DE102009051434A1 - Molded body made of highly conductive molding mass that contains a plastic and a filler incorporated into the plastic, useful as sealing including ring, bracelet and rubber gasket, as bipolar plate for an electrochemical cell, and as pipe - Google Patents

Abstract

Molded body (I) made of highly conductive molding mass that contains at least one plastic and at least one filler incorporated into the plastic, is claimed, where the mass fraction of the filler at the molding mass is at least 50% and (I) is homogeneously formed. An independent claim is included for producing (I) comprising homogeneously incorporating the filler into the plastic, and shaping the molding mass by a molding or forming process.

Description

The invention relates to a molded article of highly conductive molding composition, which contains at least one plastic and at least one filler incorporated in the plastic, wherein the molding compound is electrically conductive, thermally conductive and thermoformable, and a method for producing a molded article of highly conductive molding material.

The molding compound is a composite material, which is also referred to as a compound. Composite materials are mixtures of raw materials to which additional fillers, additives or the like are admixed. There is a distinction between homogeneous and heterogeneous mixtures. By mixing at least two substances are interconnected, the properties of the mixture by the selection of the raw materials and the fillers and their mixing ratio depending on the application can be selectively modified. In this way, for example, plastics can be mixed with fillers which are electrically and thermally conductive, whereby the resulting molding compound is electrically and thermally conductive.

Shaped bodies of electrically and thermally conductive molding compound are known for different applications and are suitable in the form of flat plates or foils, for example for use as bipolar plates in electrochemical cells, such as fuel cells. Metals segregate within electrochemical cells due to the highly corrosive environment, while a composite of a plastic and a conductive filler such as carbon meets these requirements.

In addition to high chemical resistance, molded articles which are to be used as bipolar plates in electrochemical cells must have high electrical and thermal conductivity in order to ensure high efficiency and sufficient heat dissipation. Since the electrical and thermal conductivity of a composite material containing a plastic and a conductive filler is substantially determined by the filler, relatively high levels of filler are often necessary to achieve the desired properties.

To achieve higher voltages and power several individual fuel cells are regularly combined to form a stack, also called stack, and connected in series. In this case, bipolar plates are a repeat element, which often accounts for the majority of the volume and weight of the cell. Therefore, in addition to the good electrical and thermal conductivity another requirement of bipolar plates that they are as flat and space-saving design. At the same time, the bipolar plates must be mechanically stable, since they are held together to achieve a low contact resistance to adjacent components under high pressure to stacks.

The US 2007/0125493 A1 discloses a bipolar plate consisting of two bipolar half-plates of flexible graphite layers and intended to be used in a fuel cell. The bipolar half-plates are glued together with a resin to a bipolar plate, wherein the resin forms an electrically conductive connection between the two bipolar half-plates by the addition of fillers such as carbon or metal. Furthermore, a method for the production of bipolar plates from bipolar half-plates is described in which two layers of flexible, conductive material are continuously unrolled and bonded with an electrically conductive resin.

A disadvantage of the electrical and thermal conductivity is the laminar structure of the bipolar half-plates, in which layers of different materials such as graphite and resin are joined together.

From the DD 288 076 A7 are known a conductive compound film of a mixture of ethylene-vinyl acetate, polyethylene and 35% -40% carbon black, and a method for producing and post-treating the film. In the preparation of the compound film, the components are first mixed together and granulated. Subsequently, a blown film is produced, which is then guided over different rollers and thereby irradiated and stretched in the longitudinal direction. The irradiation causes a cross-linking of the film.

On blown film lines very thin films of thermoplastic materials can be produced. A large proportion of fillers such as carbon black is indispensable for high electrical and thermal conductivity of the molding compound, but changes its suitability for further processing. Particularly in the production of blown film, it is not possible to achieve high filler proportions, since cracks or holes can easily form when air is blown into the film tube if the proportion of filler exceeds a certain limit.

The invention is therefore based on the object, the above-mentioned molded article and the process for its preparation in such a way and further that the known from the prior art disadvantages are avoided and in particular a higher thermal and mechanical conductivity in a flat design and high mechanical strength of the molding can be achieved.

This object is achieved in a molding according to the preamble of claim 1, characterized in that the mass fraction of the filler in the molding composition is at least 50% and that the molding is homogeneously formed.

The high mass fraction of the filler allows a particularly good electrical and thermal conductivity, the pure plastics usually do not have. The homogeneous formation of the shaped body also makes it possible that the properties achieved by the high filler content are present not only locally, for example in certain layers of a laminar structure, but in the entire region of the shaped body. Due to the properties thus obtained, the shaped body can be used in the area of photoabsorption, solar thermal energy and in a corrosive environment. In particular, the molding composition may be thermoplastic or polymer blend-based.

A particularly good conductivity is achieved according to an embodiment of the invention by using as filler carbon, in particular in at least one of the following manifestations: synthetic graphites, natural graphites, carbon blacks, carbon fibers, carbon nanofibers, single-walled carbon nanotubes, multi-walled carbon nanotubes, graphene.

Another teaching of the invention provides that at least one of the following substances is used as the plastic: polymers, elastomers, thermoplastic copolyesters, thermoplastic copolyamides.

In particular, amorphous, semi-crystalline and liquid-crystalline thermoplastic polymers can be used from the group of polymers. Thermoplastic elastomers have the advantage that they can be processed like thermoplastics and have elastic properties in a given temperature range. The elastomers may in particular be polyolefin elastomers of polypropylene (PP) and natural rubber (NR). Also, olefin-based thermoplastic elastomers (TPE-O or TPO), such as ethylene-propylene-diene rubber (PP / EPDM) and / or cross-linked olefin-based thermoplastic elastomers (TPE-V or TPV), such as ethylene-propylene-diene Rubber (PP / EPDM) and / or urethane-based thermoplastic elastomers (TPE-U or TPU) and / or thermoplastic copolyesters (TPE-T or TPC). Alternatively or additionally, styrene block copolymers such as SBS, SEES, SEPS, SEEPS, MBS (TPE-S or TPS) and / or thermoplastic copolyamides (TPE-A or TPA) can be used. All plastics mentioned can be used individually or in any combination with each other. In particular, can be used as a plastic PP / EPDM blend, the product properties of the thermoplastic elastomers (polypropylene, PP), such as the good heat deformation, with the good material properties of the EPDM (ethylene-propylene-diene monomer), which also is inexpensive in procurement, connects.

It is provided according to another teaching of the invention that the mass fraction of the filler in the molding composition is 50% -95%. Increasing the filler content up to 95% places increased demands on the processing of the molding compound, but allows excellent electrical and thermal conductivities. In particular, when using graphite as a filler, the mass fraction of the filler in the molding compound may be 65-90%.

In a further embodiment of the invention, it is provided that the molding compound has an electrical conductance in the range of 0.1 mS / cm to 100 S / m.

The teaching of the invention has further recognized that the molding compound has a thermal conductivity in the range of 0.1 W / mK to 30 W / mK.

A further embodiment of the invention provides that the shaped body has a hollow cylindrical shape. The shaped body can be designed, for example, as a pipe, in particular as a pipe for geothermal applications. In pipes, other applications are known in which electrically and thermally conductive pipes are advantageous compared to pure plastic pipes. For example, pipes which are thermally conductive can absorb and release heat particularly well and can thus be used, for example, as heat exchangers.

Another teaching of the invention provides that the shaped body is designed as a seal. The seal may be cord-shaped, for example designed as a ring, band or the like and - unlike a rubber seal - form an electrically and thermally conductive connection between the surfaces to be sealed. Such a seal can even produce an electrically and thermally conductive connection between relatively moving components and thus build a power supply between these components.

It is provided according to a further teaching of the invention that the shaped body is designed as a bipolar plate for an electrochemical cell. The electrochemical cell can be designed in particular as a fuel cell. This will be further proposed that the bipolar plate has a thickness of 0.5 mm-5 mm. A particularly small thickness allows a cost and space-saving design of fuel cells, which is particularly important because of the stacked arrangement of the bipolar plates to stacks. The molded body can also be designed as electrically and thermally highly conductive plastic-bonded and thermoformable film.

• – Homogenes Einarbeiten des Füllstoffs in den Kunststoff,
• – Formgebung der Formmasse durch ein Urformverfahren und
• – Formgebung der Formmasse durch ein Umformverfahren.

Procedurally, the solution of the task by the following steps:

• Homogeneous incorporation of the filler into the plastic,
• - Forming the molding material by a primary molding process and
• - Forming the molding material by a forming process.

The moldings can in principle be produced by all original and forming processes. Both a continuous process such as extrusion as well as a discontinuous processing, especially in a kneader, is possible.

The continuous processes include in particular extrusion extrusion, pipe extrusion, film extrusion, calendering and calendering embossing. In extruded extrusions, for example, profiles for the construction of heat exchangers can be produced. The pipe extrusion is used for example for the extrusion of pipes and hoses, which can be used for example as a shielding of signal lines. Film bubble extrusion can be used to produce films for lining enclosures in applications such as electromagnetic compatibility (EMC) or electrostatic discharge (ESD). Likewise, sheets or sheets may be formed by calendering the extrudate into sheets as housing parts or components of electrochemical cells. By calendering embossing, the shaping can take place simultaneously with the introduction of a structure for components of electrochemical cells.

In the batch processes, in particular injection molding, hot pressing, hot stamping and deep drawing are proposed. By injection molding or hot stamping, for example, shaping to housing parts or components of electrochemical cells can take place. The hot stamping can be used in particular for subsequent shaping of prefabricated components or semi-finished products. In particular, the shaping of calendered films and / or sheets to components or semi-finished products can be done by deep drawing.

Other methods such as embossing, thermal impressions and structure embossing are preferably used.

A teaching of the invention proposes with respect to the method that the molding material is tempered before molding. The setting of the optimum temperature can be achieved by pressure, internal friction, cooling, heating or the like and ensures the best possible production.

Further embodiments of the invention provide that the shaping of the molding compound takes place by calendering and / or extruding.

The preparation can be carried out in particular in a single-screw extruder, twin-screw extruder, multi-screw extruder, planetary roller extruder or Ko-kneader, the twin-screw extruder can be operated in the same or opposite directions. All monoextrusion tools, coextrusion tools and rubber extrusion tools can be used. The molding compound can be prepared by either direct or masterbatch compounding, including premix, split feed, or color matching variants.

It can calenders of any design with at least two rollers or rollers are used, which are preferably tempered, the gap dimensions and calendering speeds are variable shaped, and which can be equipped with mold inserts. In the manufacture of calendered bipolar plates, cycle times of less than 2 seconds are achieved.

Finally, the invention is based on the finding that a particularly high mechanical strength of the molding is achieved if the molding composition is mechanically stabilized after the molding by post-crosslinking. It is possible that the post-crosslinking takes place by radiation, which is also referred to as radiation crosslinking. In the case of radiation crosslinking, in particular alpha and / or beta radiation is used.

The high flexibility of the molding compound is necessary and desirable in the processing and shaping in order to be able to deform the molding as desired without causing cracks or the like. However, if the end product, such as a bipolar plate for electrochemical cells, in particular fuel cells, must have a high mechanical strength, the molding material should be solidified. This can be done for example by radiation crosslinking. Due to the energy of the radiation used, which is absorbed in the molding, a cross-linking takes place, which binds the molecules together and severely restricts their mobility. The plastic is thus transferred to a thermoset or thermoelastic state and remains largely dimensionally stable even with increased heat. By radiation crosslinking in particular the tear strength, the Temperature resistance, pressure resistance and chemical resistance improved.

The invention will be explained in more detail with reference to a drawing showing only a preferred embodiment. In the drawing show

1 the schematic sequence of the manufacturing process of a shaped body according to the invention, in perspective view,

2 an alternative production method of a structure-containing molding, in side view,

3 another embodiment of a shaped body according to the invention and

4A and B still further embodiments of moldings of the invention.

In 1 is schematically an extruder 1 represented in which the homogeneous molding material is produced. For this purpose, first at least one plastic and at least one filler in the funnel 2 filled. The educts are often present as granules and can thus be well dosed. A worm shaft 3 promotes the educts, ie the plastic granules and the filler granules, wherein they are melted and homogenized by heating and internal friction.

At the outlet of the extruder 1 is in the illustrated and preferred embodiment, a slot nozzle 4 mounted by the in the extruder 1 resulting molding material is pressed under high pressure. The slot nozzle 4 brings the molding compound in the form of a flat and flat track 5 indicated by dashed lines, for further processing between the rollers of a calender 6 is suitable and simplifies it.

The calender 6 has several rollers, between which a gap is formed. The distance of the gap can be regulated. The number and arrangement of rollers or rollers may vary as needed; In addition, the rollers can be heated. The through the slot nozzle 4 already preformed web 5 is through the slot between the rollers of the calender 6 guided and thereby formed into a thin tape or foil and finally to plates 7 sporadically. This process is also called calendering.

2 shows another - highly schematic - embodiment of the production of a shaped body according to the invention, which may also be provided with a structure. This will be a flat track 5 ' a pair of rollers 6 ' supplied, in which the rollers with recesses 8th are provided, so that the rollers 6 ' leaving tape corresponding unspecified surveys has. The tape can then be cut in a known manner by means of a cutting device 9 to individual structural plates 7 ' to be isolated. In the context of the invention, it is also readily possible, even if not shown, the calender rolls additionally or alternatively to the recesses 8th to design with slight elevations in order to produce in the path corresponding recesses.

In the structure having plates 7 ' For example, they may be bipolar plates that can be cut to a desired length and width after calendering.

After shaping, the bipolar plate formed from the molding compound can be mechanically stabilized.

This can be done by radiation crosslinking, whereby the mechanical, thermal and chemical properties of the bipolar plates can be varied within wide limits.

The 3 and 4 show that with a corresponding (not shown) nozzle of an extruder and hollow moldings can be produced. So is in 3 a rigid tube 10 shown, which is made endless and can be shortened to any length. In the context of the invention, however, flexible moldings are produced, so it shows 4A a flexible hose 11 who, as in 4B shown, as profiled hose 11 ' can be trained.

The few embodiments quickly make it clear that the present invention comprises almost arbitrarily shaped moldings.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• US 2007/0125493 A1 [0006]
• DD 288076 A7 [0008]

Claims (15)

Shaped body of highly conductive molding composition containing at least one plastic and at least one incorporated in the plastic filler, wherein the molding material is electrically conductive, thermally conductive and thermoformable, characterized in that the mass fraction of the filler in the molding composition is at least 50% and that the molding is formed homogeneously Shaped body according to claim 1, characterized in that carbon is used as the filler, in particular in at least one of the following manifestations: synthetic graphites, natural graphites, carbon blacks, carbon fibers, carbon nanofibers, single-walled carbon nanotubes, multi-walled carbon nanotubes, graphene. Shaped body according to claim 1 or 2, characterized in that as plastic at least one of the following materials is used: polymers, elastomers, thermoplastic copolyesters, thermoplastic copolyamides. Shaped body according to one of claims 1 to 3, characterized in that the mass fraction of the filler in the molding composition is 50% -95%. Shaped body according to one of claims 1 to 4, characterized in that the molding composition has an electrical conductance in the range of 0.1 mS / cm to 100 S / m. Shaped body according to one of claims 1 to 5, characterized in that the molding composition has a thermal conductivity in the range of 0.1 W / mK to 30 W / mK. Shaped body according to one of claims 1 to 6, characterized in that the shaped body has a hollow cylindrical shape. Shaped body according to one of claims 1 to 6, characterized in that the shaped body is designed as a seal. Shaped body according to one of claims 1 to 6, characterized in that the shaped body is designed as a bipolar plate for an electrochemical cell. Shaped body according to claim 9, characterized in that the bipolar plate has a thickness of 0.5 mm-5 mm. A process for the production of a shaped body of highly conductive molding composition which contains at least one plastic and at least one filler incorporated in the plastic, characterized by the following steps: Homogeneous incorporation of the filler into the plastic, - Forming the molding material by a primary molding process and - Forming the molding material by a forming process. A method according to claim 11, characterized in that the molding material is tempered before molding. A method according to claim 11 or 12, characterized in that the shaping of the molding material takes place by calendering. A method according to claim 11 to 13, characterized in that the shaping of the molding compound by extrusion. Method according to one of claims 11 to 14, characterized in that the molding material is mechanically stabilized after shaping by post-crosslinking.

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