Title of Invention	A METHOD OF DISPERSING CARBON NANOTUBES IN A CONTINUOUS PHASE
Abstract	The invention relates to a method for dispersing carbon nanotubes (CNTs) in a continuous phase, especially in at least one dispersing agent. In said method, the carbon nanotubes, which are especially not subjected to a preliminary treatment, are dispersed in a continuous phase, particularly in at least one dispersing agent, in the presence of at least one dispersing agent while supplying enough power for the dispersion. The invention further relates to the dispersions obtained in said manner and the use thereof. The inventive method allows the carbon nanotubes (CNTs) to be dispersed at high concentrations and with a long shelf life.

Title of Invention

A METHOD OF DISPERSING CARBON NANOTUBES IN A CONTINUOUS PHASE

Abstract

The invention relates to a method for dispersing carbon nanotubes (CNTs) in a continuous phase, especially in at least one dispersing agent. In said method, the carbon nanotubes, which are especially not subjected to a preliminary treatment, are dispersed in a continuous phase, particularly in at least one dispersing agent, in the presence of at least one dispersing agent while supplying enough power for the dispersion. The invention further relates to the dispersions obtained in said manner and the use thereof. The inventive method allows the carbon nanotubes (CNTs) to be dispersed at high concentrations and with a long shelf life.

Full Text	Dispersion method The present invention relates to a method of dispersing carbon nanotubes (CNTs) in a continuous phase, especially in at least one dispersion medium, and also to the dispersions themselves that are obtainable in this way, and to their use. Carbon nanotubes (CNTs for carbon nanotubes) are microscopically small tubular structures (i.e., molecular nanotubes) of carbon. Their walls - like those of the fullerenes or like the planes of graphite - are composed essentially exclusively of carbon, the carbon atoms occupying a honeycomblike structure with hexagons and with three bond partners in each case, this structure being dictated by the sp2 hybridization of the carbon atoms. Carbon nanotubes derive accordingly from the carbon planes of graphite which have, so to speak, been rolled up to form a tube: The carbon atoms form a honeycomblike hexagonal structure and three bond partners in each case. Tubes with an ideally hexagonal structure have a uniform thickness and are linear; also possible, however, are bent or narrowing tubes which contain pentagonal carbon rings. Depending on the way in which the honeycomb network of the graphite is rolled to form a tube ("straight" or "oblique"), there are helical (i.e., wound in the manner of a screw) and also nonmirror-symmetric structures, i.e., chiral structures. A distinction is made between _single-wall carbon nanotubes (SWCNTs or SWNTs) and multiwall carbon nanot_ubes (MWCNTs or MWNTs) , between open or closed carbon nanotubes (i.e., with a "cap", which for example is a section of a fullerene structure), and also between empty and filled (with, for example, silver, liquid lead, noble gases, etc.) carbon nanotubes. The diameter of the carbon nanotubes (CNTs) is in the region of a few nanometers (e.g., 1 to 50 nm), although carbon nanotubes (CNTs) with tube diameters of only 0.4 nm have already been prepared. Lengths ranging from several micrometers up to millimeters for individual tubes and up to a few centimeters for tube bundles have already been attained. Depending on the detail of the structure, the electrical conductivity within the carbon nanotubes is metallic or semiconducting. There are also carbon nanotubes known which at low temperatures are superconducting. Transistors and simple circuits with semiconducting carbon nanotubes have already been produced. Additionally, attempts have already been made to carry out specific production of complex circuits from different carbon nanotubes. The mechanical properties of carbon nanotubes are outstanding: CNTs have - for a density of, for example, 1.3 to 1.4 g/cm3 - an enormous tensile strength of several megapascals; in comparison to this, steel, for a density of at least 7.8 g/cm3, has a maximum tensile strength of only about 2 MPa, thus giving a ratio of tensile strength to density, arithmetically, which for some CNTs is at least 135 times better than for steel. Of particular interest for the field of electronics are the current rating and the electrical and thermal conductivities: The current rating is by estimation 1000 times higher than in the case of copper wires, whereas the thermal conductivity at room temperature is almost twice as high as that of diamond. Since CNTs may also be semiconductors, they can be used to manufacture outstanding transistors which withstand higher voltages and temperatures - and hence higher clock frequencies - than silicon transistors; functioning transistors have already been produced from CNTs. Furthermore, CNTs can be used to realize nonvolatile memories. CNTs can also be used in the field of metrology (e.g., scanning tunneling microscopes) . On the basis of their mechanical and electrical properties, carbon nanotubes can also find application in plastics: As a result, for example, the mechanical properties of the plastics are greatly improved. Furthermore, it is possible in this way to produce electrically conducting plastics. Carbon nanotubes (CNTs) are commercially available and are supplied by numerous manufacturers (e.g., by Bayer MaterialScience AG, Germany; CNT Co. Ltd., China; Cheap Tubes Inc., USA; and Nanocyl S.A., Belgium). Corresponding manufacturing processes are familiar to the skilled worker. Thus, for example, carbon nanotubes (CNTs) can be prepared by arc discharge between carbon electrodes, for example; by means of laser ablation ("vaporization") starting from graphite; or by catalytic decomposition of hydrocarbons {chemical vapor deposition, CVD for short). The properties described above for the carbon nanotubes (CNTs) and the possible applications which arise from these properties have awoken great interest. In particular, for a range of applications, there is a need for the carbon nanotubes (CNTs) to be provided in a readily manageable form, preferably in the form of dispersions. The dispersing of carbon nanotubes (CNTs) poses a great challenge, since the carbon nanotubes (CNTs) are very difficult to convert into stable dispersions, especially because the carbon nanotubes (CNTs) possess a very high aspect ratio and are present in highly agglomerated and/or coiled forms. In the prior art, therefore, there has been no lack of attempts to stably disperse carbon nanotubes (CNTs). The methods known from the prior art, however, are not very suitable for generating stable, concentrated dispersions of carbon nanotubes (CNTs): in the majority of cases the methods of the prior art do not lead to storage-stable dispersions, and, moreover, the concentration of carbon nanotubes (CNTs) in the prior- art dispersions is usually extremely small. Thus, certain prior-art methods are aimed first at modifying the surface of the carbon nanotubes (CNTs) to be dispersed, by means of a costly and inconvenient prior pretreatment, particularly for the purpose of making the surface polar in order to facilitate subsequent dispersing. Methods suitable for modifying the carbon nanotubes (CNTs) are, for example, oxidative processes, especially chemical pretreatment, halogenation, or other polarization processes for modifying the surfaces of the carbon nanotubes (CNTs). One method of this kind, which provides, for example, for prior fluorination of the surfaces of the carbon nanotubes (CNTs) prior to their dispersing, is described for example in US 6 827 918 B2. A disadvantage of these methods is the costly and inconvenient pretreatment, which particularly when implemented on an industrial scale results in more difficult implementation of the method, with significantly higher costs. Also described in the prior art have been methods which convert the carbon nanotubes into aqueous dispersions in the presence of a water-soluble polymer material (cf., e.g., US 2004/0131859 Al and WO 02/076888 Al) . These methods, however, have the disadvantage that, on the one hand, they are not universally employable, but instead are restricted to aqueous dispersion media, and, on the other hand, that they lead only to dispersions having relatively low carbon nanotube (CNT) contents. The prevailing object of the two aforementioned publications, instead, is the conversion of the dispersions described therein into a redispersible powder of carbon nanotubes (CNTs). The above-described methods of the prior art usually result in inhomogeneous dispersions, often lacking long-term stability, of carbon nanotubes (CNTs), with low concentrations or contents of CNTs. Furthermore, the prior-art dispersions - in comparison to the pure dispersion medium - exhibit a high to extreme increase in viscosity, coupled with low particle contents of carbon nanotubes (CNTs) , of only up to about 1% by weight. In relation to industrial implementation, these prior- art dispersions are associated with a great disadvantage, and consequently there is an increased demand for improved dispersions of carbon nanotubes (CNTs) in various media. It is an object of the present invention, therefore, to provide a method of preparing dispersions of carbon nanotubes (CNTs), the intention being that the disadvantages outlined above and associated with the prior art should be at least substantially avoided or else at least attenuated. A further object of the present invention is to provide dispersions of carbon nanotubes (CNTs) having properties which are improved in comparison to the corresponding prior-art dispersions, more particularly having increased storage stabilities and/or having higher carbon nanotube (CNT) contents, preferably in tandem with good manageability, such as effective fluidity, etc. The applicant has now surprisingly found that the problem outlined above can be efficiently solved if the carbon nanotubes (CNTs) are dispersed in a continuous phase, especially in at least one dispersion medium, in the presence of at least one dispersant (dispersing agent), with introduction of an energy input which is sufficient for dispersing. In an entirely surprising way it has now in fact been found that, through the combination of a suitable dispersant (dispersing agent) in interaction with high energy inputs, especially high shear forces, it is possible to provide a gentle and inexpensive method of stably dispersing carbon nanotubes (CNTs) in significantly higher concentrations and in a multiplicity of dispersion media. To solve the problem outlined above, therefore, the present invention proposes a dispersion method as per claim 1. Further, advantageous properties of the method of the invention are subject matter of the relevant dependent method claims. Further subject matter of the present invention are the dispersions of carbon nanotubes (CNTs) that are obtainable by the method of the invention, and as are defined or described in the corresponding claims directed to the dispersions themselves. Finally, a further subject of the present invention is the use of the dispersions of carbon nanotubes (CNTs) which are obtainable by the method of the invention, such use being as defined or described in the corresponding use claims. The present invention - according to a first aspect of the present invention - accordingly provides a method of dispersing carbon nanotubes (CNTs) in a continuous phase, especially in at least one dispersion medium, i.e., therefore, a method of preparing dispersions of carbon nanotubes (CNTs) in a continuous phase, especially in at least one dispersion medium, the carbon nanotubes (CNTs) being dispersed, especially without prior pretreatment of the carbon nanotubes (CNTs), in a continuous phase, especially in at least one dispersion medium, in the presence of at least one dispersant (dispersing agent), with introduction of an energy input sufficient for dispersing. With regard to the concept of the dispersion, as it is used in the context of the present invention, reference may be made in particular to DIN 53900 of July 1972, according to which the concept of the dispersion is a designation for a system (i.e., disperse system) of two or more phases, of which one phase is continuous (namely the dispersion medium) and at least one further phase is finely divided (namely the dispersed phase or the dispersoid; in this case the carbon nanotubes). In the context of the present invention the concept of the dispersion is designated exclusively in relation to the designation of suspensions, i.e., dispersions of insoluble particulate solids in liquids. The concept of the dispersant - also designated, synonymously, as dispersing agent, dispersing additive, wetting agent, etc - as used in the context of the present invention designates, generally, substances which facilitate the dispersing of particles in a dispersion medium, especially by lowering the interfacial tension between the two components particles to be dispersed, on the one hand, and dispersant, on the other hand - and so by inducing wetting. Consequently there are a multiplicity of synonymous designations for dispersants (dispersing agents) in use, examples being dispersing additive, antisettling agent, wetting agent, detergent, suspending or dispersing assistant, emulsifier, etc. The concept of the dispersant should not be confused with the concept of the dispersion medium, the latter designating the continuous phase of the dispersion (i.e., the liquid, continuous dispersion medium). In the context of the present invention the dispersant, additionally, serves the purpose of stabilizing the dispersed particles as well (i.e., the carbon nanotubes) , i.e., of holding them stably in dispersion, and of avoiding or at least minimizing their reagglomeration in an efficient way; this in turn leads to the desired viscosities of the resulting dispersions, since, in this way, readily manageable, fluid systems result in practice - even in the case of high concentrations of the dispersed carbon nanotubes. Without the use of the dispersant, in contrast, there would be such an increase in the viscosity of the resulting dispersions, as a result of unwanted reagglomeration of the dispersed CNTs, that - at least at relatively high CNT concentrations - there would in practice no longer be manageable systems resulting, since those systems would have too high a viscosity or too low a fluidity. For further details relating to the terms "dispersoid", "dispersing", "dispersant", "disperse systems", and "dispersion", reference may be made, for example, to Rompp Chemielexikon, 10th edition, Georg Thieme Verlag, Stuttgart/New York, Volume 2, 1997, pages 1014/1015, and also to the literature referred to therein, the entire disclosure content of which is hereby incorporated by reference. A particular feature of the method of the invention is to be seen in the fact that, in accordance with the invention, the dispersing operation takes place with sufficient input of energy (e.g., input of shearing energy) ; on the one hand the energy introduced must be sufficient to provide the energy needed for dispersing, especially to disrupt the agglomerates, conglomerates, coils, etc formed by the carbon nanotubes (CNTs), but on the other hand it must not exceed a certain level above which destruction of the carbon nanotubes (CNTs) begins - and this must be the case in the presence of a suitable dispersant (dispersing agent) which is capable of stabilizing the individual carbon nanotubes (CNTs) and of preventing reagglomeration occurring again, and also of facilitating the subseguent dispersing and in that way stabilizing the resultant dispersions. With the method of the invention it is possible in a surprising way to obtain relatively high concentrations of carbon nanotubes (CNTs) in the resultant dispersions. In particular the method of the invention can be used to prepare dispersions having solids contents, in terms of carbon nanotubes (CNTs), of 5% by weight or more, based on the resultant dispersions. In general the carbon nanotubes (CNTs) are dispersed in amounts of 1 x 10-5% to 30%, in particular 1 x 10-4% to 20%, preferably 1 x 10-3% to 10%, more preferably 1 x 10-2% to 7.5%, very preferably 1 x lO-1 to 5%, by weight, based on the resultant dispersions, in the continuous phase. In order to allow economically rational application, the method of the invention ought to be implemented or concluded within a certain, or relatively short, period of time, which in turn requires a particular energy input per unit time. Generally speaking, the method of the invention, or the dispersing operation, is carried out within a period of 0.01 to 30 minutes, especially 0.1 to 20 minutes, preferably 0.2 to 15 minutes, more preferably 0.5 to 10 minutes, very preferably 0.5 to 5 minutes. Nevertheless, owing to a particular case, or relative to the application, it may be necessary to deviate from the times specified above, without departing from the scope of the present invention. As outlined above, it is necessary, in order to carry out the dispersing operation, for there to be a sufficient input of energy into the dispersion medium, which on the one hand must be sufficient to ensure reliable dispersing of a carbon nanotubes (CNTs), and on the other hand must not be so high that there is destruction of the carbon nanotubes (CNTs) or of their structures. The provision of the required energy input is accomplished preferably by means of ultrasound treatment. Nevertheless, other possibilities can also be realized in the context of the present invention, an example being the application of high-pressure nozzles, although the treatment by means of ultrasound is preferred in accordance with the invention. In general, the amount of energy introduced can vary within wide ranges. In particular the amount of energy introduced, calculated as energy introduced per unit quantity of carbon nanotubes (CNTs) to be dispersed, is 5000 to 500 000 kJ/kg, especially 10 000 to 250 000 kJ/kg, preferably 15 000 to 100 000 kJ/kg, more preferably 25 000 to 50 000 kJ/kg. Nevertheless, relative to the application or as a result of a specific case, it may be necessary to deviate from the aforementioned figures, without departing the scope of the present invention. Typically the dispersing operation proper is preceded by a method step in which the carbon nanotubes (CNTs) for subsequent dispersion are contacted with the continuous phase, especially with the dispersion medium, and with the dispersant (dispersing agent), and also, where appropriate, with further constituents or ingredients of the dispersion, and these components are homogenized with one another, especially with corresponding input of energy, preferably with stirring. The energy input required for this purpose, however, is smaller than for the dispersing operation as such, and so a customary stirring or mixing operation is sufficient for this purpose. In general, the method of the invention is carried out at temperatures below the boiling temperature of the continuous phase, especially of the dispersion medium. Preferably the method of the invention is carried out at temperatures in the range from 10 to 100°C, preferably 15 to 70°C. In this case it may where appropriate be necessary to carry out the dispersing operation with cooling, since the energy input results in an increase in the temperature of the resultant dispersion. As outlined above, an advantage of the present invention is to be seen in the fact that the dispersing operation is carried out without prior pretreatment of the carbon nanotubes (CNTs) to be dispersed, especially without prior oxidation, chemical treatment (e.g., with oxidizing agents, such as nitric acid, ozone, etc) , thermal treatment, polarization, halogenation or the like. In the context of the method of the invention it is possible to use virtually any desired carbon nanotubes (CNTs), of the kind preparable by processes known from the prior art or else available as commercial products (e.g., from Bayer MaterialScience AG, Leverkusen). The carbon nanotubes (CNTs) used in accordance with the invention may be, for example, single-wall carbon nanotubes (SWCNTs or SWNTs) or multiwall carbon nanotubes (MWCNTs or MWNTs), especially 2- to 30-wall, preferably 3- to 15-wall, carbon nanotubes. The carbon nanotubes (CNTs) used in accordance with the invention may have average internal diameters of 0.4 to 50 nm, especially 1 to 10 nm, preferably 2 to 6 nm, and/or average external diameters of 1 to 60 nm, especially 5 to 30 nm, preferably 10 to 20 nm. The carbon nanotubes (CNTs) used in accordance with the invention may have average lengths of 0.01 to 1000 μm, especially 0.1 to 500 [μm, preferably 0.5 to 200 μm, more preferably 1 to 100 [m. Furthermore, the carbon nanotubes (CNTs) used in accordance with the invention may have a tensile strength per carbon nanotube of at least 1 GPa, especially at least 5 GPa, preferably at least 10 GPa, and/or an elasticity modulus per carbon nanotube of at least 0.1 TPa, especially at least 0.5 TPa, preferably at least 1 TPa, and/or a thermal conductivity of at least 500 W/mK, especially at least 1000 W/mK, preferably at least 2000 W/mK, and/or an electrical conductivity of at least 103 S/cm, especially at least 0.5 x 104 S/cm, preferably at least 104 S/cm. Typically employed carbon nanotubes (CNTs) have a bulk density in the range from 0.01 to 0.3 g/cm3, especially 0.02 to 0.2 g/cm3, preferably 0.1 to 0.2 g/cm3, and are present in the form of agglomerates or conglomerates of a multiplicity of carbon nanotubes (CNTs), especially in highly coiled form. Inventively suitable carbon nanotubes (CNTs) are available commercially, as for example from Bayer MaterialScience AG, Leverkusen, an example being the product series Baytubes® (e.g., Baytubes® C 150 P). As far as the continuous phase or dispersion medium is concerned, it is possible in the context of the present invention, in principle, to employ aqueous-based, organic-based or aqueous-organic-based dispersion media, preference being given to using organic dispersion media. Typically the continuous phase used is a dispersion medium which is present in the liquid aggregate state under dispersing conditions, especially under atmospheric pressure (101.325 kPa) and in a temperature range from 10 to 100°C, preferably 15 to 70°C. In an inventively preferred way the dispersion medium used as the continuous phase is a dispersion medium which is selected from the group of (i) alcohols, especially straight-chain, branched or cyclic, monohydric or polyhydric alcohols, such as methanol, ethanol, butanol, ethylhexanol, decanol, isotridecyl alcohol, benzyl alcohol, propargyl alcohol, oleyl alcohol, linoleyl alcohol, oxo-process alcohols, neopentyl alcohol, cyclohexanol, fatty alcohols, and diols and polyols, such as glycols; (ii) ether alcohols, such as 2-methoxyethanol, monophenyl diglycol, phenylethanol, ethylene glycol, and propylene glycol; (iii) hydrocarbons, such as toluene, xylene, and aliphatic and/or cycloaliphatic benzine fractions, chlorinated hydrocarbons, such as chloroform and trichloroethane; (iv) ethers, especially cyclic and acyclic ethers, such as dioxane, tetrahydrofuran, and polyalkylene glycol dialkyl ethers; (v) carboxylic esters, especially monocarboxylic esters, such as ethyl acetate and butyl acetate; and dicarboxylic or polycarboxylic esters, such as dialkyl esters of C2 to C4 dicarboxylic acids ("Dibasic Esters"); (vi) ether esters, especially alkylglycol esters, such as ethylglycol acetate and methoxypropyl acetate; (vii) lactones, such as butyrolactone; (viii) plasticizers, especially phthalates; (ix) aldehydes and ketones, such as methyl isobutyl ketone, cyclohexanone, and acetone; (x) acid amides, such as dimethylformamide; (xi) N-methylpyrrolidone; and also mixtures of the aforementioned dispersion media. Furthermore, it is also possible in principle to employ ionic liquids or what are known as supercritical fluids as a dispersion medium. Water as well is a suitable dispersion medium in the context of the present invention. As far as the inventively used dispersant is concerned, it is more particularly a polymeric dispersant, especially a polymeric dispersant based on a functional polymer, preferably having a number-average molecular mass of at least 500 g/mol, preferably at least 1000 g/mol, more preferably at least 2000 g/mol. In particular the inventively used dispersant may be selected from the group of polymers and copolymers having functional groups and/or groups with pigment affinity, alkylammonium salts of polymers and copolymers, polymers and copolymers having acidic groups, comb copolymers and block copolymers, such as block copolymers having groups with pigment affinity, especially basic groups with pigment affinity, optionally modified acrylate block copolymers, optionally modified polyurethanes, optionally modified and/or salified polyamines, phosphoric esters, ethoxylates, polymers and copolymers having fatty acid radicals, optionally modified polyacrylates, such as transesterified polyacrylates, optionally modified polyesters, such as acid-functional polyesters, polyphosphates, and mixtures thereof. Furthermore it is possible in principle, as dispersants suitable in accordance with the invention, to use all of the dispersants, surfactants, wetting agents, etc, that are known for that purpose. In an inventively preferred way the compounds selected as dispersants are especially those compounds of the kind described in publications EP 1 593 700 Bl, EP 0 154 678 Bl, EP 0 318 999 Bl, EP 0 270 126 Bl, EP 0 893 155 Bl, EP 0 417 490 Bl, EP 1 081 169 Bl, EP 1 650 246 Al, EP 1 486 524 Al, EP 1 640 389 Al, EP 0 879 860 Bl, WO 2005/097872 Al, and EP 1 416 019 Al, the respective disclosure content of which is hereby incorporated in full by reference. These compounds are described or defined more closely in claims 13 to 17 (= EP 1 593 700 Bl), claim 18 ( = EP 0 154 678 Bl), claim 19 (= EP 0 318 999 Bl) , claim 20 (= EP 0 270 126 Bl), claim 21 (= EP 0 893 155 Bl), claim 22 (= EP 0 417 490 Bl) , claim 23 (= EP 1 081 169 Bl), claim 24 (= EP 1 650 246 Al), claim 25 ( = EP 1 486 524 Al) , claim 26 (= EP 1 640 389 Al) , claim 27 (= EP 0 879 860 Bl), claim 28 (= WO 2005/097872 Al), and claim 29 (= EP 1 416 019 Al). As far as the method of the invention is concerned, it can in principle be carried out in continuous operation or in discontinuous operation, and this can be done in a relatively small amount of time. On account of its low level of complexity, the method of the invention can be readily employed industrially, can be carried out flexibly and economically, and can be configured adaptably up to production on the tonne scale. In principle the method of the invention can be employed for any of a very wide variety of dispersion media, of dispersants or dispersing agents, and of carbon nanotubes (CNTs), and can be readily combined with further processes or process steps. As outlined at the outset, the dispersing of CNTs poses a great challenge, because the CNTs possess a very large aspect ratio and are present in a highly coiled form: for instance, the diameters range, for example, from 3 to 25 nm, but the lengths range, for example, up to about 10 mm. On account of the high degree of coiling, very high energy inputs or shearing forces are necessary in order to separate the CNTs. Where uncoiling is accomplished only by means of high energy input, without simultaneous use of suitable dispersants, the CNTs are only size-reduced, and not sufficiently stabilized, and so the resulting dispersions are inhomogeneous and lack long-term stability. The use of dispersants is aimed on the one hand at wetting the CNTs, in order to ensure easier and more gentle uncoiling, and on the other hand at stabilizing the resulting separated CNTs by coating with the dispersant, with the consequence that, with the method of the invention, stable homogeneous dispersions are obtained. Ideally the dispersions exhibit only a slight increase in viscosity, and high activity of the CNTs. In contrast, the methods described in the prior art usually result in inhomogeneous dispersions which lack long-term stability. Furthermore, the prior-art dispersions exhibit a high increase in viscosity in tandem with low particle contents of only about 1% at most. Surprisingly it has now been found that, in the context of the method of the invention, by combining suitable dispersants with high energy inputs or shearing forces, a gentle and cost-effective method is provided for stably dispersing CNTs in any of a very wide variety of media and at significantly higher concentrations. The method of the invention leads to dispersions having high carbon nanotube (CNT) contents or with high degrees of filling (above 5% by weight, for example, based on the resultant dispersions), and it accomplishes this at the same time as low viscosities and hence ready manageability. Furthermore, the dispersions obtainable by the method of the invention exhibit high storage stabilities. Accordingly the present invention - according to a second aspect of the present invention - provides dispersions of carbon nanotubes (CNTs) in a continuous phase, especially in at least one dispersion medium, which are obtainable by the method of the invention as outlined above. For further relevant details concerning the dispersions of the invention, reference may be made to the corresponding claims directed to the dispersions themselves. The dispersions according to the present invention that are obtainable by the method of the invention have an extraordinary stability, especially storage stability; in particular the dispersions of the invention are storage-stable over at least a week, preferably at least a month, more preferably at least three months, very preferably at least six months. As outlined above, the dispersions of the invention are, furthermore, fluid at room temperature and in this way are readily manageable. The dispersions prepared in accordance with the invention exhibit a newtonian or at most thixotropic and/or structurally viscous behavior, preferably a newtonian behavior. The dispersions obtainable in accordance with the invention are suitable for a multiplicity of applications. Further provided by the present invention - in accordance with a third aspect of the present invention - is, accordingly, the inventive use of the dispersions obtainable by the method of the invention, as is defined in the corresponding use claims. Thus, for example, the dispersions of the invention are suitable for application in the field of electronics, as for example in the field of computer engineering and the computer industry, semiconductor engineering and the semiconductor industry, and metrology and the metrological industry, for the purpose, for example, of producing conducting or semiconducting structures, nanoelectric structures and devices, transistors, nonvolatile memories, displays and screens and their components, and also metrological and computer parts and components, such as circuits, diodes, and the like, etc. Additionally the dispersions of the invention are suitable for application or incorporation in plastics and polymeric compositions, coatings, paints, inks, composite materials, and the like. By way of example the dispersions of the invention can be used in order to increase the electrical conductivity and/or to improve the mechanical properties, especially the strength, preferably in relation to the aforementioned materials (i.e., plastics and polymeric compositions, coatings, paints, inks, composite materials, etc) . Thus, for example, the dispersions of the invention are suitable as reinforcing materials in the aforementioned materials. Furthermore, the dispersions prepared in accordance with the invention are suitable for producing bundles, fibers, mats, and other coherent structures of carbon nanotubes (CNTs) (e.g., after removal of the dispersion medium). Moreover, the dispersions of the invention are suitable for application in the field of aerospace technology. A further field for application of the dispersions of the invention is the field of cooling technology, especially in relation to the production of heat sinks for any of a very wide variety of applications (e.g., for GSM base stations, as CPU coolers, etc) . Finally the dispersions of the invention can also be used for shielding from electrical and/or electromagnetic radiation, especially in the aforementioned materials (i.e., plastics and polymeric compositions, coatings, paints, inks, composite materials, etc). Further embodiments, modifications, and variations of the present invention are readily evident and realizable for the skilled worker on reading the description, without departing the scope of the present invention. The present invention is illustrated by reference to the examples which follow, but which are not intended to restrict the present invention. Examples: Examples A: The particular advantages of the invention are described below, using as an example the dispersing of CNTs in PMA (propylene glycol monomethyl ether or methoxypropyl acetate) as dispersion medium, using different dispersants and an ultrasound dispersing unit. First of all various comparative experiments with and without dispersants, with only a Dispermat, were carried out, but in all cases the result was disappointing: The dispersions were very inhomogeneous and underwent complete sedimentation after a time of just a few hours to a day. Similar comparative experiments with the ultrasonic transducer, in contrast, showed better outcomes: Thus a 0.1% dispersion of CNTs without dispersant undergoes only slight sedimentation, but is still very inhomogeneous. In this case the agglomerates are in fact disrupted, but the CNTs are damaged to a high degree and are not sufficiently stabilized. A dispersion prepared in this way is not suitable for industrial use. The addition of a dispersant, though, increases the result considerably. Thus, if only ultrasound or only dispersant is used, the experiments result in unstable and inhomogeneous dispersions or suspensions with significant sedimentation behavior. In inventive experiments, different dispersants were employed in different quantities, in combination with the input of ultrasound, leading to the desired outcomes. As a first experimental series, 1% dispersions of MWCNTs in methoxypropyl acetate (PMA) were prepared with use of ultrasound (table 2) . The results were evaluated on the basis of the visual impression directly after the dispersing operation; the sedimentation behavior; and the viscosity. The dispersions are prepared in the same way as described in example B below. In order to allow better assessment of the sedimentation behavior in particular, a second step saw more highly dilute dispersions being prepared with these dispersants (table 3) . At a concentration of 0.1%, the dispersion stabilized with DISP-I showed the best result. In the course of the experiments it became apparent, surprisingly, that the combination of DISP-I and ultrasound produced very good results. The results were so good that the system could also be increased to a 5% CNT content, and the dispersions exhibited outstanding properties and excellent storage stabilities. A further increase to 10% or more CNT content was realized as well. Additionally it was observed that the method of the invention - irrespective of the mode of preparation of the CNTs - can be realized successfully, in other words that the method of the invention is suitable for use universally for CNTs and does not require prior surface modification of the CNTs (in situ or post-synthesis), thereby allowing massive cost savings. This results in immense opportunities for the industrial use of CNTs in numerous applications, since the dispersions have the following advantages: high degrees of filling, or more than 5% by weight CNTs homogeneous dispersions with long-term stability gentle dispersion method (gentle uncoiling of the CNTs) can be used universally for all commercially available CNTs cost-effective dispersing method, equally upscalable and suitable for both batch and continuous operation can be combined with further process steps low viscosities realizable if needed addition of further functionalized additives possible functionalization of the dispersant possible. In further experiments it was shown that the method of the invention can also be transposed to other solvents. When water or extremely nonpolar media are employed, of course, the requirements concerning the functional groups of the dispersant are different. Furthermore, the dispersions prepared in accordance with the invention can be processed further, for orientation of the CNTs in the dispersion medium matrix, for example. Hence it is possible to carry out parallel alignment of CNTs in an electrical field. For this purpose, however, the CNTs must be present in individualized and homogenously dispersed form, ideally at a high concentration. This is now ensured for the first time through the method of the invention. A subsequent parallel orientation is therefore possible, and for many applications is essential. A corresponding experimental system is designed as follows: In a tank, a suspension of the agglomerated CNTs in the desired dispersion medium is introduced, together with the dispersant, and is then pumped in a circuit through a flow cell, in which the dispersing operation takes place by means of ultrasound. The resulting dispersion can then either be recycled to the tank and dispersed in the circuit until the desired degree of dispersion has been achieved (batch operation) , or can be pumped into a further flow cell with ultrasound dispersing unit (continuous operation). This may then be followed by mixing, as for example with a resin (or a paint, a coating liquid, etc) , and subsequent passage through an electrical field provides for parallel alignment of the CNTs. The parallel alignment may alternatively take place at a later point in time. The prerequisite is merely a stable dispersion of individualized CNTs, something which is ensured by the method of the invention. Examples B: Preparation of a 1.0% dispersion of CNTs (Baytubes®, e.g., Baytubes® C 150 P) in methoxypropyl acetate (PMA) with 100% of DISP-I A 350 ml PE beaker is charged with 196 g of PMA and 2 g of DISP-I, and this initial charge is homogenized using a Dispermat at 1000 rpm with a toothed disc (d = 40 mm) . 2 g of CNTs are added to the mixture, and the PE vessel is placed into a stainless steel double-wall vessel, cooled to 5°C, with water as the cooling medium. Dispersing takes place using an ultrasonotrode (d = 38 mm) , which is immersed to about 2 to 3 cm in the medium. With a power of approximately (500 ± 20) W, the suspension is dispersed for 1.5 to 2 min, in such a way that the temperature remains below 70°C. The result is a homogeneous, storage-stable, black dispersion of low viscosity. Viscosities Viscosity as a function of the degree of CNT filling To illustrate the increase in viscosity with increasing degree of CNT filling, the viscosities of different dispersions in PMA, with CNT contents in the range from 0.1% to 5%, were measured (fig. 1 and fig. 2). As can be seen, the viscosity rises exponentially with the concentration, but even at concentrations above 3% is still within a manageable range. Fig. 1 shows the viscosities of PMA dispersions with different CNT contents (0.1%, 0.5%, 1.0%, 2.0%, 3.0%, and 5.0%; curves considered from bottom to top), with a constant quantity of dispersant, of 200% by weight in relation to CNTs, and fig. 2 is a corresponding logarithmic plot of the viscosities of PMA dispersions having different CNT contents against the concentration of the CNTs. Viscosity as a function of the fraction of dispersant In view of the large surface area of the CNTs and their urge to form coils, a high dispersant fraction must be used. Consequently dispersant concentrations of 50% to 200% by weight (based on CNTs) were used. The measure used for the dispersing is again the viscosity. From fig. 3 it is evident that, from a dispersant concentration of 150%, the viscosity remains still at a low level. Significantly lower concentrations lead to higher viscosities. Fig. 3 shows a comparison of the viscosities of 1% dispersions of CNTs in PMA with different amounts of DISP-I (50%, 100%, 150%, and 200%, by weight, based on CNTs; curves considered from top to bottom). Comparison of different CNTs As is evident from fig. 4, the method of the invention for dispersing CNTs can be applied almost universally to a very wide variety of different kinds of CNTs. Fig. 4 shows by way of example the viscosities of 0.1% (bottom curves) and 1% (top curves) dispersions of CNTs in PMA, on the one hand for Baytubes® C 150 P from Bayer MaterialScience AG and on the other hand for CNTs from CNT Co., Ltd.) . It is clearly apparent that the viscosities are virtually identical, irrespective of the manufacturer from which the CNTs originate. Summary of the results The present results were determined under measuring conditions which "circumvent" the "wall gliding" of the samples and allow a comparison of the low-concentration and high-concentration CNT suspensions. The resulting measurements can admittedly not be considered to be absolute values, but do serve as a basis for an empirical comparison of the samples. The 0.1% and 1.0% unstabilized suspensions, without dispersant, of Baytubes® in PMA cannot be measured, owing to the sedimentation behavior. Through the method of the invention it is possible to prepare fluid pastes having a CNT content of more than 5% by weight. Of the wetting agents tested, DISP-I showed itself to be the most effective in terms of the viscosity level. The viscosity rises exponentially with the increase in the solids content of the CNTs and with the same application of dispersant (200% by weight of DISP-I). Measuring conditions ThermoHaake RS300 with UTCE/C electrical thermal conditioning unit Measurement system: 35 mm 1° cone/plate system Experimental mode: rotation in CSR mode {Controlled Shear Rate) All of the samples exhibit a strongly pronounced yield point. The visually sensorial testing, moreover, reflected thixotropic or structurally viscous behavior on the part of the samples. Optical microscopy images In order to obtain an impression of the degree of agglomeration and the quality of the dispersion, micrographs were produced of the different dispersions. Pictured below is a selection of samples with particularly good and particularly poor dispersion. Fig. 5 shows a ten-times magnification of a 0.1% dispersion of CNTs in PMA after ultrasound treatment without dispersant (very poor dispersion, large agglomerates). Fig. 6 shows a ten-times magnification of a 0.1% dispersion of CNTs in PMA after ultrasound treatment in the presence of 50% dispersant (DISP-II) (good and stable dispersion, few agglomerates, significantly homogeneous) . Fig. 7 shows a ten-times magnification of a 0.1% dispersion of CNTs in PMA after ultrasound treatment in the presence of 100% dispersant (DISP-I) (very good and very homogeneous dispersion, no large agglomerates any more, stable). Stabilities The dispersions prepared in accordance with the invention have now been stable at room temperature for about 4 months, and are not exhibiting any sedimentation of the CNTs. Even dispersions with CNT contents of 3% or more are indeed thixotropic but show no sedimentation of the CNTs over a relatively long time period. Dispersions prepared in other ways, in contrast, frequently exhibit complete phase separation after just hours. We claim. 1. A method of dispersing carbon nanotubes (CNTs) in a continuous phase, especially in at least one dispersion medium, characterized in that first, before the dispersing operation proper, a method step is carried out in which the carbon nanotubes (CNTs) are contacted and homogenized with a continuous phase, especially a dispersion medium, and at least one dispersant (dispersing agent), and subsequently the carbon nanotubes (CNTs) are dispersed in the continuous phase, especially the dispersion medium, in the presence of the dispersant, with introduction of an energy input sufficient for dispersing, in amounts of 1 x 1CT1 % to 30 % by weight, based on the resulting dispersion, the amount of energy introduced, calculated, as energy introduced per unit quantity of carbon nanotubes (CNTs) to be dispersed, being 15 000 to 100 000 kJ/kg. 2. A dispersion of carbon nanotubes (CNTs) in a continuous phase as the dispersion medium, the dispersion being obtained by the method of Claim 1. 3. The dispersion of claim 2, characterized in that the dispersion is storage-stable for at least 1 week. 4. The use of the dispersion of claim 2 in plastics and polymeric compositions, in coatings, in paints, in inks or in composite materials. 5. The use of the dispersion of claim 2 for producing bundles, fibers, mats, and other coherent structures of carbon nanotubes (CNTs). 6. The use of the dispersion of claim 2 in the field of electronics, aerospace technology and cooling technology. The invention relates to a method of dispersing carbon nanotubes (CNTs) in a continuous phase, especially in at least one dispersion medium, the carbon nanotubes, especially without prior pretreatment, being dispersed in a continuous phase, especially in at least one dispersion medium, in the presence of at least one dispersant (dispersing agent), with introduction of an energy input sufficient for dispersing, and also to the dispersions that are obtainable in this way, and to their use. With the method of the invention it is possible for the carbon nanotubes (CNTs) to be dispersed in high concentrations and with high storage stability.

Full Text

Dispersion method
The present invention relates to a method of dispersing
carbon nanotubes (CNTs) in a continuous phase,
especially in at least one dispersion medium, and also
to the dispersions themselves that are obtainable in
this way, and to their use.
Carbon nanotubes (CNTs for carbon nanotubes) are
microscopically small tubular structures (i.e.,
molecular nanotubes) of carbon. Their walls - like
those of the fullerenes or like the planes of
graphite - are composed essentially exclusively of
carbon, the carbon atoms occupying a honeycomblike
structure with hexagons and with three bond partners in
each case, this structure being dictated by the sp2
hybridization of the carbon atoms.
Carbon nanotubes derive accordingly from the carbon
planes of graphite which have, so to speak, been rolled
up to form a tube: The carbon atoms form a
honeycomblike hexagonal structure and three bond
partners in each case. Tubes with an ideally hexagonal
structure have a uniform thickness and are linear; also
possible, however, are bent or narrowing tubes which
contain pentagonal carbon rings. Depending on the way
in which the honeycomb network of the graphite is
rolled to form a tube ("straight" or "oblique"), there
are helical (i.e., wound in the manner of a screw) and
also nonmirror-symmetric structures, i.e., chiral
structures.
A distinction is made between _single-wall carbon
nanotubes (SWCNTs or SWNTs) and multiwall carbon
nanot_ubes (MWCNTs or MWNTs) , between open or closed
carbon nanotubes (i.e., with a "cap", which for example
is a section of a fullerene structure), and also
between empty and filled (with, for example, silver,
liquid lead, noble gases, etc.) carbon nanotubes.

The diameter of the carbon nanotubes (CNTs) is in the
region of a few nanometers (e.g., 1 to 50 nm), although
carbon nanotubes (CNTs) with tube diameters of only
0.4 nm have already been prepared. Lengths ranging from
several micrometers up to millimeters for individual
tubes and up to a few centimeters for tube bundles have
already been attained.
Depending on the detail of the structure, the
electrical conductivity within the carbon nanotubes is
metallic or semiconducting. There are also carbon
nanotubes known which at low temperatures are
superconducting.
Transistors and simple circuits with semiconducting
carbon nanotubes have already been produced.
Additionally, attempts have already been made to carry
out specific production of complex circuits from
different carbon nanotubes.
The mechanical properties of carbon nanotubes are
outstanding: CNTs have - for a density of, for example,
1.3 to 1.4 g/cm3 - an enormous tensile strength of
several megapascals; in comparison to this, steel, for
a density of at least 7.8 g/cm3, has a maximum tensile
strength of only about 2 MPa, thus giving a ratio of
tensile strength to density, arithmetically, which for
some CNTs is at least 135 times better than for steel.
Of particular interest for the field of electronics are
the current rating and the electrical and thermal
conductivities: The current rating is by estimation
1000 times higher than in the case of copper wires,
whereas the thermal conductivity at room temperature is
almost twice as high as that of diamond. Since CNTs may
also be semiconductors, they can be used to manufacture
outstanding transistors which withstand higher voltages
and temperatures - and hence higher clock frequencies -
than silicon transistors; functioning transistors have

already been produced from CNTs. Furthermore, CNTs can
be used to realize nonvolatile memories. CNTs can also
be used in the field of metrology (e.g., scanning
tunneling microscopes) .
On the basis of their mechanical and electrical
properties, carbon nanotubes can also find application
in plastics: As a result, for example, the mechanical
properties of the plastics are greatly improved.
Furthermore, it is possible in this way to produce
electrically conducting plastics.
Carbon nanotubes (CNTs) are commercially available and
are supplied by numerous manufacturers (e.g., by Bayer
MaterialScience AG, Germany; CNT Co. Ltd., China; Cheap
Tubes Inc., USA; and Nanocyl S.A., Belgium).
Corresponding manufacturing processes are familiar to
the skilled worker. Thus, for example, carbon nanotubes
(CNTs) can be prepared by arc discharge between carbon
electrodes, for example; by means of laser ablation
("vaporization") starting from graphite; or by
catalytic decomposition of hydrocarbons {chemical vapor
deposition, CVD for short).
The properties described above for the carbon nanotubes
(CNTs) and the possible applications which arise from
these properties have awoken great interest. In
particular, for a range of applications, there is a
need for the carbon nanotubes (CNTs) to be provided in
a readily manageable form, preferably in the form of
dispersions.
The dispersing of carbon nanotubes (CNTs) poses a great
challenge, since the carbon nanotubes (CNTs) are very
difficult to convert into stable dispersions,
especially because the carbon nanotubes (CNTs) possess
a very high aspect ratio and are present in highly
agglomerated and/or coiled forms.

In the prior art, therefore, there has been no lack of
attempts to stably disperse carbon nanotubes (CNTs).
The methods known from the prior art, however, are not
very suitable for generating stable, concentrated
dispersions of carbon nanotubes (CNTs): in the majority
of cases the methods of the prior art do not lead to
storage-stable dispersions, and, moreover, the
concentration of carbon nanotubes (CNTs) in the prior-
art dispersions is usually extremely small.
Thus, certain prior-art methods are aimed first at
modifying the surface of the carbon nanotubes (CNTs) to
be dispersed, by means of a costly and inconvenient
prior pretreatment, particularly for the purpose of
making the surface polar in order to facilitate
subsequent dispersing. Methods suitable for modifying
the carbon nanotubes (CNTs) are, for example, oxidative
processes, especially chemical pretreatment,
halogenation, or other polarization processes for
modifying the surfaces of the carbon nanotubes (CNTs).
One method of this kind, which provides, for example,
for prior fluorination of the surfaces of the carbon
nanotubes (CNTs) prior to their dispersing, is
described for example in US 6 827 918 B2.
A disadvantage of these methods is the costly and
inconvenient pretreatment, which particularly when
implemented on an industrial scale results in more
difficult implementation of the method, with
significantly higher costs.
Also described in the prior art have been methods which
convert the carbon nanotubes into aqueous dispersions
in the presence of a water-soluble polymer material
(cf., e.g., US 2004/0131859 Al and WO 02/076888 Al) .
These methods, however, have the disadvantage that, on
the one hand, they are not universally employable, but
instead are restricted to aqueous dispersion media,
and, on the other hand, that they lead only to

dispersions having relatively low carbon nanotube (CNT)
contents. The prevailing object of the two
aforementioned publications, instead, is the conversion
of the dispersions described therein into a
redispersible powder of carbon nanotubes (CNTs).
The above-described methods of the prior art usually
result in inhomogeneous dispersions, often lacking
long-term stability, of carbon nanotubes (CNTs), with
low concentrations or contents of CNTs. Furthermore,
the prior-art dispersions - in comparison to the pure
dispersion medium - exhibit a high to extreme increase
in viscosity, coupled with low particle contents of
carbon nanotubes (CNTs) , of only up to about 1% by
weight.
In relation to industrial implementation, these prior-
art dispersions are associated with a great
disadvantage, and consequently there is an increased
demand for improved dispersions of carbon nanotubes
(CNTs) in various media.
It is an object of the present invention, therefore, to
provide a method of preparing dispersions of carbon
nanotubes (CNTs), the intention being that the
disadvantages outlined above and associated with the
prior art should be at least substantially avoided or
else at least attenuated.
A further object of the present invention is to provide
dispersions of carbon nanotubes (CNTs) having
properties which are improved in comparison to the
corresponding prior-art dispersions, more particularly
having increased storage stabilities and/or having
higher carbon nanotube (CNT) contents, preferably in
tandem with good manageability, such as effective
fluidity, etc.

The applicant has now surprisingly found that the
problem outlined above can be efficiently solved if the
carbon nanotubes (CNTs) are dispersed in a continuous
phase, especially in at least one dispersion medium, in
the presence of at least one dispersant (dispersing
agent), with introduction of an energy input which is
sufficient for dispersing.
In an entirely surprising way it has now in fact been
found that, through the combination of a suitable
dispersant (dispersing agent) in interaction with high
energy inputs, especially high shear forces, it is
possible to provide a gentle and inexpensive method of
stably dispersing carbon nanotubes (CNTs) in
significantly higher concentrations and in a
multiplicity of dispersion media.
To solve the problem outlined above, therefore, the
present invention proposes a dispersion method as per
claim 1. Further, advantageous properties of the method
of the invention are subject matter of the relevant
dependent method claims.
Further subject matter of the present invention are the
dispersions of carbon nanotubes (CNTs) that are
obtainable by the method of the invention, and as are
defined or described in the corresponding claims
directed to the dispersions themselves.
Finally, a further subject of the present invention is
the use of the dispersions of carbon nanotubes (CNTs)
which are obtainable by the method of the invention,
such use being as defined or described in the
corresponding use claims.
The present invention - according to a first aspect of
the present invention - accordingly provides a method
of dispersing carbon nanotubes (CNTs) in a continuous
phase, especially in at least one dispersion medium,

i.e., therefore, a method of preparing dispersions of
carbon nanotubes (CNTs) in a continuous phase,
especially in at least one dispersion medium, the
carbon nanotubes (CNTs) being dispersed, especially
without prior pretreatment of the carbon nanotubes
(CNTs), in a continuous phase, especially in at least
one dispersion medium, in the presence of at least one
dispersant (dispersing agent), with introduction of an
energy input sufficient for dispersing.
With regard to the concept of the dispersion, as it is
used in the context of the present invention, reference
may be made in particular to DIN 53900 of July 1972,
according to which the concept of the dispersion is a
designation for a system (i.e., disperse system) of two
or more phases, of which one phase is continuous
(namely the dispersion medium) and at least one further
phase is finely divided (namely the dispersed phase or
the dispersoid; in this case the carbon nanotubes). In
the context of the present invention the concept of the
dispersion is designated exclusively in relation to the
designation of suspensions, i.e., dispersions of
insoluble particulate solids in liquids.
The concept of the dispersant - also designated,
synonymously, as dispersing agent, dispersing additive,
wetting agent, etc - as used in the context of the
present invention designates, generally, substances
which facilitate the dispersing of particles in a
dispersion medium, especially by lowering the
interfacial tension between the two components
particles to be dispersed, on the one hand, and
dispersant, on the other hand - and so by inducing
wetting. Consequently there are a multiplicity of
synonymous designations for dispersants (dispersing
agents) in use, examples being dispersing additive,
antisettling agent, wetting agent, detergent,
suspending or dispersing assistant, emulsifier, etc.
The concept of the dispersant should not be confused

with the concept of the dispersion medium, the latter
designating the continuous phase of the dispersion
(i.e., the liquid, continuous dispersion medium). In
the context of the present invention the dispersant,
additionally, serves the purpose of stabilizing the
dispersed particles as well (i.e., the carbon
nanotubes) , i.e., of holding them stably in dispersion,
and of avoiding or at least minimizing their
reagglomeration in an efficient way; this in turn leads
to the desired viscosities of the resulting
dispersions, since, in this way, readily manageable,
fluid systems result in practice - even in the case of
high concentrations of the dispersed carbon nanotubes.
Without the use of the dispersant, in contrast, there
would be such an increase in the viscosity of the
resulting dispersions, as a result of unwanted
reagglomeration of the dispersed CNTs, that - at least
at relatively high CNT concentrations - there would in
practice no longer be manageable systems resulting,
since those systems would have too high a viscosity or
too low a fluidity.
For further details relating to the terms "dispersoid",
"dispersing", "dispersant", "disperse systems", and
"dispersion", reference may be made, for example, to
Rompp Chemielexikon, 10th edition, Georg Thieme Verlag,
Stuttgart/New York, Volume 2, 1997, pages 1014/1015,
and also to the literature referred to therein, the
entire disclosure content of which is hereby
incorporated by reference.
A particular feature of the method of the invention is
to be seen in the fact that, in accordance with the
invention, the dispersing operation takes place with
sufficient input of energy (e.g., input of shearing
energy) ; on the one hand the energy introduced must be
sufficient to provide the energy needed for dispersing,
especially to disrupt the agglomerates, conglomerates,
coils, etc formed by the carbon nanotubes (CNTs), but

on the other hand it must not exceed a certain level
above which destruction of the carbon nanotubes (CNTs)
begins - and this must be the case in the presence of a
suitable dispersant (dispersing agent) which is capable
of stabilizing the individual carbon nanotubes (CNTs)
and of preventing reagglomeration occurring again, and
also of facilitating the subseguent dispersing and in
that way stabilizing the resultant dispersions.
With the method of the invention it is possible in a
surprising way to obtain relatively high concentrations
of carbon nanotubes (CNTs) in the resultant
dispersions. In particular the method of the invention
can be used to prepare dispersions having solids
contents, in terms of carbon nanotubes (CNTs), of 5% by
weight or more, based on the resultant dispersions. In
general the carbon nanotubes (CNTs) are dispersed in
amounts of 1 x 10-5% to 30%, in particular 1 x 10-4% to
20%, preferably 1 x 10-3% to 10%, more preferably
1 x 10-2% to 7.5%, very preferably 1 x lO-1 to 5%, by
weight, based on the resultant dispersions, in the
continuous phase.
In order to allow economically rational application,
the method of the invention ought to be implemented or
concluded within a certain, or relatively short, period
of time, which in turn requires a particular energy
input per unit time. Generally speaking, the method of
the invention, or the dispersing operation, is carried
out within a period of 0.01 to 30 minutes, especially
0.1 to 20 minutes, preferably 0.2 to 15 minutes, more
preferably 0.5 to 10 minutes, very preferably 0.5 to 5
minutes. Nevertheless, owing to a particular case, or
relative to the application, it may be necessary to
deviate from the times specified above, without
departing from the scope of the present invention.
As outlined above, it is necessary, in order to carry
out the dispersing operation, for there to be a

sufficient input of energy into the dispersion medium,
which on the one hand must be sufficient to ensure
reliable dispersing of a carbon nanotubes (CNTs), and
on the other hand must not be so high that there is
destruction of the carbon nanotubes (CNTs) or of their
structures.
The provision of the required energy input is
accomplished preferably by means of ultrasound
treatment. Nevertheless, other possibilities can also
be realized in the context of the present invention, an
example being the application of high-pressure nozzles,
although the treatment by means of ultrasound is
preferred in accordance with the invention.
In general, the amount of energy introduced can vary
within wide ranges. In particular the amount of energy
introduced, calculated as energy introduced per unit
quantity of carbon nanotubes (CNTs) to be dispersed, is
5000 to 500 000 kJ/kg, especially 10 000 to
250 000 kJ/kg, preferably 15 000 to 100 000 kJ/kg, more
preferably 25 000 to 50 000 kJ/kg. Nevertheless,
relative to the application or as a result of a
specific case, it may be necessary to deviate from the
aforementioned figures, without departing the scope of
the present invention.
Typically the dispersing operation proper is preceded
by a method step in which the carbon nanotubes (CNTs)
for subsequent dispersion are contacted with the
continuous phase, especially with the dispersion
medium, and with the dispersant (dispersing agent), and
also, where appropriate, with further constituents or
ingredients of the dispersion, and these components are
homogenized with one another, especially with
corresponding input of energy, preferably with
stirring. The energy input required for this purpose,
however, is smaller than for the dispersing operation
as such, and so a customary stirring or mixing

operation is sufficient for this purpose.
In general, the method of the invention is carried out
at temperatures below the boiling temperature of the
continuous phase, especially of the dispersion medium.
Preferably the method of the invention is carried out
at temperatures in the range from 10 to 100°C,
preferably 15 to 70°C. In this case it may where
appropriate be necessary to carry out the dispersing
operation with cooling, since the energy input results
in an increase in the temperature of the resultant
dispersion.
As outlined above, an advantage of the present
invention is to be seen in the fact that the dispersing
operation is carried out without prior pretreatment of
the carbon nanotubes (CNTs) to be dispersed, especially
without prior oxidation, chemical treatment (e.g., with
oxidizing agents, such as nitric acid, ozone, etc) ,
thermal treatment, polarization, halogenation or the
like.
In the context of the method of the invention it is
possible to use virtually any desired carbon nanotubes
(CNTs), of the kind preparable by processes known from
the prior art or else available as commercial products
(e.g., from Bayer MaterialScience AG, Leverkusen).
The carbon nanotubes (CNTs) used in accordance with the
invention may be, for example, single-wall carbon
nanotubes (SWCNTs or SWNTs) or multiwall carbon
nanotubes (MWCNTs or MWNTs), especially 2- to 30-wall,
preferably 3- to 15-wall, carbon nanotubes.
The carbon nanotubes (CNTs) used in accordance with the
invention may have average internal diameters of 0.4 to
50 nm, especially 1 to 10 nm, preferably 2 to 6 nm,
and/or average external diameters of 1 to 60 nm,
especially 5 to 30 nm, preferably 10 to 20 nm. The

carbon nanotubes (CNTs) used in accordance with the
invention may have average lengths of 0.01 to 1000 μm,
especially 0.1 to 500 [μm, preferably 0.5 to 200 μm,
more preferably 1 to 100 [m.
Furthermore, the carbon nanotubes (CNTs) used in
accordance with the invention may have a tensile
strength per carbon nanotube of at least 1 GPa,
especially at least 5 GPa, preferably at least 10 GPa,
and/or an elasticity modulus per carbon nanotube of at
least 0.1 TPa, especially at least 0.5 TPa, preferably
at least 1 TPa, and/or a thermal conductivity of at
least 500 W/mK, especially at least 1000 W/mK,
preferably at least 2000 W/mK, and/or an electrical
conductivity of at least 103 S/cm, especially at least
0.5 x 104 S/cm, preferably at least 104 S/cm.
Typically employed carbon nanotubes (CNTs) have a bulk
density in the range from 0.01 to 0.3 g/cm3, especially
0.02 to 0.2 g/cm3, preferably 0.1 to 0.2 g/cm3, and are
present in the form of agglomerates or conglomerates of
a multiplicity of carbon nanotubes (CNTs), especially
in highly coiled form.
Inventively suitable carbon nanotubes (CNTs) are
available commercially, as for example from Bayer
MaterialScience AG, Leverkusen, an example being the
product series Baytubes® (e.g., Baytubes® C 150 P).
As far as the continuous phase or dispersion medium is
concerned, it is possible in the context of the present
invention, in principle, to employ aqueous-based,
organic-based or aqueous-organic-based dispersion
media, preference being given to using organic
dispersion media. Typically the continuous phase used
is a dispersion medium which is present in the liquid
aggregate state under dispersing conditions, especially
under atmospheric pressure (101.325 kPa) and in a
temperature range from 10 to 100°C, preferably 15 to

70°C.
In an inventively preferred way the dispersion medium
used as the continuous phase is a dispersion medium
which is selected from the group of (i) alcohols,
especially straight-chain, branched or cyclic,
monohydric or polyhydric alcohols, such as methanol,
ethanol, butanol, ethylhexanol, decanol, isotridecyl
alcohol, benzyl alcohol, propargyl alcohol, oleyl
alcohol, linoleyl alcohol, oxo-process alcohols,
neopentyl alcohol, cyclohexanol, fatty alcohols, and
diols and polyols, such as glycols; (ii) ether
alcohols, such as 2-methoxyethanol, monophenyl
diglycol, phenylethanol, ethylene glycol, and propylene
glycol; (iii) hydrocarbons, such as toluene, xylene,
and aliphatic and/or cycloaliphatic benzine fractions,
chlorinated hydrocarbons, such as chloroform and
trichloroethane; (iv) ethers, especially cyclic and
acyclic ethers, such as dioxane, tetrahydrofuran, and
polyalkylene glycol dialkyl ethers; (v) carboxylic
esters, especially monocarboxylic esters, such as ethyl
acetate and butyl acetate; and dicarboxylic or
polycarboxylic esters, such as dialkyl esters of C2 to
C4 dicarboxylic acids ("Dibasic Esters"); (vi) ether
esters, especially alkylglycol esters, such as
ethylglycol acetate and methoxypropyl acetate; (vii)
lactones, such as butyrolactone; (viii) plasticizers,
especially phthalates; (ix) aldehydes and ketones, such
as methyl isobutyl ketone, cyclohexanone, and acetone;
(x) acid amides, such as dimethylformamide;
(xi) N-methylpyrrolidone; and also mixtures of the
aforementioned dispersion media.
Furthermore, it is also possible in principle to employ
ionic liquids or what are known as supercritical fluids
as a dispersion medium. Water as well is a suitable
dispersion medium in the context of the present
invention.

As far as the inventively used dispersant is concerned,
it is more particularly a polymeric dispersant,
especially a polymeric dispersant based on a functional
polymer, preferably having a number-average molecular
mass of at least 500 g/mol, preferably at least
1000 g/mol, more preferably at least 2000 g/mol. In
particular the inventively used dispersant may be
selected from the group of polymers and copolymers
having functional groups and/or groups with pigment
affinity, alkylammonium salts of polymers and
copolymers, polymers and copolymers having acidic
groups, comb copolymers and block copolymers, such as
block copolymers having groups with pigment affinity,
especially basic groups with pigment affinity,
optionally modified acrylate block copolymers,
optionally modified polyurethanes, optionally modified
and/or salified polyamines, phosphoric esters,
ethoxylates, polymers and copolymers having fatty acid
radicals, optionally modified polyacrylates, such as
transesterified polyacrylates, optionally modified
polyesters, such as acid-functional polyesters,
polyphosphates, and mixtures thereof.
Furthermore it is possible in principle, as dispersants
suitable in accordance with the invention, to use all
of the dispersants, surfactants, wetting agents, etc,
that are known for that purpose.
In an inventively preferred way the compounds selected
as dispersants are especially those compounds of the
kind described in publications EP 1 593 700 Bl,
EP 0 154 678 Bl, EP 0 318 999 Bl, EP 0 270 126 Bl,
EP 0 893 155 Bl, EP 0 417 490 Bl, EP 1 081 169 Bl,
EP 1 650 246 Al, EP 1 486 524 Al, EP 1 640 389 Al,
EP 0 879 860 Bl, WO 2005/097872 Al, and EP 1 416 019
Al, the respective disclosure content of which is
hereby incorporated in full by reference. These
compounds are described or defined more closely in
claims 13 to 17 (= EP 1 593 700 Bl), claim 18 ( =

EP 0 154 678 Bl), claim 19 (= EP 0 318 999 Bl) , claim
20 (= EP 0 270 126 Bl), claim 21 (= EP 0 893 155 Bl),
claim 22 (= EP 0 417 490 Bl) , claim 23 (= EP 1 081 169
Bl), claim 24 (= EP 1 650 246 Al), claim 25 ( =
EP 1 486 524 Al) , claim 26 (= EP 1 640 389 Al) , claim
27 (= EP 0 879 860 Bl), claim 28 (= WO 2005/097872 Al),
and claim 29 (= EP 1 416 019 Al).
As far as the method of the invention is concerned, it
can in principle be carried out in continuous operation
or in discontinuous operation, and this can be done in
a relatively small amount of time. On account of its
low level of complexity, the method of the invention
can be readily employed industrially, can be carried
out flexibly and economically, and can be configured
adaptably up to production on the tonne scale.
In principle the method of the invention can be
employed for any of a very wide variety of dispersion
media, of dispersants or dispersing agents, and of
carbon nanotubes (CNTs), and can be readily combined
with further processes or process steps.
As outlined at the outset, the dispersing of CNTs poses
a great challenge, because the CNTs possess a very
large aspect ratio and are present in a highly coiled
form: for instance, the diameters range, for example,
from 3 to 25 nm, but the lengths range, for example, up
to about 10 mm. On account of the high degree of
coiling, very high energy inputs or shearing forces are
necessary in order to separate the CNTs. Where
uncoiling is accomplished only by means of high energy
input, without simultaneous use of suitable
dispersants, the CNTs are only size-reduced, and not
sufficiently stabilized, and so the resulting
dispersions are inhomogeneous and lack long-term
stability. The use of dispersants is aimed on the one
hand at wetting the CNTs, in order to ensure easier and
more gentle uncoiling, and on the other hand at

stabilizing the resulting separated CNTs by coating
with the dispersant, with the consequence that, with
the method of the invention, stable homogeneous
dispersions are obtained. Ideally the dispersions
exhibit only a slight increase in viscosity, and high
activity of the CNTs.
In contrast, the methods described in the prior art
usually result in inhomogeneous dispersions which lack
long-term stability. Furthermore, the prior-art
dispersions exhibit a high increase in viscosity in
tandem with low particle contents of only about 1% at
most.
Surprisingly it has now been found that, in the context
of the method of the invention, by combining suitable
dispersants with high energy inputs or shearing forces,
a gentle and cost-effective method is provided for
stably dispersing CNTs in any of a very wide variety of
media and at significantly higher concentrations.
The method of the invention leads to dispersions having
high carbon nanotube (CNT) contents or with high
degrees of filling (above 5% by weight, for example,
based on the resultant dispersions), and it
accomplishes this at the same time as low viscosities
and hence ready manageability.
Furthermore, the dispersions obtainable by the method
of the invention exhibit high storage stabilities.
Accordingly the present invention - according to a
second aspect of the present invention - provides
dispersions of carbon nanotubes (CNTs) in a continuous
phase, especially in at least one dispersion medium,
which are obtainable by the method of the invention as
outlined above.

For further relevant details concerning the dispersions
of the invention, reference may be made to the
corresponding claims directed to the dispersions
themselves.
The dispersions according to the present invention that
are obtainable by the method of the invention have an
extraordinary stability, especially storage stability;
in particular the dispersions of the invention are
storage-stable over at least a week, preferably at
least a month, more preferably at least three months,
very preferably at least six months. As outlined above,
the dispersions of the invention are, furthermore,
fluid at room temperature and in this way are readily
manageable. The dispersions prepared in accordance with
the invention exhibit a newtonian or at most
thixotropic and/or structurally viscous behavior,
preferably a newtonian behavior.
The dispersions obtainable in accordance with the
invention are suitable for a multiplicity of
applications. Further provided by the present invention
- in accordance with a third aspect of the present
invention - is, accordingly, the inventive use of the
dispersions obtainable by the method of the invention,
as is defined in the corresponding use claims.
Thus, for example, the dispersions of the invention are
suitable for application in the field of electronics,
as for example in the field of computer engineering and
the computer industry, semiconductor engineering and
the semiconductor industry, and metrology and the
metrological industry, for the purpose, for example, of
producing conducting or semiconducting structures,
nanoelectric structures and devices, transistors,
nonvolatile memories, displays and screens and their
components, and also metrological and computer parts
and components, such as circuits, diodes, and the like,
etc.

Additionally the dispersions of the invention are
suitable for application or incorporation in plastics
and polymeric compositions, coatings, paints, inks,
composite materials, and the like.
By way of example the dispersions of the invention can
be used in order to increase the electrical
conductivity and/or to improve the mechanical
properties, especially the strength, preferably in
relation to the aforementioned materials (i.e.,
plastics and polymeric compositions, coatings, paints,
inks, composite materials, etc) . Thus, for example, the
dispersions of the invention are suitable as
reinforcing materials in the aforementioned materials.
Furthermore, the dispersions prepared in accordance
with the invention are suitable for producing bundles,
fibers, mats, and other coherent structures of carbon
nanotubes (CNTs) (e.g., after removal of the dispersion
medium).
Moreover, the dispersions of the invention are suitable
for application in the field of aerospace technology.
A further field for application of the dispersions of
the invention is the field of cooling technology,
especially in relation to the production of heat sinks
for any of a very wide variety of applications (e.g.,
for GSM base stations, as CPU coolers, etc) .
Finally the dispersions of the invention can also be
used for shielding from electrical and/or
electromagnetic radiation, especially in the
aforementioned materials (i.e., plastics and polymeric
compositions, coatings, paints, inks, composite
materials, etc).

Further embodiments, modifications, and variations of
the present invention are readily evident and
realizable for the skilled worker on reading the
description, without departing the scope of the present
invention.
The present invention is illustrated by reference to
the examples which follow, but which are not intended
to restrict the present invention.
Examples:
Examples A:
The particular advantages of the invention are
described below, using as an example the dispersing of
CNTs in PMA (propylene glycol monomethyl ether or
methoxypropyl acetate) as dispersion medium, using
different dispersants and an ultrasound dispersing
unit.
First of all various comparative experiments with and
without dispersants, with only a Dispermat, were
carried out, but in all cases the result was
disappointing: The dispersions were very inhomogeneous
and underwent complete sedimentation after a time of
just a few hours to a day.
Similar comparative experiments with the ultrasonic
transducer, in contrast, showed better outcomes: Thus a
0.1% dispersion of CNTs without dispersant undergoes
only slight sedimentation, but is still very
inhomogeneous. In this case the agglomerates are in
fact disrupted, but the CNTs are damaged to a high
degree and are not sufficiently stabilized. A
dispersion prepared in this way is not suitable for
industrial use. The addition of a dispersant, though,
increases the result considerably.

Thus, if only ultrasound or only dispersant is used,
the experiments result in unstable and inhomogeneous
dispersions or suspensions with significant
sedimentation behavior.
In inventive experiments, different dispersants were
employed in different quantities, in combination with
the input of ultrasound, leading to the desired
outcomes.

As a first experimental series, 1% dispersions of
MWCNTs in methoxypropyl acetate (PMA) were prepared
with use of ultrasound (table 2) . The results were
evaluated on the basis of the visual impression
directly after the dispersing operation; the
sedimentation behavior; and the viscosity. The
dispersions are prepared in the same way as described
in example B below.

In order to allow better assessment of the
sedimentation behavior in particular, a second step saw
more highly dilute dispersions being prepared with
these dispersants (table 3) . At a concentration of
0.1%, the dispersion stabilized with DISP-I showed the
best result.

In the course of the experiments it became apparent,
surprisingly, that the combination of DISP-I and
ultrasound produced very good results. The results were
so good that the system could also be increased to a 5%
CNT content, and the dispersions exhibited outstanding
properties and excellent storage stabilities. A further
increase to 10% or more CNT content was realized as
well.
Additionally it was observed that the method of the
invention - irrespective of the mode of preparation of
the CNTs - can be realized successfully, in other words
that the method of the invention is suitable for use
universally for CNTs and does not require prior surface
modification of the CNTs (in situ or post-synthesis),
thereby allowing massive cost savings.
This results in immense opportunities for the
industrial use of CNTs in numerous applications, since
the dispersions have the following advantages:

high degrees of filling, or more than 5% by weight
CNTs
homogeneous dispersions with long-term stability
gentle dispersion method (gentle uncoiling of the
CNTs)
can be used universally for all commercially
available CNTs
cost-effective dispersing method, equally upscalable
and suitable for both batch and continuous operation
can be combined with further process steps
low viscosities realizable if needed
addition of further functionalized additives
possible
functionalization of the dispersant possible.
In further experiments it was shown that the method of
the invention can also be transposed to other solvents.
When water or extremely nonpolar media are employed, of
course, the requirements concerning the functional
groups of the dispersant are different.
Furthermore, the dispersions prepared in accordance
with the invention can be processed further, for
orientation of the CNTs in the dispersion medium
matrix, for example. Hence it is possible to carry out
parallel alignment of CNTs in an electrical field. For
this purpose, however, the CNTs must be present in
individualized and homogenously dispersed form, ideally
at a high concentration. This is now ensured for the
first time through the method of the invention. A
subsequent parallel orientation is therefore possible,
and for many applications is essential.
A corresponding experimental system is designed as
follows: In a tank, a suspension of the agglomerated
CNTs in the desired dispersion medium is introduced,
together with the dispersant, and is then pumped in a
circuit through a flow cell, in which the dispersing
operation takes place by means of ultrasound. The

resulting dispersion can then either be recycled to the
tank and dispersed in the circuit until the desired
degree of dispersion has been achieved (batch
operation) , or can be pumped into a further flow cell
with ultrasound dispersing unit (continuous operation).
This may then be followed by mixing, as for example
with a resin (or a paint, a coating liquid, etc) , and
subsequent passage through an electrical field provides
for parallel alignment of the CNTs. The parallel
alignment may alternatively take place at a later point
in time. The prerequisite is merely a stable dispersion
of individualized CNTs, something which is ensured by
the method of the invention.
Examples B:
Preparation of a 1.0% dispersion of CNTs (Baytubes®,
e.g., Baytubes® C 150 P) in methoxypropyl acetate (PMA)
with 100% of DISP-I
A 350 ml PE beaker is charged with 196 g of PMA and 2 g
of DISP-I, and this initial charge is homogenized using
a Dispermat at 1000 rpm with a toothed disc (d = 40
mm) . 2 g of CNTs are added to the mixture, and the PE
vessel is placed into a stainless steel double-wall
vessel, cooled to 5°C, with water as the cooling
medium. Dispersing takes place using an ultrasonotrode
(d = 38 mm) , which is immersed to about 2 to 3 cm in
the medium. With a power of approximately (500 ± 20) W,
the suspension is dispersed for 1.5 to 2 min, in such a
way that the temperature remains below 70°C. The result
is a homogeneous, storage-stable, black dispersion of
low viscosity.
Viscosities
Viscosity as a function of the degree of CNT filling
To illustrate the increase in viscosity with increasing
degree of CNT filling, the viscosities of different
dispersions in PMA, with CNT contents in the range from

0.1% to 5%, were measured (fig. 1 and fig. 2). As can
be seen, the viscosity rises exponentially with the
concentration, but even at concentrations above 3% is
still within a manageable range. Fig. 1 shows the
viscosities of PMA dispersions with different CNT
contents (0.1%, 0.5%, 1.0%, 2.0%, 3.0%, and 5.0%;
curves considered from bottom to top), with a constant
quantity of dispersant, of 200% by weight in relation
to CNTs, and fig. 2 is a corresponding logarithmic plot
of the viscosities of PMA dispersions having different
CNT contents against the concentration of the CNTs.
Viscosity as a function of the fraction of dispersant
In view of the large surface area of the CNTs and their
urge to form coils, a high dispersant fraction must be
used. Consequently dispersant concentrations of 50% to
200% by weight (based on CNTs) were used. The measure
used for the dispersing is again the viscosity. From
fig. 3 it is evident that, from a dispersant
concentration of 150%, the viscosity remains still at a
low level. Significantly lower concentrations lead to
higher viscosities. Fig. 3 shows a comparison of the
viscosities of 1% dispersions of CNTs in PMA with
different amounts of DISP-I (50%, 100%, 150%, and 200%,
by weight, based on CNTs; curves considered from top to
bottom).
Comparison of different CNTs
As is evident from fig. 4, the method of the invention
for dispersing CNTs can be applied almost universally
to a very wide variety of different kinds of CNTs.
Fig. 4 shows by way of example the viscosities of 0.1%
(bottom curves) and 1% (top curves) dispersions of CNTs
in PMA, on the one hand for Baytubes® C 150 P from
Bayer MaterialScience AG and on the other hand for CNTs
from CNT Co., Ltd.) . It is clearly apparent that the
viscosities are virtually identical, irrespective of
the manufacturer from which the CNTs originate.

Summary of the results
The present results were determined under measuring
conditions which "circumvent" the "wall gliding" of the
samples and allow a comparison of the low-concentration
and high-concentration CNT suspensions. The resulting
measurements can admittedly not be considered to be
absolute values, but do serve as a basis for an
empirical comparison of the samples.
The 0.1% and 1.0% unstabilized suspensions, without
dispersant, of Baytubes® in PMA cannot be measured,
owing to the sedimentation behavior.
Through the method of the invention it is possible to
prepare fluid pastes having a CNT content of more than
5% by weight.
Of the wetting agents tested, DISP-I showed itself to
be the most effective in terms of the viscosity level.
The viscosity rises exponentially with the increase in
the solids content of the CNTs and with the same
application of dispersant (200% by weight of DISP-I).
Measuring conditions
ThermoHaake RS300 with UTCE/C electrical thermal
conditioning unit
Measurement system: 35 mm 1° cone/plate system
Experimental mode: rotation in CSR mode {Controlled
Shear Rate)
All of the samples exhibit a strongly pronounced yield
point. The visually sensorial testing, moreover,
reflected thixotropic or structurally viscous behavior
on the part of the samples.

Optical microscopy images
In order to obtain an impression of the degree of
agglomeration and the quality of the dispersion,
micrographs were produced of the different dispersions.
Pictured below is a selection of samples with
particularly good and particularly poor dispersion.
Fig. 5 shows a ten-times magnification of a 0.1%
dispersion of CNTs in PMA after ultrasound treatment
without dispersant (very poor dispersion, large
agglomerates).
Fig. 6 shows a ten-times magnification of a 0.1%
dispersion of CNTs in PMA after ultrasound treatment in
the presence of 50% dispersant (DISP-II) (good and
stable dispersion, few agglomerates, significantly
homogeneous) .
Fig. 7 shows a ten-times magnification of a 0.1%
dispersion of CNTs in PMA after ultrasound treatment in
the presence of 100% dispersant (DISP-I) (very good and
very homogeneous dispersion, no large agglomerates any
more, stable).
Stabilities
The dispersions prepared in accordance with the
invention have now been stable at room temperature for
about 4 months, and are not exhibiting any
sedimentation of the CNTs. Even dispersions with CNT
contents of 3% or more are indeed thixotropic but show
no sedimentation of the CNTs over a relatively long
time period. Dispersions prepared in other ways, in
contrast, frequently exhibit complete phase separation
after just hours.

We claim.
1. A method of dispersing carbon nanotubes (CNTs) in
a continuous phase, especially in at least one
dispersion medium,
characterized in that
first, before the dispersing operation proper, a
method step is carried out in which the carbon
nanotubes (CNTs) are contacted and homogenized
with a continuous phase, especially a dispersion
medium, and at least one dispersant (dispersing
agent), and
subsequently the carbon nanotubes (CNTs) are
dispersed in the continuous phase, especially the
dispersion medium, in the presence of the
dispersant, with introduction of an energy input
sufficient for dispersing, in amounts of 1 x 1CT1 %
to 30 % by weight, based on the resulting
dispersion, the amount of energy introduced,
calculated, as energy introduced per unit quantity
of carbon nanotubes (CNTs) to be dispersed, being
15 000 to 100 000 kJ/kg.
2. A dispersion of carbon nanotubes (CNTs) in a
continuous phase as the dispersion medium, the
dispersion being obtained by the method of
Claim 1.
3. The dispersion of claim 2, characterized in that
the dispersion is storage-stable for at least
1 week.
4. The use of the dispersion of claim 2 in plastics
and polymeric compositions, in coatings, in
paints, in inks or in composite materials.

5. The use of the dispersion of claim 2 for producing
bundles, fibers, mats, and other coherent
structures of carbon nanotubes (CNTs).
6. The use of the dispersion of claim 2 in the field
of electronics, aerospace technology and cooling
technology.

The invention relates to a method of dispersing carbon nanotubes (CNTs) in a continuous phase, especially in at least one dispersion medium, the carbon nanotubes, especially without prior pretreatment, being dispersed in a continuous phase, especially in at least one dispersion medium, in the presence of at least one
dispersant (dispersing agent), with introduction of an energy input sufficient for dispersing, and also to the dispersions that are obtainable in this way, and to their use. With the method of the invention it is possible for the carbon nanotubes (CNTs) to be dispersed in high concentrations and with high storage stability.

Documents:

1751-KOLNP-2009-(02-02-2015)-ABSTRACT.pdf

1751-KOLNP-2009-(02-02-2015)-ANNEXURE TO FORM 3.pdf

1751-KOLNP-2009-(02-02-2015)-CLAIMS.pdf

1751-KOLNP-2009-(02-02-2015)-CORRESPONDENCE.pdf

1751-KOLNP-2009-(02-02-2015)-PETITION UNDER RULE-137.pdf

1751-KOLNP-2009-(08-02-2013)-ABSTRACT.pdf

1751-KOLNP-2009-(08-02-2013)-ANNEXURE TO FORM-3.pdf

1751-KOLNP-2009-(08-02-2013)-CLAIMS.pdf

1751-KOLNP-2009-(08-02-2013)-CORRESPONDENCE.pdf

1751-KOLNP-2009-(08-02-2013)-FORM-1.pdf

1751-KOLNP-2009-(08-02-2013)-FORM-13.pdf

1751-KOLNP-2009-(08-02-2013)-FORM-2.pdf

1751-KOLNP-2009-(08-02-2013)-OTHERS.pdf

1751-KOLNP-2009-(08-02-2013)-PA.pdf

1751-kolnp-2009-abstract.pdf

1751-kolnp-2009-claims.pdf

1751-KOLNP-2009-CORRESPONDENCE 1.1.pdf

1751-KOLNP-2009-CORRESPONDENCE-1.1.pdf

1751-kolnp-2009-correspondence.pdf

1751-kolnp-2009-description (complete).pdf

1751-kolnp-2009-drawings.pdf

1751-kolnp-2009-form 1.pdf

1751-kolnp-2009-form 13.pdf

1751-kolnp-2009-form 18.pdf

1751-kolnp-2009-form 2.pdf

1751-kolnp-2009-form 3.pdf

1751-kolnp-2009-form 5.pdf

1751-kolnp-2009-international preliminary examination report.pdf

1751-kolnp-2009-international publication.pdf

1751-kolnp-2009-international search report.pdf

1751-KOLNP-2009-PCT IPER 1.1.pdf

1751-kolnp-2009-pct priority document notification.pdf

1751-kolnp-2009-pct request form.pdf

1751-KOLNP-2009-SCHEDULE.pdf

1751-kolnp-2009-specification.pdf

1751-KOLNP-2009-TRANSLATED COPY OF PRIORITY DOCUMENT.pdf

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Patent Number

265366

Indian Patent Application Number

1751/KOLNP/2009

PG Journal Number

09/2015

Publication Date

27-Feb-2015

Grant Date

20-Feb-2015

Date of Filing

11-May-2009

Name of Patentee

BYK-CHEMIE GMBH

Applicant Address

ABELSTRASSE 45, D-46483 WESEL

Inventors:

#	Inventor's Name	Inventor's Address
1	DR. ULRICH NOLTE	WASSERBURGALLE 40 D-47533 KLEVE FEDERAL
2	DR. MICHAEL BERKEI	GINSTERSTRAßE 12 D-45721 HALTERN AM SEE FEDERAL
3	DR. THOMAS SAWITOWSKI	GUSTAV-STREICH-STRAßE 6 D-45133 ESSEN FEDERAL
4	DR. WOLFGANG PRITSCHINS	KLEISTSTRAßE 4 D-46487 WESEL FEDERAL

PCT International Classification Number

C01B 31/02

PCT International Application Number

PCT/EP2007/008193

PCT International Filing date

2007-09-20

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	10 2006 053 816.1	2006-11-14	Germany
2	10 2006 055 106.0	2006-11-21	Germany