EP2185660A1

EP2185660A1 - Printable and conductive paste and method for coating a material with said paste

Info

Publication number: EP2185660A1
Application number: EP08830858A
Authority: EP
Inventors: Gernot Frackmann; Benno Schmied; Björn HELLBACH; Michael Roth; Gunter Scharfenberger; Ansgar Komp
Original assignee: Carl Freudenberg KG
Current assignee: Carl Freudenberg KG
Priority date: 2007-09-06
Filing date: 2008-09-04
Publication date: 2010-05-19
Also published as: US20100300618A1; DE102007042253A1; WO2009033602A1

Abstract

The invention relates to a printable and conductive paste comprising dispersible thermoplastic polyurethane, a conductive filler, a water-soluble thickener, and water. The invention further relates to a method for coating a material with a paste according to one of the previous claims, wherein the paste is printed onto at least one material and subsequently dried, and the material printed with the paste is subjected to a combined heat and pressure treatment.

Description

Printable and conductive paste and method for coating a material with the paste

Technical area

The invention relates to a printable and conductive paste comprising a dispersion of a polyurethane in an aqueous solution and to a method for coating a material with the paste.

State of the art

Such pastes are known from EP 1 284 278 A2. The aqueous coating composition contains a conductive powder in which a non-conductive core is coated with a conductive layer. Preferably, a core of glass is coated with silver. The pastes described therein are used, for example, to coat flat layers, in particular textiles and nonwovens, and to equip them with electrical conductivity. Coated layers of this kind can be further processed into flexible printed conductors. It is also possible to equip the layers with the paste so that they shield electromagnetic fields. Another area of application is the use of conductive textiles in clothing. In the case of the paste known from the prior art, it is disadvantageous that it is no longer expansible and thermally deformable due to the binder after application to the material and curing. One coated with the paste Material is therefore also not stretchable. The paste can therefore not be used where stretchability of the material is required.

A screen printing paste for electrically conductive coatings based on electrically conductive polymers is described in DE 197 57 542 A1.

US 2005/0224764 relates to electrically conductive inks containing carbon fibrils. Antistatic coatings for textiles are described in US 2004/0051082.

Presentation of the invention

The invention has for its object to provide an electrically conductive paste that is easy to process and even after curing is stretchable.

This object is achieved with the features of claims 1 and 11. In advantageous embodiments, the dependent claims relate.

To achieve the object, the printable and conductive paste contains a dispersible thermoplastic polyurethane, a conductive filler, a water-soluble thickener and water. The thermoplastic polyurethane forms the binder of the paste and is both ductile and thermoformable. Thus, the paste is stretchable even after processing and can be reshaped by thermal forming processes at any time, while the stretchability is maintained. The conductive filler is mixed in such a way that the conductive particles touch each other after processing, thus establishing the conductivity. The viscosity of the paste is determined via the water-soluble thickener. According to the invention, this is between 8,000 and 150,000 mPas, preferably between 20,000 and 150,000 mPas, so that the paste can be applied to a material by a printing process, preferably screen or stencil printing.

Pastes of the invention may preferably contain from 2 to 40% by weight, preferably from 4 to 25% by weight, particularly preferably from 5 to 15% by weight, of thermoplastic polyurethane. The proportion of the conductive filler is preferably 2-40% by weight, in particular 15-40% by weight, particularly preferably 20-35% by weight. It is preferably between 1 to 5 wt.%, Preferably 1, 5 -. 3 wt.%, Thickener included. In the dry substance thus proportions of 15 to 80 wt.%, Preferably 15 to 40 wt.% Thermoplastic polyurethane, 15 to 85 wt.% Conductive filler and 0.5 to 4.5 wt.% Thickener.

The thickener is provided in a preferred embodiment as an aqueous thickener solution. The thickener solution contains, for example, 1 to 5% by weight of the thickener dissolved in water. Preference is given to using distilled or bidistilled water. In the pastes according to the invention, the proportion of thickener paste is preferably 40-80% by weight, more preferably 55-75% by weight. The paste according to the invention is preferably water-based. It thus contains no organic solvents or less than 2, 1 or 0.5 wt.% Organic solvents.

The sheet resistance of the paste after drying and calendering is preferably between 0.05 to 0.5 ohms, whereby the resistance increases by a factor of 10 to 1000 when the paste is stretched by 20% by weight, depending on the composition. In this case, the higher the proportion of the conductive filler, the lower the resistance. The paste may contain adjuvants such as humectants and rheological additives to improve processability. The thickener may contain or consist of cellulose derivatives, for example methylcellulose. Cellulose derivatives are chemical compounds derived from cellulose. The result is a hydrophilic powder which forms a viscous solution with water. Cellulose derivatives are not digestible, non-allergenic and non-toxic and therefore suitable for the production of a paste for coating clothing textiles. A suitable methylcellulose thickener is, for example, Metylan® Normal (Henkel, Dusseldorf).

The paste according to the invention contains thermoplastic polyurethanes (PU). Polyurethanes are essentially formed by the reaction of polyols (long-chain diols), diisocyanates and optionally short-chain diols. The nature of the starting materials, the reaction conditions and the proportions are responsible for the properties of the product. The polyols used are in particular polyester polyols or polyether polyols. Methods are known to the person skilled in the art to select the starting materials and the reaction conditions in such a way that polyurethanes having desired properties, for example melting point, density and hardness, are obtained. Thermoplastic polyurethane elastomers are also referred to as TPUs.

The thermoplastic polyurethane may have a melting point between 80 and 220 ⁰ C, in particular between 100 and 180 or between 110 and 150 ⁰ C. Such polyurethanes can be used without problems on textiles and can be processed and formed by conventional methods, such as calendering or thermoforming. The melting point of the polyurethane is adjusted with regard to the desired processing method and the material to be coated. Therefore, depending on the application, higher melting point polyurethanes with melting points approximately between 120 and 220 ⁰ C, in particular above 130 or 14O ⁰ C, or low melting Polyurethanes with melting points approximately between 80 and 120 ⁰ C, in particular below 110 ⁰ C ₁ used. Polyurethanes usually do not have a clearly defined melting point, but a melting range in which the material changes from the solid to the liquid state. According to the invention, the melting point is the temperature at which this melting process begins.

The polyurethanes may be aliphatic or aromatic. Aliphatic polyurethanes of comparatively low melting range have the advantage that they are generally lightfast and do not yellow.

The polyurethanes are preferably stirred into the pastes as fine powders, for example with average particle diameters of <350 μm, preferably <200 μm or <120 μm, in particular between 20 and 350 μm, between 50 and 200 μm or between 80 and 120 μm. The small particle size makes it possible to produce a homogeneous dispersion, improves the pressure behavior and accelerates the manufacturing process due to rapid melting.

In a preferred embodiment of the invention, the polyurethane used according to the invention contains no free reactive groups, in particular no free isocyanate groups. Such thermoplastic polyurethanes are obtained, for example, when the reaction between the polyol, the chain extender and the polyisocyanate is carried out with a stoichiometric excess of diol or polyol, so that the polymer has only free, for example terminal, hydroxyl groups. In this embodiment, therefore, the polyurethane is not a reactive polymer, but cured. Such a polyurethane does not react under normal conditions and in aqueous solution. The polyurethane differs from that commercially available prepolymers with free isocyanate groups. Such prepolymers are offered, for example, in the form of dispersions.

According to the invention, the polyurethanes are used as binders, while the conductivity is effected by the conductive fillers. Therefore, the paste of the invention preferably contains no conductive polymers. In a preferred embodiment of the invention, the polyurethanes are uncharged polyurethanes. Preferably, the paste contains only uncharged polyurethanes. Thus, no ionic polyurethanes are included. The paste of the invention thus differs from the

Compositions of EP 1 284 278. Uncharged polyurethanes are generally not or only poorly water-dispersible. Novel pastes with uncharged polyurethanes are preferably suspensions in which polyurethanes are finely dispersed as solids. By contrast, the ionic polyurethanes used according to EP 1 284 278, for example, are dispersed in an aqueous solution in molecular form. Commercially available polyurethane dispersions (such as the brand ROTTA WS 80525 from Rotta GmbH) are usually prepared by dispersing a liquid and still reactive polyurethane prepolymer under very high shear with an emulsifier. Often, such a dispersion still contains solvents, which are subsequently removed from the PU dispersion. The ionic groups of the polyurethane thereby increase the dispersibility and thus the storage stability, because settling of the polyurethane particles (density about 1, 1) due to the mutual repulsion is prevented or greatly reduced. Ionic polyurethanes resulting from the drying of these (emulsifier-containing) dispersions have the disadvantage that the water absorption and swelling in water due to the hydrophilicity of the ionic groups is significantly higher than nonionic polyurethanes. In principle, ionic polyurethanes can also be used according to the invention. If the viscosity of the (conductive) paste is adjusted such that the polyurethane particles and the copper flakes do not sink, neither the use of an ionic polyurethane nor the use of emulsifiers is necessary. In a preferred embodiment of the invention, the paste contains no emulsifiers.

Thermoplastic polyurethanes which are suitable according to the invention can be, for example, diphenylmethane diisocyanate (MDI), such as 2,2'-, 2,4'- and / or 4,4'-diphenylmethane diisocyanate, hexamethylene-1,6-diisocyanate (HDI), isophorone diisocyanate (IPDI), tolylene diisocyanate (TDI), naphthylene-1,5-diisocyanate (NDI), dimethyl-diphenyl-diisocyanate TODI), dicyclohexyl-methane-4,4'-diisocyanate (HMDI).

Suitable polyols are polyethers, e.g. Polytetrahydrofuran (PTHF) or polypropylene glycol (PPG), polyesters, e.g. Ethylene adipate polyol, butylene adipate polyol, NPG adipates, polycarbonate polyols and polycaprolactone polyols, and polyetherester polyols.

These are optionally used in conjunction with suitable chain extenders. Suitable chain extenders include, for example, short chain diols such as ethylene glycol, propanediol, butanediol, diethylene glycol, hexanediol, cyclohexanedimethanol (CHDM), hydroquinone hydroxyethyl ether (HQEE), as well as diamines and in minor amounts triamines or triols e.g. Trimethylolpropane.

Especially preferred is the use of polyurethanes of ethylene glycol adipic acid polyester polyol, butanediol, hexanediol and diphenylmethane-4,4 ¹ - diisocyanate. Such a TPU, for example, has a melting point of about 135 ° C. For applications at lower temperatures, for example, a TPU made of polycaprolactone polyol and 1, 6-hexamethylene diisocyanate with the chain extenders: 1, 6-hexanediol and 1, 4-butanediol extended. To achieve melting temperatures of the TPU below 110 ⁰ C polyols can be added from neopentyl glycol adipate and other isomers of butanediol.

A suitable thermoplastic polyurethane can be prepared for example from the components methylene diphenyl isocyanate, polycarbonate / hexanediol neopentyl glycol adipate and butanediol. The thermoplastic polyurethane has a melting range of 160 to 170 ⁰ C. Such higher melting polyurethanes usually have a Shore hardness of 60 to 98 Shore (A) and are due to the crystallization especially for thermoforming processes.

Another polyurethane comprises the components methylene diphenyl isocyanate, polycaprolactone and hexanediol. This thermoplastic polyurethane has a melting range of 125 to 135 ° C. Low-melting polyurethanes usually have a Shore hardness of 40 to 85 Shore (A) and are particularly suitable for use on low-melting textiles.

In one embodiment of the invention, the paste contains no crosslinker. It is then added before or during processing no crosslinker. In this way, an uncrosslinked thermoplastic coating is obtained. Due to the thermoplastic properties, the possibility of deformability (for example by deep drawing) is given. Such a post-treatment is not with crosslinked polyurethanes, for example from commercial PU dispersion or those according to EP 1 284 278 A2 possible. In a preferred embodiment of the invention, the polyurethanes have a melting point above 120 ^° C. in non-crosslinked pastes.

In a further embodiment of the invention, a crosslinker is contained in the paste, or a crosslinker is added to the paste before or during processing. The polyurethane in this embodiment contains crosslinkable hydroxyl groups. It is, for example, a polyurethane which has a low characteristic number, for example <99, <98, or <95, in particular> 80, or of 80-98 (characteristic number = n (NCO) / n (OH) * 100). In a preferred

Embodiment of the invention, the polyurethanes in crosslinked pastes have a melting point below 120 ⁰ C, in particular below 110 ⁰ C. The melting point is then for example between 80 and 120 ⁰ C or 90 and 11O ⁰ C. The crosslinker is a compound that can link hydroxyl groups, preferably a diisocyanate or polyisocyanate. Preferably, the crosslinker is a blocked isocyanate, which acts only above a defined temperature, for example 70-140 ⁰ C, crosslinking. The paste with the crosslinker is preferably storage stable at 25 ° or 40 ⁰ C, ie there is no crosslinking.

The melting point of the thermoplastic polyurethane can be adjusted to values below 12O ⁰ C or 110 ⁰ C by selecting suitable polyols and chain extender combinations. Such polyurethanes can be used if the substrate to be printed has a low melting point itself (eg in the case of a stretchable PU nonwoven fabric). One

Melting point below 110 ^° C. can be achieved, for example, with polycaprolactone polyol and additionally polyol from neopentyl glycol adipate and use of several chain extenders (1,6-hexanediol, 1,4-butanediol and 2,3-butanediol) and 1,6-hexamethylene diisocyanate. To increase the temperature stability of the coated materials, it is possible, this low to add a crosslinker to the melting paste. An inventive crosslinker which is added to this paste, for example, is ground isocyanate, such as diphenylmethane-4,4'-diisocyanate (MDI) or S.S'-DimethylbiphenyM ^ ¹ - diisocyanate (TODI), having a melting point below 110 ⁰ C. In the aqueous paste forms a thin on the isocyanate powder surface

Urea layer by reaction of isocyanate and water, which causes the water permeability and thus the urea reaction inside the isocyanate particles is slowed down very much. The paste is therefore storage stable. During the calendering process, the polyurethane and the isocyanate melt and the crosslinking reaction of the isocyanate with the free OH groups of the polyurethane occurs. In this case, the crosslinkability of advantage, since sensitive substrates can be printed and the crosslinking reaction, the temperature stability of the coating is increased.

In preferred embodiments of the invention, the conductive filler is selected from metallic particles, carbon nanotubes, low melting alloys and / or copper flakes.

The conductive filler may consist of metallic particles, preferably copper- and / or silver-based. Such metal-based particles have a particularly good conductivity. Copper and silver based particles are also corrosion resistant. The particles may be spherical, fibrous or flat. The advantage of the planar fillers is that they align themselves parallel to each other after a pressure treatment and overlap. This results in a particularly low sheet resistance. Spherical particles are particularly easy to disperse. By "metallic" particles according to the invention refers to particles which consist largely or completely of metal, ie more than 95%,> 99% or 100%. The conductive filler may comprise copper flakes. Copper flakes are flat particles. They can be aligned in parallel in a combined pressure and heat treatment. You can then overlap each other and thus have a low sheet resistance. The copper flakes which can be used according to the invention have, for example, average diameters of 5 to 100 μm, in particular 20 to 60 μm, and heights of 0.2 to 10 μm, in particular 0.5 to 8 μm. The copper flakes are preferably coated with a noble metal, in particular silver. The proportion of the coating is preferably 1 to 25, in particular 5 to 20 wt.%. Suitable copper flakes are available, for example, under the trade name Conduct-O-Fil SC230F9.5 (Potters Industries Inc.). These are flat copper plates with a mean diameter of approx. 40 μm and a height of approx. 1-5 μm. The shape of the platelets can be recognized on the SEM images (FIGS. 1 and 2). They are silvered with a weight proportion of about 9-10 wt.%.

The conductive filler may include carbon nanotubes. Carbon nanotubes (CNT) are tubular structures made of carbon. These have a diameter of 1 to 50 nm. The carbon nanotubes may be filled with metals, for example silver. Carbon nanotubes are characterized by a high current carrying capacity. It is also conceivable to form metal-coated, for example silver-coated, glass fibers as a conductive filler.

The conductive filler may include a low melting alloy. Such an alloy is, for example, a tin-bismuth alloy. Such alloys melt during a heat and pressure treatment, for example during calendering. The low melting alloy particles may be mixed with other particles, such as silver or copper. It is advantageous that the other particles through the low-melting particles are bonded cohesively and thus sets a particularly low sheet resistance. In the context of the invention "niedrigeschmelzend" means that the alloy melt at the processing temperatures of the pastes, particularly 100-220 ⁰ C, between 100 and 180 ⁰ C or between 110 and 150 ° C.

In a preferred embodiment of the invention, the paste additionally contains at least one antioxidant. Suitable examples are organic antixydants such as ascorbic acid, ascorbates such as sodium ascorbate or reducing saccharides such as glucose and inorganic antioxidants such as reducing metal salts, in particular reducing salts such as ammonium iron (II) sulfate. Preferably, in the preparation of the paste according to the invention, an aqueous solution of the antioxidants is first prepared in distilled water. This has, for example, 0.2 to 5 wt.%, Preferably 1, 5 to 3 wt.% Antioxidants on.

The preparation of the paste according to the invention is preferably carried out by first providing an aqueous solution of the thickener and optionally the antioxidant (thickener solution). Preferably, the thickener swells while being stirred for a sufficient time, for example 10 to 30 minutes. A suitable viscosity is set, for example between 1500 and 20,000 mPas.

Subsequently, the thermoplastic polyurethane, the conductive filler and optionally the crosslinker are added and mixed by stirring to a homogeneous paste. The paste is preferably degassed. If a crosslinker is used, it is preferably first mixed with the PU powder and / or the filler in order to achieve a more homogeneous distribution. In one embodiment of the invention, the paste has a pH of from 6 to 8.5, preferably from 7 to 7.5. The pH is in a preferred embodiment at about pH 7.0. These pHs are also preferably adjusted when antioxidants are included. By adjusting the pH in this range, by using antioxidants and by producing and storing in the absence of air, undesirable changes in the pastes can be avoided.

In the method according to the invention for coating a material with the paste according to the invention, the paste is printed on at least one material and then dried and subjected to the material printed with the paste of a combined heat and pressure treatment.

The paste according to the invention enables the application by means of printing processes. Decisive for the printability are the particle size and the dependent on the proportion of thickener viscosity of the paste. The printing process makes it possible to easily and inexpensively print large areas with a reproducible pattern. After the printing process, the paste is dried, for example, in a continuous furnace.

In a preferred embodiment of the invention, the paste is exposed to the conductive particles in a subsequent to the drying heat and pressure treatment, preferably a calendering. The paste is solidified, the contact and the adhesion to the material are improved and the conductive particles are aligned. The result is a smooth surface and an electrically conductive and stretchable coating of the material. In this treatment, the polyurethane melts and the copper flakes are temporarily "floating" in the PU matrix, and the applied pressure solidifies the printed paste on the substrate, compressing them to make the thin platelets parallel to the substrate Aligned to the pressure applied, they "fold over." A structure is achieved in which the platelets are more or less in one plane, overlapping each other, as can be seen on SEM images of the image panels (see Figures 1 and 2). The orientation of the platelets ensures that even with an expansion of the matrix, a sufficiently good overlap or contact of the platelets takes place, so that a good conductivity is maintained.

In a preferred embodiment of the invention, a material which has been provided with the paste is stretched in a thermal aftertreatment. For example, a deep-drawing process is suitable for this. This will be a

Elongation reached, i. The PU matrix softens under pressure and heat and is stretched. After cooling, it maintains the stretched shape. However, the silver-plated copper platelets still overlap so that the electrical conductivity is maintained. During deep drawing, the orientation of the platelets is further improved, so that even with a stretch or elongation of the substrate still enough platelets overlap.

The paste can be printed by screen or stencil printing. Depending on the choice of screen printing fabrics, large layer thicknesses of the printed paste are possible.

The material with the printed paste can be thermoformed following the combined heat and pressure treatment. An advantage of using a thermoplastic polyurethane is that such pastes can be reshaped at any time by melting the polyurethane. Therefore, the already provided with the paste materials can be repeatedly transformed later.

It can provide several materials with the paste and bonded by pressure and heat treatment through the paste cohesively become. As a result, textiles can be conductively connected to each other. This is particularly advantageous for garments, since here the conductive and cohesive connection of several clothing sections is possible with simple means.

Materials coated with the paste according to the invention are particularly suitable for automotive applications, such as dashboards and headliners having a three-dimensional, curved geometry, wherein the material provided with the paste is thermally deformed and assumes the shape of the material. Furthermore, the paste according to the invention is suitable for use in clothing, in particular functional clothing with integrated electronic components. Here the paste forms flexible tracks on the clothing. Furthermore, a use in medical clothing and medical aids is conceivable. Another field of application is the functional coating of aggregates and pipelines. It is also conceivable to produce antistatic finish with the paste according to the invention or to use the paste for heating / cooling applications.

Brief description of the drawing

The figures show SEM images of a nonwoven fabric which has been printed with the paste according to the invention and subjected to a subsequent combined heat and pressure treatment.

embodiments

In the following exemplary embodiments, the following measuring methods were used: The viscosity is determined by means of a Brookfield viscometer in accordance with DIN EN ISO 2555 (resins in the liquid state, as emulsions or dispersions, determination of the apparent viscosity by the Brookfield method, depending on viscosity, spindle 6 or 7, speed: 20 rpm) ,

The sheet resistance is determined by a straight, rectangular structure (conductor track) whose mean layer thickness is determined by means of one or more micrographs. Since the nonwoven fabric does not form a closed surface, the paste partly penetrates into the open area (see SEM images), envelops the fibers and therefore has a variable layer thickness within certain limits. The electrical conductivity / resistance is measured using a four-point method to avoid false measurements due to contact resistance.

The tensile strength of plastics (ductility) can be determined by the method of DIN 53504 or better for films according to ISO 527-3. The strain rate is set here to 1% / sec.

The determination of the elongation (up to the conductor breakage) takes place in accordance with the determination of the extensibility, wherein at the same time, by contacting the conductor track with a measuring device, the electrical conductivity is measured. As a conductor break, the increase in resistance by three orders of magnitude is considered in the present conductors. The maximum elongation reached at the conductor break is called elongation.

The melting range is determined by means of a Kofler bench. Example 1 :

The polyurethane used is a nonionic, thermoplastic, non-crosslinked, OH-terminated polyurethane. This is made from ethylene glycol

Adipic polyester polyol and diphenylmethane-4,4'-diisocyanate with the addition of chain extenders butanediol and hexanediol produced. The index, which describes the ratio of isocyanate groups to hydroxyl groups in the polymer, is less than 100. The TPU has a melting point of about 135 ° C and is used as a fine powder. To prepare the paste, an aqueous solution of the thickener methylcellulose (Metylan Normal®, Henkel) is prepared with stirring. The thickener swells with stirring for another 20 minutes. Depending on the concentration of the thickener, the aqueous solution has a viscosity of between 1500 and 20,000 mPas. In the solution, the TPU powder and the conductive filler are stirred, processed with further stirring to a homogeneous paste and then degassed under vacuum. When using a crosslinker, this is weighed together with the PU powder and / or the filler and mixed. When using antioxidants, an approximately 2.8% solution with a pH of 7.0 is first prepared with demineralized water, into which the thickener is stirred.

A first example of a paste according to the invention contains 60% by weight of a solution consisting of 1.5% Metylan® Normal (Henkel KGaA) in water, 32% by weight of a conductive filler, in this embodiment silver-coated copper flakes (Conduct-O-Fil, SC230F9 .5 of the company Potters Industries Inc.) and 8 wt.% Of a thermoplastic polyurethane having a particle size of less than 120 microns. The paste has a viscosity of 56,000 mPas and can be printed on a material, for example by screen printing. After drying in an oven and after-treatment in a heating calender, the paste has a sheet resistance of 0.19 ohms as the dried solid.

Example 2

A paste was prepared according to Example 1, wherein the following different conditions were set. The paste according to the invention contains 70% by weight of a solution consisting of 2.1% Metylan® Normal (Henkel KGaA) in water, 24% by weight of a conductive filler, in this embodiment silver-coated copper flakes, and 6% by weight of a thermoplastic polyurethane with a Particle size less than 120 μm.

The paste has a viscosity of 50,200 mPas and can be printed on a material, for example by screen printing. After drying in an oven and after-treatment in a heating calender, the paste has a sheet resistance of 0.44 ohms as the dried solid.

Example 3

A paste was prepared according to Example 1, wherein the following different conditions were set. The paste according to the invention contains 60% by weight of a solution consisting of 2.5% Metylan® Normal (Henkel KGaA) in water, 32% by weight of a conductive filler, in this embodiment copper flakes, and 8% by weight of a thermoplastic polyurethane having a particle size less than 120 μm.

The paste has a viscosity of 125,000 mPas and can be printed on a material, for example by means of stencil printing. After drying in an oven and after-treatment in a heating calender, the paste has a sheet resistance of 0.39 ohms as a dried solid.

In Examples 2 to 4 results in a distensibility of the dried and calendered paste to 25%. The extensibility of the paste is limited primarily by the large increase in resistance.

The SEM photographs of Figures 1 and 2 show a nonwoven fabric which has been printed with the paste and was subjected to a subsequent heat and pressure treatment in a calender. During calendering, the polyurethane particles were melted and the metallic platelets were aligned and overlapped, which improves conductivity. The thermoplastic polyurethane binds the particles to one another and to the nonwoven as a binder.

Example 4:

Various suitable polyurethanes have been prepared. Table 1 shows an overview of the components used. By selecting the components, the melting range can be varied.

Table 1 :

Abbreviations: Basic polyols:

D: Desmophen ™ (polyols from Bayer)

D2000: polyethylene adipate diol (Mw: 2000)

D2001 KS: polyethylene / polybutylene adipate diol (Mw: 2000) D2028: neopentyl glycol adipate (Mw: 2000) C: Capa ™ (Solvay polycaprolactone polyols)

C200: polycaprolactone (Mw: 535)

C2200: polycaprolactone (Mw: 2000) DG: Diexter ™ G (polyols from Coim)

DG200: saturated polyester oladipate: T: Terathane ™ (polyether polyol from Invista) T2000: polytetramethylene ether glycol.

Chain Comp .: B: butanediol (1,4-B: 1,4 butanediol); H: 1,6-hexanediol; D:

Diethylene glycol (3-oxapentane-1, 5-diol); N: neopentyl glycol (2,2-

Dimethyl 1,3-propanediol). Isocyanates: MDI: diphenylmethane-4,4'-diisocyanate (methylenediisocyanate)

(Phenyl)); HDI: 1,6-hexamethylene diisocyanate.

The aliphatic polyurethanes PU10, PU11 and PU12 are particularly suitable for the production of pastes with a deep melting range. They are lightfast and non-yellowing and therefore suitable for applications in the field of vision. The polyurethanes PU1 to PU9 are aromatic polymers.

Example 5

The properties of other printed and dried pastes containing different polyurethanes are examined. The resistance is measured in the initial state. In addition, the strain is measured up to the conductor break in% (relative to the original length). The conductor had a length of 90 mm and a total width of 22 mm. The result is shown in Table 2:

Table 2:

Type 1: Paste according to Example 1 using the TPU PU 2 (see Tabellei), but using each 20% TPU and 20% conductive filler (Conduct-O-fil) was used. Type 2: paste according to Example 1 using the TPU PU 2 (see Tabellei). Type 3: paste according to Example 1 using the TPU PU 3 (see Tabellei). Type 4: paste according to Example 1 using the TPU PU 3 (see Tabellei), but using 20% TPU and 20% conductive filler (Conduct-0-fιl) was used.

Example 6

Pastes were made with antioxidants. For this purpose, 2.45 g of ascorbic acid were dissolved in 98.5 g of water and the pH was adjusted with NaHCO ₃ to a value of between pH 6.5-7.5. 1.5 g of Metylan® Normal were added. Subsequently, the paste was prepared by adding 16.67 g of polyurethane and 50 g of copper flakes (Conduct-o-fil). Alternatively, ammonium iron (II) sulfate or glucose may be used as the antioxidant. A suitable formulation contains 60 g of 1.5% aqueous Metylan solution, 30 g of Cu flakes, 10 g of TPU and 0.5 to 3% by weight of antioxidant.

Claims

claims

1. Printable and conductive paste containing a dispersible thermoplastic polyurethane, a conductive filler, a water-soluble thickener and water.

2. Paste according to claim 1, characterized in that the thickener contains cellulose derivatives.

3. Paste according to claim 1 or 2, characterized in that the thermoplastic polyurethane is an uncharged polyurethane.

4. Paste according to one of the preceding claims, characterized in that the thermoplastic polyurethane particles having a particle size less than 350 microns, preferably less than 120 microns.

5. Paste according to one of the preceding claims, characterized in that the thermoplastic polyurethane has a melting point between 100 and 220 ⁰ C.

6. Paste according to one of the preceding claims, characterized in that the conductive filler of metallic particles, preferably copper and / or silver-based exists.

7. Paste according to one of the preceding claims, characterized in that the conductive filler comprises copper flakes.

8. Paste according to one of the preceding claims, characterized in that the conductive filler comprises carbon nanotubes and / or contains a low-melting alloy.

9. Paste according to one of the preceding claims, characterized in that the thermoplastic polyurethane has free hydroxyl groups and the paste contains a crosslinker.

10. A process for coating a material with a paste prepared according to one of the preceding claims, characterized in that the paste is printed on at least one material and then dried and the material printed with the paste is subjected to a combined heat and pressure treatment.

11. The method according to claim 10, characterized in that the paste is printed by screen or stencil printing.

12. The method according to claim 10 or 11, characterized in that the material with the printed paste is thermally deformed after the combined heat and pressure treatment.

13. The method according to any one of claims 10 to 12, characterized in that a plurality of materials are provided with the paste and are connected by pressure and heat treatment via the paste cohesively with each other.

14. Use of a paste according to any one of claims 1 to 9 for the coating of materials.

15. Material, in particular fabric, nonwoven fabric or garment, coated with a paste according to one of claims 1 to 9.