FR3013052A1 - ELECTRICALLY CONDUCTIVE COMPOSITION BASED ON ELECTRICALLY CONDUCTIVE NANOPARTICLES - Google Patents

Abstract

An electrically conductive composition comprising at least electrically conductive nanoparticles mixed in an aqueous medium, characterized in that said nanoparticles are carbon nanotubes (CNTs) or nanoparticles based on polyanylins or the nanoparticles comprise a core of a conductive or non-conductive material electricity and an electroconductive coating casing, and in that the composition further comprises another class of electrically conductive particles comprising graphite and / or carbon black and / or carbon fibers. The conductivity of the coating obtained from such a composition is greater than 2 S / cm, or even greater than 25 S / cm.

Description

The invention relates to an electrically conductive composition comprising at least electrically conductive nanoparticles mixed in an aqueous medium, as well as to the process for obtaining such a composition. The invention also relates to the use of the composition as an electrically conductive coating.

The invention will be more particularly described with regard to a use of the composition as a heating coating, without being limited thereto. The conductive polymeric compositions based on nanoparticles, in particular based on carbon nanotubes (also known as CNTs) or on graphene, make it possible to obtain high-performance conductive films with regard to the mechanical and conductive properties, the CNTs conferring high electrical conductivity. and thermal.

However, the performance of these compositions depends on the method of dispersion and distribution of the nanoparticles in the polymer matrix, as well as nanoparticles as such. In electrically conductive coating applications, there are also compositions based on conductive polymer as described in the French patent application 05/08172 published under FR28889197. The composition described in this patent application comprises nanocomposite particles having an alkyl polyacrylate core and a polyaniline bark. To achieve a compromise between the conductivity and film-forming properties, the synthesis of the particles gives a composition whose conductivity is however less than 2 S / cm. The object of the invention is to propose a composition based on conductive nanoparticles which have high conductivity performances while ensuring good film-forming properties (covering a surface in a homogeneous manner), in particular when they are used for low-level coatings. thickness such as less than 200 μm. The composition will further provide a silky, non-staining (i.e., non-scratch-to-touch) appearance when used as a coating. The composition of the invention also aims to minimize its manufacturing cost. The invention also relates to a process for obtaining such a composition which ensures a good dispersion of the nanoparticles in the solution containing said nanoparticles, so as not to affect the conductive properties of said solution, that is to say to reduce its conductivity. In addition, the manufacturing method of the invention remains accessible.

According to the invention, the electrically conductive composition comprises at least electrically conductive nanoparticles mixed in an aqueous medium, and is characterized in that said nanoparticles are carbon nanotubes (CNTs) or nanoparticles based on polyanylins, or the nanoparticles. comprise a core (of a non-electrically conductive material) and an electroconductive coating casing, and in that the composition further comprises another class of electrically conductive particles larger than the size of the nanoparticles.

In particular, the electrically conductive particles larger than the size of the nanoparticles have no dimension less than 100 nm regardless of their shape.

Preferably, these electrically conductive particles larger than the size of the nanoparticles (said other category of particles) comprise graphite, in particular not exfoliated, and / or carbon black, and / or carbon fibers.

All the particles (nanoparticles and larger particles in graphite or the like) are in dispersed form in water so that the particles are suspended in the aqueous medium. The composition can thus be used.

Unexpectedly, the conductivity of the composition is much higher than the conductivity that would have been expected by averaging the conductivities of two compositions each containing exclusively conductive nanoparticles or larger particles of graphite type.

In particular, the conductivity of the composition of the invention is greater than 2 S / cm, preferably greater than 5 S / cm, in particular greater than 7 S / cm, or even greater than 15 S / cm or 25 S / cm. cm.

In addition, the composition of the invention provides, when used as a coating, a silky and non-messy appearance. Furthermore, the composition is obtained by dispersing the particles in an aqueous medium, simplifying the manufacturing process, in particular with regard to the components and the operating conditions. There is no need to use solvents. The working conditions for the operator are simple, secure, without the need to comply with fire or explosion-proof standards as for the use of flammable materials of the solvent type.

According to one characteristic, the nanoparticles on the one hand, and the other category of particles (particles of a size greater than that of nanoparticles and graphite type, carbon black, or carbon fibers), on the other hand, have respectively been previously dispersed independently in water. Said other category of particles has been dispersed in water with a percentage of dry extract which depends on the desired properties, in particular the viscosity of the final composition, the conductivity, and the method of implementation. This percentage may for example be at least 25%, but may be lower. The particles of said other or second category (those larger than the nanoparticles) have for example a micrometer size. These particles are for example derived from an initial material ground. The nanoparticles of the composition may have a spherical, tubular (such as carbon nanotubes) or platelet shape such as clays or graphene, or of less specific but at least filiform or elongated form. The nanoparticles are, for example, NTCs. . They may alternatively consist of a core whose material is non-conductive for example clay, and an electrically conductive coating envelope such as metal.

Electroconductive nanoparticles can be a mixture of different types of electroconductive nanoparticles.

When the nanoparticles are CNTs, they are preferably concentrated in a polymeric compound based on a polymer such as carboxyl methylcellulose, in particular the compound comprises 45% total CNT by weight of the mixture and 55% of polymeric binder consisting of carboxymethylcellulose.

When in the second variant of the electroconductive nanoparticles, polyanylin nanoparticles are used, they are advantageously dispersed beforehand in water, preferably at a concentration of at least 15% solids, preferably at least 15% by weight. minus 30%. Once the nanoparticles and the other particles of graphite or other independently dispersed in water to form two pre-mixtures respectively, the proportions of these two premixes to form the final solution or composition are variable according to the desired conductivity and therefore the intended application. Preferably, for optimum conductivity: - For the first variant with CNTs, the proportions are 50% of a first aqueous pre-mixture based on CNT and 50% of a second aqueous pre-mixture based on particles of the second category. For the second variant with polyanylin nanoparticles, the proportions are 80% or less of polyanylin nanoparticles, and the complement of an aqueous premix based on particles of the second category. The invention also relates to a method of manufacturing a composition above, characterized in that it comprises the steps of: dispersion in an aqueous solution of CNTs or use of nanoparticles based on polyanylin already in the form of aqueous dispersion, to form a first premix; dispersion in an aqueous solution of graphite and / or carbon black and / or carbon fibers to give a second premix; - mixing the first and second premixes. The manufacturing process is thus simple to implement, safe, and affordable in terms of cost.

According to a characteristic of the manufacturing process, the composition obtained is mixed with an acrylic or vinyl emulsion, or with fluorinated products, in particular to be spread and used as a coating, for example as a paint.

The composition of the invention is advantageously used as a heating coating by depositing it directly on a compatible surface or made compatible by appropriate treatment, or included in a film intended to form a coating. The deposition of the composition on a flexible or rigid surface can be obtained by coating, screen printing, spraying with a spray gun, or any other known method. The receiving surface of the composition may be plastic, in particular a film of polyethylene terephthalate (PET), fabric 301 (textile, glass, carbon, Kevlar, etc.), paper, plaster or Placoplatre® type plaster boards. Without limitation, the composition is for example used in low voltage heating devices or usual voltage (120 or 220 volts), especially for building or industry, or in devices such as devices for heating the human body (thermotherapy), patches, belts, blankets, etc ... The composition is able to heat by Joule effect any static or mobile object. The coating based on the composition of the invention is in particular of a thickness of between 5 and 200 μm. The present invention is now described by way of example only illustrative and not limiting the scope of the invention. The invention relates to an electrically conductive composition, intended in particular to be applied in the form of a film, in particular of thickness between 10 and 60 μm. According to the invention, the electrically conductive composition comprises a first class of electrically conductive particles, which are carbon nanotubes (CNTs) or nanoparticles based on polyanylins, or the nanoparticles comprise a core made of a conductive or non-conductive material. electricity and an electroconductive coating envelope (nanoparticles hereinafter referred to as coated), and a second class of electrically conductive particles larger than the size of the nanoparticles and comprising graphite and / or carbon black and / or carbon fibers and / or coated particles made of a core and an envelope of electroconductive material. The particles of the second category are not nanoparticles.

They are larger than nanoparticles, and are preferably of micron size. They have no dimension less than 100 nm. These particles of the second category are for example derived from a ground material and being in the form of powder. The nanoparticles have a spherical, or tubular, or elongate, or platelet shape.

Polyanylin nanoparticles are rather spherical particles. Polyanylin nanoparticles are directly supplied dispersed in water as obtained in this way during their manufacture.

As for the carbon nanotubes (CNTs), they are preferably concentrated in a polymeric compound based on a polymer (to facilitate their handling) such as carboxyl methylcellulose (CMC), the polymer being water-soluble under appropriate shear. By way of example, the compound comprises 45% total weight CNT of the mixture and 55% of polymethylmethylcellulose polymer binder. Such a compound is in particular marketed under the reference CW2-45 by the company Arkema.

Carbon nanotubes (CNTs) are firstly dispersed in water for mixing with the second class of particles.

When the CNTs are concentrated in a polymeric compound, the latter (including the CNTs) is therefore previously diluted in water before mixing with the dispersion of the particles of the second category. The dilution in water of the polymeric compound is in a concentration of at least 10% solids, for example 14%. The percentage of dry extract could be greater, however giving rise to a higher viscosity. It is necessary to use the suitable tool to mix appropriately according to the viscosity of the mixture.

As for the polyanylin nanoparticles, they are previously diluted in water, preferably at a concentration of at least 15% solids. Similarly, the second class of particles has been previously dispersed in water. The percentage of dry extract is a function of the desired properties, in particular of the conductivity, the intended application and the mixing tools available. By way of example, the product referenced LB1300 at TIMCAL is a dispersion of 25% dry extract of graphite in water. Once the nanoparticles on the one hand, and the other category of particles on the other hand, have respectively been previously dispersed independently in water when they are not already in the form of an aqueous dispersion, they respectively form two pre-mixtures, the proportions of these two premixes to form the solution or final composition are variable according to the desired conductivity and therefore the intended application.

Preferably, for optimum conductivity: the proportions will be 50% of an aqueous premix based on NTC, and 50% of a second aqueous premix based on particles of the second category. - The proportions will be 80% polyanylin nanoparticles (already in the form of an aqueous mixture) and 20% of an aqueous mixture based on particles of the second category. The process for producing the composition of the invention comprises the steps of: dispersion in an aqueous solution of CNTs or the use of nanoparticles based on polyanylin already included in an aqueous solution, to form a first premix; dispersion in an aqueous solution of the electroconductive particles of the second category (in graphite for example) to give a second premix; - mixing the first and second premixes. The dispersion in water of the nanoparticles of the NTC type or the coated nanoparticles and the dissolution of the polymer in the case of bound NTCs in a polymer matrix, are carried out according to a stirring speed, a water temperature and a duration which are adapted according to the type of nanoparticles, the type of polymer, the concentration of dry extract. The stirring speed may vary during the dispersion. The temperature of the water is that ambient or greater than that ambient without however having to exceed high temperatures, in particular without exceeding the deterioration temperature detrimental to one of the components of the mixture. For example, in the case of CNT included in carboxyl methylcellulose, the temperature should not exceed 200 ° C.

The stirring time of the mixture is further reduced if the temperature of the water is high and / or the stirring speed is high. Preferably, the premix is subjected initially to a moderate stirring, for example of the order of 100 rpm, then to a strong stirring, for example of the order of 1000 rpm to finish off. burst and dissolve the nanoparticles and obtain a silky dispersion. When the particles of the second category are not already dispersed in an aqueous premix, they are thus mixed with water by a suitable stirrer and implemented under optimal conditions. The use of dispersing agents such as surfactants may be necessary. Once the two premixes obtained, they are mixed under a moderate stirring speed so as to obtain the ready-to-use composition. In a preferred first example of composition A, the two respective categories of particles used are: CNTs forming part of the ARKEMA product CW2-45, this product being mixed with 14% of dry extract in an aqueous solution to form the first premix; micrometric graphite belonging to the LB1300 product from TIMCAL which is a mixture of 25% of dry extract in an aqueous solution; this product sold under the name LB1300 and comprising graphite is used diluted to 50% in water to form the second premix. Composition A, called "diluted NTC / graphite LB1300" results from mixing the two above premixes in 50/50 proportions. In a second preferred example B of composition, the components used are: the nanoparticles with polyaniline bark described in the French patent application FR28889197 obtained at 30% solids content in an aqueous solution to form the first premix; micrometric graphite belonging to the LB1300 product from TIMCAL which is a mixture of 25% of dry extract in an aqueous solution; this product sold under the name LB1300 and comprising graphite is used diluted to 50% in water to form the second premix. Composition B, referred to as "diluted polyaniline / graphite LB1300" results from the mixing of the two above premixes in proportions 80 (polyaniline nanoparticles) / 20 (diluted LB1300). In a third preferred example C of composition, the components used are: - the nanoparticles with polyaniline bark described in the French patent application FR28889197 obtained at 30% dry extract in an aqueous solution to form the first premix; micrometric graphite belonging to the LB1300 product from TIMCAL which is a mixture of 25% solids content in an aqueous solution; this product sold under the name LB1300 and comprising graphite is directly used without being diluted at all and directly forms the second premix.

Composition C, referred to as "undiluted polyaniline / graphite LB1300" results from mixing the two above premixes in proportions 80 (polyaniline nanoparticles) / 20 (undiluted LB1300). According to the invention, the inventors have demonstrated an unexpected effect of synergy obtained by mixing two categories of particles (respectively NTC or nanoparticles of polyaniline, and graphite). Thus: the conductivity of the composition of the invention is much higher than compositions comprising only one type of particles and of equivalent proportion by weight in the composition relative to the overall quantity of the mixture; and above all the conductivity of the composition of the invention is higher than the arithmetic mean of the two conductivities that would present two separate compositions each containing only one type of particles.

Table 1 below summarizes the examples of composition A, B and C of the invention and comparative examples, and indicates the measured conductivity.

For the comparative examples: the comparative example called "polyaniline": emulsion alone in the aqueous phase of nanoparticles with polyaniline bark described in the French patent application FR28889197; the comparative example called "graphite": dispersion only in the aqueous phase of graphite, and corresponding to the only product referenced LB1300 TIMCAL company containing 25% micron graphite; the comparative example called "NTC": mixture alone in the aqueous phase of 14% of the ARKEMA product CW2-45.

For all the examples (comparative and those of the invention), the conductivity is measured in the same way: the composition is deposited using a filmograph for example on a substrate, plastic, textile or paper. For the measurements presented here, the substrate is a film of polyethylene terephthalate (PET) and the deposit is of the same thickness between 20 to 60 pm in the dry state; - After drying in the open air or in an oven, strips 1 cm wide and of a certain length are taken in order to deposit two silver lacquer electrodes 0.5 cm long and spaced apart by length of 2 cm; the resistance R between the two electrodes is measured, then the resistivity p = R xex (w / L) where "e" is the thickness of the deposit in the dry state (20 to 6011m), w is the width the band is 1 cm and "L" is the length separating the two electrodes is 2 cm, and finally the conductivity "a" which is equal to 1 / p. Table 1 Comparative Examples and Examples of the Composition of the Invention A Conductivity in S / cm Observed Aspect of "Polyaniline" Coating 1.1 Very Roughness "Graphite" Aspect 2.8 "Striking" Finger "NTC" 10.4 No staining Composition A (NTC / graphite LB1300 diluted) 29 Silky and not finger-smeared Composition B ("LB1300 polyaniline / graphite diluted) 6.2 Rough and not finger-smeared Composition C (undiluted polyaniline / graphite LB1300) 4 As a result, composition A of the invention provides a very high conductivity (29 S / cm). Compositions B and C provide a conductivity, certainly lower than for composition A, but greater than 2 S / cm (6.2 and 4.4 S / cm) respectively, or the arithmetic average of the conductivities of the "polyaniline" examples. and "graphite". The inventors have unexpectedly demonstrated a synergistic effect by mixing the conductive nanoparticles based on NTC or polyaniline and graphite particles or the like. Such conductivity values could not be expected. Indeed, one could only validly expect to obtain a much lower conductivity, at best of the order of the arithmetic mean of the conductivities of each comparative example.

In addition, the comparison between the examples "polyaniline", "graphite" and the examples of the invention B and C demonstrates the existence of a maximum conductivity lying at an undiluted LB1300 level of less than or equal to 20% . Indeed, the above values were plotted on the graph shown in the single figure, expressing the conductivity of each example as a function of the percentage of LB1300 in the mixture of polyaniline and graphite LB1300 in the solid state. It can be seen that Example B, which corresponds to 9.4% of LB1300 in the solid state and 20% of LB1300 diluted in the liquid state, is above Example C (17.2% of LB1300 in the solid state and 20% undiluted LB1300 in the liquid state), which indicates that a maximum of conductivity may even exist for a mixture of polyaniline and graphite LB1300 undiluted at a rate which n ' does not exceed 20% of the mixture in the liquid state. Finally, according to the invention, the proportions of each premix respectively based on conductive nanoparticles, and electroconductive particles larger than nanoparticles (graphite type or carbon black), will be adapted according to the desired conductivity. By way of example, Table 2 below indicates, for the example of composition A ("NTC / LB1300 graphite diluted"), the conductivity as a function of the respective proportions of the two pre-mixtures respectively based on CNTs and of graphite. Table 2 Graphite Pre-Blend% of CNT Conductivity Premix in S / cm of Composition A 80 7.2 40 40 19.5 50 50 29 40 60 17.3 20 80 11 A peak of conductivity value is observed for a 50/50 mixture of the two pre-mixtures based respectively on NTC and graphite.

Depending on the intended uses, particularly in addition to the desired electrical conductivity property, the base composition of the invention may be blended with additional products to provide, for example, a coating paint with specific properties. As additional products, mention may be made of emulsions based on acrylic (for example the product Craymul 2138 marketed by Crayvaley), or vinyl emulsions, or else based on fluorinated products (for example the product referenced Aquatec FMA12 from Arkema).

Claims (1)

REVENDICATIONS1. An electrically conductive composition comprising at least electrically conductive nanoparticles mixed in an aqueous medium, characterized in that said nanoparticles are carbon nanotubes (CNTs) or nanoparticles based on polyanylins, or the nanoparticles comprise a core and a coating envelope electroconductive, and in that the composition further comprises another class of electrically conductive particles larger than the size of the nanoparticles. Composition according to Claim 1, characterized in that the said other class of particles comprises particles of graphite and / or carbon black and / or carbon fibers and / or coated particles made of a core and an envelope of electroconductive material. Composition according to Claim 1 or 2, characterized in that the nanoparticles, on the one hand, and the other category of particles, on the other hand, have respectively been dispersed independently in water when they are not already present. in the form of an aqueous dispersion. Composition according to any one of the preceding claims, characterized in that the particles of said other category nanoparticles have no dimension less than 100 nm irrespective of their shape, preferably said particles being micrometric. Composition according to any one of the preceding claims, characterized in that prior to the dispersion of the CNTs in water, the CNTs are concentrated2. In a polymeric compound based on a polymer such as carboxyl methylcellulose, in particular the compound comprises 45% by weight total CNT of the mixture and 55% of polymeric binder consisting of carboxyl methylcellulose. 6. Composition according to any one of the preceding claims, characterized in that the nanoparticles based on polyanyline are previously diluted in water, at a concentration of at least 15% solids. 7. A method of manufacturing a composition according to any one of the preceding claims, characterized in that it comprises the steps of: - dispersion in an aqueous solution of CNT or use of polyanylin nanoparticles already included in an aqueous solution, to form a first premix; dispersion in an aqueous solution of graphite and / or carbon black and / or carbon fibers to give a second premix; - mixing the first and second premixes. 8. Manufacturing process according to the preceding claim, characterized in that the composition obtained is mixed with an acrylic or vinyl emulsion, or based on fluorinated products. 9. Use of a composition according to any one of claims 1 to 6 for the application of an electrically conductive material, in particular with a thickness of between 5 and 200 μm. 10. Use of a composition according to any one of claims 1 to 6 in low voltage heating devices or usual voltage, including for building or industry, or in devices for heating the human body, patches, belts, covers, in any static or mobile object.