A biaxially stretched film and a method for the manufacture thereof, containing at least 90 mot% of ethylene-tetrafluoroethylene copolymer, having a value of crystallization property, AT, expressed by the equationwherein
Tm (melting point) stands for the peak melting temperature (°C) found when a sample is heated at a temperature increase rate of 20°C/minute using differential scanning calorimeter (DSC), and
Tc (crystallizing temperature during fall of temperature) stands for the peak crystallizing temperature (°C) found when the sample is cooled at a temperature decrease rate of 80°C/minute from the melting point plus 20°C using said DSC,
of not less than 15°C and not more than 60°C,
prepared by a method comprising heating a thermoplastic resin containing at least 90 mol% of ethylene-tetrafluoroethylene copolymer to form a molten resin, extruding the molten resin through a die, and cooling the extruded molten resin at a cooling speed of at least 70°C/second in the range of the melting point minus 10°C to the melting point minus 100°C to thereby form a film while simultaneously biaxially stretching said film to at least two times the original size in each of the longitudinal and lateral directions.
一种双轴拉伸薄膜及其制造方法,至少含有 90%的
乙烯-
四氟乙烯共聚物,其结晶特性值 AT 用公式表示,其中
Tm(熔点)代表使用差示扫描量热仪(
DSC)以每分钟 20°C 的升温速率加热样品时发现的峰值熔化温度(°C),以及
Tc(降温过程中的结晶温度)指使用上述
DSC 以 80°C / 分钟的降温速度从熔点加 20°C 冷却样品时发现的峰值结晶温度(°C)、
不低于 15°C,不高于 60°C、
制备方法包括:加热含有至少 90 摩尔%
乙烯-
四氟乙烯共聚物的热塑性
树脂以形成熔融
树脂,通过模具挤出熔融
树脂,并在熔点负 10°C 至熔点负 100°C 的范围内以至少 70°C/ 秒的冷却速度冷却挤出的熔融
树脂,从而形成薄膜,同时在纵向和横向方向上将所述薄膜双轴拉伸至原始尺寸的至少两倍。