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CN-121989399-A - Casting apparatus

CN121989399ACN 121989399 ACN121989399 ACN 121989399ACN-121989399-A

Abstract

The present invention relates to a casting apparatus 14 and a machine 10 for producing a film. The casting apparatus includes a chill roll 142, a take-off roll 144, and a water bath 150. The chill roll 142 is configured to cool the plastic melt extruded onto its surface to produce a film F. The take-out roller 144 is disposed downstream of the cooling roller 142 and is configured to disengage the film F from the cooling roller 142. The chill roll is at least partially disposed within the water bath 150 such that the point P at which the film is detached from the chill roll 142 is above the water line of the water bath. The chill roll has a roll width B K and the take-off roll has a roll width B T , with the roll width B T of the take-off roll 144 being less than the roll width B K of the chill roll 142.

Inventors

  • A. Edward
  • A. Jabalis

Assignees

  • 布鲁克纳机械有限公司

Dates

Publication Date
20260508
Application Date
20251107
Priority Date
20241108

Claims (15)

  1. 1. A casting apparatus (14) for producing a plastic film, wherein The casting apparatus comprises a cooling roll (142), a take-off roll (144) and a water bath (150), wherein The chill roll (142) is configured to cool a plastic melt extruded onto a surface thereof to produce a film (F), wherein The take-off roller (144) is arranged downstream of the chill roller (142) and configured to disengage the film (F) from the chill 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 extraction roller (144) has a roller width (B T ), wherein The roll width (B T ) of the take-off roll (144) is smaller than the roll width (B K ) of the cooling roll (142).
  2. 2. The casting apparatus (14) of claim 1, wherein the casting apparatus (14) comprises an extrusion nozzle (126) configured to extrude the plastic melt onto a surface of the chill roll (142) at an extrusion width (B S ), and wherein The roll width (B T ) of the draw-off roll (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. 3. The casting apparatus (14) according to claim 1 or 2, wherein the cooling roll (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. 4. A casting apparatus (14) according to any one of claims 1 to 3, wherein the take-off roll (144) is coated with a polymeric material, wherein the polymeric material comprises rubber and/or at least one polyhaloolefin, in particular polytetrafluoroethylene.
  5. 5. Casting apparatus (14) according to one of claims 1 to 4, wherein the extraction roller (144) is arranged height-adjustable.
  6. 6. Casting apparatus (14) according to one of claims 1 to 5, wherein the extraction roller (144) is arranged entirely above the water line of the water bath (150).
  7. 7. Casting apparatus (14) according to one of claims 1 to 6, wherein the point (P) at which the film (F) is detached from the cooling roll (142) is above the water line of the water bath (150), flush with the water line of the water bath (150), or below the water line of the water bath (150).
  8. 8. The casting apparatus (14) according to one of claims 1 to 7, wherein the extraction roll (144) is an actively driven extraction roll (144).
  9. 9. The casting apparatus (14) according to one of claims 1 to 8, wherein the casting apparatus (14) further comprises a water removal apparatus (154), wherein The water removal device (154) is assigned to the cooling roller (142) and is arranged after the extraction roller (144) in the circumferential direction of the cooling roller (142).
  10. 10. Casting apparatus (14) according to one of claims 1 to 9, wherein the casting apparatus (14) comprises at least one water retaining element (142 a, 142 b), wherein the water retaining element (142 a, 142 b) is arranged adjacent to a shell surface of the cooling roll (142) and at the front face with respect to the extraction roll (144).
  11. 11. Casting apparatus (14) according to one of claims 1 to 10, wherein the at least one water retaining element (142 a, 142 b) protrudes beyond the front face of the cooling roll (142).
  12. 12. The casting apparatus (14) according to claim 11, wherein the at least one water retaining element (142 a, 142 b) at least partially overlaps the front face of the cooling roll (142).
  13. 13. The casting apparatus (14) according to one of claims 1 to 12, wherein the at least one water retaining element (142 a, 142 b) comprises a blow-off nozzle configured to blow off entrained water from an edge region of the cooling roll (142).
  14. 14. Machine (10) for producing a film (F), wherein the machine (10) comprises at least one extruder (12) and/or one reactor, and a casting apparatus (14) according to one of the preceding claims 2 to 13, and wherein the extruder (12) or the reactor is configured to deliver a plastic melt to the extrusion nozzle (126).
  15. 15. Machine (10) for producing a film (F) according to the preceding claim, wherein the machine (10) further comprises a stretching machine (16, 18) arranged downstream of the casting device (14) and configured to stretch the film (F) in a longitudinal and/or transverse direction.

Description

Casting apparatus Technical Field The present invention relates to a casting apparatus and a machine for producing a film, including a corresponding casting apparatus. Background In the production of thin plastic films, the plastic melt is first extruded and applied to a cooling roll, where it cools and at least partially solidifies (cast film). In order to be able to cool the extruded or cast film, which is then fed to a stretching machine, the cooling rolls are typically arranged such that a large part thereof is immersed in water. The water bath results in uniform and rapid cooling. In order to detach the casting film from the cooling roll, a so-called take-out roll is typically provided. The take-off roller is disposed downstream of the chill roller and is configured to disengage the film from the chill roller. The point at which the cast film is detached from the chill roll is generally above the water line. The detached film may then pass through another water bath and in particular be fed to a stretching machine, such as a longitudinal and/or transverse stretching machine or a simultaneous stretching machine. If the point at which the casting film is separated from the cooling roll is above the water line, the conventional casting apparatus can ensure that the center of the cooling roll covered by the casting film remains dry to a large extent. This is necessary because water that reaches the surface of the chill roll will settle between the chill roll and the newly applied plastic melt. This compromises the quality of the film and may also lead to cracking of the film during the subsequent stretching process. The thermoplastic melt may also cause evaporation of water between the melt or film and the chill roll. The resulting vapor bubbles can damage or even destroy the membrane. The general trend in the production of plastic films is to increase the production speed. This means that the surface speeds of the cooling roll and the take-off roll must also be increased. This can be achieved by a higher angular velocity and/or a larger roller diameter. Current film production machines have chill roll speeds of up to 120 m/min. Thus, after longitudinal stretching of the cast film, a film of about 500 to 600 meters per minute can be produced. At higher production speeds, such as 700 meters per minute of film, the chill roll speed has been about 140 to 150 m/min. Further increases in production speed (e.g., >800 m/min) result in a corresponding increase in chill roll speed. It has been shown that for conventional casting equipment, the chill roll and take-off roll already carry large amounts of water at chill roll speeds >120 m/min. This water carry-over results in a significant formation of splash water. The formation of splash water is so intense that the splash water impinges in particular on the surface of the cooling roll and, as described above, impairs the film quality. Disclosure of Invention It is therefore an object of the present invention to provide an improved casting apparatus and machine for producing films which provides good film quality even at high production speeds (film output >600m/min or chill roll speed >120 m/min). This object is achieved by a casting apparatus according to claim 1 and a machine for producing films according to claim. Further aspects of the invention are described in the dependent claims and in the following description. In particular, this object is achieved by a casting apparatus for producing plastic films. The casting apparatus includes at least one chill roll, a take-off roll, and a water bath. The chill roll is configured to cool the plastic melt extruded onto its surface to produce a film. The take-out roller is disposed downstream of the cooling roller in the film traveling direction a and configured to disengage the film from the cooling roller. The chill roll is at least partially disposed in the water bath. The plastic melt extruded onto the cooling roller is thus guided through a water bath with the cooling roller and cooled in the process. The chill roll may also be arranged such that the point at which the film is detached from the chill roll is above the water line of the water bath. The point at which the film is detached from the chill roll may also be flush with or below the water line of the water bath. If the point at which the film is detached from the chill roll is above the water line of the water bath, water can be prevented from flowing between the chill roll and the film. The chill roll has a roll width B K and the take-off roll has a roll width B T. The roll width B T of the take-off roll is smaller than the roll width B K of the chill roll. Thus, the following relationship applies: BK>BT the roll width here indicates the width of the shell surface of the roll (measured in the axial direction of the roll) on which the melt or film is guided. The stub shafts or other parts of the roll, which serve for example as bearings, have no influence