Multi-layer co-extrusion head and method for manufacturing multi-layer products

Abstract

Describes a coextrusion head (1) comprising a plurality of inlets (11, 12, 13, 14, 15) for fluid products; internal confluence spaces (16, 17) located downstream of said inlets and communicating with said inlets through respective delivery conduits (110, 120, 130, 140, 150) to allow the product flows to converge at said internal confluence spaces; and an outlet (18) for the final multi-layer product, said outlet being located downstream of said internal confluence spaces (16, 17). In the head (1), there is a central delivery conduit (110) provided to receive a first product flow, and two lateral delivery conduits (120, 130) designed to receive a second product flow and a third product flow respectively. The head (1) further comprises adjustable constriction means (31, 32) which act at least in the central delivery conduit (110) and are designed to vary the corresponding openings to allow adjustment of the relative position of the first flow with respect to the composite secondary flow defined by the confluence of the first, second and third flows in the confluence space (16).

Description

Technical Field

[0001] The present invention relates to a multi - layer coextrusion head (multi - layer coextrusion head).

[0002] Specifically, the present invention is designed, in particular but not exclusively, for the preparation of coextruded materials, such as those that can be used in the packaging of food products, said coextruded materials comprising, in particular, a "barrier layer", that is to say, a layer that is impermeable to oxygen. Background Art

[0003] There are prior - art coextrusion heads for manufacturing multi - layer films made of plastic materials.

[0004] More specifically, particularly in the field of packaging food products such as, for example, single - dose coffee capsules, the prior art teaches the production by coextrusion of a film that includes an outer layer of polypropylene or another polyolefin, and a central barrier layer that is joined to the previous layer by a suitable adhesive layer.

[0005] The barrier layer can be ethylene - vinyl alcohol ("EVOH") or a different type of polymer that is impermeable to oxygen.

[0006] KR 20010064788 discloses a feedblock die for manufacturing laminated films using resins of different viscosities, which can prevent encapsulation due to a flow - path adjustment device. The feedblock die has a plurality of feed ports connected to respective flow paths, and the flow - path adjustment device can operate in the flow paths. Specifically, the flow - path adjustment device includes four variable chokes that act in the respective flow paths and are all located in the same plane.

[0007] JP S5528825 describes an extrusion die for multi - layer film production, which has two inlets connected to first and second distribution channels. A first thermoplastic synthetic resin intended to form an intermediate layer passes through the first distribution channel and is intercepted by a resistance rod that can thin the intermediate layer, for example, thin it in the center. A second thermoplastic synthetic resin intended to form the front and rear layers enters the second inlet and flows through the second and third distribution channels, in which the second thermoplastic synthetic resin is intercepted by a resistance rod in the shape of a needle valve.

[0008] JP S5260853 discloses a method and a die for forming multi - layer films using thermoplastic resins of different viscosities. The die includes five chokes that act at a common confluence point where the resin flows converge and are positioned and act on a single same plane.

[0009] Depending on the type of application, it may be desirable for the barrier layer to be eccentric with respect to one or more of its transverse extension directions, inside the film, or, in any case, more generally, the centering is suitably adjusted.

[0010] The market currently does not provide a coextrusion head that allows the above-mentioned requirements to be met in an exact and general way, thus fragmenting the market with respect to the various uses that a multi-layer film can have, which range from many applications in the food sector and reach sectors such as the agricultural, biomedical or packaging sectors. Summary of the Invention

[0011] Therefore, the technical object that forms the basis of the present invention is to provide a coextrusion head capable of overcoming the drawbacks of the prior art.

[0012] This object is achieved by using a coextrusion head manufactured according to claim 1 and a coextrusion method actuated according to claim 16.

[0013] The coextrusion head according to the present invention comprises a plurality of infeed ports (infeed, transverse feed, cross-cut, feed mechanism) for fluid products, and an inner joining space located downstream of said infeed ports and in communication with said infeed ports through respective conveying ducts to allow the flow of said products to flow into said infeed ports.

[0014] Furthermore, the head according to the present invention includes an outfeed downstream of the internal joining space, a central conveying duct provided to receive a first product flow, and two or more lateral conveying ducts provided to receive a second product flow and a third product flow respectively.

[0015] Then, the head comprises adjustable narrowing means that act at least in the central conveying duct and are designed to vary the corresponding openings, thereby allowing adjustment of the relative position of the first flow with respect to the composite flow formed inside the joining space.

[0016] Since the configuration of the opening of the duct of the first flow can be changed in an adjustable manner before the first flow joins the other two flows that the first flow encounters in the joining space, and thus determines the relative position between the first flow and the other two flows within the secondary flow formed by the first flow and the other two flows, the present invention makes it possible to obtain a final multi-layer product in which the relative position of one or more inner layers is established by the user according to needs. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In the case of a strip multi-layer product with a barrier layer in the sense used in the introduction, the present invention makes it possible to precisely establish how close or far the barrier layer is from the short side of the rectangular cross-section of the strip, and provides several advantageous results that will be explained in detail in the following description of a preferred non-limiting embodiment of the co-extrusion head according to the present invention, which preferred non-limiting embodiment is shown in the drawings, wherein:

[0018] - Figure 1 is a schematic view of an apparatus using the co-extrusion head according to the present invention;

[0019] - Figure 2 is a longitudinal cross-section of the co-extrusion head according to the present invention taken in a vertical plane;

[0020] - Figure 3 is a longitudinal cross-section of the head taken in a vertical plane perpendicular to the plane of Figure 3 ; and

[0021] - Figure 4 , Figure 5 , Figure 6 and Figure 7 are schematic representations of cross-sections of multi-layer products obtainable with the present invention according to various adjustments that can be made by the user. DETAILED DESCRIPTION

[0022] Referring to the drawings, the numeral 1 indicates a co-extrusion head manufactured according to the present invention.

[0023] The head 1 according to the present invention is in particular designed for use in the co-extrusion system 10 schematically illustrated in Figure 1 , which co-extrusion system includes a plurality of feed lines 21, 22, 23, 24, said feed lines being connected to the feed ports 11, 12, 13, 14, 15 of the head 1 (as shown in Figure 2 ), each line containing an extruder 211, 221, 231, 241 designed to supply an extruded fluid product, and a pump 212, 222, 232, 242, which pumps the extruded product flow into one or more of the feed ports 11, 12, 13, 14, 15 at an adjustable flow rate.

[0024] More specifically, each of the pipelines 21, 22, 23, 24 may include extruders 211, 221, 231, 241 upstream of the pumps 212, 222, 232, 242 mentioned above, and downstream of the pumps, static mixers 213, 223, 233, 243 are connected to one or more feed ports 11, 12, 13, 14, 15 of the head 1.

[0025] In the illustrated example, the coextrusion head 1 has five feed ports 11, 12, 13, 14, 15, and the five feed ports are connected to four feed pipelines 21, 22, 23, 24.

[0026] In its preferred application, the present invention includes: a first pipeline 24 for feeding an oxygen-impermeable extruded material stream such as ethylene-vinyl alcohol, which is connected to the central feed port 11 of the head 1; a second pipeline 24 for feeding an adhesive material, which bifurcates and is connected to two lateral infeed ports 12, 13; and a third pipeline 21 and a fourth pipeline 22 for feeding a plastic material such as polypropylene or other similar polymers, which are connected to the fourth lateral feed port 14 and the fifth lateral feed port 25.

[0027] Essentially, the present invention, although not uniquely, is particularly designed for manufacturing a multi-layer product having a rectangular cross-section ( Figures 4 to 7 marked as T in the figure), that is, a so-called "strip", and the multi-layer product includes a central oxygen-barrier layer E, one or more outer propylene layers P, and one or more inner layers of glue C inserted between the barrier layer E and the polypropylene P to allow mutual adhesion of the latter.

[0028] The continuous multi-layer product exiting from the head 1 according to the present invention can be sub-packaged to manufacture, for example, single-use coffee capsules or other applications in the food industry and other applications.

[0029] As will become clearer in the following description, in the case of the preferred application described above, the present invention advantageously allows the lateral position of the barrier layer E to be adjusted along the longitudinal direction of the cross-section T of the strip, that is, the adjustment of its distances a, b from the short side L1 of the cross-section itself.

[0030] It should be noted that using some preferred but non-bonding features, the present invention also allows the adjustment of the position of the barrier layer E in a direction orthogonal to the longitudinal direction K of the cross-section T as indicated above and the adjustment of the thickness of the layer.

[0031] As has been partially mentioned, Figure 1 、 Figure 2 and Figure 3The co-extrusion head according to the present invention as shown in the figure includes a plurality of feed ports 11, 12, 13, 14, 15 for extruding fluid products; at least one internal confluence space 16, 17 of the product flow, which is positioned downstream of the feed ports 11, 12, 13, 14, 15 and is in communication with the feed ports using corresponding and separate conveying ducts 110, 120, 130, 140, 150, so as to allow the product flows to converge at the at least one internal confluence space; and a discharge port 18 for the final multi-layer product, which is located downstream of the internal confluence spaces 16, 17.

[0032] Preferably, the head 1 is made of a metallic material and can be defined by a body 100 composed of two specular half-bodies, and the joining of the two specular half-bodies defines an internal duct in which the extruded material flow travels.

[0033] The body 100 can also utilize ducts to accommodate the adjustment devices described below.

[0034] In the head 1, there are a central conveying duct 110 and several lateral conveying ducts 120, 130, 140, 150. For example, a second lateral duct 120 and a third lateral duct 130 opposite the first central duct 110, and a fourth lateral conveying duct 140 and a fifth lateral conveying duct 150 that are again opposite the first duct 110 and are located more outward relative to the other ducts.

[0035] The first duct 110 accessed by the first feed port 11 conveys a barrier material flow, the second duct 120 and the third duct 130 convey glue received from the second feed port 12 and the third feed port 13, and the fourth duct 140 and the fifth duct 150 convey polypropylene accessed through the fourth feed port 14 and the fifth feed port 15.

[0036] The head 1 is preferably oriented such that the feed ports 11, 12, 13, 14, 15 are at the top and the discharge port 18 is at the bottom. Thus, the feed direction of the material flow is downward.

[0037] The first duct 110, the second duct 120 and the third duct 130 merge into a first internal confluence space 16, and the first internal confluence space is in communication with the second internal confluence space 17 through a confluence duct 171. Thus, there is also a drawing duct 181 between the second internal space 17 and the discharge port 18.

[0038] The discharge port 18 can be quadrilateral, and preferably, it is rectangular, so as to manufacture a final product with a strip-shaped multi-layer that has a rectangular cross-section.

[0039] The various conduits within the head 1 mentioned above may also have a substantially rectangular cross-section, at least over the main part of their length.

[0040] Preferably, the central delivery conduit 110, the first converging space 16, the converging conduit 171, the suction conduit 181, and the discharge port 18 are aligned to define a continuous central hydrodynamic path.

[0041] In addition, all the conduits may be defined in the same mid-plane of the co-extrusion head 1.

[0042] According to an important aspect of the present invention, the head 1 includes adjustable constriction devices 31, 32 that act at least in the central delivery conduit 110 and are designed to vary the corresponding openings to allow adjustment of the relative position of the first flow with respect to the composite secondary flow generated by the convergence of the first, second, and third flows in the converging spaces 16, 17.

[0043] In essence, the constriction devices 31, 32, which are controllable by the user in an adjustable manner and allow variation of the shape and size of the opening of the first conduit 110, i.e., the shape and size of its transverse cross-section, act in the cross-section 111 of the first central conduit 110, which is preferably located immediately before the outlet of this first central conduit in the first converging space 16.

[0044] This adjustment preferably involves changing the position at which the first flow, which preferably contains a barrier material, enters the inner converging space 16, which is defined in a cavity made in the body of the head 1.

[0045] Still more specifically, the cross-section or stretch 111 of the first conduit 110 in which the constriction device 31 operates is provided with a taper in the feed direction of the first flow, i.e., a constriction of the transverse dimension, which in practice is the vertical direction; the taper is defined in the direction of the length of the rectangular cross-section of the first conduit, which is parallel to the length direction of the rectangular cross-section of the first converging space 16.

[0046] The constriction device 31 acts in a direction transverse to the feed direction of the first flow that is parallel to the length (or longitudinal central axis) of the rectangular cross-section of the first converging space 16, such that the position of the first flow relative to the short side of the cross-section of the space 16 can be adjusted.

[0047] The dimensions of the first converging space 16 are selected such that the space not occupied by the first flow is occupied by the second and third flows.

[0048] According to a preferred embodiment of the present invention, the constriction devices 31, 32 include at least two opposite throttling elements 311, 312, 321, 322, i.e., opposite to each other, and the opposite throttling elements are independently movable so as to change the transverse cross-section of the first conduit 110.

[0049] The throttling elements 311, 312, 321, 322 are guided in a rectilinear movement manner along the longitudinal direction of the above-mentioned cross-section 111 of the first conduit 110 and can be operated, for example, by corresponding screws 313, 314, 323, 324, the heads of which are externally accessible.

[0050] Preferably, each throttling element has a shaped head 311, 312, 321, 322 which is designed to move between a retracted position (with the shaped head positioned outside the conduit 110) and a plurality of advanced positions where the shaped head penetrates inside the conduit in the first conduit 110, thereby modifying the opening.

[0051] Still more specifically, the shaped heads 311, 312, 321, 322 of the throttling elements can be equipped with a wall facing the inner side of the conduit acting on the shaped head, and this wall is inclined with respect to the central axis of the conduit itself, i.e., inclined with respect to the vertical axis feeding the flow, so as to define a cone downwardly or in any case in the same direction as the feeding direction.

[0052] As mentioned above, the first inner confluence space 16 and the second inner confluence space 17 communicate with each other through the confluence conduit 171, and a secondary flow formed by a blocking and adhesive layer flows in this confluence conduit, and the fourth delivery conduit 14 and the fifth delivery conduit 15 also lead to the second confluence space 17.

[0053] There is also a second constriction device 32 which is preferably equivalent to the first device 31 described above and acts in the confluence conduit 171, upstream of the second confluence space 17.

[0054] Essentially, apart from the adjustment of the relative position of the above-mentioned secondary flow within the joint composite flow, preferably composed of polypropylene, formed in the second convergence space 17 together with the fourth and fifth product flows by the second constriction device 32, the things stated regarding the shape and function of the first constriction device 31, the shape and function of the cross-section 111 of the first conduit 110 in which the first constriction device acts, and the shape and function of the first convergence space 16 apply equally to the second constriction device 31, to the corresponding cross-section of the convergence conduit 171 in which the second constriction device acts (which corresponding cross-section may or may not substantially coincide with the convergence conduit 171), and to the second convergence space 17.

[0055] Due to the second constriction device 32, the distances c and d between the short side L1 of the cross-section T of the inner three-layer core glue-barrier-glue and the strip can be determined.

[0056] Furthermore, the head 1 according to the invention may also comprise means for varying the adjustable thicknesses 41, 42, 43, 44, which means are designed to act in the lateral conduits 120, 130, 140, 150 and to adjust the thickness of the second and / or third and / or fourth and / or fifth product flows.

[0057] More precisely, the varying means may comprise shaped elements 41, 42, 43, 44 which are operable individually and are equipped with a plurality of active members of different sizes, which active members can be selectively positioned in the respective lateral conduits.

[0058] For example, the shaped element may consist of shaped pins 41, 42, 43, 44 provided with a plurality of lateral surfaces of different sizes spaced at angular intervals to allow selection by rotating the pins.

[0059] Preferably, the throttling elements 311, 312, 321, 322 of the above-mentioned constriction devices 31, 32 are positioned and act in a plane transverse to the plane in which the active members of the shaped elements 41, 42, 43, 44 for varying the thickness are positioned and act.

[0060] For this reason, varying the above-mentioned surfaces, or the dimensions of other active members of the means for varying the thicknesses 41, 42, 43, 44, varies the lateral dimensions of the lateral conduits 120, 130, 140, 150 carrying the glue flow or the polypropylene flow, thereby determining the thickness in the width direction Z of the rectangular cross-section T of the strip.

[0061] The operation of the invention is described below.

[0062] Depending on the specific application of the multi-layer product, the operator adjusts the four screws 313, 314, 323, 324 of the shrinkage devices 31, 32 (or operates under a command to automatically adjust these devices), so as to properly position the forming pins 41, 42, 43, 44, and the forming pins adjust the device for varying thickness and select the flow rate of the pump, specifically referring to the flow rates of the pumps 212, 222 of the pipelines 21, 22 for feeding polypropylene.

[0063] Then, the device starts to send the extruded material flow to the feed ports 11, 12, 13, 14, 15 of the head 1 for manufacturing the multi-layer product.

[0064] The barrier layer flow descends through the first conduit 110 and encounters the first adjustment device 31; based on how the screws 313, 314 have been positioned, the intercepting elements 311, 312 define a specific configuration of the opening of the conduit 110, and this specific configuration determines the way the first flow of the barrier material enters the first confluence space 16, and thus how the first flow is positioned relative to the glue flow in the secondary flow in the length direction of the cross-section of the glue flow.

[0065] Meanwhile, based on how the pins 41, 42 of the first thickness adjustment device are oriented, the two glue flows find different openings of the corresponding conduits 12, 13, and in the composite secondary flow, the corresponding layers adopt a specific thickness, and in the direction of the width Z of the cross-section T thereof, the thickness of the barrier layer E is also automatically established at this specific thickness.

[0066] At this time, the composite flow descends along the confluence conduit 171, where the composite flow encounters the second adjustment device 32, and the second adjustment device determines the mode in which the composite flow enters the second confluence space 17, thereby also determining its position in the direction of the length J of the cross-section K of the confluence flow formed by meeting the polypropylene flow.

[0067] For a clearer understanding of how the position of the inner layer in the strip can be adjusted, reference can be specifically made to Figures 4 to 7 .

[0068] When none of the intercepting elements 311, 312, 321, 322 are fed into the corresponding conduits 110, 171 by the user, for example, by acting on the above-mentioned screws 313, 314, 323, 324, and thus the shrinkage devices 31, 32 are inactive, the layers are positioned in the product produced by the head 1 in the manner shown in Figure 7 .

[0069] In fact, in this situation, the barrier layer E is not laterally limited by the heads of the corresponding two shut-off elements 311, 312, and thus has the same length as the adhesive layer C in the transverse direction Z. If the shut-off elements 321, 322 of the second shrinking device 32 remain inactive, the same applies to the core with three central layers of adhesive-barrier-adhesive relative to the polypropylene P.

[0070] If only the first shrinking device 31 is switched on, the Figure 4 configuration is obtained. If only the second device 32 is active, the cross-section of the strip is as shown in Figure 6 , and finally, in the case where all shrinking devices 31, 32 are active, the Figure 5 configuration is achieved.

[0071] At the same time, the polypropylene has undergone two adjustments, one related to its thickness using the pins 43, 44 of the specific device described several times, and one related to the flow rate difference of the corresponding pumps 212, 222 that affects the relative position of the barrier E and adhesive C layers in the direction of the width Z of the cross-section T of the composite product stream, i.e., one perpendicular to the adjustment direction of the shrinking devices 31, 32.

[0072] In fact, based on the gradient and sign of the difference between the two flow rates, there is a greater or lesser thrust on the inner core formed by the barrier E and adhesive C layers through the polypropylene in one direction or the other.

[0073] In this way, specifically, it is possible to determine as needed the distances x, y between the barrier layer E and the long sides L2 of the cross-section T of the multi-layer or strip product.

[0074] At this time, there precisely emerges from the rectangular outlet 18 a multi-layer strip having the configuration required for use.

[0075] The present invention relates to a co-extrusion method for manufacturing multi-layer products, which can be actuated by the co-extrusion head 1 according to the present invention.

[0076] The method comprises the following steps:

[0077] - Providing at least a first extruded product stream, a second extruded product stream, and a third extruded product stream;

[0078] - Converging the three product streams such that the first product stream intervenes between the second product stream and the third product stream, thereby obtaining a composite secondary product stream having a rectangular cross-section;

[0079] - Adjusting the position of the first product stream relative to the second product stream and / or relative to the third product stream at least along the longitudinal line of the cross-section of the composite secondary product stream.

[0080] Preferably, the step of adjusting the position of the first product stream is carried out by adjusting the cross-section before the step of merging with the second and third product streams.

[0081] The third and fourth product streams can also be made available, and in this case, the method comprises the steps of:

[0082] - Merging the composite secondary product stream obtained by merging the first, second, and third product streams with the third and fourth product streams such that the secondary product stream is interposed between the third and fourth product streams, thereby obtaining a composite merged product stream; and

[0083] - Adjusting the position of the secondary product stream relative to the third and / or fourth product streams at least along the longitudinal line of the cross-section of the composite merged product stream.

[0084] Preferably, the step of adjusting the position of the secondary product stream is carried out by adjusting the cross-section before the step of merging with the fourth and fifth product streams.

[0085] In an embodiment of the method implemented by the apparatus described above, the first product stream consists of an oxygen-impermeable material, the second and third product streams consist of an adhesive material, and the fourth and fifth product streams consist of a polymer, preferably polypropylene.

[0086] Preferably, the present invention comprises the step of adjusting the thickness of the layer of adhesive C and / or polypropylene P (i.e., more generally, the thickness of the second and / or third and / or fourth and / or fifth layer), wherein the cross-section of the corresponding product stream is adjusted in a direction transverse to the direction affected by the above-mentioned step of adjusting the position before merging to define the second composite product stream and / or the third composite product stream.

[0087] Essentially, before the adhesive-converging barrier layer product stream and / or the polypropylene and adhesive-barrier-adhesive three-layer product stream are merged together, the relative product streams undergo a change in the transverse dimension of the corresponding product streams such that in the final product, there is a layer having a dimension in the direction Z parallel to the short side L1 of the cross-section T of the strip as established by the user according to need.

[0088] Furthermore, based on the principles already explained during the description of the operation of the coextrusion head 1 according to the present invention, the relative position of the inner adhesive-barrier-adhesive layer in the direction Z parallel to the short side L1 of the cross-section T of the multi-layer product can be adjusted by varying the flow rate difference of the polypropylene stream (or using other materials in the fourth and fifth product streams).

[0089] Finally, the preferred features of the apparatus according to the present invention are described below.

[0090] In the step for starting or stopping the device and in the transient step between the co - extrusion of two different types of multi - layer products, the device 10 is started for the step of cleaning the ducts, or the step of "purge", as known in the trade.

[0091] During this step, the material exiting from head 1 will be considered as waste and must be directed towards the disposal container and not towards nozzle 19; on the other hand, when the normal activity of the device restarts, the multi - layer product exiting from head 1 must be sent to distribution nozzle 19 or, in any case, to its production destination.

[0092] The routing device 5, defined as a bypass, has been designed to allow the selective routing of the product at the outlet from head 1 to nozzle 19 or to a container provided with a "gate" which comprises a movable body 51 in which two routing connectors 52, 53 are made, which allow the passage of the multi - layer product.

[0093] The first connector 52 is linear and coaxial with the feeding direction of the strip at the outlet 18 from head 1 and, therefore, is vertical in practice.

[0094] The second connector 53, located next to the first connector, can be linear and has a longitudinal axis inclined with respect to the longitudinal axis of the first connector 52.

[0095] The gate 51 can move between at least two positions upon actuation of a translation device 54 such as a hydraulic or pneumatic actuator or similar moving means, one of the at least two positions being the operating position in which the first duct 52 is aligned with the outlet 18 of head 1 and with the inlet of nozzle 19, and one of the at least two positions being the preparation position in which the inlet of the second duct 53 faces directly the outlet 18 of head 1 and allows the waste product to be directed towards the collection container.

Claims

1. A coextrusion head (1), comprising a plurality of inlets (11, 12, 13, 14, 15) for fluid products; at least one inner converging space, said at least one inner converging space being located downstream of said inlets and being in communication with said inlets through respective delivery conduits so as to allow the flow of said products to converge at said at least one inner converging space; and an outlet (18) for the final multi-layer product, said outlet being located downstream of said inner converging space, wherein, in said coextrusion head (1), there is a central delivery conduit provided for receiving a first product flow; and at least two lateral delivery conduits provided for receiving a second product flow and a third product flow respectively, said coextrusion head (1) comprising: an adjustable constriction device which acts at least in said central delivery conduit and is adapted to vary its relative opening to allow adjustment of the relative position of said first product flow with respect to a composite secondary product flow defined by the convergence of said first product flow, said second product flow and said third product flow in said inner converging space; and an adjustable thickness variation device adapted to act in said lateral delivery conduits and adapted to adjust the thickness of the second and / or third and / or fourth and / or fifth product flows; wherein said adjustable thickness variation device comprises at least respective shaping elements (41, 42, 43, 44), each of said shaping elements being provided with a plurality of movable members having different sizes, said movable members being selectively positionable in the relative conduits; The coextrusion head is characterized in that, in the same plane as the plane in which the movable members of said shaping elements (41, 42, 43, 44) of said adjustable thickness variation device are positioned and act, a throttling element of said adjustable constriction device is positioned and acts.

2. The coextrusion head (1) according to claim 1, wherein, said adjustable constriction device comprises at least two opposite throttling elements which are independently movable.

3. The coextrusion head (1) according to claim 1 or 2, wherein, each throttling element has a shaping head (311, 312, 321, 322) adapted to move between a retracted position and a plurality of advanced positions in the respective conduit, in said retracted position said shaping head being located outside the conduit and in said advanced position said shaping head penetrating the conduit.

4. The coextrusion head (1) according to claim 3, wherein, the shaping head (311, 312, 321, 322) of said throttling element is provided with a wall facing the inside of the relative conduit, said wall being angled with respect to the central axis of the same conduit so as to define a cone in the downstream direction there.

5. The co-extrusion head (1) according to claim 1 or 2, comprising at least one suction conduit (181) defined between the inner convergence space and the discharge port (18), the central delivery conduit, the inner convergence space and the suction conduit (181) being aligned to define a central continuous path towards the discharge port (18).

6. The co-extrusion head (1) according to claim 5, comprising at least five feed ports (11, 12, 13, 14, 15), wherein, one is a central feed port and four are lateral feed ports, the at least five feed ports being provided for receiving respective fluid products, the respective fluid products entering the central delivery conduit, which is the first conduit (110), and four lateral delivery conduits; and further comprising a first inner convergence space (16) and a second inner convergence space (17), the first inner convergence space and the second inner convergence space being in communication through a convergence conduit (171), wherein the second lateral delivery conduit (120) and the third lateral delivery conduit (130) on opposite sides of the first conduit (110) lead to the first inner convergence space (16), and the fourth lateral delivery conduit (140) and the fifth lateral delivery conduit (150) on opposite sides of the first conduit (110) lead to the second inner convergence space (17); first adjustable constriction means (31) and second adjustable constriction means (32) are also provided, the first adjustable constriction means and the second adjustable constriction means acting respectively in the central delivery conduit, upstream of the first inner convergence space (16), in the convergence conduit (171), upstream of the second inner convergence space (17), the second adjustable constriction means (32) being adapted to vary the opening of the convergence conduit (171) to allow adjustment of the relative position of the composite secondary product stream in the converging composite product stream, the converging composite product stream being defined in the second inner convergence space (17) and containing fourth and fifth product streams respectively entering the fourth lateral delivery conduit (140) and the fifth lateral delivery conduit (150).

7. The co-extrusion head (1) according to claim 1 or 2, wherein, the adjustable constriction means acts in the widening of the respective conduit, the respective conduit being provided with a taper in the forward movement direction of the product stream.

8. The co-extrusion head (1) according to claim 6, wherein, the convergence conduit (171) and the second inner convergence space (17) are aligned with the central delivery conduit, the convergence conduit (171) and the second inner convergence space (17) are aligned with the first inner convergence space (16) and the convergence conduit (171) and the second inner convergence space (17) are aligned with the suction conduit (181), the suction conduit being located downstream of the second inner convergence space (17), thereby defining the same central continuous path.

9. The co-extrusion head (1) according to claim 1 or 2, wherein, The discharge port (18) is rectangular.

10. The coextrusion head (1) according to claim 1 or 2, wherein, one or more of the inner converging spaces have a rectangular cross-section and the adjustable constriction means act along a line parallel to the longitudinal line of the cross-section, whereby the product streams affected by the same adjustable constriction means are adjusted as to how close or far they are from the short side of the cross-section.

11. A coextrusion apparatus, comprising the coextrusion head (1) according to any one of claims 1 to 10 and further comprising a plurality of feed lines (21, 22, 23, 24), the plurality of feed lines being connected to the feed ports (11, 12, 13, 14, 15), each of the lines comprising an extruder (211, 221, 231, 241) adapted to supply an extruded fluid product and a pump (212, 222, 232, 242) having an adjustable flow rate, the pump feeding an extruded product stream into at least one of the feed ports (11, 12, 13, 14, 15).

12. An apparatus, comprising the coextrusion head (1) according to claim 6 and further comprising a plurality of feed lines (21, 22, 23, 24), wherein, one of the plurality of feed lines (24) is connected to the central delivery conduit and two feed lines (21, 22) are respectively connected to the fourth lateral delivery conduit (140) and the fifth lateral delivery conduit (150) to allow for a change in the flow rate in the fourth and fifth product streams to change the relative position of the first, second and third product streams that are converging with respect to the fourth and fifth product streams.

13. A coextrusion method for manufacturing a multi-layer product, comprising the steps of: making at least a first product stream, a second product stream and a third product stream available; converging the three product streams such that the first product stream is between the second product stream and the third product stream, whereby a composite secondary product stream having a rectangular cross-section is obtained; adjusting the position of the first product stream at least along the longitudinal line of the cross-section of the composite secondary product stream with respect to the second product stream and / or with respect to the third product stream; making a fourth product stream and a fifth product stream available; converging the composite secondary product stream obtained by converging the first product stream, the second product stream and the third product stream with the fourth product stream and the fifth product stream such that the composite secondary product stream is between the fourth product stream and the fifth product stream, whereby a converged composite product stream is obtained; and adjusting the position of the composite secondary product stream at least along the longitudinal line of the cross-section of the converged composite product stream with respect to the fourth product stream and / or with respect to the fifth product stream, The method is characterized in that the thickness of the second layer and / or the third layer and / or the fourth layer and / or the fifth layer is adjusted, wherein, before converging to define the composite secondary product stream and / or the converging composite product stream, the transverse cross-section of the corresponding product stream is adjusted in a direction transverse to the direction affected by the step of adjusting the above-mentioned position.

14. The method according to claim 13, wherein, the step of adjusting the position of the first product stream is carried out by: adjusting the cross-section of the first product stream before the step of converging the second product stream and the third product stream.

15. The method according to claim 13 or 14, wherein, the step of adjusting the position of the composite secondary product stream is carried out by: adjusting the cross-section of the composite secondary product stream before the step of converging the fourth product stream and the fifth product stream.

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