Elastomeric layers for cables with reinforced mechanical properties

Abstract

The invention relates to a cable, typically a power cable, comprising at least one elongated conductive element, surrounded by at least one polymer layer, and characterized in that said polymer layer comprises: (a) at least one elastomer; (b) polyvinyl butyral PVB; and (c) mineral particles. Figure for abstract: None

Description

Title of the invention: Elastomeric layers for cables having reinforced mechanical properties

[0001] The present invention relates to the field of cables comprising at least one elastomer-based layer, in particular an insulating layer and / or a protective sheath based on an elastomer.

[0002] The invention applies typically, but not exclusively, to the field of cables subject to significant mechanical stresses, such as for example those used for the internal wiring of wind turbines or even industrial cables known as flexible cables.

[0003] A power and / or telecommunications cable is an electrical and / or optical cable, which is intended for the transport of power and / or the transmission of data. It conventionally comprises one or more elongated electrical and / or optical conductive elements surrounded by at least one insulating layer. This insulating layer may typically be an electrically insulating polymer layer surrounding a single electrical or optical conductor, or alternatively several electrical and / or optical conductors. Furthermore, the conductive elements insulated by one or more insulating layers are conventionally protected by an outer protective sheath which surrounds the insulated conductors.

[0004] In the case of a cable subjected to high mechanical stresses, it is well known to use elastomers for the constitution of all or part of the insulating layers and / or the protective sheath. The elasticity of the elastomers makes it possible in particular to increase the mechanical resistance performance of the cable as well as its ease of use (flexibility).

[0005] An aim of the present invention is to provide elastomer compositions which are particularly well suited to this type of application, and which have high mechanical resistance properties.

[0006] To this end, the present invention proposes adding a specific additive to the elastomers used in the cables, namely a mixture of polyvinyl butyral (PVB) and mineral particles.

[0007] More specifically, the present invention relates to a cable (typically a power cable) comprising at least one elongated conductive element surrounded by at least one polymer layer, and characterized in that said polymer layer comprises: (a) at least one elastomer; (b) polyvinyl butyral; and (c) mineral particles.

[0008] According to a preferred embodiment, the polymer layer surrounding the elongated conductive element is an insulation layer, the cable then preferably being a power cable. According to this embodiment, when the cable comprises several insulation layers, it is possible that only one or only some of them comprise the aforementioned compounds (a), (b) and (c), but it is generally preferable that all the insulation layers of the cable contain an elastomer, PVB and mineral particles. In this case, it is often more practical for all the insulation layers to be based on a single polymer composition comprising the aforementioned compounds (a), (b) and (c), but it is also conceivable for the cable to comprise several distinct types of insulating layers comprising different types of compounds (a), (b) and / or (c) or comprising the same type of compounds (a), (b) and (c) but in different proportions.

[0009] According to another embodiment, compatible with that of the preceding paragraph, the polymer layer surrounding the conductive element is an outer protective sheath, the cable then preferably being a power cable. According to this embodiment, the cable comprises at least said conductive element, an insulating layer surrounding this conductive element and said sheath surrounding the insulating layer enclosing the conductive element. The insulating layer surrounded by the protective sheath according to the invention may then or may not be an insulating layer according to the present invention, and it is preferable that it contains an elastomer; PVB; and mineral particles.

[0010] The polyvinyl butyral that is employed according to the present invention, also referred to hereinafter as "PVB" for brevity, is a well-known polymer, also referred to by the synonymous terms "poly(vinyl butyral)" or "poly(vinyl butyral)".

[0011] PVB can in particular be obtained by acetalization of a polyvinyl alcohol (PVA) with butyraldehyde (butanal).

[0012] By "polyvinyl alcohol" (or "PVA") is meant here a polymer comprising predominantly units of formula -(-CH2-CHOH-)-. This PVA polymer may be a homopolymer containing only a chain of such units, or alternatively, a copolymer (generally a random copolymer) comprising not only units of formula -(-CH2-CHOH-)- but also other units, such as for example units -(-CH2-CHOCHCH3-)-.

[0013] Typically, a PVB is derived from the acetalization of a PVA which itself is derived from a total or partial (and preferably total or almost total) hydrolysis of a polyvinyl acetate (typically by basic hydrolysis). In practice, PVB is therefore most often a random copolymer of vinyl butyral, vinyl alcohol and vinyl acetate.

[0014] Whatever its method of preparation, the PVB used according to the invention preferably comprises vinyl butyral units as the majority monomer units. Thus, the PVB used preferably comprises polymer chains including at least 70%, or even at least 80% and for example at least 90% by weight (and typically more than 75%, or even more than 80%, for example between 80 and 85% by mole) of units of formula: relative to all the monomer units present in the structure of said PVB.

[0015] When the PVB is a random copolymer of vinyl butyral, vinyl alcohol and vinyl acetate, the quantity of vinyl alcohol units of formula -(-CH2-CHOH-)- may for example be less than 25%, typically less than 20% by mole relative to all the monomer units present in the structure of the polymer. Furthermore, the quantity of vinyl acetate units of formula -(-CH2-CHOCHCH3-)- may in particular be less than 5%, for example less than 1% by mole relative to all the monomer units present in the structure of the polymer.

[0016] PVB is a well-known polymer, used in particular for the construction of laminated glazing, comprising a laminated structure with two facing glass plates, sandwiching a PVB-based sheet which allows the two sheets to be assembled, the PVB layer typically being obtained by hot lamination under pressure.

[0017] PVB is also used for the manufacture of photovoltaic cells comprising a similar laminated structure with the deposition of a photovoltaic circuit on the internal face of one of the glass plates. PVB is also known as an additive in various applications, notably as a binder in ceramics or as an adhesion promoter in inks or paints.

[0018] More specifically, PVB has also been described as an additive in a polymer, in particular to provide a thermal stability enhancing effect, as described for example in patent application DE 44 37 161.

[0019] PVB as used according to the invention, namely in conjunction with mineral particles and specifically within a layer of a cable, also proves to provide an effect not previously described to the knowledge of the inventors, namely that it improves the mechanical properties of the cable, particularly when used in insulating layers or protective sheaths, especially when used in the insulating layers of the cable.

[0020] Another advantage of the invention is that the PVB which is used can advantageously be a recycled PVB, which reduces the production cost of the cable, in addition to the positive impacts of the use of a recycled material from an environmental impact point of view.

[0021] Furthermore, some PVBs from recycling already appear to contain mineral particles suitable according to the invention. This is particularly the case for PVBs from the recycling of laminated glazing, for example, which naturally contains a small proportion of mineral glass particles particularly suitable as particles (c) for implementing the present invention. PVBs from the recycling of laminated glazing for motor vehicle windshields appear in particular to be well suited according to the invention.

[0022] The use of a layer according to the invention gives the cable interesting mechanical properties. In particular, the invention makes it possible, among other things, to improve the properties of tensile strength (expressed in MPa or N / mm2) and tensile elongation (in %), as measured under the conditions of standards NF EN 50363-1 (Materials for insulating sheath, sheathing and covering for low-voltage power cables - Part 1: Crosslinked elastomeric mixtures for insulating sheath - April 2006) and NF EN 50363-5 (Materials for insulating sheath, sheathing and covering for low-voltage power cables - Part 5: Halogen-free crosslinked mixtures for insulating sheath - April 2006)

[0023] Various aspects and advantages of the invention are described in more detail below.

[0024] Compound (a)

[0025] The compound (a) present in the polymer layer may be a single elastomer compound, or a mixture of several elastomers. Preferably, the polymer layer used according to the invention comprises this elastomer or mixture of elastomers as the main polymer constituent, namely preferably with a total content of elastomer compounds in the polymer layer of more than 50% by weight, and in general of more than 80% by weight, by weight relative to the total weight of polymers in the polymer layer. More preferably, the total content of elastomer compounds is at least 85% by weight, for example at least 90%, and in particular at least 95% by weight, relative to the total weight of polymers in the polymer layer, this content generally remaining less than 99% by weight, in particular less than or equal to 98% by weight, relative to the total weight of polymers in the polymer layer.

[0026] The elastomer compound or the mixture of elastomer compounds present as compound (a) in the polymer layer according to the invention may typically be chosen from EPDM rubbers (for "ethylene-propylene-diene monomers").

[0027] An EPDM rubber well suited to the implementation of the present invention preferably has at least one of the following characteristics (and preferably all of these characteristics): - an ethylene content of between 70% and 75% by mass; and / or - an ENB content between 2% and 10 wt%; and / or - a Mooney viscosity between 55 and 75 MU; and / or - a density between 0.860 and 0.890

[0028] According to an interesting embodiment, the polymer layer according to the invention comprises as compound (a) a mixture of at least one EPDM rubber with an EVA copolymer (ethylene and vinyl acetate copolymer), with an EVA / EPDM mass ratio which is then preferably between 60 and 40, in particular between 80 and 20.

[0029] The compound ( b )

[0030] The PVB present as compound (b) in the polymer layer according to the invention is preferably present in this layer with a total content of compound (b) of less than 5% by weight, and preferably between 1 and 5% by weight, for example between 2 and 4% by weight, relative to the total weight of polymers in the polymer layer.

[0031] The PVB used as compound (b) in the context of the present invention may, for example, be a commercial PVB available in the form of granules and generally comprising a mineral filler. An example is R-PVB BC30, designated here and in the examples by “BC30”, and marketed by the company Hainaut-Plast which contains 30% by mass of mineral filler.

[0032] Compound (b) may typically have a density of between 1.20 and 1.30 kg / dm3, for example of the order of 1.22 kg / dm3

[0033] Compound (b) may typically have a melt index as measured at 190°C of between 2.2 and 2.4°, for example of the order of 2.3 g / 10 min.

[0034] Furthermore, it is preferable that the mass ratio (b) / (a) corresponding to the total mass of compound (b) in the polymer layer, relative to the total mass of compounds (a) in said layer remains between 5 and 20, this ratio generally remaining less than or equal to 10.

[0035] Mineral particles (c)

[0036] The mineral particles (mineral fillers) present as compound (c) in the polymer layer according to the invention are preferably particles chosen from: glass particles, calcium carbonate particles, zinc carbonate, zinc stearate particles, calcium stearate particles, and mixtures of such particles.

[0037] According to a particular embodiment, the PVB used is a recycled PVB resulting from the recycling of laminated glazing. In this case, the particles (c) typically comprise the small-sized glass particles contained in this recycled PVB.

[0038] Whatever their exact nature, the particles (c) are generally included in the polymer layer of the invention at a content of 150 to 350 parts by weight, and for example between 200 and 300 parts by weight per 100 parts by weight of polymer.

[0039] A portion of the mineral particles present in the composition may be introduced via the use of a compound (b) comprising such particles, in particular glass particles from recycling. In this case, the compound (b) is typically introduced in the form of a mixture comprising PVB and mineral particles with a particle content in this mixture generally between 25 and 30% by mass relative to the mass of the mixture. The particles (c) then comprise, for a first part, the particles from this mixture, and for a second part, mineral particles introduced in addition to this mixture.

[0040] Optional additives

[0041] According to a possible embodiment, the polymer layer according to the invention consists of only compounds (a), (b) and (c). According to another alternative, the layer may optionally contain other compounds as additives.

[0042] The layer may optionally contain polymers other than elastomers. Where appropriate, it is preferable that all of the polymers present behave globally as an elastomer, in which case it is considered that the mixture of all of the polymers globally constitutes compound (a), seen as an elastomeric mixture of polymers.

[0043] In addition to compounds (a), (b) and (c), the polymer layer according to the invention may optionally comprise additives other than these compounds (a), (b) and (c), such as for example plasticizing agents or colorants. When such additives are present, the total content of additives other than compounds (a), (b) and (c) within the polymer layer is preferably less than 10% by weight relative to the total weight of the polymer layer.

[0044] Fields of application

[0045] The invention applies in particular, but not exclusively, to the fields of electric cables intended for the transport of energy, in particular to low voltage energy cables (in particular from 3 to 750 V), whether in direct or alternating current, in the fields of aerial, underwater, terrestrial electricity transport, or even aeronautics.

[0046] EXAMPLE An insulating layer according to the invention was applied as an insulating composition in a cable (3G1.5mm2 cable) comprising three cylindrical copper conductor wires each having a cross-section of 1.5mm2.

[0047] A layer of insulation with a thickness of 0.8 mm was applied by extrusion around each of the three wires which were then stranded to form an assembly with a total diameter of less than 1.75 mm.

[0048] The insulation layers around each wire were applied from a composition C, comprising: 70 parts by weight of EPDM 25 parts by weight of EVA 5 parts by weight of BC30 (PVB recycled from laminated glazing marketed by Hainault Plast comprising 30% mineral particles)

[0049] The mechanical properties of the cable obtained were measured according to the standardized tests of standards NF EN 50363-1 and 50363-5 and the results obtained are reported in the table below. Minimum median RT Maximum evolution RT Minimum median AR Maximum evolution AR Initial 5 - 200 - Oven 7 days / 100°C 4.2 ±25% 200 ±25% Oven 7 days / 135°C 5 -30% 125 ±30% Air bomb 40 hours / 127°C / ±30% / ±30% Table 1: measurements according to standards NF EN 50363-1 and 50363-5

[0050] For comparison purposes, a Control composition identical to composition C was tested, with the only difference being that it did not contain PVB. The results obtained are reported in Table 2 below. Control Composition C Viscosity (MU) 32.6 38.1 Cmax (dNm) 13.98 14.83 Ts5 (min) 0:58 0:55 T75 (min) 1:58 1:59 Median RT (MPa) 9.5 8.9 Median AR (%) 575 548 Median RT (MPa) Change (%) 8.2 -15.9 8.9 0.0 Median AR e(%) Change (%) 531 -8.3 525 -4.4 Median RT (MPa) Change (%) 8.4 -13.1 8.6 -3.5 Median AR e(%) Change (%) 539 -6.7 528 -3.8 Table 2: Comparison of composition C and the Control without PVB

Claims

Claims

1. Cable comprising at least one elongated conductive element surrounded by at least one polymer layer, and characterized in that said polymer layer comprises: (a) at least one elastomer; (b) polyvinyl butyral; and (c) mineral particles, where: - the polyvinyl butyral (b) is a polyvinyl butyral resulting from the recycling of laminated glazing and which contains glass particles; and - the total content of polyvinyl butyral (b) ranges from 1% to 5% by weight relative to the total weight of polymers in the polymer layer

2. A cable according to claim 1, wherein the polymer layer surrounding the elongated conductive element is an insulation layer.

3. A cable according to claim 1 or 2, wherein the polymer layer surrounding the conductive element is a protective outer sheath.

4. Cable according to one of claims 1 to 3, where the polyvinyl butyral (b) is a polyvinyl butyral from the recycling of motor vehicle windshields, which contains glass particles.

5. Cable according to one of claims 1 to 4, where the compound (a) is a single elastomer compound, or a mixture of several elastomers, present in the layer at a content of more than 80% by weight relative to the total weight of polymers in the polymer layer.

6. A cable according to any one of claims 1 to 5, wherein compound (a) comprises an EPDM rubber, typically in admixture with an EVA copolymer.

7. Cable according to one of claims 1 to 6, wherein the total content of polyvinyl butyral (b) ranges from 2% to 4% by weight relative to the total weight of polymers in the polymer layer

8. Cable according to one of claims 1 to 7, where the mass ratio (b) / (a) of the total mass of polyvinyl butyral (b) in the polymer layer, relative to the total mass of compounds (a) in said layer is between 5 and 20

9. Cable according to one of claims 1 to 7, where the content of particles (c) ranges from 150 to 350 parts by weight, and for example between 200 and 300 parts by weight per 100 parts by weight of polymer.