Patent Application
20160121540
The invention relates to a device and a method for thermoforming plastics, more specifically plastic sheets and films, to form spatial objects, such as receptacles.
Thermoforming three-dimensional plastic products in moulds starting from flat plastic films or sheets and in a continuous or semi-continuous process is generally known. It is also known that the actual moulding step in the mould is the slowest step in the deforming process of supplying the flat structures to the device and, via heating steps, deforming in the mould and removal of the moulded object. In order to increase the yield of the device, it is now customary to produce a plurality of spatial objects from a large sheet or film from roll, simultaneously in one large mould during the forming step. However, the large mould requires the supply of a large amount of energy for preheating the sheets and for building up the required level of pressure and/or vacuum in the mould. In addition, a superfluous amount of plastic sheet has to be heated inbetween and around the plurality of objects which are moulded simultaneously, which cannot be subsequently recovered, or only with difficulty, and thus in other words is lost as waste. This is a crucial drawback, since expensive plastics are often used, such as PC, PEI, PS, PES, CPET, biodegradable plastics etc. Finally, it is very difficult to achieve even heating across the entire large film, as the outer edges of the film stay colder than the central zone. Usually, there are also pressure differences in the forming station between the edge zones of the mould and the central zone. It is thus often difficult to achieve a precise and even form in a large mould. In addition, it is not easy to subsequently punch out the moulded objects (without burrs) correctly (inside the required tolerances) near their edges, and this also requires complicated and expensive tools.
WO 2008/090543 discloses a waste-free device for thermoforming, in one (small) mould, one single spatial object per cycle from one plastic sheet which had been cut to the required dimensions beforehand. This has the significant drawback that the device only produces one moulded object per forming cycle. The yield of the device per unit time thus remains very limited as the moulding step will always be the slowest step in the process. This device uses a pallet for the sheet which passes from the inlet side of the sheet to be deformed from a sheet stack up to the outlet of the moulded object. A large number of special and complicated grippers are fitted on the pallet for the sheet edges and have to slide horizontally inwards for the gripping operation near to the sheet edges to be gripped. Unfortunately, this sliding operation cannot guarantee a sufficiently reliable gripping operation.
In addition, in WO 2008/090543 the movement of the grippers from a non-clamping to a clamping position introduces horizontal shearing forces in the sheet edges. These forces can significantly hamper a correct positioning of these edges. Moreover, transferring each empty pallet with its gripper from the removal station back to the pick-up station for subsequent single sheets is relatively complicated and time-consuming. Finally, the machine is not very compact.
U.S. Pat. No. 7,481,640 discloses a scrapless thermoforming machine having a complex loading and unloading station.
GB1500961 discloses a process and apparatus for the production of individual rimmed plastic containers, which are filled with a product, e.g. a food product.
U.S. Pat. No. 6,086,354 discloses a twin-sheet thermoforming apparatus.
U.S. Pat. No. 5,167,969 discloses a split frame for rotary vacuum mould unit, where individual rectangular plastic sheets are clamped by means of pin bars.
It is an object of the present invention to provide a good method and a good apparatus for thermoforming spatial objects.
Surprisingly, the above object is fulfilled and the advantages are obtained by providing a method and a device for carrying out a method for simultaneously continuously thermoforming a plurality of individual plastic sheets in moulds to form an identical number of individual spatial objects and, more specifically, as described in the claims. To this end, firstly, a plurality of sheets are supplied simultaneously, each from its individual sheet stack, to a supply station and from there to a transport track extending through the device.
Subsequently, the plurality of individual sheets are simultaneously passed through on the transport track in one of a plurality of identical common holders to successively at least one heating station, a moulding station and a removal station for the individual objects. To this end, each individual sheet, in order to be thermally deformed to form its spatial object, is picked up near its outer edge and clamped into this holder for the plurality of sheets simultaneously and for the protruding edges of each of the moulded objects. During the removal of the moulded objects, these edges are then released from the holder in order to remove the objects. Thereafter, a new moulding cycle can begin for successive new series of multiple individual sheets in their holders, once these holders have been transferred to the supply station.
With a view to saving time, it is an advantageous feature of the invention that the supply of the sheets for a new cycle in the supply station occurs virtually simultaneously with the removal of the moulded objects of the preceding cycle in a removal station, which removal station is preferably situated nearby the supply station. Preferably, the supply and the removal station are even arranged closely adjacent for this purpose. This also increases the compactness of the device.
The simultaneous supply of the plurality of sheets preferably takes place from the top of each sheet stack.
Preferably, with a view to a drastic saving in energy consumption, according to another aspect of the invention, each sheet in the common holder will be heated in an individual heating cell and will be moulded in an individual moulding cell to form its object by means of its mould.
Preferably, the outer edges of the sheets and the protruding edges of the moulded objects will only be clamped transversely in the holder.
In a first aspect, the present invention provides a method for continuously simultaneously thermoforming a plurality of individual plastic sheets in moulds to form an identical number of individual spatial objects. The method comprises:
Each holder further comprises a plurality of transverse clamping pins and a clamping frame which is analogous to said middle frame and has elongated openings and protruding lips near edges of said openings, and the middle frame comprises suitable holes for receiving said clamping pins.
The method further comprises the steps of:
It is an advantage of using a plurality of individual sheets, which are pre-cut to the correct size, rather than a single (large) plastic sheet, because in this way the step of separating moulded products can be avoided, and waste material is avoided, and energy requirements (a.o. for heating such waste material) are reduced.
It is an advantage that the plastic sheets are clamped only in a transverse direction in the holder, in other words that the upper frame and middle frame between which the sheets are clamped move towards each other, or away from each other without being shifted. In this way shear forces in the plastic sheets can be avoided, and the dimensions required for clamping can be as small as 1.0 mm or even 0.5 mm of the outer edge.
It is an advantage that the plastic sheets for each holder are all picked-up simultaneously, not only because it is fast, but also because by doing so, additional components and movements can be avoided in the supply station and removal station, in particular as compared to U.S. Pat. No. 7,481,640 where sheets are loaded only three at the time (while the “transport tray” can hold 12 sheets), requiring an additional “billet shuttle” (not required in the present invention), and requiring a very complex three-dimensional construction for loading the sheets on the transport track, for removing the formed objects from the removal station, and for passing holder elements from the “unloading station” (cfr. removal station) to the “loading station” (cfr. supply station). Hence, a device for performing the method of the present invention can be made (much) more compact.
It is an advantage of using lips, in that they allow suitable clamping, even under varying temperatures.
It is an advantage that the holder can be easily fitted or unfitted by simply sliding the clamping frame, and by moving/removing the upper frame to/away from the middle frame.
Preferably the clamping frame remains connected to the middle frame. This has the advantage that only the upper frame needs to be passed on from the removal station to the supply station.
It is an advantage that the correct positioning of the upper frame on the middle frame is based on the insertion of a pen in a corresponding opening. This allows very precise positioning with very small tolerances.
In a method according to embodiments of the present invention, the supply of the sheets for a new cycle in the supply station may occur virtually simultaneously with the removal of the formed objects of the preceding cycle in the removal station which is situated nearby the supply station.
The simultaneous supply and removal saves time. By situating the removal station nearby and preferably adjacent to the supply station, the passage of the upper frame is easier, and the compactness of the device is increased.
In embodiments of the present invention, the simultaneous supply of the plurality of sheets may take place from the top of each individual sheet stack.
It is an advantage of picking-up the sheets from the top of the stacks as compared to e.g. the loading mechanism used in U.S. Pat. No. 7,481,640, because in this way so called “billet sleeves” can be avoided, as well as the transfer from said billet sleeves to the “transport tray” (cfr. holder). In other words, in the present invention the sheets are directly loaded to the holder, whereas in U.S. Pat. No. 7,481,640 the loading of the sheets is indirect.
In a method according to embodiments of the present invention, in each heating station, each sheet in the common holder may be heated in an individual heating cell and in the moulding station, each heated sheet in the holder may be moulded to form a spatial object in its individual mould. This results in a drastic saving (e.g. up to 80%) in energy consumption.
In a method according to embodiments of the present invention, the formed objects, after having been released, may be stacked in one stack per moulding cell.
It is an advantage of stacking the moulded products directly on individual stacks, as compared to some prior art devices, where the moulded products are first dropped on a conveyer belt, and only then stacked. In other words, in the present invention the moulded products are directly stacked, which is more efficient.
In a method according to embodiments of the present invention, the common holder with the formed objects may be separated in the removal station and its upper frame with the formed objects may be lifted from its middle frame while said middle frame remains on the transport track and the middle frame and the clamping frame which is slidably connected thereto, may subsequently pass to the supply station in order to repeat the cycle.
In this way, the three frames of the holder move from the removal station to the supply station: the middle frame and the clamping frame via the transport track, the upper frame via a side-track. It is an advantage of embodiments of the present invention that the latter movement does not require complex three-dimensional movements.
The lifted-up upper frame may deposit the formed objects in the removal station and may subsequently pass to the supply station in order to repeat the cycle.
In a second aspect, the present invention provides a device for continuously and simultaneously thermoforming a plurality of individual spatial objects. The device comprises:
The device is characterised in that
In a device according to embodiments of the present invention, the first pick-up means and the second pick-up means may be provided for picking up the sheets on the one hand, and for picking up the objects on the other hand virtually simultaneously.
A device according to embodiments of the present invention may further comprise control means adapted to move the clamping frame with respect to the middle frame in order to exert the clamping action on the sheet edges in the holder from the supply station to the removal station, and to move the clamping frame with respect to the middle frame in order to release the protruding edges of the moulded spatial objects in the removal station.
In a device according to embodiments of the present invention, the transport track may form a continuous path and the supply station for the sheets and the removal station for the moulded objects may be situated adjacent to one another. In particular embodiments, the path may be a circular track and the transport track may be configured as a carousel.
It is an advantage of embodiments of the present invention that, starting from plastic sheets, a waste-free continuous method and a compact device for uniform thermoforming of spatial objects are provided.
It is also an advantage of embodiments of the present invention that a significantly increased productivity can be achieved.
It is also an advantage of embodiments of the present invention that it requires much less energy per object to be moulded in each moulding cycle than is used when applying known non-waste-free thermoforming processes for a plurality of objects simultaneously starting from large films.
It is also an advantage of embodiments of the present invention to provide a simple carrier with holders for the edges of the sheets from their entry in the device to the removal of the moulded products from the device.
Furthermore, the invention makes it possible to simultaneously provide a plurality of spatial objects of mutually different shape per cycle, e.g. receptacles on the one hand and their lids on the other hand, or e.g. receptacles having different openings (e.g. round or polygonal or different still) near their protruding upper edges.
Moreover, it is a further advantage of embodiments of the present invention that the punching of the sheets and the thermoforming of the objects can be done in physically different places.
It is highly advantageous that in embodiments of the present invention pre-printed sheets can be used. Contrary to prior art systems, where pre-printed films can be used, but which need to be different at different locations of the punching machine (for obtaining similar pre-printed objects) because of a.o. different heating profiles over the punching device, in embodiments of the present invention the pre-printed sheets can all be the same. Hence it is not required to keep an accurate track of which pre-printed sheets are made for which location in the holder; any pre-printed sheet can be formed into an object at any location of the holder provided thereto. This is possible a.o. because of the presence, in a device according to embodiments of the present invention, of a dedicated heating per sheet.
This will now be described in more detail by means of an embodiment of the invention in the light of the attached figures. Numerous additional details and their advantages will thereby be explained. The protection is not limited to this embodiment. Numerous variants which are obvious to the person skilled in the art are deemed to also form part of the protection formulated and defined in the claims.
The top view from
The transport track 7 comprises a number (e.g. eight in the embodiment illustrated) of segments A to E with suitable openings 28 for receiving the holders 12 for clamping the sheets 2 to be transported and for the subsequent treatment steps to be performed on the sheets 2. In the embodiment illustrated, the continuous transport track is shown as a circular ring, but the invention is not limited thereto, and any suitable form of transport track 7 configuration may be used. Preferably the transport track 7 presents a closed configuration, including for instance a square or rectangular or polygonal configuration.
Subsequently, the transport track 7 intermittently pushes the holder 12 with sheets 2 to a sufficient series of heating cells 14 in heating stations 8 in the segments B for their first and subsequent heating steps. There, the sheets 2 are sufficiently heated in their holder 12. Each heating station 8 which is arranged so as to be stationary in the device during use comprises a plurality of separate heating cells 14 (the number of heating cells being identical to the number of sheets per holder), each with its own adjustable heat source; in the example illustrated six heating cells 14. The setting for e.g. time and temperature depends inter alia on the composition and the volume of the sheets 2. Heating is thus carried out in a very targeted manner per sheet 2 opposite its heating cell 14, as a result of which an energy saving of more than 80% can be achieved compared to the prior-art technology. In each heating station 8, the heating cells 14 may be arranged above or below, but preferably above and below the uninterrupted transport track 7 in order to achieve quicker and more even heating.
Thereafter, the transport track 7 shifts the sufficiently heated sheets 2 on to the moulding station 9 with suitable moulds 10 in segment C. In station 9 as well, each sheet 2 in the holder 12 is situated directly opposite its own mould halves (in each mould cell 10) above and below the sheet 2. As a result of this arrangement, the energy consumption (inter alia for air pressure on the one hand, and vacuum on the other hand, in the moulds) according to the invention can be further reduced to a fraction of the consumption of the prior art technology. The deformation in the cooled moulds 10 may be carried out both positive and negative. With a positive deformation, e.g. the bottom of each object (e.g. receptacle) 3 is pushed upwards by a male moulding plunger (pre-stretched) with respect to the level of the sheet edges 13. A negative deformation occurs in the opposite direction (i.e. pushed downwards). These techniques are known per se. They permit a.o. quick and accurate formation and deformation of objects 3 having relatively sharp edges and corners and having smaller tolerances with regard to their wall thickness or having large or irregular or jagged curvatures in their surface. The residence time of the sheet 2 in the mould is a few seconds at most, depending on the sheet thickness and composition of the plastic of the sheets 2.
The moulded objects 3 are then passed from the moulding station 9 to the removal station 11 in segment E and deposited there. This removal operation is described below with reference to
Then, the first temporary coupling elements 42 for the sheets 2 can descend from the first grippers 30 to the plurality of the upper sheets 2, each in their stack 5, and lift these sheets 2 (via suction). These grippers 30 can then lift the carrying frame 161 with the sheets 2 (arrow 62) and move the carrying frame 161 horizontally (arrow 63) until it is situated above the transport frame 171 on the transport track 7 (left-hand side of
Subsequently, the second temporary coupling means 44 for the moulded three-dimensional objects 3 can descend from the second grippers 32 for coupling to (a part of) these objects 3. These second grippers 32 can then lift up the carrying frame 162 and the objects 3 from the transport frame 172 on the transport track 7 (arrow 72) and transport them horizontally (arrow 73) until they are above the deposition area 45 for the objects (right-hand side of
According to a particular aspect of the invention, the deposition operation of the carrying frame 162 (right-hand side of
Overall, a cycle using the described, highly productive device therefore comprises at least three simultaneous advancing steps and three simultaneous intervals for treatment in between: heating, moulding and simultaneously supplying and removing. More treatment intervals may be provided, either for introducing further actions, or for duplicating one or more of the treatment actions, such as for instance heating. At the end of each cycle, this embodiment will thus deliver a predetermined number of receptacles, preferably as many receptacles as there are mould openings 4 in the holder 12, e.g. six receptacles 3 in the embodiment illustrated. In concrete terms, this thus means the production of a plurality of receptacles 3 at a high frequency. After all, with regard to time, the successive cycles overlap greatly as, in phase, they continue at an interval of only one advancement step. Usually, multiple heating stations will be required. However, an increase of the number of heating stations 8 does not lower the removal frequency of these six moulded objects 3. If the moulding step (which typically requires the longest time and hence defines the dwell time in each of the stations) takes e.g. 2.5 s (seconds) and an advancement step takes 0.5 s, then six objects 3 are delivered every 3 s in this example, while the total time that each sheet/object spends in the device is the number of stations×2.5 s+(the number of stations−1)×0.5 s. A device according to embodiments of the present invention provides a very low energy consumption (e.g. reduced by about 80%), without waste of plastics material and with formation of dimensionally accurate objects, with small tolerances of up to 0.1 mm. Also during start-up, compared to prior art devices, less waste is being generated.
The moulded spatial objects 3 may be simple receptacles such as e.g. cups or boxes, but may also have a shape which is much more complicated. However, their protruding edges 27 are always located in the same plane. Thus, these edges 27 can also form a useful supporting frame for subsequently (after filling) providing and attaching (e.g. by heat-sealing) cover films to the receptacles. The invention also makes it possible to reduce changeover times (or switching times) for the device for producing other object shapes to a fraction of what they were in the past, partly due to the greatly simplified holders 12 for holding the outer edges 13 of the sheets 2 and the protruding edges 27 of the objects 3 and due to the individual moulds 10.
Finally, the use of an individual heating cell 14 and an individual mould 10 for each sheet 2 and object 3 also greatly increases the flexibility of the method. Simultaneously producing different object volumes and shapes per holder 12 only requires predetermined production parameters per heating cell 14 and per mould 10, for appropriate heating and moulding, respectively. This can quickly be solved by using individualized moulds 10. In addition, the carrying frame 17 and the transport frame 16 in the holders 12 can be provided with replaceable inserts for this purpose, for the edge perimeters 13 and 27 (e.g. round or polygonal) desired (per heating cell 14 and per mould 10).
To the person skilled in the art, these and numerous other variants are deemed to form part of the protection defined in the attached claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2013/0359 | May 2013 | BE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2014/060745 | 5/23/2014 | WO | 00 |
