Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29B—PREPARATION OR PRETREATMENT OF THE MATERIAL TO BE SHAPED; MAKING GRANULES OR PREFORMS; RECOVERY OF PLASTICS OR OTHER CONSTITUENTS OF WASTE MATERIAL CONTAINING PLASTICS
  • B29B11/00—Making preforms
  • B29B11/14—Making preforms characterised by structure or composition
  • B29B11/16—Making preforms characterised by structure or composition comprising fillers or reinforcement
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C70/00—Shaping composites, i.e. plastics material comprising reinforcements, fillers or preformed parts, e.g. inserts
  • B29C70/04—Shaping composites, i.e. plastics material comprising reinforcements, fillers or preformed parts, e.g. inserts comprising reinforcements only, e.g. self-reinforcing plastics
  • B29C70/28—Shaping operations therefor
  • B29C70/40—Shaping or impregnating by compression not applied
  • B29C70/42—Shaping or impregnating by compression not applied for producing articles of definite length, i.e. discrete articles
  • B29C70/46—Shaping or impregnating by compression not applied for producing articles of definite length, i.e. discrete articles using matched moulds, e.g. for deforming sheet moulding compounds [SMC] or prepregs
  • B29C70/465—Shaping or impregnating by compression not applied for producing articles of definite length, i.e. discrete articles using matched moulds, e.g. for deforming sheet moulding compounds [SMC] or prepregs and impregnating by melting a solid material, e.g. sheets, powders of fibres
• • D—TEXTILES; PAPER
  • D04—BRAIDING; LACE-MAKING; KNITTING; TRIMMINGS; NON-WOVEN FABRICS
  • D04B—KNITTING
  • D04B1/00—Weft knitting processes for the production of fabrics or articles not dependent on the use of particular machines; Fabrics or articles defined by such processes
  • D04B1/14—Other fabrics or articles characterised primarily by the use of particular thread materials
  • D04B1/16—Other fabrics or articles characterised primarily by the use of particular thread materials synthetic threads
• • D—TEXTILES; PAPER
  • D10—INDEXING SCHEME ASSOCIATED WITH SUBLASSES OF SECTION D, RELATING TO TEXTILES
  • D10B—INDEXING SCHEME ASSOCIATED WITH SUBLASSES OF SECTION D, RELATING TO TEXTILES
  • D10B2401/00—Physical properties
  • D10B2401/04—Heat-responsive characteristics
  • D10B2401/041—Heat-responsive characteristics thermoplastic; thermosetting
• • D—TEXTILES; PAPER
  • D10—INDEXING SCHEME ASSOCIATED WITH SUBLASSES OF SECTION D, RELATING TO TEXTILES
  • D10B—INDEXING SCHEME ASSOCIATED WITH SUBLASSES OF SECTION D, RELATING TO TEXTILES
  • D10B2403/00—Details of fabric structure established in the fabric forming process
  • D10B2403/03—Shape features
  • D10B2403/033—Three dimensional fabric, e.g. forming or comprising cavities in or protrusions from the basic planar configuration, or deviations from the cylindrical shape as generally imposed by the fabric forming process
• • D—TEXTILES; PAPER
  • D10—INDEXING SCHEME ASSOCIATED WITH SUBLASSES OF SECTION D, RELATING TO TEXTILES
  • D10B—INDEXING SCHEME ASSOCIATED WITH SUBLASSES OF SECTION D, RELATING TO TEXTILES
  • D10B2505/00—Industrial
  • D10B2505/02—Reinforcing materials; Prepregs

Definitions

• TITLE PREFORM MADE BY KNITTING, COMPOSITE PRODUCT INCORPORATING SUCH A PREFORM AND MANUFACTURING PROCESSES
• the present invention relates to a preform made by knitting, said preform being intended for the manufacture of composite products, as well as a composite product obtained from such a preform.
• the present invention also relates to a method for manufacturing such a preform, as well as a method for manufacturing a composite product from such a preform.
• the composite products (or “parts”) (or “in composite material” or “in composite materials”) considered in the present invention are products comprising a matrix (generally the main constituent of the product in which the other constituents are coated) in particular with base of a polymeric material, in particular and preferably thermoplastic in the present invention, this matrix being reinforced by a material generally having a higher melting or degradation temperature than the temperature at which said matrix is made from said material polymeric (for example higher than the melting point of said polymeric material).
• Composite products incorporating a polymeric matrix and a reinforcing material are well known and make it possible to obtain interesting effects or better properties than products formed solely from said polymeric material, such as improved properties in terms of mechanical resistance or resistance corrosion, or the lightening of parts, etc.
• the reinforcing material (or material) incorporated into the matrix can be in the form of discrete or continuous elements, for example in the form of fibers which are dispersed in the matrix or in the form of threads or fibers which are assembled beforehand in fabrics, non-wovens, mats or other products obtained by textile processes, or even can be in the form of armature(s), etc.
• woven reinforcements or of fabrics of (son of) reinforcements
• polymeric material or “prepreg”.
• These fabric reinforcements are traditionally formed of weft threads and warp threads arranged perpendicularly, and typically have a planar structure.
• the fabrics are generally cut out and placed in a mold whose general shape corresponds to that of the part to be produced, the polymeric material (or resin) then being injected and polymerized in the mold in order in particular to give a rigid part.
• knitwear incorporating a polymeric material and reinforcing (or reinforcing) yarns or fibers have appeared, these knitwear being generally obtained from a continuous yarn (which can be mono- or multi-filament( s) and/or formed of discontinuous fibers bound for example by twisting or wrapping, etc.), this yarn forming interlaced stitches arranged in successive rows, the reinforcing material possibly being present in the stitch yarn(s) or possibly forming part of weft yarns added to the knit in the form of unidirectional yarns.
• Different knitting techniques in particular circular or rectilinear make it possible in particular to obtain knits forming a unitary piece, in 2D or 3D, without seams.
• knitted reinforced structures have many advantages over woven reinforced structures.
• knitting can be done if necessary from a single spool of yarn for the knit yarn, while the fabrics always require several separate coils.
• patent application FR 3065181 of the holder teaches a process for producing a dry preform for the manufacture of a product made of composite materials.
• This document describes a preform produced by knitting and incorporating at least one unidirectional reinforcing thread, this preform no longer requiring the injection of a resin because it is made up from the knitting of a mixture of threads or filaments of reinforcing material and son or filaments of thermoplastic material, the latter being intended to melt during shaping.
• preforms made by knitting still have certain drawbacks. Thus, it may be difficult for an inexperienced user to handle this flexible product or to transport it without altering it from its place of production to the place of manufacture of the composite product.
• certain high-tech products in the field for example of aeronautics, automobiles, construction, etc.
• the consolidation of knits incorporating such a material using for example the current vacuum process using a flexible support in the form of a silicone bladder is no longer possible due to degradation or wear more of said bladder above 180-200°C.
• the present invention has therefore sought to remedy the preceding drawbacks and to propose a new, more satisfactory embodiment of a textile product (formed of yarn(s) or fiber(s)) structuring and reinforcing, of improved design and implementation for the manufacture of composite products, in particular intended for high-tech applications using materials with high melting points, for example for composite parts intended for aeronautics or to be used in the field of radio frequencies (in particular for the manufacture of radomes, etc.).
• the pre-consolidated preform produced by knitting said preform being intended for the manufacture of a composite product, this preform being formed of at least one knit comprising at least one polymeric material and at least one yarn at least one reinforcing material, said knit comprising a thermoplastic polymeric material P1 constituting less than 20% by volume of said knit or of said pre-consolidated preform and acting as glue in said pre-consolidated preform.
• the present invention also relates to a process for producing (or manufacturing) a pre-consolidated preform intended for the manufacture of a composite product, said process comprising the following steps:
• the present invention also relates to a process for manufacturing a composite product from a pre-consolidated preform, this process comprising the following steps:
• the present invention also relates to a process for manufacturing a composite product from a knit, this process comprising the following steps
• thermoplastic polymeric material with the lowest melting point T1 representing less than 20% by volume of said knit or said preform
• the invention also relates to a knit intended for the manufacture of composite product(s), comprising at least one thermoplastic polymeric material P2 having a melting point T2, this polymeric material P2 being in particular intended to form the matrix of a composite product, at least one polymeric material P1 with a melting point T1 lower than the melting point T2, intended in particular to act as an adhesive, the polymeric material P1 constituting less than 20% by volume of said knit or of said preform, and at least one reinforcing material, the material P1 forming in particular one or more threads of said knit or of said preform.
• a composite product in particular a part intended for aeronautics or to be used in the field of radio frequencies, such as a radome, obtained by the method according to the invention and/or from the preconsolidated preform according to invention, said product comprising at least one polymeric material P2, forming the matrix of said composite, and comprising at least one thread of at least one reinforcing material, and at least one polymeric material P1 representing less than 10% by volume of said product has also made it possible to achieve this objective.
• the present invention therefore proposes a pre-consolidated preform produced by knitting and intended for the manufacture of a composite product, said preform being formed of at least one knit (or being formed from at least one knit or comprising at least a knit), said knit comprising at least one polymeric material (or material) and at least one thread of at least one reinforcing material, said knit comprising a thermoplastic polymeric material P1 constituting (or representing) less than 20% by volume of said knit or of said pre-consolidated preform, and acting as glue in said pre-consolidated preform, this material P1, incorporated in particular during knitting and/or initially forming yarns of the knit, binding in particular the yarn or yarns of the knit between them in the pre-consolidated preform after having been melted (and therefore appearing in a form other than a form of thread(s) in said pre-consolidated preform), in particular in the form of neck points the superficial coating(s) of yarn(s) of the knit (and not in the form of yarn(s)) within said pre-consolidated preform.
• yarn(s) is used in the present invention to designate yarn(s) and/or fiber(s) used to make knitwear (in particular knit yarn(s) or weft(s)), these threads possibly being mono- or multi-filament(s) and/or formed from discontinuous fibers bonded for example by twisting or wrapping, these threads being in particular continuous threads (as opposed to cut or short fibers) to allow their knitting knit or weft insertion according to one or the other dimension (width or length) of the knit.
• knitwear in particular knit yarn(s) or weft(s)
• these threads possibly being mono- or multi-filament(s) and/or formed from discontinuous fibers bonded for example by twisting or wrapping, these threads being in particular continuous threads (as opposed to cut or short fibers) to allow their knitting knit or weft insertion according to one or the other dimension (width or length) of the knit.
• preform we mean a textile product (that is to say made up of yarn(s) or fibre(s)), intermediate (intended to be transformed to form a final product), having a temporary shape approaching the shape of the composite product to be produced, this temporary shape being in particular and preferably according to the invention a 3D shape (thick flat or not flat), this textile product being in the present invention obtained by knitting (or from knitting(s)), more precisely by knitting at least one continuous thread where the thread forms interlaced stitches, arranged in successive rows.
• This preform is said to be “dry” (as opposed to pre-impregnated, sticky fabrics), and constitutes, where appropriate, the reinforcement of the composite product produced, this preform integrating in particular reinforcements (more precisely reinforcement threads formed of at minus the aforementioned reinforcing material) and a material intended to form all or part of the final matrix of the composite
• the preform can be formed (or made up - only - of) one or more knits (also called “pleats" in the preform), the preconsolidated preform being a more rigid (and more manipulable) form of the preform (i.e. that is to say more rigid than the initial preform simply formed of a knit or an assembly of knits).
• the knitted structure(s) according to the invention incorporate(s) one or more polymeric materials, including at least the thermoplastic material P1, intended to undergo a change of state, in particular to melt, and to form or to form part (in this modified state) of the matrix of the composite product envisaged, and at least one material intended to serve as reinforcement (and in particular not having to be melted) in the composite envisaged , this reinforcing material (or where applicable each of the reinforcing materials present) forming one or more yarns of the knitted structure, and having a state change temperature TR greater than the state change temperature of said or each of said aforementioned polymeric materials.
• the composite product corresponds to the final shape, in particular fixed, obtained by final consolidation of the pre-consolidated preform and comprising a polymeric matrix in which the reinforcements/reinforcing material(s) (or reinforcing threads formed from at least the material aforementioned reinforcement) are embedded, the polymeric matrix generally being predominant as specified later.
• state (or phase) change temperature we mean (at/for a given pressure) the temperature at or from which the material undergoes a change of shape (in particular compared to its shape in the initial knitting) such as a transition from the solid state to the liquid state or a decomposition or degradation.
• a change of shape in particular compared to its shape in the initial knitting
• thermosetting polymeric material or a reinforcing material it may be in particular (at a given pressure) the melting temperature, at or from which the material passes from the solid state to the liquid state, or the degradation temperature, at or from which the material degrades (or decomposes or burns or calcines), or, where applicable, the lower of these temperatures (melting or degradation).
• melting temperature at or from which the material passes from the solid state to the liquid state
• degradation temperature at or from which the material degrades (or decomposes or burns or calcines)
• all the polymeric materials present in the knitted structure according to the invention are thermoplastic materials, the temperature of change of the state of each of these polymeric materials being in this case their melting point,
• the knitted structure according to the invention comprises at least one (other) polymeric material P2, in particular thermoplastic , in particular forming (alone or in combination as specified later) at least one wire of said structure, this material P2 having a temperature of change of state, in particular of melting, T2, this polymeric material P2 being in particular intended to melt during the production of the composite to obtain the fixed final shape of said composite, this material then forming the matrix of said composite, the polymeric material acting as glue P1 being a different polymeric material (in particular with a different melting point) from the polymeric material P2 and having a melting point T1 (strictly) lower (preferably lower by at least 20°C, or even at least 50°C) than the change temperature state ent (in particular fusion) T2, the state change temperature ⁇ R of the reinforcing material being for its part higher than said respective temperatures T2, and a fortiori T1.
• this material P2 having a temperature of change of state, in particular of melting, T2 having a temperature of change of state, in particular melting
• the present invention thus relates in a preferred mode to a pre-consolidated preform produced by knitting, intended for the production of a composite product, this preform being formed of at least one knit comprising at least one thermoplastic polymeric material P2 (in particular forming or in the form of at least one continuous thread) having a melting point T2, this polymeric material being in particular intended to form the matrix of said composite, and this knit comprising at least one polymeric material P1 with a melting point T1 lower than the point of fusion T2, this material P1 having in particular been incorporated during knitting and/or initially forming threads of the knit, this polymeric material P1 acting as glue within said pre-consolidated preform, and constituting less than 20% by volume of said knit or of said pre-consolidated preform, said preform also comprising at least one yarn of at least one reinforcing material(s) (or reinforcing yarn), this e reinforcement material(s) having a temperature of change of state TR greater than T2, this material being intended to serve as reinforcement (and in particular not having to be melted)
• This advantageous knit where appropriate in three dimensions, intended to form the aforementioned pre-consolidated preform to subsequently produce a composite product, and which thus integrates the three aforementioned materials from the outset (three-component knit) is also considered in the present invention, as well as the preform (three-component preform) formed from said knit (and if necessary incorporating several other knits or plies, in particular similar or identical, superimposed if necessary by changing the orientation of the yarns of reinforcement(s), this knit or this preform produced by knitting therefore comprising at least one thermoplastic polymeric material P2 having a melting point T2, this polymeric material P2 being in particular intended to form the matrix of said composite, at least one (second/other) polymeric material P1, with a melting point T1 lower than the melting point T2, intended in particular to serve as an adhesive in the pre-consolidated preform intended to be made from said knit/said preform, the polymeric material P1 constituting less than 20% by volume of said knit/said preform, said knit or said preform also comprising at least one yarn
• the polymeric material P2 intended to form (the essential part of) the matrix of said composite is subsequently incorporated into the preform in the case where appropriate already pre-consolidated, in particular is added to the pre-consolidated preform during the production of the composite, in a form other than a form of threads, in particular is added by impregnating said preform/said knit by (or with) said P2 polymer material
• the present invention also proposes a method for manufacturing (or producing or obtaining) a pre-consolidated preform for (or intended for) the manufacture of a composite product, said method comprising the steps (or operations or actions) following:
• thermoplastic polymeric materials in particular at least one yarn of at least one thermoplastic polymeric material
• thermoplastic polymeric material P1 with the lowest melting point T 1 representing less than 20% by volume of said knit or said preform
• thermoplastic polymeric material P1 with the lowest melting point T1 it is meant that the melting point is the lowest compared to that of any other thermoplastic material, if any, present in the knit or the preform, in particular compared to a possible other thermoplastic polymeric material P2 intended to form the matrix of the desired composite product, whether this material P2 is present in the knit or even added later during the production of the composite. If this P1 material is the only polymeric material present in the knit or preform, it is also somehow the lowest (no other lower melting point material), and in particular is lower than the change temperature condition of the reinforcement material.
• step a) can be broken down into a first step ai) of producing one or more knits by knitting from at least one continuous yarn, each knit comprising one or more thermoplastic polymer materials (in particular at least one yarn of at least one thermoplastic polymer material) and comprising at least one yarn of at least one reinforcing material, having in particular a change of state temperature TR higher than that of the or each of the polymeric material(s) present, the thermoplastic polymeric material P1 with the lowest melting point T1 of each of the knits representing less than 20% by volume of said knit, and in a step a2) of assembling (in particular by superposition) several knits (in particular identical or similar, each obtained by knitting, in particular according to step ai ) for at least some or all of them) to form the preform.
• step ai) of producing one or more knits by knitting from at least one continuous yarn, each knit comprising one or more thermoplastic polymer materials (in particular at least one yarn of at least one thermoplastic polymer material) and comprising at least one yarn
• step b) can also, if necessary, depending on the type of composite product and the type of molding envisaged, be preceded by or consist of a step of draping around a support, for example flexible such as a silicone bladder, the assembly possibly being deposited in or on a mould.
• a support for example flexible such as a silicone bladder
• step c) can take place (and is generally carried out) on the whole of the preform within the mold (formed by a rigid part and a second part, or against mold, flexible or rigid, the treatment being carried out if necessary under vacuum, as detailed later), or possibly can be carried out locally at different points of the preform (for example using local heating means), the melting of the material thermoplastic P1 being able to operate in a more or less total or general way or possibly in a partial way (in certain points or in a certain volume in particular).
• step d) can be carried out by letting the cooling take place naturally or by accelerating the cooling.
• the knit comprises two thermoplastic polymer materials, in particular a P2 material, forming in particular one or more threads of the knit, and intended to form the matrix or the main part of the matrix of the future composite product , and a polymeric material P1 (of lowest melting point) which is the material intended to bond the thread or threads of the knit to each other in the pre-consolidated preform (this material may also be in the form of thread(s) in the knitting if applicable),
• P1 of lowest melting point
• the present invention also proposes a process for manufacturing a composite product, comprising a matrix of polymeric material(s) reinforced by reinforcing (or reinforcing) threads, the polymeric material(s) having a lower melting point at the temperature of change of state of the material constituting the reinforcing threads, from a pre-consolidated preform according to the invention, this method comprising the following steps:
• this preform being formed of at least one knit comprising one or more thermoplastic polymeric materials and at least one yarn of at least a reinforcing material, having in particular a temperature of change of state TR higher than that of the or each of the polymeric material(s), said knit or said preform comprising a thermoplastic polymeric material P1 with a melting point T1 constituting less than 20% by volume of said knit or of said preform and acting as glue in said pre-consolidated preform, said knit optionally comprising at least one other polymeric material with a melting point higher than T1,
• the treatment if necessary by heating under pressure, or the consolidation of said pre-consolidated preform, if necessary impregnated, having at least said polymeric material with a melting point T1, another polymeric material intended to form the matrix of the product composite and at least one thread of at least one reinforcing material, this treatment or this consolidation taking place either, in particular in the case where the other polymeric material is thermoplastic at a temperature greater than or equal to the melting point of this other material (and below the state change temperature of the reinforcement material TR), or, in particular in the case where the other polymeric material is thermosetting, by crosslinking of said material (this crosslinking possibly taking place depending on the material at room temperature or by heating), to obtain said composite product,
• Consolidation can take place by cross-linking in the case of certain liquid thermoplastic resins.
• the content of polymeric material P1 in the composite, produced in particular by this process is less than 10% by volume of said composite product, in particular is less than or equal to 5%.
• the process for producing the composite product from the knit or the initial preform (not pre-consolidated) also includes steps a) to d) for manufacturing the pre-consolidated preform mentioned above and then comprises the following operations:
• thermoplastic polymeric material with the lowest melting point T1 representing less than 20% by volume of said knit or of said preform
• the step of impregnation with a polymeric material in the process for producing the composite according to the invention can also allow the introduction of a third material P3, intended for example to form an overmolding according to the type of composite product sought.
• the present invention also relates to a composite product, obtained in particular according to the preceding process and/or from the preform pre- consolidated previously described, in particular in three dimensions, this composite product comprising at least one (first) polymeric material P2, in particular thermoplastic, having, where appropriate, a melting point T2 and forming the matrix of said composite, and comprising at least one thread of at least one reinforcing material, having in particular a temperature of change of state TR higher if necessary than T2, this material serving as reinforcement in said composite, and at least one (second) polymeric material P1, thermoplastic, of melting point T 1 , lower if necessary than melting point T2, this material P1 representing in particular less than 10% by volume of said product.
• first polymeric material P2 in particular thermoplastic, having, where appropriate, a melting point T2 and forming the matrix of said composite, and comprising at least one thread of at least one reinforcing material, having in particular a temperature of change of state TR higher if necessary than T2, this material serving as reinforcement in said composite
• second polymeric
• this composite product is a part intended for aeronautics or to be used in the field of radio frequencies, such as a radome.
• the polymeric material intended to form the matrix or the main part of the matrix of the composite considered is called "P2". It is either already present in the initial knit, in particular in the form of at least one yarn forming the stitches of the knit, or added later, in particular by impregnation of the pre-consolidated preform with said material P2 during the formation of the composite .
• the polymeric material acting as glue is called P1, and is part of the initial knitting, this material being able to take different forms (thread(s), wrapping, sheathing, etc.) as detailed later.
• the preform according to the invention is formed of at least one knit comprising at least one polymeric material and at least one thread of at least one reinforcing material.
• the knit is formed, as polymeric material(s), only of the polymeric material P1, which, in the initial knit, is then in the form of at least a thread (of said material P1 or optionally mixed with the reinforcing material, or in covering or sheathing of the reinforcing threads) forming the stitches of the knit and/or of the weft threads, and which, in the pre-consolidated preform, is is then in molten form (for example dots of glue or coating).
• the knit is formed, as polymeric material(s), of the polymeric material P2, which, in the initial knit and in the pre-consolidated preform, is then found advantageously in the form at least one thread (of said material P2 or optionally in mixed form with the reinforcing material, or as covering or sheathing of the reinforcing threads) forming the stitches of the knit and/or the weft threads; and polymeric material P1, which, in the initial knit, is then in the form of at least one thread (of said material P1 or possibly mixed with the reinforcing material and/or the material P2, or in covering or sheathing reinforcing threads and/or material P2) forming the stitches of the knit and/or weft threads, and which, in the pre-consolidated preform, is then in molten form.
• the polymeric material P1 forms less than 20% by volume of the knit, and respectively of the preform consisting of said knit, and preferably its volume content is less than or equal to 15%, in particular less than or equal to 10%, for example from 5 to 10%, of said knit, and respectively of said preform, this polymeric material P1 advantageously being a minority in said knit/said preform, considering its aforementioned low rate relative to the volume of the knit or that, where appropriate, its rate is considered relative to the other polymeric material P2 when it is present or that its rate is considered relative to the rate of reinforcing material.
• the content of this material P1 within the composite formed from the preform is moreover advantageously less than or equal to 10% by volume, as indicated above.
• the content of material P1 in the knit/the preform is also already advantageously less than or equal to 10% by volume.
• the material P2 intended to form the matrix or the main part of the matrix of the composite product can be described as "main” in comparison with the other polymeric material P1, its content by volume being greater (at least 2.5 times, preferably at least 5 times, higher) than that of the material P1 in the composite (and if necessary in the knit/the preform if this material P2 is already present), its rate also being higher than that of the reinforcing material present.
• the content of material P2 is advantageously at least 50% by volume, in particular at least 55% by volume, in the composite obtained from the preform. Even if the P1 material is also part of the matrix forming the final composite, the P2 material has a much higher rate. important, is considered as the main material forming the matrix or the main part of the matrix of the composite.
• the content of total polymeric material (including at least materials P1 and P2) in the composite product obtained according to the invention is preferably at least 55% by volume, in particular between 55 and 75% by volume, in particular between 60 and 70% by volume.
• polymeric material means a material formed from macromolecule(s) or from polymer(s) or copolymer(s), this material being formed either from a single type of molecule (having the same formula) or possibly from a mixture of molecules of different formula (mixture of polymers).
• the polymeric materials P1, and where appropriate P2 (or even other added polymeric materials such as P3 mentioned above) are chosen from thermoplastic materials, for example from thermoplastic polymers of the polycarbonate (PC), polyetherimide (PEI) type.
• polypropylene PP
• polyamide PA
• PMMA poly(methyl methacrylate)
• PET poly(ethylene terephthalate)
• PPS poly(phenylene sulfide)
• PEEK polyetheretherketone
• PEKK polyetherketoneketone
• the polymeric material P1 is a thermoplastic material chosen for example from the following materials: polycarbonate, polyetherimide, polypropylene, polyamide, poly(methyl methacrylate). Its melting point is for example below 225°C.
• the polymeric material P2 is a thermoplastic material, having, where appropriate, in particular for applications (such as the manufacture of radomes) requiring the use of “high temperature” fibers, a melting point greater than 250° C., in particular greater than 300° C. (thermoplastic with a high melting point), this material then being chosen, for example, from the following materials: polyetheretherketone (PEEK), polyetheretherketoneketone (PEKK), etc., the material P2 and the reinforcing material being chosen respectively so that the material P2 has a melting point lower than the temperature at which the reinforcing material changes state.
• PEEK polyetheretherketone
• PEKK polyetheretherketoneketone
• this material P2 or this material P3 can optionally be a thermosetting material chosen for example from polyurethane (PU ), epoxy resins, cyanate ester, phenolic resins, polyester, etc.,
• one and/or the other polymeric material used can comprise additives or fillers, which can be added during the step of formulating the polymer or, if necessary, of spinning threads, for example colored pigments or electric charge dissipators, flame retardants, etc.
• the rate of reinforcements/reinforcing material is preferably at least 25%, in particular at least 35%, by volume in the composite obtained from the preform, and where appropriate in the knit or the preform when the latter is already formed from the two polymeric materials P1 and P2 and when no polymeric material is added during the production of the composite, the rate of reinforcing material being, where appropriate, at least 80% by volume in the knit or the preform when the latter is formed as polymeric material(s) solely from the material P1.
• the reinforcing material may form one or more knit yarns and/or form or take the form, for example, of unidirectional yarns integrated into the knit, in particular in the weft, this reinforcing material possibly forming one or more yarns, alone or in combination with a polymeric material (mixed yarn(s)) present in the knit.
• This reinforcing material intended to form the reinforcement of the composite (and therefore not having to melt during the production of said composite), is chosen for example from the following materials: inorganic materials such as glass, quartz, alumina, carbon, basalt, metal or metallic material; natural materials, such as flax, hemp, and optionally, depending on the choice of polymeric materials P1 and P2, from synthetic, plastic or heat-resistant polymeric materials, such as aramids (para-; meta-, for example Kevlar®), polyester; polyetheretherketone (PEEK), polyetherketoneketone (PEKK), polyphenylene sulfide (PPS), etc; its nature being chosen in particular as a function of its state change temperature which must be higher than the melting point or state change point of the polymeric material(s) constituting the matrix of the final composite product.
• inorganic materials such as glass, quartz, alumina, carbon, basalt, metal or metallic material
• natural materials such as flax, hemp, and optionally, depending on the choice of polymeric materials P1 and
• the knit according to the invention is obtained from at least one continuous thread (in particular of polymeric material and/or of reinforcing material), this thread forming interlaced stitches arranged in successive rows.
• Weft yarns are also optionally added to the knit during knitting in the form of unidirectional yarns (needles passing, for example, the stitches or loops over the unidirectional yarns and holding them in place).
• Yarns other than knit(s) yarns (that is to say forming the knit stitches) or weft yarns may also be present where appropriate (seams or sewn filler yarns, etc.).
• the knitting method of the yarn or yarns used may be a weft knitting method or a warp knitting method, and is preferably a weft knitting method.
• weft knitting also called gathered stitch
• the thread follows the direction of the rows in a privileged way (weft direction by analogy to the fabric).
• Each loop in the same row is knitted one after the other, and each row is knitted one after the other, with the stitches of a new row being picked up by the stitches of the lower row.
• a single thread can achieve the entire knitting, and each needle is individually controlled, allowing a complex 3D shape to be achieved.
• the support in which the knitting needles slide is called needle bed.
• a machine can use two needle beds, the needle bed closest to the user making so-called “front” stitches, the second forming the “back” stitches.
• warp knitting also called warp stitch
• the yarn favorably follows the direction of the columns (warp direction by analogy to the fabric). All loops in one row are knitted at the same time, each row being knitted one after the other. One thread is needed per column of stitches, the needles being tied in different groups. Knits made by this method are usually flat.
• the knitting can also be carried out by circular knitting or rectilinear knitting machines. It is also possible to make multi-wall knits by knitting multiple layers simultaneously temporarily using needles for the extra walls.
• the knit or knits used are obtained by a weft, rectilinear or circular knitting technique, and preferably by a rectilinear weft knitting technique, this technique making it possible to obtain complex 3D shapes.
• the yarn or yarns used to make the knitting can be (each) of the unitary type (monofilament) or formed from a bundle of filaments (multifilaments) such as for example a yarn of the "roving" type (that is to say a set of parallel continuous filaments assembled without twisting) or a fiber yarn (i.e. a set of short staple fibers assembled by twisting), etc.
• a yarn can be an assembly of several yarns or filaments of different materials, this assembly being able to be done by twisting, wrapping, etc., or a yarn can also be a yarn of a material surrounded by another material (forming for example a sheath), this type of yarn incorporating two different materials being called mixed yarn.
• a yarn comprising polymeric material and reinforcing material for example by assembling a reinforcing yarn and a thermoplastic yarn, by wrapping a yarn of a reinforcing material by a thermoplastic yarn, etc., the knitting of mixed yarns making it possible to easily obtain a dry preform, containing both the reinforcement and the matrix.
• the reinforcing material is present in the knit according to the invention in the form of reinforcing yarn(s) or mixed yarns, in particular in the form of knit yarn(s) and/or in the form of yarn(s) unidirectional(s), called UD thread(s), inserted, in particular into weft threads, during knitting, the mesh threads including a reinforcing material ensuring in particular a better hold of the structure, while that the unidirectional yarns including a reinforcing material make it possible to obtain the expected (in particular mechanical) reinforcement.
• the knit according to the invention may also comprise knit yarn(s) and/or unidirectional and/or weft yarn(s), one or more yarns comprising at least one polymeric material (alone or in a mixture with another polymeric material or with a reinforcing material), the yarns made from polymers (in particular thermoplastics) lending themselves better to knitting (because they are not very sensitive to shearing, and have mechanical and sufficient flexibility).
• the unidirectional yarn(s) are preferably UD 90° yarns, that is to say in the weft (arranged in the direction of the rows), but where appropriate one or more unidirectional yarns of the knitting can be UD 0° yarns, that is to say arranged in the direction of the columns, perpendicular to the frame.
• the knitting can be obtained by simultaneously knitting one or more (for example from 2 to 10) knit yarns and one or more (for example from 2 to 10) UD yarns, the knit yarn(s) and the UD yarn(s) possibly understand different subjects.
• a knit yarn and/or a UD yarn can be made of one material, and around this yarn can be twisted a yarn of another material, in particular thermoplastic, or this yarn can be surrounded by a sheath of said other material, for example obtained by passing the wire(s) through a bath of thermoplastic material (with a lower melting point than the temperature of melting or change of state of the material constituting the wire ) melted, then by co-extruding the assembly.
• the knit yarn(s) and/or the UD yarn(s) can also be formed from an intimate mixture of filaments of different materials as already mentioned.
• the proportions of the different materials (polymer(s) and reinforcement) in the knit/the preform are managed in particular by the supply of the yarns, the diameter of the yarns, the choice of yarns, etc. It is also possible during knitting to vary the nature, density, composition, etc., of the yarns to obtain different zones, nevertheless, in most cases, the preform and the composite product obtained according to the invention have a uniform and homogeneous composition without differentiated zones or with different functionalities.
• the preform is advantageously made up of a single piece, without seams and has in particular a three-dimensional structure similar or adapted to the shape of the final composite product, this shape possibly being for example conical, cylindrical, etc.
• the thickness of the knit/of the preform is for example between 1 and 6 mm (without prejudging its final thickness in the composite product).
• the knit may in particular have a weight area or basis weight from 100 to 2500 g/m 2 and be produced with densities of 3 to 6 rows/cm and 2 to 4 columns/cm.
• the knitting/the preform according to the invention is generally produced by knitting at least one yarn of polymeric material P1 and/or P2 and/or reinforcement, UD yarns being added in the weft during the knitting (one can also speak of simultaneous weft knitting of at least one mesh yarn and at least one unidirectional yarn).
• the knit/the preform can also be made by knitting at least one mixed yarn comprising the polymeric material and the reinforcing material.
• the preform is then pre-consolidated by heating, in particular under pressure (at a pressure for example of the order of 1 to 20 bars), at a temperature of at least the melting temperature of the material P1, making said material viscous or liquid, the subsequent cooling of the preform making it possible to obtain a product having greater strength and rigidity than the initial preform (before pre-consolidation), and already having a shape close to the composite product to be obtained.
• pressure at a pressure for example of the order of 1 to 20 bars
• the composite product can then be directly obtained by heating, in particular under pressure (at a pressure for example of the order of 1 to 20 bars), of the pre-consolidated preform without adding additional polymeric material/resin by injection or infusion .
• the knit/the preform comprises as polymeric material(s) the material P1 only
• the polymeric material P2 is then introduced by the liquid route into a mold, as already mentioned, in particular during the production of the composite.
• the process for producing the composite product from the initial knitting operation advantageously comprises two stages of treatment and/or heating and/or melting of thermoplastic materials, the first stage (that of pre-consolidation) taking place in particular at a temperature lower than the temperature of the second stage (that of the final consolidation of the composite product).
• the first heating step to pre-consolidate the preform (step c mentioned above) is carried out by depositing the preform in or on a mould, the mold being closed if necessary and put if necessary under pressure (for example from 1 to 10 bars) and the mold being heated by heating, in particular of the induction or oven type, to a temperature greater than or equal to the melting point T1 (this temperature preferably not exceeding 225° C., or even 200° C. C, or even 180° C. or even 160° C.), the temperature being maintained for a few minutes.
• the pre-consolidated preform can be extracted or left if necessary in the mold and/or on its support, for the consolidation step.
• the first heating step can be carried out by heating locally, if necessary under pressure, as much as necessary, for example using of an ultrasound probe.
• the mold used for the first heating can be formed of a rigid part and a rigid or flexible counter mold (for example in the form of a tarpaulin).
• the preform may have been draped beforehand or alternatively be draped over a support or mandrel, in particular deformable, for example a silicone bladder or membrane, the preform/support assembly then being able to be deposited in a mold or locally heated by example by ultrasonic probes. If necessary, the vacuum can be drawn into the mold used.
• the second step of heating or consolidating the pre-consolidated preform is then carried out in a mold (if necessary formed from rigid part(s) or flexible part(s) as indicated above), this mold possibly being the same as that used for the pre-consolidation or a different mould, to carry out the consolidation (according to step g mentioned above) and obtain the desired composite product, the heating step to obtain this consolidation being, if necessary, preceded by a step of injecting a polymeric material (for example material P2) or performed simultaneously with said injection step (step f).
• a mold if necessary formed from rigid part(s) or flexible part(s) as indicated above
• this mold possibly being the same as that used for the pre-consolidation or a different mould
• the process for manufacturing the composite may not include a step (step f) of adding (in particular injection and/or infusion ) of another thermoplastic material, the preform being for example made by adapting the ratio of the thermoplastic materials and of the reinforcing material to obtain the composite directly without adding additional material.
• the pre-consolidated preform thus directly becomes the composite product after placing in the mold and heating under pressure, before removing the product from the mold and its possible support.
• a polymeric material intended to form or form part of the matrix of the composite is injected before or during the heating of step g).
• the pre-consolidated preform can for example be arranged (or “draped”) on the inner wall of a first, rigid part of the mould.
• either a second, rigid part of the mold can be closed, then the polymeric material is injected under pressure at one or different points (operation for example of the transfer molding or resin injection type), in particular to cover the entire surface of the preform, either a tarpaulin or a flexible membrane is placed as a counter-mold and the additional polymeric material is introduced by creating a depression at different points of said tarpaulin (operation for example of the infusion or infusion molding type under vacuum), in particular to cover the entire surface of the preform.
• the purpose of these various points of injection or pulling by depression is to allow the flow and the distribution of the polymeric material.
• This embodiment having an injection and/or infusion step is used in particular when the preform is mainly made up of reinforcing material, forming the reinforcement, and of material P1.
• the polymeric material added must be compatible with the materials already constituting the preform. This added material is in particular the polymeric material P2 when the preform is devoid of it or when it comprises an insufficient proportion. If necessary, another polymeric material P3 can also be added, in particular when the preform already comprises the materials P1 and P2, for example to form a more complex composite mixture and/or to form overmouldings, etc.
• a mode of addition of the transfer or injection of resin consisting in injecting, generally at low pressure (for example of the order of 1 to 4 bars), the liquid resin (or polymeric material) in a closed mould, at one or more points, the injected resin migrating in the mold cavity and impregnating the entire structure (preform) deposited in the mould, the injection of resin being stopped when the mold cavity is completely filled and the mold then being heated.
• the injection can sometimes be carried out at higher pressures (for example up to 15 or 20 bars) for very viscous resins.
• the infusion consists of placing the preform under vacuum, in a closed mould, which is subsequently impregnated with the arrival of polymeric material which is sucked up by the depression created in the mould.
• the treatment or consolidation (step g) according to the invention can be carried out in particular at a temperature above 250° C., in particular above 300° C., if necessary under a pressure of 1 to 20 bars for for example a few tens minutes. If necessary, vacuum can be used for step f) or g).
• the treatment and/or the consolidation can be carried out by operating the compaction via drawing a vacuum between a flexible membrane (silicone bladder) or a tarpaulin and a part of the mould, or by pressurizing a flexible membrane or tarpaulin in order to press the preform against the walls of the mould, or by compaction by pulling the vacuum and injecting pressure inside the membrane, or by compaction/thermoforming in a rigid mould/counter-mould(s) ( punch/die type), etc.
• the composite product obtained can then be removed from the mould, after cooling.
• the present invention has made it possible to obtain, in a simple and economical way, finished products without connection (with a good continuity of the aerodynamic profile), without loss or fall of material, and having good resistance and good resistance.
• the pre-consolidated preform according to the invention can in particular be used for the production of composite products in the fields of aeronautics (in particular for the manufacture of radomes), building, medical, furniture, automobiles, etc. .
• the preform may constitute only a specific zone of a final composite product, but advantageously it makes it possible to obtain the complete composite product directly (independently of the addition of other components and accessories).
• the composite products obtained formed from a matrix of polymeric material reinforced by reinforcing fibers, comprise in particular between 55 and 75% by volume of polymeric material, and between 25 and 45% by volume of reinforcing fibers.
• Example 1 In the first example according to the invention, a preform was produced formed from one or more tri-component knits, in three dimensions of conical shape, already having all the materials necessary for obtaining a composite product of the radome type, by knitting simultaneously, for each knit, by the weft knitting method:
• one or more mixed unidirectional yarns formed of filaments of a reinforcing material, for example glass or quartz, and filaments of a second thermoplastic polymeric material P2, for example PEEK with a melting point T2.
• the proportion of material P1 was 5% by volume, that of material P2 55% by volume and that of reinforcement material 40% by volume.
• the knit(s) (possibly superimposed) was/were then draped over a silicone bladder, this/these knit(s) then forming a preform, and the assembly was deposited in a first mold by steel for the pre-consolidation of the preform.
• the mold was closed and the vacuum pulled and the mold was heated rapidly by induction-type heating to a temperature greater than or equal to the melting temperature T1 but lower than the melting temperature T2. The temperature was maintained for a few minutes. After cooling, the bladder was removed and the preform was extracted from the mold. This obtained pre-consolidated preform could be easily handled.
• the pre-consolidated preform was then placed in a mold closed by a flexible counter-mould, then fired/consolidated/subjected to a final consolidation treatment, by carrying out a heat treatment under vacuum at a temperature greater than or equal to the temperature of fusion T2 and lower than the temperature of change of state of the reinforcement material TR to give (after cooling) a composite product, without necessarily adding resin.
• the composite product, unitary and seamless consisted of: 5% by volume of P1 material, 55% by volume of P2 material and 40% by volume of reinforcement material.
• Example 2 In this second example according to the invention, a preform formed of one or more tri-component knits, in three dimensions of conical shape, was produced, already having all the materials necessary for obtaining a composite product of the radome type, proceeding as in Example 1 except that the initial/initial knitting(s) was/were made this time by knitting simultaneously, by the weft knitting method; and only in mesh, one or more mixed yarns formed of filaments of a thermoplastic polymeric material P2, for example of PEEK with a melting point T2, and of filaments of a reinforcing material, for example of glass or quartz, this or these mixed yarns being covered by a thermoplastic material P1 with a melting point T1, for example polycarbonate or PMMA,
• the proportion of material P1 was 5% by volume, that of material P2 55% by volume and that of reinforcement material 40% by volume.
• the knit(s) were then draped over a mandrel for pre-consolidation of the formed preform of the knit(s). Using an ultrasound probe, manual heating under pressure was applied locally as many times as necessary to obtain the desired pre-consolidation.
• Example 3 In this third example according to the invention, a preform was made formed of one or more bi-component knits in three dimensions of conical shape, by knitting by the weft knitting method:
• one or more unidirectional reinforcing threads for example glass or quartz thread(s).
• the proportion of material P1 was 11% by volume, that of reinforcement material 89% by volume in the knit/in the preform.
• the knit(s) were then draped over a silicone bladder, this (these) knit(s) (possibly superimposed) thus forming a preform, and the assembly was placed in a first steel mold to pre-consolidation of the preform or preforms.
• the mold was closed and the vacuum pulled, and the mold was rapidly heated by induction type heating to a temperature greater than or equal to the melting temperature T1 but lower than the change of state temperature ⁇ reinforcement material. The temperature was maintained for a few minutes. After cooling, the bladder was removed and the preform was extracted from the mold. The pre-consolidated preform obtained could be easily handled.
• the pre-consolidated preform was then placed in a mold closed by a counter-mold, then a polymeric material P2 with a melting point T2, for example PEEK was injected, and the preform was baked/consolidated/subjected to a final consolidation treatment, by carrying out a heat treatment under vacuum at a temperature higher than the melting temperature T2 and lower than the temperature TR to give (after cooling) a composite product.
• a polymeric material P2 with a melting point T2 for example PEEK
• the final composite product, unitary and seamless, consisted of: 5% by volume of P1 material, 55% by volume of P2 material and 40% by volume of reinforcement material.
• one or more unidirectional reinforcing threads for example glass or quartz thread(s).
• the proportion of material P1 was 10% by volume, that of reinforcement material 90% by volume in the knit/in the preform.
• the knit(ies) were then draped over a silicone bladder, this(these) knit(s) (possibly superimposed) thus forming a preform.
• the first heating step is carried out by heating locally using an ultrasound probe.
• the pre-consolidated preform draped over the silicone bladder is then placed in a mold, then a thermosetting polymeric material, for example an epoxy resin, has been injected, and the preform has been baked/consolidated/subjected to a final consolidation treatment , by carrying out a heat treatment under vacuum at a temperature necessary for the crosslinking of the resin to give (after cooling) a composite product.
• the final composite product, unitary and seamless, consisted of: 5% by volume of P1 material, 50% by volume of P2 material and 45% by volume of reinforcement material.
• the pre-consolidated preforms according to the invention can in particular be used with advantage to produce new composite parts intended in particular for aeronautics or to be used in the field of radio frequencies, in particular for the manufacture of radomes, etc.

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• 2021
  • 2021-03-16 FR FR2102590A patent/FR3120812A1/fr active Pending
• 2022
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  • 2022-03-14 EP EP22713984.7A patent/EP4308356A1/de active Pending
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