SUCCESSIVELY BIAXIAL-ORIENTED POROUS POLYPROPYLENE FILM AND PROCESS FOR PRODUCTION THEREOF
申请人:NEW JAPAN CHEMICAL CO.,LTD.
公开号:EP1369221A1
公开(公告)日:2003-12-10
Disclosed is a successively biaxially stretched film obtained by successive biaxial stretching method comprising extruding a melt of a β-crystal nucleating agent-containing polypropylene-based resin composition from a T-die, cooling the extruded resin on a chill roll, and stretching the resulting web sheet longitudinally and then transversely, wherein the longitudinally stretched sheet is made to have a degree of β-crystal orientation of less than 0.3 by the following method (I) and/or (II), optionally subjected to annealing treatment, and transversely stretched:
method (I): melting the polypropylene-based resin composition containing needle crystals of a specific β-crystal nucleating agent at a temperature not lower than m.p. of the polypropylene-based resin and lower than dissolution temperature of the β-crystal nucleating agent in the polypropylene-based resin melt, and extruding the melt from the T-die at the same temperature,
method (II): adjusting neck-in ratio during longitudinal stretching to 25 to 55%.
The porous polypropylene film has good breakage resistance during manufacture, excellent thickness uniformity, high porosity and air-permeability, and is useful for battery separators.
本发明公开了一种通过连续双轴拉伸方法获得的连续双轴拉伸薄膜,该连续双轴拉伸方法包括从T型模头挤出含β晶成核剂的聚丙烯基树脂组合物的熔体,在冷却辊上冷却挤出的树脂,然后纵向拉伸所得腹板,再横向拉伸所得腹板,其中纵向拉伸的腹板通过以下方法使β晶取向度小于0.3,可选择进行退火处理,然后进行横向拉伸:
方法 (I):在不低于聚丙烯基树脂熔融温度和不低于聚丙烯基树脂熔体中 β 结晶成核剂溶解温度的条件下,熔化含有特定 β 结晶成核剂针状晶体的聚丙烯基树脂组合物,并在相同温度下从 T 型模 具挤出熔体、
方法 (II):在纵向拉伸过程中将缩颈率调整为 25%至 55%。
这种多孔聚丙烯薄膜在制造过程中具有良好的抗破损性、优异的厚度均匀性、高孔隙率和透气性,可用于电池隔膜。