EP0527092B1 - Textile reinforcement usable for making layered compositions and method for its manufacture - Google Patents

Abstract

Textile reinforcement usable for the production of laminated composites. It comprises three series of yarns (1a, 1b, 2) oriented differently in relation to one another, two (1a, 1b) being arranged slantwise, inversely to one another in relation to the length of the strip, and the yarns (2) of the third being, for their part, arranged parallel to the length and trapped between the yarns (1a, 1b). In this material the lengthwise yarns (2) consist at least partially of yarns exhibiting thermal adhesive properties, whose adhesive characteristics are developed after the braid is produced and make it possible to ensure the bonding of the two-directional outer layers (1a, 1b) without possibility of movement of the positioning of the yarns relative to one another. <IMAGE>

Description

The invention relates to an improvement made to the textile reinforcements used for the production of laminate complexes, that is to say articles based on resin (polyester or others), reinforced by a textile reinforcement structure.

To date, as a reinforcing textile reinforcement, in addition to the structures consisting of woven or nonwoven webs, possibly combined with one another (by needling, sewing / knitting, etc.), it has also been proposed to use, in particular for the production tubular hollow bodies of cylindrical or conical shape, profiles of various shapes, braided sheaths (see FR-A-2 402 730 corresponding to US-A-4 228 207, FR-A-2 455 980, 2 462 266 or 2,510,624).

Such braided sheaths which are particularly suitable for the production of tubular articles, are constituted, in a known manner, by two series of interlaced wires arranged at an angle with respect to the generator of the braid. During the manufacture of these braids, the wires are generally oriented at 45 ° relative to the generator. This material being deformable, it is therefore possible to play on this deformability in order to obtain laminated complexes of variable shapes and / or to vary the resistance either in the longitudinal direction or in the transverse direction. Thus, it is possible to considerably improve the longitudinal resistance by stretching the braid lengthwise, which causes the tubular sheath to tighten, and directs the wires which compose it in a direction which tends to approach the generator.

Such braids made up of two series of crossed threads are generally designated by the expression "bidirectional braids".

In addition to the aforementioned bidirectional braids, it has also been proposed to produce braids, designated by the expression "three-way braids", in which a third series of wires is arranged parallel to the generator and is trapped between the two series of wires arranged in bias. Such three-way braids can be used either alone or optionally have an internal core as described in FR-A-2 379 376, which can be impregnated with a thermoplastic matrix, which makes it possible to obtain directly on the machine braiding a composite tubular structure as shown in EP-A-0 327 085.

If as said previously, such reinforcing structures are suitable for the production of cylindrical elements (tubes, windsurfing masts, tennis rackets, etc.), on the other hand, they are not suitable when it is desired to make materials laminates of small thickness, flat or shaped, obtained in particular according to the technique known as "pultrusion", a technique which, in general, consists in producing profiles continuously by extruding a thermosetting resin and by continuously incorporating a reinforcement therein textile and which therefore involves significant tensioning, and therefore requires the use of non-deformable reinforcements, a property incompatible with that of a braid where, by nature, the threads can be easily moved relative to each other.

As a result, to date, for the production of laminated articles obtained by pultrusion, and more particularly in the case of articles in the form of a profile (L, U, V ..), as textile reinforcements, we therefore generally use unidirectional sheets made up of filamentary wicks held parallel to one another. These reinforcements make it possible to obtain profiles which can have complex shapes, the thickness of which is constant and in which the textile reinforcement is perfectly positioned inside the resin. The profiles thus obtained have good tensile strength taking into account the longitudinal reinforcements, but, on the other hand, may have shortcomings in resistance to torsion, in particular in the case of elements having a long length.

Now we have found, and this is what is the subject of the present invention, an improvement in textile reinforcements of the three-way braid type, which solves all of these problems and makes it possible to produce laminated articles, in particular by the technique called "pultrusion", which can have a profile (section in L, U, V ..) complex, of great length and of small thickness (of the order of a few millimeters), and in which the reinforcing wires are not moved relative to each other during shaping and extend both parallel and at an angle relative to the length of the profile produced.

Admittedly, such articles comprising wires oriented in three directions, had been proposed for a very long time (cf. US-A-3 446 25I), but, as appears from this document, their realization implied to obtain a crisscrossing of the threads between them by weaving, This is to prevent the series of elementary wires from moving relative to each other. Consequently, although no indication is given in this document on the manner in which such articles could be produced, it is clear that they require weaving looms which must be the subject of major adaptations in order to be able to orient the warp and weft son along three axes.

The three-way frame according to the invention can, for its part, be obtained according to a simple process, on conventional braiding material, without any adaptation of the latter as regards the production of the basic three-way braid entering its realization, and this according to a simple process which is also part of the invention.

In general, the reinforcement according to the invention comprises three series of wires oriented differently with respect to each other, two being arranged at an angle, in opposite directions to each other, with respect to the length , and the wires of the third being in turn arranged parallel to the length, and trapped between the two series of wires arranged at an angle, and in which said longitudinal wires consist at least in part of wires having fusible properties, the adhesive characteristics are revealed after completion of the braid, and make it possible to ensure the connection of the bidirectional external layers without the possibility of displacement of the positioning of the wires relative to each other, characterized in that said tubular braid is cut according to one of its generators and then laid flat giving a reinforcement in the form of a flexible sheet constituted by a single layer three-way.

Thanks to such a structure, a material is therefore obtained which not only has the advantages of braided textile reinforcements (orientation of the filaments at an angle relative to the length and this, at a determined angle, which can be easily adjusted during the production of said braid), but which does not have the disadvantages (deformability) which are harmful when it is desired to produce a profiled structure, the wires of the unidirectional sheet being, moreover, kept as flat and as straight as possible, without displacing the relative to each other, a necessary condition for obtaining a good quality laminate complex, especially when it is thin.

Furthermore, such a structure makes it possible to produce materials which can either be composed of yarns of the same kind (for example entirely based on son of glass, carbon, boron, silica, aromatic polyamide, etc.), or make a combination of different reinforcing threads, for example alternating glass and carbon threads, both in the bidirectional structure and in the unidirectional ply. It can also be envisaged to incorporate, in one or all of the plies, metallic wires allowing optionally to shape the reinforcement material and / or to give it specific properties.

The invention also relates to a method allowing the production of such a material, said method consisting in forming a tubular braid comprising at least two series of threads intertwined with respect to each other, and arranged at an angle with respect to the generator of the braided sheath, to be introduced simultaneously with the formation of the braid, inside the latter, between the threads arranged at an angle, a series of longitudinal, parallel threads, at least part of which consists of threads having fusible properties, the positioning of the transverse and longitudinal wires with respect to each other is fixed on the braiding machine by a heat treatment revealing the properties of the fusible wires, said heat treatment being carried out by keeping the tubular braid in shape, characterized in that, after fixing the wires relative to each other, said braid is cut according to a generator and it is laid flat, thus giving an armature constituted by a single three-way layer.

The invention and the advantages which it brings will however be better understood thanks to the exemplary embodiments given below by way of indication but not limitation, and which are illustrated by the two appended figures which are reproductions of articles produced in accordance with l he invention, part of the threads of the diapers oriented at an angle not being shown in certain zones to clearly show the way in which the different filamentary plies are arranged with respect to each other.

If one refers to the two appended figures in which the same elements are designated by the same references, the textile reinforcement according to the invention is therefore in the form of a flat strip, designated by the general reference (1 ), of very long length L compared to its width l . It comprises three series of wires oriented differently from each other. Two of these series of wires (1a, 1b) are arranged at an angle, in opposite directions to each other with respect to the length L of the strip. The wires (2) of the third series are, in turn, arranged parallel to the length L and are trapped between the two series of wires (1a, 1b) which are braided together. In the material according to the invention, the threads (2) of the undirectional sheet consist at least in part of threads having fusible properties revealed by heat treatment. Such threads (2) can be, for example, constituted by threads of the "core / sheath" type, the core being constituted by glass filaments, the sheath by a coating based on a polymer, such as a copolyamide.

Such a complex structure is obtained directly on a conventional braiding machine, making it possible to produce a tubular braid comprising two series of wires arranged at an angle (1a, 1b), between which are trapped longitudinal wires (2). The orientation of the wires arranged at an angle is obtained by adjusting, in a known manner, the braiding angle. The braiding angle can be either fixed, which makes it possible to obtain an article of determined width l , or possibly be variable during production, making it possible to obtain a braid of variable section.

In the example illustrated in FIG. 1, the tubular braid is subjected to a pressure at the outlet of the machine so that it becomes flat, the heat treatment making it possible to reveal the fusible properties of the longitudinal threads being carried out, either during this flattening phase either after this, which makes it possible to link the different layers of the complex together.

In the embodiment illustrated in FIG. 2, the heat treatment revealing the properties of the fusible wires of the unidirectional sheet, is carried out by maintaining the braid in its circular form, which then makes it possible to cut it according to a generator to return it to flat and get a larger item.

In the two embodiments illustrated in FIGS. 1 and 2, the material according to the invention is produced on a conventional braiding machine, of the "SPIRALTEX" type comprising 96 spindles and therefore making it possible to produce a bidirectional braid having two oriented plies in reverse, and each consisting of 48 wires. The son (2) of the unidirectional sheet are incorporated into the braid in a known manner.

In the two exemplary embodiments, the plies forming the threads arranged at an angle (la, lb), consist of wicks of carbon threads, having a titer of 400 tex. In the example illustrated in FIG. 1, the unidirectional sheet (wires 2) is constituted by wires of the core / sheath type, the core being based on a 22 tex glass wire and the sheath constituted by a copolyamide-based coating, the melting point of which is approximately 115 ° C. In the example illustrated in FIG. 2, the material comprises on the one hand, fusible wires (2) of the aforementioned type used as longitudinal element and, on the other hand arranged in parallel with these fusible wires, wires (2a) , made of carbon wicks.

The complexes thus produced can be used in numerous applications, such as for example as reinforcements of profiles obtained by pultrusion.

Of course, the invention is not limited to the embodiments described above, but it covers all the variants produced in the same spirit.

Claims (2)

1. A textile reinforcement usable for the production of laminated composites obtained especially by the so-called « pultrusion » technique, comprising three series of yarns (1a.1b,2) oriented differently relative to one another, two (1a, 1b) being arranged aslant, inversely to one another, in relation to the length of the strip, and the yarns (2) of the third being, for their part, arranged parallel to the length and being trapped between the two series of yarns (1a,1b) arranged aslant, in which said lengthwise yarns (2) consist at least partially of yarns exhibiting heat-adhesive properties, whose adhesive characteristics are developed after production of the braid, and make it possible to ensure the bonding of the two-directional outer layers (1a,1b) without the possibility of movement in the positioning of the yarns relative to one another, characterised in that said tubular braid is cutted along one of its generatrices and flattened producing a reinforcement formed of a supple sheet comprising a single three directional layer.
2. A process for obtaining the material as claimed in claim 1, which consists in forming a tubular braid comprising at least two series of mutually intercrossed yarns (la,lb) arranged aslant in relation to the generatrix of the braided sheath, in introducing simultaneously with the formation of the braid, inside the latter, between the yarns (1a,1b) arranged aslant, a series of parallel lengthwise yarns (2) at least part of which consists of yarns exhibiting heat-adhesive properties, in which the positioning of the transverse and lengthwise yarns relative to one another is fixed on the braiding machine by a heat treatment developing the properties of the heat adhesive yarns, said heat treatment being carried out by maintaining the braid in form characterised in that, after the yarns have been fixed relative to one another, cutting said braid along a generatrix and reflattening it, the reinforcement so realised being constituted by a single three directional layer.

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