The invention relates to a method for producing composite fibres having an improved distribution of structural fibres, e. g. filaments of carbon, boron, aramide or similar, and matrix fibres, e. g. filaments of thermoplastic.

Known art.

A method for vacuum injecting resin into structural fibres is called the"Scrimp"-method, in which by means of vacuum resin is suctioned into a layup of structural fibres, e. g. glass fibres or carbon fibres, under a vacuum bag, requires that the resin is in the fluid phase before it comes into contact with the structural fibres.

A more advanced and cleaner solution is to apply a commingled fibre fabric consisting of structural fibres and melting fibres e. g. of thermoplastic, and laying this mat directly into the mould form and vacuum melt the entire layup in order for the melting fibres melt and envelop the structural fibres, whereby a fibre composite blank is formed and may be cooled or in other ways hardened and then removed from the mould form.

EPP 0 033 244 applies a matrix on the outside of a fibre by letting the fibre pass through an extrusion press or a bath of molten thermoplastic material.

US-Patent 5 425 796 and US 5 011 523 both relate to production of glass fibre filaments and thermoplastic filaments that run together to form a yarn having relatively poor distribution of glass fibre having an enveloping cover of thermoplastic filaments, see Fig. 3a, b, and c in the actual U. S.-Patent. US 5 011 523 shows also that the final composite fibre yarn is cut into short pieces, making the fibre structure of the string inapplicable for forming composite blanks for load-bearing designs which require highest possible strength-to-weight ratio. Carbon fibres, as opposed to the illustrated U. S.-patents, may not be pulled directly from a bath, but must be formed through a somewhat more complex process in which a precursor thread, e. g. an acryl fibre, is pulled through a high temperature furnace in which it is carbonized to a non-melting carbon fibre, being one of the desired points of origin for the present invention PCT/FR97/01184 shows extrusion of glass and formation of thermoplastic covered glass fibre filament, and winding of the final material onto a bobin.

US 3 091 018 also covers a glass fibre thread with resin fibre by heating, in which a coat of resin fibre is applied on the glass fibre thread. The purpose is not to obtain a homogenous distribution of glass and resin fibres, but a core of one of the materials.

DE 20 19019 assembles two filaments of two different fibre types being collected at a comb and are then run over to rollers being arranged 90 degrees across the comb's plane, and as such collect the plane to one yarn.

EP 0 182 335 describes two yarns being twisted and, as such, thus do not provide the desired properties for the present invention's broad band which shall be generally without twisting to avoid weaknesses in the carbon-, boron-, or aramide filaments in the final composite material, and which must to a highest possible degree be free of twisting to avoid crossed structural fibre filaments and matrix filaments before joining in order to achieve a best possible distribution and mixing of these two kinds of filaments.

DE 36 34904 shows glass fibres being pulled from a melt, whereby glass fibre filaments run in onto a roller from which a seize is applied, and then the seized glass fibre yarn runs into a rotation chamber in which the fibre is slung and given a twist, whereby the twisted yarn of several filaments is wound onto a bobin.

US 4 539 249 first twines a graphite fibre and then winds this thread of graphite fibre with a resin fibre so one single yarn is formed which may be woven to hybrid fabrics for use in a form in which the melting material may be heated and for a resin-graphite laminate. The undesired twining of the graphite fibre weakens the graphite filaments in a composite fibre laminate blank that is being built from a thread formed according to the US-Patent.

Statement of problem.

The presence of"nests"where structural fibres are out of contact with resin, and the presence of areas having too much resin and a lack of structural fibres, results in a weakened composite fibre material.

The structural fibre may be present as a rather loose bundle of e. g. 1000 to 100 000 filaments, e. g. of carbon, boron, aramide, ceramic material, or metal, in which the bundle is available wound without twisting ("non-twisted") onto a bobin. The diameter of each single filament may be 5 to 20 .

The structural fibre shall be used in a process in which is it is lead adjacent to a corresponding bundle of matrix fibre of thermoplastic material as PP, PET, PBT, PEN, PEEK or others. The number of filaments in the bundle may be 1000 to 100 000 filaments having a diameter of about 10 to 40 p.

Two essential problems by joining bundles of structural fibres with bundles of matrix fibres exist: The first problem is, that if one joins the bundle having structural fibres with the bundle having matrix fibres, a composite bundle arises in which no even distribution of structural fibres and matrix fibres necessarily exists, but that the materials respectively lie in thinner bundles of structural filaments and matrix filaments which are badly distributed when seen on a filament level. Carbon fibre bundles, in particular, may have very thin filaments lying closely and which may be difficult to separate for slotting matrix fibres in between or for intrusion of molten matrix material. One reason for this incapability of matrix filaments to lie themselves between the carbon fibre filaments may be the smaller diameter of the carbon fibre filaments and their higher stiffness.

The other problem particularly associated with the use of carbon fibres, is that the filaments should lye straightest possible, without kinks on the fibres. A deviation in straightness for one single fibre filaments being more than the half filament diameter may incur an essential reduction of the filament's compression module and compression strength, and other compression properties, and also the tensile module, the tensile strength and strain at rupture, both the compression strain at rupture and the tensile strength at rupture.

Thus it is desirable to achieve an even distribution of structural filaments and matrix filaments. Additionally, it is desirable that particularly the structural filaments are as straight as possible in order to avoid kinks on the filaments. 11 the filaments lye straight and parallel, the distribution and the mixing of structural fibres and matrix fibres may also take place more easily.

Short summary of the invention.

One solution to the above mentioned problems, is a method for producing composite fibres having an improved distribution of non- melting structural fibres of carbon, boron or aramide, and matrix fibre filaments of thermoplastics, e. e. PET, PP, PCB, PEEK, in which the novelty by the invention comprises the following steps: a) spreading of at least one bundle of structural filaments to at least one first broad band having at least one flat surface and having a thickness corresponding to one or a small number of structural filaments, in which the spreading of the bundle of structural fibres form generally parallel running and continuous structural filaments; b) spreading of at least one bundle of matrix filaments to at least one second broad band having at least one flat surface and having a thickness corresponding to one or a small number of matrix filaments, in which the spreading of the bundle of matrix filaments form generally parallel and continuous running matrix filaments; that one locally, e. g. over a roller, leads the first band and the second band preferably in parallel and in the same direction, and that one in the local parallel position, e. g. on a roller's surface, join or let run together the first band with the at least one flat surface against the other band's at least one flat surface to a composite band, in which one lets the composite band maintain a large width with respect to the thickness in the further winding or use of the composite band.

The invention is also a composite fibre having an improved distribution of non-melting structural fibres of carbon, boron or aramide, and matrix fibre filaments of thermoplastic, e. g. of PET, PP, PCB, PEEK, in which the novel features of the invention are as follows: that it is produced by running together in a common direction of a first structure filament band's at least one flat surface adjacent to at least a second thermoplastic matrix filament band's at least one flat surface to a composite band, in which one lets the composite band maintain a large width relative to the thickness in the further winding-up or use of the composite band; that at least one bundle of structural filaments are spread by letting it run over rollers to at least a first broad band having the at least one flat surface and having a thickness corresponding to one or a small number of structural filaments, in which the spreading of the bundle of structural fibres form mainly parallel running and continuous structural filaments ; in which at least one bundle of matrix filaments are spread to at least a second broad band having its at least one flat surface and having a thickness corresponding to one or a small number of matrix filaments, in which the spreading of the bundle of matrix filaments forming mainly parallel and continuously running matrix filaments.

Advantages of the invention : By means of the invention, one may achieve an even distribution of structural filaments and matrix filaments. By the method of the invention it is possible to achieve that particularly the structural filaments lye straight to avoid kinks on the filaments, and that the baked-in filaments compression strength as seen on a micro-level add up to a compression strength corresponding to their number also as seen on a macro-level for the composite material. By the fact that the filaments lye straight and in parallel also the distribution and mixing of structural fibres and matrix fibres will take place more easily, and one achieves a band having very well distributed structural filaments and matrix filaments also down to a filament scale This gives good laminate properties. An even distribution of filaments as seen on a micro-scale will reduce the average flow path that each single micro volume of molten matrix shall have to wander in order to find its place in contact with structural fibres. This will reduce the processing time and the impregnating time for each particular structural filament and thus the impregnating time for the entire composite material.

Short figure captions.

Figures 1 and 2 illustrate a side elevation view and a vertical view of the invention having a set-up with a rack of bobins with structural fibre bundles and matrix fibre bundles each separately rolled off the bobins and rolled over broad rollers and spread to separate broad bands until the two bands are joined in a process according to the invention to a broad band which will then be a composite fibre.

Figure 3 is a side elevation view of the two spread bands running in onto the roller that may be called a collector or joiner or mixing station, on which a composite fibre band is formed.

Figure 4 is an imagined section through such a composite fibre band, in which one flat surface of the first band lye adjacent to one flat surface of the other band.

Figure 5 is an imagined enlarged section through such a composite fibre band in the beginning of the joining process in which one will see structural filaments 1 lying above matrix filaments 2.

Figure 6 is an imagined enlarged section through such a composite fibre band at the end of, or after, the joining process in which one may see structural filaments lying distributed between matrix filaments.

Detailed description of the invention.

The figures 1 and 2 illustrate, in a side elevation view and in a vertical view, the invention with a set-up with a rack 16 with bobins 11,12 with structural fibre bundles 9, and bobins 13, 14,15 with matrix fibre bundles 10 separately being rolled off the bundles and rolled over broad rollers 122,121,213,221,222,223 for structural fibres, and bobins 231,232,241,242,243,244 until each on their own have been spread to broad flat bands which are joined in a process according to the invention to a broad band 8 of composite fibre.

Structural filament 1 contained in the at least one structural fibre bundle 9. Rollers 211 to 223 shape the bundle 9 to a broader band 6 comprising spread structural fibres or fibre filaments 1.

Matrix filaments 2 are contained in a matrix fibre bundle 10. The rollers 231 to 244 shape the bundle 10 to a broader band 7 of spread matrix fibres or matrix filaments 2. Fig. 3 is a side elevation view of the spread bands 6 and 7 running in on a collector roller 3 on which a composite band 8 is formed. The collector roller 3 is included as a central element in the method of the invention and may also be called a collector or mixing station 3. The collector roller joins the bands 6 and 7 to a composite fibre band 8, composed of structural fibres or structural filaments 1 and matrix fibres or matrix filaments 2. One may assume that the band 6 with the structural fibres may be guided in from the outside of the band 7 containing matrix fibres because the structural fibres 1 often will be stiffer than the matrix fibres 2 and thus force themselves down between these due to the difference in stiffness. A stabiliser 4, which is not strictly required, may be used for leading the spread- mixed composite fibre band 8 in onto a composite fibre bobin 5 for the produced composite fibre band 8, or the composite fibre band 8 may be lead directly into a process in which a composite product is built.

Fig. 4 is an imagined longitudinal section, early in the joining process, through such a composite fibre band 8, in which a flat surface 18 of the band 6 lye adjacent to a flat surface 19 of the band 7. Fig. 5 is an enlarged section across a part of such a composite fibre band 8, here seen at the beginning of the joining process in which one may see structural filaments 1 lying side to side with matrix filaments 2. Fig. 6 is an imagined enlarged section through a part of such a composite fibre band 8 in the end of or after the joining process in which one see structural filaments 1 lye distributed between matrix filaments 2. in the joined state the composite fibre band may be consolidated by a partial melting of the matrix filaments so that these have adhesive properties to the structural fibre filaments, or the band may be unconsolidated.

Usually, the structural fibre bundle 9 is delivered from the manufacturer as a bobin in which the structural fibre bundle is not spread. In the same way, usually the matrix fibre bundle 10 is delivered from the manufacturers side as non-spread on a matrix fibre bobin. However one may imagine requiring that the manufacturer shall produce structural filaments 1 as a broad band wound up in crossed layers on a bobin by the production of the structural filaments, so that the in situ spreading of the bundle 9 is avoided when it shall be joined in the present process. Correspondingly, matrix fibre filaments 2 may be imagined provided as a broad band 7 on a bobin in order to avoid the step of spreading the bundle 10 to a broad band 7 before the collector roller 3.

The invention is thus a method to produce composite fibre having an improved distribution of non-melting structural fibres of carbon, boron or aramide, and matrix fibre filaments of thermoplastic, e. g. PET, PP, PCB and PEEK. Particular to the method are the following steps: a) spreading of at least one bundle (9) of structural filaments (1) to at least one first broad band (6) having at least one flat surface (18) and having a thickness corresponding to one or a small number of structural filaments (1), in which the spreading of the bundle (9) of structural fibres for generally parallel running and continuous structural filaments (1); b) spreading of at least one bundle (10) of matrix filaments (2) to at least one second broad band (7) having at least one flat surface (19) and having a thickness corresponding to one or a small number of matrix filaments (2), in which the spreading of the bundle (10) of matrix filaments (2) form generally parallel and continuously running matrix filaments (2); c) that one guide the first band (6) and the second band (7) in parallel and in the same direction; d) that one in this parallel position join or let run together the first band (6) with the at least one flat surface (18) against the second band's (7) at least one flat surface (19) to a composite band (8) r in which one lets the composite band (8) maintain a large width with respect to the thickness in the further winding or use of the composite band (8).

According to a preferred embodiment one lets the composite band (8) maintain a large width with respect to the thickness before it is wound up flat onto the bobin (5). However it may be imagined that if the main purpose of the process only is to have an even distribution of the composite fibres (1,2) and desires to have a thick bundle having a round cross-section out of the process, it may be imagined to gather the band (8) again to a bundle, e. g. in the stabiliser 4 and guide for spread-mixed composite fibres. According to the preferred embodiment of the invention the band is guided flat-lying in and onto the roller 5.

According to a preferred embodiment of the invention, generally parallel running structural filaments (1) will be formed during spreading of the bundle (9) of structural fibres. Likewise, in the preferred embodiment, during spreading of the bundle (10) of matrix filaments (2), generally parallel running matrix filaments (2) will be formed. The thickness of the structural filaments (1) and the matrix filaments (2) is preferably of the same order of size, and usually such that the structural filaments are somewhat more numerous and thinner than the fewer and melting matrix filaments, but this is not a prerequisite for the method to work. As a variation, at least one of the bands (6) with structural filaments (1) or the band (7) with matrix filaments (2) may be heated before the joining of the bands (6,7) so that the bands adhere entirely or partly after the joining. The band (7) having matrix filaments (2) may be supplied with heat so that it achieves partial melting or in other ways gets adhesion properties to the band (6) of structural filaments (1). Alternatively, the band (6) with structural filaments (1) bay be supplied with head to that it, on joining with the band (7), transfers heat and partially melts the band (7) of matrix filaments (2) or in other way supplies adhesion properties before the structural filaments (1). The advantage in heating the band (6) of structural fibres is that this band is non-melting, and one will thus not run any risk that any of the bands are entirely or partially broken before the joining on the collector roller (3). If heat is supplied to the band (7) of melting filaments (2) before the collector roller (3), there is a risk that one or more of the filaments (2) are locally weakened and may break, which would disturb the process.

According to another embodiment of the invention, at least one of the bands (6,7) of structural elements (1) or matrix filaments (2) may be charged before the joining of the bands, so that the structural filaments (1) or matrix filaments (2) are spread internally. This may be conducted by arranging brushes or electrodes by the bundles 9,10 and supplying a voltage. The bands (6,7) of structural filaments (1) and with matrix filaments (2) may be charged with opposite signs of their charges so that the at least two bands (6,7) attract each other during the joining to one composite fibre band (8).

According to the preferred embodiment of the invention the bundle (9) of structural filaments (1) is without twist. This is entirely essential for avoid kinks in the structural filaments, particularly carbon filaments. The bundle (10) of matrix filaments (2) should also be without twists, but this is less essential than the fact that the structural filaments should be without twisting, because the matrix filaments shall anyway be melted totally or partially in the end. However, it will be a considerable advantage for the mixing of the two bands (6) and (7) that both bundles are completely free of twist, i. e. without crossing to any degree after spreading.

In using distributing of several alternating layers of bands (6,7) one may build up a composite band of desired structure and thickness, having a controlled distribution of filaments.

Sensors may be arranged to check if the bands (6,7) have obtained the desired least width before the collector roller (3).

After the collector roller (3) there may be arranged rollers (not shown) to maintain the distribution and to obtain additional mixing of structural filaments (1) and matrix filaments (2). These rollers may contribute to better guiding of the band (8) in onto the composite fibre bobin (5) or to a larger bobin, or for guiding the band (8) into a desired process which utilizes such a composite band being better distributed internally. The composite fibre band (8) may also be narrowed again to a bundle, then having strongly improved distribution of matrix filaments (2) and structural filaments (1).

Different fibres require different set-up in the system to achieve a suitable spreading of the filaments. The filament diameter quotient between the structural fibre and the matrix fibre is included in the determination of numbers of bobins of different types. The weight relationship between the fibres may be defined within narrow tolerances based on tex in each of the coils.

Carbon fibre yarn which is spread or is pre-spread may in a preferred embodiment of the invention be guided through a plasma treatment in which original seizing is burned away, an by means of the plasma treatment replaced with thermoplastic molecules of e. g. the same kind as the carbon fibre later to be mixed with. This results in chemical bonding between carbon fibre and matrix fibre, which will result in a considerable increase of the strength of such composite fibres consolidated into final laminates.

1. structure filaments in a structural fibre/fibre bundle.

2. matrix filaments in a matrix fibre/matrix fibre bundle.

3. a collector or joiner or mixing station.

4. stabiliser and guide for spread-mixed composite fibres.

5. composite fibre bobin for the produced composite fibre.

6. spread structural fibres or-filaments 1.

7. spread matrix fibres pr filaments 2.

8. composite fibres, composed of structural fibres or filaments 1 and matrix fibres or-filaments 2.

9. structural fibre bundle from bobin,-not spread.

10. matrix fibre bundle from bobin,-not spread.

11. structural fibre 1 on bobin.

12. structural fibre on bobin.

13. matrix fibre on first bobin.

14. matrix fibre on second bobin.

15. matrix fibre on third bobin.

16. rack for bobin mounts.

17. tension control system, brake unit.

18. flat surface of band having structural filaments 1.

19. flat surface of band having resin/matrix filaments 2.

20. rack system for bobins.

21. separator for structural fibres and matrix fibres.

51. rotating axle for holding bobin for composite fibre 5. rack for composite fibre bobins.

53. tension control and rotation control for bobin.

54. control for way of filling of bobin.

201. guide eyes for the structural fibre bundle, fibre support out of the bobin.

202. guide eyes for the matrix fibre bundle, fibre support out of the bobin.

211. first roller in the spreader roller system for structural fibres.

212. second roller in the spreader bar system for structural fibres.

213. third roller in the spreader bar system for structural fibres.

221. fourth roller main spreader unit for the structural fibres.

222. fifth roller, main spreader unit for the structural fibres.

223. sixth roller, main spreader unit for the structural fibres.

231. first roller in the matrix fibre spreader bar unit.

232. second roller in the matrix fibre spreader bar unit.

241. third roller, main spreader bar unit for the matrix fibre.

242. fourth roller, main spreader bar for the matrix fibre.

243. fifth roller, main spreader bar for the matrix fibre.

244. roller for guiding spread matrix fibres towards the collector roller 5.

246. plasma application apparatus for shooting plasma onto the structural fibre filaments (1).