FR3078433A1 - SPECIFIC COAXIAL CABLE AND METHOD OF MANUFACTURING THE SAME - Google Patents

Abstract

The invention relates to a coaxial cable comprising: a first electrically conductive element consisting of a central cylindrical core; a second electrically conductive element surrounding said first electrically conductive element but separated therefrom by a layer of dielectric material; and an insulating sheath placed on the second electrical conducting element, characterized in that the first electrical conducting element comprises metallic nanowires.

Description

The present invention relates to specific coaxial cables which may have a very small diameter and to a method for manufacturing these.

Due to the possibility of having a very small diameter, the coaxial cables of the invention can find application in the medical field and, more specifically, in the field of invasive medicine, the small diameter implying less damage to the skin, these cables that can be associated with medical devices, such as sensors, pacemakers, diagnostic and treatment tools, probes or imaging tools (such as for x-ray or MRI).

Conventionally, coaxial cables consist of a cable comprising two conductive elements of opposite poles: a central cylindrical conductive element (or core) of a metallic element, such as copper, and a shielding element forming a hollow cylinder, generally made of a material. metallic, such as copper, surrounding said central conductive element but not in contact therewith, said central conductive element and said shielding element being separated from each other by a dielectric material. The two conductive elements have identical central axes of symmetry (hence the name of coaxial cable), which allows them to undergo the same disturbances induced by the surrounding electromagnetic fields. The shielding element is surrounded by an insulating and protective sheath, generally made of a polymer material.

Currently, coaxial cables sold have a diameter often greater than 0.5 mm, which makes them difficult to use in the context of invasive medicine, especially when it comes to accessing very narrow areas of the body. , such as a blood vessel or an area precisely located in the brain to provide neurostimulation.

Also, on the strength of what already exists, the authors of the invention set themselves the objective of developing coaxial cables and an associated manufacturing process allowing their use in the aforementioned field of application.

STATEMENT OF THE INVENTION

Thus, the invention relates to a coaxial cable comprising:

a first electrically conductive element consisting of a cylindrical central core;

a second electrically conductive element surrounding said first electrically conductive element but separated from it by a layer of dielectric material; and

an insulating sheath placed on the second electrically conductive element, characterized in that the first electrically conductive element comprises metallic nanowires.

The first electrically conductive element consists of a cylindrical central core comprising (or even composed exclusively) of metallic nanowires and more specifically of metallic nanowires comprising one or more metallic elements chosen, for example, from silver, gold, nickel, copper and the alloys thereof and, preferably, at least 50% by mass of one of these metallic elements. Advantageously, the first electrically conductive element can consist of a cylindrical central core comprising silver nanowires or even composed exclusively of silver nanowires.

The nanowires are advantageously connected together in the direction of the coaxial cable, that is to say with an electrical contact between the different nanowires ensuring electrical continuity over the entire core.

Each nanowire can have a diameter ranging from 10 nm to 1000 nm, preferably from 30 to 500 nm and, more preferably, from 20 to 100 nm.

In addition, each nanowire can have a length / diameter ratio greater than 10, preferably greater than 100, more preferably greater than 1000.

When it is produced, in particular, by electrospinning, the central cylindrical core can comprise, on its surface, a layer of polymer (s) independent of the layer of dielectric material, which one or which polymer (s) being necessary (s) the implementation of the electrospinning technique. This or these polymers can be polymers of the family of polypyrrolidones (and more specifically, polyvinylpyrrolidones). It is understood that this layer of polymer (s) thus covers the metallic nanowires, such as silver nanowires. Thus, specifically, the core can consist of silver nanowires covered with a layer of a polymer from the family of polypyrrolidones and, more specifically, polyvinylpyrrolidones.

Advantageously, the central core can have a diameter ranging from 50 to 500 nm.

Thanks to the use of nanowires to constitute the core of the coaxial cables, it is possible to access coaxial cables having a small diameter, for example a diameter less than or equal to 0.5 mm, preferably a smaller diameter or equal to 100 µm, more preferably less than or equal to 50 µm and preferably more than or equal to 5 µm.

It is specified that, by diameter, is understood taking into account the configuration of the coaxial cables of the invention, the external diameter of the insulating sheath placed on the second electrically conductive element, this sheath forming the peripheral element of the coaxial cable.

The second electrically conductive element surrounds said first electrically conductive element but is separated from it by a layer of dielectric material. From a structural point of view, the second electrically conductive element is conventionally in the form of a hollow cylinder, the internal face of which is in contact with the layer of dielectric material and the external face of which is in contact with the insulating sheath.

This second electrically conductive element can also be qualified as a shielding layer, in that it makes it possible to absorb external interference (such as parasitic signals, noise) which can come, if necessary, from other cables located nearby and also ensures the role of ground, which means that it must never be in contact with the central core at the risk of causing a short-circuit. To do this, it is separated from the central core by a layer of dielectric material.

According to the invention, the second electrically conductive element can comprise at least one first material chosen from carbon nanotubes, graphenes, graphene oxides, metallic nanowires and mixtures thereof, this or these materials being present, advantageously, in a proportion at least equal to 60% by mass relative to the total mass of the second electrically conductive element.

In addition, the second electrically conductive element may comprise a second material, for example, at least one surfactant (or surfactant additive), such as sodium dodecyl sulfate.

This second electrically conductive element may have a thickness (corresponding to the fact that it is conventionally in the form of a hollow cylinder at the difference between the external diameter and the internal diameter of the cylinder) ranging from 5 to 800 nm, preferably from 10 to 300 nm. In addition, this second electrically conductive element advantageously has a surface resistance of less than 5000 ohms per square (Ω / π), preferably less than 50 ohms per square (Ω / π).

Between the first electrically conductive element and the second electrically conductive element is disposed a layer of dielectric material, this layer possibly being in:

an organic material of the polymer type, in which case it is understood that the constituent polymer or polymers must have dielectric properties, such polymers being able to be chosen from polyolefins, polyaromatics, polyimides, acrylate polymers, silicone elastomers , elastomers of the rubber family (such as an acrylonitrile-butadiene copolymer), polyurethanes, these polymers being able to be partially or completely halogenated, in particular, with fluorine; or

an inorganic material of the oxide type (s) of metallic element (s) (for example, zirconium oxide, hafnium oxide, titanium oxide, zinc, aluminum oxide) or of metalloid element (s) (such as silicon oxide) or of the nitride type (s) (such as boron nitride).

The layer of dielectric material can also be based on a composite material comprising a polymer matrix (for example, in one or more polymers belonging to the categories mentioned above) and a filler, for example, of the oxide (s) d type. 'metallic element (s) or metalloid element (s) as mentioned above.

When the layer of a dielectric material is made of an organic material of the polymer type as mentioned above, it may have a thickness (corresponding to the difference between the external diameter and the internal diameter) ranging from 1 to 60 μm, from preferably from 1 to 6 pm.

When the layer of a dielectric material is made of an inorganic material as mentioned above, it may have a thickness (corresponding to the difference between the external diameter and the internal diameter) ranging from 1 to 1000 nm, preferably 5 at 100 nm.

Finally, the coaxial cables comprise an insulating sheath placed on the second electrically conductive element, that is to say on the shielding layer, in order to ensure physical protection of the cable.

This sheath conventionally comprises, as constituent material, a polymeric material based on one or more insulating polymers chosen, for example, from optionally halogenated polyolefins (for example, fluorinated and / or chlorinated), for example a tetrafluoroethylene copolymer and of hexafluoropropene, polyketones, silicones and mixtures thereof.

The coaxial cables of the invention can be electrical cables for transmitting digital or analog signals at high or low frequency, the first electrical conductive element and the second electrical conductive element being arranged coaxially with respect to each other (or, in other words, their axes of central symmetry merge).

The authors of the present invention have also developed a method for preparing the coaxial cables defined below, which is in particular simple to implement and generates low costs, said method comprising the following steps:

a) a step of producing the first electrically conductive element by reduction of one or more metal salts present in a solution and spinning of the nanowire (s) thus obtained;

b) a step of depositing on the first conductive element a layer of dielectric material;

c) a step of depositing on the layer of dielectric material the second electrically conductive element;

d) a step of depositing on the second electrically conductive element the insulating sheath.

Thus, the method of the invention comprises, first of all a step of preparing the first electrically conductive element constituting the central cylindrical core of the coaxial cable, this step comprising:

an operation of reduction of one or more metal salts included in a solution to form one or more metallic elements at their degree of oxidation 0 in the form of nanowires;

a spinning operation of the nanowire (s) thus obtained.

More specifically, the spinning operation can consist of an electrospinning operation (corresponding to the English terminology "electrospinning"), which makes it possible, on the one hand, to orient the metallic element or elements in the form of nanowires in a direction privileged and, on the other hand, to assemble end to end said nanowires to form the central core.

More specifically, concerning electrospinning, after the reduction operation and the possible purification operation, the nanowires obtained are advantageously dispersed in a solution comprising at least one polymer compatible with this technique, such as a polymer belonging to the family of polypyrrolidones (in particular, a polyvinylpyrrolidone called "PVP") and at least one polar protic solvent (for example, an alcoholic solvent, such as methanol). This solution advantageously comprises a concentration of nanowires ranging from 0.1 to 20 g / L, preferably from 2 to 10 g / L.

This solution is then introduced into an electrospinning device at a rate which can range from 0.1 to 10 ml / h, preferably from 0.3 to 3 ml / h and is advantageously subjected to the action. an electric field ranging from 0.1 to 10 kV / cm, preferably from 0.5 to 2 kV / cm.

At the end of this electrospinning operation, the nanowires thus oriented can be subjected to a drying operation to remove the organic solvent (s) present in the solution. The oriented nanowires thus form the cylindrical core of the coaxial cable coated with a layer of the polymer or polymers present in solution.

The cylindrical core is then covered with a layer of dielectric material.

When the dielectric material consists of a polymeric material, the deposition step may consist of an operation of extruding the polymer (s) onto the first electrically conductive element or of an operation of dipping the first electrically conductive element in a solution comprising the or the polymers constituting the dielectric material (it being understood in this case that the soaking operation will be followed by a drying operation to eliminate the volatile species present in the solution).

When the dielectric material consists of a material of the oxide (s) or nitride (s) type, the deposition step can be carried out by the solgel technique (for example, by polymerization of tetraorthosilicate, when the material consists of SiO ₂ ) or by the chemical vapor deposition technique by alternating fluxes (otherwise known as the ALD technique for “Atomic Rent Deposition”), the conditions of these techniques being advantageously fixed in order to obtain a layer having a thickness ranging from 1 to 1000 nm, preferably ranging from 5 to 50 nm.

The layer of dielectric material thus obtained is then coated with the second electrically conductive element, which can be deposited by a liquid technique, that is to say using a solution comprising the material or materials constituting the second conductive element. electric (i.e., for example, carbon nanotubes, graphene, graphene oxide, metallic nanowires and mixtures thereof and optional additives, such as a surfactant additive). Among the possible techniques, mention may be made, more specifically, of spray coating (also known under the English name "sproy-cooting"), of dip-shrinkage (also known under the English name "dip- coating ") or laminar coating (also known as" flowcoating ").

Once the deposition operation has been carried out, the layer thus obtained is advantageously subjected to a drying operation in order to remove in particular the solvent (s), for example, at ambient temperature (that is to say without application of heating other than that ambient air) for a period ranging from 5 minutes to 12 hours, preferably from 30 minutes to 3 hours, and this preferably under an atmosphere of inert gas or dry air. Alternatively, slight heating may be applied, for example, to a temperature below 100 ° C, preferably below 50 ° C.

In addition to carbon nanotubes, graphenes, graphene oxides, metallic nanowires and / or mixtures thereof, this solution can include:

one or more solvents such as water, an alcoholic solvent, a ketone solvent (such as N-methyl-2-pyrrolidone, dimethylformamide), a sulfoxide solvent (such as dimethylsulfoxide) and mixtures thereof this ; and or

one or more surfactants (such as sodium dodecyl sulfate).

Finally, the second electrically conductive element is coated by an insulating sheath, which can be deposited, when it is made of a polymeric material, by an extrusion technique. In this case, the sheath is deposited directly on the second electrically conductive element at the end of its manufacture, then cooled to ambient temperature.

The coaxial cables of the invention thanks to their small diameter have the ability to be inserted in very narrow areas, which naturally makes them perfectly suitable for use in the medical field and, in particular, for invasive applications such as , for example, in cardiology, ophthalmology or neurology, the purpose may be in vivo monitoring, the establishment of a diagnosis or neurostimulation.

Other characteristics and advantages of the invention will appear from the additional description which follows and which relates to the particular embodiment.

Of course, this additional description is given only by way of illustration of the invention and in no way constitutes a limitation.

BRIEF DESCRIPTION OF THE DRAWINGS

The single figure shows a view of a coaxial cable according to the invention.

DETAILED PRESENTATION OF PARTICULAR EMBODIMENTS

EXAMPLE

This example illustrates the preparation of a coaxial cable according to the invention comprising the preparation of the first electrically conductive element (that is to say the central core), the preparation of the layer of dielectric material, the preparation of the second electrically conductive element (that is to say the shielding layer) and the preparation of the insulating sheath, whereby a coaxial cable according to the invention results as illustrated in the single figure with a respective core central 1, a layer of dielectric material 3, a shielding layer 5 and an insulating sheath 7.

a) Preparation of the central core

In the context of this example, the central core is based on silver nanowires.

The silver nanowires are prepared by the following protocol.

Firstly, a first mixture is prepared, in a monocolor, by dissolving 3.54 g of polyvinylpyrrolidone (PVP) (of molar mass 40,000 g / mol) and 10 mg of NaCl (obtained from Sigma Aldrich, 99.0% purity) at 120 ° C (via an oil bath) in 156 mL of ethylene glycol (obtained from Sigma Aldrich, 99.0% purity).

In a second step, a second mixture is prepared, in a three-necked flask, by dissolving 1.36 g of silver nitrate (obtained from Sigma Aldrich) in 80 ml of ethylene glycol.

The first mixture is then added, during a casting time of 8 minutes, to the second mixture with stirring.

After this addition step, the temperature of the oil bath used to prepare the first mixture is increased from 120 ° C to 160 ° C.

When the temperature of the oil bath reaches 160 ° C., the three-necked flask containing the reaction mixture is immersed in this bath.

After 60 minutes of reaction, the resulting mixture is allowed to cool to room temperature.

The nanowires obtained are introduced at a rate of 3 g / L into a solution comprising 8% by mass of polyvinylpyrrolidone (PVP) in ethanol. The dispersion thus obtained is subjected to electrospinning carried out by injection of the latter into an electrospinning device at a flow rate of 0.6 ml / h for a working distance of 10 cm. The voltage used is then 6500 V (an electric field of 0.65 kV / cm). The resulting product is then dried in dry air at 50 ° C for 30 minutes.

The core thus formed comprises interlaced nanowires, the whole being covered with a PVP sheath, the core thus covered having a substantially cylindrical shape having the following dimensions: a diameter ranging from 80 to 500 nm and a height of 90 cm .

b) Preparation of the dielectric material layer

A 49% dry matter latex solution based on an acrylonitrile-butadiene copolymer (NBR Latex Zetpol®) is used (10 mL).

This solution is dissolved in acetone (500 mL) and is then concentrated. 2,5-b / s-tert-butylperoxy-2,5-dimethylhexane is added in an amount of 0.1% by mass relative to the total mass of the solution. The core obtained at the end of step a) is soaked for 30 seconds in this solution and then dried at 150 ° C for 20 seconds. The resulting product is then cooled and reeled. The layer of dielectric material obtained has a thickness of 12 μm.

c) Preparation of the shielding layer

An aqueous solution comprising water (100 ml) and carbon nanotubes and exfoliated sheets of graphene in equal mass proportion (400 mg) is first prepared. Dimethylformamide (30 mL) is added.

A surfactant, sodium dodecyl sulfate, is added up to 50 µM.

The product resulting from the previous step is soaked for 30 seconds in the solution prepared above and then dried under a flow of air heated to 150 ° C for 5 minutes.

The linear resistance measured on this sample is 250 Ω / m.

The shielding layer obtained has a thickness of 90 nm.

d) Preparation of the insulating sheath

The product resulting from the previous step is passed through an extruder to deposit a layer of tetrafluoroethylene and hexafluoropropene copolymer (called FEP copolymer) at a temperature above 300 ° C.

The coaxial cable thus formed is cooled in ambient air and wound. It has a diameter of 38 µm.

Claims (18)

1. Coaxial cable comprising: a first electrically conductive element consisting of a cylindrical central core; a second electrically conductive element surrounding said first electrically conductive element but separated from it by a layer of dielectric material; and an insulating sheath placed on the second electrically conductive element, characterized in that the first electrically conductive element comprises metallic nanowires. 2. Coaxial cable according to claim 1, in which the metallic nanowires comprise one or more metallic elements chosen from silver, gold, nickel, copper and their alloys. 3. Coaxial cable according to claim 1 or 2, wherein the metallic nanowires are silver nanowires. 4. Coaxial cable according to any one of the preceding claims, in which the cylindrical central core comprises, on its surface, a layer of polymer (s) independent of the layer of dielectric material, which one or which polymer (s) being polymers of the polypyrrolidone family. 5. Coaxial cable according to any one of the preceding claims, in which the cylindrical central core has a diameter ranging from 50 to 500 nm. 6. Coaxial cable according to any one of the preceding claims, which has a diameter less than or equal to 0.5 mm. 7. Coaxial cable according to any one of the preceding claims, which has a diameter less than or equal to 100 μm. 8. Coaxial cable according to any one of the preceding claims, which has a diameter less than or equal to 50 μm. 9. Coaxial cable according to any one of the preceding claims, in which the second electrically conductive element comprises at least one first material chosen from carbon nanotubes, graphenes, graphene oxides, metallic nanowires and mixtures thereof. this. 10. Coaxial cable according to any one of the preceding claims, in which the layer of a dielectric material is made of: an organic material of the polymer type chosen from polyolefins, polyaromatics, polyimides, acrylate polymers, silicone elastomers, elastomers of the rubber family (such as an acrylonitrile-butadiene copolymer), polyurethanes, these polymers being able to be partially or fully halogenated, in particular with fluorine; or an inorganic material of the oxide type (s) of metallic element (s) or of metalloid element (s) or of the nitride type (s). 11. Coaxial cable according to any one of the preceding claims, in which the insulating sheath comprises, as constituent material, a polymeric material based on one or more insulating polymers chosen from optionally halogenated polyolefins, polyketones, silicones and mixtures of these. 12. Method for manufacturing a coaxial cable as defined in any one of the preceding claims 1 to 11, comprising the following steps: a) a step of producing the first electrically conductive element by reduction of one or more metal salts present in a solution and spinning of the nanowire (s) thus obtained; b) a step of depositing on the first conductive element a layer of dielectric material; c) a step of depositing on the layer of dielectric material the second electrically conductive element; d) a step of depositing on the second electrically conductive element the insulating sheath. 13. The method of claim 12, wherein the spinning of step a) consists of electrospinning. 14. The method of claim 12 or 13, wherein, when the dielectric material consists of a polymeric material, the deposition step consists of an extrusion operation of the polymer (s) on the first electrically conductive element or in an operation of soaking the first electrically conductive element in a solution comprising the polymer or polymers constituting the dielectric material. 15. The method of claim 12 or 13, wherein, when the dielectric material consists of a material of the oxide (s) or nitride (s) type, the deposition step is carried out by sol-gel technique or by the technique of chemical vapor deposition by alternating flows. 16. Method according to any one of the preceding claims 12 to 15, in which the step of depositing the second electrically conductive element is carried out by a liquid technique using a solution comprising the material or materials constituting the second conductive element. electric. 17. The method of claim 16, wherein the solution comprises, in addition to carbon nanotubes, graphenes, graphene oxides, metallic nanowires and / or mixtures thereof: one or more solvents such as water, an alcoholic solvent, a ketone solvent, a sulfoxide solvent and mixtures thereof; and one or more surfactants. 18. Method according to any one of the preceding claims 12 to 17, in which the step of depositing the insulating sheath is, when the sheath is made of a polymeric material, carried out by an extrusion technique.