EP0354139A1 - Hybrid yarn for composite materials made from thermoplastic matrix and method for producing the same - Google Patents

Abstract

These yarns consist of an intimate mixture of spun threads of reinforcing fibres (2) and spun threads of thermoplastic matrix fibres (3), each of the spun threads of fibres having previously been obtained by cracking by means of a slow and progressive drawing of multifilaments. The process for obtaining them is characterised in that multifilaments of reinforcing fibres (2) and multifilaments of thermoplastic matrix fibres (3) are subjected to a separate process of cracking by slow and progressive drawing, and in that the slivers (2, 3) of discontinuous fibres thus obtained are then assembled together on a drawing machine (15) of the intersecting type, the sliver (4) leaving this drawing machine subsequently being assembled together with other identical slivers on a second drawing machine, this operation being repeated several times to produce the most intimate mixture possible, the final sliver obtained thereafter being subjected to the conventional operations of spinning long fibres: passage over a fly frame, actual spinning, winding, assembly and twisting. <IMAGE>

Description

The present invention relates to hybrid yarns for composite materials with a thermoplastic matrix, especially in the case where this matrix is made up of thermoplastic fibers as well as their process for obtaining.

It is known that, 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 .

These thermoplastic matrix fibers belong to the conventional families: polyether ether ether ketone (PEEK), polyphenylene sulfide (PPS), polyetherimide (PEI), etc.

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 of intermingling the multifilament of reinforcing fibers with the multifilament of thermoplastic fiber.

There is then an improvement in the result obtained, but the problems set out above are not completely resolved. On the other hand, the fairly high cost of this technique practically prevents its use in the case of industrial series.

The present invention has set itself the aim of proposing hybrid wires for thermoplastic matrix composites making it possible to control and solve these problems.

The hybrid yarns according to the invention are characterized in that they consist of an intimate mixture of yarns of reinforcing fibers and yarns of thermoplastic matrix fibers, each of the yarns of fibers having been obtained beforehand by cracking according to a slow drawing and progressive multifilaments.

The yarns of reinforcing fibers are chosen from yarns of carbon, aramid or glass fibers.

The yarns of thermoplastic matrix fibers are chosen from yarns of polyether ether ketone fibers (PEEK), of phenylene polysulfide (PPS), polyethersulfone (PES), polyetherimide (PEI), as well as among the other fiber yarns known for this purpose, such as polyamides and polyimides.

According to a preferred embodiment of the invention, the relative proportions of the reinforcing fibers and of the thermoplastic matrix fibers, proportions which can, of course, vary as a function of the characteristics of the matrix fibers and in particular of their viscosity when hot, are situated around 65% for reinforcing fibers and 35% for thermoplastic matrix fibers.

The invention also relates to a process for obtaining hybrid wires for composite materials according to the invention.

According to this process, multifilaments of reinforcing fibers and multifilaments of thermoplastic matrix fibers are subjected to a separate process of cracking by slow and progressive drawing, then the ribbons of staple fibers thus obtained are assembled on a drawing machine of intersecting type, the ribbon leaving this stretching machine then being assembled on a second stretching machine with other identical ribbons, this operation being repeated several times so as to produce the most intimate mixture possible, the final ribbon obtained then being subjected in conventional long fiber spinning operations: passage on a spindle bench, 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 over materials of the same type obtained according to the processes of the prior art.

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 presents itself as a monolithic solid which has "forgotten" its initial stratified structure.

The composite obtained also exhibits very good aptitudes for hot stamping.

• Figure 1 est un 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 et,
• Figure 3 est une vue très schématique de l'installation de mélange des fibres craquées conduisant à l'obtention d'un ruban de filés de fibres hybrides selon l'invention.

The process for obtaining hybrid wires for composite materials according to the invention will now be described in more detail with reference to the attached diagrammatic drawing which illustrates it without in any way limiting it. In this drawing:

• 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 cracking installation and,
• Figure 3 is a very schematic view of the installation for mixing the cracked fibers leading to the production of a ribbon of hybrid fiber yarns according to the invention.

In the figures, the reinforcing fibers are generally designated by 2 and the thermoplastic matrix fibers by 3 .

On the cracking installation shown in FIG. 2, the multifilament cables supplied from the coils 10 (whether they are multifilaments of reinforcing threads or threads of thermoplastic matrix) are subjected to a cracking operation by stretching and controlled breaking, the speeds of the stretching zones 11,12 and of the cracking zones 13,14 gradually increasing so that:
V₁₀ <V₁₂ <V₁₃ <V₁₄
which makes it possible to obtain at the outlet a ribbon of staple fibers whose average length is perfectly controlled.

This length is moreover illustrated by the diagram of FIG. 1 on which the lengths of fibers in mm are plotted on the ordinate and the abscissa is the population of fibers expressed as a percentage of the number of fibers in this population.

It is obvious that different cracking installations will be used to obtain, on the one hand, ribbons of staple fibers of reinforcement 2 and, on the other hand, ribbons of staple fibers of thermoplastic matrix 3 .

The different ribbons 2 and 3 thus obtained are then brought, by any means known per se, to the mixing device shown in FIG. 3.

It is 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 will, on leaving this machine, be assembled on an installation similar to that shown in FIG. 3 with ten other identical ribbons; this operation will be repeated approximately four times, which will make it possible to obtain the yarns of hybrid fibers according to the invention in the desired final proportions of reinforcing fibers and of thermoplastic fibers, these proportions varying, of course, depending on the characteristics of the fibers. thermoplastic matrices and in particular their hot viscosity, generally being around 65% of reinforcing fibers and around 35% of thermoplastic matrix fibers. These fiber yarns consist of an intimate mixture of reinforcing fibers and thermoplastic matrix fibers.

This ribbon then undergoes conventional spinning operations in the long fiber technique:
- passage on pin benches,
- spinning,
- winding,
- assembly,
- twisting,
which makes it possible to obtain the hybrid fiber yarn for composite materials with a thermoplastic matrix according to the invention, this fiber yarn being, of course, capable of being subsequently transformed by weaving, knitting or braiding.

This yarn has no particular mechanical characteristics, because at the time of shaping, the thermoplastic matrix fiber melts by trapping the reinforcing fibers. The performance of the composite thus obtained therefore depends only on the characteristics of the elementary fibers and their attachment to the thermoplastic matrix.

Table I below summarizes the properties of three types of hybrid fiber yarns according to the invention in which both the reinforcing fibers and the thermoplastic matrix fibers have been varied.

Table II compares the properties of different composite materials produced from hybrid fiber yarns according to the invention, compared to composites produced according to the prior art and described in the literature. TABLE II Sample references Yarn rate by volume% Density g / cm² Vacuum rate% FLEXION SHEARING TRACTION Breaking stress (GPa) Module (GPa) Breaking stress (MPa) Breaking stress (GPa) Module (GPa) 1 56 1.60 1.2 0.94 53.5 - - - 2 56.7 1.60 0.9 0.86 65.4 - - - 3 58.2 1.61 0.1 - - 57.3 - - 4 56 1.60 0.4 - - 59.3 - - 5 56.7 1.62 0.9 - - - 0.96 44.7 6 58.9 1.62 0.9 - - - 0.89 44.7 SAMPE, Jal Jan-Feb 88. p 8-10 * 51 1.54 1.6 1.19 91.6 - 1.43 120.6 53 1.58 0.5 1.34 99.9 - 1.59 122.6 COmposite N ° 3-May-June 1986 - p121-128 ** 56 - - 1.4 126 - 1.2 - *: Table IV page 10 **: Table N ° II page 123 - last column.

Claims (5)

1- Hybrid yarns for thermoplastic matrix composites, characterized in that they consist of an intimate mixture of yarns of reinforcing fibers (2) and yarns of thermoplastic matrix fibers (3), each of the yarns of fibers having been previously obtained by cracking according to a slow and progressive drawing of multifilaments. 2- Hybrid yarns according to claim 1, characterized in that the yarns of reinforcing fibers are chosen from yarns of carbon, aramid or glass fibers. 3- Hybrid yarns according to claim 1, characterized in that the yarns of thermoplastic matrix fibers are chosen from yarns of polyether ether ketone fibers (PEEK), of phenylene polysulfide (PPS), of polyethersulfone (PES), of polyetherimide (PEI), as well as among the other known fiber yarns for this purpose, such as polyamides and polyimides. 4- Hybrid yarns according to any one of claims 1 to 3, characterized in that the relative proportions of the reinforcing fibers and of the thermoplastic matrix fibers are around 65% for the reinforcing fibers and 35% for the thermoplastic matrix fibers. 5- A method for obtaining hybrid son for composite materials according to any one of claims 1 to 4, characterized in that one subjects multifilaments of reinforcing fibers (2) and multifilaments of thermoplastic matrix fibers (3) to a separate process of cracking by slow and progressive drawing, then in that the ribbons (2,3) of staple fibers thus obtained are assembled on a drawing machine (15) intersecting, the ribbon (4) coming out of this drawing machine then being assembled on a second drawing machine with other identical ribbons, this operation being repeated several times so as to produce the most intimate mixture possible, the final ribbon obtained then being subjected to the conventional operations of spinning of long fibers: passage on a bench with spindles, actual spinning, winding, assembly and twisting.

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