Method for improving thickness consistency of ETFE film

Abstract

The invention discloses a method for improving the thickness consistency of an ETFE film, and relates to the technical field of polymer films, and the method specifically comprises the following steps: extruding and melting ETFE resin through a twin-screw extruder, and mixing through a static mixer to obtain a melt; carrying out gradient stretching on the melt, firstly carrying out pre-stretching at 70-80 DEG C, then carrying out primary stretching at 80 DEG C, then raising the temperature to 118-122 DEG C, carrying out secondary stretching, and finally raising the temperature to 148-152 DEG C, and carrying out tertiary stretching; and cooling and shaping the stretched film to obtain the ETFE film. Extrusion melting conditions are effectively optimized, gradient stretching is carried out during stretching, annealing treatment is carried out after gradient stretching and before cooling, and the prepared ETFE film is consistent in thickness and good in tensile property.

Description

Technical Field

[0001] The invention relates to the technical field of polymer film preparation, and in particular to a method for improving the thickness consistency of an ETFE film. Background Art

[0002] SiC modules represent the third generation of semiconductors, boasting high-temperature resistance, high frequency, and low loss. Their breakdown electric field strength is 10 times that of silicon-based materials, and their thermal conductivity is three times that of silicon, making them suitable for the high-voltage applications of new energy vehicles. IGBT modules, consisting of chips, DBC substrates, bonding wires, and heat sinks, are core components of new energy vehicle electronic control systems, accounting for 40% of the motor controller's cost. Their packaging must meet reliability requirements across a wide temperature range of -40°C to 150°C and in high-vibration environments. To ensure optimal packaging for automotive-grade SiC / IGBT modules, the packaging material must meet the following requirements: 1. High insulation: This prevents high-voltage breakdown and enhances module reliability; 2. High-temperature resistance: SiC device junction temperatures can reach over 175°C, requiring the packaging material to withstand long-term high-temperature operation; 3. Low thermal resistance: This optimizes the heat dissipation path and reduces thermal stress on the module; 4. Chemical stability: This resists the effects of humid and corrosive environments; and 5. High mechanical strength: This withstands the vibration and shock of the in-vehicle environment.

[0003] ETFE is a high-performance fluorine material with high-temperature resistance, partially matching the high-temperature requirements of SiC modules. Its high dielectric strength makes it suitable for high-voltage insulation applications. Furthermore, ETFE film boasts high light transmittance, excellent chemical stability, heat resistance, and non-stick properties, making it a widely used plastic release film in the packaging field. Existing ETFE film preparation processes result in large variations in film thickness due to uneven melt flow, fluctuations in stretching rates, or differences in cooling gradients. Uneven stretching can lead to premature fracture at localized weak points during ultra-high stretching. Therefore, providing an ETFE film with consistent thickness is crucial. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a method for improving the thickness consistency of an ETFE film in view of the shortcomings of the prior art. The method effectively optimizes the extrusion melting conditions and uses gradient stretching during stretching. During the gradient stretching, temperature control and speed increase are performed in stages to balance the orientation and relaxation of molecular chains, thereby ensuring the thickness consistency of the ETFE film. In addition, an annealing treatment is performed after the gradient stretching and before cooling, so that the prepared ETFE film has good tensile properties.

[0005] In order to solve the above technical problems, the technical solution of the present invention is:

[0006] A method for improving the thickness consistency of ETFE film comprises the following steps:

[0007] The ETFE resin is extruded and melted through a twin-screw extruder, and then mixed in a static mixer to obtain a melt;

[0008] The melt is subjected to gradient stretching, first pre-stretching at 70-80°C, then primary stretching at 80°C, then heating to 118-122°C for secondary stretching, and finally heating to 148-152°C for tertiary stretching;

[0009] The stretched film is cooled and shaped to obtain an ETFE film.

[0010] Preferably, the molecular weight of the ETFE resin is less than 1.26×10 6 , crystallinity is 65%-85%, and impurity content is <2%.

[0011] Preferably, when the ETFE resin is extruded and melted using a twin-screw extruder, the extrusion barrel of the twin-screw extruder is divided into 5 zones for temperature control: the temperature of zone 1 is 200-220°C, the temperature of zone 2 is 230-240°C, the temperature of zone 3 is 240-250°C, the temperature of zone 4 is 245-255°C, and the temperature of zone 5 is 235-245°C. The temperature difference between each zone is ≤±1°C, and the screw speed is 40-70rpm.

[0012] Preferably, the extrusion die head of the twin-screw extruder is a coat-hanger die head, and the film thickness is monitored in real time by a β-ray thickness gauge, so that the temperature of the die lip heating zone is adjusted in real time, with a temperature difference of ≤±0.5°C; the die lip gap is dynamically adjusted (accuracy ±1μm), and the temperature of the die lip heating zone is kept consistent with the temperature of the five zones.

[0013] The control accuracy of die lip gap adjustment is ±1μm.

[0014] Preferably, the stretching speed during pre-stretching is 0.5-1 m / min, and the strain is 50-100%.

[0015] Preferably, the stretching rate during the first stretching is 0.5-1 m / min; the heating rate after the first stretching is 5-10°C / min, the stretching rate during the second stretching is 2-4 m / min; the heating rate after the second stretching is 3-5°C / min, the stretching rate for the third stretching is 5-10 m / min, and the total stretching ratio is ≥5:1.

[0016] Preferably, air knife cooling is used during cooling and shaping, the wind speed during air knife cooling is 20-30m / s, the pressure is 0.2~0.8Mpa, the air knife angle is 30°±5°, the cooling rate is controlled at 50-100℃ / s, and during air knife cooling, the temperature of the cooling roller is maintained below the crystallization temperature of ETFE and above the solidification temperature.

[0017] Preferably, when the die lip gap is dynamically adjusted, a die lip gap fine-tuning signal is output based on the feedback of melt pressure, melt temperature and real-time film thickness data.

[0018] Preferably, after gradient stretching, annealing treatment is performed before cooling and shaping.

[0019] Preferably, the annealing treatment conditions are: temperature 100°C, time 10 min, tension 0.1-0.5 N / mm 2 .

[0020] Due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0021] The present invention provides a method for improving the thickness consistency of ETFE film. The present invention adopts a twin-screw extruder to perform extrusion melting through five-zone gradient temperature control, and combines with a static mixer to ensure that the melt viscosity is evenly distributed, thereby facilitating subsequent stretching and ensuring the thickness consistency of the film.

[0022] The present invention adopts gradient stretching during stretching, and the obtained ETFE film has uniform thickness and good tensile properties. Specifically, during gradient stretching, the primary stretching is a transition zone, which ensures that the internal stress of the material is uniformly released, avoids sudden changes in crystallinity caused by sudden heating, and effectively controls the stretching speed to preliminarily orient the molecular chains. At the same time, it prevents brittle fracture caused by insufficient temperature, and can also eliminate residual stress after pre-stretching, laying a uniform molecular structure foundation for subsequent high-temperature stretching. The temperature of the secondary stretching is close to the glass transition temperature of ETFE, but lower than its melting point, and the stretching speed is increased to 2-4m / min, further orienting the molecular chains, thereby improving the longitudinal / transverse mechanical properties of the film and reducing internal stress concentration. The temperature of the tertiary stretching is close to the melting point of ETFE, but not melted, and the stretching speed is increased to 5-10m / min. The molecular chains are fully oriented by high-ratio stretching, thereby eliminating microscopic defects, improving the density and surface finish of the film, and locking the molecular orientation by high-temperature heat setting, reducing subsequent shrinkage.

[0023] The present invention also performs annealing treatment after gradient stretching, eliminates the residual stress in the molecular chain during the stretching process through thermal relaxation, stabilizes the crystal structure, and prevents the film from shrinking or warping due to subsequent stress release, thereby reducing the thickness deviation of the film and improving the tensile properties of the film. DETAILED DESCRIPTION

[0024] In order to more clearly understand the above-mentioned objectives, features and advantages of the present invention, the scheme of the present invention will be further described below. It should be noted that, in the absence of conflict, the embodiments of the present invention and the features therein can be combined with each other.

[0025] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein; it is obvious that the embodiments in the specification are only part of the embodiments of the present invention, rather than all the embodiments.

[0026] In order to further understand the present invention, preferred embodiments of the present invention are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, rather than limiting the claims of the present invention.

[0027] In the following examples and comparative examples, the twin-screw extruder features a coat-hanger die head with a screw length-to-diameter ratio of 40:1. During extrusion and melting, film thickness is monitored in real time using a β-ray thickness gauge, enabling real-time adjustment of the die lip heating zone temperature to a temperature differential of ≤±0.5°C. The die lip gap is also dynamically adjusted (with an accuracy of ±1μm). Specifically, dynamic adjustment of the die lip gap is based on feedback from melt pressure, melt temperature, and real-time film thickness data to generate a fine-tuning signal for the die lip gap.

[0028] The stretching in the following examples and comparative examples is all transverse stretching.

[0029] Example 1

[0030] A method for improving the thickness consistency of ETFE film comprises the following steps:

[0031] (1) ETFE resin (the average molecular weight of ETFE resin is 1.12×10 6 , crystallinity 70%, impurity content 0.83%) was extruded and melted by a twin-screw extruder. During the extrusion and melting, the extrusion barrel of the twin-screw extruder was divided into 5 zones for temperature control: the temperature of zone 1 was 212° C., the temperature of zone 2 was 235° C., the temperature of zone 3 was 245° C., the temperature of zone 4 was 250° C., and the temperature of zone 5 was 240° C. The temperature difference of each zone was ≤±1° C., and the screw speed was 50 rpm. The extruded and melted materials were mixed in a static mixer to control the melt temperature gradient to ≤2° C. to obtain a melt.

[0032] (2) The melt was first pre-stretched at 70°C and a stretching speed of 0.5 m / min, with a stretching strain of 50%; then the temperature was stabilized to 80°C and a stretching speed of 0.5 m / min was used for a primary stretching with a stretching ratio of 1.51; then the temperature was raised to 118°C at a rate of 5°C / min, and a secondary stretching was performed at a stretching speed of 2 m / min with a stretching ratio of 2.0; finally, the temperature was raised to 148°C at a rate of 3°C / min, and a tertiary stretching was performed at a stretching speed of 5 m / min with a stretching ratio of 1.69;

[0033] (3) The stretched film was annealed at 100°C for 10 min, and a 0.1 N / mm2 pressure was applied to the film during the annealing process. 2 tension;

[0034] (4) The film after annealing is cooled by air knife. The wind speed during air knife cooling is 20m / s, the pressure is 0.2Mpa, the air knife angle is 30°, and the cooling rate is controlled at 50℃ / s. During air knife cooling, the temperature of the cooling roller is kept below the crystallization temperature of ETFE and above the solidification temperature to obtain an ETFE film with consistent thickness.

[0035] Example 2

[0036] A method for improving the thickness consistency of ETFE film comprises the following steps:

[0037] (1) ETFE resin (the average molecular weight of ETFE resin is 1.12×10 6 , crystallinity of 70%, impurity content of 0.83%) was extruded and melted by a twin-screw extruder. During the extrusion and melting, the extrusion barrel of the twin-screw extruder was divided into 5 zones for temperature control: the temperature of zone 1 was 210° C., the temperature of zone 2 was 233° C., the temperature of zone 3 was 242° C., the temperature of zone 4 was 247° C., and the temperature of zone 5 was 242° C. The temperature difference between each zone was ≤±1° C., and the screw speed was 40 rpm. The extruded and melted materials were mixed in a static mixer to control the melt temperature gradient to ≤2° C. to obtain a melt.

[0038] (2) The melt was first pre-stretched at 75°C and a stretching speed of 0.6 m / min, with a stretching strain of 60%; then the temperature was stabilized to 80°C and a stretching speed of 0.8 m / min was used for a primary stretching with a stretching ratio of 1.48; then the temperature was raised to 120°C at a rate of 7°C / min and a secondary stretching was performed at a stretching speed of 2.5 m / min with a stretching ratio of 2.3; finally, the temperature was raised to 149°C at a rate of 3.5°C / min and a tertiary stretching was performed at a stretching speed of 6 m / min with a stretching ratio of 1.7;

[0039] (3) The stretched film was annealed at 100°C for 10 min, and a 0.2 N / mm2 pressure was applied to the film during the annealing process. 2 tension;

[0040] (4) The film after annealing treatment is cooled by air knife. The wind speed during air knife cooling is 25m / s, the pressure is 0.3Mpa, the air knife angle is 30, and the cooling rate is controlled at 60℃ / s. During air knife cooling, the temperature of the cooling roller is kept below the ETFE crystallization temperature and above the solidification temperature to obtain an ETFE film with consistent thickness.

[0041] Example 3

[0042] A method for improving the thickness consistency of ETFE film comprises the following steps:

[0043] (1) ETFE resin (the average molecular weight of ETFE resin is 1.12×10 6 , crystallinity 70%, impurity content 0.83%) was extruded and melted by a twin-screw extruder. During the extrusion and melting, the extrusion barrel of the twin-screw extruder was divided into 5 zones for temperature control: the temperature of zone 1 was 218° C., the temperature of zone 2 was 237° C., the temperature of zone 3 was 247° C., the temperature of zone 4 was 251° C., and the temperature of zone 5 was 236° C. The temperature difference between the zones was ≤±1° C., and the screw speed was 60 rpm. The extruded and melted materials were mixed in a static mixer to control the melt temperature gradient to ≤2° C. to obtain a melt.

[0044] (2) The melt was first pre-stretched at 78°C and a stretching speed of 0.7 m / min, with a stretching strain of 70%; then the temperature was stabilized to 80°C and a stretching speed of 0.7 m / min was used for a primary stretching with a stretching ratio of 1.46; then the temperature was raised to 120°C at a rate of 8°C / min and a secondary stretching was performed at a stretching speed of 3 m / min with a stretching ratio of 2.35; finally, the temperature was raised to 150°C at a rate of 4°C / min and a tertiary stretching was performed at a stretching speed of 8 m / min with a stretching ratio of 1.68;

[0045] (3) The stretched film was annealed at 100°C for 10 min, and a 0.3 N / mm2 pressure was applied to the film during the annealing process. 2 tension;

[0046] (4) The film after annealing treatment is cooled by air knife. The wind speed during air knife cooling is 28m / s, the pressure is 0.4Mpa, the air knife angle is 25, and the cooling rate is controlled at 80℃ / s. During air knife cooling, the temperature of the cooling roller is kept below the ETFE crystallization temperature and above the solidification temperature to obtain an ETFE film with consistent thickness.

[0047] Example 4

[0048] A method for improving the thickness consistency of ETFE film comprises the following steps:

[0049] (1) ETFE resin (the average molecular weight of ETFE resin is 1.12×10 6, crystallinity 70%, impurity content 0.83%) was extruded and melted by a twin-screw extruder. During the extrusion and melting, the extrusion barrel of the twin-screw extruder was divided into 5 zones for temperature control: the temperature of zone 1 was 220° C., the temperature of zone 2 was 240° C., the temperature of zone 3 was 250° C., the temperature of zone 4 was 255° C., and the temperature of zone 5 was 245° C. The temperature difference between each zone was ≤±1° C., and the screw speed was 70 rpm. The extruded and melted materials were mixed in a static mixer to control the melt temperature gradient to ≤2° C. to obtain a melt.

[0050] (2) The melt was first pre-stretched at 79°C and a stretching speed of 1 m / min, with a stretching strain of 100%; then the temperature was stabilized to 80°C and a stretching was performed at a stretching speed of 1 m / min with a stretching ratio of 1.43; then the temperature was raised to 122°C at a rate of 10°C / min and a second stretching was performed at a stretching speed of 4 m / min with a stretching ratio of 2.4; finally, the temperature was raised to 152°C at a rate of 5°C / min and a third stretching was performed at a stretching speed of 10 m / min with a stretching ratio of 1.66;

[0051] (3) The stretched film was annealed at 100°C for 10 min, and a 0.5 N / mm2 pressure was applied to the film during the annealing process. 2 tension;

[0052] (4) The film after annealing treatment is cooled by air knife. The wind speed during air knife cooling is 30m / s, the pressure is 0.8Mpa, the air knife angle is 35°, and the cooling rate is controlled at 100℃ / s. During air knife cooling, the temperature of the cooling roller is kept below the crystallization temperature of ETFE and above the solidification temperature to obtain an ETFE film with consistent thickness.

[0053] Comparative Example 1

[0054] The difference between this comparative example and Example 4 is that in step (1), no static mixer is used for mixing, and the melt after extrusion and melting is directly subjected to subsequent treatment. Other operations are the same as in Example 4.

[0055] Comparative Example 2

[0056] The difference between this comparative example and Example 4 is that: in step (1), during extrusion melting, the extrusion barrel of the twin-screw extruder is temperature-controlled in three zones: the temperature of zone 1 (feed) is 220°C, the temperature of zone 2 is 240°C, and the temperature of zone 3 (discharge) is 245°C. Other operations are the same as in Example 4.

[0057] Comparative Example 3

[0058] The difference between this comparative example and Example 4 is that in step (2), no pre-stretching is performed, and the other operations are the same as in Example 4.

[0059] Comparative Example 4

[0060] The difference between this comparative example and Example 4 is that in step (2), one stretching is not included, and the other operations are the same as in Example 4.

[0061] Comparative Example 5

[0062] The difference between this comparative example and Example 4 is that in step (2), secondary stretching is not included, and other operations are the same as in Example 4.

[0063] Comparative Example 6

[0064] The difference between this comparative example and Example 4 is that the process of step (2) is to stretch the melt at 152° C. at a stretching speed of 10 m / min, and the total stretching ratio and other operations are the same as those in Example 4.

[0065] Comparative Example 7

[0066] The difference between this comparative example and Example 4 is that in step (2), the heating rate after the first stretching is 15°C / min, and the other operations are the same as in Example 4.

[0067] Comparative Example 8

[0068] The difference between this comparative example and Example 4 is that in step (2), the heating rate after the secondary stretching is 8°C / min, and the other operations are the same as in Example 4.

[0069] Comparative Example 9

[0070] The difference between this comparative example and Example 4 is that in step (2), the stretching rates during pre-stretching, primary stretching, secondary stretching and tertiary stretching are the same, all 1 m / min, and the other operations are the same as in Example 4.

[0071] Comparative Example 10

[0072] The difference between this comparative example and Example 4 is that in step (2), the stretching rates during pre-stretching, primary stretching, secondary stretching and tertiary stretching are the same, all 4 m / min, and the other operations are the same as in Example 4.

[0073] Comparative Example 11

[0074] The difference between this comparative example and Example 4 is that in step (2), the stretching rates during pre-stretching, primary stretching, secondary stretching and tertiary stretching are the same, all 10 m / min, and the other operations are the same as in Example 4.

[0075] Comparative Example 12

[0076] The difference between this comparative example and Example 4 is that step (3) is not included, and the other operations are the same as Example 4.

[0077] The ETFE films obtained in the above examples and comparative examples were subjected to performance tests. The test methods and test results are as follows:

[0078] 1. Relative thickness deviation:

[0079]

[0080] 2. Transverse thickness consistency assessment:

[0081] Where σTD is the standard deviation of the transverse scan;

[0082] where x i is the single point thickness measurement value, is the average thickness, and N is the number of measurement points, 100.

[0083] 3. Tensile properties

[0084] The test was carried out according to the method of GB / T 1040.

[0085] The test results are shown in Table 1.

[0086] Table 1

[0087]

[0088]

[0089] It can be seen from the test results in Table 1 that, compared with the comparative example, the present invention optimizes the extrusion melting conditions and adopts gradient stretching. The film after gradient stretching is also annealed. The thickness deviation of the obtained film is less than 2%, the transverse thickness consistency is high, and the tensile performance of the film is good.

[0090] Compared to the examples, Comparative Example 1 lacked a static mixer for further melt mixing, resulting in a large melt temperature gradient and poor uniformity. This resulted in large film thickness deviations, reduced transverse thickness consistency (TU), and significantly reduced film tensile properties. In Comparative Example 2, the twin-screw extruder barrel had fewer temperature control zones, leading to large temperature fluctuations and poor melt uniformity, which in turn affected film thickness consistency and reduced film tensile properties.

[0091] Comparative Example 3 lacks pre-stretching and insufficient initial molecular orientation, which greatly reduces the thickness consistency of the film. Comparative Examples 4-6 use a single stretching, which affects the molecular orientation and causes large fluctuations in film thickness.

[0092] In Comparative Example 7, the rapid heating rate led to stress concentration, while in Comparative Example 8, the excessively high heating rate after secondary stretching affected crystallization, resulting in reduced film thickness consistency and increased thickness variation. In Comparative Examples 9-11, a single stretching speed was used, making it impossible to regulate molecular chain orientation in stages, resulting in large film thickness deviations. In Comparative Example 12, the stretched film was not annealed, resulting in high residual stress and uneven shrinkage during cooling, which affected the film's thickness consistency and reduced the film's tensile properties.

[0093] Specific examples are used herein to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core ideas, including the best mode, and also enable any technician in the field to practice the present invention, including making and using any device or system, and implementing any combined method. It should be pointed out that for ordinary technicians in this technical field, without departing from the principles of the present invention, several improvements and modifications can be made to the present invention, and these improvements and modifications also fall within the scope of protection of the claims of the present invention. The scope of patent protection of the present invention is defined by the claims and may include other embodiments that can be thought of by those skilled in the art. If these other embodiments have structural elements similar to the literal description of the claims, or if they include equivalent structural elements that are not substantially different from the literal description of the claims, then these other embodiments should also be included in the scope of the claims.

Claims

1. A method for improving the thickness consistency of ETFE film, characterized in that, The following steps are involved: The ETFE resin is extruded and melted through a twin-screw extruder, and then mixed in a static mixer to obtain a melt; The melt is subjected to gradient stretching, first pre-stretching at 70-80°C, then primary stretching at 80°C, then heating to 118-122°C for secondary stretching, and finally heating to 148-152°C for tertiary stretching; The stretched film is cooled and shaped to obtain an ETFE film.

2. a kind of method improving ETFE film thickness consistency according to claim 1, is characterized in that: The molecular weight of the ETFE resin is less than 1.26×10 6 , crystallinity is 65%-85%, and impurity content is <2%.

3. a kind of method improving ETFE film thickness consistency according to claim 1, is characterized in that: When the ETFE resin is extruded and melted by a twin-screw extruder, the extrusion barrel of the twin-screw extruder is temperature-controlled in five zones: the temperature of zone one is 200-220°C, the temperature of zone two is 230-240°C, the temperature of zone three is 240-250°C, the temperature of zone four is 245-255°C, and the temperature of zone five is 235-245°C. The temperature difference between each zone is ≤±1°C, and the screw speed is 40-70rpm.

4. a kind of method improving ETFE film thickness consistency according to claim 1, is characterized in that: The extrusion die head of the twin-screw extruder is a coat-hanger die head. The film thickness is monitored in real time by a β-ray thickness gauge, so that the temperature of the die lip heating zone is adjusted in real time, with a temperature difference of ≤±0.5°C; the die lip gap is dynamically adjusted.

5. a kind of method improving ETFE film thickness consistency according to claim 1, is characterized in that: The stretching speed during pre-stretching is 0.5-1 m / min, and the strain is 50-100%.

6. a kind of method improving ETFE film thickness consistency according to claim 1, is characterized in that: The stretching rate during the first stretching is 0.5-1m / min; the heating rate after the first stretching is 5-10℃ / min, the stretching rate during the second stretching is 2-4m / min; the heating rate after the second stretching is 3-5℃ / min, the stretching rate for the third stretching is 5-10m / min, and the total stretching ratio is ≥5:

1.

7. a kind of method improving ETFE film thickness consistency according to claim 1, is characterized in that: Air knife cooling is used during cooling and shaping. The wind speed during air knife cooling is 20-30m / s, the pressure is 0.2~0.8Mpa, the air knife angle is 30°±5°, and the cooling rate is controlled at 50-100℃ / s. During air knife cooling, the temperature of the cooling roller is kept below the crystallization temperature of ETFE and above the solidification temperature.

8. a kind of method improving ETFE film thickness consistency according to claim 1, is characterized in that: When dynamically adjusting the die lip gap, the die lip gap fine-tuning signal is output based on the feedback of melt pressure, melt temperature and real-time thickness data of the film.

9. a kind of method improving ETFE film thickness consistency according to claim 1, is characterized in that: After gradient stretching, annealing treatment is also performed before cooling and shaping.

10. A method for improving the thickness consistency of ETFE film according to claim 9, characterized in that: The annealing conditions are: temperature 100°C, time 10 min, tension 0.1-0.5 N / mm 2 .

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