EP0466618B1 - Hybrid yarn for composite materials made from thermoplastic matrix and process for producing the same - Google Patents

Abstract

This hybrid yarn is of the type comprising an intimate mixture of threads of reinforcing fibres and of threads of thermoplastic matrix fibres, each of the threads of fibres having been obtained by cracking by a slow and progressive drawing of multifilaments. According to the invention, after drawing the parallel fibres (2, 3) are overwound with a continuous filament (19) of thermoplastic material. Application to the production of hot-pressed articles. <IMAGE>

Description

The subject of the present invention is a hybrid yarn for composite materials with a thermoplastic matrix, consisting of thermoplastic fibers, as well as the process for obtaining it according to the preamble of claim 1 and according to the preamble of claim 5.

In the current processes used for the manufacture of these types of composite materials, the reinforcing fibers (carbon, aramid or glass), which are generally found in the form of multifilaments, are woven alternately with multifilaments of thermoplastic matrix fibers.

• Polyéther éther cétone (PEEK),
• Polysulfure de phénylène (PPS),
• Polyétherimide (PEI),
• Polyéthersulfone (PES),
• Polyamide.

These thermoplastic matrix fibers belong to the classic families:

• Polyether ether ketone (PEEK),
• Polyphenylene sulfide (PPS),
• Polyetherimide (PEI),
• Polyethersulfone (PES),
• Polyamide.

• une mauvaise mouillabilité,
• un taux de vide important,
• un délaminage des fibres de renfort.

This manufacturing technique has many disadvantages, among which we can cite:

• poor wettability,
• a high vacuum rate,
• delamination of the reinforcing fibers.

Another technique consists in intermingling the multifilament of reinforcing fibers with the multifilament of thermoplastic fibers, according to a process called COMINGLED.

There are also other methods, which consist of loading the reinforcing fibers with a thermoplastic pulverulent matrix, the exterior of which comprises a molten sheath which contains the powder. There are also solvent impregnation methods, the implementation of which is problematic, in particular for the safety of workers and the environment. The inclusion of residual solvents in the composite is also detrimental to good fire resistance.

• Coût de réalisation des fils,
• Difficultés au tissage ou tressage ou U.D.,
• Impossibilité de réaliser des pièces de formes complexes, car indéformabilité du réseau de fibres de renfort continues.

These different techniques have significant drawbacks in different areas in common:

• Cost of making the wires,
• Difficulties in weaving or braiding or UD,
• Impossibility of producing parts of complex shapes, because the network of continuous reinforcing fibers is indeformable.

It is known, from French patent 2,634,799 (EP-A-0 354 139) in the name of the Applicant, to produce a hybrid yarn for composite materials with a thermoplastic matrix, by an intimate mixture of reinforcing fibers and matrix fibers thermoplastics, which have previously undergone, independently of each other, a cracking operation according to a slow and progressive drawing of multifilaments.

The final ribbon obtained is then subjected to the conventional operations of spinning long fibers: passage on a bench with spindles, actual spinning, winding, assembly and twisting.

The yarns thus obtained are capable of being transformed by weaving, knitting or braiding to obtain composite materials having numerous advantages compared to materials of the same type obtained according to the processes of the prior art.

• une très bonne mouillabilité des fibres de renfort,
• un très faible taux de vide,
• une drapabilité des surfaces textiles permettant le moulage des surfaces développables ou non ;
• une très bonne isotropie du matériau dans la direction des fibres de renfort,
• une excellente résistance au délaminage. En fait, le matériau se présente comme un solide monolithique qui a "oublié" sa structure initiale stratifiée.

These are:

• very good wettability of the reinforcing fibers,
• a very low vacuum rate,
• drapability of textile surfaces allowing the molding of developable surfaces or not;
• a very good isotropy of the material in the direction of the reinforcing fibers,
• excellent resistance to delamination. In fact, the material is presented as a monolithic solid which "forgot" its initial stratified structure.

The composite obtained also has very good hot stamping skills.

Document DE-A-2 407 357 describes a yarn intended for clothing textiles obtained from a bundle of vegetable or animal fibers (cotton, wool) in intimate mixture with polyester or polyamide. The gimp spinning technique is used here to significantly improve the speed of production. This yarn comprises a covering filament which is of the same nature as the synthetic fiber in mixture for reasons of dye affinity. This covering filament which is an integral part of the thread and remains present in the garment obtained, also has the function of imparting dimensional stability to the garment and of limiting the wrinkling of the fabric.

The object of the invention is to provide a hybrid wire having all the qualities of the wire of document FR-A-2 634 790, but also having a excellent deformability allowing the production, from a textile web obtained with the yarn according to the invention, of hot stamped parts having deep shapes, without rupture and without the formation of folds detrimental to the homogeneity of such parts.

To this end, the hybrid yarn which it concerns, of the type comprising an intimate mixture of yarns of reinforcing fibers and yarns of thermoplastic matrix fibers, each of the yarns of fibers having been obtained by cracking according to a slow and progressive drawing of multifilaments , is characterized in that, after stretching, the parallel fibers are covered by a continuous filament of thermoplastic material, of the same nature as the matrix fibers of thermoplastic material, the covering thermoplastic filament represents between 10 and 25% of the total volume of thermoplastic material that the wire contains.

The structure of the yarn according to the invention makes it possible to use a bundle of organic or inorganic fibers of very high modulus to form a yarn in which each fibrous element remains rectilinear, which avoids using a twist inducing internal stresses in the fibers. . In addition, the use of a thermoplastic fiber filament to make the covering, ensures the holding of the thread during the operation of transforming the thread into a textile surface, by weaving or knitting for example, while during the transformation of the textile surface into a composite, the covering filament as well as the thermoplastic fibers of the core melt, releasing the mass of high modulus fibers which constitutes a reinforcement perfectly free from any constraint. There remains in the composite only a network of these reinforcing fibers, embedded in the organic material which has melted. There is therefore no trace of the covering filament in the final composite.

It should be noted that in the yarn in the invention the fibers are treated by cracking, while in traditional techniques the organic fibers undergo a cutting operation.

According to another characteristic, this yarn comprises from 50 to 55% of reinforcing fibers for 50 to 45% of thermoplastic fibers.

The reinforcing fibers are chosen from carbon, aramid or glass fibers while the thermoplastic matrix fibers are chosen from polyether ether ketone (PEEK), phenylene polysulfide (PPS), polyethersulfone (PES), polyetherimide fibers (PEI), as well as among the other fibers known for this purpose, such as polyamides and polyimides.

The deformability of a composite material obtained from this wire is excellent, given the very great sliding ability of the reinforcing fibers therebetween, during molding, that is to say when the thermoplastic fibers have melted.

This advantage results from the discontinuity of the reinforcing fibers and from the non-bonding between them by a twist on the original wire. These deformability characteristics are obtained without harming the other characteristics, and in particular the mechanical characteristics.

Such a wire is therefore particularly suitable for the production of complex parts in the fields of industry, the automobile and aeronautics, in particular for the interior trim parts of aircraft and helicopter cabins.

A process for obtaining this hybrid yarn consists first of all in subjecting multifilaments of reinforcing fibers and multifilaments of matrix fibers to separate cracking processes by slow and progressive drawing, in assembling the ribbons of staple fibers thus obtained on an intersecting type stretching machine, the ribbon leaving this stretching machine being assembled on another stretching machine with identical ribbons, this operation being repeated several times, in order to obtain the most intimate mixture possible , subjecting the ribbon obtained to drawing in a rolling system, and finally passing the bundle of staple fibers, mixed and parallel, inside a hollow spindle carrying a continuous filament of thermoplastic material of the same kind as matrix fibers of thermoplastic material, the thermoplastic filament represents between 10 and 25% of the total volume of thermoplastic material that e contains the yarn, to cover the bundle of fibers with the continuous filament.

In view of the low cohesion of the fibers, a zone is laminated with the fibers supported on a single strip, with a drawing rate less than 50 and a running speed reduced by 50% compared to the values set. used for the transformation of organic fibers.

• Figure 1 est une diagramme de longueurs des fibres ayant été soumises à l'opération de craquage ;
• Figure 2 est une vue très schématique de l'installation de craquage des fibres ;
• Figure 3 est une vue très schématique d'une installation de mélange des fibres craquées conduisant à l'obtention d'un ruban de filés de fibres hybrides selon l'invention ;
• Figure 4 est une vue schématique de la structure du fil selon l'invention ;
• Figure 5 est une vue du dispositif de filage.

In any case, the invention will be clearly understood with the aid of the following description of a process for obtaining the hybrid wire for composite materials according to the invention, with reference to the appended schematic drawing in which:

• Figure 1 is a length diagram of the fibers having been subjected to the cracking operation;
• Figure 2 is a very schematic view of the fiber cracking installation;
• Figure 3 is a very schematic view of a mixing installation cracked fibers leading to the production of a ribbon of hybrid fiber yarns according to the invention;
• Figure 4 is a schematic view of the structure of the wire according to the invention;
• Figure 5 is a view of the spinning device.

The yarn according to the invention contains reinforcing fibers which are designated by the general reference 2, and matrix fibers of thermoplastic material designated by the general reference 3.

Multifilaments of matrix fibers are subjected to a cracking operation using an installation shown diagrammatically in FIG. 2. Multifilaments of reinforcing fibers are also subjected to a cracking operation using an installation similarly type. This installation shown in FIG. 2 comprises coils 10 intended for supplying cables with multifilaments. These cables are subjected to a cracking operation by controlled stretching and breaking, by successive passages in zones 11, 12, 13 and 14, the speeds of the stretching zones 11, 12 and of the cracking zones 13, 14 gradually increasing by zone 11 to zone 14 which makes it possible to obtain, at the outlet, a strip of discontinuous tapes whose average length is perfectly controlled. This length is illustrated in the diagram of FIG. 1 in which the lengths of fibers in millimeters appear on the ordinate, and on the abscissa the population of fibers, expressed as a percentage of the number of fibers in this population. Separate installations of the type shown in FIG. 2 are used to obtain, on the one hand, ribbons of staple fibers of reinforcement 2 and, on the other hand, ribbons of discontinuous fibers of thermoplastic matrix 3.

These ribbons 2 and 3 are then brought, by means known per se, to a mixing device shown in FIG. 3. This device consists of an installation comprising a drawing zone 15 of the intersecting type, which makes it possible to obtain, at the outlet, a non-homogeneous ribbon 4 of reinforcing fibers 2 and of matrix fibers 3 mixed, which comprises "traces" of each of the components.

Each ribbon 4 thus obtained is, on leaving this machine, assembled on a similar machine with ten other identical ribbons. This operation is repeated several times, generally four times, which makes it possible to obtain yarns of hybrid fibers in desired final proportions of reinforcing fibers and of thermoplastic fibers. These proportions vary according to the characteristics of the free thermoplastic matrices, and in particular their hot viscosity. However, the respective proportions of reinforcing fibers and thermoplastic matrix fibers are of the order of 53% and 47% respectively.

The ribbon obtained is then subjected to a spinning operation called spinning by wrapping on a long fiber laminating system, as shown in FIG. 5. The reinforcement and matrix fibers, intimately mixed, are subjected to drawing in a system of conventional rolling, 16, 17, type SKF or SUESSEN. At the delivery point 18, the parallel fibers are covered by a continuous multifilament 19 of the same kind as the matrix fiber used. The filament 19 is carried by a hollow spindle 20, inside which passes the bundle of parallel mixed staple fibers, wrapped by the resin filament. The complete wrapped wire 22 is then taken up in receiving cylinders 23. The structure of the wrapped wire 22 is shown in particular in FIG. 4.

Under these conditions, a network of discontinuous reinforcing fibers and a perfectly straight matrix is obtained. This yarn has a very important advantage when compared to the spinning technique based on twisted yarns. Indeed, in this latter technique the fibers are deformed into helices, and are therefore subjected to a compound stress, shear and traction, which very significantly alters the mechanical properties of the composites obtained.

The yarns according to the invention are suitable for being transformed by weaving, knitting or braiding in order to obtain composite materials having excellent wettability characteristics, a very low void ratio, a very good isotropy in the direction of the reinforcing fibers , excellent resistance to delamination, and excellent capacity for deformation by sliding of the reinforcing fibers therebetween, after softening of the thermoplastic fibers.

Table I compares the properties of different composite materials produced from a mixture of carbon-based reinforcing fibers and thermoplastic matrix fibers based on phenylene polysulphide (PPS).

The samples bearing the references one to six belong to the family of discontinuous reinforcement composites, in long cracked and twisted fiber technique. The SAMPE and composites n ° 3 references correspond to the intermingled continuous wire technique (COMINGLED).

This table shows the existence of slight differences in fiber levels. The densities are also very close. On the other hand, there is a very low void rate for the hybrid wire according to the invention, which shows that the composite obtained is very homogeneous. The mechanical characteristics of the wire according to the invention are very close to those of other wires, whether at the module level and breaking stress in bending or in tension.

For their part, the deformability tests show a very clear advantage for the wire according to the invention.

As is apparent from the foregoing, the invention brings a great improvement to the existing technique by providing a hybrid wire having not only excellent mechanical characteristics, but also perfect deformability.

Claims (5)

1. Hybrid wire for composite materials with a thermoplastic matrix, of the type comprising an intimate mixture of threads of reinforcing fibres and threads of thermoplastic matrix fibres, each of the threads of fibres having been obtained by cracking by means of slow, progressive drawing of multifilaments, characterised in that, after drawing, the parallel fibres (2, 3) are covered by a continuous filament (19) of thermoplastic material, of the same nature as the matrix fibres (3) of thermoplastic material, and the covering thermoplastic filament (19) represents between 10% and 25% of the total volume of thermoplastic material contained in the wire.
2. Hybrid wire according to Claim 1, characterised in that it comprises from 50% to 55% of reinforcing fibres (2) with 50% to 45% of thermoplastic fibres (3).
3. Hybrid wire according to either one of Claims 1 and 2, characterised in that the reinforcing fibres (2) are chosen from amongst carbon, aramid or glass fibres.
4. Hybrid wire according to any one of Claims 1 to 3, characterised in that the thermoplastic matrix fibres (3) are chosen from amongst the fibres of polyether ether ketone (PEEK), phenylpolysulphide (PPS), polyethersulphone (PES) and polyetherimide (PEI), and from amongst other known fibres used for this purpose, such as polyamides and polyimides.
5. Process for obtaining a hybrid wire for composite materials with a thermoplastic matrix according to Claim 1, characterised in that it consists first of all of subjecting multifilaments of reinforcing fibres and multifilaments of matrix fibres to separate cracking processes by slow and progressive drawing, assembling the strips of discontinuous fibres (2, 3) thus obtained on a drawing machine of the intersecting type, the strip (4) emerging from this drawing machine being assembled on another drawing machine with identical strips, this operation being repeated several times, in order to obtain the most intimate mixture possible, subjecting the strip obtained to a drawing in a rolling system (16, 17), and finally causing the bunch of discontinuous, mixed, parallel fibres to pass inside a hollow spindle (20) carrying a continuous filament (19) of thermoplastic material of the same nature as the matrix fibres (3) of thermoplastic material, the thermoplastic filament (19) representing between 10% and 25% of the total volume of thermoplastic material contained in the wire, in order to cover the bunch of fibres (2, 3) with the continuous filament (19).

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