.

Example 2:

Production of dispersions Zn-doped surface modified Nano-nickel ferrites by the method according to the invention and using a conventional one Ultrasonic bath (comparison)

3.80 g NiCl ₂ · 6H ₂ O and ZnCl 3,27g ₂ are dissolved in 5 ml demineralised water and heated with stirring to 60 ° C. 21.62 g of FeCl ₃ .6H ₂ O are dissolved in 20 ml of demineralized water and also heated to 60 ° C. with stirring. 16 g NaOH are dissolved in 200 ml H ₂ O and heated to 80 ° C. Shortly before the precipitation, the metal salt solutions are combined, added to the NaOH solution with vigorous stirring and stirred at 80 ° C. for 20 minutes. After sedimentation over a permanent magnet, the precipitate obtained is washed twice with 300 ml of demineralized H ₂ O and centrifuged (3500 rpm, 10 min). The precipitate is divided into two equal portions and suspended in 100 ml of isopropanol with stirring. Sample A (comparison) is treated for 9 minutes with a conventional ultrasonic bath (power 200 W) and sample B (according to the invention) for 9 minutes with the ultrasonic homogenizer described above (power 200 W, treatment with 75% of the power). 5.0 g of hexadecyltrimethoxysilane in 20 ml of isopropanol are then added to both samples and the solutions obtained are stirred overnight at room temperature. The dispersion obtained from sample A settled completely within 10 hours after the stirring had ended. In the dispersion obtained from sample B, no solid had separated out after 7 days.

One obtained by drying Sample B Powder leaves z. B. in toluene to obtain a stable nanoscale particle dispersion redisperse.

Claims (12)

Process for producing a suspension comprising nanoscale particles suspended in a continuous phase, which have a coating on at least part of their surface, in which a) nanoscale particles are provided and suspended in a liquid forming the continuous phase, b) those in step a) suspension obtained treated with ultrasound, the energy input per 1 g dispersing ter particles and 1 minute is at least 100J, c) at least one coating agent is added and brought into intimate contact with the suspended particles. The method of claim 1, wherein the step c) suspension obtained additionally undergoes at least one workup step d) which is selected under d1) separating at least part of the continuous Phase-forming liquid, d2) Cut off at least one additional one to the surface-coated nanoscale particles contained in the continuous phase Component, d3) adding at least one suspending agent and if necessary, resuspending the nanoscale particles, and Combinations of these. Method according to one of the preceding claims, wherein the liquid used in step a) is selected under water, water-miscible organic solvents and mixtures from that. Method according to one of the preceding claims, wherein the suspension obtained in step a) has a solids content of at the most 15% by weight. Method according to one of the preceding claims, wherein in step b) the energy input is in a range from 200 to 700 J g ^-1 min ^-1 . Method according to one of the preceding claims, wherein the ultrasound power density achieved in step b) is at least 100 W / cm ³ . Method according to one of the preceding claims, wherein the coating agent used in step c) is selected among compounds with ionogenic, ionic and / or nonionic surfactants Groups. A method according to claim 7, wherein the coating agent at least one silane of the general formula (I) SiR ¹ _x R ² _4-x (I) comprises, wherein the radicals R ¹ independently of one another represent hydrolytically non-cleavable groups, it being possible for two radicals R ¹ which are bonded to two different silanes of the formula (I) to also jointly represent a group bridging these silanes, the radicals R ² independently represent hydroxyl groups or hydrolytically removable groups, and x represents an integer from 0 to 3. The method of claim 8, wherein the silane of formula (I) has one, two or three radicals R ² which are alkoxy. Method according to one of the preceding claims, wherein the nanoscale particles are paramagnetic and / or ferromagnetic Include particles. The method of claim 2, wherein in step d3) suspending agent used is selected from water, organic solvents polymerizable monomers, polymers and mixtures thereof. Process for the production of nanoscale particles, which have a coating on at least part of their surface, where you a) provides a suspension of nanoscale particles, b) the suspension is treated with ultrasound, the energy input is at least 100 J per 1 g of dispersed particles and 1 minute, c) Adds at least one coating agent and in intimate contact with the suspended particle, d) if necessary after a working up the suspension medium removed.