METHOD FOR PRODUCEING A WORKPIECE FROM COMPOSITE MATERIAL USING A THIN-WALLED MOLD

Description

FIELD OF INVENTION

[0001] The present invention relates to a method for manufacturing a part made of fiber-reinforced composite material by molding from a reactive composition, this method employing a thin-walled mold. The invention also relates to the thin-walled mold and its use for manufacturing composite material. TECHNICAL BACKGROUND

[0002] It is known to manufacture products from composite materials by molding. Resin transfer molding processes or " Resin Transfer Molding denoted RTM and the resin transfer molding processes with compression, denoted CRTM, also called ICM ( Injection Compression MoldingThese processes generally utilize a temperature-controlled press. Typically, this type of molding process is isothermal, particularly with thermosetting resins. However, for thermoplastic resins, an anisothermal process can be advantageous to facilitate fiber impregnation by reducing the viscosity of the reactive composition or polymer used to impregnate the fibers. In the case of a reactive process, an anisothermal cycle is also useful for accelerating polymerization kinetics by increasing the molding process temperature. The reinforcing fibers are then placed in the press mold. This mold is closed and then heated, if it has not already been preheated. The polymer, or the reactive composition based on the precursor(s) of this polymer, is injected in a molten state into the mold. The mold is then cooled.Then, the resulting part is removed from the mold. The press is equipped with a heating system, typically using electric heating elements or a hot fluid system, and a cooling system, typically using cold water or compressed air circuits. EP3357666A1 discloses a method and apparatus for manufacturing a part from polymer material.

[0003] It is possible to inject a composition of monomers or prepolymers. It can be advantageous to use a reactive composition based on one or more prepolymers of sufficient mass. Sufficient mass means that their mass reduces the polymerization time required to reach the final polymer mass or reduces the amount of polymerization byproducts, when the chain-elongation chemistry used releases polymerization byproducts. Prepolymers can be semi-crystalline, and when their molar mass is sufficiently high, their melting temperature is higher than the crystallization temperature of the final polymer. Prepolymers can also be amorphous, and when their molar mass is sufficiently high, their processing temperature is higher than the glass transition temperature of the final polymer.In these specific cases, thermal cycling will be necessary to cool the composite below the injection temperature of the polymer or reactive composition in order to demold it. For example, in the case of polyamides, polymerization can occur via polycondensation. The kinetics of this polymerization are relatively slow, and polymerization times approaching one minute are only observed at temperatures above 250°C.

[0004] Therefore, it is sometimes necessary to perform an anisothermal molding cycle to enable rapid polymerization, particularly above 250°C. at a minimumbeyond the melting temperature, denoted Tf, of the precursor(s) of the reactive mixture, when they are semi-crystalline and beyond their glass transition temperature denoted Tg when they are amorphous, then to cool the mold in order to be able to demold the part, to a temperature below the crystallization temperature denoted Tc for semi-crystalline polymers or Tg for amorphous polymers.

[0005] There is a real need to shorten the duration of these molding processes in order to increase production rates. Therefore, one of the goals is to shorten the mold heating and cooling phases. A molding cycle on the order of one minute is particularly desirable.

[0006] Furthermore, there is also a need to reduce the energy cost of this type of process.

[0007] This problem can be solved by increasing the number of heating circuits and cooling channels within the press. However, replacing older presses with newer, more sophisticated ones represents a significant cost. Furthermore, this solution does not address the high energy cost of this process.

[0008] Furthermore, it is important to obtain good quality molded parts, that is to say, parts with a homogeneous composition. SUMMARY OF THE INVENTION

[0009] This technical problem is solved by using a removable mold with thin walls. Claims 1, 11, 13, and 14 define the invention. The method for manufacturing a part from a composite material, said material comprising reinforcing fibers and a polymer matrix, the method comprising the following successive steps: installation in a die mounted on a press of a closed thin-walled mold in which reinforcing fibers have been arranged, closing of the press, injection in molten state into the closed thin-walled mold of a polymer or a reactive composition comprising at least one prepolymer, at least one monomer or a mixture thereof, keeping the press closed during all or part of the polymerization of the polymer matrix, when a reactive composition is used, opening of the press, removal of the thin-walled mold from the press, while maintaining a residual pressure of between 0.7 and 10 bar, preferably between 0.7 and 5 bar, in said mold, cooling of the mold under said residual pressure.

[0010] The process according to the invention has the advantage of reducing the energy cost of manufacturing. Since the cooling stage is carried out outside the press, the die mounted on the press can remain at a constant temperature. The press used according to the process of the invention is no longer subject to temperature fluctuations. Furthermore, the production cycle time, which corresponds to the time spent under the press, can be significantly reduced, since part of the polymerization and subsequent cooling takes place during masked time, outside the press. In addition, the parts produced by this process have a uniform composition, and in particular crystallinity, throughout the entire part.

[0011] The invention also relates to the thin-walled mold implemented in the process according to the invention and to its use for the manufacture of composite material. BRIEF DESCRIPTION OF THE FIGURES

[0012] There figure 1is a diagram of certain steps in the process according to the invention. figure 2 is a cross-sectional view of a thin-walled mold according to the invention. figure 3 is a perspective view of a molded part according to the examples. DESCRIPTION OF METHODS OF IMPLEMENTING THE INVENTION

[0013] Other features, aspects, objects and advantages of the present invention will become even clearer upon reading the description that follows.

[0014] It is further specified that the expressions "between... and..." and "from... to..." used in this description should be understood as including each of the mentioned limits.

[0015] The invention is now described in more detail and in a non-limiting manner in the following description.

[0016] The process according to the invention employs a thin-walled mold. For the purposes of this invention, a thin-walled mold is defined as a mold comprising two parts of complementary shapes. The wall thickness is such that the mold withstands a residual molding pressure exceeding the saturated vapor pressure of water at the injection temperature of the reactive composition. Steps in the process

[0017] The method according to the invention comprises a step of installing a thin-walled mold, in the closed position, into a die mounted on a press. Reinforcing fibers have been arranged in this mold. The press is then closed over the mold. The press is held in the closed position for a sufficient time to bring the mold to the temperature of the die mounted on the press. Generally, the time required to heat the mold is short, as the mold is designed so that contact with the die mounted on the press quickly imparts its temperature to the thin walls of the mold. The reactive composition or polymer is then injected into the mold. The press is held in the closed position to allow the polymer matrix to impregnate the reinforcing fibers.When using a reactive composition, all or part of the polymerization may also occur while the thin-walled mold remains under the press. In this case, the duration of this step depends on the reactive composition used. The press is then opened to release the mold. After removal from the press, the mold is allowed to cool before the demolding stage.

[0018] Each step of the process will be described in detail below. Laying of reinforcing fibers

[0019] Reinforcing fibers can either be placed in the thin-walled mold by a simple deposition action, or placed in the form of a preform.

[0020] According to a particular embodiment of the invention, the reinforcing fibers can be shaped into a preform. The reinforcing fibers are then mixed with an adhesion resin, also called a preform binder, and then molded, optionally by compression in a suitable mold or directly into the thin-walled mold according to the invention, to create a preform. The latter has the advantage of being easier to handle. This preform can then be easily placed in the thin-walled mold, if it is not already there.

[0021] Depending on the reinforcing fibers used and the nature of the polymer or reactive composition used for molding, the preforming step can be carried out at a temperature between 80°C and 320°C. The preform binder is chosen to withstand the applied injection temperature.

[0022] This optional preforming step can be performed on a circular device mounted on a rotating axis. Preferably, the rotation axis of the circular device is parallel to that of the press. The circular device can be positioned close to the press. For example, a carousel can be used.

[0023] According to a particular embodiment of the invention, a robotic arm can be used to place the preform in the thin-walled mold, when it has been made in another mold.

[0024] Throughout the molding process, from the installation of the mold in the press to demolding, the thin-walled mold is kept in a closed position.

[0025] This closed position maintenance can be achieved either by a vacuum pulling system or by a conventional mechanical closing system.

[0026] Preferably, the thin-walled mold is equipped with a vacuum drawing system, which exerts a residual pressure of between 0.7 and 10 bar, preferably between 0.7 and 5 bar. Advantageously, said residual pressure is from 0.7 to 0.9 bar.

[0027] Advantageously, when the residual pressure is 0.7 to 0.9 bar, polymerization is carried out by polyaddition or by radical polymerization or by nucleophilic substitution.

[0028] Advantageously, when the thin-walled mold includes a mechanical closing system, then said residual pressure is from 0.9 to 10 bars, preferably from 0.9 to 5 bars. Possible preliminary degassing step before installing the mold in the press

[0029] The process according to the invention may include a degassing step in the thin-walled mold, prior to the mold being installed in the press. This allows the thin-walled mold to remain closed during its transfer under the press. It also allows for the removal from the thin-walled mold of all or part of the air and / or any other substance whose presence could be detrimental to the manufacturing of the composite part. Indeed, degassing the fibers in the closed thin-walled mold before the start of the polymer or reactive composition injection reduces porosity caused by air bubbles.

[0030] According to a particular embodiment of the invention, the thin-walled mold is equipped with a degassing system, that is, a system for extracting gases present in the mold cavity, comprising at least one pump and one or more vents. When using a chemical polymerization system by polycondensation, the vacuum dispensing system is then closed to allow the injection of the polymer or reactive composition under conditions that limit polymerization. This is also the case when the polymer or reactive composition is sufficiently fluid at the injection temperature to risk entering and clogging the mold vents used for degassing.

[0031] Degassing can be carried out with a depression ranging from 0.010 to 0.950 bar, preferably from 0.700 to 0.900 bar, relative to atmospheric pressure. Installation of the thin-walled mold in the press

[0032] The process includes an installation step in the press-mounted die of a closed thin-walled mold, in which reinforcing fibers have been placed.

[0033] According to another particular embodiment of the invention, a robotic arm can be used to position the thin-walled mold in the die of the molding press. A combination of a carousel and a robotic arm is also possible. Press closure

[0034] Next, once the thin-walled mold is placed in the press die, the press is closed. The press is held closed for a sufficient time to allow the press die to transfer its temperature to the mold walls. The thickness of the thin mold walls is such that the thermal conductivity between the press die and the mold walls is high. Possible preliminary degassing step after the mold is installed in the press

[0035] The process according to the invention may include a degassing step in the thin-walled mold, prior to the injection step. This degassing allows for the removal of all or part of the air and / or any other substance from the thin-walled mold, the presence of which could be detrimental to the manufacture of the composite part. Indeed, degassing the fibers in the closed thin-walled mold, performed before the start of the polymer or reactive composition injection, reduces porosity caused by air bubbles. The thin-walled mold is preferably equipped with a vacuum dispensing system for this degassing. After degassing the mold, the vacuum dispensing system is closed to allow the injection of the polymer or reactive composition. Injection of the polymer or reactive composition

[0036] Next, the process according to the invention includes a step of injecting a polymer or a reactive composition comprising at least one prepolymer, at least one monomer, or mixtures thereof, in a molten state into a closed, thin-walled mold. Advantageously, the injection step lasts less than 15 seconds. Preferably, the duration of this step ranges from 1 to 10 seconds. When using a reactive composition, a short injection time limits the simultaneous or subsequent polymerization of the reactive composition during this step, thereby improving fiber impregnation.

[0037] In a particular embodiment corresponding to RTM, the injection of the polymer or reactive composition into the closed mold and the impregnation of the reinforcing fibers are simultaneous. In this embodiment, after any initial degassing, the injection and impregnation are carried out without further degassing, i.e., no vacuum is applied to the vents of the degassing system.

[0038] According to another embodiment corresponding to CRTM, the injection of the polymer or reactive composition is carried out in a closed mold having an open compression chamber, preferably without degassing during injection, after any initial degassing. The impregnation of the reinforcing fibers by the reactive composition then occurs primarily during compression induced by the closure of the compression chamber, without degassing during said compression, at a pressure applied to the mold preferably of 10 to 70 bar, and even more preferably of 40 to 60 bar. This pressure improves the impregnation of the fibers by the reactive composition.

[0039] According to a particular embodiment using a reactive composition, the temperature applied in the mold during the polymerization step is higher than the melting temperature Tf of the prepolymers, preferably higher by at least 5°C.

[0040] According to another embodiment using a reactive composition, the polymerization temperature is higher than the melting temperature of the prepolymer having the highest melting temperature, preferably higher by at least 5°C.

[0041] Preferably, the press matrix is ​​maintained at a constant temperature between 200 and 350°C, in particular between 230 and 320°C, and more particularly between 250 and 320°C. Mold closure maintenance step

[0042] Depending on the reactive composition used, the duration of this press closure step will depend on the conversion rate of prepolymers to polymers, or of monomers to prepolymers and then to polymers. Preferably, the duration of this step corresponds to the time required to double the molecular weight of the prepolymers.

[0043] Depending on the reactive composition used, it is possible to initiate polymerization during injection in the case of RTM or during compression injection in the case of CRTM, and then continue during cooling. This method reduces press time and thus significantly increases the production rate of parts without substantially increasing costs.

[0044] During the holding stage, degassing can be applied, preferably with a holding pressure below 5 bar. This degassing can be achieved by applying a vacuum ranging from 0.010 to 0.950 bar, preferably from 0.700 to 0.900 bar, relative to atmospheric pressure. The system vents located on the mold have a sufficiently small diameter and the reactive composition is sufficiently viscous to create a pressure drop at the vents, preventing the reactive composition from passing through the vents and escaping from the mold. Removing the mold from the press

[0045] The press is then opened. The thin-walled mold is then removed from the press. During these two steps, the thin-walled mold is held in the closed position by a vacuum of 0.700 to 0.900 bar. Step of maintaining the mold closure outside the press and cooling

[0046] The process then includes a step of holding the mold closed outside the press to potentially complete the polymerization of the polymer matrix from the reactive composition. This pressure is also called " holding pressure Advantageously, this pressure is lower than the pressure applied during the impregnation step. Particularly preferred, this pressure is higher than the saturated vapor pressure of water in the case of polycondensation. By the saturated vapor pressure of waterThe saturated vapor pressure of dissolved water in the composite matrix, obtained after polymerization of the reactive composition, is understood to be the saturated vapor pressure of the water at the temperature at which this polymerization occurred. Applying a holding pressure higher than the saturated vapor pressure of water prevents the water formed as a by-product during polymerization from forming bubbles, which would degrade the quality of the composite material. Preferably, the pressure applied during the holding stage is 3 to 7 bar, and even more preferably 4 to 6 bar.

[0047] In one particular embodiment, degassing is applied for substantially the entire duration of the mold closure holding step, i.e., when the mold is not under pressure. However, the pressure applied during the polymerization step must be sufficiently low to prevent the reactive composition from passing through the vents during degassing.

[0048] The duration of the mold closure step outside the press depends on the polymerization kinetics of the reactive composition. This duration is preferably less than 15 minutes, preferably less than 10 minutes, and most preferably less than 5 minutes. Cooling

[0049] The thin-walled mold is left to cool by thermal conduction with the surrounding air through its thin walls, by thermal conduction with a cold environment, within a cold room, or in a cold former, the surrounding temperature being able to go down to a temperature lower than the crystallization temperature (Tc) of the polymer formed.

[0050] According to another embodiment, the cooling consists of placing the thin-walled mold in a former, called cold, regulated at a temperature less than or equal to the crystallization temperature Tc of the polymer formed under a residual pressure of between 0.7 and 10 bars, preferably between 0.7 and 5 bars.

[0051] Advantageously, the cooling step is carried out with a cold former. Demolding

[0052] The composite material part is then removed from its thin-walled mold. Installation and Removal

[0053] According to a preferred embodiment of the invention, the steps of placing and removing the thin-walled mold, before and / or after the injection of the polymer or reactive composition, can be carried out using robotic arms. Indeed, since the process according to the invention makes it possible to maintain the press matrix at a relatively high, constant temperature, the use of robotic arms avoids any risk to the operators handling these machines.

[0054] As with the steps prior to placing the mold in the press, it is possible to use a circular device arranged on a rotation axis allowing the transfer of the molds from the press to, for example, the cold former for the cooling step.

[0055] According to a particular embodiment of the invention, it is possible to envisage a single circular device, on which would be arranged the molds comprising only the reinforcing fibers (before molding) and the molds comprising the composite material to be cooled (after molding). Polymer matrix

[0056] The composite material comprises reinforcing fibers and a polymer matrix.

[0057] According to one embodiment, the polymer matrix can be chosen from: Polymers and copolymers of the aliphatic, cycloaliphatic, or semi-aromatic polyamide (PA) family (also known as polyphthalamides (PPA)), polyureas, particularly aromatic polyureas, polymers and copolymers of the acrylic family such as polyacrylates, and more specifically polymethyl methacrylate (PMMA) or its derivatives, polymers and copolymers of the polyarylether ketone (PAEK) family such as poly(ether ether ketone) (PEEK), or polyarylether ketone ketones (PAEKK) such as poly(ether ketone) (PEKK) or their derivatives, aromatic polyetherimides (PEI), polyarylsulfides, particularly polyphenylene sulfides (PPS), polyarylsulfones, particularly polyphenylene sulfones (PPSU), polyolefins, particularly polypropylene (PP);polylactic acid (PLA), polyvinyl alcohol (PVA), fluorinated polymers, in particular poly(vinylidene fluoride) (PVDF), or polytetrafluoroethylene (PTFE) or polychlorotrifluoroethylene (PCTFE); and their mixtures.

[0058] Preferably, the polymer matrix is ​​chosen from polyamide, polyester, polyamide-imide, polyamide-ether, polyacrylic, polyolefins, polyphenylene sulfide, polyether-imide matrices.

[0059] According to an advantageous embodiment, the polymer matrix is ​​a polyamide matrix.

[0060] According to one embodiment, the polymer matrix is ​​a thermoplastic matrix.

[0061] According to a particular embodiment, the polymer matrix is ​​a semi-crystalline polymer. A semi-crystalline polymer gives the composite material, compared to amorphous polymers, significantly improved mechanical performance, particularly at high temperatures, such as resistance to creep or fatigue.

[0062] Advantageously, the polymer matrix has a glass transition temperature (Tg) of at least 80°C, preferably at least 90°C, more preferably at least 100°C, and even more preferably at least 120°C. A glass transition temperature of 80°C or higher ensures good mechanical properties of the composite over the entire temperature range of use, for example, up to 90°C for wind turbines, up to 100°C for automotive applications, and up to 120°C for aerospace applications.

[0063] In an even more advantageous embodiment, the polymer matrix is ​​semi-crystalline and has a melting temperature (Tf) above 200°C, preferably above 220°C. A melting temperature above 200°C ensures compatibility with cataphoresis treatments, particularly in the automotive industry. Preferably, the melting temperature (Tf) is less than or equal to 320°C, and even more preferably less than 290°C. A melting temperature above 320°C necessitates processing the composite material at higher temperatures, which imposes constraints on molding equipment and the associated heating system, and leads to increased energy consumption. Processing at such high temperatures increases the risk of thermal degradation of the polymer, resulting in the degradation of the properties of the final matrix and therefore of the composite material and the final composite part.

[0064] According to one embodiment, the polymer matrix has a crystallization temperature Tc such that the difference between the melting temperature Tf of the matrix and the crystallization temperature Tc, Tf-Tc, does not exceed 60°C, preferably does not exceed 50°C and more particularly does not exceed 40°C.

[0065] According to one variant, the enthalpy of crystallization of the polymer matrix is ​​between 10 and 55 J / g.

[0066] According to a particular variant, the enthalpy of crystallization of the polymer matrix is ​​between 40 J / g and 55 J / g, preferably between 20 and 35 J / g.

[0067] The mechanical performance or high-temperature resistance of the composite material can be evaluated by the variation of the bending stress at break in the direction of the fibers (or in English, "maximum strength at 0°" between ambient temperature (23°C) and 100°C, good mechanical performance at high temperatures corresponds to maintaining at least 75% of the mechanical performance, in terms of breaking stress, compared to that at ambient temperature (23°C).

[0068] According to one embodiment of the invention, the polymer matrix is ​​prepared by bulk polymerization of the reactive composition comprising at least one prepolymer, at least one monomer or a mixture thereof, in the molten state.

[0069] Advantageously, the polymer matrix has a number-average molar mass greater than 10000 g / mol, preferably ranging from 10000 to 40000 g / mol, even more preferably from 12000 to 30000 g / mol.

[0070] According to one embodiment, the polymer matrix is ​​a polyamide matrix comprising units derived from the following monomers: diterephthalic acid, isophthalic diacid, adipic acid, sebacic acid, dodecanoic acid, 1,10-decamethylene diamine, 1,6-hexamethylene diamine, 2-methyl pentamethylene diamine (MPMD), a mixture of 2,2,4 and 2,4,4-trimethylhexanediamine (TMD), 2-methyloctanediamine (8M), nonanediamine, 4,4'-diaminodicyclohexylmethane (PACM), m-xylylene diamine (MXD), 1,3-bis(aminomethyl)cyclohexyl (1,3 BAC), 1,4-bis(aminomethyl)cyclohexyl (1,4 BAC), caprolactam, 1,1-aminoundecanoic acid, 12-amino lauric acid and / or lauryl lactam.

[0071] According to an advantageous embodiment, the polymer matrix is ​​a polyamide matrix selected from PA 11 / 10T, PA5T / 10T, PA 11 / 5T / 10T, PA 6T / 10T, PA 11 / 6T / 10T, PA MPMDT / 10T, PA MDXT / 10T, PA BACT / 10T, PA 11 / BACT, PA 11 / BACT / 10T, PA 6 / 6T, PA 66 / 6T, PA 6I / 6T, PA MPMDT / 6T, PA 6T / 10T, PA 8MT / 9T, PA TMDT / 10T, PA PACM12, PA BACT / 6T, PA 11 / BACT / 6T, PA BACT / 10T / 6T, PA MXD6 and PA MXD10, BAC being advantageously the 1.3 BAC. Reactive composition

[0072] The reactive composition comprises one or more monomers capable of reacting with itself or with each other, or one or more prepolymers capable of reacting with each other during the polymerization step, to provide the matrix described above.

[0073] In an advantageous embodiment, the prepolymer(s) are polyamide prepolymers.

[0074] Each prepolymer is itself a polymer (homopolymer or copolymer), having a number-average molar mass lower than that of the matrix. In one embodiment, the prepolymer(s) included in the reactive composition have a number-average molar mass ranging from 500 to 10,000 g / mol, preferably from 750 to 6,000 g / mol, more preferably from 750 to 3,000 g / mol.

[0075] According to one embodiment, when at least two prepolymers are used, they have substantially the same number-average molar mass. By " approximately the same average molar mass in number "We understand that the difference between the two masses is less than 30%.

[0076] According to a first embodiment, the composition comprises at least one first polyamide prepolymer A1 bearing two amine groups and at least one second polyamide prepolymer A2 bearing two carboxy groups coreactive with the amine groups of the first polyamide prepolymer. The backbones of the prepolymers A1 and A2 may be of the same nature (i.e., have the same composition in repeating units) or of different natures. Preferably, they are of the same nature.

[0077] According to a second embodiment, the composition comprises at least one polyamide A3 prepolymer bearing a coreactive amine and carboxy group. In this embodiment, the composition may comprise a single polyamide prepolymer bearing a coreactive amine and carboxy group, or several different prepolymers, each bearing an amine and a carboxy group. In the latter case, the backbones of the different A3 prepolymers may be of the same nature (the different A3 prepolymers then being distinguished only by a number average molar mass), or of different natures.

[0078] According to a third embodiment, the composition comprises at least one prepolymer A1 bearing two amine functions (as described above) and at least one polyamide prepolymer A2 bearing two carboxy functions (as described above).

[0079] According to a fourth embodiment, the composition comprises at least one prepolymer A1 bearing two amine functions (as described above) or at least one polyamide prepolymer A2 bearing two carboxy functions (as described above) and at least one chain extender of formula Y-A'-Y, wherein: Y is a group bearing a reactive function by polyaddition or polycondensation with at least one function of said prepolymer A1 and / or A2; A' is a hydrocarbon biradical.

[0080] When the prepolymer carries two NH2 functions (amine functions): either the chain extender Y-A'-Y is such that --Y is chosen from the groups: maleimide, possibly blocked isocyanate, oxazinone and oxazolinone, preferably oxazinone and oxazolinone and --A' is a carbon spacer or carbon radical chosen from: ----a covalent bond between two functions (groups) Y in the case where Y is an oxazinone or oxazolinone group, or ----an aliphatic hydrocarbon chain or an aromatic and / or cycloaliphatic hydrocarbon chain, the latter two comprising at least one ring of 5 or 6 carbon atoms possibly substituted, with possibly said aliphatic hydrocarbon chain having a molecular weight of 14 to 200 g.mol -1; either the chain extender Y-A'-Y is such that Y is a caprolactam group and A' can be a carbonyl radical such as carbonyl biscaprolactam or A' can be a terephthaloyl or an isophthaloyl, or diepoxides selected from aliphatic diepoxides,cycloaliphatic or aromatic, possibly substituted. Examples of aliphatic diepoxides include diglycidyl ethers of aliphatic diols; aromatic diepoxides include diglycidyl ethers of bisphenol A such as diglycidyl ether of bisphenol A (DGEBA); and cycloaliphatic diepoxides include diglycidyl ethers of cycloaliphatic diols or hydrogenated bisphenol A. More generally, suitable examples of diepoxides according to the invention include bisphenol A diglycidyl ether (DGEBA) and its hydrogenated (cycloaliphatic) derivative, bisphenol F diglycidyl ether, tetrabromo bisphenol A diglycidyl ether or hydroquinone diglycidyl ether, ethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, butylene glycol diglycidyl ether, neopentyl glycol diglycidyl ether, 1,4-butanediol diglycidyl ether, 1,6-hexanediol diglycidyl ether, cyclohexanedimethanol diglycidyl ether, polyethylene glycol diglycidyl ether of Mn < 500,polypropylene glycol diglycidyl ether of Mn < 500, polytetramethylene glycol diglycidyl ether of Mn < 500, resorcinol diglycidyl ether, neopentylglycol diglycidyl ether, bisphenol A polyethylene glycol diglycidyl ether of Mn < 500, bisphenol A polypropylene glycol diglycidyl ether of Mn < 500, diglycidyl esters of dicarboxylic acid such as glycidyl ester of terephthalic acid or epoxidized diolefins (dienes) or epoxidized ethylenic double unsaturated fatty acids, diglycidyl 1,2 cyclohexane dicarboxylate and mixtures of the aforementioned diepoxides. said chain extender Y-A'-Y bears a cyclic anhydride group Y and preferably this extender is chosen from a cycloaliphatic and / or aromatic carboxylic dianhydride and more preferably it is chosen from: ethylenetetracarboxylic dianhydride, pyromellitic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 1,4,5,8-naphthalenetetracarboxylic dianhydride,perylenetetracarboxylic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, 1,2,3,4-cyclobutanetetracarboxylic dianhydride, bisphthalic hexafluoroisopropylidene dianhydride, 9,9-bis(trifluoromethyl)xanthenetetracarboxylic dianhydride, 3,3',4,4'-diphenylsulfonetetracarboxylic dianhydride, bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride, 1,2,3,4-cyclopentanetetracarboxylic dianhydride, 3,3',4,4'-diphenyl ether tetracarboxylic dianhydride, or mixtures thereof, A' being a carbon spacer (radical) as defined above.

[0081] When the prepolymer carries two COOH groups (carboxy groups), the chain extender Y-A'-Y is such that: -Y is chosen from among the following groups: oxazoline, oxazine, imidazoline, or aziridine, such as 1,1'-iso- or tere-phthaloyl-bis(2-methyl aziridine), or diepoxides chosen from aliphatic, cycloaliphatic, or aromatic diepoxides, possibly substituted. Examples of aliphatic diepoxides include diglycidyl ethers of aliphatic diols; aromatic diepoxides include diglycidyl ethers of bisphenol A, such as diglycidyl ether of bisphenol A (DGEBA); and cycloaliphatic diepoxides include diglycidyl ethers of cycloaliphatic diols or hydrogenated bisphenol A. More generally, suitable examples of diepoxides according to the invention include bisphenol A diglycidyl ether (DGEBA) and its hydrogenated (cycloaliphatic) derivative, bisphenol F diglycidyl ether, tetrabromo bisphenol A diglycidyl ether, hydroquinone diglycidyl ether, ethylene glycol diglycidyl ether, propylene glycol diglycidyl ether,butylene glycol diglycidyl ether, neopentyl glycol diglycidyl ether, 1,4-butanediol diglycidyl ether, 1,6-hexanediol diglycidyl ether, cyclohexanedimethanol diglycidyl ether, polyethylene glycol diglycidyl ether of Mn < 500, polypropylene glycol diglycidyl ether of Mn < 500, polytetramethylene glycol diglycidyl ether of Mn < 500, resorcinol diglycidyl ether, neopentyl glycol diglycidyl ether, bisphenol A polyethylene glycol diglycidyl ether of Mn < 500, bisphenol A polypropylene glycol diglycidyl ether of Mn < 500, diglycidyl esters of dicarboxylic acids such as glycidyl terephthalic acid ester or epoxidized diolefins (dienes) or fatty acids with ethylenic double unsaturation epoxide, diglycidyl 1,2-cyclohexane dicarboxylate, and mixtures of the aforementioned diepoxides. -A' is a carbon spacer (radical) as defined above.

[0082] In all the above statements, A' can in particular represent an alkylene biradical such as -(CH2)m- with m ranging from 1 to 14 and preferably from 2 to 10 or a substituted or unsubstituted cycloalkylene and / or arylene biradical, such as benzene arylenes, such as o-, m-, p- phenylenes or naphthalene arylenes.

[0083] According to one embodiment, the reactive composition is prepared by mixing at least two prepolymers.

[0084] Preferably, the process includes a preliminary step of heating the prepolymer(s) to a temperature above the melting point of the prepolymer(s). Preferably, the heating temperature applied is from 200 to 350°C, in particular from 230 to 320°C, and more particularly from 250 to 320°C.

[0085] Preferably, at least two prepolymers are used, in which case the process includes a step of mixing the prepolymers in the molten state, for example by means of a static mixer, a dynamic mixer, or a RIM-type mixer (in English, " Reactive Injection Molding ") to form the composition intended to be injected into the mold.

[0086] Prepolymers (particularly polyamides) can be prepared in a manner known to those skilled in the art by polymerization from their respective monomers. The polymerization can be stopped when the desired molar mass is reached, for example, by controlling the water pressure (advance of reaction) and / or the amounts of monomers. Prepolymers A1 and A2 bearing two amine or two extreme carboxy groups can, for example, be obtained using an excess of diamine monomer and an excess of diacid monomer, respectively.

[0087] The manufacture of such reactive prepolymers is described for example in document WO 2014 / 064375.

[0088] Preferably, the prepolymers contained in the reactive composition and the polymer matrix obtained by polymerization of said reactive composition have the same composition in units derived from monomers a), b) and optionally c).

[0089] According to a particular embodiment, prepolymers A1 and / or A2 or prepolymer A3 comprise units derived from the monomers: a) terephthalic acid, b1) 1,10-decamethylene diamine and b2) MPMD or MXD.

[0090] According to another particular embodiment, the prepolymers A1 and / or A2 or the prepolymer A3 comprise units derived from the monomers: a) terephthalic acid, b1) 1,10-decamethylene diamine and b2) 1,3-bis (aminomethyl) cyclohexyl (1,3 BAC), 1,4-bis (aminomethyl) cyclohexyl (1,4 BAC) or a mixture thereof, in particular 1,3-bis (aminomethyl) cyclohexyl (1,3 BAC).

[0091] According to another particular embodiment, the prepolymers A1 and / or A2 or the prepolymer A3 comprise units derived from monomer c), the latter being selected from amino-11 undecanoic acid, amino-12 lauric acid and lauryl lactam.

[0092] According to a more particular embodiment, the prepolymers A1 and / or A2 or the prepolymer A3 comprise units derived from the monomers: a) terephthalic acid, b1) 1,10-decamethylene diamine, b2) 1,6-hexamethylene diamine or MPMD or MXD or 1,3 BAC or 1,4 BAC and c) amino-11 undecanoic acid or amino-12 lauric acid or lauryl lactam.

[0093] According to a further particular embodiment, the prepolymers A1 and / or A2 or the prepolymer A3 comprise units derived from the monomers: a) terephthalic acid, b1) 1,10-decamethylene diamine, b2) 1,6-hexamethylene diamine or MPMD or MXD or 1,3 BAC or 1,4 BAC and c) amino-11 undecanoic acid.

[0094] According to a further particular embodiment, the prepolymers A1 and / or A2 or the prepolymer A3 comprise units derived from the monomers: a) terephthalic acid, b1) 1,6-hexamethylene diamine, b2) MPMD or MXD or 1,3 BAC or 1,4 BAC and c) amino-11 undecanoic acid.

[0095] According to a further particular embodiment, the prepolymers A1 and / or A2 or the prepolymer A3 comprise units derived from the monomers: a) terephthalic acid, b1) 1,10-decamethylene diamine, b2) 1,6-hexamethylene diamine and c) amino-11 undecanoic acid.

[0096] According to another particular embodiment, the prepolymers A1 and / or A2 or the prepolymer A3 comprise units derived from the monomers: a) terephthalic acid, b1) 1,10-decamethylene diamine, b2) 1,6-hexamethylene diamine and c) lauryl lactam.

[0097] According to a further particular embodiment, prepolymers A1 and / or A2 or prepolymer A3 comprise units derived from the monomers: a) terephthalic acid, b1) 1,6-hexamethylene diamine, b2) MPMD or MXD or 1,3 BAC or 1,4 BAC and c) lauryl lactam.

[0098] The reactive composition may also include monomers, said monomers being precursors of the aforementioned prepolymers.

[0099] The reactive composition may include at least one carbon-based nanofiller. Preferably, the nanofiller is chosen from: carbon black, graphene, carbon nanofibrils, and carbon nanotubes.

[0100] The reactive composition may include one or more other additives.

[0101] Additives can be those that absorb UV, infrared (IR), microwave, or induction radiation. Such additives can be used to heat the composite material, preform, or part made of composite material, prior to, for example, a further processing operation, particularly heat stamping or overmolding.

[0102] Additives can also be a specific additive such as thermal stabilizers, in particular these stabilizers are antioxidants against thermo-oxidation and / or photo-oxidation of the thermoplastic matrix polymer and are organic or mineral stabilizers.

[0103] The expression " organic stabilizer or more generally a combination of organic stabilizers" refers to a primary antioxidant of the phenol type, a secondary antioxidant of the phosphite type, for example liquid phosphites such as doverphos®, and possibly other stabilizers such as a HALS (Hindered Amine Light Stabilizer) (for example, Tinuvin 770 from Ciba), a UV blocker (for example, Tinuvin 312 from Ciba), a phenolic or phosphorus-based stabilizer. Amine-type antioxidants such as Naugard 445 from Crompton or polyfunctional stabilizers such as Nylostab S-EED from Clariant can also be used.

[0104] The organic stabilizer present may be chosen from, but not limited to, the following: -Phenolic antioxidants, for example Irganox 245, Irganox 1010, Irganox 1098 from Ciba, Irganox MD1024 from Ciba, Lowinox 44B25 from Great Lakes, ADK Stab AO-80 from Adeka Palmarole, -Phosphorus-based stabilizers, such as phosphites, for example Irgafos 168 from Ciba, -A UV absorber, such as Tinuvin 312 from Ciba, or Titanium Dioxide (TiO2), -A HALS, as previously mentioned, -An amine-type stabilizer, such as Naugard 445 from Crompton, or a hindered amine-type stabilizer such as Tinuvin 770 from Ciba, -A multifunctional stabilizer such as Nylostab S-EED from Clariant.

[0105] It is obviously possible to consider a mixture of two, or more, of these organic stabilizers.

[0106] The expression " mineral stabilizer"Refers to a stabilizer based on copper or a metal oxide as described in US patent 2008 / 0146717. Examples of such mineral stabilizers include copper halides and acetates, or iron oxides such as FeO, Fe₂O₃, Fe₃O₄, or mixtures thereof. Other metals such as silver could also be considered, but these are known to be less effective."

[0107] These mineral stabilizers are used particularly when structures need to have improved long-term thermal resistance in hot air, especially at temperatures of 100°C or higher, or even 120°C or higher, because they tend to prevent polymer chain breakage.

[0108] More specifically, by " copper-based stabilizer", we mean a compound comprising at least one copper atom, especially in ionic form, or ionizable, for example in the form of a complex.

[0109] The copper-based stabilizer can be chosen from cuprous chloride, cupric chloride, cuprous bromide, cupric bromide, cuprous iodide, cupric iodide, cuprous acetate, and cupric acetate. Halides and acetates of other metals, such as silver, can also be used in combination with the copper-based stabilizer. These copper-based compounds are typically associated with halides of alkali metals, particularly potassium. A well-known example is the mixture of copper and potassium iodide (Cul:Kl), where the Cul:Kl ratio is typically between 1:5 and 1:15. Polyad P201 from Ciba is an example of such a stabilizer.

[0110] Further details on copper-based stabilizers can be found in US document 2,705,227. More recently, copper-based stabilizers such as complexed coppers like Bruggolen H3336, H3337, H3373 from the Brüggemann company have appeared.

[0111] Advantageously, the copper-based stabilizer is selected from copper halides, copper acetate, copper halides or copper acetate in mixture with at least one alkali metal halide, and mixtures thereof, preferably mixtures of copper iodide and potassium iodide (Cul / KI).

[0112] The additive may also be a shock modifier, advantageously consisting of a polymer having a flexural modulus of less than 100 MPa measured according to ISO 178 and a glass transition temperature Tg of less than 0°C (measured according to standard 11357-2:2013 at the inflection point of the DSC thermogram), in particular a polyolefin, coupled or not with a Peba (polyether block amide) having a flexural modulus < 200 MPa.

[0113] The shock modifier polyolefin may be functionalized or non-functionalized or be a mixture of at least one functionalized polyolefin and / or at least one non-functionalized polyolefin.

[0114] Additives may also include halogen-free flame retardants, as described in US patent 2008 / 0274355, and specifically a metallic salt selected from a metallic salt of phosphinic acid and a metallic salt of diphosphinic acid, a polymer containing at least one metallic salt of phosphinic acid, a polymer containing at least one metallic salt of diphosphinic acid or red phosphorus, antimony oxide, zinc oxide, iron oxide, magnesium oxide, or metallic borates such as zinc borate, or melamine pyrophosphates and melamine cyanurates. They may also include halogenated flame retardants such as brominated or polybrominated polystyrene, brominated polycarbonate, or brominated phenol.

[0115] Advantageously, the additive is chosen from an antioxidant, a heat stabilizer, a UV absorber, a light stabilizer, a shock modifier, a lubricant, an inorganic filler, a flame retardant, a nucleating agent, including a mineral filler such as talc, and a colorant.

[0116] Nanofillers and additives can be added to the polymer(s) or prepolymer(s) in the molten state to form the polymer or reactive composition before injecting it into the mold. Reinforcing fibers

[0117] The reinforcing fibers used in the process according to the invention can be selected from mineral fibers, preferably glass, carbon or basalt, in particular glass or carbon, or from synthetic fibers, preferably aramid or polyaryl ether ketone fibers, or mixtures thereof.

[0118] Advantageously, the fibers have a length such that the L / D ratio is greater than 1000, preferably greater than 2000, where L is the average length of the fibers and D is their average diameter, determined by methods well known to those skilled in the art, particularly by microscopy.

[0119] The fibers can represent 45 to 80% by volume of the composite material, preferably 50 to 70%. Thin-walled mold

[0120] The invention also relates to a mold comprising two parts, preferably of complementary shape, intended to be assembled, characterized in that it is constituted - a first part having a groove around its entire perimeter, - a second part having a protruding rib around its entire perimeter, the positions of the groove and the rib being chosen so that they interlock when the mold is in the closed position, at least one of the parts has at least one orifice, having an axis perpendicular to the surface of the part, a seal is positioned in the groove of the first part, the parts are of a thickness which can withstand a residual molding pressure greater than the saturated vapor pressure of water at the injection temperature of the reactive composition, the parts having thermal conductivity properties.

[0121] Preferably, the residual molding pressure that the parts can withstand is between 0.7 and 5 bars.

[0122] The mold has openings, with an axis perpendicular to the surface of the part. These openings are commonly called injection points. They allow the injection of the polymer or reactive composition in its molten state into the mold. The number of openings in the mold part(s) depends on the surface area of ​​the part(s). Both parts of the mold, i.e., the lower and upper parts, can have at least one injection point.

[0123] The mold is equipped with a vacuum system that keeps it closed when removed from the press. Preferably, the vacuum system provides a vacuum of 0.7 bar to 0.9 bar.

[0124] The mold can be equipped with a mechanical system to hold it in the closed position when removed from the press. This mechanical system can withstand an internal pressure between 0.7 bar and 10 bar, preferably between 0.7 and 5 bar.

[0125] According to a particular embodiment of the invention, the thin-walled mold is provided with a degassing system, i.e., a system for sucking up the gases present in the mold cavity, comprising at least one pump and one or more vents opening into the mold cavity.

[0126] According to a particular embodiment of the invention, the first part comprising the groove and the seal is equipped with a cooling channel for cooling the seal. This cooling channel may contain a cold liquid, or be connected to a cooling system using cold water or compressed air.

[0127] Preferably, the thin-walled mold is made of a heat-conducting material that allows maximum heat transfer from the press to the reactive composition injected in molten form into the mold.

[0128] Preferably, the thermal conductivity (λ) of the walls is greater than or equal to 10 Wm-1.K-1, preferably between 0.1 and 10 Wm-1.K-1, more particularly between 0.3 and 1 Wm-1.K-1.

[0129] Thermal conductivity measurements of materials are carried out using HOT DISK technology as detailed in ISO 22007-2.

[0130] According to a specific embodiment of the invention, the thin-walled mold is made of steel.

[0131] The mold may also include one or more means of gripping or grasping, allowing for easy handling of the mold.

[0132] Preferably, the mold according to the invention comprises: - a first part having a groove around the entire perimeter of the part, a seal positioned in the groove and a cooling channel allowing the seal positioned in the groove of the first part to be cooled, - a second part having a rib protruding around the entire perimeter of the part, the positions of the groove and the rib being chosen so that they fit together when the mold is in the closed position, - at least one of the parts has at least one orifice, having an axis perpendicular to the surface of the part, - the parts being of a thickness which can withstand a residual molding pressure greater than the saturated vapor pressure of water at the injection temperature of the reactive composition, - the parts having thermal conductivity properties, the mold being equipped with - a degassing system and - a vacuum pulling system or a mechanical closing system.

[0133] Other goals, advantages, and characteristics will emerge from the description that follows, given purely as an illustrative example and with reference to the attached drawings on which: The figure 1 is a diagram of certain steps of the process according to the invention. The steps of injecting the polymer or the reactive composition: step 1A and cooling the thin-walled mold: step 1B are shown therein.

[0134] According to the process of the invention, a thin-walled mold containing reinforcing fibers is installed in a matrix mounted on a press. In step 1A, a press 12 is shown, comprising heating circuits 14 and a means 13 for injecting the reactive composition. A thin-walled mold 11 receives the reactive composition in a molten state. The press is kept closed during all or part of the polymerization of the polymer matrix. The press is then opened, and the thin-walled mold is removed. In step 1B, the thin-walled mold is placed in a cold former 15, comprising cooling circuits 16, for cooling. The thin-walled mold is then demolded.

[0135] There figure 2This illustrates an embodiment of a thin-walled mold according to the invention. The mold 1 consists of part 2, which forms the upper part of the mold 1, and part 3, which forms the lower part of the mold 1. Part 2 has a projecting rib 4 around its entire circumference. Part 2 also has two injection points 5 and 6, through which the polymer or reactive composition is injected. Part 3 has a groove 7 around its entire circumference. A seal 8 is positioned in the groove 7. This seal ensures the sealing of the mold 1. Part 3 also includes, near the seal 8 located in the groove 7, a cooling system. The cooling system extends the service life of the seals. A tube, illustrated by the openings 9, allows for the circulation of cold water or compressed air.

[0136] The invention also relates to the use of the thin-walled mold as described above for the manufacture of composite material.

[0137] The invention finally relates to a circular device arranged on an axis of rotation comprising several storage zones of identical shape, said shape being complementary to the shape of a part of a mold according to claim 11.

[0138] Other purposes and advantages of the present invention will become apparent from the following examples, which are given by way of no limitation whatsoever. EXAMPLES Comparative Example 1:

[0139] A fibrous preform is introduced into a CRTM mold, installed on a press allowing a pressure of 50 bars to be applied to the mold.

[0140] The reactive composition used is a 50 / 50 mixture of acid-terminated and amine-terminated PA 11 / 10T / 6T prepolymers, with a molar mass of 2500 g / mol and a viscosity of 1 Pa·s at 300°C. The melting point of the prepolymers is 265°C and the crystallization temperature of the final polymer is 230°C.

[0141] The thermal cycle used for molding ranges from 220°C to 300°C, resulting in a thermal amplitude of 80°C. A 1-minute hold at 300°C is performed. The pre-polymers are injected at 300°C, at the beginning of the 1-minute hold. The target cycle time is 2 minutes, meaning that every 2 minutes, the part is demolded and a new preform is introduced into the mold.

[0142] In other words, the pre-polymers are injected at 300°C, the temperature is maintained at 300°C for one minute, then the press lowers the temperature to 220°C for 30 seconds. The part is demolded. Then the press raises the temperature back to 300°C for another 30 seconds to perform another cycle.

[0143] The piece, whose shape is presented on the figure 3 , was therefore designed in a press incorporating a heating and cooling system allowing molding in 2 minutes with a cycle presenting a thermal amplitude of 80°C.

[0144] A power of 250 kW for heating and 160 kW for cooling are required to complete this cycle.

[0145] Furthermore, molding tests using a thermocouple-instrumented preform showed that temperature control from point to point within the mold is highly unsatisfactory, with a temperature difference of over 20°C observed between points during the thermal cycle. Consequently, a steady-state temperature regime is never reached within the mold. Moreover, the thermal cycle is too rapid to achieve thermal equilibrium.

[0146] In addition, samples were taken from different locations of the molded composite part and molecular mass measurements were carried out by NMR (see table 1).

[0147] There figure 3Figure 30 represents a perspective view of a molded part according to example 1. Locations 31, 32, and 33 represent the points where the analyzed samples were taken. The results show that the molar masses differ in these locations. Thus, the temperature variations encountered from one point to another in the mold lead to differences in the progress of the polymerization reaction. in situ.

[0148] Finally, it was observed that the resin crystallization in the composite is incomplete, resulting in an average enthalpy of crystallization of 17 kJ / mol compared to 32 kJ / mol for this type of polymer when fully crystallized, as measured by DSC. This difference in enthalpy of crystallization values ​​can be explained by the excessively high cooling rate applied to the mold in order to meet the 2-minute cycle time. Furthermore, temperature variations from one point to another within the mold lead to variations in resin crystallization (see Table 1). Example 2 according to the invention:

[0149] A fiber preform is introduced into a 3 mm thick, thin-walled CRTM steel mold positioned outside the press. This mold is then closed and held closed using a vacuum system consisting of a pump and a hose connected to several vents positioned around the preform. The thin-walled mold is then transferred into a die preheated to 300°C, mounted on a press. After a holding time of 30 seconds, the temperature of the thin-walled mold reaches the temperature of the heating die. The reactive composition used is the same as that described in Example 1. The reactive composition is then injected into the compression chamber of the thin-walled mold within 5 seconds. Using the press, a pressure of 50 bar is applied to the mold, which closes the compression chamber within 5 seconds and impregnates the fiber preform.

[0150] After the compression phase, the temperature is held at 300°C for one minute, then the pressure is reduced to 5 bar and the vacuum system is restarted. The press opens, and the thin-walled mold is removed from the heating matrix by a robotic arm. It is then placed in a rotating carousel until a second thin-walled mold, containing only the fiberglass preform, is positioned near the press. This second mold is then placed in the heating matrix, replacing the first mold, to receive the reactive composition. The carousel has five mold positions.

[0151] The cycle time is 2 minutes: 30 seconds of heating the thin wall mold + 1 minute of holding under pressure for the time of polymerization and impregnation of the glass fibers + 30 seconds of handling time for loading and unloading the mold.

[0152] The first thin-walled mold is then removed from the carousel by a robotic arm and placed in a cold former. This former is maintained at 220°C, allowing it to cool the thin-walled mold. It also maintains a residual pressure of 5 bar throughout the cooling process. Once the thin-walled mold reaches 220°C, which occurs after 10 minutes of cooling, it is removed from the cold former, opened, and the composite part is demolded.

[0153] The energy cost of this molding cycle is divided by 10 compared to the cycle described in example 1.

[0154] The crystallization time of the resin during cooling is considerably lengthened, while maintaining a similar cycle time, resulting in better polymerization and better crystallization of the resin (see table 1).

[0155] The temperatures recorded from one point to another in the mold and the thermal calculations indicate a variation of + / -2°C, which is very close to the variations obtained for a purely isothermal mold.

[0156] The samples of the composite material prepared in areas 31, 32 and 33 indicated on the figure 3 , allow us to observe a similar progress of the polymerization reaction: a similar molar mass, at every point of the mold and good homogeneity of crystallization (see table 1). [Table 1]: Molar mass measurements by NMR and crystallization by DSC, in zones 1, 2 and 3 of the part, for the 2 types of molding cycle. Molding type Sample collection point Molar mass (Mn, g / mol) Enthalpy of crystallization (kJ / g) Example 1 (comparative) 31 9000 13 32 12500 20 33 11200 18 Example 2 (invention) 31 18000 30 32 19100 32 33 18600 31

Claims

1. A method for manufacturing a part made of composite material, said material comprising reinforcing fibers and a polymer matrix, the method comprising the following successive steps: - installing into a matrix mounted on a press (12) a closed thin-walled mold (11) wherein reinforcing fibers have been arranged, - closing the press (12), - injecting in the molten state into the closed thin-walled mold (11) a polymer or a reactive composition comprising at least one prepolymer, at least one monomer or their mixture, - maintaining the closing of the press (12) for all or part of the polymerization of the polymer matrix, when a reactive composition is used, - opening the press (12) - removing the thin-walled mold (11) from the press (12), while maintaining a residual pressure between 0.7 and 10 bar, preferably between 0.7 and 5 bar, in said mold (11), - cooling the mold (11) under said residual pressure.

2. The method according to claim 1, characterized in that the thin-walled mold (11) is provided with a vacuum filling system facilitating a pressure of 0.7 bar to 0.9 bar.

3. The method according to claim 1 or 2, characterized in that the matrix of the press (12) is maintained at a constant temperature between 250°C and 320°C.

4. The method according to any one of the preceding claims, characterized in that the cooling step consists in cooling said mold (11) via thermal conduction with the surrounding air through its thin walls, to a temperature less than the crystallization temperature (Tc) of the polymer formed under a residual pressure between 0.7 and 10 bar, preferably between 0.7 and 5 bar.

5. The method according to any one of claims 1 to 3, characterized in that the cooling step consists in positioning the thin-walled mold (11) in a so-called cold forming machine (15) regulated at a temperature less than or equal to the crystallization temperature of the polymer formed under a residual pressure between 0.7 and 10 bar, preferably between 0.7 and 5 bar.

6. The method according to any one of the preceding claims, characterized in that, after the cooling step, the method comprises a demolding step of the composite material from the thin-walled mold (11).

7. The method according to any one of the preceding claims, characterized in that, when the injection step is carried out with a reactive composition, then the polymerization of the reactive composition is carried out in the presence of degassing, preferably, the degassing being carried out by the application of a vacuum ranging from 0.010 to 0.950 bar, preferably from 0.700 to 0.900 bar with respect to the atmospheric pressure.

8. The method according to any one of the preceding claims, characterized in that the step for maintaining the closure of the press (12) for all or part of the polymerization is carried out with compression of the mold (11), preferably at a pressure ranging from 10 to 70 bar, even more preferentially from 40 to 60 bar.

9. The method according to any one of the preceding claims, characterized in that the polymer matrix is selected from polyamide, polyester, polyamide-imide, polyamideether, polyacrylic, polyolefin, phenylene polysulfide, polyether-imide matrices, preferably a polyamide matrix.

10. The method according to any one of the preceding claims, characterized in that said reinforcing fibers are selected from mineral fibers, preferably glass, carbon or basalt fibers, in particular glass or carbon fibers, or from synthetic fibers, preferably aramid fibers or polyaryletherketone fibers, or from the mixtures thereof; and / or in which the reinforcing fibers have an L / D ratio greater than 1,000, preferably greater than 2,000, L being the mean length of the fibers and D their mean diameter.

11. A mold (1) comprising two parts intended to be assembled, characterized in that it consists of - a first part (3) comprising a groove (7) around the entire edge of the part, - a second part (2) comprising a protruding rib (4) around the entire edge of the part, the positions of the groove (7) and of the rib (4) being selected so that they fit together when the mold is in the closed position, - at least one of the parts comprises at least one orifice (5) (6), having a perpendicular axis to the surface of the part, - a seal (8) is positioned in the groove (7) of the first part (3), - the parts being of a thickness that withstands a residual molding pressure greater than the saturated vapor pressure of water at the injection temperature of the reactive composition and - the parts having heat conductive properties, the mold being equipped with a vacuum filling system making it possible to maintain it in the closed position.

12. The mold according to claim 11, characterized in that it is equipped with a cooling channel making it possible to cool the seal positioned (8) in the groove (7) of the first part (3).

13. The use of the mold as defined in any one of claims 11 or 12 for the manufacture of composite material.

14. A circular device arranged on an axis of rotation comprising several storage zones of identical shape, said shape being complementary to the shape of a part of a mold, said shape being complementary to the shape of a part of a mold (1) as defined in claim 11 or 12.