TEXTILE REINFORCEMENT SUITABLE FOR BEING USED IN A METHOD FOR IMPREGNATION BY A THERMOPLASTIC RESIN

Abstract

The invention relates to a textile reinforcement suitable for being used in a method for impregnation by a thermoplastic impregnation resin, with a view to producing composite parts, including at least one set of substantially parallel high-tenacity yarns, and a sewing yarn sewn through the one or more sets, characterized in that the sewing yarn includes filaments which have a melting temperature higher than the melting temperature of said thermoplastic impregnation resin, and filaments made from a thermoplastic material, which can be mixed into the impregnation resin, and which have a melting temperature lower than the implementation temperature of said thermoplastic impregnation resin.

Claims

1-12. (canceled)

13. A textile reinforcement suitable for use in a thermoplastic resin impregnation method, with a view to producing composite parts, comprising at least one set of high-tenacity yarns, each set comprising substantially parallel yarns, and a sewing yarn sewn through the at least one set to ensure the cohesion thereof, wherein the sewing yarn comprises a group of filaments having a melting temperature higher than the application temperature of the said thermoplastic impregnation resin, and a group of filaments produced from a thermoplastic material, miscible in the impregnation resin, and having a melting temperature lower than the application temperature of the said thermoplastic impregnation resin, the two groups of filaments being assembled by twisting or wrapping.

14. The reinforcement according to claim 13, wherein the set of yarns is a ply without crimping.

15. The reinforcement according to claim 13, wherein the reinforcement comprises two sets of yarns that are woven together.

16. The reinforcement according to claim 13, wherein the reinforcement comprises a single layer formed by a set of substantially parallel high-tenacity yarns, and a support layer formed by a fibrous material the fibers of which are not parallel to said layer of high-tenacity yarns.

17. The reinforcement according to claim 16, wherein the support layer is formed by a non-woven fabric.

18. The reinforcement according to claim 16, wherein the support layer is formed by a set of parallel yarns spaced apart from each other.

19. The reinforcement according to claim 13, wherein the reinforcement comprises at least two distinct groups of filaments produced from a thermoplastic material, miscible in the impregnation resin, and having a melting temperature lower than the application temperature of the said thermoplastic impregnation resin, each group of filaments being wrapped around the first group of filaments having a melting temperature greater than the application temperature of the said thermoplastic impregnation resin, and two of the said groups of filaments being wrapped in opposite directions.

20. The reinforcement according to claim 19, wherein the distinct groups of filaments are produced from a thermoplastic material, miscible in the impregnation resin, and have different melting temperatures.

21. The reinforcement according to claim 13, wherein the filaments having a melting temperature higher than the melting temperature of the thermoplastic impregnation resin are made of a material chosen from the group preferably comprising glass, cotton, aramid, liquid crystal polymers, carbon, quartz, basalt.

22. The reinforcement according to claim 13, wherein the filaments produced from a thermoplastic material, miscible in the impregnation resin and having a melting temperature lower than the application temperature of the said thermoplastic impregnation resin, are produced from a material chosen from the group comprising polyamides, polyphenylene sulfide, acrylic resins, polyimides, polyesters, polyaryletherketones.

23. The reinforcement according to claim 13, wherein the filaments having a melting temperature higher than the melting temperature of the thermoplastic impregnation resin, have a melting temperature or glass transition temperature of more than 250 C.

24. The reinforcement according to claim 13, wherein the sewing yarn has a yarn count of between 20 and 300 dtex.

Description

DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS

[0010] Therefore, the invention seeks to provide a reinforcement that mitigates the various disadvantages mentioned above, and which has good properties relative to fraying, which enables preforms to be produced simply, and above all which has good mechanical cohesion during molding operations at high temperature.

[0011] The invention therefore concerns a textile reinforcement suitable for use in a method of impregnation by a thermoplastic impregnation resin, with a view to producing composite parts by exposure of the reinforcement to the said resin at a temperature for implementation of the method well above the melting temperature of the impregnation resin. The said textile reinforcement comprises at least one set of substantially parallel high-tenacity yarns, typically made of glass, carbon or similar material. The said reinforcement also comprises a yarn sewn through the said set or sets of yarns to ensure the cohesion thereof.

[0012] According to the invention, the said sewing yarn comprises a group of filaments having a melting temperature higher than the application temperature of the said thermoplastic impregnation resin, and a group of filaments produced from a thermoplastic material, miscible or even soluble in the impregnation resin, and having a melting temperature lower than the application temperature of the said thermoplastic impregnation resin. These two groups of filaments of different natures are assembled by pairing, twisting or wrapping.

[0013] In other words, the invention consists of achieving the sewing of the reinforcement with a yarn including a portion resistant to the temperatures observed during the molding operations. Thus, the mechanical strength of the reinforcement is preserved during the molding, and when the resin flows transversely through the reinforcement. Complementarily, the complementary portion of the sewing yarn is heat fusible and compatible with the impregnation resin so that it does not create areas of fragility in the composite part, since this portion of the sewing yarn is embedded in the impregnation resin of the reinforcement. Moreover, because this portion of the sewing yarn is melted during the molding operation, the position it holds in the hole formed by the sewing yarn is reduced, and it allows a rearrangement of the filaments of the reinforcement in a more rectilinear configuration.

[0014] The said thermoplastic portion facilitates the sewing operations because it allows limited friction between the sewing yarn and the sewing head.

[0015] The said heat-fusible portion has other advantageous effects, since it can easily be softened or melted even before molding, thus ensuring adhesion of the yarns and filaments with which it is in contact. In particular, this makes it possible to secure the said filaments and to limit the risks of fraying at the cutting regions. The said partial adhesion of the reinforcement at the sewing yarns can also be advantageous to ensure retaining the shape of the reinforcement when it is disposed in the mold, placed on a preform.

[0016] In practice, it is possible to produce the said sewing yarn in different ways. Pairing refers to when the filaments of two different types are assembled before going through a throwing operation to obtain yarns or strands firmly combining the two types of filaments. Twisting refers to when the groups of filaments each undergo throwing in order to obtain homogeneous strands, which are then assembled by twisting to form intertwined helices. Wrapping refers to when the two strands of different natures are assembled, one of which strands is rolled around the other, called the core yarn, generally substantially straight, around which the wrapper yarn forms a helix.

[0017] The final yarn count of the assembly of the said filaments should be compatible with the utilization of said assembly as sewing yarn. The final yarn count can advantageously be between 20 and 300 dtex.

[0018] In practice, the said sewing yarn can be used on different types of reinforcements. Thus, this reinforcement can be of the NCF type with a single layer in which there is no crimping of the yarns. Such a reinforcement, unidirectional, can be associated with a support layer formed by a fibrous material, the fibers whereof are not parallel to those of the reinforcement layer. The said support layer can be non-woven, such as lightweight web, or a set of parallel yarns disposed parallel and spaced apart from each other, to form a weave that is also light, enabling the sewing yarn to be held. It is also possible to achieve the cohesion of the layer of reinforcement yarns solely by the sewing yarn with sewing produced by a knitting stitch. Of course, the reinforcement can comprise a plurality of layers each formed by a set of high-tenacity yarns that are substantially parallel, and in which the orientations of the yarns of the two adjacent layers are distinct in order to form a multi-axial reinforcement. The characteristic sewing yarn then provides a joining of the different plies to each other, which is necessary for handling, and more generally for the mechanical strength of the reinforcement.

[0019] The said sewing yarn can also be used for fabrics in which the sets of yarns are woven together. In this case, while the weaving intrinsically ensures a certain mechanical cohesion of the reinforcement, the use of the characteristic sewing yarn reinforces said cohesion during the flow of resin, but in particular makes it possible to benefit from the reduction of risks of fraying, and especially the possibility of retaining shape after being placed on a preform.

[0020] In one particular embodiment of the invention, the sewing yarn comprises at least two distinct groups of filaments produced from a thermoplastic material, miscible in the impregnation resin, and having a melting temperature lower than the melting temperature of the said thermal plastic impregnation resin. Each group of filaments is wrapped around the group of filaments having a melting temperature greater than the melting temperature of the said thermoplastic impregnation resin, and two of the said groups of filaments are wrapped in opposite directions.

[0021] In other words, the sewing yarn comprises a core yarn that has a resistance to the temperature conditions observed during impregnation, which is covered by two (or more) yarns wrapped in opposite directions, in such a way that the outer wrapper yarn somewhat locks the inner wrapper yarn, which limits the risks of raveling of said inner yarn when the sewing yarn is subjected to mechanical stresses during the operations of sewing through the reinforcement.

[0022] Advantageously in practice, the distinct groups of filaments produced from a thermoplastic material, miscible in the impregnation resin, have different melting temperatures. In other words, a first exposure to heat enables the softening of the wrapper yarn of lower glass transition temperature, in order to secure the other wrapper yarn, and thus make the assembly more resistant to raveling during sewing.

[0023] Thermal activation can also occur after sewing to secure the yarns of the reinforcement and ensure resistance to fraying of the reinforcement. In that case, the yarn of lower melting temperature will preferably be positioned at the outside.

[0024] Complementarily, the thermal activation of the other wrapper yarn can enable the reinforcement to be secured when it is in three-dimensional form.

[0025] Depending on the applications, the sewing can take place either during the manufacture of the reinforcement by traditional sewing in the plane of the reinforcement, or after forming the reinforcement on a preform by three-dimensional sewing. The characteristic sewing yarn can be used alone, and on its own ensure improvement of retention of the reinforcement. The said retention can also be supplemented by the use of other traditional sewing yarns.

[0026] In general, the filaments of the temperature-resistant sewing yarn are made of a material that can be chosen from the group preferably comprising glass, but also aramid, carbon, basalt, quartz, liquid crystal polymers and cotton. The yarn count of the yarn is chosen in accordance with the applications. It can be very low to limit the impact of said yarn in the final composite, or higher if there is a greater need for mechanical strength.

[0027] Advantageously, the material of which the miscible filaments are composed can be chosen from the same chemical family as the impregnation resin. In particular therefore, it can involve a polyamide resin, used in order to be compatible with the polyamide 6 (PA6) or 6.6 (PA66) resin used for the impregnation of the reinforcements. It can also involve an acrylic resin used in order to be compatible with an impregnation resin of methyl methacrylate or acrylonitrile butadiene styrene (ABS). For impregnation applications using polyphenylene sulfide (PPS) type resin, preferably a yarn material of PPS resin will be chosen. For impregnation applications using polyaryletherketones (PAEK), preferably a yarn material of PAEK resin will be chosen, such as the polyetheretherketones (PEEK) or polyetherketoneketones (PEKK), and for example more particularly a PEKK resin the melting point of which will be lower than that of the PEEK impregnation resin.

[0028] The coating resin forming the heat-fusible portion of the sewing yarn advantageously has a sufficiently low softening point, typically at least 20 C. lower than the melting temperature of the injected polymer, to enable the reinforcement to be secured at low temperature and to be melted during the injection procedure. For amorphous materials that do not have a melting temperature per se, for the purposes of the present patent the melting temperature will be similar to the glass transition temperature, beyond which the mechanical properties of the material become greatly reduced.

[0029] A first exemplary embodiment of a reinforcement according to the invention is as follows. The reinforcement is produced from fabric composed of carbon fibers with a yarn count of 12 K, corresponding to a surface mass on the order of 300 g/m.sup.2, like the product marketed under the reference C-WEAVE 300T 12K HS by the Applicant. The said fabric receives a sewing yarn, sewn with a chain stitch or knitting stitch at a pitch of 4 mm. The sewing yarn has a core yarn that is a glass yarn with a yarn count of 5.5 tex. The said core yarn has a melting temperature of more than 800 C. It is covered with a first wrapper yarn of polyamide 66, of 44 dtex yarn count, at 200 turns/meter in the Z (or S) direction, which has a melting point on the order of 260 C., and which has undergone a texturizing treatment. The yarn receives a second identical wrapper yarn, wrapped in equal quantity, but in the S (or respectively Z) direction. Such a reinforcement is particularly suited for producing composite parts impregnated with a PA6 or PA66 resin. Production of plates by impregnation of the said fabrics with a PA66 resin at 300 C. shows the benefit of this sewing in terms of retention of the orientation of the fibers when placed under pressure at high temperature.

[0030] A second exemplary embodiment of a reinforcement according to the invention is as follows: The reinforcement is produced from NCF and is composed of two plies of carbon fibers oriented at +45 and 45, corresponding to a surface mass on the order of 150 g/m.sup.2, as marketed by the Applicant under the reference C-PLY BX150. The sewing yarn used is similar to the one in the preceding example, with a core formed by a glass yarn of 55 dtex. It is covered with a first wrapper yarn of polyamide 66, of 44 dtex, at 200 turns/meter in the Z (or S) direction, which has a melting point on the order of 260 C., and which has undergone a texturizing treatment. The yarn receives a second wrapper yarn of polyamide 11, of 44 dtex yarn count, at 200 turns/meter in the Z (or S) direction, which has a melting point on the order of 190 C., and which has undergone a texturizing treatment. The second yarn is wrapped with a number of turns equal to the first, but in the S (or respectively Z) direction, to produce a total yarn count of the sewing yarn on the order of 150 dtex. Such a reinforcement is particularly suited for producing composite parts impregnated with a PA6 or PA66 resin.

[0031] The reactivation of the sewn product at 210 C. enables the fibers to be locked and to give an anti-fraying property to the sewn reinforcement, so that during cutting of the reinforcement, the fibers are kept together. Preforming tests of the said reinforcement by stacking 3 plies and reactivation at 210 C. show that the characteristic sewing yarn allows the plies to be bonded together.

[0032] A third exemplary embodiment of a reinforcement according to the invention is as follows: The reinforcement is produced from NCF and is composed of two plies of carbon fibers at +45 and 45, corresponding to a surface mass on the order of 150 g/m.sup.2, as marketed by the Applicant under the reference C-PLY BX150. The sewing yarn used is of a similar structure to the one in the preceding example, with a core formed from a multi-filament glass yarn of 28 dtex. It is covered with a first wrapper yarn of monofilament polyetheretherketone (PEEK), of 50 dtex yarn count, at 200 turns/meter in the Z (or S) direction, which has a melting point on the order of 340 C. The yarn receives a second wrapper yarn of monofilament PEEK, of 50 dtex yarn count, which has a melting point on the order of 340 C. The said second yarn is wrapped with a number of turns equal to the first, but in the S (or respectively Z) direction, to produce a total yarn count of the sewing yarn on the order of 130 dtex. Such a reinforcement is particularly suited for producing composite parts impregnated with a PEEK resin.

[0033] A fourth exemplary embodiment of a reinforcement according to the invention is as follows: The reinforcement is produced from NCF and is composed of glass fiber at +45 and 45, corresponding to a surface mass on the order of 600 g/m.sup.2, as marketed by the Applicant under the reference G-PLY BX600. The sewing yarn used is formed of a core formed by a multifilament glass yarn of 55 dtex. It is twisted with a texturized multifilament PPS yarn of 78 dtex, at 200 turns/meter in the Z or S direction. The PPS yarn has a melting point on the order of 280 C. The total yarn count of the sewing yarn is on the order of 130 dtex. Such a reinforcement is particularly suited for producing composite parts impregnated with a PPS resin.

[0034] It is clear from the foregoing that the reinforcement according to the invention can be used in different particular ways, such as: [0035] semi-finished product for manufacturing organo sheets, formed by stacking multiple layers of the same reinforcement, multiple layers of thermoplastic films; [0036] semi-finished product in the manufacture of thermoplastic pre-impregnates. The impregnation resin is then deposited on or in the reinforcement by a powder or impregnation procedure; [0037] semi-finished product in the manufacture of pre-impregnates intended to be used for SMC type molding, [0038] semi-finished product in the manufacture of pre-impregnates or profiled finished products, obtained by pultrusion. The said sewn reinforcement is used in transverse reinforcement in addition to yarns at 0 provided conventionally by the pultrusion method. The pressures generated in the pultrusion die containing the high viscosity resin require retention of yarns in the transverse reinforcement in order to preserve the orientation of said yarns and therefore the transverse reinforcement of the profile or pre-impregnate, [0039] principal reinforcing weave in a resin injection or infusion method.

[0040] Such a reinforcement has good mechanical strength at high temperature due to sewing with a yarn having sufficient strength during heating, as well as improvement in fraying and retention on preform because of the ability of the thermoplastic yarns forming the sewing yarn to ensure a certain locking of the yarns comprising the reinforcement.