Polyamide fibers having improved properties and their production

Abstract

A polyamide fiber excellent in strength, which is characterized by being made of a polyamide having a relative viscosity of not less than 3.5 (measured on a 96% by weight sulfuric acid solution having a polyamide concentration of 10 mg/ml at 20.degree. C.), showing an index of birefringence (.DELTA.n) of not less than 50.times.10.sup.-3 and having the following relationship between the break strength and the break elongation: Break strength (g/d).times.(Break elongation (%)).sup.1/2 .gtoreq.46.0, the index of birefringence in the section of fiber satisfying the following relationship: .DELTA.n.sub.A -.DELTA.n.sub.B .gtoreq.0.5.times.10.sup.-3 (wherein .DELTA.n.sub.A is the index of birefringence of fiber at the position of r/R=0.9, .DELTA.n.sub.B is the index of birefringence of fiber at the position of r/R=0.0, R is the radius of the section of fiber and r is the distance from the central axis of the section of fiber).

Dependencies are inferred from the claim text.