Method for producing film and system therefor

Abstract

The invention relates to a method for producing a film (A), comprising the following steps: generating a film (A) having at least one layer having 70 wt% of one or more polypropylene and 10 to 30 wt% of one or more cycloolefin polymers; and-longitudinally stretching the film (A) by means of a longitudinal stretching unit (16) having at least one pair of stretching rollers (40), a main stretching gap (S1) being formed between the stretching rollers (40) of the at least one pair of stretching rollers (40), the size of the main stretching gap (S1) being at least 30 mm. A system (10) for producing a film (A) is also shown.

Description

Technical Field

[0001] The present invention relates to a method for producing thin films and a system for producing thin films. Background Technology

[0002] Biaxially oriented polypropylene (PP) film is commonly used in film capacitors. To improve the temperature resistance of polypropylene film, a mixture of polypropylene and cyclic olefin polymers (COC) is known to be used.

[0003] However, producing such films with PP and COC is particularly challenging because cyclic olefin polymers are very brittle due to their high glass transition temperatures, making biaxial stretching difficult or even impossible.

[0004] Therefore, such thin films with very low thickness (e.g., less than 5µm) can only be produced by stretching simultaneously in the longitudinal and transverse directions, which, among other things, makes them expensive and limits their availability.

[0005] Therefore, it is desirable to produce this film containing polypropylene and cyclic olefin polymers by sequential stretching. Summary of the Invention

[0006] Therefore, the object of the present invention is to provide a method and system for producing films containing cyclic olefin polymer contents, the method and system enabling the production of such films by sequential stretching.

[0007] This objective is achieved by a method for producing thin films. The method includes at least the following steps:

[0008] - To generate a thin film having at least one layer comprising 70 wt% of one or more semi-crystalline α-olefin polymers and 10 wt% to 30 wt% of one or more cyclic olefin polymers; and

[0009] - The film is longitudinally stretched by a longitudinal stretching unit having at least one pair of stretching rollers, wherein a main stretching gap is formed between the stretching rollers in the at least one pair of stretching rollers, wherein the size of the main stretching gap is at least 30 mm.

[0010] The inventors recognized that increasing the main stretch gap in the longitudinal stretching unit by an order of magnitude from the usual few millimeters to over 30 millimeters meant that brittle films made from mixtures of α-olefin polymers (e.g., polypropylene) and cyclic olefin polymers could also be sequentially stretched in this manner. Increasing the main stretch gap by at least an order of magnitude resulted in a reduction in the stretching rate across the main stretch gap during longitudinal stretching, resulting in a smoother longitudinal stretching process. This enabled a significant increase in the draw ratio within the longitudinal stretching unit.

[0011] In particular, the stretching gap dimension between the two stretching rollers (relative to the tangent of the two stretching rollers) corresponds to the length of the tangent between the contact point of the tangent and the stretching roller. Specifically, the film runs along the tangential direction.

[0012] For example, the one or more semi-crystalline α-olefin polymers are one or more polypropylenes.

[0013] In one configuration, the film has at least 75% by weight of the one or more semi-crystalline α-olefin polymers and 15% to 25% by weight of the one or more cyclic olefin polymers, resulting in a particularly reliable achievement of a high draw ratio.

[0014] The sum of the proportions of the one or more α-olefin polymers and the one or more cycloolefin polymers is, for example, greater than 95% by weight, particularly 100% by weight. In this case, the proportion of the one or more α-olefin polymers in the film can be from 70% by weight to 90% by weight.

[0015] The film can be single-layer, double-layer, triple-layer, or multi-layer. As previously mentioned, only one, multiple, or all of the layers have one or more α-olefin polymers (particularly one or more polypropylenes) and one or more cyclic olefin polymers.

[0016] In one embodiment, the longitudinal stretching unit has a second pair of stretching rollers, wherein an auxiliary stretching gap is formed between the second pair of stretching rollers, and this auxiliary stretching gap is smaller than the main stretching gap. During longitudinal stretching, the film is first stretched in its longitudinal direction across the main stretching gap, and then stretched across the auxiliary stretching gap, or vice versa. In this way, a higher draw ratio is achieved.

[0017] To achieve a particularly high draw ratio, the main draw gap can be 50 mm or more, especially 100 mm or more.

[0018] The size of the auxiliary stretching gap can be less than 4 mm, especially less than 2 mm, which results in a particularly stable production method.

[0019] In one configuration, the stretch ratio across the main stretch gap in the longitudinal direction is greater than or equal to 3.4, particularly greater than or equal to 3.6, particularly greater than or equal to 4.0, particularly greater than or equal to 4.5, which results in the production of particularly thin films.

[0020] In one aspect, the stretch ratio across the auxiliary stretch gap in the longitudinal direction is less than or equal to 2, particularly less than or equal to 1.5, and particularly less than or equal to 1.2, resulting in a particularly reliable production method.

[0021] For example, the overall longitudinal stretching ratio is greater than 3.5, especially greater than 4.0, and even more especially greater than or equal to 5.0.

[0022] In one configuration, the film has no anti-blocking agents or additives that can be used to reduce film adhesion, resulting in particularly good dielectric properties of the film.

[0023] So-called film adhesion is specifically understood as the film surface coming into contact with or coming into contact with other films (e.g., during winding) and thus adhering to each other, which leads to problems during further processing (especially during unwinding).

[0024] As an optional configuration, it is conceivable that the film has one or more anti-blocking agents to reduce adhesion. These anti-blocking agents reduce adhesion between the film itself or other surfaces, thereby preventing adhesion. For example, a solid that acts as a spacer on the surface of the film is called an anti-blocking agent.

[0025] For example, a specific surface structure can be used to prevent film adhesion when produced using the method according to the invention. This surface structure can be generated by using process temperature, particularly by target temperature control of the cooling rollers and longitudinal stretching unit. Due to this surface structure, an average surface finish (Ra / Rmax) can be generated, which prevents adhesion and thus allows for further processing of the film. Due to the surface structure or roughness, the use of an anti-adhesion agent is not necessary in this embodiment.

[0026] In one aspect, at least one, more, or all of the polypropylenes are semi-crystalline and / or homopolymers.

[0027] For example, commercially available types such as Borclean® from Borealis (e.g., HC300BF, HC318BF) or commercially available types from The Polyolefin Company (TPC) of Singapore, KPIC - Korea Petrochemical Ind. Co., LTD, or "Prime Polymer" can be used as semi-crystalline α-olefin polymers.

[0028] In one aspect, at least one, more, or all of the cyclic olefin polymers are amorphous polymers having a glass transition temperature of 130°C to 180°C, and / or contain norbornene and ethylene as monomers.

[0029] The glass transition temperature was measured by DSC at a heating rate of 10 K / min according to ISO 11357.

[0030] For example, COC types 6013 S04, 6013 M07, 6015 S04, or 6017 S04 from Topas Advanced Polymers; COC types APL 5014CL, APL5015AL, APL5016SL, or APL 6015 T from Mitsui Chemicals; COP types Zenor 1420R, Zenor 1410R, Zeonex 162R, Zeonex 690R, or Zeonex 790R from Zeon; ViViOn CBC from USI Corporation in Taiwan; or COC type Arton from JSRCorporation can be used as cyclic olefin polymers.

[0031] It is also conceivable to mix different cyclic olefin polymers, as described in EP 4 174 120.

[0032] In one configuration, the longitudinal stretching unit has a preheating zone, wherein the temperature in the preheating zone is equal to or greater than 110°C, particularly equal to or greater than 120°C, and / or equal to or less than 155°C, particularly equal to or less than 145°C; and / or the longitudinal stretching unit has a stretching zone, wherein the temperature in the stretching zone is equal to or greater than 140°C, particularly equal to or greater than 150°C, and / or equal to or less than 165°C, particularly equal to or less than 155°C. These temperatures are higher than the typical temperatures for producing pure polypropylene films and higher than the glass transition temperatures of cyclic olefin polymers, resulting in improved stretching.

[0033] The temperature of the corresponding zone can be understood as, for example, the temperature of the roller in the corresponding zone.

[0034] To further improve cost-effectiveness, the film can be transported at a speed of 100 m / min to 400 m / min after the longitudinal stretching unit.

[0035] In one embodiment, the method further includes the following steps:

[0036] -Transferring the film from the longitudinal stretching unit to the transverse stretching unit, and

[0037] - The film is stretched laterally in the transverse stretching unit.

[0038] In particular, the film, after transverse stretching, has a width of 5 to 13 m and / or a thickness of less than 5 μm, especially equal to or less than 4 μm. In this way, the area stretching ratio can be significantly increased.

[0039] The film thickness is, for example, greater than or equal to 2 μm, and in particular, the film thickness is 3.8 μm.

[0040] For example, the film has a maximum thermal shrinkage rate of 5% in the longitudinal direction, particularly a maximum of 2.5%, and a maximum thermal shrinkage rate of 0.5% in the transverse direction, particularly a maximum of 0.05%, which is measured according to ISO 11501 at 120°C after 5 minutes.

[0041] In one configuration, the stretching ratio of the transverse stretching unit in the transverse direction is equal to or greater than 8, particularly equal to or greater than 8.5, and / or equal to or less than 10, particularly equal to or less than 9.5. In particular, the stretching ratio of the transverse stretching unit in the transverse direction is 9, resulting in a reliable production method with a high area stretching ratio.

[0042] The total stretch ratio is, for example, greater than 35, especially greater than 40.

[0043] In one embodiment, the transverse stretching unit has an oven for preheating the film prior to transverse stretching, wherein, in particular, the temperature in the stretching zone of the oven is at least partially 170°C to 175°C. This makes the production method more stable.

[0044] The temperature corresponds to the temperature in the stretching zone of the oven.

[0045] To reliably prevent film adhesion, the film, especially after transverse stretching, can have an average surface finish of 0.05µm to 0.12µm, particularly 0.06µm to 0.09µm. This can be determined by tactile measurement using a measuring device from Mahr as an orientation measurement along the transverse direction.

[0046] In one embodiment, the method further includes the following steps:

[0047] - The film is extruded onto a cooling roller, and

[0048] - The film is transferred from the cooling roller to the longitudinal stretching unit.

[0049] Specifically, the temperature of the cooling roller is kept within the range of 80°C to 100°C, and particularly within the range of 90°C to 95°C. The roughness of the film can be set by controlling the temperature of the cooling roller.

[0050] To further process the thin film, the method may also include at least one of the following steps:

[0051] - Activate the surface through corona treatment, and / or

[0052] - Wrap the film.

[0053] This is especially true after longitudinal and / or transverse stretching of the film.

[0054] Corona treatment can be performed on one or both sides.

[0055] Metallization layers can be applied to one or both sides of a fully stretched film in additional steps, especially in an offline state.

[0056] Metallization layers can be applied to one or both sides of a thin film surface. In particular, metallization layers can be made of metal or metal alloys. Furthermore, metallization layers can be applied as a single layer or multiple layers, and different layers can have different compositions.

[0057] In one aspect, the metallization layer comprises aluminum, zinc, gold, silver, magnesium, or a suitable alloy of the foregoing. The thickness of the metallization layer can, for example, range from 10 nm to 100 nm. The metallization layer may also be structured.

[0058] In particular, the corresponding metallized film can be used as a capacitor film. At least one electrode of the capacitor can be formed by or include a metallized layer.

[0059] Both electrodes of a capacitor can be formed through or include corresponding metallization layers.

[0060] This objective is also achieved by a system for producing thin films, the system having a longitudinal stretching unit, wherein the longitudinal stretching unit, and in particular the entire system, is configured to perform the method described above.

[0061] The features and advantages described for this method also apply to this system, and vice versa.

[0062] The system also includes, for example, an extrusion machine, a casting system, a transverse stretching unit (TDO, "transverse orientation device"), a processing device (e.g., a processing device for corona treatment) and / or a winding device. Attached Figure Description

[0063] Further features and advantages of the invention will become apparent from the following description and the accompanying drawings, in which the accompanying drawings are referenced. In the drawings:

[0064] Figure 1 A schematic diagram of a system according to an embodiment of the present invention is shown.

[0065] Figure 2 It shows according to Figure 1 A schematic diagram of the longitudinal tension unit of the system.

[0066] Figure 3 It shows according to Figure 2 A schematic diagram of the tensioning mechanism of the longitudinal tensioning unit.

[0067] Figure 4A flowchart of a method according to an embodiment of the present invention is shown, and

[0068] Figure 5 The graph shows the relationship between the stretching speed and the size of the stretching gap. Detailed Implementation

[0069] Figure 1 A height schematic diagram of a machine 10 for producing film A is shown, which includes several different machines and devices.

[0070] System 10 is, for example, a thin film production unit for producing thin films, such as capacitor films. This is used to explain the invention by way of example, but does not limit the scope of protection.

[0071] In the example shown, system 10 includes an extruder 12, a casting unit 14, at least one longitudinal stretching unit 16 (MDO, "machine orientation oriented"), a transverse stretching unit 18 (TDO, "transverse orientation oriented"), a processing device 20, and a winding device 24.

[0072] The extruder 12 has an extruder and is configured to generate a melt from at least one starting product, which is applied to the cooling rollers of the casting unit 14, resulting in the formation of film A.

[0073] The resulting film can have one or more layers. In the case of a multilayer film, it is conceivable that an extruder produces multiple or all of the layers, or that an extruder is provided for each layer.

[0074] For example, the extruder or multiple extruders are single-screw extruders, cascade extruders, and / or twin-screw extruders.

[0075] It is also conceivable to use other mixing and processing units, such as bus-type kneaders or planetary roll extruders.

[0076] The cooling rollers included in the casting unit 14 are temperature-controlled.

[0077] As described, for example, in DE 10 2021 128 332 A1, the transverse stretching unit 18 has an oven 25 having various zones for controlling the temperature of the film along the normal movement or removal direction of the system 10.

[0078] The transverse stretching unit 18 has a drive system for film A, the drive system having conveyor tracks to transport the film through the various regions. Multiple clamping devices are guided along each of the conveyor tracks in a manner known per se.

[0079] The clamping device can clamp the film A and move it along the conveying track by a suitable driver, so that the film A is conveyed through the transverse stretching unit 18.

[0080] The film is heated in a first region (also known as the preheating region). In a subsequent second region ("stretching region"), the film is stretched in the transverse direction, making it wider and thinner at the end of the second region than it was initially. Stretching is achieved by increasing the distance between the tracks of the drive system in the stretching region.

[0081] In the third and additional regions (referred to as the “heat treatment region,” “another heating region,” and / or “annealing region”), the film can be relaxed, for example, at high temperatures.

[0082] The film is cooled in the final region (“cooling zone”).

[0083] Another area is called the neutral zone and is used to separate the zones. For example, the neutral zone is an empty space without ventilation. The neutral zone can be located between the corresponding zones described above, such as between the annealing zone and the cooling zone.

[0084] Such a transverse stretching element 18 is known, for example, from WO 2014 / 094803 A1.

[0085] These regions of the transverse stretching unit 18 can also be divided and / or designed differently depending on their length. For example, fewer or shorter neutral regions can be provided, or neutral regions can be arranged in other locations, or even additionally. It is also conceivable to modify the remaining regions.

[0086] The processing apparatus 20 is, for example, an apparatus for activating the surface of the thin film A by corona treatment, for example, to achieve better metal adhesion. The corona treatment can be performed on one side or both sides.

[0087] The winding device 24 is used to wind the generated film A and is the last device in the take-out direction. The winding device has a winding core on which the film A is wound.

[0088] Figure 2 The longitudinal stretching unit 16 is shown in a schematic side view. The longitudinal stretching unit 16 has a feed zone 26, a preheating zone 28, a stretching zone 30, a heat treatment zone 32, and a discharge zone 34.

[0089] In the feed zone 26, at least one tension adjusting roller 36 is provided, which receives the film A and guides it to the preheating zone 28.

[0090] Tension adjusting roller 36 is used to set the film tension.

[0091] The preheating zone 28 has multiple preheating rollers 38.

[0092] The surface of the preheating roller 38 is, for example, ceramic, chrome-plated, or coated with Teflon. In the exemplary embodiment shown, a chrome-plated preheating roller 38 is used at the beginning of the preheating zone 28, while a Teflon-coated preheating roller 38 is used further along the take-out direction.

[0093] The surface of the preheating roller 38, as well as the surface of any other roller, can be heated in a controlled manner so that the film A has been heated to a specific temperature after leaving the last preheating roller 38. In this disclosure, this temperature of the film A is also referred to as the temperature of the preheating zone 28.

[0094] Adjacent to the preheating zone 28 along the extraction direction is the stretching zone 30, in which at least one pair of stretching rollers 40 are arranged. In the example shown, the longitudinal stretching unit 16 has four stretching rollers 40 in the stretching zone 30, which form two pairs of stretching rollers 40.

[0095] In addition, multiple guide rollers 42 and multiple pressure rollers 44 can be provided in the stretching zone 30.

[0096] In the exemplary embodiment shown, guide rollers 42 are positioned before and after the pair of stretching rollers 40 in the take-out direction to receive film A from preheating zone 28 and transfer film A to heat treatment zone 32.

[0097] Figure 3 The stretching zone 30, i.e. the stretching system, is shown in more detail in the area of ​​the stretching roller 40.

[0098] As can be seen, each of the front stretching rollers 40 in the pair of stretching rollers along the take-out direction is assigned to one of the pressure rollers 44, which presses the film A against the assigned stretching roller 40 in a manner known per se.

[0099] In each pair of stretching rollers 40, the rear stretching roller 40 is spaced apart from the front stretching roller 40 in the same pair.

[0100] Therefore, a stretching gap is formed between the two stretching rollers 40 in each pair of stretching rollers. The main stretching gap S1 is formed between the stretching rollers 40 in the first pair of stretching rollers (i.e., the pair of stretching rollers that are in the leading position in the take-out direction), and a stretching gap is also formed between the stretching rollers 40 in the second pair of stretching rollers (i.e., the pair of stretching rollers that are in the rear), which is called the auxiliary stretching gap S2.

[0101] The dimensions of each of the stretching gaps S1 and S2 can be determined as follows. In the side view or cross-sectional view, a tangent T is drawn across the stretching gap along the film path. The tangent T is tangent to both of the two stretching rollers 40 in the pair of stretching rollers, such that it has a contact point P with each of the stretching rollers 40. The length of the tangent T between the two contact points P is now the length of the corresponding stretching gap.

[0102] The dimension G1 of the main tension gap S1 is at least 30 mm, and particularly more than 50 mm. It is also conceivable that the dimension G1 is more than 100 mm.

[0103] The dimension G2 of the auxiliary tension gap S2 is less than 4mm, especially less than 2mm.

[0104] The stretching of film A across the main stretching gap S1 occurs because the rear ends of the two stretching rollers 40 in the first pair of stretching rollers have a high rotational speed, resulting in film A being stretched across the main stretching gap S1 in the longitudinal direction. In this process, film A becomes longer and thinner, and is subsequently referred to as film A.

[0105] Then, stretch the film A across the auxiliary stretching gap S2 in the longitudinal direction to make it thinner and longer.

[0106] The temperature in the stretching zone 30 is also controllable and corresponds to the temperature of the film.

[0107] Similar to the preheating zone 28, heating rollers 46 are disposed in the heat treatment zone 32. These heating rollers are ceramic, chrome-plated, or Teflon-coated, and their surface temperature is controllable. The resulting film A is relaxed and / or annealed in the heat treatment zone 32.

[0108] The machine 10 is configured to perform the method for producing film A as described below.

[0109] The production of a single-layer thin film A is described below.

[0110] It is conceivable that the film produced by the method according to the invention can also have multiple identical or different layers, wherein the composition and production of at least one layer of the film are as described below.

[0111] The starting product used in extruder 12 has at least 70% by weight of a semi-crystalline α-olefin polymer (particularly polypropylene) and 10% to 30% by weight of a cyclic olefin polymer.

[0112] It can also be envisioned that there are multiple types of polypropylene, with the total amount of these polypropylenes exceeding 70% by weight. One, more, or all of the polypropylenes are semi-crystalline and / or homopolymers.

[0113] For example, commercially available types such as Borclean® from Borealis (e.g., HC300BF, HC318BF) or commercially available types from Singapore's "The Polyolefin Company (TPC)," KPIC - Korea Petrochemical Ind. Co., LTD, or "Prime Polymer" can be used as semi-crystalline α-olefin polymers or as polymers.

[0114] It is also conceivable that the starting product contains multiple cyclic olefin polymers, wherein at least one, multiple, or all of the cyclic olefin polymers are amorphous polymers with a glass transition temperature of 130°C to 180°C, and / or contain norbornene and / or ethylene as monomers. The total amount of the cyclic olefin polymers is 10% to 30% by weight.

[0115] The glass transition temperature was measured by DSC at a heating rate of 10 K / min according to ISO 11357.

[0116] For example, COC types 6013 S04, 6013 M07, 6015 S04, or 6017 S04 from Topas Advanced Polymers; COC types APL 5014CL, APL5015AL, APL5016SL, or APL 6015 T from Mitsui Chemicals; COP types Zenor 1420R, Zenor 1410R, Zeonex 162R, Zeonex 690R, or Zeonex 790R from Zeon; ViViOn CBC from USI Corporation in Taiwan; or COC type Arton from JSRCorporation can be used as cyclic olefin polymers.

[0117] In particular, it is conceivable to mix different cyclic olefin polymers, as described in EP 4 174 120.

[0118] For example, the one or more polypropylenes and the one or more cyclic olefin polymers together constitute more than 95% by weight, particularly 100% by weight, of the starting product.

[0119] It is conceivable that the starting product comprises at least 75% by weight of one or more polypropylenes and 15% to 25% by weight of one or more cyclic olefin polymers.

[0120] The starting product contains no additives, which are typically used to reduce film adhesion. Therefore, it does not contain solids that would cause roughness on the film surface. Such a starting product (S1) is first prepared and then fed into the extruder 12.

[0121] The starting product can be a compound in which one or more α-olefin polymers have been mixed with one or more cyclic olefin polymers in a corresponding mixing ratio. The compound itself can be particulate.

[0122] It is also conceivable that the starting product may not be a premixed compound, but a mixture of particles of various independent components. The various particles may be mixed here by the supplier of the starting product, or they may be mixed first by the operator of machine 10, for example, when filling extruder 12.

[0123] Then, the starting product is melted and mixed by the extruder 12 and extruded as a melt onto the cooling roller of the casting unit 14 (S2). Here, the temperature of the cooling roller is kept in the range of 80°C to 100°C, especially in the range of 90°C to 95°C (S3).

[0124] The surface roughness of the produced film A can be controlled by adjusting the temperature of the cooling rollers. The mentioned temperature range results in an average surface roughness R of 0.05µm to 0.12µm, particularly 0.06µm to 0.09µm, after transverse stretching of film A. a .

[0125] In S4, film A is transferred from casting unit 14 to longitudinal stretching unit 16.

[0126] In the longitudinal stretching unit 16, the film A first passes through the preheating zone 28, where the temperature is equal to or greater than 110°C, particularly equal to or greater than 120°C, but less than 155°C, particularly less than or equal to 145°C.

[0127] Therefore, when leaving the preheating zone 28, the temperature of film A is above 110°C, especially above 120°C, but below 155°C, especially below 145°C.

[0128] Thin film A is therefore preheated (S5).

[0129] In stretching zone 30, the temperature is above 140°C, particularly above 150°C, or less than or equal to 165°C, particularly less than or equal to 155°C, which is defined as the temperature of film A in that stretching zone. This means selecting the temperature of the roller so that film A takes on the specified temperature.

[0130] Then the film A is stretched in its longitudinal direction, that is, stretched in the removal or movement direction (S6). The main stretching gap S1 is set to size G1, which is at least 30 mm, particularly 50 mm or more, or even 100 mm or more.

[0131] The size G2 of the auxiliary tension gap S2 is less than 4 mm, especially less than 2 mm, and therefore smaller than the main tension gap S1, especially by at least one order of magnitude.

[0132] Film A is first guided across the main stretching gap S1, and then across the auxiliary stretching gap S2, during which film A is stretched. However, it is also conceivable that stretching is first performed across the auxiliary stretching gap (i.e., the smaller stretching gap), and then across the main stretching gap (i.e., the larger stretching gap).

[0133] The rotational speed of the stretching roller 40 in the first pair of stretching rollers is chosen such that the rotational speed of the rear stretching roller 40 is greater, resulting in a stretch ratio across the main stretching gap S1 that is greater than or equal to 3.4, and particularly greater than or equal to 3.6. A stretch ratio greater than or equal to 4.0, and particularly greater than or equal to 4.5, is also conceivable. For even larger stretch ratios, a larger dimension G1 of the main stretching gap S1 is chosen.

[0134] After stretching across the main stretching gap S1, film A becomes longer and thinner in the longitudinal direction.

[0135] Then stretching is performed across the auxiliary stretching gap S2, wherein the rotational speed of the stretching roller 40 in the second pair of stretching rollers is selected such that the stretching ratio across the auxiliary stretching gap S2 in the longitudinal direction is less than or equal to 2, particularly less than or equal to 1.5, and even more particularly less than or equal to 1.2.

[0136] For example, the rotational speed of the front stretching roller 40 in the second pair of stretching rollers 40 corresponds to the rotational speed of the rear stretching roller 40 in the first pair of stretching rollers 40.

[0137] The rotational speed of the rear stretching roller 40 in the second pair of stretching rollers 40 is greater than the rotational speed of the corresponding first stretching roller 40, and the production speed of film A or the speed of machine 10 is determined.

[0138] The operating speed, determined by the rotational speed of the rear stretching roller 40 in the second pair of stretching rollers 40, is, for example, 100 m / min to 400 m / min.

[0139] For example, the stretch ratio MDx across the entire longitudinal stretch, i.e., across the two stretch gaps S1 and S2, is greater than 3.5, especially greater than 4.0, and even more especially greater than or equal to 5.0.

[0140] The significantly increased main tensile gap S1 makes it possible to achieve a high draw ratio MDx for inherently brittle films made of PP and COC, as shown in Table 1 below. Figure 5 The relationship diagram is shown below.

[0141] Table 1

[0142] This table shows the results of four different test series, which were conducted with different main tensile gaps S1 of G1 size. In each test series, the longitudinal tensile stretch ratio MDx gradually increased from 3.5, followed by transverse tensile stretching at a constant stretch ratio TDx of 9.

[0143] The last column displays result E, indicating whether an intact film (+) (possibly not fully stretched) or a damaged film (-) (e.g., a torn film) was obtained. The highest value of the stretch ratio MDx indicates the maximum stretch ratio. Film A was stretched to this value.

[0144] It is clear that, starting from a main tension gap S1 of 30 mm (G1), the maximum longitudinal tension ratio MDx can be increased to more than 3.5. By further increasing the main tension gap S1 (G1), the longitudinal tension ratio MDx can be further increased.

[0145] The longitudinal stretching ratio MDx can be increased because increasing the main stretching gap S1 leads to a decrease in the stretching speed D (Henky speed) of film A across the main stretching gap S1. Figure 5 As shown. Figure 5 The relationship between the stretching speed D and the size G1 of the main stretching gap S1 is shown. Therefore, a lower stretching speed D allows even brittle films to be subjected to strong stretching (MDx > 3.5).

[0146] It is conceivable that the longitudinal stretching unit 16 has more than two pairs of stretching rollers 40, thereby forming an additional auxiliary stretching gap.

[0147] After longitudinal stretching, the film is transferred from longitudinal stretching unit 16 to transverse stretching unit 18 (S7).

[0148] In the transverse stretching unit 18, the film is stretched in the transverse direction accordingly (S8).

[0149] The stretch ratio of the transverse stretching unit 18 in the transverse direction is equal to or greater than 8, particularly equal to or greater than 8.5, and / or less than 10, particularly equal to or less than 9.5. For example, the stretch ratio in the transverse direction is 9.

[0150] The area stretch ratio (i.e., the stretch ratio in the longitudinal and transverse directions) is greater than 35, especially greater than 40.

[0151] After transverse stretching, the thickness of film A is, for example, less than 5 μm, and particularly equal to or less than 4 μm. Meanwhile, the thickness of the film is greater than or equal to 2 μm.

[0152] For example, after lateral stretching, the thickness of film A is 3.8 μm.

[0153] After transverse stretching, the width of film A is 5m to 13m.

[0154] For lateral stretching, the oven 25 in the stretching zone can have a temperature of 170°C to 175°C.

[0155] Thin film A is conveyed from the transverse stretching unit 18 to the processing device 20.

[0156] The processing device 20 activates one or both surfaces of the thin film A by corona treatment (S9).

[0157] Then the film A is wound in the winding device 24 (S10).

[0158] In this manner, film A was produced by sequential stretching (i.e., by longitudinal stretching followed by transverse stretching), the film having at least one layer having 70% by weight of polypropylene and 10% to 30% by weight of one or more cyclic olefin polymers.

[0159] Table 2

[0160] Table 2 shows four examples of the produced films, with Examples 2 and 3 prepared according to the present invention as described above.

[0161] All films comprise 80 wt% polypropylene (PP) and 20 wt% cyclic olefin polymer (COC). The glass transition temperature (Tg) of the COC and the stretching type (“Type”) are indicated, i.e., whether the film is produced by sequential stretching in the longitudinal and transverse directions (“Sequential”) or by simultaneous stretching in both directions (“Simultaneous”). The stretch ratio achieved in the longitudinal direction (MDx), the achieved area stretch ratio (ASR), and the thickness (t) of the produced film are also indicated.

[0162] Sequential stretching is selected to produce films according to the first three examples, i.e., stretching in the longitudinal direction and stretching in the transverse direction are performed at different times (e.g., in two different machine segments of the same production line). The fourth example serves as a comparative example, by stretching the film simultaneously in both the longitudinal and transverse directions using a simultaneous stretching machine.

[0163] For the first three examples, the size G1 of the main tension gap S1 is specified, and the size G2 of the auxiliary tension gap S2 is 1mm to 2mm.

[0164] When producing films according to Examples 1 to 3, with other parameters remaining constant, the temperature of the cooling roller in the preheating zone 28 of the longitudinal stretching unit 16 is 95°C, and the temperature in the stretching zone of the oven 25 of the transverse stretching unit 18 is 170°C to 175°C.

[0165] The film in Example 4 was produced with a longitudinal stretch ratio of 5.5.

[0166] Clearly, increasing the stretch ratio MDx in the longitudinal direction leads to a significantly higher area stretch ratio ASR. The high area stretch ratio achieved in Examples 2 and 3 also improves the performance of film A, for example, the breakdown voltage BDV, as shown in Table 3 below:

[0167] Table 3

[0168] Table 3 lists the properties of the films obtained in this manner, namely, average surface finish (Ra), maximum roughness (Rmax), shrinkage in the longitudinal direction (MD) and transverse direction (TD), and breakdown voltage (BDV).

[0169] The films in these examples exhibit a maximum thermal shrinkage rate of 5% in the longitudinal direction, particularly a maximum of 2.5%, and a maximum thermal shrinkage rate of 0.5% in the transverse direction, particularly a maximum of 0.05%, which was measured according to ISO 11501 at 120°C after 5 minutes.

[0170] It is clear that film thicknesses of less than 4 µm can also be produced by sequential biaxial stretching using the method according to the present invention.

[0171] Meanwhile, Tables 2 and 3 clearly show the area stretch ratio and properties of the films produced according to the present invention (Examples 2 and 3), particularly the low roughness and high breakdown voltage, which are close to the properties of the films produced by simultaneous stretching (Example 4). Such simultaneously stretched films are considered as quality benchmarks.

[0172] Therefore, using the method according to the invention, it is now possible to produce films with the same quality as simultaneously stretched films, and at a lower cost, because the films are stretched sequentially, and the purchase and maintenance costs of film production machines that stretch films sequentially are much cheaper than those of machines that stretch films simultaneously.

[0173] The production of Examples 2 and 3 is extremely stable, which means that such films can be extended to lengths exceeding 30,000 m.

[0174] Due to their high breakdown voltage, the films produced using the method according to the invention can be used as dielectrics in capacitors. Such capacitors also meet the generally high requirements of the automotive and electric vehicle industries. Therefore, a further subject of the invention is the film produced according to the invention, particularly a film metallized on one or both sides, and its use as a dielectric for the production of capacitors.

Claims

1. A method for producing a thin film (A), the method comprising at least the following steps: - A thin film (A) is formed, the thin film having at least one layer having 70% by weight of one or more semi-crystalline α-olefin polymers and 10% to 30% by weight of one or more cyclic olefin polymers; as well as - The film (A) is longitudinally stretched by a longitudinal stretching unit (16) having at least one pair of stretching rollers (40), wherein a main stretching gap (S1) is formed between the stretching rollers (40) in the at least one pair of stretching rollers (40), wherein the size of the main stretching gap (S1) is at least 30 mm.

2. The method according to claim 1, characterized in that, The film (A) has at least 75% by weight of the one or more semi-crystalline α-olefin polymers and 15% to 25% by weight of the one or more cyclic olefin polymers.

3. The method according to claim 1 or 2, characterized in that, The longitudinal stretching unit (16) has a second pair of stretching rollers (40), wherein an auxiliary stretching gap (S2) is formed between the stretching rollers (40) in the second pair of stretching rollers (40), wherein the auxiliary stretching gap (S2) is smaller than the main stretching gap (S1), and During longitudinal stretching, the film (A) is first stretched in the main stretching gap (S1) in its longitudinal direction, and then stretched in the auxiliary stretching gap (S2), or vice versa.

4. The method according to any one of the preceding claims, characterized in that, The size of the main tension gap (S1) is 50 mm or more, particularly 100 mm or more, and / or wherein, The size of the auxiliary tension gap (S2) is less than 4 mm, especially less than 2 mm.

5. The method according to any one of the preceding claims, characterized in that, The stretch ratio across the main stretch gap (S1) in the longitudinal direction is greater than or equal to 3.4, particularly greater than or equal to 3.6, more particularly greater than or equal to 4.0, more particularly greater than or equal to 4.5; and / or is characterized in that the stretch ratio across the auxiliary stretch gap (S2) in the longitudinal direction is less than or equal to 2, particularly less than or equal to 1.5, more particularly less than or equal to 1.

2.

6. The method according to any one of the preceding claims, characterized in that, The film (A) contains no additives.

7. The method according to any one of the preceding claims, characterized in that, At least one, more, or all of the polypropylenes are semi-crystalline and / or homopolymers.

8. The method according to any one of the preceding claims, characterized in that, At least one, more, or all of the cyclic olefin polymers are amorphous polymers having a glass transition temperature of 130°C to 180°C, and / or contain norbornene and ethylene as monomers.

9. The method according to any one 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°C, particularly equal to or greater than 120°C, and / or equal to or less than 155°C, particularly equal to or less than 145°C; and / or The longitudinal stretching unit (16) is characterized in that it has a stretching zone (30), wherein the temperature in the stretching zone (30) is equal to or greater than 140°C, particularly equal to or greater than 150°C, and / or equal to or less than 165°C, particularly equal to or less than 155°C.

10. The method according to any one of the preceding claims, characterized in that, The film (A) is conveyed at a running speed of 100 m / min to 400 m / min after the longitudinal stretching unit (16).

11. The method according to any one of the preceding claims, characterized in that, The method further includes the following steps: - The film (A) is transferred from the longitudinal stretching unit (16) to the transverse stretching unit, and - The film is stretched laterally in the transverse stretching unit (18). In particular, the film (A) after transverse stretching has a width of 5m to 13m and / or a thickness of less than 5μm, particularly equal to or less than 4μm.

12. The method according to claim 11, characterized in that, The stretching ratio of the transverse stretching unit (18) in the transverse direction is equal to or greater than 8, particularly equal to or greater than 8.5, and / or equal to or less than 10, particularly equal to or less than 9.5, and more particularly the stretching ratio of the transverse stretching unit (18) in the transverse direction is 9.

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) prior to transverse stretching, and in particular, the temperature in the oven is at least in part between 170°C and 175°C.

14. The method according to any one of the preceding claims, characterized in that, The film (A), in particular after transverse stretching, has an average surface finish of 0.05µm to 0.12µm, especially 0.06µm to 0.09µm.

15. The method according to any one of the preceding claims, characterized in that, The method further includes the following steps: - The film (A) is extruded onto a cooling roller, and - The film (A) is transferred from the cooling roller to the longitudinal stretching unit (16). In particular, the temperature of the cooling roller is kept in the range of 80°C to 100°C, especially in the range of 90°C to 95°C.

16. The method according to any one of the preceding claims, characterized in that, The method further includes at least one of the following steps, particularly after longitudinal stretching and / or transverse stretching of the film: - Activate the surface through corona treatment, and / or -Wrap the film (A).

17. A system for producing a thin film (A), the system comprising a longitudinal stretching unit (16), wherein, The longitudinal stretching unit (16), and in particular the system (10), is configured to perform the method according to any one of the preceding claims.

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