METHOD AND DEVICE FOR PROCESSING POLYCONDENSATES

Abstract

A method for processing polycondensates, wherein the material in the form of granules or recyclate is processed to form a melt, the method including the following steps: a) feeding the material into a vacuum lock where the material is held below atmospheric pressure; b) conveying the material from the vacuum lock into a first extruder having a filling region and a feed zone that are held below atmospheric pressure, wherein the material is at least partially melted in the first extruder; c) conveying the melted material from the first extruder into a second, twin-screw extruder with two screws that turn in the opposite direction. The second extruder has at least one degassing zone and a metering zone that follows in the conveying direction. The melted material is degassed in the degassing zone and the melted material is pressurized in the metering zone and is output out of the second extruder.

Claims

1-25. (canceled)

26. A method for processing polycondensates, especially polyethylene terephthalate, wherein the material in the form of granules or in the form of recyclate is processed to form a melt, wherein the method comprises the following steps: a) feeding the material into a vacuum lock in which the material is held at a pressure lower than the atmospheric pressure; b) conveying the material from the vacuum lock into a first extruder that has a filling region and a feed zone, wherein the filling region and the feed zone are held at a pressure lower than the atmospheric pressure and wherein the material is at least partially, preferably completely, melted in the first extruder; c) conveying the at least partially melted material from the first extruder into a second extruder, wherein the second extruder is designed as a twin-screw extruder and the two screws thereof are turned in the opposite direction, wherein the second extruder comprises at least one degassing zone and a metering zone that follows in the conveying direction, wherein the melted material is degassed in the degassing zone and the melted material is pressurised in the metering zone and is output out of the second extruder.

27. The method according to claim 26, wherein a metering element is arranged between the vacuum lock and the first extruder, wherein the material being conveyed from the vacuum lock into the first extruder at a predetermined mass or volume flow.

28. The method according to claim 27, wherein the material is conveyed from the metering element into the first extruder with such a mass or volume flow that the feed zone of the first extruder is not completely filled with material, preferably with at most 95% of the maximum filling quantity, particularly preferably with at most 90% of the maximum filling quantity.

29. The method according to claim 26, wherein the pressure in the vacuum lock and/or in the filling region of the first extruder is at most 100 mbar, preferably between 0.1 mbar and 10 mbar.

30. The method according to claim 26, wherein the pressure in the degassing zone of the second extruder is at most 100 mbar, preferably at most 30 mbar.

31. The method according to claim 26, wherein a single-screw extruder is used as the first extruder.

32. The method according to claim 26, wherein the material is filtered between the first extruder and the second extruder.

33. The method according to claim 26, wherein the material is filtered after the second extruder.

34. The method according to claim 26, wherein the viscosity of the material between the first extruder and the second extruder is measured by means of a rheometer.

35. The method according to claim 26, wherein the viscosity of the material downstream of the second extruder is measured by means of a rheometer.

36. The method according to claim 34, wherein, depending on the measured viscosity of the material downstream of the first extruder and/or downstream of the second extruder, at least one process parameter is changed, preferably in a closed control loop.

37. The method according to claim 36, wherein the process parameter is the negative pressure in the filling region and/or in the feed zone of the first extruder.

38. The method according to claim 36, wherein the process parameter is the negative pressure in the degassing zone of the second extruder.

39. The method according to claim 26, wherein means for increasing the pressure, in particular a melt pump, is arranged downstream of the second extruder and the pressure in the material is increased by this means.

40. The method according to claim 26, wherein the material is dried before the material is fed into the vacuum lock, in particular by means of a vacuum dryer or an infrared dryer.

41. The method according to claim 26, wherein, after the material has been fed into the vacuum lock, an increase in the viscosity of the material is carried out by solid state polycondensation.

42. The method according to claim 26, wherein, after melting the material in the first extruder and/or in the second extruder, the viscosity of the material is increased by liquid state polycondensation.

43. A device for processing polycondensates, in particular polyethylene terephthalate, with which the material can be processed into a melt in the form of granulate or in the form of recyclate, comprising: a first extruder comprising a filling region and a feed zone, and a second extruder downstream of the first extruder, wherein the second extruder being designed as a twin-screw extruder and the second extruder having at least one degassing zone, comprising a vacuum lock in which the material can be kept under a reduced pressure compared to the atmospheric pressure, wherein the first extruder being downstream of the vacuum lock, wherein in the second extruder the two screws are designed to rotate in opposite directions and wherein the second extruder has a metering zone following the degassing zone in the conveying direction.

44. The device according to claim 43, wherein a metering element for conveying the material with a predetermined mass or volume flow is arranged between the vacuum lock and the first extruder.

45. The device according to claim 43, wherein the first extruder is a single-screw extruder.

46. The device according to claim 43, wherein a filter is arranged between the first extruder and the second extruder.

47. The device according to claim 43, wherein a filter is arranged downstream of the second extruder.

48. The device according to claim 43, wherein a rheometer for measuring the viscosity of the material is arranged between the first extruder and the second extruder.

49. The device according to claim 43, wherein a rheometer for measuring the viscosity of the material is arranged downstream of the second extruder.

50. The device according to claim 43, wherein means for increasing the pressure, in particular a melt pump, are arranged downstream of the second extruder.

Description

[0047] The drawing shows an example of an embodiment of the invention. The single FIGURE schematically shows the structure of a device for producing a melt from a granulate or recyclate of PET.

[0048] The FIGURE shows a device with which a starting material M in the form of a granulate or a recyclate is processed into a melt S. A plastic film, for example, can then be produced from the melt S, for which purpose a nozzle 12 for flat film extrusion is schematically indicated.

[0049] The material M is fed via a feed hopper 13 to a vacuum lock 1, which keeps the material M under a reduced pressure compared to the ambient pressure. It is indicated that the area of the vacuum lock 1 discharges gas G. In principle, the vacuum lock 1 operates by means of two sliders 19 and 20, through which a hermetically sealed space can be created which can be evacuated by means of a pump (not shown). By controlling the sliders 19, 20 accordingly, the material M can thus be kept under a negative pressure. When the slider 20 is opened, the negative pressure is accordingly also propagated downwards in the direction of a dosing element 8.

[0050] Following the vacuum lock 1, i.e. still under negative pressure, the material M reaches the metering element 8, which is driven by a drive motor 14 and which, in the shown embodiment, is designed as a screw conveyor unit. With the metering element 8, a predetermined amount of material M can be conveyed per time and fed to the further process. Gas G is further extracted from the material M by the vacuum that is also applied in the area of the metering element 8.

[0051] From the metering element 8, the material M enters a first extruder 2, which has a filling region 3 and a feed zone 4. The first extruder 2 is driven by a drive motor 15 and a gearing 16. In the first extruder 2, the material M is fed with such a mass or volume flow (mass or volume of material M per time) that the screw channels of the first extruder are only partially filled (underfed mode). At the same time, the material M is melted by the rotation of the screw of the first extruder 2 and by a heating of the screw barrel of the extruder 2, which is not shown.

[0052] Due to the only partial filling of the screw channels in the feed zone of the first extruder 2, an effective degassing of the material M can take place, which is indicated in the FIGURE (removal of the gas G). The degassing of the material M therefore takes place against the conveying direction of the first extruder 2. The degassing thus takes place via the feed opening or the metering element 8. In the second section of the screw of the first extruder 2, which follows the feed zone 4 in the conveying direction, the material is compressed, melted and homogenised. Furthermore, the necessary pressure build-up takes place here in order to convey the polymer melt further.

[0053] The now melted material M passes at the end of the first extruder 2 into a second extruder 5, which is designed as a twin-screw extruder with counter-rotating screws. The second extruder 5 is driven by a drive motor 17 via a gearing 18 (i.e. namely the two screws of the extruder) and has a degassing zone 6 and a metering zone 7. In the degassing zone 6, a further discharge of gas G from the melt takes place. In the metering zone 7, pressure is built up in the melt in order to convey the melt out of the second extruder 5. The second extruder 5 thus ensures degassing of the melt as well as material discharge and pressure build-up in the material M.

[0054] Behind the second extruder 5 a filter 9 is indicated, which filters the melt S. However, there is no longer a melt pump downstream of the second extruder 5, as the required pressure in the melt is built up by the second extruder 5.

[0055] A first rheometer 10 is arranged between the first extruder 2 and the second extruder 5, which measures the viscosity of the melt at this location. Similarly, a second rheometer 11 is arranged behind the second extruder 5, which also measures the viscosity of the melt.

[0056] The viscosity of the melt at the respective locations of the two rheometers 10, 11 can be taken into account in the closed loop control when controlling the system, in particular to influence the vacuum in the vacuum lock 1 and thus ensure that the melt S leaves the system with a defined quality.

[0057] Thus, starting from material M in the form of granulate or recyclate (in particular in the form of bottle or film regrind), the production of granulate, of films, of fibres, of filaments or of other plastic products and semi-finished products can take place.

[0058] Cascade extrusion can be extended, for example by implementing another filter between the first and second extruder. Likewise, instead of a single-screw extruder, a co-rotating twin-screw extruder can be used as the first extruder 2.

LIST OF REFERENCES

[0059] 1 Vacuum lock [0060] 2 First extruder [0061] 3 Filling region of the first extruder [0062] 4 Feed zone of the first extruder [0063] 5 Second extruder [0064] 6 Degassing zone of the second extruder [0065] 7 Metering zone of the second extruder [0066] 8 Metering element [0067] 9 Filter [0068] 10 First rheometer [0069] 11 Second rheometer [0070] 12 Nozzle [0071] 13 Feed hopper [0072] 14 Drive motor [0073] 15 Drive motor [0074] 16 Gearing [0075] 17 Drive motor [0076] 18 Gearing [0077] 19 Slider [0078] 20 Slider [0079] M Raw material (granulate, recycled material) [0080] G Gas [0081] S Melt