AU2008249626B2

AU2008249626B2 - Reinforcement textile armature and method for making same

Info

Publication number: AU2008249626B2
Application number: AU2008249626A
Authority: AU
Inventors: Gilbert Chomarat
Original assignee: Individual
Current assignee: Individual
Priority date: 2007-05-15
Filing date: 2008-05-14
Publication date: 2014-10-02
Anticipated expiration: 2028-05-14
Also published as: FR2916208B1; HK1139441A1; FR2916209A1; US20110151231A1; ES2362813T3; KR101518796B1; CN101680144A; IL202004A0; IL202004A; PT2145036E; PL2145036T3; DK2145036T3; EP2145036B1; ATE501294T1; SI2145036T1; AU2008249626A1; JP5185370B2; TN2009000473A1; DE602008005441D1; ZA200908582B

Abstract

The invention relates to a textile armature (1) that can be used for making composite materials or parts, and comprising: a central layer (3) containing fibre segments (3a) of a first type of synthetic material previously submitted, before the shaping thereof into a layer, to a process imparting thereto a permanent crimp; outer layers (21, 22) including a mixture of segments of chemical fibres (7) previously submitted to a process imparting thereto a permanent crimping and of segments of reinforcing fibres (4) at least some of the segments of chemical fibres (7) of the outer layers (21, 22) penetrate along a portion of their length into the central layer (3). First segments of chemical fibres (70) of the outer layers are bonded at least partially between them and to the other fibre segments (3a, 4) of the textile armature (1).

Description

1 REINFORCEMENT TEXTILE ARMATURE AND METHOD FOR MAKING SAME TECHNICAL FIELD OF THE INVENTION The present invention concerns textile armatures 5 used as products for reinforcing composite articles, i.e. articles based on resin (polyester or other resin) reinforced by a reinforcement textile armature. Reinforcement textile armatures are known from the document EP 0 395 548 which describes the use of two 10 textile reinforcement layers disposed on opposite sides of a central layer consisting of a mat based on fibers with permanent undulations. The reinforcement textile layers and the central layer are stitched/knitted together. 15 The document EP 0 694 643 for its part describes a textile armature used to produce composite articles and consisting of at least two reinforcement textile layers as such disposed on opposite sides of a central layer providing the thickness of said material, said layers 20 being stitched/knitted together, which armature includes against at least one of its external faces a synthetic fiber veil, said veil being attached either by gluing it to the outside of the complex or by stitching the various layers together. 25 Stitching/knitting techniques are relatively slow and lead to slow fabrication rates, of the order of 3 to 5 meters per minute, that cannot be speeded up. The textile armatures of the above documents also have non-uniform deformation capacities over their 30 surface because of the use of stitching/knitting means to fasten the various textile layers to each other. Also, the presence of stitching/knitting rows induces surface appearance defects in the finished part obtained after impregnating the textile armature with 35 resin.

2 The document EP 0 659 922 discloses the use of two reinforcement textile layers disposed on opposite sides of a central layer consisting of a mat based on fibers with permanent undulations with, on at least one of the reinforcement textile layers, a fibrous veil based on chemical fibers with permanent crimping and with a linear density lower than that of the fibers of the central layer. The fibrous veil or veils, the reinforcement textile layers and the central layer are needle punched together. The needle-punching technique is still slow, leading to fabrication rates of the same order as the stitching/knitting technique. Also, the connection between the layers of the armature is often insufficient. Furthermore, to ensure sufficient cohesion for the product to be handled, forceful needle punching must be used, which breaks the glass fibers. OBJECT It is the object of the present invention to substantially overcome or ameliorate one or more of the disadvantages of the prior art. SUMMARY OF THE INVENTION The present invention provides a textile armature usable for the production of composite materials or parts, comprising: - a central layer based on chopped fiber sections of a first type of synthetic material that have received before their formation into a layer a treatment communicating to them a permanent crimp, - external layers disposed on opposite faces of the central layer, wherein: - the external layers include chopped chemical fiber sections that have previously received a treatment conferring on them a permanent crimp and chopped reinforcement fiber sections, - at least some of the chopped chemical fiber sections penetrate over a part of their length into the central layer, - the chopped chemical fiber sections include at least first chopped chemical fiber sections including at least one surface layer of a thermoplastic material having a melting point 3 lower than that of the chopped fiber sections of the central layer, - the first chopped chemical fiber sections adhere, through thermal bonding, at least partly to each other and to the other adjacent chopped fiber sections in the external layers and to the other adjacent chopped fiber sections in the central layer. Such a textile armature has good deformation capacities in a number of directions. More particularly, such an armature has no preferential deformation direction and no direction in which deformation is prevented. The textile armature of the invention has homogeneous cohesion between its various textile layers in all directions. Because the chemical fibers adhere to the textile armature central layer fibers that they penetrate, it is possible to ensure efficacious interconnection of the armature layers by means of a relatively small number of such chemical fibers penetrating the central layer. The penetration of a relatively small number of chemical fibers can then be achieved using a preliminary needle- 4 punching or light needle-punching technique, consisting of less dense needle-punching. Preliminary needle punching is much faster than knitting/stitching and avoids breaking the reinforcement fibers, especially when 5 they are glass fibers. The permanent crimp of the chopped fiber sections of the central layer allows easy deformation of the textile armature when used in molding techniques. Moreover, the permanent crimp of the chopped fiber sections of the 10 central layer preserves free spaces between the chopped fiber sections, thus conferring an aerated character on the armature, which encourages flow of resin when using press molding, injection molding or vacuum molding techniques. 15 The adhesion to each other of the chopped chemical fiber sections in the external layers efficiently limits the risk of fraying of the textile armature when cut. Avoided in particular is fraying of chopped glass fiber sections that reinforce the textile armature. 20 The chemical fibers have a permanent crimp enabling homogeneous external layers to be produced from a homogeneous mixture of chopped reinforcement fiber sections and chopped chemical fiber sections, for example. The crimp of the chemical fibers avoids "settling" of the 25 mixture of fibers because of their different relative densities or sections. In a first embodiment, a homogeneous mixture can thus be obtained leading to the production of homogeneous external layers: in the external layers, the chemical fibers and the 30 reinforcement fibers are then mixed in a generally homogeneous manner. The reinforcement fibers can be glass fibers or plant (hemp, sisal, flax, etc.) fibers. The chopped fiber sections of the central layer can 35 preferably be of polypropylene, polyester or polyamide.

5 This is because these fibers are very widely used in the textile industry, of relatively low cost, easy to spin and easy to shape to produce chopped fiber sections with an elastic permanent crimp. 5 For a more regular central layer, the chopped fiber sections of the central layer can have at least two different unitary linear densities. The chopped chemical fiber sections present in the external layers advantageously have a cross section of 10 smaller diameter than the chopped reinforcement fiber sections. This diameter difference encourages entrainment and penetration along at least part of the length of at least some of the chopped chemical fiber sections of the external layers into the central layer by a preliminary 15 needle-punching process. During preliminary needle punching, the needles chosen to entrain the chopped chemical fiber sections have a small cross section, so that they do not entrain the chopped reinforcement fiber sections much, if at all. This prevents breaking of the 20 fragile chopped reinforcement fiber sections that reinforce the textile armature, specially in the case of reinforcing glass fibers. The first chopped chemical fiber sections of the external layers can advantageously be of a thermoplastic 25 material with a melting point lower than that of the chopped fiber sections of the central layer. In one advantageous embodiment of the invention, the first chopped chemical fiber sections of the external layers can be of polyethylene. 30 Polyethylene is a material very widely used in the textile industry, of relatively low cost and having a low melting point. It provides thermal bonding at lower energy cost. In another advantageous embodiment of the 35 invention, it can be provided that: 6 - the first chopped chemical fiber sections of the external layers are two-component chopped fiber sections having a central core of a first component and an external sheath of a second component, 5 - the melting point of the first component of the central core is higher than that of the second component of the external sheath. The use of such two-component fibers produces a thermal bond to connect them to the central layer without 10 risk of manifest or accidental damage to the external layers: only the external sheath of the two-component fibers is softened and participates in thermal bonding, their core remaining undamaged and retaining its mechanical properties. 15 In some cases, in particular in the case of reinforcement glass fibers, it can be relatively difficult to ensure sufficiently homogeneous mixing of the reinforcement fibers and the chemical fibers in the external layers. In this case, the external layers can 20 advantageously be produced in a stratified form, comprising an external stratum essentially of chopped chemical fiber sections, an internal stratum essentially of chopped chemical fiber sections, and an intermediate stratum essentially of reinforcement fibers. The 25 connection between the strata is provided by preliminary needle-punching followed by surface softening of the first chopped chemical fiber sections, some chemical fibers of the external stratum passing through the intermediate and internal strata of the external layer to 30 penetrate into the central layer of the textile armature. Another advantage of this embodiment is that the exterior surface of the textile armature consists essentially of chemical fibers. The thermoplastic material surface layers of these chemical fibers adhere 35 to each other and thus oppose fraying of or damage to the 7 reinforcement fibers upon subsequent handling of the textile armature when not yet embedded in resin. The possibility of eliminating the chemical fiber internal stratum will be noted. 5 According to a first variant of both embodiments, the chopped chemical fiber sections of the external layers can include only first chopped chemical fiber sections. Alternatively, according to a second variant of both embodiments, the chopped chemical fiber sections of 10 the external layers can include a mixture of first chopped chemical fiber sections and second chopped chemical fiber sections. The second chopped chemical fiber sections are of a material having a melting point higher than the melting point of the thermoplastic material of 15 the first chopped chemical fiber sections and a price very much lower than the price of the chemical fibers from which the first chopped chemical fiber sections are fabricated. For example, the chopped second chemical fiber sections are of polyamide or polyester. 20 Another aspect of the invention proposes a method of fabricating a textile armature usable for the production of composite materials or parts, including the following successive steps: a) providing a central layer based on chopped fiber 25 sections of a first type of synthetic material that have received before their formation into a layer a treatment communicating to them a permanent crimp, b) disposing on opposite sides of the central layer an external layer including chopped reinforcement fiber 30 sections and chopped chemical fiber sections with a permanent crimp including at least first chopped chemical fiber sections having at least one surface layer of a second type of thermoplastic synthetic material with a melting point lower than or equal to that of the first 35 type of synthetic material, 8 c) effecting preliminary needle-punching to cause the chopped chemical fiber sections to penetrate into the central layer over part of their length, d) heating the textile armature to soften at least 5 superficially and to render adherent the chopped chemical fiber sections. Such a fabrication process is easy to implement with technical means (machines, tooling, etc.) known and very widely used in the textile industry. The process is 10 therefore of relatively low cost. The use of thermal bonding also allows a higher production rate than using bonding by stitching/knitting or by needle-punching. During the step d), the heating can preferably be obtained by circulating hot air through the textile 15 armature. This heating method provides thermal bonding of the fibers to each other as far as the heart of the textile armature and avoids intensive heating of the lower and upper faces of the textile armature on which are disposed the external layers including chopped 20 chemical fiber sections. This therefore avoids excessive melting of the chopped chemical fiber sections of the external layers and the formation of a continuous layer of thermoplastic material after cooling, which continuous layer would compromise good impregnation of the textile 25 armature by the resin on its use in press molding, injection molding or vacuum molding techniques. Alternatively, during the step d), the heating can be effected by high-frequency microwave radiation or by infrared radiation of appropriate wavelength to soften 30 the first chopped chemical fiber sections. BRIEF DESCRIPTION OF THE DRAWINGS Other objects, features and advantages of the present invention will emerge from the following description of particular embodiments, which is given 35 with reference to the appended figures, in which: 9 - figure 1 is a diagrammatic view in longitudinal section of a textile armature of a first embodiment of the invention during its fabrication; - figure 2 is a diagrammatic view in longitudinal 5 section of the figure 1 textile armature during a preliminary needle-punching operation; - figure 3 is a diagrammatic view in longitudinal section of the figure 2 textile armature during a heating operation; 10 - figure 4 shows in perspective a chopped chemical fiber section of a two-component structure; and - figure 5 is a diagrammatic view in longitudinal section of a textile armature of a second embodiment of the invention. 15 DESCRIPTION OF THE PREFERRED EMBODIMENTS In a first embodiment shown in figure 1, a textile armature 1 of the invention includes three successive textile layers 21, 3 and 22. The central layer 3 is based on chopped fiber sections 3a of a first type of synthetic 20 material. The chopped fiber sections 3a have been treated to confer a permanent crimp on them before they are formed into a layer. To guarantee increased durability of the elasticity of the crimped chopped fiber sections 3a, the latter 25 chopped fiber sections can advantageously be fabricated from single-strand fibers. The chopped fiber sections 3a can have the same unitary linear density. It is nevertheless possible for the chopped fiber sections 3a to have at least two 30 different unitary linear densities for greater regularity of the central layer 3. Thus the central layer 3 can include chopped fiber sections 3a of 110 dTex and chopped fiber sections 3a of 70 dTex, for example. On opposite sides of the central layer 3 are 35 disposed external textile layers 21 and 22. In this 10 embodiment, the external textile layers 21 and 22 are based on a mixture of chopped reinforcement fiber sections 4 and chopped chemical fiber sections 7. The chopped chemical fiber sections 7 have been 5 treated beforehand to confer a permanent crimp on them. The external textile layers 21 and 22 are obtained from a homogeneous mixture of chopped chemical fiber sections 7 and chopped reinforcement fiber sections 4 such as glass fibers or plant fibers. Such a homogeneous 10 mixture can be obtained by means of an appropriate cutter and then will be deposited by gravity onto the two faces of the central layer 3. The homogeneity of the mixture is also a result of the permanent crimp of the chopped chemical fiber 15 sections 7, which imparts a "grab" to the mixture and prevents a phenomenon known as "settling" caused by the different relative densities or sections of the chopped reinforcement fiber sections 4 and the chopped chemical fiber sections 7. 20 Good results have been obtained with external layers 21, 22 produced from a homogeneous mixture containing from 90% by weight of chopped glass fiber sections 4 and 10% by weight of chopped chemical fiber sections 7. 25 The chopped chemical fiber sections 7 of the external textile layers 21 and 22 include at least first chopped chemical fiber sections 70 in a thermoplastic material having a melting point less than or equal to that of the chopped fiber sections 3a of the central 30 layer 3. In the state represented in figure 1, the textile armature 1 has no secure cohesion or connection allowing it to be transported. Once provided with its three textile layers 21, 3 and 22, the textile armature 1 undergoes a preliminary 35 needle-punching treatment shown in figure 2. During this 11 preliminary needle-punching operation, needles 8 cause at least some of the chopped chemical fiber sections 7 (including the first chopped chemical fiber sections 70) of each external textile layer 21 and 22 to penetrate 5 over part of their length into the central layer 3. The direction of movement of the textile armature 1 is indicated by the arrow 12 and the direction of movement of the needles is perpendicular to that direction 12 and to the surface of the textile armature 1. 10 The needles 8 used have barbs 8a of appropriate size for preferential entrainment of the chopped chemical fiber sections 7, and in particular the first chopped chemical fiber sections 70, and do not entrain the chopped reinforcement fiber sections 4 of the external 15 textile layers 21 and 22. In practice, the chopped chemical fiber sections 7, in particular the first chopped chemical fiber sections 70, have a smaller diameter than the chopped reinforcement fiber sections 4. For example, chopped chemical fiber sections 7 of 20 approximately 2 to 6 denier and chopped reinforcement fiber sections 4 of approximately 40 Tex minimum are used. It is to be understood that the thicknesses and dimensions of the lines representing the chopped fiber 25 sections 3a, 4, 7 and 70 in figures 1 to 3 are not representative of the actual thicknesses and dimensions of the chopped fiber sections 3a, 4, 7 and 70. The thicknesses and dimensions used in figures 1 to 3 are merely intended to make it easier for the reader to 30 appreciate the difference between the various fibers 3a, 4, 7 and 70 and textile layers 21, 3 and 22. Preliminary needle-punching differs from needle punching in that the textile armature 1 is passed between the needles 8 at a higher speed and the density of the 35 needles 8 is lower. By way of illustration, standard 12 needle-punching achieves a fabrication rate of at most approximately 4 meters per minute, whereas preliminary needle-punching achieves a rate of between approximately 8 meters per minute and approximately 20 meters per 5 minute. Still by way of illustrative and indicative example, a needle-punching machine conventionally has a needle density per running meter between approximately 1 600 and 32 000, whereas a preliminary needle-punching machine has a needle density per running meter between 10 approximately 900 and 1 400. The low needle density per running meter limits the risk of the chopped reinforcement fiber sections 4 of the textile layers 21 and 22 breaking when the needles 8 cause some of the chopped chemical fiber sections 7 to 15 penetrate the external layers 21 and 22 in the central layer 3, especially in the case of reinforcement glass fibers 4. The preliminary needle-punching is sufficient to ensure cohesion during transfer of the textile armature 20 blank to the next workstation but insufficient to provide the final cohesion of the textile armature 1, which is still not transportable to use as a reinforcing product following preliminary needle-punching. After the preliminary needle-punching operation 25 shown in figure 2, the textile armature 1 is heated (figure 3). During this heating step, the thermoplastic surface layer of the first chopped chemical fiber sections 70 of the external textile layers 21 and 22 is softened and renders the first chopped chemical fiber 30 sections 70 adherent. The first chopped chemical fiber sections 70 that have been entrained by the preliminary needle-punching needles 8 adhere to the adjacent chopped reinforcement fiber sections 4 of the external textile layers 21 and 22 and adhere to the adjacent chopped fiber 35 sections 3a of the central layer 3. After cooling, the 13 various textile layers 21, 3 and 22 of the textile armature 1 are thus interconnected by needle-punched and adhesively bonded fibers of the at least partly thermoplastic first chopped chemical fiber sections 70. 5 The textile armature 1 can then be transported. The adhesion of the at least partly thermoplastic first chopped chemical fiber sections 70 to the chopped reinforcement fiber sections 4 of the external textile layers 21 and 22 and to the chopped fiber sections 3a of 10 the central layer 3 compensates the inability of preliminary needle-punching to ensure sufficient cohesion of the textile armature 1 to render it transportable. In one advantageous embodiment of the invention, the chopped fiber sections 3a of the central layer 3 can 15 be of polypropylene. Polypropylene is easy to spin and easy to shape to produce chopped fiber sections with permanent elastic crimp. Chopped fiber sections 3a in polyester or in polyamide can equally be used. In one embodiment of the invention, the chopped 20 chemical fiber sections 7 include first chopped thermoplastic polyethylene fiber sections 70. First thermoplastic chopped chemical fiber sections 70 of any other material having a melting point lower than that of the chopped fiber sections 3a of the central layer 3 can 25 equally be used. Using polyethylene is advantageous because of its low melting point. The chopped polypropylene, polyester or polyamide fiber sections 3a of the central layer 3 are not damaged much, if at all, by the heating operation and 30 in this case retain all their physical and technical characteristics. On the other hand, the first chopped chemical fiber sections 70 of polyethylene drawn by preliminary needle-punching into the external textile layers 21 and 22 are softened by heating and adhere to 35 the adjacent fibers of the textile layers 21 and 22 and 14 to each other. Heating is adjusted to soften and render the thermoplastic first chopped chemical fiber sections 70 adherent, but without melting them. This avoids the 5 formation of uniform exterior layers on the upper and lower faces of the textile armature 1 that are impermeable to the resin. Such uniform and impermeable layers would compromise good impregnation of the textile armature 1 by the resin during a subsequent step of 10 shaping by press molding, injection molding or vacuum molding. In another advantageous embodiment of the invention, to avoid all risk of formation of exterior layers of low permeability to the resin, two-component 15 thermoplastic fibers can be used as the first chopped chemical fiber sections 70, as shown in figure 4, having a central core 7a and an external sheath 7b, the melting point of the central core 7a being higher than that of the external sheath 7b. 20 The two-component first chopped chemical fiber sections 70 can include a polyamide, polyester or polypropylene central core 7a and an external sheath 7b of copolyester, polyethylene or any other material having a melting point less than that of the chopped fiber 25 sections 3a of the central layer 3. In particular, good results have been obtained using a central core of polyester and an external sheath of copolyester or a central core of polypropylene and an external sheath of polyethylene. Other pairs of materials can be used in the 30 form of coaxial two-component fibers: polypropylene and copolypropylene; polypropylene and ethyl vinyl acetate. Because the central core 7a has a higher melting point than the external sheath 7b, the risk of accidental complete melting of the thermoplastic first chopped 35 chemical fiber sections 70 of the external textile layers 15 21 and 22 during fabrication of the textile armature 1 is avoided. This is also an effective way to limit the risk, during the heating step, of the thermoplastic first 5 chopped chemical fiber sections 70 being completely melted by excessive or poorly controlled heating, forming uniform layers impermeable to the resin by spreading of their constituent material over the upper and lower faces of the textile armature 1. The core of the two-component 10 fibers is not damaged much, if at all: thus the external textile layers 21 and 22 are not damaged. Furthermore, using two-component thermoplastic first chopped chemical fiber sections 70 with an external sheath 7b and a central core 7a reduces the polyolefin 15 content of the textile armature 1. This proves advantageous, the resin being not particularly compatible with polyolefins. In fact, the resin adheres badly to polyolefin fibers. If two-component thermoplastic first chopped 20 chemical fiber sections 70 are used, then the two component thermoplastic first chopped chemical fiber sections 70 can advantageously have an external sheath 7b of copolyester or polyethylene. The chopped polypropylene, polyester or polyamide fiber sections 3a 25 of the central layer 3 are thus not affected by heating. In fact, copolyester and polyethylene have melting points lower than those of polypropylene, polyester or polyamide. It is then possible to heat the textile armature 1 to a temperature just sufficient to soften the 30 copolyester or polyethylene of the two-component thermoplastic first chopped chemical fiber sections 70 without softening or otherwise affecting the polypropylene, polyester or polyamide chopped fiber sections 3a of the central layer 3. 35 In a second embodiment, shown in figure 5, a 16 textile armature 1 of the invention again includes three textile layers 21, 3 and 22 in succession. The central layer 3 has the same structure as the central layer 3 of the figure 1 embodiment described above. 5 In this second embodiment, shown in figure 5, the difference lies in the structure of the external layers 21 and 22. In this case, the external layers 21 and 22 are stratified layers each comprising a respective external stratum 21c or 22c, a respective internal 10 stratum 21a or 22a and a respective intermediate stratum 21b or 22b. The external strata 21c and 22c and the internal strata 21a and 22a consist essentially of chopped sections of chemical fibers such as the chemical fibers 7 15 of the figure 1 embodiment (which include at least first chopped chemical fiber sections 70 including at least one thermoplastic material surface layer). The intermediate strata 21b and 22b consist essentially of reinforcement fibers such as the 20 reinforcement fibers 4 of the figure 1 embodiment. During preliminary needle-punching, chopped chemical fiber sections 7, including first chopped chemical fiber sections 70, are drawn through the strata by the needles until they penetrate into the central 25 layer 3. The subsequent heating bonds the first chopped chemical fiber sections 70 to the other fibers and connects the layers and strata. In a variant of this second embodiment, an internal stratum 21a, 22a can be omitted. 30 The textile armature 1 of the invention can easily be fabricated at low cost by a method including the following steps in succession: a) providing a central layer 3 based on chopped fiber sections 3a of a first type of synthetic material 35 that have received before their formation into a layer a 17 treatment communicating to them a permanent crimp, b) disposing on opposite sides of the central layer 3 a respective external layer 21 and 22 including chopped reinforcement fiber sections 4 and chopped chemical fiber 5 sections 7 with a permanent crimp including at least first chopped chemical fiber sections 70 having at least one surface layer 7b of a second type of thermoplastic synthetic material with a melting point lower than or equal to that of the first type of synthetic material, 10 c) effecting preliminary needle-punching (figure 2) to cause the chopped chemical fiber sections 7, in particular the first chopped chemical fiber sections 70, of each external layer 21 and 22 to penetrate into the central layer 3 over part of their length, 15 d) heating the textile armature 1 (figure 3) to soften at least superficially and to render adherent at least said first chopped chemical fiber sections 70. After the step d) of heating the textile armature 1, there can advantageously follow a step e) of cold 20 rolling the textile armature 1 to give it a constant and homogeneous thickness. Rolling also encourages compacting of the fibers and bonding of the fibers to each other. The chopped chemical fiber sections 7 of the external layers 21 and 22, and in particular the first 25 chopped chemical fiber sections 70, can advantageously have a diameter less than that of the chopped reinforcement fiber sections 4. The preliminary needle punching of the step c) is then effected by means of needles 8 (figure 2) that have barbs 8a adapted to 30 entrain preferentially the chopped chemical fiber sections 7, including the first chopped chemical fiber sections 70, but not to entrain significantly the greater diameter chopped reinforcement fiber sections 4. During the heating step d), the textile armature 1 35 enters a hot-air tunnel oven 9. The hot-air tunnel oven 9 18 includes a conveyor belt 11 that moves the textile armature 1 through the oven 9 in the direction defined by the arrow 13. The conveyor belt 11 is perforated. Hot air jets 14 are directed through the textile armature 1 to 5 heat it throughout its thickness in order to cause the first chopped chemical fiber sections 70 which are at least in part of the thermoplastic type to adhere to the chopped fiber sections 3a of the central layer 3 and to the chopped reinforcement fiber sections 4 of the 10 external layers 21 and 22. To produce a textile armature 1 conforming to the embodiment of figures 1 to 3, a homogeneous mixture of chopped chemical fiber sections 7 and chopped reinforcement fiber sections 4 is obtained by means of a 15 cutter during the step b) and deposited by gravity onto the two faces of the central layer 3. To produce a textile armature 1 conforming to the embodiment of figure 5, the chemical fiber strata 21a, 22a, 21c and 22c are each produced by carding. The 20 internal strata 21a and 22a, if any, are disposed on either side of the central layer 3, after which the intermediate strata 21b and 22b of reinforcement fibers cut by a cutter are deposited by gravity, after which the external strata 21c and 22c are disposed on either side 25 of the assembly formed in this way. In a first variant of all the embodiments described above and shown in figures 1 to 5, the chopped chemical fiber sections 7 of the external layers 21 and 22 can consist only of first chopped chemical fiber sections 70. 30 In a second variant of each of these embodiments, the chopped chemical fiber sections 7 of the external layers 21 and 22 can consist of a mixture of first chopped chemical fiber sections 70 and second chopped chemical fiber sections 71. 35 The second chopped chemical fiber sections 71 are 19 chosen to have a melting point higher than that of the first chopped chemical fiber sections 70 and are of a material less costly than the material of the first chopped chemical fiber sections 70. Second chopped 5 chemical fiber sections 71 of polyester or polyamide could be used, for example. Firstly, using a mixture of first chopped chemical fiber sections 70 and second chopped chemical fiber sections 71 significantly reduces the fabrication cost of 10 the textile armature of the invention. For example, a mixture containing approximately 50% to 70% by weight of second chopped chemical fiber sections 71 can be used. Furthermore, using a mixture reduces the quantity of thermoplastic material in the external layers 21 and 15 22 to avoid, after the heating step, forming on the surface of the textile armature 1 an impermeable film of thermoplastic material preventing penetration of the resin, whilst conferring on the mixture, thanks to the second chopped chemical fiber sections 71, sufficient 20 density to be carded by a conventional carding device. It should be noted that the textile armature 1 of the invention, in particular its variant with a mixture of first chopped chemical fiber sections 70 and second chopped chemical fiber sections 71, has proven to be of 25 remarkable benefit in so-called "pre-forming" techniques. In this case, the textile armature 1 is heated during the step d) of the fabrication process that conforms it to a required shape. It is heated just sufficiently for the shape obtained to be able to be 30 transported to a resin injection molding machine with a mold corresponding to the shape obtained and enabling the textile armature to be heated again, and slightly more strongly, before or during injection of the resin. In the case of preforming a textile armature 1 with 35 exterior layers 21 and 22 in a mixture of first chopped 20 chemical fiber sections 70 and second chopped chemical fiber sections 71, it has been found advantageous to use approximately 50% by weight or more of first chopped chemical fiber sections 70. 5 Example I) On a conventional carding device, a central layer 3 is produced of chopped crimped monofilament fiber sections 3a of polypropylene with a unitary linear density of 110 dTex. The chopped fiber sections 3a have a 10 cut length of approximately 90 mm, a crimp of approximately two undulations per centimeter, and a melting point between approximately 170 0 C and 180 0 C. The central layer 3 has a mean thickness between approximately 4 and 5 mm and a weight of approximately 15 250 grams per square meter. For greater regularity of the central layer 3, chopped crimped monofilament polypropylene fiber sections 3a with a unitary linear density of 70 dTex can be mixed in a proportion from 10% to 50% by weight with chopped 20 fiber sections 3a having a unitary linear density of 110 dTex. II) There is deposited on each face of the central layer 3 an internal stratum 21a and 22a consisting of chopped chemical fiber sections 7. 25 The chopped chemical fiber sections 7 consist of a mixture comprising 70% (by weight) of second chopped crimped chemical fiber sections 71 of polyester and 30% (by weight) of two-component first chopped chemical fiber sections 70. The two-component first chopped chemical 30 fiber sections 70 have a central core 7a of polyester and a thermoplastic external sheath 7b of copolyester. The thermoplastic copolyester external sheath 7b has a melting point of approximately 1100C. The second chopped crimped chemical fiber sections 35 71 of polyester have a unitary linear density between 21 approximately 3 denier and approximately 6 denier, preferably chosen to be approximately 3.5 denier. The two-component first chopped chemical fiber sections 70 have a unitary linear density between 5 approximately 2 denier and 4 denier. III) There is deposited on each internal stratum 21a and 22a an intermediate stratum 21b and 22b consisting of chopped reinforcement fiber sections 4. The chopped reinforcement fiber sections 4 are 10 chopped glass fiber sections 4 having a unitary linear density of approximately 50 Tex and a cut length of approximately 50 mm. The diameter of the elementary fibers of the chopped glass fiber sections 4 is approximately 15 14 microns. The intermediate strata 21b and 22b have a density close to 450 g/m 2 . IV) There is deposited on each intermediate stratum 21b and 22b an external stratum 21c and 22c of identical 20 composition to the internal strata 21a and 22a. V) The textile armature 1 is introduced by means of a conveyor belt 11 into a roller-type preliminary needle puncher. The density of the needles is 4.6 per square centimeter, the separation of the rollers is 20 mm, and 25 the depth of penetration of the needles is 12 mm. The belt moves at a speed of 10 meters per minute. VI) After the preliminary needle-punching operation, the textile armature 1 is passed through a hot-air tunnel oven 9 having a heating portion 20 meters 30 long at a speed of 10 meters per minute. The temperature of the hot-air tunnel oven 9 is approximately 120 0 C. VII) On exit from the hot-air tunnel oven 9, cold rolling gives the textile armature 1 its final thickness, which is close to approximately 4 to 5 mm. 35 The present invention is not limited to the 22 embodiments explicitly described and includes variants and generalizations thereof within the scope of the following claims.

Claims

1. A textile armature usable for the production of composite materials or parts, comprising: - a central layer based on chopped fiber sections of a first type of synthetic material that have received before their formation into a layer a treatment communicating to them a permanent crimp, - external layers disposed on opposite faces of the central layer, wherein: - the external layers include chopped chemical fiber sections that have previously received a treatment conferring on them a permanent crimp and chopped reinforcement fiber sections, - at least some of the chopped chemical fiber sections penetrate over a part of their length into the central layer, - the chopped chemical fiber sections include at least first chopped chemical fiber sections including at least one surface layer of a thermoplastic material having a melting point lower than that of the chopped fiber sections of the central layer, - the first chopped chemical fiber sections adhere, through thermal bonding, at least partly to each other and to the other adjacent chopped fiber sections in the external layers and to the other adjacent chopped fiber sections in the central layer.

2. A textile armature according to claim 1, wherein the chopped fiber sections of the central layer are of polypropylene, polyester or polyamide.

3. A textile armature according to either of claims 1 or 2, wherein the chopped fiber sections of the central layer have at least two different unitary linear densities.

4. A textile armature according to any of claims 1 to 3, wherein the chopped chemical fiber sections of the external layers have a cross section with a diameter less than that of the chopped reinforcement fiber sections.

5. A textile armature according to any of claims 1 to 4, wherein the first chopped chemical fiber sections of the external layers are of a thermoplastic material with a melting point lower than that of the chopped fiber sections of the central layer. 24

6. A textile armature according to any of claims 1 to 4, wherein: - the first chopped chemical fiber sections of the external layers are two-component chopped fiber sections having a central core of a first component and an external sheath of a second component, - the melting point of the first component of the central core is higher than that of the second component of the external sheath.

7. A textile armature according to claim 6, wherein: - the central core is of polyamide, polyester or polypropylene, - the external sheath is of a thermoplastic material with a melting point lower than that of the chopped fiber sections of the central layer.

8. A textile armature according to any of claims 1 to 7, wherein the chopped chemical fiber sections in the external layers include only first chopped chemical fiber sections.

9. A textile armature according to any of claims 1 to 7, wherein the chopped chemical fiber sections in the external layers include a mixture of first chopped chemical fiber sections and second chopped chemical fiber sections.

10. A textile armature according to any of claims 1 to 9, wherein the chopped chemical fiber sections and the chopped reinforcement fiber sections in the external layers are mixed in a generally homogeneous manner.

11. A textile armature according to any of claims 1 to 9, wherein the external layers are stratified, comprising an external stratum essentially of chopped chemical fiber sections, with or without an internal stratum essentially of chopped chemical fiber sections and with an intermediate stratum essentially of reinforcement fibers.

12. A textile armature substantially as hereinbefore described with reference to any of the embodiments as that embodiment is shown in the accompanying drawings.

13. A method of fabricating a textile armature usable for the production of composite materials or parts, including the following successive steps: a) providing a central layer based on chopped fiber sections of a first type of synthetic material that have received before their formation into a layer a treatment conferring on them a 25 permanent crimp, b) disposing on opposite sides of the central layer an external layer including chopped reinforcement fiber sections and chopped chemical fiber sections with a permanent crimp including at least first chopped chemical fiber sections having at least one surface layer of a second type of thermoplastic synthetic material with a melting point lower than or equal to that of the first type of synthetic material, c) effecting preliminary needle-punching to cause the chopped chemical fiber sections, in particular the first chopped chemical fiber sections, to penetrate into the central layer over part of their length, d) heating the textile armature to soften at least superficially and to render adherent at least said first chopped chemical fiber sections.

14. A method according to claim 13, further including after the step d) a step e) during which the textile armature is cold-rolled.

15. A method according to either of claims 13 or 14, wherein: - the chopped chemical fiber sections of the external layers have a diameter less than that of the chopped reinforcement fiber sections, - the preliminary needle-punching of the step c) is effected by means of needles that have barbs adapted to entrain preferentially the chopped chemical fiber sections, in particular the first chopped chemical fiber sections, but not to entrain significantly the larger diameter chopped reinforcement fiber sections.

16. A method according to any of claims 13 to 15, wherein during the step d) the heating is effected by circulating hot air through the textile armature.

17. A method of fabricating a textile armature substantially as hereinbefore described with reference to the accompanying drawings. Gilbert Chomarat Patent Attorneys for the Applicant/Nominated Person SPRUSON & FERGUSON