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EP-4741136-A1 - CAST DEVICE

EP4741136A1EP 4741136 A1EP4741136 A1EP 4741136A1EP-4741136-A1

Abstract

The present invention relates to a casting device 14 and a system 10 for producing a film. The casting device comprises a cooling roll 142, a take-off roll 144, and a water bath 150. The cooling roll 142 is configured to cool a polymer melt extruded onto its surface in order to produce a film F. The take-off roll 144 is located downstream of the cooling roll 142 and is configured to detach the film F from the cooling roll 142. The cooling roll is at least partially submerged in the water bath 150, such that the detachment point P of the film from the cooling roll 142 is above the water level of the water bath. The cooling roll has a roll width B<sub> K</sub> , and the take-off roll has a roll width B <sub>T </sub>, wherein the roll width B<sub> T</sub> of the take-off roll 144 is smaller than the roll width B<sub> K </sub> of the cooling roll 142.

Inventors

  • Edfelder, Anton
  • GIAPOULIS, ANTHIMOS

Assignees

  • Brückner Maschinenbau GmbH

Dates

Publication Date
20260513
Application Date
20251106

Claims (15)

  1. Casting device (14) for the production of plastic films, wherein the casting device comprises a cooling roller (142), a take-off roller (144) and a water bath (150), wherein the cooling roller (142) is configured to cool a plastic melt extruded onto its surface in order to produce a film (F), wherein the take-off roller (144) is downstream of the cooling roller (142) and is designed to detach the film (F) from the cooling roller (142), and wherein the cooling roller (142) is at least partially arranged in the water bath (150), and wherein the cooling roller (142) has a roller width (B K ) and the take-off roller (144) has a roller width (B T ), wherein the roller width (B T ) of the take-off roller (144) is smaller than the roller width (B K ) of the cooling roller (142).
  2. The casting device (14) according to claim 1, wherein the casting device (14) comprises an extrusion die (126) which is configured to extrude the plastic melt onto the surface of the cooling roller (142) with an extrusion width (B S ), and wherein the roller width (B T ) of the take-off roller (144) is in the range of 70% to 105% of the extrusion width (B S ), or in the range of 75% to 100% of the extrusion width (B S ), or in the range of 80% to 95% of the extrusion width (B S ).
  3. Casting device (14) according to claim 1 or 2, wherein the cooling roller (142) is configured to rotate at a surface speed of at least 120 m/min, or at least 130 m/min, or at least 140 m/min, or at least 150 m/min or at least 160 m/min.
  4. Casting device (14) according to one of claims 1 to 3, wherein the take-off roller (144) is coated with a polymeric material, wherein the polymeric material rubber and/or at least a polyhaloolefin, in particular polytetrafluoroethylene.
  5. Casting device (14) according to one of claims 1 to 4, wherein the take-off roller (144) is arranged to be height-adjustable.
  6. Casting device (14) according to one of claims 1 to 5, wherein the take-off roller (144) is arranged completely above the waterline of the water bath (150).
  7. Casting device (14) according to one of claims 1 to 6, wherein a release point (P) of the film (F) from the cooling roller (142) is located above the water line of the water bath (150), at the level of the water line of the water bath (150), or below the water line of the water bath (150).
  8. Casting device (14) according to one of claims 1 to 7, wherein the take-off roller (144) is an actively driven take-off roller (144).
  9. Casting device (14) according to any one of claims 1 to 8, wherein the casting device (14) further comprises a water removal device (154), wherein the water removal device (154) is assigned to the cooling roller (142) and is arranged in the direction of rotation of the cooling roller (142) after the take-off roller (144).
  10. Casting device (14) according to one of claims 1 to 9, wherein the casting device (14) comprises at least one water retention element (142a, 142b), wherein the water retention element (142a, 142b) is arranged adjacent to the outer surface of the cooling roller (142) and at the end face in relation to the takeoff roller (144).
  11. Casting device (14) according to one of claims 1 to 10, wherein the at least one water retention element (142a, 142b) extends beyond an end face of the cooling roller (142).
  12. Casting device (14) according to claim 11, wherein the at least one water retention element (142a, 142b) at least partially overlaps the end face of the cooling roller (142).
  13. Casting device (14) according to one of claims 1 to 12, wherein the at least one water retention element (142a, 142b) comprises a blow-off nozzle which is configured to blow off entrained water from an edge area of the cooling roller (142).
  14. Plant (10) for the production of a film (F), wherein the plant (10) comprises at least one extruder (12) and/or one reactor as well as the casting device (14) according to any one of the preceding claims 2 to 13, and wherein the extruder (12) or the reactor is configured to supply a plastic melt to the extrusion die (126).
  15. Plant (10) for producing a film (F) according to the preceding claim, wherein the plant (10) further comprises a stretching plant (16, 18) which is connected downstream of the casting device (14) and which is configured to stretch the film (F) in the longitudinal direction and/or transverse direction.

Description

Field of invention The invention relates to a casting device and a system for producing a film, comprising a corresponding casting device. background In the production of thin plastic films, a molten plastic is first extruded and applied to a cooling roller, where it cools and at least partially solidifies (cast film). To cool the extruded or cast film and subsequently feed it into a stretching machine, the cooling roller is typically positioned so that it is mostly submerged in water. The water bath ensures homogeneous and rapid cooling. To detach the cast film from the cooling roll, a so-called take-off roll is typically used. The take-off roll is located downstream of the cooling roll and is designed to detach the film. The point at which the cast film detaches from the cooling roll is usually above the waterline. The detached film can then be passed through another water bath and, in particular, fed to a stretching machine, such as a longitudinal and/or transverse stretching machine or a simultaneous stretching machine. If the point where the cast film detaches from the cooling roller is above the waterline, conventional casting systems can largely ensure that the central area of the cooling roller, which is covered by the cast film, remains dry. This is necessary because water that gets onto the surface of the cooling roller would become trapped between the cooling roller and the reapplied plastic melt. This impairs the film quality and can also lead to film tears during further stretching processes. Furthermore, the hot molten plastic would cause the water between the melt or film and the cooling roller to evaporate. The resulting vapor bubbles can damage or even destroy the film. A general trend in plastic film manufacturing is the increase in production speed. This necessitates an increase in the surface speed of the cooling roll and the take-off roll. This can be achieved through a higher angular velocity and/or larger roll diameters. Current film production plants have a cooling roller speed of up to 120 m/min. After longitudinal stretching of the cast film, approximately 500 to 600 meters of film can be produced per minute. At higher production speeds, for example 700 meters of film per minute, the cooling roller speed is already approximately 140 to 150 m/min. A further increase in production speed (e.g., >800 m/min) leads to a corresponding increase in the cooling roller speed. It has been shown that in conventional casting equipment, the cooling roll and the take-off roll already carry over significant amounts of water at cooling roll speeds exceeding 120 m/min. This water carryover leads to a high level of splashing. The splashing is so intense that it hits, among other things, the surface of the cooling roll and, as described above, impairs the film quality. Description of the invention It is therefore an object of the present invention to provide an improved casting device and system for film production which delivers good film quality even at high production speeds (film output > 600 m/min or cooling roller speed > 120 m/min). The problem is solved by a casting device according to claim 1, as well as by the claimed apparatus for producing a film. Further aspects of the invention are described in the dependent claims and in the following description. In particular, the task is solved by a casting device for the production of plastic films. The casting device comprises at least a cooling roller, a take-off roller, and a water bath. The cooling roller is designed to cool a polymer melt extruded onto its surface in order to produce a film. The take-off roller is located downstream of the cooling roller in the film feed direction A and is designed to detach the film from the cooling roller. The cooling roller is at least partially submerged in the water bath. The polymer melt extruded onto the cooling roller is thus guided through the water bath by the cooling roller and cooled in the process. The cooling roller can also be positioned such that the film detachment point from the cooling roller is located above the water level of the water bath. It is also possible for the film detachment point to be located at or below the water level of the water bath. If the point where the film detaches from the cooling roller is above the waterline of the water bath, it can be prevented that water flows between the cooling roller and the film. The cooling roller has a roller width B <sub>K</sub> and the take-off roller has a roller width B<sub> T </sub>. The roller width B <sub>T</sub> of the take-off roller is smaller than the roller width B <sub>K</sub> of the cooling roller. Therefore, the following relationship applies: BK>BT The roller width indicates the width (measured in the axial direction of the roller) of the roller's outer surface on which the melt or film is guided. Stub shafts or other parts of the roller, such as those used for bearings, do not affect the roller width. The narrower take-off r