| 摘要 |
<p>A solution of isotactic polypropylene in a specific solvent (trichlorofluoromethane) having a pressure higher than an extinction-initiating pressure (LIE) is introduced into a vacuum chamber at a pressure of not lower than the extinction-finishing pressure (LEE), and the chamber is kept at 198°C to lower than 220°C and at a pressure not higher than the extinction-finishing pressure (LEE) to prepare a solution. The resulting solution is spun under such a condition that melt flow rate (MFR) immediately before extrusion satisfies the following relationship: 0.15-0.0014(TPF-198)«MFR/C«1.74-0.029(TPF-198) (wherein TPF represents a solution temperature, and C represents a polypropylene concentration (wt %)) to produce three-dimensionally reticulate polypropylene fibers. Nonwoven fabric is obtained by opening the fibers. The fibers have a microwave double refractive index of 0.07 or more, and the fibers and the nonwoven fabric have high thermal dimensional stability.</p> |
