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DE-102024132907-A1 - Method for producing a film and equipment therefor

DE102024132907A1DE 102024132907 A1DE102024132907 A1DE 102024132907A1DE-102024132907-A1

Abstract

A process for producing a film (A) has the following steps: - Producing a film (A) comprising at least one layer with 70 wt.% of one or more polypropylenes and between 10 wt.% and 30 wt.% of one or more cycloolefin polymers, and - Longitudinal stretching of the film (A) by means of a longitudinal stretching machine (16) with at least one pair of stretching rollers (40), wherein a main stretching gap (S 1 ) is formed between the stretching rollers (40) of the at least one pair of stretching rollers (40), wherein the main stretching gap (S 1 ) has a size of at least 30 mm. Furthermore, a system (10) for the production of a film (A) is shown.

Inventors

  • Christina Mayr
  • Roland Lund

Assignees

  • Brückner Maschinenbau GmbH

Dates

Publication Date
20260513
Application Date
20241111

Claims (17)

  1. A method for producing a film (A) comprising at least the following steps: - producing a film (A) having at least one layer comprising 70 wt.% of one or more semi-crystalline alpha-olefin polymers and between 10 wt.% and 30 wt.% of one or more cycloolefin polymers, and - longitudinally stretching the film (A) by means of a longitudinal stretching machine (16) having at least one pair of stretching rollers (40), wherein a main stretching gap (S 1 ) is formed between the stretching rollers (40) of the at least one pair of stretching rollers (40), wherein the main stretching gap (S 1 ) has a size of at least 30 mm.
  2. Procedure according to Claim 1 , characterized in that the film (A) comprises at least 75 wt.% of one or more semi-crystalline alpha-olefin polymers and between 15 wt.% and 25 wt.% of one or more cycloolefin polymers.
  3. Procedure according to Claim 1 or 2 , characterized in that the longitudinal stretching device (16) has a second pair of stretching rollers (40), wherein a secondary stretching gap (S 2 ) is formed between the stretching rollers (40) of the second pair of stretching rollers (40), wherein the secondary stretching gap (S 2 ) is smaller than the main stretching gap (S 1 ), and wherein the film (A) is first stretched over the main stretching gap (S 1 ) and then over the secondary stretching gap (S 2 ) in its longitudinal direction, or vice versa.
  4. Method according to one of the preceding claims, characterized in that the main stretching gap (S 1 ) has a size of 50 mm and more, in particular 100 mm and more, and/or wherein the secondary stretching gap (S 2 ) has a size of 4 mm and less, in particular 2 mm and less.
  5. Method according to one of the preceding claims, characterized in that the stretch ratio in the longitudinal direction over the main stretching gap (S 1 ) is greater than or equal to 3.4, in particular greater than or equal to 3.6, further in particular greater than or equal to 4.0, further in particular greater than or equal to 4.5; and/or that the stretch ratio in the longitudinal direction over the secondary stretching gap (S 2 ) is less than or equal to 2, in particular less than or equal to 1.5, further in particular less than or equal to 1.2.
  6. Method according to one of the preceding claims, characterized in that the film (A) is free of additives.
  7. Method according to one of the preceding claims, characterized in that at least one, several or all of the polypropylenes are semi-crystalline and/or a homopolymer.
  8. A method according to any of the preceding claims, characterized in that at least one, several or all of the cycloolefin polymers are amorphous, have a glass transition temperature between 130°C and 180°C, and/or contain norbornene and ethylene as monomers.
  9. A method according to one of the preceding claims, characterized in that the longitudinal drawing machine (16) has a preheating area (28), wherein the temperature in the preheating area (28) is equal to or greater than 110°C, in particular equal to or greater than 120°C, and/or equal to or less than 155°C, in particular equal to or less than 145°C; and/or that the longitudinal drawing machine (16) has a drawing area (30), wherein the temperature in the drawing area (30) is equal to or greater than 140°C, in particular equal to or greater than 150°C, and/or equal to or less than 165°C, in particular equal to or less than 155°C.
  10. Method according to one of the preceding claims, characterized in that the film (A) is conveyed after the longitudinal stretching system (16) at a running speed between 100 m/min and 400 m/min.
  11. Method according to one of the preceding claims, characterized in that the method additionally comprises: - conveying the film (A) from the longitudinal stretching machine (16) to a transverse stretching machine (18), and - transverse stretching of the film in the transverse stretching machine (18), in particular wherein the film (A) has a width of 5 m to 13 m and/or a thickness of less than 5 µm, in particular of equal to or less than 4 µm, after transverse stretching.
  12. Procedure according to Claim 11 , characterized in that the stretching ratio in the transverse direction of the transverse stretching system (18) is equal to or greater than 8, in particular equal to or greater than 8.5, and/or equal to or less than 10, in particular equal to or less than 9.5, furthermore in particular the stretching ratio in the transverse direction of the transverse stretching system (18) is 9.
  13. Procedure according to Claim 11 or 12 , characterized in that the transverse stretching system (18) has an oven for preheating the film (A) before transverse stretching, in particular wherein the temperature in the oven is at least sectionally between 170°C and 175°C.
  14. Method according to one of the preceding claims, characterized in that the film (A), in particular after transverse stretching, has a mean roughness value between 0.05 µm and 0.12 µm, in particular between 0.06 µm and 0.09 µm.
  15. Method according to one of the preceding claims, characterized in that the method additionally comprises: - extruding the film (A) onto a cooling roll, and - conveying the film (A) from the cooling roll to the longitudinal stretching unit (16), in particular wherein the cooling roll is tempered to a temperature in the range of 80°C - 100°C, in particular in the range of 90°C - 95°C.
  16. Method according to one of the preceding claims, characterized in that the method additionally comprises at least one of the following, in particular after longitudinal and/or transverse stretching of the film: - Activating the surface by means of corona treatment, and/or - Winding up the film (A).
  17. Plant for the production of a film (A) with a longitudinal stretching plant (16), wherein the longitudinal stretching plant (16), in particular the plant (10), is configured to carry out a method according to one of the preceding claims.

Description

The invention relates to a method for producing a film and to a system for producing a film. Biaxially oriented polypropylene (PP) films are typically used in film capacitors. To increase the temperature resistance of polypropylene films, it is known to use a blend of polypropylene and cycloolefin polymers (COC). However, the production of such films from PP and COC is associated with particular difficulties, since the cycloolefin polymers exhibit high brittleness due to their high glass transition temperature, making biaxial stretching difficult or impossible. For this reason, such films with very low thicknesses, e.g. of less than 5 µm, can only be produced by simultaneous stretching in longitudinal and transverse directions, which makes them very expensive and limits their availability. It is therefore desirable to produce such a film, which contains polypropylene and cycloolefin polymer, using a sequential stretching process. The object of the invention is therefore to provide a method for producing a film with a cycloolefin polymer component and a system for this purpose, which enables the production of such films by means of sequential stretching. The task is solved by a method for producing a film. The method comprises at least the following steps: - Producing a film comprising at least one layer with 70 wt.% of one or more semi-crystalline alpha-olefin polymers and between 10 wt.% and 30 wt.% of one or more cycloolefin polymers, and - Longitudinal stretching of the film by means of a longitudinal stretching machine with at least one pair of stretching rollers, wherein a main stretching gap is formed between the stretching rollers of the at least one pair, wherein the main stretching gap has a size of at least 30 mm. The inventors recognized that increasing the main stretching gap by an order of magnitude—from the usual few millimeters to 30 mm or more—in the longitudinal stretching machine allows brittle films made from a mixture of alpha-olefin polymers, e.g., polypropylene, and cycloolefin polymers to be stretched sequentially. The main stretching gap, increased by at least an order of magnitude, reduces the stretching rate during longitudinal stretching across the main stretching gap, resulting in gentler longitudinal stretching and enabling a significant increase in the stretch ratio in the longitudinal stretching machine. In particular, the size of a stretching gap between two stretching rollers, with respect to a tangent for both stretching rollers, corresponds to the length of the tangent between the points of contact of the tangent with the stretching rollers. Specifically, the film runs in the direction of the tangent. For example, one or more semi-crystalline alpha-olefin polymers are one or more polypropylenes. In one embodiment, the film comprises at least 75 wt.% of one or more semi-crystalline alpha-olefin polymers and between 15 wt.% and 25 wt.% of one or more cycloolefin polymers, thereby achieving particularly reliable high stretch ratios. The sum of the proportions of one or more alpha-olefin polymers and one or more cycloolefin polymers is, for example, more than 95 wt.%, and in particular more than 100 wt.%. The proportion of the alpha-olefin polymer(s) in the film can, in this case, be between 70 wt.% and 90 wt.%. The film can be single-, double-, triple- or multi-layered. Exactly one, several or all of the layers contain, as previously described, one or more alpha-olefin polymers, in particular one or more polypropylenes, and one or more cycloolefin polymers. In one embodiment, the longitudinal stretching machine has a second pair of stretching rollers, with a secondary stretching gap formed between the stretching rollers of the second pair. This secondary stretching gap is smaller than the primary stretching gap. During longitudinal stretching, the film is first stretched over the primary stretching gap and then over the secondary stretching gap in its longitudinal direction, or vice versa. Higher stretch ratios are achieved in this way. To achieve particularly large stretch ratios, the main stretch gap can have a size of 50 mm and more, especially 100 mm and more. The secondary corner gap can have a size of 4 mm and less, especially 2 mm and less, which makes the manufacturing process particularly stable. In one embodiment, the stretch ratio in the longitudinal direction over the main stretch gap is greater than or equal to 3.4, in particular greater than or equal to 3.6, in particular greater than or equal to 4.0, in particular greater than or equal to 4.5, which makes it possible to produce particularly thin films. In one aspect, the stretch ratio in the longitudinal direction over the secondary stretch gap is less than or equal to 2, in particular less than or equal to 1.5, in particular less than or equal to 1.2, which makes the manufacturing process particularly reliable. For example, the stretch ratio of the entire longitudinal section is greater than 3.5, in particular