Low-shrink polypropylene fibers, fabrics made therefrom, and methods of making thereof

本发明涉及对聚丙烯纤维热收缩和缩水问题的改进。这类纤维要求存在热定形后能迅速和有效地给它提供硬度的化合物。这些化合物包括这样的结构，在曝露于足够热量以熔融初始粒状聚合物，并使该熔体冷却后，这种结构能够使聚合物晶体在目标聚丙烯中成核。这类化合物必须在冷却过程中在比没有成核剂的聚丙烯高的温度下使该聚合物晶体成核。这样，这种"硬化"成核化合物就为聚丙烯晶体的生长提供了成核点。在把成核后的组合物拉伸成纤维形式(11)后，纤维被曝露于足够的热量下以产生结晶结构(26)，从而使纤维保持在一个理想的位置。优选的"硬化"化合物包括二亚苄基山梨糖醇基化合物，以及较不优选的化合物，例如苯甲酸钠，某些磷酸钠盐和磷酸锂盐(例如2，2'-亚甲基-双(4，6-二-叔丁基苯基)磷酸钠)。 This invention relates to improvements in heat and moisture-shrink problems in polypropylene fibers. Such fibers require the presence of compounds that quickly and effectively provide rigidity to the fiber after heat-setting. These compounds include structures that nucleate polymer crystals within polypropylene after exposure to sufficient heat to melt the polymer and allowing the melt to cool. The compounds must nucleate polymer crystals at higher temperatures than the polypropylene without the nucleating agent during cooling. Thus, the "rigidifying" nucleator compounds provide nucleation sites for polypropylene crystal growth. After drawing the nucleated composition into fiber form (11), the fiber is exposed to sufficient heat to grow the crystalline network (26), thus holding the fiber in a desired position. The preferred "rigidifying" compounds include dibenzylidene sorbitol based compounds, as well as less preferred compounds, such as sodium benzoate, certain sodium and lithium phosphate salts (such as sodium 2,2'-methylene-bis-(4,6-di-tert-butylphenyl)phosphate).