WO2012143256A1

WO2012143256A1 - Strand made of partial strands

Info

Publication number: WO2012143256A1
Application number: PCT/EP2012/056417
Authority: WO
Inventors: Karl-Josef Brockmanns
Original assignee: Sgl Carbon Se
Priority date: 2011-04-18
Filing date: 2012-04-10
Publication date: 2012-10-26
Also published as: DE102011007630B4; TW201313974A; DE102011007630A1

Abstract

The invention relates to a strand 1 made of a plurality of partial strands 2, wherein the partial strands 3 comprise a plurality of synthetic fibers 5 combined into a corresponding partial strand 2 by a first binding agent 6, and wherein the plurality of partial strands 2 is combined into the strand 1 by means of a second binding agent 7 intended for subsequent removal at least in areas, such that when the second binding agent 7 is acted upon, said agent can be removed or destroyed at least in areas and the strand 1 can be separated into the partial strands 2.

Description

STRAND OF PARTIAL STRINGS

The invention relates to a strand of a plurality of sub-strands, and a production method for such a strand and a use in an SMC process.

Conventional SMC (Sheet Molding Compound) processes produce plate-like composites of resin and glass fibers as reinforcing fibers which are used in many industrial fields. In the preparation of these composites, the dough-like resin is first applied to a processing belt and according to the requirements of the

Layer thickness set. Subsequently, glass fibers are singulated or applied in partial strands from the top of the resin composition and embedded in a further processing step in the resin. The resin can then be cured or partially cured, the composite being wound up on rolls and provided with further processing steps. Alternatively, the resin may also be fully cured to produce a desired end product.

When applying fibrous strands to the resin, the strands are typically removed from a roll and cut to a desired length as needed and applied to the resin compositions from above. Due to the sometimes large amounts of sub strands, which must be made available, it requires the simultaneous strand extraction of multiple roles. The removed strands must be individually cut (cut) and suitably applied to each other on the resin composition. The removal and cutting this requires a relatively large technical effort, which often makes the SMC process costly.

For this reason, in alternative manufacturing processes, the partial strands are already cut before the SMC process is carried out and fed to the processing device. The disadvantage here, however, that the already cut to length strands can only be stored in a very space consuming way. A space-saving storage on wheels is impossible for obvious reasons. In addition, there is the problem of separating individual strands, which must first be removed from a reservoir and must be applied to the resin compositions in a process that is difficult to control. This in turn requires considerable technical effort, which makes the process relatively expensive.

It is therefore an object of the present invention to propose a strand of synthetic fibers which can be processed so as to avoid the disadvantages of the prior art described above. Further, a manufacturing method for such a strand is to be specified as well as a use of such a strand in an SMC process. In particular, a strand is to be proposed, which can be processed by means of the hitherto customary technologies, but a lesser use of machinery is required.

The object is achieved by a strand according to claim 1, and a manufacturing method according to claim 17 and a use of the strand according to claim 24.

In particular, the object is achieved by a strand of a plurality of sub-strands, wherein the sub-strands comprise a plurality of synthetic fibers, which are connected by a first composite to a respective sub-strand, and wherein the plurality of sub-strands by means of a second composite, which for later at least regional removal is provided, are summarized to the strand that when acting on the second composite this at least partially removed or destroyed and the strand can be separated into the sub-strands.

Furthermore, the object is achieved by a method for producing a strand from a plurality of sub-strands, which comprises the following steps:

Providing a plurality of sub-strands of a plurality of synthetic fibers; Bonding the plurality of synthetic fibers through a first composite into a plurality of sub-strands;

Combining the plurality of sub-strands by a second

Composite to a strand, so that the second composite later removed again at least partially or destroyed and the strand can be separated into the sub strands;

Furthermore, the object is achieved by a string described above and below, which is used in an SMC method.

Synthetic fibers are here and below all types of fibers that can not be obtained by a natural manufacturing process. In particular, these are fibers of carbon, graphite, glass, aramid, polyamide, polyethylene, and of all other plastics.

An effect on the second composite for separating the strand into the partial strands may be of a thermal and / or mechanical and / or chemical and / or solvent-technical nature. Other suitable types of exposure are also possible. However, they require a chemical and / or physical interaction.

The idea according to the invention can be seen in that a strand comprises a plurality of partial strands, which can be recovered by suitable action on the strand in isolated form. The synthetic fibers of the partial strands are in this case connected by a first composite means such that the partial strands have a sufficient mechanical or physical stability in order to substantially avoid a singulation of the fibers. Furthermore, the stability is sufficient to be present even after summarizing the partial strands in a common strand as partial strands and also to be recovered as such back. The summarization of the individual partial strands takes place here by means of a second composite means. If now the second composite agent is acted upon directly or even indirectly so that it is at least partially removed or destroyed, the connection of the partial strands is eliminated and the partial strands can be recovered in isolated cases. The separation can also occur automatically when the second composite was at least partially removed or destroyed, ie the sub-strands fall apart by themselves, if they are oriented to Earth force.

This makes it possible to further process a strand of synthetic fibers in an SMC process in such a way that several partial strands can be obtained simultaneously with the processing of one strand. In particular, the cutting process is considerably easier than with conventional processes, in which each sub-strand has to be cut to length using its own cutting device. Furthermore, the strand can be stored without problems on a spool or roll, and does not require a larger storage space compared to a plurality of individual coils for the sub strands. Another advantage of such a strand is also to be mentioned that for the removal of the coil with the same number of sub-strands a significantly reduced number of coils is necessary, from which the sub-strands can be removed. This, too, provides a significant reduction in the number of machines and devices to be maintained, thereby increasing the efficiency of the SMC process.

According to a first preferred embodiment of the strand it is provided that the plurality of synthetic fibers of the partial strands are connected by a consolidated binder as the first composite. Consolidation requires at least partially curing or hardening. A complete cure, if this has not yet done, can be done in about a further processing step of the SMC process. This ensures on the one hand that the partial strands can be produced with sufficient stability against external influences and on the other hand that the partial strands are suitably available for the SMC process. According to a further embodiment of the strand, the plurality of synthetic fibers of the partial strands are connected by a powdered binder or by a liquid resin as the first composite. It should be noted that the binder or resin should be compatible with the resin of the SMC process, that allows a chemical bond with the resin of the SMC process. The first composite agents of the invention are typically easy to process and inexpensive to purchase. Particularly preferred are thermoplastic binders and resins which can be easily processed after suitable temperature adjustment.

In an alternative embodiment it is provided that the plurality of synthetic fibers of the partial strands are connected by wrapping with at least one thread or at least one band as the first composite. These bands or threads may be formed such that they can be at least partially removed or destroyed when exposed to them, so that the entire strand, or a strand section, if such is already obtained by a cutting process, can disintegrate into the sub strands , The threads or bands are in this case attached in such a way that they can be particularly easily destroyed or removed by action. This is possible, for example, in the case of mechanical action, for example by a cutting device or by a squeezing device, as a result of which the strip or the thread is mechanically destroyed. Also conceivable is a thermal action, for example on a so-called. Melt thread, after which the thread or the belt is also thermally destroyed and the sub-strands for singling free. Furthermore, even chemical or solvent-technical effects are possible, as a result of which the thread or the strip is attacked to such an extent that at least one local destruction begins and the partial strands are released. However, it is important in all cases of an impact that this does not attack the first composite for cohesion of the fibers so that the fibers are separated individually from the composite of the sub strands. Although this may be possible on a case-by-case basis, it must normally be avoided, otherwise the quality of the sub-strands for the SMC process can not be guaranteed. According to a further aspect of the invention can also be provided that the second composite means comprises a thread and / or a band, which is preferably formed from a plastic or a plastic mixture, and which under thermal, mechanical and / or chemical action and / or action can be at least partially removed or destroyed by means of a solvent.

According to another embodiment, it may also be provided that the first composite and second composite are identical. Thus, both may be about a thermoplastic material or a resin, which initially serves to impede the fibers of the partial strands. After thermal or mechanical action on the strand, the second composite can then be melted or broken, so that release of the partial strands can take place. At the same time, a partial melting of the binder may also take place as the first composite, but this melting does not jeopardize the cohesion of the fibers in the partial strands.

According to a further embodiment, at least one of the partial strands (2) may be at least partially corrugated. A corrugation can be formed as a superficial depression or region-wise compression, which regularly or irregularly varies the cross section of the partial strands. Thus, the fiber density over the cross section depending on the degree of compaction can vary over the longitudinal extent of the fibers. Due to the compression, on the one hand, the cohesion of the sub-strands is improved and, in addition, the singling of the sub-strands is promoted when the second composite is destroyed or partially dissolved. Due to the lower adhesion of the individual partial strands in the strand, fewer adhesive surfaces are formed between the individual partial strands overall, so that less separation is made against a separation of the partial strands. In addition, the individual fibers of the sub-strands remain better localized due to the compression in the sub-strands and do not dissolve out of the composite.

According to a further embodiment, it can also be provided that the multiplicity of synthetic fibers of at least one of the partial strands is wound. A turn of the partial strands increases, like a corrugation, the cohesion of the fibers in a partial strand and promotes the singulation upon removal or destruction of the second composite.

According to a continuation can also be provided that the winding of the plurality of synthetic fibers varies along the longitudinal direction of the at least one partial strand, in particular varies at regular intervals, preferably at regular intervals has a change in the winding direction. Thus, on the one hand, an intrinsic curvature of the partial strands can be prevented or controlled in a targeted manner, whereby the quality of the SMC composite to be produced can be improved. Furthermore, the separation of the partial strands from the strand can also be favorably influenced by a varying turn of the partial strands.

The partial strands have according to an embodiment a substantially circular cross-section transverse to the fiber extension direction. According to another embodiment, the cross section may also be elliptical or band-shaped. In the latter case, the strand is particularly suitably designed as a stack of individual subbands. Preferably, the cross section may also vary, such as when the substrands have corrugations.

According to one embodiment, the plurality of synthetic fibers may comprise carbon fibers, in particular comprising only carbon fibers. These are on the one hand particularly strong and thus advantageous in an SMC product, on the other hand, carbon fibers can also be well provided with a first composite, in particular a resin to form mechanically stable partial strands.

According to a further embodiment it is provided that the connection between the synthetic fibers, which is mediated by the first bonding agent, is stronger against mechanical influences than the connection between the sub-strands, which is mediated by the second bonding agent. This can ensure that after removal or destruction of the second composite, the partial strands themselves are not singled into their fibers, but in one stable bundles are present, which can be advantageously processed in an SMC process.

In another embodiment, it can also be provided that the plurality of sub-strands is arranged substantially parallel to one another in the strand. This can facilitate the separation of the partial strands. Nevertheless, the sub-strands may themselves have tortuous fibers.

According to a further embodiment, the strand can be wound onto a spool, from which it can be removed by unwinding. This storage is particularly space-saving and also allows to use SMC production devices that are already used in the prior art.

According to a particularly preferred embodiment of the production method of a strand, it can be provided that the step of providing a plurality of partial strands comprises a step of separating a single strand, in particular a heavy tow roving, into the plurality of partial strands. This can be made particularly cost-effective a isolable strand. Furthermore, the use of a single strand also ensures a uniform quality of all fibers in the sub-strands.

In a further preferred embodiment, it can also be provided that the step of separating a single strand into the plurality of partial strands comprises a step of spreading the single strand. The spreading allows a targeted optical and mechanical subdivision of the spread strand into sub-strands or sub-bands. In addition, the fiber flow can be well controlled, whereby fiber damage during the manufacturing process can be largely prevented. The spreading is also advantageous in order to apply the first composite agent to the fibers as efficiently as possible since impregnation can take place at reduced fiber layers over a larger area.

Further, the step of providing a plurality of partial strands of a plurality of synthetic fibers may comprise a shaping step in which the cross section of the sub strands is conditioned transversely to the longitudinal direction. Thus, for example, a band-shaped spread partial strand can be recombined into a partial strand, which has a round or elliptical cross section, or be corrugated. Consequently, therefore, after a successful impregnation of a partial strand, this can be brought back into a form suitable for further processing or for the connection by means of the second composite.

In a further embodiment, the step of bonding the plurality of synthetic fibers through a first composite means may comprise a step of binding. In addition, the step of bonding the plurality of synthetic fibers may include a step of compacting. Further, it is also possible that the step of bonding the plurality of synthetic fibers includes a step of twisting, compacting, and simultaneously twisting and compacting. These processing steps all allow suitable conditioning of the sub-strands which allows for improved singulation of the sub-strands and a more stable fiber composite in the sub-strands.

In the following, further embodiments will be explained with reference to some figures. Here, the individual features shown are claimed alone as well as in conjunction with each other. Like reference numerals all refer to features having the same or similar effects.

In the following show:

Fig. 1 is a schematic representation of a first embodiment of a

strand according to the invention with four sub-strands;

FIG. 2 shows a schematic illustration of a second embodiment of a strand according to the invention with four partial strands; FIG.

Fig. 3 is a schematic representation of a third embodiment of a

strand according to the invention with four sub-strands; 4 shows a schematic representation of a fourth embodiment of a strand according to the invention with four partial strands;

5 shows a schematic representation of a production line for illustrating an embodiment of the production method according to the invention;

Figure 1 shows a portion of a first embodiment of a strand 1 according to the invention with four sub-strands 2, which are taken together by means of a thread 7 as a second composite means 7 and connected thereto. The partial strands 2 themselves are constructed from a multiplicity of fibers 5, which are connected to one another by means of a first composite means 6. In the present case, the first composite 6 is preferably a resin or a thermoplastic binder which fixes and bonds the fibers 5, preferably carbon fibers 5. The resin is preferably a thermosetting resin but can also be replaced by a thermoplastic material. The cohesion of the fibers 5 in the sub-strands 2 is sufficiently good to secure the fibers 5 against mechanical release from the composite.

The second composite 7 is preferably formed as a thread 7, which can be easily and selectively separated by a mechanical action. When separated, the individual sub strands 2 and disintegrate into a loose accumulation of these partial strands 2. Thus, when feeding the strand 1 in a device for producing an SMC product shortly before applying the fibers to the resin compositions, the second composite 7 solved falling Part strands 6 on the resin composition of the SMC product and can be embedded in this in an orderly or disorderly manner. The separation is preferably carried out before application but after removal from a roll (not shown) on which the strand 1 can be wound up.

Figure 2 shows another embodiment of the strand 1 according to the invention, which differs from that in Fig. 1 only in that the partial strands 2 are not connected by a thread as a second composite means 7 but by a suitable Binderauftrag or resin application. The binder or the Resin is hardened or precured. The binder application or resin application is not shown here due to the schematic nature of the figure. For separating the partial strands 6, the strand 1 can be selectively influenced by mechanical action so that the binder application or resin application between the partial strands 2 is destroyed, for example broken, but the partial strands 2 themselves are not singulated into the fibers 5. Alternatively, the separation can also be effected by a brief intensive heating of the strand 1.

FIG. 3 shows an embodiment of the strand 1 according to the invention, which likewise has four partial strands 2 but whose fibers are not connected by means of a binder or a resin, but by means of different threads 6 as the first composite means 6. As second composite means 7 for connecting the individual partial strands 2 Bands 7 are provided, which are preferably made of a plastic, which melts when exposed to heat and thus allows to separate the partial strands 2. Preferably, the threads 6 do not melt under the influence of heat and continue to give the partial strands sufficient mechanical stability even after separation. Should it be provided to mechanically separate the bands 7, a very accurate and careful separation is required in order not to also sever the threads 6 of the sub-strands 2 and expose the fibers 5 therewith. However, to avoid this, additional adhesive bonding by means of resin or binder may be provided.

The embodiment of the strand 1 shown in FIG. 4 essentially corresponds to the embodiment shown in FIG. 1, but instead of the thread 7 a band 7 is provided which spirals around the partial strands 2. The band 7 is preferably made of a material which melts under thermal action and thus exposes the partial strands 2 for singling. For singling but also a mechanical action can be provided as shown in FIG. 1, namely by such an effect to destroy the thread 6 or 6 band gives reason and thus the substrines for singling free.

5 shows a schematic representation of a production line for illustrating an embodiment of the production method of a strand 1 according to the invention Partial strands 2. Here, a single strand 20 is first tangentially removed from a roller 21 and fed to a braking device 22. The single strand 20 in the present case is a heavy tow roving made of carbon fibers, in particular of the type 50k, ie it comprises 50,000 carbon fiber filaments (carbon fibers 5). The single strand 20 is then spread by means of a spreading device 23 to a band of defined width and provided in a subsequent binding device 24 with a bonding agent order, which is dried in a downstream drying device 25. The spreading is preferably carried out in such a way that the number of carbon fibers 5 are distributed substantially uniformly over the width dimension, ie the surface fiber density or the volume fiber density across the width are substantially constant. Optionally, a doubling of the carbon fibers 5 by spreading in two planes take place so as to improve the uniformity of the distribution yet.

The adhesive binder application first stabilizes the tape and consolidates it through the drying step. As a result of the consolidation, the adhesive binder application loses its great adhesion tendency and can now be separated in a separating device 26 into a plurality of subbands with a defined width. Adhesive binder consolidation allows good separability with reduced fiberization of the edge regions of the subbands.

The separating device is designed, for example, as a rotating knife set, but may also be designed as a stationary knife set or be an ultrasonic cutting device or a pinching cutting device.

Optionally, the subbands thus produced can be provided with a further adhesive agent application in a further downstream adhesive device 27. Alternatively, however, the adhesive binder application, which was applied by means of the binding device 24, modified or removed. Subsequently, the renewed adhesive binder order can be dried or listened to by means of a further drying device 28. In a step not shown here, an optional wrapping of the sub-bands with a thread or a band for combining and connecting the fibers 5 of the sub-strands 2 can also take place. The- However, this step does not necessarily require obstruction or adhesive application beforehand and therefore has not been shown herein.

According to the sequence in FIG. 5, the subbands are then removed by means of two rollers and subsequently taken together in a composite device 30 to form a strand 1 of sub-strands 2. Before the summary, a step of shaping by means of further pairs of rollers (not shown) is also possible, which for example forms sub-strands of the subbands which have a round or elliptical cross-section Q. The composite device 30 may cause a combination by means of a suitable second composite means 7. This can be about a thread 7, which can be wound around the sub-strands and can be defined cut or even wound off during processing of the strand 1. Optionally, the sub-bands can be conditioned by a heat treatment, a moisture treatment such that the sub-strands 2 can be adhesively bonded in a subsequent step. Alternatively, a suitable compression of the strand 1 is conceivable, which can lead to the strand 1 for the connection of the partial strands 2. A subsequent curing of the adhesive or of the adhesive binder can be advantageous in this case in order to improve the cohesion of the partial strands 2.

After subsequent guidance by a suitable roller guide 31, the strand 1 is wound on a spool 10 for storage as a roll. The roller guide can also be dancer-controlled.

As mentioned above, a step of shaping in the course of the present method may also appear meaningful. This step can be carried out in particular by means of a compacting device not shown here. The step of compacting in this case requires an at least partial solution of the adhesive binder order of the binding device 24. Subsequently, the sub-bands can be guided into the compacting device, which achieves a compaction by winding around. Alternatively, by means of a suitably shaped pair of rollers (not shown), a change false-twist can be applied to the sub-bands. The subbands are guided through the pair of rollers, that at the smallest distance from each other has a distance which is smaller than the thickness of the partial strand to be formed 2. During the implementation of the sub-bands / partial strands 2 oscillate the two rollers with adjustable amplitude and adjustable frequency. As a result, a rotation of the sub-strands is achieved with simultaneous compaction. In this case, the given rotation runs counter to the drawing-off direction / feed-through direction up to the clamping point of the partial belts / partial strands 2. By a suitable subsequent drying, the rotation thus applied can be fixed. If required, in a further subsequent step, the strand can also be treated as a complete unit with a shaping tool.

Further embodiments of the invention can be taken from the subclaims.

Reference numerals:

1 strand

2 substrand

5 fiber

6 first composite

7 second composite

10 coil

20 single strand

21 roll

22 brake device

23 spreading device

24 binding device

25 drying device

26 separating device

27 adhesive device

28 drying device

29 rolls

30 composite device Roller guide cross section

Claims

claims:

1. strand (1) of a plurality of sub-strands (2), wherein the sub-strands (3) comprise a plurality of synthetic fibers (5), which are connected by a first composite means (6) to a respective sub-strand (2), and wherein the plurality of partial strands (2) by means of a second composite means (7), which is provided for later at least regional removal, are so summarized to the strand (1) that when acting on the second composite means (7) this at least partially removed or destroyed and the strand (1) can be separated into the sub-strands (2).

2. strand according to claim 1,

characterized in that

the plurality of synthetic fibers (5) of the partial strands (2) are connected by a powdered binder or by a liquid resin as the first composite (6).

3. strand according to one of the preceding claims 1 or 2,

characterized in that

the plurality of synthetic fibers (5) of the partial strands (2) are connected by wrapping with at least one thread or at least one band as the first composite means (6).

4. strand according to one of the preceding claims,

characterized in that

the second composite (7) comprises a thread and / or a band, which are preferably formed from a plastic or a plastic mixture, and which are removed or destroyed at least partially by thermal, mechanical and / or thermal action and / or action by means of a solvent can.

5. strand according to one of the preceding claims,

characterized in that

the partial strands (2) are at least partially corrugated.

6. strand according to one of the preceding claims,

characterized in that

the sub-strands (2) have a substantially circular cross-section (Q) transverse to the fiber extension direction.

7. strand according to one of the preceding claims 1 to 5,

characterized in that

the sub-strands (2) have a substantially elliptical cross-section (Q) transverse to the fiber extension direction.

8. strand according to one of the preceding claims,

characterized in that

the plurality of synthetic fibers (5) comprise carbon fibers, in particular comprising only carbon fibers.

9. strand according to one of the preceding claims,

characterized in that

the connection between the synthetic fibers (5) mediated by the first composite (6) is stronger against mechanical impacts than the connection between the partial strands (2) mediated by the second composite (7).

10. strand according to one of the preceding claims,

characterized in that

the plurality of sub-strands (2) are arranged substantially parallel to one another in the strand (1).

11. strand according to one of the preceding claims, characterized in that

the strand (1) is wound on a spool (10), from which it can be removed by unwinding.

12. A method for producing a strand (1) from a plurality of partial strands (2), which comprises the following steps:

Providing a plurality of sub-strands (2) of a plurality of synthetic fibers (5);

Bonding the plurality of synthetic fibers through a first composite (6) into a plurality of sub-strands (2);

Combining the plurality of sub-strands (2) by a second composite means (7) to form a strand (1), so that the second composite (6) later removed again at least partially or destroyed and the strand (1) in the sub-strands (2) can be isolated;

13. The method according to claim 12,

characterized in that

the step of providing a plurality of sub-strands (2) comprises a step of separating a single strand (20), in particular a heavy tow roving, into the plurality of sub-strands (2).

14. The method according to any one of claims 12 or 13,

characterized in that

the step of separating a single strand (20) into the plurality of sub-strands (2) comprises a step of spreading the single strand (20).

15. Use of a strand (1) according to any one of claims 1 to 15 in an SMC process.