EP2848734B1 - Paper structure and its prouction from carbon fibers in a wet process - Google Patents

Paper structure and its prouction from carbon fibers in a wet process Download PDF

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Publication number
EP2848734B1
EP2848734B1 EP14180963.2A EP14180963A EP2848734B1 EP 2848734 B1 EP2848734 B1 EP 2848734B1 EP 14180963 A EP14180963 A EP 14180963A EP 2848734 B1 EP2848734 B1 EP 2848734B1
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Prior art keywords
carbon fibers
fibers
paper structure
fiber
paper
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German (de)
French (fr)
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EP2848734A1 (en
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Peter Helfer
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Helfer Peter
Reso Oberflaechentechnik GmbH
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Reso Oberflachentechnik GmbH
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    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
    • D21H13/00—Pulp or paper, comprising synthetic cellulose or non-cellulose fibres or web-forming material
    • D21H13/36—Inorganic fibres or flakes
    • D21H13/46—Non-siliceous fibres, e.g. from metal oxides
    • D21H13/50—Carbon fibres
    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
    • D21H15/00—Pulp or paper, comprising fibres or web-forming material characterised by features other than their chemical constitution
    • D21H15/02—Pulp or paper, comprising fibres or web-forming material characterised by features other than their chemical constitution characterised by configuration
    • D21H15/06—Long fibres, i.e. fibres exceeding the upper length limit of conventional paper-making fibres; Filaments

Definitions

  • the present invention relates to a method for producing a carbon fiber nonwoven fabric from an aqueous suspension and a corresponding paper structure made of carbon fibers.
  • Paper is a sheet material that consists essentially of fibers of "mostly vegetable origin” and is formed by dewatering a pulp suspension on a sieve.
  • paper is usually produced today in a continuous process, in which the pulp suspension is brought by means of a headbox on a sieve (fourdrinier) or between two sieves (former) and an initial sheet is formed.
  • the fiber structure is mechanically drained - usually under pressure - before it is then dried by means of thermal energy, for example on drying cylinders to a predetermined residual moisture content and rolled up.
  • Such methods are widely used today and are used for the production of paper, board and board in web widths up to 12 m, production speeds up to 2500 m / min and basis weights up to more than 500 g / m 2 .
  • the area weights to be produced can be further increased by bonding (gumming) several initial paper webs while still wet, so that the possible basis weight range can be extended to a very wide range.
  • carbon fiber is a hydrophobic fiber, which is usually of uniform length and very difficult to evenly distribute in water as a suspending agent in papermaking.
  • the difficulty lies, inter alia, in the fact that a stable suspension remains only very briefly without the entry of turbulence energy, or knots and spinning form in the suspension or the fibers settle very quickly in the suspension and thus in very different concentrations within the Suspension present.
  • the processing of such suspensions on a conventional paper machine is accordingly very difficult or even impossible, since a uniform distribution of the fibers in the web to be produced is not achieved.
  • Carbon fiber paper sheets are known in the art. Such a paper texture is for example the in EP 2770104 A1 discloses electrically conductive paper structures comprising cellulose-containing fibers and carbon fibers and whose resistivity is in a range between 10 -1 ⁇ • m and 10 -6 ⁇ • m. Besides, and in particular is in DE 1540949 A1 discloses a paper structure having an electrically conductive carbonaceous fiber with a resistivity between 0.036 ⁇ • cm and 0.60 ⁇ • cm. In addition, shows EP 1186704 A1 a paper structure comprising a paper base material and anti-static electrically conductive carbon fibers, the carbon fibers imparting antistatic and conductive properties to the paper structure.
  • the paper structure of carbon fibers according to the invention has at least two classes forming fibers, wherein the fibers differ at least in their length. Moreover, the amount and / or weight of the individual fiber classes in the paper structure is between 1% and 99%, preferably between 5% and 95%, and the average fiber length of the carbon fibers over all classes in the paper structure between 1 mm and 20 mm.
  • Carbon fibers also referred to as carbon fibers, are industrially produced fibers from carbonaceous raw materials which are converted to graphitic carbon by pyrolysis.
  • isotropic fibers have only low strength and less technical importance, anisotropic fibers show high strength and stiffness with low elongation at break.
  • a carbon fiber has a diameter of about 5-8 microns.
  • 1,000 to 24,000 individual fibers (filaments) are combined into a bundle (roving), which is endlessly wound on spools. This is i.a. a possible starting material for the production of the paper structure.
  • the fiber length is understood according to the present invention, the distance between the two ends of a fiber. This is given as the length of the crimped or crimped fiber length depending on the crimping state, with carbon fibers being substantially stretched due to their stiffness.
  • it is generally worked with a classification into length classes, wherein the individual length classes represent a certain length range. The width of such an area is the class width. The arithmetic mean of the two class boundaries limiting the respective class is the class center.
  • the most important task of determining the fiber lengths is to determine the fiber length distribution, i. H. at what relative frequency the fibers are represented in each length class. This class frequency, or frequency for short, indicates in which ratio in the fibrous material to be examined, which represents the population, the fibers belonging to a class belong to the fibers of this population with regard to a particular feature.
  • Frequency of fibers (frequency according to the number of fibers): The basis is the number of fibers. The ratio of the number of fibers of a length class to Total number of fibers is the fiber number frequency of this class (frequency by number of fibers); it is also called unstressed frequency. The number of fiber counts is the actual distribution of fiber lengths in the fiber, regardless of fiber cross-section, fiber density, and the interrelationships between fiber length, cross-section, and weight.
  • Fiber length frequency (frequency after the fiber length).
  • the basis is the fiber length.
  • the ratio of the total length of the fibers of a length class to the total length of all fibers is the fiber length frequency of this class (frequency after the fiber length). Lengthwise, the fibers of a length class make the more, the more and the longer they are. The fiber length frequency is therefore also called length-emphasized frequency.
  • the mean fiber length of the carbon fibers in the paper structure over all classes is between 2 mm and 10 mm, preferably between 4.5 mm and 6 mm.
  • the fiber classes are subdivided into at least one long fiber fraction and one short fiber fraction.
  • the carbon fibers of the long fiber portion for example, have a length between 25 mm and 10 mm, preferably between 5 mm and 2 mm and are in particular greater than 6 mm.
  • the carbon fibers of the short fiber fraction for example, correspondingly have a length between 10 mm and 0.1 mm, preferably between 2 mm and 0.5 mm and are in particular smaller than 6 mm.
  • the carbon fiber used for the production of the paper structure is subdivided into more than two classes.
  • a fiber content with an average fiber length (MF) or also fines (FS) can be taken into account as a separate class.
  • the fibrous material is present in at least two classes, ie two different lengths, and does not have substantially a uniform fiber length as known in the prior art. This can ensure that during the papermaking process, especially at the initial Dewatering a uniform fiber distribution is achieved and a homogeneous fleece can be provided.
  • the carbon fibers are primary and / or recycled carbon fibers.
  • the advantage of the recycled carbon fibers lies not only in the price, but also in the closure of the material cycle through the return of already used carbon fibers in the production process. Processing methods for such carbon fibers, such as the pyrolysis technique are known.
  • These carbon fibers are preferably cut by cutting and / or grinding and adjusted to the desired fiber length or fiber length distribution, this can be done for example by wet cutting (for example in a suspension or by moistening the fibers) to the at least two different lengths.
  • a possible method for shortening the fibers is a cyclic process in which, for example, the fibers are added to a Dutchman's bin with a time lag in water, so that the originally equal fibrous materials are shortened in Dutch several times to produce a pulp suspension consisting of a plurality of unequal length fibers. Accordingly, this can also be done in the circulation process with modern grinding and cutting units, wherein the pulp suspension is guided here via a pipe system with Bütte and a refiner in the circuit.
  • the addition of the starting pulp in the circulation over a certain predetermined time so that the fibers are fed to the cutting process different times.
  • the addition time of the pulp is preferably greater than the circulation time of the suspension in the milling system.
  • the crabon fibers are prepared in an upstream process step and in particular prec shortened, so that in particular an addition of these fibers in an aqueous system, as described above is possible.
  • the carbon fibers can be cut in at least two separate methods, in particular also shortened only once and then mixed in a predetermined ratio.
  • the cutting of the carbon fibers is preferably carried out by means of a grinding aggregate selected from a group comprising paper holland, papillon refiner, flat cone refiner, steep cone refiner, disc mill, deflaker, combinations thereof, and the like.
  • Such grinding units are known in the art.
  • an advantageous fiber dispersion is achieved by the grinding or cutting of the fibrous materials - preferably with one of the aforementioned grinding units - by the shearing forces acting on the fibers in the aggregates.
  • the shear forces separate the fine fiber bundles of the rovings and are then present as a single fiber so that a uniform distribution of the fibers can be achieved during papermaking and initial dewatering of the paper structure.
  • the cutting of the carbon fibers takes place in an aqueous suspension whose consistency is between 35% and 0.1%, preferably between 25% and 1% and in particular about 5%.
  • the proportion in the paper structure of the longer carbon fibers, in particular the long fibers between 10% by weight and 75% by weight, preferably 25% by weight and 50% by weight and the proportion of shorter carbon fibers, especially short fibers, between 90% and 25% by weight, preferably between 75% and 50% by weight.
  • the possibly existing remainder of the pulp is fines which have a fiber length of less than 0.5 mm or 0.1 mm.
  • the fibers are cut dry and then suspended in water for the production of the paper structure.
  • the carbon fibers have a cationic or anionic charge, which is preferably applied to the carbon fibers by a coating.
  • a cationic or anionic charge which is preferably applied to the carbon fibers by a coating.
  • the paper structure of the present invention may include other fibrous materials such as cellulosic fibers, paper fibers, recycled paper fibers, wood pulp fibers, combinations thereof, and the like.
  • Such fibers preferably have a proportion of the total weight of the paper structure between 25% by weight and 0.5% by weight, preferably between 15% by weight and 1% by weight and in particular between 10% by weight and 1.5% by weight.
  • the paper structure is made of 100% carbon fibers.
  • the paper structure according to the invention comprises, in addition to the carbon fibers, reinforcing fibers, in particular binding fibers, for example of polyethylene.
  • reinforcing fibers in particular binding fibers, for example of polyethylene.
  • These preferably have a proportion of the paper structure between 25% by weight and 0.1% by weight, preferably between 20% by weight and 1% by weight and in particular between 10% by weight and 1.5% by weight and further preferably have one Faserläge, which is between 0.1 mm and 10 mm, preferably between 0.5 mm and 7 mm and in particular between 1 mm and 5 mm.
  • Such fibers are known in the art, and are offered for example by the Black Forest textile factories.
  • These synthetic fibers are made, for example, of HD polyethylene and, in addition to a specific fiber length, in particular have a very precisely specifiable melting point. It should be noted that in the production of the paper structure, the nonwoven is dried in a dryer section of a paper machine and melted by the specific melting point, the corresponding fibers in the dryer section or group or completely melted and thus a further strength contribution to the Can provide processability of the carbon fiber nonwoven, since after cooling of the nonwoven, the re-cured plastic fibers provide a mechanical connection between the carbon fibers ready.
  • the typical melting point of such fibers is in a range between 90 ° C and 180 ° C, in particular between 110 ° C and 145 ° C and preferably in a range between 130 ° C and 135 ° C.
  • fibers, granules or particles of further or alternative thermoplastics can be used, such as acrylonitrile-butadiene-styrene (ABS), polyamides (PA), polylactate (PLA ), Polymethyl methacrylate (PMMA), polycarbonate (PC), polyethylene terephthalate (PET), polyethylene (PE), polypropylene (PP), polystyrene (PS), polyetheretherketone (PEEK), celluloid and polyvinylchloride (PVC).
  • ABS acrylonitrile-butadiene-styrene
  • PA polyamides
  • PLA polylactate
  • PMMA Polymethyl methacrylate
  • PC polycarbonate
  • PET polyethylene terephthalate
  • PE polyethylene
  • PE poly
  • the paper structure is produced without reinforcing fibers, in particular binding fibers and / or thermoplastics.
  • the paper structure in addition to the aforementioned substances, other additives such as mineral additives, in particular fillers and pigments such as calcium carbonate, kaolin, talc, special minerals, dispersants such as polyphosphates, polyacrylates and / or chemical additives such as retention aids, drainage accelerators, aluminum compounds, polyaluminum chlorides, polyacylamides , Polyethyleneimines, polyvinylamines, polyamidoamines, polydiallyldimethylammonium chloride, microparticle systems, network retention agents, natural and / or modified starch, fixatives, sizing agents, dry strength agents, wet strength agents such as melamine wet strength agents, epichlorohydrin resins, glyoxal resins, defoamers, optical brighteners, dyes, biocides, and combinations of this, to be admitted.
  • mineral additives in particular fillers and pigments such as calcium carbonate, kaolin, talc, special minerals, dispersants such as polyphosphates,
  • this comprises the production of at least two classes of carbon fibers with different fiber lengths in preferably an aqueous suspension of the carbon fibers.
  • This may preferably be done in a circulatory system with recirculation and a grinding and / or cutting unit, wherein the addition of starting carbon fibers (relatively long fibers) takes place in the water within a predetermined period of time, so that the added fibers are fed to the cutting process at different rates.
  • this method provides a relatively easily adjustable fiber length distribution.
  • the addition of the starting carbon fibers takes place in a time period which is greater than the circulation time of the carbon fibers in the circulatory system. This ensures that at least parts of the carbon fibers are fed several times to the cutting process.
  • the carbon fibers introduced into water may be cut in at least two different milling units and / or at least two different process steps to produce at least one long fiber portion and one short fiber portion and then blended in a predetermined proportion to produce the paper sheet.
  • various carbon fibers can be provided, which differ in their fiber length distribution and are assembled exactly to the needs of the paper structure to be produced.
  • the goal here is next to the relatively long Fibers also provide relatively short fibers for the production of the nonwoven fabric. Only in this way can it be ensured that a paper structure can be produced on the paper machine which fulfills the minimum requirements, in particular with regard to the uniform mass distribution.
  • Fabrication of the paper structure may be accomplished in accordance with the present invention on a dewatering apparatus selected from a group of machines including longitudinal wire machines, hybrid formers, sorters, skewers, gap formers, and hand-draw devices.
  • the paper structure besides the carbon fibers, other fibrous materials such as cellulosic fibers, paper fibers, waste paper fibers, wood pulp fibers, combinations thereof and the like can be used for the production of the paper structure, preferably in a proportion of between 25% and 0.5% by weight, preferably between 15% by weight and 1% by weight and especially between 10% by weight and 1.5% by weight can be added to the paper structure.
  • other fibrous materials such as cellulosic fibers, paper fibers, waste paper fibers, wood pulp fibers, combinations thereof and the like can be used for the production of the paper structure, preferably in a proportion of between 25% and 0.5% by weight, preferably between 15% by weight and 1% by weight and especially between 10% by weight and 1.5% by weight can be added to the paper structure.
  • the cutting of the carbon fibers is carried out according to a further particularly preferred embodiment of the method according to the invention in an aqueous suspension whose consistency is between 35% and 0.1%, preferably between 25% and 1% and in particular about 3%.
  • the paper structure additives such as mineral additives, in particular fillers and pigments such as calcium carbonate, kaolin, talc, special minerals, dispersants such as polyphosphates, polyacrylates and / or chemical additives such as retention aids, dehydration accelerators, aluminum compounds, polyaluminum chlorides, polyacylamides, polyethyleneimines, polyvinylamines, Polyamidoamines, polydiallyldimethylammonium chloride, microparticle systems, network retention agents, natural and / or modified starches, fixatives, sizing agents, dry strength agents, wet strength agents such as melamine resin wet strength agents, epichlorohydrin resins, glyoxal resins, defoamers, optical brighteners, dyes, bio
  • a device such as a paper hollander, Papillonrefiner, Flachkegelrefiner, steep cone refiner, disc mills, Entstipper used
  • the control of the device is carried out in particular by the Mahltechnik-load curve, which is for example a sinusoid.
  • the present invention also encompasses the method described above for producing a paper structure from carbon fibers with at least two classes of fibrous materials which have different lengths of carbon fibers, wherein the quantity and / or weight fraction of the individual fiber classes in the paper structure is between 1% and 99%. , preferably between 5% and 95%, and the average fiber length of the carbon fibers over all classes in the paper structure is between 1 mm and 20 mm.
  • the invention also encompasses the use of a paper structure of carbon fibers as described above for the production of fiber composite materials, in particular fiber-plastic composites, ceramic fiber composite materials, combinations thereof and the like.
  • FIG. 1 a shows a transmitted light image of a pulp which was placed in a test Dutchman (volume 15 l) with a quantity of 400 g over a picking period of 60 seconds and ground in total over a period of 180 seconds. This results in a relatively uniform fiber length distribution between 0.2 mm and 6 mm.
  • the fiber length distribution was determined in three fiber length classes. This is the long fiber content at about 20%, the proportion of medium-length fibers at about 34% and short fibers at about 46%.
  • the classes include for long fibers, pulps with a length between 7 mm and 12 mm, medium-long fibers, pulps with a length between 3 mm and 7 mm and short fibers, pulps with a length between 0.5 mm and 3 mm.
  • Figure 1 b shows a transmitted light shot of a furnish introduced in the same previously used experimental Dutchman at 50 grams for a 10 second picking period and ground in total over a period of 120 seconds.
  • the lower entry also increases the specific load of the fibers in the grinding unit, so that the proportion of short fibers also increases.
  • the long fiber content is about 16%, the proportion of medium-length fibers about 29% and short fibers about 55%.
  • Figure 1 c shows a transmitted light image of a pulp which was placed in the same previously used experimental Dutchman at a rate of 50 g over a 10 second picking period and ground in total over a period of 90 seconds. Due to the short processing time, predominantly long fibers remain, which cause considerable difficulties during processing into a paper structure. This leads to strong spinning between the fibers.
  • the long fiber content is about 17.5%
  • the proportion of medium-length fibers is about 37.5% and short fibers about 45%.
  • Figure 1d shows a transmitted light shot of a pulp which was placed in the same previously used experimental Dutchman at a rate of 50 g for a 10 second picking period and ground in total over a period of 180 seconds. After grinding for 180 seconds, there are practically no longer any long fibers.
  • the long fiber content is about 5.5%, the proportion of medium-length fibers about 33% and short fibers about 61%.
  • FIGS. 2a and 2b show two different processes for the preparation of the pulp.
  • FIG. 2a a Dutchman for grinding the pulp in a chest.
  • About the addition of 5 over the predetermined period (which is preferably greater than the Umtriebszeit the suspension in the chest) of the pulp in the with Water-filled tub 2 was added and ground over the grinder of Dutchman 4. After completing the meal, the grinder is stopped, the pulp removed and transferred to the nonwoven production.
  • FIG. 2b shows an alternative embodiment for this purpose, in which the pulp is a Bütte 10 is added via the supply line 14 and is supplied by means of the pump 12 to the grinding unit, for example, a cone refiner. Once the grinding is completed, the pulp is fed via the chest and the take-off valve 16 from the chest to the nonwoven manufacturing process.
  • the pulp is also possible for different fibrous materials with different fiber lengths to be produced one behind the other and combined for the nonwoven production after the grinding or the cutting.

Description

Die vorliegende Erfindung betrifft ein Verfahren zur Herstellung eines Kohlefaservlieses aus einer wässrigen Suspension und ein entsprechendes Papiergefüge aus Kohlefasern.The present invention relates to a method for producing a carbon fiber nonwoven fabric from an aqueous suspension and a corresponding paper structure made of carbon fibers.

Papier ist ein flächiger Werkstoff, der im Wesentlichen aus Fasern "meist pflanzlicher Herkunft besteht" und durch Entwässerung einer Faserstoffsuspension auf einem Sieb gebildet wird. Vorzugsweise wird Papier heute üblicherweise in einem Endlosverfahren hergestellt, bei welchem die Faserstoffsuspension mittels einem Stoffauflauf auf ein Sieb (Langsieb) oder zwischen zwei Siebe (Former) gebracht wird und ein initiales Blatt gebildet wird. Im Anschluss an diese Blattbildung wird das Fasergefüge mechanisch - meist unter Druck - entwässert, bevor es anschließend mittels thermischer Energie zum Beispiel auf Trockenzylindern auf eine vorgegebene Restfeuchte getrocknet und aufgerollt wird. Solche Verfahren sind heute weit verbreitet und werden für die Herstellung sowohl von Papier, Pappen als auch Karton in Bahnbreiten bis zu 12 m, Produktions-geschwindigkeiten bis zu 2500 m/min und Flächengewichten bis zu über 500 g/m2 verwendet. Die herzustellenden Flächengewichte lassen sich weiter steigern, indem mehrere initiale Papierbahnen im noch feuchten Zustand miteinander verbunden (vergautscht) werden, so dass sich der mögliche Flächengewichtsbereich auf einen sehr weiten Bereich ausdehnen lässt.Paper is a sheet material that consists essentially of fibers of "mostly vegetable origin" and is formed by dewatering a pulp suspension on a sieve. Preferably, paper is usually produced today in a continuous process, in which the pulp suspension is brought by means of a headbox on a sieve (fourdrinier) or between two sieves (former) and an initial sheet is formed. Following this formation of sheets, the fiber structure is mechanically drained - usually under pressure - before it is then dried by means of thermal energy, for example on drying cylinders to a predetermined residual moisture content and rolled up. Such methods are widely used today and are used for the production of paper, board and board in web widths up to 12 m, production speeds up to 2500 m / min and basis weights up to more than 500 g / m 2 . The area weights to be produced can be further increased by bonding (gumming) several initial paper webs while still wet, so that the possible basis weight range can be extended to a very wide range.

Es wird nun schon seit längerem versucht, diese bei der Herstellung von Papier aus natürlichen Fasern bekannten Verfahren auch für den Einsatz weiterer Papiergefüge zu verwenden, die heute noch in sogenannten Trockenverfahren u.a. durch Kämmen und Legen hergestellt werden. So werden heute zum Beispiel Carbonfaservliese trocken hergestellt, wobei hierzu besonders lange Fasern verwendet werden bzw. das Herstellungsverfahren relativ aufwendig und damit teuer ist. Auf der anderen Seite ist es ein dringender Wunsch der Industrie den vielversprechenden Werkstoff Carbonfaser noch breiter einzusetzen, wobei hierzu eine kostengünstigere, einfachere und produktivere Alternative zur Herstellung des Carbonfaservlieses dringend gesucht wird. Da es sich bei Carbonfasern auch um eine "Faser" handelt wäre es nun wünschenswert, Carbonfaservliese in einem kontinuierlichen und bekannten Nassverfahren herzustellen, um damit die Herstellungskosten zu senken und gleichzeitig die Produktivität und Verfügbarkeit dieses Basismaterials zu verbessern.It has now been tried for some time to use these known in the production of paper from natural fibers method for the use of other paper structures that are still produced today in so-called dry process, inter alia, by combing and laying. So today, for example, Carbonfaservliese produced dry, for which purpose particularly long fibers are used or the manufacturing process is relatively expensive and therefore expensive. On the other hand, it is an urgent desire of the industry to use the promising material carbon fiber even wider, in which case a more cost-effective, simpler and more productive alternative to the production of carbon fiber fleece is urgently sought. Since carbon fibers are also a "fiber", it would now be desirable to produce carbon fiber webs in a continuous and well-known wet process, thereby reducing manufacturing costs while improving the productivity and availability of this base material.

Hierbei ergeben sich jedoch große Schwierigkeiten, die bis heute noch nicht gelöst wurden. So handelt es sich bei der Kohlenstofffaser im Gegensatz zur klassischen Papierfaser aus Zellulose um eine hydrophobe Faser, welche üblicherweise in einer einheitlichen Länge vorliegt und sich in Wasser - als Suspendierungsmittel bei der Papierherstellung - nur sehr schwierig gleichmäßig verteilen lässt. Die Schwierigkeit liegt unter anderem darin, dass eine stabile Suspension nur sehr kurz ohne den Eintrag von Turbulenzenergie bestehen bleibt, bzw. sich Knoten und Verspinnungen in der Suspension bilden oder sich die Fasern sehr schnell in der Suspension absetzten und damit in sehr unterschiedlichen Konzentrationen innerhalb der Suspension vorliegen. Die Verarbeitung solcher Suspensionen auf einer klassischen Papiermaschine ist dementsprechend sehr schwierig bzw. sogar unmöglich, da eine gleichmäßige Verteilung der Fasern in dem zu erzeugenden Vlies nicht erreicht wird.However, this results in great difficulties that have not yet been solved. Thus, in contrast to the classical cellulose paper, carbon fiber is a hydrophobic fiber, which is usually of uniform length and very difficult to evenly distribute in water as a suspending agent in papermaking. The difficulty lies, inter alia, in the fact that a stable suspension remains only very briefly without the entry of turbulence energy, or knots and spinning form in the suspension or the fibers settle very quickly in the suspension and thus in very different concentrations within the Suspension present. The processing of such suspensions on a conventional paper machine is accordingly very difficult or even impossible, since a uniform distribution of the fibers in the web to be produced is not achieved.

Papiergefügen aus Carbonfasern sind im Stand der Technik bekannt. Solch ein Papiergefüge ist beispielsweise das in EP 2770104 A1 offenbarte elektrisch leitende Papiergefüge, welches cellulosehaltige Faserstoffe und Kohlenstofffasern aufweist und dessen spezifischer Widerstand in einem Bereich zwischen 10-1 Ω•m und 10-6 Ω•m liegt. Außerdem und insbesondere ist in DE 1540949 A1 ein elektrisch leitendes kohlenstoffhaltigen Fasern aufweisendes Papiergefüge mit einem spezifischen Widerstand zwischen 0,036 Ω•cm und 0,60 Ω•cm offenbart. Darüber hinaus zeigt EP 1186704 A1 ein Papiergefüge, welches ein papierenes Grundmaterial und antistatische elektrisch leitende Kohlenstofffasern aufweist, wobei die Kohlenstofffasern dem Papiergefüge antistatische und leitende Eigenschaften verleihen.Carbon fiber paper sheets are known in the art. Such a paper texture is for example the in EP 2770104 A1 discloses electrically conductive paper structures comprising cellulose-containing fibers and carbon fibers and whose resistivity is in a range between 10 -1 Ω • m and 10 -6 Ω • m. Besides, and in particular is in DE 1540949 A1 discloses a paper structure having an electrically conductive carbonaceous fiber with a resistivity between 0.036 Ω • cm and 0.60 Ω • cm. In addition, shows EP 1186704 A1 a paper structure comprising a paper base material and anti-static electrically conductive carbon fibers, the carbon fibers imparting antistatic and conductive properties to the paper structure.

Ausgehend von diesen Problemen und Schwierigkeiten des Standes der Technik ist es nun Aufgabe der vorliegenden Erfindung ein Verfahren bereit zu stellen, mit welchem die bekannten Nachteile wenigstens teilweise überwunden werden können und es möglich wird ein Papiergefüge aus Carbonfasern bereit zu stellen, welches für nachfolgende Verarbeitungsstufen wie zum Beispiel dem Imprägnieren mit Harz, der flexiblen Formgebung und Formanpassung in einem weiten Bereich geeignet ist.Based on these problems and difficulties of the prior art, it is an object of the present invention to provide a method with which the known disadvantages can be at least partially overcome and it becomes possible to provide a paper structure of carbon fibers which is suitable for subsequent processing stages For example, impregnation with resin, flexible shaping and conforming in a wide range is suitable.

Gelöst wird diese Aufgabe mit einem Verfahren zur Herstellung des Papiergefüges. Darüber hinaus wird die Aufgabe auch durch das entsprechende Papiergefüge selbst gelöst. Bevorzugte Ausführungsbeispiele des erfindungsgemäßen Verfahrens bzw. des Papiergefüges sind Gegenstand der entsprechenden Unteransprüche.This object is achieved with a method for producing the paper structure. In addition, the task is also solved by the appropriate paper structure itself. Preferred embodiments of the method and the paper structure according to the invention are the subject of the corresponding subclaims.

Das erfindungsgemäße Papiergefüge aus Carbonfasern weist wenigstens zwei Klassen bildende Faserstoffe auf, wobei sich die Faserstoffe wenigstens in ihrer Länge unterscheiden. Darüberhinaus liegt der Mengen- und/oder Gewichtsanteil der einzelnen Faserstoffklassen im Papiergefüge zwischen 1 % und 99 %, vorzugsweise zwischen 5 % und 95%, und die mittlere Faserlänge der Carbonfasern über alle Klassen im Papiergefüge zwischen 1 mm und 20 mm.The paper structure of carbon fibers according to the invention has at least two classes forming fibers, wherein the fibers differ at least in their length. Moreover, the amount and / or weight of the individual fiber classes in the paper structure is between 1% and 99%, preferably between 5% and 95%, and the average fiber length of the carbon fibers over all classes in the paper structure between 1 mm and 20 mm.

Carbonfasern, welche auch als Kohlenstofffasern bezeichnet werden, sind industriell hergestellte Fasern aus kohlenstoffhaltigen Ausgangsmaterialien, die durch Pyrolyse in graphitartig angeordneten Kohlenstoff umgewandelt werden. Man unterscheidet isotrope und anisotrope Typen: Isotrope Fasern besitzen nur geringe Festigkeiten und geringere technische Bedeutung, anisotrope Fasern zeigen hohe Festigkeiten und Steifigkeiten bei gleichzeitig geringer Bruchdehnung. Eine Kohlenstoff-Faser hat einen Durchmesser von etwa 5 - 8 Mikrometer. Üblicherweise werden 1.000 bis 24.000 Einzelfasern (Filamente) zu einem Bündel (Roving) zusammengefasst, das auf Spulen endlos gewickelt wird. Dies ist u.a. ein möglicher Ausgangsstoff für die Herstellung des Papiergefüges.Carbon fibers, also referred to as carbon fibers, are industrially produced fibers from carbonaceous raw materials which are converted to graphitic carbon by pyrolysis. A distinction is made between isotropic and anisotropic types: isotropic fibers have only low strength and less technical importance, anisotropic fibers show high strength and stiffness with low elongation at break. A carbon fiber has a diameter of about 5-8 microns. Usually, 1,000 to 24,000 individual fibers (filaments) are combined into a bundle (roving), which is endlessly wound on spools. This is i.a. a possible starting material for the production of the paper structure.

Als Faserlänge wird gemäß der vorliegenden Erfindung der Abstand der beiden Enden einer Faser verstanden. Dieser wird abhängig vom Kräuselungszustand als Länge der gekräuselten oder als Länge der entkräuselten Faser angegeben, wobei Carbonfasern aufgrund ihrer Steifheit im Wesentlichen gestreckt vorliegen. Unter anderem um das Messen der Faserlänge zu vereinfachen, wird im allgemeinen mit einer Klasseneinteilung in Längenklassen gearbeitet, wobei die einzelnen Längenklassen einen bestimmten Längenbereich darstellen. Die Weite eines solchen Bereichs ist die Klassenbreite. Das arithmetische Mittel der beiden, die jeweilige Klasse begrenzenden Klassengrenzen, ist die Klassenmitte. Die wichtigste Aufgabe einer Bestimmung der Faserlängen besteht darin, die Faserlängenverteilung festzustellen, d. h. mit welcher relativen Häufigkeit die Fasern in jeder Längenklasse vertreten sind. Diese Klassenhäufigkeit oder kurz Häufigkeit gibt an, in welchem Verhältnis im zu untersuchenden Fasergut, das die Grundgesamtheit darstellt, die zu einer Klasse gehörenden Fasern hinsichtlich eines bestimmten Merkmals zu den Fasern dieser Grundgesamtheit stehen.The fiber length is understood according to the present invention, the distance between the two ends of a fiber. This is given as the length of the crimped or crimped fiber length depending on the crimping state, with carbon fibers being substantially stretched due to their stiffness. Among other things, in order to simplify the measurement of the fiber length, it is generally worked with a classification into length classes, wherein the individual length classes represent a certain length range. The width of such an area is the class width. The arithmetic mean of the two class boundaries limiting the respective class is the class center. The most important task of determining the fiber lengths is to determine the fiber length distribution, i. H. at what relative frequency the fibers are represented in each length class. This class frequency, or frequency for short, indicates in which ratio in the fibrous material to be examined, which represents the population, the fibers belonging to a class belong to the fibers of this population with regard to a particular feature.

Faseranzahlhäufigkeit (Häufigkeit nach der Faseranzahl): Die Grundlage bildet die Faseranzahl. Das Verhältnis der Anzahl der Fasern einer Längenklasse zur Gesamtanzahl der Fasern ist die Faseranzahlhäufigkeit dieser Klasse (Häufigkeit nach der Faseranzahl); sie wird auch unbetonte Häufigkeit genannt. Die Faseranzahlhäufigkeit ist die tatsächliche Verteilung der Faserlängen im Fasergut unabhängig vom Faserquerschnitt, von der Faserdichte und den Wechselbeziehungen zwischen Faserlänge, -querschnitt und -gewicht.Frequency of fibers (frequency according to the number of fibers): The basis is the number of fibers. The ratio of the number of fibers of a length class to Total number of fibers is the fiber number frequency of this class (frequency by number of fibers); it is also called unstressed frequency. The number of fiber counts is the actual distribution of fiber lengths in the fiber, regardless of fiber cross-section, fiber density, and the interrelationships between fiber length, cross-section, and weight.

Faserlängenhäufigkeit (Häufigkeit nach der Faserlänge). Die Grundlage bildet die Faserlänge. Das Verhältnis der gesamten Länge der Fasern einer Längenklasse zur Gesamtlänge aller Fasern ist die Faserlängenhäufigkeit dieser Klasse (Häufigkeit nach der Faserlänge). Längenmäßig machen die Fasern einer Längenklasse um so mehr aus, je zahlreicher und je länger sie sind. Die Faserlängenhäufigkeit wird deshalb auch längenbetonte Häufigkeit genannt.Fiber length frequency (frequency after the fiber length). The basis is the fiber length. The ratio of the total length of the fibers of a length class to the total length of all fibers is the fiber length frequency of this class (frequency after the fiber length). Lengthwise, the fibers of a length class make the more, the more and the longer they are. The fiber length frequency is therefore also called length-emphasized frequency.

Gemäß einer besonders bevorzugten Ausführungsform des erfindungsgemäßen Papiergefüges aus Carbonfasern liegt die mittlere Faserlänge der Carbonfasern im Papiergefüge über alle Klassen zwischen 2 mm und 10 mm, vorzugsweise zwischen 4,5 mm und 6 mm.According to a particularly preferred embodiment of the paper structure of carbon fibers according to the invention, the mean fiber length of the carbon fibers in the paper structure over all classes is between 2 mm and 10 mm, preferably between 4.5 mm and 6 mm.

Darüber hinaus und insbesondere sind die Faserstoffklassen wenigstens in einen Langfaseranteil und einen Kurzfaseranteil untergliedert. Dabei haben die Carbonfasern des Langfaseranteils beispielsweise eine Länge zwischen 25 mm und 10 mm, vorzugsweise zwischen 5 mm und 2 mm und sind insbesondere größer als 6 mm. Die Carbonfasern des Kurzfaseranteils haben beispielsweise entsprechend eine Länge zwischen 10 mm und 0,1 mm, vorzugsweise zwischen 2 mm und 0,5 mm und sind insbesondere kleiner als 6 mm. Selbstverständlich liegt es auch im Sinn der vorliegenden Erfindung, dass der für die Herstellung des Papiergefüges verwendete Carbonfaserstoff in mehr als zwei Klassen untergliedert ist. Insbesondere kann hierbei neben dem Langfaseranteil (LF) und dem Kurzfaseranteil (KF) auch ein Faseranteil mit einer mittleren Faserlänge (MF) oder auch Feinstoff (FS) als eigene Klasse berücksichtigt werden.In addition, and in particular, the fiber classes are subdivided into at least one long fiber fraction and one short fiber fraction. The carbon fibers of the long fiber portion, for example, have a length between 25 mm and 10 mm, preferably between 5 mm and 2 mm and are in particular greater than 6 mm. The carbon fibers of the short fiber fraction, for example, correspondingly have a length between 10 mm and 0.1 mm, preferably between 2 mm and 0.5 mm and are in particular smaller than 6 mm. Of course, it is also within the meaning of the present invention that the carbon fiber used for the production of the paper structure is subdivided into more than two classes. In particular, in addition to the long fiber content (LF) and the short fiber content (KF), a fiber content with an average fiber length (MF) or also fines (FS) can be taken into account as a separate class.

Erfindungswesentlich ist, dass der Faserstoff in wenigstens zwei Klassen -d.h. zwei unterschiedlichen Längen - vorliegt und nicht wie im Stand der Technik bekannt im Wesentlichen eine einheitliche Faserlänge aufweist. Hierdurch kann sichergestellt werden, dass beim Papierherstellungsprozess, insbesondere bei der initialen Entwässerung eine gleichmäßige Faserverteilung erzielt wird und ein homogenes Vlies bereitgestellt werden kann.It is essential to the invention that the fibrous material is present in at least two classes, ie two different lengths, and does not have substantially a uniform fiber length as known in the prior art. This can ensure that during the papermaking process, especially at the initial Dewatering a uniform fiber distribution is achieved and a homogeneous fleece can be provided.

Gemäß einer weiteren, besonders bevorzugten Ausführungsform des erfindungsgemäßen Papiergefüges aus Carbonfasern sind die Carbonfasern primäre und/oder wiederaufbereitete Carbonfasern. Dabei liegt der Vorteil der wiederaufbereiteten Carbonfasern nicht nur im Preis, sondern auch in der Schließung des Materialkreislaufes durch die Rückführung bereits gebrauchter Carbonfasern in den Produktionsprozess. Aufbereitungsverfahren für solche Carbonfasern, wie zum Beispiel die Pyrolysetechnik sind bekannt. Diese Carbonfasern werden vorzugsweise durch Schneiden und/oder Mahlen gekürzt und auf die gewünschte Faserlänge bzw. Faserlängenverteilung eingestellt, wobei dies beispielsweise durch nasses Schneiden (zum Beispiel in einer Suspension oder durch Anfeuchten der Fasern) auf die wenigstens zwei unterschiedlichen Längen erfolgen kann.According to a further, particularly preferred embodiment of the paper structure of carbon fibers according to the invention, the carbon fibers are primary and / or recycled carbon fibers. The advantage of the recycled carbon fibers lies not only in the price, but also in the closure of the material cycle through the return of already used carbon fibers in the production process. Processing methods for such carbon fibers, such as the pyrolysis technique are known. These carbon fibers are preferably cut by cutting and / or grinding and adjusted to the desired fiber length or fiber length distribution, this can be done for example by wet cutting (for example in a suspension or by moistening the fibers) to the at least two different lengths.

Eine mögliches Verfahren zum Kürzen der Fasern ist ein Kreislaufverfahren, bei welchem zum Beispiel die Fasern in eine Bütte eines Holländers zeitlich versetzt in Wasser zugegeben werden, so dass die ursprünglich gleichlangen Faserstoffe unterschiedlich oft im Holländer gekürzt werden und so eine Faserstoffsuspension erzeugt wird, welche aus einer Vielzahl ungleich langer Fasern besteht. Entsprechend kann dies auch im Kreislaufverfahren mit modernen Mahl- und Schneidaggregaten erfolgen, wobei die Faserstoffsuspension hierbei über ein Rohrsystem mit Bütte und einem Refiner im Kreislauf geführt wird. Auch hier kann beispielsweise die Zugabe des Ausgangsfaserstoffes in den Kreislauf über eine bestimmte vorgegebene Zeit erfolgen, so dass die Fasern unterschiedlich oft dem Schneidprozess zugeführt werden. Vorzugsweise ist hierzu die Zugabezeit des Faserstoffes größer als die Umlaufzeit der Suspension im Mahlsystem.A possible method for shortening the fibers is a cyclic process in which, for example, the fibers are added to a Dutchman's bin with a time lag in water, so that the originally equal fibrous materials are shortened in Dutch several times to produce a pulp suspension consisting of a plurality of unequal length fibers. Accordingly, this can also be done in the circulation process with modern grinding and cutting units, wherein the pulp suspension is guided here via a pipe system with Bütte and a refiner in the circuit. Again, for example, the addition of the starting pulp in the circulation over a certain predetermined time, so that the fibers are fed to the cutting process different times. For this purpose, the addition time of the pulp is preferably greater than the circulation time of the suspension in the milling system.

Insbesondere bei der Verwendung von endlosen oder sehr langen Carbonfasern kann es gemäß einer weiteren, besonders bevorzugten Ausführungsform sinnvoll sein, dass die Crabonfasern in einem vorgelagerten Prozessschritt vorbereitet und insbesondere vorgekürzt werden, so dass insbesondere eine Zugabe dieser Fasern in ein wässriges System, wie vorstehend beschrieben möglich ist.In particular, in the use of endless or very long carbon fibers, it may be useful according to a further, particularly preferred embodiment that the crabon fibers are prepared in an upstream process step and in particular prec shortened, so that in particular an addition of these fibers in an aqueous system, as described above is possible.

Alternativ zu dem vorstehend beschriebenen Verfahren können die Carbonfasern in wenigstens zwei getrennten Verfahren geschnitten, insbesondere auch nur einmalig gekürzt und anschließend in einem vorgegebenen Mengenverhältnis gemischt werden. Hierbei kann insbesondere sichergestellt werden, dass die Faserstoffe gezielt bzgl. der jeweiligen Faserlänge eingestellt und somit auch sehr enge Faserlängenbereiche erzielt werden können. Das Schneiden der Carbonfasern erfolgt vorzugsweise mittels einem Mahlaggregat, das aus einer Gruppe ausgewählt wird, welche Papierholländer, Papillonrefiner, Flachkegelrefiner, Steilkegelrefiner, Scheibenmühlen, Entstipper, Kombinationen hiervon und dergleichen aufweist. Solche Mahlaggregate sind im Stand der Technik bekannt.As an alternative to the method described above, the carbon fibers can be cut in at least two separate methods, in particular also shortened only once and then mixed in a predetermined ratio. In this case, it can be ensured, in particular, that the fibrous materials can be adjusted specifically with respect to the respective fiber length and thus also very narrow fiber length ranges can be achieved. The cutting of the carbon fibers is preferably carried out by means of a grinding aggregate selected from a group comprising paper holland, papillon refiner, flat cone refiner, steep cone refiner, disc mill, deflaker, combinations thereof, and the like. Such grinding units are known in the art.

Ausgehend hiervon ist es ein Vorteil der vorliegenden Erfindung, dass durch die Mahlung bzw. das Schneiden der Faserstoffe - vorzugsweise mit einem der vorgenannten Mahlaggregate - durch die in den Aggregaten auf die Faser einwirkende Scherkräfte eine vorteilhafte Faserdispergierung erzielt wird. So werden durch die Scherkräfte die feinen Faserbündel der Rovings getrennt und liegen anschließend als Einzelfaser vor, so dass bei der Papierherstellung und initialen Entwässerung des Papiergefüges ein gleichmäßige Verteilung der Faserstoffe erzielt werden kann.Proceeding from this, it is an advantage of the present invention that an advantageous fiber dispersion is achieved by the grinding or cutting of the fibrous materials - preferably with one of the aforementioned grinding units - by the shearing forces acting on the fibers in the aggregates. Thus, the shear forces separate the fine fiber bundles of the rovings and are then present as a single fiber so that a uniform distribution of the fibers can be achieved during papermaking and initial dewatering of the paper structure.

Entsprechend einer weiteren bevorzugten Ausführungsform erfolgt das Schneiden der Carbonfasern in einer wässrigen Suspension, deren Stoffdichte zwischen 35 % und 0,1 %, vorzugsweise zwischen 25 % und 1 % und insbesondere bei ca. 5 % liegt.According to a further preferred embodiment, the cutting of the carbon fibers takes place in an aqueous suspension whose consistency is between 35% and 0.1%, preferably between 25% and 1% and in particular about 5%.

Gemäß einer weiteren, besonders bevorzugten Ausführungsform des erfindungsgemäßen Papiergefüges aus Carbonfasern liegt der Anteil im Papiergefüge der längeren Carbonfasern, insbesondere der Langfasern, zwischen 10 Gewichts-% und 75 Gewichts-%, vorzugsweise 25 Gewichts-% und 50 Gewichts-% und der Anteil der kürzeren Carbonfasern, insbesondere der Kurzfasern, zwischen 90 Gewichts-% und 25 Gewichts-%, vorzugsweise zwischen 75 Gewichts-% und 50 Gewichts-%. Der ggf. bestehende Rest des Faserstoffes ist Feinstoff, der eine Faserlänge von kleiner 0,5 mm bzw. 0,1 mm aufweist. Es liegt aber auch im Sinn der vorliegenden Erfindung, dass die Fasern trocken geschnitten und anschließend für die Herstellung des Papiergefüges in Wasser suspendiert werden.According to a further, particularly preferred embodiment of the paper structure of carbon fibers according to the invention, the proportion in the paper structure of the longer carbon fibers, in particular the long fibers, between 10% by weight and 75% by weight, preferably 25% by weight and 50% by weight and the proportion of shorter carbon fibers, especially short fibers, between 90% and 25% by weight, preferably between 75% and 50% by weight. The possibly existing remainder of the pulp is fines which have a fiber length of less than 0.5 mm or 0.1 mm. However, it is also within the meaning of the present invention that the fibers are cut dry and then suspended in water for the production of the paper structure.

Gemäß einer weiteren, besonders bevorzugten Ausführungsform des erfindungsgemäßen Papiergefüges aus Carbonfasern weisen die Carbonfasern eine kationische oder anionische Ladung auf, welche vorzugsweise durch eine Beschichtung auf die Carbonfasern aufgebracht wird. Vorteilhaft hierbei ist, dass solche modifizierten Fasern einen bestimmbaren Ladungscharakter besitzen und somit auch das Verhalten der Fasern in einer wässrigen Suspension insbesondere bei der Blattbildung durch Absstoßungs- bzw. Anziehungskräfte beeinflussbar ist. Besonders vorteilhaft lässt sich hierdurch auch die Formation, d.h. die Massenverteilung der Fasern in einem entsprechenden Faservlies beeinflussen.According to a further, particularly preferred embodiment of the paper structure of carbon fibers according to the invention, the carbon fibers have a cationic or anionic charge, which is preferably applied to the carbon fibers by a coating. The advantage here is that such modified fibers have a determinable charge character and thus the behavior of the fibers in an aqueous suspension in particular in the sheet formation can be influenced by Abstoßungs- or attraction forces. In this way, the formation, i. E. affect the mass distribution of the fibers in a corresponding nonwoven fabric.

Neben den oben bezeichneten Carbonfasern, kann das erfindungsgemäße Papiergefüge weitere Faserstoffe wie beispielsweise Cellulosefasern, Papierfasern, Altpapierfasern, Holzstofffasern, Kombinationen hiervon und dergleichen aufweisen. Solche Faserstoffe haben vorzugsweise einen Anteil am Gesamtgewicht des Papiergefüges zwischen 25 Gewichts-% und 0,5 Gewichts-%, bevorzugt zwischen 15 Gewichts-% und 1 Gewichts-% und insbesondere zwischen 10 Gewichts-% und 1,5 Gewichts-%. Selbstverständlich liegt es aber auch im Sinn der vorliegenden Erfindung, dass das Papiergefüge aus 100% Carbonfasern hergestellt wird.In addition to the carbon fibers referred to above, the paper structure of the present invention may include other fibrous materials such as cellulosic fibers, paper fibers, recycled paper fibers, wood pulp fibers, combinations thereof, and the like. Such fibers preferably have a proportion of the total weight of the paper structure between 25% by weight and 0.5% by weight, preferably between 15% by weight and 1% by weight and in particular between 10% by weight and 1.5% by weight. Of course, it is also within the meaning of the present invention that the paper structure is made of 100% carbon fibers.

Darüber hinaus und besonders bevorzugt weist das erfindungsgemäße Papiergefüge neben den Carbonfasern Verstärkungsfasern, insbesondere Bindefasern zum Beispiel aus Polyethylen auf. Diese haben vorzugsweise einen Anteil am Papiergefüge zwischen 25 Gewichts-% und 0,1 Gewichts-%, bevorzugt zwischen 20 Gewichts-% und 1 Gewichts-% und insbesondere zwischen 10 Gewichts-% und 1,5 Gewichts-% und weisen ferner vorzugsweise eine Faserläge auf, welche zwischen 0,1 mm und 10 mm, bevorzugt zwischen 0,5 mm und 7 mm und insbesondere zwischen 1 mm und 5 mm liegt. Solche Faserstoffe sind im Stand der Technik bekannt, und werden zum Beispiel von den Schwarzwälder Textil-Werken angeboten. Diese synthetischen Faserstoffe sind beispielsweise aus HD-Polyethylen hergestellt und weisen neben einer spezifischen Faserlänge insbesondere einen sehr genau spezifizierbaren Schmelzpunkt auf. Dabei ist zu berücksichtigen, dass bei der Herstellung des Papiergefüges das Vlies in einer Trockenpartie einer Papiermaschine getrocknet wird und durch den spezifischen Schmelzpunkt die entsprechenden Fasern in der Trockenpartie oder -gruppe angeschmolzen oder vollständig geschmolzen werden und somit einen weiteren Festigkeitsbeitrag für die Verarbeitbarkeit des Carbonfaservlieses bieten können, da nach dem Abkühlen des Vlieses die wiedererhärteten Kunststofffasern eine mechanische Verbindung zwischen den Carbonfasern bereit stellen. Der typische Schmelzpunkt solcher Fasern liegt in einem Bereich zwischen 90 °C und 180 °C, insbesondere zwischen 110 °C und 145 °C und vorzugsweise in einem Bereich zwischen 130 °C und 135 °C. Neben diesen Bindefasern können gemäß einer weiteren, besonders bevorzugten Ausführungsform der vorliegenden Erfindung auch Fasern, Granulat oder Partikel von weiteren oder alternativen thermoplastischen Kunststoffen eingesetzt werden, wie sie beispielsweise als Acrylnitril-Butadien-Styrol (ABS), Polyamide (PA), Polylactat (PLA), Polymethylmethacrylat (PMMA), Polycarbonat (PC), Polyethylenterephthalat (PET), Polyethylen (PE), Polypropylen (PP), Polystyrol (PS), Polyetheretherketon (PEEK), Zelluloid und Polyvinylchlorid (PVC) bekannt sind. Auch deren Schmelzpunkt sollte vorzugsweise in einem Bereich zwischen 90 °C und 180 °C, insbesondere zwischen 110 °C und 145 °C und vorzugsweise in einem Bereich zwischen 130 °C und 135 °C liegen.In addition, and particularly preferably, the paper structure according to the invention comprises, in addition to the carbon fibers, reinforcing fibers, in particular binding fibers, for example of polyethylene. These preferably have a proportion of the paper structure between 25% by weight and 0.1% by weight, preferably between 20% by weight and 1% by weight and in particular between 10% by weight and 1.5% by weight and further preferably have one Faserläge, which is between 0.1 mm and 10 mm, preferably between 0.5 mm and 7 mm and in particular between 1 mm and 5 mm. Such fibers are known in the art, and are offered for example by the Black Forest textile factories. These synthetic fibers are made, for example, of HD polyethylene and, in addition to a specific fiber length, in particular have a very precisely specifiable melting point. It should be noted that in the production of the paper structure, the nonwoven is dried in a dryer section of a paper machine and melted by the specific melting point, the corresponding fibers in the dryer section or group or completely melted and thus a further strength contribution to the Can provide processability of the carbon fiber nonwoven, since after cooling of the nonwoven, the re-cured plastic fibers provide a mechanical connection between the carbon fibers ready. The typical melting point of such fibers is in a range between 90 ° C and 180 ° C, in particular between 110 ° C and 145 ° C and preferably in a range between 130 ° C and 135 ° C. In addition to these binder fibers, according to a further, particularly preferred embodiment of the present invention, fibers, granules or particles of further or alternative thermoplastics can be used, such as acrylonitrile-butadiene-styrene (ABS), polyamides (PA), polylactate (PLA ), Polymethyl methacrylate (PMMA), polycarbonate (PC), polyethylene terephthalate (PET), polyethylene (PE), polypropylene (PP), polystyrene (PS), polyetheretherketone (PEEK), celluloid and polyvinylchloride (PVC). Its melting point should also preferably be in a range between 90 ° C and 180 ° C, in particular between 110 ° C and 145 ° C and preferably in a range between 130 ° C and 135 ° C.

Selbstverständlich liegt es aber auch im Sinn der vorliegenden Erfindung, dass das Papiergefüge ohne Verstärkungsfasern, insbesondere Bindefasern und/oder thermoplastischen Kunststoffen hergestellt wird.Of course, it is also within the meaning of the present invention that the paper structure is produced without reinforcing fibers, in particular binding fibers and / or thermoplastics.

Dem Papiergefüge können neben den zuvor genannten Stoffen auch weitere Additive wie beispielsweise mineralische Additive, insbesondere Füllstoffe und Pigmente wie Calciumcarbonat, Kaolin, Talkum, Spezialmineralien, Dispergiermittel wie Polyphospate, Polyacrylate und/oder chemische Additive wie beispielsweise Retentionsmittel, Entwässerungsbeschleuniger, Aluminiumverbindungen, Polyaluminiumchloride, Polyacylamide, Polyethylenimine, Polyvinylamine, Polyamidoamine, Polydiallyldimethylammoniumchlorid, Mikropartikelsysteme, Netzwerkretentionsmittel, natürliche und/oder modifizierte Stärke, Fixiermittel, Leimungsmittel, Trockenverfestiger, Nassfestmittel wie Melaminharz-Nassfestmittel, Epichlorhydrin-Harze, Glyoxal-Harze, Entschäumer, optische Aufheller, Farbstoffe, Biozide und Kombinationen hiervon, zugegeben werden.The paper structure, in addition to the aforementioned substances, other additives such as mineral additives, in particular fillers and pigments such as calcium carbonate, kaolin, talc, special minerals, dispersants such as polyphosphates, polyacrylates and / or chemical additives such as retention aids, drainage accelerators, aluminum compounds, polyaluminum chlorides, polyacylamides , Polyethyleneimines, polyvinylamines, polyamidoamines, polydiallyldimethylammonium chloride, microparticle systems, network retention agents, natural and / or modified starch, fixatives, sizing agents, dry strength agents, wet strength agents such as melamine wet strength agents, epichlorohydrin resins, glyoxal resins, defoamers, optical brighteners, dyes, biocides, and combinations of this, to be admitted.

Neben dem zuvor beschriebenen Papiergefüge umfasst die vorliegende Erfindung auch ein Verfahren zur Herstellung eines Papiergefüges aus Carbonfasern und Wasser mit den Schritten:

  • Bereitstellen und/oder Erzeugung wenigstens zweier Klassen von Carbonfasern mit unterschiedlichen Faserlängen, wobei die mittlere Faserlänge der Carbonfasern über alle Klassen im Papiergefüge zwischen 5 mm und 15 mm liegt;
  • Einbringen und/oder Suspendieren der Carbonfasern in Wasser, wobei der Mengen- und/oder Gewichtsanteil der einzelnen Faserstoffklassen im Papiergefüge zwischen 1 % und 99 %, vorzugsweise zwischen 5 % und 95% liegt;
  • Einstellen einer Stoffdichte zwischen 1 % bis 0,01 % und Herstellung eines Papierblatts auf einer Entwässerungsvorrichtung.
In addition to the paper structure described above, the present invention also includes a method for producing a paper structure of carbon fibers and water, comprising the steps of:
  • Providing and / or producing at least two classes of carbon fibers having different fiber lengths, the average fiber length of the carbon fibers being between 5 mm and 15 mm across all classes in the paper structure;
  • Introducing and / or suspending the carbon fibers in water, wherein the amount and / or weight content of the individual fiber classes in the paper structure is between 1% and 99%, preferably between 5% and 95%;
  • Adjust a stock consistency between 1% to 0.01% and make a paper sheet on a dewatering apparatus.

Gemäß einer weiteren bevorzugten Ausführungsform des erfindungsgemäßen Verfahrens umfasst dieses die Erzeugung wenigstens zweier Klassen von Carbonfasern mit unterschiedlichen Faserlängen in vorzugsweise einer wässrigen Suspension der Carbonfasern. Dabei kann dies vorzugsweise in einem Kreislaufsystem mit Rückführung und einem Mahl- und/oder Schneidaggregat erfolgen, wobei die Zugabe von Ausgangscarbonfasern (relativ lange Fasern) in das Wasser innerhalb einer vorgegebenen Zeitspanne erfolgt, so dass die zugegebenen Fasern unterschiedlich häufig dem Schneidprozess zugeführt werden. Wie zuvor bereits ausgeführt erhält man mittels dieser Methode eine relativ gut einstellbare Faserlängenverteilung. Gemäß einer weiteren, besonders bevorzugten Ausführungsform erfolgt die Zugabe der Ausgangscarbonfasern in einer Zeitspanne, welche größer ist als die Zirkulationszeit der Carbonfasern im Kreislaufsystem. Somit wird sicher gestellt, dass zumindest Teile der Carbonfasern mehrfach dem Schneidprozess zugeführt werden.According to a further preferred embodiment of the method according to the invention, this comprises the production of at least two classes of carbon fibers with different fiber lengths in preferably an aqueous suspension of the carbon fibers. This may preferably be done in a circulatory system with recirculation and a grinding and / or cutting unit, wherein the addition of starting carbon fibers (relatively long fibers) takes place in the water within a predetermined period of time, so that the added fibers are fed to the cutting process at different rates. As already stated above, this method provides a relatively easily adjustable fiber length distribution. According to a further, particularly preferred embodiment, the addition of the starting carbon fibers takes place in a time period which is greater than the circulation time of the carbon fibers in the circulatory system. This ensures that at least parts of the carbon fibers are fed several times to the cutting process.

Alternativ hierzu können die in Wasser eingebrachten Carbonfasern in wenigstens zwei unterschiedlichen Mahlaggregaten und/oder wenigstens zwei unterschiedlichen Verfahrensschritten zur Erzeugung wenigstens eines Langfaseranteils und eines Kurzfaseranteils geschnitten und anschließend zur Herstellung des Papierblattes in einem vorgegebenen Mengenverhältnis gemischt werden. Hiermit können verschiedene Carbonfasern bereit gestellt werden, die sich in ihrer Faserlängenverteilung unterscheiden und genau auf den Bedarf des zu erzeugenden Papiergefüges zusammengestellt werden. Ziel ist es hierbei neben den relativ langen Fasern auch relativ kurze Fasern zur Herstellung des Faservlieses bereit zu stellen. Nur so kann sichergestellt werden, dass ein Papiergefüge auf der Papiermaschine herstellbar ist, welches die Mindestanforderungen insbesondere an die gleichmäßige Massenverteilung erfüllt.Alternatively, the carbon fibers introduced into water may be cut in at least two different milling units and / or at least two different process steps to produce at least one long fiber portion and one short fiber portion and then blended in a predetermined proportion to produce the paper sheet. Hereby, various carbon fibers can be provided, which differ in their fiber length distribution and are assembled exactly to the needs of the paper structure to be produced. The goal here is next to the relatively long Fibers also provide relatively short fibers for the production of the nonwoven fabric. Only in this way can it be ensured that a paper structure can be produced on the paper machine which fulfills the minimum requirements, in particular with regard to the uniform mass distribution.

Die Herstellung des Papiergefüges kann gemäß der vorliegenden Erfindung auf einer Entwässerungsvorrichtung erfolgen, welche aus einer Gruppe von Maschinen ausgewählt wird, welche Langsiebmaschinen, Hybridformer, Rundsiebmaschinen, Schrägsiebmaschinen, Gapformer und Handschöpfvorrichtungen umfasst.Fabrication of the paper structure may be accomplished in accordance with the present invention on a dewatering apparatus selected from a group of machines including longitudinal wire machines, hybrid formers, sorters, skewers, gap formers, and hand-draw devices.

Für die Herstellung des Papiergefüges können erfindungsgemäß neben den Carbonfasern weitere Faserstoffe wie beispielsweise Cellulosefasern, Papierfasern, Altpapierfasern, Holzstofffasern, Kombinationen hiervon und dergleichen verwendet werden, wobei diese vorzugsweise mit einem Anteil zwischen 25 Gewichts-% und 0,5 Gewichts-%, bevorzugt zwischen 15 Gewichts-% und 1 Gewichts-% und insbesondere zwischen 10 Gewichts-% und 1,5 Gewichts-% dem Papiergefüge zugegeben werden können.According to the invention, besides the carbon fibers, other fibrous materials such as cellulosic fibers, paper fibers, waste paper fibers, wood pulp fibers, combinations thereof and the like can be used for the production of the paper structure, preferably in a proportion of between 25% and 0.5% by weight, preferably between 15% by weight and 1% by weight and especially between 10% by weight and 1.5% by weight can be added to the paper structure.

Das Schneiden der Carbonfasern erfolgt gemäß einer weiteren besonders bevorzugten Ausführungsform des erfindungsgemäßen Verfahrens in einer wässrigen Suspension, deren Stoffdichte zwischen 35 % und 0,1 %, vorzugsweise zwischen 25 % und 1 % und insbesondere bei ca. 3 % liegt. Darüber hinaus können dem Papiergefüge Additive wie beispielsweise mineralische Additive, insbesondere Füllstoffe und Pigmente wie Calciumcarbonat, Kaolin, Talkum, Spezialmineralien, Dispergiermittel wie Polyphospate, Polyacrylate und/oder chemische Additive wie beispielsweise Retentionsmittel, Entwässerungsbeschleuniger, Aluminiumverbindungen, Polyaluminiumchloride, Polyacylamide, Polyethylenimine, Polyvinylamine, Polyamidoamine, Polydiallyldimethylammoniumchlorid, Mikropartikelsysteme, Netzwerkretentionsmittel, natürliche und/oder modifizierte Stärke, Fixiermittel, Leimungsmittel, Trockenverfestiger, Nassfestmittel wie Melaminharz-Nassfestmittel, Epichlorhydrin-Harze, Glyoxal-Harze, Entschäumer, optische Aufheller, Farbstoffe, Biozide und Kombinationen hiervon, zugegeben werden.The cutting of the carbon fibers is carried out according to a further particularly preferred embodiment of the method according to the invention in an aqueous suspension whose consistency is between 35% and 0.1%, preferably between 25% and 1% and in particular about 3%. In addition, the paper structure additives such as mineral additives, in particular fillers and pigments such as calcium carbonate, kaolin, talc, special minerals, dispersants such as polyphosphates, polyacrylates and / or chemical additives such as retention aids, dehydration accelerators, aluminum compounds, polyaluminum chlorides, polyacylamides, polyethyleneimines, polyvinylamines, Polyamidoamines, polydiallyldimethylammonium chloride, microparticle systems, network retention agents, natural and / or modified starches, fixatives, sizing agents, dry strength agents, wet strength agents such as melamine resin wet strength agents, epichlorohydrin resins, glyoxal resins, defoamers, optical brighteners, dyes, biocides, and combinations thereof.

Für die Mahlung und/oder das Schneiden der Carbonfasern wird gemäß der vorliegenden Erfindung eine Vorrichtung wie beispielsweise ein Papierholländer, Papillonrefiner, Flachkegelrefiner, Steilkegelrefiner, Scheibenmühlen, Entstipper verwendet, wobei die Steuerung der Vorrichtung insbesondere durch die Mahlgeräte-Belastungskurve erfolgt, welche beispielsweise eine Sinuskurve ist.For the grinding and / or cutting of the carbon fibers, according to the present invention, a device such as a paper hollander, Papillonrefiner, Flachkegelrefiner, steep cone refiner, disc mills, Entstipper used, the control of the device is carried out in particular by the Mahlgeräte-load curve, which is for example a sinusoid.

Die vorliegende Erfindung umfasst darüber hinaus auch das zuvor beschriebene Verfahren zur Herstellung eines Papiergefüges aus Carbonfasern mit wenigstens zwei Klassen bildenden Faserstoffen, die unterschiedliche Längen aus Carbonfasern aufweisen, wobei der Mengen- und/oder Gewichtsanteil der einzelnen Faserstoffklassen im Papiergefüge zwischen 1 % und 99 %, vorzugsweise zwischen 5 % und 95% liegt, und die mittlere Faserlänge der Carbonfasern über alle Klassen im Papiergefüge zwischen 1 mm und 20 mm liegt.The present invention also encompasses the method described above for producing a paper structure from carbon fibers with at least two classes of fibrous materials which have different lengths of carbon fibers, wherein the quantity and / or weight fraction of the individual fiber classes in the paper structure is between 1% and 99%. , preferably between 5% and 95%, and the average fiber length of the carbon fibers over all classes in the paper structure is between 1 mm and 20 mm.

Schließlich umfasst die Erfindung auch die Verwendung eines Papiergefüge aus Carbonfasern wie es zuvor beschrieben wurde zur Herstellung von Faserverbundwerkstoffen, insbesondere Faser-Kunststoff-Verbunden, keramischen Faserverbundwerkstoffen, Kombinationen hiervon und dergleichen.Finally, the invention also encompasses the use of a paper structure of carbon fibers as described above for the production of fiber composite materials, in particular fiber-plastic composites, ceramic fiber composite materials, combinations thereof and the like.

Nachfolgend wird die Erfindung anhand verschiedener Ausführungsbeispiele beschrieben, wobei darauf hingewiesen wird, dass die Erfindung nicht auf die hier dargestellten Ausführungen beschränkt, sondern vielmehr auch entsprechende Abwandlungen im Sinne der vorliegenden Erfindung möglich sind. Weitere Merkmale der Erfindung ergeben sich aus der nachfolgenden detaillierten Beschreibung der Zeichnungen in Verbindung mit den Ansprüchen.The invention will be described with reference to various embodiments, it being understood that the invention is not limited to the embodiments shown here, but rather corresponding modifications in the context of the present invention are possible. Further features of the invention will become apparent from the following detailed description of the drawings in conjunction with the claims.

Es zeigen:

  • Figuren 1a bis 1d Durchlichtaufnahmen verschiedener Faserstoffproben von Carbonfasersuspensionen zur Herstellung eines Papiergefüges;
  • Figuren 2a und 2b Prinzipskizzen zum Schneiden der Carbonfasern.
Show it:
  • FIGS. 1a to 1d Transmitted light images of various fiber samples of carbon fiber suspensions for the production of a paper structure;
  • FIGS. 2a and 2b Schematic diagrams for cutting the carbon fibers.

Figur 1 a zeigt eine Durchlichtaufnahme eines Faserstoffes, der in einem Versuchsholländer (Volumen 15l) mit einer Menge von 400 g über einen Eintragszeitraum von 60 Sekunden eingebracht und in Summe über einen Zeitraum von 180 Sekunden gemahlen wurde. Dabei ergibt sich eine relativ gleichmäßige Faserlängenverteilung zwischen 0,2 mm und 6 mm. Bestimmt wurde die Faserlängenverteilung in drei Faserlängenklassen. Dabei liegt der Langfaseranteil bei ca. 20 %, der Anteil an mittellangen Fasern bei ca. 34 % und Kurzfasern bei ca. 46 %. Die Klassen umfassen dabei für Langfasern, Faserstoffe mit einer Länge zwischen 7 mm und 12 mm, mittellangen Fasern, Faserstoffe mit einer Länge zwischen 3 mm und 7 mm und Kurzfasern, Faserstoffe mit einer Länge zwischen 0,5 mm und 3 mm. FIG. 1 a shows a transmitted light image of a pulp which was placed in a test Dutchman (volume 15 l) with a quantity of 400 g over a picking period of 60 seconds and ground in total over a period of 180 seconds. This results in a relatively uniform fiber length distribution between 0.2 mm and 6 mm. The fiber length distribution was determined in three fiber length classes. This is the long fiber content at about 20%, the proportion of medium-length fibers at about 34% and short fibers at about 46%. The classes include for long fibers, pulps with a length between 7 mm and 12 mm, medium-long fibers, pulps with a length between 3 mm and 7 mm and short fibers, pulps with a length between 0.5 mm and 3 mm.

Figur 1 b zeigt eine Durchlichtaufnahme eines Faserstoffes, der in dem selben zuvor verwendeten Versuchsholländer mit einer Menge von 50 g über einen Eintragszeitraum von 10 Sekunden eingebracht und in Summe über einen Zeitraum von 120 Sekunden gemahlen wurde. Durch den geringeren Eintrag erhöht sich auch die spezifische Belastung der Fasern im Mahlaggregat, so dass auch der Anteil an Kurzfasern steigt. Dabei liegt der Langfaseranteil bei ca. 16 %, der Anteil an mittellangen Fasern bei ca. 29 % und Kurzfasern bei ca. 55 %. Figure 1 b Figure 12 shows a transmitted light shot of a furnish introduced in the same previously used experimental Dutchman at 50 grams for a 10 second picking period and ground in total over a period of 120 seconds. The lower entry also increases the specific load of the fibers in the grinding unit, so that the proportion of short fibers also increases. The long fiber content is about 16%, the proportion of medium-length fibers about 29% and short fibers about 55%.

Figur 1 c zeigt eine Durchlichtaufnahme eines Faserstoffes, der in dem selben zuvor verwendeten Versuchsholländer mit einer Menge von 50 g über einen Eintragszeitraum von 10 Sekunden eingebracht und in Summe über einen Zeitraum von 90 Sekunden gemahlen wurde. Durch die kurze Bearbeitungszeit bleiben überwiegend lange Fasern zurück, die bei der Verarbeitung zu einem Papiergefüge deutliche Schwierigkeiten bereiten. Es kommt hierbei zu starken Verspinnungen zwischen den Fasern. Dabei liegt der Langfaseranteil bei ca. 17,5 %, der Anteil an mittellangen Fasern bei ca. 37,5 % und Kurzfasern bei ca. 45 %. Figure 1 c shows a transmitted light image of a pulp which was placed in the same previously used experimental Dutchman at a rate of 50 g over a 10 second picking period and ground in total over a period of 90 seconds. Due to the short processing time, predominantly long fibers remain, which cause considerable difficulties during processing into a paper structure. This leads to strong spinning between the fibers. The long fiber content is about 17.5%, the proportion of medium-length fibers is about 37.5% and short fibers about 45%.

Figur 1d zeigt eine Durchlichtaufnahme eines Faserstoffes, der in dem selben zuvor verwendeten Versuchsholländer mit einer Menge von 50 g über einen Eintragszeitraum von 10 Sekunden eingebracht und in Summe über einen Zeitraum von 180 Sekunden gemahlen wurde. Nach einer Mahlung von 180 Sekunden sind praktisch keine Langfasern mehr vorhanden. Dabei liegt der Langfaseranteil bei ca. 5,5 %, der Anteil an mittellangen Fasern bei ca. 33 % und Kurzfasern bei ca. 61 %. Figure 1d shows a transmitted light shot of a pulp which was placed in the same previously used experimental Dutchman at a rate of 50 g for a 10 second picking period and ground in total over a period of 180 seconds. After grinding for 180 seconds, there are practically no longer any long fibers. The long fiber content is about 5.5%, the proportion of medium-length fibers about 33% and short fibers about 61%.

Die Figuren 2a und 2b zeigen zwei unterschiedliche Verfahren zur Aufbereitung des Faserstoffes.The FIGS. 2a and 2b show two different processes for the preparation of the pulp.

Hierbei zeigt Figur 2a einen Holländer zur Mahlung des Faserstoffs in einer Bütte. Über die Zugabe 5 wird über den vorgegeben Zeitraum (welcher vorzugsweise größer ist als die Umtriebszeit der Suspension in der Bütte) der Faserstoff in die mit Wasser gefüllte Bütte 2 zugegeben und über das Mahlwerk des Holländers 4 gemahlen. Nach Abschluss der Mahlzeit wird das Mahlwerk gestoppt, der Faserstoff entnommen und zur Vliesherstellung überführt.This shows FIG. 2a a Dutchman for grinding the pulp in a chest. About the addition of 5 over the predetermined period (which is preferably greater than the Umtriebszeit the suspension in the chest) of the pulp in the with Water-filled tub 2 was added and ground over the grinder of Dutchman 4. After completing the meal, the grinder is stopped, the pulp removed and transferred to the nonwoven production.

Figur 2b zeigt eine alternative Ausführung hierzu, bei welcher der Faserstoff einer Bütte 10 über die Zuleitung 14 zugegeben wird und mittels der Pumpe 12 dem Mahlaggregat zum Beispiel einem Kegelrefiner zugeführt wird. Sobald die Mahlung abgeschlossen ist, wird der Faserstoff über die Bütte und das Entnahmeventil 16 aus der Bütte dem Vliesherstellungsprozess zugeführt. Hierbei können selbstverständlich auch hintereinander verschiedene Faserstoffe mit unterschiedlichen Faserlängen erzeugt werden und für die Vliesherstellung nach der Mahlung bzw. dem Schneiden zusammengeführt werden. FIG. 2b shows an alternative embodiment for this purpose, in which the pulp is a Bütte 10 is added via the supply line 14 and is supplied by means of the pump 12 to the grinding unit, for example, a cone refiner. Once the grinding is completed, the pulp is fed via the chest and the take-off valve 16 from the chest to the nonwoven manufacturing process. Of course, it is also possible for different fibrous materials with different fiber lengths to be produced one behind the other and combined for the nonwoven production after the grinding or the cutting.

Claims (16)

  1. A paper structure made of carbon fibers comprising fiber materials that form at least two classes and include different lengths of carbon fibers, characterized in that
    a first class includes a proportion of long fibers whose length is greater than 6mm, and a second class includes a proportion of short fibers whose length is smaller than 6mm, and the proportion by quantity and/or weight of the individual fiber material classes in the paper structure is between 1% and 99%, preferably between 5% and 95%, and
    the mean fiber length of the carbon fibers across all classes in the paper structure is between 1mm and 20mm.
  2. The paper structure made of carbon fibers according to claim 1, characterized in that
    the mean fiber length of the carbon fibers in the paper structure across all classes is between 2mm and 10mm, preferably between 4.5mm and 6mm.
  3. The paper structure made of carbon fibers according to claim 1 or 2, characterized in that
    the fiber material classes include at least one proportion of long fibers whose fiber materials are between 25mm and 10mm in length and one proportion of short fibers whose fiber materials are between 10mm and 0.1mm in length.
  4. The paper structure made of carbon fibers according to any of the preceding claims, characterized in that
    the carbon fibers are primary and/or recycled carbon fibers and are shortened to the at least two different lengths particularly by cutting and/or refining, preferably by wet cutting.
  5. The paper structure made of carbon fibers according to any of the preceding claims, characterized in that
    the proportion in the paper structure of the longer carbon fibers, particularly of the long fibers, is between 10% and 75% by weight, preferably between 25% and 50% by weight, and the proportion of the shortercarbon fibers, particularly of the short fibers, is between 90% and 25% by weight, preferably between 75% and 50% by weight, and the rest, if any, is fines having a fiber length of less than 0.5mm or 0.1mm, respectively.
  6. The paper structure made of carbon fibers according to any of the preceding claims, characterized in that
    the carbon fibers are cut in an aqueous suspension whose stock consistency is between 35% and 0.1%, preferably between 25% and 1%, and particularly about 5%.
  7. The paper structure made of carbon fibers according to any of the preceding claims, characterized in that
    the carbon fibers have a cationic or anionic charge which is preferably applied by coating onto the carbon fibers.
  8. The paper structure made of carbon fibers according to any of the preceding claims, characterized in that
    besides the carbon fibers, there are included other fiber materials such as, for example, cellulose fibers, paper fibers, recycled-paper fibers, wood pulp fibers, combinations thereof and the like, which are preferably added to the paperstructure in a proportion of between 25% and 0.5% by weight, preferably between 15% and 1% by weight, and particularly between 10% and 1.5% by weight, and/or
    besides the carbon fibers, there are provided reinforcing fibers, particularly binding polyethylene fibers, which are preferably added to the paper structure in a proportion of between 25% and 0.1% by weight, preferably between 20% and 1% by weight, and particularly between 10% and 1.5% and which furthermore preferably have a fiber length between 0.1mm and 10mm, preferably between 0.5mm and 7mm, and particularly between 1mm and 5mm.
  9. The paper structure made of carbon fibers according to any of the preceding claims, characterized in that
    added to the paperstructure are additives such as, for example, mineral additives, particularly fillers and pigments such as calcium carbonate, kaolin, talcum, special minerals, dispersants such as polyphosphates, polyacrylates and/or chemical additives such as, for example, retention agents, dewatering aids, aluminium compounds, polyaluminium chlorides, polyacrylamides, polyethylenimines, polyvinylamines, polyamidoamines, polydiallyl dimethyl ammonium chloride, microparticle systems, network retention agents, natural and/or modified starch, fixing agents, sizing agents, dry-strength agents, wet-strength agents such as melamine resin wet-strength agents, epichlorohydrin resins, glyoxal resins, defoamers, optical brighteners, dyes, biocides and combinations thereof.
  10. A method of manufacturing a paper structure made of carbon fibers and water, the method comprising the steps of:
    - providing and/or producing at least two classes of carbon fibers having different fiber lengths, the mean fiber length of the carbon fibers across all classes in the paper structure being between 1mm and 15mm;
    - introducing and/or suspending the carbon fibers in water, the proportion by quantity and/or weight of the individual fiber material classes in the paper structure being between 1% and 99%, preferably between 5% and 95%, and
    - setting a stock consistency between 5% and 0.01% and manufacturing a paper sheet in a dewatering device.
  11. The method of manufacturing a paper structure made of carbon fibers according to claim 10, characterized in that
    the at least two classes of carbon fibers having different fiber lengths are produced in an aqueous suspension of the carbon fibers, preferably in a circulation system including recirculation and a refining and/or cutting unit, and the original carbon fibers are added to the water within a predetermined period of time, so that the added fibers are supplied to the cutting process at different frequencies and/or the carbon fibers introduced into water are cut in at least two different refining units and/or two different process steps for producing at least one proportion of long fibers and one proportion of short fibers, and are mixed at a predetermined quantity ratio for manufacturing the paper sheet.
  12. The method of manufacturing a paper structure made of carbon fibers according to either of claims 10 and 11, characterized in that
    besides the carbon fibers, there are other fiber materials used for manufacturing the paper structure, such as, for example, cellulose fibers, paper fibers, recycled-paper fibers, wood pulp fibers, combinations thereof and the like, and are preferably added to the paper structure in a proportion of between 25% and 0.5% by weight, preferably between 15% and 1% by weight, and particularly between 10% and 1.5% by weight.
  13. The method of manufacturing a paper structure made of carbon fibers according to any of claims 10 to 12, characterized in that
    the carbon fibers are cut in an aqueous suspension whose stock consistency is between 35% and 0.1%, preferably between 25% and 1%, and particularly about 3%.
  14. The method of manufacturing a paper structure made of carbon fibers according to any of claims 10 to 13, characterized in that
    the carbon fibers are refined and/or cut using a device such as, for example, a Hollander paper beater, Papillon refiner, flat conical refiner, steep-angle conical refiner, disk grinders or deflakers, the device being controlled, in particular, by the refiner load curve, which is, for example, a sinusoidal curve.
  15. The method according to any of claims 10 to 14 for manufacturing a paper structure made of carbon fibers according to any of claims 1 to 9.
  16. The use of a paper structure made of carbon fibers according to any of claims 1 to 9 for manufacturing fiber composite materials, particularly fiber-plastic composites, ceramic fiber composite materials, combinations thereof and the like.
EP14180963.2A 2013-09-06 2014-08-14 Paper structure and its prouction from carbon fibers in a wet process Active EP2848734B1 (en)

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