Method for producing composite materials

Abstract

The invention relates to a method for continuously or semi-continuously producing, by means of a multi-roller rolling mill, composite materials comprising a thermoplastic polymer; it also relates to composite materials, and to an apparatus for carrying out the method.

Description

[0001] Methods for the production of composite materials

[0002] The present invention relates to the technical field of the production of composite materials, in particular highly filled thermoplastic polymers.

[0003] In particular, the present invention relates to a method for the continuous or semi-continuous production of composite materials, preferably in the form of films.

[0004] Furthermore, the invention relates to a composite material and a device for carrying out the method.

[0005] The method according to the invention is particularly suitable for the production of films made of composite materials, which can be further processed into bipolar plates.

[0006] Bipolar plates are a key component in fuel cell technology, as they account for a large proportion of the weight and volume of a fuel cell stack. They are responsible for the full-surface electrical contact of the cells within a stack and, via integrated flow channels known as flow fields, guide the reaction gases through the cell. In doing so, they physically separate the cells from one another.

[0007] For most applications, cooling channels are integrated into the bipolar plates to dissipate the heat generated during the reaction. In addition to high electrical and thermal conductivity combined with high mechanical stability, high (electro)chemical resistance, thin material, and low material and manufacturing costs are also important in a high-rate production process. Film-like bipolar plates with thicknesses of less than 1 mm are particularly suitable for mobile applications.

[0008] In these types of bipolar plates, the flow field is introduced into the bipolar plate via a forming process, thus providing the bipolar plate with a space-saving flow structure on both sides. Two such formed plates, so-called half-plates, are then stacked, so that one plate has two outer flow structures and one inner cooling structure.

[0009] Composite bipolar plates consist of a polymeric binder matrix with a high proportion of conductive fillers, mostly carbon or metal particles. The processing of such highly filled composites is particularly challenging, as the filler content severely restricts flowability. This poor flowability means that in conventional manufacturing processes, such as injection molding or extrusion, the high shear rates make it difficult to form film-like bipolar plates, or severely limit the filler content, which directly impacts the electrical and thermal properties of the plates. While hot pressing enables the production of thin-walled bipolar plates, it is not suitable for mass production.

[0010] Homogeneous compounding for the dispersion and embedding of fillers in the polymer matrix is ​​necessary to prevent defects in the composite and to ensure a homogeneous network structure of the conductive particles. Defects can reduce mechanical strength and lead to the formation of leakage paths and thus to leaks.

[0011] Furthermore, agglomerates of the filler particles are broken up during the compounding process. This ensures uniform mechanical and electrical properties of the composite. Currently, in the production of bipolar plates, an extruder is usually used in a preliminary process step, in which shear forces disperse and embed the fillers in the plasticized polymer. Alternatively, in a premixing process, the polymer can be diluted with a solvent and dispersed with the fillers.

[0012] The production of composite materials by extrusion has the advantage that the individual components are fed directly into the extruder and mixed there, and that the process times are short. However, the high mechanical stress, especially due to shear rates of 10⁻⁶, is a disadvantage. 2 up to 10 3 s -1 and the usually necessary post-processing.

[0013] The production of composite bipolar plates using injection molding is also not ideal, as extrusion with the aforementioned disadvantages is necessary prior to the actual injection molding process, and both extrusion and the actual injection molding process subject the material to high mechanical stress. In particular, shear rates of 10 3 up to 10 4 s -1achieved. One advantage of the injection molding process is the short processing time as well as the direct production of three-dimensional objects, i.e., for example, bipolar plates with flow fields, which eliminates the need for subsequent forming steps.

[0014] Another method for manufacturing composite materials, and in particular composite bipolar plates, is compression molding. Compression molding is very flexible and gentle on materials, as it only involves shear rates of 10° to 10°. 1 s -1 This can be achieved. However, very long processing times are necessary, and the composite material itself must already be present, meaning a premixing process is required. If this premixing process is carried out, for example, by extrusion, the material is subjected to high mechanical stresses. Due to the long processing times, compression molding is not suitable for industrial production.

[0015] Another method for manufacturing bipolar plates is calendering, which is gentle on the material and cost-effective, and makes thin composite bipolar plates particularly accessible. During calendering, shear rates of only 10⁻⁶ occur. 1 up to 10 2 s -1 However, post-processing is also necessary here to obtain three-dimensionally shaped objects.

[0016] While calendering theoretically allows for the continuous production of films, particularly bipolar plates, it can only refine the surfaces or thin and smooth the material. This means it only allows for shaping the material; the individual components cannot be mixed, and therefore the composite material cannot be produced. The composite material must already exist as such and is created, for example, by extrusion and injection molding.

[0017] WO 2015 / 007544 A1 describes a manufacturing process for producing highly filled thermoplastics, in which a polymer and fillers are mixed in powder form and heated above the polymer's melting temperature using equipment such as a rolling mill or extruder. The mixture is then cooled to allow for shaping. This process can be carried out using a rolling mill or calender with at least one heated roller. The thermoplastic solidifies over a cooled roller, and the composite can then be peeled off in film form. This process is also known as the "powder-to-roll" process.

[0018] By using a rolling mill, it is possible to homogenize the individual components into a composite during the rolling process. This enables the production of highly filled composite semi-finished products, particularly films for manufacturing composite bipolar plates. The films can also be further processed into battery electrodes using dry coating methods. However, the disadvantage of rolling mills is that they always operate discontinuously.

[0019] In the powder-to-roll process, the rollers are positioned one behind the other in a horizontal arrangement, and the material web is transferred to the next roller in the roller gap by friction, i.e., the speed difference between adjacent rollers. The material is always transferred from the roller with the slower rotational speed to the roller with the higher rotational speed, all while maintaining the same roller temperature.

[0020] Homogeneous dispersion of the fillers within the polymer matrix, as well as the breaking up of filler particle agglomerates, is essential for homogeneous material properties and high composite strength, and can only be achieved under the influence of shear forces. In the rolling mill or calendering process, shear forces are deliberately introduced at the roll gap. Shear forces in the rolling mill process are generally significantly lower than in extrusion or injection molding processes. Here, the forces are generated, on the one hand, by the friction of adjacent rolls and the resulting shear. On the other hand, with narrow gap dimensions, only a portion of the material web can pass through the roll gap. The remaining portion of the material web accumulates in front of the roll gap and is kept in motion by the rotation of the rolls; this is known as kneading.

[0021] Investigations by the applicant have shown that in the powder-to-roll process, the composite web must undergo a large number of gap passes to achieve the material properties required for bipolar plates in fuel cells. In a continuous powder-to-roll process, an increase in gap passes could be achieved by using a large number of heated rollers arranged in series. Here, the friction of the rollers must be precisely adjusted so that the material web is completely transferred to the next roller. The friction range at which the material web transfers completely and without tearing from one roller to the next is very narrow and must be determined individually for each system. For a large number of rollers, the process control thus becomes very complex and cannot be optimally adjusted for the most homogeneous compounding of the components.Furthermore, for a large number of rollers, especially in a horizontal arrangement, the processing time of the composite becomes very long, during which the binder polymer is exposed to the roller temperature. This can lead to polymer degradation and impair the resulting properties of the highly filled composite film, particularly with regard to formability and weldability. Since the material transfer from one roller to the next can only occur via a controlled speed difference from a slower roller to a faster roller, a process with a large number of rollers also results in a very low rotational speed of the first roller and / or a very high rotational speed of the last roller, which further complicates process control. This makes process control so difficult that industrial implementation is unlikely.

[0022] CN 218215358 U describes a dry electrode manufacturing process with various process steps, including a multi-roll pre-compression unit with a main roll and planetary-arranged press rolls around it. The multi-roll system is intended to increase electrode compaction before the laminated film enters the final compaction stage to achieve the desired material thickness. In this process, the rolls are used solely for compacting the electrode mixture; no mixing or compounding of the components takes place.

[0023] The prior art thus still lacks a simplified, highly flexible, and universally applicable method for producing composite materials, which would significantly simplify the production of high-performance bipolar plates and shorten processing times. One object of the present invention is therefore to avoid, or at least mitigate, the disadvantages associated with the prior art described above.

[0024] In particular, an object of the present invention is to provide a method for producing a composite material which is particularly suitable for producing thin bipolar plates.

[0025] Another object of the present invention is to provide a method for the continuous production of composite materials, preferably in film form.

[0026] Furthermore, another object of the present invention is to provide an improved composite material which is particularly suitable for the manufacture of bipolar plates.

[0027] The problem set out above is solved according to a first aspect of the present invention by a method according to claim 1; further, advantageous embodiments of this aspect of the invention are the subject of the relevant dependent claims.

[0028] A further subject matter of the present invention according to a second aspect of the present invention is a composite material according to claim 17.

[0029] Finally, a further subject matter of the present invention, according to a third aspect of the present invention, is a device according to claim 18.

[0030] It goes without saying that any special features, characteristics, designs and embodiments, as well as advantages or the like, which are subsequently described in relation to only one aspect of the invention – for the purpose of avoiding unnecessary repetition – shall of course apply accordingly to the other aspects of the invention, without the need for any express mention.

[0031] Furthermore, it should be noted that all values ​​or parameters mentioned below, or the like, can generally be determined using standardized or explicitly specified determination methods, or using determination methods that are generally familiar to those skilled in the field.

[0032] Furthermore, it goes without saying that weight- or quantity-related percentages are selected by a professional in such a way that the total results in 100%.

[0033] Having said that, the present invention will now be described in more detail.

[0034] The subject matter of the present invention - according to a first aspect of the present invention - is thus a method for the continuous or semi-continuous production of composite materials comprising a thermoplastic polymer, by means of a multi-roll rolling mill, wherein the multi-roll rolling mill has at least two non-material-carrying rolls.

[0035] In the context of the present invention, a material-carrying roller is understood to be a roller on whose surface at least one web of a material adheres at least partially and which transports the web.

[0036] In the context of the present invention, a non-material-carrying roller is understood to be a roller to whose surface the material web does not adhere and which, in particular, does not transport the material web.

[0037] The process according to the invention improves the embedding and homogeneous distribution of fillers in a polymer matrix compared to known processes, particularly in the continuous powder-to-roll process. The powder-to-roll process is thus optimized by the present invention in such a way that the composite films produced can be manufactured with improved quality in terms of homogeneity and mechanical properties, and therefore become relevant for high-performance fuel cell applications with high demands on the composite.

[0038] The advantages are particularly

[0039] • improved homogenization and properties of the composite films, • simpler process control regarding the speed setting of the individual rollers, since frictions can be specifically adjusted for optimized compounding and not for material transfer, and

[0040] • Lower thermal degradation of the binder polymer.

[0041] This is achieved within the scope of the invention by using both material-carrying and non-material-carrying rollers for process control. Here, non-material-carrying rollers are preferably arranged around the material-carrying rollers and, via targeted friction, generate shearing and kneading of the composite, leading to improved homogenization and dispersion of the fillers. The fact that the additional rollers are not designed as material-carrying rollers onto which the composite web must be transferred via a controlled friction significantly simplifies material and process control in the powder-to-roll process. Furthermore, this roller arrangement enables a high number of gap passes, resulting in better homogenization of the composite and thus more suitable material properties for fuel cell applications.

[0042] The process according to the invention is preferably carried out by applying a mixture of powdered starting materials to a heated roller and forming the film over several heated rollers, with the material web being drawn off over a cooled roller. In this way, a mass-production-ready manufacturing process for thin-film composite sheets, which are ideally suited for the production of bipolar plates, is possible. In particular, a film can be formed directly from a powder mixture. The process according to the invention has the particular advantages of low shear rates and only a short-term thermal stress on the plastic. Due to the short-term thermal stress, the degradation of the polymer that typically occurs can also be avoided or at least reduced.

[0043] In particular, the present invention makes it possible to continuously compound a highly filled plastic on the rolling mill. Specifically, temperature, friction, and gap spacing are adjusted to obtain significantly improved composite materials with a much better and more homogeneous mixture in a short time. With sufficient shear and identical roll temperatures, the material web always transfers to the roll with the higher speed. If the temperature of the subsequent roll is lower than that of the preceding roll, material transfer between two rolls at the same speed is also possible. Preferably, the friction, i.e., the speed difference between two material-carrying rolls, is between 1 (i.e., no speed difference) and 4, and particularly between 1, 2, and 4.Shear forces occur only in and around the roll gap, with the material accumulating in a material bank, the so-called kneading chamber. In particular, homogenization and crosslinking in the plane of the plate occur only in the roll gap. The applicant's experiments have shown that the number of passes through the gap is essential for the homogeneity of the composite material as well as its electrical conductivity and mechanical properties, especially tensile strength and modulus of elasticity.

[0044] The process according to the invention makes it possible to obtain particularly high filler levels in polymeric masses, which is not possible in the prior art due to the high viscosity of the resulting mixture or requires higher temperatures that quickly lead to degradation of the polymeric starting material. Furthermore, the present invention eliminates the need for additives, especially flow agents. Additives, especially flow agents, are used in the prior art to increase the filler content in composite materials, but have the disadvantage of negatively affecting the thermal stability and often key properties of the composite material, such as electrical conductivity. Additives, especially flow agents, are also required in the prior art to process highly filled polymeric masses into thin composite sheets.

[0045] With the method according to the invention, in particular the in-plane conductivity, the tensile strength or the modulus of elasticity can be increased by up to 70% with 20 gap passes compared to 3 gap passes.

[0046] Furthermore, the inventive method also enables the continuous or semi-continuous production of composite materials without any reduction in the mechanical or electrical properties of the composite materials. Typically, the mechanical properties of composite films, as well as their electrical conductivity, decrease significantly during continuous production. In the prior art powder-to-roll process according to WO 2015 / 007544 A1, in which only material-carrying rollers are used and the material web is transferred from roller to roller, the roller spacing and friction do not need to be adjusted for homogeneous mixing to ensure complete transfer of the material web to the next roller.This results in composite films produced using the prior art powder-to-roll process exhibiting up to 40% lower conductivity and up to 55% lower modulus of elasticity than composites according to the invention, which are passed multiple times over non-material-carrying rollers or kneading rollers. A problem with continuous production is the large number of rollers required, and the highly complex coordination of roller speed and roller gap. Friction between the individual rollers must be optimized for material transfer at the expense of improved homogenization. Furthermore, the initial transfer is particularly problematic and frequently leads to film tears. All these factors make process control very complex when using many rollers.

[0047] The present invention addresses this issue by employing non-material-carrying rollers, so-called kneading rollers, which do not transport the composite material, particularly the film. The use of kneading rollers creates additional gap passes, leading to improved homogenization of the composite material. Furthermore, the friction between material-carrying rollers and kneading rollers during gap passes is freely adjustable, since the non-material-carrying rollers do not take over the material web but merely ensure better mixing of the composite components. This simplifies process control, as the number of roller passes—i.e., passes from one material-carrying roller to another—is decoupled from the number of gap passes.

[0048] In the context of the present invention, the continuous production of composite materials means that the composite materials are processed, in particular compounded, directly from the starting materials, in particular thermoplastic polymer, filler, and optionally further additives, to form a composite material. Further processes or process steps, in particular forming processes, may follow the production of the composite material. However, these are not considered in the context of the present invention.

[0049] A semi-continuous manufacturing process for composite materials is understood to mean that the finished composite material is produced from pre-fabricated composite materials, in particular, for example, from semi-finished products such as films, or from powdered composite materials, which are then thoroughly mixed and homogenized within the framework of the inventive process and preferably processed into a film. Continuous processing is preferred within the scope of the present invention.

[0050] As previously explained, the multi-roll rolling mill used preferably has several non-material-carrying rolls. It can be provided that the multi-roll rolling mill has at least 2, preferably at least 3, non-material-carrying rolls.

[0051] In the context of the present invention, it is further preferably provided that the multi-roll rolling mill has at most 30, preferably at most 20, preferably at most 15, preferably at most 10, particularly preferably at most 8, most particularly preferably 7, non-material-carrying rolls.

[0052] In this context, it is particularly preferred if the multi-roll rolling mill has 2 to 30, preferably 2 to 20, preferably 2 to 15, particularly preferably 3 to 10, most preferably 3 to 8, and especially preferably 3 to 7, non-material-carrying rolls.

[0053] The number of non-material-carrying rollers, as described in the present invention, makes it possible to increase the number of gap passes and thus the homogenization of the composite material without increasing the complexity of the process. This is because the non-material-carrying rollers are generally purely kneading rollers and do not transport the material, particularly the composite material, any further. The friction of the kneading rollers, i.e., the non-material-carrying rollers, is therefore freely adjustable to achieve optimal mixing of the composite and does not need to take into account the transport of the composite material to another roller. This allows for better homogenization results and improved composite materials to be obtained with fewer gap passes than when using only material-carrying rollers.

[0054] The non-material-carrying rollers can be rotating or non-rotating rollers.

[0055] Within the scope of the present invention, it is also typically and preferably provided that a non-material-carrying roll is a material feed roll. This is usually the first roll of the multi-roll mill in the direction of the process flow. This roll is required to achieve the most uniform possible melting and mixing of the starting materials, which are usually used as powders, in particular the thermoplastic polymers. Although the material feed roll is a non-material-carrying roll, since the resulting web or film is not transported by it, it is also not a kneading roll like the other non-material-carrying roll(s). Therefore, within the scope of the present invention, it is preferably provided that the multi-roll mill has 1 to 30, in particular 1 to 20, preferably 2 to 15, more preferably 3 to 10, particularly preferably 3 to 8, and most particularly preferably 3 to 7, kneading rolls.It is also possible for the multi-roll rolling mill to have at least 1, in particular at least 2, preferably at least 3, kneading rolls. Typically, the multi-roll rolling mill has at most 30, in particular at most 20, preferably at most 15, more preferably at most 10, most preferably at most 8, and most preferably at most 7, kneading rolls.

[0056] In addition to the non-material-carrying rolls, the multi-roll rolling mill generally has material-carrying rolls. These material-carrying rolls are generally rotating rolls.

[0057] The material-carrying rollers transport the material web, in particular the web of the composite material.

[0058] Within the scope of the present invention, it has proven advantageous for the multi-roll rolling mill to have at least 2, and in particular at least 3, material-carrying rolls. Furthermore, it can be provided that the multi-roll rolling mill has at most 10, and in particular at most 8, preferably at most 7, preferably at most 6, and most preferably at most 5, material-carrying rolls.

[0059] Furthermore, it is usually provided that the multi-roll rolling mill has 2 to 10, in particular 2 to 8, preferably 2 to 7, more preferably 2 to 6, particularly preferably 2 to 5, most preferably 3 to 5, material-carrying rolls.

[0060] Furthermore, it has proven advantageous to use as few material-carrying rollers as possible when there is a high number of slitting passes, since the speed, especially the friction, of the material-carrying rollers must be coordinated to ensure material transport from one roller to the next.

[0061] Within the scope of the present invention, it is generally provided that the temperature of the material-carrying rollers and / or the temperature of the non-material-carrying rollers is controllable. It is particularly preferred within the scope of the present invention if both the temperature of the material-carrying rollers and the temperature of the non-material-carrying rollers are controllable.

[0062] Generally, the roller temperature of the material-carrying rollers and the material-depositing roller is above the melting or softening temperature of the thermoplastic polymer. Preferably, the roller temperature of the material-carrying rollers and the material-depositing roller is approximately 30 °C above the melting temperature of the thermoplastic polymer. Preferably, the roller temperature of the non-material-carrying roller is also above the melting or softening temperature of the thermoplastic polymer, in particular approximately 30 °C above the melting temperature of the thermoplastic polymer.

[0063] Within the scope of the present invention, it is typically provided that the material-carrying rollers, in particular all material-carrying rollers with the exception of the last material-carrying roller in the process direction, have a temperature above the melting temperature of the thermoplastic polymer used for the production of the composite material.

[0064] Furthermore, it is preferably provided that a material-carrying roller, in particular the last material-carrying roller in the process direction, has a temperature below the solidification temperature of the polymer used for the production of the composite material. This roller is also referred to as a cooling roller.

[0065] Within the scope of the present invention, it is preferably provided that the temperature of the last material-carrying roller is lower than the temperature of the other rollers. Preferably, the temperature of the last material-carrying roller, the cooling roller, is lower than the temperature of the other material-carrying and non-material-carrying rollers.

[0066] Typically, the non-material-carrying rollers are associated with the material-carrying rollers, and in particular arranged around them. Preferably, the non-material-carrying rollers are associated with or arranged around the material-carrying rollers in such a way that a gap, a so-called roller gap, forms between the material-carrying roller and the non-material-carrying roller. The gap width and the friction between a material-carrying roller and a non-material-carrying roller can be individually adjusted.

[0067] In the context of the present invention, it is typically provided that at least one material-carrying roller, preferably each material-carrying roller except the cooling roller, is associated with one or more non-material-carrying rollers. In particular, it is preferably provided in the context of the present invention that at least one material-carrying roller, preferably each material-carrying roller except the cooling roller, is associated with 1 to 10, more preferably 1 to 8, more preferably 1 to 7, and more preferably 2 to 5, non-material-carrying rollers. By using a plurality of non-material-carrying rollers associated with a material-carrying roller, the number of gap passes can be increased and thus the homogenization of the composite material can be significantly improved without increasing the complexity of the process.

[0068] According to a particular and preferred embodiment of the present invention, non-material-carrying rollers are arranged planetarily around one or more material-carrying rollers, in particular a material-carrying roller. Within the scope of the present invention, it is typically provided that a gap between a material-carrying roller and a non-material-carrying roller is narrower than the thickness of the supplied substrate, i.e., the web of composite material that is supplied to the respective roller gap. In this way, by adjusting the gap width, the roller temperatures, and the friction, a controlled shearing effect can be achieved, which leads to the formation of a knead in front of the roller gap and further mixing of the composite material.

[0069] Within the scope of the present invention, it is therefore preferably provided that the ratio of the peripheral speed of a non-material-carrying roller to the peripheral speed of the material-carrying roller to which it is associated, i.e., the friction, is adjusted such that it is ensured that the web is not transferred to the non-material-carrying roller but remains on the material-carrying roller. Since, in addition to friction, the temperature and the surface finish of the rollers also influence whether a material web is transferred from one roller to another, the friction between material-carrying and non-material-carrying rollers can vary over a wide range. However, it is usually provided that the friction between a material-carrying roller and an associated non-material-carrying roller is between 0 and 1.5, and in particular between 0 and 1.2.

[0070] In this context, it is preferred if the friction between a material-carrying roller and an associated non-material-carrying roller is 0 to 1, in particular 0.1 to 0.5, preferably 0.1 to 0.4, preferably 0.1 to 0.3.

[0071] Similarly, within the scope of the present invention, it can be provided that the friction between a material-carrying roller and an associated non-material-carrying roller is at most 1, in particular 0.5, preferably at most 0.4, preferably at most 0.3.

[0072] In general, the composite material is obtained in the form of a web, preferably a film, when carrying out the process according to the invention. In particular, producing the composite material in the form of a web using a multi-roll rolling mill makes continuous or at least semi-continuous production of the composite material possible. Preferably, within the scope of the present invention, the composite material is obtained as a semi-finished product, in particular as a web or film.

[0073] The composite material is generally a highly filled plastic.

[0074] The composite material preferably comprises a thermoplastic polymer or polymer blend and optionally additives and fillers. Preferably, the composite material consists of a thermoplastic polymer or polymer blend and optionally additives and fillers, in particular electrically conductive particles.

[0075] Typically, the composite material is designed to include a thermoplastic polymer.

[0076] Typically, the thermoplastic polymer of the composite material is selected from the group of polyolefins, in particular polyethylene (PE), polypropylene (PP), polyetheretherketone (PEEK), polyphenylene sulfide (PPS), polyaryletherketone (PAEK), polyetherketoneketone (PEKK), polyetherimides (PEI), acrylonitrile butadiene styrene (ABS), polyamides (PA), polyphenylsulfones (PPS), polysulfone (PS), polyethersulfone (PES), polyamide imides (PAI), polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA) and mixtures thereof.

[0077] Good results are obtained within the scope of the present invention if the polymer of the composite material is selected from the group consisting of polyethylene (PE), polypropylene (PP), polyphenylene sulfide (PPS), polyvinylidene fluoride (PVDF), polyetheretherketone (PEEK), polyvinyl chloride (PVC), and polyamide (PA).

[0078] Polytetrafluoroethylene (PTFE) and mixtures thereof, preferably polyethylene (PE), polypropylene (PP), polyphenylene sulfide (PPS), polyamide (PA),

[0079] Polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE) and mixtures thereof, preferably selected from the group consisting of polyethylene (PE), polypropylene (PP), polyphenylene sulfide (PPS), polyvinylidene fluoride (PVDF) and mixtures thereof.

[0080] The composite material generally contains at least one filler.

[0081] In the context of the present invention, it is typically provided that the filler is an electrically conductive filler. The filler is preferably selected from the group consisting of carbon-containing materials, metal-organic frameworks (MOFs), covalent organic frameworks (COFs), core-shell structured mesoporous materials, in particular core-shell nanoparticles (CSNs), metals, metal oxides, nitrides, carbides, MAX phases, MXenes and mixtures thereof.

[0082] Particularly good results are obtained within the scope of the present invention when the filler is selected from the group consisting of carbon-containing materials, metals, metal oxides, nitrides, carbides and their mixtures, preferably carbon-containing materials, metals, nitrides and their mixtures, preferably carbon-containing materials, metals and their mixtures.

[0083] The filler(s) are in the form of particles, in particular in the form of fibrous particles or granular particles.

[0084] Preferably, the filler, in particular the electrically conductive filler, is a carbon-containing material.

[0085] If the filler contains or consists of metal particles, it has proven effective to select the metal from the group of nickel, titanium, platinum, ruthenium and their mixtures.

[0086] If the filler consists of or contains particles of metal oxides, it has proven advantageous for the metal oxide to be selected from the group consisting of tin(IV) oxide, manganese oxide, silver oxide, antimony oxide, cobalt(II,III) oxide, copper(II) oxide, lanthanum oxide, cerium(IV) oxide, aluminum oxide, titanium oxide, zirconium oxide, niobium oxide, and mixtures thereof. It is particularly preferred if the metal oxide is selected from the group consisting of tin(IV) oxide, manganese oxide, silver oxide, antimony oxide, cobalt(II,III) oxide, copper(II) oxide, lanthanum oxide, and mixtures thereof.

[0087] If the filler contains or consists of nitrides and / or carbides, the nitrides and / or carbides are preferably selected from metal nitrides, metal carbides and mixtures thereof.

[0088] If the filler contains or consists of nitrides and / or carbides, it has also proven advantageous if the filler is selected from nitrides and carbides of elements of the group of B, Al, Ti, Ga, In, Ti, Si, Ge, Sn, Pb, P, As, S, Cd, V, Cr, Mn, W, Co, Ni, Zn, Zr and their mixtures, preferably selected from nitrides and carbides of titanium.

[0089] As previously stated, the fillers, in particular electrically conductive fillers, are preferably carbon-containing materials. These carbon-containing materials are, in particular, particles selected from the group consisting of (conductive) carbon black, graphite, carbogels, graphene, carbon fibers, carbon nanotubes, onion-like carbons, and mixtures thereof. According to a particularly preferred embodiment of the present invention, the carbon-containing materials are carbon-based particles and are preferably selected from the group consisting of (conductive) carbon black, graphite, carbon fibers, and mixtures thereof, in particular (conductive) carbon black, graphite, and mixtures thereof.

[0090] Within the scope of the present invention, a carbogel is understood to be a carbon-containing material obtained by gel synthesis, wherein the gel is carbonized and optionally activated. Carbogels within the scope of this invention are, in particular, carbon aerogels, carbon xerogels, and carbon cryogels. Carbogels are porous particles whose specific pore volume of the mesopores, i.e., the pores with a size of 2 to 50 nm, determined by nitrogen adsorption and evaluation according to the Barrett-Joyner-Halenda and / or t-plot method, is at least 0.5 cm³. 3 / g, preferably at least 1.0 cm 3 / g, is the amount.

[0091] Furthermore, the filler may contain or consist of particles of MAX phases or MXenes, preferably MXenes. Within the scope of the present invention, MAX phases are, in particular, carbides and nitrides of the general formula M that crystallize in hexagonal layers. n +iAXn The numbers n = 1 to 3 are to be understood as follows: M represents an early transition metal from groups 3 to 6 of the periodic table, while A represents an element from groups 13 to 16 of the periodic table. A is specifically selected from Cd, Al, Ga, In, Ti, Si, Ge, Sn, Pb, P, As, S, and their mixtures, while M is preferably selected from Sc, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, and their mixtures. X is either carbon or nitrogen.

[0092] MAX phases often exhibit unusual combinations of chemical, physical, electrical, and mechanical properties, as they display both metallic and ceramic behavior depending on the conditions. This includes, for example, high electrical and thermal conductivity, high resistance to thermal shock, very high hardness, and low coefficients of thermal expansion.

[0093] MAX phases are highly resistant to chemicals and to oxidation at high temperatures.

[0094] MXenes are two-dimensional structures based on metal carbides and / or metal nitrides and can be obtained in particular by etching MAX phases, for example with HF.

[0095] It is particularly preferred if the filler, especially the electrically conductive filler, is selected from the group consisting of carbon, graphite, graphene, (conductive) carbon black, carbogels, carbon fibers, carbon nanotubes, titanium carbide, titanium nitride, metals, metal fibers, metal compounds and mixtures thereof, in particular graphite, graphene, (conductive) carbon black, carbon fibers, carbon nanotubes, nickel, titanium, platinum, ruthenium, titanium nitride and mixtures thereof, preferably graphite, (conductive) carbon black and mixtures thereof. Mixtures of graphite and (conductive) carbon black are particularly preferred.

[0096] Furthermore, it has proven advantageous within the scope of the present invention if the composite material contains the polymer in amounts of 1 to 60 wt.%, in particular 1 to 50 wt.%, preferably 2 to 40 wt.%, preferably 10 to 30 wt.%, based on the composite material.

[0097] Furthermore, it has proven advantageous within the scope of the present invention if the composite material contains the filler in amounts of 40 to 99 wt.%, in particular 50 to 99 wt.%, preferably 60 to 98 wt.%, preferably 70 to 90 wt.%, based on the composite material.

[0098] Furthermore, it is typically provided within the scope of the present invention that the resulting composite material, in particular the sheet or film, has a thickness, i.e., a material thickness, of at most 5 mm, in particular at most 2 mm, preferably at most 1 mm, and more preferably at most 0.5 mm. Likewise, it can be provided that the resulting composite material has a thickness of at least 0.02 mm, in particular 0.05 mm, preferably at least 0.1 mm, more preferably at least 0.2 mm, and most preferably 0.3 mm.

[0099] Within the scope of the present invention, it is particularly preferred if the composite material obtained has a thickness in the range of 0.02 to 5 mm, more particularly 0.05 to 2 mm, preferably 0.1 to 1 mm, more preferably 0.1 to 0.5 mm, more preferably 0.2 to 0.5 mm, and most preferably 0.3 to 0.5 mm. It is therefore preferred if the composite material is very thin. In this way, high-performance composite bipolar plates can subsequently be obtained.

[0100] Preferably, the composite material produced within the scope of the present invention is an electrically conductive composite material.

[0101] In the context of the present invention, electrically conductive means a compound or material which has an electrical conductivity of at least 1 × 10⁻⁶ at 20 °C. -11 S • m -1 exhibits.

[0102] Within the scope of the present invention, it is preferred if the composite material has an electrical conductivity of at least 10 S • rr at 20 °C. 1 , in particular 10 2 S • rr 1 , preferably 10 3 S • rr 1 . Particularly good results are obtained when the composite material has an electrical conductivity of at least 1 ≤ 10 at 20 °C. 4 S * m' 1 , especially in the range of 1 • 10 4 S • m -1 up to 5 • 10 4 S • nr 1 , exhibits. In particular, especially with composite materials that exhibit the aforementioned conductivities, particularly high-performance bipolar plates can be obtained.

[0103] The inventive method is typically used to produce composite materials for bipolar plates, heat exchangers, and chemical reactors. In particular, it is preferably intended that the inventive method is used to produce composite materials for bipolar plates and heat exchangers, most preferably bipolar plates. The bipolar plates can preferably be used in fuel cells, redox flow batteries, or electrolyzers. Within the scope of the present invention, it is typically provided that the composite material is obtained from at least one starting material selected from particles, films, or mixtures thereof.

[0104] The starting material or starting material mixtures contain the components described above, preferably in the amounts described above. Within the scope of the present invention, the proportions of the individual components of the composite material, in particular thermoplastic polymer and filler, as well as any additives, correspond to the total amounts of these components in the starting material or starting material mixtures, so that the process according to the invention only involves homogenization and shaping, but no chemical transformation.

[0105] In particular, the composite material is obtained by introducing the feedstock into a feed gap of the multi-roll rolling mill and subsequently mixing it on the multi-roll rolling mill.

[0106] Preferably, the composite material is obtained from particles as a starting material. Within the scope of the present invention, it is possible that the particles are selected from particles of thermoplastic polymers, additives, fillers, recycled composite materials, plastic compounds, and mixtures thereof.

[0107] Preferably, according to the present invention, a mixture, in particular a powder mixture, is produced from various particles consisting of the different materials contained in the composite material. These are, in particular, mixtures of particles of the thermoplastic polymer, which may optionally contain further additives, and of the filler. Optionally, particles from recycled composite materials or polymer compounds can be added to this mixture. The recycled materials can, in particular, be waste products, especially offcuts, from the production of bipolar plates, which can be processed into new bipolar plates by the inventive method without loss of quality.

[0108] Particles of the thermoplastic polymer, or of compounds and recyclates, can be obtained, in particular, by cryogenic milling. Within the scope of the present invention, films made of composite materials or polymer compounds can also be used as starting materials, which are further homogenized by the process according to the invention. This corresponds to a semi-continuous production of the composite material.

[0109] However, within the scope of the present invention, it is preferred to start with particles, in particular particle mixtures, and to produce the composite material in a continuous process.

[0110] If particles are used, it has proven advantageous for the particles to have a particle size distribution D90 in the range of 0.01 to 500 pm, particularly 0.05 to 400 pm, more specifically 0.5 to 300 pm, and preferably 0.05 to 150 pm. Within the scope of this invention, the particle size distributions are determined, in particular, by means of selective laser scattering (SLS). The aforementioned ranges apply generally to all particles. If fibrous particles are used as filler, the particle size distributions apply to the diameter of the fibers. Preferably, the fibers have a length of at most 5 mm, more particularly at most 3 mm, and more preferably at most 2 mm. Particularly good results are obtained if the fibers have a length of 0.5 to 5 mm, more particularly 0.5 to 3 mm, and more particularly 1 to 2 mm.

[0111] It can be provided that the polymer particles have a particle size distribution D90 in the range of 0.1 to 500 pm, in particular 0.5 to 400 pm, in particular 1 to 300 pm, preferably 1 to 150 pm.

[0112] Furthermore, good results are generally obtained if the filler has a particle size distribution D90 in the range of 0.01 to 300 pm, in particular 0.05 to 200 pm, preferably 0.05 to 150 pm.

[0113] However, it has proven particularly effective if the filler has a particle size distribution D90 in the range of 1 to 300 pm, in particular 1 to 200 pm, preferably 1 to 150 pm.

[0114] However, within the scope of the present invention, it can also be provided that the filler has a particle size distribution D90 in the range of 0.01 to 5 pm, in particular 0.05 to 1 pm, preferably 0.05 to 0.1 pm. According to a preferred embodiment of the present invention, the filler has a multimodal, in particular a bimodal, particle size distribution, preferably with the latter two particle size distributions of the filler. This applies particularly when mixtures of graphite and carbon black are used. The graphite typically has the larger particles, while the carbon black is more finely divided.

[0115] According to a preferred embodiment of the present invention, the inventive method is a method for the continuous or semi-continuous production of composite materials from a thermoplastic polymer comprising a thermoplastic polymer, using a multi-roll rolling mill, wherein at least one feedstock comprising at least one thermoplastic polymer is first introduced into a feed gap of the multi-roll rolling mill and is subsequently heated and mixed by means of the multi-roll rolling mill to temperatures above the melting point of the thermoplastic polymer, so that a composite material is obtained, wherein the multi-roll rolling mill has at least two non-material-carrying rolls.

[0116] For this particular and preferred embodiment of the present invention, all the aforementioned advantages, special features and characteristics apply accordingly.

[0117] Within the scope of the present invention, it is also possible for the obtained composite material to be further processed into semi-finished products by cutting and forming.

[0118] In particular, the composite material can be heated, placed in a die, and pressed into shape using a male die. This process is also known as hot stamping. Composite semi-finished products with extremely complex external shapes and / or large dimensions can easily be manufactured in this way. However, the composite material can also be formed using stamping rollers.

[0119] The figures shown in Fig. 1 depict a multi-roll rolling mill for the production of composite materials according to the state of the art;

[0120] Fig. 2 shows a multi-roll rolling mill according to the invention for the production of composite materials;

[0121] Fig. 3 shows a preferred embodiment of a multi-roll rolling mill according to the invention for the production of composite materials and

[0122] Fig. 4 shows another preferred embodiment of a multi-roll rolling mill according to the invention for the production of composite materials.

[0123] A further object of the present invention - according to a second aspect of the present invention - is a composite material comprising a thermoplastic polymer and at least one filler, in particular obtainable by a previously mentioned method, wherein the filler is anisotropic in the composite material.

[0124] A special feature of the composite material according to the invention, which is preferably obtained according to the inventive method, is that the fillers are present anisotropically, i.e., in a preferred orientation, within the composite. Typically, the particles are aligned or arranged parallel to the surface of the composite material, particularly the composite film. This is not typical for films, since, for example, extruded or injection-molded films exhibit no or several preferred directions of particle incorporation within the film cross-section.

[0125] For further details on the composite material according to the invention, reference can be made to the above descriptions of the method according to the invention, which apply accordingly to the composite material according to the invention.

[0126] Yet another aspect of the present invention is a device for producing composite materials according to a aforementioned method, wherein the

[0127] The device is a multi-roll rolling mill, comprising at least two material-carrying rolls and at least two non-material-carrying rolls. Typically, one of the at least two non-material-carrying rolls is a material feed roll. Furthermore, within the scope of the present invention, it is typically provided that one of the material-carrying rolls, in particular the one arranged last in the process direction, is a cooling roll. Preferably, the multi-roll rolling mill comprises one material feed roll and one cooling roll.

[0128] Within the scope of the present invention, it has proven advantageous if the multi-roll rolling mill has at least 2, in particular at least 3, material-carrying rolls.

[0129] Furthermore, it is preferably provided that the multi-roll rolling mill has at most 10, in particular at most 8, preferably at most 7, preferably at most 6, particularly preferably at most 5, material-carrying rolls.

[0130] Furthermore, it is preferred if the multi-roll rolling mill has 2 to 10, in particular 2 to 8, preferably 2 to 7, preferably 2 to 6, particularly preferably 2 to 5, most preferably 3 to 5, material-carrying rolls.

[0131] The material-carrying rollers are preferably arranged between the material feed roller and the cooling roller.

[0132] As previously stated, the multi-roll rolling mill preferably has several non-material-carrying rolls. In particular, the multi-roll rolling mill has at least 2, preferably at least 3, non-material-carrying rolls.

[0133] In the context of the present invention, it is further preferably provided that the multi-roll rolling mill has at most 30, in particular at most 20, preferably at most 15, preferably at most 10, preferably at most 8, particularly preferably at most 7, non-material-carrying rolls.

[0134] In this context, it is particularly preferred if the multi-roll rolling mill has 2 to 30, in particular 2 to 20, preferably 2 to 15, preferably 3 to 10, particularly preferably 3 to 8, most preferably 3 to 7, non-material-carrying rolls.

[0135] In the context of the present invention, it is therefore preferably provided that the multi-roll rolling mill has kneading rolls 1 to 30, in particular 1 to 20, preferably 2 to 15, preferably 3 to 10, particularly preferably 3 to 8, most preferably 3 to 7.

[0136] In the context of the present invention, it is typically provided that one or more non-material-carrying rollers, in particular kneading rollers, are associated with a material-carrying roller, in particular with each material-carrying roller. It is particularly preferred that one to 10, in particular 1 to 8, preferably 1 to 7, and most preferably 2 to 5, non-material-carrying rollers, in particular kneading rollers, are associated with a material-carrying roller, in particular with each material-carrying roller.

[0137] For further details on the device according to the invention, reference can be made to the above statements on the further aspects of the invention, which apply accordingly to the device according to the invention.

[0138] The subject matter of the present invention is described in more detail below in a non-limiting manner with reference to the figures.

[0139] Figure 1 shows a multi-roll rolling mill according to the prior art for the production of composite materials. The multi-roll rolling mill 1 consists of five rolls, three of which are designed as material-carrying rolls 2.

[0140] A further material-carrying roll – as the last roll in the process direction – is designed in the form of a cooling roll 4. In addition, the multi-roll rolling mill 1 has a material feed roll 3. A material feed gap 5 is formed between the first material-carrying roll 2 in the process direction and the material feed roll 3. A feed material, preferably a powder mixture containing a thermoplastic polymer and electrically conductive fillers, is introduced into the material feed gap 5 to produce a composite web 6.

[0141] The material-carrying rollers 2 and the material feed roller 3 are heatable and can be heated, in particular, to temperatures above the melting point of the thermoplastic polymer. A friction of 1 to 4, preferably 1, 2 to 2, is typically set between the material feed roller 3 and the first material-carrying roller 2, so that a composite sheet is formed which is transported from one material-carrying roller 2 to the next and finally to the cooling roller 4. The cooling roller 4 typically has a temperature below the solidification temperature of the thermoplastic polymer, so that a solid composite sheet 6 can be peeled off.

[0142] By controlling the friction and temperature of the rollers, as well as the respective gap width, it is possible to generate shearing in the gap between two rollers. This creates a material bank, a so-called kneading 7, and mixes and homogenizes the composite material. However, the multi-roll rolling mill 1 shown in Fig. 1 only has three gap passes in which the material is homogenized and mixed, so that composite materials with unsatisfactory properties are often obtained. Further increasing the number of material-carrying rollers is not practical, since a friction of 1 to 4, preferably 1, 2 to 2, must usually be set between the material-carrying rollers 2, and the contact pressure between the individual rollers also becomes increasingly complex to control.

[0143] Fig. 2 shows a multi-roll rolling mill 1 according to the invention, which in its basic structure corresponds to the multi-roll rolling mill 1 shown in Fig. 1. However, the multi-roll rolling mill 1 according to the invention additionally has kneading rolls 8, which are non-material-carrying. This means that the kneading rolls 8 in Fig. 2 create three additional gaps. Due to the freely adjustable friction of the kneading rolls 8 to the material-carrying rolls 2, which is usually in the range of 0 to 1, particularly good mixing of the knead 7 or the composite material can be achieved, whereas in the gaps between the material-carrying rolls 2, the primary focus must always be on material transport. The kneading rolls 8 are preferably heatable and are heated to a temperature above the melting point of the thermoplastic polymer during the execution of the process.

[0144] By using kneading rollers 8, it is possible to obtain significantly more homogeneous composites without complicating the process. In particular, the friction does not need to be adjusted so that the composite web is transferred from one roller to the other. Rather, the use of kneading rollers 8 allows for free adjustment of the friction.

[0145] Figure 3 shows a preferred embodiment of the multi-roll rolling mill 1 according to the invention, in which the kneading rolls 8 are arranged planetarily around a material-carrying roll 2. The multi-roll rolling mill 1 also has a material feed roll 3 and a cooling roll 4. The advantage of the arrangement of the rolls shown in Figure 3 is that the multi-roll rolling mill can be built very compactly and that the process control is very simple with regard to material transport, since only the friction between the material feed roll 3, the material-carrying roll 2, and the cooling roll 4 is determined by the material transport.

[0146] Figure 4 shows a further preferred embodiment of the rolling mill 3 according to the invention, in which several kneading rolls 8 are assigned to each material-carrying roll 2. This arrangement makes it possible to obtain particularly homogeneous composite materials, whereby the process control is no more complicated than on the five-roll rolling mill of the prior art according to Figure 1.

[0147] Reference symbol list: Multi-roll rolling mill 5 Material feed gap Material-carrying roll 6 Composite web Material feed roll 7 Kneading cooling roll 8 Kneading roll

Claims

Patent claims:

1. A method for the continuous or semi-continuous production of composite materials comprising a thermoplastic polymer, using a multi-roll rolling mill, characterized in that the multi-roll rolling mill has at least two non-material-carrying rolls.

2. Method according to claim 1, characterized in that the multi-roll rolling mill has several non-material-carrying rolls, in particular 2 to 30, preferably 2 to 20, preferably 2 to 15, particularly preferably 3 to 10, most preferably 3 to 8, particularly preferably 3 to 7.

3. Method according to claim 1 or 2, characterized in that the multi-roll rolling mill has material-carrying rolls 2 to 10, in particular 2 to 8, preferably 2 to 7, preferably 2 to 6, particularly preferably 2 to 5, most particularly preferably 3 to 5.

4. Method according to one of the preceding claims, characterized in that the temperature of the material-carrying rollers and / or the temperature of the non-material-carrying rollers is controllable.

5. Method according to one of the preceding claims, characterized in that the temperature of the last material-carrying roller is lower than the temperature of the other rollers.

6. Method according to one of the preceding claims, characterized in that the non-material-carrying rollers are assigned to the material-carrying rollers, in particular arranged around the material-carrying rollers.

7. Method according to one of the preceding claims, characterized in that a gap between a material-carrying roller and a non-material-carrying roller is narrower than the thickness of the supplied substrate.

8. Method according to one of the preceding claims, characterized in that the composite material is obtained in the form of a film.

9. A method according to any of the preceding claims, characterized in that the thermoplastic polymer of the composite material is selected from the group consisting of polyolefins, in particular polyethylene (PE), polypropylene (PP), polyetheretherketone (PEEK), polyphenylene sulfide (PPS), polyaryletherketone (PAEK), polyetherketoneketone (PEKK), polyetherimides (PEI), acrylonitrile butadiene styrene (ABS), polyamides (PA), polyphenylsulfones (PPS), polysulfone (PS), polyethersulfone (PES), polyamide imides (PAI), polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA) and mixtures thereof.

10. Method according to one of the preceding claims, characterized in that the composite material comprises at least one filler, in particular an electrically conductive filler.

11. Method according to claim 10, characterized in that the filler, in particular the electrically conductive filler, is selected from the group consisting of carbon-containing materials, metal-organic frameworks (MOFs), covalent organic frameworks (COFs), core-shell structured mesoporous materials, in particular core-shell nanoparticles (CSN), metals, metal oxides, nitrides, carbides, MAX phases, MXenes and mixtures thereof.

12. Method according to one of the preceding claims, characterized in that the composite material contains the polymer in amounts of 1 to 60 wt.%, in particular 1 to 50 wt.%, preferably 2 to 40 wt.%, preferably 10 to 30 wt.%, based on the composite material.

13. Method according to one of claims 10 to 12, characterized in that the composite material contains the filler in amounts of 40 to 99 wt.%, in particular 50 to 99 wt.%, preferably 60 to 98 wt.%, preferably 70 to 90 wt.%, based on the composite material.

14. Method according to one of the preceding claims, characterized in that the composite material is obtained from at least one starting material selected from particles, films or mixtures thereof, in particular by introduction into a feed gap of the multi-roll rolling mill and subsequent mixing on the multi-roll rolling mill.

15. Method according to claim 14, characterized in that the particles are selected from particles of thermoplastic polymers, fillers, recyclates of composite materials, plastic compounds and mixtures thereof.

16. A method for the continuous or quasi-continuous production of composite materials from a thermoplastic polymer comprising a thermoplastic polymer, using a multi-roll mill, wherein at least one feedstock comprising at least one thermoplastic polymer is first introduced into the feed gap of the multi-roll mill and is subsequently mixed by means of the multi-roll mill at temperatures above the melting point of the thermoplastic polymer, so that a composite material is obtained, wherein the multi-roll mill has at least two non-material-carrying rolls.

17. Composite material comprising a thermoplastic polymer and at least one filler, in particular obtainable by a method according to one of claims 1 to 16, characterized in that the filler is anisotropic in the composite material.

18. Device for the production of composite materials by means of a method according to one of claims 1 to 16, wherein the device is a multi-roll rolling mill, characterized in that the device has at least two material-carrying rolls and at least two non-material-carrying rolls.

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