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CN-122008579-A - Method for producing a film and system for this purpose

CN122008579ACN 122008579 ACN122008579 ACN 122008579ACN-122008579-A

Abstract

A method for producing a film (A) having the steps of-producing a film (A) having at least one layer with 70% by weight of one or more polypropylenes and 10% to 30% by weight of one or more cycloolefin polymers, and-stretching the film (A) in the machine direction by means of a machine direction stretching unit (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 30mm. A system (10) for producing the film (A) is also shown.

Inventors

  • C. MAYER
  • R. Lund

Assignees

  • 布鲁克纳机械有限公司

Dates

Publication Date
20260512
Application Date
20251110
Priority Date
20241111

Claims (17)

  1. 1. A method for producing a film (a), said method comprising at least the steps of: Forming a film (A) having at least one layer with 70% by weight of one or more semi-crystalline alpha-olefin polymers and 10% to 30% by weight of one or more cycloolefin polymers, and -Stretching the film (a) longitudinally by means of a longitudinal stretching unit (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 30mm.
  2. 2. The method according to claim 1, characterized in that said film (a) has at least 75% by weight of said semi-crystalline α -olefin polymer(s) and from 15% to 25% by weight of said cyclic olefin polymer(s).
  3. 3. The method according to claim 1 or 2, wherein the longitudinal stretching unit (16) has a second pair of stretching rollers (40), wherein an auxiliary stretching gap (S 2 ) is formed between the stretching rollers (40) of the second pair of stretching rollers (40), wherein the auxiliary stretching gap (S 2 ) is smaller than the main stretching gap (S 1 ), and Wherein during longitudinal stretching, the film (a) is stretched in its longitudinal direction first over the main stretching gap (S 1 ) and then over the auxiliary stretching gap (S 2 ) or vice versa.
  4. 4. The method according to any of the preceding claims, wherein the primary stretching gap (S 1 ) has a size of 50mm or more, in particular 100mm or more, and/or wherein the secondary stretching gap (S 2 ) has a size of 4mm or less, in particular 2mm or less.
  5. 5. The method according to any of the preceding claims, characterized in that the stretch ratio across the main stretch gap (S 1 ) in the longitudinal direction is greater than or equal to 3.4, in particular greater than or equal to 3.6, more in particular greater than or equal to 4.0, more in particular greater than or equal to 4.5, and/or in that the stretch ratio across the auxiliary stretch gap (S 2 ) in the longitudinal direction is less than or equal to 2, in particular less than or equal to 1.5, more in particular less than or equal to 1.2.
  6. 6. The method according to any of the preceding claims, characterized in that the film (a) is free of additives.
  7. 7. The method according to any of the preceding claims, wherein at least one, more or all of the polypropylenes are semi-crystalline and/or homopolymers.
  8. 8. The process according to any of the preceding claims, characterized in that at least one, more or all of the cycloolefin polymers are amorphous polymers, have a glass transition temperature of 130 ℃ to 180 ℃ and/or comprise norbornene and ethylene as monomers.
  9. 9. The method according to any of the preceding claims, characterized in that the longitudinal stretching unit (16) has a preheating zone (28), wherein the temperature in the preheating zone (28) is equal to or greater than 110 ℃, in particular equal to or greater than 120 ℃, and/or equal to or less than 155 ℃, in particular equal to or less than 145 ℃, and/or Characterized in that the longitudinal stretching unit (16) has a stretching zone (30), wherein the temperature in the stretching zone (30) is equal to or greater than 140 ℃, in particular equal to or greater than 150 ℃, and/or equal to or less than 165 ℃, in particular equal to or less than 155 ℃.
  10. 10. The method according to any one of the preceding claims, characterized in that the film (a) is conveyed at an operating speed of 100m/min to 400m/min after the longitudinal stretching unit (16).
  11. 11. The method according to any of the preceding claims, characterized in that the method additionally comprises the steps of: -transferring the film (a) from the longitudinal stretching unit (16) to a transverse stretching unit, and Transversely stretching the film in the transverse stretching unit (18), In particular, wherein the film (A) has a width of 5m to 13m and/or a thickness of less than 5 μm, in particular equal to or less than 4 μm, after transverse stretching.
  12. 12. The method according to claim 11, characterized in that the stretching ratio in the transverse direction of the transverse stretching unit (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, more in particular the stretching ratio in the transverse direction of the transverse stretching unit (18) is 9.
  13. 13. The method according to claim 11 or 12, characterized in that the transverse stretching unit (18) has an oven for preheating the film (a) before transverse stretching, in particular wherein the temperature in the oven is at least partially 170 ℃ to 175 ℃.
  14. 14. The method according to any of the preceding claims, characterized in that the film (a), in particular after transverse stretching, has an average surface finish of 0.05 to 0.12 μm, in particular 0.06 to 0.09 μm.
  15. 15. The method according to any of the preceding claims, characterized in that the method further comprises the steps of: -extruding said film (a) onto a cooling roll, and Transferring the film (A) from the cooling roll to the longitudinal stretching unit (16), In particular, the temperature of the cooling roller is brought to lie in the range from 80 ℃ to 100 ℃, in particular in the range from 90 ℃ to 95 ℃.
  16. 16. The method according to any of the preceding claims, characterized in that the method additionally comprises at least one of the following steps, in particular after longitudinal stretching and/or transverse stretching of the film: activating the surface by corona treatment, and/or -Winding said film (a).
  17. 17. A system for producing a film (a), the system comprising a longitudinal stretching unit (16), wherein the longitudinal stretching unit (16), in particular the system (10), is arranged to perform the method according to any of the preceding claims.

Description

Method for producing a film and system for this purpose Technical Field The present invention relates to a method for producing a film and a system for producing a film. Background Biaxially oriented polypropylene (PP) films are commonly used in film capacitors. In order to improve the temperature resistance of polypropylene films, it is known to use a mixture of polypropylene and cyclic olefin polymer (COC). However, the production of such films with PP and COC is particularly challenging, since cycloolefin polymers are very brittle due to their high glass transition temperature, making biaxial stretching difficult or even impossible. Thus, such films of very low thickness (e.g., less than 5 μm) can only be produced by simultaneous stretching in the longitudinal and transverse directions, which makes them expensive and limits their usability, among other things. It is therefore desirable to produce such films with polypropylene and cyclic olefin polymers by sequential stretching processes. Disclosure of Invention It is therefore an object of the present invention to provide a process for producing films containing cycloolefin polymer contents and a system therefor which enable such films to be produced by sequential stretching. This object is achieved by a method for producing a film. The method at least comprises the following steps: forming a film having at least one layer with 70% by weight of one or more semi-crystalline alpha-olefin polymers and 10% to 30% by weight of one or more cycloolefin polymers, and -Stretching the film in the machine direction by means of a machine direction stretching unit having at least one pair of stretching rollers, wherein a main stretching gap is formed between the stretching rollers of the at least one pair of stretching rollers, wherein the main stretching gap has a size of at least 30mm. The inventors have recognized that increasing the main draw gap in the machine direction draw unit from a typical few millimeters by an order of magnitude to more than 30mm means that brittle films made from a mixture of alpha-olefin polymers (e.g., polypropylene) and cyclic olefin polymers can also be drawn sequentially in this manner. An increase in the main stretch gap by at least one order of magnitude results in a decrease in the stretch speed across the main stretch gap during longitudinal stretching, with the result that a more gentle longitudinal stretching is achieved, which enables a significant increase in the stretch ratio in the longitudinal stretch unit. In particular, the dimension of the stretch gap between the two stretch rolls (relative to the tangent of the two stretch rolls) corresponds to the length of the tangent between the tangent and the point of contact of the stretch rolls. In particular, the film runs in tangential direction. For example, the one or more semi-crystalline alpha-olefin polymers are one or more polypropylenes. In one configuration, the film has at least 75% by weight of the one or more semi-crystalline alpha-olefin polymers and 15% to 25% by weight of the one or more cyclic olefin polymers, as a result of which a high draw ratio is achieved particularly reliably. The sum of the proportions of the one or more alpha-olefin polymers and the one or more cycloolefin polymers is, for example, greater than 95% by weight, in particular 100% by weight. In this case, the fraction of the one or more alpha-olefin polymers in the film may be 70 to 90% by weight. The film may be single layer, double layer, triple layer or multiple layer. As previously mentioned, only one, more or all of the layers have one or more alpha-olefin polymers (in particular one or more polypropylenes) and one or more cyclic olefin polymers. In one embodiment, the longitudinal stretching unit has a second pair of stretching rollers, wherein an auxiliary stretching gap is formed between the stretching rollers of the second pair, wherein the auxiliary stretching gap is smaller than the main stretching gap. During longitudinal stretching, the film is stretched in its longitudinal direction first over a primary stretching gap and then over a secondary stretching gap, or vice versa. In this way, a higher draw ratio is achieved. In order to achieve particularly high draw ratios, the main draw gap may be 50mm or more, in particular 100mm or more in size. The auxiliary drawing gap may have a size of 4mm or less, in particular 2mm or less, as a result of which the production process is particularly stable. In one configuration, the draw ratio across the main draw gap in the machine direction is greater than or equal to 3.4, specifically greater than or equal to 3.6, specifically greater than or equal to 4.0, specifically greater than or equal to 4.5, as a result of which particularly thin films can be produced. In one aspect, the draw ratio across the auxiliary draw gap in the longitudinal direction is less than or equal to 2, in particular less than or equal to 1.5, in particular less tha