DESCRIPTION

5

Technical field of the Invention

The present invention refers to an apparatus and a method for the manufacturing of a non-woven fabric, in particular a felt, from recycled carbon fibers.

10

Background

The high ratio between mechanical properties and weight causes Carbon Fiber- Reinforced Plastics (CFRPs) to be ever more used, in terms both of variety of 15 applications and of volumes of sale.

However, though it is true that composite materials using reinforcement carbon fibers and the related technical fabrics are increasingly considered as the materials of the future, the problem of end-of-life management of components manufactured therewith has not yet been addressed adequately.

20 For instance, to date CFRP and CF manufact manufacturing waste and scrap disposal occurs by collection, above all in a dump, or by incineration. Such solutions are very onerous, from both an economical standpoint and an environmental one.

Moreover, a few CFRP recycling techniques have been devised, some with the 25 aim of separating the resin from the carbon fibers, leaving the latter as intact as possible. An example in that sense is provided by WO 2003/089212, describing a CFRP incineration method aimed to the removal of the plastic matrix and the recovery of fibers contained therein. Said process allows to obtain recycled fibers that retain about the 80% of the mechanical properties of virgin fibers originally present in the composites treated. In general, however, such recovered fibers appear entangled and possibly contaminated by other materials and metallic and/or carbonaceous materials. Moreover, the length of recovered fibers is extremely variable. Therefore, the problem of the re-use of recycled fibers in an industrial field, i.e. of the manufacturing of semi-finished products directly usable in a primary production chain, remains open. In this connection, besides the aforementioned drawbacks there should also be considered:

- the high fragility of recovered carbon fibers, to conventional industrial processing systems which prove too invasive, breaking up, until pulverizing, a relevant part of the carbon fibers treated;

- the remarkable susceptivity of the fibers themselves to electrostatic phenomena, worsening their processing difficulties;

- the high electrical conductivity of the fibers at issue, requiring measures to safeguard processing apparatuses and machines from the risk of short circuits;

- the risks associated to the dispersion of such short fibers, in terms of salubrity and safety of the work environment.

Summary of the Invention

Hence, the technical problem set and solved by the present invention is to provide a method and an apparatus for manufacturing of non-woven fabric - in particular felt - from recycled carbon fibers, overcoming the drawbacks mentioned above with reference to the known art.

Such problems are solved by a method according to claim 1 and by an apparatus according to claim 15.

The preferred features of the present invention are set forth in the dependent claims thereof. It will be understood that, in the present context, by "recycled" carbon fibers are meant fibers recovered from other applications, in particular both pre-treated from end-of-life manufacts, and virgin fibers coming from scraps and wastes of other processings. Moreover, it will be understood that, even though the process is particularly suitable and advantageous in case of application to recycled carbon fibers, it is applicable also to commercial virgin fibers, possibly in mixture with recycled fibers.

By "virgin fibers" are meant precisely newly-produced, non-recycled commercial carbon fibers.

Moreover, as is known, by "non-woven fabric" is meant an industrial product of properties similar to those of a fabric, but obtained with processes different from weaving.

The present invention allows to obtain, starting from recovered carbon fibers, non-woven fabric suitable for the manufacturing of new finished quality products, thereby fostering recovered fibers reintroduction on the market. The method and the apparatus of the invention overcome the problems mentioned above with reference to the known art, related to the workability of recovered carbon fibers.

An example of preferred industrial application of the non-woven fabric obtained with the invention is the manufacturing of reinforcement members for composite materials, in particular having a polymer matrix, today largely used in several industrial fields, among which the aeronautical, wind energy and automotive field.

In particular, reinforcement members of non-woven fabric can be manufactured which are able to optimally adjust to complex-shape molds, giving to the composite material an adequate resistance even in zones with a very strong radius of curvature. In the known art, such complex shapes are obtained starting from elements of virgin and continuous carbon fiber, which are subjected to a lengthening process until attaining a member comprised of randomly broken filaments. However, this technology entails the limitation of a scarce predictability in fibers lengths, and of the increase in production expenses, due to the remarkable cost of yarns of virgin carbon fiber. As it will be better understood from the detailed description reported hereinafter, in the non-woven fabric produced with the invention the fibers are instead already in discontinuous form, and therefore relative motions between the fibers themselves are already allowed. Therefore, the resulting non-woven fabric exhibits a "pseudo-ductility" which greatly facilitates the formability of complex-shape components, by accelerating forming operations and remarkably reducing the onset of wrinkles in the reinforcement of the composite material.

Therefore, the method of the invention allows to obtain substantially the same features of discontinuity and alignment of the known virgin fiber elements, but at a remarkably reduced cost and with a good control of fiber length.

The semi-finished products (non-woven fabric) of recovered fibers produced with the method of the invention have a cost remarkably lower than analogous commercial products of virgin carbon fibers. Moreover, they enable to make composites with performances and mechanical properties comparable with those of the composites reinforced with virgin carbon fibers and superior to those employing fiberglass.

Therefore, the invention enables an economic exploitation of the recovered fiber and a broadening of the application field of carbon fibers to sectors where in the state of the art a use thereof would not prove economically convenient.

The invention enables a remarkable reduction of the economical and environmental costs, also for the lack of a collection in a dump or for the lack of an incineration of CFRP products or waste or, more generally, of waste deriving from the processing of objects made of carbon fiber. Other advantages, features and operation steps of the present invention will be made apparent in the following detailed description of some embodiments thereof, given by way of example and not for limitative purposes.

Brief description of the Figures

Reference will be made to the figures of the annexed drawings, wherein:

^■ Figure 1 shows a schematic flowchart illustrating a sequence of processing and/or treatment steps provided in the method of the present invention, in a preferred embodiment thereof;

^■ Figure 2 shows a schematic block depiction of a preferred embodiment of apparatus carrying out the method of Figure 1 ;

^■ Figures 3A and 3B show each a schematic illustration of a step of adding additives of the method reported in Figure 1 , with particular reference to an ensimage step carried out by bath (Fig. 3A) and spray (Fig. 3B) technique;

^■ Figures 4A and 4B show each a schematic illustration of a "veil" of recovered carbon fibers, obtained by a carding step as in the method in Figure 1 , respectively made of fibers with a respectively unidirectional and random orientation;

^■ Figures 5A and 5B refer to two alternative modes for carrying out a lap- forming step of the method of Figure 1 ; and

^■ Figure 6 shows a schematic illustration of felting means used in the method in Figure 1.

Detailed description of preferred embodiments

Referring initially to Figure 1 , it shows a sequence of steps according to a preferred embodiment of the method of the invention for the manufacturing of a non-woven fabric and in particular of a felt, from recycled carbon fibers.

As mentioned above, the method and the apparatus of the invention are also applicable to a mix of recycled fibers and virgin fibers or to virgin fibers.

Figure 2 shows a preferred embodiment of an apparatus specifically suitable for the carrying out of the above-mentioned method; such apparatus is generally denoted by 100.

In the present embodiment of the method and of the apparatus, these work on recovered carbon fibers produced according to the method reported in the afore-cited WO 2003/089212, incorporated herein by this reference. In particular, in the present example recovered carbon fibers, initially in the form of tuft or cloth, are considered.

In general, as mentioned hereto, the method and the apparatus of the invention are suitable to the treatment of carbon fibers recovered from the recycle of composite materials or waste and scraps from the processing of carbon fibers.

Thus, referring to Figures 1 and 2, in a first step of cutting the length of the recovered carbon fibers is made homogeneous.

In particular, by a feed system 101 , e.g. a conveyor belt, the flock or pieces of recovered carbon fiber are sent to a cutting system 102, e.g. a rotary cutter. The above-mentioned system, by a suitable variation of the relative rates of the two systems, enables the adjustment of the length of the fibers to be fed to the process. By making uniform the fibers to a length of 5 cm the dimensional homogenization is carried out, enabling a success of the subsequent operations required to the felting.

Cut fibers are then collected, preferably always by an automatic extraction system 103 and, e.g., of conveyor belt type, and fed to the opening unit 104 for opening the flocks/pieces, so as to blend the fibrous blanket for a first time. To this end, the device 104 is typically a rag-grinding or tigering unit. In a subsequent step of adding additiveSj and in particular of ensimaging, to the fibrous mass are added one or more products suitable to confer specific physical and/or mechanical properties to the fibers and typically water- emulsified. In particular, products suitable to foster fiber sliding and to abate the electrostatic charge thereof may be delivered. In addition or in alternative, in this step there may be envisaged the applying of a substance, referred to as "sizing", generally of epoxy type, which improves the adhesive properties of the carbon fiber. The ensimage step is of remarkable significance, as it provides fibers more mechanically protected, more sliding and less prone to charge electrostatically for the subsequent treatment and processing steps. The ensimage step therefore allows to increase the degree of safety and the workability of the recovered fibers. In Figure 2, by way of example an ensimage unit 106 has been depicted, bearing a hopper 105 for fiber inletting.

Figures 3A and 3B show respectively a specific mode of carrying out such ensimage step.

In the preferred embodiment reported in Figure 3A, the depositing of an additive product on the fibers is carried out by immersion of the latter in a suitable bath 10. To the fibers a fixed course is imposed between two conveyor belts 11 (shown as a single unit in Figure 3A) and related guide rollers, or groups of guide rollers, 1 , 2, 3 and 4. The course proposes to the fibers a pressing operation downstream of the bath - carried out, in the present example, between two compacting rollers 5 - and a subsequent drying operation carried out with means 6 based, e.g. on delivery of hot air or steam and/or by infrared lamps, a furnace or other system.

In the embodiment of Figure 3B, the depositing of an additive product on the fibers is instead carried out by spray, in particular nebulizing by means of nozzles 12.

The fibers are laid on a belt 13 bearing guide rollers 14 and 15, made so as to enable the product to wet the fibers and bearing the above-mentioned nebulizing rollers, preferably bilaterally. In this case as well, compacting rollers 5 and drying means 6 are provided.

Alternative or additional steps of adding additives, and in particular of ensimaging, may be provided also concomitantly or downstream of steps of mixing, orienting and cohesioning of fibers and/or of joining veils described in the following.

Moreover, in the step of forming the mixture, the veil and/or the lap, there may be provided the applying of solid additives, such as powders or fibers, that possibly may be fixed to the fibrous matrix by a heating step (infrared lamp, steam, furnace). Such further additives can confer to the felt the ability to make preforms, and/or to the composite to be manufactured particular characteristics, like e.g., the tenacity increase.

The fibrous mass is then subjected to a step of mixing with auxiliary fibers, in a suitable unit 107. In this case as well, the fibrous mass can be fed to the mixing unit 107 automatically, by a conveyor belt or an equivalent means.

The mixing may be carried out with a machine or with a sequence of machines known per se, e.g.: - a bale opening machine with a micro-weighing system, which enables the feeding of the individual components guaranteeing perfect control of the amounts fed (a machine suitable to said purpose is the commercial model denominated Bale opener mod. AB, produced by Cormatex),

- a belt for collecting the individual components of the mixture, suitable to form a controlled stratification, and

- rag grinding machines for the intimate mixing of the various materials (a machine suitable to said purpose is the commercial model denominated Primary Opener mod. SMF, produced by Cormatex).

The percentage of auxiliary fibers added to the mass of carbon fibers being input can be variable and adjustable, depending on the processing specifications and in particular on the non-woven fabric that is to be obtained as output. In particular, the method and the apparatus described herein provide the manufacturing of felts with 95% of carbon fibers. Of course, the method and the apparatus of the invention enable the manufacturing of felts with percentages of carbon fibers variable over a very wide range.

Auxiliary fibers may be of organic nature, as well as of inorganic nature. By way of non-limiting example, there are reported as suitable auxiliary fibers: thermoplastic fibers of polyester, Polyetheretherketone (PEEK), polytetrafluoroethylene (PTFE), polyethersulfones (PES), polyamides (PA), polypropylene (PP), polyethylene (PE), polystyrene (PS), polyvinyl alcohol (PVA) type; natural fibers of cotton, hemp, flax type; inorganic fibers of metallic, glass and aramid type.

The auxiliary fibers may have a supporting function for the subsequent steps, in particular a lap-forming step which will be introduced below in the description, and/or also confer specific functional properties to the non-woven fabric that is output and to the finished product (composite material reinforced with carbon fibers) manufactured therewith.

Moreover, as mentioned above, to the mixture may be added specific additives, both in liquid phase and in solid phase, i.e. the mixing step may be carried out concomitantly to a step of adding additives, and in particular of ensimaging, additional or alternative to that described above. Said step of adding additives may be carried out according to modes analogous to those already described in connection with Figures 3A and 3B.

The mixing step described herein may also be carried out concomitantly to the homogenizing one.

The blended fibrous mass is then subjected to a fiber arranging, or orienting operation, in a suitable unit 108 at the output of which a so-called "veil" is obtained. In a particularly preferred embodiment, such fiber orienting step is a carding step, carried out in a suitable carding machine.

The above-mentioned veil, on the basis of specific manufacturing needs and/or properties of the final product, could have a substantially predefined or random orientation of fibers. Moreover, the fibers could be oriented chiefly in a longitudinal direction, i.e. being substantially parallelized and therefore unidirectional, or be oriented bidirectionally (i.e. on a plane) or three- dimensionally.

Figure 4A shows, by way of example, a veil bearing fibers with a prevailing and predefined unidirectional orientation.

Figure 4B shows instead, always by way of example, a veil bearing fibers with a random orientation.

Typically, a machine with a higher number of carding stages produces an increase of the degree of parallelism of the fibers.

The carding machine used may be of known type, therefore it will not further be specifically dwelt upon. In such step of arranging the fibers three alternative technologies, illustrated below, are usable. According to a first "wet laid" wet deposition technique, orientation angles predefined on a plane can be imparted to the carbon fibers. In the humid phase a so-called "binder", generally of polyvinyl alcohol or of resin, is contained, to which is transferred the task of ensuring a good level of cohesion of the fibrous veil. This technique entails the advantage of not damaging the fibers. A second usable technique is that of the so-called "aerodynamic carding", which uses an air flow for veil manufacturing. Veils can be attained which are generally heavier and "nobler" compared to wet deposition products. Fiber orientation attainable with this technique is substantially three-dimensional.

An example of machine suitable to such technique is the commercial model Lap Formair, produced by Cormatex.

Aerodynamic carding entails the great advantage of preserving the length of the fibers being processed, as it reduces to a minimum the contact thereof with mechanical members and is therefore strongly advised in processes using very fragile and delicate fibers, precisely as carbon fiber. Fiber distribution to form the veil occurs by suitably controlled air flows and guaranteeing a uniformity much greater than wet processes and comparable to traditional carding techniques. The orientation of the fibers in the veil is three-dimensional and therefore less orderly compared to the traditional carding, even though, in case fragile fibers like carbon fiber are processed, such a deficit in terms of mechanical properties that can be conferred to the end product is oft-times compensated for by the ability to keep longer the fiber being processed. A further advantage of the aerodynamic carding technique, compared both to wet processes and to the traditional carding, consists in the low process costs which enable to remarkably widen the application fields of the felts manufactured with the method subject of the present invention, overcoming the limitations present today, due to the high cost of the raw material.

Finally, a further possible technique is that of traditional carding, utilizing in particular a cylinder card, allowing to obtain a mainly unidirectional orientation, thereby producing a parallelization of the fibers.

Even concomitantly to the veil forming step and/or immediately downstream of such step there may be provided the applying of additives, and in particular an ensimage step, additional or alternative to the above-mentioned ones.

The veil is then subjected to a step of lap forming in a unit 109, in which plural veils, or plural portions of a same veil, are stratified and cohesioned so as to obtain just a so-called "lap" of desired thickness and grammage.

As mentioned above, laps can be manufactured with veils having fibers of predefined or random orientation, and with fibers oriented unidirectionally, two- directionally or three-dimensionally.

Moreover, it is possible, by a suitable overlapping of the veils, to define the orientation of the fibers of the lap. For instance, by utilizing veils having chiefly unidirectional fibers, laps first - and non-woven fabrics later - having chiefly directional fibers are had.

The specific orientation of the fibers in the lap may be obtained by imparting suitable working motions to a lap-forming manufacturing machine. In particular, an overlapping of veils may be provided in a direction parallel or transversal to the advancement of the lap on such manufacturing machine. Two examples of lap manufacturing in a manufacturing machine are shown in Figures 5A and 5B. In particular, in said Figures V denotes the veil, arrows 20a, 20b the overlap direction of the veils or of the veil portions and the arrow 21 the direction of advancement of a conveyor belt 22 or equivalent means on which the veil or veils constituting the lap are laid.

In the example of Figure 5A, the resulting lap has fibers in a chiefly longitudinal direction when the starting veil has unidirectional fibers and the overlap direction 20a corresponds to the direction of orientation of the veil fibers. Therefore, in the case of Figure 5A the veils are parallely overlapped the one on the other until forming the desired lap thickness.

In the example of Fig. 5B, the veil is laid along direction 20b, transversally to the feed motion of the conveyor belt 22, enabling to obtain infinite lengths of lap. In the case of Figure 5B, the veil is therefore laid transversally to the feed motion of the lap, enabling to obtain infinite lengths of lap.

Also in the lap-forming step, or immediately downstream of such step, a step of adding additives, in particular of ensimaging, can be introduced additional or alternative to those described above.

The step of orienting fibers and that of lap-forming just described may also be carried out concomitantly the one to the other. This is possible, e.g., when using the above-mentioned aerodynamic carding.

In a subsequent step, from the lap the non-woven fabric is obtained, by an operation of further cohesioning of the veils of the lap and of forming carried out in an unit 110 and based on:

- a heating of the lap by thermal treatment, carried out e.g. by irradiation lamp, hot-air furnace, steam, etc., and

- a subsequent cohesioning and thickness calibration by rolling. The temperatures that can be utilized for the forming can range from 80 to 200 °C, according to the material utilized for veil sizing.

Figure 6 shows a diagram exemplary of the mode of carrying out such forming step, referring in particular to a felting. In that case the lap, denoted by F, is thermoformed by feeding to a heating device 30 followed by a rolling mill 31 , at the output of which precisely a non-woven fabric tnt of desired thickness is obtained.

In an alternative embodiment, the lap may be cohesioned by chemical bonds instead of by thermoforming.

According to another variant embodiment, the step of forming the non-woven fabric may be carried out by a needling, with needles or with water.

Even in the step of cohesioning and forming the non-woven fabric, or immediately downstream of such step, there may be added a step of adding additives, and in particular of ensimaging, additional or alternative to the above- mentioned ones. In case of the depositing of an additive, in particular of a sizing, on a non-woven fabric, the conveyor belt of Figure 3A may be replaced by a belt for guiding only. Moreover, downstream of the drying step of Figures 3A and 3B, the system may be completed by a device for rolling up the non- woven fabric on a spindle.

It will be understood that the devices and the units of the above-described apparatus 100 may be equipped with means, per se known, suitable to prevent the carbon fiber, particularly conductive electrically, from damaging electrical parts, control systems and/or safety devices. Hoods, shields, protections, wirings and the like are the most common known precautions for performing this task.

Moreover, the various sections of the apparatus 100 may be under negative pressure, in order to prevent the dispersion of the fibers themselves in the work environment. This contrivance eliminates the problems linked to the healthiness of the environments and to the integrity of the machines (short circuits). As afore-mentioned, the non-woven fabric obtained with the method and the apparatus described above may have mechanical and physical properties variable depending on the applicative needs, e.g. in terms of height, thickness, grammage, percentage and type of auxiliary fiber, percentage and type of additive/s and degree of fiber parallelism.

The non-woven fabric provided by the above-described apparatus and method can be managed as known non-woven fabrics and therefore can undergo subsequent processing processes, e.g. of preforming, pre-impregnation, impregnation, etc. The non-woven fabric obtained allows the design and manufacturing of composite materials and products of carbon fiber having selected high mechanical properties - in particular, strength, mechanical rigidity and tenacity - even with respect to the different directions, concomitantly optimizing the use of the material. Therefore, a composite material manufactured with the non-woven fabric of the invention proves to have mechanical features, mentioned above by weight unit, comparable to those obtained by the most performing among the materials manufactured with the known art.

As mentioned above, downstream of the step of cohesioning and forming, i.e. of the unit 110, there may be provided further steps/units for processing the non-woven fabric and/or its packaging in rolls or plates for transporting.

In particular, the non-woven fabric obtained may be utilized as is for specific applications, e.g. electro-magnetic shielding, or temperature filtering systems, or be pre-impregnated for CFRP manufacturing.

In particular, a carbon fiber-reinforced composite material starting from the non- woven fabric obtained with the above-described apparatus 100 and method can be manufactured by several known techniques, among which, purely by way of example, the following are mentioned: "manual rolling", "vacuum bag molding", "hot molding", which therefore will not specifically be dwelt upon. The present invention has been hereto described with reference to preferred embodiments thereof. It is understood that other embodiments might exist, all falling within the concept of the same invention, as defined by the protective scope of the claims hereinafter.