HK1042121B

HK1042121B - Highly oriented polyolefin fiber and the process for making the same and use thereof

Info

Publication number: HK1042121B
Application number: HK02103857.4A
Authority: HK
Inventors: Arnold Paul Maria Simmelink Joseph; Johannes Mencke Jacobus
Original assignee: Dsm Ip Assets B.V.
Priority date: 1998-10-28
Filing date: 1999-02-24
Publication date: 2004-06-25
Also published as: IL142789A; DE69904361T3; IL172893A; EP1137828A1; TW444074B; CA2348518C; DE69904361D1; WO2000024952A1; CN1332812A; EP1256641A3; HK1042121A1; EP1137828B1; EP1137828B2; DE69904361T2; CA2348518A1; CN1122124C; ES2189394T3; EP1256641A2; AU2748999A; NL1010413C1

Abstract

The invention relates to a highly oriented polyolefin fibre containing polyolefin with an intrinsic viscosity of at least 5 dl/g, which fibre has a tensile strength of at least 26 cN/dtex and a modulus of tension of at least 700 cN/dtex, a process for the preparation thereof and the use in ropes or anti-ballistic shaped articles. The invention also relates to improved ropes and anti-ballistic shaped articles. The highly oriented polyolefin fibre according to the invention has improved properties in applications such as, in particular, anti-ballistic shaped articles since the fibre contains 0.05 - 5 wt.% of a solvent for the polyolefin (relative to the total fibre weight).

Description

Highly oriented polyolefin fibers, method for the production thereof and use thereof

The present invention relates to: highly oriented polyolefin fibres comprising polyolefin having an intrinsic viscosity of at least 5dl/g, the fibres having a tensile strength of at least 26cN/dtex and a tensile modulus of at least 700 cN/dtex; a process for their preparation and their use in ropes or ballistic-resistant shaped articles. The invention also relates to an improved rope and a ballistic shaped article.

Such highly oriented polyolefin fibres are known from EP-A-0.205.960. The highly oriented polyolefin fibres described herein have very high tensile strength and modulus and low creep rate, making them particularly suitable for use in, for example, ropes and ballistic resistant shaped articles. The fibers are made by spinning a polyolefin solution into gel fibers, extracting solvent from the fibers, and drawing the extracted and dried fibers in 1 or more steps.

However, there is still a need for further improvement of the quality of such fibers, or at least for optimization of the fiber properties in order to improve the quality of products made from these fibers, such as ropes and ballistic shaped articles. It is therefore an object of the present invention to provide a highly oriented polyolefin fibre with improved properties in said applications.

Surprisingly, this object is achieved by a fiber comprising 0.05 to 5 wt.% of a solvent for the polyolefin, relative to the total weight of the fiber.

It has now been found that the fibres according to the invention are particularly suitable for use in ballistic-resistant shaped articles, since shaped articles based on such fibres have a high Specific Energy Absorption (SEA), which means that less fibres are required and therefore the same degree of protection can be obtained with less weight. It has also been found that the fibres according to the invention are particularly suitable for use in ropes, mainly because they are tight and do not lose their softness, and because they increase the strength of the rope.

The improvement in the quality of the fibres is particularly surprising since the presence of large amounts of solvent in the fibres has hitherto been considered disadvantageous since this would reduce the mechanical properties of the fibres, in particular since the creep rate of the fibres would be relatively high and their strength and modulus would be relatively low. It is also surprising that solvent-containing fibers have higher ballistic qualities than "dry" fibers of comparable strength and modulus, since the solvent itself cannot contribute to the magnitude of the protective effect, although it does increase the areal density.

Solvent-containing fibers are known in the art. However, such fibres are not highly oriented and they are not suitable for the required field of application because their mechanical properties are not good enough. Highly oriented in the context of this application is to be understood as meaning fibers having a modulus of tension of at least 700cN/dtex and a strength of tension of at least 26cN/dtex (measured in accordance with the method specified below). Solvent-containing fibers are known as an intermediate product in the process of making fibers from solution. This description clearly shows that the solvent is not desired in the final product and therefore still needs to be removed. For example, US-A-5,213,745 describes an optimal extractant for extracting mineral oil solvent from undrawn gel fibers. This publication does not describe solvent-containing, highly oriented polyolefin fibers. EP-A-0,115,192 describes fibers with ｃA high solvent content, low tensile strength and modulus. The fibers, which are likewise intermediates, are not suitable as such for the stated use.

Tensile strength (or strength) and tensile modulus (or modulus) were defined and measured as specified in ASTM D885M, using a nominal gauge length of 500mm fiber, a crosshead speed of 50%/min and an Instron 2714 clamp. Before the measurement, the fibers were twisted to 31 turns/m. The modulus can be determined as a gradient between 0.3 and 1% strain according to the measured stress-strain curve. For the calculation of modulus and strength, the tensile force measured is divided by the titer, which can be determined by weighing 10m of fiber. Creep is understood here and hereinafter as the percentage elongation after 5 hours at 50 ℃ under a load of 8.11g/dtex in relation to the original length. The elongation comprises an elastic elongation.

A fiber is understood to be a continuous or discontinuous object such as a monofilament, a multifilament yarn, a tape or a spun yarn. In principle, the filaments may have any cross-sectional shape and thickness. Preferably, the titer of the (mono) filaments is at most 5, more preferably at most 3 denier per filament. The advantage of such a low single filament number is that the fibres will have a better ballistic performance.

A variety of different polyolefins may be used in the fibers of the present invention. Particularly suitable polyolefins are homopolymers and copolymers of polyethylene and polypropylene. In addition, the polyolefins used may comprise small amounts of 1 or more other polymers, in particular other alk-1-enes. Good results are achieved when linear Polyethylene (PE) is selected as the polyolefin. Linear polyethylene is understood here to mean polyethylene having less than 1 side chain per 100 carbon atoms, preferably less than 1 per 300 carbon atoms, which may additionally contain up to 5 mol% of 1 or more alkenes copolymerized therewith, for example propylene, butene, pentene, 4-methylpentene or octene. In addition to the polyolefin and solvent, the fibers may also contain minor amounts of additives commonly used in such fibers, such as antioxidants, spin finishes, heat stabilizers, colorants, and the like.

Preferably, the polyolefin fibers, especially polyethylene fibers, should have an Intrinsic Viscosity (IV) of more than 5 dl/g. Due to their molecular chain length, polyolefin fibers with such IV have very good mechanical properties, such as high tensile strength, modulus, energy absorption at break (energy at break). This is also why it is more preferred that the polyolefin is a polyethylene having an IV of more than 10 dl/g. IV is determined according to method PTC-179(Hercules, 1982-04-29 revision) under the following conditions: dissolving in decalin at 135 deg.C for 16 hr, wherein the antioxidant is DBPC, and the amount is 2g/l solution; the viscosity at different concentrations was extrapolated to zero concentration.

To ensure good ballistic resistance, the fibers should have a tensile strength of at least 26cN/dtex and a modulus of at least 700 cN/dtex. Preferably, the modulus is at least 880cN/dtex, more preferably at least 1060cN/dtex, most preferably at least 1235 cN/dtex. The strength is preferably at least 31cN/dtex, more preferably at least 33cN/dtex, most preferably at least 35 cN/dtex. Surprisingly, it has now been found that the creep of such highly oriented fibres is only to a small extent adversely affected by the solvent at relatively low, but effective solvent concentrations for the purposes of the present invention. Preferably, the fibers of the present invention have a tensile strength of at least 26 cN/dtex; a modulus of at least 700 cN/dtex; the solvent content is 0.05-2 wt%; creep is at most 20%, more preferably at most 15%/hour, even more preferably at most 10%/hour, most preferably at most 5%. Such a low creep is advantageous in particular for use in ropes. Creep can be further reduced when copolymers having more than 2 short side chains per 1000 carbon atoms are used. Preferably, the creep at this time is at most 10, more preferably at most 5%.

Solvents here and hereinafter are understood to be substances which are capable of dissolving the polyolefin. Suitable solvents for polyolefins are known to the person skilled in the art. They can be selected, for example, from the Polymer handbook (J.Brandrup and E.H.Immergut, 3 rd edition, Chapter VII, pp.379-402). Preferably, the solvent used has a Chi-parameter of less than 0.5, more preferably less than 0.45, even more preferably less than 0.4, most preferably less than 0.35, with respect to the polyolefin, in particular polyethylene, used. The chi-parameter of the solvent is described in "solubility parameter and other cohesion parameters" 2 nd edition, published by Allan Barton, p.386. This has the advantage that the quality is improved to a greater extent for the same solvent content. The details have been modified as necessary to require less solvent to achieve the same degree of ballistic performance improvement. Examples of suitable solvents for polyolefins, in particular polyethylene, are, individually or in combination: decalin, 1, 2, 3, 4-tetrahydronaphthalene, toluene, lower n-alkanes such as hexane, (p) xylene, paraffin oil, isotridecane, mineral oil, paraffin, cyclooctane. For the reasons stated above, the solvent is most preferably a paraffin oil or decalin.

Preferably, the solvent is a non-volatile solvent, such as a paraffin oil. This has the advantage that the fibres have a better stability, that is to say that the properties of the fibres, and of the fibre-based product, do not deteriorate over time and the service life can be extended. Another advantage is that the fibres do not have such unpleasant odours, are non-toxic or do not harm health, which is particularly important as a body protection application. By non-volatile solvent is understood a solvent which does not actually evaporate at a temperature below the melting temperature of the polyolefin. Preferably, they are solvents having a boiling point substantially preferably 50 to 100 ℃ higher than the melting temperature of the fibers.

The fiber of the present invention contains 0.05 to 5 wt% of a solvent for polyolefin. If the solvent content is less than 0.05 wt%, there will be no or little effect. Above a content of 5 wt.%, the disadvantage is that they will no longer contribute substantially to the continuation of the improvement in ballistic performance, or even be harmful. SEA increases with the solvent content to an optimum solvent content, at which point the contribution to energy absorption can no longer counteract the increase in areal density, and above which SEA decreases again. Although it may be advantageous for the final shaped article to contain a solvent in an amount higher than the optimum amount, since the solvent is cheaper than the fibres, the amount of solvent is preferably selected with a view to obtaining as high ballistic performance as possible. The optimum solvent content also depends on the fiber configuration, the solvent quality chosen, and the compression conditions. The optimum level can be determined for each process condition by one skilled in the art based on the guidelines given herein. For the above reasons, the solvent content in the fiber is preferably 0.1 to 3 wt%, more preferably 0.2 to 2 wt%, further preferably 0.2 to 1.2 wt%, most preferably 0.3 to 1.0 wt%. Such low solvent contents are preferred in the case of good solvents, in particular solvents with a chi-parameter of less than 0.5 and in the case of unidirectional composites. The solvent content of the fibers can be determined in a known manner, for example directly by infrared techniques, C13NMR, or indirectly-by solvent removal, for example by extraction or headspace gas chromatography, or a combination of said techniques.

The fibers of the present invention can be prepared by contacting highly oriented "dry" polyolefin fibers with a solvent for the polyolefin, wherein the fibers absorb 0.05 to 5 weight percent of the solvent. Highly oriented "dry" polyolefin fibres can be prepared in a known manner from polyolefin polymers, for example by gel spinning (Smith and Lemstra), by solid phase processing of virgin reactor powders (Chanzy and Smith), by melt extrusion (Ward) or by extrusion of powders recrystallized from solution (Kanamoto), with 1 or more drawing steps to increase the degree of orientation.

Preferably, the fibers are made directly by a gel spinning process. The present invention also relates to a process for preparing the highly oriented polyolefin fibers of the present invention, comprising: preparing a solution of polyolefin in a solvent, extruding the solution through 1 or more spinning holes and then cooling it to obtain gel fiber to make gel fiber, removing the solvent from the gel fiber, and drawing the fiber in 1 or more steps. Such ｃA process is known from EP-A-0,205,960. To prepare the fibers of the invention, the process should be adapted as follows: instead of removing all the solvent from the formed gel fiber, the gel fiber is drawn at a temperature above the equilibrium melting temperature of the polyolefin after 1 or more drawing steps in the formation of the solvent-containing precursor, resulting in a highly oriented polyolefin fiber containing 0.05 to 5 wt% of solvent.

The advantage of the process of the present invention is that fewer steps are required to produce the fiber and the resulting fiber has better ballistic performance than fibers that would otherwise have comparable strength and modulus properties with similar amounts of solvent. Another advantage of the process according to the invention, for example compared to the process described in EP- ｃA-0,205960, is that under otherwise constant conditions, there is less fibre breakage during drawing of the solvent-containing precursor fibres into the highly oriented fibres. As a result, production downtime is less and productivity is higher.

The precursor fiber can be made in a single step by simultaneous drawing and fiber removal, or by separate solvent removal and drawing steps. The solvent content in the precursor fiber is selected such that the final product, i.e. the highly oriented polyolefin fiber, contains the required amount of solvent, i.e. between 0.05 and 5 wt% after drawing. A portion of the solvent may be left to be removed during the final draw step. Preferably, however, a non-volatile solvent is used, in which case the solvent content remains virtually constant during drawing of the precursor fiber in the final drawing step. This has the advantage that the drawing process is better controlled and thus drawability is better.

In one embodiment of the process, the solvent in the highly oriented polyolefin fiber is the same as the solvent used for the spinning solution. The solvent content of the precursor fibers can be achieved by incomplete solvent removal, for example by shortening the evaporation or extraction time or by influencing the evaporation or extraction rate.

In a particularly preferred embodiment of the process of the invention, the solvent consists essentially of a mixture of the 1 st solvent (a) and the 2 nd solvent (B), wherein (a) is to be removed; (B) is left in the fiber.

The physicochemical properties of these solvents (a) and (B) are so different that the solvent removal technique used results in the removal of (a), while the solvent (B) remains substantially within the fibers.

An advantage of this embodiment is that the content of solvent (B) in the precursor fiber can be set directly and more accurately by the choice of the spinning solvent composition, without involving significant variations in other process parameters. For the purposes of the present invention, it is not necessarily required that the entire amount of (B) present in the solution be retained in the fiber during the removal and/or drawing of (a), but for process control purposes it is advantageous that the entire amount of (B) be retained in the fiber during the removal of (a) at any rate to prevent contamination of the process. Because of this, it is preferable that the fiber is almost entirely left in the fiber even during drawing (B). (A) It is not necessary to remove all but, for process control reasons, (A) is preferably removed completely. Preferably, the content of (A) in the fibres is not higher than 0.5 wt%, preferably lower than 0.3 wt%, more preferably lower than 0.2 wt%, most preferably lower than 0.1 wt%.

In one embodiment of the process, (B) has a higher boiling point than (A), and (A) is removed at a temperature at which (B) does not evaporate or evaporates very little. Preferably, the boiling point of (B) is selected such that it does not evaporate or evaporates very little at the draw temperature. This has the advantage that the draw is better controlled because the fibre composition does not change during draw and because the fibre does not cool due to the heat removed by the solvent evaporation.

In the most preferred embodiment, (B) is a paraffin wax which is not volatile throughout the process, and (A) is a volatile solvent, preferably decalin. A further additional advantage of this embodiment compared to the previously mentioned embodiments is that the solvent mixture has a much lower viscosity than paraffin alone as solvent, so that paraffin-containing fibres of low titer per filament, in particular titer per filament below 5, preferably below 3, can be produced more easily.

In another embodiment of the process, (B) has a higher melting temperature than (A), and (A) is removed by extraction at a temperature at which no or very little extraction of (B) takes place. Preferably, (B) is paraffin and (a) is paraffin oil.

The solvent-containing precursor fiber is drawn into a highly oriented polyolefin fiber at a temperature above the approximate equilibrium melting temperature of the polyolefin. The equilibrium melting temperature is understood to be the peak temperature of the melting curve of the polyolefin powder, measured by DSC at a temperature rise rate of 10 ℃/min. In the case of polyethylene fibers, this value is preferably higher than about 140 ℃. Obviously, the drawing temperature should not be chosen so high that effective drawing can no longer be carried out. Most preferably, the draw temperature is in the range of 145 to 160 ℃ and the solvent content of the precursor fiber during the final draw step is in the range of 0.05 to 5 wt%. This has the advantage that both good productivity is achieved and very good strength and modulus are obtained.

The invention also relates to highly oriented polyolefin fibres obtainable by the process described above. Compared with other fibers which have comparable properties and are added with similar amount of solvent in different modes, the fiber has better bulletproof performance.

The invention also relates to the use of the highly oriented polyolefin fibres according to the invention for the manufacture of ropes and to ropes comprising the highly oriented polyolefin fibres according to the invention. Solvent-containing fibers are easier to process into ropes than solvent-free fibers with comparable properties. The cords are more compact, they have a lower fuzz to the touch, but are very soft. It has been found that such a rope is also stronger.

The invention also relates to the use of the highly oriented fibres according to the invention for the manufacture of a shaped ballistic-resistant article, as described above. The advantage of using the fibers is, inter alia, that the conventional methods for producing such shaped articles can be used without major modifications. Such processes are described, for example, in WO97/00766 and WO 95/00318. An additional major advantage is, for example, that the process equipment is not soiled by solvent compared to the fibers or fiber layers which are to be wetted later.

The invention also relates to ballistic resistant shaped articles comprising the highly oriented polyolefin fibers of the invention. Such shaped articles have a higher level of ballistic protection at comparable areal densities than shaped articles based on solvent-free fibers. Preferably, the ballistic resistant shaped article of the invention has at least 115J/kg/m when hit by AK47MSC bullets²More preferablyMore than 120J/kg/m²More preferably still more than 135J/kg/m²Most preferably greater than 145J/kg/m²Specific Energy Absorption (SEA).

The present invention will be explained below based on examples.

Woven fabric: comparative experiment A

SK76 Dyneema yarn without paraffin was woven as a simple fabric with a pick and a warp density of 8 pieces/cm each. The area density of the woven fabric is 318g/m².20 layers of this fabric were compressed to form flat sheets, each sandwiching a 60 μm Stamy1ex (LLDPE) film. The pressure was 10 bar, the temperature 125 ℃ and the compression time 20 min. After the compression time is over, the plate is cooled while maintaining the pressure. V50 was measured using 17 grain FSP (bullet) according to the Stanag2920 standard. The V50 is 532m/s, corresponding to 21.4J/m²Energy Absorption (SEA).

The properties of the SK76 yarn used were:

strength 36.0cN/dtex

Modulus: 1180cN/dtex

Creep deformation: 4.1 percent

Woven fabric: example 1

SK76 Dyneema yarn with specific paraffin content was prepared: a solution consisting of UHMWPE (ultra high molecular weight polyethylene) and a volatile solvent, to which a specific amount of paraffin wax is added, was made according to the gel spinning method under the conditions normally used for SK76 yarn. Dunflussig paraffin supplied from Merck, with a dynamic viscosity of 25-80 MPa/s and a density of 0.818-0.875 g/cm³As the paraffin wax. The specified paraffin content is calculated from the percentage of paraffin added to the solvent and assumes that the paraffin is completely retained in the fiber during fiber production.

Plaques were prepared and tested as in comparative example a except that SK76 yarn was used containing approximately 0.8% paraffin solvent. The yarn has the same strength, modulus and creep as solvent-free yarn. The area density of the woven fabric was 302g/m². The V50 determined on the solvent-containing plates was 560m/s, corresponding to 24J/kg/m²Energy absorption of (2).

Twill woven fabric: comparative example B

The solvent-free Dyneema SK75 yarn was woven into a 3/1 weave pattern having a weft and warp density of 3.75 threads/cm each, an areal density of 276g/m²The twill fabric of (1). 22 layers of this fabric were compressed into panels, with a 30 μm Stamylex (LLDPE) film sandwiched between each layer, and tested as specified in example 4. V50 is 534m/s, corresponding to 23.8J/kg/m²The SEA of (1).

The properties of the SK75 yarn used (determined as in comparative experiment a) were:

strength 35.1cN/dtex

Modulus: 1130cN/dtex

Twill woven fabric: example 2

Twill woven fabrics were prepared as in comparative example B except that the SK75 fiber now in use contained about 2000ppm decalin. Although the yarn properties were the same, the V50 of the sheet was increased, i.e. to 600m/s, corresponding to 28J/kg/m²The SEA of (1).

UD (unidirectional) composite: comparative example C and examples 3 to 7

SK76 and SK75Dyneema yarns of different paraffin content, prepared as described in example 1, were processed to form a single layer, consisting of unidirectionally oriented yarns incorporated in a Kraton matrix (an isopropenyl-styrene copolymer, available from shell brand). The 4 individual layers are formed into a "single-layer laminate" in which the fiber direction in each individual layer makes an angle of 90 with the fiber direction in the adjacent layer. 75 such unidirectional laminates were compressed at 125 ℃ and 165 bar pressure for 35min to make a ballistic resistant shaped article. The shaped article was cooled with water while maintaining the pressure. The shaped articles were tested according to the Stanag2920 standard using AK47MSC round-head bullets. The yarn properties were not affected by the addition of paraffin wax.

	Fiber	Paraffin wax%	V50(m/s)
	Fiber	Paraffin wax%	V50(m/s)	C	SK75	0	＜710
3	SK75	0.4	730	C	SK75	0	＜710
3	SK75	0.4	730	4	SK75	0.8	780
5	SK76	0.4	750	4	SK75	0.8	780
5	SK76	0.4	750	6	SK76	0.8	780
7	SK76	1.2	810	6	SK76	0.8	780

Rope: examples 8, 9 and 10

From SK76 Dyneema yarns of different paraffin content (prepared as in example 1, all yarns having a titer of 1760dtex per yarn), 3 braids (v1, v2 and v3) were made on a 16-position Herzog knitting machine. The braid was made with 2.75 coils/cm. The braid is very tight but very flexible. The braid was placed on a Zwick1484 tensile tester and tested using a Zwick8465 type clamp at a sliding beam speed of 150 mm/min. Nominal scale length between clamps 2600mm (see table below)

% paraffin	Tensile strength CN/dtex
% paraffin	Tensile strength CN/dtex	0.4	21.7
0.8	21.9	0.4	21.7
0.8	21.9	1.2	22.1

Claims

1. Highly oriented polyolefin fibre comprising polyolefin, said polyolefin having an intrinsic viscosity measured in decalin at 135 ℃ of at least 5dl/g, a fibre having a tensile strength of at least 26cN/dtex and a tensile modulus of at least 700cN/dtex, characterised in that the fibre comprises 0.05 to 5 solvents (relative to the total fibre weight) for the polyolefin.

2. Highly oriented polyolefin fibre according to claim 1, characterized in that the polyolefin is polyethylene.

3. Highly oriented polyolefin fibres according to claim 1 or 2, characterised in that the chi-parameter of the solvent for the polyolefin is below 0.5.

4. Highly oriented polyolefin fibres according to claim 1 or 2, characterised in that the solvent is non-volatile.

5. Highly oriented polyolefin fibre according to claim 1 or 2, characterized in that the solvent is a paraffin oil.

6. Highly oriented polyolefin fibre according to claim 1 or 2, characterised in that the fibre comprises 0.1 to 2 wt% solvent.

7. Highly oriented polyolefin fibre according to claim 1 or 2, characterised in that the creep of the fibre is at most 15%.

8. Highly oriented polyolefin fibre according to claim 1 or 2, characterised in that the fibre has a titre of less than 5 denier per filament.

9. Process for the preparation of highly oriented polyolefin fibres according to any one of claims 1 to 8, characterised in that the fibres are brought into contact with a solvent for the polyolefin, wherein the fibres absorb 0.05 to 5 wt% of the solvent for the polyolefin.

10. A process for preparing the highly oriented polyolefin fiber of any of claims 1 to 8, comprising: preparing a solution of a polyolefin in a solvent, extruding the solution through 1 or more spinning orifices and subsequently cooling it to obtain gel fibres to produce gel fibres, removing the solvent from the gel fibres and drawing the fibres in 1 or more steps, characterised in that the solvent is not completely removed from the gel fibres but is instead subjected to 1 or more drawing steps to form solvent-containing precursor fibres which are subsequently drawn at a temperature above the equilibrium melting temperature of the polyolefin to highly oriented polyolefin fibres containing 0.05 to 5 wt% solvent.

11. A method according to claim 10, characterized in that the solvent essentially consists of a mixture of a 1 st solvent (a) and a 2 nd solvent (B), wherein (a) is to be removed and (B) is left in the fibres.

12. A process according to claim 11, characterized in that (B) has a boiling point higher than that of (A), and (A) is removed by evaporation at a temperature at which (B) does not evaporate or little evaporates.

13. The process according to claim 12, wherein (B) is a nonvolatile paraffin and (a) is a volatile solvent.

14. A process according to claim 11, characterized in that (B) has a higher melting point than (a) and (a) is removed by extraction at a temperature at which no or very little extraction of (B) takes place.

15. The process according to claim 14, wherein (B) is paraffin and (a) is paraffin oil.

16. The method of any of claims 9 to 15, characterized in that the highly oriented fibers comprise 0.05 to 2 wt% polyolefin solvent.

17. A process according to any of claims 10 to 15, characterized in that the polyolefin is polyethylene and the precursor fibers thereof are drawn at a temperature above 140 ℃.

18. Highly oriented polyolefin fibres obtainable by the process according to any one of claims 9 to 17.

19. Use of the highly oriented polyolefin fibres according to any one of claims 1 to 8 or 18 for the production of ropes.

20. A rope comprising highly oriented polyolefin fibres according to any one of claims 1-8 or 18.

21. Use of the highly oriented polyolefin fibers according to any one of claims 1 to 8 or 18 for the preparation of a ballistic resistant shaped article.

22. A ballistic resistant shaped article comprising the highly oriented polyolefin fibers of any of claims 1 to 8 or 18.