Patent Application
20140167309
This application is based upon and claims priority to Italian Patent Application TO2012A001082 filed on Dec. 14, 2012.
1. Field of Invention
The present invention relates to the integration of electrical devices and connections in plastics, and in particular in components or structural parts which are made of non-conductive polymeric material and installed on-board a vehicle. More specifically, the invention relates to a method for the production of a component or a structural part made of non-conductive polymeric material, adapted to integrate electrical devices and connections.
2. Description of Related Art
In the automotive field, it is known to use non-conductive polymeric materials (for example, polyolefinic thermoplastic polymers) that are commercially available as polypropylene (PP) or high-density polyethylene (HDPE) for the realization of on-board components, including purely by way of example, fuel systems (tanks and other structural parts), the internal finishing of the passenger compartment (dashboard, door panels), and the external finishing of the vehicle body (bumpers, mouldings).
The on-board electrical or electronic devices which are installed in combination with these components (for example, sensors, devices for operating on-board systems, devices for controlling the management of the functions in the passenger compartment) are typically made as discrete elements (which are housed in seats obtained by moulding in the shape of the component) and are connected to remote power supply sources and to remote signal processing components by wiring laid along the chassis of the vehicle.
In order to avoid laying extensive lengths of wiring, different technological solutions have been developed for integrating the electrical connection lines in a plastic matrix, which forms a lining in the passenger compartment of a vehicle (or, a structural component of the vehicle). A further development involves integration of on-board electronic devices (for example, the devices for controlling the passenger compartment and bodywork functions) in the plastic components inside the passenger compartment (such as the dashboard and the door panels) where the devices may be embedded and touch-operated.
Published international patent application WO 2007/096016 describes a lining for a vehicle in which regions, including switching, sensor, or electrical or electronic signal transmission functions are formed. The on-board functional devices (such as the sensor or control devices) are formed as discrete elements which are arranged in a mould for forming the lining prior to injection of the plastic, so as to surface at the side of the lining facing the passenger compartment, once moulding has been performed, and provide a touch-operation functionality. Flexible conductor strips are embedded in the plastic matrix during moulding for connecting the devices outside of the lining formed.
Published patent application EP 1,663,720 describes a touch-operated device which can be used on-board a vehicle and which includes a capacitive sensor arranged underneath a surface of an internal lining of the vehicle, which can be touch-operated by a person present inside the passenger compartment. Such a device may be integrated in the covering surface of an air-bag, inside a steering wheel, on a dashboard, within an armrest, in a control panel, or in any other surface of a vehicle suitable for interaction with on-board electronic devices.
German utility model DE 299 07 054 relates to an instrument dashboard, in particular for a motor vehicle, with a support made at least partially of plastic, which includes display instruments and operating components which are powered by conductive tracks, in which the conductive tracks are made in electrically conductive plastic (for example ULTRAFORM® produced by Basf, or DURETHAN® and POCAN® produced by Bayer). The conductive tracks may be made in a flat form and combined with the support mechanically or chemically (for example, by an injection-moulding process).
Published patent application WO 2010/026000 describes a single-layer or multiple-layer lining for a vehicle, which has regions formed by a mixture of plastic and conductive material. The lining may be used as a part of the interior upholstery of a vehicle (for example, dashboards or insides of doors). Predetermined areas are provided with conductive tracks for performing electrical conduction functions and more complex switching, sensor or generally signal transmission functions, where the tracks are made of a mixture of plastic material forming the lining and a conductive material (for example, carbon nanotubes).
A method for producing electrically conductive and/or piezo-resistive tracks on a non-conductive, composite, polymeric substrate including a matrix of commercially available polyolefinic thermoplastic polymers, with a dispersed-phase filler of carbonization promoters such as carbon nanofibres or carbon nanotubes is known from the international patent application WO 2012/055934, which teaches how to realize the conductive tracks by laser ablation and consequent localized pyrolysis of the substrate, which results in the formation of carbonaceous conductive structures favoured by the promoters, which are able to participate in the conduction by concentration in the tracks. However, although the aforementioned document suggests, in theory and in the light of laboratory tests, using such a technology for the formation of electrical connections and simple electrical devices (such as pushbuttons, sensors, antennas, etc.) incorporated in polymeric substrates widely used in motor vehicles (such as polypropylene and polyethylene), it does not deal with the practical aspect of industrial application of this technology to the manufacture of the aforementioned elements in actual on-board components, nor the integration of the technology with the already established techniques for production of these components.
The components in the automotive field which mostly benefit from integration with electrical devices (such as the dashboard or door panels) have particular forms which are determined by the ergonomic requirements associated with their use, or simply by their position in the passenger compartment. In such cases, their shaped forms are determined exclusively by the aesthetic appearance the designer wishes to give to the passenger compartment of a vehicle, such that it may be distinguished from the design solutions of competitors. Moreover, the industrial technology of injection-moulding in the automotive field is optimized for the processing of polymeric compounds which are commonly used for the production of these components, but is not adapted to the processing of compounds with a dispersed-phase filler, the distribution of the filler affecting the electrical properties of the entire component and even more specifically the high electrical conductivity values which can be obtained by selective laser ablation of (bidimensional or tridimensional) regions of the component intended to integrate the designed electrical functions.
It is therefore desirable that the technology for the manufacturing of electrical devices and connections incorporated in non-conductive polymeric substrates should be improved for practical application thereof to specific on-board components of a vehicle and, vice versa, that the current technologies for moulding these components in the automotive field should be adapted to the new materials.
The main factors to be considered during the design of a motor-vehicle component using a polymeric material with a dispersed-phase filler having conductive properties which can be locally activated in a selective manner are strictly dependent on the suitability of the component to form conductive tracks with electrical conductivity properties, which can be controlled depending on the desired design configurations. For this purpose, during the design of a component, the following parameters must be adjusted: the minimum distance between parallel conductive tracks, in order to prevent interference and short-circuits; the curvatures and plane variations of the conductive tracks, in order to avoid the formation of discontinuities therein; the geometrical configuration of the conductive tracks (length and cross-section) depending on the electrical characteristics of the signal, the polymeric material used and the foreseen electrical load; the geometrical configuration of the component made of polymeric material in the regions designed for an electrical device, in order to define controlled-deformation zones and realize control devices which can be activated by external deformation and pressure stimuli (for example, based on the piezo-resistive effect of the conductive tracks); the geometrical configuration of the conductive tracks in the regions designed for an electrical device, in order to define capacitive proximity sensor zones and form control devices which can be operated by external touching actions (for example, based on the capacitive effect of the conductive tracks); and the technical solutions for connecting the component containing the conductive tracks to the on-board power supply and/or signal processing systems.
The object of the present invention is therefore to provide a component or a shaped structural part made of non-conductive, composite, polymeric material, in particular for installation on-board a vehicle, and integrating electrical devices and connections. In particular, the object of the present invention is to provide an optimized method for the production of a component or shaped structural part made of non-conductive polymeric material, in particular for installation on-board a vehicle, which integrates electrical devices and connections.
The general aims underlying the invention are also considered to be those of: increasing energy saving in latest-generation vehicles; increasing the degree of recyclability of the polymeric components; and reducing the costs of acquisition and assembly of accessory components, in particular switches and wiring.
According to the present invention, these objects are achieved in a method for the production of a component or a structural part made of non-conductive polymeric material, adapted to integrate electrical devices and connections, in particular for installation on-board a vehicle. The invention also relates to a system for the production of a component or a structural part made of non-conductive polymeric material, adapted to integrate electrical devices and connections. In short, the present invention is based on the technology of manufacturing components or structural parts of a vehicle using non-conductive composite polymeric material, comprising a polymeric matrix with a nano-structured dispersed-phase filler, including filamentary nano-structures, promoters of carbonization for the formation of carbonaceous conductive structures.
The invention proposes using laser ablation technology for defining, in components or structural parts of a vehicle, conductive circuits which are entirely carbon-based, so as to provide conductive tracks integrated in the polymeric material and which form electrical connections or piezo-resistive electrical devices (for example, signal switches integrated in the component) obtained by deformation of predetermined areas of polymeric surfaces containing conductive tracks.
Advantageously, a carbon nanotube filler in a matrix of polyethylene material affords a technological advantage in the method for manufacturing components, since the carbon nanotubes act as radiative absorption catalysts, locally increasing the percentage of absorption of the radiation irradiated by lasers, from 20-30% up to 80-90%, depending on the wavelength of the incident radiation.
The invention is based on the principle of producing a component or a structural part made of non-conductive polymeric material, adapted to integrate electrical devices and connections by an injection-moulding process, in which the technological parameters of the process are controlled depending on the physical properties of the material, and the distribution of the injection nozzles is established depending on the three-dimensional shape of the component or structural part and on the intended use of predefined areas, in particular with respect to the integration of electrical devices and connections.
Further characteristic features and advantages of the invention will be explained more clearly in the following detailed description of an embodiment thereof, provided by way of a non-limiting example, with reference to the accompanying drawings in which:
The step for forming the component or the structural part is denoted by 300 and, in the following, at step 400, definition of the conductive areas or tracks is carried out on the moulded part using the laser ablation writing technique described in published international patent application WO 2012/055934.
Finally, in step 500, the component or part thus produced, which has predetermined conductive areas forming the electrical devices and connections, and is assembled together with other supply components, such as the external connectors.
The provision of the composite polymeric material includes mixing, in a polyolefinic polymeric substrate (for example, commercially available polypropylene (PP) or high-density polyethylene (HDPE)) of a phase of filamentary nano-structures, promoters of conductivity, in particular carbon-based nano-structures such as carbon nanotubes or nanofibres enriched with substances which favour compatibility, namely coupling agents for the reinforcing fibres (for example alkaline hydroxides in aqueous solutions of polymer grafted with maleic anhydride) and a phase of reinforcing fillers, such as glass fibres or fillers of mineral origin. The inventors have noted that the increase in conductivity in the components made using this polymeric material is greater than the conductivity in the components made of composite polymeric material without reinforcing fibres.
The reinforcing fibres, especially those with short glass fibres, have the effect of increasing the degree of dispersion of the carbon nano-structures, which otherwise tend to reaccumulate in the melted mass, creating “islands” which overall prevent the transit of electric charges in the manufactured article, owing to the Van der Waals forces which are generated between the chains of nano-structures. This distribution effect also reduces the so-called skin effect (the formation of a surface film of non-conductive polymeric material), allowing the nanotubes to migrate towards the surface, directed by the reinforcing fibres.
The reinforcing fibres, in particular the glass fibres, are a reinforcing agent which is widely used in the polymer sector. In the tests carried out for optimization of the raw materials to be used in the process described above, it has emerged that in a polyolefin (PP, HDPE) based polymeric matrix, to which carbon nanotubes have been added, the presence of glass fibres, preferably in filaments with a length of the order of 5 mm and diameter of the order of 10 μm, increases the electrical conductivity thereof, even without further carbonization treatment, and facilitates the dispersion of the carbon nanotubes.
The results obtained show that a partially conductive interphase is formed between the glass fibre and the polymeric matrix, owing to the carbon nanotubes which tend to line the glass fibre: the local concentration of the carbon nanotubes inside the glass fibre/polymer matrix interphase provides the material with multi-functional properties, including an increase in the mechanical characteristics due to the presence of the glass fibres, and an increase in the electrical characteristics due to the presence of the carbon nanotubes.
The coupling agents used to improve the adhesion of the glass fibres in the polymeric matrix improve the distribution of the fibres in the matrix itself, making it practically isotropic: the nanotubes which line the fibres are consequently also uniformly distributed in the polymeric matrix, thereby ensuring the homogeneity of the electrical conductivity in the article.
It has been noted in tests that a component made from polyolefinic materials to which carbon nanotubes have been added, owing to the correct dispersion exerted by the glass fibres, has a conductivity at least 100 times greater than an analogous component without a dispersed glass-fibre phase. These results have been obtained with polyolefin-based polymers having carbon nanotube fillers (multiwall CNT) in an amount from 1.5% to 10% by weight, and glass fibre fillers in an amount from 10% to 20% by weight, wherein the values refer to the weight of the composite material.
During the moulding of materials of this type, the flow of the material filling a mould, (the dynamic behaviour of which is comparable to that of a high-viscosity fluid) produces complex interactions which result in: a fragmentation, such that the lengths of the fibres are distributed in a manner typical of a Weibull distribution, as shown in
In particular, the velocity profile of the flow has a high gradient zone in the vicinity of the mould walls, and a zone with a tendentially uniform profile in the central part of the thickness of the mould cavity. Consequently, in the volumes of material which in the centre are subject mainly to transverse deformation, the fibres tend to be arranged in a direction perpendicular to the injection flow, while in the vicinity of the walls the fibres tend to be arranged parallel to the flow, as a result of the shearing stresses. This condition is shown in
The fluid-dynamic conditions created during the process of injection of the composite material mixed therefore define the orientations of the fibres which in turn determine the mechanical and electrical properties of the component. Thus, in view of the foregoing, in order to avoid localized stress of the material during the injection step with an associated loss of the conductive capacities (breakage of nanotubes, deterioration of the matrix, skin effect), during design of the actual mould particular attention must be paid to the following parameters: injection layout, if necessary sequential; mould conditioning layout; and design of the movements of the carriages which are not temperature-regulated.
The component moulding step 300 is therefore dependent on a suitable design of the mould in step 200, which is dependent, in turn, on the design of the component, not only as regards the form and volume dimensions, but also the arrangement of the conductive regions where the integrated electrical connections or devices are to be formed.
The component is obtained by injection-moulding the polymeric compound defined above. Advantageously, the component or the structural part which is to be made should not have small-radius curvatures, and the forming mould should have an optimized spatial distribution of the injection nozzles, which are spatially more concentrated (compact) in the electrically functional areas of the part, and spatially more spread out elsewhere.
The moulding conditions (including, for example, temperature profiles, velocity profiles, temperature-regulation mode of the mould, injection times, pressure profiles) fundamentally determine the electrical conductivity characteristics the manufactured article will have after moulding and following definition of the conductive areas or tracks by writing or laser ablation.
The correct setting of these moulding-related parameters is of fundamental importance in order to produce a component which has sufficient levels of internal conductivity (for example, of the order of 100 ohm/cm) before laser activation of the actual conductive areas. Incorrect moulding parameters may cause a partially isolating skin effect, which would hinder the subsequent laser writing activation step.
The optimum definition of the moulding parameters is generally dependent on the geometrical configuration of the component and the layout of the mould, such that for each new component to be moulded, associated polymeric material, press type, and mould layout, it is necessary to follow a specific procedure of fine-tuning the initial parameters and defining the optimum operational parameters.
For example, in the case of production of a fuel filler nozzle of a HDPE-based composite material including carbon nanotubes and glass fibres in the percentage amounts indicated above, the tests carried out have revealed the following general setting of the parameters necessary for obtaining a good initial conductivity level: mould temperature-regulated to an average temperature of 60° C.; high injection speed; low holding pressure; and high holding time.
In particular, from the tests carried out, it emerges that the distribution of the glass fibres, and therefore the distribution of the carbon nanotubes (namely the nano-structures which promote conductivity), and consequently the homogeneity of the electrical characteristics of the moulded article, are affected by the following transformation parameters: melting temperature, mould temperature, cooling time, injection speed and time, injection pressure, plasticization speed, and holding time and pressure.
The tests carried out for components with a volume of about 300 cm3, such as the fuel filler nozzle described above, show how it is, in any case, advantageous to operate using the following moulding parameters: temperature of the material between 190° C. and 260° C.; temperature-regulation of the mould between 50° C. and 70° C.; injection speed of between about 60 and 150 cm3/s (or, an injection time of between 3 s and 5 s for a volume of 300 cm3); injection pressure of between 60 bar and 80 bar; holding/cooling time in the mould of between 30 s and 60 s; and holding pressure of between 35 bar and 60 bar.
It is noted that, with the polymeric materials to which carbon nanotubes and glass fibre fillers have been added, there is a variable dispersion of the said fillers depending on the radial distance from the injection point. In effect, the carbon nanotubes act as a fluidifying agent for the polymer chains (having a smaller size, the hot molecules of polymers “slide” on the nanotubes). This effect results, with regard to the part, in a high concentration of nanotubes close to the injection point, and a smaller concentration of nanotubes far from the injection point. For this reason, in order to ensure that a functional component is obtained, (namely one where it is possible to form conductive tracks able to form electrical connections or devices), it is preferable to arrange the injection zones close to the electrically functional areas of the part (namely the areas of the component or structural part which are to be used for formation of electrical connections or devices).
By way of example, in the case where it is required to form areas with piezo-resistive characteristics (adapted to the formation of switching devices such as the control buttons for apparatus on-board a vehicle), it has been established that the arrangement of the injection nozzles need to be within a radius of 30 cm from the area assigned so as to undergo a subsequent laser writing treatment for activation of conductive tracks. Greater distances do not ensure an adequate distribution of the glass fibres and the carbon filamentary nano-structures, irrespective of the moulding parameters envisaged.
Once the mould has been prepared, following the design of the component or structural part adapted to integrate electrical devices or connections, and after implementation of the industrial process for moulding this component or structural part, the step for definition and realization of the conductive areas (tracks) is performed. For this purpose the technique of writing by laser ablation and consequent localized pyrolysis known from international patent application WO 2012/055934 is applied.
It has been shown that the localized heating produced by a focused laser beam (which induces selective superficial ablation of the polymer matrix) causes the filamentary nano-structures, which are dispersed within the matrix, to surface and percolate, thus forming a conductive pattern. Moreover, the interaction of the laser beam with the polymer substrate favours the thermal decomposition thereof, and the consequent formation of carbon. The carbon formed in this way acts as a bridge between the nano-structures during the process of ablation of the surface layers, further favouring the formation of the electrically conductive areas (tracks). A laser beam precisely focused on the polymer matrix may be used to obtain deep and stable conductive tracks.
The parameter for the minimum distance between the conductive tracks needs to be controlled, in order to prevent interference (crosstalk) between adjacent tracks. For this purpose, it has been noted that in a polypropylene matrix with a mineral reinforcing filler (for example, talc) in an amount of 10% by weight (referred to the weight of the composite material), in order to improve the dimensional stability and the rigidity (including, if necessary, rubber for improving the impact elasticity), and carbon nanotube filler in an amount of 2.5% by weight (referred to the weight of the composite material), which ensures an electrical conductivity of 1.6 Kohm/cm, such that there be no interference between the tracks, a minimum distance of 10 mm should be maintained between adjacent tracks.
The width and depth parameters of the laser beam for ablation of the composite material need to be controlled so as to obtain a level of specific electrical resistivity of at least 1.6 Kohm/cm on an injection-moulded component with an average thickness of between 2.5 mm and 3.0 mm.
The inventors have noted that, with a laser beam having a wavelength of 10.6 μm, the optimum speed of laser ablation is 5 mm/min with an effective focal length of 135 mm and an operating power of about 30 W. In order to avoid localized combustion, which results in deterioration of the nanotubes, the laser ablation process is carried out in an inert nitrogen atmosphere. It should be noted that a modified thermal zone Z (with transverse dimensions of about 0.2 mm), where an electrical conductivity effect may still be detected, is created in the region of the groove.
In order to form electrical connections and devices, the geometrical configuration of the conductive tracks (namely the layout of the conductive region, its width, and depth), also needs to be controlled. This is of fundamental importance in the realization of electrical devices, such as switching devices in the form of control buttons integrated in the component, in order to usefully employ the piezo-resistive effect of a conductive track, the variation in resistance caused by a suitable mechanical deformation or the capacitive effect of a conductive track, and the variation in capacity caused by an external body touching a conductive electrode area (such as finger).
A cut or weakening line 20 (for example, a thinner zone of the material) is conveniently provided on the polymer substrate around the operating area, in order to facilitate the mechanical displacement (oscillation) of at least one portion of the operating area of the device, with respect to the surrounding surface of the component in which it is integrated, and amplify as far as possible the effect of varying the electrical parameter of the circuit.
During tests, the piezo-resistive effect occurred when a force of 25 N was applied, with an elastic deformation of about 3 mm. A corresponding variation in the electrical resistivity between the ends of the winding segment 10′ of the conductive track was recorded, equivalent to 10%. Where no force is applied, the resistance is equal to R=30 Kohm. Where a force of F=25 N is applied, the resistance is equal to R=33 Kohm.
The minimum variation in electrical resistivity which can be detected over a background noise, resulting from variations in the environmental conditions is in the region of 3% (for example, temperature or humidity, which also produce dimensional variations in the component).
In general, it was shown that, in order for the formed operating device to be able to work in the elastic range, the maximum permissible deformation needs to be equal to about 3 mm. Moreover, in order to obtain the piezo-resistive effect, with the aforementioned characteristics, the operating area 14 should have a thickness greater than 2 mm and preferably a thickness of 3 mm.
Finally, the component or structural part realized by applying the process steps described above and integrating electrical devices or connections is assembled together with other components forming part of a supply set, for example by successive mechanical processing operations (such as welding, gluing, etc.), able to integrate the selectively conductive component in a supply assembly for subsequent installation on the vehicle. To this end, the component or the structural part has a plurality of metal connection terminals co-moulded on the polymeric matrix, which allow connection of the conductive tracks and the control devices to electrical circuits or systems outside the component, in order to receive or distribute information or power supply current signals.
It should be noted that the embodiment proposed for the present invention in the above description is intended to be a purely non-limiting example of the present invention. A person skilled in the art may easily implement the present invention in different embodiments which do not depart from the principles illustrated here, and are therefore included within the scope of protection of the present patent, as defined in the appended claims.
The present invention has been described in an illustrative manner. It is to be understood that the terminology which has been used is intended to be in the nature of words of description rather than of limitation. Many modifications and variations of the invention are possible in light of the above teachings. Therefore, within the scope of the appended claims, the invention may be practiced other than as specifically described.
| Number | Date | Country | Kind |
|---|---|---|---|
| TO2012A001082 | Dec 2012 | IT | national |
