Composite profile with thermoplastic matrix and its manufacturing process

Abstract

According to a process for manufacturing composite profiles with a thermoplastic matrix: - a plurality of cords (30) are used, each having a core with reinforcing fibers embedded in a first thermoplastic matrix; - in an agglomeration step, the plurality of cords (30) are heated to melt the first thermoplastic material, then the cords (30) are agglomerated by passing them together through forming means (22) under tension to form the profile (3), the cords (30) having a cross-section whose perimeter-to-area ratio is less than 4 mm⁻¹. Profile thus manufactured. Figure for the abbreviation: Fig. 2

Description

Title of the invention: composite profile with thermoplastic matrix and its manufacturing method Technical field

[0001] The invention relates to a composite profile comprising continuous fibers and a thermoplastic matrix. It also relates to its manufacturing method. Prior art

[0002] It is known to produce profiles from composite material comprising continuous fibers coated in a matrix of synthetic material. The fibers are, for example, glass fibers, carbon fibers, synthetic material or plant fibers. Such profiles are known for being light and of good strength. The use of a thermoplastic matrix makes it possible to benefit from specific physical or chemical properties of thermoplastic materials, for example to subsequently transform the profiles by softening or melting the material and giving them a new shape. It also makes it easier to recycle objects constructed with these profiles.

[0003] One of the known methods for manufacturing such profiles is pultrusion, which consists of pulling a bundle of unidirectional fibers through a die making it possible to impregnate said fibers with a polymerizable resin and to polymerize the resin in the die to form a composite profile at the outlet of said die, consisting of the reinforcing fibers and a matrix incorporating the fibers. The resins used are mainly of the thermosetting type but can also be of the thermoplastic type. The bundle of fibers is typically a grouping of strands, each strand being composed of a multitude of fibers, for example glass fibers, placed side by side without intersecting. A strand is also called a "roving" in the case of glass or designated by the English term "roving".

[0004] In a particular case, the polymerization of precursors (monomers and oligomers) for obtaining thermoplastic polymers can take place in situ in the pultrusion tooling. The precursors used are then generally of low viscosity, which has the advantage of allowing the use of very high reinforcement rates while having excellent and very homogeneous impregnation of the fibers. The existing reactive systems for pultrusion are mainly based on polymerization mechanisms by ring opening of monomers / oligomers such as e-caprolactam for polyamide 6 (PA6), lauryl-lactam for polyamide 12 (PA12), cyclic oligomers of butylene terephthalate for poly(butylene terephthalate) (PBT) or radical polymerization as for poly(methyl methacrylate) (PMMA), from methyl methacrylate.

[0005] In the remainder of the document, the mixture of precursors which will form the polymer and the matrix after the reaction will be formally called resin.

[0006] The profile is formed in the pultrusion die which incorporates an impregnation zone followed by the polymerization zone which also acts as a calibration zone since it gives the desired shape to the profile, so that the profile comes out in its final shape, generally in the solid state, that is to say at a temperature below the melting point of the thermoplastic material which composes it. These tools are extremely expensive due to their dimensions. Indeed, the size of the tool is determined by the time required for polymerization and by the compromise between the length of the die and the tensile forces generated on the profile. Note that, even if the polymerization speed can be accelerated by the addition of dedicated components, it remains limited by the need to maintain a low viscosity, the time to transfer the resin mixture into the tool and to wet the fiber bundle.

[0007] Document WO 2011 / 156693 A2 shows a method for producing profiles comprising mainly two steps. In a first step, ribbons are produced from continuous fibers which are coated with molten thermoplastic material. These ribbons are then assembled in a stack and the assembly passes through a die while the thermoplastic material is melted again. This produces a profile with a rectangular section. The technique of coating fibers with molten thermoplastic material has never been convincing, because the material remains too viscous and can only impregnate a small section of fibers and with a low fiber density. Statement of the invention

[0008] The invention aims to provide a method for manufacturing thermoplastic matrix composite profiles offering simplicity of implementation, having good productivity and using inexpensive tooling. It also aims to provide thermoplastic matrix composite profiles having new properties.

[0009] With these objectives in view, the invention relates to a method for manufacturing composite profiles with a thermoplastic matrix according to which: - a plurality of cords are used comprising a core with reinforcing fibers taken in a first matrix made of a first thermoplastic material; - in an agglomeration step, the plurality of cords are heated to melt the first thermoplastic material, then the cords are agglomerated by passing them together through tensile shaping means to form the profile, characterized in that the cords have a section whose perimeter to area ratio is less than 4 mm1.

[0010] The perimeter to area ratio allows the shape and size of the cords to be characterized. With a value of 4 mm ', cords of rather massive section are selected, not very thin. For a cord of round section and diameter 1 mm, the value is 4 mm '. The criterion allows the selection of round cords with a diameter greater than 1 mm. For a cord of rectangular section of 6 x 0.6 mm, the ratio is 3.7. The selection of cords according to this criterion allows the desired sections to be obtained by limiting the constraints at the interfaces of the cords between them, and therefore by limiting the risks of fiber breakage or the creation of cracks trapping air. The limitation of constraints comes from the limitation of the number of cords, by using cords of substantial section, and by limiting the contact surface between them, with a compact shape. In the case of using a die for this process, it was found to be short and inexpensive.It generates reasonable pulling forces, which allows the use of simple pulling means. Other shaping means are also possible, for example, a combination of rollers. These means can perform the pulling function or be supplemented by dedicated pulling means that act on the profile downstream of its shaping. The beads can have various cross-sectional shapes, whether circular, elliptical, oblong, polygonal, rectangular, hexagonal or any other shape. In the case of amorphous or semi-crystalline materials, the melting temperature is understood to be a temperature above the glass transition temperature to obtain complete softening of the material. In the case of PMMA, for example, this temperature is 100 to 150K above the glass transition temperature.

[0011] According to one embodiment, the cords are produced by reactive pultrusion, the core comprising continuous fibers. The cords obtained by pultrusion are well suited for the production of elongated or continuous parts. Reactive pultrusion of thermoplastic material has the advantage of achieving excellent impregnation of the fibers by the resin before its transformation into thermoplastic material. It is thus possible to obtain cords with a high fiber density and a very good distribution of the first thermoplastic material in the fibers.

[0012] Reactive pultrusion produces the first thermoplastic material selected for example from a group comprising polyamide-6, polyamide-12, polymethyl methacrylate, polybutylene terephthalate and polyethylene terephthalate. Existing reactive systems for pultrusion are mainly based on ring-opening polymerization mechanisms of monomers / oligomers such as ε-caprolactam for polyamide 6 (PA6), lauryl-lactam for polyamide 12 (PA12), cyclic oligomers of butylene terephthalate for poly(butylene terephthalate) (PBT) or radical polymerization as for poly(methyl methacrylate) methyl methacrylate) (PMMA), from methyl methacrylate.

[0013] According to one embodiment, the profile has a final sectional area greater than the sum of the sectional areas of the beads entering the shaping means and a second thermoplastic material is added to obtain the final section of the composite part. The section of the part obtained is thus perfectly controlled, without loss of material and minimizing the risks of material defects in the part. The second complementary material is for example supplied by an extruder in the manner of coextrusion and also makes it possible to increase the pressure on the beads in order to better compact them and to coat the part with a surface layer, if necessary. This complementary material may be the same as that of the cores of the beads, or a separate material in order to provide specific surface properties, in particular resistance to aggressive environments and external appearance.During the material injection phase, the second thermoplastic material also compresses the plurality of beads. The additional material input is typically less than 5% of the total volume of the part, preferably less than 2%.

[0014] According to one embodiment, the composite part is a profiled part whose cross-sectional area is substantially equal to the sum of the cross-sectional areas of the beads entering the shaping means. It can be provided that the beads are assembled without adding material or reflux, by supplying the shaping means with just the quantity necessary and sufficient to obtain the profile.

[0015] According to one embodiment, the profile has a final section area less than the sum of the sections of the beads entering the shaping means, the shaping means comprising regulation means for regulating the pressure by allowing molten thermoplastic material to escape. In this case, the passage of the beads in the shaping means will create a reflux of molten material. Advantageously, the reflux of material is regulated in order to maintain a pressure which makes it possible to improve the compaction of the beads together. This method has the advantage of remaining simple in terms of tooling. The excess material is typically less than 2% of the section of the part.

[0016] According to a constructive arrangement, the shaping means comprise a drawing die in which the agglomeration step is carried out, the die comprising a compacting chamber followed by a calibrator making it possible to freeze the section of the profile. The material which melts is thus enclosed in the compacting chamber. The section of the compacting chamber reduces downstream in order to force the beads against each other. The calibrator makes it possible to give a precise section to the profile which is obtained, with for example cooling which makes it possible to obtain the hardening of the thermoplastic material.

[0017] According to an improvement, the die comprises a grid upstream of the compacting chamber, the grid making it possible to guide the cords towards the compacting chamber. The grid makes it possible to maintain a gap between the cords before compacting.

[0018] According to a particular arrangement, the second thermoplastic material is injected into the compacting chamber. The supply of the second thermoplastic material is carried out before the grouping of the cords so that this material is distributed between the cords and forms a second matrix. In the case of the presence of a grid, this makes it possible to retain the second thermoplastic material, preventing it from rising upstream. The second thermoplastic material is for example injected by an extruder. As in the case of supplying a second material by coextrusion, this additional material may be of the same nature as that of the cores of the cords, or a separate material.

[0019] According to one embodiment, the shaping means form the profile into a curve in order to produce a curved profile. In the case of agglomeration in a die, at least the sizer has a curve in the spinning direction, and the drawing means accompany the curvature of the profile.

[0020] The invention also relates to a composite profile, characterized in that it is obtained with a method as described above. Such profiles can incorporate cords with cores with optimized mechanical properties, in particular with a high fiber density, while being simple to manufacture.

[0021] According to advantageous characteristics, the average rate of fibers by volume is greater than 50%, preferably greater than 60%. This rate is for example calculated on a section, by calculating the ratio between the cumulative section of the fibers and that of the profile. A high rate of fibers allows significant mechanical resistance of the profile, in particular with high rigidity and resistance to breaking in bending or high traction.

[0022] According to advantageous characteristics, the continuous fibers of the core of the cords are chosen from a group comprising glass fibers, carbon fibers, vegetable fibers, metal fibers and aramid fibers.

[0023] The invention also relates to an element comprising a profile as defined above, on which at least one protrusion is added by molding over the profile. The element thus comprises a part of essentially elongated shape, such as a beam, on which the possibility of connection to an environment or of serving as a support for accessories is added. Molding over the part, or overmolding, consists of placing a part of the part in a mold and injecting molten thermoplastic material onto this part. The thermoplastic material then adheres to the part and forms the protrusion(s). Brief description of the figures

[0024] The invention will be better understood and other features and advantages will appear on reading the description which follows, the description making reference to the appended drawings among which:

[0025] - [Fig.l] is a schematic view of a cord manufacturing installation for the implementation of a method according to a first embodiment of the invention;

[0026] - [Fig.2] is a view of another part of the installation implementing the method according to the first embodiment of the invention;

[0027] - [Fig.3] is a sectional view of a first example of a profile produced with the installation of [Fig.2];

[0028] - [Fig.4] is a sectional view of a second profiled example produced with the installation of [Fig.2];

[0029] - [Fig.5] is a sectional view of an agglomeration line of the installation of the [Fig.2] ;

[0030] - [Fig.6] is a schematic view similar to [Fig.2] of a fa installation construction implementing a method according to a second embodiment of the invention;

[0031] - [Fig.7] is a view similar to [Fig.5] of a variant of the agglomeration die used on the installation of [Fig.6];

[0032] - [Fig.8] is a sectional view similar to [Fig.5] of a variant of the second embodiment;

[0033] - [Fig.9] is a schematic view similar to [Fig.2] of a fa installation brication implementing a method according to a third embodiment of the invention, for producing curved profiles. Detailed description

[0034] A method for manufacturing composite profiles with a thermoplastic matrix according to the invention is described in connection with an installation shown diagrammatically in Figures 1 and 2.

[0035] A first part of the installation comprises a spinning device 1 for manufacturing cords 30 in a spinning step, shown in [Fig.l], while a second part concerns an agglomeration device 2 for implementing an agglomeration step, shown in [Fig.2]. The spinning device 1 is in practice a pultrusion device 1 which successively comprises: a first bobbin support 10 for storing and unwinding bobbins of rovings 3010 of continuous fibers, a preheating unit 11 for the fibers 3010 which makes it possible to bring the glass fibers to a temperature close to the melting temperature of reactive monomers, i.e. approximately 80°C in the case of e-caprolactam. The fibers 3010 are heated by infrared ramps, not shown, under nitrogen flow. The pultrusion device 1 further comprises an impregnation unit 12 receiving from an injection unit 13 reactive monomers or pre-polymers which form, after polymerization, a first thermoplastic material. As illustrated, the components of the reactive system are metered separately and mixed just at the inlet of the impregnation unit 12, for example in a static mixer 14. The device then comprises a polymerization die 16 in which the bead 30 is maintained at temperature to allow the polymerization of the resin into the first thermoplastic material, so that the impregnated strands become a core forming the bead 30.The pultrusion device 1 further comprises a first pulling unit 17 which makes it possible to simultaneously advance the cord 30 hardened by cooling and to unwind the strands 3010 by the propagation of the movement through the pultrusion device 1.

[0036] The cords 30 thus produced are wound onto other reels 18 in order to accumulate a sufficient number of cords 30 for the agglomeration step.

[0037] [Fig. 2] shows the agglomeration device 2 comprising a second reel support 20 on which the reels 18 of cords 30 are placed to unwind the cords 30. A plurality of cords 30 is thus directed towards an oven 21 to heat the cords 30 to a temperature higher than the melting temperature of the first thermoplastic material. At the outlet of the oven 21, shaping means 22 assemble the plurality of cords 30 so that the cords come into contact with each other and fuse. In this example, the shaping means 22 are an agglomeration die which determines the section of the profile 3 at the outlet. The agglomeration die 22 is provided with cooling means in order to obtain the hardening of at least a part of the profile 3 thus formed.A second pulling unit 23 exerts traction on the hardened profile 3 and causes the cords 30 to unwind by the propagation of the movement through the agglomeration device 2.

[0038] In a variant not shown, the pultruded cords 30 could directly supply the agglomeration device without going through a winding step.

[0039] In a first example, cords 30 were manufactured by pultrusion with a first matrix formed by the first thermoplastic material, which is polyamide-6 obtained by the polymerization of e-caprolactam monomer, and as fibers glass fibers in a rate of approximately 84% by mass. The section of the cords 30 is circular and of diameter 3 mm. The perimeter to area ratio of the section is 1.33 mm1. The melting temperature of polyamide-6 is 220 °C. Such cords 30 could be produced at a speed of the order of 2 m / min on a pilot installation limited in size.

[0040] In the agglomeration device 2, 15 cords 30 were used by passing them through the oven 21 to raise the temperature of the cords 30 to 200°C, then to 250°C. in the die. At this latter temperature, the first thermoplastic material was melted. The plurality of cords 30 was grouped in the agglomeration die 22 to form a profile 3 of rectangular section, as shown in [Fig. 3]. The fiber content of the cords 30 by volume was 70%. Modular tooling made it possible to produce profiles with a section of 50 x 2.5 mm. Such profiles 3 could be produced at a speed of the order of 0.5 m / min.

[0041] In a second example, shown in [Fig.4], rectangular section beads were used to manufacture the profile 3'. The section of the beads 30' was 10 x 1 mm. The perimeter to area ratio of the section of the beads is 2.2 mm1.

[0042] In the sectional view of an agglomeration die 22 of [Fig. 5], there is successively, in order from upstream to downstream, a grid 223 provided to guide the cords 30 to the entrance of the die 22, a compacting chamber 224 to finish melting the thermoplastic material and agglomerate all of the cords 30, and finally a calibrator 225. The grid 223 has a hole for each of the cords 30 which enters the die 22 in order to control the relative arrangement of the cords 30 when they enter. The compacting chamber 224 is temperature-regulated so as to finish melting the thermoplastic material of the beads 30 with an injection of the material supplied by an extruder 221 just downstream of the grid 223. The compacting chamber 224 further comprises a regulating channel 2240 provided with a valve 2241 in order to evacuate the excess thermoplastic material by regulating a pressure of this material.Finally, the calibrator 225 determines the section of the final part and cools it in order to at least partially freeze this section.

[0043] According to a second embodiment, shown in [Fig.6], the shaping means 22' comprise an extruder 221 and an agglomeration die 222, a second thermoplastic material prepared by the extruder 221 being injected with the plurality of cords 30 into the agglomeration die 222.

[0044] The agglomeration die 222 for the embodiment of [Fig. 6] is shown in [Fig. 7]. It differs from the die shown in [Fig. 5] in that it no longer has a regulating channel, but a feed channel 2242 connected to the outlet of the extruder 221. The second thermoplastic material is supplied by the feed channel 2242 which opens just downstream of the grid 223, with a pressure just sufficient to bring the second thermoplastic material between the beads 30.

[0045] In a variant of the second embodiment, shown in [Fig. 8], the agglomeration die 222” differs from that of [Fig. 5] in that it no longer has a regulating channel and in that an injection chamber 2220 is located between the compacting chamber 224” and the calibrator 225”. In the injection chamber 2220, the extruder 221 injects the second thermoplastic material that is necessary for complete the section of the final part. The pressure supplied by the extruder 221 to the second thermoplastic material also makes it possible to complete the compaction of the beads 30 carried out in the compaction chamber 224”. In a variant, a third thermoplastic material is added by the extruder 221 in order to form a complete coating layer around the profile. The third thermoplastic material adds its own properties to the profile 3”, in particular its surface.

[0046] In a third embodiment, shown in [Fig.9], the installation differs from that of the first embodiment in that the die 22'” is curved in the drawing direction and the drawing means 23'” are adapted to draw a profile 3'” whose main direction is curved. It is possible that only the calibrator 225 is curved, but not the agglomeration die 222.

Claims

Claims

1. Method for manufacturing a composite profile with a thermoplastic matrix according to which: - a plurality of cords (30) are used comprising a core with reinforcing fibers taken in a first matrix made of a first thermoplastic material; - in an agglomeration step, the plurality of cords (30) are heated to melt the first thermoplastic material, then the cords (30) are agglomerated by passing them together through shaping means (22) by traction to form the profile (3), characterized in that the cords (30) have a section whose perimeter to area ratio is less than 4 mm1.

2. A method according to claim 1, wherein the cords (30) are produced in a reactive pultrusion step, the core comprising continuous fibers.

3. The method of claim 2, wherein the reactive pultrusion produces the first thermoplastic material selected from a group consisting of polyamide-6, polyamide-12, polymethyl methacrylate and polybutylene terephthalate.

4. Method according to one of the preceding claims, according to which the profile has a final section greater than the sum of the sections of the cords (30) entering the shaping means (22) and a second material is added to obtain the final section of the composite profile (3', 3”).

5. Method according to one of claims 1 to 3, according to which the composite profile has a final sectional area substantially equal to the sum of the sectional areas of the beads entering the shaping means.

6. Method according to one of claims 1 to 3, according to which the profile has a final section less than the sum of the section areas of the beads (30) entering the shaping means (22), the shaping means (22) comprising regulation means (2240, 2241) for regulating the pressure by allowing molten thermoplastic material to leak.

7. Method according to one of the preceding claims, according to which the shaping means comprise a die (22) by drawing in which the agglomeration step is carried out, the die (22) comprising a compacting chamber (224) followed by a calibrator (225) allowing the profile section to be fixed (3, 3', 3”).

8. A method according to claim 7, wherein the die comprises a grid (223) upstream of the compacting chamber, the grid (223) making it possible to guide the cords towards the compacting chamber (224).

9. A method according to claim 4 and, 7 or 8, taken in combination, wherein the second thermoplastic material is injected into the compacting chamber (224').

10. A method according to any preceding claim, wherein the shaping means (22”) form the curved profile to produce a curved profile (3”).

11. Composite profile, characterized in that it is obtained with a method according to claim 4 in combination with one of claims 1 to 3 and 7 to 10.

12. Profile according to claim 11, in which the average rate of fibers by volume is greater than 50%, preferably greater than 60%.

13. Profile according to one of claims 11 to 12, in which the reinforcing fibers of the core of the cords (30) are chosen from a group comprising glass fibers, carbon fibers, plant fibers, metal fibers and aramid fibers.

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