Patent Description:
At the state of the art it is known that following a process of cutting prepreg materials, the amount of scraps that is produced is high. Up to now, said scraps have been treated as special waste and therefore have been disposed of with specific procedures, resulting in an increase in processing costs. Only recently have some methods emerged for the reuse of prepreg scraps but these methods involve the creation of a finished product in the form of a recomposed sheet, coming from an unpeeled and interposed between two protective films prepreg cut. Said sheet can only be used in lamination processes and not in molding and pyrolysis processes. In these last two types of processes, the presence of the prepreg film would lead to the formation of interface problems, generating detachments and / or delaminations.

Furthermore, a possible manual elimination of films would involve a high increase in costs and the request for employees assigned to this specific task.

Document <CIT> describes a method for the preparation of one or more fragments of uncured composite material that allows to remove a protective film from the fragment / s by tangential jets to the prepreg kept flat. Such jets intend to peel the film while the prepreg is held in position by pressure rollers. The disadvantages of this approach are a relatively large size of the equipment that must extend in a substantially two-dimensional way since the prepreg must be positioned and held flat to identify the tangential position. Furthermore, the effectiveness is relatively poor since in the event of even small misalignments between the jet of air and the surface of the prepreg, the relative film is not detached. In greater detail, before the removal of the films, the fragment / s must be loaded onto a conveyor belt where care must be taken that the fragment / s does not overlap and that it is positioned so that the protective film contacts the belt conveyor. Finally, versatility is also relatively poor, since examples are shown for prepregs that are still large before being subsequently processed and it is complex to apply the same process in the presence of a plurality of prepreg 'chips' or scraps such as when it is necessary to recycle the scraps of a production process that has already taken place.

The basic idea of the present technical solution is to combine a cooling step of the composite material so that the polymer matrix loses tackiness, e.g. decreases its tack value, and subsequently or simultaneously undergoes an agitation action, performed in a peeling machine, to generate turbulence so as to promote separation of the film from the matrix. A repeated mechanical folding is shown but is not part of the claimed invention.

According to a preferred embodiment, the step of separating by agitation comprises the step of rotating a basket containing the two-dimensional elements. In this way, the peeling is encouraged by the continuous bumping and rubbing caused by the rotation of a basket.

According to the invention the step of separating by agitation comprises the step of agitating by means of a compressed gas directed towards the two-dimensional elements to generate turbulence, preferably a vortex. This has the advantage that the two-dimensional elements peel much more easily as the swirling motion, produced by the flow of a compressed gas, generates multiple impacts and rubs in each direction avoiding the drawback that the two-dimensional element is not peeled due to a jet directed in a tangential direction on each element.

According to a preferred embodiment during the separating step, the temperature to which the two-dimensional elements are brought is below <NUM>° and is controlled.

Controlling the temperature implies that the two-dimensional element is able to maintain its temperature without being affected by the surrounding environment resulting in the risk of not being accurately peeled.

According to a preferred embodiment said step of controlling said temperature comprises the step of closing the peeling machine in a temperature controlled cooling device. In this way, the elements to be peeled are not affected by the temperature of the surrounding environment and are all able to peel equally.

According to a preferred embodiment, the step of controlling said temperature comprises the step of providing compressed gas with cooled temperature and controlling at least one between flow rate and temperature of said compressed gas.

This implies that the control can be achieved by different means, such as valves that change temperature or flow rate. A temperature sensor may be provided within the chamber in which the elements are peeled so as to provide data to a control unit which, suitably programmed, consequently controls the valves to appropriately change the flow rate and/or temperature of the cold gas.

The resulting recycled product can be reused for the production of components for:.

In addition, the invention also finds application in first-use applications of the composite material, for example when it is necessary to remove the protective film from portions cut from a sheet cut from a roll having a width of <NUM>-<NUM>, which is carried out continuously on a cutting machine.

Further purposes and advantages of the present invention will be clear from the following detailed description of an example embodiment thereof (and its alternatives) and the appended drawings given by way of explanation only and not limitation, wherein:.

The same numbers and reference letters in the figures identify the same elements or components. The elements and features illustrated in the various preferred embodiments, including the drawings, may be combined with each other without, however, departing from the scope of protection of the present application as described below.

At the end of the cutting process of the prepreg sheets, the scraps can appear both connected and loose, sometimes even overlapping and with different shapes and sizes and equipped with a protective plastic film.

According to the method of the invention, first of all it is necessary to proceed with the on-site separation of the resin-free selvedge from the rest of the sheet, since the selvedge is a material that is not involved in the process of reusing the scraps and cannot be subsequently separated automatically. The selvedge will therefore constitute in all respects a waste and not reusable material.

In order to allow a correct processing, the scraps, obtained from a cutting operation of a prepreg sheet, are separated by type of reinforcement, fiber size, weight, texture, matrix and date of production, then bagged and labeled, so as to be easily identifiable.

The bags must then be stored at a temperature of -<NUM> until the moment to the delivery to the recovery center.

Thermosetting prepregs maintain their workability at room temperature, considering as room temperature a temperature of <NUM>, for about <NUM> days, before the resin starts the cross-linking process. This is due to the fact that the speed of the crosslinking process of the polymer matrix increases with temperature.

Therefore, in order to store prepreg scraps for a longer period of time without the matrix starting the cross-linking process, they should be stored at a temperature lower than the glass transition temperature, which in this case is about -<NUM>. In this way the useful storage period is extended to about <NUM> months.

Therefore, for proper storage of the material, it is necessary to know the type of polymeric prepreg material in order to know the exact glass transition temperature so that it is stored in the correct manner.

The first step to address in material recycling is to separate the overlapping or agglomerated material and remove the film used for cutting.

In order to be used easily for each purpose described above, the prepreg scraps must have a shape with a side dimension in the range of <NUM> - <NUM>, preferably with a side less than <NUM> and even more preferably rectangular in size <NUM>, 5x12mm. The processing machines inside the treatment cell are:.

Referring preferably to the layout of <FIG>, the steps of the method according to the present invention are:.

Going into the specifics of the various steps, taking into account <FIG> the cutting machine <NUM> comprises:.

The prepreg cuttings are fed into the blade system by means of a cutting belt <NUM> which is wound about two pulleys:.

The entire system is driven by a motor-reducer assembly.

The transmission of the motion, to the multiple drive pulley <NUM> of the belt assembly, will occur directly through the motor shaft keyed to the reducer.

The synchronization is maintained by friction of the belts. According to a form of embodiment that allows redundancies, in order to synchronize the motion of the belts with that of the cutting belt <NUM>, the motion to the driving pulley <NUM> of the belt will be transferred through a timing chain system with pinions and crown formed by: a motor pinion <NUM>, two toothed pinions and a spoked toothed crown.

The drive pinion will be splined to the end of the shaft connected to the geared motor and on which the multiple drive pulley <NUM> of the belts is also splined. This shaft will then transfer the drive torque to the entire system.

The motion to the conveyor belt drive pulley will be provided by the spoked crown wheel, which is keyed to its axis.

The motion to the conveyor belt pulley will be given by the spoked ring gear, splined to its axis of rotation.

The gear ratio of the pinion-crown system is such that the tangential speed of the conveyor belt on the driving pulley is equal to the forward speed of the trapezoidal belts.

In this way the prepreg cuttings are guided towards the blade block <NUM> without slippage between their upper and lower surfaces, thus remaining tightly adhered to the belt, thus maximizing cutting efficiency and minimizing possible jams. At the exit of the cutting machine, cuttings are obtained whose width does not exceed the distance between centres of the blades and whose length is irregular. To obtain square-shaped chips measuring <NUM>*<NUM> another cutting operation is carried out in the direction orthogonal to that of the first cut. The cuttings must therefore be aligned on the belt in such a way that the direction of their longest length is orthogonal to the direction of advancement of the cut. The cut is therefore made in two orthogonal directions, obtaining chips with a geometry within a quadrilateral.

Once the chips have passed the plurality of cutting blades, they fall by gravity and exit from the lower side of the machine.

Chips after being frozen, as per STEP <NUM>, and dosed on scales, as per STEP <NUM>, are led into a cooler where a pneumatic peeling machine <NUM> is placed. In this step a very important role is played by the temperature that must be kept below <NUM> and preferably at values close to -<NUM>. In this way the stiffness of the chips is increased and it is easier to proceed with the peeling.

According to a preferred embodiment, STEP <NUM> takes place inside an industrial freezer of suitable capacity but alternatively, and without departing from the scope of protection of the present patent application, it is possible to use more generally any other cooling device intended such as a controlled temperature cell or a climatic chamber.

Said machine <NUM> uses the mechanical agitation of the material to proceed with the peeling without mistreating the fiber fabric and degrading its properties. Therefore, the flow rate of a compressed gas is used e.g. air as a means of handling.

Chips are inserted inside the peeling machine <NUM> and rapidly rotated by the action of the compressed air exiting the nozzles <NUM>. In this way, it is not important the manner in which the chips are inserted since the peeling of the chips occurs by means of the impacts, caused by the swirling motion produced by the flow of a compressed gas, e.g. air, that each chips has with the other.

According to an embodiment not shown, the peeling machine <NUM> may provide for the presence of a rotating basket and therefore the peeling of the chips takes place both by means of agitation but also by rotation of a basket.

Further and without going beyond the scope of protection of the present patent application, liquid nitrogen or other gas supplied at a cooled temperature e.g. below <NUM>° can be used as compressed gas alternatively to air.

In the case where liquid nitrogen is used as a compressed gas, temperature control could be by means of valves that by rolling can change the temperature of the nitrogen itself or alternatively change its flow rate. In addition, temperature could consist of using a sensor inserted into the stirring chamber to control temperature.

Rotation and aerodynamic forces separate the protective films from the prepreg causing the films to be pushed by the air towards the top of the tube where they are sucked up by means of a suction system consisting of a vacuum pump.

After several tests it has been verified that the optimal quantity of chips to be inserted into the peeler is <NUM>/<NUM> gr, with a maximum size of <NUM> * <NUM> and that <NUM>/<NUM> seconds are needed with an air pressure of <NUM>-<NUM> bar and a flow rate of <NUM> liters/sec to peel the film properly. The vacuum cleaner, on the other hand, has a flow rate of <NUM> liters/sec. The high volume of air sucked in, with the consequent recall of warmer air from outside, could cause a temperature variation inside the peeling machine. In order to limit this problem as much as possible, the external air adduction duct is connected to a plate heat exchanger, inside which the air follows an obligatory path to reduce its temperature to acceptable values for the execution of the process.

During the same peeling step it is possible to add talcum powder or other lubricating and/or inert material in powder form to the chips, thus eliminating the need for a subsequent talcum powder station. The talcum powder is uniformly distributed on the peeled prepreg by the compressed air vortex.

Claim 1:
Method for treating a composite material having a polymer matrix and a filler comprising the following steps:
- receiving two-dimensional elements of composite material covered with a protective film
- bringing said two-dimensional elements to a temperature below <NUM> to approach or exceed a glass transition temperature of the polymer matrix
- at least partially separating the protective films from said two-dimensional cooled elements by agitation performed into a peeling machine (<NUM>) of the two-dimensional elements, wherein the step of separating by agitation comprises the step of agitating by means of a compressed gas directed towards the two-dimensional elements to generate a turbulence, preferably a vortex, to cause peeling by means of impacts of the two-dimensional elements; and
- aspirating, by means of a forced suction system, the removed films, which have a mass lower than the corresponding two-dimensional elements.