EP4058623A1

EP4058623A1 - Impregnated thread, ribbed thin-walled composite product comprising such an impregnated thread, and method for manufacturing this thread and this composite product

Info

Publication number: EP4058623A1
Application number: EP20807903.8A
Authority: EP
Inventors: Julien Rion; Reto Aebischer; Milos JERINIC; Christian Rytka; David BOTOR; Kunal MASANIA
Original assignee: BCOMP SA
Current assignee: BCOMP SA
Priority date: 2019-11-15
Filing date: 2020-11-13
Publication date: 2022-09-21
Also published as: US20220403563A1; WO2021094996A1; CN115298367A; FR3103199A1; FR3103199B1

Abstract

The invention relates to an impregnated thread, a ribbed thin-walled composite product comprising such an impregnated thread, and the method for manufacturing same. Such an impregnated thread (10d; 10e) comprises at least two continuous strands (10a; 10b) comprising plant fibers (11), said strands (10a; 10b) being impregnated with thermoplastic material (12a) in at least 60% of their volume, each of said strands (10a; 10b) being individually twisted (T1) and the assembly of said strands (10a; 10b) also being twisted (T2) in a configuration (10d) held by the thermoplastic material (12a).

Description

Title of the invention: Impregnated yarn, composite product with a thin ribbed wall comprising such an impregnated yarn, and method of manufacturing this yarn and this composite product [0001] Technical field

The present invention relates to the field of thin-walled composite products reinforced by ribs resulting from son, as well as impregnated son used in the manufacture of such thin-wall ribbed composite products. [0003] Such thin-walled composite products are conventionally used to form a part with improved mechanical properties while keeping a low weight for this part.

[0004] State of the art

If one seeks to strengthen the thin-walled composite product in bending, but also in compression, it is known to provide projecting reinforcements in the form of a ribbed network or grid as in WO201 7099585 in which one forms by molding these ribs above and / or below the base plate.

[0006] 0n knows certain types of thin-walled composite products from document EP2648890, in particular with son of a first thickness and son of a second thickness greater than the first thickness and which serve as reinforcement forming ribs on the one side of the thin-walled composite product. These yarns of the second thickness are composed of twisted plant fibers, this twisting in particular providing better resistance to compression of these yarns of the second thickness.

[0007] Document WO2019087141 relates to a method of impregnation with the polymer of a grid formed from an assembly of threads, which improves the quality of the impregnation, with the aim of improving the bending properties of a product A thin-walled composite comprising this grid on a base flat support, such as a mat. For this purpose, we perform a sprinkling of polymer particles on one of the faces of a lattice of crossed wires, in order to obtain a grid comprising a greater quantity of polymer on one of the faces, which in addition lightens the thin-walled composite product comprising such a grid. However, this method is not suitable when it is desired to have an impregnated thread with high mechanical performance because of the very partial impregnation of the threads of the mesh.

[0008] Document EP2813607A1 describes the passage of strands of fibers in an impregnation unit comprising a bath of liquid thermoplastic polymer, to form an impregnated yarn. It turns out that in practice the simple passage through a bath of liquid polymer does not ensure complete and perfect impregnation of the strand of fibers throughout its volume, but very partial impregnation at the surface of the strand of fibers. This random and insufficient impregnation does not guarantee optimized and reproducible properties for the reinforcing threads within the thin-walled composite product.

Brief summary of the invention

One of the aims of the present invention is to provide a solution which makes it possible to obtain an impregnated yarn for which the impregnation of the fibers is improved, whereby the mechanical properties of this impregnated yarn are increased.

Another object of the invention is to provide a method of manufacturing an impregnated yarn as well as the impregnated yarn resulting from this manufacturing process which are free from the limitations of the known manufacturing methods and impregnated yarns.

Another object of the invention is to provide a method of manufacturing a ribbed thin-wall composite product as well as the ribbed thin-wall composite resulting from this manufacturing process which are free from the limitations of the manufacturing methods and known thin-walled composites. Another object of the invention is to provide a method of manufacturing a thin-walled composite product reinforced by ribs formed by wires forming a ribbed thin-walled composite product improved with respect to the state of the technical. [0014] According to the invention, these aims are achieved in particular by means of a method for manufacturing a yarn impregnated from at least one strand comprising plant fibers, in which the following steps are implemented:

- provide at least two continuous strands comprising plant fibers,

- provide an impregnation tank delimiting a sinuous passage between an inlet and an outlet,

- supplying the tank with a bath of thermoplastic polymer material in the molten state filling said passage permanently, - arranging said strands so that they are separated from each other upstream of the impregnation tank, that they enter the tank impregnation through said inlet, that they simultaneously follow the passage by being immersed in the thermoplastic material in the liquid state and by having at least one contact zone with one face of the passage, and that they emerge from the tank of impregnation through said outlet, and

- Impregnating the strand by continuously advancing said strand so as to form a strand impregnated with the thermoplastic material, whereby an impregnated yarn is formed;

- wherein each of said strands has a twist T1 in a first orientation during their passage through the impregnation tank 20, and

- In which is also carried out, after the impregnation step, a step of twisting the yarn during which is carried out an overall twist corresponding to a twist T2 between them of all the strands downstream of the tank d 'impregnation, while the thermoplastic material is still in the liquid state, whereby the thermoplastic material forms a bond between the strands in their state twisted together, resulting in the formation of an impregnated and twisted yarn, and in which said overall twist T2 is carried out in a second orientation different from the first orientation. This solution has the particular advantage over the prior art of allowing good impregnation of the fibers by the thermoplastic material, and in particular of not obtaining an impregnated yarn in which only the surface portion of the strands is impregnated, without systematically having a core impregnation of the strands and of the impregnated yarn resulting from this process.

Such an impregnated yarn resulting from the manufacturing process according to the invention has better mechanical strength due to this improved impregnation, and in particular a more substantial impregnation, in particular by reaching the fibers of the central portion of the strand or strands. which forms the yarn, which therefore allows improved impregnation of the yarn itself thus obtained. A greater proportion of the volume of each strand is impregnated with the thermoplastic material, resulting in impregnation of a greater proportion of the volume of the entire yarn. It is in particular because of the contact with the surfaces of the impregnation tank during the passage of the strand or strands in the bath of liquid thermoplastic material, that this good impregnation is ensured, because by rubbing against hard surfaces , the strand or strands are flattened, which allows, through this opening of the strand or strands, deployment of the fibers and thereby placing all or most of the fibers of each strand in direct contact with the liquid thermoplastic material. Contact with the walls of the vessel delimiting the passage also creates a local overpressure which forces the thermoplastic material to penetrate into the strand, and to coat more fibers of the strand, or even all the fibers of the strand. Also, according to the invention there is provided an impregnated yarn comprising at least two continuous strands comprising plant fibers, with a first individual twist of the strands in a first direction (each of said strands has an individual twist in a first orientation) and a second overall twist of the strands in a second direction different from the first direction (all of said strands has an overall twist according to a second orientation different from the first orientation). Preferably, said strands are impregnated with thermoplastic material in at least 60% of their volume, each of said strands being individually twisted and all of said strands also being twisted in a configuration held by the thermoplastic material.

Thus, such an impregnated yarn therefore exhibits both an individual twist of each strand and also an overall twist. It is understood that the thermoplastic material allows the formation of a bond between all the strands both in their individual twisted configuration (individual twist of the strands) and also in their twisted configuration between them (overall twist of the strands resulting in a wire twisted).

As will be presented later in detail, an impregnated yarn with high mechanical performance is thus obtained. Among other things, such an impregnated yarn exhibits improved flexural, tensile and compressive strength due to this dual level twist, for each strand and between all strands.

According to one embodiment, the impregnated wire further comprises at least one connecting wire wound helically around all of said strands, forming an impregnated and tied wire. Such a binding wire improves the hold of the shape of the section of the wire, and will in particular help to limit the crushing of the wire intended to form a rib on the surface of a thin-walled composite product. This connecting wire is therefore optional. If this binding thread is present around the impregnated thread, one can alternatively provide two binding threads wound in a helix and which can be in the same direction, or preferably in the opposite direction. One or the other or more of the following arrangements can also be present in the impregnated yarn:

- the outer fibers of said strands form (s) an angle of between -20 ° and + 20 ° with the longitudinal or main direction of the impregnated yarn, - the strands have an individual twist of between 50 and 300 rpm, preferably between 100 and 200 rpm ,

the impregnated yarn comprises between three and six strands each having a weight of between 200 and 800 tex, preferably between 300 to 600 tex.

Also, according to the invention there is provided a method of manufacturing a thin-walled composite product comprising the following steps:

- supply of a support such as a mast

- manufacture of impregnated yarns according to the process described in this text,

- assembly of the impregnated threads to form a mesh in which the impregnated threads intersect, - stacking of the mesh and the support, and

- Compression molding of the stacked mesh and support, whereby a composite product is formed, having a ribbed face, said ribs being created at least in part by the impregnated threads.

- supply of base yarns having a size smaller than the impregnated yarns, - weaving or knitting of the base yarns with said impregnated yarns, to form a preform,

- Compression molding of the preform, whereby a composite product is formed having a ribbed face, said ribs being created at least in part by the impregnated threads. In addition, according to the invention is proposed a solution according to which there is provided a thin-walled composite product comprising impregnated son. as described in the present text, said composite product having a ribbed face, said ribs being created at least in part by said impregnated threads.

The presence of these ribs makes it possible to increase the flexural rigidity of the part formed from or incorporating such a thin-walled composite product, while slightly increasing its weight. Also, the presence of these ribs also makes it possible to improve the impact behavior of this part, the ribs slowing the propagation of cracks in the part during an impact, thus confining the damage, preventing the projection of debris and increasing by elsewhere the absorption of energy on impact.

In the present text, the expression “thin-walled” composite product means that the composite product has a wall whose thickness is at most equal to 10% of the smallest dimension of this composite product or of the article comprising this composite product. According to another possibility coming within the scope of the present invention, the expression “thin-walled” composite product means that the composite product has a wall whose thickness is at most equal to 5% of the smallest dimension of this product. composite or of the article comprising that composite product. The thin-walled composite product thus formed is intended to form in particular, and without limitation, a part or part of a part for the passenger compartment of a motor vehicle, such as an instrument panel, door covers, cover panel of the pillars and console, a roof, a trunk cover. It can also be used to make suitcase shells, vehicle bodies, etc.

[0029] The invention also relates to a method of manufacturing an article comprising a thin-walled portion wherein said thin-walled portion is formed from or comprises a thin-walled composite product produced according to the method described in the present text. , said article belonging to the group comprising: an automobile body part, in particular the doors, the roof, the hood, fenders, spoiler, spoiler, front and rear bumpers, aerodynamic kits, or automotive interior parts including door covers, dashboard, center console, pillar trims, trunk linings, the roof, or sports articles such as a canoe, kayak or light boat hull, a bicycle frame, or even a piece of furniture, or aircraft interior parts, in particular the panels side panels, ceiling panels, luggage compartments, or aerodynamic parts of light aircraft, in particular the engine cover, wheel covers, or any aerodynamic fairing of a mobile machine, or even a suitcase shell.

Brief description of the figures

Examples of implementation of the invention are indicated in the description illustrated by the appended figures in which:

[0032] Figure 1 illustrates the different steps of a process for manufacturing an impregnated yarn and the impregnated yarn resulting from this manufacturing process which are not part of the invention,

[0033] FIG. 2 represents the different stages of a method of manufacturing a yarn impregnated with two strands and the impregnated yarn resulting from this production method according to the invention,

Figure 3 illustrates the different steps of a variant with three strands of the manufacturing process of an impregnated yarn and the impregnated yarn resulting from this manufacturing process according to the invention,

Figure 4 shows a manufacturing unit of an impregnated yarn allowing the implementation of the variant of the manufacturing method of Figure 3,

[0036] FIG. 5 schematically represents an implementation possibility for the impregnation tank making it possible to carry out the step of impregnating the strand or strands which will form the impregnated yarn,

Figures 6A and 6B respectively show the first face and the second face of a composite product with thin ribbed wall according to the invention comprising impregnated son, Figure 7 is an enlarged view of zone VII of Figure 6B, showing the impregnated son forming ribs on one of the faces of the composite product of Figures 6A and 6B, and [0039] Figure 8 illustrates the different steps of a manufacturing process forming another type of impregnated yarn and which falls outside the scope of the present invention.

Example (s) of embodiment of the invention Referring to Figure 1 showing the steps in the manufacture of an impregnated yarn which is not part of the invention, from the right to the left of FIG. 1, the arrow F1 representing the entry and the arrow F2 the exit. Here, a single strand 10a is used to continuously form the impregnated yarn 10e. At the start (after the arrow F1, step A), the strand 10a is a continuous ribbon coming out of a reel and comprising plant fibers 11, the orientation of which has not necessarily been directed. For example, this strand 10a consists of short flax fibers which are essentially parallel to each other and to the general direction of the strand 10a. Next, (step B), preferably, but not necessarily, a twist T1 of the strand 10a is carried out in a first direction, which forms a twisted strand 10b according to an individual twist which orients the fibers 11 in a direction which n 'is not parallel to the general direction PO of strand 10a (angle b for the outer fibers 11 in FIG. 1). The purpose of this twisting will be to increase the resistance to tearing of the strand, and thus to prevent it from breaking during the following impregnation step. This individual twist T1 will however be small (for example an angle b of between 0 ° and 20 ° with respect to the direction PO of the strand 10b) in order to facilitate good impregnation in the following step. According to another possibility (without step A of FIG. 1), one starts directly from the strand 10b already individually twisted on the spool which feeds the production line. Next, (step C), the twisted strand 10b (or the untwisted strand 10a) is impregnated with a liquid thermoplastic material 12a, such as a thermoplastic polymer (or a mixture of polymers thermoplastics) present in an impregnation tank 20. This specific impregnation step C will be described in detail below. An impregnated strand, optionally twisted, 10c is obtained, also forming, in this case of FIG. 1 with a single strand, an impregnated yarn 10e. In the case of Figure 8, which is not part of the invention, there is shown the alternative case in which the manufacturing process comprises steps A, C described above, and step E described below. after, but not steps B and D: there is no individual torsion T1, nor additional individual torsion T1 '. This figure 8 comprises a single strand 10a with fibers 11 essentially parallel to the direction PO of strand 10a, to form the impregnated yarn 10e, but it is possible, in the context of this process of FIG. 8, to use two strands 10a, three strands 10a or even more strands 10e, which therefore remain in their untwisted state throughout the process, and in particular during impregnation step C and tying step (optional) E.

Then, as shown in Figure 1, at the outlet of the impregnation tank 20, but optionally and not imperatively, the wire 10c can be twisted (step D), and this additionally if it has already been twisted before (step B of twisting T1 or else strand already supplied twisted). This individual torsion T1 '(additional), which takes place in the same direction (first orientation of torsion) as the individual torsion T1, makes it possible to increase the resistance to radial compression of the yarn, while the lower torsion T1 (angle b) of the outer fibers 11 in the impregnation tank 20 facilitates good impregnation. A final step E, which is preferable but not imperative, in addition to or as an alternative to the twisting T1 ′ (step D) of the yarn leaving the tank, consists in placing a binding yarn 13 around the impregnated twisted strand 10c, in forming a helix, and this after passing through the impregnation tank 20, while the thermoplastic material 12a which has impregnated the impregnated yarn is still liquid and has not completely hardened. This gives an impregnated and tied 10th yarn in which the material hardened thermoplastic 12b serves as a binder to maintain the position and orientation of the fibers 11 on the one hand between them and on the other hand with the connecting yarn 13, within the impregnated and tied yarn 10e which has good cohesion giving it good radial compressive strength properties. At the exit (arrow F2), an impregnated and tied yarn 10e has been formed which can be wound on a spool for later use.

0n refers to Figure 2 showing a variant of the manufacturing process of a single strand impregnated yarn which has just been described in relation to Figures 1 and 8, constituting a process falling within the scope of the invention, in which two strands 10a (step A) or 10b (step B) are used to form an impregnated yarn according to the invention. Each twisted strand 10b is impregnated with liquid thermoplastic material 12a at the level of the impregnation tank 20 (step C) and then the two impregnated twisted strands 10c are twisted together according to a twist T2. This forms an impregnated yarn 10d larger than each individual twisted strand impregnated 10c, and this while the thermoplastic material is still liquid 12a, in all cases not hardened. In this way, this thermoplastic material provides a bond between the two impregnated twisted strands 10c, which maintains in the impregnated yarn 10d the configuration of the overall twist between the two impregnated twisted strands 10c. During the optional, but preferential, final step E of laying the binding wire 13 in a helix around the impregnated wire 10d, as the thermoplastic material 12a is still liquid and has not completely hardened, it also produces a bond retaining between them the binding wire 13 in helix around the impregnated wire 10d, and to form an impregnated and tied wire 10e. Once the thermoplastic material 12b has hardened, it maintains these bonds.

0n now refers to Figure 3 showing a variant of the manufacturing process of an impregnated yarn according to the invention, in which three flat strands 10a (step A) or three twisted strands 10b (step B) are used for forming the impregnated yarn. Each twisted strand 10b is impregnated with liquid thermoplastic material 12a at the level of the impregnation tank (step C) and then the three impregnated twisted strands 10c are twisted together (step D) according to an overall twist T2. An impregnated yarn 10d is thus formed which is larger than each impregnated twisted individual strand 10c, and this while the thermoplastic material is still liquid 12a, in all cases not hardened. In this way, this thermoplastic material 12 provides a bond between the three impregnated twisted strands 10c, which maintains the overall twist configuration between the three impregnated twisted strands 10c in the impregnated yarn 10d. If a binding wire 13 is used helically around the impregnated wire 10d, as shown in FIG. 3, and this while the thermoplastic material 12a is still liquid and has not completely hardened, this thermoplastic material 12a not only achieves a connection between the three impregnated twisted strands 10c of the impregnated yarn 10d, but also a connection retaining the connecting yarn 13 helically around the impregnated yarn 10d, and to form an impregnated and twisted yarn 10e. Once the thermoplastic material 12b has hardened, it maintains these bonds.

0n has just described in relation to Figures 1, 8, 2 and 3, the cases in which the impregnated yarn results from a single strand, two strands or three strands, but it is understood that according to the invention it is conceivable to use even more strands twisted individually and twisted together between them (4 strands, 5 strands or more strands).

Note that the expression "impregnated and tied yarn" can be replaced by "impregnated yarn" and vice versa in the present text because the use of the connecting yarn 13 arranged in a helix around the impregnated yarn is not systematic in within the scope of the present invention.

0n refers to Figure 5 illustrating one of the implementation possibilities of the impregnation step, with the impregnation tank 20 filled with liquid thermoplastic material 12a and delimiting a passage 21 between the inlet 20a and the outlet 20b of the impregnation tank 20. According to an essential arrangement to allow good impregnation of the strands 10b by the liquid thermoplastic material 12a, there exists in the passage 21 followed by each of the twisted strands 10b, one or more zone (s) of contact 20c with a wall belonging to the face of the passage 21, therefore of the internal face of the tank impregnation 20. In the case shown in FIG. 5, these contact zones 20c are located on the lateral face of the cylinders 22 placed in the impregnation tank 20 and bypassed by the twisted strands 10b which therefore run through a passage 21 in the form of a wave or a wave. Other configurations, not shown, are possible to force the individual contact of the twisted strands 10b against a face of the passage 21 while the strands 10b are bathed in the liquid thermoplastic material 12a, for example with the zig-zag walls of the tank. impregnation 20. In general, passage 21 is sinuous.

Thus, it is understood that due to this friction and the pressure of the twisted strands 10b on these contact zones, the penetration of the liquid thermoplastic material 12a into the strand 10b is favored, and this in particular because this contact tends in separating the fibers 11 of the twisted strands 10b from each other and in creating a local overpressure on the liquid thermoplastic material 12a. On leaving passage 21 and the aforementioned contacts, impregnated twisted strands 10c are obtained with an individual twist T1 in accordance with that before passing through the impregnation tank, these strands being very impregnated, or even entirely impregnated with thermoplastic material 12a. Thanks to this arrangement, an effective impregnation step is carried out which makes it possible to have, at the outlet of the impregnation tank 20, strands 10c impregnated with an impregnation of thermoplastic material in at least 60% of their volume, in general in at least 70% of their volume, preferably in at least 80%, even at least 90% or 95%. In some cases, it is possible to obtain an impregnation of thermoplastic material in the whole (100%) volume of the impregnated strands 10c. This large amount of thermoplastic material is found in the same proportion in the yarn at the end of the production line implementing the production method according to the invention.

In an embodiment corresponding to Figure 3, each of said strands has a twist T1 in a first orientation during their passage through the impregnation tank 20: this individual twist is for example between 50 and 300 rpm, from preferably between 100 and 200rpm. This first orientation is for example S. This first orientation of the twist T1 results in the formation of a strand 10b with outer fibers 11 which have an angle b with respect to the general direction PO of the strand 10a.

According to the invention, said impregnated yarn 10 d comprises at least two twisted strands 10b (preferably three twisted strands 10b) separated from one another upstream of the impregnation tank 20 and passing simultaneously through said passage 21. For example , the impregnated yarn 10 d is composed of 2 to 10 individual strands of 200 to 1500 tex, preferably 3 to 6 strands of 200 to 800 tex, preferably 3 to 6 strands of 300 to 600 tex. According to an alternative embodiment, several separate impregnation tanks working in parallel are used, one for the impregnation of each strand 10b.

For example, the twisted strands 10b enter the impregnation tank through a hole fitted at the level of the inlet 20a of the impregnation tank 20 (on the right in FIG. 5), large enough to avoid a blocking, but small enough to prevent a leak of liquid thermoplastic material, for example poly propylene (example a hole of 2.5mm in diameter for three twisted strands 10b of 555tex each). Also, for example, the impregnated twisted strands 10c emerge through a calibrated hole at the level of the outlet 20b of the impregnation tank 20 (on the left in FIG. 5) which will determine the final radius of the impregnated wire 10d and the quantity of material. thermoplastic of this 10d impregnated yarn.

(example a 2mm diameter hole for three twisted strands 10b of 555tex each). The diameter of this exit hole will be adjusted to obtain the desired fraction of thermoplastic material and fibers in the yarn impregnated 10d. The fraction will typically be between 30 and 70% by weight of thermoplastic material, preferably between 40 and 60% by weight of thermoplastic material in the impregnated yarn 10d.

According to one embodiment, the strand 10a or 10b or each of said strands 10a or 10b consists only of plant fibers. These vegetable fibers belong to the group comprising the following materials: flax, hemp, sisal, jute, abaca, kenaf, nettle, ramie, kapok, abaca, henequen, pineapple, banana, palm tree, and wood fibers.

According to one embodiment, the thermoplastic material used for the impregnation comprises a polymer which belongs to the group comprising polyolefins, polypropylene (PP), polypropylene, grafted with maleic anhydride (maPP), polyethylene (PE ), polyamide or co-polyamide, polyester or co-polyester, thermoplastic polyurethane, co-polyoxymethylene, thermoplastic cellulose esters (Cellulose acetate propionate), polylactic acid (PLA) or derivatives thereof or a mixture of these. For example, a mixture of polypropylene and polypropylene grafted with maleic anhydride (maPP) is used which promotes the adhesion of the polymer with the natural fibers. It is possible, by way of example, to use such a mixture with 3 to 10% of my PP by weight.

According to one embodiment, the thermoplastic thermoplastic material has, in the impregnation tank 20, a viscosity such that the Melt Flow Index is greater than 10 g / 10 min, preferably greater than 34 g / 10 min. By Melt Flow Index is meant a measurement in g / 10min, according to Standard IS01133, under a load of 2.16kg at 230 ° C.

According to one embodiment, the molten thermoplastic material 12a has, in the impregnation tank 20, a viscosity of between 10 and 10Ό00 Pa.s, preferably between 20 and 1000 Pa.s, and preferably between 50 and 500 Not. This viscosity corresponds to a low shear rate viscosity of 1 sec-1. In general, we are at impregnation in the impregnation tank 20 at a thermoplastic temperature of between 150 ° C and 250 ° C.

To implement the method of manufacturing an impregnated yarn as described above, in particular in relation to Figures 1 to 3, one can use a manufacturing unit 100 as shown schematically in Figure 4. We can use finds the direction of advance from right to left in FIGS. 1 to 3, between an input F1 and an output F2. At the entrance to this manufacturing unit 100, three reels 110 allow the manufacturing unit 100 to be supplied with three twisted strands 10b corresponding to step B in FIG. 3.

In the case shown, drying of the twisted strands 10b is carried out by passing through a drying module 120, which drying could be omitted in other variant embodiments. However, it is found that natural fibers still have 4-8% moisture. When these fibers 11 enter the impregnation tank which is for example brought to

190 ° C, this humidity forms water vapor and escapes from the fibers. As it escapes, the steam repels the thermoplastic material and impregnates the fibers forming the strands. The twisted strands 10b can be very easily dried by passing before entering the impregnation tank in a drying module 120 formed of a tube with a flow of hot air between 100-150 ° C. It is also possible to dry the twisted strands 10b beforehand and to keep the coils which unwind on the reels 110 in a dry atmosphere.

In this way, prior to entering the impregnation tank 20 of the strand 10b or of said strands 10b, the drying of said strand 10b or of said strands 10b is carried out.

The previously described impregnation tank 20 is arranged just downstream of the drying module 120, with an extruder 23 which supplies the tank 20 with liquid thermoplastic material. The end of the manufacturing unit 100 comprises, downstream of the impregnation tank 20, a drive module, winding and twisting 140 comprising a spool for receiving the impregnated yarn 10d (or the impregnated and tied yarn 10e). In this way, when passing the free end of the impregnated yarn 10d through the drive, winding and twisting module 140, and activating said drive, winding and twisting module 140 the impregnated yarn is advanced and its overall twist is carried out as well as its winding on a support as the impregnated yarn advances, whereby a twisted impregnated yarn 10d (and possibly tied) is obtained which is wound on a spool of the drive, winding and twisting module 140.

In this way, after step C of impregnation, a step (step D) of twisting of the impregnated yarn 10d is carried out during which an overall twist is carried out corresponding to a twist T2 between them of all the strands downstream of the impregnation tank 20, while the thermoplastic material is still in the liquid state, whereby the thermoplastic material 12a makes a bond between the strands 10c in their twisted state between them, resulting in forming an impregnated and twisted yarn 10d.

According to the invention, the overall torsion is carried out in a second orientation T2 different from the first orientation T1. Thus, if the individual twist T1 of each strand 10c is in S (anti-clockwise with respect to the direction of advance of the yarn), with said drive, winding and twisting module 140, a twist d 'whole of the wire 10d in Z (clockwise with respect to the direction of advance of the wire).

Thanks to these arrangements, the degree of twist T2 is chosen so that the outer fibers 11 of said strand 10c or of said strands 10c form an acute or zero angle d, low, between -20 ° and + 20 ° with the direction longitudinal or main P1 of the impregnated yarn 10d. According to another possibility, this angle d is between + 10 ° and -10 °, or even between + 5 ° and -5 ° and possibly between + 3 ° and -3 °. By "outer fibers" is meant the portion of the fibers of each strand which is located on the surface of the impregnated (and twisted) yarn. Indeed, in the cases where the strands 10b have fibers with a certain twist according to a first orientation (angle d if the combination of twists T1 and T1 ', or angle b if twist T1 only), by twisting the strands together according to a second orientation (overall twist T2), the angle d (and possibly e in the presence of a connecting thread 13) formed between the outer fibers of the strands and the main direction P1 of the thread 10d is reduced, or even achieved, canceling out or 10th. This is visible in particular in Figure 3 where the fibers 11, visible in portion D representing the impregnated yarn 10d with overall twist, and forming outer fibers, are substantially parallel to the main direction P1 of the impregnated yarn 10d (angle e noted as close to 0, namely e ~ 0, with respect to P1).

This situation in which the outer fibers 11 are oriented at 0 ° (longitudinal) in the impregnated yarn 10d, makes it possible to have impregnated yarns which are as rigid as possible in bending, which will generate good qualities of flexural strength when these wires are embedded as ribs on the surface in a thin-walled composite product.

As in bending, it is essentially the outer fibers of the impregnated yarn which are stressed, a yarn geometry with the outer fibers of the yarn at 0 ° (longitudinal) is advantageous. This is possible by twisting (T2 twist) several individual yarns in a reverse twist direction to the individual strands (if the individual strands have a T1 twist in S, the yarn is twisted in Z for the T2 twist) so as to obtain the fibers outside at 0 ° or close to 0 °. For example, by twisting with a twist of 73rpm three individual strands of 555tex having a twist of

158 rpm, a fiber angle of 0 ° is obtained on the outside of the 1665 tex yarn (eg linen). Thus, by working with individual strands twisted to form a large yarn, it is possible to optimize the angle of the fibers 11 in order to have good bending properties (fibers 11 outside at 0 °) and good compressive strength. radial of the yarn (inner fibers 11 with a fairly large angle of twist). Since the operation of step D of twisting all the individual wires 10c into a larger wire 10d is carried out while the thermoplastic material 12a is still in the molten state, this overall twisting creates a further compaction of the yarn 10d which further presses the thermoplastic material inside the individual yarns 10c and improves impregnation thereof.

In the embodiment shown in Figures 1 to 3, the following step is carried out (step E): a binding wire 13 is provided and said binding wire 13 is wound around the thread 10d impregnated with material thermoplastic downstream of the impregnation tank, whereby an impregnated and tied thread 10e is formed. This binding wire 13 is placed in a helix all around the impregnated wire 10d while the thermoplastic material 12a is still liquid to ensure the attachment of this binding wire 13 on the impregnated wire 10d and to obtain good cohesion for the impregnated and tied wire. 10th. For example, this binder yarn has a linear weight of between 10 and 60 tex, preferably between 15 and 45 tex. The weight added by the binder yarn will typically be 1 to 15% of the total weight of the impregnated and tied yarn 10e, preferably 2 to 10%.

Among the advantages of the presence of this connecting wire 13, it should be noted that it contributes to maintaining a circular shape to the section of the impregnated and twisted wire 10th, and mainly to increasing its resistance to radial compression. This is advantageous when the impregnated and tied yarn 10e is used in a thin-walled composite product as ribs on its surface, since during the manufacturing process of the thin-walled composite product the product is compressed either by a flexible membrane under pressure, or by a flexible pad (for example a silicone substrate). During this operation, the threads making up the ribs tend to be crushed and the effectiveness of the ribs is thus reduced. As with bending stress, the stiffness depends on the thickness of the structure to the power of three, the thickness of the ribs has a dominant influence on the bending stiffness of the thin-walled composite product. The binding thread 13 can be a thread of plant fibers (for example linen, cotton, hemp, etc.) or can be synthetic (polymer thread such as polyester, polyamide, or of glass fibers, carbon fibers , aramid). This binding wire 13 must not melt or become too flexible at the processing temperature of the composite product (180-210 ° C), otherwise the binding wire 13 will deform during the compression of the part and it loses all its usefulness in confinement and maintaining the shape of the impregnated yarn and string.

Thus, in the event of the presence of a twisted binding wire 13 in the impregnated wire 10th, this binding wire 13 is placed (step E) after step D of overall twisting of the wire, and this then that the module for depositing the connecting wire 130 is arranged upstream of (before) the drive, winding and twisting module 140. It is in fact understood that the twisting (overall twist T2) of all the strands of the yarn is produced by the drive, winding and twisting module 140 but that this overall twisting propagates to the outlet of the impregnation tank 20 (in FIG. 4, at the outlet - On the left - of the impregnation tank 20, the three impregnated twisted strands 10c are differentiated (separated) to just after being associated in the impregnated wire 10d). According to a possibility not illustrated, we provide at least two connecting son 13 downstream of the impregnation tank, and we continuously have said connecting son helically, with different directions, around the impregnated wire 10d to the as it advances through the outlet of the impregnation tank, whereby an impregnated and tied 10e thread is formed. In one embodiment, exactly two binding threads 13 are arranged in a helix around the impregnated thread 10d with a reverse direction of rotation, whereby the two binding threads 13 cross each other on the surface of the impregnated and tied thread 10e.

For the laying of this connecting wire 13 or two or more connecting son 13, different methods are possible. In a first solution, the impregnated wire passes inside the spool of the binding wire, said spool rotating at the determined speed to obtain the desired density of binding wire. With the spool rotating at high speed, the tension on the small binding wire is generated by the inertia of this binding wire rotating at high speed around the impregnated wire. Alternatively, the binding wire spool can rotate around the impregnated wire, and tension in the binding wire is generated by slowing the unwinding of the spool. In both cases, the impregnated yarn has no contact with the binding thread laying unit other than the binding thread itself, so as not to interfere with the twisting process which takes place between the drive, winding and twisting module 140 and the impregnation tank 20.

For the drive module, winding and twisting 140, one can use a winding system where the coil which winds the impregnated yarn rotates both on its own axis to wind the impregnated yarn, and on the axis of the impregnated yarn to create twist. The second way is that of the spinning wheel, with the pin spinner spinning around the spool. The speed of the spinner's rotation determines the twist, and the speed differential between the spool and the spinner controls the feed rate of the impregnated wire. The precise control of these two speeds can be done with stepping motors, with synchronous motors or with servo motors. According to another possibility visible in Figure 8, which is not part of the present invention, the initial strand 10a is in the form of a ribbon with fibers 11 aligned, with fibers 11 having an angle close to 0 ° relative to the main direction PO of the tape, passing through the bath of molten thermoplastic polymer in an impregnation tank before the binding wire 13 is laid helically around the impregnated wire 10c.

As indicated above, the invention also relates to a thin-walled composite product comprising impregnated threads as described above, said composite product having a ribbed face, said ribs being created at least in part by said threads. impregnated, and in some cases all the ribs being formed by impregnated threads.

According to one possibility, such a ribbed thin-walled composite product results from a process comprising the following steps: - providing a support such as a mat

- manufacture of impregnated yarns according to the method described above,

- assembly of the impregnated threads to form a mesh in which the impregnated threads intersect,

- stacking of the mesh and the support, and - compression molding of the stacked mesh and support, whereby a composite product is formed, having a ribbed face, said ribs being created at least in part by the impregnated threads.

An example of such a ribbed thin-walled composite product 30 is illustrated in FIGS. 6A and 6B and in FIG. 7 in the form of a portion of a part which can be used for example as a part for covering a passenger compartment. automobile. This ribbed thin-walled composite product 30 has a mesh 32 and a support 34 superimposed and interconnected. The lattice 32 is formed of impregnated and strung yarns 10e which are held together by crisscrossing by an assembly yarn, for example of polyester, for example a 10 to 100 dtex yarn, applied by sewing, knitting or weaving with the threads. impregnated and tied 10th of the lattice 32.

The connection between the mesh 32 and the support 34 is produced by the polymer itself, either during the compression molding step, or during a hot prelamination step. Alternatively, the mesh 32 can be sewn onto the support 34.

According to another manufacturing process, two supports 34 are provided and the mesh 32 is stacked with the two supports 34, the two supports 34 being on either side of said mesh 32 to form a sandwich stack. According to one embodiment, the support 34 (or both supports) is (are) chosen from among a support of woven material, a support of non-woven material or a support 34 of non-woven material belonging to the list following: a web of unidirectional fibers (11), a superposition of layers of unidirectional fibers (11) (multidirectional web), and a mat of randomly distributed fibers.

According to one embodiment, said support 34 (or both supports) is (are) prepreg (s) with a polymer (or more generally with a thermoplastic material) identical or different from the polymer (or more generally with thermoplastic material) impregnated son of the mesh.

According to one embodiment, the mesh 32 comprises a mesh with a mesh opening greater than or equal to 1 cm, preferably between 1 cm and 6 cm, preferably between 1 cm and 3 cm.

The impregnated wire described above is used to form a mesh 32 or a grid. The grid can have parallel wires in two directions to create a square, rectangular or parallelepiped mesh. It can also have three or four directions of thread. A square mesh grid will typically have a 5-100mm mesh, depending on the size of the yarn used, typically a 10-30mm mesh with a yarn made from 1500tex of impregnated linen. The grid can be produced by a textile method, with a small thread binding the impregnated threads together, for example by knitting. The grid can also be obtained by thermally welding the impregnated wires at their crossings, either by heating, or by ultrasound. To obtain the desired final composite product, the grid is then combined with other composite layers during the thermocompression step (for example mats of natural fibers and PP, or mats of polyester and PP fibers .... ) According to another possibility, there is proposed a method of manufacturing a composite product with a thin ribbed wall, comprising the following steps:

- manufacture of impregnated yarns according to one of the processes described above, - supply of base yarns having a size smaller than the impregnated yarns, - weaving or knitting of the base threads with said impregnated threads, to form a preform,

- Compression molding of the preform, whereby a composite product is formed having a ribbed face, said ribs being created at least in part by the impregnated threads.

The preform comprising the impregnated threads must be shaped in order to obtain said composite product with reinforcing ribs. Several methods are possible. For thermocompression, the preform is heated in an oven to melt the thermoplastic polymer. The base layer and the preform comprising the impregnated yarns can either be combined beforehand and heated together, if their temperature and heating method match, or else heated separately, but simultaneously. The preform and base layer are placed in the mold in a press and the press is closed to compact and form the composite product. Once the polymer has cooled and hardened, the part is demolded. The mold used is rigid on the smooth side of the part, but has a soft substrate, for example a 2-10mm layer of silicone, on the ribbed side, so as not to crush the ridges created by the impregnated threads 10d or 10e described above. . Alternatively, the pressure can be exerted by a flexible membrane pressurized on the ribbed face. Also, the heating-cooling cycle can also be done in the mold.

The ribs can be obtained at specifically chosen locations using a depositing robot which will precisely deposit the desired impregnated 10d or 10e strands on a base layer (for example a mat), according to a specific reinforcement scheme. The bond with the base layer can be done by melting the polymer, or by locally sewing the impregnated thread.

The composite product presented here has a thin wall which means that it is generally initially in the form of a sheet or of a panel, one dimension of which is much smaller (at least 10 times smaller) than the other two.

Such a composite product can take on a multitude of geometries, including a flat sheet, a non-planar sheet, and in particular a sheet with a convex face and a concave face, or even a corrugated sheet, a three-dimensional hollow shape, and in particular a hollow tube of circular section, of polygonal section or another shape, and in particular any three-dimensional shell with a thin wall.

Thus, and in a nonlimiting manner, it is proposed to manufacture an article comprising a thin-walled portion in which said thin-walled portion is formed of a thin-walled composite product produced according to one of the previously described methods. Such an article incorporating a thin-walled composite product can be used in various applications and in particular belongs to the group comprising: an automobile body part, in particular the doors, the roof, the hood, the fenders, the spoiler, the spoiler - front and rear shocks, aerodynamic kits, or automotive interior parts including door covers, dashboard, center console, pillar trim, trunk trim, roof, or sporting goods such as '' a canoe, kayak or light boat hull, a bicycle frame, or a piece of furniture, or aircraft interior parts, including side panels, ceiling panels, luggage compartments, or aerodynamic parts of light aircraft, in particular the engine cover, the wheel covers, or any aerodynamic fairing of a mobile machine, or even a suitcase shell.

[0091] [Tables 1]

Reference numbers used in figures A Strand (s) feeding step 10a B Strand (s) twisting step 10a C Strand (s) impregnation step 10b D Twisting step the set of strands 10c

E Step of laying the connecting wire 13 on the wire 10d F1 Enter

F2 Exit

T1 Individual twist of the strands

T1 'Individual additional twist of the strands

T2 Overall twist of the wire

PO Main direction of strand

P1 Main direction of the wire

A Angle between the outer fibers 11 and the strand 10a (step A)

B Angle between outer fibers 11 and strand 10b (step B)

D Angle between the outer fibers 11 and the impregnated and twisted yarn 10d (step D)

E Angle between the outer fibers 11 and the impregnated, twisted and twisted yarn (step E)

10a Flat strand

10b Twisted strand

10c Impregnated twisted strand (impregnated yarn if only one strand)

10d Impregnated yarn with overall twist

10th Impregnated and tied thread

11 fibers

12a Liquid thermoplastic material

12b Hardened thermoplastic material

13 Binding wire

20 Impregnation tank

20a Tank inlet

20b Tank outlet

20c Contact zone of the strands in the passage 21

21 Passage

22 Cylinder

23 Extruder

30 Ribbed thin-wall composite product

32 Trellis

34 Support

100 Manufacturing unit

110 Reels

120 Drying module

130 Module for removing the connecting wire

140 Drive, winding and twisting unit

Claims

1. A method of manufacturing an impregnated yarn (10d; 10e) from at least two strands (10a; 10b) comprising plant fibers (11), in which the following steps are implemented: - providing at least two continuous strands (10a; 10b) comprising fibers

(11) vegetable,

- providing an impregnation tank (20) delimiting a passage (21) winding between an inlet and an outlet,

- supplying the tank with a bath of molten thermoplastic polymer material (12a) filling said passage (21) permanently,

- Arranging said strands (10a; 10b) so that they are separated from each other upstream of the impregnation tank (20), that they enter the impregnation tank (20) through said inlet, that they simultaneously follow the passage (21) being immersed in the thermoplastic material (12a) and having at least one contact zone (20c) with one face of the passage (21), and that they emerge from the impregnation tank ( 20) through said outlet, and

- impregnating the strand (10a; 10b) by continuously advancing said strand (10a; 10b) so as to form a strand (10a; 10b) impregnated with the thermoplastic material (12a), whereby an impregnated thread is formed ( 10d; 10th),

- wherein each of said strands (10a; 10b) has a twist (T1) in a first orientation during their passage (21) in the impregnation tank (20), and

- In which is also carried out, after the impregnation step, a step of twisting the yarn during which is carried out an overall twist corresponding to a twist (T2) between them of all the strands (10a; 10b ) downstream of the impregnation tank (20), while the thermoplastic material (12a) is still in the liquid state, whereby the thermoplastic material (12a) forms a bond between the strands (10a; 10b) in their state twisted together, resulting in the formation of an impregnated (10d; 10e) and twisted yarn, and in which said overall twist (T2) is carried out in a second orientation different from the first orientation.

2. A method of manufacturing an impregnated yarn (10d; 10e) according to claim 1, wherein the following step is further implemented:

- providing a binding wire (13) and winding said binding wire (13) around the wire impregnated (10d) with thermoplastic material downstream of the impregnation tank (20), whereby an impregnated wire is formed and tied (10th).

3. thermoplastic thermoplastic A method of manufacturing an impregnated yarn (10d; 10e) according to one of claims 1 to 2, wherein the outer fibers (11) of said strand (10a; 10b) or of said strands (10a; 10b) form ( nt) an angle (d) between -20 ° and + 20 ° with the longitudinal or main direction of the impregnated yarn, preferably an angle (d) between + 10 ° and -10 °, and preferably an angle (d ) between + 5 ° and -5 °.

4. A method of manufacturing an impregnated yarn (10d; 10e) according to one of claims 1 to 3, wherein said strand (10a; 10b) consists only of plant fibers (11).

5. A method of manufacturing a yarn according to claim 4 wherein the plant fibers (11) belong to the group comprising the following materials: flax, hemp, sisal, jute, abaca, kenaf, nettle, ramie, kapok, abaca, henequen , pineapple, banana, palm tree, and wood fibers.

6. A method of manufacturing a yarn according to one of claims 1 to 5, wherein the thermoplastic polymer belongs to the group comprising polyolefins, polypropylene (PP), polypropylene grafted with maleic anhydride (maPP), polyethylene ( PE), polyamide or co-polyamide, polyester or co-polyester, thermoplastic polyurethane, co-polyoxymethylene, thermoplastic cellulose esters (Cellulose acetate propionate), polylactic acid (PLA) or derivatives thereof or a mixture of these.

7. A method of manufacturing a yarn according to one of claims 1 to 6, wherein the thermoplastic material (12a) has, in the impregnation tank, a viscosity such as the Melt Flow Index, measured according to Standard IS01133. , under a load of 2.16kg at 230 ° C, is greater than 10 ^g / 10min, preferably greater than 34 ^g / 10min.

8. A method of manufacturing a yarn according to one of claims 1 to 6, wherein the molten thermoplastic material (12a) has, in the impregnation tank, a viscosity of between 10 and 10Ό00 Pa.s.

9. A method of manufacturing a yarn according to one of claims 1 to 8, wherein the impregnated yarn (10d) comprises between 30 and 70% by weight of thermoplastic material. A method of manufacturing a yarn according to one of claims 1 to 9, wherein prior to entering the impregnation tank (20) of the strand (10a; 10b), the said strand is also dried ( 10a; 10b).

10. A method of manufacturing a yarn according to one of claims 1 to 9, wherein said following steps are also carried out:

- provide at least two connecting wires (13) downstream of the impregnation tank (20),

- Continuously having said connecting threads (13) in a helix, with different directions, around the impregnated thread (10d) as it advances through the outlet of the impregnation tank (20), whereby an impregnated and tied thread is formed (10th).

11. A method of manufacturing a yarn according to one of claims 1 to 10, wherein said following steps are also carried out:

- - provide a drive, winding and twisting module (140) disposed downstream of the impregnation tank (20),

- - pass the free end of the impregnated yarn (10d; 10e) through the drive, winding and twisting module, and

- - activate said drive, winding and twisting module (140) to advance the impregnated yarn (10d; 10e) and achieve its overall twist (T2) as well as its winding on a support as and when measurement of the advance of the impregnated thread (10d; 10e).

12. A method of manufacturing a thin-walled composite product comprising the following steps:

- provision of a support (34) such as a mat

- Manufacture of impregnated yarns according to the process of any one of claims 1 to 11,

- assembly of the impregnated threads to form a mesh (32) in which the impregnated threads intertwine,

- stacking of the mesh (32) and the support (34), and

- Compression molding of the stacked mesh (32) and of the support (34), whereby a composite product is formed, having a ribbed face, said ribs being created at least in part by the impregnated threads.

13. A method of manufacturing a thin-walled composite product according to the preceding claim, wherein the son of the mesh (32) are held together by crisscrossing by an assembly thread, for example polyester, applied by sewing, knitting. or weaving with the threads of the trellis (32).

14. A method of manufacturing a thin-walled composite product according to one of claims 12 to 13, wherein two supports (34) are provided and the mesh (32) is stacked with the two supports (34), both. supports (34) being on either side of said mesh (32) to form a sandwich stack.

15. A method of manufacturing a thin-walled composite product according to one of claims 12 to 14, wherein the support (34) is selected from a support (34) of woven material or a support (34) of non-material. -woven belonging to the following list: a sheet of unidirectional fibers (11), a superposition of layers of unidirectional fibers (11) (multidirectional sheet) and a mat of randomly distributed fibers.

16. A method of manufacturing a thin-walled composite product comprising the following steps:

- Manufacture of impregnated yarns (1 Od; 10e) according to the method of any one of claims 1 to 15,

- supply of basic yarns having a size smaller than impregnated yarns (1 Od; 10e),

- weaving or knitting of the base threads with said impregnated threads (1 Od; 10e), to form a preform,

- Compression molding of the preform, whereby a composite product is formed having a ribbed face, said ribs being created at least in part by the impregnated threads (1 Od; 10e).

17. A method of manufacturing an article comprising a thin-walled portion wherein said thin-walled portion is formed from or comprises a thin-walled composite product made according to the method of one of claims 12 to 16, said article belonging to to the group comprising: an automobile body part, in particular the doors, the roof, the hood, the fenders, the spoiler, the front and rear bumpers, the aerodynamic kits, or automobile interior parts, in particular the covers door, dashboard, center console, pillar trims, trunk liners, headliner, or sporting goods such as a canoe, kayak or light boat hull, a bicycle frame, or another piece of furniture, or aircraft interior parts, in particular the side panels, the ceiling panels, the luggage compartments, or aerodynamic parts of light aircraft, in particular the engine cover, the wheel covers, or any fairing e aerodynamics of a mobile machine, or even a suitcase shell.

18. Impregnated yarn (10d; 10e) comprising at least two continuous strands (10a; 10b) comprising vegetable fibers (11), said strands (10a; 10b) being impregnated with thermoplastic material (12a) in at least 60% of their volume, each of said strands (10a; 10b) being individually twisted, exhibiting a twist (T1) in a first orientation, and all of said strands (10a; 10b) also being twisted in a configuration maintained by the thermoplastic material (12a ), according to an overall torsion (T2) according to a second orientation different from the first orientation.

19. Impregnated yarn (10d; 10e) according to claim 18, further comprising at least one binding yarn (13) wound helically around all of said strands (10a; 10b), forming an impregnated and tied yarn (10d ; 10th).

20. Impregnated yarn (10d; 10e) according to claim 18 or 19, wherein the outer fibers (11) of said strands (10a; 10b) form an angle (d) of between -20 ° and + 20 ° with the longitudinal direction. or main (P1) of the impregnated yarn (1 Od; 10e), preferably an angle (d) between + 10 ° and -10 °, and preferably an angle (d) between + 5 ° and -5 °.

21. Impregnated yarn (10d; 10e) according to one of claims 18 to 20, wherein the strands (10a; 10b) have an individual twist (T1) of between 50 and 300 rpm, preferably between 100 and 200 rpm.

22. Impregnated yarn (10d; 10e) according to one of claims 18 to 21, comprising between three and six strands (10a; 10b) each having a weight of between 200 and 800 tex, preferably between 300 to 600 tex.

23. Thin-walled composite product comprising impregnated son (1 Od; 10e) according to one of claims 18 to 22, said composite product having a ribbed face, said ribs being created at least in part by said impregnated son (1 Od ; 10th).