EP0937271A1

EP0937271A1 - Optical fibre cable of compact composite structure

Info

Publication number: EP0937271A1
Application number: EP98942828A
Authority: EP
Inventors: Christian Lagreve; Guy Levesque
Original assignee: Acome SCOP
Current assignee: Acome SCOP
Priority date: 1997-09-05
Filing date: 1998-09-04
Publication date: 1999-08-25
Also published as: WO1999013368A1; AU9081198A

Abstract

The invention concerns an optical fibre cable with compact composite structure, characterised in that it comprises in combination three sheaths, the first ensuring that the fibres are bunched thereby facilitating the second sheath extrusion, the latter being made of an extrusible reinforced polymer capable of providing the compact composite structure with a low modulus of elasticity in tension, and a third sheath ensuring the cable external properties.

Description

CABLE WITH OPTICAL FIBERS OF COMPACT COMPOSITE STRUCTURE

The present invention relates to a fiber optic cable whose compact composite structure is intended to produce extremely dense and light cables, economical and resistant.

Fiber optic cables, or optical cables, are widely used in the field of long-distance communications and are increasingly competing with copper cables in the field of local telecommunications networks or in corporate networks. They allow light to be transmitted between two more or less distant sites and offer a transmission capacity which opens a new era of communication at very high speed for voice, data and images.

Optical cables must effectively protect optical fibers in order to maintain proper transmission of information. In the competition with copper media, however, they must also be very economical and be very easy to install. They must therefore be modular, compact, light, and have great ease of installation and connection. In addition to the cost of the cable itself, it is indeed the overall cost of the cable installed that must be competitive compared to conventional cables made with copper wires. If this cost quickly proved to be competitive for very high speed long distance links, the competition turns out to be much tougher for links in short distance local area networks, particularly in the face of the digitization of cables with symmetrical shielded pairs or no, likely to transmit over reasonable distances at high frequencies.

Furthermore, the small size of the optical fibers as well as the low expansion coefficient of the silica are at the origin of the great sensitivity of the optical fibers to mechanical and thermal aggressions.

Attempts to protect optical fibers with composite materials have already been made, in particular using a first coating of elastomeric material itself covered with a protective material of the liquid crystal polymer type. Such materials are described in US Patents 4,553,815 and 4,906,066. The use of a liquid crystal polymer makes it possible to obtain a protective sleeve whose coefficient of thermal expansion is close to that of silica.

Attempts are also known to use a liquid crystal polymer to produce the composite sheath of a small cable with a sheath composed of this material then covered with an outer polyethylene sheath. However, the mechanical properties of these polymeric liquid crystal materials are not completely satisfactory for such use. In particular, the low elongation at break induces an "straw effect" unacceptable for the generally accepted specifications for optical cables, and the high cost of these materials leads to solutions which are difficult to compete with.

We then tried to mix polymers with this liquid crystal polymer allowing its physical and mechanical properties to be modified. Thus, in European patent EP No. 0 155 070, optical fibers coated with a first layer of a rubber composition Thermoplastic of low Young's modulus are covered with a second layer of thermoplastic resin with low coefficient of linear expansion and high Young's modulus. This second layer contains a liquid crystal polymer. This process is used directly in the manufacturing line of optical fibers before they are coated with a thin layer of hard plastic material.

In addition, mixing a liquid crystal polymer with another polymer or copolymer requires the addition of compatibilizers. European patent EP No. 138 112 describes compositions comprising a polyester liquid crystal resin, a polycarbonate resin and a polyolefin or an olefinic copolymer. The polycarbonate resin allows better compatibility between the liquid crystal resin and the polyolefin or the olefinic copolymer.

In the same sense, patent application 093/24574 describes polymer blends comprising a liquid crystal polymer, a polymer matrix which can be a polyethylene terephthalate or a polybutylene terephthalate, and a compatibilizing agent which is a polymer containing reactive groups. The reactive groups of the compatibilizer react with both the liquid crystal polymer and the polymer matrix to thereby improve compatibility between the matrix and the liquid crystal polymer. However, the implementation of this mixture of polymers for the production of optical cables is complex since it requires a double extrusion.

It can therefore be seen that no satisfactory solution has so far been proposed for producing a composite cladding capable of exhibiting the qualities sought, namely a sufficiently high mechanical resistance, a stiffness capable of facilitating the installation of the cable by blowing or pushing, a reduced bulk, a great lightness, as well as the possibility of carrying out this sheathing in an economical manner in comparison with the known techniques of reinforcement of thermoplastic resins with metallic or non-metallic reinforcements.

Now, the Applicant Company has had the merit of developing such a cladding ^composite having all of these characteristics by defining a specific polymer reinforced extrudable material and by associating two thermoplastic sheaths taking said sandwich reinforced material. The subject of the invention is therefore a fiber optic cable with a compact composite structure, characterized in that it comprises:

- one or more optical fibers,

a first sheath ensuring the packaging of the optical fiber or fibers and facilitating the extrusion of the second sheath,

a second sheath made of an extrudable reinforced polymer material capable of providing the compact composite structure with a higher Young's modulus and a low coefficient of expansion,

- a third sheath guaranteeing the external qualities of the cable, such as resistance to certain aggressive agents or a coefficient of friction adapted to economical laying techniques. The invention has in fact been achieved thanks to the development and use of a particular reinforced polymer material, having physicochemical characteristics at least equal to those of the polymer alloys already known, and thanks to the combination of this particular material or alloy with on the one hand a first support layer facilitating the extrusion at very high speed of said alloy, and on the other hand a second outer layer substantially reducing the straw effect ^' and providing ^' the optical cable characteristics of the friction coefficient type adapted to economical laying techniques, such as blowing or pushing.

The coextrusion assembly thus produced leads to a composite cable structure of small dimensions, simpler, less costly than the currently existing structures, structure which can be possibly reinforced by a few load-bearing strands according to the desired tensile strength characteristics, l 'assembly obtained having performance at least equivalent to that of current optical cables.

The optical cables which are the subject of the present invention can be obtained in any form, depending on the subsequent use envisaged, for example in the form of cylindrical cables or in the form of optical ribbons.

Their connection is very easy since the optical fibers can be stripped as simply as the copper wires of conventional electric cables. In particular, obtaining a compact, high-strength composite sheath with a low expansion coefficient makes it possible to wire the optical fibers without the costly and bulky operation of elementary sheathing said tight sheathing, which also has the serious drawback of making the elementary assembly of the fibers bulky and therefore the final cable. According to the invention, the extrudable reinforced polymer material used in the constitution of the second sheath comprises at least one liquid crystal polymer, at least one polymer giving said reinforced polymer material a high flexible flexural modulus, and at least one non-copolymer ^' functional. This reinforced polymer material therefore has both a high breaking strength, a large Young's modulus, good resistance to curvature and a very low coefficient of thermal expansion. According to an advantageous embodiment, the reinforced extrudable polymeric material used for constituting the second sheath of the optical cable according to the invention comprises:

- approximately 5 to 70% by weight of at least one liquid crystal polymer,

- from 25 to 85% by weight of at least one polymer giving said reinforced polymer material a high flexural modulus,

- And from 1 to 30% of at least one non-functional copolymer, the percentages being calculated relative to the total weight of the reinforced polymer material.

Preferably, the proportion of liquid crystal polymer included in the reinforced extrudable polymer material is chosen to be between

20 and 60% and more preferably still between 30 and

50% by weight of the total weight of the reinforced polymer material. Any liquid crystal polymer can be used in the extrudable reinforced polymer material used in accordance with the invention. For any example of liquid crystal polymers, reference may be made to the article by Chaung et al. in "Handbook of Polymer Science and Technology", vol. 2, (1989), pages 625-675.

In general, the liquid crystal polymer is an aromatic polyester or an aromatic polyamide polyester having the characteristics of liquid crystal polymers. Such liquid crystal polymers are, for example, liquid crystal polymers sold under the trademark VECTRA ^® B950, VECTRA ^® A950,

VECTRA ® RD501, or those marketed by the Company

DUPONT DE NEMOURS under the ZENITE brand. In a preferred embodiment, a liquid crystal polymer is used which is commercially available and which is a copolymer of hydroxynaphthoic acid and hydroxybenzoic acid, for example a liquid crystal copolymer of the brand VECTRA® A950, containing 23% by weight of hydroxynaphthoic acid and 77% by weight of hydroxybenzoic acid.

As indicated previously, this liquid crystal polymer is preferably used in an amount ranging from approximately 20 to 60% and more preferably still from 30 to 50% by weight of the total weight of the reinforced polymer material.

The polymer giving said material a high flexural modulus is chosen from poly (C 1 -C ₄ alkylene) terephthalates and polyamides, the copolymers comprising at least one poly (C 1 -C ₄ alkylene) terephthalate block, used alone or in mixture. Copolymers of which at least one block consists of poly (Cι-C alkylene terephthalate, comprises, in addition to said poly (alkylene Cι-C _4. tereptalate) block (s), polymer sequences of any kind, for example polyester, polyolefin, polyether, etc. As examples of copolymers comprising at least one poly (Cι ~ C alkylene) terephthalate block, mention may be made of the copolymers marketed by the company DUPONT DE

NEMOURS under the HYTREL ^® brand. It is preferred to use poly (alkylene Ci-C ₄₎ terephthalates or copolymers having at least one sequence is constituted by a poly (alkylene _C: -C ₄₎ terephthalate, in particular polybutylene terephthalate or polyethylene terephthalate or their mixed. This polymer is used in amounts ranging from 25 to 85%, preferably from 25 to 65% and even more preferably from 40 to 65% by weight of the total weight of the reinforced polymer material.

By "non-functional copolymer" is meant any copolymer devoid of functional groups capable of reacting with the liquid crystal polymer and / or the polymer conferring a high flexural modulus. For example, the non-functional copolymer does not contain carboxy, anhydride, epoxy, oxazolino, hydroxy, isocyanate, acylacetate, or carbodimide groups. It is a copolymer of ethylene / alkyl acrylate in Cι_ ₈ and in particular in Cι-C or their mixtures. Preferably an ethylene / butyl acrylate or ethylene / methyl acrylate copolymer, or a mixture thereof, is used. This non-functional copolymer is used in an amount of 1 to 30%, preferably from 1 to 15% and even more preferably from 2 to 12% by weight of the total weight of the reinforced polymer material.

Of course, to the three main components of the reinforced polymer material used according to the present Invention to constitute the second sheath of the optical cable, additives such as fillers, pigments and various substances conventionally used in the polymer technique can be added in order, for example, to facilitate the processing of the material.

According to an entirely preferred embodiment, the reinforced polymer material comprises:

- approximately 60% by weight of liquid crystal polymer, - approximately 30% by weight of polybutylene terephthalate,

- And about 10% by weight of ethylene / methyl acrylate copolymer, the percentages being calculated relative to the total weight of the reinforced polymer material.

The reinforced polymer material is obtained by simple mixing of the various polymers used in the respective desired quantities.

The first sheath ensuring the packaging of the optical fiber or fibers and facilitating the extrusion of the second sheath made of the extruded reinforced polymer material described above can be made of any "technical" polymer, that is to say d a polymer having a relatively high flexural modulus such as polyethylene terephthalate or polybutylene terephthalate, polyamides, polypropylene or polycarbonate or a soft material of crosslinkable UV type, which makes it possible to improve the impact resistance, as well as the resistance to bending and which eliminates stresses on the fiber.

The third sheath ensuring the external qualities of the cable can for its part be made with in particular polyvinyl chloride, polyethylene, or flame retarded polyolefins as well as fluorine-type materials.

The composite structure of compact optical cable which is the subject of the invention therefore comprises a first sheathing of one or more fibers, the fibers retaining little freedom in the tube thus produced by extrusion of a thermoplastic material, then the implementation by extrusion of the reinforced polymer material and in tandem covering it with a very thin sheath intended to limit the residual straw effects of the compact composite structure and to provide the cables with the coefficient of friction characteristics suitable for the application considered. In a variant of the invention and very economically, it is possible to substantially reinforce the compact composite structure in tensile strength by adding aramid wicks or glass-epoxy composite wicks of small dimensions, marketed, which do not undermine because of the economic and very compact nature of the composite structure object of the invention.

By optical fiber is meant an optical fiber as sold commercially which comprises a central core of silica, or other equivalent material, covered with two hard plastic sheaths. Conventionally, the central core has a diameter of 125 μm and the overall diameter of the fiber is 250 μm. Such an optical fiber is shown in FIG. 1. However, optical fibers protected by a protective layer of another type, moisture-proof and of thin thickness (a few microns) could be used, provided, for example, that they are associate in a buffer material, the association of the buffer material and the reinforced sheath part with the liquid crystal polymer allowing to protect them effectively against mechanical and thermal actions.

In this variant of the compact composite cable structure which is the subject of the invention, the buffer material is a soft polymer of the UV-crosslinkable resin type which makes it possible to improve the impact resistance, the bending resistance and to eliminate the stresses on the fiber. By way of example, mention may be made of copolymers of styrene / butyl / styrene type and UV crosslinkable resins.

Other advantages of the invention will appear during the following detailed description of the optical cables according to the invention which can have different configurations as illustrated by the appended drawings in which:

- Figure 1 shows the cross section of a commercial optical fiber as used in the present invention;

- Figure 2 shows the cross section of a cylindrical optical cable called self-reinforced unitube cable, comprising a bundle of optical fibers;

- Figure 3 shows the cross section of a cylindrical optical cable of the self-reinforced unitube type which includes reinforcing wicks;

- Figure 4 shows a ribbon type composite cable in which the fibers are juxtaposed linearly; - Figure 5 shows the same composite ribbon type cable further comprising reinforcing wicks; - Figures 6 and 7 respectively show a compact cylindrical composite cable and a compact composite ribbon type cable.

FIG. 1 represents the optical fiber 1 used in the invention. This consists of a core la made of silica, or other equivalent material. This core is surrounded by a first sheath 1b of low modulus resin of the UV crosslinkable type, itself surrounded by a second sheath 1c of hard UV crosslinkable resin. Of course, the compact composite structure of optical cables which is the subject of the invention also applies to other types of fibers such as silica fibers sprinkled with a cladding of 500 μm for example or 900 μm or like plastic fibers.

FIG. 2 shows a simple embodiment of the optical cables according to the invention, that is to say a cylindrical cable of the self-reinforced unitube type. The cable 2 comprises a bundle 3 of optical fibers 1, the bundle preferably being slightly free inside the first sheath 4 produced by extrusion of a thermoplastic material thus forming a first elementary tube which will allow easier and high speed of the part of the sheath 5 produced with the reinforced polymer then by a tandem operation, the extrusion of the third sheath 6 forming the compact composite structure.

Of course, the bundle can be formed by a module adapted to the desired applications, for example 1, 2, 4, 6, 8, 10, 12 or 24 fibers. It can also be the result of the association of n elementary bundles and the fibers can be simply assembled or embedded in a filling jelly preventing water from penetrating. In an exemplary embodiment of the present invention, an elementary composite cable is produced compact with 12 fibers capacity for an internal diameter of approximately 1.2 mm and an external diameter of approximately 3 mm. Most optical cables having such capacities, conventionally produced by sheathing of thermoplastic materials associated with reinforcing elements, have dimensions closer to 6 to 8 mm. We see thus that the combination of the three sheaths of the composite cable leads to a cable particularly dense and therefore economical and easy to install while obtaining mechanical performance and ^'thermal perfectly suited to the desired applications, eg for inner cables or for cables in the local subscriber network laid in the pipeline. The mechanical quality of the composite is obtained by the association of the three sheaths, each making a contribution either in terms of production process, or in mechanical and thermal quality with the reinforced polymer material, or in quality of friction coefficient and finish with exterior cladding. In Figure 3, there is shown a self-reinforced unitube type cable as described above, in which are included reinforcing wicks 1, for example in aramid fibers or glass-epoxy composite fibers in small quantities, intended, while retaining the very economical in character, to significantly increase the tensile strength of the compact composite cable which is the subject of the invention. The cable thus comprises a bundle 3 of optical fibers 1, preferably slightly free in the first extruded sheath 4 and the wicks 7, here two in number, included in line at the time of the extrusion of the sheath 5 made of reinforced polymer material , followed in tandem with the extrusion of the outer protective sheath 6. In FIG. 4, a compact composite ribbon type cable has been shown in which the fibers 1 are juxtaposed linearly. The fibers are preferably slightly free inside the first sheath 8 extruded in thermoplastic material, covered with a sheath 9 in reinforced polymer material and then with an outer sheath 10 in thermoplastic material extruded in tandem. The fibers can, as in the previous embodiment, be arranged in modules of 2, 4, 6, 8, 10, 12 ^" fibers or more.

According to the embodiment of FIG. 5, the compact composite ribbon-type cable further comprises reinforcing wicks 11 intended to provide the compact composite cable with higher tensile strength characteristics.

According to the embodiment of FIG. 6, the compact composite cable comprises a bundle of optical fibers 1, which is covered with a buffer material 12 then with the sheath 13 in reinforced polymer material and with an outer sheath 14 extruded in tandem made of thermoplastic material. Of course, as in the previous embodiments and depending on the desired tensile strength, reinforcing wicks can be included, in particular when the sheath of reinforced polymer material is extruded.

According to the embodiment of FIG. 7, the compact composite cable of the ribbon type comprises fibers 1 juxtaposed linearly and covered with a buffer material 15 then with the sheath 16 in reinforced polymer material and with the outer sheath 17 extruded in tandem. It can thus be seen that the compact composite cables which are the subject of the invention have quite remarkable properties. Indeed, thanks to the association several sheaths with very different properties, a composite which brings together interesting characteristics for fiber optic cables, in particular in the spirit of low or medium capacities for cables intended for high speed cabling applications inside companies, buildings or residences, for the terminal part of future FTTH ("fiber to the home") type telecommunications networks or for applications such as digital city cabling. The realization of a compact composite structure according to the invention in fact leads to a very small footprint for modular cables which, while retaining a stiffness and a coefficient of friction well suited to laying techniques such as blowing or pushing in small pre-wired tubes, have interesting mechanical and thermal properties, thanks in particular to the combined use of a reinforced polymer, which brings both a higher Young's modulus to the composite structure and significantly reduces the coefficient of expansion of optical fibers , and two thermoplastic sheaths sandwiching this polymer. The compact composite cables thus produced, which can be cylindrical or ribbon-shaped, which can be reinforced by a reduced number of reinforcing wicks according to the desired tensile characteristics, are produced very economically by tandem extrusions with large speed and, thanks to their compactness adding to this economic character, are very easy to install, in particular through a philosophy of superposition of optical networks compared to existing and bulky copper networks. The low availability of pre-wired pipes or hoses makes composite optical cables compact objects of the invention particularly interesting for the future of the deployment of optical fibers in local networks of professional or residential subscribers.

Claims

1. Fiber optic cable with compact composite structure, characterized in that it comprises: - one or more optical fibers,

a second sheath made of an extrudable reinforced polymer material capable of providing the compact composite structure with a higher Young model and a low coefficient of expansion,

- a third sheath guaranteeing the external qualities of the cable, such as resistance to certain aggressive agents or a coefficient of friction adapted to economical laying techniques.

2. Fiber optic cable according to claim 1, characterized in that tensile reinforcing elements are embedded in the second sheath of reinforced polymer material.

3. Fiber optic cable according to either of claims 1 and 2, characterized in that it is in cylindrical form and that it comprises a fiber or one or more bundles of fibers.

4. Optical fiber cable according to either of claims 1 and 2, characterized in that it is in the form of a ribbon and comprises several fibers juxtaposed linearly.

5. Fiber optic cable according to any one of claims 1 to 4, characterized in that the reinforced extrudable material constituting the second sheath comprises:

from 5 to 70%, preferably from 20 to 60%, and even more preferably from 30 to 50% by weight of at least one liquid crystal polymer,

- from 25 to 85%, preferably from 25 to 65%, and more preferably still from 40 to 65% by weight of at least one polymer giving said reinforced polymer material a high flexural modulus, - and from 1 to 30% , preferably from 1 to 15%, and more preferably still from 2 to 12% by weight of at least one non-functional polymer, said percentages being expressed relative to the total weight of the reinforced polymer material.

6. Fiber optic cable according to any one of claims 1 to 5, characterized in that the polymer conferring on the reinforced polymer material a high flexural modulus is chosen from poly (C ₄ alkylene) terephthalates, preferably polyethylenetérephthalate or polybutyleneterephthalate, polyamides, and copolymers comprising at least one poly (C1-C6 alkylene terephthalate) block.

7. Fiber optic cable according to any one of claims 1 to 6, characterized in that the non-functional copolymer present in the reinforced extrudable polymer material is an ethylene / butyl acrylate copolymer or an ethylene / methyl acrylate copolymer.

8. Fiber optic cable according to any one of claims 1 to 7, characterized in that the liquid crystal polymer present in the reinforced extrudable polymer material is a copolymer of hydroxynaphthoic acid and hydroxybenzoic acid.

9. Optical fiber cable according to any one of claims 1 to 8, characterized in that the first sheath ensuring the packaging of the optical fiber or fibers consists of soft polymers of UV crosslinkable type, of polyesters, in particular of polyethylene terephthalate or polybutylene terephthalate, polyamides, polypropylene, or polycarbonate.

10. Fiber optic cable according to any one of claims 1 to 9, characterized in that the third sheath ensuring the external qualities of the cable consists of polyvinyl chloride, polyethylene, or flame retarded polyolefins or fluorinated polymers.

11. Use for the manufacture of optical cables of an extrudable material comprising: - from 5 to 70%, preferably from 20 to 60%, and even more preferably from 30 to 50% by weight of at least one crystal polymer liquids,

from 25 to 85%, preferably from 25 to 65%, and more preferably still from 40 to 65% by weight of at least one polymer giving said reinforced polymer material a high flexural modulus,

- And from 1 to 30%, preferably from 1 to 15%, and even more preferably from 2 to 12% by weight of at least one non-functional polymer, said percentages being expressed relative to the total weight of the reinforced polymer material. AMENDED CLAIMS

[re ^ç ues by the International Bureau 22 January 1999 (22.01 .99); claims 1 and 5-11 replaced by new claims 1 and 5-10; other claims unchanged (3 pages)]

1. Fiber optic cable with compact composite structure, characterized in that it comprises:

- one or more optical fibers,

- a second sheath ensuring the longitudinal mechanical characteristics consisting of a reinforced extrudable polymer material with a low coefficient of expansion comprising:

• from 5 to 70%, preferably from 20 to 60%, and even more preferably from 30 to 50% by weight of at least one liquid crystal polymer, • from 25 to 85%, preferably from 25 to 65% , and more preferably still from 40 to 65% by weight of at least one polymer giving said reinforced polymer material a high flexural modulus, • and from 1 to 30%, preferably from 1 to 15%, and even more preferably from 2 to 12% by weight of at least one non-functional polymer, said percentages being expressed relative to the total weight of the reinforced polymer material, - a third sheath guaranteeing the external qualities of the cable, such as resistance to certain aggressive agents or a coefficient of friction suitable for economical laying techniques.

2. Fiber optic cable according to claim 1, characterized in that tensile reinforcing elements are embedded in the second sheath of reinforced polymer material. 3. Fiber optic cable according to either of claims 1 and 2, characterized in that it is in cylindrical form and that it comprises a fiber or one or more bundles of fibers.

5. Fiber optic cable according to any one of claims 1 to 4, characterized in that the polymer giving the reinforced polymer material a high flexural modulus is chosen from poly (C ₁ -C ₄ alkylene) terephthalates, preferably polyethylenetérephthalate or polybutyleneterephthalate, polyamides, and copolymers comprising at least one poly (dC, alkylene) terephthalate block.

6. Fiber optic cable according to any one of claims 1 to 5, characterized in that the non-functional copolymer present in the reinforced extrudable polymer material is an ethylene / butyl acrylate copolymer or an ethylene / methyl acrylate copolymer.

7. Fiber optic cable according to any one of claims 1 to 6, characterized in that the liquid crystal polymer present in the material

AβDED SHEET (ARTICLE 19) reinforced extrudable polymer is a copolymer of hydroxynaphthoic acid and hydroxybenzoic acid.

8. Optical fiber cable according to any one of claims 1 to 7, characterized in that the first sheath ensuring the packaging of the optical fiber or fibers consists of a polymer having a relatively high flexural modulus, in particular polyethylene terephthalate or polybutylene terephthalate, polyamides, polypropylene, or polycarbonate, or a soft polymer of UV crosslinkable type.

9. Fiber optic cable according to any one of claims 1 to 8, characterized in that the third sheath ensuring the external qualities of the cable consists of polyvinyl chloride, polyethylene, or flame retarded polyolefins or fluorinated polymers.

10. Use for the manufacture of optical cables of an extrudable material comprising:

- from 25 to 85%, preferably from 25 to 65%, and more preferably still from 40 to 65% by weight of at least one polymer giving said reinforced polymer material a high flexural modulus, - and from 1 to 30% , preferably from 1 to 15%, and more preferably still from 2 to 12% by weight of at least one non-functional polymer, said percentages being expressed relative to the total weight of said reinforced polymer material.

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