Use of a dispersion of carbon nanotubes in a copolyamide as a conductive adhesive composition
The present invention relates to the use, as an electrically conducting adhesive composition, of a composition containing carbon nanotubes, and at least one copolyamide.
It is known that certain copolyamides have adhesive properties which make it possible to envisage their use in the manufacture of hot-melt adhesives with good resistance to hot water and to dry cleaning, in particular for the heat-sealing of textiles at low temperature (US-5,459,230; FR 2 228 813; FR 2 228 806; US 2002/0022670) or at high temperature (DE 1 594 233).
For some industrial applications, it may be advantageous to confer, on these adhesives, electrical dissipation properties so as to prevent the accumulation of electrostatic charges, capable of creating safety problems or even of attracting dust.
A solution conventionally used to confer conductive properties on polymer materials consists in dispersing therein conductive fillers such as carbon black, in amounts generally ranging from 7% to 30% by weight and, more specifically, in amounts ranging from 7% to 20% by weight for carbon blacks which are highly structured and from 15% to 30% by weight for carbon blacks which are not very highly structured.
However, it was apparent to the Applicant that the introduction of such amounts of carbon black into certain

copolyamides increases the flexural modulus of these materials and reduces the adhesion properties thereof.

It is to the Applicant's credit to have identified another solution for increasing the conductivity of these copolyamides while at the same time enabling them to conserve adhesion properties, and to thus propose a copolyamide-based composition that can be used as a conductive adhesive.
A subject of the present invention is thus the use, as an electrically conducting adhesive composition, of a composition containing: (a) carbon nanotubes and (b) at least one copolyamide that can be obtained from at least two different starting products chosen from: (i) lactams, (ii) aminocarboxylic acids and (iii) equimolar amounts of diamines and of dicarboxylic acids.
A subject of the present invention is also the use of a dispersion of said nanotubes, in said copolyamide, for producing an electrically conducting adhesive composition.
As a preamble, it is specified that the expression "between" used in the rest of this description should be understood to include the limits mentioned.
The constituents of the composition used according to the invention will now be described in detail.
Copolyamide
The composition used according to the invention comprises, as first constituent, a copolyamide which can be

formed from any monomers, provided that it has adhesive properties, in particular in hot-welding operations.
This copolyamide preferably has a melting point of between 40 and 150°C, preferably between 70 and 140°C. Particularly advantageously, the number-average molecular mass of this copolyamide may be between 5000 and 15 000 g/mol.
According to one preferred variant, a relatively fluid copolyamide will be chosen. For example, in the particular case of the copolyamide sold under the trade name Platamid® H106 by the company Arkema, the melt flow index (hereinafter MFI), which reflects this fluidity characteristic, will be at least 10, preferably at least 15 g/10 min, and more preferably at least 20 g/10 min, at 130°C under a load of 2.16 kg.
The polyamide copolymers, also denoted copolyamides, can be obtained from various starting materials: lactams, aminocarboxylic acids or equimolar amounts of diamines and of dicarboxylic acids. The obtaining of a copolyamide requires choosing at least two different starting products from those mentioned above. The copolyamide then comprises at least these two units. It may thus be a lactam and an aminocarboxylic acid having a different number of carbon atoms, or two lactams having different molecular masses, or alternatively a lactam combined with an equimolar amount of a diamine and of a dicarboxylic acid.
The copolyamide used according to the invention may, for example, be obtained from (i) at least one lactam chosen from lauryllactam and/or caprolactam, preferably a

combination of these two lactams, and at least one other polyamide precursor chosen from (ii) aminocarboxylic acids and (iii) equimolar amounts of diamines and of dicarboxylic acids.
The aminocarboxylic acid is advantageously chosen from a,co-aminocarboxylic acids such as ll-aminoundecanoic acid or 12-aminododecanoic acid.
For its part, the precursor (iii) may in particular be a combination of at least one C6-C36 aliphatic, cycloaliphatic or aromatic dicarboxylic acid, such as adipic acid, azelaic acid, sebacic acid, brassylic acid, n-dodecanedioic acid, terephthalic acid, isophthalic acid or 2,6-naphthalenedicarboxylic acid, with at least one C4-C22 aliphatic, cycloaliphatic, arylaliphatic or aromatic diamine, such as hexamethylenediamine, piperazine, 2-methyl-l,5-diaminopentane, m-xylylenediamine or p-xylylenediamine; it being understood that said dicarboxylic acid(s) and diamine(s) are used, when they are present, in equimolar amount.
The copolyamide according to the invention may advantageously comprise precursors originating from resources derived from renewable starting materials, i.e. comprising organic carbon of renewable origin determined according to ASTM standard D6866. Among these monomers derived from renewable starting materials, mention may in particular be made of 9-aminononanoic acid, 10-aminodecanoic acid, 12-aminododecanoic acid and ll-aminoundecanoic acid and its derivatives, in particular N-heptyl-11-aminoundecanoic acid, and also the diamines and diacids put forward in application PCT/FR2008/050251. The

following may in particular be envisaged:
- the diamines chosen from butanediamine (z=4), pentanediamine (z=5), hexanediamine (z=6), heptanediamine (z=7), nonanediamine (z=9), decanediamine (z=10), undecanediamine (z=ll), dodecanediamine (z=12), tridecanediamine (z=13), tetradecanediamine (z=14), hexadecanediamine (z=16), octadecanediamine (z=18), octadecenediamine (z=18), eicosanediamine (z=20), docosanediamine (z=22) and diamines obtained from fatty acids, and
- the diacids chosen from succinic acid (w=4), adipic acid (w=6), heptanedioic acid (w=7), azelaic acid (w=9), sebacic acid (w=10), undecanedioic acid (w=ll), dodecanedioic acid (w=12), brassylic acid (w=13), tetradecanedioic acid (w=14), hexadecanedioic acid (w=16), octadecanoic acid (w=18), octadecenoic acid (w=18), eicosanedioic acid (w=20), docosanedioic acid (w=22) and dimers of fatty acids containing 36 carbons.
It is preferred to use, as polyamide precursors, a combination of adipic acid and of hexamethylenediamine and/or of 11-aminoundecanoic acid.
Examples of copolyamides that may be used in the context of the present invention are, for example, the copolyamides 6/6.6/6.10, 6/6.6/6.12, 6/6.6/6.36 or else 6/6.6/10.10.
Moreover, the proportion of aromatic diacids preferably does not exceed 10 mol% relative to the total weight of the copolyamide precursors.

According to one particularly preferred embodiment of the invention, the copolyamide may be obtained from caprolactam, adipic acid, hexamethylenediamine, 11-aminoundecanoic acid and lauryllactam. In this embodiment, it may, for example, be obtained from 25% to 35% by weight of caprolactam, 20% to 40% by weight of 11-aminoundecanoic acid, 20% to 30% by weight of lauryllactam and 10% to 25% by weight of an equimolar mixture of adipic acid and hexamethylenediamine.
These copolymers can be prepared by polycondensation, according to methods well known to those skilled in the art. They are, moreover, commercially available from the company Arkema under the trade name Platamid , and in particular Platamid® H106.
The copolyamide preferably represents from 100% to 95% by weight, and more preferably from 100% to 96% by weight, relative to the total weight of the composition used according to the invention.
Nanotubes
In the composition used according to the invention, the copolyamide is combined with carbon nanotubes (hereinafter CNTs).
The nanotubes that can be used according to the invention may be of the single-walled, double-walled or multi-walled type. The double-walled nanotubes can in particular be prepared as described by Flahaut et al., in Chem. Com. (2003), 1442. The multi-walled nanotubes can, for their part, be prepared as described in document

WO 03/02456. They are preferred for a use in the present invention.
Nanotubes usually have a mean diameter ranging from 0.1 to 200 nm, preferably from 0.1 to 100 nm, more preferably from 0.4 to 50 nm, and better still from 1 to 30 nm, and advantageously a length of 0.1 to 10 urn. Their length/diameter ratio is preferably greater than 10, and most commonly greater than 100. Their specific surface area is, for example, between 100 and 300 m2/g and their apparent density can in particular be between 0.05 and 0.5 g/cm3, and more preferably between 0.1 and 0.2 g/cm3. The multi-walled nanotubes can, for example, comprise from 5 to 15 sheets, and more preferably from 7 to 10 sheets.
An example of raw carbon nanotubes is in particular commercially available from the company Arkema under the trade name Graphistrength® C100.
These nanotubes can be purified and/or treated (for example oxidized) and/or ground and/or functionalized, before they are used in the method according to the invention.
The grinding of the nanotubes may in particular be performed hot or cold, and be carried out according to known techniques implemented in devices such as ball mills, hammer mills, pug mills, knife mills, gas-jet mills or any other grinding system capable of reducing the size of the entangled mass of nanotubes. It is preferable for this grinding step to be performed using a gas-jet grinding technique, and in particular in an air-jet mill.

The raw or ground nanotubes may be purified by washing in a solution of sulphuric acid, so as to rid them of any residual inorganic and metallic impurities resulting from the method by which they were prepared. The weight ratio of nanotubes to sulphuric acid may in particular be between 1:2 and 1:3. The purification operation may, moreover, be carried out at a temperature ranging from 90 to 120°C, for example for a period lasting from 5 to 10 hours. This operation may advantageously be followed by steps in which the purified nanotubes are rinsed with water and dried.
Oxidation of the nanotubes is advantageously carried out by bringing the latter into contact with a solution of sodium hypochlorite containing from 0.5% to 15% by weight of NaOCl, and preferably from 1% to 10% by weight of NaOCl, for example in a weight ratio of nanotubes to sodium hypochlorite ranging from 1:0.1 to 1:1. The oxidation is advantageously carried out at a temperature below 60°C, and preferably at ambient temperature, for a period of time ranging from a few minutes to 24 hours. This oxidation operation may advantageously be followed by steps of filtration and/or centrifugation, washing and drying of the oxidized nanotubes.
The functionalization of the nanotubes can be carried out by grafting reactive units such as vinyl monomers at the surface of the nanotubes. The material constituting the nanotubes is used as a radical polymerization initiator after having been subjected to heat treatment at more than 900°C, in an anhydrous medium devoid of oxygen, which is intended to remove the oxygenated groups from its surface. It is thus possible to polymerize methyl methacrylate and hydroxyethyl methacrylate at the surface of carbon

nanotubes.
In the present invention, use is preferably made of optionally ground, raw nanotubes, i.e. nanotubes which are neither oxidized nor purified nor functionalized and which have undergone no other chemical treatment.
The nanotubes may represent from 0.1% to 5% by weight, preferably from 0.5% to 4% by weight, and even more preferably from 1% to 3% by weight, relative to the weight of the composition used according to the invention.
According to one advantageous version of the invention, use may be made of nanotubes fabricated from resources derived from renewable starting materials, i.e. comprising organic carbon of renewable origin determined according to ASTM standard D6866. Such a method of fabrication has in particular been described by the Applicant in patent application EP 08103248.4.
More preferably, the composition used according to the invention may comprise nanotubes and/or precursors of the copolyamide originating completely or partly from resources derived from renewable starting materials within the meaning of ASTM standard D6866.
It is preferable for the nanotubes and the copolyamide to be mixed by compounding using customary devices such as twin-screw extruders or cokneaders. In this process, the copolyamide is typically mixed in the molten state with the nanotubes, either in a single step, or in two steps where the first step is the preparation of a masterbatch and the second step consists in mixing or diluting the masterbatch

with the copolyamide. A masterbatch made up of copolyamide and nanotubes may comprise from 10% to 30% by weight, advantageously from 15% to 25% by weight, of nanotubes.
As a variant, the nanotubes may be dispersed, by any appropriate means, in the copolyamide, which is in solution in a solvent. In this case, the dispersion may be improved, according to one advantageous embodiment of the present invention, by the use of dispersion systems, such as ultrasound or rotor-stator systems, or of particular dispersing agents.
A rotor-stator system is in particular sold by the company Silverson under the trade name Silverson® L4RT. Another type of rotor-stator system is sold by the company Ika-Werke under the trade name Ultra-Turrax®.
Other rotor-stator systems are constituted of colloidal mills, deflocculating turbomixers and high-shear mixers of rotor-stator type, such as the devices sold by the company Ika-Werke or by the company Admix.
The dispersing agents may in particular be chosen from plasticizers, which may themselves be chosen from the group constituted:
of alkyl esters of phosphates or of hydroxybenzoic acid (in which the alkyl group, which is preferably linear, contains from 1 to 20 carbon atoms),
of phthalates, especially dialkyl or alkylaryl phthalates, in particular alkylbenzyl phthalates, the linear or branched alkyl groups containing, independently, from 1 to 12 carbon atoms,

of adipates, in particular dialkyl adipates, of sulphonamides, in particular arylsulphonamides in which the aryl group is, optionally substituted with at least one alkyl group containing from 1 to 6 carbon atoms, such as benzenesulphonamides and toluenesulphonamides, which may be N-substituted or N,N-disubstituted with at least one alkyl group, which is preferably linear, containing from 1 to 20 carbon atoms, and of mixtures thereof.
As a variant, the dispersing agent may be a copolymer comprising at least one anionic hydrophilic monomer and at least one monomer which includes at least one aromatic ring, such as the copolymers described in document FR-2 766 106, the ratio by weight of the dispersing agent to the nanotubes preferably ranging from 0.6:1 to 1.9:1.
In another embodiment, the dispersing agent may be a vinylpyrrolidone homopolymer or copolymer, the ratio by weight of the nanotubes to the dispersing agent preferably ranging, in this case, from 0.1 to less than 2.
According to another possibility, the mixture of carbon nanotubes and of copolyamide can be obtained by dilution of a commercial masterbatch such as the mixture Graphistrength® C M2-20 available from the company Arkema.
The adhesive composition used according to the invention may be in solid form, in particular in the form of a powder, granules, sheets, yarns, filaments, a net, etc., or in liquid or semi-liquid form, advantageously in the form of an aqueous dispersion, a solution or an

emulsion.
In addition to the copolyamide and the nanotubes described above, and also the optional plasticizers mentioned above, it may contain at least one adjuvant chosen from chain limiters, antioxidant stabilizers, light-stabilizers, colouring agents, impact-resistant agents, antistatic agents, flame-retardant agents, lubricants, and mixtures thereof.
The composition used according to the invention is more particularly used as a hot-melt adhesive, for welding together identical or different materials chosen in particular from: wood; paper; cardboard; metal; glass; synthetic or natural textiles; leather; sheets of polymer materials such as polyesters, polyolefins or polyamides; and self-adhesive cables of deflection coils for cathode tubes.
Specifically, the adhesive composition may be in the form of monofilaments, multifilaments, a web, a net or a film. This adhesive composition may also be applied to the materials to be welded according to the techniques of paste coating, powder dot coating or double dot coating, well known to those skilled in the art. This composition may thus be deposited either onto the entire surface of the materials to be welded, or only onto distinct zones of said materials, and then the laminate obtained may be compressed at high temperature, typically at 80-150°C, and subsequently cooled to ambient temperature. Subsequent drying and/or solvent evaporation steps are not generally necessary.
The invention will now be illustrated by means of the

following examples, which are given for the purposes of illustration only, and are not intended to limit the scope of the invention defined by the attached claims.
EXAMPLES
Example 1 : Preparation of an adhesive composition
Multi-walled carbon nanotubes (Graphistrength® C100 from Arkema) were added to a 6/6.6/11/12 copolyamide having a melting point of 118°C and an MFI of 22 g/10 min at 130°C under a load of 2.16 kg (Platamid® H106 from Arkema). The nanotubes were added in a proportion of 20% by weight so as to form a masterbatch, which was subsequently diluted in a matrix consisting of the same copolyamide, by means of a DSM twin-screw microextruder equipped with a flat die, the extrusion parameters being the following: temperature: 225°C; speed of rotation: 150 rpm; mixing time: 30 minutes. Composite films containing 3% by weight of nanotubes, having a thickness of 500 urn and a width of 30 mm were thus obtained. Said films were cooled at the die outlet by means of a layer of air.
Example 2 : Electrical and adhesive properties
The resistive and adhesive properties of a film according to Example 1 (hereinafter, A-CNT film) were evaluated, by comparison with similar films based on Platamid® H106 containing 22% by weight of carbon black (Ensaco® 250G from Timcal) (hereinafter, A-CB film) and with a film of Platamid® H106 free of conductive fillers (hereinafter, film A).

The surface resistances were measured using the Sefelec M1500P instrument equipped with electrodes, under the following conditions:
- applied voltage: 100 V
- charge time before reading: 15 seconds
- electrode length: 30 mm
- distance between electrodes: 50 mm.
The adhesion properties were measured after application of each of the tested films, on the one hand, to a sheet of PET of 350 urn thickness and, on the other hand, between two sheets of PET of 170 um thickness. The corresponding bilayer and trilayer structures were obtained by hot-pressing of these laminates under the conditions below:
- hotplate temperature: 150°C
- hold time between plates: 5 min
- hold pressure: low.
These structures were subjected to a peel test on a DY30 dynamometer, according to a free-geometry method, using a crosshead speed of 50 mm/min and a test cell of 100 N.
The results of these tests are given in Table 1 below.
Table 1

(Table Removed)
It emerges from this table that the film made up of the composition according to the invention (film A-CNT) is as conductive as film A-CB, while at the same time having much better adhesion properties.
Example 3 : Preparation of an adhesive composition
A film analogous to that of Example 1 was produced on a microextruder operating at 240°C (the other extrusion parameters being in accordance with Example 1), except that it contained 2% by weight of carbon nanotubes.
Example 4: Peel test
The adhesion properties of the film obtained in Example 3 (hereinafter, film B-CNT) were compared with those of a film that was identical but did not contain carbon nanotubes (hereinafter, film B), after each of these films had been applied between two sheets of PET of 175 urn thickness and the resulting laminates had been pressed as indicated in Example 2.
The trilayer structures thus obtained were subjected to a peel test on a DY30 dynamometer, according to a free-geometry method (angle of 90°), using a crosshead speed of 50 mm/min and a test cell of 100 N. The test was carried out in duplicate.
The mean of the maximum peel forces measured during

these tests is:
- for the film B: 11.5 N/15 mm
- for the film B-CNT: 9.5 N/15 mm.
The peel forces observed for the film made up of the composition according to the invention are therefore similar to those measured for the comparative film. However, the film B-CNT is conductive, whereas the film B is an insulator. In this regard, it was verified that the surface resistance of the film B-CNT was less than or equal to lxlO6 ohms, whereas that of the film B was of the order of lxlO12 ohms.
These examples thus demonstrate that the carbon nanotubes make it possible to obtain a compromise between adhesive properties and conduction.

AMENDED CLAIMS
1. An electrically conducting adhesive composition, containing: (a) from 0.1% to 5% by weight of carbon nanotubes and (b) at least 95% by weight of at least one copolyamide that can be obtained from at least two different starting products chosen from: (i) lactams, (ii) aminocarboxylic acids and (iii) equimolar amounts of diamines and of dicarboxylic acids.
2. The composition as claimed in claim 1, characterized in that the copolyamide is obtained by polycondensation of (1) at least one lactam chosen from lauryllactam and/or caprolactam, preferably a combination of these two lactams, and of at least one other polyamide precursor chosen from (ii) aminocarboxylic acids and (iii) equimolar amounts of diamines and of dicarboxylic acids.
3. The composition as claimed in claim 1 or 2, characterized in that said copolyamide has a melting point of between 40 and 150° C, preferably between 70 and 140° C.
4. The composition as claimed in any one of claims 1 to 3, characterized in that the aminocarboxylic acid is chosen from α, -aminocarboxylic acids.
5. The composition as claimed in any one of claims 1 to 4, characterized in that the precursor (iii) is a combination of at tleast one C6-C36 aliphatic, cycloaliphatic or aromatic dicarboxylic, arylaliphatic or aromatic diamine; it being understood that said dicarboxylic acid(s) and diamine(s)are used in equimolar amount.

6. The composition as claimed in claim 5, characterized in that the dicarboxylic acid is chosen from: adipic acid, azelaic acid, sebacic acid, brassylic acid, n-dodecanedioic acid, terephthalic acid, isophthalic acid and 2,6-naphthalene-dicarboxylic acid.
7. The composition as claimed in claim 5 or 6, characterized in that the diamine is chosen from: hexamethylenediamine, piperazine, 2-methyl-l, 5- diaminopentane, m-xylylenediamine and p-xylylenediamine.
8. The composition as claimed in claim 5, characterized in that said precursor (iii) comprises a combination of adipic acid and of hexamethylenediamine.
9. The composition as claimed in any one of claim 1 to 8, characterized in that said aminocarboxylic acid is 11-aminoundecanoic acid.
10. The composition as claimed in any one of claims 1 to 9, characterized in that said copolyamide is obtained from caprolactam, adipic acid, hexamethylenediamine, 11-amino-undecanoic acid and lauryllactam.
11. Dispersion of carbon nanotubes, in a copolyamide as claimed in any one of claims 1 to 10, for use in producing an electrically conducting adhesive composition as claimed in any one of claims 1 to 10.