HK1151059A - Printable composition for producing electroconductive coatings, and method for the production thereof - Google Patents

Description

Printable composition for producing electrically conductive coatings and method for producing same

The invention relates to an ink for producing electrically conductive printed images based on carbon nanotubes and at least one polymeric dispersant (dispergierhihfsmittel) in an aqueous formulation (Formulierung) and to a method for producing the same.

Surfaces with electrically conductive properties have a high prevalence in economic applications, for example in the preparation of electrical switching circuits, sensors and heating circuits.

In this regard, various methods are used to apply the conductor circuit to the surface. However, it is common for known products that the resulting conductive properties are based on metallic or semiconducting coating materials.

Essential for the aforementioned products is their generally high prevalence. The materials and methods used must therefore be able to produce the resulting assembly at the lowest possible cost to meet this high demand inexpensively. What makes this possible is, for example, the conventional screen printing process for producing conductive coatings.

This requirement has led to the use of metal conductors, in particular noble metal conductors, on components in some fields of application being disadvantageous, in particular from the point of view of price. Applications have recently become known such as so-called "radio frequency identification" tags (RFID tags for short). Which are passive or active electronic components used basically for storing and transferring data relating to the items in which they are located.

There is a study according to which in 2008 only europe there are over 2600 billions of individual products, purportedly up to 5% (i.e. 130 billion) equipped with one of these components. (News draft, "Enterme Walstrumsraten fur RFID-Markt in Europa" [ "Large growth Rate of European RFIF market" ], SOREON Research GmbH, Frankfurt am Main, 5 months and 10 days 2004)

It is particularly contemplated that for many of these products, the member is applied to a package that must be disposed of after the product contained therein has been used. Therefore, the metallic conductor or semiconductor product is disadvantageous in its disposal because it is difficult to completely burn out. On the other hand, a component consisting essentially of a substance that burns off easily would provide advantages here. Suitable examples of these would be conductive pastes or inks based on carbon black or graphite or the specific carbon nanotubes given in the present invention.

A prerequisite for good electrical conductivity of the coating is the fine dispersion of the electrically conductive particles in the formulation used for the coating in each case and its high specific conductivity.

In US 2006/124028 a1, inks for this purpose are disclosed, which use carbon nanotubes for inkjet printers. The ink is characterized by a surface tension of 0.02 to 0.07N/m and a viscosity of 0.001 to 0.03 pas at 25 ℃. The content of the disclosed carbon nanotubes is within a wide range, and is 0.1 to 30 wt%. The ink has a viscosity of not more than 0.03 pas and is therefore unsuitable for screen printing. A viscosity in the order of 1Pa · s would be required for this purpose.

In US 2005/284232 a1, an electrically conductive coating comprising carbon nanofibers is disclosed. The coating is believed to be applied by brushing, rolling or spraying a suitable ink. The possibility of using the ink for screen printing is not disclosed. The ink has a carbon nanofiber content of 4-12 wt% in a matrix similar to the substrate where, for example, polyurethane, polyimide, cyanate ester and other organics. No information is disclosed about parameters relevant to screen printing, such as viscosity or surface tension on a particular substrate. It is disclosed that the viscosity can be reduced by dissolving the matrix.

In WO 2005/119772A 2, inks are disclosed which comprise carbon nanotubes, wherein the carbon nanotubes used have an outer diameter of not more than 20nm and are used in a concentration of 10% by weight or less. The post-treatment temperature is disclosed to be greater than 75 ℃ and it should last at least 10 minutes. Furthermore, compositions of inks for e.g. screen printing are disclosed, which use, inter alia, derivatives of cellulose to achieve or obtain dispersion in the resulting formulation. The maximum surface resistance obtained for the ink after treatment according to this disclosure is 10k Ω/m.

In WO 2005/029528A 1, inks or pastes comprising carbon nanotubes are disclosed, by various printing techniques for preparing electrodes (examples)Such as screen printing) is applied to the surface. The disclosed inks are aqueous formulations comprising carbon nanotubes and an inorganic adjuvant, or formulations comprising carbon nanotubes and an organic polymeric adjuvant in an organic solvent. The carbon nanotubes used are of the type generally known to those skilled in the art. The physical properties of the ink with respect to viscosity, surface tension and conductivity are not disclosed. The disclosed inks are disadvantageous because they are either present in organic solvents and thus potentially present an environmental risk, or they include inorganic adjuvants, such as Al₂O₃、SiO₂It is not conductive and is not easily removed during post-processing. It can therefore be assumed that the conductivity of the printed image is disadvantageous compared to inks without these auxiliaries.

In the prior art listed above, cylindrical carbon nanotubes are generally used for preparing inks. These carbon nanotubes are either single-walled (called "single-walled carbon nanotubes" -SWNTs) or multi-walled (called "multi-walled carbon nanotubes" -MWNTs) carbon nanotube structures, as described by Ijima in publications (publications: S. Ijima, Nature 354, 56-58, 1991). These known carbon nanotubes are characterized in that they relate to a carbon nanotube structure in which one or more closed concentrically arranged graphene layers are the basis of the carbon nanotube structure.

There is therefore the object of providing inks comprising specific carbon nanotubes which are very suitable for industrial-scale printing processes, such as screen printing, and which exhibit improved electrical conductivity compared with the prior art and are environmentally undesirable.

Surprisingly, it has been found that this object is achieved by an ink for producing electrically conductive printed images, which comprises a specific proportion of specific carbon nanotubes having an internal structure of several graphene layers (multi-scroll type) which have not previously been described to be aggregated into stacks and rolled up and which comprises a proportion of at least one polymeric dispersant in an aqueous formulation.

The invention provides a printable composition for producing electrically conductive coatings, based on carbon nanotubes and at least one polymeric dispersant in an aqueous formulation, characterized in that at least one fifth of the carbon nanotubes consist of carbon nanotubes having a molecular structure (multiscroll type) comprising several graphene layers, said graphene layers being present in the form of assembled stacks and rolled up.

The term printed image in connection with the present invention denotes a structure on a surface, which has been applied to the surface by means of well-known printing techniques. The printed image thus also comprises conductor circuits that have been applied to the surface by printing techniques. The term should therefore not be understood in its limiting manner in its inventive aspects.

The specific carbon nanotube of the multi-scroll type refers to, for example, a carbon nanotube and an aggregate thereof provided by german patent application having official application No. 102007044031.8, which has not been disclosed so far. The content thereof with respect to the carbon nanotubes and the preparation thereof is hereby included in the disclosure of the present application. The specific carbon nanotubes of the multi-scroll type can be used in a mixture with other types of carbon nanotubes known per se, i.e. single-walled CNTs and/or multi-walled CNTs.

Unlike known CNT structures, individual graphene or graphite layers in these particular carbon nanotubes extend, seen in their cross-section, from the center of the carbon nanotube to its outer edge consecutively without interruption. This enables, for example, improved and faster insertion of other materials in the tube structure, since a more open edge can be obtained as an entry area for insertion compared to known carbon nanotubes.

Surprisingly, by these properties, in combination with the polymeric dispersant, good dispersibility and homogeneity of the resulting ink is achieved. The term ink is also used below to simplify the alternative term printable composition.

The carbon nanotubes may be present in the ink according to the invention in treated or untreated form. If it is treated, it is preferably previously treated with an oxidizing agent. The oxidizing agent is preferably nitric acid and/or hydrogen peroxide, and the oxidizing agent is particularly preferably hydrogen peroxide.

Compositions comprising carbon nanotubes having a length to diameter ratio of more than 5, preferably more than 100, are preferred.

The carbon nanotubes used preferably have an average outer diameter of from 3 to 100nm, particularly preferably from 5 to 80nm, most particularly preferably from 6 to 60 nm.

The particular carbon nanotubes are typically present at least partially as aggregates in the ink according to the invention. Preferably less than 15% by number of the carbon nanotubes are present as aggregates. It is particularly preferred that less than 5% by number of the carbon nanotubes are present as aggregates.

If the carbon nanotubes are present as aggregates in the ink, they preferably have a diameter of substantially 5 μm or less, particularly preferably 3 μm or less. Most particularly preferably, the aggregate diameter is 2 μm or less.

Small proportions of as small aggregates as possible are advantageous, since as a result of this the physical properties of viscosity and conductivity of the ink, and thus its processability, are improved when used according to the invention. Coarse and large aggregates in some cases lead to clogging of the printing apparatus during the printing process. Furthermore, coarse and large amounts of aggregates may result in some areas of the printed image having high conductivity, while other areas have no or only very low conductivity. Since it is well known to the person skilled in the art that the total resistance of a conductor circuit results from the series connection of its individual resistances, if too many and too coarse aggregates produce such an inhomogeneous resistance distribution, the resistance of the overall conductor circuit is disadvantageously high.

The preferred length-to-diameter and average outer diameter of the carbon nanotubes ensure a high specific conductivity of the resulting ink, and thus a good percolation of the conductive layer can be obtained thereby, together with the intimate contact in the aggregates present.

The proportion of the carbon nanotubes in the ink is generally from 0.1 to 15% by weight. The proportion of the carbon nanotubes in the ink is preferably 5 to 10 wt%.

A smaller proportion of carbon nanotubes results in a resulting ink with too low a viscosity, which may no longer be suitable for high throughput printing processes, such as screen printing. A higher proportion of carbon nanotubes also increases the viscosity to a level beyond that which still appears meaningful for inks used in printing processes.

The aqueous formulation in connection with the present invention means a composition in which the solvent mainly consists of water, the ink preferably comprising more than 50% by weight. The ink particularly preferably contains at least 80% by weight of water.

A high content of water as solvent is advantageous, since this means that the ink is acceptable both in the printing process and after application from the point of view of industrial hygiene with respect to the solvent.

The at least one polymeric dispersant is typically at least one agent selected from the following series: water-soluble homopolymers, water-soluble random copolymers, water-soluble block copolymers, water-soluble graft polymers, in particular polyvinyl alcohol; copolymers of polyvinyl alcohol and polyvinyl acetate; polyvinylpyrrolidone; cellulose derivatives such as carboxymethyl cellulose, carboxypropyl cellulose, carboxymethyl propyl cellulose, hydroxyethyl cellulose; starch; gelatin; a gelatin derivative; an amino acid polymer; a polylysine; polyaspartic acid; polyacrylates (polyacrylates); polyethylene sulfonate (polyethylene sulfonate); polystyrene sulfonate (Polystyrolsulfonate); polymethacrylate (Polymethacrylate); a polysulfonic acid; condensation products of aromatic sulfonic acids with formaldehyde; naphthalene sulfonate (naphalalinsulfonate); lignosulphonate (Ligninsulfonate); copolymers of acrylic monomers; a polyethyleneimine; a polyvinylamine; polyallylamine; poly (2-vinylpyridine); a block copolyether; block copolyethers with polystyrene blocks and polydiallyldimethylammonium chloride.

The at least one polymeric dispersant is preferably at least one agent selected from the following series: polyvinylpyrrolidone; block copolyethers and block copolyethers comprising polystyrene blocks; a carboxymethyl cellulose; carboxypropyl cellulose; carboxymethyl propyl cellulose; gelatin; gelatin derivatives and polysulfonic acids.

Very particularly preferably, polyvinylpyrrolidone and/or block copolyethers having polystyrene blocks are used as polymeric dispersants. Particularly suitable polyvinylpyrrolidones have a molar mass M in the range from 5000 to 400,000_n. Suitable examples are PVP K15 from Fluka (molar mass about 10000amu) or PVP K90 from Fluka (molar mass about 360000amu) or block copolyethers with polystyrene blocks having 62% by weight, based on dry dispersant, of C₂Polyether, 23% by weight of C₃Polyether and 15% by weight of polystyrene, C₂Polyethers and C₃The ratio of the block lengths of the polyethers is 7: 2 units (for example Disperbyk 190 from BYK-Chemie, Wesel).

The at least one polymeric dispersant is advantageously present in the ink in a proportion of from 0.01% to 10% by weight, preferably in a proportion of from 0.1% to 7% by weight, particularly preferably in a proportion of from 0.5% to 5% by weight.

The polymeric dispersants which are generally used and preferred are particularly advantageously present in the stated proportions, since, in addition to contributing to a suitable dispersion of the carbon nanotubes, they can also adjust the viscosity of the inks according to the invention and adjust the surface tension and film formation and adhesion of the inks to the respective substrate.

The inks according to the invention generally have a dynamic viscosity of at least 0.5 pas, preferably from 1 to 200 pas.

Such a viscosity of the ink makes it particularly suitable for high throughput printing processes, such as screen printing. Compositions with much lower viscosities generally result in the ink flowing on the surface to which it is applied in the aqueous ink formulation, thus resulting in poor printed images. This is particularly important in the printing of electrical conductor circuits for switching circuits.

In addition to the at least one polymeric dispersant, in a preferred embodiment of the novel ink, the ink can also comprise at least one conductive salt.

The at least one conductive salt in this case is preferably selected from the series of salts having the following cations: tetraalkylammonium, pyridineImidazoleTetra alkyl radicalAnd various ions ranging from simple halides through inorganic complex ions (e.g., tetrafluoroborate) to large organic ions (e.g., trifluoromethanesulfonylimide) are used as anions.

It is advantageous to add at least one conductive salt to the inks according to the invention, since these salts have a negligible vapour pressure and are electrically conductive. Thus, the salt can be used as a film former and a conductive agent even at higher temperatures and low pressures. In particular in the case of printing processes, it is therefore also possible in some cases to prevent the printed image from flowing.

In a further development of the novel ink, the ink may additionally comprise a proportion of carbon black in addition to a proportion of carbon nanotubes and polymeric dispersant.

In the context of the present invention, carbon black denotes finely divided particles of elemental carbon in graphite or amorphous form. Finely divided particles in this context are particles having an average diameter of less than or equal to 1 μm.

If carbon black is added to the ink according to the invention according to this embodiment, it may preferably be used under the name PrintexPE from EVONIC carbon black.

The addition of a proportion of carbon black to the ink is advantageous, since the conductivity of the printed image obtained from the ink can be further increased with only a slight further increase in viscosity, since the carbon black fills the potential voids between the carbon nanotubes, as a result of which a conductive connection between the carbon nanotubes is established and thus the conductive cross section of the printed image is increased.

The present invention also provides a printable composition for the preparation of electrically conductive coatings based on carbon nanotubes and at least one polymeric dispersant in an aqueous formulation, in particular a method for the preparation of a printable composition according to the present invention, characterized in that it comprises at least the following steps:

a) optionally subjecting the carbon nanotubes to an oxidative pretreatment,

b) preparing an aqueous pre-dispersion by dissolving the polymeric dispersant in an aqueous solvent, and inputting and distributing carbon nanotubes in the resulting solution,

c) at least 10 of the pre-dispersion is fed⁴J/m³Preferably at least 10⁵J/m³Particularly preferably 10⁷～10⁹J/m³Until the aggregate diameter of the carbon nanotube aggregate is substantially 5 μm or less, preferably 3 μm or less, and particularly preferably 2 μm or less.

According to step a) of the method of the present invention, the carbon nanotubes should preferably be subjected to a pretreatment, which is usually carried out by treatment with an oxidizing agent.

It is advantageous to preferably perform a pretreatment with an oxidant in which the carbon nanotubes are dispersed in a 5 to 10 wt% aqueous solution of an oxidant, and then the carbon nanotubes are separated from the oxidant and then dried. The dispersion in the oxidizing agent is generally carried out for a period of 1 to 12 hours. The carbon nanotubes are preferably dispersed in the oxidizing agent for a period of 2h to 6h, particularly preferably about 4 h. The separation of the carbon nanotubes from the oxidant is typically performed by sedimentation. The separation is preferably carried out by sedimentation under the action of gravity or in a centrifuge. The drying of the carbon nanotubes usually takes place in the atmosphere and at a temperature of 60 ℃ to 140 ℃, preferably at a temperature of 80 ℃ to 100 ℃.

The oxidizing agent is typically nitric acid and/or hydrogen peroxide, and the oxidizing agent is preferably hydrogen peroxide.

The preparation of the aqueous predispersion according to step b) of the novel process is preferably carried out by previously placing in water, dissolving at least one polymeric dispersant and then adding carbon nanotubes.

According to a preferred embodiment of the invention, it is also possible to initially add an organic solvent to the water, preferably selected from the following series: c₁～C₅Alcohol (especially C)₁～C₃Alcohols of (a), ethers (especially dioxolanes) and ketones (especially acetone).

According to a preferred embodiment of the novel ink, carbon black and/or conductive salts can also be added in the context of step b) of the novel process.

The addition of the carbon nanotubes can be carried out together with the at least one polymeric dispersant or sequentially. Preferably, the at least one polymeric dispersant is added first, followed by the addition of the carbon nanotubes in portions. It is particularly preferred that the at least one polymeric dispersant is added first and then the carbon nanotubes are added in portions under stirring and/or sonication.

If, according to a preferred embodiment of the novel ink, the ink comprises a conductive salt and/or carbon black, the carbon black is preferably added in the same manner together with the carbon nanotubes and/or the conductive salt is added in the same manner together with the at least one polymeric dispersant.

The continuous and batchwise addition of carbon nanotubes under the action of stirring and/or ultrasound is particularly advantageous for the preparation of the predispersion, since this makes it possible to improve the dispersion of the carbon nanotubes up to the final ink, wherein the carbon nanotubes are present in a stable non-settling form and thus makes it possible to reduce the energy input into the predispersion required according to step c) of the process according to the invention.

According to a preferred embodiment of step b) of the method according to the invention, at least one conductive salt is also added after the addition of the at least one polymeric dispersant and the addition of the carbon nanotubes.

The volume-based energy density, for example in the form of shear energy, which is input into the predispersion in accordance with step c) of the novel process is particularly preferably carried out by: the pre-dispersion is passed through a homogenizer at least once. In the method, the volume-based energy density can be introduced into the predispersion, for example in the region of the nozzle orifice. Any embodiment known to those skilled in the art (e.g., high pressure homogenizer) is suitable for use as the homogenizer. The principle of a particularly suitable high-pressure homogenizer is known from the following documents: chemie Ingenieur Technik, Vol.77, No. 3 (p.258-. Particularly preferred homogenizers are high-pressure homogenizers, very particularly preferred high-pressure homogenizers are jet dispersers, slit homogenizers and microfluidizersHigh pressure homogenizers of the type.

Preferably, the predispersion is passed through a homogenizer, preferably a high pressure homogenizer, at least twice. Particularly preferably, the predispersion is passed through a homogenizer, preferably a high-pressure homogenizer, at least three times.

Multiple passes through the homogenizer (preferably a high-pressure homogenizer) are advantageous because the coarse aggregates of carbon nanotubes which may remain are thereby comminuted, as a result of which the physical properties of the ink (for example viscosity and conductivity) are increased. By adjusting the inlet pressure and thus the automatic adjustment of the gap width of the homogenizer, the maximum size of the aggregates optionally retained can be influenced in a targeted manner.

This economic optimization is achieved when less than 15% by number of the carbon nanotubes in the ink are still present as aggregates of ≦ 10 μm, which corresponds approximately to passing the predispersion through the homogenizer, preferably a high-pressure homogenizer, for three times.

The homogenizer, preferably a high-pressure homogenizer, usually a jet disperser or a slit homogenizer, operates with an inlet pressure of at least 50 bar and a gap width which is automatically adjusted.

The homogenizer, preferably a high-pressure homogenizer, preferably operates with an inlet pressure of 1000 bar and a gap width which is automatically adjusted. Most particularly preferred is a high pressure homogenizer of the Micronlab type.

An alternative, likewise preferred embodiment of steps b) and c) of the novel process provides for the treatment of the predispersion in a three-roll mill.

The preferred process is characterized in that the preparation b) of the predispersion and the input c) of the shear energy are carried out by: treating the pre-dispersion in a three-roll mill with rotating rolls, wherein the method comprises at least the following steps:

b1) introducing a solution of the polymeric dispersant in the aqueous solvent with the carbon nanotubes into a first nip between first and second rollers having different rotational speeds, wherein the carbon nanotubes are pre-dispersed in the solution and coarse aggregates are comminuted;

b2) conveying the predispersion from step b1) to a second gap between a second roller and a third roller having different rotational speeds, the predispersion adhering at least partially to the roller surface during the conveying;

c1) introducing the predispersion into the second gap, wherein the aggregates of carbon nanotubes in the dispersion are comminuted to a diameter of substantially 5 μm or less, preferably 3 μm or less, particularly preferably 2 μm or less;

c2) the final dispersion was removed from the roll surface of the third roll.

An alternative embodiment of the process according to the invention is preferably operated in such a way that the ratio of the rotational speeds of the first and second roll and the ratio of the rotational speeds of the second and third roll independently of one another is at least 1: 2, preferably at least 1: 3.

The width of the gap between the first and second rollers and the width of the gap between the second and third rollers may be the same or different. The gap widths are preferably the same. The gap widths are particularly preferably the same and less than 10 μm, preferably less than 5 μm, particularly preferably less than 3 μm.

The alternative steps b) and c) of carrying out the novel process are particularly advantageous because as a result of the different rotational speeds of the rolls of the same diameter, high shear rates are achieved in the first and second gaps, which leads to a good dispersion of the carbon nanotubes. Particularly in combination with a preferably equal small gap width, the result is very advantageous. By an alternative embodiment of step c), inks with a small aggregate proportion and small aggregate size can be obtained. In a preferred embodiment, the adjustment of the gap in the homogenizer (preferably a high-pressure homogenizer) is controlled by adjusting the inlet pressure so that it is comparable to the adjustment of the gap between the rolls in the three-roll mill. In a preferred embodiment, the passage through the two slits in the three-high rolling mill can correspond approximately to two passages in a homogenizer (preferably a high-pressure homogenizer).

The inks according to the invention and their preferred and alternative embodiments obtained by the process according to the invention are particularly suitable for use in known high throughput processes for the preparation of electrically conductive printed images, such as screen printing, offset printing or the like.

The invention also provides a conductive coating which is obtainable by printing, in particular by screen printing or offset printing, a composition according to the invention onto a surface and removing the solvent or solvents.

The invention also provides electrically non-conductive or conductive coatings obtainable from the compositions of the inventionObjects of poorly performing material (surface resistance less than 10)⁴Ohm·m)。

In a further development of the use of the inks according to the invention, the electrically conductive printed images of the inks can optionally be subjected to a thermal post-treatment.

The thermal post-treatment of the printing ink in its use is preferably carried out by: drying is carried out at a temperature of from room temperature (23 ℃) to 150 ℃, preferably from 30 ℃ to 140 ℃ and particularly preferably from 40 ℃ to 80 ℃.

Thermal aftertreatment is advantageous if the adhesion between the ink according to the invention and the substrate can thus be improved and the printed ink can thus be protected against smearing by wiping (Verwischen).

In addition to the good conductivity of the printed images of the inks according to the invention and preferred embodiments thereof, the new inks have other properties, which may be advantageous for other applications.

For example, the material set of carbon nanotubes and the particular carbon nanotubes used in accordance with the present invention are known to have particularly high strength. It is therefore contemplated to use the ink by the present invention by applying it to a surface to at least partially transfer the positive mechanical properties of the particular carbon nanotube to the surface.

Furthermore, carbon nanotubes obtained according to the content of, for example, the hitherto unpublished German patent application with official application No. 102007044031.8 are characterized by a specific length-to-diameter ratio (so-called aspect ratio). With the ink according to the invention, the possibility thus arises of exposing the resulting printed image to further mechanical loads in the form of deformation loads (e.g. deep drawing, if the surface consists of a polymer material) without the carbon nanotubes losing contact with each other and therefore without the printed image losing electrical conductivity, since the carbon nanotubes align themselves in the direction of stress (ausrichten).

The following examples are for illustrative purposes and should not be construed as limiting the invention.

Examples

Example 1: (preparation of catalyst)

0.306kg of Mg (NO)₃)₂*6H₂Solution of O in water (0.35L) with 0.36kg Al (NO)₃)₃*9H₂A solution of O in 0.35 liter of water was mixed. Then, 0.17kg of Mn (NO) each dissolved in 0.5 liter of water was added₃)₂*4H₂O and 0.194kg Co (NO)₃)₂*6H₂O, the pH of the entire mixture was adjusted to about 2 by adding nitric acid while stirring for 30 minutes. This stream of solution was mixed with 20.6% by weight sodium hydroxide solution in a ratio of 1.9: 1 in a mixer and the resulting suspension was added to a 5 liter water charge (Vorlage). The pH of the charge was maintained at about 10 by controlled addition of sodium hydroxide solution.

The precipitated solid was separated from the suspension and washed several times. The washed solid was then dried in a paddle dryer over 16h, increasing the temperature of the dryer from room temperature to 160 ℃ over the first eight hours. The solid is then ground in a laboratory mill to an average particle size of 50 μm, and the intermediate fraction in the particle size range of 30 μm to 100 μm is removed for subsequent calcination, in particular for increasing fluidization in the fluidized bed and for obtaining high product yields. The solid was then calcined in a furnace at 500 ℃ for 12 hours under air introduction conditions and then cooled for 24 hours. The catalyst material was then kept for 7 more days for post oxidation at room temperature. A total of 121.3g of catalyst material was isolated.

Example 2: (preparation of CNT in fluidized bed)

The catalyst prepared in example 1 was tested on a laboratory scale in a fluidized bed apparatus. For this purpose, a quantity of catalyst is placed in a steel reactor of 100mm internal diameter heated from the outside with a heat transfer medium. The temperature of the fluidized bed is regulated by PID regulation of the electrically heated heat transfer medium. The temperature of the fluidized bed was measured by a thermocouple. Feed gas and inert diluent gas are introduced into the reactor through electronically controlled mass flow regulators.

The reactor was first rendered inert with nitrogen and heated to a temperature of 650 ℃. 24g of catalyst 1 according to example 1 are then metered in.

The feed gas was then immediately switched on as a mixture of ethylene and nitrogen. The volume ratio of the raw material mixture is ethylene to N₂90: 10. The total volume flow is adjusted to 40LN min^-1. The passage of the raw material gas over the catalyst was carried out for 33 minutes. The ongoing reaction is then terminated by interrupting the feed supply and the contents of the reactor are removed.

Example 3

25g of carbon nanotubes prepared according to example 2 were previously added to 250g of water. At RT, 334g of 10% H are added dropwise in 1.15H₂O₂. A small amount of gas was generated and the temperature rose to 29 ℃. The mixture was then stirred at RT for an additional 4h and left overnight to allow the carbon nanotubes to precipitate. The supernatant was then decanted. The precipitated carbon nanotubes were washed twice with water and then dried at 60 ℃ until a constant mass was reached. The aggregates are smaller than 200 μm after the predispersion.

0.5g of the oxidized carbon nanotubes in each case were dispersed in succession ten times in 95g of a 2% aqueous solution of PVP40 (from SIGMA-ALDRICH) using an ultrasonic finger (G.Heinemann, ultrashallund Labortechnik) at an amplitude of 30% of the maximum power, each time for 3 min. The entire dispersion was then reprocessed with the ultrasonic fingers at 40% amplitude for 6 min. The samples were treated with a high-pressure homogenizer (Gaulin Micron Lab, AVP Gaulin GmbH) in three passes, in each case with a differential pressure of 1000 bar, for further dispersion. The particles are less than 3 μm after the dispersion. The viscosity of the dispersion at a shear rate of 1/s was 1.68 pas.

The resulting paste was passed through a wire mesh (Heinen,) Application to polycarbonate (Macrolon)Bayer Material Science AG) and dried at RT. The conductivity of the resulting printed image was then measured. It is 3X 10³S/m。

A photograph of the coating under a transmission electron microscope shows that the aggregates of carbon nanotubes have a diameter of 1 μm and less.

Claims (20)

1. Printable composition for producing electrically conductive coatings, based on carbon nanotubes and at least one polymeric dispersant in an aqueous formulation, characterized in that at least one fifth of the carbon nanotubes consist of carbon nanotubes having a molecular structure comprising several graphene layers which are present in the form of assembled stacks and rolled up.

2. Composition according to claim 1, characterized in that the carbon nanotubes have a length to diameter ratio exceeding 5, preferably exceeding 100.

3. The composition of claim 1 or claim 2, characterized in that the carbon nanotubes have an average outer diameter of 3 to 100nm, preferably 5 to 80nm, particularly preferably 6 to 60 nm.

4. Composition according to one of claims 1 to 3, characterized in that the carbon nanotubes are present at least partly in the composition as aggregates, wherein the diameter of the aggregates is substantially at most 5 μm, preferably at most 3 μm, particularly preferably at most 2 μm.

5. Composition according to one of claims 1 to 4, characterized in that the proportion of all carbon nanotubes in the composition is between 0.1% and 15% by weight, preferably between 5% and 10% by weight.

6. Composition according to one of claims 1 to 5, characterized in that the carbon nanotubes have been subjected to an oxidative pretreatment, in particular with HNO₃And/or H₂O₂Preferably with H₂O₂And carrying out oxidation pretreatment.

7. Composition according to one of claims 1 to 6, characterized in that the polymeric dispersant is selected from the following series: water-soluble homopolymers, water-soluble random copolymers, water-soluble block copolymers, water-soluble graft polymers, in particular polyvinyl alcohol; copolymers of polyvinyl alcohol and polyvinyl acetate; polyvinylpyrrolidone; cellulose derivatives such as carboxymethyl cellulose, carboxypropyl cellulose, carboxymethyl propyl cellulose, hydroxyethyl cellulose; starch; gelatin; a gelatin derivative; an amino acid polymer; a polylysine; polyaspartic acid; a polyacrylate; polyethylene sulfonates; polystyrene sulfonate; polymethacrylates; a polysulfonic acid; condensation products of aromatic sulfonic acids with formaldehyde; naphthalene sulfonate; lignosulphonate; copolymers of acrylic monomers; a polyethyleneimine; a polyvinylamine; polyallylamine; poly (2-vinylpyridine); a block copolyether; block copolyether containing polystyrene blocks and polydiallyldimethylammonium chloride.

8. Composition according to one of claims 1 to 7, characterized in that the proportion of the polymeric dispersant in the composition is from 0.01% to 10% by weight, preferably from 0.1% to 7% by weight, particularly preferably from 0.5% to 5% by weight.

9. Composition according to one of claims 1 to 8, characterized in that organic solvents, preferably alcohols, ethers, ketones and dioxolanes, can be added.

10. Composition according to one of claims 1 to 9, characterized in that the composition has a dynamic viscosity of at least 0.5 Pa-s, preferably 1 to 200 Pa-s.

11. Method for the preparation of a printable composition for the preparation of electrically conductive coatings based on carbon nanotubes and at least one polymeric dispersant in an aqueous formulation, in particular a printable composition according to one of claims 1 to 9, characterized in that it comprises at least the following steps:

d) optionally subjecting the carbon nanotubes to an oxidative pretreatment,

e) preparing an aqueous pre-dispersion by dissolving the polymeric dispersant in an aqueous solvent, and inputting and distributing carbon nanotubes in the resulting solution,

f) at least 10 of the pre-dispersion is fed⁴J/m³Preferably at least 10⁵J/m³Particularly preferably 10⁷～10⁹J/m³Until the aggregates of the carbon nanotube aggregates are alignedThe diameter is substantially 5 μm or less, preferably 3 μm or less, particularly preferably 2 μm or less.

12. The method of claim 11, characterized in that the oxidative pretreatment is with HNO₃And/or H₂O₂Preferably with H₂O₂The method is carried out.

13. The method of claim 11 or claim 12, characterized in that the input of the volume-based energy density is performed by: the predispersion is passed at least once through a homogenizer, preferably a high-pressure homogenizer, in particular a jet disperser or a slit homogenizer, wherein the volume-based energy density is introduced into the predispersion in the region of the nozzle orifice.

14. The process of claim 13, characterized in that the predispersion is passed through a homogenizer, preferably a high-pressure homogenizer, in particular a jet disperser or a slit homogenizer, at least twice, preferably at least three times.

15. The process as claimed in claim 11 or claim 12, characterized in that the preparation b) of the predispersion and the input c) of shear energy are carried out by: treating the pre-dispersion in a three-roll mill with rotating rolls, wherein the method comprises at least the following steps:

b1) introducing a solution of the polymeric dispersant in the aqueous solvent with the carbon nanotubes into a first nip between first and second rollers having different rotational speeds, wherein the carbon nanotubes are pre-dispersed in the solution and coarse aggregates are comminuted;

b2) conveying the predispersion from step b1) to a second gap between a second roller and a third roller having different rotational speeds, the predispersion adhering at least partially to the roller surface during the conveying;

c1) introducing the predispersion into the second gap, wherein the carbon nanotube aggregates in the dispersion are comminuted to a diameter of substantially 5 μm or less, preferably 3 μm or less, particularly preferably 2 μm or less;

c2) the final dispersion was removed from the roll surface of the third roll.

16. The method according to claim 15, characterized in that the width of the gap between the first and second roll and the width of the gap between the second and third roll are, independently of each other, less than 10 μm, preferably less than 5 μm, particularly preferably less than 3 μm.

17. The method according to claim 15 or 16, characterized in that the ratio of the rotational speeds of the first and second roll and the ratio of the rotational speeds of the second and third roll are, independently of each other, at least 1: 2, preferably at least 1: 3.

18. Use of the printable composition according to one of claims 1 to 10 in a high throughput printing process, in particular a screen printing process or an offset printing process for the preparation of electrically conductive printed images.

19. Conductive coating obtainable by printing, in particular by screen printing or offset printing, a composition according to one of claims 1 to 10 onto a surface and removing the solvent or solvents.

20. An object of a non-conductive or poorly conductive material having a coating according to claim 19.