METHOD FOR PREPARATION AN ELECTRICALLY CONDUCTIVE STRATIFIED COMPOSITE STRUCTURE

Abstract

A process is provided for preparing an electrically conductive composite film having at least one thermoplastic polymer resin and electrically conductive particles chosen from graphene, carbon nanotubes, carbon nano-fibres, and mixtures thereof; and filiform metal nanoparticles, the electrically conductive composite film optionally impregnating fibres. The process has a step of preparing a suspension comprising a solvent and electrically conductive particles chosen from graphene, carbon nanotubes, carbon nanofibres, and mixtures thereof; and filiform metal nanoparticles. The suspension has approximately from 0.06% to 0.5% by volume of the electrically conductive particles relative to the total volume of the suspension.

Claims

1. Process for preparing an electrically conductive composite film comprising at least one thermoplastic polymer resin and electrically conductive particles chosen from: a) graphene, carbon nanotubes, carbon nanofibres, and mixtures thereof; and b) filiform metal nanoparticles, wherein said process comprises at least the following steps: 1) a step of preparing a suspension comprising a solvent and electrically conductive particles chosen from: a) graphene, carbon nanotubes, carbon nanofibres, and mixtures thereof; and b) filiform metal nanoparticles, said suspension comprising from 0.06% to 0.5% by volume of said electrically conductive particles relative to the total volume of the suspension, 2) a step of mixing a powder of thermoplastic polymer resin, having a particle size of less than or equal to 50 m, with the suspension prepared in the preceding step so as to obtain a homogeneous suspension, said homogeneous suspension comprising from 7% to 20% by volume of said thermoplastic polymer resin relative to the total volume of the suspension, 3) a step of depositing the homogeneous suspension of the preceding step on a non-stick support, 4) a drying step, 5) a step of heat treatment at a temperature greater than or equal to the melting point of the thermoplastic polymer resin when said resin is in semi-crystalline form or greater than or equal to its glass transition temperature when said resin is in amorphous form, in order to obtain an electrically conductive composite film deposited on said non-stick support, and 6) a step of removing the electrically conductive composite film from the non-stick support, and wherein said electrically conductive composite film is a self-supported film comprising at least one thermoplastic polymer resin and from 1% to 10% by volume of electrically conductive particles relative to the total volume of the electrically conductive composite film, and wherein the electrically conductive particles have an aspect ratio greater than or equal to 50.

2. Process according to claim 1, wherein the solvent of step 1) is chosen from hydrocarbon-based solvents, oxygen-bearing solvents, chlorinated solvents, water, and mixtures thereof.

3. Process according to claim 1, wherein the electrically conductive particles are filiform metal nanoparticles.

4. Process according to claim 1, wherein the thermoplastic resin of step 2) is chosen from polyaryl ether ketones (PAEKs); polyphenylene sulphides (PPSs); polyetherimides (PEIs); polyethersulphones (PESs); polysulphones (PSs); polyamides (PAs); polyamide-imides (PAIs); polycarbonates (PCs); polyvinylidene fluorides (PVdFs); copolymers of polyvinylidene fluoride and of trifluoroethylene [P(VdF-TrFE)] or of hexafluoropropene [P(VdF-HFP)]; and mixtures thereof.

5. Process according to claim 1, wherein the suspension prepared in step 2) has a viscosity ranging from 1 Pa.Math.s to 33 Pa.Math.s.

6. Process according to claim 1, wherein step 5) is carried out at a temperature ranging from 200 C. to 400 C.

7. Process according to claim 1, wherein step 3) is carried out according to the following sub-steps: 3a) a step of introducing the homogeneous suspension of step 2) into a container comprising an injection nozzle in its lower part, and maintaining the suspension under mechanical stirring, 3b) a step of applying the suspension to a non-stick support, by means of said injection nozzle and of a scraper located at the outlet of the nozzle.

8. Process according to claim 1, wherein said process further comprises at least the following steps: i-1) a step of preparing a successive stack of at least said self-supported electrically conductive composite film, and of at least one layer of fibres, and, a thermoforming step ii), so as to obtain an electrically conductive laminated composite structure comprising at least said thermoplastic polymer resin, said fibres, and said electrically conductive particles.

9. Process according to claim 1, wherein said process further comprises at least the following steps: A) a step of preparing at least one unitary stack, comprising said self-supported electrically conductive composite film as a first composite film, a layer of fibres, and optionally said second self-supported electrically conductive composite film as a second composite film, B) a thermoforming step, so as to form a first electrically conductive composite preimpregnated film, C) the repetition of steps A) and B), so as to form at least a second electrically conductive composite preimpregnated film, D) a step of preparing a stack of several electrically conductive composite preimpregnated films, which are identical or different, as obtained in steps B) and C), and E) a thermoforming step, so as to obtain an electrically conductive laminated composite structure comprising at least said thermoplastic polymer resin, said fibres and said electrically conductive particles.

10. Process according to claim 1, wherein in the suspension of step 2), the ratio of the weight of solvent to the weight of total solids (i.e. weight of thermoplastic polymer resin+weight of electrically conductive particles) ranges from 0.5 to 8

11. Process for preparing an electrically conductive composite film comprising at least one thermoplastic polymer resin and electrically conductive particles chosen from: a) graphene, carbon nanotubes, carbon nanofibres, and mixtures thereof; and b) filiform metal nanoparticles, wherein said process comprises at least the following steps: 1) a step of preparing a suspension comprising a solvent and electrically conductive particles chosen from: a) graphene, carbon nanotubes, carbon nanofibres, and mixtures thereof; and b) filiform metal nanoparticles, said suspension comprising from 0.06% to 0.5% by volume of said electrically conductive particles relative to the total volume of the suspension, 2) a step of mixing a powder of thermoplastic polymer resin, having a particle size of less than or equal to 50 m, with the suspension prepared in the preceding step so as to obtain a homogeneous suspension, said homogeneous suspension comprising from 7% to 20% by volume of said thermoplastic polymer resin relative to the total volume of the suspension, 3) a step of depositing the homogeneous suspension of the preceding step on a non-stick support, 4) a drying step, and 5) a step of heat treatment at a temperature greater than or equal to the melting point of the thermoplastic polymer resin when said resin is in semi-crystalline form or greater than or equal to its glass transition temperature when said resin is in amorphous form, in order to obtain an electrically conductive composite film deposited on said non-stick support, and 6) a step of removing the electrically conductive composite film from the non-stick support, and wherein said electrically conductive composite film is a self-supported film comprising at least one thermoplastic polymer resin and from 1% to 10% by volume of electrically conductive particles relative to the total volume of the electrically conductive composite film, and wherein in the suspension of step 2), the ratio of the weight of solvent to the weight of total solids (i.e. weight of thermoplastic polymer resin+weight of electrically conductive particles) ranges from 0.5 to 8.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0232] FIG. 1 is a diagrammatic representation of the device used to carry out the process in accordance with one embodiment;

[0233] FIG. 2 is an image of the electrically conductive composite film of example 1 in accordance with one embodiment; and

[0234] FIG. 3 is an image showing the laminated composite structure (4-ply stack) of example 2 in accordance with one embodiment.

DETAILED DESCRIPTION

[0235] The present invention is illustrated by the examples hereinafter, to which this is not however limited.

EXAMPLES

[0236] The starting materials used in the examples are listed hereinafter: [0237] polyether ketone ketone (PEKK) resin, Kepstan 6003, Arkema, powder with a particle size of approximately 20 m, Arkema, [0238] polyphenylene sulphide (PPS) resin: Fortron 0205B4, powder with a particle size of approximately 20 m, Celanese, [0239] ethanol, purity 99.8%, Sigma Aldrich, [0240] multiwall carbon nanotubes (GRAPHISTRENGTH MWNTs), Graphistrength C100, Arkema, [0241] carbon black, Sigma Aldrich, <500 nm, [0242] carbon fibre fabrics, Hexforce G0904 D1070 TCT, 193 g/m.sup.2, plain weaves from Hexcel, [0243] non-stick support: Upilex polyimide sheet, or metal sheet made non-stick using a demoulding agent, Cirex Si041WB from Sicomin.

[0244] Unless otherwise indicated, all these starting materials were used as received from the manufacturers.

[0245] The ultrasound instrument used in the examples hereinafter is sold under the trade name Vibracell 65115 by Fisherbioblock.

Example 1

Preparation of an Electrically Conductive Composite Film in Accordance with the Invention and Prepared According to the Process in Accordance with the Invention

[0246] A suspension of 2861 ml comprising 207.1 g of silver nanowires and ethanol was prepared. The silver nanowires were prepared beforehand according to a solution growth process from silver nitrate (AgNO.sub.3) and polyvinylpyrrolidone (PVP) as described by Y. G. Sun et al., Crystalline silver nanowires by soft solution processing, Nano Letters, 2002. 2(2): p. 165-168, with a PVP/AgNO.sub.3 ratio of 1.53. The silver nanowires obtained have a length ranging approximately from 10 to 100 m, and a width ranging approximately from 120 to 400 nm.

[0247] The silver nanowire suspension was mixed with 1000 g of Kepstan 6003 thermoplastic polymer resin using mechanical stirring (propeller at 100 revolutions per minute) and ultrasound at a frequency of 50 kHz and a power of 25 W per pulse of 5 seconds. A homogeneous suspension comprising ethanol, the PEKK resin and the silver nanowires was thus obtained. The suspension had a viscosity of approximately 3 Pa.Math.s.

[0248] The suspension was introduced into a container comprising an injection nozzle in its lower part, and was applied to the Upilex or Cirex Si041WB non-stick support using said injection nozzle, and a scraper located at the outlet of said nozzle.

[0249] In order to form a continuous layer of suspension, a roll which makes it possible to cause the non-stick support to continuously file past the injection nozzle and under the scraper, was used. The roll speed was approximately 2 cm/second.

[0250] The layer of suspension was then dried at a temperature of approximately 150 C. and heat-treated in a conventional oven at a temperature of approximately 350 C. for approximately 5 minutes so as to form an electrically conductive composite film deposited on said non-stick support. Said electrically conductive composite film was then detached from the non-stick support so as to form a self-supported electrically conductive composite film comprising PEKK and 2.5% by volume of silver nanowires. It had a resistivity of 0.6 ohm/square.

[0251] FIG. 1 is a diagrammatic representation of the device used to carry out the process in accordance with the first subject of the invention.

[0252] Said device comprises a roll 1 which makes it possible to cause a non-stick or fibrous support 2 to continuously file past. A homogeneous suspension comprising at least one thermoplastic polymer resin and electrically conductive particles is introduced into a container 3 comprising an injection nozzle 4 in its lower part, and is maintained under mechanical stirring. This suspension is applied to the non-stick support 2 by means of said nozzle 4, and of a scraper 5 located at the outlet of the nozzle 4 so as to form a layer of suspension 6 deposited on the non-stick support or impregnating the fibrous support. This layer is dried in a dryer 7. The vapours can be recovered by means of a system 8 of ventilation and condensation for the recovery of the solvent. The dried layer of suspension is then heat-treated in an oven 9 at a temperature greater than or equal to the melting point of the thermoplastic polymer resin so as to form an electrically conductive composite film or prepreg 10. The device may also comprise a recovery roll 11.

[0253] FIG. 2 shows the electrically conductive composite film in accordance with the invention and as obtained in this example, by scanning electron microscopy (FEG-SEM) performed with a microscope equipped with a field emission gun, sold under the trade name Jeol JSM 6700F by the company Jeol.

Example 2

Preparation of an Electrically Conductive Laminated Composite Structure in Accordance with the Invention and Prepared According to the Process in Accordance with the Invention

[0254] A laminated composite structure was manufactured by manual preparation of a successive stack of an electrically conductive composite film as obtained in Example 1, of a layer of a fibre fabric, of an electrically conductive composite film as obtained in Example 1, and of a layer of fibres (i.e. 2-ply stack: [film of PEKK-silver nanowires/layer of fibre fabric].sub.2), and by thermoforming of the stack at a temperature of 350 C. and a pressure of 0.5 MPa for 15 min, using a press sold under the trade name Carver 4128CE by the company Carver.

[0255] During the 2-ply stacking, the layers of fibres are oriented according to the successive orientations 0 and 45.

[0256] The laminated composite structure obtained had a density of 1.65 and a conductivity of 200 S/m.

[0257] A laminated composite structure was manufactured by manual preparation of a 4-ply stack: [film of PEKK-silver nanowires/layer of fibre fabric].sub.4, and by thermoforming of the stack at a temperature of 350 C. and a pressure of 0.5 MPa for 15 min using the same press as that described above.

[0258] During the 4-ply stacking, the layers of fibres are oriented according to the successive orientations 0, 45, 0 and 45.

[0259] The laminated composite structure obtained had a density of 1.805 and a conductivity of 350 S/m.

[0260] FIG. 3 shows the laminated composite structure (4-ply stack) in accordance with the invention and as obtained in this example, by scanning electron microscopy (FEG-SEM) performed with a microscope equipped with a field emission gun, sold under the trade name Jeol JSM 6700F by the company Jeol.

Example 3

Preparation of an Electrically Conductive Composite Film in Accordance with the Invention and Prepared According to the Process in Accordance with the Invention

[0261] A suspension of 5800 ml comprising 28.35 g of carbon nanotubes and ethanol was prepared by means of ultrasound at a frequency of 20 kHz and a power of 500 W per pulse of 5 seconds for 2 min.

[0262] The carbon nanotube suspension was mixed with 826 g of Kepstan 6003 thermoplastic polymer resin using mechanical stirring (propeller at 100 revolutions per minute) and ultrasound at a frequency of 20 kHz and a power of 500 W per pulse of 5 seconds. A homogeneous suspension comprising ethanol, the PEKK resin and the carbon nanotubes was thus obtained. The suspension had a viscosity of approximately 5 Pa.Math.s.

[0263] The suspension was introduced into a container comprising an injection nozzle in its lower part, and was applied to the non-stick support by means of said injection nozzle, and a scraper located at the outlet of said nozzle.

[0264] In order to form a continuous layer of suspension, a roll which makes it possible to cause the non-stick support to continuously file past the injection nozzle and under the scraper was used. The roll speed was approximately 2 cm/second.

[0265] The layer of suspension was then dried at a temperature of approximately 150 C. and heat-treated in a conventional oven at a temperature of approximately 350 C. for approximately 5 minutes so as to form an electrically conductive composite film deposited on said non-stick support.

[0266] Said electrically conductive composite film was then detached from the non-stick support so as to form a self-supported electrically conductive composite film comprising PEKK and 2% by volume of carbon nanotubes. It had a resistivity of 6000 ohm/square.

Example 4

Preparation of an Electrically Conductive Laminated Composite Structure in Accordance with the Invention and Prepared According to the Process in Accordance with the Invention

[0267] A laminated composite structure was manufactured by manual preparation of a successive stack of an electrically conductive composite film as obtained in Example 3, of a layer of a fibre fabric, of an electrically conductive composite film as obtained in Example 3, and of a layer of fibres (i.e. 2-ply stack: [film of PEKK-carbon nanotubes/layer of fibre fabric].sub.2), and by thermoforming of the stack at a temperature of 350 C. and a pressure of 0.5 MPa, using the same press as that described in Example 2.

[0268] During the 2-ply stacking, the layers of fibres are oriented according to the successive orientations 0 and 45.

[0269] The laminated composite structure obtained had a density of 1.662 and a conductivity of 0.1 S/m.

Comparative Example 5

Preparation of an Electrically Conductive Composite Film Not in Accordance with the Invention

[0270] A self-supported PEKK film was prepared according to the process as described in Example 1 using a suspension of 2500 ml comprising 1000 g of Kepstan 6003 thermoplastic polymer resin and ethanol. The suspension had a viscosity of approximately 3 Pa.Math.s. The layer of suspension was applied to the non-stick support as described in Example 1, dried at a temperature of approximately 150 C., and heat-treated in a conventional oven at a temperature of approximately 350 C. for approximately 5 minutes.

[0271] This film is not part of the invention since it does not comprise electrically conductive particles chosen from: a) graphene, carbon nanotubes, carbon nanofibres, and mixtures thereof; and b) filiform metal nanoparticles. It had a resistivity >1 000 000 ohm/square.

[0272] This self-supported film not in accordance with the invention could also be obtained by forming under a hot press (i.e. melt-forming) at a temperature of 350 C. and at a pressure of 0.5 MPa and using the same press as that described in Example 2.

Comparative Example 6

Preparation of an Electrically Conductive Laminated Composite Structure Not in Accordance with the Invention

[0273] A laminated composite structure was manufactured by manual preparation of a successive stack of a film as obtained in Comparative Example 5, of a layer of a fibre fabric, of a film as obtained in Comparative Example 5, and of a layer of fibres (i.e. 2-ply stack: [film of PEKK/layer of fibre fabric].sub.2), and by thermoforming of the stack at a temperature of 350 C. and a pressure of 0.5 MPa, using the same press as that described in Example 2.

[0274] During the 2-ply stacking, the layers of fibres are oriented according to the successive orientations 0 and 45.

[0275] The laminated composite structure obtained, not in accordance with the invention, had a density of 1.655 and a conductivity of 10.sup.12 S/m.

[0276] Thus, this laminated composite structure, not part of the invention, has an insufficient electrical conductivity and cannot therefore replace a metal structure.

Comparative Example 7

Preparation of an Electrically Conductive Composite Film Not in Accordance with the Invention

[0277] A self-supported film comprising PEKK (Kepstan 6003 thermoplastic polymer resin) and 15% by volume of carbon black was prepared by forming under a hot press (i.e. melt-forming) using the press as described in Example 2, at a temperature of 350 C. and at a pressure of 10 MPa. It had a resistivity of 200 ohm/square.

[0278] This film is not part of the invention since it does not comprise electrically conductive particles chosen from: a) graphene, carbon nanotubes, carbon nanofibres, and mixtures thereof; and b) filiform metal nanoparticles.

[0279] This same self-supported film not in accordance with the invention could not be prepared according to a process similar to that as described in Example 1, and in the invention (i.e. by preparation of a suspension, then of a layer of suspension, drying and heat-treatment). This is because the suspension comprised too great an amount of carbon black to be able to form the layer of suspension and then said film, and if the amount of carbon black is less than 15% by volume, the conductivity of the film is not sufficient.

Comparative Example 8

Preparation of an Electrically Conductive Laminated Composite Structure Not in Accordance with the Invention

[0280] A laminated composite structure was manufactured by manual preparation of a successive stack of a film as obtained in Comparative Example 7, of a layer of fibre fabric, of a film as obtained in Comparative Example 7, and of a layer of fibres (i.e. 2-ply stack: [film of PEKK-carbon black/layer of fibre fabric].sub.2), and by thermoforming of the stack at a temperature of 350 C. and a pressure of 18 MPa, using the same press as that described in Example 2.

[0281] During the 2-ply stacking, the layers of fibres are oriented according to the successive orientations 0 and 45.

[0282] The laminated composite structure obtained, not in accordance with the invention, had a density of 1.703 and a conductivity of 1 S/m. This structure has a sufficient electrical conductivity. However, it proved to be very weak and brittle, and does not therefore have mechanical properties suitable for being able to be used.

[0283] In conclusion, by virtue of the electrically conductive film in accordance with the invention comprising at least one thermoplastic resin and electrically conductive particles chosen from a) graphene, carbon nanotubes, carbon nanofibres, and mixtures thereof; and b) metal nanoparticles, a laminated composite structure with both good electrical properties and good mechanical properties can be obtained.

Example 9

Preparation of an Electrically Conductive Composite Film in Accordance with the Invention and Prepared According to the Process in Accordance with the Invention

[0284] A suspension of 2800 ml comprising 250 g of silver nanowires in ethanol was prepared as in Example 1.

[0285] The suspension of silver nanowires was mixed with 1000 g of Fortron 0205B4 thermoplastic polymer resin by means of mechanical stirring (propeller at 100 revolutions per minute) and ultrasound at a frequency of 50 kHz and a power of 25 W per pulse of 5 seconds. A homogeneous suspension comprising ethanol, the PPS resin, and the silver nanowires was thus obtained. The suspension had a viscosity of approximately 2 Pa.Math.s.

[0286] The suspension was applied to the Upilex or Cirex Si041WB non-stick support as in Example 1.

[0287] The layer of suspension was then dried at a temperature of approximately 150 C. and heat-treated in a conventional oven at a temperature of approximately 310 C. for approximately 5 minutes so as to form an electrically conductive composite film deposited on said non-stick support. Said electrically conductive composite film was then detached from the non-stick support so as to form a self-supported electrically conductive composite film comprising PPS and 3% by volume of silver nanowires. It had a resistivity of 0.9 ohm/square.

Example 10

Preparation of an Electrically Conductive Laminated Composite Structure in Accordance with the Invention and Prepared According to the Process in Accordance with the Invention

[0288] A laminated composite structure was manufactured by manual preparation of a successive stack of an electrically conductive composite film as obtained in Example 9, of a layer of a fibre fabric, of an electrically conductive composite film as obtained in Example 9, and of a layer of fibres (i.e. 2-ply stack: [film of PPS-silver nanowires/layer of fibre fabric].sub.2), and by thermoforming of the stack at a temperature of 310 C. and a pressure of 0.5 MPa for 15 min, using the same press as that described in Example 2.

[0289] During the 2-ply stacking, the layers of fibres are oriented according to the successive orientations 0 and 45.

[0290] The laminated composite structure obtained had a density of 1.68 and a conductivity of 30 S/m.