WO2013011133A1 - Ultrathin carbon fibers - Google Patents

Abstract

The invention relates to a carbon fiber which comprises at least one monofilament. At least one of the at least one filament has a filament diameter of 4 µm or less, said diameter being determined in accordance with DIN EN ISO 1973. The invention additionally relates to a method for producing such a carbon fiber, to the use thereof, and to a carbon precursor fiber.

Description

 Ultrathin carbon fibers

The present invention relates to an endless ultra-thin carbon fiber, a method for producing such an ultra-thin carbon fiber, the use of such a carbon fiber and a corresponding carbon precursor fiber.

Ultrathin fibers, also called microfibers, are used in many technological applications. These include, for example, applications in medical technology both for implants and for medical devices, in filter technology for filtering ultrafine dusts or in textile technology for producing textiles.

In textile technology, microfibers are used in a variety of applications. Examples include the use of polymer microfibers for functional textiles in the clothing industry and for industrial applications in filter technology, where such textiles are used because of their high specific reactive surface area.

For example, microfibers made of glass or carbon or carbon are used for the production of fiber composite components for lightweight structural components that have to provide supporting functions with low weight. In particular, carbon fibers are of great importance for the production of highly stable, eg highly rigid fiber composite lightweight components, which will increase in the future. For example, composite components made from carbon-fiber-reinforced plastic (CFRP) are now used in aircraft construction, in automotive engineering and in the manufacture of rotor blades for wind power plants.

For example, it is known from the prior art to produce microfibers with a fineness of 1 dtex or less by means of electrospinning. However, the result of electrospinning has the disadvantage that it is difficult to control and less productive and is therefore mainly used for special products, especially in the field of filter technology for ultrafine dusts.

In addition, the known from the prior art carbon fibers in terms of their properties are in need of improvement. In particular, there is a need for carbon fibers having better mechanical properties than the known carbon fibers and, in particular, improved fiber matrix adhesion in a composite, i. with improved bonding of the stability providing carbon fibers to the matrix system of the composite.

It is therefore the object of the present invention to provide a carbon fiber with excellent mechanical properties and with excellent fiber-matrix adhesion, which is suitable for these reasons, in particular for the production of highly rigid and lightweight components made of fiber composites. Another object of the present invention is to provide a method by which such a carbon fiber can be easily and inexpensively manufactured.

According to the invention this object is achieved by a carbon fiber, which comprises at least one monofilament, wherein at least one of the at least one filament according to DIN EN ISO 1973 certain filament diameter of 4 μπι or less.

This solution is based on the surprising finding that carbon fibers of such thin monofilaments have extremely few defects and are therefore characterized by extremely high mechanical properties, in particular an excellent tensile strength and a high modulus of elasticity. For this reason, the carbon fibers according to the invention have better mechanical properties and in particular a higher tensile strength and a higher modulus of elasticity than carbon fibers with a larger filament diameter made of the same material by the same process. A further advantage of the carbon fibers according to the invention is their excellent fiber-matrix adhesion, so that the carbon fibers according to the invention can be processed into fiber composites having a particularly high rigidity and with exceptionally good other mechanical properties. A further finding of the present invention is that, surprisingly, it is even possible at all to produce carbon fibers having a filament diameter of 4 μm or less by means of an extrusion method, without the individual monofilaments of the fiber adhering or tearing off one another immediately after their formation.

In the context of the present invention, a carbon fiber is understood to mean any carbon-containing and preferably carbon-containing, thin and flexible structure which contains at least one monofilament. The term carbon fiber is therefore understood to mean all individual fibers as well as all carbon fiber bundles or carbon fiber rovings.

According to the invention, at least one of the at least one filament of the carbon fiber, which comprises at least one monofilament, has a filament diameter of 4 μm or less determined according to DIN EN ISO 1973. If the carbon fiber has two or more filaments, such as 6,000 filaments, therefore, at least one of these 6,000 filaments has a filament diameter of 4 μπι or less.

With regard to particularly good mechanical properties and excellent fiber-matrix adhesion, it is proposed in a further development of the inventive concept that at least 50%, preferably at least 80%, more preferably at least 90%, particularly preferably at least 95%, more preferably at least 99%, and most preferably all filaments of the carbon fiber have a filament diameter of 4 μm determined according to DIN EN ISO 1973 or less.

Particularly good results are obtained, in particular, if at least one of the filaments and preferably all of the filaments of the carbon fiber has a filament diameter of at most 3.5 μm determined according to DIN EN ISO 1973, preferably of not more than 3.25 μm, more preferably of not more than three , 0 μπι, particularly preferably of at most 2.75 μπι, more preferably of at most 2.5 μπι, most preferably of at most 2.25 μπι and most preferably of at most 2.0 μπι.

Furthermore, it is preferred that at least one of the carbon fiber forming filaments and preferably all of the carbon fiber forming filaments have a filament diameter of at least 1 μπι. For example, the individual filaments of the carbon fiber can have a filament diameter of from 3.5 to 1.0 μm, preferably from 3.25 to 1.25 μm, more preferably from 3.0 to 1.5 μm, and very particularly preferably from 2, Have 75 to 2.0 μπι.

According to a particularly preferred embodiment of the present invention, the carbon fiber is obtainable by carbonizing a precursor fiber of a polyacrylonitrile homopolymer, a polyacrylonitrile copolymer or a mixture thereof. In the context of the present invention, it has been found that carbon fibers formed in particular of polyacrylonitrile and having a filament diameter of 4 μm or less are distinguished by particularly good mechanical properties and excellent fiber-matrix adhesion for matrix materials commonly used in fiber composites.

In this case, the preparation of the polyacrylonitrile can be carried out by a solution polymerization, in which the monomer, ie acrylonitrile, is dissolved in a solvent, or by a dispersion polymerization, in which the monomer is emulsified in water. To the solution or emulsion may be added one or two comonomers, such as itaconic or methacrylic acid, as well as initiators or redox systems to control the polymerization reaction, on the one hand to facilitate the spinning process and, on the other hand, those required for later thermal stabilization of the polymeric fibers in air To lower the temperature.

With regard to a particularly good fiber-matrix adhesion and particularly good mechanical properties, it has also proved to be advantageous that the carbon fiber is obtainable by carbonizing a precursor fiber of a polyacrylonitrile copolymer which i) has an acrylonitrile content of more as 90 wt .-% and preferably between 94 and 99 wt .-% and ii) has a content of itaconic or methacrylic acid of not more than 10 wt .-% and preferably between 6 and 1 wt .-%. Alternatively to or instead of itaconic or methacrylic acid can be used as comonomer methyl acrylate and / or vinyl acetate.

The polyacrylonitrile polymer may contain about 2,000 to 10,000 acrylonitrile units per polyacrylonitrile molecule. This results in a weight average molecular weight of the polymer between 50,000 and 250,000 g / mol and preferably between 100,000 and 160,000 g / mol.

According to a further particularly preferred embodiment of the present invention, at least one of and preferably all of the monofilaments of the carbon fiber has a tensile strength of 3 GPa or more, preferably 3.5 GPa or more, particularly preferably determined according to DIN EN 1007 part 4 of 5.5 GPa or more, and most preferably from 5.5 to 10.0 GPa.

An advantageous development of the invention provides that at least one of and preferably all of the monofilaments of the carbon fiber have an E modulus of 150 GPa or more determined according to DIN EN 1007 Part 4, preferably of 200 GPa or more, more preferably of 250 GPa or more, and most preferably of 300 GPa or more.

Furthermore, it is provided according to a further advantageous embodiment of the present invention that at least one and preferably all of the monofilaments of the carbon fiber measured according to DIN EN 1007 Part 4 maximum tensile strain of 1, 0% or more, preferably 1, 2 % or more and more preferably of 1.3% or more.

According to a particularly advantageous embodiment of the invention, the monofilaments of the carbon fiber according to the invention have the following properties:

 Diameter: 1, 5 to 3.5 μπι,

 Tensile strength: 3.5 to 5.5 GPa,

 Modulus of elasticity: 250 to 350 GPa and

 Maximum tensile strain: 1, 2- 1, 7%.

In a further development of the inventive concept, it is proposed that at least one of and preferably all of the monofilaments of the carbon fiber viewed in the cross-section have a length dimension L and a width dimension B, wherein the ratio of length to width (L / B) is less than 2 and 1 and preferably between less than 1, 5 and 1. As a result, not only excellent mechanical properties are obtained, but in particular also the fiber-matrix connection of the carbon fiber is advantageously influenced.

Preferably, the carbon fiber has 1,000 to 100,000 monofilaments, more preferably 6,000 to 90,000 monofilaments, and most preferably 12,000 to 64,000 monofilaments. For example, the carbon fiber may have 1,000, 3,000, 6,000, 12,000, 24,000 or 50,000 individual monofilaments. Another object of the present invention is a carbon precursor fiber comprising at least one monofilament, wherein at least one of the at least one filament according to DIN EN ISO 1973 certain filament diameter of 12 μπι or less.

From such a carbon precursor fiber can be easily, quickly and inexpensively at the time of the present invention produce non-producible carbon fibers from at least one monofilament with a diameter of 4 μπι or less, which has excellent fiber-matrix adhesion and excellent mechanical Properties and are therefore a completely new generation of carbon fibers with a variety of new application areas.

With regard to particularly good mechanical properties and excellent fiber-matrix adhesion, it is proposed in a development of the invention that at least 50%, preferably at least 80%, more preferably at least 90%, particularly preferably at least 95%, most preferably at least 99% and most preferably all filaments have a determined according to DIN EN ISO 1973 filament diameter of 12 μπι or less.

Particularly good results are obtained, in particular, if at least one of the filaments and preferably all of the filaments of the carbon precursor fiber has a filament diameter of 10 .mu.m or less, preferably 8 .mu.m or less, particularly preferably 6 .mu.m, determined in accordance with DIN EN ISO 1973 or less and most preferably of 5 μπι or less.

Preferably, the carbon precursor fiber of the present invention contains a polyacrylonitrile homopolymer, a polyacrylonitrile copolymer, or a mixture thereof. Particularly preferably, the carbon Precursor fiber of a polyacrylonitrile homopolymer, a polyacrylonitrile copolymer or a mixture thereof.

With regard to a particularly good fiber-matrix adhesion and particularly good mechanical properties, it has also proved to be advantageous that the carbon precursor fiber consists of a polyacrylonitrile copolymer which i) has an acrylonitrile content of more than 90% by weight. % and preferably between 94 and 99 wt .-% and ii) has a content of itaconic or methacrylic acid of not more than 10 wt .-% and preferably between 6 and 1 wt .-%. Alternatively to or instead of itaconic or methacrylic acid can be used as comonomer methyl acrylate and / or vinyl acetate.

In this case, the polyacrylonitrile polymer may contain about 2,000 to 10,000 acrylonitrile units per polyacrylonitrile molecule. This results in a weight average molecular weight of the polymer between 50,000 and 250,000 g / mol and preferably between 100,000 and 160,000 g / mol.

According to a further advantageous embodiment of the present invention, at least one of and preferably all of the monofilaments of the carbon fiber has a tensile strength of 50 cN / tex or more, preferably 65 cN / tex or more, and particularly preferably determined according to DIN EN ISO 5079 of 70 cN / tex or more.

Further, at least one of and preferably all of the monofilaments of the carbon fiber preferably has an E modulus of 1,100 cN / tex or more, preferably 1,200 cN / tex or more, particularly preferably 1,300 cN /, determined according to DIN EN ISO 5079. tex or more, and most preferably 1,500 cN / tex or more.

In addition, a further preferred development of the carbon precursor fiber according to the invention provides that at least one of, and preferably all of the monofilaments of the carbon fiber, one according to DIN EN ISO 5079 has a maximum tensile elongation at break of 10% or more and more preferably 12% or more.

From the carbon precursor fibers according to the invention, ultrathin carbon fibers with a diameter of the individual monofilaments of 4 μm or less, whose mechanical properties lie in the so-called high modulus range (so-called HM fibers), can be produced on the basis of their abovementioned advantageous mechanical properties which, for example, highly rigid and, due to the better fiber-matrix adhesion compared to the use of standard carbon fibers, more filigree structural components made of carbon fiber reinforced carbon (CFRC) can be produced than is possible with standard carbon fibers.

In a further development of the inventive concept, it is proposed that the monofilaments of the carbon precursor fiber have a length dimension L and a width dimension B viewed in their cross section, the ratio of the length to the width (L / B) preferably being between less than 2 and 1 and preferably between less than 1, 5 and 1.

A further subject of the present patent application is a continuous process for the preparation of a carbon fiber described above, which comprises the following steps:

a. Providing a spinning solution which contains i) a polyacrylonitrile homopolymer, a polyacrylonitrile copolymer or a mixture thereof and ii) at least one solvent,

b. Providing a spinneret which has at least one nozzle hole with a diameter of 35 μπι or less,

c. continuously extruding the spinning solution through the at least one nozzle hole of the spinneret into a precipitation bath to obtain a carbon precursor fiber and

d. Carbonizing the in step c. obtained carbon precursor fiber at a temperature of up to 1,500 ° C. In this case, the at least one nozzle hole of the spinneret forms a spinning channel, at the beginning of which the spinning solution is pressed in during extrusion and at the end of which the fiber formed emerges from the nozzle hole. The spin channel may have a varying over the length of the spin channel cross-sectional area. The term diameter of the nozzle hole is understood in the context of this invention, the diameter of the cross-sectional area of the nozzle hole at the end of the spinning channel.

To produce the at least one nozzle hole with the diameter of 35 μm or less, for example, the so-called laser spiral drilling method can be used in which a laser beam is directed onto a workpiece to be machined to produce the nozzle hole on a predetermined trajectory. In this case, the laser beam can have a wavelength in the visible or ultraviolet range and be pulsed, wherein the pulse duration can be, for example, between 1 ps and 100 ps. In order to carry out the material removal during helical drilling in a controlled manner, the pulse energy for this purpose can preferably be set to a value in the range from 1 μJ to 50 μJ, whereby the repetition rate of successive pulses of the laser beam can be set to a value in the range from 10 to 100 kHz.

According to a particularly preferred embodiment of the present invention, the diameter of the at least one nozzle hole of the spinneret used in the method according to the invention 30 μπι or less, preferably 25 μπι or less and more preferably 20 μπι or less. This makes it possible to produce particularly thin carbon precursor fibers and particularly thin carbon fibers. Experiments by the inventors have shown that surprisingly very small spinnerets can be used for the production of an extremely thin fiber in the wet spinning process, and without sticking or tearing off of the fiber in the precipitation bath or during subsequent process steps. Thus, for example, by a spinneret with nozzle holes with a diameter of 30 μπι be spun by the novel process, an endless carbon precursor fiber whose monofilaments have a diameter of 5.2 μπι. Such a carbon precursor fiber can be further processed into a carbon fiber whose individual monofilaments have a diameter of 3.07 μm.

Preferably, the fiber after step c. led out of the precipitation bath and subsequently washed, dried and stretched. The fiber formed in the extrusion is preferably left in the precipitation bath until a substantial part of the solvent contained in the fiber has diffused out of the fiber into the precipitation bath and the polymer has accumulated in the filament in such a way that the fiber solidifies sufficiently Has.

Preferably, the fiber is drawn in a first drawing step, the so-called wet drawing, wherein the wet drawing is carried out before and / or during and / or after the washing in the wet state of the fiber. In a further stretching step, the so-called dry drawing, which is carried out during and / or after the drying of the fiber, the fiber is then further drawn.

Surprisingly, an endless carbon precursor fiber can be produced in which the individual monofilaments have a diameter of at most 12 μm, preferably of not more than 10 μm, more preferably of not more than 8 μm, very particularly preferably of not more than 6 μm and most preferably of not more than 5 μm μπι, and has the excellent strength values for further processing to carbon fiber, when the fiber compared to the state that it has when leading out of the precipitation bath, when wet drawn in total by a factor between 4 and 8, preferably by a factor between 4 and 6, more preferably stretched by a factor of between 4.5 and 5.5, and in dry drawing versus the state that the fiber is after Wet stretching has a total of a factor of 1, 5 or more, preferably by a factor of 1, 7 or more, more preferably by a factor between 1, 7-2.2 further stretched.

Standard carbon precursor fibers, i. Precursor fibers with a filament diameter of 10 μm or more are usually stretched by more than a factor of 6 in the case of wet drawing and no more than by a factor of 1.2 in the case of dry drawing, since otherwise fiber breakage can occur. For the inventors, it is a surprising finding that by reducing the draw factor in wet drawing while increasing the draw factor in dry drawing over the prior art methods, a fiber having a very small filament diameter with high strength values can be produced without This leads to fiber breakage despite the fact that the fiber produced by the extrusion through the "very fine spinneret" is already very thin before the stretching process.

Applicant's experiments have shown that particularly good results for the carbon precursor fiber as well as the ultra-thin carbon fiber made therefrom can be achieved when the ratio of the stretch ratio of dry drawing to wet drawing is 0.25 or more, preferably 0.3 or more , more preferably between 0.35 and 0.45.

The drawing is preferably carried out at a temperature above the glass transition temperature of the polymer, wherein the dry drawing and / or the wet drawing are preferably carried out in each case in several stages.

Preferably, the polymer content in the spinning solution is between 5 and 30% by weight and the solvent content between 70 and 95% by weight. The preparation of the polyacrylonitrile homo- and / or copolymer used can be carried out, for example, by a solution polymerization in which the monomer, ie acrylonitrile, is dissolved in a solvent, or by a dispersion polymerization in which the monomer is emulsified in water. To the solution or emulsion may be added one or two comonomers, such as itaconic or methacrylic acid, as well as initiators or redox systems to control the polymerization reaction, on the one hand to facilitate the spinning process and, on the other hand, those required for later thermal stabilization of the polymeric fibers in air To lower the temperature.

Preferably, a poly-acrylonitrile copolymer is used whose acrylonitrile content, for example, more than 90 wt .-% and preferably between 94 and 99 wt .-% amount. The polymer may contain up to 6% by weight and preferably about 2% by weight itaconic or methacrylic acid. Other copolymers which may be included in the polymer are methyl acrylate and vinyl acetate. Preferably, in step a. a polyacrylonitrile copolymer is used, which has an acrylonitrile content between 94 and 99 wt .-% and a content of itaconic or methacrylic acid between 6 and 1 wt .-%.

The polyacrylonitrile polymer may contain about 2,000 to 10,000 acrylonitrile units per polyacrylonitrile molecule. This results in a weight average molecular weight of the polymer between 50,000 and 250,000 g / mol and preferably between 100,000 and 160,000 g / mol.

Preferably, in step c. obtained carbon precursor fiber before carbonization according to the step d. stabilized.

Good results are obtained in the step d. Carbonization obtained in particular, if this is carried out at a temperature between 800 ° C and 1500 ° C. Optionally, in step d. formed carbon fiber are then graphitized, preferably at a temperature of about 1500 ° C and more preferably at a temperature of about 2,000 ° C.

In particular for producing a fiber containing a plurality of individual monofilaments, as is the case, for example, with a carbon precursor fiber, it is preferred that the spinnerette be from 1,000 to 100,000, more preferably from 6,000 to 90,000, and most preferably from 12,000 to 64,000 nozzle holes with a diameter of 35 μπι or less, and thus by the inventive method, an endless fiber is prepared which has from 1,000 to 100,000, more preferably 6,000 to 90,000 and most preferably 12,000 to 64,000 monofilaments.

In the aforementioned spinneret with the plurality of nozzle holes with a diameter of 35 μπι or less measured from hole center to hole center distance between two adjacent nozzle holes preferably between 20 and 200 μπι, more preferably between 30 and 100 μπι and most preferably between 40 and 100 μπι. An arrangement of so many nozzle holes on the smallest surface is made possible, for example, by manufacturing technology, by using the initially described helical drilling method in which only a locally concentrated on the location of the material removal load of the material of the workpiece takes place during drilling.

In the spinneret used for the method according to the invention, the at least one nozzle hole preferably forms a spin channel with a maximum length of 500 μm and preferably of a maximum of 300 μm. In this case, the spinning channel may be at least substantially cylindrical, conical, biconical or funnel-shaped over at least part of its depth. In a further development of the concept of the invention, it is proposed that the spin channel is formed at least substantially conically, preferably with a conicity factor between more than 1: 1 and 1: 3 and more preferably between more than 1: 1 and 1: 2.

Since the density of the nozzle holes per unit area is very large and the individual nozzle holes with a diameter of 35 μπι or less are very small for the production of a fiber with 1,000 or 12,000 or more individual monofilaments, these tend very easily to clogging. To ensure a smooth production, it is therefore important that the spinnerets can be easily cleaned, which is only possible with very aggressive cleaning agents. In order to protect the spinnerets from corrosion during cleaning, a preferred embodiment of the invention provides that the spinneret is formed from a metallic material, preferably from a metal alloy, particularly preferably from a metal alloy containing one or more noble metals. For example, alloys containing platinum or gold or iridium or several of the abovementioned noble metals are conceivable.

Finally, the present invention relates to the use of a previously described carbon fiber in a textile fabric, in a prepreg or in a fiber composite component.

The textile fabric may be, for example, a fabric, a scrim, a knit, a knit or a mixture thereof.

The invention will be further elucidated with reference to the following non-limiting examples. Show it

1 shows an SEM image of a nozzle hole of a spinneret for

Carrying out the method according to the invention, FIG. 2 shows an illustration of a single method step of a preferred embodiment of the method according to the invention,

FIG. 3 shows a SEM image of a carbon fiber according to the invention

Precursor fiber,

FIG. 4 shows an SEM cross-sectional view of that shown in FIG

 Carbon precursor fiber and

FIG. 5 shows an SEM image of a carbon fiber according to the invention.

1 shows a SEM image of a nozzle hole of a spinneret for carrying out the method according to the invention. The spinneret shown in FIG. 1 has 3,000 nozzle holes, of which one nozzle hole can be seen in the present case. The nozzle hole has a diameter of 30 μηι. With the spinneret shown, a carbon precursor fiber shown in FIG. 3 was produced with the wet spinning process according to the invention described in more detail in FIG. The carbon precursor fiber shown in FIGS. 3 and 4 was subsequently processed further into a carbon fiber as shown in FIG.

In the embodiment of the process according to the invention shown in FIG. 2, a spinning solution 1 containing polyacrylonitrile and N, N-dimethylformamide solvent is continuously extruded through a spinneret 2 into a precipitation bath 3 containing a mixture of DMF and water, whereby a fiber 4 is formed.

The spinneret 2 has 3,000 nozzle openings, each with a diameter of 30 μπι. The obtained fiber 4 thus consists of 3,000 individual endless monofilaments.

Subsequently, the fiber 4 is led out of the precipitation bath 3 and subsequently washed, dried and drawn in several steps. In the presently illustrated embodiment of the method according to the invention, the fiber 4 is subjected to a washing process in a plurality of successively arranged baths 5, 6, 7 and 11, and before or between the baths 5, 6 and 7 or in the bath 11, respectively, at draw stations 8, 9, 10 and 12 wet-laid in the wet state.

In the present embodiment, the fiber 4 is thus stretched before and during the washing process in the wet state, wherein the fiber 4 is stretched in the wet drawing by a factor of 4.5 compared to the state that it has on exit from the precipitation bath 3.

In the subsequent process step, the fiber is first passed through several successively arranged, heated to 150 to 160 ° C draw stations 13 to 17. Following this, the fiber 4 is passed through a drying oven 18 and then again through a drawing station 19, before the fiber 4, which is now in the form of a carbon precursor fiber, is wound onto a bobbin by means of a winding device 20.

In the present embodiment, the fiber 4 is thus stretched before, during and after the drying process, wherein the fiber 4 is stretched in the dry drawing by a factor of 1, 9 compared to the state that it has after wet stretching.

The ratio of the degree of stretching from dry drawing to wet drawing is thus presently 0.42.

The coiled carbon precursor fiber 4 was then further processed by stabilization and carbonization to form a carbon fiber, which can be seen in FIG. The stabilization is carried out at a temperature of 220 to 280 ° C, while the carbonation, at a temperature of 1350 ° C is performed.

FIG. 3 shows the carbon precursor fiber produced by the process described in FIG. 2, in which the individual monofilaments have a diameter in the range from approximately 6.0 μm to 7.2 μm.

FIG. 4 shows an SEM cross-sectional image of the carbon precursor fiber shown in FIG. An evaluation of the cross sections reveals that the carbon precursor fiber according to the invention has a length to width ratio L / B of 1.22, i. the individual filaments have a nearly circular cross-sectional area.

FIG. 5 shows the carbon fiber produced on the basis of the carbon precursor fiber shown in FIGS. 3 and 4, in which the individual monofilaments have a diameter in the range of approximately 3.2 to 3.9 μm.

Table 1 below shows a comparative representation of the production and mechanical properties between a carbon precursor fiber or carbon fiber according to the invention and a fine carbon precursor fiber or carbon fiber known from the prior art.

Table 1 :

Filamentdurchmesser PAN-Faser [pm] 11 ,4 6,2-7,2

Filament diameter PAN fiber [pm] 11, 4 6.2-7.2

Maximum tensile strain PAN fiber [%] 13.5 1 1.9

Tensile strength PAN fiber [cN / tex] 52 70

EModule 1 PAN fiber [cN / tex] 1080 1510

Filament diameter C fiber [pm] 7.5 <4μπι

Maximum tensile strain C fiber [%] 1.7 1.3

Tensile strength C-fiber [GPa] 4, 1 5,5

Modulus of elasticity C-fiber [GPa] 240 265

Claims

Claims: 1. carbon fiber, which comprises at least one monofilament, wherein at least one of the at least one filament according to DIN EN ISO 1973 certain filament diameter of 4 μπι or less. 2. Carbon fiber according to claim 1, characterized in that at least 50%, preferably at least 80%, more preferably at least 90%, more preferably at least 95%, most preferably at least 99% and most preferably all filaments one according to DIN EN ISO 1973 certain filament diameter of 4 μπι or less. 3. Carbon fiber according to claim 1 or 2, characterized in that the at least one filament has a filament diameter determined according to DIN EN ISO 1973 of not more than 3.5 μm, preferably of not more than 3.25 μm, more preferably of not more than 3, 0 μπι, more preferably of at most 2.75 μπι, more preferably of at most 2.5 μπι, most preferably of at most 2.25 μπι and most preferably of a maximum of 2.0 μπι. 4. Carbon fiber according to one of the preceding claims, characterized in that it is obtainable by carbonizing a precursor fiber of polyacrylonitrile homopolymer, polyacrylonitrile copolymer or a mixture thereof. 5. Carbon fiber according to claim 4, characterized in that it is obtainable by carbonizing a precursor fiber of a polyacrylonitrile copolymer having an acrylonitrile content between 94 and 99 wt .-% and a content of itaconic or methacrylic acid between 6 and 1 wt .-%. 6. carbon fiber according to any one of the preceding claims, characterized Porsche Style nzeichnet that at least one of the at least one filament of the carbon fiber determined according to DIN EN 1007 Part 4 tensile strength of 3 GPa or more, preferably 3.5 GPa or more , more preferably from 5.5 GPa or more, and most preferably from 5.5 to 10.0 GPa. 7. carbon fiber according to any one of the preceding claims, characterized Porsche Style nzeichnet that at least one of the at least one filament of the carbon fiber according to DIN EN 1007 Part 4 certain modulus of elasticity of 150 GPa or more, preferably 200 GPa or more , more preferably 250 GPa or more, and most preferably 300 GPa or more. 8. Carbon fiber according to claim 1, characterized in that at least one of the at least one filament of the carbon fiber has a maximum tensile elongation of 1.0% or more, preferably of 1.2%, measured according to DIN EN 1007 Part 4 or more, and more preferably 1.3% or more. 9. carbon fiber according to any one of the preceding claims, characterized Porsche Style nzeichnet that at least one of the at least one filament of the carbon fiber considered in its cross section has a length dimension L and a width dimension B, wherein the ratio of length to width (L / B ) is between less than 2 and 1, and preferably between less than 1.5 and 1. 10. Carbon fiber according to one of the preceding claims, characterized in that it has 1,000 to 100,000 monofilaments, preferably 6,000 to 90,000 monofilaments and preferably 12,000 to 64,000 monofilaments. 1. carbon precursor fiber, which comprises at least one Monof lament, wherein at least one of the at least one filament has a determined according to DIN EN ISO 1973 filament diameter of 12 μπι or less. Carbon precursor fiber according to claim 1 1, characterized in that the at least one filament determined according to DIN EN ISO 1973 filament diameter of 10 μπι or less, preferably of 8 μπι or less, more preferably of 6 μπι or less and very particularly preferably of 5 μπι or less. A continuous process for producing a carbon fiber according to any one of claims 1 to 10, comprising the steps of:  a. Providing a spinning solution containing i) a polyacrylonitrile homopolymer, a polyacrylonitrile copolymer or a mixture thereof and ii) at least one solvent, b. Providing a spinneret which has at least one nozzle hole with a diameter of 35 μπι or less,  c. continuously extruding the spinning solution through the at least one nozzle hole of the spinneret into a precipitation bath to obtain a carbon precursor fiber and  d. Carbonizing the in step c. obtained carbon precursor fiber at a temperature of up to 1,500 ° C. Continuous method according to claim 13, characterized in that the diameter of the at least one nozzle hole of the spinneret 30 μπι or less, preferably 25 μπι or less and more preferably 20 μπι or less. 5. Use of a carbon fiber according to one of claims 1 to 10 in a textile fabric, in a prepreg or in a fiber composite component.