Abstract: The present invention provides a partially or whole flat synthetic fiber which is suitably used for preparing a high strength non-woven fabric even if the basis weight is very small, as well as a non-woven fabric prepared using such flat synthetic fibers. According to the present invention, a flat polybenzazole fiber such as PBO fiber is provided which has a flattened portion having a degree of flatness defined by the ratio of the long diameter/the short diameter of the cross section of the fiber being 2 or higher and having a short diameter being 7 &mgr;m or less. Also, a partially flat synthetic fiber is provided which has a flattened portion along the longitudinal direction of the fiber, wherein the ratio of Wmax (the maximum fiber width)/Wmin (narrowest fiber width) is 2 or higher or wherein the ratio of Wmax (the maximum fiber width)/Wav (average fiber width) is 1.5 or higher.

Abstract: The present invention provides a partially or whole flat synthetic fiber which is suitably used for preparing a high strength non-woven fabric even if the basis weight is very small, as well as a non-woven fabric prepared using such flat synthetic fibers. According to the present invention, a flat polybenzazole fiber such as PBO fiber is provided which has a flattened portion having a degree of flatness defined by the ratio of the long diameter/the short diameter of the cross section of the fiber being 2 or higher and having a short diameter being 7 &mgr;m or less. Also, a partially flat synthetic fiber is provided which has a flattened portion along the longitudinal direction of the fiber, wherein the ratio of Wmax (the maximum fiber width)/Wmin (narrowest fiber width) is 2 or higher or wherein the ratio of Wmax (the maximum fiber width)/Wav (average fiber width) is 1.5 or higher.