WO2016139527A1

WO2016139527A1 - A conductive composite material

Info

Publication number: WO2016139527A1
Application number: PCT/IB2016/000221
Authority: WO
Inventors: Giorgio Girondi
Original assignee: Ufi Innovation Center S.R.L.
Priority date: 2015-03-05
Filing date: 2016-03-02
Publication date: 2016-09-09

Abstract

A composite material comprising a polymeric matrix and a reinforcement comprises a mixture of carbon nanotubes and carbon black, wherein the car- bon nanotubes and the carbon black of the mixture are in a ratio comprised between 1.5: 1 and 2.5:1 in weight, preferably in a 2:1 ratio in weight.

Description

A CONDUCTIVE COMPOSITE MATERIAL

TECHNICAL FIELD

The present invention relates to a conductive composite material and, for example, a component of a filter cartridge and/or a filter group for filtration of fluids, for example combustible and/or lubricant fluids used in the automotive field, containing the composite material.

More in particular, the invention relates to a composite material having a polymeric matrix with a reinforcement of conductive material.

PRIOR ART

As is known, adding a polymer of a conductive material, for example, a carbon nanofiller (preferably carbon black, carbon nanotubes, graphene or the like or mixtures thereof) leads to a reduction of the original resistivity of the polymer.

For example, if the starting polymer exhibits an original resistivity substantial- ly equal to or greater than 10¹⁰ Ohm^*cm, with an addition of the carbon nano- fillers, it is possible to obtain a composite material exhibiting a resistivity that is substantially equal to or lower than 10³ Ohm^*cm, in particular suitable for the specific application for which the composite is destined.

The concentration of the reinforcement, by the effect of the reduction of the resistivity is considerably high and such as to be able to obtain a composite material having a conductivity suitable for the final application, is a concentration value known as the percolation threshold value.

As is known to a technician in the sector, the percolation threshold value relates to the distribution threshold of a reinforcement in a matrix of a compo- site material, so that a determined physical phenomenon is verified in the material. The percolation phenomenon is a geometric one, which depends on the geometry of the reinforcing grains and the relative dimensions thereof. It is further known, however, that on reaching the percolation threshold value of the reinforcement of the matrix, if on the one hand the resistivity of the composite material is considerably reduced, as mentioned above, on the other hand a considerable increase is observed in the viscosity of the composite material itself. Thus a drawback in realising composite conductive materials as described above lies in the fact that, although in order to have good conductivity of the composite material it is necessary to reach reinforcement concentrations at least equal to the percolation threshold value, these reinforcing concentrations at values close to the percolation threshold value make the conductive composite material difficult when working with the traditional working methods, for example it is observed that for these composite conductive materials it is practically impossible or in any case very difficult to work by extrusion, injection moulding or indeed spun-bond or melt-down spinning, a fact which limits use and possibility of application.

Examples of conductive composite materials are shown in documents WO 03/040224 and US 2009/0200517.

Document WO 03/040224 discloses a composition of a conductive composite material comprising a polymeric matrix (ΡΡΕ,ΡΑ) and a reinforcement comprising a conductive filler among the following: carbon black, carbon fibres (CNFs and VGCFs), carbon nanotubes, metal fillers, non-metal fillers, fillers having a metal coating, and the like, combinations comprising at least one of the foregoing electrically conductive fillers.

Document US 2009/0200517 discloses a composition of a conductive composite material comprising a polymeric matrix and a reinforcement comprising carbon nanotubes and carbon black.

An aim of the present invention is to obviate the above-mentioned drawbacks in the prior art, with a solution that is simple, rational and relative inexpensive.

The aims are attained by the characteristics of the invention as recited in the independent claim. The dependent claims delineate preferred and/or particularly advantageous aspects of the invention.

DESCRIPTION OF THE INVENTION

In particular, the invention discloses a composite material comprising a poly- meric matrix and a reinforcement comprising a mixture of carbon nanotubes

(CNT) and carbon black (CB), wherein the carbon nanotubes and the carbon black of the mixture are in a ratio comprised between 1 .5:1 and 2.5:1 in weight, preferably in a 2: 1 ratio in weight.

With this solution, it has been surprisingly observed that, thanks to the above-mentioned weight ratio between the quantity of carbon nanotubes and the quantity of carbon black which make up the reinforcement added to the polymeric matrix, the resistivity of the composite material is much lower than the resistivity of the initial polymeric matrix, advantageously improved by a quantity such as to make it suitable for the specific application, and at the same time it is possible to bring the reinforcing concentration to values equal to or greater than the percolation threshold value, while maintaining a rela- tively low viscosity of the composite material. In practice, it has been observed that a composite material thus-formulated is such as to enable good workability, including using the working techniques usually utilised for plastic materials, such as extrusion and/or injection moulding and/or spun-bond and/or melt-blown spinning.

In practice, it is observed that the above said ratio, as selectioned, is connected to a particular technical effect and no hints exist in the prior art leading the skilled person to the selection.Therefore, the composite material as above obtained may be used for heating applications and/or for dissipating electrostatic charges, for example, the electrostatic charge which accumulates on filter walls during the operation thereof.

For example, the polymeric matrix comprises a plastic material selected from a group comprising polyester (for example polyethylene terephthalate - PET, polybutylene terephthalate - PBT), polypropylene and polyamide (for example nylon PA6, PA66 or P12) or mixtures thereof.

For example, the polymeric matrix can be made up of a polymer, or a mixture of polymers, having a melting temperature of greater than 200°C.

For this selection of thermoplastic materials, in fact, this double effect of reduction of the resistivity and containing of the increase of viscosity has been seen to be advantageous, as it enables use of the deriving composite mate- rials in many applications.

In the specific case, the term "comprising" also embraces "including" as well as "constituted by", for example a composition "comprising" X can be consti- tuted by X or can include other and additional substances, for example X+Y. Still more advantageously, the polymeric matrix is a plastic material selected from a group consisting of polyester, polypropylene and polyamide (for example nylon).

For example the polymeric matrix is constituted (exclusively) by polyester (for example polyethylene terephthalate - PET, polybutylene terephthalate - PBT), or polypropylene and polyamide (for example nylon), preferably by polyester (for example polyethylene terephthalate - PET, polybutylene terephthalate - PBT).

In an aspect of the invention, the quantity of the reinforcement is at least equal to a percolation threshold value.

For example, in a case in which the polymeric matrix is constituted by polyester or by nylon (or by polypropylene), the percolation threshold value is substantially comprised between 4% and 6%, for instance equal to 6%, in weight referred to the total weight of the polymeric matrix, on the basis of the dispersion technique of the reinforcement in the polymeric matrix.

The composite material as formulated above can advantageously exhibit a Melt Flow Index, for example measured with a mass of 5kg at a temperature of 280°C, greater than 20 g/10', preferably substantially 40 g/10'.

In particular, a Quality Factor - QF - is defined using the following formula:

where MFI is the Melt Flow Index of the composite material and p is the resistivity of the composite material; as formulated above, the composite material exhibits a QF = 16 (with 4% CNT, p ¾ 10² Ohm^*cm, for example162 Ohm^*cm).

The Melt Flow Index is an indicative parameter of the viscosity of a polymeric material, in this case of the composite material.

The measurement of the Melt Flow Index (MFI) is performed for example according to the ASTM D 1238 standard.

The Melt Flow Index provides an estimated indication of the possibility of associating a polymeric material to a determined work process. In particular, a polymeric material exhibiting high Melt Flow Index values (for example com- prised between 3 and 50 g/10', preferably greater than 20 g/10') can be used in injection moulding operations (for which a lower viscosity is required).

In a further aspect of the invention, a filter cartridge is disclosed for filtering a fluid which comprises a component able to come into contact with the fluid being filtered, wherein the component comprises at least a portion made of a composite material, as described in the foregoing.

As is known, in filter groups used, for example, in the automotive field, traditionally an electric heater is inserted in the filter cartridge which carries out the function of heating the fuel (or the lubricant), for example solid paraffins contained in the diesel fuel to be filtered, so that following the first start-up of the engine the filter wall does not get clogged by the solid paraffins.

After only a few revolutions of the engine, the diesel fuel already has a temperature sufficient to melt the solid paraffins and the electric heater can be switched off, as the flow of diesel fuel towards the devices downstream of the filter group is in any case guaranteed.

The use of traditional electric heaters is not entirely free of drawbacks, not least the cost of the heater devices themselves.

With the above-described solution, it is possible to use the component (or the portion thereof) of the filter cartridge as a conductive element, which - for ex- ample by Joule effect - if crossed by an electric current can heat up, (for example uniformly in its volume) thus heating the fluid being filtered with which it comes into contact, without any need to use traditional heating elements, without any need to use traditional electric heater, with a saving in economic terms and in terms of volumes.

As an alternative or in addition, the component (or the portion thereof) of the filter cartridge can also be used for dissipating electrostatic charges, for example, the electrostatic charge which accumulates on filter walls during operation thereof.

Also when the component is Used for dissipating electrostatic charges, the conductive element (to which is requested, for instance, a lower conductivity than the conductivity requested for heating application) is connected to an electric conductor connected to the filter group (wherein, for instance, the electric conductor is connected to the casing thereof and connected typically to a ground connection), by means of this the accumulation of electrostatic charges may be avoided, as a matter of fact the electrostatic charge, if not discharged, may cause dangerous discharge phenomena with the risk of damages of the filter wall and/or the casing.

This additional application allows the composite material suitable to manufacture not only parts of filter cartridges suitable to filter fuel but also parts of filter cartridges suitable to filter the engine oil and/or oil filters for hydraulic applications.

For example, the component is one or more chosen from the components of the group comprising a filter wall, able to filter the fluid, a support plate of a filter wall and a reinforcing core of a filter wall.

The component can be conformed as a rigid jacket or a flexible sleeve posi- tionable, for example removably, about the external surface of the filter car- tridge and/or the filter wall, in the central cavity of the filter cartridge and/or the filter wall.

A still further aspect of the invention relates to a filter group for filtering a fluid, which comprises an external casing provided with an inlet and an outlet as described above, or also of a traditional type, and a filter cartridge, contained internally of the external casing so as to filter the fluid flowing from the inlet towards the outlet.

At least a portion of the external casing, able to come into contact with the fluid being filtered, can be made of a composite material, as described in the foregoing.

For example, the component might be a portion of the beaker body of the casing, the cover or the casing or a conduit fixed to the external casing, such as for example, the inlet conduit of the fluid being filtered or a fixed sleeve, removably or movably, to the lateral wall of the inlet conduit which defines the supply circuit of the fluid being filtered internally of the external casing.

Alternatively or additionally, the conductive component can be defined by a portion of a further element constituting the filter group, i.e. by a containing tank of the fluid being filtered (for example fuel or lubricant of the vehicle en- gine) serving the external casing or by an appropriately profiled element and located internally of the tank.

In this way at least a portion of the external casing (and/or the tank) can be used as a conductive element, which - for example by Joule effect - if crossed by an electric current can heat up, thus heating the fluid being filtered with which it comes into contact, without any need to use traditional heating elements, with a saving in economic terms and in terms of volumes internally of the casing.

By an alternative or in addition, the portion of the external casing (and/or the tank) may also be used for dissipating electrostatic charges, for instance the electrostatic charge which accumulates on filter walls during the operation thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

Further characteristics and advantages of the invention will emerge from a reading of the following description, provided by way of non-limiting example, with the aid of the figures of the accompanying drawings.

Figure 1 is a longitudinal section view of a filter group for fluids, for example combustible and/or lubricant fluids used in the automotive field.

BEST WAY OF CARRYING OUT THE INVENTION.

With particular reference to the figures, reference numeral 10 denotes a filter group in its entirety, for example for a combustible fluid (e.g. diesel fuel), a lubricant fluid (e.g. oil), comburent air, combustion gas coming from the base of the engine, air for conditioning the internal compartment of a vehicle or another fluid used in the automotive sector.

The filter group 10 comprises an external casing, denoted in its entirety by reference number 20, which in turn comprises a beaker body 21 and a cover 22 for closing the beaker body 21.

The cover 22 (the upper cover in the figures) is conformed, in the example, substantially as a cap and exhibits a thread (internal) able to screw into a corresponding thread (external) defined on the open edge of the beaker body

21 .

At least an inlet conduit 220 of the fluid to be filtered and an outlet conduit 221 of the filtered fluid are defined in the cover 22, in the example made at the upper wall of the cover 22, with the outlet conduit 221 , preferably in a central position.

The outlet conduit 221 is located coaxially of the cover 22 and at least partly projects internally thereof by means of a cylindrical shank 222.

The beaker body 21 comprises a bottom wall 210, substantially disc-shaped, from which support fins 21 1 and a substantially cylindrical lateral wall 212 rise.

It is possible that, alternatively, the inlet conduit and/or the outlet conduit can be made in the beaker body 21 of the external casing 20.

The external casing 20 might, further, comprise a drainage group (not illustrated) of the water which might accumulate on the bottom wall 210 of the beaker body 21 , for example by effect of a hydrophobic net and/or a coalescing wall located internally of the external casing 20.

The filter group 10 comprises a filter cartridge, denoted in its entirety by reference numeral 30, which can be housed internally of the external casing 20, for example coaxially thereto, so as to filter the fluid which enters the external casing 20 from the inlet conduit 220 and flows towards the outlet conduit 221.

The filter cartridge 30 comprises an upper support plate 31 and, for example, a lower support plate 32, which are fixed to the opposite ends of a tubular filter wall 33, in the illustrated example a porous depth wall made of a polymeric material (the filter wall might be pleated and/or composed of a plurality of superposed layers), which defines and delimits a substantially cylindrical internal volume.

The filter cartridge 30 can also comprise one or more support cores 34 (for example made of a substantially rigid material) inserted, for example substantially coaxially, internally of the filter wall 33 and provided with through-openings for passage of the fluid being filtered. In accordance with the operating conditions, for example the direction of the flow of the fluid being filtered through the filter wall 33, the support core 34 might be arranged, alternatively or additionally, externally with respect to the filter wall 33 about the external surface thereof.

The upper support plate 31 affords a central hole 310, for example delimited by a substantially cylindrical central shank, not illustrated, centred on the central longitudinal axis of the filter cartridge 33.

The central shank and therefore the central hole 310 can support an annular seal (not illustrated).

In use, the central shank and therefore the central hole 310 (with the respective annular seal) is insertable substantially snugly and sealedly on the cylindrical shank 222 of the casing 20, i.e. of the cover 22.

The lower support plate 32 is for example disc-shaped (in the example closed, but it might be appropriately pierced), which is for example located resting on the support fins 21 1 of the external casing 20).

At least a portion of a component 31 ,32,33,34,21 ,22 of the filter group 10, selected from among the filter wall 33, the upper support plate 31 , the lower support plate 32, the support core 34, but also the beaker body 21 and the cover 22 of the external casing 20, is made of a conductive material, preferably a conductive composite material (having a polymeric matrix) such as substantially to realise a heater element by Joule effect in contact with the fluid being filtered internally of the external casing 20.

At least a portion, in the specific case, might mean that the component 31 ,32,33,34,21 ,22 is exclusively realised by the conductive composite material or that the component 31 ,32,33,34,21 ,22 is made of a composite material from the conductive composite material and of other materials (for example still polymeric) joined, for example by co-moulding or in any case fixed to one another, to the conductive composite material.

For example, the conductive composite material comprises a polymeric matrix and a reinforcement comprising a mixture of carbon nanotubes and carbon black, in which the carbon nanotubes and the carbon black of the mixture are in a ratio comprised between 1.5:1 and 2.5: 1 in weight, preferably in a 2:1 ratio, as described in the foregoing.

For example, carbon black is a substance in granules, for example substantially spherical, a granulometry whereof is preferably comprised between 10 nm and 100 nm.

The carbon nanotubes are also conformed by "rolled" nano-sheets, either single-walled or multi-walled, each preferably exhibiting a diameter substantially comprised between 0.7 nm and 10 nm. For example, the ratio between the length of each carbon nanotube and the diameter thereof is in the order of 10⁴:1.

A preferred example of the composite material used for the realising of the portion of the component 31 ,32,33,34,21 ,22 comprises a polymeric polyester matrix (for example polyethylene terephthalate - PET, polybutylene tereph- thalate - PBT), and a reinforcing quantity substantially equal to the percolation threshold value of the mixture of carbon nanotubes and carbon black in the polyester, i.e. substantially 6% in weight (with respect to the weight of the polymeric matrix.

In practice, the Melt Flow Index (MFI) of the conductive composite material used is greater than 20 g/10', preferably substantially 40 g/10', enabling easily obtaining the component 31 ,32,33,34,21 ,22 by any working technique, for example by extrusion and/or injection moulding and/or spun-bond and/or melt-blown.

The filter group 10 might further comprise a temperature sensor for detecting the temperature (not illustrated) located internally of the external casing 20 and connected to a command and control circuit supported by an electronic card 40.

The electronic card 40, for example, is operatively connected to the component 31 ,32,33,34,21 ,22, for example by means of cabling 41 or conductive tracks for electric supply to the component itself, or the activating of the heater thereof.

The electronic card 40 is electrically connected to a connector (not illustrated as of known type) for connecting the electronic card itself to the control panel unit (ECU) of the vehicle.

As mentioned, the electronic card 41 comprises command and control circuit which activates the functioning of the heater of the component 31 ,32,33,34,21 ,22 according to the temperature values detected by the tern- perature sensor.

For example, the whole filter wall 33 or a portion thereof (for example the radial portion destined to be crossed first by the fluid being filtered or a longitudinal strip thereof or possibly another portion) is made, for example by spun- bond and/or melt-blown processes of the conductive material described in the foregoing.

Alternatively or in addition, the support core 34 or a portion thereof can be realised, for example by injection moulding, in the conductive composite material.

In this case, the fluid being filtered, when crossing the filter wall 33 and/or the support core 34, apart from being filtered, in the first functioning instants of the vehicle can also be heated, without the aid of additional electric heaters, by the filter wall 33 itself (and/or the support core 34) heated by Joule effect. The invention as it is conceived is susceptible to numerous modifications, all falling within the scope of the inventive concept.

Further, all the details can be replaced with other technically-equivalent elements.

In practice the materials used, as well as the contingent shapes and dimensions, can be any according to requirements, without forsaking the scope of protection of the following claims.

Claims

1. A composite material comprising a polymeric matrix and a reinforcement comprising a mixture of carbon nanotubes and carbon black, wherein the carbon nanotubes and the carbon black of the mixture are in a ratio com- prised between 1.5:1 and 2.5:1 in weight.

2. The composite material of claim 1 , wherein the carbon nanotubes and the carbon black in the mixture are in a ratio of 2: 1 in weight.

3. The composite material of claim 1 , wherein the polymeric matrix comprises at least a plastic material selected from a group comprising a polyes- ter, a polypropylene and a polyamide.

4. The composite material of claim 1 or 3, wherein the polymeric matrix consists of polyester.

5. The composite material of claim 1 or 3, wherein the polymeric matrix consists of polypropylene.

6. The composite material of claim 1 or 3, wherein the polymeric matrix consists of polyamide.

7. The composite material of any one of the preceding claims, wherein the quantity of the reinforcement is at least equal to a percolation threshold value.

8. The composite material of any one of the preceding claims, wherein the quantity of the reinforcement is at least equal to 6% in weight with respect to the weight of the polymeric matrix.

9. The composite material of claim 1 , characterised in that it has a Melt Flow Index of greater than 20 g/10', preferably 40g/10'.

10. A filter cartridge (30) for filtering a fluid which comprises a component (31 ,32,33,34) able to come into contact with the fluid being filtered, wherein the component (31 ,32,33,34) comprises at least a portion made of a composite material, according to any one of the preceding claims.

11. The filter cartridge (30) of claim 10, wherein the component (31 ,32,33,34) is a component selected from a group comprising a filter wall

(33), a support plate (21 ,32) of a filter wall and a reinforcing core (34) of a filter wall.

12. A filter group (10) for filtering a fluid, which comprises an external casing (20) provided with an inlet (220) and an outlet (221 ) and a filter cartridge (30), contained internally of the external casing (30) so as to filter the fluid flowing from the inlet (220) towards the outlet (221 ), wherein at least a por- tion of component (21 ,22) of the external casing (20), able to come into contact with the fluid being filtered, is made of a composite material according to any one of claims from 1 to 9.