EP1778905B1 - Cabled carbon-fibre thread - Google Patents

Abstract

Thread having at least two strands of continuous carbon fiber that are twisted around one another, whereby the carbon fibers of the strands are arranged approximately parallel to the thread direction. The at least two strands of continuous carbon fiber are twisted around one another and produced by direct cabling. A method for the production of the thread includes twisting each of the at least two strands of continuous carbon fiber around one another by direct cabling. An eyelet assembly with an eyelet that has a radius of at least 4 mm in the area of contact between the strands and the eyelet assembly. The thread is used as a sewing thread or a thread for reinforcing polymers, elastomers, rubber or concrete.

Description

The invention relates to a yarn of at least two mutually wound strands of continuous carbon fibers, a process for the preparation and the use of such yarns.

For the increasing production and application of so-called textile preforms, for example for technical applications, such as fiber composites, filter media, u.a. suitable sewing threads necessary. These yarns are intended to fix the preform, but increasingly also structurally reinforce, even at very high temperatures, as required for example in the production of fiber ceramics or when used as filter media in chemically and / or thermally highly loaded processes.

The mechanical properties as well as the thermal and chemical resistance of carbon fibers make this material particularly suitable for sewing threads especially for the above-mentioned applications.

Due to the many and especially strong thread deflections during sewing, the sewing thread is damaged and usually does not reach its original mechanical strengths in the later composite. Especially brittle carbon fibers can be sewn only conditionally. The theoretically possible mechanical properties of the fibers are not achieved in the component after sewing.

In the past, there was a Toray Torayca T900 product on the market, which can be partially sewn. This yarn is made with 1000 filaments or two components each with 1000 filaments or three components with 1000 filaments each. The fermentation rotation of the individual components is about S222-224 t / m. When two or three components are connected together as strands, these strands are wound around each other at approximately Z162-Z164 t / m. The production of this twist is probably possible in a normal twisting process with many abrasive thread deflections only with thin and thus flexible filaments in a diameter of about 5.5 microns or less. The production of carbon fibers with a diameter of less than 6 microns, however, is very expensive, so that this type of yarn is very expensive.

Alternatively, sewing threads have been developed which have a core of carbon fibers and are additionally sheathed with another yarn (see, for example, US Pat JP-A 2133632 or JP-A 1061527 ). This sheathing can be done by various methods, for example by winding or crocheting. Since wrapping means a heavy burden on the yarn material, this z. As polyester or polyamide yarns used. However, these yarns have a low composite adhesion to the plastic matrix and reduce the fiber volume fraction of carbon fibers in a fiber composite material by the proportion of Umwindegarne. In addition, the core materials of the sewing yarns can not be placed close enough to the fabric because the bulky sheath is located therebetween.

EP-A-0 303 381 describes a yarn of two, mutually wound strands of continuous carbon fibers at about 50 t / m.

At the same time, glass twists, aramid or so-called PBO fibers are used for sewing, since they have a higher transverse strength than carbon fibers and in this way survive damage to the abrasive sewing process. However, their printing properties or their mechanical properties in combination with a matrix, such as plastic, are considerably lower than at Carbon fibers, so that a real structural reinforcement can not be achieved.

As a rule, the filaments of filament yarn fibers are parallel in the yarn after production and thus form only a small cohesion to a closed yarn structure. In particular, for sewing threads, however, it is important that they have a closed yarn bond, as only then is it ensured that a perfect seam is formed.

In order to achieve a closed yarn structure, twists are introduced into filament yarns. This usually additional manufacturing step means a first damage to the filaments, which then in the subsequent sewing process cause further filament damage to the thread breakage.

The object of the present invention is therefore to provide yarns of endless carbon fibers in which the disadvantages described above are at least reduced. In particular, the yarns should be better suited for use as sewing threads than those previously available on the market.

The object of the invention is achieved in that the yarn has at least two, mutually wound strands of endless carbon fibers, wherein the carbon fibers of the strands are arranged at least almost parallel to the yarn direction.

For the purposes of the present invention, carbon fibers are understood to mean endless carbon fibers (carbon fiber filaments). The arrangement of the carbon fiber in a single processing step, which is selected almost parallel to the yarn axis, achieves that the loss of strength as a result of the filament breaks during the two-stage twisting process caused by the mutual winding of the strands in the two-stage twisting process Production or otherwise unavoidable skew of the filaments in the yarn in a single-stage twisting method significantly lower fails.

The yarns according to the invention can be produced by producing them by direct cabling of at least two carbon fiber strands. This direct cabling has hitherto been used only for the production of tire cord (see, for example WO 02/103097 ). However, it is necessary to modify the direct cabling machines available on the market today in order to obtain the yarns according to the invention. In particular, it is necessary that the Zusammenführöse, by which the strands used to produce the yarn according to the invention are wound around each other, in the region in which a contact with the strands, a radius of at least 4 mm, preferably 4 to 40 mm, especially preferably at least 6 to 12 mm. It has also been found to be particularly advantageous that each of the thread guide elements used in a direct cabling machine has a radius of at least 4 mm, preferably 4 to 40 mm, in the region in which contact takes place with one or more of the strands or with the finished yarn , more preferably 6 to 12 mm. By adhering to this measure, the yarn of the invention can be produced with the normal knowledge required for direct cabling.

In order to allow a particularly filament-friendly processing of the carbon fibers, the surface of the Zusammenungsöse is coated with a plasma coating in the composition of 97% Al2O3 and 3% TiO2, which is subsequently polished.

In the case of direct cabling, two strands are wound around each other in one work step without giving the individual strands a turn. Due to the then almost stretched and parallel filaments very high yarn strengths are possible just with carbon fibers. In addition, the thread tensions of the two strands can be controlled by the so-called cord regulator set very precisely, so that at least almost equally long strands are interconnected. In this way, both strands absorb the same amount of the total load. Maximum utilization of both yarn components becomes possible.

Another advantage of direct cabling in the processing of a generally brittle carbon fiber is the small number of necessary thread guide elements in this process, which should, however, be adapted to the dimensions indicated above. The filaments are then significantly less damaged than in the previously known twisting.

Tests have shown that carbon fibers having a filament diameter of from 5 to 8 μm and a filament number of from 100 to 2,000, preferably from 500 to 1,000 filaments, are particularly suitable as starting material for the production of the yarns according to the invention. If a rotation number of 50 to 1000 T / m, preferably from 150 to 250 T / m is set in direct cabling, particularly useful yarns are obtained, which can be used in particular as sewing yarns. Turning numbers of 150 to 400 T / m, in particular 160 to 290 T / m have proven particularly useful here.

The direct cabling of the precursor, that is to say of the fibers which are further processed by oxidation and / or carbonization into carbon fibers, can also take place, after which the oxidation and / or carbonization takes place. It is also conceivable to withdraw all intermediate products of carbon fiber production from the process, to direct-cofacilitate and then to feed it back into the carbon fiber production at the removal point. In particular, the intermediates prior to carbonization are particularly suitable for this purpose.

The yarn according to the invention is characterized in particular by an average abrasion resistance of from 50 to 350, preferably from 175 to 300.

The abrasion resistance is measured by the following method:

To determine the yarn rub resistance, a yarn G is clamped in a yarn clamp 7 and, corresponding to the yarn course in FIG FIG. 1 passed through a sewing needle 5 and loaded on the other, free yarn end with a weight 6 of 10 g. During the scouring test moves a crosshead 1 with the sewing needle 5 cyclically and horizontally by a stroke of about 75 mm. For this purpose, the cross member 1 is mounted on a bearing 2 via a bearing 4. The stroke of about 75 mm is limited by stops 3 'and 3 ", which process about 60 strokes per minute.

Since the one yarn end is fixed in the yarn clamp, the yarn G - due to the ever-changing distance between the yarn clamp 7 and needle eye of the needle 5 - is moved through the needle eye of the needle 5 and thus undergoes a scuffing load. After a yarn is torn, the number of strokes executed until then is recorded. This measurement is performed on eight different yarn sections. At the end of the test, all eight values are averaged and rounded to an integer number. This integer number is given as a measure of the average rub resistance.

Since the yarn is often passed through the sewing needle under load and under high bending, similarly to the sewing process, the measurement of the average abrasion resistance is excellent for judging the sewing properties of the tested yarn.

wobei

S

die durchschnittliche Scheuerfestigkeit und

D

die Drehungen der Stränge pro m ist und

A

Werte zwischen 170 und -35 einnimmt.

The yarn of the invention is characterized in particular in that it satisfies the following condition: $$\mathrm{S}\mathrm{=}\mathrm{-}\mathrm{35}\mathrm{*}{\mathrm{10}}^{\mathrm{-}\mathrm{4}}<figure-callout\; id="2"\; label="\; D"\; filenames="imgf0001.png"\; state="\{\{state\}\}">\; </figure-callout>{\mathrm{D}}^{}{\mathrm{}}^{\mathrm{2}}\mathrm{+}\mathrm{2}\mathrm{D}\mathrm{-}\mathrm{A}\mathrm{.}$$

in which

S

the average rub resistance and

D

the turns of strands per m is and

A

Values between 170 and -35.

wobei

K

die durchschnittliche Knotenfestigkeit in MPa und

D

die Drehungen der Stränge pro m ist und

B

Werte zwischen 250 und 450 einnimmt.

The yarn of the invention is characterized in particular in that it satisfies the following condition: $$\mathrm{K}\mathrm{=}\mathrm{-}\mathrm{105}\mathrm{*}{\mathrm{10}}^{\mathrm{-}\mathrm{4}}<figure-callout\; id="2"\; label="\; D"\; filenames="imgf0001.png"\; state="\{\{state\}\}">\; </figure-callout>{\mathrm{D}}^{}{\mathrm{}}^{\mathrm{2}}\mathrm{+}\mathrm{590}\mathrm{-}\mathrm{B}$$

in which

K

the average knot strength in MPa and

D

the turns of strands per m is and

B

Values between 250 and 450 occupies.

The knot strength is measured according to DIN 53842, however, the yarn ends are fixed with cardboard hoppers before they are clamped in the tensile testing machine. In addition, no preload force is adjusted due to the brittleness of the material.

Furthermore, the yarn according to the invention is distinguished by the fact that the carbon fibers in the strands have a diameter of 3 to 10 μm, in particular 6 to 10 μm.

The invention will be explained in more detail with reference to the following examples.

Two carbon fiber strands, Tenax HTA 5641 67tex f1000 Z15, Applicant's yarn on the market, each having 1000 carbon fiber filaments, were cabled by direct cabling, with the strands cabled with different rotations. The cross-sectional opening of the Zusammenführöse has a curved course in the area in which yarns touch the Zusammenführöse, wherein the smallest radius of the curved course is about 15 mm. The Gamein- and - austaufbereiche the Zusammenführöse are rounded with smaller radii in the range of 1 to 3 mm. The other yarn guides in turn have a curved course in cross section, wherein the smallest radius is about 8 mm.

The abrasion resistance and knot strength exhibited by the yarns prepared in this way are shown in Table 1. <b> Table 1 </ b> yarn A B C D applied rotations [T / m] 150 200 250 300 average rub resistance 106 206 229 190 Knot strength [MPa] 234.6 441.6 467.3 405.4

It can be seen from the table that yarns B and C give the best results in terms of shear strength and knot strength. They are therefore also ideally suited as sewing threads.

In addition to the actual sewability of a yarn, especially for the three-dimensional reinforcement of fiber composite materials, the fiber-matrix connection, especially in the region of a seam, is particularly important for the mechanical material potential. In order to detect the fiber-matrix bonding without disturbing influences (such as sewing), a prepreg was prepared from yarns B and C in conjunction with a resin film, and the compressive strength was measured according to EN 2850-B2 and the apparent interlaminar shear strength according to EN 2563 ,

To carry out the test, the following steps are necessary: Firstly, a prepreg film (HexPly 6376 prepreg film from Hexcel Composite, Dagneux (US Pat. France)) with a basis weight of 72 g / m ² applied. The yarn is wound on this film with a laboratory winding machine perpendicular to the winding axis with a yarn tension of 500 cN and a winding speed of 23.1 mm / s so that a UD structure is formed. The layers are again wound with a prepreg film having a basis weight of 72 g / m ² .

This entire UD structure and the metallic core are heated in an oven under constant rotation - in 20 minutes at 80 ° C, held for 20 minutes below 80 ° C and cooled to room temperature in 60 minutes. The resulting UD body is cut open at the eight edges, resulting in 8 platy preprep materials. These prepreg materials are further processed according to the standards EN 2850-B2 and EN 2563 into multilayer laminates in an autoclave and a conventional vacuum structure and tested under standard conditions.

• ein Kohlenstofffasergarn E (Tenax HTA 5131 400tex f6000 t0, ein bei der Anmelderin erhältliches Garn),
• mit Polyesterfasern umhäkelte Kohlenstofffasern F (Mit Polyesterfasern (PES 84 dtex f12) umhäkelte Kohlenstofffasern F (Tenax HTA 5641 67tex f1000 Z15) und
• PBO - Fasern G aus poly(p-phenylene-2,6-benzobisoxazole, Handelsname PBO Fiber Zylon der Firma Toyobo, Osaka Japan

hergestellt.For comparison, further multilayer laminates were prepared in the same way, using as yarns

• a carbon fiber yarn E (Tenax HTA 5131 400tex f6000 t0, a yarn available from the Applicant),
• Carbon fibers crocheted with polyester fibers F (Carbon fibers F (Tenax HTA 5641 67tex f1000 Z15) and crocheted with polyester fibers (PES 84 dtex f12) and
• PBO - fibers G from poly (p-phenylene-2,6-benzobisoxazole, trade name PBO Fiber Zylon from Toyobo, Osaka Japan

produced.

The test results of the apparent interlaminar shear strength (ILSF) according to EN 2563 and the results of the compressive strength test according to EN 2850-B2 are shown in Table 2. <b> Table 2 </ b> yarn B C e F G Fiber volume fraction [%] 57.2 56.2 59.0 38.5 66.9 apparent interlaminar shear strength [MPa] 123.2 120.5 113.3 50.5 40.3 Compressive strength [MPa] 1,118.6 989.1 1,215.6 383.3 178.6

It will be appreciated that yarns B and C of the invention have similar high apparent interlaminar shear strength and compressive strength to conventional carbon fiber yarn E. The cabling process of the present invention does not significantly deflect the filaments of the yarn from their orientation parallel to the yarn longitudinal axis otherwise the pressure characteristics would have dropped.

In contrast, Comparative yarn F, which has a core of carbon fiber filaments and a crocheted jacket of polyester yarn, exhibits significantly poorer compressive strengths. The load-absorbing carbon fiber filaments are therefore no longer stretched along the yarn longitudinal axis and therefore fail faster at a pressure load. In addition, the polyester sheath obstructs the necessary adhesion between load-bearing carbon fiber and matrix material.

Although the second comparative yarn G is outstandingly sewn on account of its high transverse strength and its ductile material behavior, it has very low shear and compressive strengths, so that a reinforcing effect in fiber composite materials is not to be expected.

In order to demonstrate the advantage of suturing fiber composites, especially under impact loads, test specimens are produced and tested in accordance with EN 6038. Notwithstanding EN 6038, the test specimen produced has a wall thickness of 4 mm, while the test was carried out with a span of 15 mm. To this end, four layers of quasi-isotropic, four-layered multiaxial layers (NCF, 267 g / m ² fiber surface weight of the scrubland cell) are sutured. The sewing is done with the above-mentioned yarn C with a stitch length of 4 mm, a seam spacing of 3 mm and a stretched lower thread in the lockstitch (also yarn C).

The resulting textile preform with a square base area of 315 mm ² and a wall thickness of 4 mm is impregnated with RTM6 resin from Hexcel in compliance with the resin manufacturer specifications so that a pore-free fiber composite material with a fiber volume fraction of 60 ± 4% , Test specimens were sawn and tested from this plate according to the test standard EN 6038 (hereinafter referred to as "NCF sewn").

Corresponding specimens were with the aid of the above-mentioned Multiaxialgelege (four times four-ply) without suturing (hereinafter "NCF unsewn" referred to) and

of an analogously constructed prepreg laminate (16 layers each with 267 g / m ² fiber surface weight of the prepreg single layer, mirror symmetrical to the median plane of a resin film (HexPly 6376 from Hexcel Composite, Dagneux (France)) and carbon fibers (Tenax HTS 5631 800tex applicant's application number f12000 t0) (hereinafter referred to as "prepreg").

Table 3 shows the results of the test (residual compressive strength after impact according to EN 6038 in [MPa]) with the yarn according to the invention (NCF sewn) in comparison to an unvarnished multiaxial fabric (NCF unwown) and an analogously constructed laminate (prepreg). <b> Table 3 </ b> Impact energy [J] prepreg NCF unsewn Sewn NCF 0 342.9 305.2 290.6 20 208.1 209.6 265.1 30 196.9 172.8 253.6 40 160.4 139.9 267.0

It can be clearly seen that especially at higher impact energies the suturing contributes to an almost constant course of the residual compressive strength. By contrast, the conventional non-stitched comparative laminates have a high dependence of the residual compressive strength on the previously introduced impact energy. Accordingly, until now components without suturing had to be dimensioned sufficiently larger and thus heavier against this load case.

The yarn of the present invention can be used in virtually all matrices reinforced with fibers. Suitable matrix materials include polymers such as thermoplastics (eg, polyethyleneimine, polyetherketone, polyetheretherketone, polyphenylene sulfide, polyethersulfone, polyethersulfone, polysulfone), duromers (eg, epoxies), elastomers, and rubbers. The use in ceramic materials (eg silicon carbide or boron nitride) or metallic materials (eg steel (alloys), titanium) is possible due to the very good temperature resistance of carbon fibers.
Thermoplastics and thermosets are particularly suitable because the necessary fiber-matrix adhesion between these polymeric materials and the carbon fiber is particularly good.
But also the reinforcement of elastomers and rubber with the yarns according to the invention is advantageous since normally carbon fibers have a high strength but not those in these materials usual elongation properties. Due to the yarn structure of the yarns according to the invention an improved extensibility is possible and in this way an improved reinforcing effect in elastomer and rubber materials.

The direct cabling of carbon fibers can be used not only for the production of sewing threads but also, for example, for the production of yarns for concrete reinforcement. For example, if strands are selected for direct cabling, of which one strand has a higher thread tension than the other strand, then in direct cabling the one or more strands having the lower thread tension will wrap around the strand or strands with the higher thread tension. In this way, a yarn with a kind of ribbing, as they have, for example, reinforcing bars for the reinforcement of reinforced concrete. Thus, a mechanical anchoring of the yarn in the concrete is possible.

For this yarn construction, various components would be interesting: For the core, which consists of one or more elongated strands, carbon fibers are suitable with a filament count of over 6,000 filaments, preferably over 24,000 filaments. For the outer strand or the outer strands, however, offer finer yarns, which need not necessarily be made of carbon fibers. The rotation value should be in the range of very few turns per meter, preferably below 10 T / m.

Claims (19)

1. A thread comprising at least two strands of continuous carbon fiber that are twisted around one another, characterized in that the carbon fibers of the strands are arranged at least approximately parallel to the thread direction.
2. A thread according to claim 1 producible by direct cabling.
3. A thread according to claim 1 or 2, characterized in that the strands are twisted around one another at 150 to 400 turns per meter.
4. A thread according to claim 3, characterized in that the strands are twisted around one another at 160 to 290 turns per meter.
5. A thread according to claims 3 or 4, characterized in that the thread has an average abrasion resistance of 50 to 350.
6. A thread according to claim 5, characterized in that the thread has an average abrasion resistance of 175 to 300.
7. A thread according to one or more of the claims 3 to 6, characterized in that the following condition is fulfilled: $$\mathrm{S}\mathrm{=}\mathrm{-}\mathrm{35}\mathrm{*}{\mathrm{10}}^{\mathrm{-}\mathrm{4}}{\mathrm{D}}^{\mathrm{2}}\mathrm{+}\mathrm{2}\mathrm{D}\mathrm{-}\mathrm{A}\mathrm{,}$$

   

   whereby

   S is the average abrasion resistance and

   D is the strand turns per meter and

   A ranges between 170 and -35
8. A thread according to one or more of the claims 3 to 7, characterized in that the following condition is fulfilled: $$\mathrm{K}\mathrm{=}\mathrm{-}\mathrm{105}\mathrm{*}{\mathrm{10}}^{\mathrm{-}\mathrm{4}}{\mathrm{D}}^{\mathrm{2}}\mathrm{+}\mathrm{590}\mathrm{-}\mathrm{B}$$

   

   
   whereby

   K is the average knot strength in MPa and

   D is the strand turns per meter and

   B ranges between 250 and 450.
9. A thread according to one or more of the claims 1 to 8, characterized in that the carbon fibers in the strands have a diameter of 6 to 10 µm.
10. A thread according to one or more of the claims 1 to 9, characterized in that the thread is a sewing thread.
11. A method for the production of a carbon fiber thread according to one or more of the claims 1 to 10, characterized in that at least two strands consisting of continuous carbon fibers are twisted around one another by direct cabling, whereby the assembly eyelet is an eyelet that has a radius of at least 4 mm in the area of contact between the strands and the assembly eyelet.
12. A method according to claim 11, characterized in that the assembly eyelet is an eyelet that has a radius of 4 to 40 mm at least in the area of contact between the strands and the assembly eyelet.
13. A method according to claim 11, characterized in that the assembly eyelet is an eyelet that has a radius of 6 to 12 mm at least in the area of contact between the strands and the assembly eyelet.
14. A method according to one of the claims 11 to 13, characterized in that thread guides are used that have a radius of at least 4 mm, at least in the area of contact between the strands and the thread guide.
15. A method according to claim 14, characterized in that thread guides are used that have a radius of at least 4 to 40 mm, at least in the area of contact between the strands and the thread guide.
16. A method according to claim 14, characterized in that thread guides are used that have a radius of at least 6 to 12 mm, at least in the area of contact between the strands and the thread guide.
17. Use of a thread according to one or more of the claims 1 to 9 as a sewing thread.
18. Use of a thread according to one or more of the claims 1 to 9 in fiber composite materials, such as thermoplasts, duromers, elastomers, particularly rubber, or ceramic materials.
19. Use of a thread according to one or more of the claims 1 to 9 to reinforce concrete.

Images