BE1001610A4 - EXTRUDER DIE FOR MANUFACTURING A MULTI-blown film. - Google Patents

Abstract

... from several laminated thermoplastic materials comprising a lower part of the die (1) equipped with a device for supplying several flows of plastic material via several supply conduits (2) an upper part of die (3) with annular outlet slot (4) for the exit of a flow of multilayer plastic material in the form of a sheath, a die core (5) and a laminating device (6). Transfer channels (7, 8) in the form of an annular slot are arranged in the upper (3) and lower (1) parts of the die.

Description

       

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  "Extruder die for the production of a multi-layer blown sheet"
The invention relates to an extruder die for the production, by co-extrusion, of a multi-layer blown sheet from several laminated thermoplastic materials, comprising a lower die part equipped with a device for feeding multiple streams. of plastic material via several supply conduits, an upper part of the die with an annular outlet slot for the exit of a flow of plastic material. multilayer in the form of a sheath, a die core and a laminating device, transfer channels in the form of an annular slot being arranged in the lower and upper parts of the die.

   The term stratification device is understood to mean the sum of the mechanical measurements which ensure stratification without mixing. This includes taking into account the mass fluxes which add up during the stratification and the prevention of the appearance of shearing forces between the different layers by differences in speeds or similar measurements. It goes without saying that in the extruder die of the aforementioned kind, the lower and upper parts of the die are arranged in symmetry of revolution about the axis of the die, with the exception of the supply conduits. Similarly, the transfer channels and the annular outlet slit are also shaped to be symmetrical in revolution.

   In addition, it goes without saying that the core may include a supply air supply system and possibly also a supply air exhaust system when it comes to the production of blown sheets.

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   In the extruder die of the type described, well known in the art, the supply conduits of the lower part of the die open respectively into a particular transfer channel. The stratification device is located in the upper part of the die. 11 consists of a plurality of helical distributors corresponding to a plurality of plastic flows, which are nested one inside the other and connected to the plurality of transfer channels which is followed by a channel narrowing conically in the direction of the annular outlet slot in which the actual stratification occurs.

   The propeller distributors are mounted upstream because the transfer channels for the plurality of plastic flows are divided in the upper part of the die by core bars which immobilize or support the core. Inconvenient influences on the plastic flows must be removed in the vane distributors before they can be laminated in such a way that, on this point, the vane distributors are part of the laminating device and make it complicated and expensive. Failure-free service time is often insufficient because plastic can become trapped in the vane valves.

   In this case, it is necessary to carry out an expensive disassembly of the propeller valves fitted together; cleaning and reassembly.



   The object of the present invention is to improve an extruder die of the aforementioned kind in such a way that it is no longer necessary to provide an upper die part with a plurality of nested propeller distributors.



   According to the invention, this object is achieved by the fact that the supply conduits open into a single transfer channel in the form of an annular slot devoid of core strips and surrounding the core of the die, said transfer channel being shaped as layering device, and

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 that the annular outlet slot is connected to the laminating device by means of a single transfer channel, without core bars, from the upper part of the die. The invention takes advantage of the discovery that it is not necessary for an extruder die of the type described above to place the laminating device in the upper part of the die, shortly before the annular outlet slot.

   By accommodating the stratification device in the lower part of the die and by adopting, moreover, the arrangement described, it is astonishing to note that no mixing occurs on the subsequent course of the flow of multilayer plastic material, between th device laminate and the annular outlet slot.



  In addition, the invention takes advantage of the fact that bars are no longer necessary for holding or fixing the core of the die when the supply conduits open into the single transfer channel in the form of an annular slot which surrounds the core of the industry.



   For the extruder die according to the invention, it may be advantageous to adapt the thickness of the annular outlet slot to the special operating conditions and to the plastics used. For this, it is provided according to the invention that the annular outlet slot is shaped as the mouth of a conical section of the transfer channel in the upper part of the die, which is arranged between an upper nozzle element and a lower nozzle element. The width of the annular outlet slot can then be variable by adjusting or replacing at least one of the nozzle elements. This Operation can also be carried out during production and influenced by measurements relating to the adjustment technique.

   To ensure uniform conditions everywhere on the circumference of the blown sheet, which also includes a regular resistance to flow for the flow of laminated plastic material, the invention recommends placing in the transfer channel, in the direction of flow of the multilayer plastic flow and upstream of the conical section of the transfer channel, undulations which extend essentially in the circumferential direction.

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   The advantages obtained reside in the fact that, while dispensing with vane distributors nested one inside the other, the extruder die according to the invention allows without difficulty the production of multi-layer blown sheets produced from the most thermoplastic materials. various. In addition, the extruder die according to the invention can be produced easily and maintained without great expense.



   The description which follows, with reference to the attached drawing by way of nonlimiting example, will make it possible to understand clearly how the invention can be put into practice.



   The single figure shows an axial section of one half of an extruder die according to the invention comprising the supply conduits.



   The extruder die shown in the figure is intended for the manufacture, by co-extrusion, of a multi-layer blown sheet from several laminated thermoplastic materials. It basically comprises a lower part of the die 1 with a device for supplying several plastic material flows, via a plurality of supply conduits 2, an upper part of the die 3 with an annular outlet slot. 4 for the outlet of a flow of multilayer plastic material in the form of a sheath, a die core 5 and a stratification device 6.



   There are, moreover, transfer channels 7,8 one of which 7 is arranged in the lower part of die 1, while the other 8 is located in the upper part of die 3. The transfer channel 8 of the upper die 3 opens into the annular outlet slot 4.



   The supply conduits 2 open into the single transfer channel 7, in the form of an annular slot, in the lower part of die 1, which surrounds the die core 5 and which is devoid of core bars. It is clear from the drawing that this transfer channel 7 is configured as a stratification device 6, that is to say in such a way that the mass fluxes can add up.

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  In terms of design, care was then taken to ensure that shear forces between the different plastic flows are avoided by differences in speed or similar measures. The annular outlet slot 4 is connected to this laminating device 6 by means of a single transfer channel 8 without core bars in the upper part of the die.

   In the embodiment and according to a preferred embodiment of the invention, the arrangement has been chosen in such a way that the annular outlet slot 4 is shaped into a mouth of a conical section 9 of the transfer channel 8 in the upper part of die 3, which section is arranged between an upper nozzle element 10 and a lower nozzle element 11. The width of the annular outlet slot 4 can therefore be modified by adjusting or replacing at least 1 'one of the nozzle elements 10,11.

   Viewed in the direction of flow of the multilayer plastic flow, corrugations 1. which extend essentially in the circumferential direction and are visible in the part of the drawing shown on a larger scale, are arranged in the transfer channel 8 , upstream of the conical section 9 of the transfer channel 8.


    

Claims (3)

 CLAIMS 1. Extruder die for the production, by co-extrusion, of a multi-layer blown sheet from several laminated thermoplastic materials comprising a lower die part equipped with a device for feeding several plastic flows by the intermediary of several supply conduits, an upper part of a die with an annular outlet slot for the exit of a flow of multilayer plastic material in the form of a sheath, a die core and a laminating device, transfer channels in the form of an annular slot being arranged in the lower and upper parts of the die, characterized in that the inlet conduits (2) open into a transfer channel (7)  single in the form of an annular slot in the lower die part (1), said transfer channel (7) surrounding the die core (5) and being shaped as a laminating device (6), and that the annular outlet slot ( 4) is connected to the stratification device (6) via a single transfer channel (8) without core bars provided in the upper die part (3).  2. extruder die according to claim l, characterized in that the annular outlet slot (4) is shaped as a mouth of a conical section (9) of the transfer channel (8) in the upper die part ( 3) and arranged between an upper nozzle element (10) and a lower nozzle element (11), and that the width of the annular outlet slot (4) can be modified by adjusting or replacing at least one nozzle elements (10, 11).  3. Extruder die according to claim 2, characterized in that, seen in the direction of flow of the flow of multilayer plastic material, corrugations (12), which extend essentially in the circumferential direction. are arranged in the transfer channel (8), upstream of the conical section (9) of said transfer channel (8).